resilient modulus testing for pavement components astm special technical publication 1437

8/20/2019 Resilient Modulus Testing for Pavement Components ASTM Special Technical Publication 1437

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S T P 1 4 3 7

Resi l i en t M odu lu s T est i n g o r

Pavem en t Componen ts

Ga ry N. Durham , W. Al len M arr , and

W il lard L. DeG roff , edi tors

A S T M S t oc k N u m b e r: S T P l 4 3 7

INTERN TION L

A S T M I n t e r n a t i o n a l

1 0 0 B a r r H a r b o r D r i v e

P O B o x C 7 0 0

W e s t C o n s h o h o c k e n , P A 1 9 4 2 8 -2 9 5 9

Pr in ted in th e U .S .A.



L i b r a r y o f C o n g r e s s C a t a l o g i n g - i n - P u b l i c a t i o n D a t a

I S B N : 0 - 8 0 3 1 - 3 4 6 1 - 4

C o p y r i g h t 9 2 0 0 3 A S T M I n t e r n a t io n a l , W e s t C o n s h o h o c k e n , P A . A l l r i g h ts r e s e r v e d . T h i s m a t e r i a l

m a y n o t b e r e p r o d u c e d o r c o p i e d , i n w h o l e o r i n p a r t , i n a n y p r i n t e d , m e c h a n i c a l , e l e c t r o n i c , f i l m ,

o r o t h e r d i s t r i b u t i o n a n d s t o r a g e m e d i a , w i t h o u t t h e w r i t t e n c o n s e n t o f t h e p u b l i s h e r .

P h o t o c o p y R i g h ts

A u t h o r i z a ti o n t o p h o t o c o p y i t e m s f o r i n te r n a l, p e r s o n a l , o r e d u c a t i o n a l c l a s s r o o m u s e , o r

t h e i n te r n a l, p e r s o n a l , o r e d u c a t i o n a l c l a s s r o o m u s e o f s p e c i fi c c l ie n t s , is g r a n t e d b y A S T M

I n t e r n a ti o n a l ( A S T M ) p r o v i d e d t h a t t h e a p p r o p r i a t e f e e i s p a i d to t h e C o p y r i g h t C l e a r a n c e

C e n t e r , 2 2 2 R o s e w o o d D r iv e , D a n v e r s , M A 0 1 9 2 3 ; T e l: 9 7 8 - 7 5 0 - 8 4 0 0 ; o n l in e : h t t p : / /

w w w . c o p y r i g h t . c o m / .

P e e r R e v i e w P o l i c y

E a c h p a p e r p u b l is h e d in th is v o l u m e w a s e v a l u a t e d b y t w o p e e r r e v i e w e r s a n d a t l e a s t o n e e d i -

t or . T h e a u t h o r s a d d r e s s e d a ll o f t h e r e v i e w e r s ' c o m m e n t s t o t h e s a t i s f a c t i o n o f b o t h t h e t e c h n i c a l

e d it o r( s ) a n d t h e A S T M I n te r n a ti o n a l C o m m i t t e e o n P u b l ic a t io n s .

T o m a k e t e c h n i c a l i n f o r m a t i o n a v a i l a b le a s q u i c k l y a s p o s s i b le , t h e p e e r - r e v i e w e d p a p e r s i n t h is

p u b l i c a t i o n w e r e p r e p a r e d " c a m e r a - r e a d y " a s s u b m i t t e d b y t h e a u t h o r s .

T h e q u a l i t y o f th e p a p e r s i n t h is p u b l i c a t i o n r e f l e c t s n o t o n l y t h e o b v i o u s e f f o r t s o f t h e a u t h o r s

a n d t h e t e c h n i c a l e d i to r ( s ), b u t a l s o t h e w o r k o f t h e p e e r r e v i e w e r s . In k e e p i n g w i t h l o n g - s t a n d i n g

p u b l i c a t io n p r a c t ic e s , A S T M I n te r n a t io n a l m a i n t a i n s th e a n o n y m i t y o f t h e p e e r r e v i e w e r s . T h e A S T M

I n te r n a t io n a l C o m m i t t e e o n P u b l i c a t io n s a c k n o w l e d g e s w i t h a p p r e c i a t i o n t h e i r d e d i c a t i o n a n d c o n -

t r i b u t i o n o f ti m e a n d e f f o r t o n b e h a l f o f A S T M I n t e r n a t io n a l .

Pr in ted in Ann Arbor , MI

2003



o rewo rd

T h e S y m p o s i u m o n R e s i li e n t M o d u l u s T e st in g f o r P a v e m e n t C o m p o n e n t s w a s h e l d in S a lt

L a k e C i ty U t a h o n 2 7 - 2 8 J u n e 2 0 0 2. A S T M I n te r n at io n a l C o m m i t t e e D 1 8 o n S o i l a n d R o c k

a n d S u b c o m m i t t e e D1 8 . 0 9 o n C y c l i c a n d Dy n a m i c P r o p e r ti e s o f S o i ls s e r v e d a s s p o n so r s .

S y m p o s i u m c h a i r m e n a n d c o - e d i to r s o f th i s p u b l i c a ti o n we r e Ga r y N . Du r h a m Du r h a m Ge o -

E n t e r p ri s e s S t o n e M o u n t a i n Ge o r g i a ; W. A l l e n M a r t Ge o c o m p I n c o r p o r a te d B o x b o r o u g h

M a s s a c h u s e t ts ; a n d W i l la r d L . De G r o f f F u g r o S o u t h Ho u s t o n T e x a s .



onten ts

O v e r v i e w

v i i

SESSION I :

THEORY AND DESIGN CONSTRAINTS

U s e o f R e s i l ie n t M o d u l u s T e s t R e s u l t s in F l e x i b le P a v e m e n t D e s i g n -

s . NAZARIAN~ L ABDALLAH~ A. M ESH KAN , AND L. KE

A A S H T O T 3 0 7 - - B a c k g r o u n d and Dis cus sio n-- J . L. GROEGER, G. R. RADA, AND

A. LOPEZ

R e p e a t a b i l i t y o f t h e R e s i l i e n t M o d u l u s T e s t P r o c e d u r e - - R . L. BOUDREAU

I m p l e m e n t a t i o n o f S t a r t u p P r o c e d u r e s i n t h e L a b o r a t o r y - - J . L. GROEGER,

A. BRO, G. R. RADA, AND A. LOPEZ

16

3 0

41

SESSION : TESTING CONSTRAINTS AND VARIABLES

R e s i l i e n t M o d u l u s V a r i a t i o n s w i t h W a t e r C o n t e n t - - J . LI A ND B. S . Q UBA IN

E f f e ct o f M o i s t u re C o n t e n t a n d P o r e W a t e r P r e s s u r e B u i l d u p o n R e s i l i e n t

M o d u l u s o f C o h e s i v e S o i l s i n O h i o - - T , s . B U T A UA , J. H UA N G , D .-G . K IM ,

AND F. CROFT

D e s i g n S u b g r a d e R e s i l ie n t M o d u l u s f o r F l o r i d a S u b g r a d e S o i l s - - N . B ANDARA

AND G. M. ROWE

5 9

7 0

85

SESSION 3: ASPHALT AND ADMIXTURES

R e s i l i e n t M o d u l u s o f S o il s a n d S o i l - C e m e n t M i x t u r e s - - T . P. TR IN DA DE ,

C. A. B. CA RVA LHO , C. H. C. SI LVA, D. C. DE LIM A, AND P. S. A. BARBOS A

G e o t e c h n i c a l C h a r a c t e r i z a t i o n o f a C l a y e y S o i l S t a b i l i z e d w i t h P o l y p r o p y l e n e

F i b e r U s i ng U n c o n f i n e d C o m p r e s s i o n a n d R e s i l ie n t M o d u l u s T e s ti ng

D a t a - - I

IASB IK, D. C. DE LIM A, C. A. B. CAR VAL HO, C. H. C. SILV A,

E. MINETTE, AND P. S. A. BARBOSA

9 9

i 1 4



S E S S IO N 4 : E Q U I P M E N T , T E S T P R O C E D U R E S , A N D Q U A L I T Y C O N T R O L I SS U E S

A Low-Cost High-Performan ce Alternative for Controlling a Se rvo-I lydra ulic

System for Triaxial Resilient Modulus Apparatus--M. o. BEJARANO,

A . C . H E A T H , A N D J . T . H A R V E Y

A Fully Automated Computer Controlled Resilient Modulus Testing System--

W . A . M A R R , R . H A N K O U R A N D S . K . W E R D E N

A Simple Method for Determining Modulus of Base and S ubgra de

Mater ia ls--s .

N A Z A R I A N , D . Y U A N , A N D R . R . W I L L I A M S

Resilient Modulus Testing Using Conventional Geotechnical Triaxial

Equipment--J.-M.

K O N R A D A N D C . R O B E R T

Resilient Modulus Tes t-Triaxial Cell Int er ac ti on -- R. L. BOUDREAU AND J. WANG

129

141

152

165

176

S E S S I O N 5 M O D E L I N G D A T A R E D U C T I O N A N D I N T E R PR E T A T I O N

Comparison of Laboratory Resilient Modulus with Back-Calculated Elastic

Moduli from Lar ge-Scale Model Experiments and FWD Tests on

Gran ular Materials--B. F.

T A N Y U , W . H . K I M , T . B . E D I L ,

A N D C . H . B E N S O N

Resilient Modulus Testing of Unbound Materials: LTPP s Learning

Experience--G. R. R A D A , J . L . G R O E G E R , P . N . S C H M A L Z E R , A N D A . L O P E Z

Resilient Modulus-Pavement Subgrade Design Value--R. L. BOUDREAU

T h e U s e o f C o n t i n u o u s I n t r u s i o n M i n i a t u r e C o n e P e n e t r a t i o n T e s t i n g i n

Est ima ting the Resilient Modulus of Cohesive Soi ls- -L. MOHAMMAD,

A . H E R A T H , A N D H . H . T I TI

Charac teriza tion of Resilient Modulus of Coar se-Gr ained Materi als Using the

Intrusion Technology- -H. H. TITI, L. N. MOHAMMAD, AND A. HERATH

191

209

224

233

252



verv iew

R e s i l i e n t M o d u l u s i n d i c a te s t h e s t i ff n e s s o f a s o i l u n d e r c o n t r o l l e d c o n f i n e m e n t c o n d i t io n s

a n d r e p e a t e d l o a d i n g . T h e t e s t i s i n t e n d e d t o s i m u l a t e t h e s t r e s s c o n d i t i o n s t h a t o c c u r i n t h e

b a s e a n d s u b g r a d e o f a p a v e m e n t s y s t e m . R e s i l i e n t M o d u l u s h a s b e e n a d o p t e d b y t h e U . S .

F e d e r a l H i g h w a y A d m i n i s tr a t io n a s t h e p r i m a r y p e r l b r m a n c e p a r a m e t e r f or p a v e m e n t d e s ig n .

T h e c u r r e n t s t a n d a r d s f o r r e s i li e n t m o d u l u s t e s ti n g ( A A S H T O T 2 9 2 - 0 0 a n d T 3 0 7 - 9 9 f o r

s o i l s a n d A S T M D 4 1 2 3 f o r a s p h a l t ) d o n o t y i e l d c o n s i s t e n t a n d r e p r o d u c i b l e r e s u l t s . D i f -

f e r e n c e s i n t e s t e q u i p m e n t , i n s t r u m e n t a t io n , s a m p l e p r e p a r a t i o n , e n d c o n d i t i o n s o f t h e s p e c -

i m e n s , a n d d a t a p r o c e s s i n g a p p a r e n t l y h a v e c o n s i d e r a b l e e f f ec t s o n t h e v a l u e o f r e s il i e n t

m o d u l u s o b t a i n e d f r o m t h e te s t: T h e s e p r o b l e m s h a v e b e e n t h e to p i c o f m a n y p a p e r s o v e r

t h e p a s t t h i rt y y e a r s ; h o w e v e r , a c o n s e n s u s h a s n o t d e v e l o p e d o n h o w t o i m p r o v e t h e t e s ti n g

s t a n d a r d t o o v e r c o m e t h e m . T h e s e c o n d i t i o n s p r o m p t e d A S T M S u b c o m m i t t e e D I 8 t o o r -

g a n i z e a n d h o l d a s y m p o s i u m t o e x a m i n e t h e b e n e f i t s a n d p r o b l e m s w i t h r e s i l i e n t m o d u l u s

t e s ti n g . T h e s y m p o s i u m w a s h e l d J u n e 2 7 - 2 8 , 2 0 0 2 in S a l t L a k e C i ty , U t ah . I t c o n s i s t e d o f

p r e s e n t a t i o n s o f t h e i r f i n d i n g s b y e a c h a u t h o r , t b l l o w e d b y q u e s t i o n a n d a n s w e r s e s s i o n s .

T h e s y m p o s i u m c o n c l u d e d w i th a r o u n d t a b l e d i s c u s s i o n o f t h e c u r r e n t s ta t u s o f t h e r e s i li e n t

m o d u l u s t e s t a n d w a y s i n w h i c h t h e t e s t c a n b e i m p r o v e d . T h i s A S T M S p e c i a l T e c h n i c a l

P u b l i c a t i o n p r e s e n t s t h e p a p e r s p r e p a r e d f o r t h a t s y m p o s i u m . W e w e r e f o r t u n a t e t o r e c e i v e

g o o d q u a l i t y p a p e r s c o v e r i n g a v a r i e t y o f t o p i c s f r o m t e s t e q u i p m e n t t o u s e o f t h e r e s u l t s i n

d e s i g n .

O n t h e t es t m e t h o d , G r o e g e r , R a d a , S c h m a l z e r , a n d L o p e z d i s c u s s t h e d i f fe r e n c e s b e tw e e n

A A S H T O T 3 0 7 - 9 9 a n d L o n g T e rm P a v e m e n t P e r f o r m a n c e P r o to c o l P 4 6 a n d t he r e a so n s fo r

t h o s e d i f f e r e n c e s . T h e y r e c o m m e n d w a y s t o i m p r o v e t h e T 3 0 7 - 9 9 s t a n d a r d . B o u d r e a u e x -

a m i n e s t h e r e p e a t a b i l i ty o f th e t e s t b y t e s ti n g r e p l i c a t e d te s t s p e c i m e n s u n d e r t h e s a m e

c o n d i t i o n s . H e o b t a i n e d v a l u e s w i t h a c o e f f i c i e n t o f v a r i a t i o n o f r e s i l i e n t m o d u l u s l e s s t h a n

5 u n d e r t h e s e v e r y c o n t r o l l e d c o n d i t io n s . G r o e g e r , R a d a , a n d L o p e z d i s c u s s t h e b a c k -

g r o u n d o f t e st s ta r t u p a n d q u a l i ty c o n t r o l p r o c e d u r e s d e v e l o p e d in t h e F H W A L T P P P r o t o c o l

P 4 6 t o o b t a i n r e p e a t a b l e , r e l i a b l e , h i g h q u a l i t y r e s i l i e n t m o d u l u s d a t a . T a n y u , K i m , E d i l , a n d

B e n s o n c o m p a r e d l a b o r at o r y t es ts to m e a s u r e r e s i li e n t m o d u l u s b y A A S H T O T 2 9 4 w i th

l a r g e - s c a l e te s t s i n a p it . T h e y m e a s u r e d l a b o r a t o r y v a l u e s u p t o t e n t i m e s h i g h e r th a n t h e

f i e l d v a l u e s a n d t h e y a t t r i b u t e t h e d i f f e r e n c e s t o d i s p a r i t i e s i n s a m p l e s i z e , s t r a i n a m p l i t u d e s ,

a n d b o u n d a r y c o n d i t i o n s b e t w e e n t h e t w o t e s t t y p e s . R a d a , G r o e g e r , S c h m n a l z e r , a n d L o p e z

r e v i e w t h e L T P P t e st p r o g r a m a n d s u m m a r i z e w h a t h a s b e e n l e a r n e d f r o m t h e la s t 1 4 y e a r s

o f t h e p r o g r a m w i t h r e g a r d t o te s t p r o t o c o l , l a b o r a t o r y s t a rt u p , a n d q u a l i t y c o n t r o l p r o c e d u r e s .

C o n s i d e r i n g t h e t e s t e q u i p m e n t , B e j a r a n o , H e a t h , a n d H a r v e y d e s c r i b e t h e u s e o f o f f - th e -

s h e l f c o m p o n e n t s t o b u i l d a P I D c o n t r o l l e r f o r a s e r v o - h y r a u l i c s y s t e m t o p e r f o r m t h e r e s i li e n t

m o d u l u s t es t. B o u d r e a u a n d W a n g d e m o n s t r a t e h o w m a n y d e t a i l s o f t h e te s t c e l l c a n a f f e c t

t h e m e a s u r e m e n t o f r e si li e n t m o d u l u s . M a r r , H a n k o u r , a n d W e r d e n d e s c r i b e a fu l ly a u t o m a t e d

c o m p u t e r c o n t r o l l e d te s t in g s y s t e m f o r p e r f o r m i n g R e s i l i e n t M o d u l u s t e st s. T h e y u s e a P I D

a d a p t i v e c o n t r o l l e r t o i m p r o v e t h e q u a l i t y o f t h e t e s t a n d r e d u c e t h e l a b o r r e q u i r e d t o r u n

t h e t e s t. T h e y a l s o d i s c u s s s o m e o f t h e d i f f ic u l t i e s a n d t e c h n i c a l d e t a i l s f o r r u n n i n g a R e s i l i e n t

M o d u l u s t e s t a c c o r d i n g t o c u r r e n t t e s t s p e c i f i c a t i o n s .

T e s t r e s u lt s a r e c o n s i d e r e d b y L i a n d Q u b a i n w h o s h o w t h e e ff e c t o f w a t er c o n t e n t o f t h e

s o i l s p e c i m e n s o n r e s i li e n t m o d u l u s f o r t h r e e s u b g r a d e s o i ls . B u t a li a , H u a n g , K i m , a n d C r o f t

e x a m i n e t h e e f f e c t o f w a t e r c o n t e n t a n d p o r e w a t e r p r e s s u r e b u i l d u p o n t h e r e s i l ie n t m o d u l u s

vii



v i i i RESILIENT MODULUS TESTING FOR P VEM ENT COMPONENTS

of unsaturated and saturated cohesive soils. Bandara and Rowe develop resilient modulus

relationships for typical subgrade soils used in Florida for use in design. Trindale, Carvalho,

Silva, de Lima, and Barbosa examine empirical relationships among CBR, unconfined com-

pressive strength, Young s modulus, and resilient modulus for soils and soil-cement mixtures.

Titi, Herath, and Mohammad investigate the use of miniature cone penetration tests to get a

correlation with resilient modulus for cohesive soils and describe a method to use the cone

penetration results on road rehabilitation projects in Louisiana. Iasbik, de Lima, Carvalho,

Silva, Minette, and Barbosa examine the effect of polypropylene fibers on resilient modulus

of two soils. Konrad and Robert describe the results of a comprehensive laboratory investi-

gation into the resilient modulus properties of unbound aggregate used in base courses. :

The importance of resilient modulus in design is addressed by Nazarian, Abdallah, Mesh-

kani, and Ke, who demonstrate with different pavement design models the importance of

the value of resilient modulus on required pavement thickness and show its importance in

obtaining a reliable measurement of resilient modulus for mechanistic pavement design.

Nazarian, Yah, and Williams examine different pavement analysis algorithms and material

models to show the effect of resilient modulus on mechanistic pavement design. They show

that inaccuracies in the analysis algorithms and in the testing procedures have an important

effect on the design. Boudreau proposes a constitutive model and iterative layered elastic

methodology to interpret laboratory test results for resilient modulus as used in the AASHTO

Design Guide for Pavement Structures.

The closing panel discussion concluded that the resilient modulus test is a valid and useful

test when run properly. More work must be done to standardize the test equipment, the

instrumentation, the specimen preparation procedures, and the loading requirements to im-

prove the reproducibility and reliability among laboratories. Further work is also needed to

clarify and quantify how to make the test more closely represent actual field conditions.

We thank those who prepared these papers, the reviewers who provided anonymous peer

reviews, and those who participated in the symposium. We hope this STP encourages more

work to improve the testing standard and the value of the Resilient Modulus test.

Gary Durham

Durham Geo-Enterprises

Willard L DeGroff

Fugro South

W

Allen Marr

GEOCOMP/GeoTesting Express



SESSION : THEORY AND DESIGN CONSTRAINTS



S o h e i l N a zar i an , l Im ad A b d a l l ah , 2 A m i t i s Me sh k an i , 3 an d L iqu n K e 4

U s e o f R e s i li e n t M o d u l u s T e s t R e s u l ts i n F l e x ib l e P a v e m e n t D e s i g n

Re fe r e nc e : N aza r i an , S . , A b d a l l ah , I . , Me sh k an i , A . , an d Ke , L . , " U se o f Re s i l i e n t

M o d u l u s T e s t R e s u l ts i n F l e xi b le P a v e m e n t D e s i g n ,"

Resilient Modulus Testing or

Pavement Components, ASTMSTP 1437,

G . N . D u r h a m , W . A . M a r t , a n d W . L .

D e G r o f f, E d s ., A S T M I n t er n a ti o n a l, W e s t C o n s h o h o c k e n , P A , 2 0 0 3 .

Abs tr a c t : T h e s t a te o f p rac t i ce in d es ign in g pav em en t s in th e U n i t ed S ta t es i s p r im a r i ly

b a s e d o n e m p i r ic a l o r s i m p l e m e c h a n i s t ic - e m p i r i c a l p r o c e d u r e s. E v e n t h o u g h a n u m b e r o f

s t a te an d f ed e ra l h igh w ay agen c ies pe r fo rm res i l i en t m o d u lu s t e s ts , o n ly f ew in co rpo ra t e

th e r e su lt s i n th e pa v em en t d e s ign in a r a t io n a l m an n er . A c o n cen t ra t ed n a t io n a l e f fo r t is

o n th e way to d ev e lo p an d im p lem en t m ech an i s t i c pa v em en t d es ign in a l l st a te s . In th i s

p a p e r , r e c o m m e n d a t i o n s a r e m a d e i n t e rm s o f t h e u s e o f t he r e s il ie n t m o d u l u s a s a

fu n c t io n o f t h e an a lys is a lgo r i th m se l ec t ed an d m ate r i a l m o d e l s u t il i z ed . T h ese

reco m m e n d a t io n s a re a l so in f lu en ced b y th e sen s i t i v i ty o f t h e c ri t ica l pav em en t r e spo n ses

to th e m a te r i a l m o d e l s fo r typ ica l f l ex ib l e pav em en t s . T h e in accu rac ies in l ab o ra to ry an d

f i e ld t e s t in g as we l l a s t h e acc u racy o f th e a lgo r i th m s sh o u ld b e ca re fu l ly co n s id e red to

ad o p t a b a l an ce an d r easo n ab le d es ign p ro ced u re .

K e y w o r d s : r e s i li en t m o d u lu s , pav e m en t d es ign , l ab o ra to ry t e s t in g , b ase , su b grad e ,

asph a l t

A n i d ea l m e c h a n i s t i c p a v e m e n t d e s i g n p r o c e s s i n c l ud e s ( 1 ) d e t e rm i n i n g p a v e m e n t -

re l a t ed ph ys ica l co n s t an t s , su ch as t ypes o f ex i s t in g m a te r i a l s an d en v i ro n m en ta l

co n d i t io n s , ( 2 ) l ab o ra to ry an d f i e ld t e s t in g to d e t e rm in e th e s t r en g th an d s t i f fn ess

pa ram ete r s an d co n s t i t u t iv e m o d e l o f each l aye r , an d (3 ) e s t im a t in g th e r em a in in g l i f e o f

t h e p a v e m e n t u s i n g a n a p p r o p r i a te a l g o ri th m . P a v e m e n t d e s i g n o r e v a l u a t i o n a l g o r it h m s

c a n b e b a s e d o n o n e o f m a n y l a y e r t h e o r y o r f in i te e l e m e n t p r o g r a m s . T h e m a t e ri a ls c a n

b e m o d e le d as l i n ea r o r n o n l in ea r an d e l a s ti c o r v isco e las t i c . T h e app l i ed lo ad can b e

c o n s i d e r e d a s d y n a m i c o r s ta t ic . N o m a t t e r h o w s o p h i st i c at e d o r s i m p l e t h e p r o c e s s i s

m ad e , t h e m a te r i a l p ro per t ie s sh o u ld b e m eas u red in a m a n n er th a t i s co m pa t ib l e w i th th e

1 P r o f e s s or , 2 R e s e a r c h E n g i n e e r, C e n t e r f o r H i g h w a y M a t e r ia l s R e s e a r c h , T h e U n i v e r s i t y o f

T ex as a t E1 P aso , E1 P aso , T X 7 9 9 68 .

3 A s s i s ta n t E n g i n e e r , F l ex i b le P a v e m e n t B r a n c h , T e x a s D e p a r t m e n t o f T r a n s p o r ta t i on , 9 5 0 0

L a k e C r e e k P a r k w a y , B l d g 5 1 , A u s ti n , T X 7 8 7 1 7 .

4 S en io r En g in ee r , N ich o l s C o n su l t in g En g in ee r s , C h td ., 1 10 1 P ac i f i c A v e S te 3 0 0 , S an ta

C r u z , C A 9 5 0 6 0 .

3

Copyright9 by ASTM International www .astm.org



RESILIENTMODULUS TESTING FOR PAVEMENT COMPONENTS

a lgo r i t hm used . I f a ba l an ce be tw een the ma te r i a l p rope r t i e s and ana ly t i ca l a lgo r i t hm i s

no t s t r uck , t he r e su lt s m ay be un re l i ab l e .

The s t a te o f p r ac t i ce i n t he Un i t ed S t a t e s is p r imar i l y ba sed on emp i r i ca l o r s imp le

m e c h a n i s ti c -e m p i r ic a l p a v e m e n t d e s i g n p r o c e du r e s. U n d e r t h e A A S H T O 2 0 0 2 p r o g r a m ,

a c o n c e n t r a t e d n a ti o n a l e f f o r t i s u n d e r w a y t o d e v e l o p a n d i m p l e m e n t m e c h a n i s t i c

pav em en t de s ign i n al l s t a te s . The i n t en t i on o f t h i s pape r i s no t t o p rov ide a d i a logue o n

t h e t ec h n i c a l a s p ec t s o f p a v e m e n t d e s i g n s i n c e t h e m e t h o d o l o g i e s d e s c r i b e d h e r e a r e b y

n o m e a n s n e w o r n o v e l t o th e a c a d e m i c c o m m u n i t y . R a t h e r, t h e p a p e r i s w r it t en f o r t h e

p rac t i t i one r s t ha t a re i n t e r e s ted i n eva lua t i ng t he p r ac t i ca l impac t s o f imp lem en t ing

re s i li en t mo du lu s t e s t i ng i n to in t he i r day - to -d ay ope ra t i ons . I n gene ra l , t he d i s cus s ions

a re l imi t ed t o t he base an d subg rade l aye r s beca use o f space l imi t a t ions . H ow eve r , a s

r e f l ec t ed i n o the r pape r s i n t h i s manusc r ip t , t he v i s co -e l a s t i c and t empe ra tu r e - r e l a t ed

va r i a t i on i n the s t i f fne s s pa r ame te r s o f t he a spha l t conc re t e (AC ) l aye r shou ld be

cons ide red .

In t h i s pape r , d i f f e r en t pavemen t ana lys i s a lgo r i t hms and ma te r i a l mode l s a r e b r i e f l y

desc r ibed . Th e sens i t i v i ty o f t he c r it i c a l pav em en t r e spon ses t o t he non l inea r ma te r i a l

m o d e l s f o r t y p ic a l p a v e m e n t s i s q u a n t if ie d . T h e t r a d e o f f b e t w e e n t h e c o m p u t a t i o n t im e a s

a f u n c t i o n o f a p p r o x i m a t i o n i n th e a n a l y s i s a n d m a t e r i a l m o d e l s a r e d e m o n s t r a te d .

Theo re t i ca l l y speak ing , t he more soph i s t i c a t ed t he ma te r i a l mode l s and t he ana lys i s

a lgo r i t hm s a r e , t he c lo se r t he ca l cu l a t ed r e spon se sh ou ld be t o the ac tua l re spo nse o f t he

pavemen t . Howeve r , t he i naccu rac i e s i n l abo ra to ry and f i e ld t e s t i ng a s we l l a s t he

i n a d e q u a c ie s o f th e a l g o r i t h m s s h o u l d b e c a r e f u l l y c o n s i d e r e d t o a d o p t a b a l a n c e d d e s i g n

sys t em. I f t he mod e l i s no t ca l i b r a t ed we l l , i r r e spec t ive o f i ts deg ree o f soph i s t i c a t i on , t he

r e su l ts m ay be un re l i ab l e .

a t e r i a l o d e l s

B r o w n ( 1 9 9 6 ) d i s c u s s e d a s p e c tr tt rn o f a n a l y ti c a l a n d n u m e r i c a l m o d e l s t h a t c a n b e

used i n pave m en t de s ign . W i th t he se mode l s , t he c ri t ic a l s t re s se s , s t ra in s and

de fo rma t ions wi th in a pavemen t s t r uc tu r e and , t he r e fo re , t he r ema in ing l i f e can be

e s ti m a t ed . M a n y c o m p u t e r p r o g r a m s w i t h d i ff e r e n t le v e l s o f s o p h is t ic a t io n e x is t. T h e

f o c a l p o i n t o f al l th e s e m o d e l s i s th e m o d u l i a n d P o i s s o n s r a ti o o f d i ff e r e n t la y e rs .

Th e l i nea r e la s t i c m ode l i s r a the r s imp le s i nce t he m odu lus i s cons ide red a s a

c o n s t a n t v a lu e . I n t h e s ta t e o f p r a c t ic e , t h e m o d u l u s i s a l s o a s s u m e d t o b e i n d e p e n d e n t o f

t h e s ta t e o f s tr e ss a p p l i e d t o t h e p a v e m e n t . A s s u c h , t h e m o d u l u s o f e a c h l a y e r d o e s n o t

c h a n g e w i t h th e v a r i a t io n i n l o a d a p p l i ed t o a p a v e m e n t . M o s t c u r r e n t p a v e m e n t a n a l y s i s

a n d d e s i g n a l g o r i t h m s u s e t h i s t y p e o f s o lu t io n . T h e a d v a n t a g e o f t h e s e m o d e l s i s t h a t

t hey can r ap id ly y i e ld re su l ts . T he i r m a in l im i t a t ion i s tha t t he r e su l ts a r e r a the r

app ro x im a te i f t he l oads a r e l a rge enough fo r t he ma te r i a l t o exh ib i t a non l inea r behav io r .

I n t he con t e x t o f t he r e s il i en t mo du lus t e s ti ng , t he r e l evan t i n fo rma t ion i s the

r ep re sen t a t i ve va lue t o be u sed i n t he des ign . Spec i f i ca l l y , t he re s i l ien t mo du lu s a t wha t

c o n f i n i n g p r e s su r e a n d d e v i a t o r i c s t re s s s h o u l d b e u s e d i n t h e d e s i g n ? T h i s w i ll b e

discussed la te r .

T h e n o n l i n e a r c o n s ti t u ti v e m o d e l a d o p t e d b y m o s t a g e n c i e s a n d i n s ti tu t io n s c a n b e

gene ra l i zed a s :



NAZARIAN ET AL ON FLEXIBLE PAVEMENT DESIGN 5

k

E = k l O c k Z a d

( l )

w h e r e ~ c a n d ~ d a r e t h e c o n f i n i n g p r e s s u r e a n d d e v i a t o r i c s t re s s , r e s p e c t i v e l y a n d k l , k z

a n d k 3 a r e c o e f f i c i e n t s p r e f e r a b l y d e t e r m i n e d f r o m l a b o r a t o r y t e s ts . I n E q u a t i o n 1 , t h e

m o d u l u s a t a g i v e n p o i n t w i t h i n t h e p a v e m e n t s t r u c tu r e i s r e l a t e d t o th e s t a t e o f s tr e s s .

T h e a d v a n t a g e o f t h is t y p e o f m o d e l i s th a t i t is u n i v e r s a l l y a p p l i c a b l e to f i n e - g r a i n e d a n d

c o a r s e - g r a i n e d b a s e a n d s u b g r a d e m a t e r i a ls . T h e a c c u r a c y a n d r e a s o n a b l e n e s s o f t h is

m o d e l a r e e x t r e m e l y im p o r t a n t b e c a u s e t h e y a r e th e k e y s t o s u c c e s s f u l l y c o m b i n e

l a b o r a t o r y a n d f i e l d r e s u lt s . B a r k s d a l e e t a l. ( 1 9 9 7) h a v e s u m m a r i z e d a n u m b e r o f

v a r i a t i o n s t o th i s e q u a t i o n . U s i n g p r i n c i p l e s o f m e c h a n i c s , a l l t h o s e r e l a t i o n s h i p s c a n b e

c o n v e r t e d t o th e o t h e r w i t h e a s e . T h e s o - c a l l e d t w o - p a r a m e t e r m o d e l s a d v o c a t e d b y t h e

A A S H T O 1 99 3 d e s i g n g u i d e c an b e d e r i v e d f r o m E q u a t i o n 1 b y a s s i g n i n g a v a l u e o f z e r o

t o k 2 ( f o r f i n e - g r a i n e d m a t e r i a l s ) o r k3 ( f o r c o a r s e - g r a i n e d m a t e r i a l s ) . A s s u c h ,

c o n s i d e r i n g o n e s p e c i f i c m o d e l d o e s n o t i m p a c t th e g e n e r a l i ty o f t h e c o n c l u s i o n s d r a w n

f r o m t h i s p a p e r .

U s i n g c o n v e n t i o n s f r o m g e o t e c h n i c a l e n g i n e e r in g , t h e t e r m k l (r ck2 co r r e sp on ds t o

t h e i n i t i a l t a n g e n t m o d u l u s . S i n c e n o r m a l l y p a r a m e t e r k 2 i s p o s i t iv e , t h e i n i t ia l t a n g e n t

m o d u l u s i n c r e a s e s a s th e c o n f i n i n g p r e s s u r e i n c r e a s e s . P a r a m e t e r k3 s u g g e s t s t h a t th e

m o d u l u s c h a n g e s a s t h e d e v i a t o r i c s t r e s s c h a n g e s . B e c a u s e k 3 i s u s u a l l y n e g a t i v e , t h e

m o d u l u s i n c r e a s e s w i t h a d e c r e a s e i n t h e d e v i a t o r i c s t re s s ( o r s tr a in ) . T h e m a x i m u m

f e a s i b l e m o d u l u s f r o m E q u a t i o n 1 i s e q u a l t o k lc rc k2, i .e . t h e i n i t ia l t a n g e n t m o d u l u s .

I n a ll th e s e m o d e l s , t h e s ta t e o f s t re s s i s b o u n d b e t w e e n t w o e x t r e m e s , w h e n n o

e x t e r n a l lo a d s a r e a p p l i e d a n d u n d e r e x t e r n a l l o a d s i m p a r t e d b y a n a c t u a l tr u c k. W h e n n o

e x t e r n a l l o a d i s a p p l i e d t h e i n i t ia l c o n f i n i n g p r e s s u r e , a ~ in it, i s

l + 2 k 0

O C i n i t - - - - O v

( 2 )

3

w h e r e Cyv s t h e v e r t i c a l g e o s t a t i c s t r e s s a n d k o i s t h e c o e f f i c i e n t o f l a t e r a l e a r t h p r e s s u r e a t

r e s t . T he i n i t i a l dev i a t o r i c s t r e s s , O d in it C an be w r i t t en a s

_ 2 2 k 0

o - ~ _ ~ . , , ~ ~ r ~ 3 )

W h e n t h e e x t e r n a l l o a d s a r e p r e s e n t , a d d i t i o n a l s t r e s s e s , ~ x , Cry a n d cy z, a r e i n d u c e d i n t w o

h o r i z o n t a l a n d o n e v e r t i c a l d i r e c ti o n s u n d e r t h e a p p l i c a t i o n o f a n e x t e r n a l l o ad . A m u l t i-

l a y e r e la s t ic p r o g r a m c a n c o n v e n i e n t l y c o m p u t e t h e s e a d d i t i o n a l st re s s e s . T h e u l t i m a t e

co nf in i ng pr es su re , ~c_u~t i s

l + 2 k 0 c r x + C r y + C r~

ere = 3 cry + (4 )

3

and t he u l t i m a t e de v i a t o r i c s t r e s s , (Yd u lt, i s eq ua l t o

2 - 2 k o 2crz - crx - Cry

Cru_,l , - 3 C rv+ 3 (5 )

U n d e r a c t u a l t r u c k l o a d s , t h e m o d u l u s c a n b e c o m e n o n l i n e a r d e p e n d i n g o n t h e a m p l i tu d e

o f c o n f i n i n g p r e s s u r e ~ r a n d d e v i a t o r i c s t r e s s o f ~ d_ ult. I n t h a t c a s e



RESILIENT MODULUS TESTING FOR PAVEMENT COMPONENTS

k k~

E = k lo- ~- . , - c r d_ . , (6 )

nalysis Options

The ana lys i s a lgo r i t hm c an be e i t he r a mu l t i - laye r l i nea r sy s t em, o r a mu l t i - l aye r

e q u i v a l en t - li n e a r s y s t e m , o r a f in i te e l e m e n t c o d e f o r a c o m p r e h e n s i v e n o n l i n e a r d y n a m i c

sys t em. A mu l t i - laye r l i nea r sy s t em is t he s imp le s t s im u la t i on o f a f lex ib l e pave me n t . I n

th is sy s t em, a ll l aye r s a r e cons id e red t o behave l i nea r ly e l as t ic . W E SL E A (V an

C a u w e l a e r t et al. 1 9 8 9 ) a n d B t S A R ( D e J o n g e t a l. 1 9 7 3 ) a r e tw o o f t h e p o p u l a r p r o g r a m s

in th is ca tegory .

The equ iva l en t - l i nea r m ode l i s ba se d on t he s t a t i c l inea r e l a s ti c l aye red t heo ry .

Non l inea r cons t i t u t i ve mode l s , such a s t he one desc r ibed i n Equa t ion 1 , c an be

i m p l e m e n t e d i n t h e m . A n i te r a ti v e p r o c e s s h a s to b e e m p l o y e d t o i m p l e m e n t t h is m e t h o d .

No n l inea r l aye r s a re d iv ided i n to s eve ra l sub l aye r s . On e s t r e ss po in t i s cho sen fo r each

non l inea r sub - l aye r . An in it ia l mo du lu s i s a s s igned t o each s t r e s s po in t . The s t r e s ses an d

s t ra in s a r e ca l cu l a t ed fo r a ll s t re s s po in t s u s in g a mu l t i - l aye r e l a st i c com pu te r p rog ram .

The c on f in ing p r e s su re a nd dev i a to r i c s tr e s s can t hen be ca l cu l a t ed fo r each s t re s s po in t

u s i n g E q u a t i o n s 2 th r o u g h 5 . A n e w m o d u l u s c a n t h e n b e o b t a in e d f r o m E q u a t i o n 6 . T h e

a s s u m e d m o d u l u s a n d t h e n e w l y c al c u l a te d m o d u l u s a t e a c h s tr e ss p o i n t a r e c o m p a r e d . I f

t he d i f fe r ence i s l a rge r t han a p r e - a s s ign ed t o l e r ance , t he p roces s w i l l be r epea t ed u s ing

u p d a t e d a s s u m e d m o d u l i . T h e a b o v e p r o c e d u r e i s re p e a t e d u n t il t h e m o d u l u s d i f f e r e n c e is

wi th in t he t o l e r ance and , t hus , conve rgen ce is reached . F ina l ly , t he r equ i r ed s t r e s se s and

s t r a in s a r e compu ted us ing f i na l modu l i f o r a l l non l inea r sub - l aye r s . Th i s me thod i s

r e l a t i ve ly r ap id ; howe ve r , t he r e su l t s a r e app rox im a te . I n a laye red so lu t i on , t he l a t e ra l

v a r i a ti o n o f m o d u l u s w i t h i n a l a y e r c a n n o t b e c o n s i d e r e d . T o c o m p e n s a t e t o a c e r ta i n

ex t en t f o r t h i s d i s advan tage , a s e t o f s t re s s po in t s a t d i ff e r en t r ad i a l d i s t ances a r e

cons ide red . A bda l l ah e t a l. ( 2002) de sc r ibe s s uch an a lgo r i t hm.

T h e a l l -p u r p o s e f i n it e e le m e n t s o f t w a r e p a c k a g e s , s u c h a s A B A Q U S , c a n b e u s e d

f o r n o n l i n e a r m o d e l s . T h e s e p r o g r a m s a l l o w a u s e r to m o d e l t h e b e h a v i o r o f a p a v e m e n t

i n t h e m o s t c o m p r e h e n s i v e m a n n e r a n d t o s e l e c t t h e m o s t s o p h i s t ic a t e d c o n s t i t u ti v e

m o d e l s f o r e a c h l ay e r o f p a v e m e n t . T h e d y n a m i c n a tu r e o f t h e l o a d i n g c a n a l s o b e

cons ide red . The cons t i t u t i ve mode l adop ted i n non l inea r mode l s i s t he s ame a s t ha t i n t he

equ iva l en t - l i nea r mode l , a s de sc r ibed i n Equa t ion 1 .

The g oa l w i th a l l t he se mo de l s i s o f cou r se t o ca l cu l a t e t he c r i ti c a l s t re s se s and

s t ra in s and f i na l l y t he r em a in ing l if e . W e w i l l concen t r a t e o n t he t ens i le s t r a in a t the

b o t t o m o f th e A C l a y e r an d c o m p r e s s i v e s tr a in o n t o p o f t h e s u b g ra d e . T h e s e t w o

p a r a m e t e r s c a n b e i n c o r p o r a t e d i n t o a d a m a g e m o d e l ( e. g. , th e A s p h a l t I n s ti tu t e m o d e l s )

t o e s ti m a t e t h e r e m a i n i n g l iv e s d u e t o a n u m b e r o f m o d e s o f f a il u re ( e . g ., r u t t in g a n d

f a ti g u e c r a c k in g ) . T h e s e e q u a t i o n s a re w e l l k n o w n a n d c a n b e f o u n d i n H u a n g ( 1 9 9 3 )

a m o n g o t h e r s o u rc e s .



NAZARIAN ET AL ON FLEXIBLE PAVEME NT DESIGN 7

A p p r o p r i a t e M o d u l u s P a r a m e t e r f o r M o d e l s

A s i n d i c a t e d b e f o r e , th e s t r u c tu r a l m o d e l a n d t h e i n p u t m o d u l i s h o u l d b e

c o n s i d e r e d t o g e t h e r . D i f f e r e n t s tr u c t u r a l m o d e l s r e q u i r e d i f f e r e n t i n p u t p a r a m e t e r s . F o r

t h e e q u i v a l e n t l i n e a r a n d n o n l i n e a r m o d e l s , a l l th r e e n o n l i n e a r p a r a m e t e r s a r e r e q u ir e d .

T h e p r o c e s s o f d e f i n i n g th e s e p a r a m e t e r s c a n b e c a t e g o r i z e d a s m a t e r i a l c h a r a c te r i z a ti o n .

F o r t h e l i n e a r m o d e l , a r e p r e s e n t a ti v e l in e a r m o d u l u s h a s t o b e d e t e r m i n e d . T h e p r o c e s s

o f a p p r o x i m a t i n g t h e m o d u l u s i s c a ll e d th e d e s i g n s i m u l a ti o n .

O n e s i g n i f i c a n t p o i n t to c o n s i d e r h a s to d o w i t h th e d i f f e r e n c e s a n d s i m i l a r i t i e s

b e t w e e n m a t e r i a l c h a r a c t e r i z a t io n a n d d e s i g n s i m u l a t io n . I n m a t e r i a l c h a r a c t e ri z a t io n o n e

a t t e m p t s i n a w a y t h a t i s t h e m o s t t h e o r e t i c a l l y c o r r e c t t o d e t e r m i n e t h e e n g i n e e r i n g

p r o p e r t i e s o f a m a t e r i a l ( su c h a s m o d u l u s o r s t r en g t h ). T h e m a t e r i a l p r o p e r t i e s m e a s u r e d

i n th i s w a y , a r e f u n d a m e n t a l m a t e r i a l p r o p e r t i e s th a t a r e n o t r e l a t e d t o a s p e c i f i c m o d e l i n g

s c e n a r io . T o u s e t h e s e m a t e r i a l p r o p e r t i e s in a c e r t a i n d e s i g n m e t h o d o l o g y , t h e y s h o u l d b e

c o m b i n e d w i t h a n a p p r o p r i a t e a n a ly t i c a l o r n u m e r i c a l m o d e l t o o b t a i n t h e d e s i g n o u t p u t .

I n t h e d e s i g n s i m u l a t io n , o n e t ri e s t o e x p e r i m e n t a l l y s i m u l a t e t h e d e s i g n c o n d i t io n , a n d

t h e n e s t im a t e s o m e m a t e r i a l p a r a m e t e r t h a t i s re l e v a n t t o t h a t c o n d i ti o n . B o t h o f t h e s e

a p p r o a c h e s h a v e a d v a n t a g e s a n d d i s a d v a n t a g e s . I n g e n e r a l, th e f i r st m e t h o d s h o u l d y i e l d

m o r e a c c u r a t e r e s u lt s b u t a t t h e e x p e n s e o f m o r e c o m p l e x i t y in c a l c u l a t io n a n d m o d e l i n g

d u r i n g t h e d e s i g n p r o c e s s .

T h e i m p l i c a t i o n o f th i s m a t t e r is b e s t s h o w n t h r o u g h a n e x a m p l e . W e c o n s i d e r a

t y p i c a l p a v e m e n t i n T e x a s . T h e a s p h a l t l a y e r i s t y p i c a l l y 7 5 m m t h i c k w i th a m o d u l u s o f 3 .5

G P a . F o r s i m p l i c i t y , l e t u s a s s u m e t h a t t h e s u b g r a d e i s a l i n e a r - e l a s t i c m a t e r i a l w i t h a

m o d u l u s o f 70 M P a . T h e b a s e i s a s s u m e d t o b e n o n l i n e a r a c c o r d i n g t o E q u a t i o n 1 w i t h k l ,

k 2 a n d k 3 v a l u e s o f 5 0 M P a , 0 . 4 a n d - 0 .1 , r e s p e c t iv e l y . T h e t h i c k n e s s o f t h e b a s e o f 2 0 0 m m

i s a ss u m e d . T h i s p a v e m e n t s e c t io n i s s u b j e c t e d t o a n 8 0 k N w h e e l l o a d . I n th e f i r s t ex e r c i s e,

t h e th i c k n e s s o f t h e b a s e i s v a r i e d b e t w e e n 1 00 m m a n d 3 0 0 m m . T h e v a r i a t io n in b a s e

m o d u l u s w i t h d e p t h i s s h o w n i n F i g u r e 1 i n a n o r m a l i z e d f a s h io n . I n a ll th r e e c a s e s , t h e

m o d u l i a r e n o t c o n s t a n t a n d d e c r e a s e w i t h d e p t h w i th i n t h e b a s e . A s t h e t h i c k n e s s o f t h e

b a s e i n c r e as e s , th e c o n t r a s t b e t w e e n

t h e to p a n d b o t t o m m o d u l u s

b e c o m e s m o r e e v i d e n t .

I n a s i m i l a r f a s h i o n , t h e

i m p a c t o f p a r a m e t e r s

k l k2

an d k3

a r e a l s o s h o w n i n F i g u r e 2 . In t h is

c a s e , th e m o d u l i a r e n o r m a l i z e d t o

t h e m o d u l u s d e t e r m i n e d a t m i d -

h e i g h t o f t h e b a s e (E av g) . O n c e a g a i n ,

t h e s e p a r a m e t e r s i m p a c t t h e

v a r i a t io n i n m o d u l u s w i t h d e p t h . I n

s o m e c a s e s , th e d i f f e r e n c e b e t w e e n

t h e m o d u l i o f t h e m i d d l e o f t h e l a y e r

a n d t h e t o p a n d t h e b o t t o m i s as

m u c h a s 2 0 . S i n c e t h e d e s i g n i s

b a s e d o n t h e i n t e r f a c e s t r e s s e s o r

s t r a in s , i f o n e d e c i d e s t h a t t h e

0 .0 T o p o f B a s e

0 .1 / 2.2 7 / ~ ' ~

~ 0 .4 0.5 / / /

~ 0 .6 = 1 0 0 m m

~ 0 . 7 /

z 0 .8 / / [ / t 2 = 2 0 0 m m

0 . 9 f o p ' o fB a ~ ' / . . . . . i t 2 = 3 0 0 m m

1 . 0

1 5 0 2 0 0 2 5 0 3 0 0

M o d u lu s , M P a

F i g u r e 1 - Impa c t o f l ayer t h i ckness on var ia ti on

in modulus wi thin base layer



R E S I L I E N TMOD ULUS TESTING FOR PAVEMENT COMPO NENTS

m o d u l u s i n t h e m i d d l e o f th e l a y e r is

a p p r o p r i a t e f o r a l i n e a r e l a s t i c b a s e d

d e s i g n , h e / s h e m a y i n t ro d u c e l a r g e ~ ,

e r r o r s i n t h e a n a l y s i s , s i n c e i n m o s t

m o d e l s t h e e s t i m a t e d s t ra i n s h a v e t o -~

b e r a i s e d t o a p o w e r o f a b o u t f o u r.

A s a n e x a m p l e , t h e r e s p o n s e s B

o f t h e t y p i c a l p a v e m e n t d e s c r i b e d ~

a b o v e f o r d i f f e r e n t s t r u c t u ra l a n d Z

m a t e r ia l m o d e l s a r e s u m m a r i z e d in

T a b l e 1 . T o g e n e r a t e T a b l e I , t h e

s u b g r ad e w a s a l so a s s u m e d t o b e

n o n l i n e a r w h e n a p p l i c a b l e . V a l u e s o f

k l , k 2 a n d k 3 o f 5 0 M P a , 0 . 2 a n d - 0 .2

w e r e r e s p e c t i v e l y a s s u m e d f o r t h is

l a y er . T h e s e v a l u e s a r e r e p r e s e n t a t iv e ~ .

o f m a t e r i a l s i n e a s t T e x a s . I n t h e

t a b l e , t h e l in e a r s t a t i c m o d e l r e f e r s t o

t h e s t a t e o f p r a c t i c e . I n t h e l i n e a r

d y n a m i c m o d e l t h e d y n a m i c n a tu r e o f

t h e l o a d i s c o n s i d e r e d i n t h e a n a l y s i s .

I n t h e e q u i v a l e n t - l i n e a r m o d e l , t h e Z

n o n l i n e a r n a t u r e o f t h e b a s e a n d

s u b g r a d e i s c o n s i d e r e d i n a n

a p p r o x i m a t e f a s h i o n , b u t t h e d y n a m i c

n a t u r e o f t h e l o a d i s ig n o r e d . T h e

n o n l i n e a r s t a t ic c o n d i t i o n i s s im i l a r t o

t h e e q u i v a l e n t l i n e a r s o l u t i o n w i t h t h e

e x c e p t i o n t h a t th e n o n l i n e a r b e h a v i o r

o f e a c h m a t e r i a l i s r i g o r o u s l y ~ .

m o d e l e d . F i n a l l y , i n t h e n o n l i n e a r

d y n a m i c a n a l y s i s b o t h t h e d y n a m i c

n a t u r e o f t h e l o a d a n d t h e n o n l i n e a r -~

t~

n a t u r e o f t h e b a s e a n d s u b g r a d e a r e

c o n s i d e r e d .

Z

T h e s u r f a c e d e f l e c ti o n s t h a t

w o u l d h a v e b e e n m e a s u r e d u n d e r a

f a l l i n g w e i g h t d e f l e c t o m e t e r ( F W D )

a t a 4 0 k N l o a d , a n d c r i ti c a l s t r a in s ,

a n d r e m a i n i n g l iv e s o f t h e t y p i c a l

p a v e m e n t s e c ti o n u n d e r a n 8 0 k N

d u a l t a n d e m l o a d a r e p re s e n t e d i n t h e

t a b l e . T h e r e s p o n s e u n d e r t h e F W D i s

0 . 0

0 . 2

0 . 4

0 . 6

0 . 8

1 .0

a ) k l ~ / "

/~j/

/ i k = 2 5 M P a

, ~ // k l = 5 0 M P a

- / . . . . . . k l = 1 00 M P a

0 . 5 0 0 . 7 5 1 . 0 0 1 . 2 5 1 . 5 0

N o r m a l i z e d M o d u l u s E /E av g)

0 . 0 T

0 . 2

i b ) k 2

0 . 4

0 . 6

0 . 8

1 .0

0 . 5 0

, ~ t - - - k 2 = 0 . 3

,, ] k2 = 0.4

. / f - ~ - - - k 2 = 0 . 5

I t I t

0 . 7 5 1 . 0 0 1 . 2 5 1 . 5 0

N o r m a l i z e d M o d u l u s (E /Eavg)

0 . 0

0 . 2

0 . 4

0 . 6

0 . 8

1 .0

0 . 5 0

(C ) k 3 , : ' / / /

/ ~ ,

k 3 = 0

/ ; k3 = -0 .1

~

k 3 = - 0 .2

- - I r / r

0 . 7 5 1 . 0 0 1 . 2 5 1 . 5 0

N o r m a l i z e d M o d u l u s E /E a vg )

F i g u r e 2 - Impact of nonlinear parameters on

variation in modulus within base layer

d e m o n s t r a t e d b e c a u s e A A S H T O 1 99 3 a l l o w s t h e u se o f t h e s u rf a c e d e f le c t io n t o

b a c k c a l c u l a t e m o d u l i . T h e i m p a c t o f t h e n o n l in e a r b e h a v i o r o f t h e b a s e a n d s u b g r a d e



NAZARIAN ET AL ON FLEXIBLE PAVEMENT DESIGN

Material

Model

(Approximate

Computation

time)

Linear

Static

(2 see)

Linear

Dynamic

(600 see)

Equivalent -

Linear

(120 sec)

Nonlinear

Static

(1500 sec)

Nonlinear

Dynamic

(2400 sec)

T a b l e 1 Pavement responses under di

Surface Deflections (microns)

Radial Distance (m)

0 0.3 0.6 0.9 1.2 1.5 1.8

541 333 213 147 104 76 58

(-15)e ( -14) ( -10 ) ( -8) ( - 1 1 ) ( -19) ( -29 )

523 328 213 152 114 91 76

- 1 7 ) - 1 5 ) - 1 0 ) - 5 ) - 2 ) - 3 ) - 3 )

673 396 226 147 104 76 58

-6 -2 ( -4) ( -7) ( - 1 1 ) ( - 2 0) ( -27)

638 384 229 150 104 74 56

-1 (-1) (-3) (-6) ( - 1 1 ) (-22) (-29)

632 386 236 160 117 94 79

rerent models.

Critical Strains

(micro-strain)

tc gcd

204 587

(-33) ( -21)

203 596

(-33) ( -20)

282 844

(-7) (14)

307 702

(1) (-5)

304 764

Remaining

Livesb

(103 EASL s)

Fatigue Rutting

Cracking

1505 401

(271 ) (185 )

1532 373

(278 ) (165 )

518 79

(28) ( -44)

392 120

(-3) (28)

406 141

a u s i n g a 5 0 0 M H z P C

b e s t i m a t ed f rom A sp ha l t In s t i tu t e E qua t i ons

c t ens i l e s t r e s s a t bo t t om o f A C l aye r

d c o m p r e s s i v e s t r en g t h o n t o p o f s u b g r a d e

e pe rcen t d i f f e r ence be t w ee n t h i s quan t i t y and quan t i t y f rom no n l i nea r dynam i c m ode l .

m a t e r i a l s o n th e b a c k c a l c u l a t e d m o d u l i i s b e y o n d t h e s c o p e o f t h is p a p e r . H o w e v e r , f r o m

t h e c h a n g e i n t h e m a g n i t u d e o f t h e d e f l e c t i o n s a s a f u n c t i o n o f m o d e l , i t is i n t u i t iv e th a t i t

i m p a c t s t h e b a c k c a l c u l a t e d v a lu e s .

A s s u m i n g t h e r e s u lt s f r o m t h e n o n l i n e a r d y n a m i c m o d e l a r e th e m o s t a c c u r a t e o n e s ,

t h e d i f f e r e n c e s in t h e r e s u lt s o f t h e o t h e r m o d e l s f r o m t h o s e o f th e n o n l i n e a r d y n a m i c

m o d e l a r e a l s o g i v e n i n T a b l e 1. F o r t h e l i n e a r e l a s t ic m o d e l u s i n g t h e m i d - d e p t h m o d u l u s

f o r b a s e , t h e s u r f a c e d e f l e c t io n s a r e a b o u t 8 - 3 0 l e ss t h a n t h o s e f r o m th e n o n l i n e a r

d y n a m i c m o d e l . F o r t h e f ir s t t h r e e s e n s o r s , m o s t o f th e d i f f e r e n c e s i n d e f l e c t io n s c a n b e

a t t r ib u t e d t o m a t e r i a l n o n l i n e a r i t y . F o r t h e o t h e r s e n s o r s , o n t h e o t h e r h a n d , t h e

d i f f er e n c e s c a n b e m a i n l y f r o m t h e d y n a m i c e f f e ct s . A s a r e s u l t o f i g n o r i n g m a t e r i a l

n o n l i n e a r i t y i n t h e l i n e a r s t a t ic m o d e l , th e c r i ti c a l t e n s i l e s t r a i n i s a b o u t 3 0 s m a l l e r a n d

t h e c r i ti c a l c o m p r e s s i v e s t ra i n i s a b o u t 2 0 s m a l l e r t h a n th o s e in th e n o n l i n e a r d y n a m i c

m o d e l . C o r r e s p o n d i n g l y , th e f a ti g u e r e m a i n i n g l if e a n d t h e r u t ti n g r e m a i n i n g l i f e a re

o v e r e s t i m a t e d b y 2 7 0 a n d 1 85 , r e s p e c t i v e ly .

S i n c e t h e m a t e r i a l n o n l i n e a r i t y a ff e c ts t h e s u r f a c e d e f l e c t io n s n e a r t h e l o a d

a p p l i c a t i o n a n d t h e d y n a m i c e f f e c ts m a i n l y a f f e c t th e s u r f a c e d e f l e c t io n s a t t h e o u t e r

s e n s o r s , t h e l a s t f o u r s u r f a c e d e f l e c t i o n s a r e v e r y c l o s e t o th o s e f r o m t h e n o n l i n e a r

d y n a m i c m o d e l . H o w e v e r , t h e f ir s t t h r e e s u r f a c e d e f l e c t io n s a r e 1 0 - 1 7 l e ss t h a n t h o s e

f r o m t h e n o n l in e a r d y n a m i c m o d e l . A s c o m p a r e d w i t h t h e n o n l i n e a r d y n a m i c m o d e l , t h e

c r i t ic a l t e n s i l e s t r a i n i s 3 3 s m a l l e r a n d t h e c r i t ic a l c o m p r e s s i v e s t r a i n i s 2 0 s m a l l e r .

C o r r e s p o n d i n g l y , th e f a t ig u e r e m a i n i n g l i f e a n d t h e r u t t i n g r e m a i n i n g l i fe a r e

o v e r e s t i m a t e d b y 2 7 8 a n d 16 5 , r e s p e c t iv e l y . T h e c o m p u t a t i o n o f t h e l i n e a r d y n a m i c



1 RESILIENTMODULUS TESTING FOR PAVEMENT COMPONENTS

m ode l i s a lso r e l a t i ve ly r ap id . Ho we ve r , t he l eve l s o f app rox ima t ion i n t he c ri t ic a l s t r a in s

and r em a in ing l i ve s a r e s imi l a r to t hose i n t he l i nea r s t a t ic mo de l , an d t he r e su l ts a r e no t

sa t i s fac tory .

In t he equ iva l en t - l i nea r m ode l , t he ma te r i a l non l inea r i t y is taken i n to cons ide ra t i on

in an app rox ima te f a sh ion , wh i l e t he dynamic e f f ec t s a r e no t cons ide red . The l a rges t

d i f f e r ences i n de f l ec t i ons occ u r a t t he t h r ee ou t e r s enso r s , 11 -2 7 sma l l e r t han t hose

f rom the non l inea r dy nam ic mod e l . The d i f f e r ence s i n the su r f ace de f l ec t i ons a t t he f i r st

fou r senso rs a re sma l l . Th e cr i t ica l tens i le s tra in i s 7 sm al le r and the c r i t ica l

com pres s ive s tr a in i s 14 l a rge r t han t he r e su l t s f r om the non l inea r dyn am ic mo de l .

Co r r e spon d ing ly , the f a t i gue r em a in ing l i fe and t he ru t t i ng r ema in ing l i f e a r e

u n d e r e s t im a t e d b y 2 8 a n d 4 4 , r e s p e ct i v el y . T h e l e v e ls o f a p p r o x i m a t i o n i n t h e

c r i ti c a l s t r a in s a nd r em a in ing l i ve s a r e r e l a t ive ly l a rge bu t , g ive n t he s t at e o f p r ac t i ce ,

pe rhaps accep t ab l e .

In t he non l ine a r s t a t ic m ode l , t he m a te r i a l non l inea r i t y i s t aken i n to cons ide ra t i on ,

bu t t he dynam ic e f f ec t s ar e no t cons ide red . T he l a rges t d i f f e r ences i n de f l ec t i ons oc cu r a t

t h e t h re e o u t e r s e n s o rs , w h e r e t h e y a r e 1 1 - 2 9 s m a l l e r t h a n t h o s e f r o m t h e n o n l i n e a r

d y n a m i c m o d e l . T h e s e d i f f e r e n c es a r e s i m i l a r i n m a g n i t u d e t o t h o s e o f t h e e q u i v a l e n t-

l i nea r mo de l . The c r it i c a l t ens i le s t ra in is 1 l a rge r and t he c r i ti c a l com pres s iv e s tr a in i s

5 s m a l l er t h a n t h e r e s u lt s fr o m t h e n o n l i n e a r d y n a m i c m o d e l . C o r r e s p o n d i n g l y , t h e

f a t igue r em a in ing l i fe is unde re s t ima ted b y 3 , and t he ru t t i ng r em a in ing l i fe i s

ove re s t im a ted by 28 . The r e su l ts f r om the non l inea r s ta t ic mode l a r e c lo se t o t hose

f rom the non l in ea r dyn am ic mode l , i n t h i s ca se , excep t f o r t he t h r ee su r f ace de f l ec t i ons a t

t he ou t e r s enso r s .

To be p r ac t i ca l, t he so lu t i on sho u ld be ob t a ined i n a t ime ly manne r . T ab l e 1 a l so

c o n t a in s t h is i n f o r m a t i o n w h e n a 5 0 0 M H z p e r s o n a l c o m p u t e r i s u s e d . T h e c o m p u t a t i o n

t i m e o f t h e l in e a r s t a ti c m o d e l i s v e r y r a p i d ( a b o u t 2 s ec ). H o w e v e r , w i t h o u t c o n s i d e r i n g

ma te r i a l non l inea r i t y and d yna m ic e f fec t s , t he r e su l ts a r e r a the r app rox im a te . On the o the r

h a n d , t h e r ig o r o u s n o n l i n e a r d y n a m i c a n a ly s i s m a y b e t o o t i m e c o n s u m i n g ( a b o u t 4

hour s ) .

B a s e d o n t h e e x a m p l e s h o w n f o r a t y p i ca l p a v e m e n t i n T e x a s , t h e c o n s e q u e n c e s o f

s e l ec t in g d i f fe r e n t m o d e l s o n t h e a c c u r a c y o f t h e e s t i m a t e d s t ra i ns a n d r e m a i n i n g l iv e s

s h o u l d b e c l ea r . A b a l a n c e b e t w e e n t h e a c c e p t a b l e l e v e l o f m o d e l s o p h i s ti c a ti o n a n d t h e

c o m p u t a t i o n a l t im e s h o u l d b e s tr u c k. T h e d e c i s i o n o n h o w s o p h i s ti c a te d t h e a n a ly s i s

s h o u l d b e m a d e h a s t o b e m a d e b a s e d o n t h e i m p o r t a n c e o f t h e p ro j e c t. A s s o o n a s a

d e c i s i o n o n t h e m o d e l i s m a d e , t h e l e v e l o f s o p h i s t ic a t io n i n t h e l a b o r a t o r y t es t in g c a n b e

d e t e rm i n e d . T h i s d e c i s i o n i s al s o g o v e r n e d b y d e t e r m i n i n g w h i c h p a v e m e n t p r o p e r t y w i l l

imp ac t t he r e su lt s o f a g iven ana lys i s s i gn i f i can t ly . T o answ er t h i s ques t i on , K e e t a l.

( 2001) and Meshkan i e t a l . ( 2002) have conduc t ed an ex t ens ive s ens i t i v i t y ana lys i s t o

i d e n t i fy t he m o s t c r i ti c al p a r a m e t e r s. A b r i e f s u m m a r y o f t h e ir c o n c l u s i o n s i s d e s c r i b e d

b e l o w .

T h e f o c u s o f b o t h s t ud i es h a s b e e n o n f o u r ca t eg o r ie s o f p a v e m e n t s : T h i c k A C -

Th ick Base ( e . g . , i n t e r s t a t e roads ) , Th i ck AC-Th in Base ( e . g . , f a rm to marke t r oads ) , Th in

A C - T h i c k B a s e ( e .g ., s e c o n d a r y r o a d s ) a n d T h i n A C - T h i n B a s e ( e .g ., s t r ee t r o a d s) . T h e

sens i ti v i ti e s o f r em a in ing l i ve s due t o f a t i gue c r ack ing a nd ru t t i ng fo r d i f f e r en t pa r am e te r s

a n d f o r th e f o u r p a v e m e n t c a t eg o r i es a r e i n c l u d e d i n F i g u r e s 3 a n d 4 . T h e s e g r a p h s c a n



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b e u s e d a s g u i d e li n e s d u r i n g t h e d e s i g n , e v a l u a t i o n o r c o n s t r u c t io n o f p a v e m e n t s . T h e

c a s e s t h at t h e d y n a m i c a n a l y s e s a re p e r f o r m e d a r e n o t c o n s i d e r e d a n y f u r th e r b e c a u s e o f a

l a c k o f w i d e s p r e a d u s e .

In F igu re s 3 an d 4 , the x - ax i s i s t he r e levan t pa r am e te r s f o r d i f fe r en t mod e l s an d

the y - ax i s i s t he s ens i t i v i ty o f t he r em a in ing l i fe e i t he r due t o f a t i gue c r ack in g o r r u t t ing t o

tha t pa r am e te r . To d e t e rmine t he s ens i t iv i t y o f a g iven pa rame te r , t he pa r t i cu l a r pa r am e te r

w a s a l lo w e d t o v a r y b y 2 5 a b o v e a n d b e l o w t h e a s s i g n e d v a l u e. B a s e d o n o u r

e x p e r i e n c e w i t h p a v e m e n t a n a l y s i s a n d d e s i g n a n d l a b o r a t o r y t e st in g , t h i s v a lu e s e e m e d

r e a s o n a b l e f o r T e x a s. F i v e h u n d r e d s e ts o f i n p u t d a t a w e r e g e n e r a t e d u s i n g a M o n t e C a r l o

s i m u l a ti o n . T h e v a lu e s w e r e u n i f o r m l y d i s tr ib u t e d w i t h i n th e m i n i m u m a n d m a x i m u m

v a l u e s a s s i g n e d t o a p a ra m e t e r . T h e i m p a c t o f a p a r a m e t e r o n t h e r e m a i n i n g l i fe w a s

quan t i f i ed u s ing a pa r ame te r t e rm ed the s ens i t i v i t y index . The sens i t i v it y i ndex (S i) i s

d e f i n e d a s t h e r a ti o o f th e p e r c e n t a g e c h a n g e i n t h e t a r g et p a r a m e t e r ( o n e o f th e t w o

rema in ing l i ve s ) t o t he pe rcen t age change i n t he pe r tu rbed i npu t pa r ame te r .

M a t h e m a t i c a l l y ,

Si = Percentage Ch ang e in Target Parameter (7)

Percentage Ch ang e in Perturbed Inp ut Parameter

w h e r e

P e r c e n t a g e C h a n g e - I C a l c u l a t e d ~ U s e d Q u a n t i t y - O r i g i n al Q u a n t i ty I • 1 0 0 ( 8 )

O r i g i n al Q u a n t i t y

The re fo re , t he l a rge r t he s ens i t i v i t y i ndex i s , t he mo re s ens i t ive t he t a rge t pa r am e te r w i l l

be t o t he va r i ed pa rame te r .

A s e t o f li m i ts w a s u s e d t o d e f in e t h e s i g n i f i c a n c e o f a g i v e n p a ra m e t e r . T h e s e

l eve l s a r e de f ined i n Tab le 2 . The i n t e rp re t a ti on o f t he se l eve l s o f s ens i t i v it y i n t e rms o f

t h e ir a p p l i c a b il i ty t o t h e l a b o r a t o r y a n d f i el d m e a s u r e m e n t s i s a ls o s u m m a r i z e d i n T a b l e

2 . Fo r examp le , f o r a pa r am e te r t ha t i s l abe l ed no t s ens i t i ve , i ts va lue can be e s t ima ted

f rom l i te r a tu re and t he r e i s no nee d t o spend e f fo r t and funds t o measu re t hem accu ra t e ly .

H o w e v e r , w h e n a p a r a m e t e r i s v e r y s e n s it iv e f o r a g i v e n m o d e l , t h e a g e n c y i n v o l v e d i n

t h e p a v e m e n t d e s i g n e i t h e r s h o u l d s p e n d n e c e s s a r y ti m e a n d e f f o r t t o m e a s u r e t h e m

Table 2 -

Leve l s o f sens i t iv i t y ass igned to each param eter base d on sens i t iv i t y i ndex

L e v e l o f

Sens i t i v i t y

N o t S e n s i t i v e

ms)

M o d e r a t e l y

Sens i t i ve

( M S )

Sens i t i ve

s)

V e r y S e n s i ti v e

( V S )

Sens i t i v i t y

I n d e x

< 0 .25

>_0.25

and < 0 .5

> 0 .5

a n d < 1 . 0

~>1.0

S i g n i f i c a n c e t o P a v e m e n t D e s i g n

C a n b e p r o b a b l y e s ti m a t e d w i t h s m a l l e r r o r i n

f ina l resu l t s

M u s t b e m e a s u r e d t o l i m i t e r ro r s i n d e s i g n

M u s t b e m e a s u r e d w i t h r e as o n a b le a c c u r a c y

fo r s a t i s f ac to ry des ign

M u s t b e m e a s u r e d v e r y a c c u r at e ly

o r d e s i g n m a y n o t b e c o n s i d e r e d a p p r o p r i a t e




a c c u r a te l y o r s h o u l d u s e a s i m p l e r s t r u ct u ra l m o d e l . I t s h o u l d b e m e n t i o n e d t h a t t h e

c o n c l u s i o n s d r a w n h e r e a r e o n l y a p p l ic a b l e t o t h e m o d e l s t h a t a r e s i m i la r t o th e A s p h a l t

In s t it u t e mo de l s . S hou ld an agen cy adop t d i f f e r en t f a il u r e mode l s o r ma te r i a l m ode l s , t h i s

e x e r c is e s h o u l d b e r e p e a te d . T h e c o m m e n t s m a d e h e r e m a y n o t b e v a li d f o r t h o s e m o d e l s .

M e s h k a n i e t al. ( 2 0 0 2 ) d e m o n s t r a te o n e p r o c e s s t h a t c a n b e c a r r i e d o u t to e s t a b li s h

impor t an t pa r ame te r s .

F r o m t h e t w o f i g u re s t h a t c o r r e s p o n d t o t y p i c a l p a v e m e n t s i n E a s t T e x a s ,

d e p e n d i n g o n t h e th i c k n e s s o f t h e b a s e a n d A C l a y er s , t h e m a t e r ia l m o d e l u s e d a n d t h e

m o d e o f fa i lu r e c o n s i d e r e d , d i f fe r e n t p a r a m e t e r s b e c o m e i m p o r t a n t . F o r e x a m p l e , f o r a

th in A C and th in base , the non l inea r pa r ame te r s k2 and k i m p a c t t h e r e s p o n s e o f t h e

p a v e m e n t s i g n if i ca n t ly . O n t h e o t h e r h a n d , w h e n t h e b a s e a n d A C a r e t h i ck , o n e s h o u l d

n o t b e c o n c e r n e d a b o u t t h e s e p a r a m e t e r s i n t h e f a t ig u e c r a c k i n g m o d e .

F o r t h e f a t i g u e c r a c k i n g m o d e , t h e l e a s t s i g n i fi c a n t p a r a m e t e r i s th e P o i s s o n s r a t io

o f t h e s u b g r a d e. O n t h e o t h e r h a n d , f o r t h e r u t ti n g f a i lu r e m o d e , o n e o f t h e m o s t

s i g n if i c a n t p a r a m e t e r s i s th e P o i s s o n s r a t io o f s u b g ra d e . T h e o t h e r i m p o r t a n t o b s e r v a t i o n

f r o m F i g u r e 3 is t h at th e m o d u l u s o f th e b a s e s h o u l d b e m e a s u r e d m o r e c a r e f u l l y w h e n

the l i nea r e la s t ic m ode l i s u sed . Fo r th i s mo de o f f a i lu r e , t he non l inea r pa r am e te r s k2 and

k 3 s h o u l d b e m e a s u r e d m o r e c a r e f u l l y f o r th e t h i n n e r p a v e m e n t s . F o r a n i n te r st a te t y p e

p a v e m e n t s e c ti o n , i t m a y n o t b e n e c e s s a r y t o c o n d u c t a n y l a b o r a t o r y te s ts t o d e t e r m i n e t h e

n o n l i n e a r p a r a m e t e r s o f t h e s u b g r a d e . T h i s s t a t e m e n t m a y b e c o u n t e r in t u i ti v e . B u t

c o n s i d e r i n g t h a t t h i c k l a y e rs o f A C a n d b a s e h a s t o b e p l a c e d o n t o p o f t h e s u b g r a d e t o

e n d u r e t h e l a rg e n u m b e r o f v e h i c u l a r l o a d s , t h e s t r es s e s w i t h i n t h e s u b g r a d e m a y b e t o o

sma l l t o i nduce non l ine a r behav io r . I n th i s ca se , a cco rd ing to F igu re 3 , any mi se s t ima t ing

o f t h e n o n l i n e a r p a r a m e t e r s o f th e b a s e m a y s i g n i f i c a n tl y im p a c t th e e s t i m a t e d r e m a i n i n g

life.

F o r t h e r u t ti n g m o d e o f fa i lu r e , a s s h o w n i n F i g u r e 4 , t h e m o s t s i g n i f ic a n t

p a r a m e t e r s a r e t h e m o d u l u s ( o r p a r a m e t e r k l f o r t h e n o n l i n e a r m a t er i al m o d e l s ) a n d

P o i s s o n s r a ti o o f t h e s u b g r a d e 5. T h e m o d u l u s o f t h e A C l a y e r i s a l s o r e a s o n a b l y

i m p o r t a n t. O n t h e o t h e r h a n d , t h e n o n l i n e a r p a r a m e t e r s o f t h i n b a s e s a r e o f l im i t e d

s ign i f i cance . Bu t f o r t h i cke r ba se s , the se pa ram e te r s shou ld be cons ide red .

T h e s e g r a p h s , a n d a l a r g e n u m b e r o f si m i l a r o n e s p r e s e n t e d i n M e s h k a n i e t al.

( 2002) c l ea r ly dem ons t r a t e t ha t one t e s t i ng p ro g ram does no t f it a l l p ro j ec t s . Du r ing t he

i n it ia l p h a s e s o f d e s ig n , b a s e d o n t h e s t r u c tu r a l m o d e l a d o p t e d b y t h e a g e n c y a n d b a s e d

on the t yp i ca l laye r ma te r i a ls and t h i cknes se s t ha t the ag enc y is comfo r t ab l e w i th ,

adequa t e and app rop r i a t e l abo ra to ry t e s t i ng shou ld be cons ide red .

Th i s s t udy , and o the r s imi l a r ones i n M eshk an i e t a l . ( 2002) , a l so dem ons t r a t e s t ha t

i f the l i nea r e l a s t ic l aye red t he o ry i s cons ide red fo r t he ana lys i s , pe rhaps t he r e s i l ien t

m o d u l u s t e s ts c a n b e s i m p l i fi e d s o t h at t h e l a rg e n u m b e r o f s t ep s n e c e s s a r y u n d e r c u r r e n t

p r o t o c o l c a n b e o p t im i z e d . T e s ts c a n b e p e r h a p s p e r f o r m e d u n d e r c l o se t o z e ro c o n f i n i n g

p r e s s u re ( c o r r e s p o n d i n g t o t h e u n l o a d e d c o n d i t io n ) a n d o n e o t h e r c o n f i n i n g p r e ss u r e t h a t

5 P o i s s o n s r at io b e c o m e s i m p o r t a n t w h e n a v a l u e g r ea t e r t h a n 0 . 4 is a s s u m e d . S i n c e th e

so i l s in ea s t Tex as a r e gene ra l l y s a tu ra t ed , a cen t r a l va lue o f 0 .45 wa s a s sum ed d u r ing

the s imu la t i on .




i s reasonably c lose to the con f in ing pres sure induced in the pa r t i cu la r pavem ent l aye r

unde r the des ign veh icu la r loads . On the o the r hand , i t s eems tha t fo r s a tu ra ted or nea r

sa tura ted subgrades , efforts are need ed to determ ine the in-place Poiss on ' s ra tio .

Conclus ions

In th is paper an a t t emp t has been made to b r ing to the a t t en tion of those who a re

involved in p avem ent des ign the impor tance o f ha rmoniz ing the l abora tory t es ting ,

espec ia l ly re s il i en t mo dulus t es ting , wi th the des ign procedu re used b y the agency .

S impl i f i ed des ign procedures ma y no t requ i re a s much emphas i s on some o f the s t i f fnes s

proper t i e s o f som e laye rs . A pro toc o l i s p roposed to iden t i fy the s ign if i can t pa ramete rs a s

a funct ion o f pav em ent s t ructure and s t ructura l m odel an d mater ia l mod el used.

cknowledgment s

This work w as suppo r ted by the Texas D epar tment o f T ranspor ta tion . The au thors

wou ld l ike to expres s the ir s incere apprec ia t ion to M ark M cDanie l , Joe Tho mp son , and

John Rantz fo r the i r eve r -presen t suppor t and va luab le adv ice . The conten t s o f th is pape r

re f lec t the v iew o f the au thors , wh o a re re spons ib le fo r the fac ts and the accuracy of the

da ta p resen ted he re in . The con ten t s do no t n ecessa r i ly re f lec t the o f f i c ia l v iews or po l ic ie s

o f the fu nding agencies .

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J o n a t h a n L . G r o e g e r, 1 G o n z a l o R . R a d a , 2 A r a m i s L o p e z 3

A A S H T O T 3 0 7 - B a c k g r o u n d a n d D is cu s si o n

R e f e r e n c e : G r o e g e r , J . L ., R a d a , G . R . , a n d L o p e z , A . , " A A S H T O T 3 0 7 -

B a c k g r o u n d

a n d D i s c u s s io n , " Res i l i en t Modu lus Tes t i ng or Pa veme n t Componen ts , A ST M STP

1437,

G . N . D u r h a m , W . A . M a r r, a n d W . L . D e G r o f f , E d s ., A S T M I n te r n a ti o n al , W e s t

C o n s h o h o c k e n , P A , 2 0 0 3 .

A b s t r a c t : T h e c u r r e n t A A S H T O p r o t o c o l f o r d et e r m i n a t io n o f r e si li e n t m o d u l u s o f s o il s

a n d a g g r e g a t e m a te r ia l ( T 3 0 7 - 9 9 ) i s b a s e d l a r g e ly o n L o n g T e r m P a v e m e n t P e r f o r m a n c e

( L T P P ) P r o t o c o l P 46 . T h e L T P P p r o t o c o l e v o l v e d o v e r a n u m b e r o f y e a r s a n d ha s h a d

n u m ero u s co n t r ib u to r s ( in c lu d in g s ign i f ican t gu id an ce an d in pu t f ro m th e au th o r s o f t h is

paper ) . T o -d a te , o v e r 3 0 0 0 sam ples h av e b een t e s t ed wi th P 4 6 an d r esu l ts o f th i s t e s t in g

e f f o rt w i ll h a v e f a r - re a c h i n g i m p l i c a ti o n s i n t h e d e v e l o p m e n t o f p e r f o r m a n c e m o d e l s f o r

p a v e m e n t s t ru c tu r es . M a n y l e s s on s w e r e l e a r n e d d u r in g d e v e l o p m e n t o f P 4 6 a n d t h is

h i s t o ry is d o c u m e n t e d i n a c o m p a n i o n p ap e r . T h e p r e s e n t p a p e r p r o v id e s a b a c k g r o u n d

o f t h e r e as o n s a n d r a t i o na l e b e h i n d s o m e o f t h e m a j o r t e c hn i c a l a s p e c ts o f P 4 6 , a n d b y

d i re c t a s s o c ia t io n , A A S H T O T 3 0 7 . T h e p a p e r a l s o o f f e r s s u g g e s t i on s f o r i m p r o v e m e n t

o r m o d i f i ca t io n o fT 3 0 7 . I t i s h o p ed th a t t h is d i scu ss io n wi l l l ead to a d eepe r

u n d er s t an d in g o f t h e t e s t p ro ce d u re an d p e rh aps f ac i l it a t e a d i scu ss io n o f t h e d i r ec t io n th e

T 3 0 7 p ro ced u re sh o u ld fo l lo w in th e fu tu re .

K e y w o r d s : r e s i li en t m o d u lu s , l ab o ra to ry t es t ing , u n b o u n d m ate r i a l s , su b grad e ,

g u i de l in e s , L T P P , T 3 0 7 , L T P P P r o t o c o l P 4 6

I n t r o d u c t i o n

T h e c u rr e n t A A S H T O S t a n d a r d M e t h o d o f T e s t f o r D e t e r m i n i n g t h e R e s i l ie n t

M o d u l u s o f So i ls a n d A g g r e g a t e M a t e r ia l s , A A S H T O D e s i g n a t i o n ( T 3 0 7- 9 9 ) is b a s e d

l a r g e ly o n L o n g T e r m P a v e m e n t P e r f o r m a n c e ( L T P P ) P r o t o c o l P 4 6 , R e s i l ie n t M o d u l u s

o f U n b o u n d G r a n u l a r B a s e / S u b b a s e a n d S u b g r a d e M a t e ri a ls . T h e L T P P p r o t o c o l

e v o l v e d o v e r a n u m b e r o f y e ar s a n d h a s h a d n u m e r o u s c o n t ri b u to r s ( i n c l u d i ng s i g n if i c a nt

gu id an ce an d in pu t f ro m th e au th o r s o f t h is paper ) . T o d a te , o v e r 3 0 0 0 sam ples h a v e

b een t e s t ed wi th P 4 6 an d r esu l t s o f th i s t e s tin g e f fo r t w i l l h av e f a r - r each in g im p l i ca t io n s

i n t h e d e v e l o p m e n t o f p e r f o rm a n c e m o d e l s f o r p a v e m e n t s t ru c tu r es .

M a n y l e s s o n s w e r e l e a rn e d d u r i n g d e v e l o p m e n t o f P 4 6 a n d t h is h i s t o r y is

d o c u m e n t e d i n a c o m p a n i o n p a p e r ( R a d a e t al . 2 00 3 ) . T h e p r e s e n t p a p e r p r o v i d e s a

b a c k g r o u n d o f th e r e a s o n s a n d r a t io n a le b e h i n d s o m e o f t he m a j o r t e c hn i c a l a s p e c t s o f

t Vice President, Axiom Decision Systems, Inc., 6420 D obbin Road, Su ite E, C olumbia, MD 21045.

2 Assistant Vice President, LAW PCS , 12104 Indian Creek Court, Suite A, Beltsville, MD 20705.

3 LTPP Team Leader, Federal HighwayAdministration, 6300 G eorgetown Pike, M cLean, VA 22101.

1 6




G R O EG E R E T A L O N A A SH T O T 3 7 1 7

P 4 6 , a n d b y d i r e c t a s s o c ia t io n , A A S H T O T 3 0 7 . T h e p a p e r a ls o o f f e r s s u g g e s t i o n s f o r

i m p r o v e m e n t o r m o d i f i c a t i o n o f T 3 0 7 . I t i s h o p e d t h a t t h is d i s c u s s io n w i l l le a d t o a

d e e p e r u n d e r s t a n d i n g o f t h e t es t p r o c e d u r e a n d p e r h a p s f o s te r a d i s c u s s io n o f t h e

d i r e c t io n t h e p r o c e d u r e s h o u l d f o l l o w i n t h e f u t u re .

T h e p a p e r w i l l f ir s t d i s c u s s t h e s im i l a ri ti e s a n d d i f f e re n c e s b e t w e e n L T P P

P r o t o c o l P 4 6 a n d A S S H T O T 3 0 7 . T h i s d i s c u s s i o n f r a m e s t h e v a r i o u s te c h n i c a l is s u e s

i n v o l v e d w i t h t h e c u rr e n t p r o c e d u r e s . T h e t o p i c s c o v e r e d i n c lu d e t h e f o l l o w i n g :

9 L o a d i n g s y s te m 9 N u m b e r a n d t y p e o f L V D T s

9 L o a d c e ll l o c at io n 9 N u m b e r o f p o i n ts p e r c y c l e

9 D e f o r m a t i o n m e a s u r e m e n t 9 S p e c i m e n s iz e

9 C o n f i n i n g f l u i d 9 C o m p a c t i o n p a r a m e t e r s

9 L o a d p u l s e s h a p e 9 C o m p a c t i o n p r o c e d u r e s

9 L o a d a n d c y c l e d u r a t i o n 9 Q u i c k s h e a r t e s t

E a c h t o p i c i s c o v e r e d i n d e t a il t o g i v e th e r e a d e r a n u n d e r s t a n d i n g o f

w y

t he t e s t

p r o c e d u r e w a s d e v e l o p e d a s i t w a s , a n d n o t j u s t

ow

i t i s pe r fo rm ed . Th i s d i s cus s io n is

c r i ti c a l to c o m p r e h e n s i o n o f t h e l im i t a t io n s o f T 3 0 7 a n d i s i n t e n d e d t o f a c il it a te

d i s c u s s i o n o f p o s s i b l e i m p r o v e m e n t s t h a t c a n b e m a d e i n t h e f u tu r e . I t i s i n t e n d e d t h a t

t h i s w i l l l e ad t o a more rob us t t e s t p roc edu re t ha t c an be u sed t o gene ra t e r epea t ab l e ,

a c c u r a te , a n d c o n s i s t e n t re s il ie n t m o d u l u s d a t a f o r u s e i n p a v e m e n t d e s i g n a n d e v a l u a ti o n .

R e s i l i e n t M o d u l u s C o n d e n s e d H i s t o r y

P a v e m e n t t h i c k n e s s d e s i g n p r i o r t o W o r l d W a r I I w a s b a s i c a l ly e m p i r i c a l, b a s e d

on expe r i ence , so i l c l a s s if i c a t ion , and r e s pon se o f a pav em en t s t r uc tu r e t o s t a t ic l oad ,

( e .g . , a p l a t e l o a d o r C B R t es t) . A m i n i m u m t h i c k n e ss f o r a s u rf a c e c o u r s e w a s o f t e n

s e l e c te d b a s e d o n p l a s t ic d e f o r m a t i o n a s th e o n l y f a il u re c r i te r io n . E l a s t ic d e f o r m a t i o n s

w e r e n o t e v e n c o n s i d e r e d ( V i n s o n 1 9 8 9 ).

Shor t l y t he r ea f t e r , s eve ra l i nves t i ga to r s u sed r epea t ed p l a t e l oad t e s t s on mode l

p a v e m e n t s e c t io n s w i t h t h e n u m b e r o f l o a d r e p e t it i o n s a r o u n d 1 0 . T h e p r i m a r y o b j e c t i v e

o f t h e ir i n v e s t i g a ti o n s w a s t o d e t e r m i n e t h e e f f e c t o f r e p e t it i o n o f lo a d o n t h e d e f o r m a t i o n

a n d n o t t o d e t e r m i n e t h e r e si li e n t m o d u l u s . T h e c o l l e c t i v e w o r k o f t h e s e i n v e s t ig a t o r s

f o c u s e d o n t h e d e t e r m i n a t i o n o f t h e d e f o r m a t i o n c h a r a c te r i st i c s a n d r e si li e n t m o d u l u s o f

c o m p a c t e d s u b g r a d e s . T h e i n v e s t i g a to r s c a m e t o t h e c o n c l u s i o n th a t th e b e h a v i o r o f s o i ls

u n d e r tr a f fi c l o a d i n g c o u l d o n l y b e o b t a i n e d f r o m r e p e a te d l o a d t es ts . T h i s c o n c l u s i o n

w a s f u r th e r s u p p o r t e d w i t h d a t a o b t a i n e d b y t h e C a l if o r n i a D e p a r t m e n t o f H i g h w a y s t h a t

i ll u s tr a te d a la r g e d i f f e r e n c e i n p a v e m e n t d e f l e c ti o n s o c c u r r i n g u n d e r s t a n d i n g a n d s l o w l y

m o v i n g w h e e l l o a d s ( V i n s o n 1 9 8 9) .

T h i s w o r k c o n t i n u e d i n t h e 1 9 6 0 s a n d 7 0 s . I t w a s n o t e d t h a t v e h i c l e s p e e d a n d

d e p t h b e n e a t h t h e p a v e m e n t s u r f a c e a r e o f g r ea t i m p o r t a n c e i n s e l e c t i n g th e a p p r o p r i a t e

ax i a l com pre s s ive s t r e s s pu l se t ime to u se i n r epea t ed l oad t e s ti ng . Ba sed o n the r e su lt s

o f a l i nea r e la s t ic f i n i t e e l emen t r ep re se n t a t i on o f a t yp i ca l pav em en t s t r uc tu r e ,

r e l a ti o n s h i p s c o n c e r n i n g t h e v a r i a t io n o f e q u i v a l e n t v e r t ic a l s t r e ss p u l s e t i m e w i t h v e h i c l e

v e l o c i t y a n d d e p t h w e r e e s t a b l is h e d ( V i n s o n 1 9 8 9) .



8 RESIL IENT MODULUS TESTING FOR PAVEMENT COMPONENTS

All of this work led to the adoption of AASHTO T274 in 1982. This standard

was the first modern procedure used to define the test method for resilient modulus. The

concept of resilient modulus was subsequently incorporated into the 1986 AASHTO

Guide for Design of Pavement Structures. During this time, the standard had varying

degrees of acceptance throughout the materials testing community.

In 1988, a thorough review was conducted of ASTM T274 by the LTPP Materials

Expert Task Group ETG) and the LTPP team. This group identified areas within the

standard that were ambiguous or that offered alternatives. Through this process, LTPP

Protocol P46,

Resilient Modulus of Unbound Granular Base/Subbase Materials and

Subgrade Soils, was developed and issued in 1989. Over the years, the protocol was

revised and amended and was issued in its final form in 1996. Subsequently, in 1999 P46

was balloted through the AASHTO process and was adopted with some modification) as

AASHTO standard T307-99, Determining the Resilient Modulus of Soils and Aggregate

Materials.

Over the past quarter o f a century, a great deal of practical research has been

undertaken in the pavement design and management community regarding resilient

modulus. All of this research cannot be documented herein, however, suffice it to say

that the reader can find ample research results in the literature. There is no doubt that the

state o f the practice of resilient modulus testing will be advanced through the adoption of

new technology and testing procedures. The reader is directed to Vinson 1989) for a

more detailed treatment of the history of resilient modulus.

O v e r v i e w o f R e s i l i e n t o d u l u s P r o t o c o ls

Protocol P46

P46 contains many conditions and requirements that apply only to the LTPP

program. For example, measurement of deformation outside of the test chamber is a

requirement that is very specific to the goals and objectives of the LTPP program.

Because o f the large numbers o f samples to be tested, the ETG that reviewed the protocol

decided that this was the most practical and efficient method. However, this method may

not apply to all test conditions. In addition, the compaction procedures were specifically

chosen for similar reasons.

Protocol P46 covers the following topics:

Scope

Testing Locations

Definitions

Applicable Documents

Unbound Materials Testing Prerequisites

Apparatus

Preparation of Test Specimens

Test Procedures

Calculations

Reporting

Compaction of Test Specimens



GROEGER ET AL ON AASHTO T307 19

Th e P46 pro toc o l i s su it ab l e fo r use by o rgan iza t i ons wi sh ing to pe r fo rm the i r

t e s t s exac t ly a s t hey we re cond uc ted b y LT PP for cor re l a t ion o r o the r purposes .

Ho we ver , i ts use a s a genera l te s t me thod b y o the r o rgan iza t i ons shou ld be con s ide red

careful ly .

A A S H T O T 3 0 7

A s m e n t i o n e d p r e v i o u s l y , T 3 0 7 w a s d e v e l o p e d p r i m a r i l y b y m o d i f y i n g L T P P

Pro toco l P46 . M any f ea tu res o f t he st andard a re s imi l a r t o P46 whi l e som e sec t ions have

b e e n m o d i f i e d t o f a c il it a te u s e o f t h e p r o c e d u r e b y a b r o a d e r r a n g e o f o r g a n iz a t io n s . A t

the t ime o f t he dev e lopm ent o f t h i s paper , t h i s is t he on ly t e s t s t andard a dopted b y

A A S H T O t o d e t e rm i n e r e s il ie n t m o d u l u s v a l u e s f r o m p a v e m e n t m a t e ri a ls .

A A S H T O T 3 0 7 c o v e r s th e f o l lo w i n g t o p ic s :

S c o p e

R e f e re n c e d D o c u m e n t s

T e r m i n o l o g y

S u m m a r y o f M e th o d

S ign i f i cance and Use

A p p a r a t u s

P r e p a r a ti o n o f T e s t S p e c i m e n s

T e s t P r o c e d u r e s

R e p o r t i n g

C o m p a c t io n o f T e st S p e c i m e n s

O f pa r t i cu l a r no t e , t he s t andard i nc ludes t he use o f e i the r hydrau l i c o r pneu m at i c

t e s t sys t em s and inc ludes add i ti ona l sec t i ons de t a i li ng com pac t ion by use o f a knead ing

appara tus .

P4 6 T30 7 S imi lar i ti e s and Di f fe rences

Bec ause T3 07 i s a d i r ec t descendan t o f P46 , i t st ands to r eason tha t t hey sha re

m an y s imi la r i ti e s . H ow eve r , t hey a l so con ta in som e d i f f e rences . Ta b le 1 h igh l igh t s t hese

s imi lar i t ies and di f ferences .

O t h e r P r o c e d u r e s

There a re severa l o the r t e s t p rocedu res deve loped , o r under deve lop m ent ,

t h r o u g h o u t t h e w o r l d . E a c h p r o c e d u r e h a s i ts o w n s t r en g t h s a n d w e a k n e s s e s . F o r

exam ple , N CH RP 1-28 Barksda l e e t a l. 1998) has p ropo sed new proced ures fo r t e s t ing

aspha l t and unboun d m ate r ia l s . Severa l o the r r e sea rcher s have a l so pu t fo r th rev i sed t e s t

p r o c e d u r es . F o r n o w , it s e e m s th a t A A S H T O T 3 0 7 , b a s e d p r i m a r i l y o n L T P P

dev e lopm ent e f fo r t s , i s t he s t a t e o f t he p rac t i ce wi th in t he U ni t ed S t a tes .



20 RESILIENT MO ULUS TESTING F O R P V EM E N T C O M P O N E N T S

Table l - Comparison of P46 and T3 7

Protocol Specification P46 T307

Type of Loading System Hydraulic Hydraulic/Pneumatic

Load Control Closed Loop Closed Loop

Load Cell Location External External

Deformation Measurement External External

Confining Fluid Air Air

Load Pulse Shape Haversine Haversine

Load Duration 0.1 s 0.1 s

Cycle Duration 1.0 s 1.0 to 3.0 s

Number of LVDTs 2 2

# ofpts per cycle 500 200

Specimen L/D Ratio >= 2:1 > = 2:1

Type of Compaction Static/Vibratory Static/Vibratory/Kneading

The next portion of this paper will involve a detailed discussion of various

technical aspects of the protocol.

oading System

LTPP protocol P46 and AASHTO T307 require a haversine loading waveform

with varying frequencies and magnitudes. Equipment manufacturers have gone

exclusively to fluid power to apply these loads. Mechanical testers employing cams,

levers, gear or screw drive, while suitable for static or slow displacement testing, prove

too cumbersome for repeated load, especially in a load-controlled mode.

Electromagnetic drive systems, while well suited for metal fatigue testing in resonant

drive machines at frequencies much higher than 10 Hz are not suitable for resilient

modulus testing. The high currents needed to produce repeated loads at 1 Hz and below

create a noisy environment to nearby electronic instrumentation. Fluid power options

open to the designer include:

9 fluid medium: air or hydraulic oil

9 control mode: open or closed-loop

A brief discussion of advantages and disadvantages of each follows:

Fluid Medium

Compressed air is a logical choice as a source of load power. It is non-messy, non-toxic,

and readily available in most labs. As an additional advantage, the noisy compressor can

be placed remote from the test lab. At normal line pressures, however, (100-125 psi)



GROIEGER ET AL ON AASHTO T307 21

upp e r l oad l imi t s a re 1 000 to 2000 lb fo r r ea so nab ly s i zed ac tua to r s . A l so , s i nce a i r i s

h i g h l y c o m p r e s s i b l e , c o n s i d e r a b l e e n e r g y i s e x p e n d e d t o c y c l e h i g h l o a d s c o n t i n u o u s l y .

C o m p r e s s i b i l i ty a l s o p l a c e s a l i m i t o n t h e q u i c k n e s s o f l o a d a p p l i c a t io n ( ri se t i m e t o

a t ta in fu l l load) .

Hy drau l i c f l u id (o i l) is we l l su i t ed a s a m eans o f f l u id pow er . Fo r example , a t

w o r k i n g p r e s s u r e s o f 2 5 0 0 t o 3 0 0 0 p s i , i t c a n b e v e r y q u i c k i n l o a d r is e t i m e , a n d a 5 k i p ,

2 i n . s tr o k e a c t u a t o r c a n b e v e r y s m a l l . T h e f ir st c o s t o f h y d r a u l i c s y s t e m s i s h i g h , th o u g h

t h e s e s y s t e m s a re m o r e c o m p l e x t h a n p n e u m a t i c s y s te m s . A d d i t i o n a l l y , t h e p u m p u n i t

u s u a l l y r e s id e s c l o s e t o t h e t e s t a p p ar a tu s , a n d m a y r e q u i r e e x t e r n a l c o o l i n g a s w e l l a s

n o i s e r e d u c i n g c a b i n e t r y . O i l l e a k a g e c a n p o t e n t i a l l y b e a p r o b l e m i n il l -m a i n t a i n e d

e q u i p m e n t .

P r o t o c o l P 4 6 a l lo w s o n l y h y d r a u l i c s y s te m s . T h i s t y p e o f s y s t e m w a s c h o s e n a s it

w a s b e l ie v e d b y t h e E T G t h at t hi s ty p e o f m a c h i n e w a s t h e b e s t t o p r o d u c e c o n s i s te n t a n d

r e p e a t a b l e r es i li e n t m o d u l u s v a l u e s . I t w a s a l s o c h o s e n t o r e d u c e a p o t e n t ia l s o u r c e o f

v a r i a b i li t y i n th e t e st i n g p r o c e s s . T h e L T P P p r o g r a m p r o c u r e d t h r e e l a b o r a to r i e s t o

con du c t so il s r e s i li en t mod u lu s t es t ing . As such , i t w as des i r ed t ha t e ach l ab u se t he s am e

t y p e o f e q u i p m e n t . B a s e d u p o n t h e s e r a t io n a l e , it w a s d e c i d e d th a t e a c h la b s h o u l d b e

e q u i p p e d w i t h a s e r v o - h y d r a u l i c te s t in g s y s t e m .

A s m e n t i o n e d , t h e s e s y s te m s a re r a t h e r e x p e n s i v e a n d s o m e D O T a n d u n i v e r s i t y

l a b o r a to r i e s d o u b t l e s s s ti ll e m p l o y p n e u m a t i c s y s t e m s s i n c e t h e y a r e a m u c h c h e a p e r

a l te r n a ti v e t o a h y d r a u l i c s y s te m . T h e r e b y , i t i s s u r m i s e d t h a t t h e A A S H T O c o m m i t t e e

t h a t d e v e l o p e d T 3 0 7 a l l o w e d th e u se o f s u c h s y s t e m s a s a c o m p a r a b l e s o lu t i o n . T h i s m a y

b e a v a l i d r at io n a l e . T o t h e a u t h o r s k n o w l e d g e t h e r e h a s n e v e r b e e n a c o m p a r i s o n s t u d y

c o n d u c t e d t o c o m p a r e t h e tw o a l te r n a ti v e s t o d e t e r m i n e t h e i r c o m p a r a b i l i ty . I t i s s tr o n g l y

s u g g e s t e d t h a t s u c h a s t u d y b e i m p l e m e n t e d p r i o r t o r e - d e v e l o p m e n t o f t h e T 3 0 7 t e st

p ro ced ure a s it i s exp ec t ed t he r e w i l l be s i gn i f i can t d i f f e r ences i n t he r e su l ts ob t a ined

f r o m a h y d r a u l i c v e r s u s p n e u m a t i c s y s t e m . M o s t s y s t e m s s o l d f o r r e s il ie n t m o d u l u s

t e s t in g t o d a y a r e o f t h e h y d r a u l i c v a r i et y .

C o n t r o l S y s t e m s

O p e n l o o p c o n t r o l s y s t e m s r e s p o n d t o a c o m m a n d i n p u t w i t h o u t r e g a r d t o c u r r e n t

o u t p u t s t a tu s o f l o a d o r d i s p l a c e m e n t o f t h e a c t u a to r . A g o o d e x a m p l e i s a c o n s t a n t - ra t e

t ri a xi a l l o a d f r a m e ( o l d e r st y le w i t h o u t s e r v o - m o t o r ) . T h e c o m m a n d i n p u t i s a s e t t in g a t a

c o n s t a n t s p e ed . O n c e s ta r te d t h e p l a t en m o v e s u n t il s h u t o ff . N o s e l f - a d ju s t i n g ta k e s

p l a c e t o m a i n t a i n s p e e d .

R e p e a t e d l o a d m a c h i n e s o f t h e o p e n - l o o p v a r i e t y u s e a s o u r c e o f c o n s t a n t p re s s u r e

t o d e r iv e t h e l o a d p u ls e . T y p i c a l l y , t h e a c t u a t o r c y l i n d e r is t o g g l e d b y a v a l v e b e t w e e n a

h i g h p r e s s u r e s o u r c e a n d a l o w p r e s s u r e s o u r c e t o g a i n t h e d e s i re d t r a i n o f l o ad p u l s es .

T h e c h i e f a d v a n t a g e s a r e s i m p l i c it y , re l ia b i li t y a n d l o w c o s t. T h e v a l v e s u s e d a r e r u g g e d

o n / o f f d e v i c e s w h i c h a r e e a s y t o s e r v i c e o r r e p l a ce , a n d t h e a c t u a t o r c a n b e s i n g le a c t i n g

( u n id i r ec t io n a l ). P r e s s u r e r e g u l a to r s w i t h o u t p u t g a u g e s c a n s u p p l y t h e h i g h a n d l o w

p r e s s u re ; t h e g a u g e s g i v e t h e o p e r a t o r a r o u g h i d e a o f a p p li e d l o a d s .

D u e t o a la c k o f

o n g o i n g c o n t r o l n o m o d e r n r e s i li e n t m o d u l u s s t a n d a r d a l l o w s u s e o f s u c h a s y s t e m .

C l o s e d l o o p c o n t r o l s y s t e m s e m p l o y a s e n s o r a t t h e a c t u a t o r o u t p u t t h a t c a n

m o n i t o r t h e d e s i re d v a r i a b le , e i t h e r lo a d o r d i s p la c e m e n t . T h e s i g n a l t h a t r e p o r t s th e




cu r r en t ou tpu t s ta tu s i s c a l l ed the f eedb ack s igna l . I t i s com par ed t o ano the r s i gna l , inpu t

c o m m a n d , a t a s u m m i n g p o in t . T h e d i ff e re n c e b e t w e e n t h e i n p u t c o m m a n d a n d o u t p u t

s t a tu s i s t h e e r r o r a n d i s u s e d t o d r i v e t h e a c t u a to r c o n t r o l v a l v e t o r a p i d l y m i n i m i z e t h e

e r ro r . T h e c h i e f a d v a n t a g e o f c l o s e d l o o p c o n t r o l is it s ab i l it y to f o l l o w c o m m a n d s i g n a l

i npu t chang es , w i th in the speed and amp l i t ude capab i l i ti e s o f t he ac tua to r . I ndeed , a

l a r g e i n d u s t r y h a s e v o l v e d i n t h e f i el d o f s t ru c t u ra l r e s p o n s e t e s ti n g , b o t h d e s t r u c ti v e a n d

n o n d e s t r u c t i v e , b a s e d o n t h e c a p a b il i ti e s o f c lo s e d l o o p c o n t r o l l e d a c t u a t o r s t o s i m u l a t e

f ie l d p h e n o m e n a . H o w e v e r , c l o s e d l o o p s y s t e m s a r e i n h e r e n t l y m o r e c o m p l e x a n d

e x p e n s i v e t h a n o p e n l o o p s y st e m s . A s e r v o a m p d r i v e s th e s e rv o v a l v e ; d y n a m i c

r e s p o n s e o f t h e c o m p l e t e s y st e m w i t h f e e d b a c k m u s t b e o p t i m i z e d o r t u n e d f o r t h e

m a t e r i a l s a n d t o a d f r a m e u s e d . P e r f o r m a n c e o f a n i m p r o p e r l y a d j u s te d s y s t e m c a n r a n g e

f r o m s l u g g i s h t o w i l d l y u n s t a b le a n d c a n p o t e n t i a ll y b e e x t r e m e l y d a n g e r o u s ( B r i c k m a n

1 9 8 9) . F o r t h e s e re a s o n s , n e i th e r P 4 6 n o r T 3 0 7 a l l o w s u s e o f o p e n - l o o p s y s t e m s .

L o a d e l l L o c a t i o n

B o t h P 4 6 a n d T 3 0 7 r e q u i r e t h e u s e o f a l o a d c el l m o u n t e d o u t s i d e t h e tr i ax i a l

c h a m b e r . T h i s i s o n e a r e a o f T 3 0 7 t h a t s h o u l d u n d e r g o s c r u t in y . F o r L T P P , th e r e w e r e a

l a r g e n u m b e r o f s a m p l e s t h a t n e e d e d t o b e te s te d . T h e r e f o r e , a f t er a p e r i o d o f p i l o t

t e s t in g a n d f o r e f f ic i e n c y c o n c e r n s , it w a s d e c i d e d t o m o u n t t h e l o a d c e l l a n d d e f o r m a t i o n

t r a n s d u c e r s o u t s i d e t h e c o n f i n i n g c h a m b e r . M a k i n g t h i s d e c i si o n m e a n s t h a t a g r e a t d e a l

o f e f f o r t m u s t b e e x p e n d e d e n s u r i n g t h a t t h e r e i s n o f r i c ti o n o r e x t r a n e o u s d e f o r m a t i o n s

i n t h e s y s t e m . T h i s t o p i c w a s a s o u r c e o f g r e a t a n g u i s h w i t h in L T P P d u e t o t h e v e r y ti g h t

t o l e r ances t ha t r e su l ted .

U n d e r n o r m a l c i r c u m s t a n c e s , i t s h o u l d b e e n t i r e ly a p p r o p r i a te , a n d p e r h a p s

adv i sed , t o m ou n t t he l oad ce ll w i th in t he t e s t cham ber . I n f ac t , t h i s is t he app ro ach used

b y s e v e r a l m a n u f a c t u r e rs . M o u n t i n g t h e lo a d c e ll w i t h i n th e c h a m b e r a l lo w s f o r m o r e

p r e c i s e c o n t r o l a n d a m o r e a c c u r a te r e a d i n g o f e x a c t l y t h e l o ad th e s p e c i m e n i s f e e l i n g .

T h e u p l i f t a d j u s t m e n t n e c e s s a r y t o a c c o u n t f o r t h e c o n f i n i n g p r e s s u r e c a n a l s o b e

n e g a t e d . A l l i n al l, m o u n t i n g t h e l o a d c e ll w i t h in t h e c h a m b e r s h o u l d b e c o n s i d e r e d a s a

su i t ab l e a l t e rna t i ve i n T307 .

W i t h t h a t b e i n g s a id , h o w e v e r , i f t h e l o a d c e l l i s m o u n t e d w i t h i n t h e c h a m b e r ,

t h e n t h e d e f o r m a t i o n m e a s u r e m e n t d e v i c e s m u s t b e m o u n t e d i n s i d e t h e c h a m b e r a s w e l l

(u sua l l y on t he spec imen) . Th i s i s nec es sa ry bec aus e a t yp i ca l l oad ce l l i s e s sen t i a l l y a

d e v i c e t h a t p r o v i d e s i t r e a d i n g s t h r o u g h s t r a in m e a s u r e m e n t s . T h e r e b y t h e l o a d c e ll h a s

t o d e f l e c t t o re a d l o a d . I f th e d e f o r m a t i o n d e v i c e s a r e m o u n t e d o u t s i d e t h e c h a m b e r , t h is

s tr a in w i ll b e c o m e p a r t o f t h e s p e c i m e n s t ra i n re a d i n g . O b v i o u s l y , t h is i s n o t a d e s i r e d

o u t c o m e . T h e r e b y , i f t h e l o a d c e ll is m o u n t e d i n t e rn a l ly , c a r e s h o u l d b e t a k e n t o l o c a t e

t h e d e f o r m a t i o n m e a s u r e m e n t d e v i c e s i n a n a r e a t h a t w i l l n o t s e e t h is d e f o rm a t i o n .

D e f o r m a t io n M e a s u r em e n t

S i m i l a rl y , b o t h P 4 6 a n d T 3 0 7 r e q u i r e u s e o f d e f o r m a t i o n d e v i c e s m o u n t e d o u t s i d e

t h e t r ia x i al c h a m b e r . T h i s is a n o t h e r a r e a o f T 3 0 7 t h a t s h o u l d u n d e r g o s c r u t in y . T h e

s a m e r a t io n a l e a p p l i e s h e r e a s w a s d i s c u s s e d f o r th e l o a d c e ll s. F o r L T P P , i t w a s e f f i c ie n t

a n d r e a s o n a b l e t o u se tr a n s d u c e r s m o u n t e d o n l y o n t h e o u t s i d e o f t h e c h a m b e r . O n e



GR OEGER ET AL ON AASH TO T 3 0 7 2 3

o v e r r i d i n g re a s o n f o r t h is d e c i s i o n w a s t h a t L V D T s m o u n t e d o n t h e s p e c i m e n m a y s li p

d u r i n g t es t in g . T h i s a c t i o n m a y o r m a y n o t b e r e a d i ly a p p a r e n t t o t h e o p e r a to r . I f t h is

happ ens , t he t e st m us t be ha l t ed and t he en t i r e p roc edu re r epea t ed . Th i s ha s t he po t en t i a l

t o c a u s e a g r e a t d e a l o f i n e f f i c i e n c y w h e n t e s ti n g n u m e r o u s s a m p l e s .

H o w e v e r , i t h a s b e e n t h e a u t h o r ' s r e c e nt e x p e r i en c e t h a t m o u n t i n g t h e L V D T s

d i r e c t l y o n t h e s a m p l e h a s it s m e r i ts . T h i s a p p r o a c h n eg a t e s a n y s l o p i n t h e s y s t e m t h a t

m a y a p p e a r a s s p e c i m e n s t r ai n w h e n m e a s u r i n g o u t s i d e t h e c h a m b e r . I t a l s o a ll e v i at e s

c o n c e r n s w i t h s t re s s c o n c e n t r a t i o n s t h a t a r e e v i d e n t a t t h e e n d s o f t h e s p e c i m e n s .

H o w e v e r , g r e a t c a re m u s t b e u s e d w i t h t h is a p p r o a c h . T h e o p e r a t o r m u s t e n s u r e t h a t t h e

d e f o r m a t i o n m e a s u r e m e n t d e v i c e s d o n o t s li p d u r in g t h e t es t. A l s o , d e p e n d i n g o n t h e

c o n f i g u r a t io n , t h e y m u s t b e r e m o v e d p r i o r t o c o n d u c t o f a n y t y p e o f s h e a r te s t.

I t i s v e r y s t r o n g l y r e c o m m e n d e d t h a t t hi s i s s u e b e re v i s it e d d u r i n g a n y p r o p o s e d

r e v i s io n t o T 3 0 7 . I n t e rn a l d e f o r m a t i o n m e a s u r e m e n t c a n w o r k a n d u n d e r c e r t a in

c i r c u m s t a n c e s m a y p r o v i d e m o r e a c c u r a t e v a l u e s t h a n m e a s u r i n g o u t s i d e th e c h a m b e r .

F ina l l y , P46 r equ i r e s t he bo t tom o f t he t ri ax i al c e l l be bo l t ed d ow n to t he te s t t ab l e

w h i l e T 3 0 7 d o e s n o t c o n t a i n s u c h a p r o v i s io n . I f t h e c o n f i g u r a t io n s h o w n i n T 3 0 7 i s u s e d

( d e f o r m a t i o n m e a s u r e d o u t s id e t h e c h a m b e r ) i t h a s b e e n d e m o n s t r a t e d t h a t it is v e r y

i m p o r t a n t t o b o l t t h e c h a m b e r d o w n . I n th i s t e st p r o c e d u r e w e a r e m e a s u r i n g v e r y , v e r y

s m a l l st ra in s . I f t h e b o t t o m o f t h e p l a t e i s a l l o w e d to f l o a t , s m a l l d e f o r m a t i o n s a r e

p i c k e d u p b y t h e d e f o r m a t i o n tr a n s d u c e r s m o u n t e d o u t s id e o f t h e c h a m b e r . B o l t i n g t h e

s y s t e m d o w n w i l l h e l p t o re d u c e t h is p r o b l e m . T h i s i s a v e r y i m p o r t a n t p a rt o f th e

p r o c e d u r e a n d s h o u l d b e s t ri c tl y f o l l o w e d . I t i s r e c o m m e n d e d t h a t T 3 0 7 b e r e v i s e d t o

a c c o m m o d a t e th i s re q u i r em e n t .

onfining Fluid

L T P P P r o t o c o l P 4 6 a n d A A S H T O T 3 0 7 b o t h r e q u ir e t h e u s e o f a ir a s t h e

c o n f i n i n g f l u id . P r a c t ic a l ly , th is i s t h e b e s t r e c o m m e n d a t i o n . H o w e v e r , t o p l a y d e v i l ' s

a d v o c a t e , u n d e r c e r t a i n c i r c u m s t a n c e s w a t e r c a n b e a p p r o p r i a t e a s a c o n f i n i n g m e d i u m .

I n th e f i n a l a n a l y s is , h o w e v e r , p r a c t i c a l ly s p e a k i n g w a t e r c a n b e m e s s y a n d m a y

c o m p r o m i s e t h e s p e c i m e n ' s i n t e g r i ty i f a le a k o r o t h e r f a il u re o c c u r s . I t i s r e c o m m e n d e d

t h a t a ir r e m a i n t h e o n l y c h o i c e i n th i s r eg a r d . P r e s s u r e t r a n s d u c e r s t h a t c a n a u t o m a t i c a l ly

r e g u l a t e t h e a ir p r e ss u r e w i t h in a c h a m b e r a r e r e l a ti v e l y c h e a p a n d p r o v i d e f o r a c c u r a t e

c o n t r o l o f p re s s u re . I n a n y c a s e, th e t e s te r s h o u l d m o n i t o r th i s i te m v e r y c a r e f u l l y a n d

r e c o r d t h e a c t u a l p r e s s u r e i n t h e c h a m b e r , n o t t h e n o m i n a l p r e s su r e . E x p e r i e n c e h a s

s h o w n t h a t s o m e u s e r s o n l y r e c o r d w h a t t h e p r es s u r e s h o u l d b e , a n d n o t w h a t i t a c t u a l ly

i s. T h i s c a n h a v e d i r e c o n s e q u e n c e s w h e n a n a l y z i n g t e st r es u lt s.

Load Pulse Shape

B o t h p r o to c o l s a ll o w o n l y a h a v e r si n e w a v e f o r m . T h i s ty p e o f w a v e f o r m h a s

b e e n p r o v e n t h r o u g h r e s e a r c h t o b e f a i rl y re p r e s e n t a ti v e o f th e e f f e c t o f a m o v i n g w h e e l

l o a d o v e r a p a v e m e n t s e c t i o n ( V i n s o n 1 9 8 9 ). T h e r e s h o u l d b e n o a r g u m e n t a s t o th e

v a l i d i t y o f th i s p re m i s e . H o w e v e r , o n e t o p i c th a t h a s b e e n a s u b j e c t o f d e b a t e w i t h i n t h e

L T P P p r o g r a m is - w h a t c o n s t it u te s a h a v e r s in e w a v e f o r m ? H o w c l o s e m u s t y o u b e t o

t h e t h eo r e t ic a l e q u a t i o n t o h a v e i t b e c o n s i d e r e d c o r r e c t ? S o m e s y s t e m s o n t h e m a r k e t




t o d a y c o m e w i t h " a c c e p t a n c e b a n d s " a n d a u t o m a t i c P I D s e t t in g s . B u t e a c h i s d i ff e re n t .

T h i s c a n p o t e n t i a ll y h a v e a s i g n i f i c an t i m p a c t o n m o d u l u s v a l u e s d u e t o d i f f e r e n c e s i n

app l i ed ene rgy .

T o a n s w e r t h i s q u e s t i o n w i t h i n L T P P , t h e f o l l o w i n g a c c e p t a n c e c r i t e ri a w e r e

a d o p t e d :

P lo t t he l oad va lues ( r ead ings f rom the l oad ce l l ) ve r sus t ime fo r a r ep re sen t a t i ve

c y c l e ( s ) a t e a c h l o a d . S u p e r i m p o s e a n i d e a l l o a d o v e r th i s t y p i c a l lo a d p u l s e .

C o m p a r e t h e a c tu a l l o a d p u l s e w i t h t h e id e a l l o ad p u ls e . F o r r e s il ie n t m o d u l u s

t e s t ing , t h i s c ri t e r i on is a s f o l l ows : Co ns t ruc t a t heo re t i ca l i dea l l oad ing pu l se fo r

e a c h l o a d s e q u e n c e f r o m t h e m a x i m u m l o a d an d t h e 0 .1 s e c o n d l o a d i n g d u r a t i o n

s p e c i f ie d i n th e p r o t o c o l . T h e p e a k t h e o r et i c al l o a d i s m a t c h e d i n ti m e w i t h t h e

p e a k r e c o r d e d l o a d o f a g i v e n s e q u e n c e . A n a c c e p t a n c e t o l e ra n c e b a n d i s t h e n

c rea t ed a ro und the t heo re t i ca l l oad pu l se t ha t i s u sed t o f l ag suspec t da t a f a l l ing

o u t s id e o f t h e b a n d. T h e d e v e l o p m e n t o f t h e m i n i m u m a n d m a x i m u m v a lu e s o f

t h e a c c e p t a n c e b a n d i s b a s e d o n t h e f o l l o w i n g c o n s i d e r a t i o n s :

9 A c c e p t a n c e t o l e ra n c e r a n g e . A • 1 0 p e r c e n t v a r i a t io n f r o m th e t h e o r e ti c a l l o a d

i s j u d g e d t o b e a c c e p t a b le . I n c o m b i n a t i o n w i t h t h e o t h e r c h e c k s , t h is r a n g e i s

e f f e c t iv e a t h i g h e r l o a d l e v e ls a n d t h o s e n e a r th e p e ak . H o w e v e r , a t l o w l o a d

l e v e ls t h is r a n g e m a y c r e a t e a n u n r e a s o n a b l y t i g h t t o le r a n c e .

9 Se rv o va lve r e sponse time . A 4- 0 .006 secon d t ime sh i ft i n l oad f rom the

theo re t i ca l l oad pu l se i s r ea son ab le t o a l l ow fo r the phy s i ca l l imi t a t i ons on t he

r e s p o n s e t i m e o f t h e s e rv o h y d r a u l i c s y s t e m . T h i s w i l l p r o v i d e a r e a s o n a b l e

t o l e ra n c e b a n d t h a t w i l l b e e f f e c t iv e a t i n t e rm e d i a t e l o a d i n g a n d u n l o a d i n g

p o r t i o n s o f t h e l o a d c y c l e .

9 R e s o l u t i o n o f t h e e l e c tr o n i c lo a d c e ll . T h e r e s o l u t io n o f t h e e l e c t ro n i c l o a d

ce l l gene ra l l y u sed i n r e s i li en t m odu lus t e s t i ng fo r t he se ma te r i a l s i s + 4 .4 N .

T h e r e f o r e , a r a n g e o f t w i c e t h e m i n i m u m r e s o l u t io n o f t h e l o a d c e l l is u s e d ;

i .e . , 4- 8 . 8 N . Th i s r ange p rov id es acce p t ab l e t o l e r ances fo r t e s t i ng a t l ow loa d

leve ls .

9 L o g i c . T h e m i n i m u m l o a d a l l o w e d i s 0 N .

F o r e a c h t i m e s te p i n t h e l o a d c u r v e , th e t o l e r a n c e r a n g e f r o m a l l o f t h e s e

c o m p o n e n t s i s c o m p u t e d . T h e m a x i m u m v a l u e o f t h es e th r e e c o m p o n e n t s is

s e l e c te d a s t h e u p p e r t o l e r a n c e l im i t , w h i l e t h e m i n i m u m v a l u e i s u s e d f o r th e

low er l imi t a t e ach t ime s t ep . Ov e r the en t i r e r ange o f l oad ing , f i ve po in t s a r e

a l l o w e d t o b e o u t o f t o l e ra n c e b e f o r e t h e l o a d c y c l e i s c o n s i d e r e d f a i l e d ( A l a v i e t

al . 1997).

T h i s i s b u t o n e a p p r o a c h t o d e te r m i n i n g i f a w a v e f o r m i s a c c e p ta b l e . I n g e n e ra l ,

i t i s r e c o m m e n d e d t h a t a c c e p t a n c e c ri t er i a b e e s t a b l is h e d i n T 3 0 7 a s w e l l . T h i s w i l l w o r k

to a s s i s t i n r epea t ab i l i t y and l ower va r i ab i l i t y bo th w i th in and be tween l abo ra to r i e s .



GR OE GE R E T A L ON A A S H TO T3 0 7 2 5

L o a d a n d y c l e D u r a t i o n

P 4 6 a n d T 3 0 7 b o t h a ll o w 0 .1 s e c o n d lo a d i n g p er i o ds . H o w e v e r , P 4 6 o n l y a ll o w s

a c y c l e d u r a t io n o f 1 .0 s e c o n d w h i l e T 3 0 7 a l lo w s 3 . 0 s e c o n d s . I t i s b e l i e v e d t h a t th e

d i f f e re n c e i n t h e s e t w o s p e c i f ic a t i o n s i s p r i m a r i l y r e l a te d t o t h e u s e o f h y d r a u l i c a n d

p n e u m a t i c t e st s y s te m s . D u e t o t h e c o m p r e s s i b i l i ty o f ai r, p n e u m a t i c s y s t e m s g e n e r a l l y

r e q u i re m o r e t im e t o r a m p u p f o r e a c h lo a d c y c l e . T h e r e f o r e t h e y r e q u i re a n a d d i t io n a l

t w o s e c o n d s to p e r f o r m t h e c y c le . H y d r a u l i c s y s te m s a r e im m e d i a t e l y r e a d y t o p e r f o r m

t h e n e x t l o a d c y c l e . I f p n e u m a t i c s y s t e m s a r e r e t ai n e d w i t h i n T 3 0 7 , t h e n t h is r e q u i r e m e n t

s h o u l d b e r e t ai n e d . I f, h o w e v e r , t h e s t a n d a r d i s m o d i f i e d t o o n l y a l l o w h y d r a u l i c

s y s t e m s , i t i s r e c o m m e n d e d t h a t t h e st a n d a r d c o n t a i n e d in P 4 6 b e a p p li e d. T h e r e i s s o m e

c o n c e r n o n t h e a u t h o r ' s p a r t t h a t u se o f b o t h p n e u m a t i c a n d h y d r a u l i c s y s t e m s i n a

m a t e r i a ls s t u d y o r i n t e r - la b o r a t o r y c o m p a r i s o n m a y y i e l d a g r e a t d e a l o f v a ri a b i li t y

a l t h o u g h a d m i t t e d l y w e h a v e n o d a t a to b a c k u p t h is c l a im . T h e r e b y , t h i s i ss u e s h o u l d b e

g ive n cons ide ra t i on a t a la t e r t ime .

N u m b e r a n d T y p e o f L V D T s

B o t h p r o t o c o l s r e q u i r e th e u s e o f t w o s p r i n g - l o a d e d L V D T s . I n t h e c a s e o f P 4 6 ,

t h is i s r e q u i r e d d u e t o e f f i c i e n c y a n d a c c u r a c y c o n si d e r a ti o n s . T h e o u t p u t s o f t h e L V D T s

w e r e u s e d t o d e t e r m i n e i f t h e s a m p l e w a s r o c k i n g ( a n i n d i c a ti o n t h a t t h e s a m p l e i s

i n c o r r e c t l y m o u n t e d i n th e t r ia x ia l c h a m b e r ) . T h e r e i s n o r e a l r e a s o n h o w e v e r to l i m i t th e

n u m b e r t o tw o . T h e r e a r e s o m e t e st i n g c o n f i g u r a t i o n s th a t u t i li z e th r e e o r m o r e L V D T s .

I t i s o u r r e c o m m e n d a t i o n t h a t t h e s p e c i f ic a t i o n al l o w tw o o r m o r e L V D T s . T h i s

r e c o m m e n d a t i o n g o e s h a n d - i n - h a n d w i t h t h e p r io r d i s c u s s i o n re l a te d t o i n s i d e v e r s u s

o u t s id e L V D T p l a ce m e n t .

A s f a r a s t h e ty p e o f L V D T is c o n c e rn e d , i t i s h i g h l y r e c o m m e n d e d t h at L V D T s

o t h e r th a n s p r i n g - l o a d e d b e a l l o w e d i n t h e te s t p r o c e d u r e . T h e r e a r e m a n y t y p e s o f

L V D T s o n th e m a r k e t t o d a y a n d e a c h h a s it s a d v a n t a g e s a n d d i sa d v a n t a g e s . A l s o , t h e

t e c h n o l o g y i s a l w a y s e v o l v i n g a n d th e u s e o f n o n - c o n t a c t d e f o r m a t i o n t r a n s d u c e r s i s

p r o b a b l y n o t f a r o f f. O t h e r t y p es o f d e f o rm a t i o n m e a s u r e m e n t d e v i c e s s h o u l d b e a l l o w e d

i n t h e p r o t o c o l . T h e s p e c i f i c a t io n s h o u l d b e re d e v e l o p e d w i t h a p e r f o r m a n c e b a s e d

s c o p e . T h e p r o t o c o l s h o u l d o n l y s p e c i f y t h e a c c u r a c y o f t h e d e v i c e a n d l e a v e t h e c h o i c e

t o a p p l ic a t i o n e n g i n e e r s w h o c a n b e s t d e t e rm i n e h o w t o g e t t h e j o b d o n e . T h i s p o i n t

need s a g r ea t dea l o f a t t en t ion i n t he cu r r en t T30 7 p ro toc o l .

N u m b e r o f P o i n ts p e r y c l e

T h e r e h a s b e e n m u c h d i s c u s s io n c o n c e m i n g t h e n u m b e r o f d a t a p o i n ts t h a t m u s t

b e c o l l e c t e d d u r i n g o n e c y c l e o f a r e si li e n t m o d u l u s t e st . P 4 6 r e q u i r e s 5 0 0 p o i n t s p e r

s e c o n d w h i l e T 3 0 7 r e c o m m e n d s a m i n i m u m o f 2 0 0 p o in t s p e r s ec o n d . W i t h in t h e L T P P

p r o g r a m , a g r e a t d e a l o f e ff o r t w a s d e d i c a t e d t o th i s i ss u e . F r o m o u r e x p e r i e n c e , i t w a s

d e t e r m i n e d t h a t 2 0 0 p o i n t s ( a s s u m i n g a c o n s t a n t s a m p l i n g r at e) w a s N O T a d e q u a t e t o

f u l ly c h a ra c t er i ze t h e t ru e s h a p e o f th e c u r v e. S o m e s y s t e m s e m p l o y a s y s t e m w h e r e b y

100 po in t s a r e co l l ec t ed wi th in t he f i r s t 0 .1 s eco nd and 100 po in t s a r e co l l ec t ed i n t he

r em a in ing cyc l e du ra t i on (o r som e s imi l a r log i c ) . W hi l e i t i s ag reed t ha t th i s s e rves a




comparable goal as the LTPP option, it is not implemented consistently among software

developers. Thereby the 500 points per second criteria serves to standardize this part of

the procedure. Modem data acquisition systems and software data reduction programs

should have no problem performing this task. The authors would argue that systems that

employ data acquisition systems that cannot perform this requirement should not be used

for resilient modulus testing. In any case, these criteria should be formalized and

minimums should be avoided. Standardization is the key to producing solid resilient

modulus results.

Specimen Size

Sample size was an important issue for the LTPP program. The sample size

chosen was highly dependent on the amount of material that could be obtained from a

given layer in the pavement structure. Therefore, the smallest sample sizes possible were

selected. However, the sample sizes were determined by using the criteria outlined in

T307 which is still very much relevant today. For LTPP procedures, Type 2 (generally

cohesive) samples are molded in 2.8 inch diameter molds (to replicate a thinwall tube

sample) and type 1 (generally non-cohesive) materials are molded in 6 inch molds. In

T307, various specimen sizes are allowed as long as the diameter is greater than five

times the nominal aggregate size. Additionally, both protocols require the L/D ratio to be

greater than 2:1.

For LTPP, it was necessary to be extremely precise in this regard to ensure

repeatability and consistency. The AASHTO approach makes a lot of sense for general

testing and it is recommended that it be retained in the procedure in its current form.

ompaction Param eters

Each protocol has a similar approach to specifying target density and moisture

parameters. For LTPP General Pavement Studies (and thus P46), the first choice was to

compact specimens to approximate the in situ wet density and moisture content. This

requirement was instituted in an attempt to better correlate laboratory test results and

those from the analysis of deflection measurements performed immediately prior to

sampling. It is important to recognize that establishing this correlation is an important

objective of the LTPP program. Where in situ information was not available, a consistent

and repeatable compaction density/moisture was desired. Therefore, after consultation

with many experts, it was decided to compact all other specimens, including Specific

Pavement Studies (SPS) samples, at optimum moisture and 95 percent maximum dry

density. This was done to approximate construction specifications for most materials.

T307 requires a similar approach except that reconstituted specimens that have no

field density/moisture data are compacted to parameters selected by the agency.

It should be noted that the compaction parameters selected for P46 were based

upon the unique needs of the program. It is suggested that T307 be revised to allow

compaction parameters that suit the objective of the testing process. For example, i f in

situ testing conditions are most important then these compaction parameters should be

specified, if standard density and moisture parameters are appropriate, then these should

be used. The way in which T307 is currently worded may be able to accommodate this



GR OEGER ET AL ON AASH TO T 3 0 7 2 7

sub t le ty ; how ever , the ve rb i age cou ld be imp roved . For exam ple , t he i r does no t need to

b e a h i e r a r c h y in t h e s a m p l e c o m p a c t i o n a re a to d u p l i c at e P 4 6. E a c h s e t o f c o m p a c t i o n

param ete r s is appropr i a t e fo r a g iven si tua t ion . In o the r words , t he r ange o f com pac t ion

param ete r s used i s h igh ly dependen t on t he purpose beh ind the r e s i li en t mod ulus t e s t i ng

p r o g r a m . I t m a y b e u n s u i t a b le t o u s e i n s it u m o i s tu r e / d e n s it y p a r a m e t e r s f o r p a v e m e n t

des ign . A m ore su i t ab l e se t o f pa ram ete r s wou ld be r e la t ed to t he mo i s tu re and dens i t y

upon l aye r p l ace m ent o r impro vem ent . In genera l , th i s is sue should be r ev i s i ted i f T307

is revised .

ompact ion Procedures

Pro toco l P46 a l l ows s t a ti c comp ac t ion fo r t ype 2 ma te r i a l s (genera l l y cohe s ive )

a n d v i b r a t o r y c o m p a c t i o n f o r t y p e 1 m a t e r i a ls ( g e n e r a ll y n o n - c o h e s i v e ). A A S H T O T 3 0 7

a l lo w s s i m i la r r e q u ir e m e n t s w i t h t h e a d d i t io n o f a l lo w a n c e o f k n e a d i n g c o m p a c t i o n f o r

type 2 ma te r i a l s . On ce aga in , t he te s t pa ram ete r s fo r P46 w ere chosen fo r e f fi c i ency ,

cons i s t ency , and r epea t ab i l i t y concerns . These p roced ures a r e ve ry spec i f i c t o t he

p r o g r a m . T h e r e f o r e , i t w a s v e r y p r u d e n t f o r t h e c o m m i t t e e th a t a d o p t e d T 3 0 7 t o a l lo w

u s e o f k n e a d i n g c o m p a c t i o n a s t h is t y p e o f c o m p a c t i o n h a s b e e n s h o w n t o b e s t r e p r e s e n t

the conf igura t i on o f i n s i tu pa r ti c l e s in a subgrade . Ho we ver , g rea t ca re shou ld be

exerc i sed fo r in t r a - o r in t e r - labora to ry t e st i ng comp ar i son programs . I t s eem s obvious ,

b u t t h e s a m e c o m p a c t i o n p r o ce d u r e s, e q u i p m e n t , a n d p a r a m e t e r s s h o u ld b e u s e d t o

per fo rm the compa r i son . The T307 p ro toco l appear s to be so l id in th i s a r ea and the

a u t h o r ' s h a v e n o r e c o m m e n d a t i o n s i n th i s r eg a r d.

Q u i ck S h ea r T es t

B o t h P 4 6 a n d T 3 0 7 re q u i re a Q u i c k S h e a r T e s t t o b e p e r f o r m e d . T h i s p a r t o f

t h e p r o c e d u r e w a s a d d e d t o P 4 6 v e r y l at e in t h e p r o t o c o l d e v e l o p m e n t p r o c e s s b e c a u s e o f

shor t com ings i n t he overa l l LTPP ma te r i a ls cha rac t e r i za t ion p ro gram ( i.e . a so i l s t r eng th

t es t wa s needed) . I t i s no t a necessa ry pa r t o f t he re s i li en t mo dulus p rocedure . B y

spec i fy ing the qu i ck sh ea r te s t, the con f igura t ion o f t he equ ipm ent used to pe r form the

t es t chang es d ram at i ca l l y and the re su l t ing sens i t i v it y o f t he sys t em suf fe rs . In genera l ,

t he use r mu s t use a l oad ce l l m uch l a rge r t han wou ld be need ed to pe r fo rm the t e s t in t he

f i rs t p l ace . There fore , t he re i s a po t en t i a l l os s o f accuracy in pe r form anc e o f the

procedure .

I t is h ig h l y r e c o m m e n d e d t h a t t h e Q u i c k S h e a r T e s t b e d e l e te d f r o m A A S H T O

T307. I t i s a t o t a l l y sepa ra t e p roced ure t ha t was t acked on to P46 and r ea l l y has no

bus iness a s a pa r t o f t he p rocedure . I t s use can ac tua l ly com prom ise t he accu racy and

sens i t i v i ty o f the eq u ipm ent used to pe r f orm the r e s il i en t mo dulus p roced ure . I f a

s t reng th t e s t is des ir ed , cons ide ra t i on should b e g iv en to us ing d i f f e ren t equ ipm ent and

sam ples to pe r form the te s t. Ge nera l l y speak ing , t he equ ipme nt used to pe r fo rm res il i en t

m odu lus t e s t i ng should no t be used fo r pe r fo rm ing s t reng th t e st s .



8 RESILIENT MODULUS TESTING FOR PAVEMENT COMPONENTS

S u m m a r y a n d o n c lu s i on s

T h e c u r r en t A A S H T O p ro t o c o l f o r d e t erm i n a ti o n o f r e s il ie n t m o d u l u s o f s o i ls a n d

aggrega te ma te r ia l (T307-99) i s based l a rge ly on Lo ng Term Pav em ent Pe r fo rma nce

(LTP P) P ro toco l P46 . This paper has p rov ided a background o f the reasons and ra tiona le

b e h i n d s o m e o f t h e m a j o r t e c h n ic a l a s pe c ts o f P 4 6 , a n d b y d i r e ct a s s o ci a ti o n , A A S H T O

T307. The paper a lso of fe red sugges t ions fo r impro vem ent o r mo di f ica t ion of T3 07 . I t i s

hop ed tha t th i s d i scuss ion wi l l l ead to a d eeper unders tand ing of the t e s t p roce dure and

perhaps fos te r a d i scussion o f the d i rec t ion the p rocedure should fo l low in the fu ture .

I t is hoped tha t the reader has deve loped an und ers tand ing o f why the tes t

p roced ure was de ve loped as i t was , and no t jus t

how

i t i s perfo rme d. This discuss ion is

c r i ti ca l to com prehens ion o f the l imi ta tions o f T307 and w as presen ted to fos te r a

d i scuss ion o f poss ib le improvem ents tha t can be m ade in the fu ture. I t is in tended tha t an

open d i scuss ion of the s treng ths and weaknesses o fT 30 7 w i ll l ead to a more robus t t e s t

p roc edure tha t can b e u sed to genera te repea tab le , accura te , and cons i s ten t re s i li en t

mo dulus da ta fo r use in pavem ent des ign and eva lua t ion .

R e f e r e n c e s

Alavi , S . , M erport , T . , W ilson, T . , G roeger , J ., Lope z, A. , Janu ary 1997, LT PP Ma teria ls

Charac te r iza t ion P rogram: Res i l i en t M odulus o f Unb ound M ate r ia ls (LT PP

Pro toco l P46) Lab ora tory S ta rtup and Qu a l i ty Cont ro l P roced ure , Rep or t No.

F H W A -R D -9 6 -1 7 6 , U . S . D e p a r t m e n t o f T ra n sp o r ta t io n , F e d e ra l H i g h w a y

Ad minis t ra t ion, M cLe an, Virginia.

Bark sdale , R. D. , Alba, J . , Kh osla , N. P . , Kim, R. K. , Lamb e, P . C. , and R ahm an, M . S . ,

1998,

NCHRP Web Document 14 Laboratory Determination of Resilient

Modulus for Flexible Pavement Design,

Pro jec t 1 -28 F ina l Repo r t , Na t iona l

C o o p e ra t i v e H i g h w a y R e s e a rc h P ro g ra m , T ra n s p o r t at io n R e s e a rc h B o a rd ,

Na t iona l Resea rch Counc i l , Washing ton , D.C.

Br ickman , A. , 1989, An O verv iew o f Res i l ien t M odulus Tes t Sys tem s , Proceedings of

the Workshop on Resilient Modulus Testing,

Orego n S ta te Un ive rs ity , Corva l l i s ,

Oregon .

L A W P C S , a D i v i s i o n o f L a w E n g i n e e r in g & E n v i ro n m e n t a l S e rv i c e s, I n c. , a n d

Ax iom Dec is ion Sys tems , Inc , 2002 , G uide for De te rm in ing Des ign Res i l i en t

M odulus Va lues fo r Unb ound M ate r ia ls , LTPP CD-ROMProduct, L T P P T e a m ,

Federa l H ighw ay A dminis t ra tion , Mc Lean , Vi rg in ia .

Rada , G . R . , Groeg er , J . L . , Schm alze r , P . N. , and Lop ez , A. , 2003 , Res i l i en t M odulus

Tes t ing of Un boun d Mate rial s: LT PP ' s Learn ing Exp er ience ,

Resilient Modulus

Testing or Pavement Components, ASTM STP 1437,

G.N. Durham, A.W. Marr ,

and W .L . De Gro f f , Eds. , A mer ican S oc ie ty fo r Tes t ing and Mate r ia ls , W es t

C o n s h o h o c k e n , P A .



GROEGER ET AL ON AASHTO T307

9

Vinson, T. S., 1989, Fundam entals o f Resilient M odulus Testing ,

Proceedings of the

Workshop on Resilient Modulus Testing Oregon State University, Corvallis,

Oregon.



Richard L . Bo udreau t

R e p e a t a b i l i t y o f t h e R e s i l i e n t M o d u l u s T e s t P r o c e d u r e

R e f e r e n c e : Boudreau, R. L., "Repeatability o f t h e R e s i li e n t M o d u l u s T e s t

P r o c e d u r e , " A ST M S TP 1437, Res i l i en t Modu lus Tes t ing f or Pavem en t Componen ts ,

G. N. Durham, W. A. Marr, and W. L. De Groff, Eds., ASTM International, West

Conshohocken, PA, 2003.

A b s t r a c t : Through the work of the Strategic Highway Research Program (SHRP, 1987-

1992) and the Federal Highway Administration (FHWA, 1992-present), the government

has provided financial and technical assistance to develop and improve a laboratory test

method to determine the resilient modulus properties of unbound materials. Although the

work -par t of the Long Term Pavement Performance (LTPP) study - has led towards

the adoption of test procedure T307-99 in the current release of the American Association

of State Highway and Transportation Officials (AASHTO) Tests, many skeptics insist

that the method does not lend itself towards repeatable, reproducible test results.

This paper acknowledges that the work conducted by SHRP and FHWA focused

primarily upon developing a test method that would be relatively simple and highly

productive with less variability inherent in the previous, existing test procedure.

Variables not investigated included compaction methodology, instrumentation location

and sensitivities to other influencing factors such as precision of confining pressure,

waveform control, membrane thickness and porous stone properties. Additionally, the

testing program did not successfully establish a precision and bias statement for the test

method utilized.

The repeatability of the test is examined by utilizing eight replicated test specimen

sub sampled from a homogenous Alabama soil and nineteen replicated test specimen sub

sampled from a homogenous Georgia soil. Each test specimen was prepared using the

five-lift static compaction method. All specimens were tested within the range of el

pound per cubic foot density and e0.4 percent moisture content, thus minimizing

variations o f results due to material variation. Averages, standard deviations, and

coefficients o f variation (c.v.) were determined for resilient modulus values calculated at

each load sequence, resulting in c.v.s of below 4.5%. The resilient modulus values were

_ K2 K5 -

calculated using the constitutive model: Mr - KI (So) ($3) in order to normalize the

data for comparative purposes.

The test method can promote repeatable test results, although much more testing is

recommended to produce precision and bias statements within and between laboratories.

K e y w o r d s :

resilient modulus, soil stiffness, subgrade

1President, Boudreau Engineering, Inc., 5392 Blue Iris Court, Norcross, GA 30092.

30

Copyright9 by ASTM International www.astm.org



BOUDR EAU ON REPEATABILf F Y OF A TEST PROCE DURE 31

Introduction

R e s i li e n t m o d u l u s t e st in g o f c o h e s i v e a n d c o h e s i o n l es s u n b o u n d m a t e r i a ls b e g a n t o

ga in m om en tum in t he h ighw ay mate r i a l s cha rac t e ri za t ion d i sc ip l i ne in t he mid-1970s .

By 1982, t he Am er i can Assoc i a t i on o f S t a t e Hig hw ay and Transpor t a t i on Of f i c i a ls

( A A S H T O ) a d o p t e d t es t m e t h o d T - 2 7 4 . I n 1 9 8 6, A A S H T O a d o p t e d a p a v e m e n t s tr u c tu r e

th i ckness des ign man ua l t ha t r equ i red r es i l ien t mod ulus a s the p r im ary respo nse i npu t fo r

subgrade suppor t .

S ince i ts i ncep t ion , t he t e s t p rocedu re has ev o lved , ma in ly t h rough the ac t i v i t y o f

t h e S t r at e g ic H i g h w a y R e s e a r c h P r o g r a m ( S H R P ) . T h e f ir s t t e st p r o to c o l o f S H R P f o r

r es i li en t modu lus t e s t i ng o f unbound base / sub base m a te r i a ls and sub grade so i l s, P ro toco l

P46 , was i n t ended to p rov ide a s impl i f i ed ve r s ion o f T -274 tha t wo uld l ead t o impro ved

repea t ab i l it y and r e li ab il it y . M any f ac to r s we re be l i eved to h ave con t r ibu ted t o t he n on-

repea t ab i l it y o f t he t e st , such as mo i s tu re con ten t, dens i t y , com pac t ion m ethodo logy ,

wa vefo rm con t ro l and num erous o the r s . Skep t i c s hav e l ong c l a imed tha t t he t e st appear s

to be ex t r em ely use r - sens t i ve , and va r i a t i on seem s too e xcess ive fo r t he t e s t to be

pract ica l or useable .

W hi l e a l l t hese concerns hav e been c red ib l e and war ran t ed t h rougho ut t he yea r s , t he

w o r k d o n e u n d e r t h e L o n g T e r m P a v e m e n t P e r fo r m a n c e ( L T P P ) s t u d y t o g e th e r w i th t h e

t r emend ous t echnolog ica l adv ances i n i ns trumenta t i on as d ig i ta l has r ep l aced ana log

c o n t ro l s a n d a c q u i si ti o n , h a v e l e d t o b o t h b e t t e r e q u i p m e n t a n d m o r e k n o w l e d g e a b l e

ind iv idua l s t o p e r form the t e s t ing .

Eve n so , seve ra l round- rob in p rof i c i ency t e s t p rogram s have be en in i t ia t ed r ecen t ly ,

a n d r e s u l ts h a v e b e e n s o w i d e s p r e a d t h a t p o t e n ti a l p a v e m e n t d e s i g n p r o f e s si o n a l s r e m a i n

skep t i ca l t ha t the p ro cedu re and l abo ra to r ie s pe r form ing the t e s ts can not p rov id e r e li ab l e

t es t da t a t o base a s t ruc tu ra l pave m ent des ign .

V o n Q u i n tu s a n d K i l l in g s w o r t h ( 1 9 9 8 ) d e s c r ib e a r e c o m m e n d e d f ie l d s a m p l i n g a n d

labora to ry te s t p rogram to p rov ide suf f i c i en t da ta fo r sub grade s t r eng th ch a rac t e r iza t i on

in t ended fo r use i n se l ec t i ng a des ign subg rade r es il i en t mo dulus . The i r r epor t sugges t s

va r i a t ions a s h igh as 25% a t any g iven s t r e s s leve l a r e poss ib l e , and r eco m m end s t ha t

p e r h a p s t h r e e r e p l ic a t e d s p e c i m e n s f o r e a c h m a t e r i al e n c o u n t e r e d m a y b e n e c e s s a r y t o

accura t e ly cha rac t e r i ze t he ma te r i a l .

Th e p resen t pape r addresses t he concerns r a i sed ab out t he t e s t no t be ing a b l e to

reprod uce s im i l a r r e su lt s . Th i s s t udy i s i n tended to dem ons t r a t e t ha t r e su l t s ob t a ined f rom

tes t ing r ep l i ca ted sp ec im ens can be r epea t ed ; how ever , fu r the r eva lua t ion i s

r ecom m end ed as t h is wo rk on ly inc ludes a s ing l e t e s t ope ra to r and s ing l e t e s t sys tem.

xperimentation

T h i s r e p e a t a b il i ty s tu d y c o m m e n c e d a c c i d e n t a ll y i n t h e s u m m e r o f 2 0 0 0 , a n d h a s

procee ded w i th in t en t ion un ti l M arch 2002 . The s tud y has i nc luded tw o so i ls , each

repl icated nu m erou s t im es to t ight toleranc es o f den si ty (_+ 1 lb/cu. f t .) and m ois tu re

conten t (_+ 0.5% ). Th is den si ty toleran ce i s t ighter than the req ui rem ent s t ipula ted b y

A A SH TO T30 7-99 (+_ 3% of t a rge t , which t r ans l a te s t o • 3 l b / cu . f t fo r a 100 lb / eu . ft t a rge t

dens i ty ) . The fo l l owing sec t ions desc r ibe t he t e s t i ng p rocess an d con t ro l.



3

RESILIENTMODULUS TESTING FOR P VEMENT COMPONENTS

Soils

Both So i l A , sampled f rom Alab am a , and So i l B , sam pled f rom Geo rg i a , a r e

desc r ibed as san dy s i lt s (AA SH TO ) or c l ayey sands (Un i f ied So i l C lass if i ca ti on) . A

sum m ary of p roper t i e s fo r each so i l is p rov ided in Tab le 1 .

Tab le 1 -

Summary o f So il Properties

Physical Property Soil A Soil B

Liquid Limit, LL 21 36

Plastic Limit, PL 16 27

Plasticity Index, PI 5 9

P4 ( ) 94 100

Plo ( ) 92 96

P2oo ) 47 48

M axim um D ry De nsity, Ym~x pcf) 119.8 113.3

Op timum M oisture Co ntent, coopt ) 12.0 15.0

AASH TO Classification A-4 A-4

Unified Soil Classification SC SC

Maximum dry density and optimum m oisture content as determined by

AA SHT O T-99 (standard Proctor).

A p p r o x i m a t e l y 1 50 0 g r a m s o f s oi l w a s s u b s a m p l e d f r o m e a c h s o i l s a m p l e in o r d e r

to p repare / co m pac t each t e s t spec imen r ep l i ca te .

ompaction Methodology

Based on wo rk done under the in i ti a l SHRP con t r ac t, a doub le -p lunge com pac t ion

m e t h o d o f w a s f ir st u s e d f o r r e m o l d i n g p u r p o s e s , s im i l a r t o A S T M T e s t M e t h o d f o r

M a k i n g a n d C u r i n g S o i l -C e m e n t C o m p r e s s i o n a n d F le x u r a l T e s t S p e c i m e n s i n t h e

L a b o r a t o r y ( A S T M D 1 6 3 2 ) . T h i s m e t h o d y i e l d e d s p e c i m e n s v i s ib l y u n c o m p a c t e d i n t h e

cen te r he igh t w hi l e exh ib i t ing r e l a t i ve ly dense ends . A th ree - l if t sys t em was eva lua t ed ,

which im prov ed the condi t ion o f t he s ing l e li f t sys t em, bu t d id no t p rov ide en ough

conf idence t ha t a un i fo rm condi t ion ex i s ted . Th i s l ed t o a f i ve - l i ft st a ti c com pac t ion

m e t h o d o l o g y , w h i c h i s c u r r en t ly c o n ta i n e d in A A S H T O T - 3 0 7 a s A n n e x A 3 . T h i s

m e t h o d p r o v i d e s f o r u n i f o rm c o m p a c t e d h e ig h t s u s i n g t h e s a m e m a s s o f s o i l f o r e a c h l if t.

A f iv e - l if t s ta t ic c o m p a c t i o n m e t h o d o l o g y w a s u s e d f o r e a c h s p e c i m e n t e s te d . T h e

com pac t ion dev ice u t il ized , s im i l a r t o t ha t show n in F igure 1 , was a 50 000-1b f r am e

cons t ruc ted on a tr i pod s t ee l - f r ame bas e wi th a 30- inch to ta l s t roke , bo t tom -mo unted r am

energ i zed by a 115V s ing l e -phase pump . Thi s dua l -use un i t i n tegra t es a conven ien t , easy

r ing as se m bly to gu aran t ee ve ry l it tl e r isk o f over com pac t ing spec imen l if t s, whi l e

a l l owing the opera to r t o qu i ck ly tr ans form the un i t fo r ex t rus ion purposes . No m ina l 2 .8 -

inch d i amete r by 5 .6 - inch t a ll cy l i ndr ica l t e s t spec ime ns w ere p rep ared fo r t h i s s t udy .

Den s i ty g rad ien t ve r i f i ca t ion i s no t r equ i r ed fo r t he f i ve - l i ft s ta t ic c om pac t ion

m e t h o d o l o g y p e r A A S H T O r e q u ir e m e n t s , a n d d e n s i ty g r a d ie n t s w e r e n o t m e a s u r e d f o r

any o f t he spec imen s p repared fo r th i s s t udy .



BOUDRE U ON REPE T BILITY OF TEST PROCEDURE

Figure 1 -

Static Compactor photograph compliments of

Durham Geo-Enterprises)

Test System

Resilient modulus testing was perform ed on an Instron Mo del 8502 test frame,

utilizing Instron s 8800-Series digital controller. The 50 000-1b capacity test frame

house s a crosshead-m ounted 10-inch stroke servo-hydraulic actuator, operating with a 5

gallon per minute water-cooled hydraulic pump. Although a 50 000-1b capacity ma chine

is certainly not required to p erform repeated load testing of soil specimens, in the

auth or s e xperience a 50 000-1b capacity machine convincingly outperform s 5 000-1b and

20 000-1b capacity servo-hydraulic mach ines w ith respect to wav eform control.

Calibrated com ponents include two 0.2-inch stroke spring linear variable

displacem ent transducers (LV DTs, S olartron Mode l AG 2.5), a 1000-1b dynam ic load cell

(Ilastron Dynacell Model 2527-103) and a 120 psig automated electronic pressure

controller (Testcom M odel ER 3000). Th e load cell is instrumented with an internally

mounted accelerometer which is used in compensat ion mode to negate the ef fects of

inertial forces resulting from rapid directional changes o f the load cell mass. This control




is better capable of keeping the load feedback signal within the tolerances prescribed by

AASHTO T307.

The instrumentation configuration consisted o f externally moun ted load cell

(attached to the top crosshead actuator) and ex ternally mou nted LV DTs. T his typical

configuration is shown in the photo graph belo w (Figure 2).

Figure 2 - Resilient odulus Test System

This system possesses au tomated pressure control for applying, adjusting and

measuring confining pressure throughout the duration o f a test through software control.

This transducer capab ility is helpful but not required. Th e system opera tor must ensure

that appropriate pressures are provided and maintained fo r each load sequence if manual

pressure control is utilized.

The test system was self-evaluated using procedures described in the Federal

High way Admin istration s Startup Procedur es (Alavi et al. 1997). The ev aluation was

limited to only the physical testing requirements of the Report , and w as conducted using

a 2,000-1b Moreho use proving ring. The e valuation conc luded that the test system

performs at an acceptable level of ac curacy and precision.



B O U D R E U O N R E P E T B IL IT Y O F T E S T P R O C E D U R E 5

Remolding Requirements

V a l u e s o f 9 5 o f t h e m a x i m u m d r y st a nd a r d d e n s it y a t o p t i m u m m o i s tu r e

c o n d i t i o n s w e r e t a r g e te d . H y g r o s c o p i c m o i s t u r e c o n t e n t s w e r e d e t e r m i n e d f o r e a c h

s a m p l e o n d a y on e . O n d a y tw o , e a c h i n d e p e n d e n t l y m e a s u r e d b u l k s a m p l e w a s m o i s t u r e -

c o n d i t io n e d , p l a c e d i n a p l a s ti c b a g a n d a l l o w e d t o a b s o r b t h e m i x e d w a t e r o v e r n ig h t . A

m o i s t u r e c o n t e n t w a s t a k e n f r o m e a c h m i x e d s a m p l e a t t h e c o n c l u s i o n o f d a y t w o .

S p e c i m e n s w e r e c o m p a c t e d o n d a y th r e e , a ft e r a m o i s t u r e c o n t e n t t o l e r a n c e c h e c k w a s

d e t e rm i n e d . I m m e d i a t e l y af te r c o m p a c t i o n , t h e s p e c i m e n s w e r e e x tr u d e d , m e a s u r e d f o r

d im ens ion s (u t i l i z ing a Mi tu to yo 8 - inch d ig it a l c a l i pe r) and ma ss , p l aced i n a l a tex

m e m b r a n e w i t h p a p e r d i s k s a n d p o r o u s s t o n e s , a n d t es te d . F o l l o w i n g t h e t es t, t h e e n t ir e

s a m p l e w a s m e a s u r e d f o r m o i s t u r e c o n t e n t.

Testing

A l l t e s t in g w a s c o n d u c t e d i n a h i g h - b a y w a r e h o u s e n e a r A t l a n t a, G e o r g i a . T h i s

s p a c e d i d n o t h a v e t e m p e r a t u r e c o n t r o l s t o m o d e r a t e t e m p e r a t u re s d u r i n g t h e e x t r e m e h o t

a n d c o l d s e a s o n s c h o s e n f o r t h e s e c o n d p h a s e o f t h e w o r k . T e s t s w e r e c o n d u c t e d f o r t h e

e i g h t S o i l A s p e c i m e n s b e t w e e n A u g u s t 1 a n d 9 , 2 0 0 0 . B a s e d o n t h e p r o m i s i n g

r e p e a t ab i l it y a c h i e v e d o n t h i s s m a l l g r o u p o f r e p li c a te d s p e c i m e n s , a s e c o n d t e s t i n g p h a s e

w a s i n it ia t ed t o m e a s u r e t h e r e p e a t a b i l it y o v e r a l o n g p e r i o d o f t im e , i n o r d e r t o e v a l u a t e

t h e e f f ec t s o f a m b i e n t l a b o r a t o r y c o n d i t i o n s. T h u s , t e s ts f o r S o i l B w e r e c o n d u c t e d o v e r a

p e r i o d o f e ig h t m o n t h s , f r o m A u g u s t 2 0 0 1 t o M a r c h 2 0 0 2 . T e m p e r a t u r e s i n t h e t e s t

f a c i li t y r a n g e d f r o m 9 5 ~ i n t h e la t e s u m m e r to 5 0 ~ i n t h e w in t er .

e su l t s

In o rde r to eva lua t e t he r epea t ab i l i t y o f t he t e s t r e su l ts , i t i s impo r t an t t o m easu re

t h e p h y s i c a l re p e a t a b i li t y o f t h e s p e c i m e n s u s e d f o r t e s t in g a n d e v a l u a ti o n . N o a t t em p t s

w e r e m a d e t o m e a s u r e t h e s e n s i ti v it y o f t h e t e s t to s i g n i fi c a n t v a r i a ti o n s o f d e n s i ty o r

m o i s t u r e c o n t e n t. T h u s r e a s o n a b l e t o l e r a n c e s o f d e n s it y a n d m o i s t u r e w e r e c o n t r o l le d .

T h e f o l l o w i n g t a b l e ( T a b l e 2 ) i ll u st ra t es t h e d e n s i t y a n d m o i s t u r e c o n t r o l a c h i e v e d f o r

b o t h s a m p l e g r o u p s .

Ta b le 2 - Remolded Test Specimen Summary

M easurement Soil A Soil B

Dry Density

A vera ge (pcf) 113.5 107.1

Standard De viatio n (pcf) 0.3 0.3

Coefficient o f Variation ( ) 0.3 0.2

M inimum Valu e (pcf) 113.0 106.5

M axim um Value (pcf) 114.1 107.5

Moisture ontent

Av erage ( ) 12.2 15.0

Standard D eviatio n ( ) 0.1 0.2

Coefficient o f Va riation ( ) 0.4 1.2

M inimum Va lue ( ) 12.1 14.7

M aximum Value ( ) 12 .2 15 .4

No. o f Test Specimens 8 19



6 RESIL IENT MODULUS TESTING FOR P VEMENT COMPONENTS

A s c a n b e r e a d i l y o b s e r v e d , t h e s p e c i m e n s u s e d f o r th i s s t u d y a r e w e l l r e p l ic a t e d .

T h e d e n s i t i e s o b t a i n e d a r e w e l l w i t h i n t h e s t u d y g o a l t o l e r a n c e s o f_ + 1 l b /c u . f t, a n d _+ 0 . 5 %

m o i s t u r e c o n t e n t. T h i s d e m o n s t r a t e s th e r e p e a t a b i l i t y i n w h i c h s a m p l e s c a n b e p r e p a r e d

u s i n g th e p r o c e d u r es o f A A S H T O T 3 0 7 - 99 , A n n e x A 3 . T h e a v e r a g e d r y d e n s i t y d e v i a te d

f r o m t h e t a rg e t v a l u e o f 9 5 p e r c e n t o f t h e s t a n d a r d P r o c t o r m a x i m u m d r y d e n s i t y b y 0 .3

p c f fo r S o i l A a n d 0 .5 p c f f o r S o i l B . S i m i l a r ly , t h e a v e r a g e m o i s t u r e c o n t e n t d e v i a t e d

f r o m t h e t a r g e t o p t i m u m m o i s t u r e c o n t e n t b y 0 . 2 p e r c e n t f o r S o i l A a n d 0 . 01 p e r c e n t f o r

S o i l B . A l t h o u g h d e n s i t y g r a d i e n t s w e r e n o t m e a s u r e d t o a s s u r e n e g l i g i b l e v a r i a t io n o f

d e n s i t y a n d m o i s t u r e t h r o u g h o u t e a c h t e s t s p e c i m e n , t h e r e a r e r e a s o n a b l e a s s u r a n c e s t h a t

r e s i li e n t m o d u l u s t e st v a r i a ti o n s m e a s u r e d s h o u l d b e m a i n l y a t t r i b u te d t o t e s t v a r ia t i o n s ,

n o t m a t e r i a l v a r i a b i l i ty .

T h e s t re s s le v e l t a r g e ts p r e s e n t e d i n T a b l e 1 o f A A S H T O T 3 0 7 a r e n o m i n a l l e v e l s

s u g g e s t e d t o a c h i e v e . T h i s t a b l e c o n s i s t s o f 1 5 d i ff e r e n t c o m b i n a t i o n s o f c y c l ic a x i a l

s t re s s a n d c o n f i n i n g p r e s s u r e , e a c h c o m b i n a t i o n r e f e r r e d to a s a s e q u e n c e . I t w o u l d b e

h a r d t o b e l i e v e th a t th e s e t a r g et s c o u l d b e e x a c t l y m a t c h e d b e t w e e n c o m m a n d a n d

f e e d b a c k s i g n a l s. B e c a u s e o f t h e d i f f i c u l t y i n a c h i e v i n g p r e c i s e f e e d b a c k , a c o n s t i tu t i v e

m o d e l i s n e c e s s a r y i n o r d e r to c o m p a r e r e s u l ts o f t e s ts . T h e c o n s t i tu t i v e m o d e l u s e d i n

t h is s t u d y i s t h a t w h i c h w a s f i rs t i n t r o d u c e d b y S H R P i n t h e e a r l y 1 9 9 0 ' s :

M r = K 1 S c ~ S 3 ~5 ( 1 )

w h e r e

M r = r e s i li e n t m o d u l u s , p s i

S c = c y c l i c s t r e s s , p s i

3 = c o n f i n i n g p r e s s u r e , p s i

K 1 , K 2 a n d K 5 = n o n l i n e a r e la s t ic r e g r e s s i o n c o e f f i c i e n t/ e x p o n e n t s

R e s u l t s o f t h e t e s ti n g f o l l o w i n g t h e r e g r e s s i o n o f d a t a f r o m e a c h s p e c i m e n t o f i t t h e

c o n s t i tu t i v e m o d e l a r e p r o v i d e d i n T a b l e 3 . I n o r d e r t o c o m p u t e t h e r e g r e s s i o n c o n s t a n t

a n d c o e f f i c ie n t s , t h e d e p e n d e n t v a r i a b l e , M r a n d i n d e p e n d e n t v a r i a b l e s S c a n d 3 m u s t

f ir s t b e t r a n s f o r m e d t o a L o g l 0 b a s e . T h i s a l l o w s a l i n e a r re g r e s s i o n t o b e p e r f o r m e d .

O n c e c o m p l e t e d , th e y - i n t e r c e p t i s u s e d a s a 1 0 - b a s e e x p o n e n t i a l to d e r i v e t h e K 1

c o n s t an t , w h i l e th e K 2 a n d K 5 c o e f f i c ie n t s a re u s e d a s e x p o n e n t i a ls i n E q u a t i o n 1 .

T a b l e 3 - No nl inear E las t i c oe f fi c ien t~Exponen t s

Regre ssion Coe fficients

Sample No. K1 K2 K5 R2

A-1 9 838 -0.13196 0.22194 0.99

A-2 9 873 -0.14194 0.21102 0.99

A- 3 10 121 -0.14167 0.21493 0.99

A-4 9 335 -0.12725 0.23100 0.98

A-5 10 387 ~ 0.23229 0.98

A-6 9 463 -0.11857 0.20279 0.98

A-7 10 294 -0.10049 0.17310 0.98

A-8 8 780 -0.07114 0.21455 0.97



BOUDRE_ U ON REPE T BILITY OF TEST PROCEDURE 7

B-1 7 515 -0.17220 0.21615 0.98

B-2 7 922 -0.18555 0.22319 0.98

B-3 7 762 -0.18606 0.21680 0.98

B-4 7 898 -0.19693 0.24964 0.99

B-5 7 859 -0.18428 0.25522 0.99

B-6 8 321 -0.19894 0.23261 0.99

B-7 7 905 -0.20854 0.25953 0.99

B-8 7 872 -0.22103 0.26367 0.98

B-9 8 178 -0.19842 0.25590 0.99

B-10 7 938 -0.21171 0.23770 0.99

B-11 6 956 -0.21025 0.30340 0.99

B-12 7 775 -0.20790 0.25843 0.99

B-13 8 484 -0.21230 0.23373 0.99

B-14 8 118 -0.20199 0.23251 0.98

B-15 7 592 -0.20140 0.25691 0.98

B-16 7 911 -0.22068 0.25496 0.99

B-17 7 904 -0.20062 0.27061 0.99

B-18 7 597 -0.21391 0.26113 0.99

B-19 7 468 -0.21679 026751 0.99

The constitut ive model selected provides an excellent fit for the data, as can be

observed by the multiple-cor relation coefficient, R 2. Although the regression constant,

K1, and the coefficients, K2 and K5, seem to be quite variable for supposedly replicated

specimens, there is no conclusive evidence of precision and bias that would indicate how

much variability is acceptable.

Once satisfied that the constitutive model Equation 1) was reasonable based on the

good R 2, the results for each test specime n were calcula ted or predicted for resili ent

modulus at the exact stresses for each of the 15 sequences tested. This is done for the

purpose of e xamining the differences in resilient modulus values from sample to sample

or collec tively as a group o f replicated specimens.

As an illustration of importance, a test performed on a specimen targeted for a

cyclic stress of 6 psi at a c onfin ing pressure of 4 psi sequence number 8 of 15) may have

achieved a cyclic stress of 5.75 psi, whereas another sample tested at the same targets

may have achieved only a 5.4 psi value. If the material is sensitive to stress stress

dependent), comparing the raw resilient modulus value s will not be ideal, or appropriate.

Tables 4 and 5 present the calculated resilient modulu s values of each specime n

tested for both soils at each of the 15 sequences. Summar y information consisting of

average, standard deviation, coefficient of variation and number o f tests or observations

are provided for each of the 15 sequences table columns).



8 R E S I LI E NT M O D U L U S T E S T IN G F O R P V EM E N T C O M P O N E N T S

S a m p l e

N o .

T a ble 4

E s t i m a t e d R e s i l ie n t M o d u l u s D a t a S o i l ,4 )

R e s i l ie n t M o d u l u s ( p r e d i c t e d b y C o n s t i t u t i v e M o d e l a t e a c h t e s t l o a d i n g s e q u e n c e) , p s i

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

A-I 13,362 12,194 11,559 11,129 10,806 12 21 2 11,145 10,564 10,171_ 9,876 10,471 9,556 9,058 8,721 8,468

A-2 13,059 11,836 11,174 10,727 10,392 11,989 10,865 10,258 9,847 9,540 10,357 9,387 8,862 8,507 8,242

A-3 13,484 12,223 11, 541 11,080 10,735 12,359 11,203 10,578 10,155 9,839 10,648 9,652 9,113 8,749 8,477

A-4 12,929 11,837 11,242 10,838 10,535 11,773 10,779 10,237 9,86 9 9,593 10,031 9,t8 4 8,722 8,40 9 8.173

A-5 14,146 12,707 11,933 l l A 14 11,026 12,875 11,564 10,8 61 10,388 10,035 10,960 9,845 9,246 8,843 8.543

A-6 12,535 11,546 11.004 10,635 10,358 11,546 10,635 10,136 9,796 9.540 10,032 9,240 8,807 8, 5l l 8,28 9

A-7 13,093 12,212 11,724 11,390 11,t3 8 12,205 11,384 10,930 10,618 10,383 10,825 10,097 9,694 9,41 8 9,20 9

A-8 122 75 11,685 II t35 2 11,122 10,947 11,253 10,7 11 10,407 10,196 10,035 9,698 9,231 8,96 9 8,787 8,648

avg. 13 ,1 1 1 12,030 11,441 11 042 10,742 I2,026 11,036 10,496 10,130 9,855 10,378 9,524 9,059 8,743 8,506

s .dev . 578 375 306 288 292 506 338 291 286 295 435 327 308 314 326

c.v. 4.41 3.12 2.68 2.61 2.72 4.21 3.07 2.78 2.82 3.00 4.19 3.43 3.40 3.59 3.84

obs. 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8

S a m p l e

N o .

T a ble 5

E s t i m a t e d R e s i l i e n t M o d u l u s D a t a S o i l 17)

R e s i l ie n t M o d u l u s ( ,p r e di c te d b y C o n s t i t u t i v e M o d e l a t e a c h t e s t l o a d i n g s e q u e n c e ) , p s i

1 2 3 4 5 6 7 8 9 1 11

1 2 1 3 1 4 1 5

B-I 9,8 24 8,719 8,131 7,738 7,4 46 9,00 0 7,987 7,448 7,088 6,821 7,747 6,876 6,412 6,102 5,872

B-2 1 0, 3 91 9,137 8,475 8,034 7,708 9,492 8,346 7,741 7,339 7,041 8,131 7,150 6,632 6,287 6,032

/3 -3 10,062 8,844 8,202 7,774 7,458 9,215 8,100 7,511 7,120 6,830 7,929 6,970 6,463 6,12 6 5,877

B-4 10,777 9,402 8,680 8,202 7,850 9,739 8,497 7,845 7,413 7,094 8,192 7,147 6,598 6,235 5,967

B-5 10,927 9,617 8,924 8,463 8,122 9,853 8,671 8,047 7,631 7,324 8,255 7,265 6,74 2 6,394 6,136

B-6 10,998 9,581 8,838 8,347 7,984 10,008 8,719 8,043 7,596 7,266 8,517 7,420 6,845 6,465 6,184

B-7 10 ,8 9 1 9,425 8,661 8,157 7,786 9,803 8,484 7,796 7,342 7,008 8,189 7,087 6,513 6,133 5,854

B-8 10,832 9,294 8,497 7,974 7,590 9,734 8,351 7,635 7,165 6,820 8,108 6,956 6,360 5,968 5,681

B-9 11,273 9,825 9,065 8,562 8,191 10,162 8,85 6 8,172 7,718 7,384 8,510 7,417 6,844 6,46 4 6,18 4

B-10 10 ,494 9 ,062 8 ,316 7 ,825 7 ,464 9 ,530 8 ,229 7 ,552 7 ,106 6 ,778 8 ,082 6 ,979 6 ,405 6 ,027 5 ,749

B- II 10,355 8,951 8,219 7,73 7 7,382 9,157 7,915 7,268 6,841 6,528 7,420 6,414 5,890 5,544 5,290

13 -12 10,696 9,260 8,512 8,018 7,654 9,63 2 8,339 7,665 7,220 6,893 8,052 6,97 2 6,40 8 6,036 5,762

B-13 11,132 9,609 8,816 8,29 4 7,91 0 10,125 8,740 8,019 7,544 7,195 8,611 7,433 6,820 6,41 6 6,119

/3-14 10,705 9,306 8,574 8,090 7,734 9,742 8,469 7,803 7,362 7,038 8,292 7,208 6,641 6,267 5,990

B-15 10,463 9,09 9 8,38 6 7,914 7,566 9,428 8,199 7,556 7,131 6,818 7,890 6,862 6,324 5,968 5,706

B-16 10,720 9,200 8,412 7,895 7,515 9,667 8,296 7,586 7,119 6,777 8,101 6,952 6,35 7 5,966 5,679

B-17 11,169 9,71 9 8,960 8,458 8,087 10,009 8,709 8,02 9 7,579 7,247 8,297 7,2 20 6,656 6,28 2 6,007

B-I 8 10,458 9,017 8,268 7,774 7,412 9,407 8,111 7,437 6,993 6,667 7,850 6,768 6,206 5,835 5,563



BOUDREAU ON REPEATABIL ITY OF A TEST PROCEDURE 9

B-1 9 10,378 8,930 8,178 7,684 7,321 9,311 8,012 7,338 6,894 6,569 7,735 6,656 6,096 5,727 5,457

avg . 10,660 9,263 8,532 8,049 7,694 9,632 8,370 7,710 7,274 6,953 8,101 7,040 6,485 6,118 5,848

s.dev. 376.8 311A 287.3 275.4 268.5 328.8 280.7 264.3 256 .7 252.5 296.2 266.5 256.6 251.8 249.1

c . v . 3 . 5 3 . 4 3 . 4 3 . 4 3 . 5 3 . 4 3 . 4 3 . 4 3 . 5 3 . 6 3 . 7 3 . 8 4 . 0 4 . 1 4 . 3

obs . 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19

O b s e r v a t i o n s

T h e d a t a c a n b e a n a l y z e d f a i r ly e a s il y b y o b s e r v i n g t h e c .v . t e rm s u m m a r i z e d a t th e

b o t t o m o f e a c h o f th e t a b le s a b o v e . T h e c . v . te r m d e r i v e d f o r a n y s e q u e n c e i s b e l o w

4 . 5 . T h e s e s m a l l c .v . s i n d ic a t e v e r y g o o d r e p ea t ab i li ty . T h i s m a r g i n a l l y l o w s p r e a d o f

d a t a re f u t e s th e a r g u m e n t t h a t 3 s p e c i m e n s m a y b e r e q u i r e d t o p r o p e r l y c h a r a c t e r iz e a

p a r t ic u l a r s o il t y p e , a s s u g g e s t e d b y V o n Q u i n t u s a n d K i l l in g s w o r t h ( 1 9 9 8 ) b a s e d o n

an t i c ipa t ed c .v . s o f up t o 25 .

o n c l u s i o n s a n d R e c o m m e n d a t i o n s

T h e f o l l o w i n g c o n c l u s i o n s c a n b e m a d e f r o m t h is l i m i te d s t u d y :

1 . T h e 5 - l if t s ta t ic c o m p a c t i o n m e t h o d o l o g y c a n r e a d i l y p r o d u c e s p e c i m e n

prope r t i e s w i th in t i gh t t o l e r ances . Th e ab i l it y t o r emo ld spe c im en con s i s t en t l y i s

b e s t s e r v e d b y w e l l - c r a ft e d a n d m a i n t a i n e d e q u i p m e n t a n d n o r m a l l a b o r a t o r y

s t a n d a r d o f c a r e p r a c ti c e s. A w e l l - d e s i g n e d d a t a w o r k s h e e t t o p r e p a r e s p e c i m e n s

is requi red .

2 . T h e t e s t s y s t e m m u s t b e p r o p e r l y a n d p r e c i s e ly c a li b ra t e d. T h i s n o t o n l y in c l u d e s

c o m p o n e n t c a l i b ra t io n s , b u t a l s o s h o u l d c o n s i s t o f a s y s t e m e v a l u a t i o n s i m i l a r to

t ha t d o c u m e n t e d in F H W A - R D - 9 6 - 1 7 6 .

3 . I f p r e c a u t i o n s a r e t a k e n t o e l i m i n a te c o n c e r n s re g a r d i n g s p e c i m e n v a r i a b il i ty a n d

e q u i p m e n t v a r i a b il it y , t h e t e s t p r o c e d u r e i s c a p a b l e o f p r o d u c i n g r e s u lt s t h a t a r e

repea table .

4 . O n ly one spec im en (no t 3 ) i s r equ i r ed t o adeq ua t e ly cha rac t e r i ze t he r e s i li en t

b e h a v i o r o f a g i v e n s o il .

T h e s t u d y c o n c l u s i o n s a r e li m i t ed t o t h e f a c t th a t o n l y A - 4 s o i ls w e r e e v a l u a t e d ,

p r e p a r e d b y o n l y o n e r e m o l d i n g m e t h o d , b y o n l y o n e t es t o p e r a t o r p e r f o r m i n g t es t s i n a

s i n g le t ri ax i al c h a m b e r o n o n e t e s t s y s te m . E x p e r i e n c e h a s s h o w n t h a t a n y v a r i a t io n o f

t h e s e m e n t i o n e d f a c t o r s c a n l e ad t o v a r i a ti o n s o f r e su l ts , e v e n i f s p e c i m e n s a r e m e a s u r e d

t o w i t h i n t h e s a m e t o l e ra n c e s o f d e n s i t y a n d m o i s t u r e c o n t en t .

I t i s r e c o m m e n d e d t h a t a p r o g r a m b e d e v e l o p e d a n d a d m i n i st e r e d t o e v a l u a t e a

p r e c i s i o n a n d b i a s s t a te m e n t t h a t w o u l d i n c l u d e m a t e r i a ls c o v e r i n g a w i d e r r a n g e o f

expec t ed r e s il i en t p rope r t ie s . T hese sh ou ld i nc lude A -4 , A-5 , A-6 an d A-7 so i l s , a s a

m i n i m u m . O n c e s e le c t ed , s e v e r a l l a b o r a to r i e s th a t c a n d e m o n s t r a t e c o n f o r m a n c e ( b y o n -

s i g h t e v a lu a t i o n ) t o th e p r e c i s e r e q u i re m e n t s o f th e t e st p r o c e d u r e s h o u l d t e s t a m i n i m u m

o f s i x r e p l ic a t e s f r o m e a c h m a t e r ia l c o m b i n a t i o n t o d e v e l o p b o t h w i t h i n - la b o r a t o r y

( r epea t ab i li t y ) and be tw een- l a bo ra to ry ( r ep roduc ib i l i ty ) va r i a t ion . I t w ou ld be




advantageous to eva lua te the e f f ec t s o f compa c t ion method olog y dur ing th i s

r ecom me nded program as we l l a s e f f ec t s o f mo is tu r e and dens i ty va r ia t ions . This

addi t iona l eva lua t ion i s r ecomm ended as a second phase , f o l lowing the deve lopm ent o f

an accura te and accep tab le p r ec is ion and b ias o f the t e s t p rocedure .

e f e r en c e s

Alavi , S ., M erpor t , T . , Wilson, T. , Gro eger , J ., and Lopez , A. , 1997, LT PP Ma ter ia ls

Charac te r iza t ion P rogram: R es i li en t Modulus o f Unbound M ate ria ls (LT PP

Pro toco l P46) L abora tory S ta r tup and Qua l i ty Cont ro l P rocedures , Federal

Highway Administration Report No. FHWA RD 96 176.

Vo n Quin tus, H. and Ki l lingswor th , B . , 1998 , An a lyses Re la t ing to Pavem ent Mate ria l

Charac te riza tions and The i r E f fec t s on P avem ent Pe r forman ce ,

Federal Highway

Administration Publication No. FHWA RD 97 085.



Jona than L . G roeger , 1 Ander s Bro , 2 Go nza lo Rada , 3 Aram is Lop ez4

Imp lementation of Startup Procedures in the L aboratory

Reference:

G r o e g e r , J . L . , B r o , A . , R a d a , G . , L o p e z , A . ,

"Implementation of

Startup Procedures in the Laboratory,"

ASTM STP 1437, Resilient Modulus Testing

for Pavement Components,

G . N . D u r h a m , W . A . M a r t , a n d W . L . D e G r o f f , E d s . ,

A S T M I n t er n a ti o n a l, W e s t C o n s h o h o c k e n , P A , 2 0 0 3 .

Abstract: A s p a r t o f t he F e d e r a l H i g h w a y A d m i n i s tr a ti o n 's ( F H W A ) L o n g - T e r m

P a v e m e n t P e r fo r m a n c e P r o g r a m ( L T P P ) M a t e r ia l s C h a r a c te r i z at io n e f f o r t , a q u a l it y

c o n t ro l /q u a l it y a s s u r a n c e ( Q C / Q A ) p r o c e d u r e w a s d e v e l o p e d t o v e r i f y th e p r o f i c i e n c y

of l abora to ry equ ipment and pe r sonne l i n pe r f o rm ing r es il ien t mo dulus t e s ti ng . Th i s

e f f o r t i s d o c u m e n t e d in r e p o r t F H W A R D - 9 6 - 1 7 6 ,

Resilient Modulus of Unbound

Materials (LTPP Protocol P46) Laboratory Startup and Quality Control Procedure

( Alav i , e t a l . 1997). S ince i ssuance o f tha t r epo r t , a g r ea t dea l o f exper i ence has been

ga the red i n us ing t he p rocedure . Th i s p resen t pap er p rov ides an ou t li ne o f t he

p rocedure , t he r a ti ona l e beh ind t he p rocedure , and docum ent s r ecen t changes t ha t have

been d eve loped by the au thor s. The pap er a l so d i scusses i s sues t o l ook f o r w hen

implem ent ing the s t a r tup p rocedure . F ina ll y , a b r i e f l is t o f is sues t ha t have b een f ound by

us ing t he p ro cedure i s p r esen t ed .

Keywords: r e s il ien t m odulus , l abora to ry te s ti ng , unb ound mate r i a l s , qua l it y con t ro l and

qual i ty assurance, guidel ines , LTPP

Introduction

T h e L o n g - T e r m P a v e m e n t P e r f o rm a n c e ( L T P P ) r e s il ie n t m o d u l u s t e s t p r o t o c o ls w e r e

deve lop ed t o a sce r t a in s t i f fness o f pav em ent su r f ace ( a spha l t concre te ) , base , subbase ,

and subgrade m a te r ia l s . The r e s i l ien t mo dulus t e s t i ng p rocess , genera l l y rega rded as a

r esea rch- type p rocedure , has h i s t o ri ca l ly been p e r f o rm ed in a un ive r s i t y se tt i ng and on a

' Vice P res iden t , Ax iom Dec i s ion S ys t em s , Inc ., 6420 D obb in Road , S u i te E , Colum bia ,

M D 2 1 0 4 5 .

2 P r inc ipa l , Geo Tes t Unl imi t ed , Inc . , 27069 N . B loo mf i e ld Rd . , N eva da C i ty , CA 95959 .

3 Assis tant Vice Pres ident , L AW PCS , 12104 Indian Cree k Cour t , Sui te A, Bel t svi lle ,

MD 20705.

4 L T P P T e a m L e a d e r , F e d e ra l H i g h w a y A d m i n i s tr a ti o n , 6 3 0 0 G e o r g e t o w n P i k e , M c L e a n ,

VA 22101.

41

Copyright9 by ASTM Internationa l w ww .astm.org




r e l a ti v e l y s m a l l n u m b e r o f s p e c im e n s . B e c a u s e t h e m o d u l u s v a l u e d e r iv e d f r o m t h i s

t e s ti n g p r o c e s s i s a k e y p a r a m e t e r f o r p a v e m e n t d e s i g n , t h e t e st i s b e i n g p e r f o r m e d f o r t h e

L T P P p r o g r a m i n a p r o d u c t i o n t e st in g e n v i r o n m e n t i n w h a t m a y b e t h e l a r g e st s in g l e

res i li en t mod ulus t e s t i ng p rogra m eve r under t aken .

I t is o f p a ra m o u n t i m p o r t a n c e to p r o v i d e L T P P r e s ea r c h e rs w i th t h e h i g h e s t q u a l i t y

da t a poss ib l e . As such , a qua l i t y con t ro l / qua l i ty a s surance QC /QA ) proce dure was

deve loped to ve r i fy t he ab i l i t y o f labora to ry equ ipmen t and pe r sonn e l t o pe r for m res i li en t

m o d u l u s t e st in g f o r L T P P . T h e o r ig i n a l p r o c e d u r e, d o c u m e n t e d in F H W A - R D - 9 6 - 1 7 6 ,

LT PP Materials Characterization Program: Resilient Modulus o f Unbound Ma terials

LT PP Protocol P46) Laboratory Startup and Q uality C ontrol Procedure

w a s d e v e l o p e d

pr im ar i l y fo r the ve r i f i ca t i on o f base , subbase , and su bgrade r es i l ien t m odu lus p rocedure .

S i n c e i s s u a n c e o f t h at r e p o rt , m a n y l e ss o n s h a v e b e e n l e ar n e d a n d p r o c e s s e s h a v e b e e n

a d d e d i n a n o n g o i n g p r o c e s s i m p r o v e m e n t cy c le . A n u p d a t e d a n d r e v i s e d v e r s io n o f t h is

proced ure i s p roposed to be i s sued in 2002 .

The pu rpose o f th i s pap er is no t t o r epea t a desc r ip t i on o f t he p rocedure p resen t ed i n

t h e a b o v e re f e re n c e . R a t h e r t he p a p e r p r o v i d e s a m o r e d e t a il e d b a c k g r o u n d o f th e

proce dure i n o rde r to fos t e r a deeper under s t and ing o f t he p rocess . I t s con ten t r epresen t s

m ore o f a d i scuss ion o f t he p rocedu re r a the r than a s t a teme nt o f p rocedura l f ac t s .

I t i s r e c o m m e n d e d t h a t r e a d er s o f t h is d o c u m e n t h a v e a c o p y o f th e s t a rt u p p r o c e d u r e

h a n d y a s t h is p a p e r c a n b e c o n s i d er e d a c o m p a n i o n d o c u m e n t .

P r o c e d u r e v e r v i e w

The s t a r tup and qua l i t y con t ro l p roced ure was dev e loped to ensure accurac y and

re l i ab i li t y o f r aw m easure m ent s p roduced w hi t e t e s ti ng mate r i a l s us ing c losed - loop

se rvo-hy drau l i c sys tems . I t is based on the p remise t ha t any eng inee r ing ana lys i s r equ ir es

re l iab l e r aw da t a , and the p re requ i s i te fo r r e l iab l e r aw da t a i s p rop er ly conf igured

equipm ent . Th e p rocedu re i s des igned to ve r i fy t he opera t i ng accurac y o f a ll e ssen t i a l

sys t em com pon ent s i n a l og i ca l man ner . Each pa r t o f t he sys t em i s ve r i f i ed i nd iv idua l ly

and then the en t i r e sys t em i s checked to m ake sure a l l pa r t s work tog e the r p roper ly .

The p rocedu re i s d iv ided in to t h ree d i s ti nc t compo nent s :

1 . E l ec t ron i cs sys t em per form ance ve r if i ca t ion p rocedure .

2 . Ca l ib ra t i on check and overa l l sys t em per fo rm ance ve r if i ca t ion p rocedure .

3 . P rof i c i ency procedure .

As p a r t o f t he e l ec t ron i cs sys t em ver i f i ca t i on p rocedure , s i gna l condi t i on ing chann e l s ,

da t a acqu i s i ti on p rocesses , and tr ansducer s a r e checked fo r p rop er opera t i on . Fo l lowing

the e l ec t ron i cs sys t em v er i f ica t i on p rocedure , t he ca l i b ra t i on check and overa l l sys t em

p e r f o r m a n c e v e r i fi c a ti o n p r o c e d u r e i s p e r f o r m e d . L o a d a n d d i s p l a c e m e n t m e a s u r i n g

dev ices ; i .e ., l oad ce l l s, l inea r va r i ab l e de form at ion tr ansdu cer s -LV DT s) a re checked fo r

l i nea r i ty and pro per ca l i b ra t i on . The ab i l i ty o f so f tware to con t ro l and acqu i r e da t a i s a lso

a s s e ss e d . W h e n t h e p r o c e s s o f v e r if y i n g in d i v id u a l s y s t e m c o m p o n e n t s is c o m p l e te , th e

overa l l capab i l i t y o f the m achine t o condu c t a spec i f ic exper im ent is a s sessed th rough

spec i a l l y des igned s t a ti c and cyc l i c exper im ent s on mate r i a l s wi th kno wn p roper t i e s .

O n c e t h e s y s t e m h a s b e e n e v a lu a te d , t h e p r o f ic i e n c y p h a s e o f t h e p r o c e d u r e a d d r e s se s



GROEGER ET AL ON STARTUP PROCEDURES 43

c o m p e t e n c e o f l a b o ra t o r y p e rs o n n e l t o p re p a r e a n d t e st s p e c im e n s . T h r o u g h u s e o f t h is

p r o c e d u r e , a l l c o m p o n e n t s n e c e s s a r y t o o b t a i n r e p e a t a b l e , a c c u r a t e t e s t r e s u l ts a r e

v e r i f i e d .

T h e p r o c e d u r e e n a b l e s l a b o r a to r i e s t o v e r i f y t h e i r t e s ti n g s y s t e m s p r i o r to t h e s t a r t o f

p r o d u c t i o n t e s t in g b y u s i n g a c o m p r e h e n s i v e a n d l o g i c a l p r o c e s s . I t c a n a l s o b e u s e d t o

p e r f o r m o n g o i n g q u a l i t y c o n tr o l c h e c k s o f e q u i p m e n t a n d t e s t in g p r o c e s s e s b e i n g u s e d b y

t h e l a b o r a t o r y d u r i n g t h e p r o d u c t i o n t e s ti n g p r o c e s s .

I t s h o u l d b e n o t e d t h a t t h e tw o p r i m a r y g o a l s o f th i s p r o c e s s a r e 1 ) to e n s u r e t h a t th e

t e st s y s t e m a n d t e c h n i c i a n s a r e c a p a b l e o f p e r f o r m i n g a t e s t p r o c e d u r e , a n d 2 ) t o d e v e l o p

a b e n c h m a r k p e r f o r m a n c e s t a n d a rd a g a i n st w h i c h t h e l a b o r a t o ry c a n b e e v a l u a te d o n a n

o n - g o i n g b a s i s . T h i s i s a v e r y i m p o r t a n t p a r t o f a n y q u a l i ty c o n t r o l / q u a l it y a s s u r a n c e

s y s t e m .

T h e p r o c e d u r e s h o u l d b e u s e d p r i o r t o st a r ti n g a te s t in g p r o g r a m , e v e r y y e a r d u r i n g

p r o d u c t i o n t es ti n g, , a n d a f t e r p e r i o d s o f s y s t e m i n a c t i v i ty i .e ., s i x w e e k s o f d o w n - t i m e ) .

I t c a n a l s o b e u se d w h e n e q u i p m e n t is re p l ac e d , m o v e d , o r w h e n e v e r a s u s p e c te d

o v e r l o a d o r m a l f u n c t i o n o c c u r s . A n o t h e r i m p o r t a n t u s e o f t h e p r o c e d u r e i s t o v e r i f y

o p e r a t io n o f n e w m a c h i n e s b e i n g d e l i v e re d b y a m a n u f a c tu r e r. C o n v e r s e l y , th e

p r o c e d u r e c a n b e u s e d t o v e r i fy th e a b i l i t y o f o ld e r m a c h i n e s t o p e r f o r m n e w

a p p l i c a t i o n s .

T h e r e a r e s e v e r a l o b v i o u s b e n e f i t s o f u s in g c o n c e p t s d e t a i le d h e r e i n . T h e f i r st is t h a t

t h e p r o c e d u r e p r o v i d e s g u i d e l i n e s f o r st a n d a r d i z a t io n o f a n e n ti re t e s t p r o c e s s . I t a l s o

p r o v i d e s a b e n c h m a r k p e r f o r m a n c e s t a n d ar d f o r e q u i p m e n t . I f i m p l e m e n t e d c o r re c t ly , i t

c a n m i n i m i z e e q u i p m e n t a n d o p e r a t o r v a r i a b i l i t y a n d t h u s p r o v i d e g r e a t e r c o n f i d e n c e i n

t e s t r e s u l t s a n d t h e i r a p p l i c a t i o n i n r e s e a r c h o r d e s i g n .

l e c t r o n i c s S y s t e m s P e r f o r m a n c e V e r i fi c a t io n P r o c e d u r e

T h e

electronics system perform nce verific tion procedu re

c h a r a c t er i z e s f r e q u e n c y

r e s p o n s e o f s i g n a l c o n d i t i o n e r s a n d t h e d a t a a c q u i s it i o n s y s t e m . T h i s p r o c e d u r e i s

g e n e r a l l y u s e d p r i o r t o in i t ia t io n o f a r e s il ie n t m o d u l u s t e s ti n g p r o g r a m . A s l o n g a s a l l

e l e c t ro n i c p a r t s o f th e t e s t s y s t e m r e m a i n t h e s a m e , t h is p r o c e d u r e d o e s n o t n e c e s s a r i l y

n e e d t o b e r e p e a t e d o n a c o n t i n u i n g b a s is . H o w e v e r , i t m a y b e c o n d u c t e d y e a r l y t o v e r i fy

e q u i p m e n t m e e t s a c c e p t a n c e c r i t e ri a o r w h e n a n y p a r t o f t h e e le c t r o n i c s i s r e p l a c e d o r

m o d i f i e d . A l s o , th e p r o c e d u r e c a n b e p e r fo r m e d w h e n o t h e r c i r c u m s t a n c e s s u g g e s t t h a t

e l e c t r o n i c s a r e s u s p e c t. G e n e r a l l y , a n e le c t r o n i c s t e c h n i c ia n w e l l - v e r s e d i n d a t a

a c q u i s i ti o n s y s t e m s is n e e d e d t o p e r f o r m t h e s e e x p e r i m e n t s .

B a s e d u p o n e x p e r i e n c e o f m u l t ip l e s y s t e m e v a l u a t i o n s , it h a s b e e n f o u n d t h a t t h e

e l e c t r o n i c s v e r i f i c a t io n p r o c e d u r e i s b y f a r t h e m o s t c o m p l e x a n d d i f f ic u l t p o r t i o n o f t h e

e v a l u a t i o n p r o c e d u r e .

W h e n p e r f o r m i n g a te s t, i t i s g e n e r a l l y a c c e p t e d t h a t te s t t r a n s d u c e r s b e c a l i b r a te d .

T h i s i s a p r o c e d u r e i n w h i c h o u t p u t o f t h e tr a n s d u c e r i s c o m p a r e d t o a k n o w n t e s t v a lu e

e . g . , a l o a d , p r e s s u r e , o r d i s p l a c e m e n t ) , a n d a r e l a t i o n s h i p u s u a l l y li n e a r ) is d e v e l o p e d

b e t w e e n t r a n s d u c e r o u t p u t a n d k n o w n a p p l i e d t e st v a l u e s . T h e r e s u l t in g c u r v e i s t h e

t r a n s d u c e r c a l i b r a t i o n . T h i s c a l ib r a t io n p r o c e d u r e i s a r e q u i r e d e l e m e n t i f t h e u s e r i s t o

k n o w t e s t v a l u e s b e i n g a p p l i e d to a s p e c i m e n u n d e r t e st . B u t t h i s c a l i b r a ti o n i s b y n o

m e a n s t h e o n l y f a c t o r w h i c h i n f l u e n c e s te s t r e a d i n g s . T h e c a l i b r a ti o n p r o c e d u r e m a y n o t



RESIL IENT MODULUS TESTING FOR PAVEMENT COMPONENTS

a c c o u n t f o r s y s t e m e l e c tr o n i c s, a n d i t c e r t a i n ly d o e s n o t a c c o u n t f o r t im e v a r y i n g t e s t

c o n d i t io n s . I f t e st s y s t e m e l e c t r o n ic s a r e i m p r o p e r l y c o n f i g u r e d , t e st r e a d i n g s m a y b e

qu i t e wro ng , even i f t r ansduce r s a r e ca l ib r a t ed .

T h e p u r p o s e o f t h e e l e c t ro n i c s v e r i f i c a ti o n p r o c e d u r e i s t o a s s es s c y c l i c s y s t e m

p e r f o r m a n c e o f t h e d a t a a c q u i s i ti o n s y s t e m ( D A S ) s o th a t t h e u s e r is c o n f i d e n t t h a t v a lu e s

m e a s u r e d b y t h e c o m p u t e r a r e in f a c t l o a d s , d is p l a c e m e n t s a n d p r e s s u r e s b e i n g a p p l i e d t o

t h e s p e c i m e n . T o p e r f o r m t h is v e r i f ic a t i o n te s t o n t h e d a ta a c q u i s i ti o n s y s t e m , k n o w n

s i g n a ls ( k n o w n i n ti m e a n d m a g n i t u d e ) a r e a p p l ie d t o e a c h c o n d i t i o n e d c h a n n e l i n

s u c c e s s i o n , a n d r e s p o n s e o f e a c h c h a n n e l is c o m p a r e d t o a k n o w n a p p l i e d s ig n a l. T h e s e

v e r i f i c a ti o n te s ts a r e p e r f o r m e d i n - s y s t e m t o as g r e a t a n e x te n t a s p o s s i b l e s o t h a t t h e

en t i r e t r ansduce r / cond i t i on ing / acqu i s i t i on sys t em i s i nco rpo ra t ed i n t he ve r i f i c a t i on t e s t .

A n a d d i t io n a l b e n e f i t o f p e r f o r m i n g t h e s e v e r i f ic a t i o n t es ts i s t h a t t h e t e s t s y s t e m i s

e x e r c i s e d a n d o p e r a t o r s b e c o m e m o r e f a m i l i a r w i t h b o t h s o f t w a r e a n d h a r d w a r e o f t h e

s y s t em . I f an o p e n m i n d i s u s ed t o a n a l y z e s o u r c e s o f er r o r a n d a b e r r a ti o n s w h i c h a r e

e x h i b i te d d u r i n g t h e s e t e st s, t h e n o t h e r i n te r r el a te d s h o r t c o m i n g s o f t h e s y s t e m c a n o f t e n

b e d e d u c e d a n d r e c ti f ie d , r e s u l ti n g i n a m o r e r o b u s t a n d p r o p e r l y o p e r a t i n g s y s t e m .

T h e r e f o r e , t h e p r o c e d u r e s h o u l d n o t b e u s e d i n a c o o k b o o k m a n n e r . I n s t e a d t h e o b j e c t i v e

o f e a c h t a s k a n d r e s p o n s e o f th e s y s t e m s h o u l d a l s o b e u n d e r s t o o d , r a t h e r t h a n a p p l y i n g a

g o / n o - g o m e n t a l i t y .

T h e p r o c e d u r e h a s b e e n d e v e l o p e d t o e v a l u a te f il te r s e tt in g s o f s i g n a l c o n d i t i o n e rs .

W he n a s i gna l pa s se s t h roug h a f il t e r ( i n mos t ca se s t h is i s a low -pas s f i lt e r) , t he s i gna l i s

d e l a y e d b y a c o n s ta n t a m o u n t ( t h e d e l a y o f w h i c h is f o r t h e m o s t p a r t i n d e p e n d e n t o f

f r equen c i e s u sed i n t he se t e s ts ) . I n add i t i on , t he s i gna l is a t t enua t ed a s t he s i gna l

f r e q u e n c y i n c r e a s e s p a s t th e f i l te r c u t o f f f re q u e n c y . I f th e i n p u t t o t h e c o n d i t i o n e r i s

c o m p a r e d t o t h e o u t p u t s i g n a l o v e r a r a n g e o f f re q u e n c i e s, t h e u s e r c a n i d e n t i f y t h e ty p e

o f f i lt e r a n d f i l te r c u t o f f f r e q u e n c y . M o r e i m p o r t a n t ly , t h e u s e r c a n e v a l u a t e w h e t h e r t h e

c o n d i t i o n e d s i g n a l c l o s e l y d u p l ic a t e s ( b o t h i n m a g n i t u d e a n d i n ti m e ) t h e p h y s i c a l

p r o c e s s e s b e i n g m o n i t o r e d .

T h e p r o c e d u r e u s e d t o e v a l u a t e f i lt e r se t ti n g s w a s i n i t ia l ly d e v e l o p e d u s i n g a w h o l l y

e l e c tr i ca l a p p r o a c h i n w h i c h t r a n s d u c e rs w e r e e l e c tr i c a ll y s im u l a t e d . T h i s a p p r o a c h

w o r k s w e l l f o r D C t y p e s i g n a l c o n d it i o n e rs , b u t h a s s e r i o u s d r a w b a c k s f o r t r a n s d u c e r s

w h i c h r e l y o n A C e x c i t a t i o n (e .g ., L V D T s ) . F o r t h e s e A C e x c i t e d tr a n s d u c e rs , a n e w

s i m u l a t i o n i n t e r f a c e c i r c u it h a s t o b e d e s i g n e d , b u il t, a n d t e s t e d f o r e a c h t y p e o f A C

s igna l cond i t i one r . Th e new con s t ruc t i on and t e s t i ng o f t he t e s t c i r cu i t is i n i t s e l f a ta sk

w hic h i s qu i t e l abo r i n t ens ive and t he f i na l t e s t c i r cu i t cou ld po t en t i a l l y i n t rodu ce no i se .

I n a d d i ti o n , a n y e r r o rs i n t r o d u c e d b y t h e c i r c u i t n e e d t o b e q u a n t i fi e d . A n o t h e r i s s u e w i t h

t h is a p p r o a c h i s t h a t t h e n e w c i r c u it n e e d s t o b e t e s t e d i n t h e s y s t e m b e f o r e i t is d e e m e d

a c c e p t a b le . T h i s a p p r o a c h i s v e r y ti m e - c o n s u m i n g .

T o w o r k a r o u n d t h e s e s h o r t c o m i n g s , a m e c h a n i c a l a p p r o a c h w a s d e v e l o p e d t o a c t u a te

s y s t e m L V D T s a n d t e st th e A C c o n d i t io n i n g s y st e m b y c o m p a r i n g m o v e m e n t o f a

r e fe r e n ce L V D T t o d i sp l a c e m e n t o f t h e s y s te m L V D T b e i n g te st ed . ( T h is m e c h a n i c a l

L V D T a c t u a to r c o u l d b e f u r th e r m o d i f ie d t o i n cl u d e a s t ra in g a u g e d m e m b e r w h i c h

w o u l d b e m e c h a n i c a l l y fl e x e d a n d re s u l t i n a W h e a t s t o n e b r i d g e o u t p u t w h i c h c o u l d b e

used t o s imu la t e a l oad ce l l. Thus , w i th t h i s mech an ica l a c tua to r , no e l ec t r i ca l

s i m u l a t i o n s w o u l d b e r e q u i r e d t o p e r f o r m t h e v e r i f ic a t i o n t e st s. )




A n a l t e r n a ti v e p r o c e d u r e t o e l e c tr i c a l si m u l a t i o n h a s b e e n d e v e l o p e d f o r e v a l u a t i n g

l o a d c e ll c h a n n e l s . I n th i s a p p r o a c h t h e l o a d ce l l is p h y s i c a l l y a c t u a t e d u s i n g t h e

h y d r a u l i c l o a d i n g s y s t e m . T h e h y d r a u l i c l o a d i n g r a m a p p l i e s a s i n u s o i d a l lo a d a t

f r e q u e n c i e s u p t o 5 0 H z . G e n e r a l l y m o s t s y s t e m s e n c o u n t e r e d t o d a te s e e m t o b e l i m i t e d

t o a fr e q u e n c y o f 2 0 H z o r s o ( a lt h o u g h t h is m a y b e s o f t w a r e l i m i t e d r a th e r t h a n b e i n g

l i m i t e d b y h a r d w a r e ) . D u e t o t h is i n a b i li t y t o r e a c h 5 0 H z , D C c o n d i t i o n e r s w i l l h a v e to

b e e l e c t r i c a l l y s im u l a t e d u n l e s s t h is l i m i t a ti o n c a n b e o v e r c o m e .

A n o t e c o n c e r n i n g f i lt e r s e t t i n g s is w a r r a n t e d i n t h i s d i s c u s s i o n . L o w p a s s f i l t e rs a r e

a n i n te g r a l p a r t o f m o s t s i g n a l c o n d i t i o n i n g s y s t e m s . T h e y a r e u s e d t o s m o o t h o u t d e s i r e d

s ig n a ls a n d t o b l o c k h i g h f r e q u e n c y n o i s e w h i c h m a y b e s u p e r i m p o s e d o n t h e d e s ir e d

s ig n a l . I n th e c a s e o f A C c o n d i t i o n i n g s y s t e m s , t h e y a l s o fi lt e r o u t a n y r e s id u a l n o i s e d u e

t o t h e c a r r i e r f r e q u e n c y . W i t h s u c h b e n e f i t s t o b e g a i n e d f r o m f i lt e r s, it i s t e m p t i n g t o

a d d a s m u c h f i lt e r in g a s p o s s ib l e . T h e p r o b l e m w i t h th i s a p p r o a c h i s t h a t f il te r s a ls o

i n t r o d u c e a t im e d e l a y a n d t e n d t o a t te n u a t e t h e d e s i r e d s i g n a l a s th e f r e q u e n c y o f t h e

d e s i g n e d s i g n a l s t a r ts t o a p p r o a c h t h e f i l t e r c u t - o f f f r e q u e n c y . I t i s b e s t t o se t th e s e l o w

p a s s f i l te r s a s h i g h a s p o s s i b l e a n d y e t st il l o b t a i n a s m o o t h s i g n a l . T h e s e f i lt e r se t t i n g s

s h o u l d b e r e c o r d e d a n d t e st s p e r f o r m e d w i t h t h e s e f i l te r s e tt in g s .

B e f o r e s e t tl in g o n t h e s e f il te r se t ti n g s , t h e u s e r s h o u l d o p e r a t e t h e t e s t s y s t e m u n d e r

v a r i o u s c o n d i t io n s t o a s c e r t a in t h e s e t ti n g s w h e n a v a r i e t y o f o p e r a t i n g e n v i r o n m e n t s a r e

e n c o u n t e r e d . S t a r t in g a n d s t o p p i n g o f la r g e i n d u c t i v e m o t o r s c r e a te a p a r t i c u l a r ly l a r g e

a m o u n t o f e l e c tr i c a l in t e r fe r e n c e . T o a c c o u n t f o r t h e s e p o te n t i a l s o u r c e s o f e l e c t ri c a l

n o i s e , a ir c o n d i t i o n e rs , c o m p r e s s o r s , h y d r a u l i c p u m p s , a n d o t h e r l a r g e m o t o r s s h o u l d b e

s t a rt e d a n d s t o p p e d w h e n t a k i n g d a t a in a n a t t e m p t t o i d e n t i fy s o u r c e s o f n o i s e w h i c h

m i g h t i m p a c t t h e s y s t e m . F i l te r c u t - o f f f r e q u e n c i e s s h o u l d b e s e t t o r e d u c e t h is n o i s e t o a

t o l e r a b l e l e v e l . I f r e d u c i n g f i lt e r s e t t i n g s d o e s n o t r e d u c e n o i s e s u f f i c i e n t l y , t h e te s t

s y s t e m s h o u l d b e i s o l a t e d f r o m t h e s o u r c e o f e l e c t ri c a l n o is e .

T y p i c a l l y a t e st s y s t e m w i ll u s e f i lt e rs o f th e s a m e t y p e o n e a c h o f it s c h a n n e l s . I n th i s

i n s ta n c e , i t m i g h t b e a g o o d p o l i c y t o s e t c u t - o f f f r e q u e n c i e s o f th e f i l te r s to t h e s a m e

v a l u e s . T h u s , e v e n t h o u g h f il te r s m i g h t i n t r o d u c e a d e l a y to e a c h c h a n n e l , r e l a t iv e d e l a y

b e t w e e n c h a n n e l s w o u l d b e n e a r l y z e r o , a n d w o u l d s ti ll re s u l t i n a sa t i s f a c t o r y c h a n n e l -

t o - c h a n n e l d e l a y ( a s l o n g a s t h e r e i s n o a p p r e c i a b l e a t te n u a t io n ) .

F i l te r s c a n b e s e t u s in g s o f t w a r e o r b y p h y s i c a l l y c h a n g i n g c o m p o n e n t s i n th e f i lt e r

s e c t i o n o f t h e si g n a l c o n d i t io n e r . U s u a l l y f il te r s a r e n o t p h y s i c a l l y m o d i f i e d d u e t o a

n a t u r a l h e s i ta t i o n o n t h e p a r t o f a te c h n i c i a n t o p h y s i c a l l y e n t e r in t o t h e c o m p u t e r o r

s i g n a l c o n d i t i o n i n g s y s t e m a n d m o d i f y th e s y s t e m . S i n c e it r e q u i r e s a k n o w l e d g e a b l e

e f f o r t t o m o d i f y a f i l te r , o n c e p h y s i c a l f i lt e rs a r e s e t t h e y a r e n o t u s u a l l y m o d i f i e d

( a l th o u g h t h e y m a y b e u n i n t e n t io n a l l y c h a n g e d w h e n a s i g n a l c o n d i t i o n i n g m o d u l e i s

c h a n g e d ) . O n t h e o t h e r h a n d , so f t w a r e f i lt e rs m a y b e e a s i ly m o d i f i e d , w h e t h e r

i n t e n t io n a l l y o r n o t, s i m p l y w i t h a f e w k e y s t r o k e s . D i l i g e n c e i s t h e r e f o r e r e q u i r e d o n t h e

p a r t o f th e t e s t o p e r a t o r to b e a w a r e o f w h a t f i lt e r se t ti n g s a r e, h o w t o c h a n g e t h e m , a n d

w h a t th e y s h o u l d b e f o r e a c h te s t. T e s t p r o c e d u r e s s h o u l d b e p e r f o r m e d u s i n g f i lt e r

s e t ti n g s f o r w h i c h i t i s a n t ic i p a t e d t h e t e s t w i l l b e n o r m a l l y r u n . A n y f i lt e rs s e t w i t h

d i f f e re n t c u t o f f f r e q u e n c i e s t h a n u s e d i n th e v e r i f i c a ti o n p r o c e d u r e w o u l d p o s s i b l y

i n v a l i d a t e a n y t e s t p e r f o r m e d w i t h t h e s e f i lt e r se t ti n g s.

O f t e n q u e s t i o n s a r is e r e g a r d i n g c h o i c e o f f r e q u e n c i e s u s e d i n t h i s v e r if i c a t io n

p r o c e d u r e . A t e s t e r s f o c u s i s g e n e r a l l y t h e t e s t b e i n g p e r f o r m e d . B u t c o n c e r n w i t h t h is




p o r t i o n o f th e v e r i fi c a ti o n p r o c e d u r e i s n o t p e r f o r m a n c e o f th e u l t im a t e t e st b e i n g

p e r f o r m e d , b u t c h a r a c t er i za t io n o f t h e e l ec t r o n ic s s y s t e m . T o t h i s e n d , u s e rs n e e d t o

m easu re r e sponse o f t he e l ec tr i ca l sys t em. Th e use r pe r form s ve r if i ca t ion a t l ow

f requenc i es to eva lua t e sys t em low f r equen cy r esponse . Un less s igna l condi t i oner s a r e

im pro per ly conf igured , t h i s low f r eq uenc y t e s t w i l l measure una t t enua t ed s igna l

th roughput . The h ighes t f r equen cy of 50 H z i s used to me asure s igna l de l ay t h rough

s igna l condi t ion ing / f i lt e r ing m odules . Th e f i lt e r ing sec t i on i n t roduces a con s t an t time

de lay wh ich i s f a i r l y i ndependent o f f r equency . Th i s smal l t ime de l ay i s obse rved wi th

be t t e r r e so lu t ion i f a h igh f r equ ency i s used . The re fore a ve r i fi ca t ion te s t a t 50 H z i s used

to accura t e ly cha rac t e r i ze s igna l de l ay due t o the f i lt e r ing / condi t ion ing mo dule . The t e s ts

a t in t e r m e d i a te f r e q u e n c ie s o f 1 0 a n d 2 0 H z a r e p e r f o r m e d t o m o r e t h o r o u g h l y

charac t e r i ze f r equen cy /a t t enua t ion o f t he channe l be ing t e s ted .

As d ocu m ented in t he p rocedure , t he fo l lowing c r i te r i a mu s t be me t i n o rde r to pass

the tes t .

9 Al l channe l s shou ld have m atched inpu t - to -ou tpu t de l ays . De lay s de r ived f rom

dig i ta l da t a shou ld i nd i ca t e ma tched inpu t - to -ou tpu t de l ays wi th in + 0 .000400 s a t

50 Hz .

9 T h e m a x i m u m d e v i a ti o n i n a m p l i t u d e ( s ig n a l a t te n u a ti o n ) fr o m 2 H z t o 1 0 H z f o r

a s ing l e channe l shou ld be l e s s t han 0 .5 pe rcen t a s de t e rmined f rom d ig i t ized da t a.

I f abov e c r it e r i a a re no t me t , p rob l e m s such as i nadequ a t e f i lt e rs (o r unm atched f i lt e r s)

o r i nadequac i es i n da t a acqu i s it i on ha rdware / sof tware shou ld be i nves t i ga t ed and t e s t s

should be r epea t ed . F i l t e r cha rac t e r is t ic s shou ld no t cause excess ive amp l i tude o r phase

e r ror s i n t he s igna l s . F i l te r se tt ings shou ld r em ain unchan ged a f t e r t he e l ec t ron i cs sys t em

has pa ssed the acce p tance c r i te r ia .

Th ere a re no easy ru l es t o use i n choos ing the bes t ve r i f i ca ti on t e s t conf igura t i on . The

e l ec t ron i c s imula t i on o f LV DT s can be d i f f icu l t t o under s tand , w hereas m echan ica l

ac tua t ion i s qu i t e easy t o comprehend . So more t han any th ing e lse , use r ' s cho ice o f

conf igura t i on depen ds on equ ipm ent which i s ava i l ab l e and des ign o f t he da t a acqu i s i t ion

sys t em , a s we l l a s t he approa ch wi th w hich the i nves t i ga to r f ee ls com for t ab l e .

I f t he re i s no t i ceab l e s igna l a t tenua t ion , t hen f i lt e r cu t -o f f se t ti ngs a re gen era l l y se t t oo

low and need to be m odi f i ed . I t i s ve ry ins t ruc tive fo r the pe r son pe r form ing the te s t to

exp er ime nt wi th f i l t e r se t t ings and se t t hem to sequen t i a ll y l ower and lowe r va lues . Th e

outpu t s i gna l wi l l be seen to ge t smal l e r and sm al l e r even thoug h inpu t s i gna l s rem ain t he

same . Th i s exe rc i se dem ons t r a t e s the im por t anc e o f p rop er f il t e r se t ti ngs , and ho w

imp rope r f i lt e r se t ti ng can r esu l t i n use l es s da t a .

a l ib r a t io n h e c k a n d O v e r a l l S y s t e m P e r f o r m a n c e V e r i f ic a t io n P r o c e d u r e

C y c l i c te s t in g p r o c e d u r e s r e q u i re a s y s t e m m a d e u p o f m a n y d i f fe r e n t p i e c e s o f

equ ipm ent : l oad f r ame , l oad ce l l s, hydrau l i c sys t em , de form at ion dev ices , t ri ax i a l

p ressure cham ber , t emp era tu re cham bers , com pute r , e tc . For t he

calibration check and

overall system performance verification procedure

i nd iv idua l e l em ent s o f t e s t equ ipm ent

a re chec ked f i rs t fo l l owed by overa l l t e s t s etup . Th i s ve r i f ie s tha t the t e s t sys t em i s

prod uc ing ex pec t ed r esponses . B y f ir s t check ing ind iv idua l com pon ent s o f t he t e s t




s y s t e m , i t i s e x p e c t e d t h a t m a n y p r o b l e m s t h a t w o u l d b e e n c o u n t e r e d d u r i n g a c t u a l c y c l i c

t e s t in g c a n b e i d e n t i fi e d a n d e l i m i n a t e d p r i o r to c h e c k i n g th e o v e r a l l s y s te m . T h i s

p r o c e d u r e i s g e n e r a l l y u s e d p r i o r t o i n it i at io n o f a t es t in g p r o g r a m a n d s u b s e q u e n t l y o n a

c o n t i n u i n g b a s i s (i.e . m o n t h l y ) t o v e r i f y s y s t e m r e s p o n s e .

T h e f o l l o w i n g s e c t i o n is b r o k e n d o w n i n t o e ig h t c o m p o n e n t s a s f o l l o w s :

1. D e f o r m a t i o n m e a s u r e m e n t d ev i c e

2 . L o a d c e l l z e r o

3 . Lo ad ce l l c a l i b r a t i on

4.. Ve r i f i ca t i on o f l oad ce l l c a l i b r a t i on ( s t a ti c )

5 . L o a d v e r s u s d e f o r m a t i o n r e s p o n s e c h e c k ( c y c l ic )

6 . S y s t e m c y c l ic r e s p o n s e c h e c k

7 . T r i ax i a l p r e s su r e cha m ber

8 . E n v i r o n m e n t a l c h a m b e r

eformation Measurement evices

On e o f t he m os t c r i t ic a l a spec t s o f a cyc l i c ma te r i a l s t e s t i ng sy s t em i s t he s t r a in , o r

d e f o r m a t i o n tr a n s d u c er , u s e d to m e a s u r e m o v e m e n t o f t h e sp e c i m e n . T h e s e c a n c o n s i s t

o f L i n e a r V a r i a b l e D i f f e re n t ia l T r a n s d u c e r s ( L V D T s ) , e x t e n s o m e t e r s , s t r ai n g a u g e s , a n d

o t h e r t y p e s o f d e v ic e s . T h e p u r p o s e o f t h is e x p e r i m e n t i s to v e r i f y t h a t th e d e f o r m a t i o n

m e a s u r e m e n t d e v i c e i s p r o p e r l y c a li b r a te d a n d p e r f o r m i n g i n a n a c c e p t a b l e m a n n e r . T h e

p r o c e d u r e w a s d e v e l o p e d f o r L V D T s o r e x t e ns o m e t e rs ; h o w e v e r a s im i l a r a p p r o a c h c a n

b e u s e d f o r o t h e r ty p e s o f d e f o r m a t i o n m e a s u r e m e n t e q u i p m e n t .

T h e d e f o r m a t i o n m e a s u r e m e n t d e v i c e m u s t b e m a t c h e d t o t h e a p p l ic a t io n . F o r a m o r e

d e t a i le d e x p l a n a t i o n o f t h e t y p e s o f d e f o r m a t i o n m e a s u r e m e n t d e v i c e s a n d t h e i r

a p p l i c a ti o n , t h e r e a d e r i s r e f e rr e d t o t h e c y c l i c t e st s y s t e m m a n u f a c t u r e r o r v a r i o u s

d e f o r m a t i o n m e a s u r e m e n t d e v i c e m a n u f a c tu r e rs . M u c h o f th is i n f o r m a t io n c a n b e

o b t a i n e d f r o m t h e m a n u f a c t u r e r ' s w e b s ite .

A s d o c u m e n t e d i n th e p r o c e d u r e , t h e f o l l o w i n g c r it e ri a m u s t b e m e t i n o r d e r t o p a s s

the test .

9 T h e b e s t f i t c u r v e s h a l l h a v e a z e ro i n te r c e p t ( + 0 . 0 2 5 4 m m ) , a n d a R 2 v a l u e o f a t

leas t 0 .99 .

9 T h e m a x i m u m d i f f er e n c e i n r e a d in g s b e t w e e n m i c r o m e t e r a n d d e f o r m a t i o n d e v i c e

c a n n o t e x c e e d o n e p e r c e n t o f d e v i c e f u ll s c a le tr a v el . F o r e x a m p l e , f o r a

d e f o r m a t i o n d e v i c e w i t h a f u l l s c a l e ra n g e o f 2 .5 4 r a m , t h e m i c r o m e t e r v e r s u s

d e f o r m a t i o n d e v i ce r e a d in g s s h o u l d b e w i t h i n + 0 . 0 2 5 4 m m

9 T h e d e f o r m a t i o n d e v i c e s h a ll b e f r ee o f v i s u a l d e f e c t s a n d s h o u l d o p e r a t e i n a n

a c c e p t a b l e m a n n e r ( n o v i s ib l e d a m a g e a n d n o s t ic k i n g o f d e v i c e , e t c. ).

I n a p r o d u c t io n t e s ti n g m o d e , i t is r e c o m m e n d e d t h a t L V D T s b e v e r i fi e d e v e r y t w o

w eeks o r a ft e r eve ry 50 r e s i li en t mod u lu s te s t s, wh ich eve r com es f ir s t. I n add i t ion , i t i s

h i g h l y r e c o m m e n d e d t h a t t h e m i c r o m e t e r u s e d t o c h e c k c a li b r a t io n b e N I S T c a l ib r a t e d o r

c a l ib r a t e d u s i n g N I S T t r a c ea b l e g a u g e b l o c k s .




Load ell Zero

I t i s n o t u n c o m m o n i n a l a b o r a t o r y t o o v e r l o a d a l o a d c e ll . O v e r l o a d i n g c a n o c c u r d u e

t o a c c i d e n t a l l y e x c e e d i n g t h e r a t e d c a p a c i t y o f th e l o a d c e ll , o r b y d r o p p i n g i t. I n

add i t i on , i f a ce l l is l oaded t o nea r i ts r a ted capa c i t y , and t he spec ime n f a i l s b r i t tl ey , t hen

t h e c y c l i c s tr e ss w a v e w h i c h p a s s e s t h r o u g h t h e d e v i c e c a n a l s o o v e r s tr e s s t h e c e ll . S u c h

o v e r l o a d i n g n e e d s t o b e e v a l u a t e d p e r i o d ic a l ly . I t i s o ft e n e r r o n e o u s l y t h o u g h t t h at t h e

c e l l n e e d o n l y b e r e c a l ib r a t e d i n e v e n t o f a n o v e r l o a d . I n s o m e c a s e s o f m i l d o v e r l o a d i n g ,

t h is a p p r o a c h m a y b e a c c e p ta b l e , b u t o f t e n t h e o n l y r e c o u r s e i s t o d i sp o s e o f t h e l o a d c e ll .

A n o v e r l o a d e d l o a d c el l c a n a c q u i re s o m e v e r y u n d e s ir a b l e c h a r a ct e ri s ti c s. F i r st o f

a l l, the l oad ce l l z e ro w i l l u sua l l y sh i f t due t o ove r load ing . Th i s i s t he mo s t obv ious s i gn

o f a n o v e r l o a d e d c e l l. A g a i n , i t i s c o m m o n l y b e l ie v e d t h a t o n e c a n j u s t r e - z e r o t h e c e l l

a n d c o n t i n u e t e s ti n g . U n f o r t u n a t e l y , b y o v e r l o a d i n g t h e c e ll , a p o r t i o n o f t h e s e n s i n g

m e m b r a n e i n t h e c e l l h a s g o n e i n to p la s t ic i ty . T h i s p e r m a n e n t d e f o r m a t i o n c h a n g e s t h e

e l a st ic b e h a v i o r o f th e c e l l s e n s i n g m e m b e r . I n a d d i t i o n t o z e r o o f fs e t , th e c e l l m a y n o w

have a d i f f e r en t ca l i b r a t i on f ac to r , and more impor t an t l y , i t may we l l exh ib i t hys t e r e s i s

a n d c r e e p . T h u s t h e l o a d i n g c u r v e ( o f l o a d c e ll v o l t a g e v s . k n o w n l o a d ) w i l l n o t f o l l o w

t h e u n l o a d i n g c u r v e . C r e e p b e h a v i o r i s m a n i f e s te d b y n o t r e t u m i n g t o z e r o a f te r b e i n g

u n l o a d e d , a n d t h e n g r a d u a l l y s e tt li n g d o w n t o a z e r o re a d i n g. O r a f t e r a p p l y i n g a l ar g e

load , t he ce l l w i l l s l ow ly d ri f t t o a s t eady r ead ing . Th ese t r a it s a r e una ccep t ab l e fo r any

t r a n s d u c e r, a n d s u c h a n o v e r l o a d e d c e l l s h o u l d b e r e p a i r e d o r r e p la c e d .

W he n a l oad ce l l i s f ab r ica t ed and se t up a t the f ac to ry , t he whe a t s tone b r idge i s

ba l anc ed , e i t he r u s ing l a se r t r imm ed s t r a in gaug es o r add i ti ona l r e s i s to r s , t o r ead a nea r

z e r o v o l t s w h e n t h e b r i d g e i s ex c i te d . W h e n t h e c el l is o v e r l o a d e d , th i s b a l a n c e i s

d e s t r o y e d .

A s d o c u m e n t e d i n t h e p r o c e d u r e , t h e f o l l o w i n g c r i te r ia m u s t b e m e t i n o r d e r t o p a s s

the tes t .

9 L o a d c e ll z e ro r e a d in g s h o u l d b e w i t h in 1 .5 p e r c e n t o f i ts f u ll - sc a l e f a c t o r y

ind i ca t ed s ens i t iv i t y .

I f l oad ce l l z e ro r ead ing e xceed s 1 .5 pe rcen t o f i ts f u l l -s ca l e f ac to ry ind i ca t ed

sens i t iv i t y , t hen i t sho u ld be r e tu rned t o t he man ufac tu r e r f o r eva lua t i on . I f t he l oad ce l l

m e e t s s p e c i f ic a t i o n s u s i n g m a n u f a c t u r e r 's t e st e q u i p m e n t t h e n t h e l o a d c e l l i s c o n s i d e r e d

s u i ta b l e f o r u s e . I f it d o e s n o t m e e t m a n u f a c t u r e r ' s s p e c i fi c a ti o n s , t h e n i t s h o u l d b e

r e p a i re d o r r e p l a c ed . I t i s r e c o m m e n d e d t h a t t h e l o a d c e ll z e r o c h e c k b e c o n d u c t e d o n a l l

l o a d c e l ls a t l e as t y e a r l y o r w h e n e v e r a s u s p e c t e d o v e r l o a d h a s o c c u r r e d .

Load ell alibration

L o a d c e l l c a li b r a ti o n i s e q u a l ly i m p o r t a n t a s th e l o a d c e ll z e r o c h e c k . A s p a r t o f a n y

s t a n d a r d l a b o r a t o r y q u a l i t y c o n t r o l p l a n , l o a d c e l l s s h o u l d b e e v a l u a t e d a t l e a s t y e a r l y

e i t h er i n - h o u s e , b y t r a in e d s t a f f a n d N I S T t r a c e a b le s t an d a r d s, o r u s i n g a c a l i b ra t i o n

s e r v i c e w i t h a N a t i o n a l I n s t it u t e o f S ta n d a r d s a n d T e c h n o l o g y ( N I S T ) t r a c e a b l e c e ll . I n

e i th e r c a s e , t h e c a l i b r a ti o n s h o u l d b e c o n d u c t e d u s i n g t h e l a t es t v e r s i o n o f S t a n d a r d

P r a c t i c e s f o r F o r c e V e r i f i c a ti o n o f T e s t i n g M a c h i n e s ( A S T M E 4 ) . T h e c a l i b r a t io n s h o u l d




b e p e r f o r m e d f o r t h e e n t ir e l o a d c e l l o p e r a t i n g ra n g e . T h e l o a d i n g d e v i c e s h o u l d b e

v e r i f ie d a n n u a l l y a n d / o r i m m e d i a t e l y a f t e r a n y r e p a i r o r a n y r e l o c a t i o n o f t h e t e s t i n g

m ach ine r ega rd l e s s o f t ime in t e rva l s i nce t he l a s t ve r i f i c a ti on .

D u r i n g t h i s p o r t i o n o f t h e p r o c e d u r e , l o a d c e l l c a l i b r at i o n c e r ti f ic a t e s a r e s i m p l y

r e v i e w e d t o d e t e r m i n e i f t h is c a l i b r a ti o n h a s o c c u r r e d w i t h i n o n e y e a r .

A s d o c u m e n t e d i n t h e p r o c e d u r e , th e f o l l o w i n g c r it e ri a m u s t b e m e t i n o r d e r to p a s s

the tes t .

T h e l o a d c el l m u s t h a v e b e e n c a li b r a te d w i t h i n o n e y e a r o f i n s p e c ti o n . A m i s s i n g

ce r t i f i c a t e i s c ause fo r r e j ec t i on o f l oad ce l l f o r t e s ti ng un t i l t he nece s sa ry

ca l i b r a t i on has t aken p l ace .

Verification of Load Cell Calibration Static)

T h e v e r i f i c a ti o n o f t h e l o a d c e l l s ta t ic c a l ib r a t io n i s c o n d u c t e d w i t h t h e s y s t e m f u l l y

a s s e m b l e d a s i f a p r o d u c t i o n t e st w a s a b o u t t o b e p e r f o rm e d . I n t h is e x p e r i m e n t , a

p r o v i n g r i n g ( s p e c i m e n w i t h k n o w n p r o p e rt i es ) , o r o t h e r su i ta b l e d e v i c e , is u se d . T h i s

p r o c e d u r e d o e s n o t t a k e t h e p la c e o f t h e N I S T t r a c e a b l e c a l ib r a t io n m e n t i o n e d p r e v i o u s l y .

I t i s s i m p l y a c h e c k o f t h e e n t ir e s y s t e m v e r s u s a s p e c i m e n o f k n o w n p r o p e r ti e s .

Ve r i f i ca t i on o f l oad ce l l c a l i b r a t i on i s con duc t ed fo r two r ea sons : ( 1 ) t o ensu re t ha t

l o a d c e ll is p e r f o r m i n g a s e x p e c t e d in t h e s y s te m , a n d ( 2 ) t o c h e c k f o r u n w a n t e d s y s t e m

d e f o r m a t i o n s .

T w o m e t h o d s m a y b e u s e d t o p e r f o r m t h is p r o c e d u r e d e p e n d i n g o n t h e u s e r s t e st

r equ i r emen t s . I f ve r i f i c a t i on o f s t a ti c ca l i b r a t ion i s a ll tha t i s r equ i r ed , t he n a p rov ing

r i n g o r e x te r n a l l o a d c e l l c a n b e u se d . A s , in L T P P P r o t o c o l P 4 6 ( A A S H T O T - 3 0 7 ) ,

d e f o r m a t i o n t ra n s d u c e r s a r e m o u n t e d o u t s i d e t h e te s t c h a m b e r , t h u s th e u s e r w o u l d w a n t

t o m e a s u r e t h e d i f f e r e n c e b e t w e e n d e f o r m a t i o n m e a s u r e d i n s i d e th e s y s t e m v e r s u s t h a t

m e a s u r e d o u t s i d e t o d e t e rm i n e i f t h e r e is u n w a n t e d f r ic t i o n o r d e f o r m a t i o n s i n th e s y s te m .

I n t h is c a s e , a p r o v i n g r i n g w i t h a n i n t e r n a ll y m o u n t e d d i a l g a u g e o r d i g i ta l r e a d o u t i s

p r e f e r re d s o a s t o m a k e d e f o r m a t i o n c o m p a r i s o n s .

T h e r e a r e m a n y p r o v i n g t i n g s o n t h e m a r k e t t o d a y . I f t h e u s e r is g o i n g to p e r f o r m a n

i n s i d e d e f o r m a t i o n v e r s u s o u t s i d e d e f o r m a t i o n c h e c k u s i n g a p r o v i n g r i n g , i t i s

r e c o m m e n d e d t h a t t h e u s e r o b t a in a h i g h - q u a l i ty p r o v i n g r i n g t h a t c o n s is t s o f o n e s o l i d

p i e c e o f m e t a l r a t h e r th a n t h e t y p e t h a t h a s s e p a r a te u n i ts f o r t o p b o s s , r in g , a n d b o t t o m

b o s s . P a s t e x p e r i e n c e h a s s h o w n t h a t t h e s e m u l t i - p i e c e t in g s a r e u n s u i t a b l e f o r t h is

a p p l i c a t io n a s t h e y c o n t a i n m a n y m e t a l - t o - m e t a l i n te r f a c e s th a t c a n a d d t o m e a s u r e d

ou t s ide de fo rm a t ion , t hus mak ing r e su l ts d i f f i cu l t t o i n te rp re t . Th e s ing l e p i ece t i ngs do

n o t h a v e t h e s e e x t r a i n t e rf a c e s a n d t h e r e f o r e e r ro r s d u e t o e x t r a n e o u s d e f o r m a t i o n s o f

t i ngs a r e min im ized . I f l oad ve r i f i c a t i on i s al l t ha t is de s i r ed , a m u l t i - p i ece p ro v in g r i ng

i s a d e q u a t e f o r t h e ap p l i c at i o n . E q u i p m e n t u s e d t o a c c o m p l i s h t h is p r o c e d u r e d e p e n d s

en t i r e ly on use r goa l s .

I n o r d e r to p e r f o r m t h is p r o c e d u r e , t h e p r o v i n g r i n g o r o th e r l o a d m e a s u r e m e n t d e v i c e

m u s t b e m a t c h e d t o t h e a p p li c a ti o n . M a n y p r o v i n g r in g s a r e o n l y g u a r a n t e e d t o b e l i n e a r

f r o m 1 0 to 1 0 0 p e r c e n t o f t h e i r r a t ed c a p a c i t y . T h e r e f o r e , i f t h e t es t p r o c e d u r e

c o n t e m p l a t e d r e s u l ts i n l o a d s u p t o 4 .5 k N , t h e p r o v i n g r i n g s h o u l d b e m a t c h e d t o t h i s




r equ i r eme n t . Th e use r shou ld ve r i fy t he l oad ce l l c a l i b r a t i on fo r a l l l oads an t i c ipa t ed fo r

a pa r t i cu l a r t e s t app l i ca t i on .

A s d o c u m e n t e d i n t h e p r o c e d u r e , th e f o l l o w i n g c ri te r ia m u s t b e m e t i n o r d e r to p a s s

the tes t .

9 T h e te s t s y s t e m l o a d m u s t b e w i t h i n • p e r c e n t o f p r o v i n g r i n g l o a d.

9 T h e t e st s y s t e m d e f o r m a t i o n m u s t b e w i t h in :k 5 p e r c e n t o f p r o v i n g ri n g

d e f o r m a t i o n .

I f , u s ing t he ac cep t an ce c r i te r i a , t he sys t em f a il s th i s check , t he p ro ced ure i s repea t ed .

I f t he sys t e m f a il s s econd r ep l ica t e , t he sys t em f a il s. I f t he sys t e m pas se s t he s econ d t es t ,

t hen a t h i rd r ep l ica t e shou ld be run to de t e rmine a ccep t ance o r f a il u r e. Th e appa ra tu s

s h o u l d b e d i s a s s e m b l e d a n d r e - a s s e m b l e d i n - b e t w e e n e a c h r e p li c a te . I f t h e s y s t e m f a il s

t h i s check , t he l oad ce l l shou ld be reca l i b r a t ed , o r a ne w loa d ce l l sho u ld be i n s t a l l ed on

t h e te s t s y s t e m a n d t h e p r o c e s s r e pe a t e d . I f t h e s y s t e m d o e s n o t p a s s th e d e f o r m a t i o n

c r i te r i a , che ck sys t em f o r f r i c ti on i n tr i ax ia l p i s t on , m i sa l i gnm en t , l oose t r i ax ia l c e l l ,

l o o s e d e f o r m a t i o n d e v i c e s , e tc .

Lo ad versus Deformation Respo nse Check Cyclic)

I n o r d e r t o p r o p e r l y e v a l u a t e s u i t a b il i ty o f a p a r t i c u la r t e s t s y s t e m t o a g i v e n

a p p l i ca t i o n , i t i s e ss e n ti a l th a t th e m a c h i n e b e c o m p a r e d a g a i n s t a s p e c i m e n o f k n o w n

p r o p e r t ie s . T h i s c o m p a r i s o n w i l l a l l o w u s er s t o a s s e ss p e r f o r m a n c e o f e q u i p m e n t i n n e a r-

t e st c o n d i t i o n s w i t h o u t r e p e a t a b il i ty a n d a c c u r a c y l im i t a ti o n s i m p o s e d b y t e s t i n g a r e a l

s p e c i m e n . T h e r e b y , t h e p u r p o s e o f t h is e x p e r i m e n t i s t o si m u l a t e a n a c t u a l te s t a s c l o s e l y

a s p o s s i b l e a n d e n s u r e s y s t e m p e r f o r m a n c e m e e t s a n t ic i p a te d u s e r n e e d s . T h i s

e x p e r i m e n t i s d e s i g n e d t o p r o v id e a b e n c h m a r k p e r f o r m a n c e s t an d a r d t h a t c a n b e

repea t ed i n t he fu tu r e t o ensu re t he sys t em i s pe r fo rming in a cons i s t en t manne r .

I n o r d e r to p e r f o r m t h is p r o c e d u r e , a p r o v i n g r i n g w i t h a n i n t e r n a ll y m o u n t e d

d e f o r m a t i o n d e v i c e i s re q u i re d . A l t e r n a ti v e l y , i f m e a s u r i n g d e f o r m a t i o n o u t s i d e a tr ia x ia l

ce l l ( f o r a so i l s r e s i l i en t modu lus t e s t ) , de fo rma t ion can be mon i to r ed u s ing ex t e rna l

d e f o r m a t i o n d e v i c e s ( a s s u m i n g t h e s y s t e m h a s p a s s e d e x t e r n al v e r s u s i n t e rn a l

d e f o r m a t i o n te s t p r e s e n t e d p r e v i o u s ly ) . S i m i l a r r e q u i r e m e n t s r e g a r d i n g p r o v i n g r i n g s a s

p re sen t ed ea r l i e r app ly t o th i s te s t. I t i s a s su me d he re in t ha t t he p rov ing r i ngs u sed fo r

t h is t e s t p r o c e d u r e h a v e c a p a c i t y to p e r f o r m t e s ti n g i n a s i m i l a r m a n n e r a s t h e t e s t

p r o c e d u r e r e q u ir e s . N e v e r o v e r l o a d p r o v i n g r i n g s o r l o a d c e l ls w h e n p e r f o r m i n g th i s

p r o c e d u r e .

A s d o c u m e n t e d i n th e p r o c e d u r e , t h e f o l l o w i n g c r it e ri a m u s t b e m e t i n o r d e r to p a s s

the tes t.

9 G e n e r a t e d h a v e r s in e w a v e f o r m is c l o s e t o i d ea l h a v e r s i n e w a v e f o r m .

9 L o a d a n d d e f o r m a t i o n c o n s is t o f 5 0 0 p o i n t s p e r c y c le .

9 G e n e r a t e d d e f o r m a t i o n o u t p u t is w i t h i n 1 0 p e r c e n t o f i d e al h a v e r s i n e w a v e f o r m .

9 T i m e l a g b e t w e e n l o a d p e a k a n d d e f o r m a t i o n p e a k is l e ss t h a n 0 . 0 0 8 -s .

9 D e f o r m a t i o n i s o c c u r r i n g a f te r l o a d .

9 M a x i m u m a n d c y c l i c l o a d s w i t h i n 5 p e r c e n t o f t a rg e t.

9 Co n tac t l oad i s w i th in 10 pe rcen t o f t a rge t .




9 D e f o r m a t i o n d e v i c e s m e a s u r i n g w i t h i n 1 0 p e r c e n t o f e a c h o t h e r .

9 M ean de fo rm a t ion va lues ve r sus mea n app l i ed l oad wi th in 4 -5 pe rc en t li ne s.

9 R 2 o f be s t f i t l i ne shou ld be g r ea t e r t han 0 .99 .

I f , u s ing a ccep t ance c r i te r i a t he sys t em f a i l s t h i s check , t he p ro ced ure i s r epea t ed . I f

t he sys t em f a i ls the s e con d r ep l ica t e , t he sys t em f a i ls the check . I f t he sys t em pas se s t he

seco nd te s t , t hen a t h i rd r ep l i ca t e shou ld be run t o de t e rmine accep t ance o r f a i lu r e . Th e

a p p a r a t u s i s d i s a s s e m b l e d a n d r e - a s s e m b l e d i n - b e t w e e n e a c h r e p li c a te .

I f t h e s y s t e m f a il s th e l o a d i n g o r d e f o r m a t i o n c h e c k , o p e r a t o r s s h o u l d a d j u s t m a c h i n e

s e t ti n g s t o o b t a i n a b e tt e r w a v e f o r m . I f t h is d o e s n o t c o r r e c t t h e p r o b l e m , t h e

m a n u f a c t u r e r s h o u l d b e c o n t a c t e d t o a s s is t i n p r o b l e m r e s o lu t i o n .

I f th e s y s t e m f a il s ti m e l a g c h e ck , s y s t e m e l e c t r o n i c s a n d s o f t w a r e s h o u l d b e e v a l u a t e d

t o d e t e r m i n e t h e c a u s e o f t i m e d e l a y s . A l s o , c h e c k t h e s y s t e m f o r f r i c ti o n i n tr ia x i a l

p i s t o n , m i s a l i g n m e n t , l o o s e c o n n e c t i o n s , l o o s e d e f o r m a t i o n d e v i c e s , e t c.

System yclic Respo nse heck

T o i n v e s t ig a t e s y s t e m c y c l i c r e s p o n s e a n d i n v e s t i g a te t h e p o s s i b i l i t y o f e x c e s s i v e

f r i c t iona l f o r ce s , t r iax i a l f i x tu r e mi sa l i gnm en t , and m ach ine i nduc ed t ime l ag be tw een

l o a d a n d d i s p l a c e m e n t , a s e ri e s o f f re q u e n c y s w e e p s i n u s o id a l c y c l i c lo a d i n g e x p e r i m e n t s

i s c o n d u c t e d . T o p e r f o r m t h is te s t, c y c l i c l o a d a n d d e f o r m a t i o n r e a d i n g s a r e a c q u i r e d

f r o m t h e d a t a a c q u i s i ti o n s y s t e m u s i n g t h e l o a d ce l l a n d th e d e f o r m a t i o n d e v i c e m o u n t e d

o n t h e p r o v i n g ri n g . T h e d e f o r m a t i o n c a n a l s o b e o b t a i n e d f r o m d e f o r m a t i o n d e v i c e s

l o c a t e d e l s e w h e r e o n t h e s y s t e m s u c h a s o n t o p o f th e t r ia x ia l c e l l.

T h e p u r p o s e o f t h is t e st i s to a s c e r ta i n t h e t im e d e l a y b e t w e e n l o a d a n d d e f o r m a t i o n

d e v i c e c h a n n e l ( s ) a n d t o c h e e k f o r a t te n u a t i o n o f lo a d a n d d e f o r m a t i o n v a l u e s o v e r a

r a n g e o f lo a d i n g f r e q u e n c ie s . T h i s c h e c k n o t o n l y r e -v e r if i e s th e e l e c t r o n i c s c h e c k s , b u t

i t a l so iden t i f i e s f ri c t i on i n t he sys t em, mi sa l i gnm en t and ove ra l l sy s t em func t ion . Th i s

e x p e r i m e n t c a n n o t t a k e t h e p l a c e o f e le c t r o n ic s c h e c k s a s i t d o e s n o t f u l l y c h a r a c t e ri z e

t h e e l e c tr o n i c s s y s t em . I t c a n h o w e v e r b e u s e d a s a r o u g h c h e c k o f s y s t e m e l e c t r o n i c s.

C a u t i o n i s a d v i s e d i f t h is p r o c e s s i s u s e d t o c h e c k e l e c t r o n i cs o f t h e s y s t e m a s o t h e r

ca sua l f ac to r s such a s f r i c t i on and mi sa l i gnmen t can cause t he r e su l t s t o f a i l t h i s check .

T h e r e f o r e , a m o r e i n - d e p t h e v a l u a t i o n w o u l d h a v e t o b e u n d e r t a k e n t o d e t e r m i n e t h e

c a u s e o f fa i lu r e t h a n i f t h e e l e c tr o n i c s p r o c e d u r e a n d s y s t e m c y c l i c r e s p o n s e c h e c k w e r e

r u n i n d e p e n d e n t l y .

A s d o c u m e n t e d i n th e p r o c e d u r e , t h e f o l l o w i n g c r i te r ia m u s t b e m e t i n o r d e r t o p a ss

the test .

9 T h e p h a s e a n g l e m e a s u r e m e n t s h o u l d r e m a i n c o n s i s t e n t f o r a ll f i v e p e r i o d s a t a

g ive n f r eq uen cy (wi th in 4 -0.5 deg ree ) .

9 P h a s e a n g l e m e a s u r e m e n t le s s t h a n 2 . 8 d e g r e es .

I f , u s ing t he a ccep t a nce c r i te r i a, t he sys t em f a i l s t h i s check , r epea t t he p rocedu re . I f

t h e s y s t e m f a il s th e s e c o n d r e p li c at e , t h e s y s t e m f a il s th e c h e c k . I f t h e s y s t e m p a s s e s t h e

seco nd t es t , t hen a t h i rd r ep l i ca t e shou ld be run to de t e rmine a ccep t ance o r fa i lu r e . Th e

a p p a r a t u s s h o u l d b e d i s a s s e m b l e d a n d r e - a s s e m b l e d i n - b e t w e e n e a c h r e p li c a te .

I f th e s y s t e m f a il s th i s c h e c k , th e s y s t e m e l e c tr o n i c s a n d s o f t w a r e a r e e v a l u a t e d t o

d e t e r m i n e t h e c a u s e o f t i m e d e l a y . A l s o , th e s y s t e m s h o u l d b e c h e c k e d f o r f ri c t io n i n

t r i ax i a l p i s t on , mi sa l i gnmen t , l oose connec t ions , l oose de fo rma t ion dev i ce s , e t c .




Triaxial Pressure Chamber

E a c h t r ia x i a l p r e s su r e c h a m b e r t o b e u s e d f o r t e s ti n g s h o u l d b e a b l e to m a i n t a i n

p re s su re i n acco rd anc e wi th te s t i ng pa rame te r s . I t i s a l so ve ry impor t an t t ha t t e s t r e su l t s

r epo r t a c tua l p r e s su re u sed fo r t he te s t. I n s eve ra l in s t ances , i t ha s been fou nd tha t u se r s

r e p o r t n o m i n a l p r e s s u r e, o r p r e s s u r e t h a t w a s p r o g r a m m e d f o r th e te s t. F o r s o m e t e s t

s y s t e m s , p r e s s u r e u s e d f o r th e t es t m a y v a r y f r o m t h a t s p e c if i ed . I n th i s c a s e , u s e o f

n o m i n a l p r e s s u r e c a n c a u s e e r ro r s i n te s t r es u l ts w h e n c o m p a r e d w i t h o t h e r t e s t re s u lt s.

I n o r d e r t o p e r f o r m t h is t e st p r o c e d u r e , a s e p a ra t e N I S T t r a c e a b le p r e s s u r e g a u g e o r

t r a n s d u c e r i s n e c e s s a r y . T h i s g a u g e i s u s e d t o p e r f o r m a n in d e p e n d e n t s y s t e m c h e c k .

A l s o , i t i s v e r y i m p o r t a n t t h a t t h e c e l l p r e s s u r e i s z e r o b e f o r e a p p l y i n g t h e s y s t e m

c o m m a n d t o p r e ss u r iz e t h e c h a m b e r .

T h e p r e s s u r e s u s e d f o r th i s e x p e r i m e n t a r e s i m i l ar t o t h o s e u s e d f o r t h e a c t u a l t e s t

p r o c e d u r e . T h i s e x p e r i m e n t c a n b e c o n d u c t e d d u r i n g p r o f i c i e n c y t e s t in g a s w e l l i f t h a t i s

d e e m e d m o r e e f f i c ie n t th a n r u n n i n g t h e e x p e r i m e n t i n d e p e n d e n t l y .

A s d o c u m e n t e d i n t h e p r o c e d u r e , t h e f o l l o w i n g c r i te r ia m u s t b e m e t i n o r d e r t o p a s s

the tes t .

9 A l l s y s t e m p r e s s u r e r e a d i n g s s h o u l d b e w i t h i n • p e r c e n t o f t h e t a rg e t .

9 A l l N I S T g a u g e p r e s s u re r e a d i n g s s h o u l d b e w i t h i n • p e r c e n t o f t h e t a rg e t .

9 A l l s y s t e m a n d g a u g e r e a d i n g s s h o u l d b e w i t h i n • p e r c e n t o f e a c h o t h e r .

9 T h e t a r g e t p r e s s u r e m u s t b e a c h i e v e d w i t h i n 3 0 s e c o n d s .

L i k e o t h e r p o r t io n s o f a s e r v o - h y d r a u l i c s y s te m , s y s t e m p r e s s u r e s y s t e m i s e x t r e m e l y

impo r t an t . I r a p r e s su re t r ansd uce r i s u sed , it i s ve ry imp or t an t t ha t t he tr ansd uce r i s

m a t c h e d t o t h e te s t s y s t e m a s c l o s e l y as p o ss i b le . I t m a y n o t b e a d v i s a b l e t o u s e a 1 0 3 4

k P a p r e s s u r e t r a n s d u c e r t o p e r f o r m s o il s a n d a g g r e g a t e t e s ti n g u n l e s s i t c a n b e s c a l e d t o a

s u i ta b l e r a n g e w i t h o u t l o s s o f a c c u r a c y . C o n t a c t t h e s y s t e m m a n u f a c t u r e r f o r a ss i s ta n c e

in s e l ec t i ng a su i t ab l e p r e s su re t r an sduce r fo r u se i n a pa r t i cu l a r t e s t p rocedure .

I f , u s ing t he acc ep t an ce c r it e r ia , t he sys t e m f a i ls th i s check , r epea t t he p rocedure . I f

t h e s y s t e m f a il s th e s e c o n d r e p li c at e , t h e s y s t e m f a il s th e c h e c k . I f t h e s y s t e m p a s s e s t h e

seco nd t es t , t hen a t h i rd r ep l i ca t e shou ld be run t o de t e rm ine acc ep t an ce o r fa i lu r e . The

a p p a r a t u s s h o u l d b e d i s a s s e m b l e d a n d r e - a s s e m b l e d i n - b e t w e e n e a c h r e p l i c at e .

I f p r o b l e m s a r e f o u n d w i t h s y s t e m p r e s s u re , t h e m a n u f a c t u r e r s h o u l d b e c o n t a c t e d t o

a s s i st i n de t e rm ina t ion o f p rob ab le cause s and e f f i c i en t so lu t ions .

rof ic iency rocedure

T h e a b i l it y o f l a b o r a t o r y p e r s o n n e l t o c o n d u c t c y c l i c te s t in g i s e v a l u a t e d i n th e

prof iciency procedure W h i l e t h is p r o c e d u r e h a s b e e n d e v e l o p e d p r i m a r i l y f o r r e si li e n t

m o d u l u s t e st in g , t h e c o n c e p t s c a n b e a p p l i e d to m a n y t e st p r o g r a m s . T h i s p r o c e d u r e i s

g e n e r a l l y u s e d p r i o r t o i n i ti a ti o n o f a t e s ti n g p r o g r a m a n d s u b s e q u e n t l y o n a c o n t i n u i n g

bas i s ( i .e . , qua r t e r l y ) t o ve r i fy op e ra t o r ' s ab i l i t y t o conduc t r e s i l ien t m odu lus t e s t ing . Th e

p r o c e d u r e r e q u i r e s a p p r o x i m a t e l y 2 d a y s t o c o m p l e t e .

I n o r d e r t o p e r f o r m a c o m p l e t e a n a l y s is o f t h e l a b o r a t o r y ' s a b i l it y to p e r f o r m a

p a r t i c u l a r te s t, a l l f a c et s o f th e t e st p r o c e s s m u s t b e r e v i e w e d . T o p e r f o r m t h is p r o c e d u r e ,

a p e r s o n w i t h a d e q u a t e e x p e r i e n c e i n p e r f o r m a n c e o f th e te s t m u s t b e e n l i s te d t o p e r f o r m




t h is r ev i e w . T h e p r o f i c i e n c y p r o c e d u r e b r i n g s t o g e t h e r al l o f e x p e r i m e n t s m e n t i o n e d

pre v iou s ly to ensu re accu ra t e , r epea t ab l e t e st va lues a r e de t e rmined .

T h e p r o f i c i e n c y p r o c e d u r e s h o u l d n o t b e c o n d u c t e d u n t i l al l o f m e c h a n i c a l a n d

e l e c tr ic a l s y s t e m e v a l u a t i o n p r o c e s s e s h a v e b e e n c o m p l e t e d t o t h e s a t i s fa c t i o n o f t h e

e v a l u a t i o n te a m . I n o r d e r to p e r f o r m t h is p r o c e d u r e , a w e l l- w r i t te n c o m p r e h e n s i v e t e s t

p r o c e d u r e m u s t b e a v a i la b l e t o d o c u m e n t t e st p r o c e s se s .

S e v e r a l f u n d a m e n t a l p r o c e d u r e s s h o u l d b e e v a l u a t e d d u r i n g a p r o f i c i e n c y t e s ti n g

r e v i e w a s f o l l o w s :

* M a te r i a l p r epa ra t i on

9 T e s t p e r f o r m a n c e

9 Ca lcu l a t i ons

9 D a t a r e p o r t i n g

9 D a t a r e a s o n a b l e n e s s

T h e e n t i r e t e st p r o c e d u r e i s o b s e r v e d b y p e r s o n n e l t h a t a r e v e r y f a m i l i a r w i t h t h e

t e s t in g p ro c e s s . T h i s s h o u l d c o m m e n c e w i t h s p e c i m e n p r e p a r a t io n t h r o u g h t o d a t a

a n a l y s is a n d r e p o r t in g . I t sh o u l d b e n o t e d t h a t s o m e o f t h e a c c e p t a n c e c r i te r ia n o t e d

h e r e i n a r e s u b j e c t i v e - th u s t h e n e c e s s i t y f o r a k n o w l e d g e a b l e i n d i v id u a l t o p e r f o r m t h is

p r o c e d u r e .

Fo r th i s expe r im en t , t he u se r i s look ing fo r t he fo l l ow ing c r it e r ia :

9 G e n e r a t e d h a v e r s i n e w a v e f o r m i s w i t h i n t o l er a n c e .

9 L o a d c o n s i s ts o f 5 0 0 p o i n t s p e r c y c l e .

9 G e n e r a t e d d e f o r m a t i o n o u t p u t i s w i t h i n t o le r a n c e.

9 D e f o r m a t i o n c o n s i s ts o f 5 0 0 p o i n t s p e r c y c l e .

9 M a x i m u m d e f o r m a t io n i s o c c u r r in g a f te r m a x i m u m l o ad

9 A l l m a n u a l l y c al c u l a te d v a lu e s s h o u l d b e w i th i n 5 p e r c e n t o f a u t o m a t e d

ca l cu l a t ed va lues .

9 A l l t e s t p a r a m e t e r s s h o u l d b e w i th i n 5 p e r c e n t o f t es t r e q u i re m e n t s .

9 V e r t i c a l d e f o r m a t i o n r e a d i n g s f r o m e a c h s e q u e n c e s h a ll b e c h e c k e d t o e n s u r e t h a t

d e f o r m a t i o n d e v i c e s a r e r e c o r d i n g v a l u e s w i t h a v e r a g e s t h a t ( f o r c o l le c t e d c y c l e s )

hav e a coe f f i c i en t o f va r i a t i on l e s s t han 2 .5 pe rcen t .

9 D e f o r m a t i o n v a l u e s w i t h i n 3 0 p e r c e n t o f e a c h o t h e r s h o u l d b e o b s e r v e d f o r a ll t e st

s equences .

9 A l l f ina l t e s t r e su l t s shou ld be r ea sonab le a s de t e rm ined by t he r ev i e w t eam.

I f , u s ing t he accep t ance c r i t e r ia , t he sy s t em f a i l s t h is check , t he p ro ced ure i s r epea t ed .

I f th e s y s t e m f a il s th e s e c o n d r e p l ic a t e, t h e s y s t e m f a il s t h e c h e c k . I f th e s y s t e m p a s s e s

the s econ d t es t , t hen a th i rd r ep l i ca te sho u ld be run t o de t e rm ine ac cep t ance o r f a il u r e .

T h e a p p a r a t u s s h o u l d b e d i s a s s e m b l e d a n d r e - a s s e m b l e d i n - b e t w e e n e a c h r e p li c at e .

A l a b o r a t o r y p e r f o r m i n g r e s i li e n t m o d u l u s t e s t i n g s h o u l d g i v e c o n s i d e r a t i o n t o

p a r t i c ip a t i o n i n a n i n t e r l a b o r a t o r y t e s ti n g p r o g r a m t o v e r i f y c a li b r a t io n o f e q u i p m e n t a n d

p r o c e d u r e s w i t h r e s p e c t to o t h e r la b o r a to r i es . A l s o , i t m a y b e d e s i r ab l e t o m a n u f a c t u r e o r

p r o c u r e a s t a n d a r d s p e c i m e n t o t es t o n a c o n t i n u i n g b a s i s t o d e te c t g r o s s c h a n g e s i n

p e r f o r m a n c e o f t h e s y s t e m o v e r t im e .




W h a t C a n G o W r o n g

T h e p r o c e d u r e d i s c u s s e d h e r e i n h a s b e e n d e v e l o p e d t o v e r i f y o p e r a t i o n o f c l o s e d - lo o p ,

se rvo -hyd rau l i c sy s t em s fo r spec i f i c app l i ca t i on t o the r e si l ien t mo du lus p roces s . I t i s

e m p h a s i z e d t h a t u s e rs s h o u l d i m p l e m e n t t h is p r o c e d u r e w i t h a n o p e n - m i n d a n d n o t i n a

c o o k b o o k a p p ro a c h .

F r o m u s e o f t h e p r o c e d u r e , m a n y p o te n t i a l s o u r c e s o f e rr o r h a v e b e e n i d e n t i fi e d a n d

r e c t if i e d p r i o r to s t a r ti n g a t e s ti n g p r o g r a m , t h u s p o t e n t i a l l y s a v i n g a l a rg e a m o u n t o f

e f f o r t a n d r e s o u rc e s . F r o m t h e a u t h o r s ' e x p e r i e n c e i n a n u m b e r o f l ab o r a t o ri e s , t h e

f o l l o w i n g p r o b l e m s h a v e b e e n i d e n t if i e d t h r o u g h i m p l e m e n t a t io n o f th i s p r o c e d u r e :

lectronics

9 O v e r - r a n g e d l o a d c e ll s

9 Inad equ a t e f i lt e r s ( ampl i t ude a t t enua t ion )

9 U n m a t c h e d f il te r s ( e x c e s s i v e t i m e d e l a y b e t w e e n ch a n n e l s )

Software

9 I n a d e q u a t e s o f t w a r e c o n t r o l o f l o a d

9 I n a d e q u a t e s a m p l i n g r a te s

9 R a w d a t a w i t h o u t u n i ts

9 L a c k o f g a i n c o n t r o l a d j u s t m e n t d u r i n g t e s ti n g

9 I m p r o p e r r a w d a t a f o r m a t , c o m m a n d v a lu e s w e r e s a v e d r a t h e r t h a n f e e d b a c k

v a l u e s

Mechanical

9 S y s t e m n o t f a s t e n o u g h t o a p p l y p r o p e r h a v e r s i n e lo a d s

9 O v e r s i z e d s e r v o - v a l v e

9 F r i c t i o n i n s e r v o - v a l v e p i s t o n

9 Fr ic t io n in t r iax ia l ce l l sea ls

9 M i s a l i g n m e n t c a u s e d b y i m p r o p e r l y d e s i g n e d t ri a x ia l c e ll

9 E x c e s s i v e d e f o r m a t i o n , u p to 7 6 % o f d e f o r m a t i o n d u e t o b e n d i n g o f t r i a x i a l c e l l

b a s e p l a te

9 E x c e s s i v e d e f o r m a t i o n d u e t o u n r e s tr a i n e d f i x tu r e

9 S l ip p a g e o f L V D T h o l de r s

9 L a c k o f c o n t ro l o f p r e s s u r e t r a n s d u c e r

9 A i r p r e s s u r e r e g u l a t o r m a l f u n c t i o n

T h e s e e x a m p l e s a r e n o t m e a n t t o p r o d u c e f e a r o r a n x i e t y in p o te n t i a l u s e rs . R a t h e r

t h e y a r e i l lu s t ra t iv e o f t y p e s o f p r o b l e m s a u s e r c a n f a c e w h e n i m p l e m e n t i n g a r es i li e n t

m o d u l u s t e s t in g p r o g r a m . U s e o f t h e v e r if i c a ti o n p r o c e d u r e c a n a le r t u s e r s to p r o b l e m s

w i t h t h e s y s t e m a n d l a b o r a t o r y p r o c e s s e s q u i c k l y a n d e f f i c ie n t ly .




S u mm a r y a n d o n c lu s io n s

T h e L T P P R e s il ie n t M o d u l u s S t ar tu p a n d Q u a l i ty C o n t r o l P r o c e d u r e w a s d e v e l o p e d t o

ensure h igh qua l i ty , repea t ab l e t e s ti ng fo r LT PP resea rcher s . U se o f t h i s p roce dure has

y i e lded s ign i f ican t ga ins in ach i ev ing th i s goa l. Th e p rocedure has a l so been

i m p l e m e n t e d i n m a n y D O T , u n i v e r s it y , a n d c o m m e r c i a l la b o r at o ri e s.

F r o m e x p e r i e n c e g a in e d w i th i n th e L T P P p r o g r a m a n d f r o m t h e a u t h o r s ' e x p e r i e n c e

imp leme nt ing th i s p roced ure t h roughou t t he count ry , we found i t is c r i ti ca l tha t use r s

imp lem ent each phase o f the p rocedu re in a sys t emat i c and log i ca l man ner . In add i ti on ,

pe r son s sk i l l ed in e l ec t ron i cs a s they a pp ly t o t hese t e s t sys t ems a re nece ssa ry t o fu l l y

imp lem ent th i s p rocedure . P l ease use ca re wi th t he p rocedu re and do no t im plem ent the

p r o c e s s e s i n a c o o k b o o k m a n n e r . T h e p u r p o s e o f t h is p a p e r i s t o p r o v i d e a d e e p e r

under s t and ing o f t he p rocedure i n o rde r t o p rom ote i ts use in a wa y so as to a s sure

success wi th implem enta t i on o f t he S ta r tup and Q ua l i t y Con t ro l p rocedure . The r eader i s

r e fe r r ed t o t he l a t es t ve r s ion o f t he p rocedu res fo r m ore i n form at ion in t h is r ega rd .

References

Alavi , S ., M erpor t , T . , W i l son , T . , Groeg er , J ., Lopez , A . , J anua ry 1997 , LT PP M ate r i a ls

C h a r a c t e ri z a ti o n P r o g r a m : R e s i l ie n t M o d u l u s o f U n b o u n d M a t e r i a ls ( L T P P

Pro toco l P46) Lab ora to ry S t a r tup and Qua l i ty Cont ro l P roce dure , Re por t No .

F H W A - R D - 9 6 - 1 7 6 , U . S . D e p a r t m e n t o f T r a n s p o r ta t io n , F e d e r al H i g h w a y

Adm ini s tr a t ion , M cLean , Vi rg in i a .



SESSION : TESTING CONSTRAINTS

AND VARIABLES



J i an ch ao L i I an d B ash ar S . Q u b a in 2

R e s i li e n t M o d u l u s V a r i a t io n s w i t h W a t e r C o n t e n t

R e f e r e n c e :

Li , J . , and Qub ain , B . S . ,

" R e s i l i e n t M o d u l u s V a r i a t i o n s w i t h W a t e r

C o n t e n t , " Res i l ien t Modu lus Tes ti ng o r P aveme n t Componen ts , A ST M STP 1437,

G . N . D u r h a m , W . A . M a r t , a n d W . L . D e G r o f f , A S T M I n t e r n a t i o n a l , W e s t

C o n s h o h o c k e n , P A , 2 0 0 3 .

A b s t r a c t : R e s i li e n t m o d u l u s ( M R ) v a r ia t io n s w i t h w a t e r c o n t e n t w e r e c a r e f u l ly

e x a m i n e d f o r th r ee s u b g r a d e s o i l s - - l e a n c l a y , c l a y e y sa n d , a n d c l a y e y g r a v el . F o r e a c h

so il t ype , f o u r MR tes ts w ere pe r fo rm ed a t t h e fo l lo w in g wa te r co n ten t s : 2 to 3 % d ry o f

o p t i m u m , a t o p t i m u m ; 2 t o 3 % w e t o f o p t i m u m ; a n d a t fu ll b a c k p r e s s u re s a tu r a ti o n. T h e

b a c k p r e s s u r e - s a t u r a t e d s a m p l e s w e r e m o l d e d a t o p t i m u m a n d g a i n e d u p t o 6 % m o i s t u r e

d u r in g sa tu ra t ion . T h e M a t e s t in g o f t h e n o n -sa tu ra t ed spe c im en s was co n d u c te d

a c c o r d i n g t o A S S H T O T 3 0 7 - 9 9 a n d s p e c i f i c t e s t i n g a d j u s t m e n t s w e r e d e v e l o p e d f o r t h e

b ack pressu re - sa tu ra t ed o n es . A f t e r ach iev in g sa tu ra t io n , t h e spec im en s were co n so l id a t ed

a t a co n f in in g p ressu re equ iv a len t t o th e s tr e s s l ev e l o f pav em en t su rch arge an d th en

su b jec t ed to f iv e l ev e ls o f d ev ia to r s tr e s ses u n d er u n d ra in ed co n d i t io n s . T h e t e s t r e su l ts

were u t i l i z ed to ge th e r w i th in s i tu s t r e s ses to d ev e lo p d es ign cu rv es fo r r e s i l i en t m o d u lu s

v er su s w a te r co n ten t .

K e y w o r d s : Res i l i en t m o d u lu s , seaso n a l m o i s tu re v a r i a t io n s , b ack pressu re sa tu ra t io n ,

su b grad e s t r e s ses , pav em en t d es ign


T h e m e c h a n i s ti c - e m p i r ic a l m o d e l i n t he l a te s t G u i d e f o r D e s i g n o f P a v e m e n t

S t ruc tu res (A A S H T O 1 9 9 3 ) u ti l iz es th e r e s i li en t m o d u lu s (MR) o f t h e su b grad e so i l a s th e

fu n d am e n ta l m a te r i a l p ro per ty fo r pav em en t d es ign . I t f o llo ws th a t an accu ra t e

d e te rm in a t io n o f t h is im po r t an t pa ram ete r i s e s sen t ia l . Res i l i en t m o d u lu s h as lo n g b een

r e c o g n i z e d t o b e s tr e ss a n d m o i s t u re d e p e n d e n t ( T h o m p s o n a n d R o b n e t t 1 9 76 , F r e d l u nd

et a l . 1977 , El l io t t and Th orn t on 1988 , Pe zo e t a l. 1992). T ypic al ly , MR is dete rm ined

f ro m e i th e r f i e ld o r l ab o ra to ry t e s t s, b o th o f wh ich in co rpo ra t e th e in f lu en ce o f st r es ses.

F i e ld m e a s u r e m e n t s o f p a v e m e n t d e f l ec t i on u s i n g t h e f a ll in g w e i g h t d e f l e c t o m e t e r

(FWD ) in d ica t e th a t t h e su b grad e r e s i l i en t m o d u lu s v a r i e s w i th lo ad o r s t r e s s l ev e l

(N o u re ld in 1 99 4) . L ab o ra to ry t e st s a l so sh o w th a t MR v ar i e s w i th b o th d ev ia to r an d

co n f in in g s t r e s ses , an d v a r io u s co n s t i t u t iv e m o d e l s h av e b een p ro po sed to r e l a t e th e

JA sso c iat e , Geo S t ru c tu res , In c ., 9 8 5 O ld Eag le S ch o o l Ro ad , W ayn e , P A 1 9 0 8 7. E -m ai l :

j c l i~g eo s t ru c tu res .n e t .

2 P resid ent , Geo S t ru c tu res , In c ., 9 8 5 O ld Eag le S ch o o l Ro a d , Wa yn e , P A 1 9 0 8 7. E -m ai l :

b qu b a in ~ ,geo s t ru c tu res .n e t .

59





res i l ient m odu lus to the s ta te o f s t ress (Fredlund e t a l. 1977, Uza n 1985, Hou ston e t a l.

1993, Santha 1994).

The i n f luence o f wa t e r con ten t , on t he o the r hand , i s no t a s eas i l y addressed . For

e x a m p l e , f ie l d te s ts s u c h a s F W D m e a s u r e t h e p a v e m e n t d e f l e c ti o n a n d b a c k c a lc u l a te t h e

res i li en t mod ulus a t t he t ime o f t he t e s t w i thou t a ccoun t ing fo r m oi s tu re va r i a ti ons .

Labora to ry r e s i l i en t modulus t e s t s a r e a l so usua l l y pe r fo rmed a t op t imum wate r con t en t

wh ich m ay no t be r epresen t a t i ve o f the i n s i tu mo i s tu re th rough out t he yea r .

T o o v e r c o m e t h e se s h o r tc o m i n g s , t h e 1 9 9 3 A A S H T O G u i d e p r o p o s e d a p r o c e d u r e fo r

ad jus t ing M R based o n seasona l m oi s tu re va r i a ti ons . A l thou gh a s tep in the r igh t

d i r ec t i on , t he sugges t ed p rocedure t r ea t s a l l so i l t ypes i n t he same manner and does no t

of f e r a r a ti ona l eva lua t i on approach . F red lund e t a l. ( 1977) r ecogn ized t he r e la t i onsh ip

be tween wa te r con t en t and r es i l i en t modulus bu t t hey d id no t pe r fo rm t es t s under fu l l

sa tu ra t i on- - a condi t i on which would r esu l t i n a h igh wa te r con t en t and a l ow M R.

M uhanna e t a l . ( 1999) u t i l i zed a soak ing appara tus t o s imula t e fu l l s a tu ra t i on bu t t he

se tup on ly ach i eved about 90 sa tu ra ti on and took two we eks to reach tha t leve l .

Th i s paper p resen t s a l abora to ry t e s t i ng p rogram to eva lua t e r e s i l i en t modulus

var i a t i ons wi th wa te r con t en t fo r t h r ee subgrade so i l s a long t he Pennsy lvan i a Turnp ike .

As a r e su l t , modi f i ca t i ons t o ex i s t i ng t e s t me thods a r e p roposed t o enab l e t he

de t e rmina t i on o f M R a t fu l l s a tu ra t ion . The fo l l owing ques t i ons a r e a lso addressed

here in : W ha t a r e t he upper and l owe r limi t s o f M R? What a r e t he upp er and l ow er l imi t s

of wa t e r con t en t ? I s soak ing adequa t e t o s imula t e wor s t - case mo i s tu re condi t ions?

Testing rogram

Res i l i en t modu lus t e s t s a re conduc t ed on l ean c l ay (CL) , c l ay ey sand (SC) , and

c l a y e y g r a v e l ( G C ) s u b g r a d e s o i ls a s p a r t o f t w o p a v e m e n t d e s i g n p r o j e c ts a l o n g t h e

Penn sy lvan i a Turnpike -- --one i n the Ph i l ade lph i a a r ea and t he o the r i n S om erse t County

in the wes t e rn pa r t o f the s ta te . To exa mine t he e f f ec t s o f moi s tu re va r i a t ions , each so il

t ype is t e s t ed a t t he fo l lowing wa te r con t en ts : 2 t o 3 d ry o f op t im um , a t op t imu m; 2 t o

3 we t o f op t imu m; and a t fu ll backp ressure sa tu ra t ion . W ate r i s added and t horoug hly

mixed wi th t he va r ious so i l s and a sp l i t mold (71 mm d i amete r and 142 mm he igh t ) i s

used t o p repare r emo lded spec im ens a t t he ta rge t ed wa te r con t en ts . The so i l is p l aced i n

f ive l if t s, each com pac t ed wi th a s t ee l rod to ach i eve 100 of t he s t andard P roc tor.

Res i l i en t modulus t e s t i ng fo r non- sa tu ra t ed spec imens i s conduc t ed accord ing t o

A S S H T O M e t h o d f o r D e t e r m i n i n g t he R e s i li e n t M o d u l u s o f S o il s a n d A g g r e g a t e

M ate r ia l s (T307-99) . Spec i f i c t e s t ing de t a il s, howe ver , a r e deve lope d fo r t he sa tu ra ted

s p e c i m e n s t h a t a r e r e m o l d e d a t o p t i m u m w a t e r c o n t e n t a s d e s c r ib e d l a te r in t h i s p a p e r .

The r es i l i en t modulus t e s t i ng se tup used fo r t h i s work i s an e l ec t ro -hydrau l i c se rvo-

con t ro l sys tem. The cyc l i c l oad ing is app l ied th rough an ac tua to r pow ered by a c losed-

loop hydrau l i c sys t em. Th e conf in ing a i r p r es sure i n t he t ri ax i a l cha m ber i s m easured by

a p res sure t r ansducer and con t ro ll ed t h rough a r egu l a to r . De form at ions a r e m easured by

two ex t e rna l l y m oun ted LV DT s on t he actua to r. For sa tu rat ion , wa t e r is in t roduced t o the

spec imen by backpressure t h rough a p res sure con t ro l pane l and a da t a acqu i s i t i on un i t

(ADU) . Pore p res sure i s measured t h rough a p res sure t r ansducer connec t ed t o t he l ower

d r a in a g e l in e o f t h e s p e c im e n . B o t h b a c k a n d p o r e p r e ss u r e s a r e c o n t in u o u s l y m e a s u r e d

a n d m o n i t o r e d o n a c o m p u t e r s c r e en t h ro u g h t h e A D U .



LI AND QUBAIN ON VARIATIONS W ITH WATER CONTENT 6

Standard Resilient Modulus Test Methods

Cur ren t l y , t he re a r e two p r ima ry s tandards fo r r e s i li en t mod ulus t e s t i ng i n t he con t ex t

o f p a v e m e n t d e si g n : T 3 0 7 a n d A A S H T O M e t h o d f o r R e s il ie n t M o d u l u s o f S u b g ra d e

Soi l s and Unt r ea t ed B ase /Subb ase M ate r i a l s (T292-96) . Th e p rocedure o f T307 i s

app l i cab l e t o bo th f i ne -gra ined and coa r se -gra ined subgrade so i l s . I t i nc ludes a

precondi t i on ing sequence (1000 cyc l es ) and 15 l oad ing sequences (100 cyc l es pe r

sequence) w i th a com bina t i on o f 3 l eve l s o f conf in ing p res sures (41 .4 , 27 .6 , and 13 .8

kP a) and 5 levels of dev ia tor s tresses (12.4, 24.8, 37.3, 49.7, an d 62.0 kPa) . Th e dra inage

l ines a r e kep t open t o t he a tmosp her i c p res sure dur ing app l i ca t ion o f cyc l i c load ing . Th i s

m ethod r ecognizes t he i n f luence o f conf in ing p res sure on M R for f i ne -gra ined as we l l a s

coar se -gra ined so i ls bu t does no t i nc lude a ny prov i s ions fo r sa tu ra t ion .

Unl ike t he p rev ious t e s t me thod , T292 has d i f f e r en t t r ea tment s fo r f i ne -gra ined

(cohes ive ) and coa r se -gra ined (g ranu l a r ) subgrade so i l s and i t s cyc l i c l oad ing i s app l i ed

under undra ined condi t i ons wi th a l l t he d ra inage l i nes c losed . Th i s me thod main t a ins ,

t he smal l r ange o f conf in ing p res sure expec t ed wi th in subgrades has on ly a min imal

e f f ec t on M R va lues ob t a ined f rom cohes ive spec imen s . Ac cord ing ly , cohe s ive so i ls a r e

t e s t ed a t a s i ng l e conf in ing p res sure o f 21 kP a bu t t he spec im en i s conso l ida t ed under t ha t

sam e pres sure p r io r t o l oad ing . A precondi t i on ing sequen ce and 5 l eve l s o f dev i a to r

s t resses are included s imi lar to T307, except wi th di f ferent devia tor s t resses (21, 34, 48,

69, and 103 kPa) . A sa tura t ion proced ure is a l so includ ed for coh es iv e soi l s. I t i s s imi lar

to that ut i l i zed in s tandard t r iaxia l t es t ing but requi res ful l sa tura t ion wi thout speci fying a

m i n i m u m v a l u e f o r t he p o r e p r e s s u re p a r a m e t e r B .

mplemented Procedure or Saturation and Mn Testing

Sa tura t ion fo r t h i s wo rk is pe r fo rm ed th rough backpre ssure i nc rement s . P r io r t o

app ly ing a i r p r es sure , t he tr i ax ia l ce l l i s f il led wi th wa te r up t o 15 m m of f i ts t op . Ce l l

p res sure i s app l i ed t h rough a i r abo ve t he wa te r su r f ace , Du r ing the i nc remen t s o f

backpressure app l i ca t i on , pore p res sure i s r ecorded i n o rde r t o ca l cu l a t e B pa ramete r .

Sa tura t ion i s cons ide red ach i eved wh en a B va lue o f 0 .90 o r g rea t e r is r eached . Fu l l

sa tura t ion (B greater than 0.95 as in convent ional t r iaxia l t es t ing) i s not targeted here in

for two r easons : (1 ) fo r B equa l t o 0 .9 o r g rea t e r , t he degree o f sa tu ra ti on i s 98% or mo re

(B lack and Lee 1973) an d t he subg rade i s no t l i ke ly t o be sa tu ra t ed t o such a h igh d egree ;

and (2 ) t he t e s ti ng se tup l imi t s t he backpressure t o ab out 3 l 0 kPa and fu l l s a tu ra t ion fo r

r e m o l d e d s p e c i m e n s w o u l d r e q u i re m u c h h i g h e r v a lu e s .

Af t e r s a tu ra t ion i s comple t ed , t he spec ime n i s conso l ida t ed t o a co nf in ing p res sure o f

17 kPa , wh ich cor r espon ds t o the e s t ima ted s t r e ss l eve l o f a 580 m m p ave m ent sec ti on .

Af t e r conso l ida t i on i s comple t ed , a l l d r a inage va lves a r e c losed and t he spec imen i s

sub j ec t ed to 500 cyc l es o f p recondi t i on ing a t a dev i a to r st r e s s o f 25 kPa . The spec im en i s

t h e n t e s t e d i n t h e s t a n d a r d m a n n e r - - 1 0 0 c y c l e s a t 5 l e v e l s o f d e v i a t o r s t r e s s e s - - a s

spec i f i ed i n T307 . The f i na l wa t e r con t en t i s me asured upo n co mp le t i ng the t e st .

Resul t s and na lyses

Figure 1 shows a typ i ca l p lo t o f

R versus

devia to r and co nf in ing s t r e s ses fo r a lean

c l a y s p e c i m e n r e m o l d e d a t 2 % w e t o f o p t i m u m a n d F i g u r e 2 d e p i c ts a t y p i c a l p l o t



6 R E S IL IE N T M O D U L U S T E S TI N G F O R P A V E M E N T C O M P O N E N T S

1 0 0 0 0 0

9 0 0 0 0

~ . 8 0 0 0 0

v

7 0 0 0 0

O

O

" E 60000

r r 5 0 0 0 0

4

3 0 0 0 0

2

i I I ]

9 9 41 . 4 kP a con f i n i ng s t r ess

- - = - - 2 7 . 6 k P a c o n f in i n g s t r e s s

I / . . . . . . 1 3 .8 k P a c o n f in i n g s t r e s s

4 5 6 7 8 9

D e v i a t o r S t r e s s ( k P a )

1 0

F i g u r e 1

T y p i c a l P l o t o f R e s i l ie n t M o d u l u s v s D e v i a t o r a n d C o n f i n i n g S t r es s e s f o r L e a n C l a y

110000

1

90000

v 80000 ~

0

o 70000

~ 6 0 0 0 0

n ~

50000

4 0 0 0 0

\

. . . .

3 0 0 0 0

0 1 2 3 4 5 7

D e v i a t o r S t r e s s ( k P a )

8 9 10

F i g u r e 2

Res i l i en t Modu lus vs De v ia tor S t r es s fo r Sa tur a ted C layey Gr a ve l a t crc = 17 kPa



LI AN D Q UBA N ON VARIAT IONS WITH WA TER CON TENT 6

for a saturated clay ey gravel specimen. Both of these figures illustrate that MR decreases

with the increase in deviator stress

ad

The decrease is more pronounced at lower values

of ad and level s of f at values greater than 35 kPa. Figure 1 also shows that MR increases

with the increase in confining stress ac for lean clay, which is in agreement with T307 but

contrary to the posit ion maintained by T292. The MR testing results are summarized in

Table 1 for the Pennsylvania Tumpik e project in the Philadelphia area and in Table 2 for

the Somerset project.

Table 1 - Summ ary o f Resi lient Modulus Testing Results fo r Philadelphia Area Project

Remolded Remo[ded Compaction Moisture Degree of Moisture Design

Soil Type/ Dry Density Moisture Level Variat ion Saturation at Test MR

Specimen (g/cm3) ( ) ( ) ( ) ( ) (kVa)

CL-Dry of optimum L94 8.5 99 3.0 dry 57 8.3 110,649

CL-Optimum 1.96 11.8 100 Optimum 85 11 .8 83,534

CL-Wet of optimum 1.90 13.4 97 1.9 wet 85 13 .2 59,241

CL-Saturated 1.96 11.8 I00 6.3 wet 100 17.6 38,080

SC-Dry of optimum 2.04 8.2 101 1.6 dry 68 8.2 110,411

SC-Opfimum 2.03 llA 101 Optimum 91 11.1 125,391

SC-Wet of optimum 1.97 14.2 97 3.0 wet 95 14 .2 56,298

SC-Saturated 2.03 11.1 101 1.9 wet 100 13.1 87,976

GC-Dry of optimum 2.I6 7.1 I0I 1.3 dry 84 7.7 103,831

GC-Optimum 2.15 9.4 100 Optimum 90 9.4 69,771

GC-Wet of optimum 2.05 11.6 96 1.6 wet 90 10.6 52,737

GC-Saturated 2.15 9.4 100 2.1 wet 100 11.1 62,465

Table 2 -

Sum mary o f Resilient M odulus Testing Results fo r Som erset Co unty Project

Soil Type

Clayey sand

Sandy lean

clay

Sandy lean

clay with

gravel

Sandy lean

clay

Clayey sand

with gravel

Clayey sand

with gravel

Remolded Remolded Compaction Moi sture Deg ree f Moisture

Dry Density Moisture Le vel Var iat ion Saturation at Test

(g/cm3) ( ) ( ) ( ) ( )

Optimum 78 12.81.87 12.8 99

Saturation 1O0 16.4

Optimum 81 12.2

1.92 12.2 102

Saturation 100 15.5

Optimum 92 13.6

1 93 13.6 99

Saturation 100 15.2

Optimum 82 11.3

1 96 11 3 100

Saturation 100 14.2

Optimum 67 12.0

1.87 12.0 100

Saturation 100 17.5

Optimum 81 12.4

1.91 12.4 98

Saturation 100 15.0

Design

MR

(kPa)

108,330

50,370

96,600

71,070

90,390

54,510

137,310

57,960

132,480

41,400

91,080

53,820




T h e b a c k p r e s s u re - s a tu r a t e d sp e c i m e n s w e r e m o l d e d a t o p t i m u m a n d g a i n e d u p t o 6

mo i s tu re fo r t he l ean c l ay so i l dur ing sa tu ra t ion as show n in Tab l e 1 . Th e r esu l ti ng wa te r

con t en t s fo r t he d i f f e r en t spec ime ns va r i ed f rom 8 t o 18 wi th t he sa tu ra t ed spec ime ns

gene ra l l y r epresen t i ng t he uppe r boun d o f wa t e r con ten t . The bas i s fo r r emold ing t he

sa tu ra t ed spec imens a t op t imum i s t ha t subgrade so i l s a r e usua l l y compac t ed c lose t o

o p t i m u m a n d a b s o r b m o i s tu r e u p o n p r o l o n g e d e x p o s u r e t o r a in t o t h e l im i t o f th e i r

e f f ec t i ve conso l ida t i on s t re s ses . I n con tr as t, a r emolded l ab ora to ry spec im en a t m oi s tu re

c lose t o fu l l s a tu ra t i on would no t l i ke ly ach i eve p roper compac t ion and t he re fore would

not r ea l is t i ca ll y s imu la t e t he subgrade so il. Ev iden t ly , the dens i t y o f t he r emolded

s p e c i m e n a t h i g h w a t e r c o n te n t w o u l d b e m u c h l o w e r t h a n t h a t o f th e s u b g r a d e .

Design MR

As show n in F igure 1 , t he l abora to ry t e s ts p roduc e a se t o f curves t ha t r e l a t e M R to

d e v i a t o r a n d c o n f i n in g s t re s se s . H o w e v e r , p a v e m e n t d e si g n a c c o r d in g t o th e A A S H T O

Guide r equ i r es a s i ng l e i npu t va lue fo r t he r e s il i en t mod ulus . Th i s i s ca l l ed the e f f ec t i ve

roadbe d r es i li en t mod ulus and i t is de t e rmined b y t h ree p rocesses : (1 ) se l ec t i ng a des ign

M R va lue bas ed o n t he i n s i t u s t r e ss s t at e ; (2 ) de t e rmin ing t he up per an d l ow er l imi t s o f

r es i li en t modu lus an d w a te r con t en t va r i a ti ons ; and (3 ) ad jus ti ng t he d es ign M R to r e f l ec t

t he seasona l moi s tu re va r i a t i ons t h roughout t he yea r .

In s i t u s t r e s ses a r e ca l cu l a t ed us ing

KENL YER

c o m p u t e r p r o g r a m ( H u a n g 1 9 9 3 ) ,

which i s base d on a mul t i - l aye r e l a s ti c mode l . T ra f f i c l oads i nc lud ing v a r ious 80 kN ax l e

load com bina t i ons t oge the r wi th surcharge f rom the pav em ent sec t i on a r e u t il ized . For a

580 mm pavement sec t i on , t he ana lys i s r e su l t s i n dev i a to r and conf in ing s t r e s ses i n t he

range o f 14 to 21 kPa , and a bu lk s t re s s on t he o rde r o f 60 kPa . The se i n s i tu s t r e s ses a r e

d i r ec t l y used i n a cons t i t u t i ve r e l a t i on be tween M R ver sus dev i a to r and bu lk s t r e s ses t o

es t ab l i sh t he des ign M R. Thi s r e l a t i onsh ip i s deve loped t h rough a non l inea r r egres s ion

ana lys i s o f t he l abora to ry r e s il i en t mo dulus da t a t o f i t t he cons t i t u t ive m ode l p ro pose d by

Uz an (1985) and d i scussed by San tha (1994) . The r egres s ion ana lys i s (no t i nc luded

here in ) i s s imi l a r t o t ha t i l lus t r a ted b y V on Quin tus and K i l li ngsw or th (1997) .

On the bas i s o f the es t im ated in s i tu s t ress s ta te , a des ign

R

i s de t e rmined fo r each

spec imen as shown in Tab l e 1 fo r t he Pennsy lvan i a Turnp ike p ro j ec t i n t he Ph i l ade lph i a

a rea and Tab le 2 fo r the Som erse t p ro j ec t . Thes e des ign M R va lues cor r espo nd to t he

spec i f i c wa t e r con t en t s a t t he t ime o f t e s t ing and on ly r eprese n t t he f i r s t p rocess . The

upp er and l ow er l imi t s o f re s i li en t modulus an d w a te r con t en t va r i a t ions a r e de t e rmined

as fol lows.

Resilient Modulus and Water Content Variations

The R

va lues i n Tab l e 1 a r e p lo t t ed aga ins t the cor r espo nding m oi s tu re con t en t s fo r

each sub grade so i l a s show n in F igures 3 th rough 5 . The cu rves c l ea r ly sugges t a genera l

t r end or r e l a ti onsh ip t ha t app l i e s t o a l l t e s ted so i l types . The l ean c l ay and c l ay ey grave l

M R t es t r e su l t s p roduce d good f i t to t he s ugge s t ed t r end wi th mu l t i p l e cor r e l a ti on

coeff ic ien ts R 2 = 0.97, and 0.85, resp ect ively. Th e c lay ey sand tes t resul t s w ere not as



L i A N D Q U B A I N O N V A R IA T IO N S W I T H W A T E R C O N T E N T 6 5

160,000

1 2 0 , 0 0 0

(3.

o 80,000

E

tY

40,000

0

5.0

10.0 15.0 20.0

W a t e r C o n t e n t ( )

Figure 3 - Resilient Modulus vs Water Content for Lean Clay

f f

v

o

O

tw

200,000

160,000

120,000

80,000

40,000

0

5.0

I

\ i

\ \ L i

9 ~ 125,391 I '

9 56,298

I i

15.0

W a t e r C o n t e n t (%)

1 0 0

Figure 4 - Resilient Modulus vs Water Content fo r Clayey Sand

2 0 0



R E S I LI E NT M O D U L U S T E S T I N G F O R P A V E M E N T C O M P O N E N T S

160,000

1 2 0 , 0 0 0

13.

~ 80,000

E

40,000

0

5.0

10.0

W a t e r C o n t e n t

( )

15.0

Figure 5 - Resilient Modulus vs Water Content for Clayey Gravel

wel l co nform ing as i nd i ca ted by t he i r cor r e l a ti on coe f f i c i en t o f 0.51 . I t is a l so no t ed tha t

t h e s a t u ra t ed c l a y e y s a n d s p e c i m e n d i d n o t p r o v i d e t h e u p p e r l im i t o f w a t e r c o n t e n t a s

e x p e r i e n c e d b y t h e o t h e r s p e c im e n s . T h i s m a y e x p l a i n t h e l a c k o f c o n f o r m i t y o f t h e

c l aye y sand da ta .

A c l o se e x a m i n a t io n o f T a b l e 1 s h o w s t h a t t h e b a c k p r e s s u r e - s a tu r a t e d s p e c im e n s

genera l l y r e su l ted i n t he l owes t r e s i li en t m odulus va lues . A l so , a l l s a tu ra t ed spec imen s

ach i eve d a degree o f sa tu ra t ion equa l t o 100 . Sa tu ra ted M R va lues , on ave rage ,

r epresen t 50 o f t he op t im um res i li en t mo dulus va lues fo r t he l ean c l ay soi ls . I n

compar i son , t he soak ing appara tus p roposed by M uhanna e t a l . ( 1999) r e su l t ed i n 15 t o

25 r educ t i on in t he r e s il i en t mo dulus va lues . The te s t r e su l ts in Tab l e 2 fo r t he

Som erse t p ro j ec t a l so i nd i ca te t ha t fo r a ll bu t the seco nd sam ple o f the sandy l ean c l ay o r

c l aye y sand subgrade , M R va lues a t s a tu ra ti on a r e abou t 50 o f t hose a t op t imum . The

da t a i n Tab l e 2 a r e p lo t t ed i n F igure 6 , which shows tha t i t conforms t o t he genera l

r e l a t ionsh ip i nd i ca ted b y t he o the r subgrade so i l s p r esen t ed i n Tab l e 1 and F igures 3 t o 5 .

The mu l t ip l e co r r e l a ti on coe f f i c i en t fo r the c urve i n F igure 6 i s 0 . 88 .

I t is no t ed t ha t t he sa tu ra t ed c l ayey sand and c l ayey grave l re s i l ien t m odul i a r e on ly

30 and 10 l ow er t han t he M R va lues a t op t imu m. Thi s i s exp l a ine d by t he l e ss

depen dence o f t hese s l igh t l y g ranu l a r so i ls on wa te r con t en t va r i a t ions . The c l ayey sand

and san dy l ean c l ay o f the So merse t p ro jec t , how ever , beha ved i n a ma nne r c lose t o t ha t

o f the l ean c l ay due t o t he i r borde r l i ne c l a s s i f ica t ion .



LI AND QUBAIN ON VARIATIONS WITH WA TER CONTENT 7

150000 ,I

o t

130000 \

\

\ .

~ - , 1 o o o o . ~ i "

9

.~

70000

50000

3 i I

10 11 12

I

_

i

' -

,

. . . . . . . .

~ l ~ -

J 1

' i

I i

9

14 15 16 1713 18

Wate r C on ten t ( % )

Figure 6 - Resilient Modulus vs Moisture Content for Sandy Lean Clay~Clayey Sand

o n c l u s i o n s

Perhaps t he m os t impo r t an t ou t co m e of t he re s i li en t mod ulus t e s t i ng r esu l t s p resen ted

here in i s t he i ns igh t ga ined con cern ing the i n f luence o f wa te r con ten t on M R va lues . As

prev ious ly exp la ined , t h ree p rocesses a r e necessa ry t o u l t ima te ly de t e rmine t he e f f ec t i ve

roadb ed r es i li en t mod ulus . Th i s paper p resen t ed a de t a i led t r ea tmen t o f t he f ir s t and

second ones . The th i rd p rocess r equ i r es seasona l co l lec t i on o f subgrad e mo i s tu re da t a .

F igures 3 t h rough 6 dep i c t the va r i a t i on o f the subgrade r es i l ien t m odu lus wi th w a te r

con ten t . As c l ea r ly shown, t he da t a sugges t a genera l t r end or r e la t i onsh ip be tween the

res i l i en t modulus and wa te r con ten t . M oi s tu re va r i a t i ons may be de t e rmined by d i r ec t

m easu rem ent o f the su bgrade m oi s tu re , f rom h i s to r ica l da t a , i f ava i l ab l e , o r based on

loca l exper i ence . Reg ard l ess o f how m oi s tu re va r i a t i ons a re de te rmined , such a

re l a ti onsh ip can a lwa ys be used to de t e rm ine t he e f f ec t i ve roadb ed r es i l ien t mod ulus .

The t e s t i ng r esu l t s i nd i ca t e t ha t t he backpressure - sa tu ra t ed spec imens p roduced the

h ighes t poss ib l e wa te r con ten t s and the l owe s t re s i li en t mo dul i l i ke ly t o be exper i enced in

p a v e m e n t s u b g ra d e s . S a t u ra t ed M R v a l u e s a r e a p p r o x i m a t e l y 5 0 o f t h e o p t i m u m

res i li en t m odulus va lues fo r the t e s t ed l ean c l ay so il s. The c l ayey sand a nd c l ay ey grave l

soi l s , however , exhibi ted less reduct ion in the res i l ient modulus values a t ful l sa tura t ion.

Al though f r eeze and thaw e f f ec t s a r e no t cons ide red he re , t he t yp i ca l r educ t ion due t o

sa tu ra ti on fo r t he t e s t ed so i l s appear s t o be s imi l a r t o t ha t sugg es t ed fo r f r eeze and thaw

condi t ions .




cknowledgment

The laboratory tests presented in th is paper w ere performed at Valley Forge

Laboratories, Inc . Kenneth M . Heirendt of the Pennsylvania Turnpike C omm ission is

acknow ledged fo r his technical suggestions and enthusiasm towards improving pavemen t

subgrade evaluation practices.

References

AASHTO, Guide or Design o f Pavement Structures W ashington, D.C ., 1993.

Black, D. K., and Lee, K. I., 1973 , Saturating Lab oratory Sam ples by Ba ck Pressure,

Journal o f Soil Mech anics a nd Foundation D ivision ASCE. Vol. 99, No. SM1, pp.

75-93.

Elliott, R. P., and Thornton, S. I., 1988, Simplification o f Subgrade R esilient Modulus

Testing, Transportation Research Record 1192 TRB National Research Council,

Washington, D.C.

Fredlund, D. G., Bergan, A. T., and Wong, P. K., 1977, Relation between Resilient

Modulus and Stress Conditions for Cohesive Subgrade Soils, Transportation

Research Rec ord 642 TRB, National Research Council, Washington, D.C.

Houston, W . N., Houston, S. L., and Anderson, T. W ., 1993, Stress State Considerations

for Resilient M odulus Testing of Pavement Su bgrade, Transportation Research

Record 1406 TRB, National Research Council, Washington, D.C.

Huang, u H., 1993, Pavem ent Analysis a nd Design Prentice Hall, Englewood, NJ.

Muhanna, A. S., Rahman, M. S., and Lambe, P. C., 1999, Resil ient Modulus

M easurement o f Fine-Grained S ubgrade Soils, Transportation Research Record

1687 TRB National Research Council, Washington, D.C.

Noureldin, A. S., 19 94 , Influence o f Stress Levels and Seasonal Va riations on In Situ

Pavement Layer Properties, Transportation Research Record 1448 TRB, National

Research Council, Washington, D.C.

Pezo, R. F., Carlos, G., Hudson, W. R., and Stokoe, II, K. H., 1992, Development o f a

Reliable Resilient Modulus Test fo r Subgrade an d Non-G ranular Subbase Ma terials

for Use in Routine Pavement Design Report II 77-4F, Center for Transportation

Research, University o f Texas at Austin.

Santha, B. L., 1 99 4, Resilient Modulus of Subgrade Soils: Comparison of Two

Constitutive Equations, Transportation Research Record 1462 TRB, National

Research Council, Washington, D.C.



L I AND QUBAIN ON VARIATIONS WITH WA TER CONTENT 9

Thom pson, M. R ., and Robnett, Q. L., 1976,

Resilient Properties o f Subgrade Soils Fina l

Report - Data Summary Transportation Engineering Series No. 14, Illinois

Cooperative Highway Research and Transportation Program Series No. 160.

University o f Illinois at Urbana-Cham paign.

Uzan, J., 19 85, Characterization of Granular Materials, Transportation Research

Record 1022

TR B, National Research Council, W ashington, D.C.

Von Q uintus, H. and K illingsworth, B, 1997, Design Pamphlet fo r the Determination o f

Design Subgrade in Support o f the 199 3 AA SH TO Guide fo r the Design o f Pavement

Structures FHW A-RD -97-083, Federal Highway Adm inistration, W ashington, D.C.



T aru n j i t S . B u ta l ia , l Ju n H u an g , 2 D o n g -G yo u Kim , 3 an d F ran k C ro f t 4

E f f e c t o f M o i s t u r e C o n t e n t a n d P o r e W a t e r P r e s s u r e B u i l d u p o n R e s il i e n t M o d u l u s

o f C o h e s i v e S o i ls in O h i o

R e f e r e n c e :

Butal ia , T . S . , Huang, J . , Kim, D.-G. , and Crof t , F . ,

" E f f e ct o f M o i s t u r e

C o n t e n t a n d P o r e W a t e r P r e s s u r e B u i l d u p o n R e s i l i en t M o d u l u s o f C o h e s i v e

S o i l s , "

Resilient Modulus Testing or Pavement Components, ASTM STP 1437, G . N . D u r h a m ,

W . A . M a r t , a n d W . L . D e G r o f f , E d s ., A S T M I n te r n at io n a l, W e s t C o n s h o h o c k e n , P A ,

2 0 0 3 .

A b s t r a c t : H ig h po s i t i v e po re p ressu res in su b grad e so i ls can b e ex pe c ted to co n t r ib u te to

red u c t io n in so il s t r en g th an d s t i f fn ess . M easu re m e n t o f e l ev a ted po re wa te r p ressu res in

th e su b grad es o f i n s t ru m en ted sec t io n s o f S pec i f i c P av em en t S tu d ies co n d u c ted in O h io

o v er th e pas t sev e ra l yea r s h av e r a i sed co n ce rn s ab o u t t h e lo n g - t e rm s t ab i li t y o f t h ese t e s t

sec t ion s . T h e o b j ec t iv e o f t h is s tu d y w as to id en t i fy th e e f f ec t s o f m o i s tu re co n te n t an d

po re w a te r p ressu re o n th e re s i li en t m o d u lu s (Mr) o f u n sa tu ra t ed an d sa tu ra t ed co h es iv e

so il s . T es t r e su lt s co n d u c te d o n u n sa tu ra t ed co h es iv e so i ls a t t h ree d i f f e ren t m o i s tu re

c o n t e n ts ( o p t i m u m , 2 t o 4 % d r y o f o p t i m u m , a n d 1 89 t o 3 % w e t o f o p t i m u m ) s h o w e d t h a t

th e r e si l ien t m o d u lu s an d th e e f f ec t o f co n f in in g s t re s s d ec reased wi th in c reas in g

m o is tu re co n ten t . L ab o ra to ry t e st s o n fu l ly sa tu ra ted co h es iv e so i l s sh o w ed th a t t h e

res i li en t m o d u lu s o f sa tu ra t ed so i l s d ec reased to l e s s th an h a l f t h a t o f so i l spec im en s

tes t ed at o p t im u m m o is tu re co n ten t . Res id u a l po re wa te r p ressu re in c reased wi th an

in c rease in th e d ev ia to r s t re s s , an d a d ec rea se in th e lo ad in g pe r io d . T h e t im e to d i s sipa t e

res idu a l po re w a te r p ressure , w h ich w as l a rge in co m par i s o n to th e lo ad ra t e , i n c reased

wi th in c reas in g d ev ia to r s t re s s . T h e r esi l ien t m o d u lu s o f fu l ly sa tu ra ted co h es iv e so i l

wa s m u ch l e s s u n d er f a s t e r (1 seco n d pe r cyc le ) cyc l i c l o ad in g th an s lo wer (8 seco n d s pe r

cyc le ) cy c l i c l o ad in g .

K e y w o r d s : co h e s iv e so i l, l o ad in g pe r io d , m o i s tu re co n ten t , po re w a te r p ressu re , r e s i li en t

m o d u lu s , r e s id u a l, s a tu ra t ed , su b grad e , u n sa tu ra t ed

R e s e a r c h S c ie n ti st , D e p a r t m e n t o f C iv i l a n d E n v i r o n m e n t a l E n g i n e e r i n g a n d G e o d e t i c

S c ien ce , T h e O h io S ta t e U n iv e r s i ty , 2 0 7 0 N e i l A v en u e , C o lu m b u s , O H 4 3 2 1 0 .

2 Geo tech n ica l En g in ee r , F u gro -M cC le l l an d Mar in e Geo sc ien ces , In c . , 61 0 0 H i l l c ro f l,

H o u s t o n , T X 7 7 0 8 1 .

3 G r a d u a t e R e s e a r c h A s s o c i a te , D e p a r t m e n t o f C i v i l a n d E n v i r o n m e n t a l E n g i n e e r i n g a n d

G e o d e t i c S c i e n c e , T h e O h i o S t a t e U n i ve r s it y , 2 0 7 0 N e i l A v e n u e , C o l u m b u s , O H

4 3 2 1 0 .

4 A s s o c i a t e P r o f e s s o r, D e p a r t m e n t o f C i v il a n d E n v i r o n m e n t a l E n g i n e e r i n g a n d G e o d e t i c

S c ien ce , T h e O h io S ta t e U n iv e r s i ty , 2 0 7 0 N e i l A v en u e , C o lu m b u s , O H 4 3 2 1 0 .

7O

Copyright9 by ASTM lntcrnational www .astm.org



B U T AL IA E T A L O N O H IO S O IL 7

n t r o d u c t i o n

A mec hani s t i c ana lys i s me thod , r equ i ri ng an accu ra t e de t e rmina t i on o f t he r e s il i en t

m o d u l u s o f s u b g r ad e s o il s, h a s b e e n a d o p t e d b y t h e A m e r i c a n A s s o c i a t i o n o f S t a te

H i g h w a y a n d T ra n s p o r t a ti o n O f f i ci a ls A A S H T O ) f o r d e s i g n in g ro a d w a y p a v e m e n t

s y s te m s . T h i s m e t h o d o f p a v e m e n t d e si g n i s b a s e d o n t h e o r i g in a l w o r k b y S e e d e t a l.

1962) w ho sugg es t ed tha t som e f lex ib l e pav em ent f a il u r es , such as t he c r ack ing o f t he

pav em ent su r f ace , may b e cau sed by e l a s t ic o r r ecov erab l e s t r a in o f t he subg rade so il s.

For ov er 40 yea r s , man y r esea rcher s have s tud i ed and do cum ented t he cha rac t e r is t i c s o f

r es i li en t r e sponse o f va r ious coh es ive so i l s used as subgrade . T hese r e sea rch e f fo r t s have

show n tha t the r e s i l ien t modu lus o f cohes ive so i l s dec reases wi th i nc reas ing dev i a to r

s t ress e .g . , Bro dsk y 1989, D rum m et a l. 1990, Fredlun d e t a l. 1977, H ua ng 2001, K im

1999, M oh am m ad et a l . 1994, Seed e t a l. 1962, W oo ls t rum 1990), increases wi th

inc reas ing conf in ing s t r e ss e . g ., B rod sky 1989 , K im 1999), and dec reases wi th

increa s ing mo is ture content e .g . , Bu rczy k e t a l. 1994, D ru m m et a l. 1997, Fredlund e t al .

1977, Huang 2001, Kim 1999, Lee e t a l . 1997, Mohammad et a l . 1996, Seed e t a l . 1962,

W ool s t rum 1990). M oh am m ad e t a l. 1996 a tt r ibu t ed t h is r educ t i on i n t he r e s il i en t

mo dulus t o an i nc rease i n pos i t i ve pore p res sures wi th an i nc rease i n mo i s tu re con t en t

as soc i a t ed w i th g rea t e r l eve l s o f sa tu ra ti on .

A s p a r t o f a n o v e r a l l p r o g r a m t o m o d e r n i z e h ig h w a y d e s i g n , th e F e d e r a l H i g h w a y

A d m i n is t ra t io n F H W A ) d e v e l o p e d t h e S t ra t eg i c H i g h w a y R e s e a r c h P ro g r a m S H R P ) in

1993. As pa r t o f i ts suppor t fo r SHRP, the Ohio Dep ar tmen t o f T ranspor t a t i on OD OT ) ,

w i t h F H W A , c o n s t ru c t e d a c o m p r e h e n s i v e te s t r o a d c o n s i st in g o f fo u r e x p e r i m e n t s 4 0

sec t ions ) on U .S . Rou te 23 nea r De l awa re , Ohio . In th i s p ro j ec t , impor t an t pave m ent

r esponse pa ram ete r s we re m easured . The purpo se o f th i s p ro j ec t was t o eva lua t e t he

p e r f o r m a n c e o f s p e c if i c p a v e m e n t d e s i g n s u n d e r t r a ff ic l o a d in g . A t a l im i t e d n u m b e r o f

sec t ions , the f i e ld moni to r ing i nc luded mea sur ing t he pore wa te r p res sure . A t each o f

these l oca t i ons , po re wa te r p res sures obse rved under t r a f f i c l oad ing were h igh er t han

expe c t ed and t oo k a l ong t ime to d i ss ipa te . Th i s pore w a te r p res sure bu i l dup i n the so i l s

wo uld r ed uce t he e f f ec t i ve conf in ing s t r e s s, l ead ing t o a d ec rease i n t he r e s i li en t modulus .

T h e r e f o r e , t h e c u r r e n t m e t h o d o f c a l c u la t in g r e s il ie n t m o d u l u s o f s u b g r a d e s o i l m a y n o t

be ad equa t e w i thou t cons ide ra t i on o f t he e f f ec t s o f pore wa te r p res sure bu i l dup i n

subgrade so i ls Hu ang 2001 , K im 1999).

I f pa r t i a l l y sa tu ra t ed cohes ive so i ls cons t ruc t ed a t op t im um m oi s tu re con t en t beco m e

sa tura t ed , t he pore w a te r p res sure wi l l bu i l dup un der t r a f f ic l oad ing du e t o t he l ow

perm eabi l i t y o f cohes ive soi ls . T h i s can r esu l t i n a r educ t i on i n e f f ec t i ve conf in ing s t r e s s

and poss ib ly t he re s i li en t modulus . Som e r esea rcher s have o bse rve d t ha t pore wa te r

pres sure bu i l dup i n a cohe s ive so i l is r e la t ed t o the d ev i a to r s t r e ss l eve l s and t he n um ber

o f l o a d in g c y c l e s u n d e r d y n a m i c l o a d in g A n s a l a n d E r k e n 1 98 9, M e n d o z a a n d

He rnand ez 1994, Og aw a e t al . 1977). C yc l i c load ing o f d i f f e r en t f r equenc i es c r ea t ed

d i f f e ren t l eve l s o f pore w a te r p res sure bu i l dup i n sa tu ra ted so i l s amples i n t he f i rs t f ew

load ing cyc les An sal e t a l. 1989).



7 RESILIENT MODULUS TESTING FOR P VEMENT COMPONENTS

bjectives and Scope

T h e o b j e c t iv e s o f t h is s t u d y a r e t o e v a l u at e t h e e f f e c t o f m o i s t u r e c o n t e n t o n t h e

r e s il ie n t m o d u l u s o f u n s a t u r a t ed c o h e s i v e s o il s, a n d t o i n v e s t ig a t e t h e e f f e c t o f p o r e w a t e r

p re s su re on t he r e s il i en t mod u lus o f s a tu r a t ed cohe s ive so il s . To ach i ev e t he se ob j ec t i ve s ,

s ix c o h e s i v e s o il s, r e p r e s e n t in g m a j o r s o i l s u b g r a d e t y p e s i n O h i o , w e r e c o l l e c t e d f r o m

r o a d c o n s t r u c t i o n s it es i n f i v e c o u n ti e s i n O h i o b y t h e O h i o D e p a r t m e n t o f T r a n s p o r ta t io n .

I n a d d i ti o n , o n e c o h e s i v e s o i l sa m p l e w a s s e l e ct e d f r o m t h e S p e c i f i e d P a v e m e n t S t u d i e s

t e s t p r o g r a m o n U . S . R o u t e 2 3 . A t o t a l o f s e v e n s o il s a m p l e s w e r e i n v e s t i g a te d i n t h is

s tudy .

Soil Properties and Specimen Preparation

Propert ies o f Ohio Subgrade Soils

T h e s e v e n s o i l s a m p l e s c a m e f r o m W a s h i n g t o n , A t h e n s , S h e l b y , C r a w f o r d , a n d

D e l a w a r e C o u n t i es . A l l s o i l s a m p l e s w e r e p l a c e d i n a n o v e n , w h i c h w a s m a i n t a i n e d a t

6 0 ~ f o r 2 4 h o u r s , a n d t h e n w e r e a i r- d r ie d i n t h e l a b o r a t o r y o v e r a t w o - w e e k p e r io d .

A t t e r b e r g l i m it s, S i e v e A n a l y s i s , H y d r o m e t e r , S t a n d a r d P r o c t o r C o m p a c t i o n , a n d

S p e c i f i c G r a v i t y t e st s w e r e c o n d u c t e d t o d e t e r m i n e t h e e n g i n e e r i n g i n d i ce s o f t h e s e l e c te d

so i l s ample s .

T a b l e 1 s h o w s t h e s a m p l e n a m e , s o i l t y p e a n d b a s i c e n g i n e e r i n g i n d i c e s f o r th e

p r e d o m i n a n t l y g l a c i a l s o il s a m p l e s . T h e l i q u id l i m i t f o r t h e s a m p l e s e t r a n g e d f r o m 2 5

t o 6 0 , a n d p l a s t ic i t y i n d e x r a n g e d b e t w e e n 9 a n d 3 1 . T h e sa m p l e s w e r e p r i m a r i l y

s il t ( 4 5 - 8 1 ) w i t h l e s se r a m o u n t s o f s a n d ( 0 - 1 7 ) a n d c l a y ( 7 - 3 9 ) . T h e s a m p l e s w e r e

c l a s si f ie d a s e i t h e r A - 4 , A - 6 o r A - 7 - 6 . T h e r e w e r e t w o s a m p l e s i n th e A - 4 g r o u p , t h r e e

s a m p l e s i n t h e A - 6 g r o u p , a n d tw o s a m p l e s i n t h e A - 7 - 6 g r o u p . A c c o r d i n g t o U S C S s o il

c l a s s i f i c a t ion , s i x o f t he so i l s am ple s w e re c l a s s i f i ed a s CL ( low p l a s t i c i t y c l ay ) . On e

s a m p l e f r o m A t h e n s C o u n t y w a s c l a s s if i e d a s C H ( h i g h p la s t ic i t y c l ay ) .

Sample

Tab le 1 - Soil Classification and Engineering Indices

Soil Classification Liq uid Pl as tic ity Perc ent f Pe rcentof Percent f

AA SH TO U S C S Limit Index Sand Silt Clay

WA S-7 A-4 CL 29 10 3 56 7

SHE-47 A-4 CL 26 9 17 66 14

WA S-821 A-6 CL 32 11 13 56 21

ATH -50-Cool A-6 CL 33 13 8 45 39

DEL -23 A -6 CL 38 17 14 70 13

CRA W -Beal A-7-6 CL 41 21 7 81 12

ATH -7 A-7-6 CH 59 31 0 66 34

Specimen Preparation

T a b l e 2 s h o w s t h e m o i s t u r e c o n t e n t a n d d r y d e n s i t y o b t a i n e d f o r e a c h s o i l sa m p l e a s a

r e su l t o f S ta n d a rd P r o c t o r C o m p a c t i o n te s t ( A S T M D 6 9 8 ) . T h e o p t i m u m m o i s t u re

c o n t e n t s r a n g e d f r o m 1 4 t o 2 5 w h i l e t h e m a x i m u m d r y d e n s i t y v a r i e d f r o m 1 5 0 0 t o

2 0 0 0 k g / m 3.



B U T AL IA E T A L O N O H IO S O IL

7

Six samp les were each t e s t ed a t t h r ee d i f fe r en t mo i s tu re con t en ts , d ry o f op t im um

m o i s t u r e co n t e n t (D R Y ) , o p t i m u m m o i s t u r e co n t e n t (O M C ) , a n d w e t o f o p t im u m

m ois tu re con t en t (W ET) , t o eva lua t e t he e f f ec t o f moi s tu re con t en t on r es i li en t modulus

of unsa tu ra ted so il s. The r ange o f mo i s tu re con t en ts were chosen t o cor r espon d to t yp i ca l

m o i s t u r e c o n te n t s d u r in g f i e ld c o m p a c t i o n . T h e D R Y s a m p l e s w e r e 2 t o 4 % b e l o w t h e

o p t i m u m c o nd i ti o n , a n d W E T s a m p l e s w e r e c o m p a c t e d a t 18 9 o 3 % a b o v e o p ti m u m .

The n a tu ra l moi s tu re con t en t s fo r the so i l s a t t he t ime o f sam ple co l l ec t ion w ere genera l l y

h igher t han t he op t im um m oi s tu re con t en ts .

The sam ples fo r re s i l ien t modu lus t e s ti ng were p rep ared us ing a cons t an t mas s o f so i l

ma te r i a l t ha t was t ho rough ly mixed w i th d i s ti ll ed wa te r t o ob t a in t he des i r ed mo i s tu re

con t en t and d ry dens i ty . Th e m ixed so i l ma te r i a l wa s p l aced i n a g l as s bowl w i th p l as ti c

cover , and s to red in a humid bo x fo r twen ty- four hour s . Th i s ensured a un i fo rm ly

d i s t ri bu t ed m oi s tu re i n t he so i l ma te r ia l . Af t e r twen ty- four hour s , t he m a te r i a l was

c o m p a c t e d i n t h e m o l d i n f i v e l a y e rs o f a p p r o x i m a t e l y e q u a l m a s s . E a c h l a y e r o f t h e

s p e c i m e n w a s c o m p a c t e d u s in g a m a n u a l r a m m e r i n a H a r v a r d M i n i a tu r e C o m p a c t i o n

a p p a r at u s . T h e c o m p a c t i v e e ff o r t a p p l ie d p e r u n i t v o l u m e f o r t h e H a r v a r d M i n i a tu r e

C o m p a c t i o n T e s t w a s t h e s a m e a s t h at f o r th e S t a n da r d P r o c t o r C o m p a c t i o n T e s t. A f t e r

t h e s a m p l e w a s c o m p a c t e d i n f i v e la y e r s , e a c h s p e c i m e n w a s c a r e f u ll y e x tr u d e d f r o m t h e

c o m p a c t i o n m o l d , a n d i t s d i a m e t e r a n d h e ig h t w e r e m e a s u r e d .

Tab l e 2 - Summ ary o f Soil Specimen roperties

Dry of Optimum Optimum Wet of Optimum Saturat ion

(DRY) (OMC) (WET) (SAT)

S a m p l e M o i s t u r e D ry M o i s tu r e D ry M o i s t u r e D r y M o i s t u r e D ry

C o n t en t D e n s i t y C o n t e n t D e n s i t y C on te nt D e n s i t y C o n t e n t D e n s it y

( ) (k~/m3) ( ) (k~ m3) ( ) (k~ m 3) ( ) (k~ m3)

W A S-7 11.0 1906 14.0 1937 16.0 1896

SH E-4 7 12.5 1814 14.5 1864 16.0 1828 -

W AS -821 10.8 1860 14.8 1897 17.8 1850

AT H-5 0-Coo l 14 .0 1840 16.0 1879 18.0 1840

DEL -23 16.6 1813 18.8 1,813

CR AW -Bea l 15 .7 1684 17.7 1720 19.7 1686

AT H -7 21.2 1513 24.2 1541 27.2 1508

DE L-23 sam ples we re t e s ted a t two d i f f e r en t mo i s tu re con ten t s , op t imu m moi s tu re

con t en t (OM C) , and 100% of sa tu ra t ion (SAT) t o eva lua t e t he e f f ec t o f pore wa te r

pres sure on r es il i en t mod ulus . DEL-23 sam ple fo r SAT cond i t ion w as f i rs t com pac t ed a t

m a x i m u m d r y d e n s i ty a n d o p t i m u m m o i s tu r e c o n te n t , a n d t h e n w a s f u l ly s a t u ra t ed i n a

t r iax i a l te s t chamber . Sa tu ra t i on was ach i eved by app ly ing a back pressu re o f 227 kP a .

Th e ce l l p r es sure w as 248 k Pa , fo r an e f fec t i ve conf in ing p res sure o f 21 kPa , which w as

a lm os t the sam e e f f ec t ive p res sure a s tha t o f subgrade so i l a t a dep th o f 0 .6 m be low the

p a v e m e n t .

q u i p m en t a n d T es t Pro ced u re

The m ajor com pon ent s fo r t he r e s il i en t m odulus t e s t s a s pe r fo rm ed in the So i l

M e c h a n i c s L a b o r a t o r y at T h e O h i o S t at e U n i v e r si ty a r e s h o w n F i g u r e s 1 an d 2 . T h e

s p e c i fi e d l o a d w a s a p p l i ed b y a n a x i a l- to r s io n l o a d i n g s y s t e m m a n u f a c t u r e d b y M T S

S y s t e m s C o r p o r a ti o n . A n I B M c o m p a t i b l e p e r s o n a l c o m p u t e r in c l u d in g a n i n t er n a l D a t a




Acquisition Board DAQ) and LabVIEW software, a triaxial chamber, a loadcell, a

Linear Variable Differential Transformer LVDT), and a pore water pressure transducer

were used in the test set up. The system used in this study was developed for measuring

resilient modulus o f subgrade soils according to AASHTO Method of Test for Resilient

Modulus of Unbound Granular Base/Subbase Materials and Subgrade Soils-SHRP

Protocol P46 T294-94).

Loading System and Data cquisition

All the resilient modulus tests in this study were conducted using an axial-torsion

loading system developed by MTS Systems Corporation. This system comprised of a

servohydraulic control system and a load frame with an actuator as shown in Figure 1.

The force capacity of the load frame was 250 kN. The internal interface DAQ and the

graphic language program software, LabVIEW, were used to control the system and to

collect all data from the loadcell, LVDT, and pore water pressure transducer. The applied

load was controlled by the servohydraulic control system. The applied load generally

consisted ofa haversine with a load duration of 0.1 sec and cycle duration of 1.0 sec as

per AASHTO T294-94), except for the modified testing sequences. This wave was

generated and sent to the servohydraulic control system by a program coded using

LabVIEW. Signals were recorded and generated at a rate of 100 points per second.

Figure 1 - Resilient Modulus Testing System

Triaxial pparatus and Measurement Systems

The triaxial pressure chamber was modified to include the loadcell and the LVDT to

facilitate the determination of the resilient modulus. Figure 2 shows a modified triaxial

pressure chamber mounted in the load frame. The loadcell was mounted inside the



BUTALIA ET AL ON OHIO SOIL 75

t r iaxial pressure chamber between the steel piston and the top platen on the soi l specimen.

The capa ci ty of the load cell was 441 N . The LV DT was m ounted on the external s teel

rod in the top cove r o f the tr iaxial pressure c ham ber as sho wn F igure 2. This external

LVDT was a DC-DC miniature LVDT wi th a range of+/ - 5 .08 mm. The pore water

pressure t ransducer was m ounted on the bot tom drainage valve. The capaci ty of the pore

water pressure transducer was 345 kPa. I t was only used to measure the pore water

pressure in the saturated DEL-23 samples.

Figure 2 - Triaxial ell or Resilient Modulus Test

Testing Procedure

In this study, two procedures w ere used to measure resi lient mod ulus for the soi l

samples . The f i rs t was the tes t ing sequence for Material Type 2 in A AS HT O T294 -94

test ing procedure. The resi lient modulus o f unsaturated soi l samples w as obta ined using

this test ing sequence. During this test , the two bottom drainage valves were open and no

pore pressures were measured. The other was the modified test ing sequence for ful ly

saturated soi l sample as show n in Table 3. This test consisted o f two different types o f

test ing procedure s. M odified Test ing I was to meas ure resi l ient mo dulus o f ful ly

saturated specimen at 21 kPa effect ive confining stress, and Modified Test ing II was

deve loped to invest igate the buildup an d dissipat ion o f pore w ater pressure at four

different load rates. In the Modified T est ing II procedu re, the num ber o f loading cyc les

was reduced to 30. The loading per iod was var ied to chec k the ef fect of length of unload

time on the pore pressure buildup and degradation of resil ient modulus. In these tests, the

actual load t ime w as kept constant as 0.1 sec, but the unload t ime w as varied as the

loading period changed. Fo ur load cycles 1, 4, 6, and 8 sec) were em ploy ed in the



7 RESILIENT MODU LUS TESTING FOR P VEMENT COMPONENTS

M o d i f i e d T e s t i n g I I p r o g r a m . A l o a d i n g p e r i o d o f 1 s e c c o n s i s t e d o f 0 .1 s e c o f lo a d i n g

t i m e a n d 0 . 9 s e c o f u n l o a d i n g t im e . A l o a d i n g p e r i o d o f 4 s e c c o n s i s t e d o f 0.1 s e c o f

l o a d i n g t i m e a n d 3 . 9 s e c o f u n l o a d i n g t i m e . D u r i n g t h e M o d i f i e d T e s t i n g I a n d II

p r o c e d u r e s , t h e t w o b o t t o m d r a i n a g e v a l v e s w e r e c l o s e d to e n s u r e u n d r a i n e d c o n d i t io n s .

A f t e r t h e r e s i l ie n t m o d u l u s t e s t o n u n s a t u r a t e d a n d s a t u r a t e d s o il s a m p l e s , t h e l e n g t h o f

e a c h s p e c i m e n w a s m e a s u r e d . T h e s p e c i m e n w a s th e n w e i g h e d to d e t e r m i n e th e m o i s t u r e

con t en t .

T a b l e 3 - Mod tTed Test ing Sequences or Saturated Sam ples

Number of

T es tin g S e q u e n c e C o n f i n i n g L oa din g L oa din g D e via to r

Proced ure Pressure, kPa Cyc les Periods, s Stress, kPa

M odified 1 21 1000 1 14

Testing I, 2 21 100 1 14

Saturated 3 21 100 1 28

Soil 4 21 100 1 41

drainage 5 21 100 1 55

valve closed) 6 21 100 1 69

Modified

Testing II,

Saturated

Soil

drainage

valve closed)

21 1000 21

2 21 30 1 14

3 21 30 1 41

4 21 30 1 55

5 21 30 1 69

6 21 30 4 41

7 2I 30 4 55

8 21 30 4 69

9 21 30 6 41

10 21 30 6 55

11 21 30 6 69

12 21 30 8 41

13 21 30 8 55

14 21 30 8 69

T e s t R e s u l t s a n d D i s c u s s i o n

Test Resu lts

F i g u r e s 3 a n d 4 s h o w t y p i c a l r e s u lt s o f r e s i li e n t m o d u l u s t e s t s o n s a m p l e s W A S - 7 ,

W A S - 8 2 1 , C R A W - B e a l a n d A T H - 5 0 - C o o L T h e r e s u lt s i ll u st ra t e t h e e f fe c ts o f v a r y i n g

d e v i a t o r s t r e ss e s , c o n f i n in g s t r e s s e s, a n d m o i s t u r e c o n t e n ts . F i g u r e 3 w a s d e v e l o p e d u s i n g

a l i n e a r s c a l e f o r b o t h a x e s a n d F i g u r e 4 p r e s e n t s t h e r e s i li e n t m o d u l u s t e s t d a t a u s in g a

l o g s c a le f o r b o t h a x e s i n a c c o r d a n c e w i th t h e A A S H T O T 2 9 4 - 9 4 . F i g u r e 4 s h o w s t h e

c o e f f i c i e n t o f d e t e r m i n a t i o n , R 2 , a n d r e g r e s s i o n c o e f f i c i e n t s , k a a n d k 2 , as p e r t h e s i m p l e

l in e a r r e g r e s s io n m o d e l f o r T y p e 2 M a t e r ia l re c o m m e n d e d i n A A S H T O T 2 9 4 - 9 4 f o r

t h r e e d if f e r e n t m o i s t u r e c o n t e n t s o f A T H - 5 0 - C o o l . T a b l e 4 a l s o s h o w s t h e c o e f f i c i e n t o f

d e t e r m i n a t i o n , R 2, a n d r e g r e s s i o n c o e f f i c i e n t s , k~ a n d k ~ d e t e r m i n e d f r o m t h e r e s i l i e n t

m o d u l u s t e s t r e s u l ts f o r s i x o f th e s o i l sa m p l e s , k l , k 2 , a n d R 2 w e r e d e t e r m i n e d f o r e a c h



BUTALIA ET AL ON OHIO SOIL 7 7

case f rom 15 da t a po in t s us ing s imp le li nea r r egress ion mo de l fo r Typ e 2 M ate r i a l a s

r e c o m m e n d e d in A A S H T O T 2 9 4 -9 4 .

D eviato r Stress Con fining Stress and M ois ture Content

Res i l i en t modu l i measu red in the s ix so i l s am ples wi th t h ree d i f f e ren t moi s tu re

con ten t s were ana lyzed o n the bas i s o f dev i a to r s tr e s ses , conf in ing s t r e s ses and m oi s tu re

con ten t. A s show n in F igure 3 , r e si l ien t mo dulus o f t he coh es ive so i l s g radua l ly

dec reased w i th an i nc rease i n dev i a to r s tr es s. In m any cases , t he dec rea s ing r a t e a t the

low dev ia to r s t r e s s wa s m ore p rono unced than tha t a t the h igh dev ia to r st r es s . Res i l ien t

mo dulus fo r each o f t he s ix so i l s amples i n t h is s t udy inc reased s l i gh t ly wi th an i nc rease

in conf in ing s t re s s . As show n in F igure 4 and Ta b le 4 , t h i s beh av io r is eas i l y exp la ined by

eva lua t ing t he r e su l ts o f a l i nea r r egress ion ana lys i s o f t he da t a po in t s me asured dur ing

the r es il i en t mo dulus t e s t on each spec imen . The coe f f i c i en t o f de t e rmina t ion f ro m

res i li en t modu lus fo r t he s ix so i l s amp les had a r ange be twe en 0 .0018 and 0 .6646 . On ly

f o u r s p e c im e n s , t w o a t o p t i m u m m o i s tu r e c o n t e n t a n d w e t o f o p t i m u m m o i s tu r e c o n t e n t

i n W A S - 8 2 1 , a n d o n e s p e c i m e n e a c h w i t h w e t o f o p t im u m m o i s t u r e c o n te n t i n A T H - 5 0 -

Cool and AT H -7 had a coe f f i c ien t o f de t e rmina t ion g rea t e r t han 0 .5 . T he a ve rage o f t he

c o e f f ic i e n t o f d e t e r m i n a ti o n f o r s a m p l e s w i t h d r y o f o p t i m u m m o i s t u r e c o n t e n t, o p t i m u m

mo is tu re , and w e t o f op t im um m oi s tu re con ten t were 0 . I 13 , 0 .258 , and 0 .45 , r e spec t ive ly .

Thi s r e su l t ma y be an e f f ec t o f g radua l ly dec reas ing e f f ec t i ve conf in ing s t r e ss wi th an

inc rease i n t he moi s tu re con ten t . A l though the r ange o f the coe f f i c ien t s o f de t e rmina t ion

in each m oi s tu re con ten t wa s s l i gh t ly h igh , i t can be cons ide red t ha t t he co nf in ing s t r e s s

m ay in f luence r es i l i en t modu lus fo r coh es ive subgrade soi ls .

As m ent ioned prev ious ly , i t i s no t ed t ha t r e s i li en t modu lus fo r co hes ive so i l s i s c lose ly

re la ted to the m ois ture con tent in sub grad e soi ls . A s show n in F igu re 3 , the res i l ient

m odu lus o f t he so i l s am ples dec reased wi th an i nc rease i n m oi s tu re con ten t s . F igure 5

shows the r e l a ti onsh ip be tw een th ree mo i s tu re con ten ts and va lues o f r e s il i en t m odulus ,

m easured a t a dev i a to r s tr e s s o f 41 k Pa and a conf in ing s t r e s s o f 21 kP a , fo r the s ix

u n s a t u ra t e d s a m p l e s. R e s i li e n t m o d u l u s o f s a m p l e s d r y o f o p t i m u m m o i s tu r e c o n t e n t a r e

10 to 76 g rea t e r t han tha t o f sam ples a t op t im um moi s tu re con ten t, and the r e s il i en t

m o d u l u s o f s a m p l e s w e t o f o p t i m u m m o i s t u r e c o n t en t a r e 2 0 to 7 0 l o w e r t h a n t h a t o f

sam ples com pac ted a t op t imu m moi s tu re con ten t . The r esu l ts o f t h is s t udy c l ea r ly show

tha t an i nc rease i n moi s tu re con ten t causes s ign i f ican t degrada t ion o f r e s i li en t mod ulus o f

cohe s ive so i ls .

F igure 6 show s the re s i li en t mo dul i o f t he sam ple wi th op t im um m oi s tu re con ten t and

fu l ly sa tu ra t ed so i l s ample fo r DEL-23 . The r es i l ien t mod ulus o f t he sa tu ra t ed so i l s ample

i s l e s s t han ha l f t ha t mea sured a t op t imu m for each co r responding dev ia to r s tr e s s l eve l. In

the r e s i li en t mod ulus t e s t ing pe r fo rm ed in th i s s t udy on sa tu ra ted so i l s am ples , pore wa te r

pressure i nc reases were obse rved . There fore , i t is poss ib l e t ha t t he r educ t ion i n r e s il i en t

mo dulus , r e su l ti ng f rom pore w a te r p ressure bu i ldup , can be m easured .

Pore Pressure Bui ldup

The f i rs t g roup o f te s t s was ca r r ied ou t a f t e r the pore w a te r p ressure t ha t was b u i l t up

in t he condi t i on ing process had d i s s ipa ted . Th e load ing pe r iod wa s va r i ed f ro m 1 to 8 sec



8 R E S IL IE N T M O D U L U S T E S TING F O R P A V EM E N T C O M P O N E N T S

150

100

5 o

0

0

150

~ 1 0 0

150

. ]oo

N 5O

a)

~- Confining Stress of 41 kPa ]

-~ - Confmh~gStress of 21 kPa

- I - Confining Stress of 0 kPa

~

. . . . . . . . . . _ _ . . . . . . . . . . . .

9

i . _ _ 2 ~ : : _:Ir.~: ::::.

2 0 4 0 6 0

D e v i a t o r S t r e s s ,

kPa

b)

~ [ - o- C onfining Stress o f 42 kPa

-~ - Confining Stress of 21 kPa

-u - Confining Stress of 0 kPa

Q . 9 1 4 9

9 . . . . . . . .

: l ~ : :

. . . . . . . 9 . . . . . . . . . 9 . . . . . . . . . 9

. . . . . . . . . -o . . . . . . 9 . . . . . . . . . . 9

' ' ' I ' ' ' t ' ' ] ' ' '

2 0 4 0 6 0

D e v i a t o r S t r e s s , k P a

c)

~ [ --O -C onfiningStress of 42 kPa

Confining Stress of 21 kPa

O. - I - Conf ining St ress of 0 kPa

9 . . . "o . . . .

- . - . . . . .

9 -m . . . . ~ . . . . . 2 1 ~ I S ~ 2 ~ _ : t

. . . . . . " . . . . . H D - . . . . . . . 9 m

' I ' I ' ' ' I '

2 0 4 0 6 0

D e v i a t o r S t r e s s , k l ? a

80

8 0

80

F i g u re 3 - R e s i l i e n t M o d u l u s

Test Re sultfo r a) W AS-7 A-4), b) W AS-821 A-6), c)

CRA W-Beal A-7-6)



B U T A L IA E T A L O N O H I O S O I L 9

1000

100

10

9 Confining Stress of 41 kPa



DRY OMC WET

y = 104.4x o.o33 y = 102,4x o-~ y = 271.7x o.515

R2 = 0.025 R2 = 0.1003 R2 = 0.6646

~

. . . . . . . . - ~ . . . . . ~ - - - ~ - - - ~

10 100

D e v i a t o r S t r e s s k P a

F i g u r e 4

Resilient Modulus Test Result or A TH-50-Cool A-6), Log Scale

T a b l e 4 Regression Constants

am ple k l k2 R 2 k l k2 R 2 k l k2 R 2

WAS -7 111.09 -0.153 0.285 96.35 -0.183 0.249 76.46 -0.270 0.459

SHE- 47 144.77 -0.207 0.272 90.2 -0.256 0.426 13.43 -0.044 0.01

WAS -82 1 84.26 -0.04 0. 008 171.84 -0.312 0.61 160.71 -0.448 0.595

AT H-5 0- Co ol 104.36 -0.033 0.025 102.38 -0.068 0.1 271.7 -0.515 0.665

CR AW -B ea l 111.43 -0.087 0.047 122.53 -0.214 0.158 108.96 -0.341 0.458

ATH -7 109.41 -0.064 0.043 79.18 -0.01 0.002 129.42 -0.222 0.51l



8 R E SIL IE N T M O D U L U S T E S T IN G F O R P A VE M EN T C O M P O N E N T S

1 0 0

8 0

6 0

4 0

2 0

0

- - E - - W A S - 7 - - O -- S H E - 4 7 - - -I I -- W A S - 8 2 1

- o - - A T H - 5 0 - C o o l - I - C R A W - B e a l - 9 A T H - 7

1 0

' ' t ' ' I ' ' ' I ' ' ' I ' ~ I ' ' ' I ' ' ' I ' ' ' I ' ' '

1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8

Moisture Content %

0

~0

Figure 5 - Resilient Modulus versus Moisture Content deviator stress of 41 kPa and

confining stress of 21 kPa)

9 0

8 0

7 0

60

5

4 0

9- 3 0

2 0

1 0

, , , , i , , , , [ , , , , i , r , , i , , ,

1 0 2 0 3 0 4 0 5 0 6 0

Deviator S t r e s s , k P a

F i g u r e 6 Resilient Modulus fo r DEL-23 with Optimum Moisture Content and Saturation



BUTALIA ET AL ON OH IO SO IL 81

6

5

~ 4

~ 3

g 2

0

0

~ Dev ia to r S t r e ss o f 41 k Pa

. . . .

L . . . . I . . . . ] ' ' ' / . . . .

2 4 6 8 10

L o a d i n g P e r i o d

s / c y c l e

F i g u r e 7 - Residual Pore Pressure Loading Period and Deviator Stresses or Saturated

DEL-23

2 5 0 0

2 0 0 0

N 1 5 0 0

1 0 0 0

o .

5 O 0

- -e - D ev ia to r S t r e ss o f 5 5 k Pa

~ f 6 9 k P a ]

i . . . . I . . . . I 1

0 2 4 6 8 10

L o a d i n g P e r i o d

s / c y c l e

F i g u r e 8 - Dissipation Time Loading Period and Deviator Stress for Saturated DEL-23




25

2O

g

o 5

-m- Loading Period 4 s/cycle

35 45 55 65 75

D e v i a t o r S t r e s s kPa

Figure 9 - R e s i li e n t M o d u l u s v e r s u s L o a d i n g P e r i o d f o r S a t u r a t e d D E L 2 3

a n d t h e n u m b e r o f l o a d in g c y c l e s w a s c h o s e n t o b e 3 0. F o u r s e q u e n c e s o f t es t in g w e r e

car r ied out a t d i f feren t dev ia tor s t ress levels 14 41 55 and 69 kPa. Each tes t ing

sequence was ca r r i ed ou t a f t e r t he pore wa te r p res sure c r ea t ed by t he p rev ious t e s t i ng

sequence d i s s ipa t ed . Res idua l po re wa te r p res sure bu i l t up a f t e r s eve ra l cyc l es o f l oad ing

and i t t ook som e t ime to d i s s ipa te com ple t e ly . Res idua l pore w a te r p res sure he re in i s

de f ined as t he pore w a te r p res sure m easured j us t a f t e r t he l oad ing cyc l e i s imposed . In

genera l h igher dev i a to r s tr e s s c r ea t ed h igher dynam ic pore w a te r p res sure bu i l dup .

F igure 7 show s the i n f luence o f l oad ing pe r iod and dev i a to r s t re s s on the bu i l dup o f

the r e s idua l po re wa te r p res sure . The r es idua l pore wa te r p res sure i nc reased as t he pe r iod

of l oad ing dec reased . L arge r dev i a to r s t r es ses t ended t o c r ea t e h igher r e s idua l pore wa te r

pres sures . F igure 8 show s how the d i s s ipa t i on t ime i s r e l a t ed to l oad ing pe r iod and

dev ia to r s t r e ss l eve l . The r equ i r ed d i s s ipa t i on time dec reased as t he l oad ing p e r iod

inc reased a t each dev i a to r s t re s s l eve l and i nc reased as t he de v i a to r s t re s s l eve l inc reased

a t each l oad ing pe r iod . Sho r t e r l oad ing pe r iods c r ea t ed h igher po re wa te r p res sure

bu i ldups a nd r equ i r ed l onger d i s s ipa ti on t ime .

F igure 9 show s the degrada t i on o f r e s il ien t mod ulus due t o t he pore w a te r p res sure

bu i ldup a t d i f f e r en t l oad ing pe r iods and dev i a to r s t re s s l eve ls . The r es i l i en t mo dulus o f

the sa tu ra t ed so i l was h igher a t l onger l oad ing pe r iod a t each dev i a to r s t re s s l eve l.

o n c l u s i o n s

Base d on t he r e s il i en t mo dulus t e s t ing o f t he seven coh es ive so i l s amp les i t can be

conc luded t ha t:

1 . Res i l i en t mo dulus fo r unsa tu ra t ed and fu l l y sa tu ra ted cohes ive so i ls dec reases wi th an

increas e in the dev ia tor s t ress .

2 . The con f in ing s tr e s s a f f ec t s r e s i li en t mo dulus fo r unsa tu ra t ed coh es ive so i ls and the

so i l s amp les exh ib i t an i nc rease i n the r e s i li en t modu lus w i th an i nc rease i n t he

conf ining s t ress .



BU T AL IA ET AL ON OH I O SOI L 8 3

3 . Th e r esi l ien t mo dulus fo r cohes ive so i ls i s cons ide rab ly a f fec ted by the m ois ture

con tent in the coh es ive soil mater ia l . An increase in mois ture con tent resul ted in a

s ignif icant degradat ion in the res i l ient modulus .

4 . Th e r es il i en t mo dulus o f the sa tura ted so il reduce d to l e ss than ha l f tha t o f the so i l

spec imen a t op t imum m ois ture con ten t . Some reduc t ion wou ld poss ib ly be caused by

the bu i ldup o f pore w a te r p res sure , which i s shown b y the m odi f ied r es i li en t mod ulus

tes t ing un der lab oratory cy cl ic loading.

5 . The pore wa te r p res sure bu i ldup in sa turated cohes ive so i ls depends on the un load

t ime be twe en two spikes o f load ing cyc les . Shor te r load ing pe r iod tend to c r ea te

h igh er r e s idua l pore wa te r p r es sure . Larg e r dev ia tor st re s ses t end to c r ea te h igher

r es idua l po re wa te r p r es sure . Thus , i t t akes longer t ime for the r e s idua l po re w a te r

pressure to diss ipate a t shor ter loading pe r iod and hig her devia to r s tresses . Th e

res i li en t mod ulus o f fu l ly sa tura ted cohes ive so il was mu ch le s s under f a s te r (1

second pe r cy c le ) cyc l ic load ing than s lower (8 seconds pe r cyc le ) cyc l ic loading .

6 . The e f f ec t o f conf in ing st re ss seems to g r adua l ly dec rease wi th an inc rease in the

m ois ture conten t . Th is aspect needs to be inv es t igated fur ther .

Acknowledgments

This r e sea rch was pa r t i a lly suppor ted by the Oh io De par tment o f Transpor ta tion and

t h e F e d e r a l H i g h wa y Ad m i n i st ra t io n . T h e g u i d a n c e a n d r e v i e w c o m m e n t s p r o v id e d b y

Professor Wi l l iam E . W olfe o f The O hio S ta te Un ive r s i ty a re g r ea t ly apprec ia ted .

e f e r e n c e s

AA SH TO Guide for Des ign of Pavem ent S t ruc tures , 1993,

Am erican Association o f State

Highway and Transportation Officials

W ashington , D. C .

Ansa l , A. M. , E rken , A. , 1989 , Un dra ined Beh avior o f Clay und er Cyc l ic Shear

Stresses , Journal o f Geotechnical Engineering Vo l. 115 , N o. 7, pp. 968-983.

Brodsk y , N. S . , 1989 , Res i l i en t M odulus Measurem ents on Co hes ive Soi ls a s a Func t ion

o f De via tor S t res s and C onf in ing P ressure ,

Resilient M odu li o f Soils: Laboratory

Conditions

ed i ted by David J . E l ton and Richard P . Ray , Ne w York , N.Y. ,

Am er ican So c ie ty o f Civ il Enginee r s , pp . 15-30 .

Bu rczyk , J . M . , Ksaibat i , K. , An derson-S precher , R. , and Far rer , M.J ., 1994, Fac tors

Inf luenc ing De te rmina t ion o f a Subgrade Res i li en t Modu lus V a lue ,

Transportation Research Record No. 1462 Transpor ta t ion Resea rch Board ,

Na t ional Rese arch Co unci l , pp. 72-78.

Drum m, E . C ., Boa teng-Poku , Y. and P ie rce , T . J., 1990, Es t ima t ion of Subgrade

res i li en t Modulus f romStandard Tes t s ,

Journal o f Geotechnical Engineering

V ol. 116, N o. 5, pp. 774-789.

Dru mm , E. C. , Ree ves , J . S . , M adget t , M . R. , and Trol inge r , W . D. , 1997, Sub grad e




Resi l ient M odulus C orrect ion for Saturat ion Effects , Journal of Geotechnical

and Geoenvironmental Engineering Vol. 123 , N o. 7, pp. 663-670.

Fredlund, D. G. , Bergan, A. T. and Wong , P. K. , 1977, Re lat ion Betw een Resi lient

M odulu s and Stress Research Conditions for Cohesive Subgrade Soils,

Transportation RecordNo. 642 Transportation Re search Board, Na tional

Rese arch Co uncil , pp. 73-81.

H uang , J., 2001, Degradation of Resilient Modulus of Saturated Clay Due to Pore Water

Pressure Bulidup under Cyclic Loading Master Thesis Departm ent of Civil and

Env ironm ental Eng ineering and Geo detic Science, Th e O hio State University.

K im, D. G., 1999, Engineering Properties Affecting The Resilient Modulus of Fine-

Grained Soils as Subgrade Master Thesis

Depar tmen t o f C iv il and

Env ironm ental Engin eering and Geodetic Science T he O hio State University.

Lee, W., Bohra, N. C. , Altschaeffi , A. G . , and White , T . D., 1997, Resi l ient mo dulus of

cohesive soils, Journal of Geotechnical and Geoenvironmental Engineering Vol.

123, No . 2, pp. 131-136.

M endoza, M. J ., Hernandez, V. M . , 1994, Pore-pressure Build-up unde r Cycl ic Load ing

in Mexico C i ty Clay , XI11ICSMFE Proceedings 13 h International Conference

on Soil Mechanics and Foundation Engineering New Delhi, India, Vol. 1, pp.

181-186.

M oha m m ad, L. N. Puppala, A. J. and Alavill i, P. , 1994, Influ enc e o f Testing Procedure

and L VD T Locat ion on Res i li en t Modulus o f So i l s , Transportation Research

Record No. 1462 Transportation Rese arch Board, Nation al Research C ouncil , pp.

91-101.

M oha mm ad, L. N. Puppala, A. J. and Alavill i, P. , 1996 , Re silient Properties o f

Labo ratory Com pacted Subgrade Soi ls , Transportation Research Record No.

1504 Transportation Rese arch Board, N ational Resea rch Co uncil , pp. 87-102.

Ogaw a, S. , Shibayama, T. , and Yamaguchi, H. , 1977, Dy nam ic Strength of Saturated

Cohesive Soi l , XIII ICSM FE, Proceedings 9th International Conference on Soil

Mechanics and Foundation Engineering Vol. 2, pp. 317-320.

Seed, H. B., Chan, C. K., and Lee , C. E., 1962, Re silience Characteristics o f Subgrade

Soils an d Their Relat ion to Fat igue Fai lure in Asphal t Pav em ent , Proceedings

International Conference on Structural Design of Asphalt Pavement Univers i ty

o f M ichigan , A nn Arbor, pp. 611-636.

W oolstrum, G. 1990 , Dy nam ic Test ing of Nebraska Soi ls and Aggregates ,

Transportation Research Record No. 1278 Transportat ion Research Board,

Na tional Resea rch Council, pp. 27-34.



N i s h a n t h a B a n d a r a 1 a n d G e o f f r e y M . R o w e 2

Des ign Sub grade Res i l ient M odulus for F lor ida Subgrad e So i l s

Reference: B an d ara , N . an d Ro we , G . M. , "Design Sub grade Res i l ient Mod ulus for

Flor ida Sub grade S o i l s , "

Res i l ien t Modu lus Tes t ing f or Pavem en t Component s, A S TM

STP 1437,

G . N . D u r h a m , W . A . M a r l a n d W . L . D e G r o f f , E d s ., A S T M I n te r n a ti o n a l,

W e s t C o n s h o h o c k e n , P A , 2 0 0 3 .

Abstract: Man y agen c ies s t i l l u se em pi r i ca l co r re l a t io n s d ev e lo ped to d e te rm in e d es ign

su b grad e r e s i l i en t m o d u lu s b ased o n C a l i fo rn ia B ear in g Ra t io (C B R) , R-Va lu e o r S o i l

S u pp o r t Va lu e (S S V ) fo r pav em en t d es ign p ro j ec t s . T h ese r e l a t io n sh ips d o n o t co n s id e r

th e s tr e s s d epen d en c y o f t h e l ab o ra to ry d e te rm in ed r es i li en t m o d u lu s v a lu e .

B a c k c a l c u l a t e d su b g r a d e m o d u l u s v a l u e s f r o m F a l l in g W e i g h t D e f l e c t o m e t e r ( F W D )

tes ts a re a l so u sed fo r t h is pu rpo se . T h i s s tu d y was co n d u c ted to d e t e rm in e th e

re l a t io n sh ips b e tween l ab o ra to ry d e te rm in ed su b grad e r e s i l i en t m o d u lu s an d th e r e su l t s o f

L i m e R o c k B e a r i n g R a t i o ( L B R ) a n d F W D t es ts f o r c e rt a in F l o r i d a s u b g r a d e s o il s.

Lab o ra to ry r e s i li en t m o d u lu s v a lu es were d e te rm in ed u s in g su b grad e so i l s am ples

c o l l e ct e d f r o m ni n e p a v e m e n t s e c t io n s . T h e r e s il ie n t m o d u l u s v a l ue s w e r e c o m p u t e d b y

co n s id e r in g s t r e s s l ev e ls u n d e r a s t an d ard d u a l wh ee l i n th ree typ ica l pav em en t sec t ion s .

T h e ro ad w ay sec t io n s were se l ec t ed f ro m v ar io u s lo ca t io n s in P o lk C o u n ty , F lo rid a ,

F W D t es ts w e r e c o n d u c t e d a l o n g t he s e l e c te d r o a d w a y s a n d L B R t e st s w e r e c o n d u c t e d

o n b u lk su b grad e so i l s am ples . P re l im in a ry r e l a tio n sh ips to d e t e rm in e d e s ign su b grad e

r e s il ie n t m o d u l u s e q u i v a le n t t o A A S H T O R o a d T e s t s u b g ra d e f r o m F W D a n d L B R t e st s

w e r e d e v e l o p e d f o r c o n si d e r e d t y p i c a l p a v e m e n t s e c t i o ns .

Keywords: r e s i li en t m o d u lu s , ca l i fo rn ia b ea r in g r a t io , b ack ca lc u la t io n

Introduct ion

T h e res i l ien t m o d u lu s o f su b grad e (Mr) is u sed to ch a rac te r i ze th e ro ad b ed so il f o r

p a v e m e n t d e s i g n in t he 1 9 93 A A S H T O f le x i bl e p a v e m e n t g u i d e a s a d ir e c t i n p u t

pa ram ete r an d in d i rec t ly in th e r ig id pav em en t a s th e co e f f i c i en t o f su b gr ad e r e ac t io n (k) .

T h e e l a s t ic m o d u lu s b a sed o n th e r eco v erab le s t r a in u n d er r epea ted lo ad s i s ch a rac t e r i zed

b y th e r e si l ien t m o d u lu s (Mr) a s g iv en b e lo w (H u an g 1 99 3) .

M =aj_~

(1)

E

1

Pavement Engineer, Dynatest Consulting Inc., Route 5, B ox 1510, Starke, FL 32091.

2 President, Aba tech, Inc. 73, Old Dublin Pike, #31 2, Doylestow n, PA 18901.

85





In the ab ove equa t i on , t yd i s the devia to r s tress and

c ,

i s t he r ecoverab l e s t ra in und er

r epea t ed load ing . A l though the l abora to ry me thod o f de t e rmin ing o f r e s i li en t mo dulus i s

desc r ibed in the AA SH TO Tes t M ethod T 307-99 , m an y agenc ies s til l use empi r i ca l

cor r e l at i ons t o de t e rm ine r es i li en t m odulus base d on Ca l i fo rn i a Bear ing Ra t io CB R) or

L im erock Bear ing Ra t io LBR ) , R-Value , So i l Suppo r t Va lue SSV) . The fo l l owing

re l a ti onsh ips a r e genera l l y used i n F lor ida t o de t e rmine t he des ign subgrade mo dulus i n

lbs pe r square i nch) fo r road way cons t ruc t i on o r r ehab i l it a t ion p ro j ec t s .

S S V = 4 .596 x L O G ~ o L B R ) - 0 .576

2 )

( S $ V + 1 8 . 7 2 ~

M r

= 10~ g ~ - ; 3 )

In add i t ion t o t he ab ove r e l a t ionsh ips , o the r co r r e la t ions be tween

Mr

C B R a n d R -

Value are a l so avai lable .

M = 1500 C B R )

4)

M = 1 1 5 5 + 5 5 5 R 5 )

In the r e l a t ionsh ip g iv en i n the Eq ua t ion 4 , t he coe f f i c i en t 1500 m ay va ry f rom 750 to

3000 , and i s more su i t ab l e fo r fi ne g ra ined so i ls t han g ranu l a r ma te r i a l. Gene ra l ly , the

Equa t ion 4 i s su i tab l e fo r fi ne g ra ined so i l s w i th C BR o f le s s t han 25 and Equa t ion 5 i s

su i tab l e fo r ma te r i a ls w i th R-Value o f l e s s t han 60 Hu ang 1993). Acc ord ing t o t he

abov e d i scussion , i t can be seen t ha t a va s t va r i a ti on ex i s t s i n e s t ima t ing r es i li en t mod ulus

us ing conven t iona l so i l p roper ti e s .

The p ro j ec t i nvo lved de t e rmina t i on o f labora to ry re s i li en t mod ulus fo r n ine road

sec t ions sca t t e r ed a round Po lk County , F lo r ida and w as a im ed a t deve lop ing re l a t ionsh ips

for subgrade mod ulus fo r F lo r ida subgrade so i ls . Se l ec t ed pav em ent sec ti ons were

cons t ruc t ed wi th open-graded aspha l t cour se on a com pac t ed subgrade . A c l aye y sand

s u b - b a s e w a s e n c o u n t e r ed b e l o w t h e o p e n - g r a d e d a s p h a lt c o u r s e a t a f e w r o a d w a y

sec ti ons . Labo ra to ry r e s i li en t m odu l i va lues were d e t e rmined fo r t he roadw ay sec ti ons

us ing bu lk so i l s amples ob t a ined f rom represen t a t ive subgrade mate r i a ls . LB R t es t s fo r

the subgrade so i l s to de t e rm ine t he subgrade so i l s to de t e rmine t he sub grade so i l m odu lus

us ing em pi r i ca l r e l a ti onsh ips and FW D t es ts on t he pavem ent sec t ions t o de t e rmine

backca l cu l a t ed so il mod ulus we re a l so pe r fo rm ed to e s t ab l i sh re l a t ionsh ips w i th

l abora to ry r e s il i en t modulus , L BR t es ts and F W D resu lt s .

escription of Sites

Tw enty- f i ve roadw ay sec t ions were v i sua l l y eva lua t ed . Pav em ent coring , so il bor ings

and h and pen e t rom ete r t e s t ing were pe r fo rm ed to de t e rm ine t he represen t a t i ve s it e s fo r

l abora to ry r e s i li en t m odulus an d LB R t es t s. So i l bor ings pe r fo rm ed on the se l ec t ed

road wa y sec ti ons i den ti f ied c l ean f i ne sands A-3) and c l ean to s l i gh t l y s i lt y fi ne sands

A-2-4) undernea th t he pav em ent sec ti ons . These so i l t ypes a r e t yp i ca l subgrade so i l s in



BAN D AR A AN D R O WE ON F LOR ID A SOI L 8

Flor ida . Based o n the soi l bor ing results, nine road w ay sections were se lected to obta in

bulk soi l samples for LB R and res i l ient mod ulus tes ting.

a b o r a t o r y T e s t f o r t h e R e s i l i e n t M o d u l u s o f S u b g r a d e S o i ls

Th e res i l ient mo dulus tes t for granular ma ter ia l and f ine gra ined soi ls is sp ecif ied in

t h e AA S HT O T 3 0 7 - 9 9 R e s il ie n t M o d u l u s o f S o il s a n d Ag g re g a te M a t er ia l s . T h e

res il i en t mo dulus i s de te rmined by the r epea ted load t r i ax ia l com press ion te st on the t e s t

specimen. R esi l ient mod ulus (Mr) is the ra t io o f the am pli tude o f the repeated ax ia l s t ress

to the amp li tude o f the resul tant recoverab le axia l s train.

S tandard P roc tor com pac t ion te s ts were pe r formed on the each subgrade so i l s ample

to de te rmine the op t im um m ois ture con ten t and m axim um dry dens i ty va lues. These so i l

p roper t ie s were used to p r epare a r em olded sample w i th a d iamete r o f 73 .6 mm (2 .9

inches) and a he igh t o f 144 .8 m m (5.7 inches) . A r em old ing ta rge t va lue of 95% of the

ma ximu m d ry dens ity was used fo r the sample prepara t ion . The r es i li en t mod ulus t e s t ing

for each sample uses a ser ies o f devia tor st resses , con f ining pressures and loading cyc les

as g iven in Table 1 . A r epea ted ax ia l cyc l ic s t re s s o f f ixed magni tude , load dura t ion of

0.1 second s was app l ied to the rem olde d cyl indr ical sample . On e hundred repet i t ions o f

the cor respo ndin g cyc l ic axia l s tress us ing a ha vers ine-shap ed load pulse we re appl ied.

Av erage r ecovered de format ion for each de format ion measur ing dev ice fo r the l a s t f ive

cyc les were separa te ly r ecorded . These va lues w ere used to ca lcu la te the ave rage

res il i en t mo dulus a t each sequence . Af te r com ple t ion of the r e s i li en t mo dulus t e s t, a

qu ick shea r t e s t using a conf in ing pres sure o f 27 .6 (4 ps i ) was pe r form ed for each sample .

A typical res il ient modu lus verses c ycl ic-s t ress plot in En gl ish uni ts is i l lus tra ted in

Figure 1.

T A B L E 1 - - T e s t in g Sequence fo r Resil ient M odulus Test

Sequence No. Con f in ing P ressure Dev ia tor S tr es s Nu mb er o f Load

(kPa) (kPa) Ap plicat ions

0 (condi t ioning s tep) 41.4 (6 ps i) 27.6 (4 ps i) 500 -1000

1 41 .4 (6 psi) 13.8 (2 psi) 100

2 41.4 (6 ps i) 27.6 (4 ps i) 100

3 41.4 (6 ps i) 41.4 (6 ps i) 100

4 41.4 (6 ps i) 55.2 (8 ps i) 100

5 41.4 (6 ps i) 68.9 (10 ps i) 100

6 27 .6 (4 psi) 13.8 (2 psi) 100

7 27.6 (4 ps i) 27.6 (4 ps i) 100

8 27.6 (4 ps i) 41.4 (6 ps i) 100

9 27.6 (4 ps i) 55.2 (8 ps i) 100

10 27.6 (4 ps i) 68.9 (10 ps i) 100

11 13.8 (2 psi) 13.8 (2 psi) 100

12 13.8 (2 psi) 27.6 (4 psi) 100

13 13.8 (2 psi) 41 .4 (6 psi) 100

14 13.8 (2 psi) 55.2 (8 psi) 100

15 13.8 (2 psi) 68.9 (10 psi) 100



8 8 R E S I L I E N T M O D U L U S T E S T I N G F O R P A V E M E N T C O M P O N E N T S

'3

O

O

1 0 0 0 0 0 0

1 0 0 0 0 0

1 0 0 0 0

1 0 0 0

4 J

p i

9 $ 3 = 1 3 .7 9 k P a _ _

] 9 $ 3 = 2 7 . 5 8 k P a , ~

I

~ $ 3 = 4 1 . 3 7 k P a

r

r I I I ,

1 1

C y c l ic S t r e s s k P a )

F i g u r e 1 - - A Typica l Re silient Mod ulus Vs. Cyclic Stress plot.

Based on s imi l a r p lo t s deve loped fo r each s i t e , f o l l owing cons t i t u t i ve r e l a t i onsh ip fo r

r e s i l i en t modu lus Mr) n lb s pe r squa re i nch ps i ) w i th cyc l i c s t r e ss and con f in ing s t r e ss

w a s o b t a i n e d u s i n g r e g r e s s io n t e c h n iq u e s .

g : KI S ) 2 S3y

6)

w her e Sc : cy c l ic s t ress, ps i

3 - - con f in ing p r e s su re , p s i

Mr = r e s i li en t m odu lus , p s i

T h e c o r r e la t i o n c o e f f i c i e n t R e f o r e a c h s o il s a m p l e i s p r e s e n t e d i n T a b l e 2 a l o n g w i t h

t h e v a l u e s f o r K1, K 2 and K5 .

T A B L E

S i ~ N o . K 1

2--R esi l ien t M odulus Coeff ic ien ts for Eac h S ite.

K 2 K 5 R 2

1 6053 0 .1314 9 0 .33581 0 .98

2 5 9 9 7 0 . 1 1 8 1 8 0 . 3 3 1 4 4 0 . 9 8

3 5 1 0 8 0 . 1 1 1 1 3 0 . 4 0 06 1 0 . 9 8

4 6 4 6 2 0 . 1 2 3 2 6 0 . 3 1 1 8 2 0 . 9 7

5 6 0 3 4 0 . 1 0 2 6 3 0 . 3 5 4 8 2 0 . 9 8

6 6 1 5 5 0 . 1 0 3 4 7 0 . 3 6 5 7 2 0 . 9 8

7 4 9 2 5 0 . 0 6 7 2 7 0 . 3 7 8 0 2 0 . 9 2

8 5895 0 .1071 6 0 .36371 0 .98

9 5 8 3 6 0 . 0 6 3 9 7 0 . 3 6 3 5 2 0 . 9 8

L a b o r a t o r y T e s t f o r t h e L i m e r o c k B e a r i n g R a t i o ( L B R )

L B R t es t s a n d m o d i f i e d P r o c t o r te s ts w e r e p e r f o r m e d i n a c c o r d a n c e w i t h t h e F l o r i d a

D e p a r t m e n t o f T r a n s p o r t a t i o n S t a n d a r d F M 5 - 5 2 5 . T h e L B R t e s t i s a m e a s u r e o f t h e



BAN D AR A AN D R O WE ON F L ORID A SOI L 9

bearing capacity of soil as relating to pavement design. The test consists of measuring

the load required to cause a standard circular plunger with an area of 1 935 mm2) to

penetrate a specimen at a specified rate. The LBR is the load required to force the

plunger into the soil 2.54 mm 0.1 inches) expressed as a percentage of the load required

to force the same plunger the same depth into a standard sample of crushed limerock.

The average penetration load for a typical crushed limerock found in Florida has been

standardized to 5 516 kPa 800 psi). Based on the above LBR values and employing

Equations 2 and 3, the subgrade modulus value for each selected roadway section was

estimated. The test results and estimated subgrade modulus values for each roadway

section are presented in Table 3.

TABLE

3--L im eroc k Bearin~ Ratio LBR) Values.

Site No. LBR Estimated Subgrade Modulus MPa)

1

23 56.1

2 37 79.7

3 49 98.0

4 32 71.6

5 32 71.6

6 40 84.4

7 75 134.0

8 35 76.5

9 35 76.5

Fall ing W eight Deflectometer FW D) Testing

FWD tests were performed on the selected roadways to evaluate the in-situ subgrade

moduli values at each site. These tests were performed using Dynatest 8082 equipment

at an approximate spacing of 304.8 meters 1 000 feet). In the roadway sections shorter

than 304.8 meters, minimum of three locations were tested. Three tests were conducted

at each location at load levels of 26.7, 40.05, 66.75 kN 6 000, 9 000, 15 000 lbs) which

corresponds to stress levels o f approximately 378, 567 and 945 kPa over a 300 mm

diameter loading platen) to check for linearity of the pavement structure. Deflections

were measured using seven geophones located at 0, 200, 300, 600, 900, 1200, 1500 mm

from the center of the loading plate.

Backcalculation of FW D Data

Deflection Analysis of Pavement Structures DAPSTM was used for backcalculation

of subgrade modulus values from the FWD data. Three soil models rigid half-space and

subgrade thickness RHSST), known half-space stiffness KHSS) and non-linear A,B

subgrade A,B Sg) are included with DAPSTMbackcalculation algorithm. In the RHSST

model, a rigid base beneath the subgrade bedrock) is assumed. This allows for known

effects of non-linearity within the subgrade soil. In the KHSS model, a rigid base

beneath the subgrade is not assumed and is suitable for unusual situations with very soft

underlying materials etc. The non-linear soil model for the subgrade modulus Esub) uses

following relationship for the analysis.



9 0 R E S IL IE N T M O D U L US T E S T I NG F O R P A V E M E N T C O M P O N E N T S

(7)

w h e r e p

q

A,B

= m e a n n o r m a l e f f e c ti v e s tr e ss d u e t o s e l f w e i g h t o f th e p a v e m e n t

s t ruc ture

- - dev i a to r s t re s s due t o whee l l oad ing

= so i l cons t an t s

The u se r can s e l ec t t he be s t su i t ab l e so i l m ode l f o r t he ana lys is cons ide r ing t he

ge o lo gy and so i l p rope r t i e s i n t he a r ea . A l ea s t - squa re so lu t i on p roces s i s app l i ed ,

e m p l o y i n g a l l m e a s u r e d d e f l e ct i o n s a s p a r a m e t e r s c h a r a c t e r i z in g t h e d e f l e c t i o n b o w l .

S e e d v a l u e s f o r t h e a s p h a R c o n c r e t e ( A C ) a n d s u b g r a d e s t if f n es s w e r e o b t a i n e d f r o m

em pi r i ca l co r r e l a t i ons and a r e u sed t o gene ra t e t r a il va lues fo r t he pa ram e te r s

c h a r a c t e ri z i n g t h e b o w l . A s e t o f s i m u l t a n e o u s e q u a t i o n s w a s s e tu p a n d s o l u t i o n s t o th e s e

s i m u l t a n e o u s e q u a t io n s w e r e o b t a i n e d b y a n i te r a ti v e p r o c e s s . T h e R H S S T m o d e l a n d

n o n - l i n e a r A , B s u b g r a d e m o d e l w e r e c o n s i d e r e d f o r t h e a n a l y s is a s f o l lo w s .

F o r t h e R H S S T m o d e l a t w o - l a y e r el a st ic s y s t e m w i t h a h a l f -s p a c e s t i f fn e s s o f 2 0 0 0

M P a w a s c o n s i d e r e d f o r t h e a n a l ys i s. T h e n o n - l i n e a r s u b g r a d e ( A , B S g ) w a s m o d e l e d b y

fou r l aye rs w i th t h i cknes se s o f 0 .6 m , 0 .9 m , 1 .2 m , an d 1 .8 m on a com pres s ib l e h a l f -

s p a ce . T h e s u b g r a d e s t i ff n e s s w a s c a l c u la t e d a t a d e p t h o f O . 3 m b e l o w t h e u n d e r s id e o f

t he a spha l t l aye r u s ing t he A and B pa ram e te r s d e t e rm ined by t he ana lys i s . Fu r the r , a

l e a s t- s q u a r e s o l u t i o n p r o c e s s w i t h a r o o t m e a n s q u a r e e r r o r v a lu e o f le s s th a n 4 % w a s

e m p l o y e d t o e v a l u a t e t h e q u a l i ty o f th e b a c k c a l c u l a t e d r e s ul ts .

I n a d d it i o n t o th e a b o v e b a c k c a l c u l a t io n p r o c e s s , t h e s u b g r a d e m o d u l u s w a s

b a c k c a l c u l a t e d b y u s i n g t h e fo l l o w i n g e q u a t i o n g i v e n i n t h e 1 9 93 A A S H T O g u i d e .

0 . 2 4 P

M r - (8)

drr

w h e r e P

dr

r

= app l i ed l oad i n l b s

= m easu red de f l ec t i on a t r ad ia l d i s t ance r , i nches

= r ad i a l d i s tance a t wh ic h t he de f l ec t i on i s mea su red , i nches

A m i n i m u m d i s ta n c e f o r dr, to p e r f o r m t h e b a c k c a l c u l a t i o n u s i n g E q u a t i o n 8 i s

r e c o m m e n d e d i n t h e A A S H T O d e s i g n g u id e a s g i v e n in th e f o l l o w i n g r el a ti o n s h ip .

r~O.7a~

(9)

w h e r e , ae

a

D

z / [ a 2 / o / 2 1

= F W D l o a d p l at e r ad i u s , i n c h es

= t o t al t h i c k n e s s o f p a v e m e n t l a y e r s a b o v e t h e s u b ~ ' a d e , i n c h e s



BANDARA AND ROWE ON FLORIDA SOIL 91

E p -- effective modulus of all pavement layers above the subgrade, psi

The effective modulus of all pavement layers can be backcalculated from the following

relationship.

o = 1 .5pa~ , 1 2

] M r / l + D ~ e[-g -f

a M ,J

1 - D 2

+

E p

where, do

P

= deflection measured at the center of the load plate, inches

= FWD load plate pressure, psi

(lO)

The backcalculated subgrade modulus values were averaged to determine a

representative value for each roadway section. The average backcalculated subgrade

modulus values from the above analysis methods and other related statistics are presented

in Table 4.

TABLE

4 ~ B a c k c a l c u l a t e d S ub ~ , ra de M o d u l u s V a lu es .

DAPSTM-A,B Sg Model

(MPa)

Mean Min. Max.

169 98 212

183 129 252

172 94 280

213 164 214

186 164 203

153 135 170

171 143 202

167 96 244

144 42 189

Site No. AASHTO Equ~ion DAPSVM-RHSSTModel

(MP~ (MPa)

Mean Min. Max. Mean Min. Max.

1 128 76 181 154 104 207

2 171 122 231 184 133 242

3 149 89 258 163 97 258

4 136 134 139 162 160 165

5 138 119 165 164 152 180

6 148 131 165 170 159 183

7 145 122 176 180 157 208

8 151 91 200 167 102 229

9 120 86 192 131 59 193

I n t e r p r e t a t i o n o f R e s u l t s

As shown in Equation 6, the constitute model for the laboratory resilient modulus is a

function of the deviator stress and the confining pressure. To compare the subgrade

modulus obtained using FWD tests and LBR tests with the laboratory determined values,




t he r e s il ien t m odu l us f r o m t he cons t i tu t e m od e l shou l d be de t e r m i ned f o r t he equ i va l en t

f i e ld st re s se s. E l a s t i c L aye r ed Sys t em S of t wa r e ( EL SY S

T M )

was used t o ca l cu l a t e t he

s t r e s se s on the subgr ad e due t o s t anda rd dua l w hee l . Th i s p r og r a m ca l cu l a te s t he s t re s se s

and s tr a in s , a t any r eques t ed p o i n t due t o a g i ven l oad i ng , by i npu t ti ng l aye r t h i cknes se s ,

dens i ti e s and P o i s so n ' s r a t i o s o f e ach l aye r.

Thr ee t yp i ca l pav em en t s ec ti ons we r e cons i de r ed f o r t he ana l ysi s . Th ese s ec t ions

i nc l uded t h r ee d i f f e r en t a spha l t ic l aye r t h icknes se s cons i s t i ng o f 50 m m ( 2 i nches ) , 75

m m ( 3 i nches ) and 100 m m ( 4 i nches ) and 228 . 6 m m ( 9 inches ) o f g r anu l a r ba se . The se

l aye r t h i cknes se s a r e cons i de r ed a s the m i n i m um t h i cknes se s r equ i r ed f o r t yp i ca l m a jo r

r o a d w a y a s re c o m m e n d e d b y t h e F l o ri d a D e p a r t m e n t o f T r a n s p o r ta t io n . A n e l as ti c

m o du l i va l ue o f 3 125 MP a a t 20~ f o r a spha l t i c m a t e r i a l s and 100 M Pa f o r g r anu l a r

m a t e r i a l s we r e a s sum ed f o r the s t r e ss ca l cu la t ions .

Th e ve r t i c a l s tr e s s ( o r z ) on t he subgr ade l aye r w as a s su m e d t o b e equa l t o t he

dev i a t o r st r e ss o f the l abo r a t o r y m ode l . The co n f i n i ng s t re s s was a s sum ed t o be equa l t o

t he no r m a l oc t ahed r a l st r e ss in t he subgr ade l aye r ( Naza r i an e t al. 1998). Th e no r m a l

oc t ahed r a l s t r e ss can b e ca l cu l a t ed a s f o l lows .

crc = aocr = { a x +cry

+ o - z ) / 3

I n i ti a ll y , dev i a t o r and co nf i n i ng s t r e s se s o f 13 .8 kP a ( 2 p s i ) we r e u sed t o c om pu t e t he

co r r e spond i ng r e s i l ien t m odu l us u s i ng t he cons t i tu t i ve equa t i on g i ven i n Equa t i on 6 . The

ca l cu l a t ed re s i li en t m odu l us va l ues we r e t hen em pl oye d in EL SY S t o ca l cu l a t e

co r r e spon d i ng subgr ade s t re s s va l ues . Th ese ca l cu l a t ed s t r es s va l ues we r e u se d i n t he

cons t i tu t i ve m ode l t o ca l cu l a te r e su l ti ng subg r ade r e s i li en t m odu l us va l ues . Th i s

p r ocedu r e was r epea t ed un t il t wo suc ces s i ve ca l cu l a ti on s t eps p r oduce d equa l pave m en t

s t re s s va l ues . Us i ng t he abov e d i s cus sed p r ocedu r e , t he f o l l ow i ng l abo r a t o r y re s i li en t

m o d u l u s v a l u e s f o r e a c h a s p h a l t la y e r th i c k n es s w e r e c o m p u t e d a s p r e s e n t e d i n T a b l e5

T A B L E

5 --C om pute d Resi l ient Modulus B ased on Laboratory Results.

Si te No . L ab or a t o r y Res i l i en t M odu l us ( MP a)

5 0 m m A C 75 m m A C 1 00 m m A C

1 96.3 85.0 75.3

2 91.1 80.8 71.7

3 83 .7 72 .6 62 .9

4 97 .2 86 .7 77 .4

5 91 .4 80 .9 71 .5

6 95.5 84.2 74.4

7 68.4 60.3 53.2

8 90.5 80.6 71.1

9 80 .4 71 .4 63 .6

Com parison o f Resu l ts

A t y p i ca l c o m p a r i s o n o f la b o r a t o ry re s il ie n t m o d u l u s w i t h F W D e s t im a t e d m o d u l u s

u s i n g th e R H S S T m o d e l a n d L B R e s t i m a t e d m o d u l u s a r e i ll u st ra t ed i n F i g u re 2 a n d

Figure 3 , respec t ive ly .



B A N D A RA A N D R O W E O N F L O R ID A S O I L 9 3

A ccor d i ng t o Tab l e s 4 and 5 , t he ave r age va l ue o f the backca l cu l a t ed subgr ade

m o du l us , u s i ng t he cons i de r ed t h r ee ana l ys is m ode l s w as a l way s h i ghe r t han t he

l a b o r a to r y r e si li e n t m o d u l u s . T h e A A S H T O ( 1 99 3 ) d e s ig n g u i d e r e c o m m e n d s m o d i f y i n g

t he backca l cu l a t ed m o du l us u s i ng a co r r ec t i on f ac t o r t o ob t a i n de s i gn sub gr ade r e s i li en t

m o d u l u s v a l u e e q u iv a l e n t t o A A S H T O r o a d t e st s u b g ra d e . T h e A A S H T O d e s i g n g u i d e

r e c o m m e n d s a c o r re c t io n f a c t o r o f n o m o r e t h a n 0 .3 3 t o m o d i f y th e b a c k c a l c u l a te d

s u b g r a d e m o d u l u s v a l u e s. H o w e v e r , A A S H T O r o a d t es t d a ta s h o w t h a t th e r e si li e n t

m o d u l u s o f t h e A A S H T O r o a d t e s t s o il i s s t re s s s e n s it iv e a n d c o n s is ts o f m a i n l y f i n e -

g r a i ned so il s. The AA SH TO des i gn gu i de a l so sugges t s the g r anu l a r subgr ades wou l d

no t r equ i re a co r r ec t i on f ac t o r a s g r ea t a s t ha t requ i r ed f o r f i ne - g r a i ned cohes i ve

subgr ades . A ccor d i ng t o t he so i l bo r i ng da t a , t he subgr ades o f t he s i te s cons i de r ed f o r

t h i s s t udy m a i n l y cons i s t s o f non- co hes i ve s an dy m a t e r i a l s and a co r r ec t i on f ac t o r a s

g r ea t a s 0 .33 m ay no t be r equ i r ed t o ad jus t t he backca l cu l a t ed subgr ade m odu l us va l ues

a p p r o p r ia t e f o r u s e i n d e s ig n w i t h t h e A A S H T O m o d e l .

- ~ 1 0 0

" ~ 9 0

IE

8 0

7 0

e ~ 6 0

~ = g ~ 5 0

4 0

~ ' 3 0

o

2 0

~ o

- I

5 0 1 0 0

A m

9 7 5 m m A C / -

100

wwnA C ] _ ~

1 5 0 2 0 0

S u b g r a d e M o d u l u s F r o m F W D ( M P a )

F I G .

2- -Co mp ariso n o f Laboratory Resilient Modulus with Average Subgrade M odulus

Est imated from FW D Data Using RH SST M odel .

o

o

I

o

o

100

9

8 0

70 . . . . . . . . . . . . . ] -

6 0 . . . . . . . . . . 9 - - -

5 0 - -

~ . 5 0 r n rn A C I

3 0 7 5 m m A C - -

2 0 ! ~ e ~ f r -q , ,~ ,

1 0 / 1 0 0 r f f n A C _

0

0 5 0 1 0 0 1 5 0 2 0 0

S u b g r a d e M o d u l u s F r o m L B R ( M P a )

F I G .

3---Comparison o f Labo ratory Resilient Modulus w ith Average Sub grade M odulus

Estimated fro m LB R Results.




Similarly, laboratory resilient modulus values were compared with subgrade modulus

calculated from LBR results and reasonable correlations were observed as illustrated in

Figure 3.

TABLE

6- - -Aver a~ ,e R a t io s B e tw een Lab or a tor y an d F ie ld S ub~ , rade M o du lus Va lues .

AC Layer

Thickness

(mm)

Correction Factor for FWD Backcalculated Subgrade

Modulus

RHSST Model Non-linear A,B AASHTO

Sg. Model Equation

Avg. Std. Avg. Std. Avg. Std.

Dev. Dev. Dev.

50 0.54 0.07 0.51 0.07 0.62 0.09

75 0.48 0.07 0.45 0.06 0.55 0.08

100 0.42 0.06 0.40 0.05 0.48 0.07

Correction

Factor for

Estimated

Subgrade

Modulus from

LBR

Avg. Std.

Dev.

1.14 0.33

1 . 0 0 0.3

0.89 0.26

As illustrated in Table 6, the ratio for FWD backcalculated subgrade modulus varied

from 0.62 to 0.40 based on the considered models for the considered pavement structures.

The LBR estimated subgrade modulus is matched with the laboratory resilient modulus

for 75 mm (3-inch) asphalt layer thickness.

The relationships were developed to obtain the ratios between laboratory and field

subgrade modulus from backcalculated subgrade modulus and LBR estimated subgrade

modulus as follows:

Ratio for FWD backcalculated subgrade modulus = A x e 8(Ac ,h~c~,e,s) (12)

Ratio for LBR estimated subgrade modulus = C • e D(AC-thic~ness) (13)

where,

A,B,C,D are model constants

AC-thickness -- Asphalt concrete surface thickness in mm

The A,B parameters obtained for different models used for FWD backcalculation

and C,D parameters obtained for LBR estimated subgrade modulus are given in Table 7.

TABLE 7 - - M o d e l P a r a m e t e r s t o E s t i m a t e C o r r e c ti o n F ac t o r s.

Model

Parameter

FWD Backcalculated Subgrade Modulus

RHSST Model A,B Subgrade AASHTO

Model Equation

0.6961 0.6495 0.803

-0.005 -0.0049 -0.0051

LBR

Backcalculated

Subgrade

Modulus

A

B

C 1.4567

D -0.005



B A N DA R A A N D R O W E O N F LO R ID A S O I L 9 5

T h e s e r e l a t io n s h i p s s h o u l d b e c o n s i d e r e d p r e l i m i n a r y a s m o r e r e s e a r c h i s n e e d e d t o

o b t a i n g e n e r a l i z e d r e la t io n s h i p s. T h e d i f fe r e n c e s c a n b e d u e t o s e v e r a l r e a s o n s i n c l u d i n g

s a m p l i n g d i s t u rb a n c e , n o n - r e p r e s e n ta t i v e s p e c i m e n s , e tc . T h e a b o v e a n a l y s e s a re b a s e d

o n h y p o t h et ic a l p a v e m e n t s e c ti o n s c o n si s ti n g o f 5 0 m m , 7 5 m m a n d 1 00 m m o f a s p ha l t

l a y e rs w i t h 2 2 9 m m o f g r a n u l a r b a s e . T h e s e a s p h a l t la y e r t h i c k n e s se s a r e a p p r o x i m a t e l y

r e l at e d t o m i n i m u m s t ru c t u ra l c o u r s e f o r l im i t e d a c c e s s , E q u i v a l e n t S i n g l e A x l e L o a d s

( E S A L s ) o f g re a te r th a n 3 5 0 0 0 0 0 a n d E S A L s b e t w e e n 3 0 0 0 0 0 t o 3 5 0 0 0 0 0 r o a d w a y s .

C o n c l u s i o n s

C B R o r L B R a n d F W D t e st s a re w i d e l y u s e d t o o b t a i n s u b g r a d e so i l p r o p e r ti e s f o r

p a v e m e n t d e s i g n a s a n a l t e rn a t iv e t o t h e d e t e r m i n a t i o n o f su b g r a d e r e s il ie n t m o d u l u s

us ing l abo ra to ry re s i l ien t mo du lu s t e st ing . As a s t anda rd p r ac t i ce , emp i r i ca l co r r e l a t i ons

a r e u s e d t o o b t a i n d e s ig n r es i li e n t m o d u l u s u s i n g C B R o r L B R t e st r e su l ts . I n A A S H T O

( 1 9 9 3 ) p a v e m e n t d e s i g n g u i d e , a c o r r e c t i o n f a c t o r o f 0 . 33 i s d e fi n e d a s a c o r r e c t io n f a c t o r

f o r F W D b a c k c a l c u l a t e d s u b g r a d e m o d u l u s v a l u e s f o r fi n e - g r a in e d s u b g r a d e s o il s.

T h e p r i m a r y o b j e c t i v e o f t h is s t u d y w a s t o o b t a i n r e l a t io n s h i p s f o r d e s ig n r e s il ie n t

m o d u l u s b a s e d o n F W D a n d L B R t e st s. S i n c e t h e la b o r a t o r y - d e t e r m i n e d r e s il ie n t

m o d u l u s i s st re s s d e p e n d e n t , a p a v e m e n t l a y e r s tr e ss a n a l y s is w a s c o n d u c t e d t o q u a n t i f y

the s t r e ss dep end enc y fo r t he empi r i ca l co r r e l a t i ons t o e s t ima te de s ign sub grade r e s i l i en t

m o d u l u s u s in g F W D a n d L B R t es ts .

T h e l a b o r a t o r y -d e t e r m i n e d s u b g r a d e m o d u l u s v a l u e s w e r e g e n e r a l l y l es s t h a n th e

F W D b a c k c a l c u l a t e d su b g r a d e m o d u l u s v a lu e s . T h e b a c k c a l c u l a t e d m o d u l u s v a l u e s w i t h

D A P S u s i n g d i f f e r en t s o i l m o d e l s g e n e r a l l y p r o d u c e d s i m i la r r e s u lt s f o r s e l e c t ed

p a v e m e n t th i c k n e ss e s . T h e r a ti o s b e t w e e n l a b o r a t o r y a n d F W D b a c k c a l c u l a t e d m o d u l u s

v a r i e d f r o m 0 .4 0 t o 0 . 6 2 . T h e s t a n d a r d d e v i a ti o n v a r i e d f r o m 0 .0 5 t o 0 . 0 9 . T h e s e

d i f f e r ences can be due t o s eve ra l r ea sons , i nc lud ing s ampl ing d i s t u rbance , non -

r ep re sen t a t i ve spec im ens e tc . M ore r e sea rch is nee ded t o ob t a in gene ra l i zed r e l a t i onsh ips

w i t h l a b o r a t o r y a n d f i e l d s u b g r a d e m o d u l u s v a l u e s.

T h e r a ti o s b e tw e e n l a b o r a t o r y a n d L B R e s t i m a t e d s u b g r a d e m o d u l u s v a r i e d f r o m - 0 . 8 9

to 1 .14 . Th e s tanda rd dev i a t i on va r i ed f rom 0 .26 t o 0 .33 . The L B R es t im a ted r e si l ien t

m o d u l u s m a t c h e d w i t h th e l a b o r a t o r y d e t e r m i n e d r e s i li e n t m o d u l u s f o r a p a v e m e n t

s e c t io n w i t h 7 5 m m o f a s p h a lt la y e r. T h i s p a v e m e n t s e c t i o n c a n b e c o n s i d e r e d a s th e

m i n i m u m p a v e m e n t s e c t i o n re q u i r e d f o r a ty p i c a l ar te r ia l r o a d w a y s e c ti o n . T h e r e f o r e ,

t h e e m p i r i c al r e l a t io n s h i p t o d e t e rm i n e t h e d e s i g n s u b g r a d e m o d u l u s b a s e d o n L B R t e st s

c a n b e c o n s i d e r e d a s v a l id f o r ty p i c a l s u b g r a d e s o i l s i n F lo r id a . H o w e v e r , m o d i f i c a ti o n s

f o r th e e s t i m a t e d v a l u e s a r e n e c e s s a r y f o r th i n n e r o f t h i c k e r p a v e m e n t s e c ti o n s .

Acknowledgments

T h e a u t h o r s w o u l d l i k e to o f f e r t h e ir s i n c e re a p p r e c i a t i o n t o R e e s N i c k e r s o n w i t h

Pro fe s s ion a l Se rv i ce Indus t r i e s , Tam pa , F lo r ida fo r p rov id ing t he da t a fo r t h i s s t udy .




R e f e r e n c e s

Abatech, Inc., 2001, "Deflection Analysis of Pavement Structures (DA PS T M ) Software

Us er M anual," D oylestown, PA.

Abatech, Inc., 2001, "Elastic Layered System Software (ELSY S

T M )

Software User

M anual," D oylestown, PA.

AA SHT O, 1993, "Guide for the Design of Pavement Structures," A merican Association

o f State Highway and Transportation Officials, W ashington, D.C.

Florida D epartment o f Transportation (FDOT ), 2000, "Flexible Pavem ent Design

Manual," Tallahassee, FL.

Huang, Y. H., 1993, Pavem ent Analysis and Design, Prentice H all, In c., Englewood

Cliffs, NJ.

Nazarian, S., Ro jas, J., Pezo, R., Yuan, D., Abdu llah, I., and S cullion, T., 19 98, "Re lating

Laboratory and Field M oduli o f Texas B ase M aterials," Preprint C D-RO M , 7 7 h

Annual M eeting, Transportation Research Board, Washington, D .C.

Tam , W . S. and Brow n, S. F., 1998, "Back-analyzed Elastic Stiffness: Comparison

Between Different Evaluation Procedures," First International Symposium on

Nondestructive Testing o f Pavements and B ackcalculation o f M oduli, Baltimore,

MD.

Thom pson, M . R., 1989, "Illi-pave Based ND T A nalysis Procedures,"

Nondestructive

Testing of Pavements and Back calculation of M oduli,

ASTM STP 1026, A.J .

Bush III and G .Y. Baladi, Eds., Am erican So ciety for Testing and M aterials,

Philadelphia, PA.

V on Q uintus, H. L., Killingsworth, B. M., 1998, "Com parison o f Laboratory and Insitu

Determined Elastic Layer M oduli," P reprint C D-RO M ,

77 th

Annual Meeting,

Transportation R esearch B oard, Washington, D .C.



SESSION 3: ASPHALT AND ADMIXTURES



Tiag o P . Tr indad e, l Car los A. B. Carv alho, 2 Cl fiudio H. C. S i lva , 3 Da r io C . de Lim a,4 and

P aulo S . A . Barbo sa5

R e s i l ie n t M o d u l u s o f S o i ls a n d S o i l - C e m e n t M i x t u r e s

R e f e r e n c e :

Trindad e, T . P ., Carv alho, C. A. B. , S i lva , C. H. C. , Lim a, D. C., and

Barb osa , P . S . A. , " R e s i l ie n t M o d u l u s o f S o i l s a n d S o i l - C e m e n t M i x t u r e s , " ASTMSTP

1437, Resilient Modulus Testing or Pavement Components,

G. N . Durham , W . A . M ar r ,

and W . L . DeG rof f , Eds., A S TM In te rna ti ona l, W e s t Conshoh ocken , P A, 2003.

A b s t r a c t :

K n o w l e d g e o f th e r e s il ie n t m o d u l u s

(MR)

o f the sub -g rade so i ls and m a te r i a l s

t ha t com pos e t he l aye r s o f road pavem ent s i s mand a tory f o r an e f f i c i en t ana lys i s o f t he i r

s truc tu ra l beha v ior a s a wh ole . How ever , l abora to ry de t e rmina t i on o f

MR

requi res

em ploym ent o f r e l a ti ve ly soph i s t ica t ed l oad ing sys t em s and da t a acqu i si ti on , be s id es

dem anding cons ide rab l e t e s t ing t ime . Th ere f ore , it i s des ir ab l e t o l ook f o r s tandard t e s t

me thod s t ha t can be used t o e s t ima te t h is eng inee r ing pa ram ete r . Th i s pap er p resen t s

geo t ec tmica l eng inee r ing pa ram ete r s o f two so i ls and t he i r so i l - cemen t mix tures , and

prov ides empi r i ca l cor r e la t i ons be tw een CB R, unco nf ined com press ion s t reng th

de t e rmined a t 1 % o f ax i a l str ain , Y ou ng ' s t angen t mo dulus , and measu red va lues o f M R

o f t hese so i l s and m ix tures .

K ey w ord s : r e s i li en t mo dulus , r epea t ed- load ing t r iax i a l t e s t, CBR , unconf ined

com press ion te s t , so il s and so i l - cement mix tures

J M .S c . S tuden t, Dep ar tmen t o f C iv i l Eng inee r ing , Federa l U nive r s i t y o f Vigosa ,

36571-000 Vi9osa , M G , Braz il .

2 Assoc i a t e P rof essor , De par tm ent o f C iv i l Eng inee r ing , Federa l U nive r s i t y o f Vi~osa ,

36571-000 Vigosa , M G , Braz il .

3 Assoc i a t e P rof essor , Depar tm ent o f C iv il En g inee r ing , F edera l Unive r s i t y o f Vi~osa ,


4 P rof essor , Depar tme nt o f C iv i l Eng inee r ing , F edera l Un ive r s i t y o f Vigosa ,


s Ass i s t an t P rof essor , Depar tme nt o f C iv il Eng inee r ing , F edera l Un ive r s i t y o f Vigosa ,

36571-000 Viqosa , M G , Braz il .

99




1 0 0 R E S I L I E N TM O D U L U S T E S T I NG F OR P A V E M E N T C O M P O N E N T S

N o m e n c l a t u r e

A A S H T O

H R B

M C T

T R B

U S C

a, b

C B R

ET

KI , K2

L L

L V D T

P I

P L

MR

Su

Sul.O%

Wi '

Wopt

Sa

3,a

~'clm~ix

Ga

O'd

(J2

0

A m e r i c a n A s s o c i a t i o n o f S t a t e H i g h w a y a n d T r a n s p o r t a t i o n

O f f i ci a ls D N E R B r a z i li a n N a t i o n a l H i g h w a y O f f i c ia l s

H i g h w a y R e s e a rc h B o a r d

M i n i a tu r e , C o m p a c t e d a n d T r o p i c al

Tr anspor t a t i on Resea r ch Boa r d

Uni f ied Soi l Class i f i ca t ion

C o n s t a n ts f o r d e t e rm i n a t io n o f Y o u n g ' s t a n g e n t m o d u l u s

Ca l i f o r n i a Bea r i ng Ra t i o

I n it ia l o r Y o u n g ' s t a n g e nt m o d u l u s

Cons t an t s de t e r m i ned expe r i m en t a l l y f o r each m a t e r ia l

Liquid l imi t

L i nea r va r i ab l e d i f fe r en t ia l t r ans f o r m er

Plas t i c i ty index

Plas t i c l imi t

Res i l i en t m odu l us

Un conf i ned com pr es s i on s t reng t h a t fa i lu r e

U n c o n f i n e d c o m p r e s s io n s t re n g t h a t 1 % o f s tr a in

Wat e r con t en t

O p t i m u m w a t e r c o n t e n t

A x i a l s t r a in

D r y u n i t w e i g h t

M a x i m u m d r y un it w e ig h t

Axia l s t ress

D ev i a t o r s t r e s s

M a jo r p r i nc i pa l s t re s s

I n t e r m ed i a t e p r i nc i pa l s t r e s s

M i nor p r i nc i pa l s t r es s , o r con f i n i ng p r e s su r e

Bulk s t ress


Reg a r d i ng t he Br az i l i an h i ghw ay sys t em , i t is m anda t o r y to an a l yze t he r e s il i en t

beha v i o r o f t he sub - g r ade so i l s, e spec i a l l y w hen cons i de r i ng t he need f o r pe r f o r m i ng

pav em en t r e in f o r cem en t o f t he paved r oad ne t. D a t a f r om 1999 d i s c l osed t ha t t he

B r a z i li a n p a v e d r o a d s y s t e m a m o u n t e d f o r a p p r o x i m a t e l y 1 60 0 0 0 k m ( n e a rl y 8 % o f th e

t o t a l Br az i l ian r oad sys t em ) . Resea r ch r epo r t ed by Fe l i pe ( 1999), and b ased on s am pl i ng

i nvo l v i ng nea r l y 43 000 km o f th i s ne t, s t a te s t ha t a t l e a s t 77 .5 % we r e i n poo r o r

de f i c i en t cond i t ions , and r equ i r e pavem en t m a i n t enan ce and , m a i n l y , r e i n f o r cem en t . An

e l uc i da t ive i n f o r m a t i on on t he i m p or t ance o f t h is sy s t em t o the B r az i li an eco no m y is t ha t

t h is ne t i s r e spons i b l e f o r 65 % o f a l l tr anspor t ed l oad and 95 % o f a l l tr anspor t ed peop l e

i n t he coun t r y , co r r e spond i ng t o , app r ox i m a t e l y , 70 % o f t he Br az i l ian G r os s Do m es t i c

Product (Rei s , 2002) .



TRINDADE ET AL. ON SOILS AND SOIL-CEMENT MIXTURES 101

I t i s we l l kn ow n that the s tructura l degrad at ion of bi tum inous pav eme nts , and even

of the ce men ted base l aye r s , is s t r ongly as soc ia ted w i th the r e s i l ien t r e sponse o f the sub-

grade so i ls . Genera l ly , de te rmina t ion of the r e s il i en t modulus (MR) o f h ighway

enginee r ing mater ia ls is based on labora tory repeated- load ing t r iaxia l tes ting.

Co ncern ing the res i l ient response o f soils, i t i s know n that granular mater ia ls sho w

an increase in MR with an increase in the con f ining pressure; on the o ther hand, this

param eter is less inf luence d by the ap pl ied axia l devia tor st ress, for st ress levels belo w

those co r respon ding to fa i lure (Fossberg, 1969). Fo r coh es ive soils, th is autho r refers that

the con f ining pressure less inf luences the res i l ient mod ulus , and conv ersely, the axia l

dev ia tor st ress plays a remarka ble role in the res i l ient soi l response .

In Braz il , re sea rch works d i r ec ted to the de te rmina t ion o f MR for pavemen t des ign

begun in 1978, wi th the agreem ent be tween the Braz i l i an Inst itute fo r Highw ay Resea rch

( IPR) and the Po s t Gradua t ion P rogram in E nginee r ing a t the Federa l Unive r s i ty o f R io

de Jane iro (COPP E-RJ) , a s repor ted by M ot ta and Mac~do (1998). The f i rs t p roced ure

for l abora tory de te rmina t ion of MR was pu bl i shed by the B raz i li an Na t iona l Highw ay

Of f ice -DNER , in 1986 , under the des igna tion DN ER -ME 131/86 "S tandard Method fo r

De te rmin ing the Res i l i en t Modu lus o f So i l s ," and l a te r r ev i sed by th is Of f ice in 1994

under the des igna t ion DNE R-M E 131/94 .

His tor ica lly , determinat ion of MR for highw ay des ign purpose requires equipm ent

with re la t ively high d egree o f comp lexi ty that has be en res t r ic ted to a few technical

insti tutions. This fac t has led researchers to prop ose empir ical correlations betw een MR and

othe r soil parameters m ore easily determ ined in laboratory, as internationally reported by

Jones and W itczak (1977), Dru mm et al . (1990) , Cardo so and W itczak (1991), an d mo re

recen tly by L ee et al . (1997). D eve lop m ent o f correlations obtain ed from Brazilian soils

database are reported b y M edina an d Preusller (1980), M otta et al. (1985), F ranzo i (1990),

No gam i and Vill ibor (1995), Be m ucc i (1995), and Parreira et al . (1998).

Cons ide r ing the impo r tance of deve lop ing eng inee r ing cor r e la t ions on a r eg iona l

bas is , th is pap er focuses on two soils o f the C oun ty of Vi~osa , M inas Ge rais S ta te , Brazi l ,

and presen t s cor r e la tions deve loped be tween MR and some geo technica l eng inee r ing

paramete r s o f these so il s (CB R and un conf ined com press ion s tr eng th), and us ing

spec imens pr epared f rom p la in so i l s and so i l cement m ix tures .

Methodology

Th e two soi l samp les used in this s tudy represen t typical gneiss ic res idual soi ls f rom

the Co unty o f Vigosa , loca ted in the So utheas t o f Minas Gera i s S ta te , Braz i l. I n t e rms o f

ped olog y, the f i r s t one is a mature sandy -s i l ty-c layey soi l c lass i fied as yel low an d reddish

latosol , predo m inant ly found in smo oth s lopes , and cons t i tuted bas ical ly o f 1:1 c lay

minera ls , i r on and a luminum oxides . The second on e i s a y oung c layey- s i l ty - sandy so i l,

c lass i f ied as a saprol ite , gray colored, cons t i tuted main ly by qua r tz wi th presen ce o f mica .

Table 1 p r esen t s in format ion rega rd ing so i l type , s ample ho r izon and sampl ing dep th ;

Tables 2 and 3 sh ow so i ls geo tec lmica l eng inee r ing index pa ramete r s , and T able 4 dep ic t s

so i ls c la s s if i ca tion accord ing to HR B (Highw ay Resea rch B oard) and USC (Uni f ied So i l

Clas s if i ca t ion) sys tems , and acco rd ing to the M CT (Minia tur e , Com pac ted and Tropica l )

me thod ology (Nogami and Vi l l ibor , 1995).




TABLE 1--Soil samples description.

Soil Designation Pedological Formation Soil Horizon Sampling Depth (m)

01 Yellow Reddish Latosol B 6.00

02 Saprolite C 11.20

TABLE 2--Grain size distribution.

Clay Silt Sand

Soil Designation

(% < 0.005 mm) (0.074 < % < 0.005 ram) (2 < % < 0.074 mm)

01 54 24 22

02 7 18 75

TABLE 3--A tterb erg l imits .

Soil Designation LL (%) PL (%) PI (%)

01 68 35 33

02 30 19 11

TABLE ~ -S o il c lassif ication systems: HR B , U SC, and MC T ~ og am i and Vill ibor,

1995).

Soil Classification Systems

Soil Designation

HRB USC MCT

01 A-7-5 (20) MH LQ'

02 A-2-4 (0) SM-SC NA '

Compacted soil specimens prepared from soils and soil-cement mixtures were used

throughout this study. The cement used in the mixtures was the Brazilian Portland CPII-

E-32 type. Optimum cement contents referred to soil dry weight determined according to

the Brazilian standards released by DNER (Ferraz, 1994) were added to the soils, as

follows: 11% to soil 01, and 5 % to soil 02. Specimen preparation and testing procedures

were carried out as follows:

9 CBR tests: Compaction of specimens at the AASHTO Intermediate compaction

effort, and determination of CBR and Expansionc~R curves. Specimen acceptance

criteria were: water content of(Wi + 0.3 %), and compaction degree of(100 + 0.3 %);

9 Unconfined compression and repeated-loading triaxial tests:

9 Compaction of specimens 10 cm high and 5 cm in diameter at the

AASTHO Intermediate compaction effort, at water contents o f Wopt-2 %,

Wopt and Wopt + 2 %. Specimens acceptance criteria were: sample height

of 10 + 0.05 cm, sample diameter of 5 cm, water content of Wi + 0.3 %,

and degree of compaction of 100 + 0.3 %;

9 After molding, the specimens were involved in plastic bags, in order to

maintain their water content, and properly stored in wet chamber until

beginning of tests;



T R I ND A D E E T A L . O N S O I LS A N D S O I L- C E M E N T M I X T U R E S 1 0 3

9 U n c o n f i n e d c o m p r e s s io n te s ts o f so i ls a n d so i l -c e m e n t m i x t u r e s w e r e

pe r f o r m ed a t the s t r a in r a te o f 1 m m /m i n . So i l spec i m ens wer e t e s t ed r i gh t

a f t e r be i ng m ol ded , wh i l e so i l - cem e n t m i x t u r e s we r e t e s t ed a f t e r a 7 days

cu r i ng pe r iod . U nconf i ned com pr es s i on s t r eng ths ( Su ) a r e r e f e r r ed t o 1%

s t ra i ns and f a i lu r e s t re s se s , fo l l owi ng m e t ho do l o gy p r opose d by L ee e t a l .

( 1997) . Fo r eac h spec i m en wa t e r con t en t , t h r ee spec i m e ns wer e t e s t ed and

t he f i na l va l ue o f Su was adop t ed a s t he ave r age ;

9 Rep ea t ed - l oad i ng t ri ax i a l t e s ts we r e p e r f o r m ed acco r d i ng t o t he f o l low i ng

s e q ue n c e : ( 1 ) p la c e m e n t o f t h e s p e c i m e n i n v o l v e d b y a l a t e x m e m b r a n e i n

t he t r i ax ia l cham ber ; ( 2 ) i n s t a l la t i on o f d i sp l acem en t t ransduce r s

( L V D T's ) ; ( 3 ) f ina l s e tup ad jus t m en t s and r eco r d i ng o f in i ti a l r e ad ings

r e g a rd i n g s p e c i m e n p o s i t io n ; ( 4) p e r f o r m i n g o f te s ts a c c o r d i n g t o D N E R -

M E 13 U94 , a s p r e sen t ed i n T ab l e 5 .

T A B L E 5- -R epea ted - load ing t r iax ia l te s t s t eps acc ord ing to the Braz i l ian S tanda rd

D N E R - M E 1 3 1 / 9 4 .

T y p e o f s o il s S a m p l e c o n d i ti o n in g

t~ 3 ( kPa ) ~d ( kPa )

C l a y e y a n d

21 70

s i l ty so i l s

S t eps

St ra in regi s t ra t ion

~ 3

( kPa )

~ d

( kPa )

21 21

21 35

21 52.5

21 70

21 105

21 140

21 210

70 70

S a n d y a n d

70 210

gr ave l l y so i ls

105 315

21 21

21 42

21 63

35 35

35 70

35 105

52.5 52.5

52.5 105

52.5 157.5

70 70

70 140

70 210

105 105

105 210

105 315

140 140

140 280

140 420




T h e B r a z il ia n S t a n d a rd D N E R - M E 1 31 /9 4 i s b a s e d o n t h e A A S H T O " S t a n d a r d

M e t h o d o f T e s t fo r R e s i li e n t M o d u l u s o f S u b g ra d e S o i l s ( A A S H T O T 2 7 4 - 8 2 ) . "

H ow eve r , i t u se s t we n t y cyc l e s and l oad i ng t im e o f 0 ,1 s f o r e ach load i ng s equence . The

so i l spec i m en i s cond i t i oned by app l y i ng t wo hu ndr ed r epe t i t i ons o f t he spec i f i ed

dev ia tor s t ress a t a cer ta in conf in ing pressu re . Af te r cond i t ioning , the so i l spec im en i s

sub j ec t ed to d i f fe r en t dev i a t o r s tr e s s s equences a t t he s a m e co nf i n i ng p r e s su r e a s

i n f o r m ed i n T ab l e 5 . F i gu r e 1 dep i c t s t he Fede r a l Un i ve r s i t y o f V i gosa ( U FV ) ' s r epea ted -

l oad i ng tr i ax ia l t e s ti ng appa r a t us , wh i ch wa s f unde d by t he M i nas G e r a i s S t a te Re sea r ch

Fund i ng A gency , Br az i l, th r ough t he g r an t TE C 2431 /97 .

F I G . I - - U F V ' s

Repeated-loading triaxiat test apparatus.

Data Analysis

Tab l e s 6 an d 7 p r e sen t so i l s and so i l - cem en t m i x t u r e s t e s ti ng da t a r ega r d i ng t he

f o l l owi ng pa r am e t e r s : m ax i m um dr y un i t w e i gh t (Tdm ax),op t i m u m w a t e r con t en t ( Wopt),

CB R an d expa ns i on de t e r m i ned i n t he CB R t e s ts . I nd i v i dua l t e s t ing da t a ana l yse s a r e a s

fo l lows:



T R IN D A D E E T A L . O N S O I LS A N D S O I L -C E M E N T M I X T UR E S 1 0 5

Compaction and CB R T esting Da ta

T e s t i n g d a t a p r e s e n t e d i n t hi s w o r k s h o w t h a t a d d i t io n o f c e m e n t p r o m o t e s a s l ig h t

incr eas e in W opt, an d a sm all de cre ase in ?din*x,a s dep i c t ed i n Tab l e s 6 and 7 . It i s a lso

n o t i c e a b le s i g n i fi c a n t in c r e a se s i n C B R o f t h e te s t e d s o i l - c e m e n t m i x t u r e s c o m p a r e d t o

the so i ls up t o 730 % a nd 5 30 % r e spec t i ve ly fo r so i l s 01 and 02 .

Unconfined Compression Testing Data

M a n y c o n v e n t i o n a l d e v i c e s u s e d i n c o m m o n g e o t e c h n i c a l la b o r a t o r y t e s ti n g p r a c ti c e

a re ne i the r ab l e no r p r ec i s e eno ugh t o measu re ve ry l ow s t r a in s and t he r e spec t i ve l oads

i n o r d e r t o a s se s s t h e i n it ia l t a n g e n t m o d u l u s . T h e r e f o r e , t o o v e r c o m e o r m i n i m i z e t h is

d r a w b a c k t h e m e t h o d d e s c ri b e d b y D u n c a n a n d C h a n g ( 1 9 7 0 ) w a s u s e d i n t h is s t u d y ,

a s sum ing a hyp e rbo l i c r e la t i onsh ip be twee n ax i a l s t r a in s and s t r e sse s , a s fo l l ows :

ga a + b . c , (1 )

O" a

T h e i n i ti al t a n g e n t m o d u l u s c a n b e a p p r o x i m a t e d b y :

1

E 0 = - ( 2 )

a

F i g u r e 2 s h o w s t h e re s u lt s o f u n c o n f i n e d c o m p r e s s i o n t e st s, f r o m w h i c h i t c a n b e

obse rved t ha t so i ls s t ab i l i z ed wi th cem en t p r e sen t sub s t an t ia l i nc r ea se s i n t he i r s S~

m eas ure d a t fa i lure a nd a t 1 % o f ax ia l s t ra in (So~.0~/o), as wel l as in the i r s in i t i a l t ang ent

m o d u l u s c o m p a r e d t o t h e c o r r e s p o n d i n g v a l u e s d e t e r m i n e d f o r p l a i n s o i ls . T e x t u r a l s o i l

c o m p o s i t i o n h a s r e v e a l e d t o b e a n i m p o r t a n t p a r a m e t e r t o c h a r a c te r i z e t h e m e c h a n i c a l

r e sponse o f so i ls and so i l - ceme n t mix tu re s . F igu re 2 s how s t ha t so il 01 an d i ts so i l-

c e m e n t m i x t u r e s p r e s e n t m a x i m u m v a l u e s o f s tr e ss a t f ai lu r e, a t 1 % o f s tr a in a n d i n i ti a l

t a n g e n t m o d u l u s a t th e o p t i m u m w a t e r c o n t e n t , w h i le s o i l 0 2 a n d i t s s o il - c e m e n t m i x t u r e s

e x h i b i t m a x i m u m v a l u e s a t th e d r y s i d e o f t h e c o m p a c t i o n c u r v e .

Repeated-Loading Triaxial Testing Da ta

MR

o f s o i ls c a n v a r y w i d e l y m a i n l y a c c o r d i n g t o l o a d i n g c o n d i t io n s , s t r e ss s ta t e a n d

so i l t ype (Pa r r e i r a e t a l ., 1998) . M ode l s have b een p ro pos ed t o r ep re sen t va r i a t i on

of MR

a c c o r d i n g t o t h e v a r i a t i o n o f th e s ta t e o f s tr e ss . S u c h m o d e l s , i n t h e i r g r e a t m a j o r i ty , w e r e

de r ived t ak ing i n to acc oun t t he so i l type . Fo r i n s t ance , t he r e a r e spec i f i c m ode l s fo r

d e s c r i b i n g th e b e h a v i o r o f s a n d a n d c l a y s oi ls . I n th e s e m o d e l s t h e m o s t s i g n i f i ca n t

va r i ab l e s a r e , r e spec t i ve ly , t he con f in in g p re s su re and t he de v i a to r s t r e ss .



1 0 6

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(~m/N~l) +q~!+AX ~!Ufl ~ ( l

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1 0 8

R E S IL IE N T M O D U L U S T E S T IN G F O R P A V E M E N T C O M P O N E N T S

L e g e n d

g~ Soi l 01 0 So i l 02

, lk S o i l 0 1 S t a b i li z e d w i t h 1 1 % o f C e m e n t + S o il 0 2 S t a b il i z ed w i t h 5 % o f C e m e n t

4 0 0 0 4 0 0 0 6 0 0 0 0 0

\ -

2 0 0 ~ ~ ~ , 3 2 0 0 , ~ 4 5 0 0 0 0

240 0 ~ ,~ 240 0 ~ ,~

X ~ ' ~ ~ 3 0 0 0 0 0

= 1 6 0 0 ' = 1 6 0 0

r~ ~" r~

r ~ 8 0 0 1 5 0 0 0 0

o ~ - - - ~ ' - - ~ ' o

2 6 2 8 3 0 3 2 3 4 2 6

Wa t er Co nt ent

(%)

80 0 A -- '-'~--~

0 ' L ~ ,

2 6 2 8 3 0 3 2 3 4

Wa t er Co nt ent (%)

3 0 0 0

0 - . . .

2 4 0 0

1 2 0 0

60 0 O--- "- -O--- - '- tD

0 i i i i

8 10 12 14 16


3 0 0 0

2 4 0 0

1 8 0 0

1 2 0 0

6 0 0

0

8

L I

9 -- ~ - - - m ,

10 12 14 16


.---%

I t

4 0 0 0 0 0

~r " "" - ] '~ - - -- .. ,r ,

2 8 3 0 3 2 3 4

Wa t er Co nt ent

(%)

3 0 0 0 0 0 " ~

2 0 0 0 0 0 v

[...

1 0 0 0 0 0

o ~ - - - ~ '

8 10 12 14 16


F I G .

2 - -U nc on f ined comp ress ion t e s ting da ta o f so i l s and so i l - cemen t m ixture s."

Stress a t fa i lure , a t axia l s t ra in o f l %, and in i tia l tangen t modu lus

T h e f o l l o w i n g m o d e l s w e r e u s e d i n th i s s t u d y t o r e p r es e n t v a r i a t i o n o f M R o f s oi ls

a n d s o i l -c e m e n t m i x t u r e s :

9 M o d e l r e fe r r e d b y th e m e t h o d D N E R - M E t 3 1 / 9 4 , a n d h e r e re p r e s e n te d b y e q u a t i o n

3 , is d i r ec t ed t o c l ayey so i l and m ix tu re s , w h i l e e qua t i on 4 i s d i r ec t ed t o s an dy so i l

a n d m i x t u r e s .

MR = K l "o'd K' (3 )

MR = K I 9o'3 K-' (4 )

w h e r e :

M R -= res i l i en t m od ulu s (k Pa) ,

CYd =

dev i a to r s t r e s s (kPa ) ,

~r3 = co nf in ing s t ress (kPa ) , an d

K 1 and K 2 = cons t an t s de t e rm ined expe r im en ta l l y fo r each m a te r ia l .

F igu re s 3 and 4 show r ep ea t ed - load ing t r iax i a l t e s t i ng da t a o f so i l s and so i l - ce me n t

mix tu re s t e s t ed a t wa t e r con t en t s o f W op t - 2 %, W op t and W op t+ 2 % wi th t he cons t an t s



T R IN D A D E E T A L. O N S O I LS A N D S O I L -C E M E N T M I X T U R E S 1 0 9

K l a nd K 2 tha t f i ts expe r imen ta l da t a fo r equa t i ons 3 and 4 . I t i s obse rved r e l a t i ve ly h igh

coe f f i c i en t s o f de t e rmina t i on (R 2 ) i n a lmo s t a l l o f t he t e s t ed so i l s and mix tu re s ,

r e p r e s e n ti n g a l s o t h e g o o d q u a l i t y o f t e s ti n g d a ta . M o l d i n g w a t e r c o n t e n t o f s o i ls a n d

m i x t u r e s s p e c i m e n s a f f e ct s M R , e sp e c i a ll y a t th e w e t s i d e o f t h e c o m p a c t i o n c u r v e ,

n o t i c i n g a d e c re a s e i n t h is p a r a m e t e r w i t h c o r r e s p o n d i n g i n c r e a s e i n s p e c i m e n w a t e r

con t en t .

8000000

6000000

4000000

~" 2000000

~oooooo

800000

o

600000

400000

200000

100000

80000

60000

40

60 80 100 200

D e v i a t o r

S t r e s s ( k P a )

400

M R

= Kl~d K2 (DN ER 131/ 94)

L e g e n d ]

[ ] Soil 0t - Wopt -2% /

O Soil OI - Wopt |

A Soil 01 - Wopt +2% [

--~ Soil 01 Stabilized with I 1% of Cement - Wopt -2% ]

Soil 01 Stabilized with 11% of Cement - Wopt |

AL Soil 01 Stabilized with 11% of Cement - Wopt +2%)

E q u a t i o n s

[ ] M R = 47,557,110.80" d 1"0597 and R 2 = 0.9757

O M R = 278,2 69,19 0.4Gd I-5128 and R 2 = 0.9966

A MR=728, 330.9Gd ~ and R2=0. 8481

Z MR = 20,836,100.2(~d ~176 and R 2 = 0.99 52

~= M R = 38,364,620.50"d ~176 and R 2 = 0.9641

& MR = 35,757,531.8CYd ~ and R 2 = 0.9743

FIG .

3--Re silie nt modulus versus deviator stress of soils and mixtures.

9 M o d e l d e s c r i b e d b y C a r d o s o a n d W i t c z a k ( 1 9 9 1 ), a n d h e r e p re s e n t e d i n e q u a t i o n 5 .

MR = 7 6 1. 79 . (C B R ) '~ 9 0) L4383

( 5 )

( o - , ) 1 , 8 6 0

w h e r e

MR = r e s i l ien t m od u lus (kPa ) ,

C B R = C a l i f o r n ia b e a r in g r a t io ( % ) ,

0 = o l + c2 + o3 = bu lk s t r e s s (kPa ) , and

Ol = m a jo r p r i nc ipa l s t r es s (kPa ) .



1 1 0

R E S IL IE N T M O D U L U S T E S T I N G F O R P A VE M EN T C O M P O N E N T S

4 0 0 0 0 0 0

2 0 0 0 0 0 0 - -

1 0 0 0 0 0 0

~,~ 800000

. ~ 6 0 0 0 0 0

o 4 0 0 0 0 0

2 0 0 0 0 0

f I

M R = K1 G 3 ~ ( D N E R 1 3 1 /9 4 )

1 7 So i l 0 2 - Wo p t - 2 % |

0 So i l 02 - Wop t |

t~x So i l 02 - Wo pt +2% |

So i l 0 2 S t a b i l i z e d w i t h 5 % o f Ce m e n t - Wo p t - 2 % |

So i l 0 2 S t a b i l i z e d w i t h 5 % o f Ce m e n t - Wo p t |

S o i l 0 2 S t a b i l i z ed w i th 5 % o f C e m e n t - W o p t + 2 % )

1 0 0 0 0 0

8 0 0 0 0

6 0 0 0 0

4 0 0 0 0

4 0

I

6 0 8 0 1 0 0

C o n f i n i n g S t r e s s ( k P a )

2 0 0

E q u a t i o n s

E | M R = 1 7 , 8 0 0 . 1 0 - 3~ a n d R 2 = 0 . 8 8 8 8

O M R = 1 0 , 99 4 . 9G 3 0 " 5 0 7 8 a n d R 2 - 0 . 8 9 2 5

' M R = 3 , 9 9 6 . 3 0 - 3 0 . 7 0 8 6 a n d R 2 = 0 . 9 7 3 9

M R = 4 8 8 , 6 6 5 . 2 0 " 3 ~ a n d R 2 = 0 . 8 6 3 4

M R = 4 0 8 , 9 2 0 . 7 0 " 3 o 3 8 2 3 a n d R 2 = 0 . 9 6 2 3

A M R = 1 0 0, 55 1 .4 0 "3 0 -6 5 72 a n d R 2 = 0 . 9 1 3 6

FIG . 4--Resilient modulus versus confining stress of soils and mixtures.

9 M ode l p ro pose d by L ee e t a l. (1997) , and he re r ep re sen t ed by equa t i on 6 .

MR = 645.40(SuLovo ) - 0.86(S,Loo~)z

(6)

w h e r e

MR = r e s i li en t mo du lus (kPa ) , f o r a g iven dev i a to r s t r e s s , and

Sul.0% - - s t r e ss (kPa ) caus ing 1 % o f s t r a in du r ing t he con ven t iona l unco nf ined

compres s ion t e s t .

9 M ode l p ropo sed b y Pa r r e i r a e t a t. (1998) , and he re r ep re sen t ed by equa t i ons 7 and 8 .

w h e r e

4,52 3.12 . (E r )o.3~58. (0)~.,393

M R -- (O'00"3436

MR = 84 8.1 5" (E T)~ + 1,1 47 .24 " (0 ) o.8630

(7)

( 8 )

MR ~- res i l i en t m od ulu s (kPa) ,

E T = Y o u n g ' s t a n g e n t m o d u l u s ( k P a ),

0 = bu lk s t r e ss (kPa ) , and

Crd = de via tor s tress (kPa ).



T R IN D A D E E T A L . O N S O I L S A N D S O IL -C E M E N T M I X T U R E S 111

I n t h e p r e s e n t w o r k , a s t a ti s ti c a l a n a l y s i s w a s c a r r i e d o u t to s t u d y th e p e r f o r m a n c e o f

t h e a b o v e - m e n t i o n e d m o d e l s w h e n a p p l i e d to s o i l s a n d m i x t u r e s e x p e r i m e n t a l d at a .

C o r r e l a t io n s b e t w e e n M R a n d C B R , s t re s s d e t e r m i n e d a t 1 % a x i a l s tr a in , in i t ia l t a n g e n t

m o d u l u s , d e v i a t o r s tr e s s , fi r st s t re s s i n v a r i a n t a n d c o m b i n a t i o n s o f t h e se v a r i a b l e s w e r e

c o n s i d e r e d i n t h e s t u d y , a s p r e s e n t e d i n T a b l e 8 . A n a l y s i s o f t h e d a t a p r e s e n t e d i n t h is

t a b l e s h o w s t h a t t h e v a r i a b l e s c o n s i d e r e d i n t h e a n a l y s i s c o r r e l a t e w e l l w i t h t h e r e s i l i e n t

m o d u l u s , M R , o f s o il s a n d m i x t u re s . T h e c o e f f i c i e n t o f d e t e r m i n a t i o n r a n g e d f r o m

0 . 85 04 t o 0 . 95 67 .

T A B L E 8--Ap plication o f models fo r estimating the MR o f soils and m ixtures.

Sam pl es R ep r e sen t a t ive m o de l

C oe f f i c ien t o f

D e t e r m i n a t i o n

(R 2)

and S t anda r d E r r o r

So i l 01

natura l and

s t ab i l i zed

w i t h 1 1 % o f

cem en t

53,038.92- (Su~.OO/o)"1837 R2 = 0.9235

M R = F (0, SuLo~)

M R

(0)0.9902 E rr o r = 0.146 4

1,031,965.89. (ET)1"~176

R2 = 0 .9567

MR = F (0, Ev)

MR (0)0.9779

Erro r = 0.1137

412,233.75. (CBR~5~ R2 = 0.9 09 9

MR = F (0 , CBR) M R

=

0 ~ , 2 3 9 6 Error = 0 .1760

M , = F (0 , t~d, Su,.oo/.) MR 48"78(0)~ R2 = 0.8504

(~d)0 '2 '

oi l 02 Er ror = 0 .1858

natura l and 103 .28.(0 ) 0"9110 .( E v) 1-07'4 R 2 = 0.9338

sta bi liz ed MR = F (0, (2rd,ET)

MR =

w i t h 5 % o f ( ad )~176 Er ro r = 0.0839

cem en t R 2

M R :

F (0,

Od,

C B R )

MR = 12"47(0)0"9T09 "(CBR ~'7476 =

0.9249

(O'd)0"4055 E rr or =

0.1013

N o t e : M R = R e s i l i e n t m o d u l u s ( k P a ) , S ul.0 % -- s t r e s s a t 1 % o f s t r a i n d u r i n g t h e

c o n v e n t i o n a l u n c o n f i n e d c o m p r e s s i o n t e s t ( k P a ) , E T -- Y o u n g ' s t a n g e n t m o d u l u s

( k P a ) , C B R : C a l i f o r n i a b e a r i n g r a ti o ( % ) , 0 - - b u l k s t r e s s ( k P a ) , a n d 6 d =

d e v i a t o r s t r e s s ( k P a ) .


I t c o u l d b e p r e m a t u r e t o m a k e f i n al c o n c l u s io n s b a s e d o n d a t a p r e s e n t e d i n th i s

s t u d y , m a i n l y c o n s i d e r i n g t h a t it w a s c a r r i e d o u t o v e r o n l y t w o s o i l t y p e s. H o w e v e r , o n a

p r e l i m i n a r y b a s i s , a n a l y s i s o f t h e l a b o r a t o r y te s t in g p r o g r a m d a t a s u g g e s t s t h a t:

H i g h e r v a l u e s o f C B R , u n c o n f i n e d c o m p r e s s i o n s t r e n g th , i n i ti a l t a n g e n t m o d u l u s

a n d r e s i l ie n t m o d u l u s a r e re l a t e d t o s o i l a n d m i x t u r e s s p e c i m e n s c o m p a c t e d a t t h e

o p t i m u m o r a t t h e d r y s id e o f t h e c o m p a c t i o n c u r v e ;




Figures 3 and 4 show tha t re s i li en t modulus d ec reases wi th the inc r ease in wa te r

con tent for the soi ls tes ted;

App ly ing DNE R-M E 131/94 m ode ls , i t can be seen tha t MR decreases wi th the

increase of devia tor s t ress and increases with the increase o f con f ining s tress . Also ,

MR always decreases with the increase in wa ter content ; and

Ac ceptable s ta tist ica l cor re la t ions w ere develo ped betwe en MR and the fol low ing

variables: s tress at 1 % o f axia l s train, initial tang ent m odu lus, CB R, bulk stress,

and dev iato r stress.

Acknowledgment

The au thor s wish to ex pres s the i r g r a t itude to FAP EM IG, th rough the g r an t TEC

2431/97 , U FV and CN Pq tha t con t r ibu ted wi th scho lar sh ips , ma te r ial s , l abora tory t e s ting

device s and the required f inancia l suppor t to deve lop this s tudy.

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I s r ae l I a sb ik ] Dar io C . de L ima ,2 Car los A . B . C arv a lh o) C l~iud io H . C . S i l va ,4 En iva ldo

M ine t t e, 5 and P au lo S . A . B arbosa 6

G e o t e c h n ic a l C h a r a c t e r i z a t io n o f a C l a y e y S o il S t a b i li z e d w i t h P o l y p r o p y l e n e F i b e r

U s i n g U n c o n f i n e d C o m p r e s s i o n a n d R e s i li e n t M o d u l u s T e s t i n g D a t a

R e f e r e n c e :

Iasbik, I ., Lim a, D. C. , Carv alho, C. A. B. , S i lva , C. H. C. , Minet te , E. , and

Barbosa , P .S .A. ,

" G e o t e c h n i c a l C h a r a c t e r i z a t i o n o f a C l a y e y S o i l S t a b i l i z e d w i t h

P o l y p r o p y l e n e F i b e r U s i n g U n c o n f i n e d C o m p r e s s i o n a n d R e s i li e n t M o d u l u s T e s t i n g

D a t a , " Res i l i en t Mod u lus Tes ting fo r P avem en t Componen t s, A ST M STP 1437 , G . N .

Durham, W . A . M ar r , and W . DeGrof f , Eds . , AS TM In t e rna t i ona l , W es t Conshohocken ,

PA, 2003.

A b s t r a c t :

Thi s pap er f ocuses o n t he g eo t echn i ca l cha rac t e r iza t i on o f a c l ayey so i l and i t s

m ix ture wi th po lyp ropy lene f i be r. The l abora to ry t e s t ing p rog ram w as d i r ec t ed t o : ( i)

ana lys i s o f t he i n f luence o f fi be r con t en t and f i be r l eng th on t he uncon f ined com press ion

s t r eng th o f a c l ayey so il i n o rde r t o de t e rmine o p t im um param ete r s to be used i n

repea ted- load ing t r iaxia l t es t s , and ( i i ) analys i s o f the inf luenc e o f f iber on the res i l ient

mo dulus o f t he c l ayey so i l, accord ing t o the Braz i l ian S t andard D NE R -M E 131/ 94 . T he

l abora to ry te s t ing d a t a suppor t t hat: ( i) t he m echan i ca l r e spo nse o f the co m pos i t e i s f i be r

con t en t and f i be r leng th dependen t ; ( ii ) add i t i on o f f ibe r t o t he so i l imp roves sub s t an t ia l l y

i ts uncon f ined c om press ion s t reng th ; and ( ii i) add i t i on o f f i be r to t he so i l is a l so

respons ib l e f o r subs t an t ia l dec rease i n i t s M R va lues , and p roduces a com pos i t e t ha t can

be u se f u l i n road eng inee r ing p rac t ice .

1 M . S c ., D epar tm ent o f C iv il Eng inee r ing , Federa l U nive r s i t y o f Vigosa , 36571-000

Vi~osa , M G , Braz i l .

2 P rof essor , Depar tm ent o f C iv i l Eng inee r ing , Federa l Un ive r s i t y o f Vigosa , 36571-000

Vigosa , M G , Braz i l.

3 Assoc i a t e P rof essor , Depar tm ent o f C iv i l Eng inee r ing , Federa l Un ive r s i t y o f Vigosa ,

36571-000 Vi~osa , M G , Braz il .

4 Assoc i a t e P rof essor , Depar tm ent o f C iv i l Eng inee r ing , Federa l Un ive r s i ty o f Vi~osa ,

36571-000 Vigosa , M G , Brazi l.

5 Assoc i a t e P rof essor , Depar tm ent o f C iv i l Eng inee r ing , Federa l Un ive r s i ty o f Vigosa ,

36571-000 Vi~osa , M G , Braz il .

6 Ass i s t an t P rof essor , Dep ar tmen t o f C iv i l Eng inee r ing , Federa l U nive r s i t y o f Vigosa ,

36571-000 Vigosa , M G , Brazi l.

114




I A S B IK E T A L , O N A C L A Y E Y S O I L 1 1 5

K ey w or d s" r e s i li en t m odu l us , r epea t ed - l oad i ng t ri ax ia l t es t, so i l - po l yp r opy l ene f i be r

m i x t u r e s , so i l r e i n f o r cem en t

N o m e n c l a m r e

A A S H T O

D N E R

H R B

M C T

U S C

L V D T

C B R

P I

L L

P L

MR

Su

W i

Wopt

Er

"~drn~x

~3d

(51

(Y3

A m e r i c a n A s s o c i at io n o f S t a te H i g h w a y a n d T r a n s p o rt a ti o n

Of f i c i a l s

Br az i l i an Na t i ona l H i ghw ay Of f i c ia l s

H i g h w a y R e s e a rc h B o a r d

Mi n i a t u r e , Com pac t ed and Tr op i ca l

Un i f i ed So i l C l a s s if i c a ti on

L i nea r va r i ab l e d i f f e ren t i a l t r ans f o r m er

Ca l i f o r n i a Bea r i ng R a t i o

Plas t i c i ty index

L i qu i d l im i t

Plas t i c l imi t

Res i l i en t m odu l us

Fa i l u r e s t re s s ob t a i ned in t he uncon f i ned com pr es s i on t e s t

W a t e r c o n t e n t

O p t i m u m w a t e r c o n t e n t

Elas t i c ax ia l s t ra in

Sol id uni t weight

M a x i m u m d r y u n it w e i g h t

De v i a t o r s t r e ss

M a jo r p r i nc i pa l s t r e ss

In te rmedia te pr inc ipa l s t ress

Minor pr inc ipa l s t ress , or conf in ing pressure

Introduct ion

I n t he pa s t t wo decades , da t a f r om l abo r a t o r y r e sea r ch d i rec t ed t o t he geo t echn i ca l

cha r ac t e r iza t i on o f so i l- f i be r m i x t u r e s hav e em p has i zed t he i r g r ea t po t en ti a l t o i m p r ove

so il shea r s t reng t h , com pr es s i b i l i ty and pe r m eab i l i t y f r om a c i v i l eng i nee r i ng pe r spec t i ve .

Typ i ca l app l i ca t ions encom pass sha l l ow f ounda t i ons , s te ep s l ope em bank m en t s , and

pav em en t l aye rs , am ong o t he r s .

Th i s p ape r i s d i rec t ed t o t he geo t echn i ca l eva l ua t i on o f so i l -f i be r m i x t u r e s

cons ider ing h ighway-engineer ing appl ica t ions . A mature gne i ss ic res idua l so i l ,

pedo l og i ca l l y c la s s i f ied a s a ye l l ow and r edd i sh l a t o so l f r om t he No r t h Fo r e s t o f Mi nas

Ger a i s S t a t e , Br az i l , was used t h r oughou t t he s tudy . So i l and so i l m i x t u r e s w e r e t e s ted

unde r r epea t ed - l oad i ng t r i ax ia l t e s ts f o l l owi ng t he Br az i l ian S t anda r d M e t hod f o r

D e t e r m i n i ng t he Res i l ien t Modu l us o f So i l s ( DNE R- M E 131/94 ).




L i t e r a t u r e R e v i e w

Introduction

R e i n f o r c e m e n t o f s o i ls b y a d d i t i o n o f f i b er s c r e a te s a n a t tr a c ti v e c o m p o s i t e t o b e u s e d

in geo t echn i ca l and road eng inee r ing . As i n o the r s so i l r e i n fo rcemen t t e chn iques ,

c o m p o s i t e d e s i g n r e q u i r es d e t e r m i n i n g i n l a b o r a t o ry t h e o p t i m u m f i b e r c o n t e n t f o r e a c h

spec i f i c app l i ca ti on . I t dem and s so i l t ype and f i be r t ype and geom e t ry cons ide ra t i ons .

Pa ram e te r s t ha t a f f ec t f i be r so il de s ign a r e a s fo l l ows : so i l type , f i be r t ype and geom e t ry ,

com pac t i on e f fo r t , wa t e r con t en t , and f i be r a spec t r at io .

Reg a rd ing so i l and l oad ing t ypes , t he ma jo r i t y o f pape r s on t h i s t op i c a r e d i r ec t ed t o

the ana lys i s o f eng ine e r ing be hav io r o f s ands t e s t ed unde r s ta t i c loads . Few o f t he se

pape r s dea l s w i th r e in fo rced c l ayey so il s , and ma in ly w i th the se so i l s t e s ted un de r

r epea t ed - load ing . Rese a rches on c l ayey so il s te s t ed unde r s t a t ic l oads a r e repo r t ed by

An de r s l an d and K ha t t ak (1979) , M ahe r and Ho (1994) , Te ixe i r a e t al . ( 1994) , S i l va e t a l.

( 1995 ) , L im a e t a l. ( 1996) an d L im a e t a l. ( 1999) , and unde r r epea t ed - load ing b y Ho

(1992) , and Bu zze l l i ( 1995 ) .

Highway Engineering Resilient Modulus

Af te r S eed e t a l . ( 1962) , mo s t l y o f t he r e sea rches d i r ec t ed t o t he ana lys i s o f t he

behav io r o f h ighw ay eng inee r ing ma te r ia l s ha s been based on l abo ra to ry r epea ted - load ing

tes t ing da ta in order to de term ine the i r res i l ien t m od ulus (Mr0. In Braz i l , these s tudies w ere

f i rs t pe r fo rmed i n 1978 , a s r epo r t ed by M ot t a and M ac~do (1998). MR i s de f i ned a s the r a t io

be tw een the app l ied rep ea ted axia l dev ia tor s t ress (o0 = cyl - 63) an d the e las t ic ax ia l s train .

The re fo re , t h i s pa r am e te r i s unde r s tood a s:

M R = cr--La (0 1 )

s

w h e r e

MR = Res i l i en t m odu lus (kPa o r K gf f cm2) ,

Od = A xia l repe a ted dev ia tor s t ress (Od = Ot - Or3, kPa) ,

C l = M a jo r p r i nc ipa l s t r e s s ,

o3 = Min or p r i nc ipa l s t r e ss , and

8r = Elas t ic ax ia l s t ra in .

H i s to r i ca l l y , i t is kno w n tha t t he ax i a l dev i a to r s t r e ss p l ays a s i gn i f i can t r o l e i n the

so i l re s i li en t r e s ponse (MR) o f f i ne -g ra ined so i ls . O n t he o the r hand , i n t he se so i l s t h is

pa ram e te r i s l e ss i n f l uenced by t he app l ied con f in ing s t r e s s (Fossbe rg , 1969) .



I ASB I K ET AL . O N A C L AY EY SO I L 1 1 7

M e t h o d o l o g y

Materia ls

The t e s t ed so i l s amp le i s a gne i s s i c r e s idua l so i l f r om the Co un ty o f V igosa , l oca t ed i n

the N or th R eg io n o f M inas G era i s S t a t e , Braz i l. I t is a s andy- s i l t y c l ay w i th c l ay f r ac t ion

cons t i t u t ed by 1 :1 c l ay mine ra l s, i r on and a lum inum ox ides .

R and om ly d i s tr i bu t ed po ly p rop y l ene s t ap le f ibe r s w i th l eng ths o f 10 , 15, 20 and 30

r a m , 1 .2 m m w i d e , 0 . 0 1 6 m m t h i c k ( l in e a r m a s s o f 0 . 1 1 6 8 g / m ) , a n d f i b e r c o n t e n t s o f

0 .25 , 0 .5 0 and 0 ,75 % r e f e r en ced t o soi l d ry un i t we igh t we re u sed t h ro ugh ou t t he s t udy .

Testing P roced ures

T h e l a b o r a t o r y - te s t in g p r o g r a m i n c l u d e d s p e c i m e n c o m p a c t i o n , a n d u n c o n f i n e d

compres s ion and r epea t ed - load ing t r i ax i a l t e s t s , a s f o l l ows :

9 S p e c i m e n c o m p a c t i o n a c c e p ta n c e c r it e ri a : H e i g h t . o f 1 00 + 0 . 5 m m , d i a m e t e r o f

5 0 m m , w a t e r c o n t e n t o f ( W i + 0 .3 % ) , a n d d e g r e e o f c o m p a c t i o n o f ( 1 0 0 + 0 . 3

%);

9 U n c o n f i n e d c o m p r e s s i o n t es ts :

o S p e c i m e n c o m p a c t i o n :

9 A A S H T O I n te r m e d ia t e c o m p a c t i o n e f fo r t;

9 F ib er lengths : 10 , 15 , 20 and 30 ram;

9 F ibe r con t en t s : 0 , 0 . 25 , 0 .5 0 and 0 .75 %;

9 W ate r con t en t : Wop t (op t im um w a te r con t en t ), (Wopt - 2 %) , and

(Wopt + 2 %); and

9 Af t e r mo ld ing , t he spec im ens were i nvo lved i n p l a s t ic bags in

o rde r t o ma in t a in t he i r wa t e r con t en t , and t hen p rop e r ly s t o r ed in

the we t chamber un t i l beg inn ing o f t e s t s .

o Tes t s pe r fo rm ed a t t he s t ra in r a t e o f lm m /m in (Head , 1982) ;

o U n con f ined com pres s io n s tr eng ths a t f a i lu r e (Su ) a r e r e f e r r ed t o t he

a v e r a g e o f th r e e t e st e d s p e c i m e n s ; a n d

o O p t i m u m f i b e r c o n t e n t a n d o p t i m u m f i b e r l e n g th : d e f i n e d as t h e

p a r a m e t e r s a s s o c i a t e d t o t h e c o m p o s i t e h i g h e r u n c o n f i n e d c o m p r e s s i o n

s t rength .

9

Repea t ed - load ing t r i ax i a l t e s t s :

o S p e c i m e n c o m p a c t i o n :

9 A A S H T O I n te r m e d ia t e c o m p a c t i o n e f fo r t;

9 W a t e r c o n t e n t: Wopt o p t i m u m w a t e r c o n t e n t) ;

9 F ibe r l eng th : 20 m m , i. e. , op t im um f ibe r l eng th de f ined f rom

u n c o n f i n e d c o m p r e s s i o n t e st in g d a t a ;



1 18 RESILIENTMODULUS TESTING FOR PAVEMENT COMPONENTS

9 F ibe r con t en t : 0 . 25 %, i .e ., op t im um f ibe r con t en t ob t a ined f rom

t h e u n c o n f i n e d c o m p r e s s i o n t e s ti n g d a ta ; a n d

9 A f t e r m o l d i n g , t h e s p e c i m e n s w e r e i n v o l v e d in p l a s ti c b a g s in

o rde r t o ma in t a in t he i r wa t e r con t en t , an d t hen p rop e r ly s t o r ed i n

cha mb er un t il beg in n ing o f te s ts .

P l ace m en t o f two l inea r va r i ab l e d if f e ren t i a l t ransduce r s (L V DT s) i n t he

m idd l e h a l f leng th o f the spec im en i n s ide t he tr i ax i a l cham ber ;

T e s t i n g p r o c e d u r e s c o n d u c t e d a t c o n f i n i n g p re s s u r e s a n d d e v i a t o r s t re s se s

s h o w n i n T a b l e 1 , f o l l o w i n g t h e B r a z i li a n S t a n d a r d D N E R - M E 1 3 1 / 9 4 ;

a n d

MR va lues a r e r e f e r r ed t o one t e s t ed spec im en .

F igu re 1 dep i c t s t he r epea t ed - load ing t r iax i a l t e s t ing appa ra tu s u sed t h rough ou t t h is

s tudy.

F igu re 1 - Repeated-loading triaxial test apparatus

T h e B r a z il ia n S t a nd a r d D N E R - M E 1 3 1 /9 4 is b a s e d o n t h e A A S H T O " S t a n d a rd

M e t h o d o f T e s t f o r R e s il ie n t M o d u l u s o f S u b g ra d e S o i ls ( A A S H T O T 2 7 4 - 8 2 ). "

H o w e v e r , i t u s e s t w e n t y c y c l e s a n d l o a d i n g t i m e o f 0,1 s f o r e a c h l o a d i n g s e q u e n c e . T h e

s o il s p e c i m e n i s c o n d i t io n e d b y a p p l y i n g tw o h u n d r e d r e p e ti ti o n s o f t h e s p e c i f ie d

dev i a to r s t re s s a t a c e r t a in con f in ing p re s su re . A f t e r cond i t i on ing , t he so i l spec im en i s



I A S B IK E T A L . O N A C L A Y E Y S O I L 119

sub j ec t ed t o d i f f e ren t dev i a t o r s t r es s s equences a t the s am e conf i n i ng p r e s su r e a s

informed in Table 1 .

Tab l e 1 -

Repeated-loading triaxial tes t procedures app lied to clayey and silty soils

according to DN E R-ME 131/94

So i l t ype

C l a y e y a n d

si l ty soi ls

Tes t i ng s equence

S a m p l e c o n d i ti o n in g S t ra in m e a s u r e m e n t

~3 (kPa) ~d (kPa)

21 70

~ 3 ( k P a ) o d ( k P ~

21 21

21 35

21 52.5

21 70

21 105

21 140

21 210

Data A nalysis

T h e o p t i m u m c o m b i n a t i o n o f f ib e r l en g th , f i b e r c o n t e n t a n d c o m p a c t i o n p a r a m e t e r s

wh i ch l ed t o the h i ghes t unconf i ned com pr es s i on s t reng t h o f the com pos i t e was

de t e r m i ned , an d r epea t ed - l oad i ng t r i ax ia l t e s ts w e r e pe r f o r m ed a t t h is i dea l com bi na t i on .

Soil and Composite Laboratory Testing Data: Compaction and Unconfined Compression

Tests

Ta ble 2 and Fig ure 2 presen t geotechnica l so i l l abora to ry t es t ing da ta . Th e so i l is

c l a s s if i ed a s A- 7 - 5 ( 20 ), M H, and L G ' f o l l owi ng , r e spec ti ve l ly , t he Hi gh w ay Resea r ch

Bo a r d ( H RB ) Cl a s s i fi c a t ion S ys t em , the Un i f ied So i l C l a s s if i c a ti on ( US C) S ys t em , and

t h e M i n i a tu r e , C o m p a c t e d a n d T r o p i c a l ( M C T ) M e t h o d o l o g y d e v e l o p e d b y N o g a m i a n d

Vil l ibor (1995).

Reg a r d i ng t he r ang e o f f i be r con t en t u sed in t h is r e sea r ch , com pac t i on t e s t i ng d a t a

supp or t tha t addi t ion o f fiber to so i l l ead to ins igni f i cant chan ges in i ts Wopt in accord ance

wi t h p r ev i ous s t udy deve l o ped by Buen o e t a l (1997). W or k i ng w i t h t he s am e c l ayey so il

and s am e r ange o f po l yp r op y l ene f i be r con ten t , t he se au t ho r s r epo r t va r i a t ions i n W opt o f

so il and co m p os i t e sm a l l e r than 1% . The r e f o r e , f o r p r ac t ica l pu r pose s am e Wopt was

adop t ed i n t h i s r e sea r ch f o r so i l and com pos i t e .



120

R E S I L IE N T M O D U L U S T E S T I N G F O R P A V E M E N T C O M P O N E N T S

Table 2 - So il characterization testing da ta

Soil Parameter Value

LL (%) 65

PL (%) 33

Pi (%) 32

Ys (kN/m3) 27.25

Wopt (%, AASHTO Standard compaction 31.40

effort)

~'dmax kN/m 3, AASHTO Standard compaction 14.06

effort)

Su (kPa, AASHTO Standard compaction effort) 293

CBR (%, AASHTO Standard compaction 10

effort)

ExpansioncBR (%, AASHTO Standard 0.1

compaction effort)

e~

100

90

80

70

60

50

40

3O

2O

10

0

0.000 0.00l 0.010 0.100 1.000 10.000

Grain Size (ram)

Figure 2 -

Grain s i ze d is t r ibut ion o f the c layey soi l

Figure 3 presents soil and composite variations of Su versus fiber content for all

tested fiber lengths. Data support that both parameters are major factors in the mechanical

response of the composite, and that maximum Su is associated to fiber content of 0.25 %

and fiber length of 20 mm.



500

400

%- 300

200

500

100

i

0.2

[ 3 - - -

I , I . . _ l I i I i I J m

0.3 0.4 0.5 0.6 0.7 0.8

F i b e r C o n t e n t ( % )

Legend 1

- F i be r l O m m l o n g

F ib er 1 5 m m l o n g |

8 _ _ F ib er 2 0 m m l o n g

F ib er 3 0 m m l o n g )

Figu re 3 - Unc on f ined compress ion s t reng th (Su ) ve rsus f i b e r con ten t a t d i f fe ren t f i b e r

lengths

Figu re 4 d i sp l ays va r i a t i ons o f Su wi th wa t e r con t en t o f so i l and com pos i t e .

M a x i m u m v a l u e s o f S u c a n b e a s s o c ia t e d t o th e d r y si d e (W o p t - 2 % ) a n d t o th e o p t i m u m

wa te r con t en t (Wopt ) o f t he com pac t i on cu rves o f so il and com pos i t e , r e spec t i ve ly .

400

%-

300

200

100

0

29 34

, J r . . I , I i I ,

30 31 32 33

W a t e r C o n t e nt ( % )

I A S B I K E T A L . O N A C L A Y E Y S O I L 121

Legend

[ ] Clayey so il

C) Soil-fiber mix

Figu re 3 -

Unc on f ined com press ion s t reng th (Su ) ve rsus w a te r con ten t o f so il and

c o m p o s i te a t f i b e r c o n t en t o f 0 . 2 5 % a n d f i b e r l en g th o f 2 0 m m



1 2 2 RESILIENTMODULUS TESTING FOR PAVEMENT COMPONENTS

Repea ted -Load ing Tes ting Da ta

F i g u r e 4 i n t r o d u c e s t r e n d o f M R v e r s u s d e v i a t o r st r e ss .

5 0 0 0 0 0

4130000

3O00O0

2OOOO0

1 0 0 0 0 0

0 ~ I - , ,_ ~ i I i ,

40 80 120 160 240

Deviator Stress (kPa)

2o0

f

L e g e n d

! [ ] C l a y e y s o i l

[ f 3 S o i l - f i b e r m i x

[ ]

0

Equations ]

M R = 1 5 5 , 0 0 0 + 6 , 4 2 1 ( 1 0 0 - o ' d) ; Oa < 100 I

M n= 15 5 ,00 0- 682(o ', j - 100) ; ~d > 1(30

|

M R = 9 2 ,00 0 + 1 ,13 1(12 5 - 6d) ; cr~ < 125 [

M R = 9 2 ' 0 0 0 - 1 8 (O d - 1 2 5 ) ; Od > 1 2 5

F i g u r e 4 -

M e versus dev ia tor s t re ss o f so il and m ix ture s o f so i l and f i b e r a t f i b e r con ten t

o f 0 .2 5 % a n d f i b e r l en g th o f 2 0 m m

F i g u r e 4 i l l u s t r a te s th a t M R v a l u e s o f s o i l a n d c o m p o s i t e f o l l o w a b i l i n e a r t r e n d t h a t

d e c r e a s e s w i t h i n c r e a s e s i n th e d e v i a t o r s tr e s s , a s e x p e c t e d a n d r e p o r t e d b y D u n c a n e t al .

( 1 9 6 8 ) f o r c l a y e y s o i l s . D a t a p r e s e n t e d i n t h is f i g u r e s u p p o r t t h a t:

9 M R v a l u e s o f t h e s o il r a n g e s f r o m 4 6 0 0 0 0 t o 8 0 0 0 0 k P a , r e a c h i n g a d e c r e a s e o f

6 7 % b e t w e e n i ts m a x i m u m a n d m i n i m u m v a l u e s in t h e fi r st p a r t o f t h e b i l in e a r

m o d e l ;

9 M R o f t h e c o m p o s i t e r a n g e s f r o m 1 60 0 0 0 t o 9 0 0 0 0 k P a ;

9 T h e b i l i n e a r m o d e l s o f s o i l a n d c o m p o s i t e a re c h a r a c t e r i z e d b y d e v i a t o r s t re s s e s

o f 1 0 0 a n d 1 3 0 k P a , r e s p e c t i v e l y ; a n d

9 I n f l u e n c e o f t h e d e v i a t o r s t r e s s o n t h e M R o f th e c o m p o s i t e i s l e s s s i g n i f i c a n t t h a n

o n t h e M R o f t h e s o i l , s u g g e s t i n g t h a t a d d i t i o n o f f i b e r i s r e s p o n s i b l e f o r s h i f t i n g

t h e b e h a v i o r o f t h e c l a y e y s o i l in t h e d i r e c t i o n o f s a n d y s o i l s .

F u r t h e r c o m m e n t s o n t h is t o p i c a r e a s f o ll o w s :

I t c a n b e i n f e r r e d t h a t a t h i g h d e v i a t o r s t r e s s e s c o n t r i b u t i o n o f f i b e r is m o r e

e v i d e n t i n a b s o l u t e t e r m s . T h e r e f o r e , th e o b s e r v e d M R r e d u c t i o n i s m o r e

s i g n i f i c a n t i n th e c o m p o s i t e t h a n i n th e s o i l ;



IASBIK ET AL. ON A CLAYEY SOIL 123

Ho we ve r , a t l ow s t ra in va lues it c an be e s t ima ted t ha t t he dynam ic mo du lu s o f the

l i gh twe igh t com pos i t e w i l l be l e s s than t he so i l becau se f i be r i s l igh t e r t han so i l ;

a n d

Ad d i t i on o f f i be r t o the so i l m akes i t beha ve a s a more r e s i s t an t and m ore f l ex ib l e

ma te r i a l . F rom an eng inee r ing pe r spec t i ve , and unde r spec i f i c de s ign

r e q u i re m e n t s , t h e m e c h a n i c a l r e s p o n s e o f th e c o m p o s i t e u n d e r r e p e a t e d l o a d i n g

can b e t echn i ca l l y u se fu l. Ce r t a in ly , a pav em en t l aye r mor e t o l e r an t t o s e tt l emen t s

a n d m o r e r e s is t a n t t o c r a c k i n g w i l l m i n i m i z e i n f l u e n c e o f l o a d i n g r e p e t i ti o n o n t h e

l o n g - t e r m b e h a v i o r o f p a v e m e n t l ay e rs .

Conclusions

Th e l abo ra to ry - t e s t i ng p rog ra m w as d i r ec t ed to t he geo t echn i ca l cha rac t e r i za t i on o f a

c l a y e y s o il s t a b i li z e d w i t h p o l y p r o p y l e n e f i b e r u s in g u n c o n f i n e d c o m p r e s s i o n t e s ti n g a n d

re s il i en t mod u lus da t a . Repea t ed l oad ing t r iax i a l t e st s f o l l owin g t he Braz i l i an S t anda rd

D N E R - M E 1 3 1 / 9 4 w e r e p e r f o r m e d a t th e o p t i m u m f i b e r c o n t e n t a nd f i b e r l e n g th ,

r e s p e c ti v e ly , o f 0 .2 5 % a n d 2 0 m m .

A l t h o u g h t h e s c o p e o f th e t e s ti n g p r o g r a m is s o m e w h a t l i m i te d , a n d t h e c o n c l u s io n s

d raw n a r e no t conc lus ive , t he l abo ra to ry t e s t i ng da t a sugges t t ha t :

9 T h e m e c h a n i c a l r e s p o n se o f t h e c o m p o s i t e is f i b e r c o n t e n t a n d fi b e r l e n g th

d e p e n d e n t ;

9 Ad d i t i on o f f i be r t o t he so i l imp roves subs t an t i a ll y i ts unc onf in ed comp res s ion

s t r eng th ; and

9 MR va lues o f so i l and com pos i t e p r e sen t typ i ca l b i l i nea r t r end o f coh es ive

so i ls ; MR va lues o f t he com pos i t e a r e gene ra l l y sma l l e r t han t hose o f the so i l,

a n d m a j o r d e c r e a s e s i n M R v a l u e s o f t h e c o m p o s i t e a r e o b s e r v e d a t d e v i a t o r

s t r es se s up t o 100 kPa .

Acknowledgement

T h e a u t h o r s w o u l d l ik e to e x p re s s t h e ir g ra t it u d e to F A P E M I G , F I E M G , C A P E S a n d

the Fede ra l U n ive r s i t y o f V iqosa , who suppo r t ed t h is r e sea rch .

References

An der s l and , O . B . , and K ha t t ak , A . S . , 1979 , " Sh ea r S t r eng th o f K ao l in i t e /F ibe r S o i l

M i x t u r e s , "

I n te r na t iona l Con fe r ence on S o i l R e in fo r cemen t , I ,

Par i s , France , pp . 11-

16.



1 2 4


Bu eno , B. S .; Lim a, D. C. ; Teixeira , S . H. , and M inet te , E ., 1997,

"The Mechan i ca l

Response o f Re in forced So i l s Us ing S hor t Randomly D i s tr i bu t ed P las t i c S t r i ps , "

Recen t Deve lop me nt in So i l and Pavem ent Mechanics , Ed i ted by Marc io Almeida ,

Ba lkem a , Rot te rdam, pp . 401-408 .

Buzzelli , P. , 1995,

"Dyna mic Triaxia l Test ing o f Unrein forced and Reinforce d SoiL"

New York , Thes i s (M.S .) , T he Coop er Union Alber t Nerken S choo l o f Enginee r ing ,

220 p.

Du ncan, J . M. , and Chang, C. Y. , 1970, "No nl inea r Analys is of S tress and Stra in in

Soi ls ,"

Journa l o f t he So i l Mec han i cs and Fou nda t ion Div i sion ,

ASC E, V ol . 96 ,

No. SM5, pp. 1629-1653.

Fossberg, P . E . , 1969, "Som e De form at ions Character is tics of a Lim e Stabi l ized Clay,"

Highw ay Research Record ,

Vol. 1192, pp. 1-7.

He ad, K. H. , 1982,

M anu al o f Soi l Lab oratory Test ing - Volume 2 - Permeabi li ty , Shear

Streng th an d Compressibil i ty Tests, New York , John W i ley & Sons , 418 p .

Ho, Y. C., 1992,

B ehavior o f Fiber-Reinforced, Cem ented Soi l s U nder Sta t i c and Cycl ic

Loads,

New Jersey, Thes is (Ph.D.), Th e Sta te Univers i ty of Ne w Jersey, 152 p.

Lim a, D. C. , Bueno , B. S ., Ma rques , E . T . , and Minet te , E ., 1999, " Inf luence of Ad di t ion

of Po lypropy lene F ibe r s and Com pac t ion Ef for t on the M echanica l Response o f

Soi l -L ime M ixtures ,"

First South Americ an Sym posium on G eosyntheti cs,

R i o d e

Janeiro, October 19-22, pp. 177-182. (In Portuguese) .

L ima , D. C . , Buen o , B . S . , and Thomas i , L . , 1996 , "The M echanica l Response o f So i l-

L im e M ixtures Re inforced wi th Sh or t Synthe ti c F ibe r s , " Third In ternat ional

Sym posium on E nvironme ntal Geotechnology,

June 10-12, San Dieg o, Cal i fornia ,

pp. 868-877.

M aher , M. H. , and H o, Y. C. , 1994, "M echan ical Proper t ies of Kaol ini te /F iber Soil

C o m p o s i t e , " Journa l o f G eo techn ica l E ngineer ing , Vo l. 120, No . 8, pp. 1381-1393.

M otta , L. M. G. , and Mac~do, J . A. G. , 1998, "Dy nam ic Tr iaxia l Tes t for Pav em ents -

N e w T e n d e n c i e s ," X I Braz i li an So i l Mechan i cs a nd Founda t ion Engineer ing

Congress,

Brasflia, N ov em be r 5 - 10, Vo l. 1, pp. 623-628. (In Portugu ese) .

No gam i, J . S . , and V il l ibor , D. F . , 1995,

Low-Cost Pavement Using Lateri t i c Soi l s ,

Vil l ibor , Sao P aulo-SP, B razi l , 213 p. ( In Por tuguese) .

Seed, H. B. , Chan, C. K. , and Lee, C. E ., 1962, "Re s i l ience Character is tics of Sub grade

Soi l and their Rela t ion to Fat igue Fai lures in Asph al t Pavem ents ,"

In ternat ional

Conference on the Structural De sign o f Asp hal t Paveme nt ,

Un ivers i ty o f Michigan.

Silva, W. R., 1998, Be hav ior o f Co ld -Mixed Dense-Graded Aspha l t Mix R ein forced wi th

Random ly D i s tr i bu t ed Syn the ti c F iber ,

Viqosa-Brazil, Th esis (M.S.), Fed eral

Un ivers i ty of Viqosa , U nivers i ty Press, 91 p. ( In Por tugu ese) .

S i lva , M. A . , Buen o, B. S ., and Lima, D. C. , 1995, "Soi l S tabi l iza t ion Using S hor t

F ibe r s , "

Geosynthet ics 95 - B razi l ian Congress on Geosynthet ics,

S~o Paulo, B razi l,

Vo l. 1, pp. 327-335. (In Portug uese) .



IASBIK ET AL. ON A CLAYEY SOIL

1 2 5

Teixe ira , S . H. , Bu eno , B. S . , and Lima , D. C . , 1994, "Ana lys is of the Beh avio r of Soi ls

Re inforced w i th F ibe r s ," First Civil E ngineering Congress, Federa l Unive r s i ty o f

Juiz de Fora, August, pp. 54-64. (In Portuguese) .



SESSION 4: EQUIPMENT, TEST PROCEDURES,

AND QUALITY CONTROL ISSUES



M anue l O . Be j a rano , 1 An drew C . H ea th , 1 and Jo hn T . H arvey2

A L o w - C o s t H i g h - P e r f o r m a n c e A l t e r n a ti v e f o r C o n t r o l l in g a S e r v o - H y d r a u l i c

S y s t e m f o r T r i ax i a l R e s il ie n t M o d u l u s A p p a r a t u s

R e f e r e n c e :

Bej a rano , M . O . , Hea th , A . C . , and Harve y , J . T ., "A

L o w - C o s t H i g h -

P e r f o r m a n c e A l t e r n a ti v e f o r C o n t r o l l in g a S e r v o - H y d r a u l i c S y s t e m f o r T r i a x ia l

R e s i li e n t M o d u l u s A p p a r a t u s , "

Resilient Modulus Testing or Pavement Components,

ASTMSTP 1437,

G . N . D u r h a m , W . A . M a r t, a n d W . L . D e G r o f f , E d s ., A S T M

Inte rna t iona l , W es t Con shohock en , P A , 2003.

Abstrac t :

A t r iax i a l t e s t appara tus f o r t he cha rac t e r i za ti on o f pav em ent ma te r ia l s was

des igned and bu i l t a t t he P ave m ent Resea rch Cen te r (P RC ) a t t he Unive r s i t y o f

Ca l i f o rn ia , Berke l ey ( UCB) . T he sy s t em was d es igned f o r h igh qua l i t y t e s t ing o f

unbound , s t ab il iz ed , and aspha l t i c ma te r i a ls . The de s ign p rocess i nc luded t he des ign o f

the ha rdware and t he se rvo-con t ro l li ng sys tems . An impo r t an t s t ep i n the des ign o f t he

sys t em w as t he d es ign o f t he con t ro l l e r f o r the se rvo -hydrau l i c sys t em. Al t e rna t ives f o r

con t ro l le r s o f se rvo-hydrau l i c sys t ems f o r wa vef o rm genera t i on i nc luded t he use o f t he

da t a acqu i s i ti on sys t em a lon g w i th p ropor t i ona l , i n teg ra l, and de r iva t i ve ( P ID) a lgor i t hms

f o r se tt in g t h e m i n i m u m a n d m a x i m u m l o a d s / d is p l ac e m e n t . S o f tw a r e p r o g r a m m i n g f o r

these so lu ti ons was v e ry com plex w i th l imi t ed sa t i s fac to ry cons i s tency . Co mm erc i a l

r eady- to -use con t ro ll e r s a r e exp ens ive and l imi t ed t o t he spec i f ica t i ons o f t he

m a n u f a c tu r e r. T h e r e fo r e , a c o m m e r c i a l l y a v a il a b le p r o g r a m m a b l e m o t i o n c o n t r o ll e r P I C

card was im p lem ented f o r con t ro ll i ng t he se rvo-hydrau l i c sys tem. The m ot ion con t ro l l e r

r equ i r ed on ly one P ID con t ro l l e r t o genera t e r epea t ed wa vef o rm s or mon oton i c l oad ing .

An ava i l ab l e com m erc i a l t e s t so lu t ion sof tware com pa t ib l e wi th t he mo t ion con t ro l l e r

ca rd was use d t o p rog ra m the m ot ion con t ro l l e r and da t a acqu i s i ti on sys t em. Thi s

capab i l i t y wa s p re f e rab l e t o p rov ide f l ex ib i li t y i n mod i f y ing t he sys t em ba sed o n r e sea rch

needs . S of tware p rog ra m m ing was s imp le . In add i ti on , t he cos t o f the new sys t em was

reduced b y about 80 pe rcen t w i th r e spec t to t he r eady- to -use mo t ion con t ro ll e r s.

The pa per desc r ibes the imp lemen ta t i on o f t he mo t ion con t ro ll e r , t he ph i l osophy o f

the so f tware p rog ram , and the success ob t a ined wi th t he new sys t em. The sys t em mee t s

a l l the qu a l it y con t ro l p rov i s ion o f the LT TP P ro toco l P -46 . C ur ren t ly t he t r iax i a l

appara tus i s be ing use t o i nves t i ga t e the r e s i li en t r e sponse and pe rm anen t de f orm at ion

per f orm ance o f t yp i ca l Ca l i f o rn i a aggrega t e base and subbases .

K e y w o r d s :

res i l ient modulus , t r iaxia l t es t ing , servo-hydraul ic sys tem, mot ion cont rol ler ,

t e s ti ng equ ipm ent

~Assi st an t Rese a rch Eng inee r and G radua t e S tuden t R esea rche r , r e spec t ive ly , P av em ent

Resea rch Cente r , Unive r s i t y o f Ca l i fo rn i a , 135 3 S . 46 th S t., R i chm ond, CA 94804 .

2Assoc i at e P rof essor , Unive r s i t y o f Ca l i fo rn i a , D avi s , C A 95616 .

1 2 9





Introduction

Th e Ca l i f o r n i a D epa r t m en t o f Tr anspor t a t i on ( Ca l t rans ) u se s t he r e s i s tance " R"

va l ue ob t a i ned f r o m t he H ve em s t ab i l om e t e r te s t f o r t he cha r ac t e r i za ti on o f un t r ea ted and

t r ea t ed unbou nd m a t e r i a l s ( Ca l i f o r n i a Tes t 301 2000) . Th e R- va l ue g i ves an i nd i ca t ion o f

pe r f o r m a nce o f pav em en t ba se s , subbases , and t he subgr ades sub j ec t ed to t r a ff i c l oad ing .

The cu r r en t Ca l tr ans de s i gn p r oced ur e i s a s em i - t heo r e t ica l m e t ho d t ha t u se s the R- v a l ue

a l o n g w i t h m a t e r ia l e q u i v a l e n c y f a c t o rs t o d e s i g n t h e p a v e m e n t s t ru c t u re ( H v e e m a n d

Car m any 1948) .

M a t e r ia l equ i va l ency f ac t o r s w e r e dev e l oped f o r s tanda r d C a l i f o r n i a m a t e r i a l s ba sed

on co r r e l a t ions o f fi e l d pe r f o r m anc e wi t h t he m a t e r i a l p r ope r t i e s ob t a i ned w i t h t he

s t ab i l om e t e r t e st . Ex t r apo l a t i ons f r om t he em pi r i ca l equ i va l ency f ac t o r s and pavem en t

s tr u c tu r e s to a c c o m m o d a t e n e w a n d i n n o v a t i v e p a v e m e n t m a t e r ia l s ( s u ch a s r e c y c le d

m a t e r i a l s ) m a y r e su l t i n ques t i onab l e de s i gns .

Bec ause o f t he se and o t he r l i m i t a ti ons wi t h em pi r i ca l m e t hods , C a l t rans ha s pu t

c o n s i d e ra b l e a t t en t io n o n t h e d e v e l o p m e n t o f m e c h a n i s t ic - b a s e d a p p r o a c h e s f o r th e

d e s i g n a n d e v a l u a ti o n o f p a v e m e n t s i n r e ce n t y e a r s . M o s t m e c h a n i s t ic - b a s e d d e s i g n

m e t hods u se t he r e s il ien t m o du l us o f each l aye r in t he de s i gn p r oces s . T he r e s i l ien t

m o du l us o f pav em en t m a t e r i a l s is u sua l l y ob t a i ned us i ng r epea t ed l oad t r i ax i a l t e s t s and

h a s b e e n s h o w n t o b e a f u n c t io n o f b o t h c o n f i n in g a n d d e v i a to r i c s tr e s s ( H i c k s a n d

M oni sm i t h 1970; Uzan 1985).

The t r i ax i a l equ i pm en t de sc r i bed i n th i s pap e r was d eve l op ed du r i ng t he yea r 2000

i n o r d e r t o p r o v i d e a t e s t a p p a r a t u s to s t u d y t h e m e c h a n i c a l p r o p e r t ie s o f p a v e m e n t

m a t e r i a l s . The t e s t appa r a t us ha s been used t o d e t e r m i ne t he r e s i l ien t m od u l us , s t at ic

shea r and pe r m anen t de f o r m a t i on cha r ac t e ri s t ic s o f Ca l i f o r n i a ba se s , subbases , and

subgr ades . Th e equ i pm en t ha s been s l igh t l y m od i f i ed f r om i t s in i ti a l con f i gu r a ti on t o

i nc lude a t em per a t u r e con t r o l sys t em i n t he con f i n i ng ce l l t o de t e r m i ne v i s coe l a s t i c

p r ope r t i e s o f a spha l t boun d m a t e r i a ls . F i gu r e 1 show s the t e s t sys t em wi t hou t t he

t em p er a t u r e con t r o l sy s t em i ns t a ll ed .

Test Apparatus and Loading System

The com pone n t s o f t he tr i ax i a l t e s t ing sy s t em i nc l ude t he f r am e , t he hydr au l i c

ac tua tor , the t ri ax ia l ce ll , and e lec t ronic equipm ent (Figure 1). Th e f ram e and hyd raul ic

ac t ua t o r w e r e ob t a i ned f r om ou t da t ed t e s ti ng equ i pm en t . The t r iax i a l c e ll w as de s i gned

and cons t r uc t ed i n - house . The ce l l top and bo t t om p l a t e s we r e cons t r uc t ed us i ng

a l um i num and the ce ll i s a 25 . 4 m m (1 i nch ) t h i ck p l ex i g l a s s cy li nde r . A l um i nu m wa s

chosen f o r t he t op and bo t t om p l a t e s a s s ta i n le s s s t ee l wo u l d ha ve bee n t oo heavy .

A 150 m m d i am e t e r , 300 m m h i gh cy l i nd r i ca l spec i m en is cove r ed wi t h a la t ex

m em br an e and p l aced i n t he t r iax i a l c e ll wh i ch i s p r e s su r i zed us i ng a ir . The ax i a l load i ng

sys t em has a capab i l it y o f 44 . 4 kN ( 10 000 l b f ). Ce l l p r e s su r e s a r e app l ied i n the r ange o f

0 t o 700 kP a ( 0 t o 100 ps i ). A p r e s su r e t r ansduce r i s u sed t o con t r o l the p r e s su r e i n t he

triaxial cell .

T w o load ce l l s a re provid ed, o ne ins ide the t es t ce l l and the o ther ou t s ide the ce ll .

Th e i n t e r na l l oad ce ll i s no t a f f ec t ed by l oad i ng r od f r ic t i on o r con f i n i ng p r e s su r e

changes , w h i l e t he ex t e r na l l oad ce l l wi l l g i ve h i ghe r r ead i ngs a s con f i n i ng s t r e s s and



BEJARANO ET AL. ON A SERVO-HYDRAULIC SYSTEM 131

f r i c t i o n i n c r e a s e . D u r i n g l o a d - c o n t r o l l e d t e s t in g , th e l o a d s a r e a p p l i e d u s i n g t h e i n t e r n a l

l o a d c e l l r e a d i n g s , w h i c h a r e c o n s i d e r e d m o r e a c c u r a te .

F i g u r e 1 -

UCB Triaxial Testing System or Pavement Materials

T w o L V D T s a r e m o u n t e d o n t he s p e c i m e n a n d t w o m o r e o n t o p o f s a m p le . R a d i a l

d i s p l a c e m e n t s a r e m o n i t o r e d u s i n g a c h a i n d e v i c e . P o o r s i g n a l t o n o i s e r a ti o s f o r th e

r a d i a l c h a i n s u g g e s t t h e u s e o f n o n - c o n t a c t p r o x i m e t e r s t o m e a s u r e r a d i a l d i s p l a c e m e n t s .

T h e o n - s a m p l e i n s t ru m e n t a t i o n i s i l lu s t r a t e d i n F ig u r e 2 . D a t a f r o m t h e i n s tr u m e n t a t i o n

a r e c o l l e c t e d b y m e a n s o f s i g n a l c o n d i t i o n i n g a n d d a t a a c q u i s i t io n s y s t e m s .

Servo C ontroller System Description

T h e a x i a l l o a d i s a p p l i e d t o t h e s p e c i m e n u s i n g a h y d r a u l i c a c tu a t o r a n d i s

m o n i t o r e d w i t h a d i s p l a c e m e n t tr a n s d u c e r i n s i d e t h e a c t u a to r , o r w i t h t h e i n t e r n a l l o a d

c e ll . D u r i n g r e p e a t e d l o a d i n g , t h e f e e d b a c k s i g n a l i s c o m p a r e d w i t h t a r g e t v a l u e a n d



1 3 2 R E S I L IE N T M O D U L U S T E S T I N G F O R P A V E M E N T C O M P O N E N T S

a d j u s t m e n t s m a d e i n th e c o n t r o l l e r t o m i n i m i z e t h e e r ro r b e t w e e n t h e f e e d b a c k s i g n a l a n d

t h e t a rg e t v a lu e . F i g u r e 3 s h o w s a d i a g r a m o f t h e f o u r c o m p o n e n t s o f t h e e l e c t ro n i c

s y s t e m o f t h e t ri a xi a l a p p a r a tu s . A d e s c r ip t i o n o f e a c h c o m p o n e n t f o l l o w s .

F igu re 2 -

On-Sample Instrumentation

Signal Subsystem

T h e s i g n a l s u b s y s t e m i s c u r r e n t ly c o m p o s e d o f t w o f e e d b a c k s i g n a ls , a n d o n e i s

s e l e c te d d e p e n d i n g o n w h e t h e r t h e t e s t is r u n u n d e r d i s p l a c e m e n t o r l o a d c o n t ro l .

D i s p l a c e m e n t c o n t r o l is a c c o m p l i s h e d u s i n g a s i g n a l f r o m t h e L V D T m o u n t e d i n s id e t h e

a c t u a t o r p i s to n . L o a d c o n t r o l is c a r r i e d o u t u s in g a s ig n a l f r o m t h e l o a d c e l l m o u n t e d o n

top o f t he s ample , i n s ide t he t r iax i a l c e l l. N o n- f e edb ack s i gna l s a r e t hose ob t a ined f rom

t h e e x t er n a l ly m o u n t e d l o a d c e ll a n d f r o m t h e i n t e rn a l ly m o u n t e d r a d i a l a n d L V D T

t r an s d u c e rs . C u r r e n tl y , t h e s e n o n - f e e d b a c k s i g n a ls c a n b e u s e d a s f e e d b a c k s i g n a ls i f

requi red .



B E J A R A N O E T A L . O N A S E R V O - H Y D R A U LI C S Y S T E M 1 3 3

D at a

S i g n a l C o n d i ti o n in g M o t io n C o n t r o l

S u b s y s t e m a n d A c q u i s it io n S u b s y s t e m

S u b s y s t e m

Feedback Signals

Axial Actuator [ / S ig n al ~

oad Ce ll Internal Motion

Controller

Axial Actuator ] "]

LVDT ~! Data

Acquisition

Non-Feedback n ~ Conditioning Card

Signals

Loa d C ell External

Ra dial Transducers

LVDT 1

LVDT 2

LVDT 3

LVDT 4

Figure 3 - Components of the Electronic System

S e r v o - V a l v e

S u b s y s t e m

Axial

Actuator

Servo-valve

Signal Conditioning and Data Acquisition (SCDA) Subsystem

Signal con di t ioning is prov ided by a program ma ble mu l t i-channel chass is -based

sys tem. T he sys tem co ns is ts of two m odu les that am pl i fy, f il te r , i solate, and m ul t iplex the

load/pressure and L VD Ts s ignals . The d ata acquis i tion i s provided by a h igh performan ce

data acquis it ion card wi th 16-single ended analog inputs capable o f a samp l ing ra te of up

to 100 thous and samples per seco nd and a 16-bit resolut ion. The d ata acquis i tion card

also inclu ded twol6 -bi t analog outputs and e ight input /output digi ta l l ines (Nat ional

Instruments 2002). D igital l ines were use d to con trol switches th at op en an d close the

hydrau l ic l ines and chang e the tes t mod e from/to displacement control to/ f rom load

control.

Motion Control Subsystem

During the ea r ly developm ent of the sy s tem severa l a lternat ives were tes ted in ord er

to control the sys tem for wav eform and m ono tonic loading tes ting. The a l temat ives

included 1) us ing the a nalog inputs and outpu ts of the data acquisi tion card, 2) us in g a

com m ercia l ly available ready-to-use servo-control ler typica l ly used in this type o f

applications, or 3) usin g a com m ercia l ly available m otio n controller card that requires

program m ing to develop the applica tion.

Alternative 1 requ ired proportional, integral, deriva tive (PID) algo ri thm s to contro l

the sys tem. The a l ternative was acceptable for mon oton ic loading because the target or

se t values were ea sy to fol low. A s ingle p oint genera t ion approach wa s used. Ho wev er ,

wav eform s wi th f reque ncies high er than 0.03 Hz could not be genera ted because the loop




u s e d i n th e s o f t w a r e t o c o n t r o l e a c h p o i n t o f t h e w a v e f o r m w a s t o o s l o w f o r t h e

app l i ca t i on . Th e f a s t e st P IE) l oop r a t e w as o f 5 5 mi l l i s econ ds pe r s a mple . A r ea l - t ime da t a

a c q u i s i t io n c a r d s h o w e d n o s i g n i fi c a n t i m p r o v e m e n t . O t h e r s o l u ti o n s u s i n g t h e d a t a

acqu i s i t i on ca rd i nc luded a bu f f e r ed ana log i npu t /ou tpu t so lu t i on . Howeve r , t he r e su l t s

w e r e n o t s a t i s f a c to r y b e c a u s e i t r e q u i re d s e v e r a l P I D a l g o r i th m s t o s e t t h e m a x i m u m ,

m i n i m u m , a n d s h a p e o f t h e w a v e f o r m s . B a s e d o n t h e r e s u lt s o f t h e d a t a a c q u i s it i o n c a r d

o p t i o n , a v i a b le a l t e r n at iv e w a s t o p u r c h a s e a r e a d y - t o - u s e m o t i o n c o n t r o l le r ( a l t e m a t i v e

2 ). T e c h n i c a l l y , t h e r e a d y - t o - u s e m o t i o n c o n t r o l l e r w o u l d p r o v i d e e x c e l l e n t c o n t r o l o f a

s i n g l e s e r v o - h y d r a u l i c c h a n n el . T h e c o s t o f a s i n g le u n i t w a s a b o v e $ 1 0 0 0 0 d o l la r s

w h i c h w a s o v e r t h e b u d g e t a l lo c a t e d f o r d e v e l o p i n g t h e s y s t e m i n - h o u s e . I n a d d it i o n ,

a n o t h e r m o t i o n c o n t r o l l e r w o u l d h a v e t o b e p u r c h a s e d i f o t h e r c h a n n e l s n e e d e d t o b e

con t ro l l ed ( e .g . , con f in in g p re s su re , sh ea r ac tua to r , e t c ).

B e c a u s e o f b u d g e t c o n s t r a in t s a n d h i g h e r c a p a b i l it ie s e x p e c t e d f r o m t h e m o t i o n

c o n t r o l l e r i t w a s d e c i d e d t o p u r c h a s e a m o t i o n c o n t r o l le r c a r d w i t h p r o g r a m a b l e

c o m p a t i b i l it i e s w i t h t h e s o f tw a r e u s e d f o r d a t a a c q u i s it io n . A m o n g t h e m a n y f e a tu r e s i n

the mo t io n con t ro l l e r , the m os t s i gn i f i can t f o r t he t r iax i a l app l i ca t i ons w e re a fou r

chann e l con t ro l l e r PC I ca rd ( r a the r t han on e chann e l w i th a l t e rna t i ve 2 ) , 62 x 10 9

secon ds P I D loop up da t e r a t e ( r a the r t han 5 5 x 10 -3 s econ ds w i th a l t em a t ive 1 ),

c o n t o u r i n g , a n d o n - b o a r d p r o g r a m m i n g . T h e c o n t o u r i n g f e a tu r e o f t h e m o t i o n c o n t r o l l e r

a l lo w s t h e u s e r t o s p e c i fy a n y t y p e o f c o m p l e x w a v e f o r m a n d h a v e t h e m o t i o n c o n t r o ll e r

c r e a t e a s m o o t h p a t h t h r o u g h th e m . T h e o n - b o a r d p r o g r a m m i n g w a s a l s o d e s ir a b l e, a s th e

w a v e f o r m m o t i o n c a n b e p r o g r a m i n t h e p r o c e s s o r o f th e m o t i o n c o n t r o ll e r i ns te a d o f t h e

h o s t c o m p u t e r (N a t i o n a l I n s tr u m e n t s 2 0 0 2 ) . R u n n i n g t h e o n - b o a r d p r o g r a m s o f f e r s

r e l i ab i l it y and p red i c t ab i l i t y o f t he t e s ts su ch a s a r epea t ed l o ad ing t e s t w i th no r e s t

p e r i o d s a t f r e q u e n c i e s a b o v e 1 0 H z . M a n y o t h e r f e a t u re s a r e a v a i la b l e f o r t h e

p r o g r a m m a b l e m o t i o n c o n t r o ll e r s w h i c h a r e p r o p e r l y d e s c r i b e d i n t h e m a n u f a c t u r e s

t echn i ca l f ac t shee t s.

Servo- Valve Subsystem

A h i g h p e r f o r m a n c e s e r v o - v a l v e t h a t c o v e r s a ra n g e o f r a t ed f l o w s f r o m 0 . 0 6 3 t o

0 .946 1 /s ( 1 t o 15 gpm ) a t 6 .89 M Pa (1000 ps i ) i s u sed i n t he hyd rau l i c sy s t em . Inpu t

s i g n al s a r e i n t h e ra n g e o f ~ : 1 5 m A . S i n c e t h e o u t p u t s i g n a l o f th e m o t i o n c o n t r o l l e r c a r d

a r e in th e ra n g e o f i l 0 V , a b u f f e r a m p l i fi e r w a s o b t a i n e d t o b r i d g e th i s d if f e re n c e .

Temperature Control Subsystem

T h e t e m p e r a t u r e c o n t r o l s u b s y s t e m i s o n l y u s e d f o r t e s ti n g a s p h a l t ic m a t e ri a l s a n d i s

i n d e p e n d e n t o f t h e o t h e r c o n t r o l sy s t e m s . T h e a i r e n te r i n g t h e c el l is h e a t e d w i t h a 4 0 0 W

in- l i ne a i r hea t e r , c apab l e o f hea t i ng a i r a t p r e s su re s o f up t o 700 kPa (100 ps i ) . A n a i r

b l e e d v a l v e s l o w l y r e m o v e s a i r f r o m t h e c e ll , a n d t h e r e p l a c e m e n t a ir i s h e a t e d b e f o r e

en t e r i ng t he ce ll . Tw o sm a l l f ans c i r cu l a t e t he a ir in s ide t he ce ll to ensu re un i fo rm

t e m p e r a t u r e d i s tr i b ut io n . T h e t e m p e r a t u r e i s c o n tr o l l e d u s in g a s e p a ra t e , c o m m e r c i a l l y

ava i l ab l e e l ec t ron i c t empera tu re con t ro l l e r t ha t c an con t ro l t he a i r t emp era tu re t o w i th in

0.55 C (1 F).

B e c a u s e t h e h e a t tr a n s fe r t h r o u g h t h e a l u m i n u m t o p a n d b o t t o m c a p s w a s h i g h , i t

w a s n e c e s s a r y to i n s ta l l a t e m p e r a t u r e c o n t r o l b o x a r o u n d t h e a p p a r a t u s a n d h e a t t h e a i r



B E J A R A N O E T A L . O N A S E R V O - H Y D R A U LI C S Y S T E M 1 3 5

a roun d t he ce l l u s ing a sma l l f an hea t e r and a t he rmos t a t . Th i s ensu re s t ha t t emp era tu re s

o f ove r 40 C can be ma in t a ine d i n s ide t he ce ll . The t e s t sy s t em wi th t empera tu re con t ro l

box i s i l lus t ra ted in Figure 5 .

Figure 4 -

Tr iax ia l Sy s tem wi th Tempera ture C on t ro l B ox In s ta l l ed

Performance o f Hydraulic System

C u r r e n t l y th e p e r f o r m a n c e o f t h e s y s t e m i s e x c e l l en t a n d i t h a s b e e n u s e d n o t o n l y t o

c o n d u c t l a b o r a to r y t es t in g u n d e r t h e P - 4 6 t e st p r o t o c o l s ( F e d e ra l H i g h w a y A d m i n i s t r a ti o n

1997) fo r g r anu l a r ma te r i a l s bu t a l so o the r l ab o ra to ry t e st s . Resu l t s o f t he se t e s t

p r o c e d u r e s h a v e b e e n u s e d t o c a li b r at e a b o u n d i n g s u r f ac e p l a s t ic i ty c o n s t i tu t i v e m o d e l

f o r u n s a tu r a t e d g r a n u l a r p a v e m e n t m a t e r ia l s. T h e s y s t e m i s b e i n g u s e d t o c a li b r at e a

cons t i t u t i ve mode l fo r a spha l t conc re t e ma te r i a l s . The n eed fo r a l te r i ng t he so f tw a re and

the ha rdware b ased on r e sea rch need s was a f ea tu r e tha t was r equ i r ed fo r t he

d e v e l o p m e n t o f t h e s y s te m .

T h e s y s t e m a l lo w s v e r y a c c u ra t e c o n t ro l o f lo a d s d u r i n g d y n a m i c te s ti n g . T h e

s y s t e m w a s c h e c k e d a g a i n s t t h e P - 4 6 l a b o r a t o r y s t ar t up p r o c e d u r e s ( F e d er a l H i g h w a y

Ad min i s t r a t i on 1997) and f el l w i th in t he a l l owab le r ange fo r phas e sh i f t and a l l o the r

r equ i r ed spec i f i ca t ions . Ap p l i ed s t r e sse s and mea su red s t r a in s du r ing two typ i ca l t e s t

b lock s du r ing a P -46 t e s t a r e i ll u s tr a t ed i n F igu re s 6 and 7 . Th e app l i ed wa ves a r e

i n t e n d e d t o b e 0 .1 s e c o n d h a v e r s i n e p u l s e s w i t h a 0 . 9 s e c o n d r e s t p e r io d b e t w e e n p u l s e s




( n o t sh o w n ) . B o t h f i g u r e s s h o w t h r e e w a v e s s u p e r i m p o s e d o n e a c h o t h e r, a n d th e d a t a i s

unf i l te red .

.=,

2=

r13

0.06 120

100

0.04 , ' ~ 80

0.03

0 .02 60

0.01

4 0

0 "

't ~ .~ ~,..~r.~ ~ 20

-0.01 x. "~x.-~-~- ~ -x -• 2 1 5

-0.02 . . . . ' . . . . ' . . . . . . . . . 0

0 0.05 0.1 0.15 0.2

T i m e ( s )

F igu re 5 - S t r e s s e s a n d S t r a i n s w i t h T i m e f o r a H i g h D e v i a t o r i c S t r e s s

' * Ax ial s t rain

o --a- 9Radial s t rain

'~ - ~<- Stres s

r ,

A s s h o w n , t h e r e p e a t a b i li t y o f t h e w a v e s i s e x c e ll e n t, a n d t h e c o n t r o l s y s t e m a n d

h y d r a u l i c a c t u a t o r c o n t r o l t h e w a v e s w e l l, w i t h v e r y l i tt le d e v i a t io n f r o m a tr u e h a v e r s i n e

shape . The d ev i a to r i c s t r e s s is c a l cu l a t ed u s ing t he i n t e rna l l oad ce l l, t he ax i a l s tr a in is

c a l c u l a te d u s i n g t h e o n - s a m p l e L V D T s , a n d t h e r a d i a l s t r ai n i s c a l c u la t e d u s i n g t h e r a d i a l

cha in .

P e r f o r m a n c e o f t h e I n s t r u m e n t a t i o n a n d D a t a A c q u i s i ti o n S y s t e m

A s s h o w n i n F i g u r e s 5 a n d 6 , th e l o a d c e ll a n d L V D T s h a v e e x c e l l e n t re p e a t a b i l it y

and l i tt l e no i se , wh i l e t he no i se f rom the r ad i a l t ransd uce r i s e a s i l y no t i ceab l e , e sp ec i a l l y

a t l ow s t r e s s leve l s . Fo r t h i s r ea son , i t i s an t ic ipa t ed t ha t t he r ad i a l t r ansduce r w i l l be

r e p l a c e d w i t h p r o x i m i t y s e n s o rs .

T h e r e i s a sl i g h t t i m e l a g b e t w e e n t h e l o a d a n d d i s p l a c e m e n t c u r v e s i n F i g u re s 5 a n d

6 , bu t t h i s i s a tt r i bu ted t o non - l i nea r , t im e dep ende n t m a te r i a l beha v io r r a the r t han t o t he

d a t a a c q u i s it i o n s y s te m . T h e r a d i a l tr a n s d u c e r i s c o n n e c t e d t o t h e s a m e d a t a a c q u i s i ti o n

m o d u l e a s th e l o a d c e ll , w h i l e t h e L V D T s a r e c o n n e c t e d to a n o t h e r m o d u l e . F o u r i e r

a n a l y s i s o f t h e h a v e r s in e w a v e s i n d i c a t e d a n a v e r a g e p h a s e l a g o f 9 . 2 m s b e t w e e n t h e

L V D T s a n d l o a d ce l l, a n d 7 .4 m s b e t w e e n t h e ra d i a l t r a n s d u c e r a n d l o a d c e ll . T h e

w a v e l e n g t h w a s a l so d i ff e r en t , in d i c a t i n g t i m e d e p e n d e n t m a t e r ia l b e h a v i o r . T h e a v e r a g e



B E J A R A N O E T A L . O N A S E R V O - H Y D R A U L I C S Y S T E M 1 3 7

w a v e l e n g t h f o r t h e l o a d p u l s e w a s 1 1 .1 m s ( t a r g e t = 1 0 m s ) , w h i l e i t w a s 1 2 .1 a n d 1 2 . 5

m s f o r t h e L V D T s a n d r a d i a l t r a n s d u c e r r e s p e c t iv e l y .

0 . 02

"-" 0.01

0 . 005

4 0

0 .01 5 ; / ~ 3 0

r~

20 "~

o

15 .~

0

, % t , ,

- 00 0 5. . . . . . . . . . . ' . . . . ' . . . . 0

0 0 .05 0 .1 0 .15 0 .2

T i m e ( s )

F i g u r e 6 -

St re sse s and S t ra ins w i th T ime fo r a Low D ev ia tor i c S t re ss

3 0 0 ~ . : . ~

~ /

2 5 0

9 2 0 0

150

N

E lOO

0

o 50

0 5 0 100 15 0 200 25 0 300

L o a d f r o m i n t e r n a l l o a d c e ll ( k P a )

F i g u r e 7 -

Compar i son o f In t e rna l and Ex te rna l Load Ce l l Read ings

' A x i a l s t r a i n

' Rad ia l s t r a in [

- ; L S e s s j

[

P e a k s t re s s ( kP a )

o S e a t i ng l oa d I

1 : 1 l ine j




The reading from the internal and external load cell were compared to assess the

effect of load road friction and confining stress on measured loads. The results from P-46

testing on four different Caltrans class 2 aggregate base materials (California Department

of Transportation 1999) are illustrated in Figure 7.

As shown, the external load cell readings are generally higher than for the internal

load cell, because of load road friction and uplift pressure on the load rod. While this

difference is usually small, this is not always the case, particularly at higher loads where

the external load cell can read over 15 percent higher. The load rod friction was

minimized as much as practically possible by using a low friction linear bearing system

in the top cap, and a single o-ring. O-ring grease was applied before testing to further

minimize friction. This indicates that while many triaxial test apparatus use only an

external load cell, this may not yield acceptable results. There does not appear to be a

constant relationship between internal and external load cell reading, and it is likely that

this is affected by sample stiffness, confining stress and test system compliance.

The measured resilient modulus (Mr) calculated using the on-sample, top cap and

actuator LVDTs is compared in Figure 8. The data are from the same four aggregates

used to determine the difference between internal and external load cell readings.

Figure 8 - Comparison o f Measured Resilient M odulus from Different L VDTs

As shown, the resilient modulus measured using the on-sample LVDTs is

consistently higher than for the other LVDTs. This is because the top-cap LVDTs are

influenced by sample end effects. The actuator LVDT is influenced by sample end

effects and compliance in the load cells, actuator and frame. For these reasons, the

resilient modulus measured using the on-sample LVDTs is expected to be highest, while

that measured using the actuator LVDT is expected to be lowest. The difference



BEJARANO ET AL ON A SERVO-HYDRAULIC SYSTEM 139

i nc r ea se s w i th i nc r ea s ing s ample s t i f fne s s a s t he compl i ance wi l l have a g r ea t e r e f f ec t

r e l a t i ve t o t he t r ue s ample de fo rma t ions .

Th i s i s a l so an a spec t t ha t i s o f t en no t cons ide red i n r e s i l i en t modu lus t e s t i ng o f

p a v e m e n t m a t e r i a ls , a l t h o u g h s o m e l a b o r a t o ri e s a p p l y a n e m p i r ic a l c o r r e c t i o n f a c t o r t o

a c c o u n t f o r c o m p l i a n c e . A s s h o w n i n F i g u r e 8 , t h e r e is n o c o n s i s te n t r e la t i o n sh i p

b e t w e e n t h e m e a s u r e m e n t s f r o m t h e d if f e re n t L V D T s a s s a m p l e e n d e f f e ct s a re s p e c i f ic

t o t h e a c tu a l s a m p l e . T h e u s e o f an e m p i r ic a l c o r r e c t i o n f a c t o r i s t h e r e fo r e u n l i k e l y t o

y i e ld a ccu ra t e r e su lt s .

O t h e r T e s ts

A n i m p o r t a n t a s p e c t o f t h e t r ia x i al s y s t e m d e v e l o p m e n t w a s t o i n c l u d e f l ex i b i li t y

t o a l l o w t h e d e v e l o p m e n t o f n e w t e s ts f o r b o u n d a n d u n b o u n d p a v e m e n t m a t e r ia l s. I n

add i t i on t o r e s il i en t m od u lu s t e s ts , l oad co n t ro l s t a t ic sh ea r t e st s , vo lum e t r i c s t r a in t e s ts

a n d p e r m a n e n t d e f o r m a t i o n t e st s w e r e r e q u i re d o n u n b o u n d m a t e r ia l s .

The vo lume t r i c s t r a in t e s t s enab l e t he t ime i ndependen t vo lume t r i c e l a s t i c and

h y s t e r e ti c b e h a v i o r t o b e m e a s u r e d . T h i s b e h a v i o r i s c u r re n t l y b e i n g i m p l e m e n t e d i n to a

b o u n d i n g s u r f a c e p l a s t ic i t y m o d e l f o r u n s a t u r a te d g r a n u l a r p a v e m e n t m a t e r ia l s . T h e o n -

s a m p l e i n s t r u m e n t a t i o n e n a b l e s a c c u r a t e m e a s u r e m e n t o f s m a l l v o l u m e t r i c s t r ai n s w i t h

c h a n g e s i n c o n f i n i n g s tr e ss e s. T h i s b e h a v i o r w a s t r a d i t io n a l l y d i ff i c u lt to m e a s u r e , a n d a s

a re s u l t m a n y r e s e a r c h e r s a s s u m e d l it tl e o r n o v o l u m e t r i c h y s t e r e s is f o r g r a n u l a r

m a t e r ia l s. T h e b e h a v i o r i s m e a s u r e d b y s l o w l y c y c l i n g t h e c o n f i n i n g s tr e s s to d i f f e re n t

s t r e s s leve l s . A n exa m ple o f t he t e s t r e su l t s is il l u s tr a t ed i n F igu re 9 .

F igu re 9 -

Typical V olumetric Test Resu l t




Because the v o lumet r ic te s t s a re run b y changing on ly the conf in ing s tr es s and on ly

a ve ry smal l cons tan t dev ia to r ic s tr e ss i s app l ied to ho ld the sam ple up t igh t , the bu lk

behav ior can be separa ted f rom the shea r behav ior wh ich i s impor tan t f o r de te rmin ing

mo de l pa r amete r s fo r advanced cons t i tu tive mode ls .


A t r iax ia l te s t appara tus was des igned and bu i l t a t the Pave me nt Resea rch C ente r at

the U nive r s i ty o f Ca l i fo rn ia , Berke ley fo r the cha rac te r iza t ion of un t r ea ted and t r ea ted

granula r ma te r ia ls and o the r ma te ria ls . T he sy s tem co nforms to the P4 6 qua l i ty

r equ i rements . A p rogramm able mo t ion con t ro l l e r PCI ca rd co n t ro l s the se rvo-hydrau l ic

sys tem. T he mo t ion con t ro l l e r was in tegra ted wi th the da ta acquis i t ion to have a comp le te

easy to p rogram sys tem w i th the f l ex ib i l i ty to a l low sys tem mo di f ica tions , based on

research needs .

Th e pe r form ance o f the t e s t appara tus i s cons ide red exce l l en t , p rov id ing q ua l i ty da ta

for inves t igat ing dif ferent aspects reg arding res i l ient mod ulus tes t ing, m ater ia l

cha rac te riza t ion , and cons t i tu t ive mode l ve r i f i ca tion . The sys tem i s cur r en t ly be ing used

to ch a rac te r ize va r ious Ca l i fo rn ia pavem ent ma te r ia ls and to ve r i fy cons t i tu tive mode ls

for bo th granu lar and asphal t ic mater ia ls .

Re fe r e nc e s

Cal i fo rn ia Dep ar tment o f T ransporta t ion , Ju ly 1999, "S tand ard Sp ec i f i ca t ions . "

Ca l i fo rn ia Tes t 301 , March 2002 , "Res i s tance "R " V a lue o f T rea ted and Un t r ea ted Bases,

Subbases , an d Ba sem ent Soi ls (S tabi lo m eter ) ."

Federa l Highw ay Adminis t r a tion , January 1997 , "LT PP M ate ria l s Charac te riza t ion

P r o g ra m : R e s i li e n t M o d u l u s o f U n b o u n d M a t e r ia l s ( L T P P P r o t o c o l P 46 ) L a b o r a t o r y

S ta rt -Up and Q ua l i ty Cont ro l P roced ure , " Publ ica t ion No. FH W A-R D-96 -176 , U .S .

Dep ar tment o f T ranspor ta t ion , Federa l High wa y Adm inist r a tion . Resea rch and

D e v e l o p m e n t , M c L e a n , V A .

Hicks , R . G . and M onismi th C . L . , 1971 , "Fac tor s In f luenc ing the Res i l i en t P roper t i e s o f

Granula r M ate r ia l s ,"

Highway Research Record

345, 15-31.

Hv eem , F .N. , and Carm any R. M. , 1948, "Th e Fac tor s Un der ly ing the Ra t iona l Des ign of

P a v em e n t s, " P r o c e e d i n g s

Highway Research Board

Vol. 28.

Na t iona l I nst ruments , 2002 , "The Mea surement and A utom at ion Ca ta log . "

Uzan , J . , 1985, "C harac te r iza tion of G ranula r Mate r ia l , " Transportation Research Reeord

1022, 52-59.



W . A . M ar r , I R . H an k o u r , : an d S . K . W erd en 3

A Fu l ly Autom ated Com puter Contro l led Res i lient M odulus Tes t ing Sys tem

Reference: MalT , W . A . , H an k o u r , R . , an d W erd en , S . K . , " A F u l ly A u t o ma t e d

Com puter Contro l led Res i lient M odulus Tes t ing S y s t e m , " Resilient Modulus Testing

for Pavement Components', ASTMSTP 1437, G . N . D u r h a m , W . A . M a r t , a n d W . L .

D e G r o f f, E d s ., A S T M I n te r n at io n a l, W e s t C o n s h o h o c k e n , P A , 2 0 0 3 .

Abstract: T h is paper d esc r ib es a fu l ly au to m ated co m pu te r co n t ro l l ed t e s t in g sys t em fo r

pe r fo rm in g res il i en t m o d u lu s t e s t s. I t d esc r ib es th e u se o f a P ID a d ap t iv e co n t ro l l e r t o

im p ro v e th e qu a l i t y o f th e t e s t an d r ed u ce th e l ab o r r equ i red to ru n th e t e st . I t a lso

ad d resses s o m e o f th e d i f f i cul t ie s an d t ech n ica l d e t a i l s fo r ru n n in g a r e s i l ien t m o d u lu s t e s t

acco rd in g to cu r ren t t e s t spec i f i ca t io n s .

Keywords:

r e s il i ent m o d u lu s t e s t in g , P ID co n t ro l , t e st au to m at io n

Introduct ion

A res i li en t m o d u lu s t e s t i s a co m pl i ca t ed c yc l i c te s t i n w h ich th e s t i f fn ess o f t h e sam ple

ch an ges wi th lo ad in g . T h ese ch an ges a re cau sed b y th e n o n l in ea r s t i f fn ess b eh av io r o f

t e s t ed m a te r i a l s fo r d i f f e ren t s t r e ss l ev e l s an d th e ch an ge o f s t i ffn ess o f te s t ed m a te r i a l

d u r in g cyc l i c s t re s s in g wi th th e sam e lo ad . S in ce th e co n t ro l pa ram ete r s o f a cyc l i c

lo ad in g sys t em d e pen d o n th e s t if fn ess o f t h e sam ple , m o s t sys t em s f a il t o app ly the

co r rec t l o ad th ro u gh o u t th e te s t. A sys t em ad ju s t ed to g iv e th e spe c i f i ed lo ad a t t h e

b e g i n n i n g o f th e t es t m a y b e o f f a t t h e e n d o f t h e te s t. S o m e p e o p l e m a k e m a n u a l

ad ju s tm en t s to th e equ ip m e n t th ro u g h o u t th e te s t t o m a in ta in th e co r rec t l o ad. O th e r s

ign o re th is p ro b lem , wh ich p ro d u c es r e su l ts t h a t d o n o t co n fo rm to th e t e s t spec i f i ca tio n s .

In co r rec t se t ti n gs o f t h e lo ad co n t ro l equ ipm en t can p ro d u ce lo ad o v er sh o o t , l o ad

u n d er sh o o t , o r s lo w lo ad r espo n se so th a t th e app l i ed lo ad d ev ia t e s f a r f ro m th a t d e f in ed

by the tes t s tandards .

T h e s y s t e m p r e s e n te d i n th is p a p e r u s e s r e a l -t im e a d j u s t m e n t o f a P I D c o n t r o l l e r to

c h a n g e t h e s y s t e m c o n t r o l p a r am e t e r s a s t h e s t if f n es s o f t h e s p e c i m e n c h a n g e s . P I D s t an d s

fo r P ro po r t io n aM n teg ra l -D er iv a t iv e . T h i s i s a f eed b ack co n t ro l l e r wh o se o u tpu t , a

c o n t r o l v a r ia b l e , i s b a s e d o n t h e e r r o r b e tw e e n s o m e u s e r - d e f in e d s e t p o i n t a n d s o m e

m e asu red p ro c ess v a r i ab le . T h i s f ea tu re pe rm i t s t h e app l i ca t io n o f an accu ra te lo ad f ro m

th e b eg in n in g to th e en d o f t h e t e st w i th o u t m a n u a l ad ju s tm en t . T h ere fo re , t h i s sys t em

m e e t s t h e r i g id A A S H T O T - 2 9 4 / T - 3 0 7 , a n d L T P P P r o t o c o l P 4 6 s p e c i f ic a t io n s f o r

1

CEO , GE OCOM P Corporation, 1145 Massachusetts Ave, Boxborough, MA 01719.

2 G eotechnieal Engineer, G EOCO MP Corporation.

Senior Systems Engineer, G EOCO MP C orporation.

141





p r e c i s i o n o n l o a d i n g t h r o u g h a ll s t a g e s o f t h e te s t w i t h o u t r e q u i r in g m a n u a l a d j u s t m e n t

du r ing t he t e s t. A s i l lu s t r a t ed i n F igu re 1 , t h i s t e st p ro toco l r equ i r e s t he l oad t o be app l i ed

a n d r e m o v e d i n 0 .1 s e c a c c o r d i n g t o a h a v e r s i n e s h a p e , f o l l o w e d b y a 0 . 9 s e c o n d r e s t

p e r i o d f o r h y d r a u l i c l o a d i n g s y s t em s .

P n e u m a t i c s y s t e m s d o n o t c o m e c l o s e t o a p p l y i n g a h a v e r s i n e w a v e f o r m t h a t m e e t s t h e

A A S H T O s t a n d ar d s r e q u ir e m e n t s ( T - 3 0 7 S e c t i o n 4.1 a n d T - 2 9 4 S e c t i o n 6 .2 . 2) . A s a

r e s u lt t h e c u r re n t A A S H T O s t a n d a rd T 3 0 7 - 9 9 S e c t i o n 6 .2 i s m o r e f o r g i v i n g f o r

p n e u m a t i c s y s t e m s . T h e r e s t p e r i o d c a n s t r e t ch f r o m 0 . 9 t o 3 . 0 s e c o n d s .

iN) 180

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a d (P~rr~u~)

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* T h e r e s t p e r i o d w i l l be O . 9 s f o r h y d r a u l i c l o a d i n g

d e v i c e s a n d 0 . 9 t o 3 . 0 s f o r p n e u m a t i c l o a d i n g d e v i c e s .

F IG .

1--Load Shape rom AASHTO T-307.

T h e s y s t e m d e s c r i b e d i n t h i s p a p e r f u l l y a u t o m a t e s t h e c o n d u c t o f a re s i li e n t

m o d u l u s t es t a c c o r d i n g t o A A S H T O T 2 9 2 / T 3 0 7 , an d L T P P P r o t o c o l P 4 6 . O n c e a

ma te r i a l spec ime n i s i n p l ace an d t he t e s t cond i t i ons s e l ec ted , t he sys t em w i l l r un the

en t i r e te s t f r om s t a rt to f i n i sh w i thou t manu a l i n t e rven t i on . Tes t da t a w i ll be s t o r ed i n a



MARR ET AL. ON AN AUTOMATED TESTING SYSTEM 143

f i le f o r subsequen t r educ t i on and p l o t t i ng by t he s ys t em so f t wa r e . A t t he end o f the t e s t ,

t he sys t em gene r a t e s t he t e s t da t a i n a va r i e t y o f ou t pu t f o r m a t s so u se r s can ge t t he m o s t

use ou t o f t he da t a. O p t i ons i nc l ude a c om pl e t e f ina l t e s t r epo r t wi t h a l l app r op r i a t e

ca l cu l a ti ons on t he da t a , t ex t f i le o f r aw da t a and a t ex t f i l e o f da t a i n eng i nee r i ng un i t s ,

e i t he r o f wh i ch can b e i m por t ed i n t o a sp r eadshee t f o r f u r t he r da t a ana l ys is .

Coe f f i c ien t s f o r t he r e s il i en t m o du l us cons t i tu t i ve r e la t i onsh ips d e f i ned i n FH W A

D e s i g n P a m p h l e t ( F H W A - R D - 9 7 - 0 8 3 ) a r e a u t o m a t ic a l ly c o m p u t e d i n t h e r e p o r t o p t io n s .

F u l l y A u t o m a t e d R e s i l i e n t M o d u l u s H a r d w a r e

Fi gur e 2 sho ws t he new sys t em desc r i bed i n t h is pape r . I t cons i s t s o f a load f r am e , a

hydr au l i c pum p , and a s e r vo - v a l ve wi t h a hydr au l i c cy l i nde r, an ex t e r na l s i gna l -

cond i t i on ing un i t, and a com pu t e r wi t h a ne t wo r k ca r d and an A /D ca r d f o r da ta

F I G .

2--Automated resilient modulus system.

Th e hydr au l i c com pon en t s cons i s t o f a cy l inde r , coup l ed wi t h a s e r vo - con t r o l va l ve and a

hydr au l i c ac t ua t o r d r i ven by a 2.5 gp m a t 3000 ps i ( 10 L /m i n a t 21 M Pa) a i r - coo l ed

hydr au l i c pum p f o r app l y i ng the cyc l i c load . Th e hydr au l i c ac t ua t o r p r ov i des t he cyc l i c

com pon en t o f ve r ti c a l f o r ce . Th e sys t em w or ks a s a c l o sed - l oop e l ec t r o - hydr au l ic sys t em

f or app l y i ng r epea t ed ax i a l dev i a t o r s t re s s o f f i xed m agn i t ude , l oad du r a t i on ( 0 .1 s econd) ,

and cyc l e du r a ti on ( 1 s econd) . These cyc l i c l oad pa r am e t e r s can be cha nged t h r oug h t he

so f t wa r e p r o g r am t o p r ov i de f l ex i b i l it y i n cyc l i c l oad i ng pu l s e and r e s t du r a ti ons .

An e l ec t r o - pneum a t i c cel l p r e s su r e r egu l a to r app l i e s and ad jus ts t he spec i f i ed ce ll

p r e s su r e au t om a t i ca l l y f r om on e s t ep to t he o t he r . P r e s su r e is con t i nua l l y m on i t o r ed a nd




m a i n t a i ned a t the r equ i r ed va l ue t h r oughou t t he t es t. T he e l ec t r o - pneu m a t i c p r e s su r e

con t r o l l e r i s a p r opo r t i ona l r egu l a t o r wi t h bu i l t - in f eedbac k . The i npu t s i gna l is 0 - 5V D C

vol t age p r ov i ded by t he A/D ca r d t h r ough so f t wa r e con t r o l. P r e s su r e i s con t ro l l ed to

w i th in 0 .1 ps i (0 .7 kPa) .

T h e e q u i p m e n t i s c o n tr o ll e d w i t h a p e r s o n a l c o m p u t e r r u n n i n g t h e W i n d o w s

TM

ope r a t i ng sys t em . A 16 - b it ana l og - to - d i g i t a l c a r d p l aced i n s i de t he c om pu t e r co l l ec t s da t a

f r om t he s enso r s and s ends con t r o l s igna l s t o t he s e r v o - va l ve con t r o ll e r .

F u l l y A u t o m a t e d R e s i li e n t M o d u l u s S o f t w a r e

Th e sys t em so f t wa r e cons i s t s o f a s i ng le p r og r am t ha t r uns t he t e s t , co l lec t s da t a f o r the

t e s t and s t o r es t he da t a i n a f i le . I t a lso pe r f o r m s t he n eces sa r y ca l cu l a t ions an d p r epa r e s

t he f i na l t ab l e s and g r aphs o f t he t e s t r e su lt s . Th i s p r o g r am wi l l r un on any PC us i ng t he

W i n d o w s

TM

NT , X P o r 2000 ope r a t i ng sys t em s . The co n f i gu r a t ion f o r any p r ev i o us t e s t

can be u sed t o e s t ab l ish t he i n i ti a l cond i t ions o f a subsequen t t e s t by l oad i ng t he ex i s t i ng

t e s t f il e . Th i s c apab i l i t y a ll ows an op e r a t o r to s e t up and s t a r t a t e s t wi t h i n a ve r y sho r t

t ime.

F I G . 3--M ain window fo r system software.

Th e so f t w a r e a l low s the u se r t o de f i ne the con d i t ions f o r con t r o ll i ng the eq u i pm en t and

r unn i ng t he t e s t. F i gu r e 3 i l l u s tr a t e s t he m a i n w i ndow . S pec i m en spec i f i c i n f o r m a t i on can

be en t e r ed f o r i nc l us ion o n t he t abu l a t ed and g r aphed r e su lt s. Th i s w i ndow i s com pos ed



M A R R E T A L . O N A N A U T O M A T E D T E S T IN G S Y S T E M 1 4 5

of a me nu bar at the top and a property sheet with five tabs. Each of the menu s (File,

View, Run, etc.) can be selected in the standard way of clicking on the me nu word or

using short-cut keys. Each tab on the property sheet (Project, Specimen, Water Content ,

etc.) specifies a property page, which can be displayed by clicking on the tab. Informat ion

for a test is typed into the ent ry fields on each property page after clicking on the field

where information is to be entered. Once a test has been defined, the test can be started

with a single mouse click. During the test, real time data and status information are

displayed on the monitor in numeric form or graphical form by accessing menu options.

PID

C o n t r o l o f

Load

Resilient modulus testing requires precise control of the applied load, which must

change rapidly. The applied load va lue is part of a measurab le process that uses a

feedback contro ller designed to generate an output that causes some corrective effort to

be applied so that the target load is obtained accurately. Control of the load is

accomplished by usi ng a dose d loop controller. At equally spaced time intervals, called

the control loop period, the controlle r compares the applied load measured with a load

cell to the target load. The load error is the difference between the two. The cont roller

uses this error to compute and send a signal to the servo valve to reduce the load error in

the next loop period.

The signal to the servo valve controls the val,ee's spool position. Assumi ng constant

pressure drop across the valve, flow to the hydraulic cylinder is proportional to the spool

position, which in turn is also proportional to the signal. The constant flow to the cylinder

produces a constant displacement rate of the actuator. The resulting loading rate will be

proportional to the stiffness of the test specimen. Table 1 summarizes the key

relationships that define a PID controller.

TABLE

1--PID Controller.

1 Load Error

2 DisplacementRate

3 Load Rate

4 Signal

5 Load Error Rate

6 Signal

7

8

9 Signal(I)

10 Signal(D)

t 1 Signal

= Target Load - Actual Load

= Signal * Valve Constant

= SpecimenStiffiaess * DisplacementRate

= SpecimenStiffness * Signal * Valve Constant

= Load Rate / SpecimenStifliiess Valve Constant

= Load Error / Control Loop Period

= Load Error / ControlLoop Period / SpecimenStiffness

/ Valve Constant

Proportional Gain (GP)= 1 / Control Loop Period / SpecimenStiffness Valve Constant

Signal (P) = Load Error * Proportional Gain

= Sum (Load Errors) * Integral Gain

= Change Load Error * Derivative Gain

= Signal(P) + Signal(I)+ Signal(D)

These equations contain two physical unknowns, the valve constant and the speci men

stiffness, and three system unknowns, the proportional, integral and derivative gains. The

valve constant is constant onl y if the pressure drop across the valve is constant. The



1 4 6


p r e s s u re d r o p d e p e n d s o n t h e a b il i ty o f t h e h y d ra u l i c p u m p t o m a i n t a i n t h e s u p p l y

p re s su re fo r a g iven f l ow. I t a lso depend s o n t he l oad app l i ed t o t he spec imen .

T h e s p e c i m e n s t if f n es s i s o b v i o u s l y u n k n o w n ; o t h e r w i s e w e w o u l d n o t b e r u n n i n g t h e

t e st . An e s t ima te o f t he s t i f fne s s i s no t enou gh t o run t he t e s t a ccu ra t e ly f rom s t a rt t o

f i n ish . As t he l oad ing p rog re s se s , t he s t i ffne s s o f t he spe c im en chang es .

The va r i ab l e s e rvo cons t an t and va r i ab l e spec imen s t i f fne s s r equ i r e s t ha t t he

p r o p o r t i o n a l g a i n m u s t b e c h a n g e d t h r o u g h o u t t h e t e s t t o m a i n t a in t h e t a r g e t l o a d .

C h a n g i n g t h e g a i n s e t t in g d u r i n g t h e t e s t t o i m p r o v e p e r f o r m a n c e i s c al l e d " a d a p t i v e

c o n t r o l ." T h e c o n t r o l le r c o m p u t e s a n d u s e s n e w v a l u e s o f g a i n a s t h e t es t r u n s t o a d j u s t t o

the chan g ing s t i f fne s s o f t he sys t em. S im p le P ID co n t ro l l e r s cons ide r on ly t he e r ro r in t he

load t o con t ro l t he va lve . Th ese a r e p ropor t i ona l con t ro l le r s . M ore r e f i nem en t i n t he

c o n t r o l c a n b e o b t a i n e d b y c o n s i d e r i n g t h e b e h a v i o r o f t h e l o a d e r r o r o v e r t im e . I f th e s u m

o f t he p r ev iou s l oad e r ro r s i s i nc r ea s ing , we m igh t w an t t o ad jus t t he s i gna l to t he va lve .

Th i s i s c a l l ed " i n t eg ra l ga in . " I f t he l oad e r ro r i s inc r ea s ing , w e m igh t wan t t o ad jus t t he

s igna l t o t he va lve . Th i s i s c a l l ed " de r iva t i ve ga in . " A con t ro l l e r t ha t u se s a l l th r ee

m easu re s o f e r ro r i s r e f e r r ed t o a s a P ID con t ro l le r .

As i t tu rns ou t , a sy s t em w i th P ID adap t i ve con t ro l c an ad jus t f o r chan ges i n t he va lve

cons t an t t h rou gho u t t he te s t a s we l l . The re fo re , a sy s t em w i th adap t i ve co n t ro l c apab i l i t y

on ly needs i n i ti a l e s t ima te s o f t he p ropor t i ona l , i n t eg ra l and de r iva t i ve ga ins t o s t a rt t he

t e st . The ad ap t i ve co n t ro l l e r w i l l conve rge t o t he co r r ec t ga in s e t t ings i n t he f i r s t f ew

c y c l e s o f t h e te s t a n d c o n t i n u e t o a d j u s t t h o s e s e t t in g s t h r o u g h o u t t h e t es t t o m a t c h t h e

ac tua l l oad t o t he t a rge t l oad a s c lo se ly a s pos s ib l e . F igu re 4 i l l u s tr a t e s t he t yp i ca l

ad jus tmen t s t o p ropo r t i ona l ga in du r ing one l oad s equ ence o f a r e s i li en t mo du lu s t e st .

I_2

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FIG . 4~-Proportional gain with time.



M A R R E T A L . O N A N A U T O M A T E D T E ST IN G S Y S T E M 1 4 7

T yp i ca l T es t Resul t s

The so f twa re p rog ram m enu has o p t i on t o p rodu ce a r epo r t o f t he cyc l i c phase r e su l t s i n

g raph i ca l f o rm o r i n t abu l a r f o rm and t o choo se t he s e t t i ngs fo r the g r aphs i nc luded i n t he

g raph i ca l r epo r t . I t a l so p rov ides a n op t i on fo r ed i t ing t he da t a , wh ich wi l l be u sed i n the

r epo r t . F igu re 5 shows a t yp i ca l s e t o f r e su l t s f o r a Type 1 pe r AA SH TO T-307 . F igu re 6

s h o w s a ty p i c al s e t o f r es u l ts f o r T y p e 2 p e r A A S H T O T - 3 0 7 l o ad i n g. T h e s e s i n g le p a g e

t e s t r epo r t s a r e p rodu ced au tom a t i ca l l y by the sys t em us ing da t a r educ t i on t echn iques

d i c t a t ed by t he te s t s tanda rd . T he t abu l a t ed da t a show tha t t he adap t i ve con t ro l l e r i s

con t ro l l i ng t he app l i ed dev i a to r s tr e s s t o w i th in a va r i a t i on < 1 .0 % wh en c om par ing t he

n o m i n a l m a x i m u m d e v i a t o r s tr e ss ( c o l u m n N o . 2 ) to t h e ac t u al m e a n d e v i a t o r s t re s s

( co lumn N o . 3 ) .

T A B L E 2--Nominal versus applied deviator stresses.

N o m i n a l M a x . t M e a n D e v i a t o r V a r i a t io n

De v ia to r S t r e ss S t r e ss

(kea ) (kPa ) (%)

13.8 (2ps i ) 13 .7 (1 .997 ps i ) -0 .15

27.6 (4ps i ) 27 .6 (4 .002 ps i ) 0 .05

41.4 (6ps i ) 41 .1 (5 .962 ps i ) -0 .63

55 .2 (8 ps i ) 54 .8 (7 .943 ps i ) -0 .71

68 .9 ( i 0 p s i ) 68 .6 (9 .946 ps i ) - 0 .5 4

13.8 (2ps i ) 13 .7 (1 .997 ps i ) -0 .15

27.6 (4ps i ) 27 .6 (3 .982 ps i ) -0 .45

41.4 (6ps i ) 41 .1 (5 .961 ps i ) -0 .65

55 .2 (8 ps i ) 54 .8 (7 .940 ps i ) -0 .75

68.9 (10 ps i ) 68 .4 (9 .921 ps i ) -0 .79

13.8 (2ps i ) 13 .8 (1 .998 ps i ) -0 .10

27.6 (4ps i ) 27 .5 (3 .982 ps i ) -0 .45

41.4 (6ps i ) 41 .2 (5 .971 ps i ) -0 .48

D a t a f r o m T e s t o n T y p e 1 S o il f r o m F i g u re 5

Th i s i s exce l l en t con t ro l com pare d t o o the r va r i ab l e s i n t he r e s i li en t mo du lus t e st . A

sys t em l i ke t he one desc r ibed g rea t l y r educes t he l abo r r equ i r ed t o run a re s i l ien t mo du lu s

t e s t t o p r im ar i l y t ha t r equ i r ed t o p r epa re and se t up t he te s t spec imen . T he au tom a ted

sys t em r equ i r e s m uch l e s s manua l t r i a l and e r ro r t o f i nd t he r i gh t s e t ti ngs fo r con t ro l l i ng

t h e l o ad . A d a p t i v e c o n t ro l g i v e s m u c h i m p r o v e d l o a d c o n t r o l o v e r t he c o m p l e t e d u r a t io n

o f the t e st . These f ac to r s reduce t he t e chn i c i an t ime r equ i r ed t o run t he t e st and im prov e

the tes t qua l i ty .



1 4 8 R E S I L I E N T M O D U L U S T E S T I N G F O R P A V E M E N T C O M P O N E N T S

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Con f l n ing N or a , M a x . M ean S t d . D m r M eon M e on S t d . O ev . M ean S t d . D ev .

S t r eg s D ev ia t o r D ev ia t o r O ev la t o r B u l k R e~ $ ien t R es }l len t R es i li en t R es i l i en t

S 3 S t r es s S t res . ~ S t r o s s S t r es s S t r o rn S t r a in M odu lus M odu lus

(psi) (p= ) (psr) (p~ ) Cpsi) (~) (L9 (p=i) 0 ~

5 . 9 9 9 2 1 ,9 9 7 0 . 0 0 2 9 1 9 .9 9 0 . 0 3 0 . 0 0 5 9 6 8 . 8 9 9 . 8 1 9

5 . 9 9 7 4 4 , 0 0 2 0 . 0 0 2 5 2 1 . 9 9 0 , 0 5 0 . 0 0 6 9 9 4 . 6 4 5 . 9 19

6 .0 0 1 6 5 . 9 6 2 0 . 0 0 6 6 2 3 . 9 7 0 . 0 7 0 . 0 0 7 2 8 4 . 5 5 2 . 54 . 5

6 . 0 0 8 8 7 , 9 4 3 0 . 0 0 7 5 2 5 . 9 6 0 . 0 9 0 . 0 0 7 8 5 8 .1 4 9 . 5 2 7

5 , 9 9 5 1 0 9 , 9 4 6 0 . 0 0 7 4 2 7 , 9 3 0 ,1 1 0 . 0 0 8 5 0 3 , 7 5 2 , 6 0 7

4 . 0 1 5 2 1 . 9 9 7 0 , 0 0 3 0 1 4 . 0 4 0 . 0 3 0 . 0 0 6 0 1 6 . 6 8 7 . 9 4

4 . 0 1 4 4 3 . 9 8 2 0 . 0 0 5 2 16 . 0 2 0 . 0 5 0 . 0 0 6 8 2 9 , 9 7 3 . 1 1 6

4 . 0 0 7 6 5 . 9 8 1 0 . 0 0 2 1 1 7. 9 8 0 . 0 7 0 . 0 0 7 3 3 2 . 1 7 3 . 1 9 9

4 . 0 2 5 R 7 . 9 4 0 . 0 0 3 0 2 0 . 0 1 0 . 0 9 0 . 0 0 8 t 2 0 . 8 6 1 . 5 0 5

4 . 0 1 5 1 0 9 . 9 2 1 0 . 0 1 0 3 2 1 , 9 6 0 . 1 0 0 , 0 0 8 7 1 3 . 1 4 r

2 , 0 1 2 2 1 , 9 9 6 0 , 0 0 2 7 6 . 0 3 2 0 , 0 3 0 , 0 0 6 0 8 0 6 8 , 9 0 4

2 . 0 3 7 4 3 . 9 8 2 0 . 0 0 2 9 1 0 ,0 9 0 . 0 5 0 , 0 0 6 7 9 3 . 5 3 2 . 9 1 4

2 . 04 -1 6 5 . 9 7 1 0 . 0 0 2 9 1 2 .1 0 . 0 8 0 . 0 0 7 1 9 4 . 5 5 6 . 8 8 6

2 . 0 0 6 5 7 . 9 4 3 0 . 0 0 2 4 - 1 3 , 9 6 0 . 0 9 0 . 0 0 7 8 5 4 . 8 4 8 .0 7 1

2 . 0 2 9 1 0 g . 9 3 6 0 . 0 0 5 7 1 6 . 0 2 O . 1 0 0 . 0 0 8 6 6 9 . 7 4 -5 .9 4- 1

P r o j e c t : R o o d I m p r o v e m e n t s L o c o t i o n : B o x b o r o u g h , M A P r o j e c t N o .: G I ~ - A B C

9B o r in g No ,: . . . . T e l t e d By :. r h C hec ked ~ ilkw

S a m p l e N o .: M - 3 T e ~ rt D o t e : 0 6 / 2 7 / 2 0 0 1 D e~ pth :

TI~rt N o, : R M 6 S a m p le T ) I pe : Co m p ac t ed E lev o tr on :

D es c r ip t ion : M o is L r edd i s h b rown s i l t y eond w i t h g r ov e l

R e m a r k| 9 5 ~ : o f 1 2 3 . 8 p o f O ' 8 . B Z / S u b g m d e M a t e r i a l

R l e : D : \ h e l p b o c k u p \ r r n \ 3 4 7 9 - r m 6 . d o ~

FIG. 5 - -T es t repor t f o r R M t es t ( subgrade soi l, t ype 1) pe r AA SH TO T307-9 .



M A R R E T A L. O N A N A U T O M A T E D T E S T I NG S Y S T E M

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Conf ln ing Norn. Max, Mer Std.

D ~ .

M ean M ean S t d . D ay . M ~ n S t d . D ev .

St re ss Dev iator DL, ~J r J to r Dev)ator Bulk Re~l lent Res l t ]ant Res i l rent Reoi l lent

5 3 S ~ r ~ S V e s e S t r e s s S t r e w S t ro r n S t ra i n M o d u l us M o d u l us

( P = O ( P ~ ) ( p= i ) ( p s i) ( p = O ( ~ ) ( z ) ( p = O ( ~ ' )

5 . 9 9 2 1 . 9 6 8 0 , 0 0 9 1 1 9 . 9 6 0 . 0 1 O .O 0 1 3 5 5 0 8 9 1 . 3 2

8 4 3 . 9 7 8 0 . 0 0 7 2 2 1 . 9 8 0 . 0 3 0 . 00 1 1 0 8 0 2 2 3 7 . 3 4

5 .0 0 1 6 5 . 9 6 3 0 . 0 1 0 2 2 3 . 9 9 0 . 0 6 0 . D0 8 1 1 7 . 7 5 8 . 4 5 5

6 . 0 0 6 B 7 . 9 9 2 0 . 0 0 6 5 2 6 . 0 2 0 . 1 0 0 . 0 0 8 8 6 3 .9 3 7 . 3 5 8

6 , 0 5 2 1 0 1 0 0 . 0 1 3 0 2 8 . 1 6 0 . 1 4 0 . 0 0 6 2 9 1 . 6 5 5 .2 1 1

4 , 0 0 9 2 1 . 9 9 2 0 . 0 1 t 7 1 4 . ~ 0 . 0 2 0 . 00 1 1 0 4 7 3 2 4~ .. 9 7

4 . 0 1 4 4 3 . 9 9 3 0 . 0 1 2 3 1 6. 0 3 0 . 0 4 0 . 0 0 8 0 4 2 . 4 3 1 8 . 7 5

4 . 0 4 4 6 5 . 9 7 5 0 . 0 0 9 5 1 8. 11 0 . 0 6 0 . 0 0 5 3 ,3 2 .4 6 5 . 6 5 4

4 8 7 . 9 8 3 0 . 0 1 1 9 1 9 . 9 8 O . 1 2 0 . 0 0 5 6 2 7 . 4 4 7 . 1 9

4 . n 2 9 1 0 1 0 . 0 6 0 . 0 2 B 4 2 2 . 1 5 O . 1 7 0 . 0 0 5 3 0 6 . 9 1 3 . 2 6

2 . 0 4 1 2 1 ~ 8 7 0 , 0 2 1 3 8 . 1 0 8 0 . 0 2 0 . 0 0 8 8 3 8 3 4 1, 81

2 . 0 6 4 3 , 9 8 8 0 . 0 1 2 6 1 0 .1 7 0 . 0 6 0 . 0 0 6 2 1 0 . 6 2 1 . 7 6 7

2 , 0 3 5 6 6 . 0 3 2 0 , 0 1 4 9 1 2 .1 ~ 0 . 1 i 0 . 0 0 4 8 9 7 . 1 1 9 , 8 2 2

2 . 0 4 8 8 7 . 9 7 6 0 . 0 0 6 7 1 4 . 1 2 0 . 1 6 0 , 0 0 4 4 4 5 . 6 2 8 , 1 3 6

2 , 0 4 7 1 0 1 9 . 9 5 4 0 , 0 1 1 3 1 6 .1 0 . 2 0 0 . 0 0 4 3 2 6 . 9 1 5 . 6 5 4

I

P r o j e c t R oad I m l~ rov em en t ~ L oc o tT on : B D ~ or o uc j h . M A

Borir~l No .: . . . . T e a t e d By :. rh

P r o j ec t N o . : G ' T X - A B C

Check ed By: . =kw

S a m p le N o .: M - 5 T e s t D o te : 0 6 / 2 7 / 2 0 0 1

T e s t N o .: R M 1 S a m p l e T y p e : ~ p o c t e d E l m /a l l' on : - - -

De~r Mois t , gray ish b r ow n ck~

R em ar k s : 9 5 ~ o f 1 05 . 5 po f 0 1 8 .63K / S ubgr ade I da t ~ do l

F i l e : D : ~ h e l p b a c k u p \ r m \ , 3 4 7 9 - n - n l = . d o t

. I~ lp t h: . . . .

F I G , 6- - -Tes t repor t f o r R M t es t ( subgrade soi l, t ype 2 ) pe r A AS H TO T307-99 .




I s s u es W i t h C u r r e n t T e s t S t a n d a r d s

T h e r e q u i r em e n t o f t he A A S H T O t es t s ta n d ar d s t o a p p l y a n d r e m o v e t h e d e v ia t o r lo a d

in 0.1 s ec is d i ff i cu l t and ex pens iv e t o ach ieve . I t r equ i r e s h igh pe r fo rm anc e s e rvo -va lv e

a n d f a s t e l e ct r o n ic s w i t h l it tl e n o is e . F r o m o u r o w n t e s t i n g e x p e r i e n c e d y n a m i c e f f e ct s

m a y b e c o m e s i g n if i c a n t fo r 1 2 i n c h ( 3 0 0 m m ) h i g h s p e c i m e n s w i t h a s t if f n es s t e s s t h a n

2 0 , 0 0 0 p s i ( 1 4 0 M P a ) a n d f o r 6 i n c h ( 1 5 0 m m ) h i g h s p e c i m e n s w i t h a s ti f fn e s s le s s th a n

1 0 , 0 0 0 p si ( 7 0 M P a ) . W h i l e t h e r a p i d l o a d i n g ra t e is u s e d t o m o d e l m o v i n g v e h i c l e s o n a

pav em en t sys t em, i t is no t c l ea r tha t t h i s f a s t load in g r a t e is neces s a ry t o ob t a in a

m e a n i n g f u l s t if f n es s o f a so il s p e c i m e n . T h e t e s t w o u l d b e a l o t s i m p l e r t o ru n a n d t h e

e q u i p m e n t l e s s e x p e n s i v e i f th e l o a d i n g p e r i o d c o u l d b e i n c r e a s e d t o 0 .5 s e c o n d s .

A n a c c u r a t e m e a s u r e m e n t o f t h e a x ia l d e f o r m a t i o n o f t h e s p e c i m e n is k e y to o b t a i n i n g

r e li a b le r e s il ie n t m o d u l u s r e s u lt s. W h e n t h e f ir s t A A S H T O s t a n d ar d ( T 2 9 2 - 9 1 ) c a m e o u t ,

t h e v e rt ic a l d e f o r m a t i o n w a s m e a s u r e d w i t h t w o L V D T s m o u n t e d i n t e rn a l ly a n d 1 8 0 ~

d i a m e tr i ca l ly o p p o s e d a b o u t t h e s p e c i m e n ' s a x is b y m e a n s o f c la m p s . T h i s m e t h o d m a d e

i t e x t r e m e l y d i f f ic u l t to s e t - u p a te s t s p e c i m e n . L a t e r o n , t h e t w o L V D T s w e r e c l a m p e d t o

t h e p i s to n r o d i n s id e t h e c h a m b e r . B e c a u s e o f t h e p o t e n ti a l f o r t h e t o p c a p t o r o c k , i t m a d e

s e n s e t o u s e t h e a v e r a g e v a l u e o f th e t w o L V D T s . E v e n w i t h t h i s c h a n g e , i t w a s s ti ll

d i f f i cu l t t o s e tup a t es t sp ec im en e sp ec i a l l y i f i t i s a so f t s ample . Th e m os t cu r r en t

A A S H T O s ta n d a rd s ( T 3 0 7 - 9 9 a n d T 2 9 2 - 9 4 ) u s e s tw o L V D T s e x t e rn a l ly m o u n t e d t o t h e

p i s t o n r o d . T h e t w o L V D T s n o w r e s t o n a r i g id s u r f ac e . T h e r e f o r e , th e r e i s n o n e e d t o u s e

t w o L V D T s . O n e t r a n s d u c e r w o u l d b e m o r e c o n v e n i e n t a n d s u ff i c ie n t to d e t e r m i n e t h e

ax i a l de fo rma t ion .

A A S H T O s t a n d a rd ( T 3 0 7 - 9 9 ) s p e c i f ie s l o a d c e ll c a p a c i ti e s f o r d i f fe r e n t s a m p l e s i z es

a s s u m m a r i z e d i n T a b l e 3 . T h e s p e c i fi e d c a p a c i t y is t w o t o f o u r t i m e s t h e r e q u i r ed

c a p a c it y . T h i s r e d u c e s t h e s e n s i t iv i t y o f t h e l o a d c e ll a n d m a k e s i t m o r e d i f f ic u l t t o

a c h i e v e p r e c i se c o n t r o l o f th e l o a d d u r i n g t h e te s t. T h e s t a n d a rd s h o u l d b e c h a n g e d t o

s p e c i f y t h e r e q u i re d a c c u r a c y i n t h e l o a d m e a s u r i n g s y s t e m a s a p e r c e n t o f t h e m a x i m u m

app l i ed l oad .

T A B L E 3 - - A A S H T O T 3 0 7 -9 9 l o a d c e l l c a p a c it ie s.

S p e c i m e n D i a m e t e r L o a d C e l l C a p a c i t y R e q u i re d M a x i m u m L o a d

m m k N k N

71 2.2 1.1

1 0 0

8.0 2 .2

1 5 2 2 2 . 2 5 . 0

A S T M D 4 1 2 3 p r o v i d e s a s ta n d a r d t o m e a s u r e t h e re s il ie n t m o d u l u s o f a s p h a l t s p e c i m e n s

wi th t he i nd i r ec t t ens ion t e s t. Th e t e s t i s u sed t o s t udy t he e f f ec t s o f t empera tu re , l oad in g

r a te , r e s t p e ri o d s a n d s p e c i m e n o r i e n t a ti o n o n r e s il ie n t m o d u l u s o f b i t u m i n o u s m i x t u r e s .

T h e s t a n d a r d re q u i re s d e f o r m a t i o n s t o b e m e a s u r e d t o 0 . 0 0 0 0 1 i n c h ( 0 .4 m i c r o m e t e r s ).

Th e s t anda rd s t a t e s t ha t co re s shou ld have r e l a t i ve ly sm oo th and pa ra l l e l su r f aces . I t i s no t

c l ea r w h a t r e la t iv e l y s m o o t h a n d p a r al le l m e a n s . W e k n o w f r o m w o r k i n r o c k m e c h a n i c s

u s e d f o r A S T M s t a n d a rd s D 2 9 3 8 , D 2 2 1 6 a n d D 4 5 5 3 t h a t t h e s tr e n g t h an d s t if f n e ss o f

r o c k i s s e n s i t iv e t o t h e u n i f o r m i t y o f th e t e s t s p e c im e n s . T h e s e s t a n d a rd s r e q u i r e t h e e n d s

o f t h e t e st s p e c i m e n a n d t h e l o a d i n g p l a t e n s t o b e f l a t a n d p a r al le l t o w i t h i n 0 .0 0 1 i n c h



M A R R E T A L . O N A N A U T O M A T E D T E S T IN G S Y S T E M 1 5 1

( 40 m i c r om e t e r s ) to m i n i m i ze t he e f f ec t s o f a spe r i ti e s on t he t e s t r e su lt s. I t s eem s

r easonab l e t ha t a s im i l a r r equ i r em en t shou l d be used f o r b i t um i nou s spec i m ens ,

e spec i a l l y i f one i s exam i n i ng t he e f f ec t s o f t em per a t u r e , spec i m en o r i en t a ti on , l oad i ng

r a te , and r e s t pe r i ods on r e s il i en t m odu l us .

S u m m a r y a n d C o n c l u si o n s

Hi s t o r i ca l l y t he re ha ve b een t h r ee m a i n de t e r r en ts t o r unn i ng t he r e s i li en t m o du l us te st:

t he com pl ex i t y o f t he t e s t, t he h i gh cos t o f t he equ i pm en t , and t he va r i ab i l it y o f t e s t

r e su lt s . The au t om a t ed sys t em d esc r i bed i n t h is pap e r m a kes t he t e s t e a s i e r t o r un , cos t s

l e s s than o t he r s e r vo - hydr au l i c sys t em s , and p r ov i des c ons i s t en t t e s t re su l ts b ecause o f the

u s e o f a d a p t i v e c o n tr o l. T h e s e i m p r o v e m e n t s h a v e r e s u lt e d f r o m t h e u s e o f r e ce n t

advan ces i n e lec t ron i c s , com p u t e r s and so f t w a r e toge t he r wi t h t he app l i ca t i on o f sys t em

cont ro l theory to run the t es t.

A u t om a t i on o f the t e s t ha s r educed t he m an t i m e r equ i r ed t o r un t he t es t. A u t om a t i c

r epor t i ng o f t he t e s t re su l ts r em ove s ano t he r l abo r - i n t ens i ve ta sk . D e t a il ed da t a a r e s aved

f o r each l oad cyc l e, wh i ch pe r m i t s subsequen t exam i na t i on o f any suspec t o r ques t i onab l e

tes t resul t s . Ada pt ive co nt ro l im pro ves the qua l i ty and con s i s tency o f the t est .

Tes t i ng e r r o r s can s ti ll occu r . Sp ec i m e n p r epa r a t ion r em a i ns a cha l l enge t o ob t a i n a

spec i m en a t cond i t ions r ep r e sen t a ti ve o f f ie l d cond i t ions . Th i s r equ i re s ca r e f u l

cons i de r a t ion o f com pac t i on m e t hod , den s i t y and m oi s t u r e con t en t t o ob t a in a l abo r a t o r y

spec i m en t ha t r e fl ec ts f i e l d cond i ti ons . C a r e m us t be t aken t o m i n i m i ze de f l ec ti ons ,

w h i ch can occ u r ou t si de t he spec i m e n bu t a r e inc l uded i n t he de f l ec t ion m easu r em en t ,

e spec i a l l y f o r spec i m ens w i t h h i gh r e s il ien t m od u l us . T h i s r equ i r es r i g i d connec t i ons and

f ia t, para l l e l spec im en end s to the degree poss ib le .

Res i l ien t m od u l us t e s t ing r equ i re s a know l edgeab l e t e chn i c i an who unde r s t ands t he

equ ipm ent and the t es t . The t es t resul t is qui t e sens i t ive to the cond i t ion o f the t es t

equ i pm en t , m e t hods o f spec i m en p r epa r a ti on , and de t a i l s o f the t e s t s e t up . U n l e s s t he se

de ta i l s a re carefu l ly cont ro l l ed , on e shou ld exp ec t cons iderab le var ia t ion in t es t resul t s

ob t a i ned by d i f f e ren t l abo r a to r i e s.

R e f e r e n c e s

A A S H T O 1 99 3. G u i d e f o r D e s ig n o f P a v e m e n t S tru ctu re . A m e r i c a n A s s o c i at io n o f S ta te

H i g h w a y a n d T r a n s p o r ta t io n O f f i c ia l s ( A A S H T O ) , W a s h in g t o n , D . C .

A A S H T O 1 99 7. S t a n d a r d T e s t M e t h o d f o r D e t e rm i n i n g t h e R e s il ie n t M o d u l u s o f S o il s

and Agg r ega t e Ma t e r ia l s . Assoc i a t i on o f S ta t e Hi gh w ay and Tr anspor t a t i on

Of f i c i a l s ( AASHTO) , Wash i ng t on , D . C .

A A S H T O 1 99 7. S t a n d a r d T e s t M e t h o d f o r D e t e rm i n i n g t h e R e s il ie n t M o d u l u s o f S o il s

and Agg r ega t e Ma t e r ia l s . Assoc i a t i on o f S ta t e Hi gh w ay and Tr anspor t a t ion

Of f i c i a l s ( AASHTO) , Wash i ng t on , D . C .

F H W A - R D - 9 7 - 0 8 3 . D e s i g n P a m p h l e t f o r t h e D e t e rm i n a t i o n o f D e s i g n S u b g r a d e i n

S u p p o r t o f t h e 1 9 9 3 A A S H T O G u i d e o f P a v e m e n t S tr u ct u re s . U .S . D e p a r t m e n t o f

Tr anspor t a ti on . Fede r a l H i ghw ay Adm i n i st r a ti on . Resea r ch and De ve l opm en t .

T u r n e r - F a r ib a n k H i g h w a y R e s e a r c h C e n t er , 6 3 0 0 G e o r g e t o w n P i k e . M c L e a n , V A

22101- 2296 .



S o h e i l N azar i an , 1D e r e n Y u a n , 2 a n d R o b e r t R . W i l l i a m s 3

A S imp le M e t h o d f o r D e te r min in g M o d u lu s o f B a s e a n d S u b g r a d e M a t e r ia l s

Reference: N azar i an , S . , Y u an , D . , an d Wi l l i am s , R . R . , " A S imp le M e t h o d f o r

Determining M odulu s o f Base an d S ubgrade M ater ia ls ," Resilient Modulus Testing

for Pavement Components, ASTMSTP 1437, G . N . D u r h a m , W . A . M a r r , a n d W . L . D e

G r o f f , E d s. , A S T M I n te r n at io n a l, W e s t C o n s h o h o c k e n , P A , 2 0 0 3 .

Abstract: T h e r e s il ie n t m o d u l u s t e s t is c o m m o n l y u s e d t o d e t e rm i n e t h e m o d u l u s o f b a s e

o r su b grad e m a te r ia l s a s we l l a s t o e s tab l i sh th e i r n o n l in ea r b eh av io r . S in ce th e re s i l ien t

m o d u l u s t e s t is t im e c o n s u m i n g , t h e n u m b e r o f t e st s p e r f o r m e d f o r a g i v e n p r o j e c t i s

l im i t e d. F o r d a y - t o - d a y o p e r a t i o n o f h i g h w a y a g e n c i es , a m o r e r a p i d te s t m e t h o d i s

n eed ed . T h e s t r e s s w av e (o r se i sm ic ) m e th o d i s b e in g co n s id e red in T ex as fo r t h is

p u r p o s e . S e i s m i c m e t h o d s o f t e s ti n g c a n r a p i d ly a n d n o n d e s t r u c ti v e l y p ro v i d e

fu n d am en ta l ly co r rec t m o d u l i a t k n o w n s t a t es o f s t re s s . U n l ik e th e r e s il i en t m o d u lu s t e s t ,

co m para t iv e f i e ld t e s t in g m e th o d s a re av a i l ab le fo r se i sm ic m e th o d s th a t can p ro v id e

s im i l a r re su l ts u n d er s im i l a r co n d i t io n s . T h i s paper d esc r ib es th e se i sm ic t e s t p ro ce d u re

an d i t s r e l a t io n sh ip to th e re s i l ien t m o d u lu s t e s t re su lt s . A l so d i sc u ssed a re th e

repea tab i l i ty an d r e p ro d u c ib i l i t y o f t h e r e su lt s a s a fu n c t io n o f o pe ra to r ex pe r i en ce , t ype

o f so i l, an d p repa ra t io n m e th o d .

Keywords: se i sm ic m o d u lu s , r e s i l ien t m o d u lu s , l ab o ra to ry te s t in g , b ase , su b grad e ,

qu a l i t y co n t ro l , qu a l i t y a s su ran ce

A s id e f ro m t r a f fi c an d en v i ro n m en ta l l o ad in g , t h e p r im ary pa ram ete r s th a t a f f ec t th e

p e r f o r m a n c e o f p a v e m e n t s a r e t h e m o d u l i o f i ts d i f fe r e n t la y e rs . C u r r e n t m e c h a n i s t i c -

em pi r i ca l d es ign p ro ce d u res fo r s tru c tu ra l d es ign o f f l ex ib l e pav em en t s t y p ica l ly ca l l f o r

t h e se p a r am e t e r s . T h e p r o p o s e d 2 0 0 2 A A S H T O d e s i g n g u id e s e e m s t o h e a v i l y r e l y o n

th ese pa ram ete r s a s we l t. U n fo r tu n a te ly , co n s t ru c t io n spec i f i ca t io n s a re n o t b ased o n

t h e se e n g i n e e r i n g p r o p e rt ie s . T o s u c c e s s f u l l y i m p l e m e n t a n y m e c h a n i s t i c p a v e m e n t

d es ign p ro ced u re an d to m o v e to ward pe r fo rm an ce-b ased spec i f i ca t io n s , i t i s e s sen t i a l t o

d e v e l o p t o o l s t h a t c a n m e a s u r e t h e m o d u l u s o f e a c h l a y e r in a r a p id m a n n e r . F o r a

c o m p r e h e n s i v e q u a l i ty m a n a g e m e n t o f p a v e m e n t l a y e r s, f r o m t h e d e s i g n s t a g e t o th e

co m ple t io n o f th e p ro j ec t , l ab o ra to ry an d f i e ld t e s ts sh o u ld p re f e rab ly b e ca r r i ed o u t o n a

d a i ly b as i s t o en su re a co n s i s t en t an d d u rab le h igh way . W e h av e s tu d ied a m e th o d b ased

~P ro fessor , 2 Resea rch En g in ee r , an d 3 G rad u a te Res ea rch A ss i s t an t, C en te r fo r H ig h w ay

Mate r i a l s R esea rch , T h e U n iv e r s i ty o f T ex as a t E1 P aso , 5 0 0 W . U n iv e r s i ty , E1

P aso , T X 7 9 9 68 .

152




NAZARIAN ET AL. ON DETERMINING MODULUS 153

o n s t r e ss w a v e p r o p a g a t i o n t h a t is q u i te s u i t ab l e f o r th i s p u r p o s e . T h e r e s u lt s o f o v e r f o u r

y e a r s o f e f f o rt i n d e v e l o p i n g a u s e r - fr i e n d l y s u r r o g a t e t o t h e r e s i li e n t m o d u l u s t e st s a r e

s u m m a r i z e d h e r e .

A r e v i e w o f t h e f u n d a m e n t a l s o f r e s il ie n t m o d u l u s t e s ti n g a n d t h e s t a t e -o f - p r a c t ic e i n

p e r f o r m i n g t h e s e te s ts c a n b e f o u n d i n B a r k s d a l e e t al. ( 1 9 9 7 ) a s w e l l a s a n u m b e r o f

pape r s i n t h i s pub l i ca t i on . Th e s tep -by - s t ep p roc edu re u sed to de t e rmine t he r e s i li en t

m odu l i o f d i f f e r en t ma te r i a l s i n t h i s s t udy can be foun d i n N a za r i an e t a l. ( 1999) . E i t he r

1 0 0 m m b y 2 0 0 m m ( 4 in . b y 8 in ., f o r s u b g ra d e ) o r 1 5 0 m m b y 3 0 0 m m ( 6 in . b y 1 2 i n. ,

f o r b a s e ) s p e c i m e n s w e r e c o m p a c t e d i n c y l i n d ri c a l m o l d s t o t h e m o d i f i e d p r o c t o r e n e r g y .

Th e r e si l ien t m odu lus t e s t s cons i s t ed o f app ly ing va r ious dev i a to r i c s t r e s se s a t d i ff e r en t

c o n f i n i n g p r e s su r e s . T a b l e 1 c o n t a i n s t h e s e q u e n c e f o r b a s e m a t e r ia l s . T h e l o a d i n g

s e q u e n ce u s e d w a s a m o d i f ie d f o r m o f t h e se q u e n c e f o u n d in A A S T H O T P 4 6 - 9 4 . T h r e e

t e st s a t z e r o c o n f i n e m e n t w e r e a d d e d .

Tab l e 1 -

Loading Sequence or Resilient Modulus Test

C o n f i n i n g P r e s s u r e ( k P a ) D e v i a t o r i c S t re s s ( k P a )

15 15 ( con d i t i on in g cyc l e )

0 7

0 14

0 21

21 21

21 41

21 62

3 4 3 4

3 4 6 9

34 103

6 9 6 9

69 138

6 9 2 0 7

103 69

103 103

103 207

138 103

138 138

138 276

T h e a x i a l d e f o r m a t i o n s w e r e m e a s u r e d a l o n g t h e m i d d l e o n e - t h i r d o f t h e s p e c i m e n

w i t h s ix n o n - c o n t a c t p r o x i m i t o r s e n s o r s as s h o w n i n F i g u r e 1 . T w e n t y - f i v e c y c l e s o f

l o a d i n g a r e a p p l ie d a t e v e r y s t ag e t o o p t i m i z e t e s t in g t i m e , a n d t o m i n i m i z e t h e

d e g r a d a t i o n o f t h e s p e c im e n . F r o m t h e m e a s u r e d a x i al d i s p l a c e m e n t s a t a p a r t ic u l a r

d e v i a t o r ic s t r e ss a n d c o n f i n i n g p r e ss u r e , t h e r e si li e n t m o d u l u s o f t h e s p e c i m e n w a s

de t e rmined .




F i g u r e 1 - Pho tograph and schem at i c o f re s i li en t modu lus t e s t se tup

T h e c o n s t i tu t i v e m o d e l u s e d t o d e s c r i b e t h e r e s u lt s o f t h e r e s i l ie n t m o d u l u s t e st s i s

M R = k l ~Jdk2 IJck3 (1)

w h e r e O d a n d O c a r e t h e d e v i a t o r i c s t re s s a n d c o n f i n i n g p r e s s u r e , r e s p e c t i v e l y .

P a r a m e t e r s k L , k 2, a n d k 3 a r e s ta t i s t i c a I I y - d e t e r m i n e d c o e f f i c i e n t s . T y p i c a l r e s u l t s f r o m

o n e t e st a r e s h o w n i n F i g u r e 2 , S i n c e s e i s m i c te s t s a re p e r f o r m e d a t a c o n f i n i n g p r e s s u r e

o f z e r o , a s e t o f t h r e e r e s i l ie n t m o d u l u s t e st s w a s p e r f o r m e d a t z e r o c o n f i n i n g p r e s s u r e t o

f a c i l i t a t e t h e e s t a b l i s h m e n t o f r e l a t i o n s h i p s .

~ , 2000

15oo

"~ 1000

E

.~ 500

o F

0

~ 1 0 5 k P a

~ 2 1 k P a 3 5 k P a " 7 0 k P a

?

. . . . I ' ' - ~ + ' ' ' i . . . . . . . I . . . .

I

50 100 150 200 250

De via tor i c S t r ess (kPa)

o No Conf inement * Conf inement - -Pr ed icte d Modulus i

F i g u r e 2 - Typical resi l ien t mo dulus tes t resul ts

T h e d i s a d v a n t a g e o f t h e s e i s m i c m e t h o d s i s t h a t t h e y p r o v i d e m o d u l i a t s m a l l s tr a in s

a n d t h u s r e q u i re a d j u s t m e n t f o r d e s ig n p u r p o s e s . S e i s m i c m o d u l i a r e l o w - s t ra i n , h i g h -

s t r a in - r a t e v a l u e s ; w h e r e a s t h e d e s i g n m o d u l i a r e b a s e d o n h i g h - s tr a i n , l o w - s t r a i n - r a te

v a l u e s . N u m e r o u s i n v e s t ig a t o r s i n t h e f i e ld o f g e o t e c h n i c a l e n g i n e e r i n g h a v e a d d r e s s e d



N A Z A R IA N E T A L . O N D E T E R M I NIN G M O D U L U S 1 5 5

t h is m a t t e r i n t h e p a s t 2 5 y e ar s . H o r h o t a ( 1 9 9 6 ) a n d K e e t a l. ( 2 0 0 0 ) h a v e s h o w n t w o

a p p r o a c h e s t o t h is p r o b l e m i n p a v e m e n t d e s i g n . F o r t h e s a k e o f b r e v i ty , t hi s s u b j e c t h as

n o t b e e n p u r s u e d a n y fu r th e r. T h e r e a d e r s a re e n c o u r a g e d t o r e v i e w t h e p u b l i c a t io n s

m e n t i o n e d a b o v e . B r i e f l y u n d e r th e K e e t a l. ( 2 0 0 0 ) a p p r o a c h , th e s e i s m i c m o d u l u s a n d

n o n l i n e a r p a r a m e t e r s o f e a c h l a y e r a re i n p u t t o a s tr u c tu r a l m o d e l . T h e s t ru c t u r al m o d e l

c a n b e b a s e d o n e i t h e r n o n li n e a r, l a y e r e d s o l u ti o n s o r f i n it e e l e m e n t a l g o r i t h m s . T h e

n o n l i n e a r m a t e r ia l m o d e l f o r b a s e a n d s u b g r a d e , w h i c h i s a d o p t e d f r o m B a r k s d a l e e t al .

( 1994) , i s i n t he fo rm o f :

E design = g seis ( a cu lt ) k 2 ( ( l d ul t ) k 3 (2)

(~ c_init (I d init

w h e r e E d e s i g n a n d E s e is a r e t h e d e s ig n m o d u l u s a n d s e i s m i c m o d u l u s , r e s p e c t i v e l y .

S u b s c r i p ts " u l t " a n d " i n i t " c o r r e s p o n d t o th e c o n d i t i o n w h e n t h e m a x i m u m t r u c k l o a d i s

a p p l i e d to th e p a v e m e n t a n d t h e fr e e - fi e ld c o n d i t io n , r e s p e c t iv e l y . T h e d e r i v a t io n o f

Eq ua t i on 2 can be fou nd i n K e e t a l. Pa ram e te r s k2 and k3 a r e r eg re s s io n pa ram e te r s t ha t

a r e p r e f e r a b l y d e t e r m i n e d f r o m r e si li e n t m o d u l u s l a b o r a t o r y t e s ts o n t h e s p e c i m e n . A

r e l at i o n sh i p c a n b e d e t e r m i n e d b y c o n d u c t i n g s e i s m i c t e s ts o n s p e c i m e n s t o b e t e s t e d

wi th t he t r ad i t i ona l r e s i li en t mo du lu s s e tup .

I n th i s p a p e r, t h e e x p e r i m e n t a l a n d t h e o r e ti c a l b a c k g r o u n d o f t h e s e i s m i c m o d u l u s t e st

i s de sc r i be d f i rs t . The t y p i ca l r e su lt s and t r ends a s we l l a s t he r epea t ab i l i t y o f t he t e s t

m e t h o d s a r e d e m o n s t r a te d . F i n a ll y , t h e c o r r e la t i o n b e t w e e n t h e s e i s m i c a n d r e si li e n t

m odu lus t e s t r e su l t s i s p rov ided .

Seismic Modulus Test

T h e f r e e - fr e e r e s o n a n t c o l u m n t e s t is a s i m p l e l a b o r a t o r y t e s t f o r d e t e rm i n i n g t h e

m o d u l u s o f p a v e m e n t m a te r ia ls . T h e m o d u l u s m e a s u r e d w i t h th i s m e t h o d is th e l o w -

s t ra i n s e is m i c m o d u l u s . T h e m e t h o d w a s o r i g i n a l l y d e v e l o p e d f o r t e s t in g P o r t l a n d

c e m e n t c o n c r e t e s p e c i m e n s ; h o w e v e r , w i t h a p p r o p ri a te m o d i f i c a t i o n s in h a r d w a r e a n d

so f twa re , i t i s a l so app l i cab l e t o spec ime ns o f ba se an d subgrad e ma te r i a l s . S ince t he

s e i sm i c t e s ts a r e n o n d e s t ru c t i v e , a m e m b r a n e c a n b e p l a c e d a r o u n d t h e s p e c i m e n s o t h a t it

c an be t e s t ed la t e r f o r s t i ffne s s ( re s i li en t modu lus ) . Pe r f o rm ing bo th t e s ts s im u l t ane ous ly

w i l l a l lo w h i g h w a y a g e n c i e s t o d e v e l o p a d a t a b a s e th a t c a n b e u s e d t o s m o o t h l y u n i f y t h e

des ign pa rame te r s and cons t ruc t i on qua l i t y con t ro l a s de sc r ibed i n N aza r i an e t a l . ( 2002) .

W h e n a c y l in d r i c a l s p e c i m e n i s s u b j e c t e d t o a n i m p u l s e l o a d a t o n e e n d , s e i s m i c

e n e r g y o v e r a la r g e r a n g e o f f r e q u e n c i es w i l l p r o p a g a t e w i t h i n t h e s p e c i m e n . D e p e n d i n g

o n t h e d i m e n s i o n s a n d t h e s ti f fn e s s o f t h e s p e c i m e n , e n e r g y a s s o c i a te d w i t h o n e o r m o r e

f r e q u e n c i es a r e t r a p p e d a n d m a g n i f i e d ( r e s o n a te ) a s t h e y p r o p a g a t e w i t h in t h e s p e c i m e n .

The go a l w i th t h is t e st is t o de t e rm ine t he se r e son an t f r equenc i e s . S ince t he d im ens ion s

o f t h e s p e c i m e n a r e k n o w n , i f o n e c a n d e t e r m i n e t h e f r e q u e n c y ( i e s ) t h a t a re r e s o n a t i n g

( i.e . t h e r e s o n a n t f r e q u e n c ie s ) , o n e c a n r e a d i ly d e t e r m i n e t h e m o d u l u s o f th e s p e c i m e n

u s i n g p r i n c i p le s o f w a v e p r o p a g a t i o n i n a s o l i d r o d ( s e e R i c h a r t e t a l. , 1 9 7 0 f o r th e

theo re t i ca l background) .

T h e p r o c e d u r e u s e d i n t h e s e is m i c t e st is to f i n d t h e Y o u n g ' s m o d u l u s b y m e a s u r i n g

t h e v e l o c i t y t h a t a w a v e p r o p a g a t e s t h r o u g h a c y li n d r i c a l s p e c i m e n a n d c o m b i n i n g t h o s e

r e s ul ts w i t h o t h e r m e a s u r a b l e p r o p e r ti e s . T h e s c h e m a t i c o f t h e te s t s e t u p i s s h o w n i n

F i g u r e 3 . T o p e r f o r m t h e t e s t an a c c e l e r o m e t e r i s p l a c e d s e c u r e l y a t o n e e n d o f a



1 5 6 R E S I LI E N T M O D U L US T E S T I N G F O R P A V E M E N T C O M P O N E N T S

spec i m e n , and t he o t he r end i s t apped w i th a ham m er t ha t ha s a l oad ce l l a tt a ched t o i t.

The t w o senso r s a r e connec t ed t o a da t a acqu i s i ti on sys t em p l ace d i n a lap t op com pu t e r .

S o f t w a r e h a s b e e n d e v e l o p e d t o a c q u i re a n d m a n i p u l a t e t h e t i m e r e c o r d s f r o m t h e

acce l e r om e t e r and the l oad ce ll . Typ i ca l t i m e r eco r ds a r e show n i n F i gu r e 4 . The l oad

cons i s t s o f a sho r t - du r a t ion ha l f - s ine pu ls e . The r e spo nse m ea su r ed w i t h t he

acce l e r om e t e r con t a i ns an osc i ll a t ion t ha t co r r e spon ds t o t he s t and i ng w ave en e r gy

t r apped wi t h i n t he spec i m en .

Figure 3 -

Photograph and schematic o f ree-free resonant column te st setup

Load Cell

~

~ m e t e r

I . . . . I I . . . . I r

0 10 20 30 40 50

Tim e (msec)

F i gu r e 4 -

Typical load cell and accelerometer responses fro m free-free tes t

A m o r e c o n v e n i e n t w a y o f d e te r m i n i n g th e f r e q u e n c y o f o s ci ll a ti o n c o n s i s ts o f

t r ans f o r m i ng the t wo s i gna ls i n to t he f r equenc y- dom a i n us ing a f a s t - Four i e r t r ans f o r m

and t hen no r m a l i z i ng the acce l e r a t i on am pl i t ude wi t h t he l oad am pl i t ude . Th e va r i a ti on

of no r m a l i zed am p l i tude a s a f unc t ion o f f r equency , wh i ch i s c a l l ed a t r ans f e r func t i on ,

con t a i ns peaks t ha t co r r e spond t o t he o sc i l la t i on o f t he s t and i ng wa ves . A t yp i ca l t r ans f e r

f u n c t io n i s s h o w n i n F i g u re 5 w i t h th e p e a k f r e q u e n c y c l e a r ly m a r k e d . K n o w i n g t h e



N A Z A R IA N E T A L . O N D E T E R M I NI NG M O D U L U S 1 5 7

r e s o n a n t f r e q u e n c y , fp , m a s s d e n s it y , p , a n d t h e l e n g t h o f t h e s p e c i m e n , L , Y o u n g ' s

m o d u l u s , E , c a n b e f o u n d u s i n g :

E : p (2 fp L)2 : P (Vp)2

(3)

w h e r e V p is t h e c o m p r e s s i o n w a v e v e l o c i t y .

Longitudinal Resonance ( f p ~

/ \

' ' ' I . . . . I . .. .. .. + - - ~ ' ' I . . . . ', . . . . I . . . . I ~ ' .- -- + -~ ' ' I . . . . . .

0 100 200 300 400 500 600 700 800 900 1000

Frequenc y (Hz)

F igu re 5 - Typical free-fr ee test transfer fun ct ion

Th e sam ple p r epa ra t i on desc r ibed fo r t he r e s i li en t mo du lus t e s t i s a l so app l i cab l e he re .

S i m i l a r t o th e r e s il ie n t m o d u l u s t e st s, a h e i g h t - t o - d i a m e t e r r a t io o f 2 i s r e c o m m e n d e d f o r

s p e c i m e n s . H o w e v e r , i f n e c e s s a r y , th i s c a n b e r e l a x e d t o 1 .5 . A n o t h e r i m p o r t a n t p r a c ti c a l

i s su e is s e c u r i n g th e a c c e l e r o m e t e r t o t h e s p e c im e n . W e h a v e f o u n d th a t a ro o f i n g n a i l

e m b e d d e d i n t h e s p e c i m e n d u r i n g c o m p a c t i o n p r o v i d e s a c o n v e n i e n t p e d e s ta l f o r

s e c u r i n g t h e a c c e l e r o m e t e r w i t h a m a g n e t . W e h a v e a l s o f o u n d t h a t a n a i l p l a c e d o n t h e

o p p o s i t e s i d e w i l l p r o v i d e a n i c e a n v i l f o r t h e h a m m e r .

P r e s e n t a t i o n o f R e s u l t s

M a j o r c o n c e r n s w i t h a n y t e s t p r o c e d u r e a r e t h e r o b u s t n e ss , r e p e a t a b i l i ty o f t h e

me asu rem en t s . Th ese ma t t e r s a r e r epo r t ed he re fi r st . Th ree ma te r i a l s ( a t yp i ca l ba se , a

s a n d , a n d a c la y ) w e r e u s e d f o r t h is p u r p o s e . T h e b a s e s p e c i m e n s w e r e n o m i n a l l y 1 5 0

m m ( 6 i n. ) i n d i a m e t e r b y 3 0 0 m m ( 1 2 in .) i n l e n g th w h i l e t h e s a n d a n d c l a y s p e c i m e n s

w e r e n o m i n a l l y 1 0 0 m m ( 4 in .) b y 2 0 0 m m ( 8 in .). T h e c l a y m a t e r i a l i s a h i g h l y -p l a s t ic

c l a y f r o m D a l l as a r e a , a n d m a i n l y c o n s i s t e d o f m a t e r i a ls p a s s i n g N o . 2 0 0 s ie v e . T h e

l iq u i d a n d p l a st i c l im i t s o f t h a t m a t e r ia l w e r e 6 5 % a n d 2 4 % , r e s p e c t i v e ly . T h e s a n d i s

p r i m a r i l y f in e a n d m e d i u m s a n d w i t h s o m e s m a l l a m o u n t o f si lt a l s o f r o m t h e D a l la s a r e a .

T h e o p t i m u m m o i s t u re c o n t e n ts o f th e t w o m a t e r ia l s w e r e a b o u t 1 8 % a n d 8 % f o r t h e

f i ne -g ra ined and coa r se -g ra ined ma te r i a l s , r e spec t i ve ly .




Best Test Conf igurat ion

A l e x a n d e r e t al. ( 1 9 9 6 ) e s t i m a t e t h a t th e r e p e a t a b i li t y o f t h e m e t h o d o n c o n c r e t e

s p e c i m e n s i s b e t te r t h a n 1 % . B u t b e c a u s e o f t h e a t te n u a t io n o f s i g n a ls i n s o f t e r g r a n u la r

m a t e r ia l s a n d th e s e n s i t i v it y o f t h e m o d u l u s t o c h a n g e i n m o i s t u r e a n d u n i f o r m i t y o f

c o m p a c t i o n , s u c h a l e v e l o f r e p e at a b i li t y c a n n o t b e a c h i e v e d i n b a s e a n d s u b g r a d e

ma te r i a l s . Ev en t hou gh t he r e sonan t f r equen c i e s i n t he s e i smic t e st s a r e no t s ens i t i ve t o

t h e l o c a t io n s o f t h e a c c e l e r o m e t e r a n d i m p a c t o n t h e s p e c i m e n e n d s , t h e a m p l i tu d e

a s s o c i a te d w i t h e a c h r e s o n a n c e v a r i e s w i t h th e s e t w o p a r a m e t e r s . F o r t u n a t e ly , t h e

a m p l i t u d e s a r e n o t i m p o r t a n t a t a ll a n d o n l y t h e f r e q u e n c i e s a t w h i c h t h e p e a k a m p l i t u d e s

( r e sonan t f r equenc i e s ) o ccu r a r e s i gn i fi can t . H ow eve r , it i s de s i r ab l e t o p ro pos e l oca t i ons

w h e r e t h e r e s u l ts a r e m o r e r o b u s t .

A s e r ie s o f t e s ts w e r e c o n d u c t e d o n a b o u t e i g h t - d o z e n s p e c i m e n s t o s t u d y t h is

p h e n o m e n o n . A s r e f l e c t e d in F i g u re 6 , t h i r ty - f i v e p o s s i b l e c o m b i n a t i o n s o f i m p a c t ( l o a d

c e ll ) a n d r e c e i v e r ( a c c e l e ro m e t e r ) l o c a t i o n s t h a t w o u l d p r o d u c e a p r i m a r y w a v e w e r e

t r ie d o n e a c h s p e c im e n . F o r c o n v e n i e n c e , t h e s p e c im e n s w e r e i m p a c t e d o n t o p .

T h u m b t a c k s w e r e p l a c e d i n a s i d e w a y s " T " s h a p e t o d i s t in g u i s h t h e d i f f e r e n t lo c a t i o n s

a n d t o p r o v i d e a p la c e t o h i t t h e s p e c i m e n . T h e b o t t o m o f t h e s p e c i m e n , w h e r e t h e

r e c e i v e r is p l a c e d c o n s i s ts o f a n " L " s h a p e w i t h l o c a t io n A b e i n g a c r o s s f r o m 1 , B f r o m 2 ,

a n d s o o n .

T O P

e j

BOTTOM

\ \

Figure 6 -

Source and re c e i ve r loca tions

Sta t is t i c a ll y , the ma jo r i t y o f t he te s t s con f igu ra t i on s y i e lded repea t ab l e r e su l t s. Th e

b e s t t e st s e t u ps s e e m t o b e w h e n t h e s o u r c e i s p l a c e d n e a r t h e c e n t e r o f t h e s p e c i m e n

( w i t h in o n e - t h ir d o f t h e ra d i us ) . T h e l o c a t io n o f t h e r e c e i v e r w o r k e d b e s t w h e n i t w a s

p l a c e d o n t h e s a m e h a l f o f t h e s p e c i m e n a s t h e s o u r c e b u t n o t b e y o n d t w o - t h i r d s r a d iu s

o u t f r o m t h e c en t e r. L o c a t i o n s A 1 , C 1 , a n d E 1 p r o v e d t o p r o v i d e r es u l ts t h a t w e r e h i g h l y

repea t ab l e . I f on ly t he A1 ( cen t e r - t o - cen t e r ) t e s t com bina t i on i s u sed , t he r e i s l e s s o f a

c h a n c e t o g e n e r a t e d e te c t a b le s h e a r e n e r g y . T h u s , i t is r e c o m m e n d e d t o t e st w i t h t h e C 1

o r E 1 c o n f i g u r a t i o n i n a d d i ti o n t o A 1 .



N A Z A RI A N E T A L . O N D E T E R M IN IN G M O D U L U S 1 5 9

Repeatability o f Tests

T h e v a r i a ti o n i n m o d u l u s w i t h m o i s t u r e f o r th e c l a y , s a n d a n d b a s e m a t e r i al s a r e

s h o w n i n F i g u r e 7 . F r o m F i g u r e 7 a , t h e c l a y e x h i b it s a p e a k s e i s m i c m o d u l u s a t w a t e r

c o n t e n t o f a b o u t 1 3 % . A r e l a t iv e l y la r g e n u m b e r o f s p e c i m e n s w e r e p r e p a r e d t o

d e m o n s t r a t e t h e r e p e a t a b i li t y a n d re p r o d u c i b i l i ty o f t h e te s t m e t h o d . T h e g o a l w a s t o

p r e p a r e t h e s p e c i m e n s a t s ix d i sc r e te w a t e r c o n t e n t s. S o m e v a r i a b i li t y b e t w e e n t h e ta r g e t

a n d a c t u a l m o i s t u r e c o n t e n t s a re o b s e r v e d . N e v e r t h e l e s s , t h e r e su l ts f o l l o w a re a s o n a b l y

t i gh t tr end , dem ons t r a t i n g t he r ep rod uc ib i l i t y o f t he re su l ts .

T h e s a n d y m a t e ri a l d e m o n s t r a t e s a d if f e re n t t r e n d a s re f l e c t e d in F i g u r e 7 b . T h e

m o d u l u s i n c r e a s e s w i t h a d e c r e a se i n m o i s t u r e c o n t e n t u n t il a p o i n t ( s a y 3 % ) . B e l o w t h a t

m o i s t u r e c o n t e n t , t h e s p e c i m e n s a r e so f r a g il e th a t t h e y c o u l d n o t s t a n d a l o n e w i t h o u t

c r a c k in g . A s s u c h , t h e ir m e a s u r e d m o d u l i a r e q u i t e l o w . I g n o r i n g t h e m o d u l i f r o m

s p e c i m e n s w i t h m o i s t u r e c o n t e n t s b e l o w 3 % , t h e r e s u lt s a r e a g a i n r e a s o n a b l y r e p e a t a b l e

and fo l l ow a ti gh t t r end .

The base ma te r i a l , a s shown in F igu re 7c , exh ib i t ed l a rge va r i ab i l i t y i n ou r

expe r im en t . S ince the te s t m e tho d is r epea t ab l e on o the r ma te r i a ls , t he va r i ab i l i t y wa s

a t tr i b u te d t o t h e s p e c i m e n p r e p a r a t i o n m e t h o d . A v i s u a l o b s e r v a t i o n o f t h e s p e c i m e n

d e m o n s t r a t e d s e g r e g a t i o n o f m a t e r ia l s d u r i n g s p e c i m e n p r e p a r a ti o n . S e v e r a l s te p s w e r e

t a k e n to a d d r e ss t h is i ss u e. T h e s a m p l e p r e p a r a ti o n m e t h o d w a s m o d i f i e d t o in c o r p o r a t e

a t h o r o u g h m i x i n g o f t h e m a t er i a ls b e f o r e a n d d u r i n g t h e s p e c i m e n p r e p a r a t io n . T h e

ma te r i a l s u sed fo r each l i ft wa s ensu red t o v i sua l l y con t a in a ba l an ced d i s t r i bu t i on o f a l l

a g g r e g a t es . A g g r e g a t e la r g e r t h a n 2 5 .4 m m (1 i n .) w a s a l s o r e m o v e d f r o m t h e s a m p l e .

E a c h l i f t w a s d e e p l y s c a r i f ie d t o e n su r e i n t im a t e a n d s e a m l e s s c o n t a c t b e t w e e n e a c h

layer.

T h e o t h e r p a r a m e t e r t h a t w a s s t u d ie d w a s t h e m e t h o d o f c o m p a c t i o n - m a n u a l ( h a n d )

o r m e c h a n i c a l ( m a c h i n e ) . W e d e t e r m i n e d t h a t t h e tw o m e t h o d s p r o v i d e c o n s i s t e n t r e s u lt s

a s l o n g a s th e c o m p a c t i o n d e v i c e i s ro u t i n e l y a n d c a r e f u l l y m a i n t a i n e d a n d i t s ca b l e s w e r e

s t r e t ched p rope r ly . Af t e r t he se m od i f i ca t i on s , ano th e r r epea t ab i l i t y s t ud y w as ca r r i ed ou t .

T h e s p e c i m e n s p r e p a r e d u s i n g th e m a c h i n e y i e l d s i m i l a r r e s u lt s w i t h a m u c h s m a l l e r

c o e f f i c i e n t o f v a r ia t io n . A s i s e v i d e n t in F i g u re 8 , " i d e n t i c a l " s p e c i m e n s p r e p a r e d w i t h

p r e c a u t i o n y i e l d r e p e a t a b l e r e su l ts w i t h o n l y o n e o u t li e r. T h e c o e f f i c i e n t o f v a r i a ti o n

d r o p s f r o m 1 8 % t o 9 % w h e n t h e o u t l ie r is r e m o v e d . I n s u m m a r y , t h e s e c o r re c t i v e

m e a s u r e s n o t o n l y h a v e s i g n i f ic a n t l y im p r o v e d t h e r e p e a t a b i l it y o f t h e s e i s m i c t e s ts o n

b a s e m a t e r i a ls , t h e y h a v e a l s o i m p r o v e d t h e re p e a t a b i l it y o f t h e r e s il ie n t m o d u l u s a n d

t ri a x ia l t es ts c o n d u c t e d . M a c h i n e c o m p a c t i o n i s r e c o m m e n d e d b e c a u s e t h e r e i s l e ss

v a r i a ti o n f r o m s p e c i m e n - t o - s p e c i m e n a n d o p e r a t o r - t o - o p e r a t o r t h a n a r i se s w i t h h a n d

c o m p a c t i o n .

Th e o the r pa ram e te r t ha t shou ld be con t ro l l ed i n t h is and o the r t e s ts i s the t ime

b e t w e e n t h e p r e p a r a t i o n o f t h e s p e c i m e n a n d te s ti n g . O n o n e h a n d , th e s p e c i m e n " c u r e s "

wi th t ime ; t ha t is i ts s tr eng th and m odu lus i nc r ea se s . On t he o the r hand , t he spec ime n

" d r ie s o u t " w i t h t im e . T o m i n i m i z e t h e l o s s o f m o i s t u r e w i t h ti m e , i t is e s se n t ia l t o c o v e r

t h e s p e c i m e n a s s o o n a s it is p r e p a re d . F i g u r e 9 d e m o n s t r a t e s t h e i m p a c t o f ti m e f r o m

s p e c i m e n p re p a r a t i o n o n t h e m e a s u r e d m o d u l u s f o r a s a n d y m a t e ri a l w h e n p r o p e r

p recau t i ons a r e no t t aken t o m in im ize mo i s tu r e l o s s . As a no t e , t he se t e st s we re

c o n d u c t e d i n E1 P a s o w h e r e t h e r e l a ti v e h u m i d i t y i s n o r m a l l y e x t r e m e l y l o w ( le s s t h a n



160

R E S I L I E N T M O D U L U S T E S T I N G F O R P A V E M E N T C O M P O N E N T S

600

500 9149

400

, , o : o

300 " " "

9 9 0 0 9

" ~ 2 0 0 8 9

100

o - L ~ . .. .. . ~ J ~ . . . .. .. + ~ . .. .. . . .. . ~ . .. .. I ,,

0% 5% 10% 15% 20% 25%

Moisture (%)

a) Clay

30%

700

600

500

400

T

b) Sand

O 0 O

I %

.~ 300 9 " ~

200 .

~ 5 ,

100 9 w o

0% 2% 4% 6% 8% 10% 12% 14% 16%

Moisture (%)

600

500

,~ 400

300

7 200

100

; 9 9

c ) B a s e

9 oo

0

. . . . 1- . . . F ~ I . . . . I . . . . I ' ' ~ - ~ = - ~ - H = ~ - ~ + ~ - = ~ - ~

0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10%

Moisture (%)

F i g ur e 7 - M o i s t u r e - m o d u l u s plots fo r a) clay, b) sand, and c) base

1 5 % ). T h e m o d u l u s c h a n g e d f r o m d a y - t o - d a y i n m a g n i t u d e . S p e c i m e n s d r y o f a n d n e a r

t h e p e a k o n t h e m o d u l u s - m o i s t u r e c u r v e t en d e d t o h a v e m o d u l i t h a t i n c r e a se d s l ig h t ly a s

t h e d a y s p r o g re s s e d . S p e c i m e n s w e t o f t h e p e a k g e n e r a l l y h a d m o d u l i t h a t d e c re a s e d

s l i gh tl y o r s t ayed t he s am e wi t h ti m e . W i t h the i nc r ea se in ti m e be t w een s pec i m en



NAZARIAN ET AL. ON DETERMINING MODULUS 161

300

250

' 7 2 0 0

. o l O O

5oT

0 A_

[ 9 Modulus o Out lier - -A ve rag e /

F igu re 8 -

Seismic modulus of samples prepared with precautionary measures

p r e p a r a t i o n a n d t e s t in g t h e d a t a b e c a m e i n c r e a s i n g l y s c a tt e re d . F o r t h e f i r st 2 4 h o u r s ,

s i m i la r s p e c i m e n s y i e l d si m i l a r m o d u l i . A c a r e f u l o b s e r v a t i o n o f F i g u r e 9 d e m o n s t r a t e s

tha t d i f f e r en t spec imens p r epa red a t s imi l a r wa t e r con t en t l o se mo i s tu r e a t d i f f e r en t r a t e s ,

h e n c e m o r e s c a t t e r in th e t e s t r e su l ts . B a s e d o n th i s s t u d y , w e r e c o m m e n d t h a t e i t h e r

s a n d s p e c i m e n s b e t e s te d a b o u t 2 4 h o u r s a f te r p r e p a r a t i o n o r th e s p e c i m e n s b e m a i n t a i n e d

i n a m a n n e r t h a t t h e m o i s t u r e l o s s i s m i n i m a l .

v

00

~ 5 0 0 ;

400 '~

9 +

300 ~ . . ~ "~

200 a

100 ~ ~ S

i ! , , ~ ~ ~

0 % 2 % 4% 6 % 8 % 10% 12% 14% 16%

Moisture (%)

i . D a y 0 x D a y l o D a y 2 + D a y 3 ]

F igu re 9 - Overall modulus-moisture plot for sand material

A s i m i l ar e x p e r i m e n t w a s c a r r ie d o u t f o r t h e cl a y . E v e n t h o u g h n o t s h o w n h e r e, t h e

c l a y m a t e r ia l c a n b e t e s t e d o n a n y d a y w i t h v i r t u a l ly n o d i f fi c u lt i es a n d w i t h r e l a t iv e l y

s m a l l c h a n g e s i n t h e m o d u l u s f r o m d a y t o d a y a s l o n g a s it is p r o t e c t e d f r o m m o i s t u r e

l o ss . O v e r t h e fo u r d a y s o f t e st in g , t h e m o d u l u s c h a n g e d v e r y li tt le a n d t h e d a t a d i d n o t

sca t te r f o r ind iv idua l spec imen s .

U n d e r t h e n e w s p e c i m e n p r e p a r a t io n p r o t o c o l , t h e b a s e b e c a m e e a s i e r t o t e s t a s t h e

d a y s p r o g r e s s e d s i n c e t h e s p e c i m e n w a s m a t u r i n g . T h e o p t i m u m t i m e t o te s t t h e b a s e

m a t e r i a l w a s t h e f ir s t 4 8 h o u r s a f te r th e p r e p a r a t i o n o f t h e s p e c i m e n w i t h a p p r o p r i a t e

a t te n t i o n t o m i n i m i z i n g t h e l o s s o f m o i s tu r e .




R e l a t in g S e i sm i c M o d u l u s t o O t h e r S t r e n g th a n d S t i f fn e s s P a r a m e t e r s

On e im por t an t qua l i t y i nd i ca to r o f t he ma te r i a l s i s t he t r iax i a l s t r eng th o f a ma te r ia l .

N a z a r i a n e t al. ( 2 0 0 2 ) d e s c r i b e a n a t t e m p t b y a h i g h w a y a g e n c y t o re l a te s e i s m i c m o d u l u s

t o th e s t r e n g th o f a b a s e m a t e ri a l. T h e v a r i a t i o n i n c o m p r e s s i o n w a v e v e l o c i t y , V p, w i th

the a ngle o f in te rna l f r ic t ion , d~, i s sho w n in Fig ure 10 .

A s E q u a t i o n 3 i n d ic a t es , t h e c o m p r e s s i o n w a v e v e l o c i t y a n d s e is m i c m o d u l u s a r e

r e l a te d t h r o u g h d e n s i ty . S i n c e th e c o m p r e s s i o n w a v e v e l o c i t y i s a n i n d e p e n d e n t v a r i a b l e

w h e r e a s t h e m o d u l u s i s re l a te d t o t w o i n d e p e n d e n t v a r i ab l e s ( c o m p r e s s i o n w a v e v e l o c i t y

and dens i t y ) , it i s m ore des i r ab l e t o dev e lop co r r e l a t i ons ba se d on th i s pa r am e te r . Th i s

w i l l e li m i n a t e t h e e f f ec t s o f d e n s i t y w h e n c o m p a r i n g t h e c o m p r e s s i o n w a v e v e l o c i t y t o

the ang l e o f i n t e rna l f r i c t ion . The co r r e l a t i on be tw een t he se tw o pa ra me te r s (V p and d~) i s

q u i te r e a so n a b l e , e s p e c i a l l y f o r s t r o n g e r b a s e s. C o r r e l a t io n s s u c h a s th e o n e s h o w n c o u l d

p e r m i t a n e v o l u t i o n a r y t r an s i ti o n f r o m t h e s t a n d a r d q u a l i ty c o n t r o l b a s e d o n m o i s t u r e -

d e n s i t y t o a m o r e m e c h a n i s t i c - b a s e d a p p r o a c h t h a t t a k e s i n t o a c c o u n t o t h e r p a r a m e t e r s

such a s mo du lu s and i n t e rna l f r i c ti on .

z

r,.)

350

300

250

200

150 I

100

50

0 ' '

0

Vp =0 .116 42-3.54 ~b + 139

Rz = 0.82

I ~ ' - ~ -

'

'

~ -

20 30 40

Angle of InternalFriction,~ (degrees)

Z

~a2

~ H - - - . . . . . . . I

10 50 60

Figure 10 -

Corre la tion b e tween s t reng th par am e te r a nd com press ion w ave ve loc i t y o f a

base f ro m one d i s t r ic t

T h e r e s i li e n t a n d s e i s m i c m o d u l i w e r e a l s o c o m p a r e d t o d e v e l o p a m o d e l t h a t r e la t es

the se two t e s ts . A d e t a i l ed desc r ip t i on o f p roce s s can be fou nd i n W i l l i ams e t a l. ( 2002) .

F o r t h e sa k e o f b r e v i t y , w e h a v e d e m o n s t r a t e d a n e x a m p l e . S i n c e t h e s p e c i m e n s a r e n o t

s u b j e c t e d t o c o n f i n e m e n t w h e n t h e s e i s m i c t es t i s p e r f o r m e d , r e s il ie n t m o d u l u s v a l u e s f o r

t h e u n c o n f i n e d t e s t w e r e u s e d i n t h is a n a l y s i s e v e n t h o u g h t h e r e s il ie n t m o d u l u s t e s t w a s

p e r f o r m e d a t s e v e r al d i f f e re n t c o n f i n i n g p re s s u re s . T h e r e s u l ts f r o m t e s ts o n a b o u t t w o -

d o z e n s o i l s ar e s h o w n i n F ig u r e 1 1. T h e r e l a t io n s h i p b e t w e e n t h e t w o m o d u l i i s m o r e o r

l e s s l inea r . A s i nd i ca t ed be fo re , t he unc onf in ed MR t e s ts we r e adde d t o t he te s t p ro to co l

f o r t h is p u r p o s e . T h i s d o e s n o t i m p a c t t h e g e n e r a l i t y o f t h e r e si li e n t m o d u l u s d a t a s i n c e

t h e c o n s t it u t iv e m o d e l d e s c r i b e d i n E q u a t i o n 1 , c a n b e u s e d t o d e t e r m i n e t h e m o d u l u s a t

a n y o t h e r s t at e o f s tr es s . T h e r a t io o f s e i s m i c m o d u l u s t o r e s i li e n t m o d u l u s i s

a p p r o x i m a t e l y t w o t o o n e w i t h a n R 2 v a l u e o f a b o u t 0 . 8 . F i g u r e 1 1 c o n ta i n s d a t a f r o m

tes ts on seve ra l d i f fe r en t ma te r i a ls and ma te r i a l t ypes . Th e co r r e l a t i on can be imp rov ed



N A Z A R I A N E T A L . O N D E T E R M I N IN G M O D U L U S 1 6 3

7 0 0

600 I

~ 5 0 0

400

300

.~ 200

1 o o [

0

MR = 0.4713

E

R2 = 0.7771

9 | 9 9 9

i i i i , i i i

0 100 200 300 400 500 600 700 800 900 100 0

Seismic Modulus (MPa)

Figure 11 -

U n c o n f i n e d r e s i l i e n t m o d u l u s a v e r a g e v s. s e i s m i c m o d u l u s

b y d e v e l o p i n g r e la t io n s h i p s f o r in d i v i d u a l m a t e r ia l t y p e s . T h e s e m e t h o d s a n d o t h e r

m e t h o d s c a n b e u s e d t o f u r th e r e x p l o r e th e r e l at i o n s h ip b e t w e e n t h e r es i li e n t m o d u l u s a n d

t h e s e is m i c m o d u l u s , a n d e x p l o r e d t h o r o u g h l y in W i l li a m s e t al. ( 2 0 0 2 ) .

S u m m a r y a n d C o n c l u s io n s

T h e s e i s m i c m o d u l u s t e s t is a r a p i d a n d a c c u r a te w a y t o d e t e r m i n e t h e m o d u l u s o f

b a s e a n d s u b g r a d e m a t e ri a ls . T h i s m e t h o d w i l l a i d in th e i m p l e m e n t a t i o n o f a

m e c h a n i s ti c p a v e m e n t d e s i g n p r o ce d u r e a n d t o m o v e t o w a r d p e r f o r m a n c e - b a s e d

spec i f i ca t i ons .

I n th i s p a p e r , t h e s e i s m i c m o d u l u s t e s t w a s a n a l y z e d u n d e r s e v e r a l d i f f e r e n t c o n d i ti o n s

a n d c o m p a r e d w i t h s e v e r a l p a r a m e t e rs . T h e p r a c t i c a l it y o f t h e te s t i n re l a t io n t o m o i s t u r e

c o n t e n t, ti m e , a n d p r e p a r a t io n m e t h o d w a s e x a m i n e d t o d e t e r m i n e t h e b e s t w a y to

p e r f o r m s e i s m i c t es t s o n b a s e a n d s u b g r a d e m a t er ia l s. F u r t h e r m o r e , s e i s m i c m o d u l u s t e st

d a t a w e r e c o m p a r e d w i t h d a t a f r o m o t h e r t es ts i n a n a t t e m p t t o d e v e l o p c o r r e l a t io n s

a m o n g t h e m . T h e r e s il ie n t m o d u l u s a n d t h e an g l e o f i n te r n a l f r i c ti o n w e r e c o m p a r e d

wi th t he s e i sm ic t e s t r e su l ts t o sh ow the a pp l i ca t i ons o f t he s e i smic t e s t i n r e l a t i on t o

those tes t s .

T h e b e s t t e s t c o n f i g u r a t i o n c o n s i s ts o f t h e s o u r c e w i t h i n o n e - t h i r d r a d i u s o f t h e c e n t er .

T h e r e c e i v e r c a n b e p l a c e d a n y w h e r e w i t h i n t w o - t h i rd s r a d i u s o f t h e c e n t e r i f t h e s o u r c e

i s i n th e c e n t er . F r o m t e s t i n g e x p e r ie n c e , i t i s r e c o m m e n d e d t o p l a c e t h e s o u r c e o n t h e

cen t e r and o ne r ece iv e r a t the cen t e r and o ne a t two- th i rd s r ad ius ou t f o r r egu l a r t e s ti ng .

In gene ra l , i t is be s t t o pe r fo rm se i smic t e s t s w i th in 24 h ou r s o f p r epa ra t i on , o r the

s p e c i m e n s s h o u l d b e p r o t e c t e d f r o m m o i s t u re l o s s.

T h e r e l a ti o n s h i p b e t w e e n c o m p r e s s i o n w a v e v e l o c i t y f r o m s e i s m i c t e s ts a n d a n g l e o f

in te rna l f r ic t ion f rom t r iax ia l t es t s i s qui te reasonable .

A c o m p a r i s o n o f r e s il ie n t m o d u l u s a n d s e i s m i c m o d u l u s s h o w s t h a t t h e r e s il ie n t

m o d u l u s i s a p p r o x i m a t el y h a l f o f th e s e i sm i c m o d u l u s w h e n d a t a f o r a n u m b e r o f

m a t e r i a ls a n d m a t e r ia l t y p e s a r e u s e d . B e t t e r re l a ti o n s h i p s c a n b e d e v e l o p e d f o r

i nd iv idua l ma te r i a l t ypes .



1 6 4 R E S I L I E N TM O D U L U S T E S T I N G F O R P A V E M E N T C O M P O N E N T S

Acknowledgments

The work being reported herein is part of Project 0-1735 funded by the Texas

Department of Transportation at the University of Texas at El Paso. The authors would

like to offer their sincere appreciation to the Advisory Committee of that Project,

especially Steve Smith, Mike Arellano, and Mark McDaniel for their support. We would

also like to thank Eddy Rodriguez, Thomas Driscoll, and Pradeep Ghuge for their

assistance in data collection and reduction.

R e f e r e n c e s

Alexander, D. R., 1996, "In Situ Strength Measurements with Seismic Methods," Report

from U. S. Army Engineer Waterways Experiment Station, Vicksburg,

Mississippi for the U. S. Air Force Civil Engineering Support Agency, Tyndall

AFB, Florida.

Barksdale, R. D., Alba, J., Khosla, P. N., Kim, R., Lambe, P. C., and Rahman, M. S.,

1997, "Laboratory Determination of Resilient Modulus for Flexible Pavement

Design," Interim Report Project 1-28, Federal Highway Administration,

Washington, DC.

Horhota, D. J., 1996, "Evaluation of SASW Test Method for Florida Department of

Transportation Applications," Ph.D. Thesis, University of Florida, Gainesville,

FL, 444 p.

Ke, L., Nazarian, S., Abdallah, I., and Yuan, D., 2000, "A Sensitivity Study of

Parameters Involved in Design with Seismic Moduli," Research Report 1780-2,

Center for Highway Materials Research, The University of Texas at E1 Paso.

Kramer, S. U, 1996, Geotechnical Earthquake Engineering, Prentice Hall, Inc., Upper

Saddle River, California.

Nazarian, S., Yuan, D., and Tandon, V., 1999, "Structural Field Testing of Flexible

Pavement Layers with Seismic Methods for Quality Control," Transportation

Research Record 1654, Washington, DC, pp. 50-60.

Nazarian, S., Yuan, D., and Arellano, M., 2002, "Quality Management of Base and

Subgrade Materials with Seismic Methods," Journal of Transportation Research

Board Washington, DC, 2002.

Richart Jr., F. E., Woods, R. D., Hall Jr., J. R., 1970, Vibrations of Soils and Foundations,

Prentice-Hall, Inc., Englewood Cliffs, New Jersey.

Williams, R. R., Nazarian, S., Yuan, D., 2002, "Methods of Data Analysis for Correlating

Resilient Modulus and Seismic Modulus Test Results," submitted to Journal of

Materials in Civil Engineering, American Society of Civil Engineers, New York,

NY.



J e a n - M a r ie K o n r a d 1a n d C l a u d e R o b e r t2

Res i l ient M odulu s Tes t ing Us ing Con vent iona l G eotechnica l Tr iax ial E qu ipm ent

Reference:

Ko nrad , J .-M . and Rob er t , C .,

"Res i l ient Mod ulus Tes t ing Us ing

Con vent iona l G eotechnica l Tr iax iai

E q u i p m e n t , "

Resilient Modulus Testing or

Pavement Components, ASTMSTP 1437,

G. N . Du rham , W . A . M ar r , and W . L . De

Grof f , Eds . , AS T M In t e rna t iona l , W es t Con shohoc ken , P A , 2003 .

Abstract:

Thi s pa per p resen t s t he r e su l t s o f a com prehen s ive l abora to ry i nves t iga t i on

p r o g r a m o n t h e m e c h a n i c a l p r o p er ti e s o f a n u n b o u n d a g g r e g a te u s e d i n p a v e m e n t b a s e

cour ses . Rep ea t ed l oad t r iax i a l te s t s were used t o a s sess the i n f luence o f te s t cond i t ions

( spec ime n s i ze , deg ree o f sa tu ra ti on , pu l se l oad ing an d l oad ing sequence ) on r e s i li en t

mod ulus . A con ven t iona l t ri ax i al s e tup , used by mos t geo t echn i ca l l abora to r i e s , was

a d a p t e d f o r t h e te s t in g o f 1 0 0 - m m - d i a m e t e r a n d 2 0 0 - m m - h i g h s p e c i m e n s . T h e m a t e ri a l

r e s p o n s e u n d e r a s in u s o id a l v a r ia t io n o f lo a d w a s c o m p a r e d w i t h t h e A A S H T O p r o c e d u r e

on l a rge r samples and d i f f e r en t pu l se l oad ing . The t e s t p rog ram sh ow ed tha t the r e s i li en t

mo dulus ob t a ined f rom the d i f f e r en t l oad ing sequences ag reed we l l f o r g iven dens i t y and

mo i s tu re con t en t cond it ions . Conv en t iona l tr i ax ia l equ ipme nt can be used t o de t e rmine

the re s i li en t modulus o f unbound aggrega t es p rov id ed accura t e d i sp l acemen t gauges a r e

used i n the m idd l e - th i rd o f t he spec imen .

Keywords:

aggrega te , ba se course , t r iaxia l t est , repeated loading, res i l i ent m odu lus

l P rof essor , Dep t . C iv i l Eng inee r ing , Unive r s it 6 Lav a l , Quebec C i ty , QC, C anada ,

G 1 K 7 P4 .

2 P ro j ec t man ager an d r esea rch sc i en t is t , M in i s t ry o f T ranspo r t a t ion o f Qurbe c ,

2700 E ins t e in S t r ee t, S t e -Foy , QC, Canada , G1 P 3W 8.

165






P a v e m e n t d e s i g n re q u i re s a k n o w l e d g e o f t h e m a t e ri a l p r o p e r t ie s o f e a c h l a y e r . F o r t h e

b a s e c o u r s e m a t e r ia l , w h i c h i s u s u a l ly a w e l l- g r a d e d c r u s h e d s t o n e w i t h m a x i m u m p a r ti c le

s i ze o f abou t 20 m m , e l a s t ic p r ope r t i e s m ay be o b t a i ned f r o m r epea t ed l oad t r i ax i a l t e s ts .

S e v e r a l e q u i p m e n t a n d t e s t p r o c e d u r e s h a v e b e e n d e v e l o p e d b y d i f fe r e n t c o u n t ri e s a n d

t he r e is no s t anda r d t e s t o r st anda r d p r ocedu r e to da t e . I n 1989 , SH RP i n t r oduced a

t e s ti n g p r o c e d u r e f o r t h e d e t e r m i n a ti o n o f re s i li e n t m o d u l u s o f b a s e c o u r s e m a t e r i a ls , a n d

a c o m p r e h e n s i v e c o m p a r i s o n a n d p e r f o r m a n c e o f re p e a t e d tr ia x i a l te s t e q u i p m e n t f o r

unb ound g r anu l a r m a t e r i a l was d one b y Pa u t e e t a l. ( 1996).

A c o m m o n f e a tu r e o f a ll t h e s e h i g h w a y - o r i e n t e d tr ia x i al e q u i p m e n t s i s t h e s i z e o f th e

s p e c im e n u s ed : 1 50 m m x 3 0 0 m m a t t h e U n i v e r s it y o f N o t t i n g h a m ( U K ) , 3 0 0 m m x 6 0 0

m m a t t he L N E C ( P o rt ug a l) , t 6 0 m m x 3 2 0 m m a t t h e L C P C ( F ra n c e) , 4 0 0 m m x 8 0 0 m m

a t D e l f t U n i v e rs i ty o f T e c h n o lo g y a n d g e n e r a ll y 1 50 m m x 3 0 0 m m f o r t h e S H R P

equ i pm en t . Fu r t he r m o r e , m os t o f t he labo r a t o r i e s u se hydr au l i c ac t ua t o r s t o app l y ax i a l

l oads a t f r equenc i e s up t o 10 Hz .

I n v i e w o f t h i s b r i e f r e v i e w o f r e p e a te d t r ia x i a l t e st in g i n h i g h w a y e n g i n e e ri n g , i t

b e c a m e e v i d e n t th a t m o s t g e o t ec h n i c a l la b o r a to r i es i n Q u e b e c w o u l d n o t b e a b l e t o

p u r c h a s e e q u i p m e n t c a p a b l e o f u s i n g la r g e u n b o u n d g r a n u l a r s p e c i m e n s . H o w e v e r , m o s t

o f t he se l abo r a t o r i e s a r e we l l equ i ped w i t h conven t i ona l t r i ax ia l sys t em s ab l e to t e s t 100

m m x 2 0 0 m m s a m p l e s . S i nc e t h e A A S H T O t ri ax ia l t es t m e t h o d r e c o m m e n d s a

m i n i m u m d i a m e t e r o f s a m p l e 5 ti m e s th e m a x i m u m a g g re g a te s iz e , 1 0 0 m m d i a m e t e r

a p p e a r s to b e s u f f ic i e n tl y la r g e to t e s t g ra n u l a r m a t e r i a l u p t o 2 0 m m m a x i m u m a g g r e g a t e

size.

T h e p u r p o s e o f t h is p a p e r is t o r e p o r t t h e re s u l ts o f a c o m p a r a t i v e s tu d y o f t r i a x i a l

t e s t ing on a t yp i ca l c r ushed s t one used i n ba se cou r se s u s i ng a m od i f i ed conve n t i ona l

t ri a x ia l te s t in g e q u i p m e n t d e v e l o p e d b y t h e U n i v e r s i t y L a v a l N S E R C r e s e a r c h c h a i r

( C R E I G ) a n d a S H R P e q u i p m e n t a v a i l a b le a t t h e m i n i s t r y o f T r a n s p o r t io n o f Q u e b e c

( M T Q ) .

M a t e r i a l T e s t e d

A c r u s h e d g r a n it ic a g g r e g a t e f r o m th e Q u e b e c r e g i o n , a p p r o v e d f o r g r a n u l ar m a t e r i a l

b a s e c o u r s e , w a s s e l ec t e d f o r t h is s t u d y . T h e a g g r e g a t e s a m p l e d o n t h e q u a r r y s t o c k p i l e

w as cu t a t 20 m m and f rac t iona ted in 20/14 , 14/10 , 10/5, 5/2 .5 , 2 .5/1 .25, 1 .25/0 .63 ,

0 . 63 /0 .315 , 0 . 315 /0 . 16 , 0 . 16 /0 . 08 and pas s i ng 0 .08 m m . Sam pl e s w e r e p r ep a r ed by

r e c o m b i n i n g t h e a g g r e g a t e f r a ct io n s to m e e t t h e a v e r a g e c u r v e o f t h e M G - 2 0 ( b a s e

c o u r s e m a t e r ia l ) s p e c i f ic a t io n s o f th e m i n i s t r y o f T r a n s p o r t a t io n o f Q u e b e c ( F i g u r e 1 ).



K O N R A D A N D R O B E R T O N G E O T E C H N I C A L T R IA X IA L E Q U IP M E N T 1 6 7

i

1 0 0

9 0

8 0

7 0

6 0

5 0

4 0

3 0

2 0

10

0

1 0 0

1 0 1 0 , 1 0 , 0 1

A g g r e g a t e d i a m e t e r ( m m )

Fi gur e 1 -

Grain size distribution of material tested.

Test ing E quipm ent and Exp er imental Procedure

T h e t e st in g a p p a r a t u s u s e d a t C R E I G i s c o m p o s e d o f a s t a n d ar d g e o t e c h n ic a l t ri a x ia l

c e ll a n d lo a d i n g f l a m e b y W y k e h a m & F a r ra n c e . T h e c e ll is d e s ig n e d f o r c y li n d r ic a l

s a m p l e s 1 00 m m i n d i a m e t e r b y 2 0 0 m m i n h e i gh t .

The appa r a t us u sed a t MT Q was m anuf ac t u r ed by t he A m e r i can f ir m S tr uc tu ra l Beh av i o r

Eng ineer ing Labo ra tor ies , Inc . , and i s co m pos ed of an adap ted t r iax ia l ce l l des igned to

r ece i ve 15 0- m m - d i am e t e r by 300- m m - he i gh t s am pl e .

Sample Preparation

D r i e d a g g r e g a te s w e r e f i r s t r e c o m b i n e d f r o m t h e 1 0 f r a c ti o n s to m e e t p r e c i s e ly t h e

g r ada t i on o f th i s s tudy . Fo r the conv en t i ona l t ri ax ia l c e l l, s am p l e s w e r e p r epa r ed i n a

c y l in d r ic a l P V C m o u l d c o m p o s e d o f t w o h a l f c y l in d e r s b o l t e d to g e t h er . T h e m o u l d i s

i n te r n a ll y l in e d w i th a l a t e x m e m b r a n e w h i c h p u r p o s e i s t o f a c i li ta t e u n m o u l d i n g a n d

pr o v i de p r o t ec t i on f o r a s econd l a t ex m e m br an e used du r i ng t r i ax i a l t e s ti ng .

S a m p l e s w e r e c o m p a c t e d i n 6 l a y e r s u s i n g 2 5 b l o w s o f P r o c t o r h a m m e r f o l lo w e d b y a

v i b r a t o r y p n e u m a t i c h a m m e r . E a c h l a y e r b a t c h is c a r e f u ll y w e i g h te d a n d t h e

c o r r e s p o n d i n g l a y e r t h i c k n e s s r e c o r d e d d u r in g c o m p a c t io n . N u m b e r o f b l o w s a n d t i m e

o f v i b r a ti o n h a v e b e e n a d j u s te d t o r e a c h m a x i m u m d e n s i ty a s d e f i n e d b y a m o d i f i e d

P r o c t o r t es t. T h e h e i g h t o f t h e s a m p l e w a s m o n i t o r e d d u r in g c o m p a c t i o n . F o r th e S H R P

c e ll , s a m p l e s w e r e p r e p a r e d i n a m e t a l s p l i t m o u l d w i th o u t l a t e x m e m b r a n e ; t h e

m e m b r a n e w a s p u t o n t h e s a m p l e a f te r t h e e x t ra c t io n f r o m t h e m o u l d .




Repeated L oading Tests

For the conventional triaxial equipment, the mechanical loading system of the triaxial

frame was locked and vertical cyclic loads were applied to the sample using a pneumatic

Bellofram piston. The following configuration was used:

* A 7 cm diameter Bellofram attached to the top of the loading frame. The

loading was sinusoidal with a frequency of 0.2 Hz.

9 Load measured by a load cell installed inside the triaxial cell.

9 Vertical displacements of the sample recorded by 2 LVDTs attached on the

sample at mid-height with a recording distance of 100 ram, i.e. about 5 times

the maximum grain size. Each LVDT has a stroke of+ 0.5 mm with an

accuracy of 0.7/am as specified by the manufacturer. Actual measurements

on calibration dummies indicate a precision of+ 0.5 gm.

9 Stress path selected for this study was composed of three levels of axial

loading (q = 100, 200 and 280 kPa) and three levels o f cell pressure (~c' = 50,

70 and 120 kPa). For each combination of axial load and confining pressure,

deformations were recorded for the last three cycles after 97 load repetitions.

All samples were subjected to 1000 initial cycles for conditioning under a cell

pressure of 150 kPa and an axial repeated loading of 55 kPa.

9 Tests were carried out in the drained mode (bottom and top valves open).

For the SHRP equipment used at the MTQ, the axial stress is applied by a hydraulic

servo-system with a function generator capable of applying a Haversine-type pulse in

which the signal crest corresponds to the load application time (0.1 seconds), followed

by a relaxation period of 0.9 seconds. Vertical displacements were measured by 2

LVDTs attached on either side of the sample to the top platen and the bottom platen.

Each LVDT has a stroke of +-_2.54 mm with an accuracy of 6.35/am.

The tests were done in accordance with the AASHTO T 307-99 "Determining the

Resilient Modulus of Soils and Aggregate Materials" test method for specimen of

Type 1. For each of the five predefined confinement stresses, representing the minor

principal stress ~3, three different deviator stresses ~d are successively applied to the

sample (Table 1). The sum of the principal stresses, refers to as 0 in the model K-0,

varied from about 84 kPa to 690 kPa.

Table 1 - Stresses applied to the sample in the AASHTO T307-99 test method

Confinement stress, a3 Deviator stress, ~d

(kPa) (kPa)

21 21 41 62

35 35 69 103

69 69 138 207

103 69 103 207

138 103 138 276



KONRAD AND ROBERT ON GEOTECHNICAL TRIAXIAL EQUIPMENT 169

T h e s a m p l e w a s s u b j e ct e d to p r e - l o a d in g o f at le a s t 2 0 0 c y c l e s u n d e r c o n f i n e m e n t a n d

dev i a t o r s t re s se s o f 103. 4 kPa . Fo r each co n f i nem en t s t re s s , t he ax i a l l oad is app l i ed f o r

100 cyc le s . I t i s a s sum e d t ha t, beyo nd t he 9 5 t h cyc l e , the so i l beha v i o r i s p r ac t i ca l l y

e l a st ic . Con sequen t l y , on l y t he r e su l t s o f t he l a s t f i ve cyc l e s a r e t aken i n t o con s i de r a t ion

i n ca l cu l a t ing t he r e s il i en t m o du l us . A n a ve r ag e va l ue f o r the se l a s t f i ve cyc l e s is u sed .

T h e l a te r al d e f o r m a t i o n o f t h e s a m p l e w a s n o t m e a s u r e d .

T a b l e 2 s u m m a r i z e s t h e m a i n d i f f e r en c e s b e t w e e n b o t h e q u i p m e n t s u s e d h e r e i n .

Ta b l e 2 -

Charac teristics o f testing equipment use d

E q u ip m e n t S H R P E q u i pm e n t C R E I G

S a m p l e d ia m e t e r

S a m p l e h e i g h t

T y p e o f l o ad i n g

D i s p l a c e m e n t

m e a s u r e m e n t

1 5 0 m m

3 00 m m

have r s i ne pu l s e ( 0 .1 s econd)

2 L V D T s b e t w e e n p l at en s

1 00 m m

2 00 m m

s i nuso i da l w av e (5 s econds )

2 L V D T s a t s a m p l e ' s m i d h e ig h t

T e s t R e s u l t s

Typical Data Using the Conventional Triaxial Cell (CREIG)

Ty p i ca l r eco r d i ng f r om t he i n t e r na l L V D Ts p r e sen t s t he ax i a l load ve r sus s t r a in f o r the

l a s t 3 cyc l e s a f t e r t he 97 t h l oad r epe t i t ion und e r a m a x i m um dev i a t o r s tr e s s q = 75 kPa

a n d a c o n s t a n t c o n f in i n g p r e s su r e o f 5 0 k P a . T h e m o d u l u s v a l u e f o r t h e s e s t re s s

c o n d i ti o n s w a s d e t e r m i n e d f r o m t h e s l o p e o f t h is q / s t ra i n r e la t io n s h i p a n d w a s 3 1 2 M P a

a n d 3 91 M P a u s i n g d a t a f r o m L V D T 1 ( F ig u r e 2 ) a n d L V D T 2 ( F i g u r e 3) , r e s p e c t iv e l y .

T h e m o d u l u s o f s am p l e 1 7 1.1 w a s t h u s d e f i n ed b y t h e a v e r a g e m o d u l u s d e t e rm i n e d f r o m

t h e t w o L V D T r e c o r d in g s a s 3 5 1. 5 M P a f o r a m e a n p r i n c ip a l e f f e c t iv e st r es s o f 9 1 .6 k P a .

Typical Da ta Using the SH RP Equipment (MTQ)

W i t h t h e S H R P e q u i p m e n t , t h e g r a p h o f t h e a x i a l lo a d v e r s u s s t r ai n i s p r e s e n t ed f o r th e

l a st c y c l e o f 1 0 0 c y c l es u n d e r a m a x i m u m d e v i a t o r s t re s s q = 8 5 k P a a n d a c o n f i n i n g

p r e s s u r e o 3 = 6 4 k P a . T h e m o d u l u s v a l u e s f o r t h e s e s tr e ss c o n d i ti o n s w a s 2 7 2 M p a a n d

4 5 4 M p a u s i n g d a t a f r o m L V D T 1 ( F ig u r e 4 ) a n d L V D T 2 ( F i g u re 5 ), r e s p e c ti v e ly . T h e

r e s u lt s o b t a i n e d w i t h t h e L V D T 2 a r e e x p l a in e d b y a p r o b l e m o f p a r a l le l i sm o f t h e p l at e n s.

T h e d i s p l a c e m e n t m e a s u r e d b y t h e L V D T 1 r e a c h e s 0 .0 8 5 n u n , a h ig h e r v a l u e th a n t h e o n e

m e a s u r e d a t m i d - h e ig h t o f t h e s a m p l e b y C R E I G . T h e a v e r a g e m o d u l u s m e a s u r e d b y



1 7 0 R E S I L I E N TMODULUS TEST ING FOR P AVEM ENT COMP ONENTS

S a m p l e 1 7 1 .1 L V D T 1

0,7 ~ i

s a L.J ~ ~

0 0,005 Displa~176 mm 0 015 0,02

Figu re 2 - Typical data obtained fro m L V DT 1, fo r sa mp le 171.1 with a c onfining

pressure of 50 kPa and dry densi ty o f 2250 kg/m 3.

S a m p l e 1 7 1 . 1 L V D T 2

0 ,7

0 ,6

0 ,5

~ 0 , 4

~ 0 ,2

0,1

0

0 0,005 0,01 0,015

D i s p l a c e m e n t , m m

-

0,02

Figu re 3 -

Typical data obtained from LV D T 2, fo r sample 171.1 with a confining

pressure o f 50 k Pa and a dry densi ty of 22 50 kg/m 3.



KONRAD AND ROBERT ON GEOTE CHNICAL TRIA XlAL EQUIPME NT

171

S a m p l e M T Q - S H R P , L V D T 1

" O

5

1,60

1,40

1,20

1 , 0 0

0,80

0,60

0,40

0,20

0,00 k l

0 ,000

I 9

0 ,020

$

P

0,040 0,060 0,080 0,100

D i s p l a c e m e n t ( m m )

F i g u r e 4 - M e a s u r e m e n t

o f the axial deformation obtained fro m L V DT 1, fo r the

sample MT Q-SH RP w ith a eonfining pressure o f 64 kPa and a dry densi ty

of 22 60 kg/m J.

S a m p l e M T Q - S H R P , L V D T 2

1,60

J

"o

o

1,40

1 , 2 0

1,00

0,80

0 ,6 0 i ~ 9

0,40

0,20

0 ,00

0,000

~ I

9 I

0,020 0,040 0,060 0,080 0,100

D i s p l a c e m e n t ( r a m )

F i g u re 5 - Measu rement o f the axial deformation obtained from L VD T 2, fo r the

sample MTQ -SH RP w ith a eonfining pressure o f 64 kPa an d a dry densi ty

o f 226 0 kg/m 3.



1 7 2

R E S IL IE N T M O D U L U S T E S T I N G F O R P A VE M E N T C O M P O N E N T S

M T Q i s 3 6 3 M p a , a v a l u e h i g h e r t h a n t h e m o d u l u s o f C R E I G , f o r a s l ig h t l y h i g h e r s t r es s

level .

T h e v a l u e s o f t h e r e si li e n t m o d u l u s a r e p r e s e n t e d v e r s u s t h e s u m o f p r in c i p a l s t re s se s ,

and f i t ted based o n t he K -0 m ode l (F ig u re 6 ). Th i s g r a ph a l l ows t o s ee t ha t t he re su l ts

o b t a i n e d f o r lo w s tr es s l e v el s m u s t b e e x c l u d e d b e c a u s e t h e v a l u e s o f t h e m o d u l u s a r e n o t i n

acco rda nce wi th t he o the r va lues ob t a ined a t h ighe r s t r e ss l eve ls . A t l ow s t r e s s leve ls , t he

L V D T s a r e m a y b e n o t e n o u g h a c c u r a t e t o m e a s u r e s m a l l s tra in s. T h e v a l u e s o b ta i n e d b y

the L V D Ts a r e no t r ea l is t ic va lues , and l ead t o an ove re s t im a t ion o f t he re s i li en t modu lus .

1 0 0 0

1 0 0 , 0

10 0 - , , , t I

1 0 , 0 1 0 0 0 , 0

Su m o f p r inc ipa l s t r esses , 0 (kPa )

Figu re 6 -

R e s i l ie n t m o d u l us v a lu e s o f M G - 2 0 a g g r e g a t e m a t e r i a l o b t a i n ed w i t h

S H R P e q u i p m e n t a c c o r d i ng t o th e A A S H T O T 3 0 7 - 9 9 t e s t m e th o d.

C o m p a r i s o n o f R e su l ts

T h e r e s il ie n t m o d u l u s v a l u e s o b t a i n e d f r o m t h e d a t a w i t h t h e c o n v e n t i o n a l C R E I G

t ri ax i al e q u i p m e n t a r e c o m p a r e d w i th t h o s e o b ta i n e d f r o m t h e M T Q S H R P e q u i p m e n t

( F i g u r e 7 ) . T h e r e s il ie n t m o d u l u s d a t a w e r e p l o t t e d a g a i n s t t h e m e a n e f f e c t i v e s t re s s

p ' = ( o ' 1 + 2 o '3 ) / 3 f o r s a m p l e s c o m p a c t e d a t d i ff e r e n t d e ns i ti e s. I n t h e C R E I G c e l l , M r

v a l u e s w e r e o b t a i n e d f o r t h r e e d i f f e re n t d r y d e n s i t y v a l u e s o f 2 1 6 0 , 2 2 1 0 a n d 2 2 5 0 k g / m 3

r e sp e c ti v el y ,, w h i l e t h e s a m p l e s p r e p a r e d f o r t h e S H R P e q u i p m e n t h a d a d r y d e n s i t y o f

2 2 6 0 k g / m . A s a n t i ci p a te d , r e si li e n t m o d u l i o f b a s e c o u r s e m a t e r i a l s i n c r e a se w i t h

i n c r e a s i n g d e n s i t y a n d m e a n s tr e ss . C l o s e e x a m i n a t i o n o f t h e d a t a f o r s a m p l e s a t a b o u t

t h e s a m e d e n s i t y ( 2 2 5 0 k g / m 3 f o r C R E I G a n d 2 2 6 0 k g / m 3 f o r M T Q - S H R P ) r e v e al s t h a t



KONRAD AND ROBERT ON GEOTECHNICAL TRIAXIAL EQUIPM ENT 1 73

the resilient moduli obtained with the convential triaxial equipment used by CREIG are

about 1.2 to 1.5 times higher than those obtained on the same soil using the MTQ-SHRP

equipment. However, in both cases, Mr increases with increasing stress level at about the

same rate. Mohammed et al. (1994) observed that the values of resilient modulus

measured at mid-third of the sample are 1.1 to 1.2 times higher than the values obtained

with the measures of the displacements between the end platens.

_=

O

@

"3

1 0 0 0

9 r

# I ~ I I

j,

#

I I O [ ' q l

t

[!CREIG

d = 2 1 6 0

kg/m3

],,, T Q d= 22 06 kg /m3

JC RE IG d=2210 kg/m3

• CREI G d=22 50 kg/m3

IOO ] I

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0

p ' k P a

Figure 7 - Resilien t modulus values fo r M G- 20 at different dry densities.

D i s c u s s i o n

This section provides some valuable insight into why there is a lot of scatter on the low

strain results for stiffsamples. It is well known that the stiffness parameters measured in

the laboratory depend on many factors including : the fabric of the sample, the loading

path and rate of testing, as well as location and performance of instruments. Major

sources of error in the measurement of stiffness in triaxial tests can be associated with

seating errors and misalignments o f the loading ram with the top platen (Baldi et al.

1988). These errors can be minimised by using local gauges attached to the sample

(Jardine et al. 1984). The use of displacement transducers between the platens as

presently done by the MTQ procedure leads to an overestimation of the soil strain, hence




an underestimation of the resilient modulus for a given stress condition. Furthermore, it

must be emphasized that the actual AASHTO loading procedure may also result in strains

too low to be accurately measured by LVDTs which have a stroke that is too large in

order to accomodate the displacements between platens distant of 300 mm. For instance,

consider a base course material with a resilient modulus value of 250 MPa subjected to a

vertical stress o f 25 kPa, the resulting axial strain would be 0.01% and the actual

displacement 0.03000 ram. Considering that the stroke of the LVDT in the SHRP

equipment is +_2.5 mm with a linearity of+ 0.25%, the precision of the LVDT of

+ 0.00625 mm may not provide sufficient accuracy for the determination of resilient

modulus at low stress levels. For the same granular material in the CREIG set-up, the

actual displacement between the rings attached to the sample would be 0.01 mm which

can be accurately measured using the 0.5 mm stroke LVDT since its precision is

~: 0.5 ~m.

C o n c l u s i o n

A comparative study of repeated triaxial loading using two different equipments and

procedures was undertaken to validate the use of a conventional triaxial equipment using

100 mm x 200 mm samples for the determination of resilient modulus for unbound

granular base course materials. The study led to the following conclusions:

9 Axial strain must be measured with displacement gauges attached to the sample,

usually over the middle third, at least over a diameter length.

9 Displacement gauges need to be accurate enough to record the desired small

strains for the lowest load level. Small samples require therefore relatively

accurate displacement gauges.

9 Reducing the frequency of loading permits to increase the accuracy of

measurements, especially at low stress levels.

9 Provided special attention is paid to these basic requirements, it was shown that

conventional triaxial equipment with 100 mm x 200 mm samples are adequate to

provide resilient modulus values for unbound granular materials.

9 Modifications might be brought about the AASHTO T 307-99 test method to get

accurate values of resilient modulus of granular materials, especially concerning

the location of the LVDTs and to eliminate the lower stress levels.

Acknowledgements

This research work was funded through the NSERC industrial chair and its 22 partners,

particularly the ministry o f Transportation of Quebec. The authors want to express their

appreciation to Mr. Nelson Dub6 from the MTQ, and Mr. Francois Gilbert from

University Laval for his assistance in instrumentation with both the repeated load and

static triaxial tests.



KONRAD AND ROBERT ON GEOTECHNICAL TRIAXIAL EQUIPMENT 175

R e f e r e n c e s

Baldi , G. , High t , D. and Tho m as , G. E., 1988, A Re-ev aluat ion o f Co nven t ional Triaxia l

Tes t Methods ,

In Advanced Triaxial Testing of Soil and Rock, ASTM STP 9 77,

p p

219-263.

Jardine , R. J ., Sym es , M. and Burland, J .B., 1984, Th e M easurem ent o f Soil S t i f fness in

Th e Triax ial Apparatus, G~oteehnique 34, No 3, pp 323-340.

M oham m ed, L. N. , Puppala , A. J . and Alavi l li , P . , 1 994, Inf luence of Tes t ing Proced ure

and LV DT Loca t ion on R es i li en t Modulus o f So il s, Transportation Research

Record 1462, Transpo rta t ion Research Board, Nat ional Research Cou nci l ,

W ashington , D.C. , pp 91-101.

Paute , J .-L. , Daw son, A. R. , Galjaard, P . J ., 1 996 , Re com m enda t ions for Rep eated Lo ad

Triaxia l T es t Equipm ent and Procedure fo r Un bou nd G ranular Mater ia ls ,

Flexible Pavements, Go me s Corre ia (ed.) Balkem a, Ro t terdam .



R i c h a r d L . B o u d r e a u t a n d J i a nr e n W a n g 2

R e s i l i e n t M o d u l u s T e s t - T r i a x i a l C e l l I n t e r a c t i o n

R E F E R E N C E : B o u d reau , R . L . an d W an g , J . , " R e s i l i e n t M o d u l u s T e s t - T r i a x i a i C e l l

I n t e r a c t i o n , "

Res i l ien t Modu lus Tes t i ng f or Pavem en t Component s, A ST M ST P 1437 , G .

N . D u r h a m , W . A . M a r r, a n d W . L . D e G r u f f , E d s ., A S T M I n te r n a ti o n al , W e s t

C o n s h o h o c k e n , P A , 2 0 0 3 .

A B S T R A C T : D u r i ng d e v e l op m e n t a l w o r k b y t he S t ra te g ic H i g h w a y R e s e ar c h P r o g r a m

( S H R P , 1 9 8 7 -1 9 9 2 ) a n d th e F e d e ra l H i g h w a y A d m i n i s t r a ti o n ( F H W A , 1 9 9 3 -p r e s en t ), i t

w a s r e c o m m e n d e d th a t k n o w l e d g e a n d a s s e s s m e n t o f t r i a x i a l e q u i p m e n t a n d s a m p l e

in t e rac tio n b e co r rec t ly app l ied to b o th t e s t co m m an d an d d a ta r ed u c t io n ro u t in es fo r t h e

a c c u r a te m e a s u r e m e n t o f r e si li e n t m o d u l u s p r o p e rt i es o f u n b o u n d m a t e r ia l s u s i n g

ex te rn a l i n s t ru m en ta t io n co n f igu ra t io n . T h i s co n cern i s b r i e f ly ad d ressed in th e A m e r ican

A s s o c i a t i o n o f S ta t e H i g h w a y a n d T r a n s p o r ta t i o n O f f i c ia l s ( A A S H T O ) t e st m e t h o d

T 3 0 7 -9 9 , u n d er pa rag rap h 8 .3 .2 .1 . T h e pa rag raph r e f e r s o n ly to ca l cu la t io n s n ecess a ry to

c o r r e c t fo r th e p r o p e r m a g n i t u d e s o f s e a ti n g l o a d b a s e d o n k n o w n p r o p e r ti e s o f th e

t r iax ia l ce ll . T h e m e th o d d o e s n o t co n ta in in fo rm at io n d esc r ib in g th e m e th o d s an d

ca lcu la t io n s n eed e d to co n s id e r th ese pa ram ete r s in th e d a ta r ed u c t io n po r t io n o f t h e t e st .

Fu r th e r , t h e te s t m e th o d d o e s n o t ad d ress o th e r in f lu en ces u n iqu e to a tr i axia l t e s t in g ce l l ,

n a m e l y f r ic t io n a l f o r c e s r e s ul t in g f r o m p o o r l y m a n u f a c t u r e d o r i m p r o p e r l y d e s i g n e d

sea ls , a l i gn m en t i s su es an d co m pl i an ce .

T h i s paper ad d resses th e sen s i t iv i ti e s o f th e r e su l t s d u e to app ro p r i a t e an d

in appro p r i a t e in t e rp re t a t io n o f t h e co r rec t io n f ac to r s n ecessa ry , a s we l l a s i n f lu en ces o f

sea l d rag fo rces . T h e sen s i ti v i ti e s h av e b e en ca l cu la t ed fo r two spe c i f i c t ri ax ia l ce l ls .

N o te th a t each t r iax ia l ce l l an d in s t ru m en ta t io n co n f igu ra t io n po ssesse s u n iqu e v a lu es

n eed e d fo r t h e co r rec t io n . G en era l ly , th e l a rge r th e t r i axia l ce l l ( l a rge r ro d d i am ete r ,

l a rge r m a ss o f ro d ) , th e g rea t e r t h e in f lu en ces o f t h e u p l i ft an d s t a t i c we igh t co m po n en t s

o f lo ad .

U s e r s m u s t b e k n o w l e d g e a b l e a b o u t t h e i r t es t e q u i p m e n t a n d t h e a b i li t y o f th e

so f tware to co r rec t ly app ly p ro p er lo ad s an d p ro p er ly a s sess th ese lo ad s fo r t h e co r rec t

ca l cu la t io n o f r e s i li en t m o d u lu s . Fu r th e r, ph ys ica l to l e ran ces m u s t b e d ev e lo ped fo r

t r iax ia l ce l ls w i th r e spec t t o sea l d rag , a l i gn m en t a n d co m pl i an ce . T h ese i s su es a re

ex t rem ely im po r t an t wh en co m par in g r esu l t s b e tween l ab o ra to r i e s , a s t h e e r ro r s

asso c ia t ed wi th m isca lcu la t io n , m is in t e rp re t a t io n o r in co r rec t m easu re m e n t o f l o ad s can

resu l t in var ia t ions ou ts ide the pre cis ion o f the tes t i t se l f .

K E Y W O R D S : r e si li e nt m o d u l u s , t ri a xi a l te s t, s e a l d r a g , c o m p l i a n c e , s u b g r a d e

i President, Boudreau Engineering, Inc., 5392 B lue Iris Court, Norcross, GA 30092.

2 Branch Manager, GeoTesting of GA, 2658 HolcombBrid ge Rd., Alpharetta, GA, 30022.

176




BOUDREAU AND WANG ON TRIAXlAL CELL INTERACTION 177

Introduction

A s t h e m u c h - a n t ic i p a te d r e le a s e o f th e 2 0 0 2 P a v e m e n t D e s i g n G u i d e l i n e d r a w s

n e a r, m a n y S t at e D e p a r t m e n t s o f T r a n s p o rt a ti o n h a v e b e g u n t h e i m p l e m e n t a t i o n p h a s e o f

l abo r a t o r y re s i li en t m o du l us t e st ing . R esu l t s o f the r e s i l ien t m o du l us t e s t wi l l m os t

ce r t a i n ly be u t i l i z ed i n t he de s i gn m e t hod o l og i e s con t a i ned i n th i s new gu i de li ne . Th e use

i s an t i c ipa ted in the form o f s ti f fness charac te r iza t ion fo r unb oun d m ater ia l s ( i. e. ,

subgr ade so i ls and agg r ega t e ba se / subb ase m a t e r i a ls ) .

T h e c u r re n t an d p e r h a p s m o s t a c c e p t ed a n d w i d e s p re a d t e st m e t h o d , A A S H T O T -

3 0 7 , h a s b e e n a d o p t e d b y A A S H T O f o l lo w i n g n u m e r o u s y e a r s o f m o d i f i c at i o n s a n d

p r o d u c t io n - l e v e l w o r k a s p a r t o f th e S t ra t e g ic H i g h w a y R e s e a r c h P r o g r a m ( S H R P ) a n d

F e d er al H i g h w a y A d m i n i s tr a ti o n 's ( F H W A ) L o n g T e r m P a v e m e n t P e r f o rm a n c e ( L T P P )

s tudy. Th e p r i m a r y ob j ec t i ve in dev e l op i ng an accep t ed t e s t m e t hod wa s t o p r ov i d e a

re la t ive ly s imple , useable , prec i se , repea table , reprod ucib le and prod uct ive t est .

A l t h o u g h t h e te s t m e t h o d p r o v i d e s f o r a u n i fo r m m e t h o d o l o g y i n w h i c h t o m e a s u r e

l oad and de f o r m a t i on ( s tr e s s and r e s i l ien t s t r a in behav i o r ) , it i s r e cogn i zed a s an

ex t r em e l y sens i t i ve t e st , m easu r i ng r e l a t i ve l y sm a l l s t r a in m agn i t udes a t l ow t o m ode r a t e

s t re s s l eve ls . To t h is end , t he m e t hod f a l ls sho r t i n r ecogn i z i ng ce r t a i n i n f luences o f

equ i pm en t va r i ab l e s tha t cou l d l e ad t o p r ec i s i on e r r o r s t ha t wi l l in t u r n l e ad t o b i a sed

r e su l ts . S om e o f the p r ec i s i on e r r o r s a r e sm a l l, wh i l e o t he r s cou l d b e s i gn i f ican t .

H istorical Developm ent

Si nce 1944 , wh en t he Fede r a l - Ai d H i ghw ay Ac t c r ea ted a b l uep r i n t f o r a 40 000-

m i l e " N a t i o n a l S y s t e m o f H i g h w a y s , " s ig n i fi c an t d e v e l o p m e n t s h a v e b e e n a c h i e v e d w i th

r e spec t t o the s t r uc tu r a l de s i gn o f pave m en t s . Th e p r i m ar y in t en t o f th i s b l uep r i n t w as and

s ti ll r e m a i n s t h e f u n d a m e n t a l c o n c e p t o f p r o v i d in g a n d p r o m o t i n g a u n i f o r m m e a n s t o

des i gn pavem en t s . The f i r s t si gn i fi can t a ch i evem en t inc l uded a n em pi r i ca l - ba sed des i gn

m e t h o d o l o g y d e r iv e d p r i m a r i l y f r o m d a t a o b t a in e d a t th e A A S H O R o a d T e s t i n t h e la t e

1950s.

A s o u r i n d u s t ry h a s e v o l v e d , th e p r o c e s s o f p a v e m e n t d e s i g n h a s a d v a n c e d . T h e

1 98 6 A A S H T O P a v e m e n t D e s i g n G u i d e p r o v i d e d a m e c h a n i s t ic - e m p i r ic a l b a s i s f o r t h e

des i gn o f pav em en t s t ruc t u re s . Th i s gu i de r equ i r ed t he u se o f r e s i li en t m od u l us i n p l ace

o f s o il s u p p o r t a s t h e p r i m a r y in p u t f o r s u b g r a de . A d v a n c e s m a d e i n t e c h n o l o g y a n d

k n o w l e d g e g a i n e d p r i m a r i l y th r o u g h r e s e a r c h a l lo w e d t h is p a r a m e t e r to b e d i r e c tl y

m easu r ed i n t he l abo r a to r y ; howev e r , ve r y f ew l abo r a t o ri e s acqu i r ed t he cap ab i l i t y t o

conduc t t he t e s t, r e ly i ng on co r r e la t i ons t o de r i ve re s i li en t m od u l us f r om o t he r m o r e

com m on so i l p r ope r t ie s .

Th e f i r st s tanda r d i zed t e s t m e t hod t o m eas u r e t he r e s il ien t m od u l us p r ope r t ie s o f

s o il w a s A A S H T O T e s t M e t h o d T - 27 4 . W h e n S H R P b e g a n t h e 2 0 - y ea r L T P P e f fo r t in

1987 , th i s m e t hod w as used a s t he founda t i on t ha t c r ea ted SH RP Tes t P r o t oco l P46 . Th e

p r i m a r y o b j e c t iv e o f t h is p r o t o c o l w a s t o p r o v i d e f o r a s t a n d a r d iz e d m e t h o d t h a t c o u ld b e

pe r f o r m e d ea s il y , wi t h a h i gh deg r ee o f p r odu c t i v i t y and p r ec i s i on . The dec i s i on t o

m e a s u r e l o a d a n d d e f le c t io n o u t s id e t h e c h a m b e r w a s m a d e p r i m a r i ly to p r o m o t e t h e

p r odu c t i v i t y a spec t o f t he ob j ec t ive .




During the work conducted by SHRP, numerous attempts were made to measure the

quality of data being measured at the contracted laboratories. The first effort was to

administer a round-robin proficiency test program. Numerous laboratories volunteered

for this effort, which included laboratories from academia, DOT, industry and private test

labs. Cylindrical test specimens comprised of materials ranging from extruded urethanes,

teftons and nylons were sent to participating laboratories, and results were examined by

the program administrator.

The data obtained from these early rounds o f testing were widely scattered. Under

close examination, numerous problems existed, both with the test procedure as well as

with the specimens utilized. First, it was recognized that, by developing a static stiffness

envelope for each material, a minimum stiffness threshold could be realized. Data

provided by laboratories furnishing dynamic stiffness values less than these minimum

threshold values could be eliminated. Still, the variability in data from labs that were not

eliminated was still unacceptable. Many of the participating laboratories were utilizing

antiquated equipment using "black-box" software, could not demonstrate waveform

control, and even misinterpreted the intent of deviator stress. The misinterpretation of

stress levels required to apply to the test specimen, and how to calculate the measured

response load magnitude for resilient modulus resulted in an inherent 20 percent error of

the result.

Following the evaluation of the synthetic round-robin testing, the LTPP Team

included a graph in Protocol P46 illustrating seating loads, cyclic loads and haversine

shape, in an effort to minimize errors associated with misinterpretation. In addition, the

Team recognized certain influences that act on the rod of the triaxial cell. Because of the

external mounting of the system load cell, knowledge and compensation is required for

both the static weight of the load rod and deformation measurement assembly above the

test specimen as well as the uplift forces caused by the confining pressure applied to the

test specimen, which act on the cross-sectional area of the load rod. Neglected was the

measurement or understanding of the influence of seal drag, alignment and triaxial cell

compliance on the results.

Objectives

This paper examines the influences of the parameters that may affect the resilient

modulus results derived from actual test measurements made in various triaxial

chambers. An understanding of these influences should be considered in any future

modification of a standardized test method. These influences may better enable a

potential user, test operator or even software designer a quick enlightenment and

appreciation for variables that can be better specified or controlled in order to minimize

or eliminate variations of results that are not considered material variations (i.e.,

mineralogy, density, moisture content).

The primary goal of this paper is to heighten awareness that a tightly controlled

tolerance for triaxial test equipment is necessary. This necessity pertains to external

instrumentation, which represents a secondary goal. With the development of the stated

triaxial cell tolerances, the authors anticipate that the test standard will be capable of

providing results with a high degree of precision and productivity, both essential for the

ultimate acceptance of the standard. Recognizing that internal instrumentation may



B O U D R E A U A N D W A N G O N T R I A X IA L C E L L I NT E R A C T I O N 1 7 9

alleviate or minimize these influences, this mode of instrumentation is much more

difficult than the external instrumentation configuration, thus a trade off for higher

precision while sacrificing productivity (and cost) should be examined. Additionally, if

backpressure saturation becomes important, internal instrumentation may not be an

option. By eliminating variables that contribute to result variations, our industry should

be capable of providing and promoting a more uniform and productive standardized test

method with an acceptable precision and bias.

Influencing Factors

Many factors are known to influence the resilient behavior of soils. These factors

can be broadly categorized as material variables and equipment variables. Material

variables may include such items as the geological makeup, density level, moisture

content and compaction methodology of the test specimen. These variables can be

controlled to a predetermined value and tolerance. Equipment variables are less known as

to their affects on resilient modulus values. These factors include load waveform shape,

duration, frequency (each of which can be controlled), test operator and other specific

equipment variables.

The specific equipment variables consist of the test system, the electronic

transducers (load cell and linear variable deflection transducers or LVDTs), and the

triaxial cell. In addition, proper quality management including equipment calibration and

software verification and validation is important in the resilient modulus testing process.

If two laboratories remold a soil obtained by splitting a bulk sample, each lab would

expect to get the same result, when testing in accordance with AASHTO T-307. Let us

assume that both laboratories produced the remolded test specimens to yield the exact

same density and moisture content, using the same compactive effort and methodology to

achieve the density. First, how close should the answer be to consider both labs equal?

Unfortunately, we do not know what the tolerance or anticipated difference should be.

Secondly, if the labs produce values that are significantly different, which lab, if either,

has produced the correct result? Unfortunately, this is the scenario that develops each

time a round-robin program is initiated.

There is no simple, inexpensive answer to these questions. The short answer is that

both laboratories should be fully evaluated for proper implementation of their respective

resilient modulus test systems, its components, the proper application of the test method,

and the correct processing of the acquired data resulting from the test.

The current test procedure, AASHTO T-307, contains provisions that provide

control tolerances on material variables and some of the equipment variables (limited to

accuracy and precision of the electronic transducers). In addition, a report (Alavi 1997)

addresses the integrated function of the system and software. Neither of these references

adequately address the variables associated with the triaxial chamber used to test the

specimen. A provision included in T-307 (paragraph 8.3.2.1) recognizes certain

influences acting on the triaxial chamber 's load rod. This provision requires that

adjustments be made to account for both the static weight of the rod and deformation

measurement system as well as the uplift force on the load rod due to the confining

pressure applied within the triaxial cell. This provision is not restated anywhere in the

standard that would require that this adjustment be accounted for again during data



1 8 0 R E S I L I E N TM O D U L U S T E S T I N G F OR P A V E M E N T C O M P O N E N T S

r educ t i on and r epo r ti ng . Fu r the r , ne i t he r o f t he r e f e r ences add re s se s i n f l uences o f s ea l

d r a g f o r c e s , al i g n m e n t o f t o p a n d b o t t o m p l a te n s , o r s y s t e m c o m p l i a n c e .

Th e pu rpo se o f t he t r iax i a l cham ber i s two- fo ld : f i rs t t o p rope r ly a l i gn t he

cy l i nd ri ca l s am ple unde r t he ax i a l l y app l i ed l oad , and s econd t o a l l ow a cons t an t

app l i ca t i on o f con f in ing p re s su re t o be he ld du r ing t he r epea t ed l oad ing po r t i ons o f t he

t e st . I n o rde r t o me e t bo th o f t he se ob jec t i ve s , a l oad rod i s ex t ended f rom the ou t s i de o f

t h e c h a m b e r , t h o u g h a c o l l a r h o u s i n g l in e a r T h o m p s o n b a l l b us h i n g s , t o t h e s a m p l e

l o a d i n g c a p o r to p p l a t en . T h e T h o m p s o n b a ll b u s h i n g k e e p s t h e s y s t e m p r o p e r l y a li g n e d

th roughou t t he t e s t ing s equences . T h i s bush ing a l l ows fo r ve ry minu t e l a t e ra l o r

h o r i zo n t a l m o v e m e n t w h i l e a l l o w i n g t h e r o d t o m o v e f r e e ly in t h e v e r ti c a l d i re c t io n w i t h

neg l i g ib l e l oad . I n o rde r t o p rov ide fo r cons t an t con f in ing p re s su re , t he l oad rod m us t be

sea l ed i n s ide t he cham ber so a s to no t a l l ow l eaka ge t h rough t he co l l a r hous ing . Th i s i s

t yp i ca l l y ach i eved us ing a l ip s ea l , o - r i ng s ea l o r o the r t ype o f s ea l .

Tha t s a id , i f two o r mor e i nd iv idua l l abo ra to r i e s w e re fu l l y eva lua t ed fo r t he i r

r e spec t i ve sy s t ems , t hen t e s t ed sp l it s o f t he s am e bu lk so i l a s be fo re , wou ld w e exp ec t

t h e m t o g et th e s a m e r e su l t? M a y b e n o t . R e m e m b e r , n o n e o f t h e l ab o r a t o ri e s w o u l d h a v e

had t he i r r e spec t i ve t r iax i a l c e ll measu red fo r t he am oun t o f s ea l f ri c ti on , a l i gnm en t o f

t op and bo t t om p l a t ens o r sy s t em compl i ance . The re cu r r en t l y i s no spec i f i ca t i on t ha t

wo u ld l imi t the s ea l d r ag fo r ce , the a l l ow ab le eccen t r i c i t y o f t he t op and bo t t om p l a t en o r

a l l o w a b l e s y s t e m c o m p l i a n c e o f th e t r ia x i al c e l l, t h u s a n e x a m i n a t i o n o f h o w t h e s e f a c t o rs

m ay a f f ec t the r e su l t s i s wor thwh i l e .

Sens i t i v i ty o f V ar i abl es

In o rde r t o unde r s t and and app rec i a t e t he po t en t i a l s ens i t i v i ti e s o f t he se t r i ax i a l

cha mb er i n f l uences , an a t t emp t to i l lu s t r a te and com pare da t a fo r ac tua l o r t heo re t ica l

t e s ts h a s b e e n p e r f o r m e d . B r e a k i n g t h e r e s i li e n t m o d u l u s d o w n t o i t s m o s t b a s i c f o r m i s

neces sa ry .

Mr = o / e , , o r (P/A)/(AJL)

(1)

whe re :

Mr = r e s il i en t modu lus , p s i

= cyc l ic s t ress , ps i

e r = rec ov erab le s t ra in , in . / in .

P = appl ied cyc l ic load , lb

A = spe c im en cr oss se c t iona l a rea , in. 2

Ar = r eco ve rab l e de fo rm a t ion , i n.

L = spec ime n he igh t , i n.

Uplifting F orce

Fa i lu r e t o accoun t fo r and ad jus t t he s t a ti c we igh t and up l i f t f o r ce s ac t i ng on t he

l o a d r o d w o u l d b e e x p e c t e d t o o n l y a f f e ct t h e P t e r m s h o w n i n E q u a t i o n 1 . T h e s e e f fe c t s,

how eve r , on ly app ly to t he s ea t i ng l oad p r io r to t he app l i ca t i on o f cyc li c load . Thu s , t hey

wi l l neve r en t e r the equa t i on t o a f f ec t t he r e su l t ing r e s i l i en t modu lus . I f t he i n f l uences a r e



BOUDREAU AND WANG ON TRIAXIAL CELL INTERACTION 181

s igni f ic ant ( i. e. , a rod wh ich w eigh s 12 to 15 lb , and i s 1 to 1 .5 inche s in d iameter ) , th i s

c o u l d re s u l t i n a s p e c i m e n t h a t h a s a n e x c e s s i v e a m o u n t o f s e at i n g lo a d ( o r o v e r b u r d e n

p r e s su r e ), w h i c h m a y i n t u r n s l i g h t ly ' s t i f f e n ' a s a m p l e p r i o r t o t h e re p e a t e d l o a d p o r t i o n

o f t h e t es t. W o r s e y e t , in s o m e i n s ta n c e s t h e l o a d i n g r e q u i r e m e n t m a y b e s u c h t h a t th e

l o a d r o d l o o s e s c o n t a c t w i t h t h e t o p p l a t e n i f t h e s t a ti c w e i g h t o f t h e r o d a n d u p l i f t f o r c e

i s n o t p r o p e r l y a c c o u n t e d f o r. T h i s w i ll m o s t c e r t a in l y re s u l t i n e r r o n e o u s d e f o r m a t i o n

m e a s u r e m e n t s . F u t u r e m o d i f i c a t i o n s to a s t a n d a rd i z e d t e s t m e t h o d s h o u l d e m p h a s i s t h i s

i s sue t o ensu re p rope r am oun t s o f s ea t i ng l oad a r e app l i ed r ega rd l e s s o f ce ll p rope r ti e s .

SealDrag

I n a s im i l a r m a n n e r , o n e c a n p r e d i c t t h e e f fe c t s o r e v e n a c c u r a t e l y m e a s u r e t h e

e f f ec t s o f r e s i li en t mo du lus va lues t e s t ed i n a t r iax i a l c e l l t ha t exh ib i t som e mag n i tud e o f

sea l d r ag . An expe r imen t was pe r fo rmed u t i l i z i ng two d i f f e r en t t r i ax i a l chamber s ,

i den t i f i ed a s Ce l l A an d Ce l l B . F ir s t, e ach ch am ber was i n s t rum en ted such t ha t t he

a m o u n t o f s e a l d r a g c o u l d b e m e a s u r e d , a s s h o w n i n F i g u r e 1 .

F IG . 1--Configuration o f seal drag test.

Th e sea l d r ag was m easu red by i n s t a l li ng each t r iax i a l c e l l w i th ou t a spec im en , w i th

t h e l o a d r o d t h r e a d e d t i g h t l y to t h e b o t t o m o f t h e a c t u a t o r - m o u n t e d l o a d c ell. T e s t i n g w a s

p e r f o r m e d w i t h e a c h t r i ax i a l c e l l p re s s u r i z e d t o 0 , 2 , 4 a n d 6 p s i o f c o m p r e s s e d a i r u s i n g

1 , 5 and 10 mi l s ( lm i l = 0 .001 i nch ) o f con t ro l l ed m ov em en t a t e ach l eve l o f a ir p r e s su re .




L o a d r e a d i n g s w e r e m e a s u r e d d u r i n g p u l s e d e f o r m a t i o n s ( d e f o r m a t i o n a m p l i t u d e

w ave fo rm con t ro l , 0.1 s ec l oad ing fo l l ow ed by 0 .9 s ec r e s t pe r i od ) .

R e c o g n i z i n g t h e p o t e n ti a l f o r i n e rt ia r e s u l t in g f r o m t h e l o a d c e l l m a s s r a p i d l y

m o v i n g u p a n d d o w n w h e n a t t a c h e d t o th e m o v i n g a c t u at o r , a p r e l i m i n a r y e f fo r t w a s

m a d e t o m e a s u r e t h i s f o r c e . T h i s w a s a c c o m p l i s h e d b y a t t a c h i n g t h e tr ia x ia l c e l l l o a d r o d

t o t h e l o a d c e l l w i t h o u t t h e t ri a xi al c e ll a s s e m b l e d . A l t h o u g h s o m e a m o u n t o f i n e rt ia f o r c e

was measu red , t he sys t em u t i l i z ed - I n s t ron 85 02 /8800 Se r i e s Con t ro l l e r - con t a in s an

i n t e r n a l ly - m o u n t e d a c c e l e r o m e t e r i n t h e lo a d c e ll , w h i c h i s in t e g r at e d i n t h e s y s t e m ' s

f eedb ack capab i l i t y , t hus t he i ne rt i a a f f ec ts a r e au toma t i ca l l y compe nsa t ed .

C e l l A w a s m e a s u r e d t o h a v e a p p r o x i m a t e l y 0.5 1b o f f r ic t io n w h i l e C e ll B h a d

s l i gh t l y mor e t han 21b o f f r ic t i on .

O n c e t h e a m o u n t o f fr i ct io n a l f o r c e s w a s d e t e r m i n e d f o r e a c h tr ia x i al c h a m b e r , a n

e x p e r i m e n t w a s p e r f o r m e d o n a n A - 4 s o i l f r o m G e o r g i a . N i n e t ee n t e s t s p e c im e n s w e r e

r e p l ic a t e d t o n e a r l y th e s a m e r e m o l d e d v a l u e s o f 95 p e r c e n t o f t h e m a t e r i a l ' s m a x i m u m

s t a n d a r d d r y d e n s i t y a t o p t i m u m m o i s t u re , a n d t e s te d p e r A A S H T O T - 3 0 7 i n C e l l A . T h e

t r iax i a l c e l l con f igu ra t i on fo r t he te s t s pe r fo rm ed i n C e l l A i s show n in F igu re 2 .

F I G .

2--Triaxial cell configuration

T h e s t re s s le v e l ta r g e ts p r e s e n te d i n T a b l e 1 o f A A S H T O T 3 0 7 a r e n o m i n a l l e v e l s

sugges t ed t o ach i eve . Th i s t ab l e cons i s t s o f 15 d i f f e r en t comb ina t i on s o f cyc l i c ax ia l



B O U D R E A U A N D W A N G O N T R I A X I A L C E L L I N T E R A G T I O N 1 8 3

stress and confi ning pressure, each combination referred to as a sequence. It would be

hard to believe that these targets could be exactly matched between command and

feedback signals. Because of the difficulty in achieving precise feedback, a constitutive

model is necessary in order to compare results of tests. The constitutive model used i n

this study is that which was first introduced by SHRP i n the early 1990's:

Mr =- K1 ScmS3 K5 (2)

where

Mr = resilient modulus, psi

Sc = cyclic stress, psi

$3 = conf ining pressure, psi

KI, K2 and K5 = nonli near elastic regression coefficient/exponents

Results of the testing following the regression of data from each specimen to fit the

constitutive model are provided in Table 1. In order to compute the regression constant

and coefficients, the dependent variable, Mr and independent variables Sc and $3 must

first be transformed to a Log~0 base. This a llows a linear regression to be performed.

Once completed, the y-intercept is used as a 10-base exponential to derive the K1

constant, while the K2 and K5 coefficients are used as exponentials in Equa tion 2.

TABLE

1-- No nlin ear elastic coefficient~exponents.

RegressionCoefficients

Sample No. K1 K2 K5 R2

1 7 515 -0.17220 0.21615 0.98

2 7 922 -0.18555 0.22319 0.98

3 7 762 -0.18606 0.21680 0.98

4 7 898 -0,19693 0.24964 0.99

5 7 859 -0.18428 0.25522 0.99

6 8 321 -0,19894 0.23261 0.99

7 7 905 -0,20854 0.25953 0.99

8 7 872 -0.22103 0.26367 0.98

9 8 178 -0,19842 0.25590 0.99

10 7 938 -0.21171 0.23770 0.99

11 6 956 -0.21025 0.30340 0.99

12 7 775 -0.20790 0.25843 0.99

13 8 484 -0.21230 0.23373 0.99

14 8 118 -0.20199 0.23251 0.98

15 7 592 -0.20140 0.25691 0.98

16 7 911 -0.22068 0.25496 0.99

17 7 904 -0.20062 0.27061 0.99

18 7 597 -0.21391 0.26113 0.99

19 7 468 -0.21679 0.26751 0.99

The constitu tive model selected provides an excellent fit for the data, as can be

observed by the multip le-correlat ion coefficient, R 2. Although the regression constant,

KI , and the coefficients, K2 and K5, seem to be quite variable for supposedly replicated

specimens, there is no conclusive evidence of precision and bias that would indicate how

much variability is acceptable.



1 8 4 R E S I L IE N TM O D U L U S T E S T IN G F O R P A V E M E N T C O M P O N E N T S

Once sat i s f i ed that the cons t i tut ive model (Equat ion 1 ) was reasonable based on the

go od R 2 , the resul ts for ea ch tes t sp ecim en wer e calculated or predicted for res il ient

mo dulu s at the exact s t resses for each o f the 15 seq uence s t es ted . T hi s i s done for the

p urp os e o f exam i n i ng t he d i ff erences i n resi li ent m odul us va l ues f rom s am p l e t o s am p l e

or col l ect iv e ly as a group o f rep l i cated specim ens .

As an il lus tration o f importance , a t est performed on a spe cime n targeted for a

cyc l i c s t res s o f 6 p s i a t a conf i n i ng p res sure o f 4 p s i ( s eq u ence n um ber 8 o f 1 5 ) m ay have

achieved a cycl i c s t ress o f 5 . 75 p s i , whereas another samp le t es ted at the same targets

m ay ha ve ac hieved on ly a 5 .4 ps i value . I f the materia l i s s ens i t ive to s t ress ( s t ress

dependen t ) , com paring the raw res i li ent mo dulu s valu es wi l l no t be ideal, or appropriate .

Table 2 presents the calculated res i l i ent modulus values of each specimen tes ted at

each o f the 15 sequ ences . Su mm ary informat ion con s i s t ing of average, s tandard

deviat ion, co ef f i c i ent of variat ion and number o f tes ts or observat ions are pro vided for

each o f t he 1 5 s eq uences ( t ab l e co l um ns ) .

T A B L E

2--Estimated resilient modulus data.

Sam ple Resil ient Mod ulus (predicted by Constitutive Model at each test loading seque nce), psi

No. 1 2 3 4 5 6 7 8 9

10 11

12 13 14 15

1 9,824 8,719 8,131

2 10,391 9,137 8,475

3 10,062 8,844 8,202

4 10,777 9,402 8,680

5 10,927 9,617 8,924

6 10,998 9,581 8,838

7 10,891 9,425 8,661

8 10,832 9,294 8,497

9 11,273 9,825 9,065

10 10,494 9,062 8,316

I1 10,355 8,951 8,219

12 10,696 9,260 8,512

13 11,132 9,609 8,816

14 10,705 9,306 8,574

15 10,463 9,099 8,386

16 10,720 9,200 8,412

17 11,169 9,719 8,960

18 10,458 9,017 8,268

19 10,378 8,930 8,178

a v g . 10,660 9,263 8,532

s .dev .

376.8 311.4 287.3

c.v. 3.5% 3.4% 3.4%

obs.

19 19 19

7,738 7,446 9,000 7,987 7,448 7,088

8,034 7,708 9,492 8,346 7,741 7,339

7,774 7,458 9,215 8,100 7,511 7,120

8,202 7,850 9,739 8,497 7,845 7,413

8,463 8,122 9,853 8,671 8,047 7,631

8,347 7,984 10,008 8,719 8,043 7,596

8,157 7,786 9,803 8,484 7,796 7,342

7,974 7,590 9,734 8,351 7,635 7,165

8,562 8,191 10,162 8,856 8,172 7,718

7,825 7,464 9,530 8,229 7,552 7,106

7,737 7,382 9,157 7,915 7,268 6,841

8,018 7,654 9,632 8,339 7,665 7,220

8,294 7,910 10,125 8,740 8,019 7,544

8,090 7,734 9,742 8,469 7,803 7,362

7,914 7,566 9,428 8,199 7,556 7,131

7,895 7,515 9,667 8,296 7,586 7,119

8,458 8,08 7 10,009 8,709 8,029 7 ,579

7,774 7,412 9,407 8,111 7,437 6,993

7,684 7,321 9,311 8,012 7,338 6,894

8,049 7,694 9,632 8,370 7,710 7,274

275.4 268.5 328.8 280.7 264.3 256.7

3.4% 3.5% 3.4% 3.4% 3.4% 3.5%

19 19 19 19 19 19

6,821 7,747 6,876 6,412 6,102 5,872

7,041 8,131 7,150 6,632 6,287 6,032

6,830 7,929 6,970 6,463 6,126 5,877

7,094 8,192 7,147 6,598 6,235 5,967

7,324 8,255 7,265 6,742 6,394 6,136

7,266 8,517 7,420 6,845 6,465 6,184

7,008 8,189 7,087 6,513 6,133 5,854

6,820 8,108 6,956 6,360 5,968 5,681

7,384 8,510 7,417 6,844 6,464 6,184

6,778 8,082 6,979 6,405 6,027 5,749

6,528 7,420 6,414 5,890 5,544 5,290

6,893 8,052 6,972 6,408 6,036 5,762

7,195 8,611 7,433 6,820 6,416 6,119

7,038 8,292 7,208 6,641 6,267 5,990

6,818 7,890 6,862 6,324 5,968 5,706

6,777 8,101 6,952 6,357 5,966 5,679

7,247 8,297 7,220 6,656 6,282 6,007

6,667 7,850 6,768 6,206 5,835 5,563

6,569 7,735 6,656 6,096 5,727 5,457

6,953 8,101 7,040 6,485 6,118 5,848

252.5 296.2 266.5 256.6 251.8 249.1

3.6% 3.7% 3.8% 4.0% 4.1% 4.3%

19 19 19 19 19 19



B O U D R E A U A N D W A N G O N T R I A X l A L C E L L I N T E R A C T I O N 185

T h e c o e f f i c i e n t o f v a r i a n c e , c . v ., i s r e l a t i v e l y s m a l l f o r e a c h o f t h e 1 5 s e q u e n c e s .

T h i s s m a l l v a r i a ti o n p r o v i d e s a l e v e l o f c o n f i d e n c e t h a t a n y o f th e 1 9 r e s u l ts a r e

r e p r e s e n t a t i v e o f t h e s o i l t e s te d .

N e x t , a s p e c i m e n w a s p r e p a r e d t o a s i m i l a r l e v e l o f w e t d e n s i t y a n d m o i s t u r e

c o n t e n t a n d te s t e d p e r A A S H T O T - 3 0 7 i n C e l l B . T h e r e s u l ts w e r e r e g r e s s e d w i t h t h e

s a m e E q u a t i o n 2 m o d e l .

F i n a l l y , t h e r e s u l t s o f t h e te s t i n g a r e s u m m a r i z e d i n T a b l e 3 . I n c l u d e d a r e r e s u l t s f o r

T e s t A ( t e s t e d i n C e l l A , S p e c i m e n N o . 1 0 ), T e s t B ( t e s t e d in C e l l B ) , a n d T e s t B ad j ( s a m e

a s T e s t B w i t h 2 l b o f l o a d r e m o v e d f r o m t h e a c q u i r e d l o a d t r a n s d u c e r r e a d i n g s , p r i o r to

i n p u t i n t o E q u a t i o n 2 ) . P e r c e n t d i f f e r e n c e s o f T e s t B a n d T e s t B ad j c o m p a r e d w i t h T e s t A

a r e a l s o p r o v i d e d .

T A B L E

3-- Su mm ary o f test results fo r seal drag sensitiviO;.

P a r a m e t e r T e s t A T e s t B % d i f f T e s t B adi % d i f f

K1 7938 10 365 7973

K 2 -0.21171 -0.26330 -0.15495

K3 0.23770 0.24074 0.24064

Seq 1 10 494 13 294 27 11 021 5

Seq 2 9062 11 076 22 9899 9

Seq 3 8316 9954 20 9296 12

Seq 4 7825 9228 18 8891 14

Seq 5 7464 8702 17 8589 15

Seq 6 9530 12 057 27 9997 5

Seq 7 8229 10 046 22 8979 9

Seq 8 7552 9029 20 8432 12

Seq 9 7106 8370 18 8064 13

Seq 10 6778 7892 16 7790 15

Seq 11 8082 10 204 26 8461 5

Seq 12 6979 8502 22 7599 9

S e q l3 6405 7641 19 7137 11

Seq 14 6027 7084 18 6825 13

Se~ 15 5749 6679 16 6593 15

I t s h o u l d b e n o t e d t h a t b o t h t h e t r i a x i a l c h a m b e r s u s e d f o r T e s t A a n d T e s t B t r i a l s

p o s s e s s a 0 . 5 - i n c h d i a m e t e r l o a d r o d

A l t h o u g h 2 l b s e e m s l i k e s u c h a n e g l i g i b l e a m o u n t o f s e a l d r a g , i t s p o t e n t i a l

i n f l u e n c e o n r e s u l ts c a n a p p r o a c h 3 0 % . T h e s e e r r o r s a re m o s t p r o n o u n c e d a t l o w l o a d

i n t e r v a l s th a t t a r g e t o n l y 8 - 1 0 l b o f c y c l i c l o a d a t 2 p s i c y c l i c s tr e s s l e v e l s o n 2 . 8 - i n c h

d i a m e t e r t e st s p e c i m e n . C o r r e c t i n g f o r k n o w n a m o u n t s o f s ea l d r a g is a d a n g e r o u s

p r o p o s i t i o n as w e l l, a s t h e a m o u n t o f s e al d r a g d e v e l o p e d m a y b e n o n - l i n e a r , t h u s c o u l d

d e p e n d o n t h e a m o u n t o f r o d m o v e m e n t a s l o a d s a re p u l se d o n t h e s p e c i m e n .

A d d i t io n a l l y , s e a l d r a g m a y c h a n g e w i t h t i m e a s t h e s e a l w e a r s .

E x p e r i e n c e h a s s h o w n t h a t s e a l d r a g i n c r e a s e s a s lo a d r o d d i a m e t e r in c r e a s e s ( m o r e

c i r c u m f e r e n t i a l a r e a i n c o n t a c t b e t w e e n t h e p r e c i s i o n s ta i n l e s s s te e l r o d a n d t h e s e a l ) th u s

t h e s e p o t e n t i a l e r r o r s a r e e x p e c t e d t o i n c r e a s e i n m a g n i t u d e w i t h l a r g e r c ells ;.




System Compliance

System compliance can be a significant factor since the LVDTs are mounted

outside the triaxial chamber. Not only will the LVDTs measure test specimen

deformation, they may also measure system deformation that is not solely specimen

deformation. System deformation could consist of load rod compression, load rod

bending, compression of porous stones, contact points or interfaces such as top and

bottom loading platens, and base bending. Current resilient modulus test procedures do

not specify a tolerance for system compliance. ASTM Standard Test Method for the

Determination of the Modulus and Damping Properties of Soils Using the Cyclic Triaxial

Apparatus (ASTM D 3999) has a similar physical test configuration as the resilient

modulus test and involves measurements of very small amounts of specimen deformation

(on the order of 1 mil or less). Experience has shown that the system compliance could be

more than 10% of the deformation measured. This could significantly affect the results.

In fact, ASTM D 3999 requires that the system compliance be evaluated to ensure the

compliance is less than 10 % of the deformation measured and reported. A similar

tolerance for the system compliance should be established for the resilient modulus test.

No efforts were made to determine the system compliance for Triaxial Cell A or B

in the experiment described in the previous section. An attempt was made to correct the

results for seal drag, which did lead to a better match between Test A and Test B. It is

quite possible that system compliance could explain more of the variation between the

two tests.

Some may argue that if intemally mounted LVDTs and load cell are used, system

compliance will not be an issue. While this argument has valuable merit, a system with

internally mounted transducers has inherent problems too, such as sensitivity of the

transducers to pressure and difficulties of assembling these transducers inside the triaxial

cell. Further, when saturation of a specimen is desired, the triaxial cell will be required to

fill with water as the confining medium. This issue will make internal instrumentation

extremely difficult, expensive and time consuming.

Alignment of Load Rod and Top~Bottom Platens

Alignment of the load rod and top/bottom loading platens is an important issue.

Misalignment of the load rod and platens will result in eccentric loading that may in turn

lead to erroneous deformation measurements. There is no specific requirement on the

tolerance of alignment in the current AASHTO T-307 test standard. A tolerance for the

alignment has been established as part ofAS TM D 3999. Like system compliance, a

tolerance pertaining to alignment may be warranted.

Physical Dimension Measurements of Test Specimen

Another point of potential sensitivity is the accurate measurement of diameter and

height. The diameter measurement will affect the stress term while the height

measurement will affect the strain term in Equation 1. By incorrectly measuring these

dimensions, or neglecting to measure these dimensions and using nominal specimen

dimensions or mold dimensions, can lead to final resilient modulus result errors o f up to 5



B O U D R E A U A N D W A N G O N T R IA X I A L C E L L I NT E R A C T I O N 1 8 7

%. N o t on ly cou ld t h i s t ype o f neg l ec t l e ad t o e r roneo us r e s i li en t m od u lus da t a , it w i l l

a l so c o m p u t e e r r o n e o u s v o l u m e t r i c d a t a in t h e f o r m o f d e n s it y ,

C o n c l u s i o n s a n d R e c o m m e n d a t i o n s

Thi s pap e r s t r e sse s t he imp or t anc e o f i n f l uenc ing f ac to r s a s soc i a t ed wi th t he t r iax i a l

c e ll u s e d t o c o n d u c t r e si li e n t m o d u l u s t e s ti n g b a s e d o n y e a r s o f e x p e r ie n c e i n t h e a r e a o f

dyn am ic t e s t ing o f so i ls . These f ac to r s a re no t adequa t e ly add re s sed i n t he cu r r en t

r e s i li en t mod u lus t e s t st anda rd . Fo l l o win g ca r e fu l r ev i ew o f t he spec i f ica t i on , ana ly z ing

the e f f ec ts o f va r i ous t r i ax ia l c e l l in f l uences , and d ra win g upo n expe r i en ce spa nn ing

s e v e ra l y e a r s a n d n u m e r o u s t es ts , t h e f o l l o w i n g c o n c l u s i o n s a r e p r o v i d e d .

9 Th e r e s il i en t mo du lus t e s t is an ex t r em e ly s ens i t i ve te s t, me asu r ing sma l l s t r a in s

a t l o w t o m o d e r a t e l o a d s .

9 In o rde r t o be a s p rodu c t i ve a s pos s ib l e , ex t e rna l i n s t rum en ta t i on i s a l l owa b le t o

m easu re l oad ( s tr e s s ) and de fo rm a t ion ( s t ra in ).

9 C a r e m u s t b e t a k e n w h e n i m p l e m e n t i n g a r e s il ie n t m o d u l u s t e st s y s te m .

A s s u r a n c e s m u s t b e a t ta i ne d t o p r o v i d e a c c u r a t e l o a d a n d d e f o r m a t i o n

m e a s u r e m e n t s t h a t w i ll l e a d t o t h e m o s t a c c u r a t e c a l c u l a ti o n o f r e s il ie n t m o d u l u s .

9 In t ema l mea su rem en t s fo r l oad ( s tr e s s) and s t r a in (de fo rm a t ion ) can e l imina t e o r

r educe t he i nhe ren t e r ro r s a s soc i a t ed wi th equ ipmen t va r i a t i on . Th i s dec i s i on

s h o u l d r e c o g n i z e h o w d i f fi c u lt a n d t i m e - c o n s u m i n g i n te r n a l i n s t ru m e n t a t io n is .

F u r th e r , i t s h o u l d b e r e c o g n i z e d t h a t t h e u s e o f b a c k s a t u r a t i o n t e c h n i q u e s w o u l d

make i n t e rna l i n s t rumen ta t i on ex t r eme ly d i f f i cu l t .

9 L abora to r i e s t ha t hav e no t exe rc i s ed ca u t i on t oward s t he se s ens i t iv i t ie s , t ho se t ha t

h a v e n o t b e e n e v a l u a t e d f o r s y s t e m c o n f o r m a n c e , a n d t h o s e t h a t d o n o t a d h e r e t o

a s a t i sf a c t o r y q u a l i t y s y s t e m p r o g r a m s h o u l d n o t p a r t ic i p a te i n r o u n d r o b i n t e s t

p rog rams . Wi thou t t he se con t ro l s , va r i a t i on no t a t t r i bu t ed t o ma te r i a l va r i a t i on i s

pos s ib l e , p robab l e and uncon t ro l l ab l e .

I t i s r e c o m m e n d e d t h a t a s p e c i fi c a t io n b e d e v e l o p e d t h a t w o u l d p r o v i d e t ig h t

t o l e r ance con t ro l f o r m anufa c tu re r s o f t r iax i a l t e s ti ng equ ipmen t . T he spec i f i ca t i on

s h o u l d , a t a m i n i m u m , l im i t t h e a m o u n t o f s e a l d r a g f o r c e w h i l e a t t h e s a m e t i m e l i m i t th e

a m o u n t o f c o m p r e s s e d a i r l e a k ag e . I f th e s e p a r a m e t e r s a r e c o n tr o l le d , i n s t r u m e n t a ti o n c a n

b e m a d e e x t e r n a l ly a n d t h e s e i n fl u e n c e s c a n b e n e g le c t ed . S o m e o f th e s e m e a s u r e s h a v e

b e e n a d d r e s s e d i n A S T M D 3 9 9 9 a n d s h o u l d b e c o n s i d e r e d f o r th i s te s t m e t h o d a s w e ll .

I t i s fu r t h er r e c o m m e n d e d t h a t a p r o g r a m b e d e v e l o p e d a n d a d m i n i s t e re d t o

eva lua t e a p r ec i s i on and b i a s s t a t emen t fo r a s t anda rd i zed t e s t p rocedure t ha t wou ld

i n c l u d e m a t e r ia l s c o v e r i n g a w i d e r a n g e o f e x p e c t e d r e si li e n t p r o p e rt ie s . T h e s e s h o u l d

inc lude

A-4 , A-5 , A-6 , and A-7 so i l s , a s a min imum. Once s e l ec t ed , s eve ra l l abo ra to r i e s

t h a t c a n d e m o n s t r a t e c o n f o r m a n c e ( b y o n - s i g h t ev a l u a ti o n ) t o t h e p r e c i s e re q u i r e m e n t s o f

t h e t e st p r o c e d u r e s h o u l d t e st a m i n i m u m o f si x r e p li c a te s f r o m e a c h m a t e r i a l

c o m b i n a t i o n t o d e v e l o p b o t h w i t h i n - l a b o r a t o r y a n d b e t w e e n - l a b o r a t o r y v a r i at io n . I t

w o u l d b e a d v a n t a g e o u s t o e v a l u a t e th e e f f e ct s o f c o m p a c t i o n m e t h o d o l o g y d u r i n g t h is

r e c o m m e n d e d p r o g r a m a s w e l l a s e f fe c t s o f m o i s t u r e a n d d e n s i t y v a ri a ti o n s . T h i s



1 8 8 R E S I L I E N TM O D U L U S T E S T IN G F OR P A V E M E N T C O M P O N E N T S

addi t ional evaluat ion i s recomm ended as a secon d phase, fol low ing the developm ent o f

an accurate and acceptable precision and bias o f the test procedure.

R e f e r e n c e s

Alavi, S. , Merport , T. , Wilso n, T., Groeger, J ., and Lope z, A., 1 997 , "L TP P Materials

Character iza tion Program: Res i l ient M odulus o f Un boun d M ater ia ls (LTPP

Protocol P46) L aboratory Star tup and Qu al i ty Con trol Proced ures ," Federal

Highway Administration Report No. FHWA-RD-96-176.



SESSION 5: MODELING DATA REDUCTION

AND INTERPRETATION



B. F . T anyu , l W . H . K im , 2 T . B . Ed i l , 3 and C . H . B enso n 3

C o m p a r i s o n o f L a b o r a t o r y R e s i li e n t M o d u l u s w i t h B a e k - C a l e u l a t e d E ~ a st ic M o d u l i

f r o m L a r g e- S c a le M o d e l E x p e r i m e n ts a n d F W D T e s ts o n G r a n u l a r M a t e r ia l s

Reference :

Tanyu , B . F . , Kim, W . H . , Ed i l , T . B . , and Benson , C . H . ,

" C o m p a r i s o n o f

L a b o r a t o r y R e s il i e n t M o d u l u s w i t h B a c k - C a l c u l a t e d E l a s t ic M o d u l i f r o m L a r g e -

S c a l e M o d e l E x p e r i m e n t s a n d F W D T e s t s o n G r a n u l a r M a t e r i al s ,"

Resilient

Modulus Testing fo r Pavement Components, AS TM STP 143 7,

G . N . D u r h a m , W . A .

M a r r , a n d W . L . D e G r o f f , E d s ., A S T M I n te r n a ti o n a l, W e s t C o n s h o h o c k e n , P A , 2 0 0 3 .

Abstrac t : A c o m p a r i s o n i s m a d e b e t w e e n r e s i l i e n t m o d u l i o b t a i n e d f r o m ( i ) a

conven t iona l sma l l - sca l e r e s i l i en t modulus t e s t , ( i i ) a l a rge - sca l e mode l exper iment

( LS M E) , and (i ii ) a f a ll ing w e igh t de f l ec tomete r ( FW D) in t he f i eld . Th e LS M E i s a

l a rg e p r o t o t y p e - s c a l e t e s t s im u l a t i n g a p a v e m e n t se c ti o n . T h e F W D t e st s w e r e c o n d u c t e d

on a h igh w ay t e s t s ec t i on . A l l te s t s we re conduc t ed on a t yp i ca l bas e cour se ma te r i a l and

two g ranu l a r i ndus t r ia l by -p rodu c t s used as subbase . Re l a t i onsh ips be tw een e l a st ic

m o d u l u s a n d b u l k s t r e ss w e r e d e r i v e d f r o m th e L S M E d a t a b y m o d e l i n g t h e s e t - u p a s a

n o n l in e a r e l a st ic la y e r e d s y s t e m u s i n g t h e c o m p u t e r p r o g r a m K E N L A Y E R . E l a st ic

m o d u l i w e r e b a c k - c a l c u l a t e d f r o m t h e F W D d a t a u s i n g t h e p r o g r a r n M O D U L U S .

R e a s o n a b l e c o r r e s p o n d e n c e b e t w e e n t h e e la s ti c m o d u l i m e a s u r e d a t d i ff e r e n t sc a l e s w a s

o b t a i n e d w h e n e m p i r i c a l c o r r e c t i o n s w e r e m a d e f o r s t r a i n a m p l i t u d e u s i n g a b a c k b o n e

c u r v e f o r g r a n u l ar m a t e r ia l s a n d b y m a t c h i n g st re s s le v e ls . H o w e v e r , e v e n w h e n

cor rec t i ons a r e app l i ed , t he l ow-s t r a in ( o r maximum) e l a s t i c modulus f o r t he i ndus t r i a l

bypro duc t s i n f e r r ed f rom the l ab ora to ry r e s i li en t m odu lus t e s t t ends t o be l owe r ( by a

f ac to r o f 1 . 5 t o 4 ) t han t he ope ra t i ve e l a s t i c modulus i n f e r r ed f rom the LS M E and t he

FW D tes ts . I n add i ti on , the min im um bulk s t r e s s p rov ided by t he l abora to ry r e s i li en t

mo dulus t e s t can be h igh er t han t he bu lk s t r e s s ex i s t i ng in t he f i eld . In such cases , the

e l as t i c modulus a t t he f i e ld bu lk s t r e s s can be e s t ima ted by ex t r apo l a t i on us ing a power

funct ion.

K e y w o r d s :

r e s i li en t mod ulus , e l a s ti c modulus , g r ave l , f oundry s l ag , bo t t o m ash , f a l li ng

weigh t de f l ec tomete r t e s t , l a rge - sca l e mode l exper iment , i ndus t r i a l

b y p r o d u c t s , p r o t o t y p e t e s t

1 G ra d. R e s . A s s t. , G e o l o g i c a l E n g i n e e r i n g P r o g r a m , U n i v e r s i ty o f W i s c o n s in - M a d i s o n ,

M a d i s o n , W I , 5 3 7 0 6 , U S A , b f t a n y u @ s t u d e n t s .w i s c . e d u

2Grad . Res . Ass t . , Dep t . o f C iv i l & En vi ronm enta l Eng inee r ing , U nive r s i t y o f W iscons in -

M a d i s o n , M a d i s o n , W I , 5 37 0 6 , U S A , w k i m @ c a e . w i s c . e d u

3prof essor , G eolog i ca l Eng inee r ing P ro gram and Dep t . o f C iv i l & Envi rormaenta l

E n g i n e e ri n g , U n i v e r s i t y o f W i s c o n s i n -M a d i s o n , M a d i so n , W I , 5 3 7 0 6 , U S A ,

ed i l@engr .wi sc . edu , benson@engr .wi sc . edu

191




1 9 2



T h e r e s i l i e n t m o d u l u s i s a m a t e r i a l p r o p e r t y u s e d i n p a v e m e n t e n g i n e e r i n g t h a t

d e s c ri b e s t h e d e f o r m a t i o n o f m a t e r ia l s c o m p r i s i n g a p a v e m e n t s t r u ct u r e s u b j e c t e d t o

r e p e ti ti v e l o a d s s i m i l a r to t h o s e i m p o s e d b y v e h i c l es . T h e r e s i li e n t m o d u l u s i s ty p i c a l l y

m e a s u r e d i n t he l a b o r a to r y o n s p e c im e n s o f p a v e m e n t m a t e ri a ls c o m p a c t e d u s i n g

l a b o r a to r y c o m p a c t i o n e q u i p m e n t . A l o a d i n g p r o t o c o l is f o l l o w e d w h e r e th e c o n f i n i n g

p re s su re an d t he r epe t i t i ve dev i a to r s t r e ss a r e va r i ed t o s im u la t e d i f f e r en t s t a t e s o f s tr e ss .

C h a n g e s i n t h e l o a d i n g p r o t o c o l h a v e b e e n m a d e p e r i o d i c a l l y s i n c e t h e t e s t m e t h o d w a s

i n it ia l ly d e v e l o p e d . H o w e v e r , t h e g e n er a l c h a r a c t er i s ti c s o f t h e t es t m e t h o d h a v e

r e m a i n e d t h e s a m e .

U n l i k e m a n y o t h e r m e c h a n i c a l p r o p e r t ie s o f ea r t h e n m a t e r ia l s , t h e r e i s n o d i r ec t

w a y o f v e r i f y i n g t h a t t h e r e s il ie n t m o d u l u s m e a s u r e d i n th e l a b o r a t o r y i s r e p r e s e n ta t i v e o f

e l a st ic modu l i ope ra t i ve i n t he fi e l d und e r wh ee l l oads . The re fo re , t he r e i s unce r t a in ty

r e g a r d i n g h o w f a i th f u l l y th e r e s il ie n t m o d u l u s m e a s u r e d i n th e l a b o r a t o r y c o r r e s p o n d s t o

t h e o p e r a t iv e e l a s ti c m o d u l u s i n th e f ie ld . D i r e c t c o m p a r i s o n o f t h e r es i li e n t m o d u l u s

w i t h e l a st ic m o d u l i o b t a i n e d f r o m o t h e r m e t h o d s i s a ls o d i f f ic u l t b e c a u s e o f d if f e r e n c e s i n

s tr e ss a n d s t r ai n c o n d i t io n s , f r e q u e n c y o f d y n a m i c l o a d i ng , a n d o t h e r f a c to r s . T h i s p a p e r

p r e s e n t s a s t u d y f o c u s e d o n c o m p a r i n g t h e r e s i l i e n t m o d u l u s m e a s u r e d i n t h e l a b o r a t o r y

o n t e st s p e c i m e n s o f g r a n u l a r m a t e ri a ls w i t h e l a st ic m o d u l i b a c k c a l c u l a t e d f r o m a l a rg e -

s c a l e m o d e l e x p e r i m e n t ( L S M E ) a n d f a l l i n g w e i g h t d e f l e c t o m e t e r ( F W D ) t e s t s c o n d u c t e d

i n t h e fi el d. T h e l a b o r a t o r y te s ts w e r e c o n d u c t e d u s i n g a c o n v e n t i o n a l r e s il ie n t m o d u l u s

t e s t p r o c e d u r e ( A A S H T O T 2 9 4 - 9 4 ) , w h e r e a s b a c k - c a l c u l a t i o n m e t h o d s w e r e u s e d t o

o b t a in e l as ti c m o d u l i f r o m t h e L S M E a n d F W D t es ts .

A t y p i c a l g r a n u l a r b a s e c o u r s e a n d t w o g r a n u l a r i n d u s tr i al b y - p r o d u c t s w e r e u s e d

f o r a ll th r e e m e t h o d s o f ev a l u a ti o n . P r o p e r ti e s o f t h e m a t e ri a ls a r e s u m m a r i z e d i n T a b l e

1 . G r a d e 2 g r a v e l is a n a t u r al m a t e r ia l c o m m o n l y u s e d a s b a s e c o u r s e i n W i s c o n s i n .

B o t t o m a s h a n d f o u n d r y s l a g a r e g r a n u l a r in d u s t ri a l b y - p r o d u c t s t h a t a r e u s e d a s s u b b a s e

o v e r s o ft s u b g r a d e s t o e n a b l e c o n s t ru c t i o n . B o t h o f t h e i n d u s tr i al b y p r o d u c t s a r e w e l l-

g r aded coa r se -g ra ined s and - l i ke ma te r i a ls . A l l o f t he ma te r i a l s a r e nea r ly i n sens i t i ve t o

w a t e r c o n t e n t d u r i n g c o m p a c t i o n ( F i g. 1 ).

Tab l e 1 -

P r o

Specific D m D60

Material Gra vity ( ) (ram) Cu

Gr ade 2 2.65 0.09 6.0 66.7

Bo t tom

2.65 0.06 1.9 31.7

A s h

Fou ndry 2.29 0.13 2.0 15 .4Slag

Note: N M = not measured.

"Industrial Byproducts and Grade 2 Gravel .

Maximum D ry U n i t W e igh t Op t imum

USCS (kN/m3)

Sym bol Com pact ion Vibra tory

p er A S T M p e r A S T M

G W

SW

SP

D 698 D 4253

22 .6 N M

15.1 13.7

10.0 8.4

Wate r

Con ten t CBR

per D 698

(%)

8 .2 N M

-- 21

-- 17



T A N Y U E T A L . O N T E S T C O M P A R I S O N S 1 9 3

.E

"E:

s

E

Uz

E:

c ~

Z-

C 3

25

20

15

10

25

20

15

10

5

30

2 5

2 0

1 5

. . . . r . . . . i . . . . i . . . . 1 . . . . r . . . .

( a ) B o t t o m A s h

99 9 ~ i r Vo id . ';

]

9 Std. Procter |

9 R e s i l ie n t M o d u l u s T e s t

]

S M E

9 F i e l d S e c t i o n

. . . . P . . . . I . . . . i . . . . i . . . . i , , i i

0 5 10 15 20 25 30

W ate r Con ten t (% )

T e s t ' ' ~ . . . . , . . . . w . . . .

S td . P r o c t or ( b ) F o u n d r y S l a g

9 R e s i l ie n t M o d u l u s

o L S M E

9 F i e ld S e c t i o n

Zero A i r Vo ids

A A A A 9 A 41 ~A 9

- ~ o

5 35

0 15

. . . . i . . . . i , , i i I i , i , i . . . . i = , , i

10 15 20 25 30


i i

( c ) G r a d e 2

~ , ~ Ze ro A ir Vo ids

9 S t d . P r o c t o r

9 R e s i l i e n t M o d u l u s T e

L S M E

I =

' 5 1~0


F i g . 1 - Compac tion C urves and Test Unit Weights fo r (a) B ottom Ash, (b) Foun dry

Slag, and (e) Grade 2 Gravel.




Laboratory Resil ient M odulus Test (AASH TO T294)

R e s il ie n t m o d u l i o f t h e g r a nu l a r m a te r ia ls w e r e e v a l u a te d u s i n g A A S H T O T 2 9 4 -

9 4 f o l l o w i n g th e p r o t o c o l f o r T y p e 1 m a t e r ia l s ( u n b o u n d g r a n u l a r b a s e a n d s u b b a s e

ma te r i a ls ) . The ce l l u sed fo r t he r e s i li en t mo du lu s t e s t wa s i den t i ca l t o a t r iax i a l c e l l u sed

fo r shea r s t r eng th t e s t ing , excep t a i r wa s u sed a s the con f in ing f l u id i n s t ead o f wa t e r a s i s

r e qu ir e d in A A S H T O T 2 9 4 .

D i m e n s i o n s o f t h e t e st s p e c i m e n s w e r e s e l e c te d b a s e d o n t h e p a r ti c l e s iz e

d i s tr i bu t io n o f t h e m a t e r i a l s b e i n g t e s te d f o l l o w i n g t h e c r it e ri a i n T 2 9 4 . S p e c i m e n s o f

f o u n d r y sl a g a n d b o t t o m a s h s a m p l e s h a d a h e ig h t o f 1 52 m m a n d a d i a m e t e r o f 7 6 m m ,

w h e r e a s s p e c i m e n s o f G r a d e 2 g r a v e l h a d a h e ig h t o f 30 5 m m a n d a d i a m e t e r o f 1 52 m m .

A l l sp e c i m e n s w e r e c o m p a c t e d t o 9 5 % o f t h e m a x i m u m d r y u n i t w e i g h t p e r s t an d a rd

P r o c to r . T h i s d r y u n i t w e i g h t i s c o m p a r a b l e t o t h a t a c h i e v e d i n th e f ie l d a n d i n th e L S M E

(Fig. 1).

A l o a d i n g s y s t e m m a n u f a c t u r e d b y C o x & S o n s I n c . w a s u s e d t h a t i n c l u d e d a

t e m p e r a t u r e - c o n t r o ll e d t e s t c h a m b e r . L o a d s w e r e a p p l i e d u s i n g a h y d r a u l i c l o a d a c t u a to r

a n d w e r e m e a s u r e d u s i n g a 2 2 - k N l o a d c e l l m o u n t e d e x t e r n a ll y . D e f l e c t i o n s w e r e

m e a s u r e d u s in g tw o L V D T s m o u n t e d e x te rn a ll y . T h e l o a d in g s e q u e n c e w a s a p p li ed

u s i n g a h a v e r s i n e l o a d p u l s e w i t h a f r e q u e n c y o f 1 H z . T h e l o a d w a s a p p l i e d f o r 0 .1 s a t

t h e b e g i n n i n g o f e a c h c y c l e , a n d w a s f o l l o w e d b y a 0 . 9 -s re s t p e r i o d . R e s i l ie n t m o d u l i

w e r e c o m p u t e d f r o m t h e m e a s u r e d l o a d s a n d d e f l e c ti o n s u s in g t h e m e t h o d i n T 2 9 4 .

Large-Scale M odel Experiment (LS M E)

T h e L S M E i s a m e t h o d d e v i s e d t o m o d e l a p a v e m e n t s t r u c t u re ( o r p a r ts o f it) a t

p ro to type s ca l e i n a m ann e r t ha t r ep l i ca t e s fi e l d cond i t i ons a s c lo se ly a s p r ac t ica l . A

p h o t o g r a p h o f t h e L S M E i s i n F i g . 2 a n d a s c h e m a t i c is s h o w n i n F i g . 3.

A p ave m en t p ro f i l e i s cons t ruc t ed i n a 3 m x 3 m x 3 m t e s t p i t (F ig . 3 ) by p l ac in g

th ree d if f e r en t l aye r s o f ma te r i a l s ( f rom bo t t om to top ) : ( i) a 2 .5 -m th i ck l aye r o f dense

u n i f o r m s a n d , ( i i ) a 0 . 4 5 - m - t h i c k s i m u l a t e d s o f t s u b g r a d e ( e x p a n d e d p o l y s t y r e n e f o a m ) ,

and ( ii i) a l aye r o f coa r se g r anu l a r t e s t ma t e r i a l ( 0 .22 t o 0 .90 -m th i ck ) s imu la t i ng subbase .

T h e s u r f a c e o f t h e s o f t s u b g r a d e i s n e a r l y at th e t o p s u r f a c e o f th e p it . T h e u p p e r l a y e r

s i m u l a t in g s u b b a s e l i e s a b o v e t h e s u r f a c e o f t h e te s t p it . W o o d e n w a l l s 1 m h i g h c o n f i n e

the subbase m a te r i a l a l o ng t he boun da r i e s o f the t e s t p i t.

A r i d i n g s u r f a c e a n d a b a s e c o u r s e l a y e r a r e n o t i n c o r p o r a t e d i n t h e L S M E , b u t

t he i r e f f ec t i n t r ansmi t t i ng whee l l oads i s cons ide red , a s de sc r ibed subsequen t ly .

Repe t i t i ve l oads a r e app l i ed t o t he su r f ace o f t he p ro f i l e w i th a s tee l p l a t e u s ing a 90 -k N

hydrau l i c ac tua to r (F ig . 2 ) .



T A NY U E T A L . O N T E S T C O M P A R I S O N S 1 9 5

F i g . 2 - Setup of LSME Showing Hydraulic Actuator, Load Frame, and Data Acquisition

System.

F i g . 3 - Schematic Cross Section of Large-Scale Model Experiment (LSME).




Materials

Dense Uniform Sand -

T h e d e n s e u n i f o r m s a n d l a y e r a t t h e b a s e o f th e p r o f i le

p r ov i des a f ir m f oun da t i on f o r t he expe r i m en t , and s i m u l a t e s a deep e r s t i f f l aye r . Th e

sand has an e f f ec t i ve g r a i n s i ze o f 0 . 22 r am , a co e f f i c ien t o f un i f o r m i t y o f 1 .8 , a d r y un i t

w e i g h t o f 1 7 .4 k N / m 3 , and a vo i d r a ti o o f 0 .49 . Th i s vo i d r a ti o co r r e spo nds t o a r e l a t i ve l y

dens i t y o f 85% . Th e s and w as o r i g i na l ly p l aced us i ng a loade r , and has been i n u sed i n a

v a r i e ty o f e x p e r i m e n t a l p r o g r a m s o v e r t h e l as t d ec a d e . T o h o m o g e n i z e th e s a n d , t h e p o r e

wa t e r p r e s su r e i s e l eva t ed un ti l t he s and i s l ique f ied . Pu m ps l oca t ed ben ea t h t he p i t a r e

used to app l y t he po r e wa t e r p r e s su r e . A f t e r l ique f ac ti on , t he s and i s d r a i ned and

com pr es se s unde r i t s s e l f - we i gh t and t he m a t r i c suc t i on t ha t deve l ops du r i ng d r a i nage .

B e f o r e u s e in t h is t e s t p r o g r a m , t he u p p e r 4 50 m m o f th e s a n d w a s c o m p a c t e d w i t h a

v i b r a t o ry p l a t e c o m p a c t o r .

Simulated Soft Subgrade -

E x p a n d e d p o l y s t y r e n e ( E P S ) f o a m w a s u s e d t o

s i m u l a t e a so f t subgr ade s i m i l a r t o a s il ty cl ay . EPS w as used i n l ieu o f so i l t o ensu r e

un i f o r m i t y , and to r educe t he t i m e and e f f o r t r equ i r ed to p r epa r e exp e r i m en t s . EPS i s a

g e o f o a m , a n d h a s b e e n u s e d i n a v a r i e ty o f g e o t e c h n ic a l a p p l i c a ti o n s i n c lu d i n g p a v e m e n t

s tr uc tu re s. Fo r exam pl e , one - d i m ens i ona l com pr es s i on t e s t s condu c t ed by Ne gu ssey and

Jahanand i sh ( 1993) show t ha t t he s t r e s s - s t r a i n behav i o r o f l ow- dens i t y EPS ( 21 . 0 kg /m 3)

is com p ar ab l e t o t ha t o f so f t ino r gan i c c l ay o f m ode r a t e p la s t i c it y . I n add i ti on , Neg ussey

and Jahanand i sh ( 1993) r epo r t t ha t con f i nem en t and l oad i ng f r equency have m i n i m a l

e f f e c t o n t h e c o m p r e s s i b i li t y o f E P S .

A n a p p r o p r i a t e E P S m a t e r i a l w a s s e l e c t e d f o r t h e L S M E b y i d e n t i f y i n g t h e

dens i t y o f EPS t ha t ha s s i m i l a r s t r e s s - s t r a i n behav i o r a s a t yp i ca l so f t subgr ade so i l i n

W i scons i n ( m o i s t An t i go s i lt l oam , t he Wi scons i n s t a te so il ). Un conf i n ed cyc l i c l oad ing

t e s t s w e r e conduc t ed on spec i m ens o f EP S ( 300 m m t a ll, 150 m m d i am e t e r ) and r e s i li en t

m o du l us te s t s w e r e conduc t ed on t he An t i go s i lt l oam . A c om par i so n o f t he s tr e s s -

beh av i o r o f the A n t i go s i lt l oam and t ha t o f the l ow - dens i t y EPS ( 17 .1 kg /m 3) s e l ec t ed f o r

use in the L S M E i s show n i n F i g . 4 . The E PS ha s s i m i l a r s t r e s s -s t r a in behav i o r a s t he

An t i go s i lt l oam , and has s i m i l a r m od u l us .

The EPS does unde r go s i gn i f i can t p l a s t i c de f o r m a t i on a t an ax i a l s t r e s s o f 100-

120 kPa , wh e r eas t he An t i go s i l t l oam does no t . Ho w eve r , c a l cu l a t ions i nd i ca t ed t ha t t he

s t re s s a t t he l eve l o f t he EPS i n t he L SM E w ou l d nev e r exceed 100 kPa . Thu s , the EPS

i n be l i eved t o r em a i n wi t h i n i t s e l a s t i c r ange i n t he L SME, wi t h an e l a s t i c m odu l us

s imi la r to tha t o f a sof t c lay .

T h e s i m u l a te d s o f t s u b g ra d e i n th e L M S E w a s p l a c e d a s t h re e l a y e r s o f E P S

pane l s , e ach 0 . 15- m t h i ck , to f o r m a 0 . 45- m t h i ck so f t l aye r . Th i s ap p r oac h was used i n

l ie u o f a s in g l e b l o c k o f E P S t o s i m p l i f y c o n s tr u c ti o n a n d r e d u c e c o s t s. U s e o f p a n e l s

r a t he r t han a s i ng l e b l ock i s no t exp ec t ed to a f f ec t de f o r m a t i on o f the p r o f i l e . Z ou e t al.

( 2000) show t ha t b l ock s i ze and l a te r a l re s t ra i n t do no t s i gn i f i can t l y a f f ec t de f o r m a t i on

b e h a v i o r o f E P S .

Granular Subbase Layer -

T h e c o a r s e g r a n u l a r l a y e r s i m u l a t i n g s u b b a s e w a s

p l aced i n 0 . 11 - m - t h i ck l if ts . Eac h l i f t w as com p ac t ed wi t h a v i b r a t o r y p l a t e com pac t o r t o



TANYU ET AL. ON TEST COMPARISONS 197

o b ta i n a d r y u n it w e i g h t i n e x c e s s o f 9 5 % o f m a x i m u m d r y u n i t w e i g h t b a s e d o n s t an d a rd

P r o c to r . A n u c l e a r g a u g e w a s u s e d t o m e a s u r e t h e d e n s i t y o f e a c h lift. T h e d r y u n it

w e i g h t s t h a t w e r e a c h i e v e d a r e s im i l a r t o t h o s e u s e d f o r t h e l a b o r a t o r y r e s i li e n t m o d u l u s

t e st s and i n t he f i e ld (F ig . 1 ). G ran u l a r subbase l aye r s w e re con s t ruc t ed w i th t he G rade 2

g r a v e l a n d b o t h i n d u st ri a l b y p r o d u c t s . A t l e as t tw o t h i c k n e s s e s o f e a c h m a t e r i a l w e r e

evalua ted .

2 00

150

. • 1 0 0

5 0

0

0.0

' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' '

Antigo Silt Loam

......... EPS

1.0 2.0 3.0 4.0

Axial Strain (%)

Fig. 4 - Stress-Strain Behavior of 3OO-mm-Thick EPS and Antigo Silt Loam.

Loading

G ranu la r subbase ma te r i a l s a r e sub jec t ed t o two l oad ing l eve l s : ( i ) h ighe r i n t ens i t y

s h o r t d u r a t i o n l o a d s d u r i n g c o n s t r u c t i o n c a u s e d b y h e a v y t r u c k t r a f f i c d i r e c t l y o n t h e

subbase an d ( ii ) l ow er i n t ens i t y l oads t ha t pe r s i s t f o r m an y yea r s due t o t r a f f ic on t he

f i n is h e d p a v e m e n t . T h e s e l o a d i n g c o n d i t io n s w e r e s i m u l a t e d f o r a t y p i c a l r u r a l h i g h w a y

(i.e ., W i s c o n s i n S t a te T r u n k H i g h w a y 6 0 , r e fe r r e d t o h e r e in a s S T H 6 0 , w h i c h i s th e s i te

o f th e f ie l d te s ts ) b y a p p l y i n g d i f fe r e n t s t re s se s t o t h e s u r f a c e o f t h e c o m p a c t e d s u b b a s e

l a y er i n th e L S M E .

T h e c o n s t r u c t i o n l o a d s w e r e s e l e c t e d t o s i m u l a t e t h e lo a d a p p l i e d b y 4 - a x l e d u m p

t r uc k s a p p l y i n g a lo a d o f 7 0 k N p e r a x l e d i r e c t ly o n t h e s u b b a se . T h e s e t r u c k s n o r m a l l y

h a v e a t i re p r e s s u r e o f a p p r o x i m a t e l y 7 0 0 k P a , w h i c h r e s u l t s i n a c o n t a c t a r e a o f 0 .0 5 m 2

unde r a 35 kN load . The re fo re , a c i r cu l a r st ee l p l a t e hav in g a d i am e te r o f 25 0 m m ( i.e .,

a n a r ea o f 0 .0 5 m 2 ) a n d a t h i c k n e s s o f 2 5 m m w a s u s e d t o a p p l y t h e w h e e l l o a d. L o a d s




app l i ed by t he se t r ucks r ep re sen t t he heav i e s t r epe t i t i ve l oads app l i ed t o t he subbase

dur ing cons t ruc t i on .

C o n v e n t i o n a l t r a f f i c l o a d s w e r e e s t i m a t e d b y c o n d u c t i n g a m u l t i l a y e r e l a s t i c

a n a ly s is o f t h e p a v e m e n t s t r uc tu r e a t S T H 6 0 u s i n g t h e p r o g r a m K E N L A Y E R ( H u a n g

1 99 3). T h e p r o g r a m w a s u s e d t o d e t e r m i n e th e l o a d i n g o n t h e s u b b a s e c a u s e d b y a n

e q u i v a le n t s i n g le a x l e l o a d ( E S A L ) o n t h e s u r fa c e o f t h e p a v e m e n t s t r u c tu r e . T h e a s p h a lt

w a s a s s u m e d h a v e a n e l as ti c m o d u l u s o f 3 5 4 0 M P a , a P o i s s o n ' s r a t io o f 0 . 3 0 , a n d a

t h ic k n es s o f I 2 5 m m . T h e b a s e co u r s e w a s a s s u m e d t o b e 2 5 5 - m m t h ic k a n d t o h a v e a

Po i s so n ra t i o o f 0 .35 ( c o r r e sp ond ing t o a a t -r e s t e a r t h p r e s su re coe f f i c i e n t o f 0 .5 4 ).

M o d u l i o f th e b a s e a n d s u b b a s e a n d l a y e r s w e r e a s s u m e d t o f o l l o w t h e n o n - l i n e a r e l as ti c

p o w e r f u n c ti o n m o d e l :

M = k lc r b k~ (1 )

where k~ and k2 a r e em pir ica l cons tants an d Orb i s the bulk s t ress . Th e bulk s t ress equals

CYO 3a3, wh ere cyd i s the d evia tor s t ress and c3 i s the m ino r pr inc ipa l s t ress . Fo r the base

cour se , k l was a s s um ed to be 15.3 M Pa and k2 w as 0 .5 0. Fo r t he subbase , k l was 3 .3

M P a a n d k2 w a s 0 . 6 2. T h e s o f t s u b g r a d e w a s a s s u m e d t o b e l i n e a r l y e l as ti c w i t h a

m o d u l u s o f 69 M P a a n d a P o i s s o n ' s r at io o f 0.4 5 .

T h e K E N L A Y E R a n a ly s i s in d i ca t e d th a t st re s s a p p l ie d t o t h e s u b b a s e b a s e l a y e r

is 1 4 0 k P a , o r a p p r o x i m a t e l y 2 0 % o f t h a t a p pl ie d t o t h e s u r f a c e o f t h e p a v e m e n t . T h i s

s tr e ss w a s s i m u l a t e d b y a p p l y i n g a f o r c e o f 7 k N t o t h e l o a d i n g p l a te .

L o a d s w e r e a p p l i e d u s i n g a h a v e r s in e l o a d p u l se c o n s i s t i n g o f a 0 . 1 - s l o a d p e r i o d

f o l lo w e d b y a 0 . 9 - s re s t p e r io d , w h i c h i s t h e s a m e l o a d p u l s e s p e c i f i e d i n t h e l a b o r a t o r y

r e si li e nt m o d u l u s te s t. T h e d y n a m i c m o t i o n o f t h e a c tu a t o r w a s p r o v i d e d b y a 2 8 0 - L / m

M T S h y d r a u l ic p u m p . T h e 3 5 - k N l o a d w a s a p p l i e d f o r t h e fi rs t 1 0 0 0 c y c l e s t o s im u l a t e

c o n s t r u c t io n t ra f fi c . T h e n 1 0 , 00 0 c y c l e s o f t h e 7 - k N l o a d w e r e a p p l i e d t o s i m u l a t e p o s t -

c o n s t r u c t io n tr a f fi c lo a d s . A C R - 9 0 0 0 d a t a l o g g e r m a n u f a c t u r e d b y C a m p b e l l S c i e n t i fi c

I n c . w a s u s e d f o r r e c o r d i n g v e r t ic a l d i s p l a c e m e n t o f t h e l o a d i n g p l a t e a n d t h e a p p l i ed

l o a d as a f u n c ti o n o f t im e . F o r e a c h l o a d c y c l e , 9 6 d a t a p o in t s w e r e r e c o r d e d , i n c l u d i n g

t h e m i n i m u m a n d m a x i m u m a p p l i e d l o a d s a n d c o r r e s p o n d i n g d e f l e c t i o n s .

Inversion of Elastic Modulus from the LSME

K E N L A Y E R w a s u s e d t o i n v e rt th e e la s ti c m o d u l u s o f t h e s u b b a s e l a y e r i n th e

L S M E f r o m t h e m e a s u r e d l o a d s an d d e f e ct io n s . T h e s i m u l a t e d s o ft s u b g r a d e w a s

a s s u m e d t o b e l i n e a r ly e l a s ti c , w h e r e a s t h e e l a st ic m o d u l u s o f t h e s u b b a s e w a s a s s u m e d

to fo l l ow the e la s t ic po w er func t i on i n Eq . 1 . Th e subbase w as d iv ided i n to sub l aye r s 5 0 -

m m t h i c k in t h e a n a l y s is .

T h e p a r a m e t e r k2 v a r i e s i n a n a r r o w r a n g e f o r a w i d e v a r i e t y o f g r a n u l a r m a t e r ia l s.

T h u s , k 2 w a s f i x e d u s i n g t h e v a l u e o b t a i n e d f r o m t h e r e s il ie n t m o d u l u s t e s t c o n d u c t e d p e r

T 2 9 4 . T h e p a r a m e t e r k i, w h i c h v a r i es o v e r a b r o a d r a n g e , w a s a d j u s te d u n t il t h e

m e a s u r e d a n d p r e d i c t e d e l a st ic d e f le c t i o n s m a t c h e d . T h e k l t h a t p r o v i d e d m a t c h i n g

de f l ec t i ons wa s a s sum ed to be t he ope ra t i ve k~ o f t he subbas e l aye r . Th e e la s t ic




de f l ec t i ons u sed a s i npu t t o KENL AYER wer e de r i ved f r om t he t o t a l de f l ec t i ons ( e l a s t i c

and p l a s t i c ) m easu r ed i n t he L SME by sub t r ac t i ng t he accum ul a t ed p l a s t i c ( non-

r ecove r ab l e ) de f l ec t ions f r om t he t o t a l de f l ec ti ons .

Field E xperiment

Test Section

A 654- m t e s t s egm en t con t a i n i ng s eve r a l t e s t s ec t i ons was cons t r uc t ed du r i ng

r econs t r uc ti on o f STH 60 be t w een L od i and P r a i r i e du Sac , W i scons i n ( Ed i l e t al . 2002) .

Th i s s egm en t con t a i ned f ou r te s t s ec t ions cons t r uc t ed wi t h t he g r anu l a r m a t e r i a l s u sed i n

t he L SM E. P l an and c r os s - s ec t i ona l v i ew s o f the te s t s ec t ions a r e shown i n F i g . 5. Tw o

of t he te s t s ec ti ons ( a t t he ends ) a r e con tr o l s. Th e con t r o l s we r e co ns t r uc t ed us i ng

c r ushed r ock f o r subbase , wh i ch i s t he s am e m a t e r i a l u sed f o r t he po r t i on o f STH 60 t ha t

was r e - cons tr uc t ed . Th e o t he r t wo t e s t s ec t ions i nco r po r a t ed g r anu l a r i ndus tr i al by -

p r oduc t s , i .e ., f oun dr y s l ag and bo t t om ash as subbase . Al l s ec t i ons had a 12 5- m m - t h i ck

a s p h al t s u r fa c e a n d a b a s e c o u r s e c o n s i st in g o f 1 15 m m o f G r a d e 2 g r a v e l a n d 1 4 0 m m o f

sa l vaged a spha l t (t o t a l ba s e cou r se t h i cknes s = 255 m m ) .

Und i s t u r bed s a m pl e s o f the subg r ade wer e co l l ec t ed a l ong t he l eng t h o f t he t e s t

s ec t i on a t a dep t h o f 1 m be l ow g r ound su r f ace us i ng t h i n - wa l l s am pl i ng t ubes hav i ng a

d i am e t e r o f 75- m m . Th e subgr ade cons i s ted o f le an s il t ( M L ) o r le an c l ay ( CL ) .

Unconf i ned com pr es s i on t e s t s i nd i ca t ed t ha t t he subgr ade was r ea sonab l y un i f o r m , wi t h

unconf i ned com pr es s i v e s t r eng ths (qu ) r ang i ng be t w een 100 and 160 kPa . M easu r em en t s

m ade wi t h a dynam i c cone pene t r om e t e r ( DCP) and a so i l s t i f f ne s s gauge ( SSG) a l so

indica ted tha t the subgrade was uni form (Edi l e t a l . 2002) .

The t wo i ndus t r i a l by - p r oduc t s ( bo t t om ash and f oundr y s l ag ) we r e u sed a s a

s u b b a s e m a t e ri a l, p r o v i d i n g a s t ab l e w o r k i n g p l a t f o r m o v e r t h e s u b g r a d e d u r in g p a v e m e n t

cons t ruc t ion . Gr ad e 2 g r ave l w as used a s ba se cou r se a l ong wi t h a l aye r o f s a l vaged

aspha lt , wh i ch has e s sen t i a l l y t he s am e p r ope r t i e s a s Gr ade 2 g r ave l . Th e bo t t om ash and

f oundr y s l ag we r e u sed i n bu l k f o r m ( a s a laye r r a t he r t han be i ng m i xed w i t h soi l) . Bo t h

wer e p l aced i n 150- m m - t h i ck l i f t s t ha t we r e com pac t ed wi t h a t am pi ng f oo t r o l l e r t o

a c h i e v e a d r y u n it w e i g h t e x c e e d i n g 1 0 0 % o f m a x i m u m d r y u n it w e i g h t p e r s ta n d a rd

Pr oc t o r ( F ig . 1 ). Th e d r y un i t we i gh t o f e ach l aye r w as m ea su r ed pe r i od i ca l l y wi t h a

nuc l ea r dens i ty gage . A f t e r p l ace m en t and com pac t i on o f t he l a s t l if t , t he top o f each

s u b b a s e l a y e r w a s c o m p a c t e d a g a i n w i th s t e el - d ru m a n d r u b b e r - t ir e c o m p a c t o r s to

p r o v i d e a s m o o t h a n d u n i f o r m s u r f a c e f o r t h e r e m a i n i n g p a v e m e n t l a y e r s.




~ , ~ NV e s t t o P r a i r i e d u S a c

C o n t r o l F o u n d r yl a g

1 2 2 m 1 5 2 m

( 2 4 0 + 0 0 ) ( 2 4 4 + 0 0 )

. I . 1 5 2 m = l=

I

( 2 4 9 + 0 0 ) ( 2 5 4 + 0 0 )

6 5 4 m

E a s t T o L o d i - - ~ !

B o t t o ms h

C ~ 1 7 6 I

1 5 2 m _ ,_ 7 6 m

~ 1 ~ l = I

( 2 5 9 + 0 0 ) ( 2 6 1 + 5 0 )

- I

F o u n d r y S l a g

1 2 5 m m A C

1 1 5 m m G r a d e 2

Grave l Base

1 4 0 m m S a l v a g e d

A s p h a l t B a s e

8 4 0 m m

F o u n d r y S l a g

S u b b a s e

w = 1 2 . 5 %

~'d = 12 .4 k N /m 3

D P I = 2 5 m m / b l o w

S t i f f n e s s ( S S G ) =

3 .8 M N / m

S u b g r a d e

M L - C L ( A - 4 )

w = 2 4 . 5 %

L L = 3 0

P L = 2 2

"(d = 14 .2 k N /m 3

q u = 1 3 9 k P a

D P I = 3 9 m m / b l o w


5 .3 M N / m

/

/ . /

B o t t o m A s h

1 2 5 m m A C

1 1 5 m m G r a d e 2

Grave l Base


Aspha l t Base

6 0 0 m m

B o S o m A s h

S u b b a s e

w = 2 . 6 %

7 d = 1 7 . 1 k N / m 3

D P I = 2 2 r a m / b l o w


4 . 0 M N / m

S u b g r a d e

C L ( A - 6 )

w = 2 4 . 9 %

L L = 3 7

P L = 2 3

Yd = 1 4 . 4 k N / m 3

q u = 1 6 1 k P a

D P I = 6 9 r a m / b l o w


4 . 4 M N / n l

\ . \

'N

C o n t r o l

1 2 5 m m A C

1 1 5 m m G r a d e 2

G r a v e l B a s e


A s p h a l t B a s e

8 4 0 m m o r m o r e

E x c a v a t e d R o c k

S u b b a s e

w = 6 .3 %

Yd = 2 0 . 1 k N / m 3

D P I = 2 8 m m / b l o w


1 0 .0 M N / m

S u b g r a d e

C L ( A - 6 )

w = 2 5 . 2 %

L L = 4 6

P L = 2 6

~,~ = 14.1 kN /m 3

q u = 9 8 k P a

D P I = 7 9 m m / b l o w


5 . 6 M N / m

( N o t t o s c a l e

Fig . 5 -

P a v em en t S t ru c t u re a n d P r o pert ie s o f Su b gr a d e a n d Su b b a s e a t ST H 6 0. D P I =

Dynam ic Penet ra t ion l ndex From Dynamic C one Penet rometer . S ti ff ness Was

M easur ed U sing a Soi l Sti ffness Gage (SSG).



T A N Y U E T A L . O N T E S T C O M P A R I S O N S 2 0 1

Falling W eight Deflectometer Tests

F a l l in g w e i g h t d e f l e c t o m e t e r ( F W D ) t e st s w e r e p e r f o r m e d a t S T H 6 0 t o d e te r m i n e

t h e o p e r a t iv e e l a st ic m o d u l i o f t h e G r a d e 2 s u b b a s e , b o t t o m a s h , a n d f o u n d r y s la g . T h e

F W D t e s ts w e r e c o n d u c t e d s e m i - an n u a l l y fo r t w o y e a r s b y t h e W i s c o n s i n D e p a r t m e n t o f

T r an s po r ta ti on ( W i s D O T ) u s in g a K U A B M o d e l 2m - 3 3 F W D . T h e K A U B 2 m - 3 3 F W D

i s t r a il e r -m o u n t e d a n d i s t o w e d b y a l ig h t t ru c k . T h e F W D i s a u t o m a t i c a l l y c o n t r o l l e d b y

a c o m p u t e r i n t h e to w i n g v e h i c le . L o a d s a n d d e f l e c t io n s a r e r e c o r d e d a n d s t o r ed i n th e

compu te r .

T h e F W D w a s u s e d t o d r o p a 4 9 k N w e i g h t o n t o a 3 0 0 - m m - d i a m e t e r p l a t e i n

c o n t a c t w i t h t h e p a v e m e n t s u r f a c e . T h e d r o p a p p l i es a l o a d w i t h a r is e t i m e o f 1 7 t o 2 5

m s a n d d u r a ti o n o f 3 4 t o 5 0 m s . T h e p e a k l o a d im p o s e d o n t h e p a v e m e n t s u r f a c e b y t h e

f a ll in g w e i g h t w a s m e a s u r e d u s i n g a l o a d t r an s d u c e r. S u r f a c e d e f l e c t io n s w e r e m e a s u r e d

w i t h s e v e n v e l o c i t y t ra n s d u c e r s l o c a t ed a t t h e c e n t e r o f t h e l o a d a n d a t d i st a n c e s o f 0 .3 0

(edge o f l oad p l a te ) , 0 . 45 , 0 .60 , 0 .90 , 1 .20 , and 1 .5 2 m f rom the cen t e r o f t he l oad .

Elastic Modulus from FW D D ata

E l a s ti c m o d u l i o f t h e s u b b a s e a n d b a s e l a y e r s w e r e c o m p u t e d u s i n g t h e l o a d s a n d

d e f le c ti o n s m e a s u r e d w i t h th e F W D . T h e l ay e r e d e la s ti c a n al y s is p r o g r a m M O D U L U S

( T e x a s T r a n s p o r t a t i o n I n s t i t u t e 1 9 9 1 ) w a s u s e d f o r t h e a n a l y s i s b e c a u s e i t p r o v i d e s

r o u t in e s f o r b a c k - c a l c u l a t i n g e l as t ic m o d u l i f r o m F W D d a t a . E a c h p a v e m e n t l a y e r i s

a s s u m e d t o b e h o m o g e n e o u s , i s o t r o p ic , a n d l i n e ar l y e la s ti c a n d t o e x t e n d i n f i n i t e ly i n t h e

h o r i z o n ta l d i re c t io n . T h e b o t t o m l a y e r i s a l so a s s u m e d t o e x t e n d d o w n w a r d i n f in i te l y .

E l a s t i c modu l i a s s igned t o each l aye r a r e ad jus t ed i t e r a t i ve ly un t i l t he measu red and

pred i c t ed de f l ec t i ons m a tch w i th in an accep t ed t o l e r ance (U zan e t a l. 1988) .

A f o u r - l a y e r s y s t e m ( a s p h a l t , b a s e c o u r s e , s u b b a s e c o u r s e , a n d s u b g r a d e ) w a s

u s e d f o r t h e b a c k - c a l c u l a t i o n m o d e l . E a c h l a y e r w a s a s s i g n e d i ts a v e r a g e t h i c k n e s s ( F i g .

5 ). Th e two base co u r se l aye r s (G rade 2 g r ave l and s a lvaged a spha l t , F ig . 5 ) we re t rea t ed

a s s in g l e la y e r w i th a c o m b i n e d t h ic k n e s s o f 2 5 5 ra m . A P o i s s o n ' s r a t io o f 0 . 3 0 w a s u s e d

f o r t h e a s p h al t s u r f a c e la y e r. T h e P o i s s o n ' s r at io w a s s e t at 0 .3 5 F o r t h e c o m b i n e d b a s e

cour se laye r . Po i s so n ' s r a t i o s o f 0 .33 , 0 .25 , and 0 .30 we re u sed fo r t he subbase l aye r s

c o n s t r u c te d f r o m f o u n d r y sl a g, b o t t o m a s h , a n d c r u s h e d r o c k . T h e P o i s s o n ' s r a ti o s f o r

t h e b a s e a n d s u b b a s e m a t e r i a l s w e r e e s t i m a t e d u s i n g e l a s t i c t h e o r y a n d t h e a t - r e s t e a r t h

p r e ss u r e c o e f fi c i e n t c o m p u t e d u s i n g J a k y ' s eq u a t io n . D e p t h t o t h e " r ig i d la y e r " w a s

f i x ed a t 6 m t o s i m u l a t e t h e a p p r o x i m a t e d e p t h o f b e d r o c k a t t h e site . B u s h a n d

A l e x a n d e r ( 1 9 8 5 ) i n d i c a t e t h a t t h e r i g i d l a y e r h a s l i t t l e e f f e c t o n t h e b a c k - c a l c u l a t e d

e l a st ic m odu l i wh en t he dep th i s a t l e a s t 6 m .

O n c e t h e f i e l d e l a s t i c m o d u l i w e r e b a c k - c a l c u l a t e d u s i n g M O D U L U S , a n

a d d it io n a l a n a ly s is w a s c o n d u c t e d w i t h K E N L A Y E R t o d e t e r m i n e t h e r a n g e o f b u l k

s t re s se s and ve r t i c a l s t r a in s ope ra t i ve i n t he ba se and subb ase l aye r s i n the f i e ld . A

s u r fa c e l o a d e q u a l t o th a t a p p l i ed b y t h e F W D w a s i n c l u d e d t o s i m u l a t e t h e s t r es s e s

i m p o s e d d u r i n g t h e F W D t es t. T h e e l as ti c m o d u l i b a c k - c a lc u l a te d w i t h M O D U L U S w e r e



202 R E S IL IE N T M O D U L U S T E S T I N G F O R P A VE M EN T C O M P O N E N T S

3 0 0

400

~ 3oo

(3

.,~ 200

(3

(3

100

0

500

~ " 4 0 0

0..

3 0 0

o

"E 200

(3

(3

t~

1 0 0

0

5 0 0

~ " 4 0 0

(3-

~ 30o

5

"o

o

"E 209

(3

100

. . . . I . . . . i . . . . i . . . . i . . . . i . . . . i . . . .

( a ) B o t t o m A s h

L S M E ( h = 0 . 8 0 m , R C = 9 6 % )

L S M E ( h = 0 . 9 2 m , R C = 9 7 % ) 4 f L S M E ( h = 0 . 69 m , R C = 9 3 % )

FW D (h = 0 .60 m , RC = 10 8% ) ~ ~ ~ o

/ ~ ~ o t Modu,us estRC=9~'/o)

~ = 96'/.)

. . . . i . . . . i . . . . ] , , ~ 9 t . . . . i . . . . ! . . . .

. . . . i i . . . . r . . . . i . . . . i . . . . i . . . .

( b ) F o u n d r y S l a g

Res i l i en t Modu lus Tes t (RC = 95%)

FWD (h = 0 .84 m, RC = 120% ))

J / LSME (h = 0 .92 m , RC = 100%) -

. . . . . , . . . . . R c = o 6 7 !

. . . .

. . . . i . . . . I . . . . i . . . . I . . . . I . . . . ~ . . . .

(r G r a d e 2

Res i li en t Mod u lus Tes t (RC = 95%)

FWD (h = 0 ,115 m, RC = NA) ~ o

. ~ M E ( h = 0 .2 3 m m , RC = 8 9Y o )

r - , t , r t t I i i r , , i i , f 9 9 * . . . . ~ . . . . i . . . .

1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0

Bulk Stress (kPa)

F i g . 6 -

E l a s t ic M o d u l i f o r ( a ) B o t t o m A s h , ( b ) F o u n d r y S l ag , a n d ( e) G r a d e 2 G r a v e l ( h

= T h i c k n es s, R C = R e l a ti v e C o m p a c t i o n, N A = D a t a N o t A v a il a b l e ).




used a s i npu t. Th e bu lk s t r es s and ve r t i c a l s t r a in a t m id -de p th o f each l aye r we re

as sum ed to be r ep re sen t a t i ve o f t he ope ra t i ve c ond i t i ons i n t he f i e ld .

R e s u l ts a n d D i s c u s s i o n

T h e e l a s ti c m o d u l i m e a s u r e d i n t h e la b o r a t o ry , L S M E , a n d t h e f i el d a r e s h o w n i n

F ig . 6 . E l a s t i c m odu l i de t e rmined f rom the l abo ra to ry r e s i l ien t mo du lus t e s t and t he

L S M E a re s h o w n a s f u n c ti o n s o f b u l k s t re ss . T h i s r e la t io n s h i p w a s d e t e r m i n e d d i r e c tl y

f r o m th e I a b o r a t o r y r e s il i en t m o d u l u s t es t. F o r t h e L S M E , t h e r e l a t io n s h i p w a s o b t a i n e d

f r o m t h e K E N L A Y E R a n a l y s is d e s c r ib e d p r ev i o u s l y . O n l y a si n g l e e la s ti c m o d u l u s i s

p r e s e n t ed f o r th e F W D t e st s b e c a u s e o n l y o n e l o a d i n g c o n d i t i o n w a s a p p l i e d i n t h e f ie ld .

T h e e r r o r b a r s r e p re s e n t t h e r a n g e o f m o d u l i o b t a i n e d f r o m t h e f o u r s e m i - a n n u a l F W D

t es ts th a t h a v e b e e n c o n d u c t e d . T h e b u l k s t re s s o p e r a t iv e d u r i n g t h e F W D t e s t w a s

c o m p u t e d u s i n g K E N L A Y E R , a n d r e p re s e n ts t h e s t r es s a t m i d - d e p t h i n t h e s u b b a s e l a y er .

E a c h o f th e e v a l u a t i o n m e t h o d s p r o v i d e s a d i f f er e n t m o d u l u s f o r a g i v e n b u l k

s tr es s. F o r e x a m p l e , t h e e la s ti c m o d u l i m e a s u r e d i n th e l a b o r a t o r y u s i n g A A S H T O T 2 9 4

and i n the f i e l d w i th t he FW D d i f f e r by a s m uch a s a f ac to r o f f ou r a t t he f i e l d bu lk s tr es s.

Th i s d i f f e r ence i s cons i s t en t w i th o the r r epo r t s i nd i ca t i ng t ha t e l a s t i c modu l i ob t a ined

u s i n g t h e s e m e t h o d s m a y d i f f er b y a s m u c h a s a f a c to r o f 1 0 ( N e w c o m b 1 9 8 6 , A l i a n d

K h os l a 1987 , Hou s ton e t al . 1990 , Da l e id en e t a l. 1994) . Th e ma te r i a l s u sed i n a ll t h r ee

m e t h o d s w e r e p r e p a r e d a t c o m p a r a b l e d r y u n it w e i g h t a n d w a t e r c o n t e n t ( F ig . 1 ). T h u s ,

d i f f e r ences i n t he e l a s ti c m odu l i f o r a g iven ma te r i a l a r e a s sum ed to be du e t o d i f fe r ences

in s t at e o f s t re s s , s tr a in leve l , nu m ber o f l oad ing cyc l e s , and s ca l e . Th e e s t ima ted bu lk

s tr e ss a n d n u m b e r o f l o a d i n g c y c l e s i n e a c h t e st m e t h o d a r e s u m m a r i z e d i n T a b l e 2 .

Fo r a l l ma t e r i a l s , t he e l a s t i c modu lus i nc r ea se s app rec i ab ly w i th i nc r ea s ing bu lk

s tre ss . F o r e x a m p l e , t h e e la s ti c m o d u l u s o f G r a d e 2 g r a v e l m e a s u r e d i n t h e l a b o r a t o r y

r e s i l i e n t m o d u l u s t e s t i n c r e a s e s f r o m 1 4 0 M P a t o 4 0 0 M P a a s t h e b u l k s t r e s s i n c r e a s e s

f rom 70 kPa t o 670 kPa . Th e s ens i t i v i ty o f e l a s ti c mo du lus t o s t r e ss s t a t e i l lu s t r a te s t he

i m p o r t a n c e o f m a i n t a i n i n g a c o n s i st e n t s t re s s s ta te w h e n c o m p a r i n g e l a s ti c m o d u l i

measu red a t d i f f e r en t s ca l e s and wi th d i f f e r en t me thods .

T h e e l a s ti c m o d u l u s m e a s u r e d i n th e L S M E i s se n s i ti v e t o t h e th i c k n e s s o f t h e

subbase l aye r (h ) be ing eva lua t ed ( i . e . , t h i cke r l aye r s have a h ighe r e l a s t i c modu lus a t a

g iven bu lk s t r e ss ) . Th e s ens i t i v i t y t o t h i cknes s i n t he L S M E re f l ec t s t he d i f f e r en t leve l s

o f s tr a in i n l a y e r s h a v i n g d i f fe r e n t t h ic k n e s s, w h i c h i s k n o w n t o a f f e c t t h e e l as t ic m o d u l u s

o f g r a n u la r m a t e r ia l s ( S e e d a n d I d r i s s 1 9 7 0 , H a r d i n a n d D r n e v i c h 1 9 7 2 , E d il a n d L u h

1 97 8). V e r t i ca l s tr a in s d e t e rm i n e d f r o m t h e K E N L A Y E R a n a l y s i s a re s u m m a r i z e d in

Tab l e 3 . L o w er ve r t ic a l s t r a in s ex i s t in t he t h i cke r l aye r s due t o g r ea t e r s t r e s s d i s tr i bu t i on

t h a t o c c u r s in a t h i c k e r l a y e r u n d e r t h e s a m e a p p l ie d s u r f a c e l o ad .




T a b l e 2 - Stress and Loading Conditions in FWD, LSME, and

Resilient Modulus Test.

T e s t i n g M e t h o d ] L o a d i n g C y c l e s [ B u l k S t r e s sb ( k P a )

B o t to m A s h

F W D 1 0 , 0 0 0 a 3 1

L SM E ( 0 .46 m ) 10 , 000 28

L SM E ( 0.69 m ) 10 , 000 22

L SM E ( 0.80 m ) 10 , 000 18

LSM E (0 .92 m) 10 ,000 19

A A S H T O T 2 9 4 1 ,5 0 0 8 4 - 7 1 8

F W D

F o u n d r y S la g

1 0 , 0 0 0 a 35

L SM E ( 0 .46 m ) 10 , 000 25

LSM E (0 .92 m) 10 ,000 13

A A S H T O T 2 9 4 1 , 50 0 8 4 - 7 1 8

G r a d e 2 G r a v e l

F W D 1 0 , 0 0 0 a 104

LSM E (0 .23 m) 10 ,000 75

L SM E ( 0.30 m ) 10 , 000 5 9

L SM E ( 0 .46 m ) 10 , 000 0

A A S H T O T 2 9 4 1 , 50 0 8 4 - 7 1 8

N o t e s : % s t i m a t e d t r a f fi c l o a d i n g b y th e ti m e o f m e a s u r e m e n t ; b m i d -

d e p t h o f t h e s u b b a s e a n d b a se l a y er s f or F W D a n d L S M E .

T ab l e 3 -

Resilient Modulus and Vertical Strain at Field Bulk Stress.

Bulk S t r ess E las t i c M odulus Ver t i ca l S t r a in

M e t h o d

( kPa ) ( M Pa) ( % )

B o t to m A s h

FW D 31 108 0.030

31 28 0.140

SM E ( 0 .46 m )

L SM E ( 0 .69 m )

L SM E ( 0 .80 m )

LSME (0 .92 m)

A A S H T O T 2 9 4

31

60

0.050

31 68 0.042

31 72 0.036

31 32 0.018

Foundr y S l ag

FW D 35 119 0 .022

35 20 0.265

35

L SM E ( 0 . 46 m )

LSME (0 .92 m)

A A S H T O T 2 9 4

29

0.130

35 30 0.022

G r a d e 2 G r a v e l

FWD 104 143 0.038

104 28 0.770

SME (0 .23 m)

L SM E ( 0 .30 m )

L SM E ( 0 .46 m )

A A S H T O T 2 9 4

104 60 0.140

104 68 0.058

104 157 0.014




To com par e t he e l a s t ic m odu l i u nde r s i m i l a r l eve l s o f st r a in an d s t r e s s , t he sm a l l -

s t ra i n m o du l us ( Mm ax) o f each m a t e r i a l was e s t i m a t ed f o r the ave r a ge s t r e s s cond i t i on

ex i s t i ng i n t he f i e l d ( t he f i e l d bu l k s t r e s se s a r e sum m ar i zed i n Tab l e 2 ) u s i ng t he

backb one cu r ves in Seed e t al. (1986). The back bon e cu r ves de sc r i be t he ra t i o o f shea r

m o du l us a t a g i ven shea r s t ra i n ( Gv , ) t o t he m ax i m um shea r m o du l u s (Gm ~x) a s a f unc t ion

o f shea r str ain . Th e shea r s tr a i n in each t e s t wa s com pu t ed us i ng :

r'=O+o) v (2)

wher e u i s t he Po i s so n ' s r a t io and ev i s the ve r t i c a l e la s t ic s t r a i n i n t he subb ase l ay e r (K i m

and S t okoe 1992) . The i m p l i c i t a s sum pt i on in th i s app r oach is t ha t t he r a ti o M/Mmax s

com par ab l e to r a ti o Gy '/Gm a• Th e backb one cu r ve f o r s and i n Seed e t a l. ( 1986) wa s used

f o r t he s and- li ke bo t t o m ash and f ou ndr y s lag , wh e r eas t he backb one cu r ve f o r g r ave l was

used f o r t he Gr ad e 2 g r ave l . Fo r t he bo t t om ash and f o und r y s lag , t he f i e ld bu l k s t r e s s i s

l ower than t he l ow es t bu l k s t re s s app l i ed in t he l abo r a t o r y r e s i li en t m od u l us t e st . Thus ,

f o r t he se m a t e r i a l s , t he e l a s t i c m odu l us a t t he f i e l d bu l k s t r e s s was e s t i m a t ed by

ex t r apo l a t ion us i ng t he po w er f unc t i on i n Eq . 1 .

The M m ~ ob t a i ned u s i ng t h is app r oach a r e t abu l a t ed i n Tab l e 4 f o r each m a t e r i a l.

F o r th e L S M E , t h e

Mrnax

or a g i ven m a t e r i a l a r e s i m i l a r r ega r d l e s s o f the l aye r t h icknes s ,

excep t f o r t he th i nnes t l aye r o f Gr ad e 2 g r ave l ( h = 0 . 46 m ) . Th i s s i m i l a r i ty suppor t s the

e f f ec ti venes s o f t he co r r ec t i on m e t ho d t o accoun t f o r s t ra i n e f fec t s . Th e

Mmax

f r o m t h e

FW D i s sl i gh t ly ( app r ox i m a t e l y 1 .6 t i m es ) h i ghe r t han t he Mm ax ob t a i ned f r om t he L SM E

f or a ll m a t e r ia l s , and i s app r ec i ab l y h i ghe r ( app r ox i m a t e l y 4 t i m es ) t han

Mmax

ob t a i ned

f r o m th e l a b o r a t o r y t e s t fo l lo w i n g A A S H T O T 2 9 4 f o r t h e b o t t o m a s h a n d f o u n d r y s la g.

For G r ade 2 g r ave l , Mm ax f r om t he F W D i s s li gh t ly ( app r o x i m a t e l y 1 . 3 t im es ) h i ghe r t han

Mmax

o b t a in e d f r o m t h e l a b o r a t o ry t e st fo l lo w i n g A A S H T O T 2 9 4 . T h e s i m i la r it y o f th e

Mmax

f r o m t h e F W D a n d t h e L S M E s u g g e s t s t h a t t h e L S M E p r o v i d e s a r e a l i s t i c

a s se s sm en t o f e l a s ti c m odu l i ope r a t i ve i n t he f ie ld .

T h e c a u s e o f t h e d i f f e r e n c e b e t w e e n t h e l a b o r a t o r y - m e a s u r e d r e s i l i e n t m o d u l u s

and t he e l a s t i c m odu l i back ca l cu l a t ed f r om t he L SME and f i e l d t e s t s f o r t he i ndus t r i a l

bypr od uc t s is no t know n . I nacc u r acy i n t he ex t r apo l a t ion to l ow er bu l k s t re s se s m ay be

r e sp o n s ib l e. T h e r e m a y a l s o b e s o m e a s p e c t o f th e p a rt ic l e c o m p o s i t io n o f t h e

bypr od uc t s t ha t is d i f f e r en t f r om t hose cha r ac t e ri s ti c o f the p r ed om i nan t l y s i l i c a - based

sands t ha t f o r m t he ba s i s f o r t he power f unc t i on i n Eq . 1 and t he backbone cu r ve f o r

s ands i n Seed e t a l. ( 1986). Nev e r t he l e s s , m odu l i f o r t he bypr o duc t s ob t a ined us i ng t he

l abo r a t o r y r e s i l i en t m odu l us t e s t t end t o be l ower t han t hose ope r a t i ve a t t he p r o t o t ype

and f ie l d s ca le s . Thus , pa vem en t de s i gns inco r po r a t i ng s i m i l a r byp r odu c t s tha t hav e

em pl oyed m odu l i f r o m l abo r a t o r y r e s i li en t m odu l us t e s ts shou l d be con se r va t i ve .

C o n c l u s i o n

The da t a f r om t h i s s t udy i nd i ca t e t ha t t he e l a s t i c m odu l us o f g r anu l a r m a t e r i a l s

used i n pavem en t sys t em s depends on t he s t a t e o f s t r e s s and t he s t r a i n am pl i t ude .

Com par i son o f e l a s t i c m odu l i m easu r ed i n a conven t i ona l l abo r a t o r y t e s t t o t hose



2 0 6 R E S IL IE N T M O D U L U S T E S T I NG F O R P A V E M E N T C O M P O N E N T S

o p e r a t i v e at t h e p r o t o t y p e a n d f i e ld s c a l e s r e q u ir e s t h a t s t a te o f s t r e ss a n d s t r a in a m p l i t u d e

b e c o m p a r a b l e . D i f f e r e n c e s i n s t ra i n a m p l i tu d e c a n b e d e a l t w i t h b y a p p l y i n g an

e m p i r i c a l c o r r e c t i o n u s i n g b a c k b o n e c u r v e s f o r g r a n u l a r m a t e r i a l s . T h e e f f e c ts o f s t re s s

a r e h a n d l e d b y l i m i t in g c o m p a r i s o n s o n l y to e l a s t ic m o d u l i m e a s u r e d a t a c o m p a r a b l e

s ta t e o f s tr e s s. H o w e v e r , t h e l a b o r a t o r y re s i li e n t m o d u l u s t e s t d o e s n o t a l w a y s p r o v i d e

e l a s t ic m o d u l i f o r t h e r a n g e o f b u l k s t r e s s e s e n c o u n t e r e d i n t h e f i e ld . I n s u c h c a s e s , a n

e s t im a t e o f t h e e l a s ti c m o d u l u s a t t h e f i e l d st a te o f s tr e s s c a n b e o b t a i n e d b y e x t r a p o l a t i o n

u s i n g a p o w e r f u n c t i o n .

T a b l e 4 - L o w S t ra i n E l a s t ic M o d u l u s O b t a i n ed a t F i e M B u l k S t r e s s

M e t h o d

Elas t i c Shear

Mo dulus S t r a in , 7 '

( M Pa) ( % )

Shea r

M o d u l u s

R a t i o

M a x i m u m

M odu l us ,

M , ~ ( M P a )

Bot tom A sh, Bulk S t r ess = 31 kPa

FW D 108 0.038 0.48 225

28 0.175 0.18 156

SME (0 .46 m)

L SM E ( 0 .69 m m )

LSME (0 .80 m)

LSME (0 .92 m)

A A S H T O T 2 9 4

60

68

72

0.063

0.053

0.39

0.44

0.045 0.46

32 0.018 0.60

Fou ndry S lag , Bulk S t r ess = 35 kPa

154

155

157

53

F W D

L SM E ( 0 .46 m )

LSME (0 .92 m)

A A S H T O T 2 9 4

119

20

29

30

0.029

0.352

0.173

0.029

0.57

0.15

0.23

0.57

209

t 33

130

53

Grad e 2 Gravel , Bulk S t r ess = 104 kPa

FW D 143

LSM E (0 .23 m) 28

LSM E (0 .305 m) 60

LSM E (0 .46 m) 68

A A S H T O T 2 9 4 1 57

0.049

1 . 0 0 1

0.182

0.075

0.018

0.30 [

0.07

0.16

0.23

0.43

477

400

375

296

365

E v e n w h e n c o r r e c t i o n s a r e a p p l ie d , t h e e l a st ic m o d u l u s o b t a i n e d f r o m a l a b o r a t o r y

r e s i li e n t m o d u l u s t e s t t e n d s t o b e l o w e r th a n t h e o p e r a t i v e e l a s t i c m o d u l u s o b t a i n e d b y

b a c k - c a l c u l a t io n f ro m p r o t o t y p e t e s ts ( e .g . , t h e L S M E ) a n d f i e l d t e s ts u s i n g t h e F W D .

F o r c o n v e n t i o n a l g r a v e l s u s e d a s s u b b a s e m a t e r i a l s , t h e d i f f e r e n c e b e t w e e n t h e e l a s t i c

m o d u l i m e a s u r e d i n t h e l a b o r a t o r y a n d f i e ld i s s m a l l . H o w e v e r , f o r s a n d - l i k e i n d u s t r ia l

b y p r o d u c t s , t h e f i e l d e l a s t i c m o d u l i c a n b e a s m u c h a s f o u r t i m e s h i g h e r t h a n t h a t

m e a s u r e d i n a l a b o r a t o r y r e s il i e n t m o d u l u s t es t.




Acknowledgment

The Wisconsin Highway Research Program provided financial support for the

study described in this paper. However, he conclusions and recommendations are those

of the authors and do not reflect the opinions or policies of WisDOT. Alliant Energy

Corporation supplied the bottom ash, Grede Foundries Inc. supplied the foundry slag, and

Yahara Materials supplied the Grade 2 gravel. The assistance provided by Alliant

Energy, Grede Foundries, and Yahara Materials is greatly appreciated. The LSME

experiments described in this paper were conducted in the University of Wisconsin

Structures and Materials Testing Laboratory (SMTL). Professor Steven Cramer (Director

of SMTL) and Mr. William Lang (Manger of SMTL) provided valuable assistance during

the study.

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Go nza lo R . Rada , l Jona than L . Groeger , 2 P e t e r N . S chm alze r , 3 and Aram is L opez 4

Res i l ient M odulus Tes t ing o f Un bou nd Mater ia ls : L TPP's L earning Exp er ience

Reference:

Rad a, G. R. , Gro eger , J . L ., Schm alzer , P . N. , and L opez , A.,

"Resi l ient

M odulus Tes t ing o f Un bou nd Mater ia ls : L TPP's L earning Exp er ience," Resilient

Modulus Testing or Pavement Components, ASTM STP 1437, G. N . Du rham , W . A .

M ar r , and W . L . De G rof f , Eds . , AS TM In t e rna t iona l , W es t Con shohock en , P A , 2003 .

Abstract:

Res i l ien t modu lus i s a key da t a e l emen t f o r cha rac t e r iz ing unboun d pav em ent

ma te r ia l s wi th in t he LT P P p rog ram. Al though the t e s t has been a round f o r nea r ly th ree

decades , i ts imp lem enta t i on wi th in t he p rog ram ha s been a cha l lenge . A su i t ab l e t e s t

p ro toco l was no t ava i l ab l e when t he p rog ram bega n i n 1987 . I t was i nco r r ec t ly a s sume d

in the ea r l y yea r s tha t equ ipm ent man uf ac tu red f o r ' t he te s t would w ork as i n t ended . I t

w a s a l so i n c o r r e c tl y a s su m e d t h a t p r o p e r l y o p e r a ti n g e q u i p m e n t a n d k n o w l e d g e a b l e

p e r s o n n e l im p l y g o o d d a ta . T h i s p a p e r h a s b e e n p r e p a r e d t o s h a re L T P P ' s e x p e r i e n c e

ov er t he pas t 14 yea r s i n ach i ev ing r epea t ab l e , h igh-qua l i ty r e s i li en t mo dulus da t a .

S pec i f ic i s sues addressed i n t he pape r i nc lude t he t e s t p ro toco l , l abora to ry s t a r tup and

qua l i ty con t ro l p rocedures , qua l i t y con t ro l and qua l i ty a s surance p rocesses , and

com prehen s ive gu ide l ines con t a ined in an easy - to -use , i n t e rac t ive CD -RO M .

Keywords:

r e s il ien t mo dulus , l abora to ry te s ti ng , unbo und mate r i a l s , qua l i t y con t ro l and

qua l i t y a s surance , gu ide l ines , L TP P

Introduct ion

T h e L o n g - T e r m P a v e m e n t P e r fo r m a n c e ( L T P P ) p r o g r a m i s a 2 0 - y e a r s tu d y o f

pav em ent pe r f o rm ance and t he f ac to r s t ha t a f f ec t it . It s m a in go a l i s to p rov id e t he da t a

n e c e s s ar y to e x p l a in h o w p a v e m e n t s p e r f o r m a n d w h y t h e y p e r f o r m a s t h e y d o . T o m e e t

this goa l , the p rog ram has e s t ab l ished nea r ly 2500 t e s t s ec ti ons on i n - se rv i ce h ighw ays

throughout No r th Am er i ca . The da t a co l l ec t ed a t each o f t hose t e s t s ec ti ons a r e i n t ended

to cha rac t e ri ze pavem ent pe r f o rma nce and t he condi t i ons a s soc i a t ed wi th t ha t

1 Ass i s t an t Vice P res iden t , LA W P CS , 12104 Ind i an Creek C our t , S u i te A , Be l t sv il le ,

M D 2 0 7 0 5 .

2 Vice P res iden t, A xiom Dec i s ion S ys t ems , Inc . , 6420 Dob bin R oad , S u i t e E , Colum bia ,

M D 2 1 0 4 5 .

3 P ro j ec t Eng inee r , LA W P CS , 1575 De lucch i Lane , S u i te 201 , R eno , NV 89502 .

4 L T P P T e a m L e a d e r, F e d e r al H i g h w a y A d m i n i s tr a ti o n , 6 3 0 0 G e o r g e t o w n P i k e , M c L e a n ,

VA 22101.

209

Copyright9 by ASTM lntcrnational w ww .astm.org




p e r f o r m a n c e .

D a t a cha r ac t e r iz i ng t he pavem en t m a t e r i a ls ob t a ined v i a s am pl i ng and l ab o r a t o r y

t e s ti n g a r e o f p a r a m o u n t i m p o r t a n c e to m e e t in g t h e p r o g r a m ' s g o a l. I n th e c a s e o f

unb ound m a t e r i a l s , one o f the m os t i m p or t an t da t a e l em en t s is the r e s i li en t m od u l us ( Mr) .

Th i s va l ue i s a key i npu t to t he cu r r en t A A SH TO des i gn p r ocedur e s . I t i s a lso a ba s i c

m a t e r i a l p r ope r t y t ha t c an be used i n m ech an i s t ic ana l ys i s o f m u l t i- l aye r ed sys t em s f o r

p r ed i c t i ng e l a s t ic d e f o r m a t i ons t ha t u l ti m a t e l y co r r e la t e to p avem en t pe r f o r m ance .

Al t hou gh t he t e s t ha s been a r ound f o r ahnos t t h ree decades , i t s i m p l em e n t a t i on wi t h i n

t he p r og r am was a cha l lenge . Fo r s t ar te r s , t he r e was no su i t ab le t e s t p r o t oco l w hen t he

p r og r am b egan i n 1987, w h i ch m ean t a s i gn i fi can t l eve l o f e f f o r t wa s spen t i n t he

p r epa r a t i on o f such a p r o t oco l . It wa s a l so i nco r r ec t ly a s sum e d ea r l y i n the p r o g r am t ha t

equ i p m e n t m an uf ac t u r ed f o r Mr t e s ti ng wou l d w or k a s in tended . The l e s son l ea r ned f r om

t h i s m i s t ake l ed to de ve l op m e n t o f t he L T PP l abo r a t o r y s t a rt up and qua l i t y con t ro l ( QC )

pr ocedur e , w h i ch i s de s i gned t o ve r i f y t he ope r a t i ng accu r acy o f a ll e s s en t ia l sys t em

com pon en t s i n a l og i ca l m a nne r an d i nc r ea se t he u se r ' s con f i dence i n the r e su l t i ng da t a.

Bes i des i ts rou t i ne u se wi t h i n the p r og r am , t he p r ocedu r e ha s a l so been i m p l em en t ed b y a

num ber o f s ta t e s a s we l l a s academ i a and p r i va t e labo r a t o ri e s .

L T P P ' s e f f o r t s to en su r e t he h i ghes t qua l it y Mr da ta d i d no t s t op a f t e r t he

i m p l em e n t a t i on o f the s t a r tup and Q C p r ocedur e . I ndeed , ano t he r l e s son l ea r ned sho r t l y

a f t e r i ts i m p l em en t a t i on was no t to a s sum e t ha t p r ope r l y ope r a t i ng equ i pm en t and

kno w l edgeab l e pe r sonne l i m p l y good da ta . M or e t o the po i n t , a t ho r ough r ev i ew o f the

da t a r evea l ed , a l be i t i n f requen t ly , t he p r e sence o f anom a l i e s. Th i s l ed t o t he dev e l opm en t

o f de t a i led qu a l i ty con t r o l and qua l it y a s su rance ( QC /QA ) p r oces se s and so f t wa r e t o

check o ve r 2000 da t a com pone n t s to ensu r e accu r acy and cons is t ency .

Cl ea r l y , m uch has be en l ea r ned wi t h in t he L TP P p r og r am i n the pa s t 14 yea r s wi t h

r ega r ds t o t he Mr cha r ac te r i za ti on o f unbou nd m a t e r ia l s . M any o f the l e s sons l e a r ned

hav e been sha r ed wi t h t he pavem en t com m uni t y , bu t c e rt a i n l y no t a ll. T o add r e s s t ha t

sho r t com i ng , an e f f o r t t o dev e l op com pr ehen s i ve gu i de li ne s on t he Mr t e s t f o r unbo und

m a t e r i a l s w as r ecen t l y com pl e t ed . Th e gu i de l ine s a r e con t a i ned i n an ea sy - t o - use ,

i n t e r ac ti ve CD - R O M and t hey a r e be i ng d i s tr i bu ted t o a wi de aud i ence - h i ghw ay

agen cies , univers i t i es , indus t ry , and co nsul tant s .

Th i s pap e r expand s on each o f the t op i c s add r e s sed abo ve - t e s t p r o t oco l , l abo r a t o r y

s t a r tup an d qua l i ty con t r o l p r ocedur e , qua l i t y con t ro l and a s su r ance p r oces se s , and

Mr

gu i de l i ne s on CD - RO M . I t s m a i n o b j ec t i ve i s t o sha r e L T PP ' s l e a r n ing exp e r i ence i n

cons i s t en t l y ach i ev i ng r epea t ab l e , h i gh - qua l i ty Mr da t a wi t h t he pave m e n t com m u ni t y .

T e s t P r o t o c o l

At t he ou t s e t o f L T PP, p r og r am p l anne r s de s i gna t ed Mr t e s t ing a s a ke y i npu t f o r t he

p r o j e ct . Th i s was de t e r m i ned because o f t he u se f u l nes s o f the t e s t r e su lt s i n em pi r i ca l and

m e c h a n i s ti c p a v e m e n t d e si g n p ro c e d u re s . D u r in g t h is t im e , A A S H T O T 2 7 4 w a s t h e

p r edo m i n an t p r o t oco l u sed f o r Mr t e s ti ng o f unbound pav em en t m a t e r i a ls . Af t e r c a r e f u l

r ev i e w o f t he p r ocedu r e by a g r ou p o f m a t e r ia l s te s t i ng expe r t s , it was de t e r m i ned t ha t t he

S t a n d a rd M e t h o d o f T e s t f o r R e s i li e n t M o d u l u s o f S u b g ra d e S o i ls , A A S H T O D e s i g n a t i o n

T 274 ( d i s con t inued i n 1990) was no t adequa t e fo r t he L TPP p r og r am . The s t anda r d



R A D A E T A L . O N U N B O U N D M A T E R I A LS 2 1 1

con t a i ned t oo g r ea t a r isk o f po t en t ia l va r i ab i l it y because o f i t s wo r d i ng . A s such , i t w as

d e c i d ed t h a t a n e w p r o c e d u r e w a s n e e d e d f o r th e L T P P p r o g r a m .

I n 1989 , a g r oup o f m a t e r i a l s t e s t ing expe r t s aga i n conven ed t o p r oduce w ha t i s now

k n o w n a s th e L o n g - T e r m P a v e m e n t P e r f o r m a n c e P r o t o c o l P 4 6: R e s i l ie n t M o d u l u s o f

Un bou nd Gr anu l a r Base /Sub base M a t e r ia l s and Subgr ade So il s. T he f i rs t ve r s i on

a t t em p t ed t o m ake t he p r ocedur e a s s t anda r d a s pos s i b le and e l i m i na t ed m an y o f the

oppo r t un i t ie s f o r dev i a t i on i nv i t ed by T 274 . A f t e r a l eng t hy r ev i ew p r oce s s , the f i r s t

ve r s i on o f P46 w as i s sued l a t e r t ha t yea r. Four l abo r a t o r ie s unde r con t r ac t t o L T PP used

t he p r o t oco l f o r s eve r a l m o n t hs i n a p il o t s tudy. F r om t he r e su l ts o f t h i s p i lo t s t udy , m a ny

r e c o m m e n d a t i o n s f o r im p r o v e m e n t t o th e p r o c e d u r e w e r e d e v e l o p e d . B a s e d u p o n t h e s e

r ecom m enda t i ons , the p r o t oco l was t ho r oug h l y rev i s ed and r e - i s sued i n 1992 .

T h e 1 99 2 p r o t o c o l w a s u s e d f o r se v e r al y e a r s i n t h e L T P P p r o g r a m a n d m a n y

addi t iona l l essons w ere l earned as a resul t. In 1996, anoth er s igni f i cant rev iew and

r e v i s io n c y c l e w a s u n d e r ta k e n . M a n y i m p r o v e m e n t s w e r e m a d e b a s e d u p o n t h e

expe r i ence o f f ou r yea r s o f t es t ing . T he r eby , t he f i na l ve r s i on o f t he p r o t oco l , a s i t ex i s t s

t oday , was i s sued by L TPP. The p r o t oco l in i t s ex i s t ing cond i t i on i nco r po r a t e s a va s t

am oun t o f t heo r e ti ca l and p rac t ica l knowl edg e g l eaned f r om t e s t ing ov e r 3000 s am pl e s .

The p r o t oco l con t a ins m any cond i t ions and r equ i r em en t s tha t app l y on l y t o t he L TP P

p r o g r a m . F o r e x a m p l e , m e a s u r e m e n t o f d e f o rm a t i o n o u t si d e o f t h e t e s t c h a m b e r i s a

r equ i r em en t t ha t i s ve r y spec i f ic t o t he goa l s and ob j ec t i ve s o f t he L T PP p r og r am .

Beca use o f t he l a r ge num ber s o f s am pl e s to be t e s ted , the ex pe r t t a sk g r oup t ha t r ev i ew ed

t he p r o t oco l dec i ded t ha t t h i s was t he m o s t p r ac t ica l and e f f i c i en t m e t hod . Ho w eve r , t h i s

m e t hod m ay no t a pp l y to a ll t e s t cond it ions .

S u b s e q u e n t t o t h e p u b l ic a t io n o f th e f i n a l p r o t o c o l, a n A A S H T O c o m m i t t e e u n d e r t o o k

t he t a sk o f u s i ng the L T PP p r o t oco l to deve l op a new r e s il ien t m od u l us p r o t oco l f o r u se

i n th e A A S H T O m a t e r i a ls s p e c if ic a ti o n s d o c u m e n t. T h i s p r o to c o l w a s m e a n t to r e p l a c e

t h e T 2 7 4 p r o t o c o l. T h i s n e w p r o t o c o l, S t a n d a rd M e t h o d o f T e s t f o r D e t e r m i n in g t h e

R e s i l ie n t M o d u l u s o f S o i ls a n d A g g r e g a t e M a t e r ia l s, A A S H T O D e s i g n a t i o n T 3 0 7 , w a s

i s sued i n 1999 . W hi l e t he s t anda rd con t a i ns m a ny s i m i l a ri t ie s to P46 , t he au t ho r s o f t

307 t o ok g r ea t c a re t o i nco r po r a t e o t he r p r ac t ica l app l i ca t i ons to t he p r oced ur e t o m ak e i t

u se r - f r iend l i e r f o r a wi de v a r i e t y o f u se rs . An exa m p l e is the a l l ow ance o f t he u se o f

pneu m a t i c sys t em s in T 307 , wh i ch a r e p r oh i b i t ed i n P46.

P46 desc r i be s t he l abo r a t o r y p r epa r a t ion and t e s t i ng p r ocedu r e s f o r Mr de t e r m i na t i on

of unbo und g r anu l a r ba se and sub base m a t e r i a l s and subgr ade so i ls unde r spec i f i ed

cond i t i ons r ep r e sen t i ng s t re s s s ta t e s benea t h pavem en t s sub j ec t ed to m ov i ng w hee l l oads .

The m e t hods desc r i bed i n the p r o t oco l a r e app l i cab le t o und i s tu r bed s am pl e s o f na t u r a l

a n d c o m p a c t e d s u b g r a d e s o i ls a n d to d i s tu r b e d s a m p l e s o f u n b o u n d b a s e a n d s u b b a s e a n d

subgr ade so i ls com pac t ed i n t he l abo r a t o ry . S t r e ss l eve l s u sed f o r te s t i ng spe c i m e ns a r e

based up on t he l oca t i on o f t he spec i m en wi t h in t he pavem en t s tr uc tu r e . Sa m p l e s l oca t ed

wi t h i n t he ba se and sub base a r e sub j ec ted t o d i f f e ren t s tr e s s leve l s a s com par e d to t hose

spec i m ens t ha t a r e f r om t he subgr ade . Gene r a l l y , spec i m en s i ze f o r t e s t ing depen ds u pon

t he t ype o f m a t e r i a l ba sed upon t he g r ada t i on and t he p l a s t i c l i m i t o f the m a t e r i a l .

Pro tocol P46 covers the fo l lowing topics : scope , t es t ing loca t ions , def in i t ions ,

app l i cab l e docum en t s , unbou nd m a t e r i a l s t e s ti ng p r e r equ is i te s , appa r a t us , p r epa r a t i on o f

t e s t spec i m en s , t e s t p r ocedur e s , c a l cu l a ti ons , r epo r t ing , and com pac t i on o f t e s t

spec i m ens . I t is su i t ab l e f o r u se by o r gan i za t ions w i sh i ng t o pe r f o r m t he i r t e s ts ex ac t l y a s



2 1 2 R E S IL IE N T M O D U L US T E S T I NG F O R P A V E M E N T C O M P O N E N T S

t hey wer e con duc t ed b y L TP P f o r co r re l a t ion o r o t he r pu r poses . Ho w eve r , i ts u se a s a

gene r a l t e s t m e t hod f o r u se by a l l o r gan i za ti ons shou l d be co ns i de r ed ve r y ca r e fu l l y .

A s m e n t i o n e d p r e v i o u s ly , T 3 0 7 w a s d e v e l o p e d p r i m a r il y b y m o d i f y i n g L T P P

Pr o t oco l P46 . M any f ea t u r e s o f t he s t anda r d a r e s i m i l a r t o P46 w h i l e som e sec t i ons have

been m od i f i ed t o f ac i li t a te u se o f t he p r ocedur e b y a b r oade r r ange o f o r gan i za t i ons . A t

t he t i m e o f t he de ve l op m e n t o f t h i s too l , th i s i s t he on l y t e s t st anda r d ado p t ed b y

A A S H T O t o d e t e r m i n e r es il ie n t m o d u l u s v a l u e s f r o m p a v e m e n t m a t er i al s .

The r e a r e s eve r a l o t he r te s t p r ocedur e s dev e l oped , o r unde r dev e l opm en t , t h r ough ou t

t h e w o r l d . E a c h p r o c e d u r e h a s it s o w n s t re n g th s a n d w e a k n e s s e s . F o r e x a m p l e , N C H R P

1-28 [Ba r ksda l e e t al . 1998] ha s p r opo sed new p r ocedur e s f o r t e s ti ng a spha l t and

unbo und m a t e r i a l s . Seve r a l o t he r re sea r che r s have a l so pu t f o r t h r ev i s ed t e s t p r ocedur e s .

Fo r now , i t s eem s tha t AA SH TO T 307 i s t he s ta t e - o f - the - p r ac t i ce wi t h i n t he Un i t ed

S t at es . P 4 6 c a n b e d o w n l o a d e d f r o m th e F e d e ra l H i g h w a y A d m i n is t ra t io n ( F H W A ) L T P P

w e b s i te , w h i le T 3 0 7 i s a v a il a b le f r o m A A S H T O .

La boratory S tartup and Quality Control Procedure

R e s i l ie n t m o d u l u s t e s ti n g o f u n b o u n d m a t e r ia l s w i t h i n th e L T P P p r o g r a m b e g a n

shor t l y a ft e r com pl e t i on o f t he P46 t e s t p r o toco l . A s i gn if i can t leve l o f e f f o r t had been

spen t o n d eve l op i ng t he p r o t oco l , t hus h i gh - qua l i t y t e s t r e su l ts w e r e an t ic i pa t ed .

Unf o r t una t e l y , i t wa s i nco r r ec t ly a s sum ed a t t he t i m e t ha t equ i pm en t m an uf ac t u r ed f o r Mr

t e s t ing wo u l d w or k a s in tended . A r e v i ew o f t he da t a ob t a ined a f t e r t e s t ing co m m enc ed

i den t if i ed num er ous p r ob l em s , wh i ch i n t u rn r a i s ed ques ti ons ov e r t he accu r ac y and

re l i ab i l i ty of the col l ec ted da ta .

A subsequ en t i nves t i ga t ion r evea l ed t ha t m os t o f t he p r ob l em s cou l d be t r aced t o

incor rec t se t tings in the equ ipm ent e lec t ronic f il te rs . Th ese inco r rec t se t tings resul t ed in

p r ob l em s such a s non - sym m e t r i ca l l oad i ng cond i ti ons , peak de f o r m a t i on occu r r i ng p r io r

t o pea k l oad i ng , de f o r m a t i on re sponse occu r r i ng f o r sho r te r ti m e pe r i od t han l oad i ng ,

de f o r m a t i on r e sponse f l uc tua t ions , and a de f o r m a t i on - c l i pp i ng phen om enon . F i gu r e s 1

and 2 i l lu s t r a te a cou p l e o f t he p r ob l em s i den t if i ed du r i ng t he i nves t iga t i on .

Th e l e s sons l e a r ned f r om t h i s i nves t i ga ti on l ed t o t he deve l op m en t o f the l abo r a t o r y

s t a r tup and qua l i ty con t r o l p r ocedur e , wh i ch i s i n t ended t o ensu r e t he ac cu r acy and

r e l iab i l it y o f the r a w da t a p r oduced wh i l e te s t ing m a t e r i a ls u s i ng c l o sed - l oop s e r vo -

hydr au l i c sys t em s . T he p r oce dur e i s de s i gned t o v e r i f y t he ope r a t i ng acc u r acy o f a ll

e s sen t i a l sys t em com pon en t s i n a l og ica l m anne r . Ea ch pa r t o f t he sys t em i s ve r i f i ed

i nd i v i dua l l y and t hen t he en t i r e sys t em i s checked t o m ake su r e a l l o f the pa r t s w or k

together .

The p r oced ur e i s d iv i ded i n to t he t h r ee d is t inc t com pon en t s de sc r i bed be l ow . A m or e

de t a i led desc r i p t i on o f the p r ocedu r e and i t s com p onen t s is p r e sen t ed i n [Al av i e t a l.

1997].

E l ec t r on i c s Sys t em Pe r f o r m ance Ver i f i c a t ion P r oced ur e - Th i s p r ocedur e

cha r ac t e r i ze s the f r equency r e sponse o f t he s i gna l cond i t ione r s and da t a acqu i s i t i on

com pon en t o f t he t e s t sys t em . The p r oced ur e i s gene r a l ly u sed p r i o r t o the i n i ti a t ion o f

a Mr t e s t ing p r og r am . As l ong a s a l l o f the e l ec t r on i c s o f the t e s t sys t em r e m a i n t he

sam e , t h i s p r ocedur e does no t need t o be r epea t ed on a con t inu i ng bas i s . Ho w eve r , t he



RADA ET AL. ON UNBOUND MATERIALS

2 1 3

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Figure 2 - Exam ple o f Typ ica l De format ion C l ipp ing Phenomeno n




pr oced ur e shou l d b e conduc t ed a t le a s t eve r y yea r o r wh en an y pa r t o f t he e l ec t r on i c s

i s r ep l aced o r m o d i f ied . A l so , th i s p r ocedur e i s pe r f o r m ed wh en o t he r c i r cum s t ances

sugges t t ha t the e l ec tr on i c s m a y be suspec t. An e l ec t ron i c s t e chn i c i an we l l v e r s ed i n

da t a acqu i s i ti on sys t em s i s needed to pe r f o r m t he p r ocedur e . The am oun t o f t i m e

r equ i r ed t o pe r f o r m t h is p r ocedur e dep ends on t he co m p l ex i t y o f the t e s t sys t em and

expe r i ence o f t he te chn i c ian , bu t o n ave r age , i t t akes abo u t 8 t o 10 hour s to com pl e t e .

9 Ca l i b r a t i on Ch eck and Ove r a l l Sys t em Pe r f o r m ance Ver i f ic a t i on P r ocedu r e -

D y n a m i c t e st in g p r o c e d u r e s r e q ui re a s y s t e m m a d e u p o f m a n y d i f f e re n t p ie c e s o f

equ i pm en t : l oad f r am e , l oad ce l l s, hyd r au li c sys t em , de f o r m a t i on dev i ce s , t r iax i a l

p r e s su r e cham ber , tem per a t u r e cham b er s , com pu t e r , e tc . Fo r t he ca l ib r a t i on check and

ove r a l l sy s t em p e r f o r m an ce ve r i f ic a t i on p rocedur e , i nd i v i dua l e l em en t s o f the t e s t

equ i pm en t a r e check ed f i r s t f o l l owed b y the ove r a l l t e s t s e t up t o ve r i f y t ha t t he sys t em

i s p r oduc i ng t he exp ec t ed re sponses . The i nd iv i dua l subco m p onen t s add r e s sed

i nc lude : ve r i f i c a t ion o f d i sp l acem en t t ransduce r ca l i b ra t i on check , l oad ce l l z e r o

check , load ce l l ca l ibra t ion check, ver i f i ca t ion of load ce l l ca l ibra t ion ch eck ( s ta ti c ) ,

l o a d v e r s u s d e f o r m a t i o n r e s p o n s e c h e c k ( d y n a m i c) , s y s t e m d y n a m i c r e s p o n s e c h e c k ,

and t r i ax ia l p r e s su r e cham ber check . By f ir s t check i ng t he i nd i v idua l co m pon en t s o f

t he t e s t sys t em , m an y p r ob l em s t ha t wo u l d be encoun t e r ed du r i ng ac t ua l dynam i c

t e s t i ng can be i den t if i ed an d e l i m i na t ed p r i o r to ch eck i ng t he ove r a l l sy s t em . Th i s

p r oced ur e i s gene r a l l y u sed p r i o r t o i n i ti a ti on o f a t e s ti ng p r og r am and su bsequen t l y on

a con t i nu i ng b as i s ( i.e ., m o n t h l y ) t o ve r i f y t he sys t em r e sponse . O n ave r age , t he

p r ocedu r e r equ i r e s app r ox i m a t e l y 16 hour s t o com p l e t e

9 P r o f i c i ency P r ocedur e - The ab i l it y o f labo r a t o r y pe r sonne l t o conduc t dynam i c

t e s t ing i s eva l ua t ed i n t h is p r ocedu r e , p r i o r t o i n i ti a ti on o f a t e s ti ng p r o g r am and

subsequ en t l y on a con t i nu i ng bas i s to ve r i f y t he ope r a t o r ' s ab i l i ty to c ondu c t Mr

t e s ti ng . The p r oced ur e r equ i re s app r o x i m a t e l y 2 days to com pl e t e . The p r i m ar y goa l s

o f t he p r ocedur e a r e ( 1) t o ensu r e t ha t the t e s t sys t em and t echn i c i ans a r e cap ab l e o f

pe r f o r m i ng a te s t p rocedur e , and ( 2 ) t o deve l op a ben chm ar k pe r f o r m ance s t anda r d

aga i ns t wh i ch t he l abo r a t o r y can be eva l ua t ed on an on - go i ng bas i s. Th i s i s a ve r y

i m p o r t a n t p a r t o f a n y Q C / Q A s y s te m .

As pa r t o f the e l ec t ron i c s sys t em ve r i fi c a t ion p r ocedur e , t he s i gna l con d i t ion i ng

channe l s , d a t a acqu i s i t ion p r oces se s , and t r ansduce r s a r e check ed f o r p r ope r ope r a t i on .

On com pl e t i on , the ca l i b r a ti on check and ove r a l l sy s t em pe r f o r m ance ve r i f i c a t i on

pr oced ur e i s pe r fo r m ed . L oad and d i sp l acem en t m easu r i ng dev i ce s ; (i.e ., l oad ce l l s , l inea r

va r i ab l e de f o r m a t i on tr ansduce r s o r L VD Ts) a r e checked f o r l inea r i ty and p r ope r

ca l i b ra t i on . Th e ab i l i ty o f t he so f t wa r e t o con t r o l and acqu i r e d a t a i s a l so a s se s sed . W hen

t he p r oc es s o f ve r i f y i ng t he i nd i v i dua l sys t em com pon en t s i s com pl e t e , the o ve r a l l

capab i l i t y o f t he m a ch i ne t o co nduc t a spec i f i c expe r i m en t is a s se s sed t h r ough spec i a l l y

des i gned s t a t ic and dyn am i c expe r i m en t s on m a t e r i a l s wi t h kno w n p r ope r t ie s . On ce t he

sys t em has b een ev a l ua t ed , t he p r o f i c i ency phase o f the p r oced ur e add r e s se s t he

c o m p e t e n c e o f t h e l a b o r a t o ry p e rs o n n e l to p r e p a r e a n d t e s t s a m p l es . T h r o u g h t h e u s e o f

t h i s p r ocedur e , a l l o f t he com pone n t s neces sa r y to o b t a i n r epea t ab le , a ccu r a t e Mr t es t

resul t s a re ver i f i ed .

The s t a r tup an d Q C p r ocedur e enab l e s l abo r a to r i e s t o ve r i f y t he i r te s t i ng sys t em s and

pr oced ur e s p r i o r t o t he s t a r t o f p r oduc t i on t e s t ing by us i ng a com pr ehen s i ve and l og i ca l



R A D A E T A L . O N U N BO U N D M A T E R I A LS 2 1 5

p r o c e s s. I t c a n a l s o b e u s e d t o p e r f o r m o n g o i n g Q C c h e c k s o f t h e e q u i p m e n t a n d t e s t in g

p roces se s be ing used by t he l abo ra to ry du r ing t he p roduc t i on t e s t i ng p roces s . F rom use o f

t he p roced ure t o da t e , man y po t en t ia l sou rces o f e r ro r have been i den t i f i ed and r ec t i f i ed

p r io r t o s t a rt i ng a t es t i ng p rog ram , t hus po t en t i a l ly s av ing a l a rge amou n t o f e f fo r t and

re sou rces . T hey i nc lude :

E l ec t ron i c e r ro r s - ove r - r an ged l oad ce l ls , i nadequa t e f i l te r s ( ampl i t ude a t t enua t ion ) ,

and unma tched f i l t e r s ( exces s ive t ime de l ay be tween channe l s ) .

So f tw a re e r ro r s - i nadequa t e so f tw a re con t ro l o f l oad , i nadequa t e s am pl ing r a t e s , r aw

da t a w i tho u t un i t s , l a ck o f ga in con t ro l ad jus tm en t du r ing t e s t ing , and imp rope r r aw

d a t a f o r m a t , c o m m a n d v a l u e s w e r e s a v e d r a t h er t h a n f e e d b a c k v a l u e s .

Me chan i ca l e r ro r s - sy s t em no t f a s t enoug h t o app ly p rope r have r s ine l oads , ove r s i zed

se rvo -v a lve , f r i c t ion i n s e rvo -va lv e p i st on , f r i c t ion i n t r iax i a l c e l l s ea l s, m i sa l i gn me n t

caused by imprope r ly de s igned t r i ax i a l c e l l , exces s ive de fo rma t ion , up t o 76% o f

de fo rm a t ion due t o bend ing o f t r iax i a l c e ll ba se p la t e , exces s iv e de fo rm a t ion due t o

un re s t r a ined f i x tu re , s l i ppage o f L V D T ho lde r s , l a ck o f con t ro l o f p r e s su re t r ansduce r ,

and a i r p r e s su re r egu l a to r ma l func t i on .

In sum ma ry , t he r e a re s eve ra l obv io us bene f i t s o f u s ing t he s t a r tup and Q C p roc edure .

The f i r st i s t ha t the p rocedu re p rov ide s gu ide l i ne s fo r s tanda rd i za t i on o f an en t i re t e s t

p r o c e s s . I t a l s o p r o v id e s a b e n c h m a r k p e r f o r m a n c e s t a n d a rd f o r e q u i p m e n t . I f

imp lemen ted co r r ec t l y , i t c an min imize equ ipmen t and ope ra to r va r i ab i l i t y and t hus

p rov id e g r ea t e r con f idence i n the t e s t re su l t s and t he i r app l i ca t i on i n re sea rch o r de s ign .

Q u a l i ty C o n t r o l a n d A s s u r a n c e o f D a t a C o m p o n e n t s

The l abo ra to ry s t a r t up and Q C p rocedure i s i n t ended t o ensu re t he accu racy and

re l i ab i li t y o f t he r aw Mr da t a. I t s imp lem en ta t i on , how eve r , d oes no t im p ly t ha t Mr da t a

p r o d u c e d b y p r o p e r l y o p e ra t i n g e q u i p m e n t a n d k n o w l e d g e a b l e p e r s o n n e l w i ll b e e r r o r

f r ee. I ndeed , s t ud i e s conduc t ed sho r t l y a f t e r imp leme n ta t i on o f the s t a r t up and Q C

proced ure r evea l ed , a l be i t in f r equen t ly , t he p r e sence o f da t a anom a l i e s .

D u e t o t he i n h e re n t c o m p l e x i t y o f t h e Mrt e s t p rocedure and t he a s soc i a t ed equ ipmen t ,

qua l i t y con t ro l and qua l i t y a s su rance i s pa r amoun t t o p roduc ing r e l i ab l e , r epea t ab l e Mr

t e s t va lues . The re a r e seve ra l t ypes o f Q C/Q A checks t ha t shou ld be add re s sed i n t h i s

p r o c e s s . T h e f o l l o w i n g o u tl in e s s o m e o f t h e Q C / Q A p r o c e s s e s i m p l e m e n t e d w i t h i n t h e

L T P P p r o g r a m b a s e d o n l e s s on s l e a r ne d o v e r t he p a s t 1 4 y e a rs . I m p l e m e n t a t i o n o f t h es e

p r o c e s s e s i s r e c o m m e n d e d f o r e v e r y l a b o r a to r y p e r f o r m i n g t h e M r te s t.

9 G ene ra l Q C /Q A - A labo ra to ry pe r fo rm ing Mr t e s t ing shou ld g ive cons ide ra t i on to

pa r t i c i pa t i on i n an i n t ra and i n t e r - l abo ra to ry t e s ti ng p ro g ram to ve r i fy t he ca l i b r a t i on

o f t he equ ipm en t and p rocedure s w i th r e spec t t o o the r labo ra to r i e s. I t m ay a l so be

des i r ab l e t o manufac tu re o r p rocu re a s tanda rd sp ec im en t o t e st on a con t i nu ing bas i s

t o de t ec t g ros s changes i n the pe r fo rm ance o f t he sys t em ove r t ime .

9 Sam ple P repa ra t i on - I t i s h igh ly r eco m me nde d t ha t a s t anda rd p r epa ra t i on wo rkshe e t

be u t i l i z ed t o w a lk t he t e chn i c i an t h rough t he p roces s. I t i s be s t i f t he p roces s can be

au toma ted t h rough Exce l o r some o the r so f twa re . Th i s a l l ows t he t e chn i c i an t o



2 1 6 R E S IL IE N T M O D U L US T E S T IN G F O R P A V E M E N T C O M P O N E N T S

a u t o m a t i c a l l y p e r f o r m s t a n d a r d m a t h e m a t i c a l c o m p u t a t io n s , t h u s e l i m i n a t i n g t h e

p o s s i b i l it y o f c a lc u l a t io n e rr o rs . A f t e r s a m p l e p r e p a r a t i o n a n d c o m p a c t i o n , a n o t h e r

t e c h n i c i a n o r s u p e r v i s o r s h o u l d c h e c k th e e n t r ie s f o r c o m p l e t e n e s s a n d a c c u r a c y .

O p e r a t o r C h e c k s - T h e M r t e st i s n o t a " p u s h t h e b u t t o n a n d w a l k a w a y " t y p e o f t e s t

p r o c e d u r e . T h e r e a r e m a n y t h i n g s t h a t h a p p e n d u r i n g t h e te s t in g p r o c e s s t h a t m u s t b e

m o n i t o r e d o n a n o n g o i n g b as i s. T h e s e i n c l u d e th e f o l l o w i n g i t e m s :

+ L o a d P u l s e R e a s o n a b l e n e s s - M a n y m o d e m t e st s y s te m s a l lo w t h e o p e r a t o r t o f u l l y

a u t o m a t e t h e t e st i n g p r o ce s s . H o w e v e r , c l o s e d - l o o p s e r v o - h y d r a u l i c s y s t e m s a l s o

r e l y h e a v i l y o n t h e a p p r o p r ia t e s e tt in g a n d m a i n t e n a n c e o f t h e P I D c o n t r o l s ( a l s o

k n o w n a s " g a i n " s e t ti n gs ). T h e P I D s e tt in g s m u s t b e " t u n e d " f o r e v e r y s a m p l e a n d

t e s t c o n f ig u r a t io n . O n e o f t h e r e a s o n s f o r th e n u m b e r o f c o n d i t i o n i n g l o a d p u l s e s

n e c e s s a r y t o c o n d u c t M r te s t in g i s t o g i v e t h e o p e r a t o r a c h a n c e t o t u n e t h e s y s t e m

fo r a pa r t i cu l a r s am ple . Th i s t un ing i s no t s t a ti c ; a s t he t e s t p rog re s se s , t he P ID

v a l u e s n e e d t o b e a d j u s t ed t o e n s u r e a n a d e q u a t e h a v e r s i n e w a v e f o r m . T h i s

ad jus tm en t i s c r it i c a l t o ob t a in r epea t ab l e Mr t e s t va lues . D ur ing t e s t i ng , t he l oad

p u l s e s h o u l d b e v e r y c l o s e to a h a v e r s in e s h a p e ; w i t h in 1 0 p e r c e n t o f th e e x p e c t e d

shape . I n add i ti on , t he l oad pu l se shou ld be w i th in 10 pe rcen t o f t he exp ec t ed

m a x i m u m l o ad . F i n a ll y , t h e r eq u i r ed c o n t a c t lo a d s h o u l d b e a d h e r e d t o a s c l o s e a s

p o s s i b l e b u t n o t f u r t h e r t h a n 1 0 p e r c e n t f r o m t h e i n t e n d e d v a l u e . M a n y t e s t s y s t e m s

t o d a y a l l o w t h e o p e r a t o r t o m o n i t o r lo a d a n d d i s p l a c e m e n t o n t h e c o m p u t e r s c r e e n

a n d s o m e e v e n p r o v i d e e r r o r b a n d s a r o u n d t h e l o a d t o a le r t t h e u s e r o f o u t o f

t o l e ra n c e l o a d i n g . T h e s e " s c o p e s , " a s t h e y a r e s o m e t i m e s r e f e rr e d t o , s h o u l d b e

c l o s e l y m o n i t o r e d b y t h e t e c h n i c i a n d u r i n g c o n d u c t o f t h e t e st . I f th e l o a d p u l s e i s

no t a s p r e sc r i bed t he o pe ra to r ha s a g r ea t dea l o f con t ro l u s ing t he P ID se t t ings t o

ad jus t t he con t ro l s t o p roduce a su i t ab l e wave fo rm.

+ D e f o r m a t i o n R e s p o n s e R e a s o n a b l e n e s s - L i k e th e lo a d p u l s e , t h e d e f o r m a t i o n

r e s p o n s e o f t h e s y s t e m s h o u l d b e m o n i t o re d . A l t h o u g h t h e o p e r a t o r h a s n o d i r e c t

c o n t r o l o v e r t h e d e f o r m a t i o n r e s p o n s e , t h e y s h o u l d b e m o n i t o r e d t o d e t e c t L V D T s

o u t o f ra n g e, s li pp a g e o f t h e L V D T h o ld e r, " s t ic k i n g " o f t h e L V D T , L V D T s o u t o f

ba l ance , e t c . I f any abnorm a l i t ie s a r e de t ec t ed wi th t he de fo rm a t ion t r ansduce r s , t he

ope ra to r shou ld s t op t he t e s t and co r r ec t the p rob l em . U sua l l y i n t he se ca se s t he t e s t

w i l l hav e t o be r e - run .

+ C o n f i n i n g P r es s u r e C o n f o r m i t y - T h e c o n f i n i n g p r e s s u re s h o u l d b e m o n i t o r e d t o

ensu re t ha t t he p rope r p r e s su re i s ma in t a ined , an d t ha t t he sys t em i s r each ing t he

t a r g e te d p r e s s u r e i n a t im e l y m a n n e r . M r v a l u e s a r e v e r y s u s c e p t i b le t o c h a n g e s i n

c o n f i n i n g p r e s s u re v a l u e s a n d t h e a c h i e v e m e n t o f a c c u r at e , c o n s i s t e n t p r e ss u r e s i s

c r i ti c a l i n m od u lus t e s t ing . Th e ac tua l con f in ing p re s su re shou ld be w i th in 5 pe rcen t

o f t he t a rge t ed va lue . I f t he co r r ec t p r e s su re s a r e no t a ch i eved , o r a r e no t r eached i n

a r e a s o n a b l e a m o u n t o f t im e , t h e t e s t s h o u l d b e s t o p p e d a n d t h e o p e r a t o r s h o u l d f i x

t h e p r o b l e m .

+ S a m p l e I n t e g r it y - D u r i n g t h e te s t p r o c e d u r e , th e o p e r a t o r s h o u l d m o n i t o r t h e

sam ple t o ensu re t ha t i t ha s no t f a il ed . Th i s i s p r imar i l y acc om pl i she d by

m o n i t o r i n g t h e t ot a l p e r m a n e n t d e f o r m a t i o n e x p e r i e n c e d b y t h e s p e c i m e n . I f t h e

spec imen i ncu r s g r ea t e r t han 5 pe rcen t s t r a in , t he spec imen i s cons ide red f a i l ed and

t h e t e st s h o u l d b e s t op p e d . U s u a l l y s p e c i m e n f a i lu r e c a n n o t b e s e e n b y t h e n a k e d

eye - r a the r it i s de t e rm ined by mon i to r i ng t he ave rage de fo rm a t ion va lues . I n o rde r




t o p e r f o r m t h e

Mr

t e s t a ccu ra t e ly , t he ope ra to r mus t be cog n i zan t o f t he t e s ti ng

p roce s s a nd m on i to r t he t e s t a s i t p rog re s se s . Th i s i s c ri t ic a l t o ensu r ing accu ra t e ,

cons i s t en t Mr t e s t i ng va lues .

P o s t P r o c e s s i n g - F o l l o w i n g c o m p l e t i o n o f t h e te s t p r o c e d u r e , i n t h e L T P P p r o g r a m

t h e r e s u lt a n t d a t a is a n a l y z e d u s in g a n a u t o m a t e d Q C / Q A p r o g r a m . M o s t l a b o r a t o r ie s

h a v e n o t p r e p a r e d s u c h a p r o g r a m n o r d o e s o n e e x i st o n t h e m a r k e t t o d a y . A n o u t l i n e

o f c h e c k s t h a t c o u l d b e c o n d u c t e d b y s u c h a p r o g r a m f o l lo w s :

+ Da ta Com ple t enes s - F i l e shou ld be r ead t o ensu re it i s com ple t e and i s no t co r rup t .

+ L o ad Pu l se Rea sonab l en es s - V e r i fy t ha t l oad pu l se i s w i th in a l l owab le t o l e r ance

range . T o do t h i s , p lo t a c tua l t oad va lues ve r sus t ime fo r a r ep re sen t a t i ve cyc l e ( s ) a t

each l oad . N ex t , cons t ruc t a theo re t i ca l i dea l load ing pu l se fo r each l oa d s equ ence s

f r o m t h e m a x i m u m l o a d a n d th e 0 . 1 - s e c o n d l o a d in g d u r a t i o n s p e c i fi e d i n t h e L T P P

P 4 6 p r o t o c o l . T h e p e a k t h e o r et i ca l l o a d i s m a t c h e d i n t im e w i t h t h e p e a k - r e c o r d e d

l o a d o f a g i v e n s e q u e n c e . A n a c c e p t a n c e t o l e ra n c e b a n d i s t h e n c r e a t e d a r o u n d t h e

theo re t i ca l l oa d pu l se t ha t i s u sed t o f l ag suspec t d a t a f a l li ng ou t s ide o f the ban d .

D e v e l o p m e n t o f th e m i n i m u m a n d m a x i m u m v a l ue s o f t h e a c c e p ta n c e b a n d i s

b a s e d o n t h e f o l l o w i n g c o n s i d e r a ti o n s :

9 A c c e p t a n c e t o l e r a n c e r a n g e :

~ :10 pe rcen t v a r i a t i on f ro m the t heo re t i ca l l oad i s

j u d g e d t o b e a c c e p t a b le .

9 S e r v o v a l v e r e s p o n s e t i m e : ~= 0.006 secon d t ime sh i f t i n l oad f r om the t heo re t i ca l

l oad pu l se i s r ea sonab l e t o a l l ow fo r t he phys i ca l l imi t a t i ons on t he r e s pon se

t i m e o f t h e s e r v o - h y d r a u l ic s y s t e m .

9 R e s o l u t i o n o f t h e e l e c t r o n i c l o a d c e l l:

R e s o l u t i o n o f e l e c t ro n i c l o a d c e i l s u s e d i n

M r te s t in g o f u n b o u n d m a t e r ia l s i s g e n e r a l l y + 4 . 4 N . T h e r e f o r e , a r a n g e o f t w i c e

the min imum load ce l l r e so lu t i on (+ 8 .8 N ) i s cons ide red accep t ab l e .

9 L o g i c :

M i n i m u m l o a d a l lo w e d i s 0 N .

For ea ch t ime s t ep i n t he l oad cu rve , the t o l e r ance r ange f rom a l l o f t he se

c o m p o n e n t s i s co m p u t e d . T h e m a x i m u m v a l ue o f t h es e t h re e c o m p o n e n t s i s

s e l e c te d a s t h e u p p e r t o l e r a n ce l im i t, w h i l e t h e m i n i m u m v a l u e i s u s e d f o r t h e l o w e r

l imi t a t e ach t ime s tep . Ov e r the en t i r e r ange o f l oad ing , f i ve po in t s a r e a l l ow ed t o

b e o u t o f t o l e ra n c e b e f o r e t h e l o a d c y c l e i s c o n s i d e re d f a i le d . A n e x a m p l e o f t h is

c h e c k i s s h o w n i n F i g u re 3 .

+ D e f o r m a t i o n R e s p o n s e R e a s o n a b l e n e s s - V e r i f y t h a t d e f o r m a t i o n p u l s e is w i t h i n

a l l owab le t o l e r ance r ange . To do t h i s , p lo t a c tua l de fo rma t ion va lues ve r sus t ime

fo r a r ep re sen t a t i ve cyc l e ( s ) a t e ach l oad l eve l . N ex t , u s ing t he equa t i on fo r a

h a v e r s i n e w a v e f o r m , c o n s t r u c t a th e o r e ti c a l id e a l d e f o r m a t i o n p u l s e f o r e a c h l o a d

s e q u e n c e s f r o m t h e m a x i m u m l o a d a n d t h e 0 . 1 - s e c o n d l o a d i n g d u r a ti o n s p e c i f i ed i n

t h e L T P P P 4 6 p r o t o c o l . T h e p e a k t h e o re t ic a l d e f o r m a t i o n i s m a t c h e d i n t i m e w i t h

t h e p e a k - r e c o r d e d d e f o r m a t i o n o f a g i v e n s e q u en c e . A n a c c e p t a n c e t o l e r a n c e b a n d

i s t hen c r ea t ed a roun d t he theo re t i ca l de fo rm a t ion pu l se t ha t i s u sed t o f l ag suspec t

d a t a fa ll in g o u t s id e o f th e b an d . D e v e l o p m e n t o f t h e m i n i m u m a n d m a x i m u m

v a l u e s o f t h e a c c e p t a n c e b a n d i s b a se d o n t h e f o l l o w i n g c o n s i d e r a t i o n s :

9 A c c e p t a b l e t o l e r a n c e r a n g e : 4=10 pe rcen t va r i a t i on f rom the t he o re t i ca l

d e f o r m a t i o n i s j u d g e d t o b e a c c e p ta b l e .

9 L o g i c :

M i n i m u m d e f o r m a t i o n a l l o w e d i s 0 .

F o r e a c h s t ep i n th e d e f o r m a t i o n c u r v e , t h e to l e r a n c e r a n g e f r o m t h e s e c o m p o n e n t s



2 1 8 R E S IL IE N T M O D U L U S T E S T IN G F OR P A V E M E N T C O M P O N E N T S

L o a d v s . T i m e , R i n g L o a d 5 0 0 0 I b s , R e p l i c a t e 1 ,

S e q u e n c e 0 1 , C y c l e 3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . i

] - - ~

L o a d o T h e o r e t i c a l i

! - M i n M a x i

2 5 . 0 0

2 0 . 0 0 1

Lo

a d i

Ob 15 .00 i

s ) 10 .00 t

5 . 0 0

o o o l

2 6 . 9 5

T i m e I s )

t . . . . . . . . i - - t . . . . . . . . .

2 7 2 7 . 0 5 2 7 .1 2 7 . 1 5

+

+

Figure 3 - Example of Load Pulse Response Reasonableness Check

i s c o m p u t e d b a s e d u p o n t h e m a x i m u m d e f o r m a t i o n p o in t f o r t h e c y c l e. T h e

m a x i m u m v a l u e o f t h e se c h e c k s i s s el e ct ed a s th e u p p e r t o l e ra n c e a n d t h e m i n i m u m

va l ue o f t he se check s i s s e lec t ed a s the l ow er l i m i t f o r e ach t i m e s t ep . Th e ac t ua l

de f o r m a t i on is then c om par ed wi t h t he to l e r ances a t e ach t i m e s t ep t o de t e r m i ne

conf o r m ance . O ve r the en t i r e r ange o f load i ng , f i ve po i n t s a r e a l low ed t o be ou t o f

t o l e r ance be f o r e t he de f o r m a t i on cyc l e i s cons i de r ed f a il ed . Th i s t e s t is pe r f o r m ed

f o r a l l de f o r m a t i on dev i ce s .

L o a d v e r s u s D e f o r m a t i o n T i m e L a g - D e t e r m i n e th e m a x i m u m l o a d p o i n t f o r a

g i v e n c y c le a n d e x t r a c t t h e c o r re s p o n d i n g t im e s t a m p . D e t e r m i n e t h e m a x i m u m

def o r m a t i on f o r t he s am e cyc l e and ex t r ac t t he co r r e spond i ng t i m e s t am p . Sub t r ac t

t h e m a x i m u m d e f o r m a t io n p o i nt ti m e s t a m p f r o m t h e m a x i m u m l o a d p o i n t t i m e

s t am p . Th i s va l ue shou l d b e pos i t i ve and I e s s t han 0 . 008 s . I f t he t i m e d e l ay i s

g r ea t e r t han 0 . 008 s , m os t l i ke ly t he re i s a p r ob l em w i t h t he sys t em e l ec t r on i c s o r

so f t wa r e . I f t he t i m e de l ay i s nega t i ve , it m eans t ha t t he m a x i m um de f o r m a t i on i s

occu r r i ng p r i o r t o t he m ax i m um l oad , a p r ac ti ca l im po ss i b i li t y , wh i ch aga i n w ou l d

l ead t o t he susp i c i on t ha t t he r e i s a p r ob l em w i t h t he sys t em e l ec t ron i c s o r so f t wa r e .

Th i s ana l ys i s shou l d be pe r f o r m ed f o r each de f o r m a t i on dev i ce .

R e v i e w o f D a t a C o m p u t a t i o n P r o c e ss - I n th i s a n a ly s is , t h e r a w d a t a a r e m a n u a l l y

r e d u c e d a n d t h e r e s u lt s c o m p a r e d t o th e s u m m a r y d a ta d e v e l o p e d b y t h e c o m p u t e r

so f t wa r e sys t em . Fo r Mr te s ti ng , t he f o l low i ng va l ues shou l d be an a l yzed a s i s

p r ac t ica l : cyc l i c l oad , m a x i m um l oad , con t ac t ( s ea ti ng ) l oad , de f o r m a t i on r e spon se

( f o r a ll d e f b r m a t i on dev i ce s ) , con f i n i ng p r e s su r e ( so il s and agg r ega t e t e s t ing ) ,

t em pera ture (asphal t ) , devia tor s t ress ( so i l s and aggreg a te t es ting) , s t ra in ( so i l s and




a g g r e g a t e t es t in g ) , a n d r e s i li e n t m o d u l u s . T h e s e v a l u e s s h o u l d b e d e r i v e d f r o m t h e

r a w d a t a u s i n g p r o c e d u r e s s t a te d i n t h e p r o t o c o l .

+ C o n f o r m a n c e t o T e s t P a r a m e t e rs - A f t e r t h e s u m m a r y d a t a h a v e b e e n v e r i f ie d b y

h a n d , a d h e r e n c e t o t h e p r o t o c o l p a r a m e t e r s s h o u l d b e a n a l y z e d . T h i s a n a l y s i s i s

u n d e r t a k e n t o d e t e r m i n e h o w c l o s e t h e l a b o r a t o r y is t o th e p r o t o c o l t e s t

r e q u i r e m e n t s . A l l t e s t p a r a m e t e r s s h o u l d b e w i t h i n 5 % o f th e t e s t r e q u ir e m e n t s . T h e

f o l l o w i n g i t e m s s h o u l d b e c h e c k e d a s a p p r o p r i a te f o r a p a r t ic u l a r p r o to c o l : t a r g e t

d e v i a t o r s t r e s s a n d t a r g e t c o n f i n i n g p r e s s u r e .

+ D e f o r m a t i o n D e v i c e V a r i a t io n - T h e d e f o r m a t i o n d e v i c e s s h o u l d b e s ta b l e w i t h i n a

g i v e n l o a d i n g r e g i m e a n d t e s t cy c l e . In t h i s a n a l y s i s , t h e c o e f f i c i e n t o f v a r i a t i o n o f

t h e d e f o r m a t i o n d e v i c e s i s c a lc u l a t e d a t a g i v e n t e s t s eq u e n c e . T o p e r f o r m t h i s

a n a l y s i s , s e l e c t t h e d e f o r m a t i o n v a l u e s f o r a ll c o l l e c t e d c y c l e s o f d a t a a t a g i v e n t e s t

s e q u e n c e . D e t e r m i n e t h e c o e f f i c ie n t o f v a r i a ti o n o f t h e v a l u e s . R e p e a t f o r a l l te s t

s e q u e n c e s a n d d e f o r m a t i o n d e v ic e s . V e r t i c a l d e f o r m a t i o n r e a d i n g s f r o m e a c h o f t h e

s e q u e n c e s s h o u l d b e c h e c k e d t o e n s u r e t h a t t h e d e f o r m a t i o n d e v i c e s a r e r e c o r d i n g

v a l u e s w i t h a v e r a g e s t h a t h a v e a c o e f f i c i e n t o f v a r i a t i o n l e s s t h a n 2 . 5 p e r c e n t .

+ D e f o r m a t i o n B a l a n c e - T h i s t e s t i s o n l y c o n d u c t e d i f m o r e th a n o n e d e f o r m a t i o n

d e v i c e i s m o u n t e d o n t h e s y s te m . A l l d e f o r m a t i o n d e v i c e s u s e d f o r t h is c o m p a r i s o n

s h o u l d b e m o u n t e d i n a p p r o x i m a t e l y t h e s a m e l o c a t i o n i n t h e s y s t e m , s u c h a s o n t o p

o f t r i a x i a l c h a m b e r o r o n t e st s p e c i m e n . I n t h i s a n a l y s i s, th e b a l a n c e o f t h e

d e f o r m a t i o n d e v i c e s i s ev a l u a te d . I f d e f o r m a t i o n d e v i c e s a r e m o u n t e d i n

a p p r o x i m a t e l y t h e s a m e l o c a t i o n o n th e s a m p l e o r i n th e s y s t e m , it c a n b e

r e a s o n a b l y e x p e c t e d t h a t t h e y w o u l d e x p e r i e n c e s i m i l a r d e f o r m a t i o n m e a s u r e m e n t s .

F o r a g i v e n d e f o r m a t i o n c y c le , e x tr a c t th e c y c l i c d e f o r m a t i o n v a l u e f r o m t h e

s u m m a r y ( c a l c u l a te d ) d a ta . T h e c o l l e c te d d e f o r m a t i o n r e a d i n g s a r e c h e c k e d t o

e n s u r e t h a t a c c e p t a b l e v e r ti c a l d e f o r m a t i o n r a ti o s a r e b e i n g m e a s u r e d . A c c e p t a b l e

v e r t i c a l d e f o r m a t i o n r a t i o s ( R v) a r e d e f i n e d a s R v

=

Ymax/Ymin < 1.30, w he re

Ymax

e q u a l s t h e l a r g e r o f t h e t w o v e r t ic a l d e f o r m a t i o n s a n d

Ymin

e q u a l s t h e s m a l l e r o f th e

t w o v e r t i c a l d e f o r m a t i o n s . T h i s a n a l y s i s s h o u l d b e p e r f o r m e d f o r e a c h d e f o r m a t i o n

d e v i c e i n o r d e r . I f m o r e t h a n t w o d e f o r m a t i o n t r a n s d u c c r s a r e u s e d , o n e s h o u l d b e

s e l e c t e d a s t h e r e f e re n c e a n d t h e o t h e r s c o m p a r e d t o t h is r e f e r e n c e. A l l v a l u e s

s h o u l d b e w i t h i n + 3 0 % o f th e r e f e r en c e .

+ R e a s o n a b l e n e s s o f T e s t R e s u lt s - T h e f i n a l r e s u l ts o f t h e t e s t p r o c e d u r e s h o u l d b e

r e v i e w e d f o r r e a s o n a b l e n e s s . T h is c h e c k c a n o n l y b e c o n d u c t e d b y p e r s o n n e l w h o

a r e f a m i l i a r w i t h t h e t e s t p r o c e d u r e . F o r s o i l s a n d a g g r e g a t e te s t i n g , a b a s i c c h e c k

c a n b e m a d e o f t h e M r v e r s u s c o n f i n i n g p r e s s u r e re s u l ts . G e n e r a l l y , M r v a l u e s a t

l o w e r c o n f i n in g p r e s s u r e s s h o u l d b e l o w e r th a n t h o s e a t h i g h e r c o n f i n i n g p r e s s u r e s

( f o r a g i v e n d e v i a t o r s tr e s s ). I n th i s e x p e r i m e n t , th e r e s u l t s s h o u l d l o o k r e a s o n a b l e

t o t h e u s e r. A n y a n o m a l i e s s h o u l d b e i n v e s t i g a te d .

R a n g e C h e c k s - I n th e L T P P p r o g r a m , a g r e a t d e a l o f e f f o rt w a s u s e d t o d e f i n e v a l i d

r a n g e s f o r t h e d a t a p r o d u c e d . O t h e r M r te s t in g a g e n c i e s m a y f i n d t h e s e r a n g e c h e c k s

u s e f u l t o p e r f o r m t h e i r o w n q u a l i t y c o n t r o l p r o c e d u r e s . T a b l e 1 c o n t a i n s a l i s t o f a l l

t e s t p a r a m e t e r s a l o n g w i t h t h e i r a p p l i c a b l e r a n g e c h e c k s . T h e s e r a n g e s a p p l y p r i m a r i l y

t o L T P P P r o t o c o l P 4 6 b u t c a n a ls o b e a p p l i e d t o A A S H T O T 3 0 7 . T h e d e f i n i ti o n s o f

t h e t e r m s i n T a b l e 1 a r e c o n t a i n e d i n P r o t o c o l P 4 6 .




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Mr G u i d e l i n es o n C D - R O M

M a n y o f t h e l e s so n s l e a r n ed w i t h in t h e L T P P p r o g r a m i n t h e p a s t 1 4 y e a r s r e g a r d i n g

M r t e s ti n g h a v e b e e n s h a r e d w i t h t h e p a v e m e n t c o m m u n i t y , b u t c e r ta i n l y n o t a ll. T o

a d d r e s s t h is s h o r t c o m i n g , c o m p r e h e n s i v e g u i d e l in e s o n t h e M r t e st f o r u n b o u n d g r a n u l a r

m a t e r i a l s w e r e r e c e n t ly c o m p l e t e d a n d a r e c o n t a i n e d i n a n e a s y - t o - u se , i n t e ra c t iv e C D -

R O M . T h e g u i d e li n e s i n c l u d e d e t a il s o n t h e u s e f u l n e ss o f t e st r e su l ts i n p a v e m e n t d e s i g n ,

b a c k g r o u n d a n d u s e f u l n e ss o f t e st p r o c e d u r e , a n d te c h n i q u e s t h a t c a n b e u s e d t o r e d u c e

the w i th in - and be tween- l abo ra to ry va r i ab i l i t y .

T h e C D - R O M h a s b e e n d e v e l o p e d a s s e v e n e d u c a t io n a l m o d u l e s t h a t d e s c r ib e t h e

sa l i en t f ea tu r e s o f t he Mr t e st . Th ey a r e : (1 ) f undam en ta l s o f r e s i li en t m od u lus t e s t ing , ( 2 )

i m p l e m e n t a t i o n o f a r e s il ie n t m o d u l u s t e s t in g p r o g r a m , ( 3 ) re s il ie n t m o d u l u s s t a rt u p a n d

qua l i t y con t ro l p rocedure s , ( 4 ) r epea t ed l oad t ri ax i a l t e s t i ng , ( 5 ) qua l i t y con t ro l /qu a l i t y

a s su rance , ( 6 ) keys to a succes s fu l re s i l ien t m odu lus t e s t i ng p rog ram , and (7 ) r e s i li en t

m o d u l u s i n p a v e m e n t d e s ig n . E a c h o f t h e s e m o d u l e s c o v e r s f u n d a m e n t a l i s s u e s t h a t




s h o u l d b e a d d r e s s e d p r i o r to a n d d u r i n g Mr t es ti n g . M o s t o f t h e k e y i s s u e s c o v e r e d i n t h e

m o d u l e s h a v e b e e n a d d r e s s e d e a r li er i n th i s p a pe r , b u t n o t a s u m m a r y o f th e k e y s t o

s u c c e s s f u l te s t in g a s c o n t a i n e d i n th e L T P P M r C D - R O M . T h e f o l l o w i n g i s a l is t o f th e

top t en i s sues t o add re s s t o he lp ensu re a succe s s fu l

Mr

t e s ti n g p r o g r a m .

9 I m p l e m e n t I n t en s i v e T r a in i n g - T h e r e a r e t w o p r i m a r y t y p e s o f t r a in i n g t h a t s h o u l d b e

a d d r e s se d . F i rs t, t h e e q u i p m e n t m a n u f a c t u r e r s h o u l d p r o v i d e a m p l e t r a in i n g t o

l abo ra to ry pe r son ne l i n t he ope ra t i on , ma in t en ance , c a l i b r a t i on , and s a f e ty p r ecau t i ons

su r rou nd ing t he equ ipm en t u sed fo r Mr t e s ti ng . Th i s t r a in ing shou ld a l so be

d o c u m e n t e d s o t h a t t h e l a b o r a t o r y c a n t r ai n o t h e r o p e r a to r s . S e c o n d l y , l a b o r a t o r y

p e r s o n n e l s h o u l d b e t r a i n e d i n t h e c o n d u c t o f t h e t e st , i n c l u d i n g s a m p l e p r e p a r a t i o n

a n d c o m p a c t i o n , a n d d a t a a n a l y s is p r o c e d u r e s. T h i s t r a i n in g s h o u l d b e r e - e m p h a s i z e d

e v e r y s o o f t e n a s o p e r a t o r s h a v e a t e n d e n c y t o d e v e l o p h a b i t s t h a t m a y b e d e t r im e n t a l

t o t h e a c q u i s i ti o n o f q u a li t y M r d a t a o v e r t im e . I n te r n a l t ra i n in g s h o u l d b e d o c u m e n t e d

so a s t o c r ea t e an i n s t it u t iona l kno w ledg e base fo r f u tu r e u se .

9 U s e t h e R i g h t E q u i p m e n t - M r t e st e q u i p m e n t s h o u l d b e t a i lo r e d to d o t h e j o b . O n e o f

t h e l e a d i n g c a u s e s o f p r o b l e m s w i t h Mr t e s ti n g i s th e u s e o f e q u i p m e n t t h a t i s n o t

co r r ec t l y con f igu re d . U sua l l y th i s mean s t ha t l oad cel ls , s e rvo -va lves o r p r e s su re

t r ansduce r s a r e no t o f t he p rope r r ange a nd capac i t y . Fo r exam ple , t he r e i s l it tl e nee d

t o u s e a 5 ,0 0 0 -1 b l o a d c el l fo r a s u b g r a d e M r te s t i n w h i c h t h e m a x i m u m l o a d i s a r o u n d

6 0 l b . I f c o n f i g u r a t i o n is n o t p e r f o r m e d p r o p e r ly , t h is m a y l e a d t o p o o r c o n t r o l o f t h e

s y s t e m a n d p o s s i b l e i n s ta b i li ty o f t h e t e s t e q u ip m e n t . U s i n g t h e r i g h t t o o l f o r t h e j o b

wi l l g r ea t l y ea se p rob l ems a s soc i a t ed wi th sys t em con t ro l and da t a acqu i s i t i on .

9 I m p l e m e n t S ta r tu p a n d Q u a l it y C o n t r o l P r o c e d u r e s - A n im p o r t a n t l e s s o n l e a r n e d

f r o m t he L T P P Mrt e s t i ng expe r i ence w as t ha t i t i s imp e ra t i ve t ha t e l ec t ron i c s an d

m e c h a n i c s o f th e t e s t s y s t e m a r e t h o r o u g h l y v e r if i e d p r i o r t o t e s ti n g a n d p r o f i c i e n c y o f

o p e r a t o r s b e e v a l u a t e d t h r o u g h a p r o f ic i e n c y p r o g r a m . T h i s s h o u l d b e d o n e e v e n i f th e

m a n u f a c t u r e r a s s u r e s t h e l a b o r a t o ry th a t th e e q u i p m e n t m e e t s s p e c i fi c a ti o n s . T h e

v e r i f i c a ti o n a n d e v a l u a t i o n is a c c o m p l i s h e d b y p e r f o r m i n g t h e L T P P S t a rt u p a n d

Q u a l i t y C o n t r o l P r o c e d u r e . M a n y i m p o r t a n t c h a r a c te r is t ic s o f t h e te s t s y s t e m a r e

e v a l u a t e d t h r o u g h t h e s t a rt u p p ro c e s s . I n f a ct , s o m e p r o b l e m s w o u l d n e v e r b e f o u n d b y

m e r e l y p e r f o r m i n g n o r m a l c a l ib r a ti o n s o r s e le c t iv e p o r t i o n s o f t h e s t a r tu p p r o c e d u r e s .

9 P e r f o r m E q u i p m e n t C a l i b ra t io n - T h i s it e m g o e s h a n d - i n - h a n d w i t h t h e

i m p l e m e n t a t i o n o f th e s t ar tu p p r o c e d u r e b u t i s r e la t e d m o r e c l o s e l y t o f r e q u e n t

c a l ib r a t io n s r e q u i re d b y t h e e q u i p m e n t m a n u f a c t u r e r a n d t h e t e s t p r o t o c o l s . L o a d c e l ls

a n d t r a n s d u c e r s h a v e t h e p o t e n ti a l to b e d a m a g e d a n d f a t i g u e d d u r in g n o r m a l t e s t in g

ope ra t i ons . T hese i t ems need t o be ca l i b r a t ed on a r egu l a r ba s i s to ensu re t ha t t hey a r e

r e a d i n g c o r r e c t l y a n d e n s u r e t h e s a f e o p e r a t io n o f t h e t e s t m a c h i n e . R e g u l a r c a l i b r a t io n

o f s e n s it i v e c o m p o n e n t s i s s o m e t i m e s o v e r l o o k e d , b u t i t is a v e r y i m p o r t a n t p a r t o f th e

e q u i p m e n t m a i n t e n a n c e a n d o p e r a t o rs s h o u l d b e v e r y c o n s c i e n t i o u s o f t h is t a s k .

9 O r g a n i z e S y s t e m D o c u m e n t a t i o n - L a b o r a t o r y s h o u l d k e e p al l t e s t s y s t e m

d o c u m e n t a t i o n i n a s a fe p la c e . T h i s d o c u m e n t a t i o n i s e x t r e m e l y h a n d y s h o u l d

m a i n t e n a n c e n e e d t o b e p e r f o r m e d o r t h e s y s t e m o t h e r w i s e m a l f u n c t i o n s . W i t h o u t t h i s

d o c u m e n t a t i o n , t r a in i n g o f n e w o p e r a t o r s a n d t r o u b l e - s h o o t i n g b e c o m e v e r y d i ff i cu l t.

9 V e r i f y t h e D a t a A n a l y s i s S o f t w a r e - M a n y e q u i p m e n t v e n d o r s s u p p l y d a t a a n a l y s i s

s o f t w a r e w i t h t h ei r p r o d u c t. T h i s s o f t w a r e s h o u l d b e c h e c k e d p r i o r to i m p l e m e n t a t i o n



222

R E S I L I E N T M O D U L U S T E S T I N G F O R P A V E M E N T C O M P O N E N T S

t o ensu re t ha t t he ca l cu l a t i ons pe r fo rm ed by t he so f twa re a r e cons i s t en t w i th t he te s t

p r o t o c o l . I n a d d i ti o n , m a n y p r o g r a m s u s e t h e " M a x / M i n " a p p r o a c h t o d a t a a n a l y si s .

W hi l e t h i s is a conv en i en t app roach fo r t he so f twa re dev e lope r , i t ha s t he po t en t i a l f o r

p r o b l e m s w h e n a n a l y z i n g M r d a ta . D u r i n g t e s ti n g , i t is p o s s i b le t h a t t h e s y s t e m m a y

e x p e r i e n c e a s i g n i fi c a n t o v e r s h o o t o f t h e l o ad , a n d t h u s d e f o r m a t i o n . I f t h is o c c u r s a n d

t h e m a x / m i n a p p r o a c h i s u se d , t h e l o a d a n d d e f o r m a t i o n v a l u e s c a n b e s i g n i f ic a n t l y

a f f e ct e d . T h e r e f o r e t h e m e t h o d o f d a ta a n a l y si s p re s e n t e d i n L T P P P r o t o c o l P 4 6 a n d

A A S H T O T 3 0 7 i s p r e fe r re d a n d h i g h ly r e c o m m e n d e d t o d e te r m i n e m a x i m u m ,

m i n i m u m , a n d c y c l i c s tr e ss e s a n d s tr a in s . T h i s m e t h o d u t i l iz e s a " m a x i m u m a n d

a v e r a g e " a l g o r i t h m t h a t t a k e s c a r e o f a n y p o t e n ti a l o v e r s h o o t i s su e s i n d a t a a n a l y si s .

* I n v o l v e Y o u r s e l f i n t h e T e s t in g P r o c e s s - S o m e c o n s i d e r M r a " p u s h t h e b u t t o n a n d

w a l k a w a y " p r o c e d u r e . I t i s h i g h l y r e c o m m e n d e d , h o w e v e r , t h a t t h e o p e r a t o r m o n i t o r

t he t e s t a s i t p rog re s se s i n a ca r e fu l manne r . Many po t en t i a l p rob l ems can occu r du r ing

the co ndu c t o f the t e s t tha t w i l l no t be r ead i l y appa ren t i f t he op e ra to r i s no t

m on i to r i ng t he r e su l ts . I n add i ti on , f o r ma ny t e s t sy s t ems , i t is r equ i r ed t ha t t he

ope ra to r ad jus t s mac h ine s e t t ings du r ing t he t e st . Th i s i s a ve ry im por t an t pa r t o f the

Mr t e s t ing p roces s .

9 P a y C l o s e A t t e n t io n to C o m p a c t i o n P r o c e d u r e s - O n e o f t h e g re a t e s t i n f l u e n c e s o n M r

v a l u e s i s t h e c o n s i s t e n c y o f s a m p l e c o m p a c t i o n . I t c a n n o t b e o v e r s t a te d h o w i m p o r t a n t

i t i s t o have p rope r ly t r a ined , co nsc i en t i ous i nd iv idua l s pe r fo rm th i s c ruc i a l r o l e . I n

add i t i on , i f the l ab o ra to ry i s pa r t i c i pa t ing i n a rou nd rob in o r s im i l a r t e s t ing exe rc i s e , i t

i s e x t r e m e l y i m p o r t a n t t h a t sa m p l e s b e c o m p a c t e d u s i n g s i m i l a r e q u i p m e n t ,

p r o c e d u r e s a n d c o m p a c t i o n t a r g e ts ( d e n s i ty a n d m o i s t u re ) a s t h e o t h e r l a b o r a t o ri e s .

W hi l e t h i s ma y seem obv iou s , i t i s ve ry d i f f icu l t to im p lem en t i n r ea l li fe .

9 Fac to r i n t he Resu l t an t Fo rce - W hen p e r fo rm ing Mr t e s ts , i t i s e a sy t o i gno re t he

fo rce s o the r t han t he ax i a l l oad on a spec imen . Howeve r , i t i s ex t r eme ly impor t an t t o

f ac to r i n t he r e su l tan t f o r ce wh en t e s t i ng l a rge s ample s . The t e s t con f igu ra t i on and /o r

t h e d a t a a n a l y s i s p r o g r a m m u s t ta k e i n t o a c c o u n t t h e f o r c e s r e s u l ti n g f r o m t h e w e i g h t

o f t h e a c t u a t o r r o d a n d t o p c a p a s w e l l a s th e i n f l u e n c e o f t h e c o n f i n i n g p r e s s u re . A

d e t a il e d d e s c r i p ti o n o f t h e i n f l u en c e o f t h e s e f o r c e s is c o n t a i n e d i n L T P P P r o t o c o l P 4 6

a n d A A S H T O T 3 0 7 . A t t e n t io n t o th i s d e ta i l is a m u s t.

9 P rac t i ce , P r ac t i ce , P r ac t i ce - Ju s t li ke a go od spo r t s t e am, p r ac t i ce m ake s pe r f ec t . The

M r t e s ti n g p r o c e d u r e s h o u l d b e p r a c t i c e d m a n y t i m e s p r i o r t o f u l l- s c a le

i m p l e m e n t a t i o n w i t h in a n o r g a n i z a t io n . T h i s p r a c ti c e w i l l h e lp w o r k o u t b u g s i n t h e

s y s t e m , f a m i l i a ri z e o p e r a t o r s w i t h t es t p a ra m e t e r s , a n d l e ad t o r a p i d a c k n o w l e d g e m e n t

o f p r o b le m s i f t h e y o c c u r.

W hi l e t h i s l is t i s no t mean t t o be an a ll - i nc lu s ive run dow n o f a l l t he i s sues t o keep an

e y e o n w h e n c o n d u c t i n g M r t e st in g , i t i s ai m e d a t p r o v i d i n g t h e r ea d e r w i t h a s u m m a r y o f

the mo s t impo r t an t i s sues t ha t shou ld be add re s sed . Succes s fu l Mr t e s t i ng i s h igh ly

d e p e n d e n t o n a t t e n t io n t o d e ta il. A c k n o w l e d g i n g a n d c o n f r o n t i n g t h e se i s s u e s p r i o r t o

i m p l e m e n t a t i o n o f a M r p r o g r a m c o u l d s a v e v a l u a b le t i m e a n d r e s o u r c e s .

A d d i t io n a l i n f o r m a t io n a b o u t th e L T P P M r C D - R O M , t it le d Guide or Determining

Design Resilient Modulus Values or Unbound Materials

[ L A W P C S 2 0 0 2 ] , c a n b e

o b t a i n e d b y c o n t a c t i n g th e F e d e r a l H i g h w a y A d m i n i s t r a t i o n a t lt p p i n f o @ f h w a . d o t . g o v .



R A D A E T A L . O N U N B O U N D M A T E R IA LS 2 2 3

S u m ma r y a n d C o n c lu s io n s

T h e p u r p o s e o f t h is p a p e r w a s t o s h a r e L T P P ' s e x p e r i e n c e o v e r t h e p a s t 1 4 y e ar s w i t h

r ega r ds t o t he Mr cha r ac te r i za ti on o f unbound pav em en t m a t e r i a ls . Tow ar ds t ha t end , t he

f i rs t pa r t o f the pap e r add r e s sed the L TP P P46 t e s t p r o t oco l , inc l ud i ng i t s deve l op m en t

t h r ough m an y yea r s o f expe r i ence a we l l a s the va r i ous t op i c s cove r ed b y the p r o t oco l .

T h i s p r o t o c o l s e rv e d a s th e p r i m a r y b a si s f o r d e v e l o p m e n t o f t h e A A S H T O T 3 0 7

pr o t oco l , w h i ch i s a t p r e sen t t he s t a te - o f - the - p r ac t i ce i n t he U n i t ed S t a te s .

The l abo r a t o r y s ta r tup and qua l i t y con t r o l p r ocedur e deve l oped b y L TP P t o ensu r e t he

a c c u r a c y a n d r e l ia b i li ty o f t h e r a w M r d a ta w a s a l s o c o v e r e d i n th e p a p e r . D e v e l o p m e n t o f

t h i s p r ocedur e w as t r i gge r ed by f ind i ngs ea r l y in t he p r og r am t ha t equ i pm en t

m a nuf ac t u r ed f o r Mr t e s ti ng wa s no t wor k i ng a s i n tended . T he r e su l t ing p r oc edur e

enab l e s l abo r a t o r i e s to v e r i f y t he i r t e s ti ng sys t em s and m e t hods p r i o r to t he s t a r t o f

p r odu c t i on t e s t i ng and , i f neces sa r y , t o i den t if y and co r r ec t e l ec tr on i c , so f t wa r e a nd /o r

m e chan i ca l e r ro r s .

Qua l i t y con t r o l and qua l i t y a s su r ance p r oces se s deve l op ed and i m p l em en t ed wi t h i n

t he L TP P p r o g r am b ased on l e s sons l ea r ned s i nce 1988 wer e ou t l i ned i n t he pape r . The se

p r oces se s i nc l uded gen e r a l qua l it y con t ro l and qua l i ty a s su r ance , s am pl e p r epa r a t i on ,

ope r a t o r checks , da t a pos t - p r oces s i ng , and da t a r ange checks .

F i na l ly , an ea sy - t o - use , i n t er ac ti ve CD - RO M con t a i n i ng com p r ehens i ve gu i de l ine s on

t he Mr t e s t f o r unbou nd g r anu l a r m a t e r i a ls was d i s cus sed . Pa r t i cu l a r em pha s i s was p l aced

on a l i s t o f the t op t en i s sues t ha t need t o be add r e s sed t o he l p en su r e a succ es s f u l Mr

t e s t ing p r og r am .

The i n f o r m a t i on con t a i ned o r r e f e r enced i n th i s pape r wi l l he l p o t he r s ach i eve

r epea t ab l e , h igh - qua l i t y Mr da t a f o r unbound pav em en t m a t e r i a ls . I t i s a lso t he au t h o r s '

op i n i on t ha t such r epea t ab l e , h i gh - qua l it y da ta wou l d no t ha ve been p os s i b l e w i t hou t t he

m any exp e r i ences and l e s sons l e a r ned i n the cou r se o f t he L T PP p r og r a m t o da t e.

References

Al av i , S ., Mer po r t , T ., W i lson , T . , Gr oege r , J. , L opez , A . , J anua r y 1997 , " L TP P M a t e r i a ls

C h a r a c t e ri z a ti o n P r o g r a m : R e s il ie n t M o d u l u s o f U n b o u n d M a t e ri a ls ( L T P P P r o t o c o l

P 4 6 ) L a b o r a t o r y S t ar tu p a n d Q u a l it y C o n tr o l P r o c ed u r e , " R e p o r t N o . F H W A - R D - 9 6 -

176, U . S . Dep a r t m en t o f Tr anspor t a ti on , Fede r a l Hi gh w ay Ad m i n i s t r a t ion , M cL ea n ,

Vi rg in ia .

Bark sda le , R. D. , A lba , J ., Kh os la , N. P . , Kim , R. K. , La m be, P . C. , and R ahm an, M . S . ,

1988,

NCHRP Web Document 14 Laboratory Determination of Resilient Modulus or

Flexible Pavement Design,

Pr o j ec t 1 - 28 F ina l Repor t , Na t i ona l C oop e r a t i ve H i ghw ay

Resea r ch P r og r am , Tr anspor t a t i on Resea r ch Boa r d , Na t i ona l Resea r ch Counc i l ,

Wash i ng t on , D . C .

L A W P C S , a D i v i s io n o f L a w E n g i n e e r in g & E n v i r o n m e n t a l S e r v ic e s , I n c ., an d A x i o m

Decis ion Sys tems, Inc . , 2002,

Guide or Determining Design Resilient Modulus

Values or Unbound Materials,

L T P P C D - R O M P r od u c t, L T P P T e a m , F e d e ra l

H i ghw ay Ad m i n i s t r a ti on , M cL ean , V i r g in i a .



Richard L . Boud reau 1

R e s i li e n t M o d u l u s - P a v e m e n t S u b g r a d e D e s ig n V a l u e

R e f e r e n c e : B o u d r ea u , R . L . , " R e s i li e n t M o d u l u s - P a v e m e n t S u b g r a d e D e s i g n

V a l u e , " A S TM ST P 1437, Res i l ien t Modu lus Tes t i ng o r Pa vemen t Component s, G . N .

Durham , W . A . M ar l and W . L . De G rof f , Eds., A S T M In t e rna t iona l , W es t

Conshohocken , P A, 2003 .

A b s t r a c t :

M uch r es i li en t modu lus r e sea rch w ork has been co mp le t ed recen t l y , m os t l y as

p a r t o f th e L o n g T e r m P a v e m e n t P e r f o rm a n c e ( L T P P ) s tu dy . T h i s w o r k h a s l ed t o w a r d s

the adop t ion o f the r e s i l ien t m odulus t e s t p rocedure , T3 07-99 , i n t he cur ren t r e l ease o f t he

A m e r i c a n A s s o c ia t io n o f S t a te H i g h w a y a n d T r a n s p o r ta t io n O f f i ci a ls ( A A S H T O ) T e s ts .

Ne i the r t he t e s t p rocedu re nor t he cur ren t des ign gu ide l ine addresses h ow to approac h

se l ec ti ng a des ign r e s il ien t m odu lus va lue f ro m the f i f t een s tr e s s -dependen t num ber s

gen erated b y the lab oratory tes t.

Coh es ive and n on-co hes ive subgrade so i ls a r e genera l l y non l inea r i ne l as ti c

m ater ia l s , thus thei r s t i ffness i s depe nden t on the s t ress condi t ion subjected to .

Rec ogniz ing t h i s , the p ro j ec t - spec i f i c case s t udy d i scussed i n t h i s paper ex am ines t he

s t r e s s-dependen cy o f so i l s encoun te red t h rough l abora to ry de t e rmina t i on o f r e s i li en t

modulus .

Thi s pape r uses a r ecogn i zed cons t it u t ive m ode l and l aye red el a s ti c me tho dolo gy

approach ( i te r a t ive so lu t ion) t o ob j ec t i ve ly in t e rp ret r e su l ts f rom a l abora to ry te s t

p r o g r a m a n d a p p l y th e r e s u lt s f o r in p u t i n to t h e 1 9 9 3 A A S H T O D e s i g n G u i d e f o r

P a v e m e n t S t ru c tu r e s ( o r D a r W I N ) .

Throu gh the use o f the s t r e s s -dependen t cons t i tu t i ve mode l : M r = K I ( S c) w ($3) K5

and s imple 85 th pe rcen t i le s t a t is t ic s , t he p rocess c r ea t ed uses t he p red i c t ed subgrade

mo dulus va lues a t an a s sum ed s t re s s s ta te . T he 85 th pe rcen t i le va lue i s s e l ec t ed as i npu t

in to t he 1993 AAS HTO s t ruc tu ra l number ( S N) r equ i r ement . A conven t iona l pavement

sys t em ( l aye r t ype and t h i ckness ) i s then d eve lop ed us ing t yp i ca l me chan i s t i c p roper t i e s

of a spha l t concre te and aggrega t e base , which sa t i s fy the S N. Th e l aye red e l a st ic m ode l

EL S YM 5 i s t hen used t o app rox im ate ve r ti ca l and hor i zon t a l s t re s ses a t t he t op o f t he

subgrade l aye r . These s t r e s ses a r e com pared t o t hose a s sum ed va lues u sed i n t he i n iti al

i tera tion. Ad jus tm ents are m ade an d i tera t ions cont inue unt i l the values used to predic t

subgrade mod ulus r eason ab ly ma tch t he ca l cu l a t ed s tr e s ses i n the pav em ent sys t em.

The f inal i t era ted value fo r res i l ient m od ulus i s the des ign res i l ient mo dulus . I t i s

r e c o m m e n d e d t h a t th i s d e s i g n v a l u e b e u s e d t o c a l cu l a te p a v e m e n t t h ic k n e s s

requ i r emen t s f o r a ll pavem ent t ypes under cons ide ra t i on f o r t he p ro jec t .

K e y w o r d s :

subgrade , r e s il ien t modulus , pa vem ent des ign

i President, Boud reau Engineering, Inc ., 5392 Blue Iris Court, Norcross, GA 30092.

224

Copyright9 by ASTM Internationa l ww w .astm.org



BOUDREAU ON PAVEMENT SUBGRADE DESIGN VALUE 225

T h e A m e r i c a n A s s o c i a t i o n f o r S t a te H i g h w a y a n d T r a n s p o r ta t i o n O f f i c i a ls

( A A S H T O ) re l e a se d a r e v o l u t i o n a r y d e s i g n m a n u a l i n 1 9 8 6 th a t i n te g r a te d m e c h a n i s t i c

des ign p r inc ip l e s w i th gene ra l l y accep t ed empi r i ca l r e l a ti onsh ips . T h i s manu a l , r e f e r r ed

to as the

AASHTO 1986 Pavement Design Guide,

r e p l a c e d t h e p u r e e m p i r i c a l- b a s e d

i n t e ri m d e s i g n g u i d e f r o m 1 9 7 2. P e r h a p s t h e m o s t s i g n i fi c a n t c h a n g e i n th i s n e w g u i d e

w a s t h e r e q u i re m e n t f o r s u b g r a d e s u p p o r t, c h a n g i n g f r o m a C a l i f o r n i a B e a r i n g C a p a c i t y

( C B R ) d e r i v e d s o i l s u p p o r t n u m b e r ( S S N ) t o t h e re s i li e n t m o d u l u s .

A l t h o u g h t h e p r e f e rr e d m e t h o d o f d e t e r m i n i n g t h e s u b g r a d e r e s i li e n t m o d u l u s w a s

t h r o u g h a d i re c t la b o r a t o r y t es t m e a s u r e m e n t ( A A S H T O T - 2 7 4 ) , a c o n v e r s i o n f a c t o r o f

15 00 xC BR w as a l l owab le . L abora to r i e s tha t we re unw i l l i ng t o i nves t i n t he soph i s t i c a t ed

e q u i p m e n t n e c e s s a r y t o p e r f o r m a r e s il ie n t m o d u l u s t e st o p t e d t o c o n t i n u e t o p e r f o r m

C B R t e s ti n g a n d u s e t h e c o n v e n i e n t c o r r e la t i o n f a c to r . T h o s e l a b o r at o r ie s t h a t m a d e t h e

inves tm en t t o d i r ec t l y me asu re t he r e s i li en t mo du lu s f aced a new cha l l enge . I n t e rp re t a t i on

o f a C B R t e s t w a s f a i rl y si m p l e , p i c k i n g e i th e r th e v a l u e a t 0.1 o r 0 .2 i n c h e s o f

pene t r a t ion . Re cog n iz in g tha t so i l is gene ra l l y a non l i nea r i ne l a s ti c ma te r i a l , a r e s i l ien t

m o d u l u s t e s t i s c o n d u c t e d o v e r a r a n g e o f 1 5 d if f e re n t s t a te s o f st re s s ( c o m b i n a t i o n s o f

ve r t i c a l and ho r i zon t a l s t r e s se s r ep re sen t i ng pos s ib l e i n - s i t u cond i t i ons i n a pavemen t

sys tem) .

A s t h e p a v e m e n t d e s i g n i n d u s t r y h as e v o l v e d , t h e d e s i g n g u i d e h a s b e e n u p d a t e d

( A A S H T O 1 9 9 3 P a v e m e n t D e s i g n G u i d e ) a n d t h e la b o r a t o r y t e st m e t h o d t o d i re c t l y

m e a s u r e t h e r e si li e n t m o d u l u s h a s g o n e th r o u g h c h a n g e s ( A A S H T O T - 3 0 7 ) .

U nfo r tun a t e ly , t he t e st me thod s ti ll r e su l ts i n 15 va lues , an d t he gu ide s t il l requ i r e s a

s i n g u la r v a l u e f o r i n p ut . T h e c h a l l e n g e b e c o m e s w h i c h o f t h e 1 5 v a l u e s s h o u l d b e

se l ec t ed fo r de s ign i npu t ? T o fu r the r com pl i ca t e t he s i t ua t i on , i f a p ro j ec t con s i s t s o f t es t

r e su l ts f o r num erou s t e s ts , s ay 10 d i f f e r en t spec imens , wh ich o f t he 15 0 va lues shou ld be

se l ec t ed? Th i s dec i s i on has no t been add re s sed i n a t e chn i ca l documen t , t hus p r ac t i t i one r s

h a v e b e e n l e ft to c h o o s e t h e ir o w n v a l u e .

Th i s pape r i s i n t ended t o b r i dge t h i s l ongs t and ing gap . A p rac t i ca l app roach t o

s e l e ct a d e s i g n s u b g r a d e r e s i li e n t m o d u l u s v a l u e f r o m a l a b o r a t o r y te s t in g p r o g r a m i s

out l ined .

D e v e l o p m e n t o f a M o d e l

In a s cena r io t ha t ha s r epea t ed i t s e l f num erou s t imes ove r t he pa s t decade , a

l abo ra to ry t e s ti ng p rog ram i s com ple t ed and t e s t r e su l t s a r e fu rn i shed t o t he de s ign

e n g in e e r. T h e m o s t c o m m o n l y a s k e d q u e s t i o n i s:

Q : W h a t v a l u e o f r e s il ie n t m o d u l u s s h o u l d I u s e ?

A : D e p e n d s .

Bec ause so i l i s gene ra l l y a non l i nea r i ne l a s t ic m a te r i a l, i t is s t r e ss depend an t . Thus ,

t h e a n s w e r " d e p e n d s " d e s e r v e s s o m e a t t en t io n . W h a t d o e s i t d e p e n d o n ? S e v e r a l f a c to r s .

L e t u s a s s u m e t h a t t h e la b o r a t o r y t e st p r o g r a m w a s c o n d u c t e d o n s o il r e m o l d e d t o

a p p r o p r i a te d e n s i t y a n d m o i s t u re c o n d i t i o n s t h a t a re a c c e p t a b l e t o t h e d e s i g n e n g i n e e r

( i.e ., w i th in acce p t ab l e t o l e r ance o f i n t ended t a rge t s ). T he de s ign r e s il i en t mo du lus

depends on t he an t i c ipa t ed s t r e s s s t a t e i n t he subg rade l aye r . Thus , a p rope r a s se s smen t o f



226


i n - s i t u st r e s s i s r e q u i r e d . T h i s s t r e s s m u s t b e c a l c u l a t e d f o r th e d e s i g n t r a f f i c tr a v e r s i n g

o v e r a c o n s t r u c te d p a v e m e n t c r o s s s e c t i o n b u i l t o n t h e s e s t r e ss d e p e n d a n t s u b g r a d e s o i ls .

Example

F o r d e m o n s t r a t io n , l e t us a s s u m e t h a t a l a b o r a t o r y s a m p l i n g a n d t e s t p r o g r a m h a s

b e e n c o n d u c t e d . T h e m a t e r i a l s a m p l e d f o r t h is n e w a l i g n m e n t p r o j e c t h as b e e n t e s t e d a n d

a n a l y z e d . B a s e d o n t h e l e n g t h o f t h e p r o je c t , th e b o r i n g l o g i n f o r m a t i o n r e c o r d e d i n t h e

f i e l d , a n d t h e s o i l c l a s s i f i c a t i o n t e s t i n g f r o m t h e l a b o r a t o r y , e i g h t s o i l s w e r e s e l e c t e d f o r

s t i f f n e s s c h a r a c t e r i z a t i o n .

E a c h o f t h e e i g h t so i ls s e l e c t e d w e r e r e m o l d e d t o a p p r o x i m a t e l y 9 5 % o f t h e ir

s t a n d a r d P r o c t o r m a x i m u m d r y d e n s i ti e s at o p t i m u m m o i s t u r e c o n t e n t ( t a rg e t s e s t a b li s h e d

b y t h e c o n s t r u c t io n s p e c i f i c a t io n s ) u s i n g p r o c e d u r e s s e t fo r th i n A n n e x A 3 o f t e st m e t h o d

A A S H T O T - 3 07 . R e s i li e n t m o d u l u s t es ts w e r e c o n d u c t e d o n e a c h o f th e e i g h t r e m o l d e d

t e s t s p e c im e n s . T h e d e s i g n a s s u m e s t h at e a c h o f th e s e e i g h t s o i l s w i l l b e e q u a l l y

r e p r e s e n t e d i n t h e f i n is h e d , p r e p a r e d r o a d b e d p r o f i le .

I n o r d e r to p r o p e r l y h a n d l e t h e d a t a , e a c h t e s t r e s u l t m u s t b e c o n v e r t e d o r f i t i n a

c o n s t i tu t i v e m o d e l . U s i n g a c o n s t it u ti v e m o d e l f ir s t i n t ro d u c e d d u r i n g t h e S H R P w o r k

( E q u a t i o n 1 ), t h e d a t a is t r a n s f o r m e d i n t o a f o r m i n w h i c h m o d u l u s v a l u e s c a n b e

c o m p u t e d f o r a n y l e v e l o f s t r e s s d e s i r a b l e ( T a b l e 1 ).

M r = K I ( S c ) K 2 ( S 3 ) K5 ( 1 )

w h e r e

M r = r e s i l i e n t m o d u l u s , p s i

S c -- c y c l i c a p p l i e d a x i a l s t r e ss , p s i

$ 3 - - c h a m b e r c o n f i n i n g p r e s s u r e , p s i

K 1 , K 2 , K 5 - - n o n l i n e a r r e g r e s s i o n c o n s t a n t / c o e f f i c i e n t s

I n o r d e r t o c o m p u t e t h e r e g r e s s i o n c o n s t a n t a n d c o e f f ic i e n t s, th e d e p e n d e n t v a r i a b l e ,

M r a n d i n d e p e n d e n t v a r i a b l e s S c a n d $ 3 ( a s m e a s u r e d f r o m t h e 1 5 - s eq u e n c e l o a d i n g

r e g i m e r e q u i r e d b y th e A A S H T O T - 3 0 7 t e s t s ta n d a r d ) m u s t f ir s t b e t r a n s f o r m e d t o a

L og 10 b a s e . T h i s a l l o w s a l i n e a r r e g r e s s i o n to b e p e r f o r m e d . O n c e c o m p l e t e d , t h e y -

i n t e r c e p t i s u s e d a s a 1 0 - b a s e e x p o n e n t i a l to d e r i v e t h e K 1 c o n s t a n t , w h i l e t h e K 2 a n d K 5

c o e f f i c i e n t s a r e u s e d a s e x p o n e n t i a l s i n E q u a t i o n 1 .

T a b l e 1 Summaryof Test Results

Sample Dry Moisture

No. D ensity(pcO Con tent,% K1

1 118.3 15.5 9838

2 120.3 17.2 6259

3 117.8 18.9 13 123

4 115.2 16.3 7502

5 113.6 12.2 10 387

6 119.7 17.8 9463

7 113.0 12.1 10 294

8 118.6 16.1 8670

i

Regres sion Coefficients

K2 K5 R 2

-0.13187 0.2219 4 0.99

-0.14293 0.2110 2 0.99

-0.14 105 0.21493 0,98

-0.12825 0.2310 0 0.99

-0.15483 0.23 229 0.98

-0.05394 0.29379 0.98

-0.10049 0.1731 0 0.99

-0.23156 0.21455 0.98



B O U D R E A U O N P A V E M E N T S U B G R A D E D E S I G N V A L U E 2 2 7

T h e c o n s t i tu t i v e m o d e l s e l e c t e d p r o v i d e s a n e x c e l l e n t f it f or t h e d a t a , a s c a n b e

o b s e r v e d b y t h e m u l t i p l e - c o r r e l a t i o n c o e f f i c i e n t , R 2. I n o r d e r t o m a k e u s e o f t h e d a t a , t h e

s u m m a r y r e s u l t s a r e b e s t s e rv e d i n a s p r e a d s h e e t fo r m w i t h a n a d d i t io n a l c o l u m n a d d e d

t h a t c a n r e a d i l y c o m p u t e t h e r e s i l i e n t m o d u l u s a t a n y l e v e l o f v e r t i c a l (S o) a n d h o r i z o n t a l

( $ 3) s t re s s . T h e c a l c u l a t e d o r p r e d i c t e d r e s i l i e n t m o d u l u s w i l l h a v e v e r y s m a l l e r r o r s

a s s o c i a t e d w i t h i t, b a s e d o n t h e g o o d R 2 v a l u e s .

O n c e t h e p r e d i c t e d r e s i li e n t m o d u l u s v a l u e s a r e c o m p u t e d f o r e a c h s o i l m o d e l e d i n

t h e p r o j e c t - s p e c i f i c s o il p r o f i l e , a s i n g u l a r v a l u e i s s e l e c t e d a n d u s e d i n t h e i t e r a t i v e

s e q u e n c e d e s c r i b e d b e lo w . T h i s s i n g u l a r v a l u e c o u l d b e t h e a v e r a g e , t h e a v e r a g e m i n u s a

c o u p l e o f s ta n d a r d d e v i a t i o n s , a m e d i a n o r 5 0 t h p e r c e n t i l e v a l u e , o r s o m e o t h e r p r e f e r r e d

v a l u e . T h i s e x a m p l e u s e s t h e 8 5 t h p e r c e n t i l e v a l u e . B y s e l e c t i n g th i s v a l u e , th e d e s i g n e r

i s w i l l in g t o a c c e p t p o t e n ti a l p r e m a t u r e f a i lu r e s o v e r 1 5 % o f th e d e s i g n e d a n d c o n s t r u c t e d

p a v e m e n t a r e a. T h e s e f a i lu r e s a r e a n t i c ip a t e d o n l y i n t h a t t he t h i c k n e s s d e s i g n w i l l b e

i n s u f f ic i e n t f o r p o t e n t i a l ly 1 5 % o f t h e s u b g r a d e s o i l s th a t c o u l d b e e n c o u n t e r ed .

P r e m a t u r e f a i l u r e s a r e a n t i c i p a t e d to o c c u r p r i o r to t h e e n d o f t h e a n a l y s i s p e r i o d , a n d

c o u l d b e r e p a i r e d i n t h e f o r m o f p a t c h e s . M o r e c o n s e r v a t i v e d e s i g n s c o u l d b e

i m p l e m e n t e d ( b y s e l e c t in g th e m i n i m u m v a l u e ), b u t t hi s s e l e c t io n m a y l e a d t o a m u c h

g r e a t er p a v e m e n t t h i c k n e s s t h at i s e x c e s s i v e f o r t h e m a j o r i t y o f t h e p a v e m e n t p r o f i l e .

D e s i g n e r s s h o u l d d e v e l o p t h e i r o w n a c c e p t a b l e l e v e l o f r i sk , a n d m a k e t h e i r s e l e c t io n

a c c o r d i n g l y .

T h e s e l e c t i o n o f t h e d e s i g n r e s i l i e n t m o d u l u s i s a n i te r a t i v e s o l u t io n . I n o r d e r t o f i n d

t h e p r o p e r s o l u t io n , i n p u t p a r a m e t e r s f o r d e s i g n a r e r e q u i r e d . T h e d e s i g n p o l i c y u t i l i z e d

w i l l b e t h e A A S H T O 1 99 3 G u i d e f o r f l e x i b le p a v e m e n t s . T h e s e i n p u t s c a n b e d e t e r m i n e d

t h r o u g h l a b o r a t o r y t e st in g , e x p e r i e n c e o r p o l i c y . T h e p a r a m e t e r s a n d v a l u e s u s e d i n th i s

e x a m p l e a r e l i s t e d i n T a b l e 2 .

T a b l e 2 - Design Assumptions

Material~Layer

Par am e t e r V a l ue U n i t s

Asphaltic Concrete

Lay er coef f i c i en t , a 0 .44

Mo dulus , E 400 000 ps i

Po i sso n ' s r a t io , v 0 .35

U ni t W e i gh t , 7 145 pe r

Graded Aggregate Base

Lay er coef f i c i en t , a 0 .14

M odulus , E 40 000 ps i

Po i sso n ' s r a t io , v 0 .40

Uni t W eight , y 138 pc f

Subgrade

Po isso n' s rat io, v 0.45

Traffic

V ol um e 1 000 000 E SA L s

Tire pre ssu re, cYc 80 ps i

Serviceability, APSI

2.5



2 2 8


T h e f o l l o w i n g s t e p s h a v e b e e n c r e a t e d i n o r d e r to i l l u s t r a te th e i t e r a t i v e p r o c e s s .

Step I (T r ia l 1 ) - S e l e c t a c o m b i n a t i o n o f v e r t ic a l a n d h o r i z o n t a l s t r e s s e s

a n t i c i p a t e d i n t h e s u b g r a d e l a y e r . F o r t h i s e x a m p l e , a f i r s t t r ia l i te r a t i o n o f 4 p s i v e r t i c a l

a n d 4 p s i h o r i z o n t a l s t r e s s is a s s u m e d ( T a b l e 3 ) , r e s u l t i n g i n a n 8 5 t h p e r c e n t i l e r e s i l ie n t

m o d u l u s v a l u e o f 8 4 77 p s i ( u s e 8 5 0 0 p s i) .

Sample

No.

I

2

3

4

5

6

7

8

T a b l e 3 - C o m p u t e d 8 5 t h P e r c e n t i l e V a l u e (T r i a l 1 )

Dry M o i s m r e Reg~ssion Coeff icients Est . Resil ient

Den si ty(pc0 Content,% K1 K2 K5 M od ulu s, s i ~

118.3 15.5 98 38 -0 .1 31 8 7 0.2219 4 11 146

120.3 17.2 62 59 -0 .1 42 93 0.2110 2 6879

117.8 18.9 13 123 -0 .1 4 1 0 5 0.2 14 93 14 538

115.2 16.3 75 02 -0 .1 28 25 0.2310 0 8650

113.6 12.2 10 387 -0 .1 54 8 3 0.23 22 9 11 564

119.7 17.8 94 63 -0 .0 53 94 0.2937 9 13 196

113.0 12.1 10 294 -0 .1 00 49 0.17 31 0 11 384

118.6 16.1 86 70 -0 .2 3 1 56 0.21455 8468

AV G 10 728

StDev 2568

85th % 8477

Note 1: Resilient mod ulus estimated at axial stress = 4 psi, confining stress = 4 psi.

Step 2 (Tr ia l 1 ) - U s i n g t h e d e s i g n v a l u e s p r o v i d e d i n T a b l e 2 a n d a s u b g r a d e

r e s i li e n t m o d u l u s o f 8 5 0 0 p s i , d e t e r m i n e t h e r e q u i r e d s t r u c tu r a l n u m b e r ( S N ) f r o m e i t h e r

t h e e q u a t i o n o r t h e n o m o g r a p h t h a t s o l v e s t h e e q u a t io n . T h e S N r e q u i r e d f o r th i s f ir s t

i t e r a t i on i s 3 . 2 .

Step 3 (Tr ia l 1 ) - P r o v i d e a p a v e m e n t c r o s s s e c t i o n th a t s a t i s f ie s t h e r e q u i r e d S N .

A n a s p h a l ti c c o n c r et e ( A C ) t h ic k n e s s o f 5 .0 i n c h e s o n a g r a d e d a g g r e g a t e b a s e ( G A B )

t h i c k n e s s o f 8 .0 i n c h e s p r o v i d e s a n a d e q u a t e S N j u s t i n e x c e s s o f th e r e q u i r e d 3 . 2 . O n c e

c o m p l e t e d , s im u l a t e t h e d e s i g n l o a d o n t h e p a v e m e n t s u r f a c e a n d c r o s s s e c t io n , a n d

p e r f o r m c o m p u t a t i o n s b a s e d o n l a y e r e d e l a s t i c t h e o r y t o d e t e r m i n e t h e h o r i z o n t a l ( A fr x,y )

a n d v e r t i c a l (A c rz ) s t r e s s c h a n g e s a t th e t o p o f t h e s u b g r a d e t h a t r e s u l t f r o m t h e l o a d i n g .

T h e c o m p u t e r p r o g r a m E L S Y M 5 ( S R A T e c h n o l o g i e s 1 9 85 ) c a n r e a d il y c a l cu l a te t h es e

v a l u e s .

Step 4 (Tr ia l 1 ) - U s i n g E L S Y M 5 , t h e v e r ti c a l a n d h o r i z o n t a l s tr e s s c h a n g e s o f 5.3

p s i a n d 0 . 9 4 p s i , r e s p e c t i v e l y , a r e e s t i m a t e d . T h e s e v a l u e s m u s t b e a d d e d t o t h e s t a t ic , in -

s i tu p r e s s u r e s e x i s ti n g f r o m t h e p a v e m e n t s y s t e m o v e r b u r d e n . T h e s t at ic p a v e m e n t

o v e r b u r d e n v e r t i c a l ( ~ z ) a n d h o r i z o n t a l ( ~ x.y ) s t r e s s e s c a n b e e s t i m a t e d u s i n g t r a d i t i o n a l

s o i l m e c h a n i c s p r i n c i p l e s ( S o w e r s 1 9 79 ). T h e v e r t ic a l p r e s s u r e i s s i m p l y th e s u m m a t i o n

o f e a c h l a y e r d e n s i t y m u l t i p l ie d b y t h e l a y e r t h i c k n e s s a b o v e t h e s u b g r a d e . T h e h o r i z o n t a l

p r e s s u r e c a n b e c a l c u l a t e d u s i n g t h e l a t e r a l a t - r e s t e a r t h p r e s s u r e c o e f f i c i e n t , k 0 ( e s t i m a t e d

b y t h e s u b g r a d e s o i l s P o i s s o n ' s r a t io , v , i n th e f o r m k 0 = v / l - v ) m u l t i p l ie d b y t h e v e r t i c a l



B O U D R E A U O N P A V E M E N T S U B G R A D E D E S I G N V A L U E 229

o v e r b u r d e n p r e s s u r e a t t h e t o p o f t h e s u b g ra d e . T h e d e t e r m i n a t i o n o f s t re s s r e s u lt i n g f r o m

T r i a l 1 d a t a i s s u m m a r i z e d i n T a b l e 4 .

T a b l e 4 -

Determinat ion o f Stress (Tria l 1)

L a y e r

P r o p e r t y u n i t s

T h i c k n e s s i n c h

D e n s i t y l b / c u f t

Ve r t i ca l Ov erbu rden P res su re , cyv ps i

P o i s s o n ' s r a t i o - S u b g r a d e v

S u b g r a d e 1% = ( v / l - v )

H oriz on tal Pres sure ~x,y = (1% x ~z) ps i

V e r t i c a l P r e s s u r e c h a n g e , A ~ v p s i

H oriz on tal Pre ssur e cha ng e, AC~x,y ps i

In-s i tu Ver t ical S tress ( (Yv+ Acyv) ps i

In-s itu H or iz on ta l Str ess (~x,u + Ac~,~y) psi

A C G A B T o ta l

5.0 8 .0 13.0

145.0 138.0

0.42 0 .64 1 .06

0 . 45

0 . 818

0 . 866

5.31

0 . 9 4

6 . 37

1.81

Step 5 (Trial 1) - C o m p a r e t h e re s u lt s o f t h e c o m p u t a t i o n w i t h t h e v a l u e s u s e d t o

e s t i m a t e t h e t r i a l r e s i l i e n t m o d u l u s . T h e s e v a l u e s o f 6 . 4 p s i ( 4 p s i u s e d f o r t r ia l ) a n d 1 .8

p s i ( 4 p si u s e d f o r tr ia l ) a r e n o t a p a r t i c u l a r l y c l o s e m a t c h , t h u s a s e c o n d i t e r a t i o n i s

r e q u i r e d .

T h e 5 - s t e p p r o c e s s i s r e p e a t e d u s i n g a n e s t i m a t e o f 6 . 4 p s i v e r t i c a l s t r e ss a n d 1 .8 p s i

h o r i z o n t a l s t r e s s .

Step 1 (Tria l 2) - A s e c o n d t r ia l i te r a t i o n u s i n g 6 . 4 p s i v e r t i c a l a n d 1 .8 p s i

h o r i z o n t a l s t re s s is a s s u m e d ( T a b l e 4 ), r e s u l t in g i n a n 8 5 t h p e r c e n t i l e r e s i l ie n t m o d u l u s

v a l u e o f 6 4 1 8 p s i ( u s e 6 4 0 0 p s i ) .

T a b l e 5 - Com puted 85th Percent i le Value (Tria l 2)

Sam ple Dry Mo istum Regression Coefficients Est. Resilient

No. De ns i~ (pc 0 C on ~n t ,% K1 K2 K5 Modulus, ps i I

1 118.3 15.5 9838 -0.13187 0.22194 8775

2 120.3 17.2 6259 -0 .1 4 2 9 3 0 .21102 5434

3 117.8 18.9 13 123 -0.14105 0. 21 49 3 11 460

4 115.2 16.3 7502 -0.12825 0.23100 6773

5 113.6 12.2 10 387 -0 .1 5 4 8 3 0.23229 8932

6 119.7 17.8 9 4 6 3 -0.05394 0.29379 10 175

7 113.0 12.1 10 294 -0.10049 0.17310 9457

8 118.6 16.1 8670 -0.23156 0.21455 6399

AVG 8426

StDev 2053

85th% 6418

Note 1 Resilient mo dulus estimated a t axial stress = 6.4 psi, confining stress = 1.8 psi.

Step 2 (Trial 2) -

U s i n g t h e d e s i g n a s s u m p t i o n s p r o v i d e d i n T a b l e 2 a n d a su b g r a d e

r e s il i e n t m o d u l u s o f 6 4 0 0 p s i , d e t e rm i n e t h e r e q u i r e d s t r uc t u ra l n u m b e r ( S N ) f r o m e i t h e r




t h e e q u a t io n o r t h e n o m o g r a p h t h a t s o l v e s th e e q u a t i o n . T h e S N r e q u i r e d f o r t h is s e c o n d

i t e r a t i on i s 3 . 5 .

Step 3 (Trial 2) - P r o v i d e a p a v e m e n t c r o s s s e c t i o n t h a t s a t i s f ie s t h e r e q u i r e d S N .

A n a s p h a l t ic c o n c r e te ( A C ) t h ic k n e s s o f 5.5 i n c h e s o n a g r a d e d a g g r e g a t e b a s e ( G A B )

t h i c k n e s s o f 8 .0 i n c h e s p r o v i d e s a n a d e q u a t e S N j u s t i n e x c e s s o f th e r e q u i r e d 3 .5 . O n c e

c o m p l e t e d , s im u l a t e t h e d e s i g n l o a d o n t h e p a v e m e n t s u r f a c e a n d c r o s s s e c t io n , a n d

p e r f o r m c o m p u t a t i o n s b a s e d o n l a y e r e d e l a s ti c t h e o r y to d e t e r m i n e t h e h o r i z o n t a l a n d

v e r t i c a l s t r e s s c h a n g e s a t t h e t o p o f th e s u b g r a d e t h a t r e s u l t f r o m t h e l o a d i n g . T h e

c o m p u t e r p r o g r a m E L S Y M 5 c a n r e a d i ly c a l c u l a te th e s e v a lu e s .

Step 4 (Trial 2) -

U s i n g E L S Y M 5 , t h e v e r ti c a l a n d h o r i z o n t a l s t re s s c h a n g e s o f 4 . 2

p s i a n d 0 . 7 3 p s i , r e s p e c t i v e l y , a r e e s t i m a t e d . A g a i n , t h e s e v a l u e s m u s t b e a d d e d t o t h e

s t at ic , i n - s it u p r e s s u r e s e x i s t i n g fr o m t h e p a v e m e n t s y s t e m o v e r b u r d e n , a s s h o w n i n T a b l e

6 .

T a b l e 6 - Dete r mina t ion o f S t re s s (T r ia l 2 )

L a y e r

Propert-/ units

Thickness inch

Densi ty lb /cu f t

Ver t i ca l Ove rburden Pressure , ~v ps i

Po i sson ' s r a tio - Subgrade v

Subgr ade k0 = ( v / l - v )

Ho r izontal Press ure % = (k0 x ~z) psi

Ver t i ca l Pressure change , A~v ps i

Ho r izontal Press ure chang e, Acrx,y psi

In-s i tu V ertic al Stre ss (~v + ACyv) ps i

In-si tu H or izo ntal St ress (~xTy+ Acy,ry) ps i

A C G A B T o t al

5.5 8.0 13.5

145.0 138.0

0.46 0.64 1.10

0.45

0.818

0.900

4.20

0.73

5.30

1.63

Step 5 (Tr ia l 2) - C o m p a r e t h e re s u l ts o f t h e c o m p u t a t i o n w i t h t h e v a l u e s u s e d t o

e s t i m a t e t h e t r i a l r e s i l i e n t m o d u l u s . T h e s e v a l u e s o f 5 .3 p s i ( 6 . 4 p s i u s e d f o r t r ia l ) a n d 1 .6

p s i ( 1 . 8 p s i u s e d f o r t r i a l) a r e s t il l n o t a c l o s e e n o u g h m a t c h , b u t a r e g r e a t l y i m p r o v e d

f r om t he f i r s t tr i a l . A t h i r d i t e r a t i on i s r equ i r ed .

T h e 5 - s t e p p r o c e s s i s r e p e a t e d u s i n g a n e s t i m a t e o f 5. 3 p s i v e r t i c a l s t re s s a n d 1 .6 p s i

h o r i z o n t a l s t r e s s .

Step 1 (Trial 3)

- A t h i r d t r ia l i te r a t i o n o f 5 .3 p s i v e r t i c a l a n d 1 .6 p s i h o r i z o n t a l

s t re s s i s a s s u m e d ( T a b l e 5 ) , r e s u l ti n g i n a n 8 5 th p e r c e n t i l e r e s i li e n t m o d u l u s v a l u e o f

6 5 2 9 p s i ( u s e 6 5 0 0 p s i ) .

,, Ta ble 7 - Corn[rated 85th Perc ent i le Value (Tr ia l 3 )

Sample Dry M o i s t u r e R eg res s io n oeff ic ien ts Es t. Res il ien t

No. Density (pcf) Content, % K1 K2 K5 M od ul us , si i

1 118.3 15.5 98 38 -0 .1 3 18 7 0.2219 4 8764

2 120.3 17.2 62 59 -0 .1 42 93 0.2110 2 5446

3 117.8 18.9 13 123 -0 .1 41 05 0.21 493 11 475

4 115.2 16.3 75 02 -0 .1 28 2 5 0.2310 0 6752



B O U D R E A U O N P A V E M E N T S U B G R A D E D E S I G N V A L U E 2 3 1

5 113.6 12.2 I0 387 -0 .1 54 8 3 0.23 22 9 8949

6 119.7 17.8 94 63 -0 .0 53 9 4 0.2937 9 9930

7 113.0 12.1 10 294 -0 .1 00 49 0.17 310 9444

8 118.6 16.1 86 70 -0 .2 31 56 0.21455 6518

AVG 8410

StDev 2011

85th % 6529

Note 1: Resilient modulus estimated at axial stress -- 5.3 psi, co nfining stress = 1.6 psi.

Step 2 (Trial 3) - U s i n g t h e d e s i g n a s s u m p t i o n s p r o v i d e d i n T a b l e 2 a n d a s u b g r a d e

r e s i li e n t m o d u l u s o f 6 5 0 0 p s i , d e t e r m i n e t h e r e q u i r e d s t ru c t u ra l n u m b e r ( S N ) f r o m e i th e r

t h e e q u a t i o n o r t h e n o m o g r a p h t h a t s o l v e s t h e e q u a t io n . T h e S N r e q u i r e d f o r th i s t h i r d

i t e r a t i on i s 3 . 5 .

Step 3 (Trial 3) - P r o v i d e a p a v e m e n t c r o s s s e c t i o n t h a t s a ti s f i e s t h e r e q u i r e d S N .

A n a s p h a l ti c c o n c r e te ( A C ) t h i c k n e s s o f 5.5 i n c h e s o n a g r a d e d a g g r e g a t e b a s e ( G A B )

t h ic k n e s s o f 8 .0 i n c h e s p r o v i d e s a n a d e q u a t e S N j u s t i n e x c e s s o f th e r e q u i r e d 3 . 5. O n c e

c o m p l e t e d , s im u l a t e t h e d e s i g n l o a d o n t h e p a v e m e n t s u r f a c e a n d c r o s s s e c ti o n , a n d

p e r f o r m c o m p u t a t i o n s b a s e d o n l a y e r e d e la s t ic th e o r y t o d e t e r m i n e t h e h o r i z o n t a l a n d

v e r t i c a l s t re s s e s a t t h e t o p o f th e s u b g r a d e . U s i n g E L S Y M 5 , t h e v e r t ic a l a n d h o r i z o n t a l

s t r e s s e s o f 4 .2 p s i a n d 0 . 73 p s i , r e s p e c t i v e l y , a r e d e t e r m i n e d .

Step 4 (Trial 3) - U s i n g E L S Y M 5 , t h e v e r t i c a l a n d h o r i z o n t a l s tr e s s c h a n g e s o f 4 . 2

p s i a n d 0 . 7 3 p s i , r e s p e c t i v e l y , a r e e s t im a t e d . A g a i n , t h e s e v a l u e s m u s t b e a d d e d t o t h e

s t at ic , i n - si tu p r e s su r e s e x i s t i n g f r o m t h e p a v e m e n t s y s t e m o v e r b u r d e n , a s s h o w n i n T a b l e

8.

T a b l e 8 - Determ inat ion o f S tress (Tr ia l 3 )

L aye r

Proper ty uni t s

Thickness inch

Den si ty lb /cu f t

Ver t i ca l Overb urden Pressure , Ov ps i

Po i sson ' s r a t io - Subgrade v

Subgr ade k0 = ( v / l - v )

H oriz on tal Pre ssu re cyx,v (k0 x oz) psi

Ver t i ca l Pressure change , Ao~ ps i

Ho r izontal Pressu re chang e, Aox,v psi

In-si tu Ve r t ical St ress (~v + Aov) psi

In-si tu Hor izo ntal St ress (ox,y+ AgxTy) p si

A C G A B T o t al

5.5 8.0 13.5

145.0 138.0

0.46 0.64 1. I0

0.45

0.818

0.900

4.20

0.73

5.30

1 .63

Step 5 (Tr ia l 3 ) C o m p a r e t h e r e s u l ts o f th e c o m p u t a t i o n w i t h t h e v a l u e s u s e d t o

e s t i m a t e t h e t r i a l r e s i l i e n t m o d u l u s . T h e s e v a l u e s o f 5. 3 p s i ( 5 .3 p s i u s e d f o r t r ia l ) a n d 1 .6

p s i ( 1 . 6 p s i u s e d f o r tr i a l ) a r e a c l o s e e n o u g h m a t c h t o c o n s i d e r th e i t e r a t i v e s o l u t i o n

c l o s e d . A n o t h e r i t e r a t i o n w i l l n o t c l o s e t h i s s o l u t i o n a n y f u r th e r .

B a s e d o n t h is f i n a l it e ra t io n , th e d e s i g n s u b g r a d e r e s i l i e n t m o d u l u s s h o u l d b e 6 5 0 0

ps i .




Dis c us s io n

Thi s i s a f a i r ly s i m p l e app r oach t ha t does no t t ake a g r ea t dea l o f t im e . F r om t he

beg i nn i ng o f Tr i a l 1 t o t he com pl e t i on o f Tr i a l 3 r equ i r e s app r ox i m a t e l y 20 m i nu t e s . Th i s

p r oces s cons i de r s and u t il iz e s t he s t r e s s - st r a in be hav i o r o f the p r o j ec t - spec i f ic so i l s

encou ntered . I t should b e rec ogn ized tha t cer ta in e r rors a re inherent in th i s process . F i rs t,

t he e s t i m a t e o f re s i li en t m od u l us a t any g i ven l eve l o f s tr e s s is an app r ox i m a t i on . The

e r r o rs a s soc i a t ed wi t h t h i s app r ox i m a t i on a r e a t tr i bu ted b y how we l l t he con s t it u t ive

mo del f it s the da ta (R 2 r e su l ti ng f r om t he Eq ua t i on 1 reg r e s s ion ) . O bv i ous l y , t he l a r ge r

t he R 2, t he m or e accu r a t e t h i s app r ox i m a t i on i s. Second l y , t he de s i gn a s sum es t ha t e ach

so i l i s r ep r e sen t ed equa l ly . I f t h is a s su m p t i on i s no t va l i d ( f o r exam p l e , i f so i l s am pl e

num ber 2 wi l l no t be u t i l iz ed du r i ng cons t r uc t ion , o r so i l s am pl e num ber 5 w i ll be u sed

f o r an e s t i m a t ed 50% o f t he p r o j ec t) app r op r i a t e ad jus t m en t s a r e r equ i red p r i o r to t he

i t e ra t i ve p r oces s . A we i gh t ed ave r ag e can be used , o r a d i f f e r en t pe r cen t i l e va l ue . As

s t a ted ea r l ie r , de s igne r s shou l d de ve l op t he i r ow n accep t ab l e l eve l o f r isk , and m ake t he i r

se lec t ion accordingly .

Th e va l ues u t i l iz ed i n th i s de s i gn exa m p l e do no t cons i de r s ea sona l a f f ect s . E f f o r ts

shou l d b e m ade t o i nco r po r a t e s ea sona l va r i a t ion o f subgr ade s t i ff ne s s.

Re fe r e nc e s

Sowers , George F . , 1979,

In t roduc tory So i l Mechan i cs a nd Founda t ions : Geo techn i ca t

Engineering, Four t h Ed i t ion , M acm i l l an Pub l i sh ing , Ne w Yor k , pp 383- 384 .

S R A T e c h n o l o g i es , 1 9 85 , E L S Y M 5 C o m p u t e r P r o g r a m , V e r si o n 1 . 0 , " P a v e m e n t D e s ig n

a n d A n a l y si s P r o c e d u re s o n M i c r o c o m p u t e r s , " S t u d y C o n t r a c t e d b y t h e F e d e r a l

H i ghw ay Adm i n i st r at i on .



Louay N. Mohammad, ~Ananda Herath, e and Hani H. Titi 3

T h e U s e o f C o n t i n u o u s I n t r u si o n M i n i a tu r e C o n e P e n e t r a t io n T e s t in g i n E s t i m a t i n g

t h e R e s il i en t M o d u l u s o f C o h e s i v e S o i ls

Re fe r e nc e :

Mohammad, L. N., Herath, A., and Titi, H. H.,

" T h e U s e

o f

C o n t i n u o u s

I n t r u s io n M i n i a t u re C o n e P e n e t r a t io n T e s t in g i n E s t i m a t i n g t h e R e s il ie n t M o d u l u s

o f C o h e s i v e

Soils," Res i l ien t Modu lus Tes t ing f or Pavem en t Componen ts , A ST M ST P

1437, G. N. Durham, W. A. Marr, and W. L. De Groff, Eds., ASTM International, West

Conshohocken, PA, 2003.

Abstract:

This paper presents an application o f the continuous intrusion miniature cone

penetration testing in evaluating the resilient modulus of cohesive soils. Four cohesive

soils were selected for the field and laboratory testing program. The field tests were

performed on these soils using the continuous intrusion miniature cone penetration test

system. The laboratory testing program included repeated load triaxial tests on

undisturbed soil samples, and soil physical and strength properties testing. A statistical

analysis was performed on the test results of two soils to develop a correlation among the

resilient modulus, cone penetration test parameters, in-situ stresses, and soil properties.

The model was used to predict the resilient modulus of other two soils. The predicted

and measured values of the resilient modulus were in agreement.

K e y w o r d s : resilient modulus, cone penetration testing, cohesive soil


The American Association of State Highway and Transportation Officials (AASHTO)

guide for design of pavement structures (AASHTO 1993) recommends the use of the

resilient modulus (Mr) for characterization of base and subgrade soil and for design of

flexible pavements. The subgrade soil characterization, based on the resilient modulus,

is a realistic way to analyze the moving vehicle loads on a pavement. The resilient

modulus represents the dynamic stiffness of pavement materials under the repeated loads

of vehicles.

Associate Professor, Department of Civil & Environmental Engineering and Louisiana

Transportation Research Center, Louisiana State University, 4101

Gourrier Ave., Baton Rogue, LA 70808.

Postdoctoral Researcher, Louisiana Transportation Research Center, 4101 Gourrier

Ave., Baton Rogue, LA 70808.

3 Assistant Professor, Department o f Civil Engineering and Mechanics, University of

Wisconsin - Milwaukee, P.O. Box 784, Milwaukee, WI 53201.

233

Copyright9 by ASTM International www.astm.org




The r e s i l i en t modu lus can be e s t ima ted f rom the empi r i ca l co r r e l a t i ons , i n - s i t u

nond es t ruc t i ve t e st me thod s (N DT ) , and l abo ra to ry t e s t i ng on so il s ample s . Th e

l a b o r a to r y p r o c e d u r e s a r e c o n s i d e r e d l a b o r i o u s , t i m e c o n s u m i n g , a n d h i g h l y e x p e n s i v e.

The f i e l d nondes t ruc t i ve t e s t p rocedure s have ce r t a in l imi t a t i ons w i th r e spec t t o

r epea t ab i l i ty o f t e s t r e su lt s . The sho r t co min gs o f the se t e s t m e thod s s i gn i fy t he need fo r

an i n - s i tu t e ch no lo gy fo r de t e rm in ing t he r e s i l ien t cha rac t e r is t i c s o f subg rade and base

so i l s unde rnea th a pavemen t .

Th e con e pene t r a t i on t e s t i ng (CPT ) i s pop u l a r i n t he geo t echn i ca l f i e ld fo r so ft

cha rac t e r i za ti on . T h i s i s becau se t he CP T is e con om ica l , f a s t, and p rov ides r epea t ab l e and

re l iab l e r e su l ts . Th e CP T i s condu c t ed by advan c ing a cy l i nd r i ca l r od w i th a con e t i p in to

the so i l and m easu r ing t he t ip r e s i s tance and s l eeve f r i c t i on due t o t h is i n t ru s ion . T he

cone r e s i s t ance pa ram e te r s , t i p r e s i s tance and s l eeve f r i c t ion , a r e u sed t o c l a s s i fy so i l

s t ra t a and t o e s t ima te s t r eng th an d de fo rma t ion cha rac t e r i s t ic s o f so i ls .

Th i s pape r p r e sen t s t he r e su l t s o f a s t udy pe r fo rme d t o i nves t i ga t e t he app l i cab i l i ty o f

t he i n t ru s ion t echn o log y in eva lua t i ng t he r e s il i en t m odu lus o f subg rad e so i l s.

L abo ra to ry and f i e l d - t e s ti ng p rog ram s were co ndu c t ed a t t h r ee si te s com pr i s i ng fo u r

cohe s ive so i ls i n L ou i s i ana . The f i e l d t e s ts cons i s t ed o f con t i nu ous i n t ru s ion min i a tu r e

cone pene t r a t i on t es t s. The se te s t s we re condu c t ed u s ing a con t i nu ous i n t ru s ion

m i n i a t u re c o n e p e n e t r a t io n t e s t ( C I M C P T ) s y s t em . T h e l a b o r a t o ry t e st s c o n s i s te d o f

r epea t ed l oa d t r iax i a l t e s t on und i s tu rbed so i l s ample s t o eva lua t e t he r e s il i en t

cha rac t e r i s ti c s o f t he se so il s . O the r so il te s t s we re co ndu c t ed t o cha rac t e r i ze t he so il s

such a s phys i ca l p rope r t i e s , co m pac t i on cha rac te r i s t ic s , and s t r eng th pa ram e te r s .

S t a t is t ic a l ana lyse s we re pe r fo rm ed t o co r r e l a t e t he cone pene t r a t i on t e st pa r ame te r s ,

and t he re s i l ien t cha rac t e r i s ti c s and phys i ca l p rope r t i e s o f t he i nves t i ga t ed so il s . A m ode l

w a s p r o p o s e d i n w h i c h t h e r e s il ie n t m o d u l u s o f s u b g r ad e s o il i s p r e d i c te d f r o m t h e c o n e

t ip r e s is t ance , s l eeve f r i c t ion , mo i s tu r e con t en t , un i t we igh t , and t he in - s i t u s tr e s se s . Th e

m o d e l w a s d e v e l o p e d u s i n g t h e t e s t r es u l ts o f tw o s o i ls a n d u s e d t o p r e d i c t t h e r e s i li e n t

m odu lus o f t he o the r two i nv es t i ga t ed so i ls .

Objective and Scope

T h e o b j e c t iv e o f t h is s t u d y w a s t o d e v e l o p a n d v a l id a t e a c o r r e l a ti o n a m o n g t h e

con t in uou s i n t ru s ion min i a tu r e co ne pene t r a t i on t e s t pa r ame te r s , r e s i li en t cha rac t e r i s t ic s

o f subg rade so i ls , i n - s i t u s t r e s se s , a nd so i l p rope r t i e s .

T h e m i n i a tu r e c o n e p e n e t r a t io n t e s ts w e r e p e r f o r m e d u s i n g t h e 2 - c m ~ min i a tu r e

f r i c ti on con e pene t rom e te r . The l abo ra to ry r epea t ed l oad t r iax i a l te s t s we re pe r fo rm ed on

the und i s tu rbed so i l s ample s .

Background

The r e s i l ien t m odu lus o f so i ls i s i n f l uenced b y man y f ac to r s i nc lud ing t he so il t ype ,

t he va r i a t i on o f mo i s tu r e con t en t , un i t we igh t , and t he i n - s i tu s t re s se s. I nves t i ga to r s have

a t t em p t e d a v a r i e ty o f m e t h o d s t o e v a l u a t e t h e d y n a m i c r e s il ie n t p r o p e r t ie s o f s u b g r a d e

so i l and t o i nves t i ga t e t he d i f f e r en t f ac to r s a f f ec t i ng the r e s i l ien t m odu lus . The t e s t

m e t h o d s i n c l u d e d l a b o r a t o r y as w e l l a s in - s it u t e st m e t h o d s . T h e l a b o r a to r y m e t h o d s a r e

m a in ly cond uc t e d u s ing tr i ax ia l sy s t em s , s imp le shea r , r e sonan t co lumn , gy ra to ry , and

t h e h o l l o w c y l i n d e r te s t d e v i c e . M o h a m m a d e t a l. ( 1 9 9 4 ) p r e s e n t e d a s u m m a r y o f th e



M O H A M M E D E T A L . O N E S T I M A T I N G R E S I L IE N T M O D U L U S 2 3 5

r e s e a r c h r e s u l t s c o n d u c t e d u s i n g t h e s e d e v i c e s . B e c a u s e o f it s s i m p l i c i t y , r e p e a t a b i l i ty ,

a n d a c c u r a c y , t h e t r ia x i a l c e l l i s t h e m o s t p o p u l a r r e s i l i e n t m o d u l u s l a b o r a t o r y - t e s t i n g

d e v i c e . T h e r e s i l i e n t m o d u l u s ( M r ) in a r e p e a t e d l o a d t e s t is d e f i n e d a s t h e r a t i o o f th e

m a x i m u m d e v i a t o r s tr e s s ( @ j ) a n d t h e r e c o v e r a b l e e l a s ti c s t r a in ( T r) a s f o l l o w s :

Mr = " ~ (1)

s

F i g u r e 1 il l u s t ra t e s t h e d e f i n i t i o n o f th e r e s i l i e n t m o d u l u s i n a r e p e a t e d l o a d t r i a x i a l

t e s t. G e n e r a l l y , t h e r e s i li e n t m o d u l u s d e t e r m i n e d f r o m t h e l a b o r a t o r y t e s ts i s i n f l u e n c e d

b y m a n y f a c to r s i n c l u d i n g m o i s t u r e c o n t e n t, d r y u n i t w e i g h t , c o n f i n i n g a n d d e v i a t o r

s t r e s s e s , s i z e o f t h e s p e c i m e n , s t r e s s p u l s e s h a p e , d u r a t i o n , f r e q u e n c y a n d s e q u e n c e o f

s t re s s l e v e l s, te s t in g e q u i p m e n t a n d s p e c i m e n p r e p a r a t i o n a s w e l l a s c o n d i t i o n i n g

m e t h o d s ( F r e d l u n d et a l. 1 9 7 7, N a t a a t m a d j a a n d P a r k i n 1 9 8 9 , M o n i s m i t h 1 9 89 , M c G e e

1 98 9 , A l l e n 1 9 8 9, K a m a l e t a l. 1 99 3 , M o h a m m a d e t a l. 1 9 94 , M o h a m m a d a n d P u p p a l a

1995 , D r um m e t a l . 1997 ) .

(Yd

Resil ient modulus, M -

gr

6

r/3

Dev iator stress, o d

Stress

~ - - S t r a i n

d

Re silient stra in, g~

41 Pla stic stra in, %1

Time, t

F i g u r e 1 - Definition of Resilient Modulus



2 3 6 R E S IL IE N T M O D U L US T E S T I NG F O R P A V E M E N T C O M P O N E N T S

Seve ra l i n - s i t u me thods have been deve loped t o de t e rmine t he r e s i l i en t modu lus .

N o n d e s t r u c t iv e t e st m e t h o d s s u c h a s t h e D y n a f l e c t a n d F a l l i n g W e i g h t D e f l e c t o m e t e r

( F W D ) h a v e a l s o b e e n s u b j e c t e d t o a lo t o f sc r u ti n y . D e f l e c t i o n s o f p a v e m e n t m a t e r i a ls

a r e measu red i n t he f ie l d by such equ ipmen t , and t he se de f l ec t i ons a r e u sed wi th

back ca l cu l a t i on su b rou t i ne s fo r e s t ima t ing t he r e s il i en t p rope r t i e s . Seve ra l t ypes o f

back ca l cu l a t i on so f twa re a r e a lr eady ava i l ab l e and r epo r t ed i n t he li te r a tu r e . Resu l t s

o b t a i n e d f r o m t h i s s o f t w a r e a r e n o t r e p e at a b le a n d a p p e a r t o b e a f f e c t e d b y f a c t o rs s u c h

as t he t e s ti ng l oad , the r e l a t i ve s t if fne s s be twe en l aye r s and en v i ronm en ta l co nd i t i ons .

B o t h l a b o r a to r y a n d i n -s i tu m e t h o d s a r e i m p r o v i n g w i t h d e v e l o p m e n t s i n h a r d w a r e

t echno log i e s , pa r t i cu l a r l y i n a r ea s such a s da t a acqu i s i t i on sys t ems and compu te r

t e c h n o l o g y . H o w e v e r , t h e la b o r a t o r y m e t h o d s a r e r a t h e r la b o r io u s , t i m e c o n s u m i n g , a n d

expens ive and t hey r equ i r e a h igh ly soph i s t i c a t ed t e s t i ng sys t em. Moreove r , t he se

m e t h o d s a r e s ti ll b e i n g m o d i f i e d t o m a k e t h e m m o r e a c c u r a t e a n d r e li ab l e. T h e s e

l im i t a ti o n s i n l a b o r a t o r y a n d i n -s it u N D T m e t h o d s s i g n i f y t h e n e e d t o d e v e l o p a m o r e

rea l is t ic , r e l iab l e and e con om ica l i n - s it u me thod fo r de t e rmin ing t he r e si l ien t p rope r t i e s

o f su b g r a d e s o i ls . T h e i n - si tu m e t h o d s h o u l d b e a b l e t o s a v e a s i g n i fi c a n t a m o u n t o f t i m e

a n d m o n e y , w h i c h w o u l d h a v e b e e n s p e n t o n s a m p l i n g a n d l a b o r a t o r y t e st in g .

S e v e r a l t y p e s o f i n- s it u t e s ti n g e q u i p m e n t h a v e b e e n u s e d i n g e o t e c h n i c a l

i nves t i ga t i ons fo r t he pa s t two d ecades . The co ne pene t r a t i on t e s t ha s been r eco gn i z ed a s

one o f t he mos t w ide ly u sed i n - s i tu t e st s . I n t he U .S . , con e pene t r a t i on t e s t ing has ga in ed

rap id popu l a r i t y i n t he l a s t decade an d i s cu r r en t l y r ep l ac ing t he t r ad it i ona l s t anda rd

pene t r a t i on t e s t (Tu m ay e t a l . 1998) . Cone pen e t r a t i on t e s t i ng is an in - s i tu m e tho d used

fo r c l a s s i f i c a ti on an d i n t e rp re t a t ion o f eng inee r ing p rope r t i e s o f so i ls i n t he f i e l d o f

g e o t e c h n i c a l e n g i n e e r in g . T h e c o n e p e n e t r a t i o n t e s t c o n s i s t s o f a d v a n c i n g a c y l i n d ri c a l

rod wi th a con i ca l t i p i n to t he so i l and me asu r in g t he fo r ce s r equ i r ed t o push t h i s r od .

The re a r e two fo rce s m easu re d d u r ing t he CP T: t he co ne t i p r e s is t ance (qc) i s t he so i l

r e s i s tance t o advan ce t he cone t ip and t he s leeve f r i c t i on ~ ) i s t he f r i c ti on deve lope d

b e t w e e n t h e s o i l a n d t h e s l e e v e o f t h e p e n e t r o m e t e r b e c a u s e o f t h e p en e t ra t io n . T h e

f r i c ti on r a t io (Rfl is de f i ned a s t he r a t i o o f the s l eeve f r i c ti on an d t i p r e s i s t ance a nd i s

e x p r e s s e d i n p e r c e n t. T h e s e c o n e - m e a s u r e d p a r a m e t e r s a r e u s e d t o i d e n t i f y t h e s o i ls a n d

de t e rmine t he i r p rope r t i e s .

A p p l i c a t i o n s o f C P T i n th e f ie l d o f p a v e m e n t e n g i n e e r i n g , p a r t ic u l a r ly r e l a te d t o

s u b s o il s , h a v e a l so b e e n a t t em p t e d . B a d u - T w e n e b o a h e t al. ( 1 9 8 9 ) c o n d u c t e d c o n e

p e n e t r a t io n t es ts o n v a r i o u s h i g h w a y p a v e m e n t s i n F l o ri d a . T h e y c o r r e la t e d t h e c o n e t es t

r e s u lt s w i t h M , re s u lt s f r o m N D T m e t h o d s . I n a c c u r a c i e s a n d u n c er t a in t ie s i n v o l v i n g N D T

back ca l cu l a t i on sub rou t i ne s m ay a f f ec t t he r e l iab i l i ty o f t he se co r r e l a t ions . I n sp i te o f t h is

l imi t a ti on , t h i s s t udy r evea l ed t he po t en t i a l o f CP T in de t e rmin ing r e s il i en t p rope r t ie s .

T h e c o n c e r n r e g a r d i n g t h e u s e o f th e c o n e p e n e t r a t io n t e st m e t h o d t o d e t e r m i n e t h e

re s i li en t mo du lu s o f subso i l s i s w i th r e spec t t o the d i f f e r ences i n t he mo des o f t e s t i ng

used . T he t i p r e s is t ance an d s l eeve f r i c t i on a re ob t a ined f rom the con e pene t r a t i on t e st ,

wh ich i s cons ide red a quas i - s t a t i c t e s t me thod , whe reas t he r e s i l i en t modu lus i s a p rope r ty

o b t a i n e d f r o m a d y n a m i c r e p e a t e d l o a d t e st . I t is o f t e n a s s u m e d t h a t t e st p a r a m e t e r s

o b t a i n e d f r o m d i f f e r e n t te s t b a c k g r o u n d s m a y n o t p r o v i d e r e a s o n a b l e c o r r e l a t io n s w i t h

one ano the r . Howeve r , t h i s i s no t a lways t he ca se . Ea r l i e r s t ud i e s (Tumay 1985 , Puppa l a

e t al . 1 9 9 5 ) s h o w e d t h e p o t e n ti a l o f t h e q u a s i- s ta t ic C P T m e t h o d i n d e te r m i n i n g t h e l o w

s t ra i n d y n a m i c s h e a r m o d u l u s a n d l i q u e f a c ti o n o f s o il . T h e d y n a m i c s h e a r m o d u l i a n d



MOHAMMED ET AL. ON ESTIMATING RESILIENT MODULUS 237

CP T pa ram e te r s a r e l e s s i n f l uenced by s t r e s s and s t r a in h i st o ry . I n fac t , t he se pa ram e te r s

a r e c o n t ro l l e d b y th e s a m e s o il v a ri a b le s , w h i c h m a y h a v e l e d to t h e d e v e l o p m e n t o f

b e t te r c o r r e la t io n s b e t w e e n t h e m . T h e r e si li e n t m o d u l u s i s c o n s i d e r e d a n a l o g o u s a n d a l s o

re l a ted t o the shea r mo du lus . The re fo re , t he i n f l uence o f s t re s s and s t r a in behav io r on

r e s il ie n t m o d u l u s w i ll b e s i m i l a r to t h a t o f s h e a r m o d u l u s . P r e v i o u s s t u d i es M o h a m m a d e t

a l. ( 1994) a l so i nd i ca t ed t ha t t he r e s il i en t p rope r ty o f subg rade so i l is l e s s dependen t o n

s t re s s and s t ra in h i s t o ry . Th e s t r a in h i s t o ry i n f l uence i s a l so exp ec t ed t o be i n s ign i f i can t

i n a nondes t ruc t i ve r epea t ed l oad t r i ax ia l t e s t. Fu r the rmore , t he cone pene t r a t i on t e s t s and

repea t ed l oad r e s il i en t m odu lus t e s ts we re co ndu c t ed on so i l und e r i den t i ca l

env i ronmen ta l cond i t i ons . Th i s imp l i e s t ha t bo th t e s t pa r ame te r s we re sub jec t ed t o s imi l a r

env i ronmen ta l va r i ab l e s such a s dens i t y , mo i s tu r e con t en t , and geoma te r i a l f ab r i c . I n

such cond i t i ons , t he con e pene t r a t i on te s t and re s i l ien t m odu l i pa r ame te r s depe nd o n t he

sam e so i l va r iab l e s . The re tb r e , i t i s r ea sonab l e t o a s sum e tha t a co r r e l a t i on i s pos s ib l e

be tween cone pene t r a t i on t e s t pa r ame te r s and r e s i l i en t modu lus .

M e t h o d o l o g y

F i e ld a n d l a b o r a t o ry te s t in g p r o g r a m s w e r e c o n d u c t e d o n c o h e s i v e s o il s f r o m t h re e

d i f f e r en t s it e s com pr i s i ng t b u r coh es ive so i l s i n L ou i s i ana . T he l oca t i on o f t he t e s t s it e s i s

sho wn on L ou i s i ana m ap i n F igu re 2 . Th e f i e ld t e st s c a r r i ed ou t a t t he i nves t i ga t ed s it e s

cons i s t ed o f con t i nu ous i n t ru s ion min i a tu r e cone pene t r a t i on te s ts . U n d i s tu rbed an d

d i s tu rbed so i l s amp le s we re ob t a ined f rom these s i t es u s ing a conve n t iona l d r i l l i ng r ig .

F igu re 3 dep i c t s a t yp i ca l p l an fo r t he fi e ld t e s ts co ndu c t ed a t t he i nve s t i ga t ed s i te s . Th e

l a b o r a to r y - t e st i n g p r o g r a m w a s c o n d u c t e d o n t h e u n d i s t u r b e d a n d d i s t u r b e d s o i l s a m p l e s

to de t e rmine t he i r re s i li en t mo du lus , phys i ca l p rope r t i e s , s t r eng th pa rame te r s , and

c o m p a c t i o n c h a r ac t e ri s ti c s. T h e l a b o r a t o r y te st s c o n d u c t e d a r e: R e s i l i en t M o d u l u s o f

U n b o u n d G r a n u l a r B a s e / S u b b a s e M a t e r i a l s a n d S u b g r a d e S o i l s - S H R P P r o t o c o l P 4 6

( A A S H T O 1 9 9 5) , D e t e r m i n i n g t he A t t e r b e r g L i m i ts o f S o i ls , D e t e r m i n a t i o n o f M o i s t u re

C o n t e n t , M o i s t u r e D e n s i t y R e l a t io n s h i p s , M e c h a n i c a l A n a l y s i s o f S o i ls , O r g a n i c M a t e ri a l

i n S o il , T e s t M e t h o d f o r S p e c i fi c G r a v i t y o f S o il s , T e s t M e t h o d f o r C o n s o l i d a t e d

U n d r a i n e d T r i a x i a l C o m p r e s s i o n T e s t o n C o h e s i v e S o i l , T e s t M e t h o d f o r C l a s s i fi c a t io n

o f S o i l F o r E n g i n e e r i n g P u r p o s e s ( U n i f i e d S o i l C l a s s if i c a ti o n S y s t e m ) , a n d

C l a s s i fi c a ti o n o f S o il a n d S o i l A g g r e g a t e M i x t u r e s f o r H i g h w a y C o n s t r u c t i o n P u r p o s e s .

T h e s e t e st s w e r e p e r f o r m e d i n a c c o r d a n c e w i t h th e c o r r e s p o n d i n g te s t p r o t o c o l s o f A S T M

a n d /o r L o u i s ia n a D e p a r tm e n t o f T r an s p o r ta t io n a n d D e v e l o p m e n t ( L A D O T D ) .

Char acter i za t i on o f the Inves t igated S o i l s

Pavement Research Faci l i . ty S i te , Por t Al len

The f i r s t s i te s e l ec t ed was t he Pa vem en t R esea rch Fac i l i t y (PR F) i n Po r t A l l en ,

L ou i s i ana . Th i s s i t e is l oca t ed on s i x ac r e s o f m a in ly a na tu ra l so i l depos i t o f he av y c l ay

w i t h 1 .5 2 m t h i c k e m b a n k m e n t c o n s t r u c t e d o f s i lt y c l a y c o n s t r u c t e d o n p a r t o f t h e s i te .

The se two so i ls we re s e l ec t ed fo r th i s s t udy . The s i l t y c l ay cons i s t s o f 23 pe rcen t c l ay and

70 pe rcen t s i l t and 4 .7 pe rcen t o rgan i c con t en t . Th e c l ay i s c l a s s i f i ed a s CL -M L ( s i lt y

c l a y ) a c c o r d i n g t o t h e U S C S a n d A - 4 ( s il ty s o il ) a c c o r d i n g t o t h e A A S H T O c l a s s i f ic a t i o n




sys t em. S t anda rd P roc to r t e s t on t he s i l t y c l ay showed tha t t he op t imum moi s tu r e con t en t

o f t he so i l (Wopt) s 18 .0 pe rcen t and t he co r r e spon d ing m ax im um d ry un i t we igh t ( (dmax) i s

16 .7 kN /m 3.

Figure 2 - Location o f the Inv estiga ted Soil Sites

T h e h e a v y c l a y c o n si s ts o f m e d i u m g r a y s o ft n o r m a l l y c o n s o l id a t e d c l a y w i t h t r a c e s o f

o rgan i c ma te r i a l s and i ron ox ide . T he t opso i l l aye r w i th an ave rag e dep th o f 0 .5 m i s

m a i n l y s o f t c la y m i x e d w i t h o r g a n i c m a t e r ia l s a n d t r a c e s o f r o ot s . A p p r o x i m a t e l y a 6 . 0 m

deep so f t no rma l ly conso l i da t ed c l ay l aye r unde r l i e s t h i s l aye r. Th e heav y c l ay cons i s t s

o f 2 pe rcen t s and , 14 pe rcen t s il t, 84 pe rcen t c l ay and co l lo id s . Th e so i l pos se s se s h igh

mo i s tu r e con t en t w i th an ave rage o f 51 pe rcen t ( ave rag e L L = 93 and ave ra ge PL = 27 ) .

Th e ave rage un i t we igh t o f t he so i l is 17 .2 kN /m 3. The heav y c l ay i s c l a s s i fi ed a s C H ( f a t

c l a y) u s i n g t h e U S C S a n d A - 7 - 6 ( c l ay ) a c c o r d i n g t o t h e A A S H T O c l a s si f ic a t io n s y s t e m .

S t a n d ar d P r o c t o r t e s t o n th e h e a v y c l a y s h o w e d t h at t he o p t i m u m m o i s t u r e c o n t e n t o f t h e

soi l (Wopt) s 31 .4 pe rcen t and t he co r r e spon d ing m ax im um d ry un i t we igh t ((dmax) i s 13 .6

kN /m 3. U nco nso l i da t ed und ra ined t r i ax i a l (U U ) t e s t was conduc t ed t o eva lua t e t he

undra ined shea r s tr eng th o f the heavy c l ay . Tes t r e su lt s sho wed tha t t he ave rage

undra ined shea r s t r eng th i s 51 .5 kPa . Th e p rope r t i e s o f t he s i l ty c l ay and hea vy c l ay a r e

s u m m a r i z e d i n T a b l e 1.



M O H A M M E D E T A L . O N E S T IM A T I N G R E S IL IE N T M O D U L U S

T ab le 1 - Properties of the Investigated Cohesive Soils

2 3 9

PRF-Silty

c l ay

93

P RF-H eav y

clay

98

LA-15 clay

Passing sieve #20 0 (% ) 98

Clay ( ~ 23 84 44 33

Silt (% ) 70 14 54 65

Organic content (%) 4 .7 9 .2 N A NA

Liquid limit, LL (%) 28 93 52 35

Plastic limit, PL (%) 22 27 25 23

Plasticity index, PI 6 66 27 12

Specific gravity,

G

2.67 2.68 2.70 2.69

An gle o f friction, ~b(o) 22.0 14.0 14.0 19.2

Optimum wa ter content, Wop~% ) 18.0 31.4 28.1 17.5

3

Max. d ry unit weight

(kN/m)

16.7 13.6 15.1 17.0

Soil classification, USCS

Soil c lassification, AASHTO

C H

(Fat clay)

A-7-6

(Clay ey soil)

C L - M L

(Silty clay)

A-4

(Silty soil)

C H

(Fat clay)

A-7-6

(Claye y soil)

Siegen Lane

c lay

98

C L

(Lean c lay)

A-6

(Sil ty clay)

State Route LA-15, Deer Park

T h e e m b a n k m e n t o f S t a te R o u t e L A - 1 5 i n C o n c o r d i a P a r is h i s l o c a t e d a p p r o x i m a t e l y

1 5 m i l es so u th o f V id a li a . T h e em b an k m en t a t t h i s l o ca t io n i s pa r t o f t h e Miss i s s ipp i

R iv e r Lev ee . T h e so il co n s id e red in th i s s tu d y i s lo ca ted a t t h e u p s lo pe o f th e ro ad w ay o n

th e Lev ee . T h e so i l co n s i s t s o f 4 4 pe rcen t c l a y an d 5 4 pe rcen t s ilt . T h e av e rag e L iqu id

L im i t (LL) i s 5 2 pe rcen t an d th e av e rage P las t i c i ty In d ex (P / ) i s 27 . T h e so i l i s c l a s s i f ied

as C H ( f a t c l ay ) u s in g th e U n i f i ed S o i l C lass i f i ca t io n S ys tem a n d A -7 -6 ( c l aye y so i l)

u s i n g t h e A A S H T O c l a s si f ic a t io n s y s t e m . T h e o p t i m u m m o i s t u r e c o n t e n t o f th e s o i l is

2 8.1 pe rcen t an d th e co r respo n d in g m ax im u m d ry u n i t we igh t 1 5.1 k N /m 3. P ro per t i e s o f

L A - 1 5 c l a y a re s u m m a r i z e d i n T a b le 1.

Siegen Lane, Baton Rouge

T h e t e s t s it e is l o ca ted a t t h e in t e r sec t io n o f S iegen L an e an d th e In d u s t r ip l ex in B a to n

Ro u ge . T h e so i l a t th i s s i te co n s i s t s o f 3 3 pe rcen t c l ay an d 65 p e rcen t s il t. T h e so i l is

c l a s si f ie d a s l e a n c l a y ( C L ) a c c o r d i n g t o t h e U S C S a n d s i l ty c l a y ( A - 6 ) a c c o r d i n g t o t h e

A A S H T O c l a ss i fi c at io n . T h e a v e r a g e L i q u i d L i m i t o f t h e s o il i s 3 5 p e r ce n t a n d t h e

av erag e P las t ic i t y In d ex is 1 2 . C o m pac t io n ch a rac te r i s t i c s o f t h e so i l sh o w ed th a t th e




o p t i m u m m o i s t u r e c o n t e n t is 1 7 .5 p e r c e n t a n d t h e c o r r e s p o n d i n g m a x i m u m d r y u n it

we igh t i s 17 .0 kN / m 3 .

C o n t i n u o u s I n t r u s io n M i n i a t u r e C o n e P e n e t r a ti o n T e s t

T h e c o n e p e n e t r a t i o n t e st s y s t e m s u s e d t o e x e c u t e t h e f i e l d -t e s ti n g p r o g r a m i s t h e

c o n t i n u o u s i n t r u si o n m i n i a t u r e c o n e p e n e t ra t i o n t e s t s y st e m , w h i c h w a s d e v e l o p e d a t t h e

L o u i s ia n a T r a n sp o r ta t io n R e s e a r ch C e n t e r ( L T R C ) b y T u m a y a n d c o - w o r k e r s ( T u m a y e t

a l. 1998 , Tu m ay and T i t i 2000 , T i f f e t al . 2000) fo r sha l l ow s i t e cha rac t e ri za t i on . T he

s y s t em , s h o w n i n F i g u r e 3 , c o n s i s ts o f c o n t i n u o u s p u s h d e v i c e , h y d r a u l ic m o t o r ,

m i n i a t u r e c o n e p e n e t ro m e t e r , a n d d a t a a c q u i s i t io n s y s te m . T h e c o n e i s a t ta c h e d t o a

c o i le d p u s h r o d , w h i c h a l lo w s a c o n t i n u o u s p e n e t ra t io n , a n d i s m e c h a n i c a l l y s t r ai g h t e n e d

as t he cone i s push ed i n to t he so il . Th e min i a tu r e cone pen e t rom e te r ha s a c ros s s ec t iona l

a r ea

of 2

c m 2 , t he f r i c t i on s l eeve a r ea i s 40 cm 2 , and t he co ne a pex ang l e i s 60 deg rees .

Resea rch e r s a t L TR C (T um ay e t a l. 1998 , T um ay and T i t i 2000 , T i t i e t a l. 2000)

c o n d u c t e d f ie l d a n d l a b o r a t o r y t e st s t o c a l i b ra t e a n d e v a l u a t e t h e r e s u l ts o f t h e C I M C P T

w i t h r e s p e c t t o t h e re s u l ts o f t h e 1 0 a n d 1 5 c m 2 cone pe ne t rom e te r s i n d i f f e r en t so il t ypes .

R e s u l t s s h o w e d t h a t th e C I M C P T r e s u l ts a r e c o n s i s te n t w i t h t h o s e o b t a i n e d b y t h e 1 0 a n d

1 5 c m 2 c o n e p e n e t r o m e t e rs . G e n e r a l ly , t h e C I M C P T s y s t e m t e n d s t o r e c o r d h i g h e r ti p

r e s is t a n c e a n d l o w e r s l e e v e f r ic t io n i n t h e a m o u n t o f 1 0 p e r ce n t c o m p a r e d t o t h e 1 0 a n d

15 cm 2 cone pene t rom e te r s .

T h e C I M C P T p r o c e d u r e d e s c r i b e d h e r e i n w a s u s e d a t a ll si te s. D u r i n g C I M C P T , t h e

c o n e w a s a d v a n c e d i n to t h e g r o u n d a t a ra t e o f 2 c m / s e c w i th c o n t i n u o u s m e a s u r e m e n t s

o f t h e t ip r e s is t a n ce ( qc ) a n d s l e e v e f ri c ti o n ~ ) . T h e C I M C P T s w e r e c o n d u c t e d a r o u n d

t h e b o r e h o l e f r o m w h i c h t h e l a b o r a t o r y sa m p l e s w e r e o b t a i n e d f o r r es il ie n t m o d u l u s

de t e rmina t i on . Th i s i s t o ensu re t ha t t he CIMCPT sound ings r ep re sen t t he so i l t e s t ed i n

the l abo ra to ry . A typ i ca l cone pen e t r a t i on t e s t p l an a t t he i nves t i ga t ed s i te s i s p r e sen t ed i n

F igu re 4 .

F igu re 5 dep i c t s t he r e su lt s o f CIM CP T o n t he s i l ty c l ay fo r f ie l d te s t s e t 1 . A s sh ow n

in t he f i gu re , the t i p r e s is t ance and s l eeve f r i c t i on (o f t he s i l t y c l ay l aye r ) meas u red by t he

C I M C P T s y s t e m a r e c o n s i s t e n t a n d r e fl e c t s im i l a r p a t te r n s. R e s u l ts o f C I M C P T s

c o n d u c t e d o n t h e h e a v y c l a y a re p r e se n t ed i n F i g u re 6 . T h e C I M C P T s o u n d i n g s o f t h e

h e a v y c l a y a re a l s o c o n s is t en t . T h e c o n e p e n e t r a ti o n t e s t p a r a m e t e rs (q s a n d f ) w e r e u s e d

t o d e v e l o p a m o d e l f o r p r e d i c ti n g t h e r e si li e n t m o d u l u s o f c o h e s i v e s o i ls f r o m t h e c o n e

p a r a m e t e rs . T h e r e f o r e , i t is i m p o r t a n t t o e v a l u a t e t h e v a r i a b i li t y o f t h e C I M C P T p r o f i l e s

a t s ame s i t e u s ing s t a ti s ti c a l ana lys i s . Th e so i l p ro f i l e was d iv ide d i n to t h in 20 -m m so i l

l a y e rs a n d t h e C I M C P T p a r a m e t e r s ( qc a n d f s ) o f e a c h t e st w e r e a v e r a g e d a l o n g t h e 2 0 -

m m l aye rs . Fo r each 20 - r am so i l laye r ( a t e ach t e s t s e t) , t he r e a r e fou r va lues fo r q~ and

f o u r v a l u e s f o r f . T h e a v e r a g e o f th e s e f o u r v a l ue s , t h e s ta n d a r d d e v i a ti o n , a n d t h e

c o e f f i c ie n t o f v a r ia t i o n a r e c a l c u la t e d . T h e a v e r a g e v a l u e s o f th e c o e f f i c ie n t o f v a r i a t io n

o f q ~ a n d f s a r e p re s e n t e d i n T a b l e 2 . T h e a v e r a g e c o e f f i c ie n t o f v a r ia t i o n f o r q c r a n g e s

f rom 17 t o 20 fo r t e s t s e t #1 a t t he PR F s ite . G ene ra l l y , t he r e su l t s p r e sen t ed i n Tab l e 2

quan t i fy t he na tu ra l va r i ab i l i ty o f t he so i l a t t he s a me t e s t s it e . I n add i t ion , t h e se r e su l t s

i nd i ca t e t ha t t he CIM C PT repea t ab i l i ty i s f unc t i on o f t he so i l va r i ab i li t y and i s s i te

spec i f ic .



M O H A M M E D E T A L . O N E S T I M A T I N G R E S IL IE N T M O D U L U S 2 4 1

F i g u r e 3 - The Cone Penetration Test Systems Used in the Study

t

CIMC

(

CIMCPTI CIMCPT5

r T x r T~ _ _

/

~PT3 CI M ( ~aT8 DH2 CI

O

T4 CIM

BH1

Q

CIMCPT2

1.0

m

se t 1

1.0 m

r'LN

MLJ

CIMCPT6

1.0 m

) l

s e t 2

ICPT7 CIMC

1 . 0 m

CIMCPT9

q'12 BH3 C PTI 1

M.]

C|MCPT10 I

1 . 0 m

~

se t 3

9 BH 1 Borehole (undisturbed soil sampling)

~) CIM CPT: Continuou s Intrusion Miniature Cone Penetration Test

F i g u r e 4 - A Typical Layout fo r the Field Testing



242


Tip resistance, q, S le ev e riction, Fr ict io n atio,

Rf

Soil profile (MPa) (MPa) (%)

F i g u r e 5 -

Cone Penetration Test Results of Silty Clay

F i g u r e 6 - Cone Penetration Test Results of Heavy Clay



M O H A M M E D E T A L . O N E S T I M A T I N G R E S I LI E N T M O D U L U S 243

Table 2 - S t a t i s ti c a l A n a l y s i s C o n d u c t e d o n t h e P e n e t r a t i o n T e s t R e s u l t s

Test Site Test Depth (m) Cone esistance, qc Sleeve riction,f

Set COV average (%) COV average (%)

PRF-Silty Set 1 0.8 20 22

clay 1.0 17 15

PRF-

Heavy

clay

LA-15

clay

Siegen

Lane clay

Set 2

Set 3

0.8

1.0

0.8

1.0

0.8

22

19

26

27

30

25

16

16

25

14

Set 1

1.0

33

5

0.8 31 11

Set 2

1.0 11 28

Set 3 0.8 14 39

1.0 23

21.8

22

34

Set 1

1.0

26 36

Set 2 0.8 21 23

1.0 23 19

0.8 27 38

Set 3

18

.0

0.8

44

26

43

Set 1

1.0 39 42

0.8 18 38

Set 2

1.0

27 39

0.8 10 9

Set 3

13.0 11

R e s i l i e n t M o d u l u s

The resilient modulus o f the investigated soils was determined using the repeated load

triaxial test. The test was conducted using an MTS model 810-closed loop servo-

hydraulic material-testing system as shown in Figure 7. The major components of this

system are the load ing system, digital controller, and load unit control panel.

The undisturbed soil samples were trimmed and prepared for the laboratory resilient

modulus test. The repeated loading triaxial tests were conducted accord ing to the

AASHT O procedure T 294-94 "Resilient modulus of Unbou nd Granular Base/Subbase

Materials and Subgrade Soils - SHRP Protocol P46." The soil samples were conditioned

by applying one thousand repetitions of a specified deviator stress at a certain confi ning

pressure. Conditi oning eliminates the effects of specimen disturbances from sampling,

and specimen preparation procedures and minimi zes the imperfect contacts between end

platens and the specimen. The spec imen is then subjected to different stress sequences.

The stress sequence is selected to cover the expected in-service range that a pavement or

subgrade material experiences under traffic loading. Some of the investigated soils are

very soft and possesses low unconfined compressive strength. These soil specimens could

not be tested at high stress levels, therefore, the max imum deviator stress was limited to

less than half of the unconfined compressive strength of the specimen as specified by

AASHT O T 294-94.




Figure 7 -

The M TS Tes t Sy s t em

Th e r e su l t s o f the r epea t ed l o ad t r iax i a l t e s t on t he so i l s ample s f rom the PR F t e s t s i t e

a r e s h o w n i n T a b l e 3 . In s p e c t i o n o f T a b l e 3 s h o w s t h a t t h e c o e f f i ci e n t o f v a r i a ti o n o f th e

ca l cu l a t ed r e s i li en t mod u lus r ang es f rom 0 to 2 .0 . Th i s i nd i ca t e s t ha t t he repea t ed t oa d

t r iax i a l t e s t on t he i nves t i ga t ed so il s amp le s w as r epea t ab l e. Th e va r i a t i ons o f t he r e s i li en t

m o d u l u s (Mr)wi th dev i a to r s t re s s a t d i f f e r en t con f in ing p re s su re s fo r t he s amp le s a r e

s h o w n i n F i g u r e 8 . T h e r e s i li e n t m o d u l u s a t a c o n s ta n t c o n f i n i n g p r e s s u r e d e c r e a s e s a s

the dev i a to r s t r e s s inc r ea se s , whe reas , t he r e s il i en t mo du lu s a t a cons t an t dev i a to r s tr e s s

inc rea se s a s t he con f in ing p re s su re i nc r ea se s . Th i s r e f lec t s a t yp i ca l beh av io r o f the e f f ec t

o f s t r e sse s on t he re s i l ien t m odu lu s . I n spec t i on o f F igu re 8a i nd i ca t e s t ha t the s i l t y c l ay

e x h i b i te d h i g h r e s i li e n t m o d u l u s v a l u es . T h e i n -s i tu m o i s t u r e c o n t e n t o f s il t y c l a y r a n g e s

f r o m 2 0 . 8 t o 2 5 . 4 p e r c e n t a n d t h e u n i t w e i g h t v a r ie s b e t w e e n 1 9 .9 a n d 2 0 . 8 k N / m 3. T h e s e

v a l u e s a r e c lo s e to t h e o p t i m u m m o i s t u r e c o n t e n t ( w = l 6 . 5 % ) a n d t h e c o r r e s p o n d i n g u n i t

w e i g h t ( ( = 19 . 8 k N / m 3 ) o b t a i n e d f r o m t h e l a b o r a t o r y c o m p a c t i o n t e st . H o w e v e r , t h e

r e si li e nt m o d u l u s o f t h e h e a v y c l a y is l o w c o m p a r e d t o t h e s i l t y cl a y, F i g u r e 8 b . T h e

h e a v y c l a y i s a s o f t so i l w i th a r a n g e o f i n - s i t u m o i s t u r e c o n t e n t b e t w e e n 5 9 a n d 6 5 . 1

p e r c e n t a n d t h e u n i t w e i g h t r a n g e s f r o m 1 6 t o 1 6 ,4 k N / m 3. T h e o p t i m u m m o i s t u r e c o n t e n t

o f t h e h e a v y c l a y o b t a in e d i n t h e l a b o r a t o r y is 3 1 . 4 p e r c e n t a n d t h e c o r r e s p o n d i n g u n i t

w e i g h t i s 1 7 .8 k N / m 3 . T h e h i g h a m o u n t o f m o i s t u r e i n t h e h e a v y c l a y i s th e m a i n r e a s o n

fo r the l ow er r e s il i en t mo du lus o f t h i s so i l.

Th e r e s il i en t m od u lu s o f t he i nves t i ga t ed f i ne -g ra ined so i l s r e f l ec ts a t yp i ca l beh av io r

w h e r e t h e v a l u e s o f t h e r es il ie n t m o d u l u s a t c o n s t a n t c o n f i n i n g p r e s s u r e d e c r e a s e w i t h t h e

inc rea se o f t he dev i a to r s tr e s s. I n add i t i on , t he r e s i l ien t m odu lus va lues a t a cons t an t

dev i a to r s t r e s s i nc r ea se w i th t he i nc r ea se o f t he con f in ing p re s su re .



M O H A M M E D E T A L . O N E S T IM A T I N G R E S IL IE N T M O D U L U S 245

T a b l e 3 - Results of the Repeated Load Triaxial Test

S oi l t ype ~ D ep th (m )

0 . 8

P R F - s i l t y c l a y

1.0

0 . 8

P R F - h e a v y c l a y

1.0

oc (kP a ) ~ d (kP a ) M r (M P a)

4 1 . 8 2 6 . 4 3 7 . 8

41 . 4 13 . 1 45 . 0

41 . 5 26 . 3 38 . 5

4 1 . 5 3 8 . 4 3 3 . 6

4 1 . 5 5 1 . 0 2 9 . 9

4 1 . 5 6 3 . 9 2 7 . 9

20.7 13. I 40.5

20 . 7 25 . 8 32 . 1

2 0 . 7 3 7 . 9 2 8 . 3

2 0 . 7 5 0 . 8 2 6 . 7

2 0 . 7 6 3 . 9 2 6 . 1

0 . 4 12 . 8 33 . 8

0 . 4 2 5 . 2 2 6 . 7

0 . 4 3 7 . 4 2 4 , 2

0 . 4 5 0 . 6 23 . 5

0 . 4 6 3 . 7 2 3 . 7

41 . 3 26 . 1 43 . 7

41 , 3 13 . 0 5 0 . 4

41 . 3 26 . 2 44 . 1

4 1 . 4 3 8 . 2 3 7 . 7

41 . 3 5 0 . 8 32 . 5

41 . 3 63 . 5 30 . 1

2 0 . 6 1 2 .9 4 2 . 9

20 . 6 25 . 6 34 . 1

2 0 . 7 3 7 . 7 3 0 . 0

2 0 . 6 5 0 . 7 2 8 . 4

2 0 . 6 6 3 . 7 2 7 . 9

0.3 12.7 35 .1

0 . 3 25 . 1 28 . 4

0 . 3 37 . 3 25 . 6

0 . 3 5 0 . 5 24 . 9

0 . 3 63 . 5 25 , 1

41 . 6 12 . 0 6 . 2

41 , 7 5 .8 8 . 3

41 . 7 11 . 8 6 . 3

41 . 7 17 . 4 5 . 5

20 . 9 5 . 8 8 . 2

20.9 t 1 .7 6 .2

21 , 0 17 , 4 5 . 4

0 , 6 5 . 7 7 . 9

0.5 I 1.6 6.1

0 . 6 17 . 2 5 . 3

41 . 4 12 .1 7 . 0

41 . 5 5 . 9 8 . 6

41.5 12.3 7 .1

41 .4 17.3 5 .8

20 . 9 5 . 9 8 . 8

20 . 9 12 .1 6 . 8

20 .9 17.3 5 .8

0 . 6 5 , 8 8 . 2

0 . 6 11 . 9 6 . 5

0 , 6 17 . 2 11 . 7

c o v ( % )

0 , 4

0.1

0 , 3

0 . 2

0.1

0,1

0 . 3

0 . 2

0.1

0.1

0.1

0 . 2

0 . 2

0 . 0

0 , 2

0 . 2

0 . 5

0 . 4

0 , 3

0 . 3

0 . 2

0.1

0 . 4

0 . 2

0.1

0 . 2

0 . 2

0 . i

0,1

0.1

0 . 0

0 . 0

1.0

0 . 2

0 . 4

0.3

0 . 2

0 . 4

0.1

2 . 0

1,0

0 , 3

2 . 0

2 . 0

1.0

0 . 3

1.0

1.0

0 . 2

0 . 4

0 . 4

0 . 2



2 4 6 R E S I L IE N T M O D U L US T E S T I N G F O R P A V E M E N T C O M P O N E N T S

e~

_=

O

1 0 0 1 0 0

10

depth=0.8 m

w= 25.4 %

L~ 15.9 kN/m3

10

' ' ' '

' ' ' 1 0

100 10

D e v i a t o r s t r e s s , a a ( k P a )

, , l , J f

depth= 1.0 m

w= 23.0 %

~,~= 16.5 kN /m3

Con{)ning st ress

9 o ~41.3 kPa

9 o, -20.7 kPa

u a u I I

D e v i a t o r s t r e s s , o d ( k P a )

I i t

1 0 0

( a ) R e s u l t s o f th e r e p e a t e d l o a d t r i a x i a l t e s t o n t h e s i l ty c l ay .

1 0 0

l 0

c~

. . . . . . . . I . . . . . . . 1 0 0

depth=0.8 m

w = 6 1 . 6 %

yj= 9.9 kN/m~

, ~ , , L , , ~ I ' ' ' ' ' ' ' l

1 0 1 0 0

D e v i a t o r s t r e s s , c a ( k P a )

, * , iin ,, ' I i i i I~, 1

depth= 1.0 m

w= 65.1%

"r,~ 9.9 kN/m3

t t .~ ill ,l[ 1 a i mil l

1 0 1 0 0

D e v i a t o r s t r e s s , c~d ( k P a )

( b ) R e s u l t s o f th e r e p e a t e d l o a d t r i ax i a l t e s t o n t h e h e a v y c l a y .

F i g u r e 8 - Resilient Modulus

D e v e l o p m e n t o f t h e R e s i l i e nt M o d u l u s M o d e l

T h i s s t u d y a i m e d t o e s t a b l i s h a c o r r e l a t i o n b e t w e e n t h e c o n e p e n e t r a t i o n t e s t

p a r a m e t e r s ( qc a n d f i ) a n d t h e r e s i l ie n t m o d u l u s o f c o h e s i v e s o i l a n d to v a l i d a t e t h e

p r o p o s e d c o r re l a t i o n . T h e r e f o r e , a n e x p e r i m e n t a l p r o g r a m w a s c a r r i e d o u t in w h i c h c o n e

p e n e t r a t i o n t e s t s w e r e c o n d u c t e d n e a r b o r e h o l e s f r o m w h i c h u n d i s t u r b e d s o i l s a m p l e s

w e r e t e s t e d to d e t e r m i n e t h e i r r e s i l ie n t m o d u l u s .

I n o r d e r t o e s t a b l i s h a c o r r e l a t i o n b e t w e e n t h e c o n e p e n e t r a t i o n t e s t p a r a m e t e r s a n d t h e

r e s i l ie n t m o d u l u s , t h e v a r i a b l e s a f f e c t b o t h t e s t s a r e id e n t i f ie d . T h e c o n e t i p r e s i s t a n c e



M O H A M M E D E T A L. O N E S T IM A T IN G R E S IL IE N T M O D U L U S 2 4 7

(qc), s leev e frict ion (fss) and res i l ient m od ulu s (Mr) are affected by the soi l typ e, unit

weigh t ( 0 , mois ture co ntent of the so i l (w) , and s tate of s t res s (~0). Therefore , an at tempt

wa s m ade in thi s s tudy to account for the ef f ect s o f the con e res is tance , s l eeve f r ict ion,

soi l propert i es and s tres ses o n the predict ion o f resi l ient m odulus .

G r o u n d l e v e l

~-E y - unit weight of soi l

Confining stress, er~

= K,, G,

E

100

9 0

8 0

7 0

6 0

5 0

4 0

Insita confining stress Ievel

'~ ~ Confining stress

2 0 - -

9 ~, =41.3 kPa

'~ ~ 9 o~, =20.7 kP a

i 9 cr =0.0 kPa

1 0

2 0 3 0 4 0 5 0 6 0 7 0 8 0

9 0 1 0 0

Deviator stress, er ( k P a )

Figure 9 -

Estimation of the Field Resilient Modulus

The res il ient m odu lus obtained from the laboratory repeated loading t r iaxial t es t vary

with deviator s tress . Therefore, i t i s necessary to ident i fy a s ingle value of the res i l ient

m od ulu s from the laboratory test that correspon ds to the in-s i tu s tress condit ion s . Th is

value of the res il i ent mo dulus i s determined from the repeated load tr iaxial t es t and i s

referred to as the field res i l ient m od ulu s M r f ) . A p rocedure w as d eve l op ed t o de t erm ine

the f ield res i lient mod ulu s for the invest iga ted soi ls and is i l lustrated in Figure 9. Th e



2 4 8


ave rag e dep ths o f t he und i s tu rbed so i l s ample s w e re 0 .8 and 1 .0 m . A t t he se dep ths , the

s t re s s es a c t i n g o n a s o i l e le m e n t w e r e c o m p u t e d . T h e n , t h e r e s il ie n t m o d u l u s v a l u e s w e r e

in t e rpo l a t ed f ro m the l abo ra to ry t e s t r e su l t s ba se d o n t he s t re s se s o f each so i l s am ple a s

i l lu s t r a ted i n F igu re 9 . Th e so i l is cons ide red un de r i n - s i t u (K o) cond i t i on , wh e re t he i n -

s i tu s t r e s se s a r e ca l cu l a t ed f ro m the so i l un i t we igh t and t he dep th o f t he so i l e l emen t

u n d e r c o n s i d er a t io n . A s u m m a r y o f t h e f i el d a n d l a b o r a t o r y t e s t r e s u lt s a n d t h e a n a l y s is

fo r t he i nves t iga t ed so i l s is p r e sen t ed i n T ab l e 4 . The se r e su l t s r ep re sen t t he r e s i l ien t

m o d u l u s v a l u e s c o r r e s p o n d i n g t o t h e i n - si tu s t re s s c o n d i t i o n s

(Mrf).

T h e v a r ia b l e s p r e s e n te d i n T a b l e 4 a r e c o n s i d e r e d i n t h e a n a l y si s t o d e v e l o p a m o d e l

fo r p r ed i c t i ng t he r e s il i en t m odu lus u s ing the CIM C PT ou tpu t . S t a t is t ic a l ana lys i s wa s

p e r f o r m e d u s i n g t h e S ta t is t ic a l A n a l y s i s S y s t e m ( S A S ) p r o g r a m . T h e m o d e l i s d e v e l o p e d

f o r t h e f i n e - g a i n e d s o i ls u n d e r i n - s it u c o n d i t i o n s . T h e v a r i a b le s f o r t h e P R F - s i l t y c l a y a n d

P R F - h e a v y c l a y w e r e u s e d t o d e v e l o p t h e m o d e l s i n c e t h e y re p r e s e n t t h e s t i f f a n d t h e s o f t

so i l types , r e spec t i ve ly . B ased on t he r e su l t s o f t he s t a t is t ic a l ana lys i s , t he fo l l ow ing

m o d e l w a s p r o p o s e d t o p r e d ic t t h e r e si li e n t m o d u l u s o f f i n e -g r a i n e d s o i ls u s i n g t h e c o n e

pene t r a t i on t e s t :

M~r - 1 ( 3 1 . 7 9 q c + 7 4 . 8 1 f s l + 4 . 0 8 Y d

O 0'55 O" w J Yw

where , M r i s t he r e s i li en t mo du lu s (MP a) , q c i s t he cone t ip r e s is t ance ( M Pa ) , f s i s t he

s leeve f r ic t ion (M Pa) , Crc i s the con f in i ng s t ress (kP a) , or,, s the ver t ica l s t ress (kP a) , w i s

t he w a t e r con t en t ( dec ima l ) , Ya i s the d ry un i t we ig h t ( kN /m3) , an d yw i s th e u n i t w e i g h t o f

t h e w a t e r ( k N /m 3 ) . T h e r o o t m e a n s q u a r e d e r r o r f o r t h is m o d e l i s R M S E = l . 3 7 a n d t h e

c o e f f i c ie n t o f d e t e rm i n a t i o n i s R 2 = 0 .99 .

90

80

7O

r 60

so

o 40

30

20

10

I

T I ' ~ ' i ' I ' I ' I ' 0 1 ' ~

, PR F-SiIty O / t

9 PR F-H eavy / -~

- [ ] . _ -

F * S,ogon Lano O " f -_

7"

0 10 20 30 40 50 60 70 80 90

Predicted Mrp (MPa)

F igu re 10

-Measured versus Predic ted Res i l ient Modulus



MOHAMMED ET AL. ON ESTIMATING RESILIENT MODULUS 249

T a b l e 4 - S u m m a r y o f th e L a b o r a t o r y a n d F i e l d T e s ts

Test Soi l Depth qc f~ w Ya crcy aay Mrt

s i te s a mpl e (m) (MP a ) (MP a ) (% )

(kN/m3)

(kPa) (kPa) (MP a)

BH1 0.8 2 .50 0 .066 25 .4 15 .9 12.4 4 .5 48.4

PR F- BH1 1.0 3.20 0.071 23.0 16.5 15.7 5.3 50.4

silty BH 2 0,8 2.69 0.091 20.8 16.8 12.4 4.5 54.1

clay BH3 0.8 2.82 0.073 23.2 16.9 12.4 4.5 63.4

BH 3 1.0 3.15 0,092 21.5 17.0 15.7 5.3 60.7

BH I 0.8 0.28 0.019 61.6 9.9 11.9 1.3 14.3

PR F- BH1 1.0 0.31 0.02 0 65.1 9.9 14.9 1.6 14.6

heav y BH 2 0.8 0.32 0.023 60.4 10.2 11.9 1.3 24.7

clay BH 2 1.0 0.40 0.023 62.5 10.0 14.9 1.6 26.2

BH3 0.8 0.39 0.019 59.0 10.2 11.9 1.3 24.8

BH 3 1.0 0.38 0.018 59.5 10.3 14.9 1.6 24.5

BH 1 0.8 2.85 0.151 24.1 17.3 13.0 4.1 77.4

BH I 1 .0 2 .08 0 .114 23.0 16.2 15 .1 4 .8 58.3

LA-15 BH 2 0.8 2.07 0.123 28.4 16.8 13.1 4.1 52.8

clay BH 2 1.0 2.14 0.097 27.3 15.3 14.8 4.7 53.0

BH 3 0.8 3.07 0.135 18.8 17.8 12.9 4.1 83.3

BH 3 1.0 2.05 0.110 31.4 15.2 15.2 4,8 56.9

BH1 0.6 3.10 0.124 9.5 18.3 8.1 4.0 54.6

Sieg en B H I 1.2 1.32 0.156 22.5 17.1 16.8 8.3 35.9

Lane BH 2 0.8 3.36 0.113 16.7 17.1 10.7 5.3 61.1

clay BH 3 t .3 1.61 0.105 23.1 15.4 16.3 8.0 33.2

Legend: qc - t ip resistance,f~ - sleeve fric t ion, w - mo isture content , Yd - dry unit weight , cr~r -c omput e d

con fining stress,

~Ydf--

om puted d eviator stress, M~r - fie ld resi l ient modulus, B H - borehole.

V e r i f ic a t io n o f th e R e s i li e n t M o d u l u s M o d e l

T h e m o d e l I b r p r e d i c t i n g t h e r e s il i e n t m o d u l u s o f c o h e s i v e s o i l s b y t h e c o n e

p e n e t r a t i o n t e s t w a s d e v e l o p e d b a s e d o n t h e f i e ld a n d l a b o r a t o r y te s t r e s u l t s o n t h e P R F -

s i lt y cl a y a n d h e a v y c l ay . T h e m o d e l w a s t h e n v e r i f i e d b y p r e d i c t i n g t h e r e s i l i e n t

m o d u l u s o f t h e o th e r c o h e s i v e s o il s a n d c o m p a r i n g t h e m o d e l p r e d i c t io n s a n d l a b o r a t o r y

a n d f i e l d t e s t r e s u lt s . T h e r e s u l t s o f t h e p r e d i c t e d v e r s u s m e a s u r e d r e s i l ie n t m o d u l u s a r e

s h o w n i n F i g u r e 1 0 . T h e p r e d i c t e d a n d m e a s u r e d v a l u e s o f re s i li e n t m o d u l u s a r e in g o o d

a g r e e m e n t .


T h i s p a p e r p r e s e n t e d a p i l o t i n v e s t i g a t i o n t o a s s e ss t h e a p p l i c a b i l i t y o f th e i n t r u s i o n

t e c h n o l o g y f o r e s t i m a t i n g t h e re s i l ie n t m o d u l u s o f s u b g r a d e s o i ls . F i e ld a n d l a b o r a t o r y

t e s t i n g p r o g r a m s w e r e c o n d u c t e d o n f o u r c o h e s i v e s o i ls i n L o u is i an a . C o n e p e n e t r a t io n

t es t s w e r e c o n d u c t e d u s i n g t h e c o n t i n u o u s i n t r u s i o n m i n i a t u r e c o n e p e n e t r a t i o n t e s t w i t h

m e a s u r e m e n t s o f t h e c o n e t ip r e s i s t a n c e a n d s l e e v e f r ic t io n . U n d i s t u r b e d a n d d i s t u r b e d

s o i l s a m p l e s w e r e o b t a i n e d f r o m d i f f e r e n t d e p t h s n e x t t o t h e c o n e p e n e t r a t i o n t e st s .

R e p e a t e d l o a d t ri a x ia l t e s t s w e r e c o n d u c t e d o n t h e u n d i s t u r b e d s o il s a m p l e s t o d e t e r m i n e




the r e s i li en t modulus . O the r l abora tory t e s ts w ere conduc ted a l so to de te rm ine the

s t rength parameters , phys ical proper t ies , and com pact io n character is tics . Resul ts o f both

f ie ld and labo ratory tes t ing programs w ere analyze d and cr i t ica l ly evaluated.

Stat is tica l analys is was cond ucted on the con e penetra t ion tes t prof i les and the

repeated load t r iaxia l tes t resul ts to evalu ate the qual i ty o f the f ie ld and la borato ry tes ts . A

sta tist ica l mo del for predic t ing the res i l ient mo dulu s was d evelo ped based o n the f ie ld

and lab oratory tes t resul ts o f two soils, wh ich co m pr ise s t i f f and so f t cohes iv e soi ls . T he

mo del cor re la tes the res i l ient mo dulu s to the co ne penetra t ion tes t parameters , bas ic soi l

proper t ies , and in-s i tu s tress cond i t ions o f the soi l. P redic t ing the res i l ient modu lus o f the

o the r two so i ls and comp ar ing the r esu l ts w i th l abora tory and f i e ld measurem ents

val idated the model .

Acknowledgments

This r e sea rch pro jec t i s f inanc ia lly suppor ted by the U .S. Dep ar tment o f

Transpor ta t ion , Federa l Highw ay Adm inis tr a t ion /P r io r ity Tec hno logy P rogram (USD OT

F H W A /P T P ) C o n t r ac t N o . D T F H 7 1 - 9 7 - P T P - L A - 1 4 , t h e L o u i s ia n a D e p a r t m e n t o f

Transpor ta t ion and Deve lop men t (LAD OT D) S ta te P ro jec t No. 736-99-0773 , and the

Louis iana Transpor ta t ion Resea rch C ente r P ro jec t No. 98 -8GT.

The e f for t o f Wi l l i am T . T ie rney , Resea rch S pec ia l is t /LTR C, in con duc t ing the c one

pene tra t ion tes ts and soi l samp ling is apprecia ted. Th e ass is tance o f A m ar Rag havend ra ,

Resea rch Asso c ia te /LT RC , in ge t ting the MT S sys tem opera tiona l f o r the r e si l ien t

mo dulus t e s ts i s acknowledged . M ark M orvant , Geotechnica l M anager /LTRC , e f for t s and

coopera t ion dur ing the f i e ld and l abora tory t e s ting program s i s g r a te fu lly apprec ia ted .

Paul B rady , M elba Bounds , and Kenne th Johnson , LTRC Geotechnica l Labora tory

helped in con duct ing va r ious soi l tests.

References

AA SH TO , 1993, Guide fb r Des ign o f Pavem ent S t ructures, Am er ican Assoc ia t ion of

S ta te Highw ay and Transpor ta t ion O f f ic ia ls , W ashing ton D.C.

AA SH TO , 1995, "Res i li en t M odulus o f Unbound G ranula r Base /Subbase Mate r ia ls and

Subgrade So i l s , " SHR P Pro toco l P -46 , Am er ican Assoc ia t ion of S ta te High way

and Transpo r ta t ion Off ic ia ls , W ashington D .C. , pp. 794-807.

Al len , D. U , 1989, "Mr Tes t ing in Ken tucky , " W orkshop on Res i l i en t M odulus T es t ing ,

Orego n S ta te Unive r s i ty , Corva l l is , O regon .

Badu-Tw eneboah , K ., Manz ione , C .W. , Ruth , B .E . , and Mi ley , W .G. 1989, "P red ic t ion

o f F l e x ib l e P a v e m e n t L a y e r M o d u l i f r o m D y n a f le c t a n d F W D D e f l e c t io n s . "

Am er ican Soc ie ty for Tes t ing and Materials: Non-destructive Testing of

Pavements and Back calculation ofM oduli . A.J. B ush III and G .Y. Bald i, Eds. ,

AST M 1026, Philadelphia, pp. 245-277.

D rum m, E. C. , Reeves , J. S . , M adget t , M. R. , and Trol inger , W. D . , 1997, "Subg rade

Res i l ien t M odulus Cor r ec t ion fo r Sa tura t ion E f f ec t s , " Journal o f Geotechnical

and Geoenvironmental Engineering, Vol. 123, No.7, pp. 663-670.

Fredlund, D. G. , Bergan, A. T. , and Wo ng, P . K. , 1977, "Re la t ion Betw een Resi l ient

Mo dulus and S t r ess Condi t ions fo r Cohes ive Subgrade So i l s " , Transportation

Research Record, No , 642, pp. 73-81.



M O H A M M E D E T A L . O N E S T I M A T IN G R E S IL IE N T M O D U L U S 2 5 1

Kam al , M. A. , Daw son, A. R. , Farouki , O. T. , Hu ghes , D. A. B. , and Sha 'a t, A. A . , 1993

" F i e ld a n d L a b o r a t o ry E v a lu a t io n o f t h e M e c h a n ic a l B e h a v i o r o f U n b o u n d

Granula r Mate r ia l s in Pavem ents , " Transportation Research R ecord, No. 1406,

pp. 88-97.

M cGee , N . , 1989 , "Co ld Region Fac i l i ty - Subgrade So i l s , " Workshop on Res i l ien t

M odulus T es t ing, Oregon Sta te Univers i ty , Corval l is , Oregon.

M oham mad , L. N. , Puppala , A. J ., and Alavi ll i, P . , 1994, " Inf luen ce o f Tes t ing Proc edu re

and LV DT Loca t ion on Res i l i en t M odulus o f So i ls " , Transportation R esearch

Record, No. 1462, pp. 91-101.

M oham mad , L. N. , Puppala , A . , and Alavi l l i , P . , 1994, "Effec t o f S tra in M easurem ents

on R es i li en t Modulus o f Granula r So i l s , " Dynamic Geotechnical Testing: S e c o n d

V o l u m e , AST M STP 1213, ASTM, pp .202-221 .

M oham mad, L . N . and Puppa la , A. , 1995, "Res i l i en t P roper t ie s o f Labora tory Com pac ted

Subgrade So i l s ,"

Transportation Research R ecord,

No. 1504, pp. 87-102.

M onism ith, C. L. , 1989, "M r tes t ing- Interpre ta t ion o f Labora tory Resul ts fo r Design

Purposes , " W orkshop o n Res i l i en t M odulus T es t ing , Oreg on S ta te Unive r s ity ,

Corval l is , Oregon.

Nataatmadja , A. and Parkin, A . , 1989, "Ch aracter iza t ion o f Granu lar M ater ia ls for

P a v e m e n t s , " Canadian Geotechnical Journal, Vol.26, N o.4, pp. 725-730.

Puppa la , A. J ., Acar Y . B . , and Tum ay, M. T . 1995, "C one Pene t r a t ion in Very We akly

C e m e n t e d S a n d s ." Journal o f Geotechnical Engineering, AS CE , Vol . 121 , No. 8 ,

pp. 589-600.

Rada, G . and W i tczak , M. W . , 19 81 , " Com prehens ive Eva lua t ion o f Labo ra tory

Res i l ien t M odul i Resu l ts f o r Granula r M ate r ia l , "

Transportation R esearch

Record, No. 810, pp. 23-33.

T i t i, H . H. , M oham mad, L . N . , and Tum ay, M. T . , 2000 , "M in ia tur e Con e Pene t r a t ion

Tes t s in Sof t and S t i f f C lays , " Geotechnical Testing Journal, AS TM , Vol . 23 , No.

4, pp.432-443.

Tum ay, M. T. , and Ti ti , H. H . , 2000, "R esearch Pays Off : Louis iana ' s Co nt inuou s

In t rus ion Min ia tur e Cone Pene t r a t ion Tes t S ys tem," TR News, Transpor ta t ion

Resea rch Board, I ssue 207, pp. 26-27.

Tum ay, M. T. , and Kurupp , P . U. , and Boggess , R. L., 1998, "A C ont inuo us Intrus ion

Elec t ron ic M in ia tur e C one Pene t r a tion Tes t Sys tem for S i te C harac te r iza t ion , "

Geo techn ical S i te Character iza t ion, Proc . 1st Internation al Co nf. O n site

character iza t ion - ISC'98, At lanta , Vol . 1 , pp. 118 3- t 188.

Tum ay, M. T . 1985 , F ie ld Ca l ib r a tion of E lec t r i c Con e Pen e t romete r in S of t So il -

E x e c u t i v e S u m m a r y , R e p o rt F H W A /L A - L S U - G E 8 5/0 2, L o u i s ia n a

Transp or ta t ion Research C enter , Baton Ro uge, Louis iana.



H a n i H . T i t i t , Lo u a y N . M o h a m ma d 2, a n d A n a n d a H e r a t h 3

Cha r a c te r iz a t io n o f Re s i li e n t Mo d ulus o f Co a r s e -Gr a ine d M a te ria l s Us ing the

I n tr usio n Te c hn o lo g y

Reference:

T i t i, H . H . , Mo h a m ma d , L . N . , a n d H e r a th , A . ,

"Character izat ion of

Re s i li e n t M o dulus o f Co a r s e -G r a ine d M a te ria ls Us ing the I n tr us ion Te c hno lo g y ,"

Resil ient M odulus Testing fo r Pav eme nt Components, A ST M STP 1437, G . N . D u r h a m , W

A . Ma r r , a n d W. L . D e G r o f f , Ed s . , A S T M I n t e rn a t i o n a l, W e s t C o n s h o h o c k e n , P A , 2 0 0 3 .

Abstract:

T h e o b j e c t i v e o f t h i s s t u d y w a s t o i n v e s t iga t e th e a pp l i c a b i l i t y o f t h e c o n e

pe n e t r a t i o n t es t t o d e t e r m i n e t h e r e s i l ie n t mo d u l u s o f c o a r s e - g r a i n e d ma t e r i a ls . F i e l d a n d

l a b o r a t o r y in v e s t i ga ti o n s w e r e c o n d u c t e d a t t h e s i te s o f t w o pa v e m e n t p r o j e c t s in

Lo u i s i a n a . F i e l d t e s ts c o n s i s t e d o f c o n t i n u o u s i n t r u s io n m i n i a t u r e c o n e pe n e t r a t i o n t e s ts

a n d s o i l s ampl i n g . La b o r a t o r y te s t s i n c l u d e d t h e r e pe a t e d l o a d t r i a x ia l t e s t a n d o t h e r t e s t s

f o r ma t e r i a l s c h a ra c t e r iza t i o n . T h e t e s t r e s u l ts w e r e u s e d t o d e v e l o p a c o r r e l a t io n f o r

p r e d i c t i n g th e r e s i l i e n t mo d u l u s o f c o a r s e - g r a i n e d ma t e r i a l s u s i n g t h e c o n e pe n e t r a t i o n

t e s t pa r a me t e r s a n d b a s i c s o i l p r o pe r ti e s . A n o t h e r l a b o r a t o r y i n v e s t iga t i o n w a s c o n d u c t e d

t o i n v e s t i ga t e t h e e f f e c t o f mo i s t u re c o n t e n t a n d u n i t w e i gh t o n t h e c o n e p e n e t r a t io n t e s t

pa r a m e t e r s a n d r e s il i e n t mo d u l u s . T e s t r e s u l ts w e r e u s e d t o v a l i d a t e t h e mo d e l d e v e l o pe d

f o r p r e d i c t i n g t h e r e s i l i e n t mo d u l u s . T h e r e s i l ie n t mo d u l u s v a l u e s p r e d i c t e d w e r e

c o n s i s t e n t w i t h t h o s e o b t a i n e d u s i n g t h e r e p e a t e d l o a d t r i a x i a l t e s t.

Ke y wo r ds :

r e s i li e n t mo d u l u s , c o a r s e - g r a i n e d ma t e r i a l s , c o n e pe n e t r a t i o n t e s t

Introduction

T h e m e t h o d s o f d e t e r mi n i n g t h e r e s i li e n t mo d u l u s o f s u b g r a d e s o i l s a n d pa v e m e n t -

u n b o u n d ma t e r i a l s a re b a s e d o n l a b o r a t o r y a n d f i e l d t e s ts . La b o r a t o r y t e s t me t h o d s

i n c l u d e t h e r e pe a t e d l o a d t r i a x i a l t e s t, s i m p l e s h e a r , r e s o n a n t c o l u mn , gy r a t o r y , a n d t h e

i A s s i s t a n t P r o fe s s o r , D e p a r t me n t o f C i v i l En g i n e e r i n g & M e c h a n i c s , U n i v e r s i t y o f

W i s c o n s i n - M i l w a u k e e , P .O . B o x 7 8 4 , Mi l w a u k e e , W I 5 3 2 01 .

2 A s s o c i a t e P r o f e s s o r , D e p a r t me n t o f C i v i l & En v i r o n m e n t a l E n g i n e e r i n g a n d" Lo u i s i a n a

T r a n s po r t a t io n R e s e a r c h C e n t e r, Lo u i s i a n a S t a t e U n i v e r s i ty , 4 1 0 1 G o u r r i e r A v e . , B a t o n

R o gu e , L A 7 0 8 0 8 .

3 P o s t d o c t o r a l R e s e a r c h e r , Lo u i s i a n a T r a n s po r t a t io n R e s e a r c h C e n t e r, 4 1 0 1 G o u r r i e r

A v e . , B a t o n R o gu e , L A 7 0 8 08 .

2 5 2

Copyright9 by ASTM In te rna t iona l ww w.as tm.org



TITI ET AL. ON INTRUSION TECHNOLOGY 253

ho l l ow- cy l i nde r te s t ing d ev i ce . These l abo r a t o r y t e s t s r equ i r e adv anced t e s t i ng equ i pm en t

and sk i l l ed pe r sonne l , and a r e cons i de r ed exp ens i ve , l abo r ious , and t i m e consum i ng .

F i e l d t e s ts i nc lude t he nond es t r uc t ive t e s t ing ( N DT ) us i ng dev i ce s such a s t he dyna m i c

d e f l ec t io n d e t e r m i n a ti o n s y s t e m ( D Y N A F L E C T ) a n d t h e f a ll in g w e i g h t d e f l e c t o m e t e r

( F W D ) . N o n d e s t r u c ti v e t e st in g o f p a v e m e n t s i s q u i c k a n d e a s y to p e r f o r m ; h o w e v e r ,

t he r e i s a conce r n r ega r d i ng r e li ab i li ty o f u s i ng t he se m e t hod s t o ev a l ua t e pav em en t

l ay e r s m o d u l i . T h e N D T m e t h o d s u s e b a c k c a l c u la t io n p r o c e d u r e s t o d e t e rm i n e t h e

pav em en t l aye r s m o du l i . Ana l ys i s u s ing t he se p r ocedu r e s does no t r e su l t in a un i que

so l u ti on ; m or e ove r , the m a ny p r ov i ded so l u t ions depe nd on t he i npu t pa r am e t e r s .

The r e f o r e , t he r e i s a need f o r a r e li ab le , f a s t , and econo m i ca l i n - s i tu t e s t m e t hod t o

e s t i m a t e t he r es i li en t m odu l us o f subgr ade so i l s and pavem en t unbo und m a t e r i a l s .

Th e co ne pene t r a t i on t e s t ( CPT) , an i n t eg ra t ed m e t h odo l ogy f o r s i te cha r ac t e ri za ti on ,

has been u sed f o r a wi de r ange o f app l i ca t ions i n geo t echn i ca l and pave m en t eng i nee r ing .

The CP T t echno l og y is f a s t, cos t e f f ec t ive , and can e f f ec t i ve l y be used d u r i ng t he

d i f f er en t de s i gn and cons t r uc t i on phase s o f a pav em en t p r o j ec t.

Th i s pa pe r p r e sen t s t he r e su l ts o f a s t udy conduc t ed t o de t e r m i ne t he r e s il ien t

cha r ac t e ri s ti c s o f coa r se - g r a i ned m a t e r i a ls ( cohes i on l e s s subg r ade so i l s and unbo und

gr anu l a r pavem en t m a t e r i a l s ) u s ing t he co ne pene t r a t i on t e st . F i e ld and l abo r a t o r y t e s t ing

p r og r am s wer e cond uc t ed a t t wo pa vem en t p r o j ec t si te s i n L ou i s iana . F i e l d t e s ts

cons i s t ed o f cone pene t r a t i on t e st s and so i l s am p l i ng , w h i l e l abo r a t o r y t e s ts cons i s t ed o f

t he r epea t ed l oad t r i ax i al t e s t and o t he r l ab o r a t o r y te s t s f o r m a t e r i a ls cha r ac t e r iza t ion . Th e

f i e ld t e s ts we r e con duc t ed o n t he pavem en t m a t e r i a l s unde r t he ir na t u ra l cond i t i ons o f

m oi s t u r e con t en t and un i t we i gh t . Tes t re su l t s w e r e ana l yzed and u sed t o p r opo se a

co r r e l a t ion be t w een t he r e s i li en t m od u l us and t he cone pen e t r a t ion t e s t pa r am e t e r s . A

l abor a t o r y inves t i ga t ion w as a l so con duc t ed t o i nve s t i ga t e t he e f f ec t o f t he m o i s t u r e

con t en t and u n i t we i gh t o f t he se m a t e r i a l s on the r e s i li en t m odu l us de t e r m i ned us i ng t he

cone pene t r a t i on t e st .

B a c k g r o u n d

A m on g t he d i f f e ren t l abo r a t o r y m e t hods , t he r epea t ed l oad t r iax i a l t e st is t he m o s t

pop u l a r f o r de t e r m i na t i on o f the r e s i li en t m odu l us . The r e s i li en t m od u l us ( Mr) in a

r epea t ed l oad t r i ax i a l t e s t i s de f i ned a s t he r a t io o f the m ax i m um dev i a t o r s t r e s s

(are) and

the rec ov erab le e las t ic s t ra in (c r) as fo l low s:

M r - era

- - - ( 1 )

Er

F i gu r e 1 i ll u s tr a te s t he de f i n i ti on o f the r e s i l ien t m odu l us i n a r epea t ed l oad t r iax i a l

t es t. The r e s i l ien t m odu l us de t e r m i ned f r om t he l abo r a t o r y te s t s i s in f l uenced by m an y

f ac t o r s i nc lud i ng t he m a t e r i a l t ype ( coa r se - g r a ined , f i ne -g r a i ned ), m o i s t u r e con t en t , un i t

we i gh t , s i z e o f the spec i m en , s t r e ss pu l s e shape , du ra t ion , f r equency and s eque nce o f

s t re s s l eve ls , t e st i ng equ i pm en t , and spec i m en p r epa r a t ion , a s we l l a s cond i t i on ing

m e t hods ( F r ed l und e t al . 1977 , Rada and W i t czak 1981 , Al l en 1989 , McG ee 1989,




M oni sm i t h 1989, Na t aa t m ad ja and Pa r k i n 1989 , K am a l e t a l. 1993 , Mo ham m ad e t al.

1994, D ru m m et a l. 1997).

O

~ 0 . I ~

0 . 9

T im e ( s )

s

o

Time, t

Fi gur e 1 - The

def in i tion o f the resi l ien t modulus in a repeated loading tr iaxia l tes t

Th e i m p or t ance o f r e l iab l e de t e r m i na t i on o f the r e s i l ien t m odu l us i s il l u s tr a t ed i n

F i g u r e 2 . T h e A A S T H O 1 9 9 3 p r o c e d u r e f o r f l e x ib l e p a v e m e n t d e s ig n r e q u ir e s th e

r e s i li en t m odu l us o f subgr ade so i l a s an i npu t pa r am e t e r . As sh ow n i n F i gu r e 2 , f o r t he

g i ven des i gn pa r am e t e r s , t he va r i a t ion o f t he ove r l ay des i gn t h icknes s i s i n f luenced b y t he

va l ue o f t he r e s il i en t m o du l us . U nde r e s t i m a t i ng t he r e s i li en t m od u l us o f subgr ade so i l by

10 MP a w i ll r e su l t i n an add i t i ona l 37 m m i nc r ea se o f th i cknes s o f t he ove r l ay .

The r e f o r e , de t e r m i na t i on o f a p r ope r re s i li en t m odu l us i s de s i r ed i n pave m en t de s i gn .



T IT I E T A L . O N I N T R U S I O N T E C H N O L O G Y 2 5 5

o

o

1 5 0

1 0 0

5 0

- 5 0

- 1 0 0

- 1 5 0

Pavement ypical section

H M A C

layer

D 1 = 1 0 2 m m . a = 0 0 1 6 5 4 / m m

B~ e course layer

D : = 2 4 1 r a m , a : = 0 0 0 6 3 / r a m

Subbase layer

D j = 4 5 7 r am , a = 0 0 0 4 0 / m m

S ubgvade oil

[ ' , I , I L I L I ~ I I I ~ [ ~ l

" k

- 3 0 - 2 0 - 1 0 0 ~ . 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0

~

M , ( M P a )

W j s = 5 , 0 0 0 , 0 0 0 E S A L s

R = 9 5 %

A P S I = 1 . 9

S O = 0 . 3 5

D e s i g n M r = 3 4 . 5 M P a

D e s i g n

S N = 5

L e g e n d

W ; a = predicted number o f equiva lent s ing le ax le load ( E S A L )

R -

reliabil ity

A P S I = di f ference between the in i t ia l des ign serv iceabi l i ty

index and the des ign termina l s erv iceabi l i ty index

S O = combin ed s tandard error o f the tra ff i c predict ion and

performance predict ion

M r = res i l ient mod ulus o f subgrade so i l

S N = structural number

Figure 2 - Th e ef f ec t o f var y in g th e r esi l ien t modulus

o f subgrade soil

on th e

overlay

design

thickness

The c on e penetrat ion t est has bee n su ccess ful ly used for character izat ion of

geomateria l s . T he co ne p enetrat ion t es t cons i s t s of push ing a cyl indrical rod wi th a

conical t ip into the so i l and measuring the res i st ing forces . There are two forces measured

during the penetrat ion: the cone t ip res is tance (qc) , which is the soi l res is tance to advance

t he cone t ip , and the s l eeve f ri c ti on ~ ) , w h i ch i s the f r ic t ion deve l op ed be t w een t he s o il

and the s l eeve o f the penetrometer . The f r ict ion rat io Rf) s the rat io o f the s l eeve f r ict ion

and tip res is tance and i s exp ressed in percent. T hese measured parameters are used to

c las s i fy the so i l s and determine their propert ies .

Ap pl i cat ions o f the CP T in the f ie ld o f pa vem ent e ngineering, part i cularly re lated to

s ubs o il s , have a l s o been a t tem p t ed . B adu- T w eneb oah e t a l. ( 1 9 8 9 ) conduct ed C PT t e s ts

on various high wa y pave men ts in Florida . Th ey correlated the con e t es t result s wi th the

res il ient mod ulus determined from N D T m ethods , Inaccuracies and uncertaint ies

i nvo l v i ng N D T back ca l cu l a ti on s ubrout ines m a y have a f fec t ed t he re li ab il it y o f t hes e

correlations . In sp i te o f this l imi tat ion, thi s s tudy revea led the potent ia l of CPT in

determining the res i li ent propert i es of subgrade soi l s and unbou nd pav em ent m ateria l s.

There i s a concern regarding the use o f the con e penetrat ion t est to determine the

res il ient mo dulu s ofgeo ma teria l s . The t ip res is tance and s l eeve f r ict ion are obtained from

the cone p enetration t est , which i s cons idered a quas i - s tati c t es t method, wherea s the

res il ient m odu lus i s a prop erty obtained from a dynam ic repeated loa d test . I t i s of t en




assumed that test parameters obtained from different test backgrounds may not provide

reasonable correlations with one another. However, this is not always the case. Earlier

studies (Tumay 1985, Puppala et al. 1995) showed the potential of the quasi-static CPT

method in determining the low strain dynamic shear modulus and liquefaction of soil.

The dynamic shear moduli and CPT parameters are less influenced by stress and strain

history. In fact, these parameters are controlled by the same soil variables, which may

have led to the development of better correlations between them. The resilient modulus is

considered analogous to the shear modulus. Therefore, the influence of stress and strain

behavior on the resilient modulus will be similar to that o f the shear modulus.

Previous studies also indicated that the resilient property of subgrade soil is less

dependent on stress and strain history (Mohammad et al. 1994). The strain history

influence is also expected to be insignificant in a nondestructive repeated load triaxial

test. Furthermore, the cone penetration tests and repeated load resilient modulus tests

were conducted on soil Under identical environmental conditions. This implies that both

test parameters were subjected to similar environmental variables such as density,

moisture content, and geomaterial fabric. In such conditions, the cone penetration test and

resilient moduli parameters depend on the same soil variables. Therefore, it is reasonable

to assume that a correlation is possible between the cone penetration test and resilient

moduli parameters.

O bjective o f Research

The objective of this study was to evaluate the applicability of the cone penetration

test in determining the resilient modulus of coarse-grained materials such as granular

base course layers and embankments, and cohesionless subgrade soils. Moreover, this

study attempted to develop and validate a model to determine the resilient modulus of

these materials from the cone penetration test results and basic soil properties.

Field and Laboratory Testing Programs

The research approach adopted is divided into two parts:

(1) Conducting field and laboratory testing programs at the sites of pavement projects

to assess the applicability of the cone penetration test in determining the resilient

modulus of coarse-grained materials. The field tests of this phase consisted of cone

penetration tests and material sampling. The laboratory tests consisted of repeated load

triaxial test in addition to other laboratory tests for material characterization.

(2) Conducting a detailed laboratory investigation to evaluate the effect of the unit

weight and moisture content on the resilient modulus determined by the cone penetration

test. This phase was completed in the laboratory and included miniature cone penetration

tests conducted on materials prepared under different conditions of moisture content and

unit weight. Repeated load triaixial tests were conducted on samples under the specified



T IT I E T A L . O N I NT R U S IO N T E C H N O L O G Y

m o i s t u r e c o n t e n t a n d u n i t w e ig h t . O t h e r l a b o r a t o r y t e st s w e r e a l s o c o n d u c t e d t o

de t e rmine t he phys i ca l p rope r t ie s and com pac t i on cha rac t e r i s ti c s o f t he se ma te r i a l s .

2 5 7

E qu ipmen t fo r F ie ld and Labora tory Tes t ing

Con t inuous In t rus ion M in ia ture Cone Pene t ra t ion Tes t ( C IM CP T) Sy s t em -

T h e

s y s t e m w a s d e v e l o p e d , c a l i b ra t ed , a n d i m p l e m e n t e d ( T u m a y e t a l. 1 9 9 8 , T u m a y a n d T i ti

2000 , T i ti e t al. 2000 , T i t i and M orv an t 2001 ) fo r sha l l ow dep th s i t e cha rac t e r iza t i on . T he

s y s t e m c o n s i s t s o f a c o n t i n u o u s p u s h d e v i c e , c o i l in g / u n c o i l i n g m e c h a n i s m , h y d r a u l i c

m o t o r , a n d d a t a a c q u i s i t io n s y s t e m . T h e c o n e i s a t ta c h e d t o a c o i l e d p u s h r o d , w h i c h

a l l o w s a c o n t i n u o u s p e n e t r a t io n o f t h e c o n e . T h e c o i l i s m e c h a n i c a l l y s t ra i g h t e n e d a s t h e

c o n e i s p u s h e d i n t o t h e s 0il. T h e c o n t i n u o u s p u s h d e v i c e o f th e C I M C P T s y s t e m i s s h o w n

i n F i g u re 3 a . T h e s y s t e m p u s h e s a m i n i a t u r e c o n e p e n e t r o m e t e r ( F i g u r e 3 b ) w i t h a c r o s s

s e c ti o n a l a r e a o f 2 c m 2 , a f r i c ti on s l eeve a r ea o f 40 cm 2, a n d a c o n e a p e x a n g l e o f 6 0

deg rees .

Min ia ture Cone Pene t ra tion Tes t (MC PT) Sy s t em -

T h i s s y s t e m w a s f a b r ic a t e d to

c o n d u c t t h e m i n i a t u r e c o n e p e n e t r a t io n t e st s o n t h e p a v e m e n t m a t e r i a ls u n d e r c o n t r o l l e d

u n i t w e i g h t a n d m o i s t u r e c o n t e n t. T h e M C P T s y s te m , s h o w n i n F i g u r e 3 c , c o n s is t s o f a

hydrau l i c push sys t em, a dep th encode r , a r eac t i on f r ame , a min i a tu r e cone pene t rome te r ,

and a da t a acqu i s i t i on sys t em.

Materia l Test ing System (MTS)

- a m o d e l M T S - 8 1 0 c l o s e d l o o p se r v o - h y d r a u l i c

m a t e r i a l t e s ti n g s y s t e m w a s u s e d t o p e r f o r m t h e r e p e a t e d l o a d t ri a x ia l t e st . T h e m a j o r

com po nen t s o f t h i s sy s t em a re t he l oad ing f r ame , d ig i t a l con t ro l l e r , hyd rau l i c ac tua to r ,

l oad ce l l, t ri ax i a l c e l l, L V DT s , and p re s su re con t ro l pane l .

Fie ld and L abora tory Inve s t iga t ion

T h e f i el d - te s t in g p r o g r a m w a s c o n d u c t e d a t t w o p a v e m e n t p r o j e c t s i te s i n L o u i s ia n a .

De sc r ip t i on o f t he t e s t si t es i s g iven be low.

Sta te Rou te LA-28 , S impson -

Thi s s i te i s l oca t ed nea r t he i n t e r sec t i on o f t he S t a t e

R o u t e L A - 2 8 a n d H i g h w a y 4 6 5 n e a r S i m p s o n , V e r n o n P a r is h . T h e s it e is u s e d b y t h e

L o u i s i a n a D e p a r t m e n t o f T r a n s p o r t a t io n a n d D e v e l o p m e n t a s a b o r r o w p i t f o r

c o n s t r u c t i o n o f r o a d w a y e m b a n k m e n t s . T h e s o il a t t h e s i te c o n s i s t s o f 6 0 p e r c e n t s a n d , 1 8

pe rce n t s i lt , and 12 pe rcen t c l ay . The so i l is c l a s s i fi ed s i l t y sand (SM ) a cco rd ing t o t he

U S C S a n d s i lt y s a n d ( A - 2 - 4 ) a c c o r d i n g to t h e A A S H T O s o il c la s s i fi c a t io n s y s t e m .

S t a n d a r d P r o c t o r t e s t u s in g t h i s s o i l s h o w e d t h a t t h e o p t i m u m m o i s t u r e c o n t e n t o f t h e s o i l

i s 1 1 . 4 p e r c e n t a n d t h e c o r r e s p o n d i n g m a x i m u m d r y u n i t w e i g h t i s 1 8.3 k N / m 3.




( a ) T h e c o n t i n u o u s i n tr u s io n m i n i a t u r e c o n e p e n e t r at i o n t e s t ( C I M C P T ) s y s t e m u s e d

fo r f i el d and l abo ra to ry i nves t i ga t i on

( b ) T h e m i n i a tu r e c o n e p e n e t r o m e t e r

( c ) The min i a tu r e con e pene t r a t i on t e st (M CP T) sys t em and t he te s t se tup used fo r

l abo ra to ry i nves t i ga t i on

Figure 3 - F ie ld and lab or a tor y t e s t eq u ip men t u s ed in the inve s tig a t ion



T IT I E T A L . O N IN T R US I O N T E C H N O L O G Y 2 5 9

State Route LA-89, New lberia -

T h e t e s t s it e is a n e m b a n k m e n t l o c a t e d o n S t a t e

R o u t e L A - 8 9 , N e w I b e ri a . T h e e m b a n k m e n t c o n s i s t s o f r e c y c l e d s o il - c e m e n t b a s e

(g ranu l a r ma te r i a l) , w h ich exh ib i t ed a behav io r s imi l a r to t ha t o f g r anu l a r ma te r i a l s un de r

r epea t ed l o ad t ri ax i a l te s t. Th e so i l is c l a s s if i ed s i l ty g r ave l (G M ) ac co rd ing t o the U S C S

a n d g r a v e l a n d s a n d ( A - l - b ) a c c o r d i n g t o t h e A A S H T O s o il c la s s i fi c a ti o n s y s t em .

T h e C I M C P T s y s t e m w a s u s e d t o c o n d u c t th e c o n e p e n e t r a t io n t e s ts a t e a c h si te . C o n e

p e n e t r a t i o n t es ts w e r e c o n d u c t e d b y c o n t i n u o u s l y a d v a n c i n g t h e c o n e i n t o th e g r o u n d a t a

r a te o f 2 c m / s e c . C o n t i n u o u s m e a s u r e m e n t s o f c o n e t ip r e s i st a n c e ( qr a n d s l e e v e f ri c ti o n

~ ) w e r e o b t a i n ed . A s s h o w n i n F i g u r e 4 a , c o n e p e n e t r a ti o n t e st s w e r e c o n d u c t e d a t a

c e r ta i n p a t t e m c l o s e t o t h e b o r e h o l e l o c a t i o n f r o m w h i c h t h e m a t e r ia l s a m p l e s w e r e

ob t a ined fo r labo ra to ry te s t ing . T h i s was t o ensu re t ha t t he cone pene t r a t i on t e s t s

r ep re sen t t he m a te r i a l t e s ted i n t he l abo ra to ry .

M a t e r i a l s a m p l e s w e r e o b t a i n e d f r o m b o r e h o l e s a t e a c h te s t s it e d o w n t o a d e p t h o f 2 . 0

m . S a m p l e s w e r e e x t r a c te d , s e a l ed , a n d k e p t i n a h u m i d i t y r o o m . M a t e r i al s a m p l i n g a n d

con e pene t r a t i on t e s ts we re ca r r i ed ou t a t t he s am e da y i n o rde r t o ensu re s im i l a r in - s i t u

cond i t i ons . S o i l s ample s , un de r t he i r na tu r a l mo i s tu r e c on t en t and un i t we igh t , we re

sub jec t ed t o l abo ra to ry t es t s to de t e rmine t he r e s il i en t m odu lus , phy s i ca l p rope r ti e s , and

c o m p a c t i o n c h a r a c te r is t ic s . T h e r e s i li e n t m o d u l u s t e s t w a s c o n d u c t e d a c c o r d i n g t o

A A S H T O T 2 9 4 - 9 4 : R e si li e nt M o d u l u s o f U n b o u n d G r a n u l ar B a s e /S u b b a s e M a t er ia l s

a n d S u b g r a d e S o i l s - S H R P P r o t o c o l P 4 6 . O t h e r l a b o r a t o r y t e st s i n c l u d e d d e t e r m i n i n g t h e

At t e rb e rg l imi t s o f so i ls , mo i s tu r e con t en t , mo i s tu r e co n t en t -un i t w e igh t r e l a t i onsh ips ,

gra in s ize d i s t r ibut ion , and spec i f ic gravi ty .

Laboratory Investigation

T w o c o a r s e - g r a in e d m a t e ri a ls ( s il ty s a n d a n d s a n d) , w h i c h a r e c o m m o n l y u s e d i n

p a v e m e n t l a ye r s, w e r e s e l ec t e d f o r l a b o r a t o ry i n v e s t ig a t i o n u n d e r c o n t r o l le d c o n d i t i o n s o f

m o i s t u r e c o n t e n t a n d u n i t w e i g h t. T h e s e m a t e ri a ls w e r e c o l l e c t e d a n d s u b j e c t e d t o v a r ie t y

o f t e s ts t o de t e rmine t he i r p rope r t i e s and t o e s t ab l i sh t he i r mo i s tu r e c on t en t -un i t we ig h t

r e l a t ionsh ips . I n o rde r t o pe r fo rm co ne pene t r a t i on t e s t s on the se m a te r i a l s und e r

c o n t r o l l e d m o i s t u r e c o n t e n t a n d u n i t w e i g h t , a t e st s e t u p w a s a s s e m b l e d a s s h o w n i n

F i g u r e 3 c . E a c h m a t e ri a l w a s c o m p a c t e d i n a 5 5 - g a l l o n ri g i d - w a l l m e t a l c o n t a i n e r u n d e r

t h r e e d i ff e r e n t v a lu e s o f m o i s t u r e c o n t e n t a n d u n i t w e i g h t . T h e s e v a l u e s a r e ( 1 ) t h e d r y

s i d e ( b e l o w t h e p o i n t o f o p t i m u m m o i s t u r e c o n te n t ), ( 2 ) t h e p o i n t o f o p t i m u m m o i s t u r e

c o n t e n t, a n d ( 3 ) th e w e t s i de ( a b o v e t h e p o i n t o f o p t i m u m m o i s t u r e c o n t e n t) .

E a c h m a t e r i al w a s s u b j e c t e d t o f i v e m i n i a t u r e c o n e p e n e t r a t io n t e s ts u n d e r e a c h

m o i s t u r e c o n t e n t a n d u n i t w e ig h t . T h e m i n i a tu r e c o n e p e n e t r o m e t e r w a s a d v a n c e d i n to

t h e c o n t a i n e r at a r a te o f 2 0 m m / s e c i n t h re e s t r ok e s . C o n t i n u o u s m e a s u r e m e n t s o f c o n e

t ip r e s i s tance (qc) and s l eeve f r i c ti on ~ ) we re ob t a ined . T he min i a tu r e co ne pene t r a t i on

t e st s w e r e c o n d u c t e d a c c o r d i n g t o t h e l a y o u t s h o w n i n F i g u r e 4 b . T h e t e s t l a y o u t w a s

s e l e ct e d t o a v o i d t h e c o n t a i n e r b o u n d a r y e f f e c ts o n t h e r e s u lt s o f th e m i n i a tu r e c o n e

pene t r a t i on t e st .

A f t e r t h e m i n i a t u re c o n e p e n e t r a t io n t e s ts w e r e c o n d u c t e d , s o i l s a m p l e s w e r e c o l l e c t e d

a t d i ff e r en t dep ths fo r the l ab o ra to ry r e s il i en t mo du lu s an d so i l p rope r ty te s ts .




CIMCPT1 CIMCPT5 CIMCPT9

(1) 9 |

~ f 4.d BHI CIM~ 3 CIMIT8 ~ CI~CPT7 CIMCf'2 n~ C+CPT[

9 , . | 9 . . . .

IMCPT2 k CIMCPT6 CI PTI0

1.0m 1,0m 1.1Dm L0m .0m )

I ~1 ~ )- ~1~ "7"

set 1 set 2 set 3

9 BHI:Borehole sampling)

CIMCPT:Continuous ntrusionMiniatureConePenetrationTest

(a): Field testing and ma terial sam pling or the field and laboratory nv estigation

@ MCPT:Miniature onepenetrationest

9 BH:material ampling

(b): Laboratory esting and material samplingfor the laboratory n vestigation

F i g u r e 4 -

Typical configuration fo r f ie ld and laboratory con e penetrat ion tes ts and

mater ia l sampl ing

A n a l y s i s o f F i el d a n d L a b o r a t o r y T e s t R e s u lt s

Fie ld and Lab ora tory Inves t iga t ion

T h e r e s u l ts o f t h e l a b o r a t o r y t e st s c o n d u c t e d t o e v a l u a t e t h e p h y s i c a l p r o p e r t i e s o f t h e

i n v e s t i g a t e d m a t e r i a l s a re s u m m a r i z e d i n T a b l e 1. A l l m a t e r i a l s c o n si d e r ed a r e c o a r s e -

g r a in e d , w h i c h w e r e u s e d i n h i g h w a y e m b a n k m e n t s o r b a s e c o u r se p a v e m e n t l ay e r s.

T h e c o n t i n u o u s i n t r u s i o n m i n i a t u r e c o n e p e n e t r a t i o n t e s t r es u l t s ( s e t # 1 ) o n t h e s i l t y

s a n d , L A - 2 8 s i t e a r e s h o w n i n F i g u r e 5 a . I n s p e c t i o n o f t h e f i g u r e s h o w s t h at t h e t ip

r e s i s ta n c e a n d s l e e v e f r i c t i o n p r o f i l e s a r e c o n s i s t e n t a m o n g t h e f o u r te s ts i n s e t # I a n d

r e f l e c t s i m i l a r pa t t e r n . S t a t i s t i c a l a n a l ys i s w a s c o n d u c t e d t o qu a n t i t a t iv e l y e v a l u a t e th e

r e p e a t a b i l i t y o f t h e m i n i a t u r e c o n e p e n e t r a t i o n t e s ts . E a c h p r o f i l e w a s d i v i d e d i n to t h in

2 0 - m m s o i l la y e r s i n w h i c h t h e c o n e p e n e t r a t i o n te s t p a r a m e t e r s ( qc a n d f s ) w e r e a v e r a g e d

a l o n g t h e 2 0 - m m l a y e r s. F o r e a c h 2 0 - m m d i v i d e d l a y e r , t h e r e a r e f o u r v a l u e s fo r q c a n d

f o u r v a l u e s f o r f i . T h e a v e r a g e o f t h e s e f o u r v a l u e s , t h e s t a n d a r d d e v i at io n , an d t h e

c o e f f i c i e n t o f v a r i a t i o n w e r e d e t e r m i n e d . T h e a v e r a g e v a l u e s o f t h e c o ef fi ci en t o f



T IT / E T A L . O N IN T R US I ON T E C H N O L O G Y 261

v a r i a t i o n f o r q c a n d f i a r e s h o w n i n F i g u r e 5 b . T h e v a r i a t i o n o f q c r e f l e c ts t h e v a r ia b i l it y

o f e a c h m a t e r i a l a t t h e s a m e t e s t s it e . I t i s n o t e x p e c t e d t o h a v e i d e n t i c a l m a t e r i a l s a t t w o

d i f f e r e n t l o c a t i o n s a t t h e s a m e s i te . G e n e r a l l y , t h e c o n e p e n e t r a t i o n t e s t r e s u l ts s h o w e d

g o o d c o m p l i a n c e a n d a r e c o n s is t e n t w i t h i n t h e s a m e g r o u p a n d r e f l e c t e d s i m i l a r p a t te r n s.

T a b l e 1 - Prop ert ies o f the invest igated materia ls

LA-28,

Simpson

LA-89, New

Material Type (Laboratory testing)

Property Iberia Silty Sand Sand

Description Base course Base course Embankm ent Base course

Passing sieve #200 (%) 30 24 39 2

iClay (%) 12 16 9 0

!Silt (%) 18 8 30 2

Sp ec ific gravity, Gs 2.68 2.69 2.67

Optimum wa ter content (Wopt) % ) 11.4 15.2 8.1

M aximum dry unit weight, Yd .. .

( kN/ m3) 18.3 17.2 16.4

Un ified Soil Classification System GM SP

-

(USCS) SM Silty gravel with SM Poorly graded

Silty sand sand Silty sand sand

P~.ASHTO Soil Classification A-2-4 A -l -b A-4 A-3

Silty sand G ravel and sand Sandy loam Fine sand

F i g u r e 5 - Resu l t s o f cone pene t ra t ion t e s ting a t LA-28 pa vem en t pro je c t s i te




Th e r e su l ts o f t he r epea t ed l oad t r i ax ia l t e s t on t he s i l ty s and a t L A -28 , S impso n , a r e

s h o w n i n F i g u r e 6 . T h e f i g u re s h o w s a t y p i c a l v a ri a t io n o f t h e r e si li e n t m o d u l u s w i t h t h e

bu lk s t r es s fo r coa r se -g ra ined ma te r i a l s whe re t he re s i l ien t m odu lus i nc r ea se s w i th t he

i n c r ea s e o f b u l k s t re s s. T h e r e si li e n t m o d u l u s v a r i e s b e t w e e n 4 8 a n d 2 0 2 M P a , d e p e n d i n g

on t he s t re s s l eve ls . W he n t he bu lk s t r e s s i nc r ea se s , the ma te r i a l pa r t i c l e s be co m e c lo se r

to each o the r , wh ich r e su l t i n be t t e r i n t e r l ock ing and f r i c ti ona l cha rac t e r i st i c s .

1000 . . . . . . . 1000 ~ I . . . . . r - r :

w= I1.0% w= 16.3 %

7 = 19.4 kN/m~ y = 17.2 kN/m

100 100

10 10 1~1 ~ . . . . . '

100 1000 100 1000

Bu lk s t re s s , c b (kPa ) Bu lk s t re s s , c b (kPa )

Figure 6 - R es u l t s o f the r ep ea ted load t r iax ia l t e s t on si l t y s and b as e co ur s e laye r a t the

S t a te R o u t e L A - 2 8 p ro j ec t , S i m p s o n

R e s i l ie n t M o d u l u s - C P T C o r r e l at io n

Th e r e s il i en t mod u lu s ob t a ined f rom the l abo ra to ry r epea t ed l oad t r iax i a l t e s t va r i e s

wi th t he bu lk s t re s s . The re fo re , i t is neces sa ry t o de t e rmine a s i ng l e va lue o f t he re s i l ien t

m o d u l u s f r o m t h e l a b o r a t o r y te s t th a t c o r r e s p o n d s t o t h e p a v e m e n t s t re s s c o n d i t i o n s i n t h e

f ie ld . Th i s r e s i l ien t m od u lu s va lues i s i den t i fi ed a s t he f i e l d r e s il i en t m odu lus (Mrf ). A

p r o c e d u r e w a s d e v e l o p e d t o d e t e r m i n e t h e f i e ld r e s il ie n t m o d u l u s f r o m l a b o r a t o r y t es t

r e su l t s a s il l u s tr a t ed i n F igu re 7 . The i n - s i t u s t r e sse s ac t i ng on an e l em en t l oca t ed a t a

d e p t h D u n d e r t h e p a v e m e n t s u r f a c e w e r e d e t e r m i n e d f r o m t h e u n i t w e i g h t o f t h e m a t e r ia l

a n d t h e d e p t h o f t h e e l e m e n t . A t r af f ic l o a d i n g c o r r e s p o n d i n g t o 2 0 - k N s t a n d a rd s i n g le

w h e e l l o a d i n g w a s a p p l i e d o n t h e p a v e m e n t s u r f a ce . T h e s t r es s e s i n d u c e d o n t h e m a t e r ia l

e l e m e n t d u e t o t h e a p p l ie d t r a f fi c l o a d in g w e r e d e t e r m i n e d u s i n g a c o m p u t e r p r o g r a m f o r

a n a l y si s o f l in e a r -e l a st ic p a v e m e n t s y s t e m s c a l l e d E L S Y M 5 ( 1 9 8 5 ) . T h e c o n f i g u r a t i o n o f

the d i f f e r en t pavem en t l aye r s cons ide red i n t he e l a st i c ana lys i s is p r e sen t ed i n F igu re 7 .

T y p i c a l v a l u e s o f t h e m o d u l u s o f e l a st ic i ty a n d P o i s s o n ' s r a t io w e r e u s e d i n th e a n a l y s is .

Th e s t r e s se s ac t i ng on t he ma te r i a l e l em en t due t o i n - s i t u s t re s se s and t r a f f i c l oad ing were

added . These s t r e s se s a r e cons ide red t he h ighes t s t r e s s l eve l s t ha t t he pavemen t sys t em

w i l l e x p e r ie n c e . T h e l e v e l s o f th e b u l k a n d c o n f i n i n g s t re s s e s w e r e d e t e r m i n e d a n d

l o c a t ed o n t h e g r a p h s h o w n i n F i g u r e 7 . F in a l ly , t h e r e si li e n t m o d u l u s c o r r e s p o n d i n g t o

the s t r e s s l eve l s o f t he i n - s i t u and t r a f fi c l oad ings w as d e t e rm ined a s il l u s tr a t ed i n t he



T IT I E T A L . O N I N T R U S I O N T E C H N O L O G Y 2 6 3

Figure 7 . A summ ary of the f i e ld and laboratory t est resul ts for the coarse-grained

materia ls i s presented in Table 2 . Th ese resul t s represent the res i li ent mo dulu s valu es

corresponding to the in-s i tu and traff ic s tresses .

T a b l e 2 - Sum ma ry o f the laboratory and f ie ld tes t result s on the invest igated coarse-

gra ined m aterials (in-si tu an d traf fic)

T e s t S o i l D e p t h q c f ~ w Y d ~ o a M , f

s i te s am p l e ( m ) ( M P a ) ( M P a ) ( % ) (kN/ m ) ( k P a ) ( k P a ) ( M P a )

L A - 8 9 B H 1 0 . 4 6 . 5 0 . 3 2 4 18 . 8 1 5 .8 1 . 02 9 . 6 9 5 2 . 2

B H 3 0 . 4 8 . 1 0 . 3 6 9 1 7 . 9 1 7 . 9 1 0 . 6 9 . 8 5 7 5 . 0

BH 1 0 .8 2 .30 0 .015 11 .0 17 .2 13 .4 13 .7 43 .3

L A - 2 8 B H 1 1 . 0 2 . 1 0 0 . 0 2 5 16 .3 1 7 .2 1 4 . 9 1 5 . 0 3 4 . 8

BH 2 0 .8 2 .30 0 .02 17 11 .1 17 .7 13 .5 13 .8 44 .4

BH 3 0 .8 2 .40 0 .023 8 10 .3 17 .5 12 .5 12 .8 38 .9

10

10

100 1000

B u l k s t r e s s, % ( k P a )

9 a =207kPa

9 ~ 345 kPa

9 a -689kPa

O" ~, = 1034kPa

4 " o - 1378 k Pa

Confining tress

~ cL~ ~r0esksNre= 689 kPa

Asphalt concrete surface ( Ej ,v~)

Base course (E:,vz)

Embankment ( E ,% )

Subgrade (E~,%)

Y" unit weight of soiI

h4

/

Traffic stress, o,

/

lns im s tress, ~ r = 7 hi

I 1 ~ ~

Confining insitu stress Lateral traffic stress

%

F i g u r e 7 - Determ inat ion o f the f ie l d resi lient modulus value un der in-s itu and t ra ff ic

stresses




I n o r de r t o e s t ab l ish a co r r e l a t ion be t w een t he co ne pene t r a t i on t e s t pa r am e t e r s and t he

r e s il i en t m o du l us , t he va r i ab l e s tha t a f f ec t the r e su l t s o f bo t h t he cone pen e t r a ti on t e s t and

r e s il ien t m odu l us w e r e i den t if ied . The t ip r e s i s t ance

(qc),

s l eeve f r ic t ion ~ ) , and r e s i li en t

m odu l us ( Mr ) ar e a f f ec t ed by t he m a t e r i a l type ( f i ne - g r ai ned , coa r se - g r a i ned ) , un i t we i gh t

( g ) , m o i s t u r e con ten t ( w) , and t he s t r e ss l eve l (a ) . Th e r e f o r e , any p r opo sed m ode l shou l d

cons i de r t he e f f ec t s o f t he se va r i ab l e s on t he r e s i l ien t m o du l us . The va r i ab l e s p r e sen t ed i n

Tab l e 2 we r e u sed i n t he ana l ys is t o co r r e la t e t he r e s il i en t m odu l us and t he con e

pene t r a t i on t e s t pa r am e t e r s . S t a t is t ic a l ana l yse s ( m u l t ip l e r eg r e s s i on ) we r e pe r f o r m ed

us i ng t he S t a t is t ic a l Ana l ys i s Sys t em ( SA S) p r og r am . Fo r war d s e l ect ion , backw ar d

e l i m i na t ion , a l l pos s i b l e r eg r e ss i on , and s t epwi se p r ocedur e s w e r e u sed t o s e l ec t t he

va r i ab l e s in t he se co r r e la t ions . Th e f o l l owi ng r e l a t ionsh i p w as dev e l oped base d on t he

stat is t ical analysis :

0.55

M r = 18.95q < or3 Crb ~_0.41tr0.55 Y d

Wyw (2)

w here M r i s the res il i en t mo du lus (M Pa) , or3 i s the co nf in ing s t ress (kPa) , t r l is the

ver t i ca l s t ress (kPa) , qc i s the t ip res i s t ance (M Pa) , w i s the w ater con tent , ya i s the dry

uni t w eigh t (kN/m3), ywiS the un i t weig ht o f w ater (kN/m3), and cro i s the bu lk s t ress

( kPa ) . Fo r t h i s m od e l , t he coe f f i c i en t o f m u l t i p l e de t e r m i na t i on , R 2= 0 . 99 and r oo t m ean

squa r ed e r ro r , RM SE =l . 25 . The m o de l p r e sen t ed i n Equ a t i on 2 does no t i nc lude t he

s l eeve fr i c ti on ~ ) . M ode l s t ha t inc l u de f i w e r e a t t em pt ed and d i s r ega r ded due t o the i r low

v a lu e o f R 2 a n d h i g h R M S E .

Laboratory Investigation

Th e r e su l ts o f t he f i e l d and l abo r a t o r y inves t i ga t ion w er e used t o dev e l op a co r r e l a t i on

f o r p r ed i c t i ng t he r e s il ien t m odu l us o f coa r se -g r a i ned m a t e r i a l s f r om t he co ne pene t r a t i on

t e s t pa r am e t e r s and bas i c so i l p r ope r t ie s . Th e l abo r a t o r y inves t i ga t ion i n t ended t o

i nves t i ga t e t he e f f ec t s o f the un i t we i gh t and m oi s t u r e con t en t o f t he m a t e r i a l on t he

p r ed i c t ed r e s il ien t m odu l us . I n add i ti on , i t wi l l p r ov i de d a t a r equ i r ed t o va l i da t e t he

p r o p o s e d m o d e l .

An a l ys i s was cond uc t ed o n t he re su l t s o f t he l abo r a t o r y m i n i a t u r e con e pene t r a t ion

t e s ts on t he i nves t i ga t ed m a t e r i a ls unde r con t r o l led cond i t ions o f m o i s t u r e con t en t and

un i t we i gh t . F i gu r e 8 sho ws t he co ne pene t r a t i on t e s t p r o f i l e s f o r t he s and unde r t h r ee

d i f fe r en t cond i ti ons o f m o i s t u r e con t en t and un i t w e i gh t . The coa r se - g r a i ned m a t e r i a l s

s h o w e d h i g h e r

qc

v a l u e s f o r th e s a m p l e s p r e p a re d a t t h e o p t i m u m m o i s t u r e c o n te n t a n d

m ax i m um d r y un i t we i gh t . Th i s i s expec t ed s i nce the m a t e r i a l pos se s se s a h i ghe r s t r eng th

unde r t he se cond i t ions and t he r e f o r e h i ghe r r e si s t ance t o pene tr a t ion . T he s am pl e s on t he

w e t s i de o f t he m o i s t u r e con t en t- un i t we i gh t cu r ve sho w ed t he l ow es t qc va l ues . The

s t reng t h o f the se m a t e r i a ls dec r ea se s wi t h t he i nc r ea se o f t he m o i s t u r e con t en t and t he

dec r ea se o f the un i t w e i gh t. I t i s ev i den t t ha t t he t ip r e s i s t ance was i n f luenced by t he

m ois ture con tent and the uni t weight . S ta t i s t i ca l ana lys i s (descr ibed ear l i e r) w as a l so



T IT I E T A L . O N I N T R US I ON T E C H N O L O G Y 2 6 5

c o n d u c t e d t o e v a l u a t e t h e r e p e a t a b i l i ty o f t h e m i n i a t u r e c o n e p e n e t r a t i o n t e s ts . T h e

a v e r a g e c o e f f i c i e n t o f v a r i a t i o n f o r q~ r a n g e s f r o m 7 to 1 6 f o r c o a r s e - g r a i n e d m a t e r i a l s .

T h e c o n e p e n e t r a t i o n te s t p r o f i l e s s h o w e d g o o d c o m p l i a n c e a n d a r e c o n s i s te n t w i t h i n th e

s a m e g r o u p a n d r e f l e c t e d s i m i l a r p at te r n s .

T h e r e s u l ts o f t h e r e p e a t e d l o a d t r i a x ia l te s t o n t h e m a t e r i a l s u n d e r c o n t r o l l e d

c o n d i t i o n s o f m o i s t u r e c o n t e n t a n d u n i t w e i g h t a r e p r e s e n t e d i n T a b l e 3 . I n s p e c t i o n o f

T a b l e 3 i n d i c a te s t h a t t h e m a t e r i a ls w i t h o p t i m u m m o i s t u r e c o n t e n t a n d m a x i m u m d r y

u n i t w e i g h t e x h i b i t e d th e h i g h e s t v a l u e s o f th e r e s i l i e n t m o d u l u s . T h e r e s u l ts o f t h e

r e p e a t e d l o a d t r i a x i a l t e s ts o n t h e s a n d u n d e r c o n t r o l l e d c o n d i t i o n s o f m o i s t u r e c o n t e n t

a n d u n i t w e i g h t a r e s h o w n i n F i g u r e 9 . T h e v a r i a t i o n o f t h e m o i s t u r e c o n t e n t o f th e s a n d

( f r o m 5 t o 1 1 p e r c e n t ) s l i g h t l y a f f e c t e d th e r e s i l i e n t m o d u l u s . T h i s i s d u e t o e f f e c t o f

o t h e r f a c t o r s o n t h e r e s i l ie n t m o d u l u s o f c o a r s e - g r a i n e d m a t e r i a ls s u c h a s s t r e s s l e v e l s

( c o n f i n e m e n t ) , p a r t i c l e s h a p e , a n d p a r t i c l e s i z e .

L~y=6 ~ ~ O p t i m u m W e t s i d e

(excluded)

w = 8 . 1 % w = 1 1 .0 %

0 . 1 2 5 3 1 1, y j = I 6 . 4 k N /m ~ Yd = 1 5 . 7 k N/ m 3

Layer 5 f ~ .

~y~, 0.250

s s~ in ~

0.750 l I I , I , I , I I

Layers 0 5 10 15 20 0 5 10 15 20 0 20

q r ( M P a )

qc

( M P a )

qc

( M P a )

F i g u r e 8 -

Results o f the miniature cone penetration tests conducted on sand under

controlled conditions of moisture content and unit weight

1 0 0 0 1 0 0 0

100

10

' i Dry side

w = 5 .0 %, Yd = 16.1 kN/m 3

100

10

1 0 00 ~ ' 1 ~ t i m ~ m . . . . .

~ . K 1% " Yd = 16"4 kN /m 3 ,

100

a = 2 0 7 k P a

a e = 3 4 5 k Pa

a = S S 9 k P a

e l = 1 0 3 4 k Pa

Conf ining s t~ s

4 -

~ e = 1 3 7 ~ k P a

10 t I I ]

I I

i i I i

1O 0 1 0 0 0

Bulk stress, ~b (kPa)

7 Wet side

w = I1 .0 %, yd= 15 .7 kN/m 3

_ _ _ - _ -

[ I I I I I I I ] I t i t i i i

1 0 0 1 0 0 0 1 0 0 1 0 0 0

Bulk stress, c b (kPa) Bulk stress, a b (kPa)

F i g u r e 9 -

Results o f the repeated load triaxial test on sand under controlled conditions

of moisture content and unit weight



266

R E S IL IE N T M O D U L U S TE S T IN G F O R P A V E M E N T C O M P O N E N T S

Table 3 -

Resi l ient modulus tes t resul ts fo r coarse-grained m ateria ls under con trol led

moi s ture c on ten t and un i t weigh t

o~ crd M, (MPa) COV Mr (MPa) COV Mr (MPa) COV

(kPa) (kPa) dry side (%) optimum (%) wet side (%)

21 21 58.94 4.1 56.25 5.3 33.94 9.5

21 41 60.51 3.2 56.82 5.6 34.80 7.2

21 62 64.27 4.6 57.39 9.0 35.42 4.7

34 34 78.03 2.9 76.98 4.3 60.82 4.2

34 69 80.81 3.0 77.62 3.6 61.92 4.2

Silty 34 103 82.37 4.6 78.39 4.6 63.27 5.0

sand 69 69 121.33 3.3 110.21 2.8 103.52 2.5

69 138 126.62 4.3 111.23 3.6 104.70 2.8

69 207 126.45 3.0 113.71 3.2 105.12 3.1

103 69 155.98 3.1 135.29 2.4 146.27 1.7

103 103 157.93 2.0 136.35 2.5 148.48 2.3

103 207 164.00 1.6 137.40 3.4 151.41 1.7

138 103 187.01 1.5 165.13 2.0 180.67 1.7

138 138 189.94 1.8 167.21 1.7 182.84 2.3

138 276 191.98 1.8 167.90 2.8 184.16 1.9

21 21 75.51 2.2 79.17 3.1 42.92 7.6

21 41 75.97 2.1 79.79 4.2 43.74 3.0

21 62 76.71 2.3 80.49 3.8 45.04 3.3

34 34 105.00 2.0 107.68 3.0 70.20 3.7

34 69 106.00 2.1 108.39 3.2 70.75 5.5

34 103 107.15 1.9 110.00 2.3 72.06 4.6

69 69 172.58 1.3 174.07 1.4 143.99 2.7

69 138 171.05 1.4 174.76 1.8 144.17 2.7

69 207 165.74 1.5 171.34 1.3 146.58 1.5

103 69 220.66 1.0 234.07 1.9 213.99 1.6

103 103 225.22 0.9 237.06 1.1 217.50 1.6

103 207 220.71 0.8 234.30 1.3 214.19 1.5

Sand 138 103 257.80 0.9 271.46 1.4 251.97 1.8

138 138 262.22 0.8 276.17 1.5 255.39 1.2

138 276 252.64 1.1 271.56 0.9 246.28 1.0

Verif ica tion o f the Pro pos ed M ode l

Equation 2 presented a model pr oposed for predicting the resilient modulus of coarse-

grained materials using the co ne penetration test parameters and basic soil properties.

This model was develop ed using statistical analysis on field and laboratory test results of

materials un der its natural condi tions. It is necessary to validate the model by predi cting

the resilient modulus of materials that were not used to develop the model. Therefore, the

model was us ed to predict the resilient modulus o f the coarse-grained materials used in

the laboratory investigation. Comparison o f predicted and measure d resilient modulus

values are depicted in Figure lOa. Inspection of Figure 10a shows the agreem ent of the

predicted and meas ured resilient modulus values. In order to quantify the deviation of the

predicted resilient modulus from the measured values, the absolute relative error was



T IT I E T A L . O N I NT R U S IO N T E C H N O L O G Y 267

d e t e r m i n e d a n d d e p i c t e d in F i g u r e 1 0 b. T h e m o d e l p r e s e n t e d i n E q u a t i o n 2 p r e d i c t e d th e

r e s i l ie n t m o d u l u s o f c o a r s e - g r a i n e d m a t e r i a l s a n d i s c o n s i d e r e d a s t e p f o r w a r d i n t h e

d i r e c t io n o f i n - s i tu c h a r a c t e r i z a ti o n o f p a v e m e n t m a t e r i a l s.

10 0 , [ v I ' f " I ' -

~ : 6o

4 0 *

.2O

c o a r s e - g r a i n e d

0 , I ~ I J I r I , /

0 2 0 4 0 6 0 8 0 I 0 0

P r e d i ct e d M , ( M P a )

(a) Com parison of predicted and m easured M

~ l k L A 2 8

9D ' L A 8 9

O Cont ro l l ed t es t - sand

A Cont ro l l ed -s i lt y sand

(b) Ab solute relative error in predicting the m easured resilient mo dulus.

F i g u r e 1 0 - Validation of the proposed model


T h i s p a p e r i n v e s t i g a t e d t h e a p p l i c a b i l i ty o f t h e c o n e p e n e t r a t i o n t e s t i n d e t e r m i n i n g t h e

r e s i l ie n t m o d u l u s o f c o a r s e - g r a i n e d m a t e r i a l s . C o n e p e n e t r a t io n t e s t s w e r e c o n d u c t e d a t

t w o p a v e m e n t p r o j e c t s it e s in L o u i s ia n a . M a t e r i a l s s a m p l e s w e r e o b t a i n e d a n d s u b j e c t e d

t o l a b o r a t o r y te s t s i n c l u d i n g t h e r e p e a t e d l o a d t r i a x i a l te s t a n d o t h e r t e s t s f o r m a t e r i a l

c h a r a c t er i z a ti o n . A n a l y s i s w a s c o n d u c t e d o n t h e t e s t r e s u l ts , w h i c h w e r e u s e d t o d e v e l o p

a m o d e l f o r p r e d i c t i n g th e r e s i l ie n t m o d u l u s o f c o a r s e - g r a i n e d m a t e r i a l s u s i n g t h e c o n e

p e n e t r a t i o n t e s t p a r a m e t e r s a n d b a s i c s o i l p r o p e r t ie s .

A n a d d i t i o n a l l a b o r a t o r y i n v e s t i g a ti o n w a s c o n d u c t e d o n c o a r s e - g a i n e d m a t e r i a l s

p r e p a r e d u n d e r c o n t r o l le d c o n d i t io n s o f m o i s t u r e c o n t e n t a n d u n i t w e i g h t . T h e r e s u l t s o f

t h e l a b o r a t o r y t e st s w e r e u t i li z e d to i n v e s t ig a t e t h e e f f e c t o f m o i s t u r e c o n t e n t a n d u n i t




weight o n the cone pene t r a t ion t e s t pa r amete rs and r es il i en t modulus . T he r esu l ts w ere

a l so used to ve r i fy the m ode l deve loped for p r ed ic t ing the r e si l ien t modulus . T he

pred ic ted res i li en t mo dulus va lues were cons i s ten t wi th those ob ta ined us ing the r epea ted

load t r iaxia l test . T his s tud y demon stra ted the appl icabi l i ty o f con e penetra t ion tes t in

predic t ing the res i l ient mo dulu s o f coarse-gra ined mater ia ls .

Acknowledgments

This r e sea rch pro jec t is f inanc ia lly suppor ted by the U .S . D epar tment o f

Transpor ta tion , Federa l Highw ay Adm inis tr a t ion /P r io r ity Tec hno logy P rogram (USD OT

F H W A /P T P ) C o n t ra c t N o . D T F H 7 1 - 9 7 - P T P - L A - 1 4 , t h e L o u i s ia n a D e p a r tm e n t o f

Transpor ta t ion and Deve lop men t (LAD OT D) S ta te P ro jec t No. 736-99-0773 , and the

Louis iana Transpor ta t ion Resea rch C ente r P ro jec t No. 98-8GT .

Th e e f for t o f Wi l l iam T . T ie rney , Resea rch Spec ia l i st and Am ar Raghavendra ,

Resea rch A ssoc ia te /LT RC i s acknowledged . M ark M orvant , Geotechnica l and Pavem ent

Adm inis tr a to r/LTRC , e f for t s and coo pera t ion dur ing the f i e ld and l abora tory t e s ting

programs i s g r a te fu l ly apprec ia ted . Pau l B rady , M elba Bo unds , and Ken ne th Johnson ,

LTR C Geotechnica l Labora tory he lped in co nduc t ing va r ious so i l te st s.

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STP1437-EB/Jan. 2003

A u t h o r I n d e x

A

Abdallah , Imad, 3

B

Ba ndara , Nishantha, 85

Barbosa, Paulo S. A., 99, 114

Bejarano, Manuel O. , 129

Benson, C. H., 191

Bou dreau, Richard L. , 30 , 176 , 224

Bro, Anders , 41

Butal ia , Tarunj i S . , 70

C

Carvalho, Carlos A. B., 99, 114

Crof t , Frank, 70

D

de Lima, Dario C., 99, 114

E

Edil, T. B., 191

G

Groeger , Jona than L . , 16, 41 ,20 9

H

Hankour, R., 141

Ha rvey , John T., 129

Heath , Andrew C. , 129

Hera th , Ananda , 233 , 252

Huang, Jun, 70

Iasbik, Israel, 114

K

Ke, L iqun , 3

Kim , D o n g - Gy o u , 7 0

Kim, W. H., 191

Konrad, Jean-Marie , 165

L

Li, J ianchao, 59

Lopez , Aramis , 16 , 41 ,209

M

Marr, W. A., 141

Meshkani , Amit is , 3

Minet te , Enivaldo, 114

Mohammad , Louay N. , 233 , 252

N

Nazarian, Soheil, 3, 152

Q

Qubain , Bashar S. , 59

R

Rada, Gonza lo R. , 16, 41 ,2 09

Ro bert, Claud e, 165

Row e, Geo f f rey M. , 86

S

Schmalzer , Peter N. , 209

Silva , Cl~iudio H. C., 99, 114

T

Tanyu, B. E, 191

Tit i , Hani H. , 233, 252

Tr indade , T iago R , 99

W

Wang, J ianren , 176

Werden, S. K., 141

W ill iams, Rob er t R. , 152

Y

Yuan, Deren, 152

2 7 1

Copyright9 by ASTM Intern ation al ww w.astm .org



STP1437-EB/Jan. 2003

Subject Index

A

A AS HT O T30 7, 16, 30 , 59 , 176, 224

Aggregate , 165

Asphalt , 3

B

Backcalculat ion , 85

Backpressure saturat ion , 59

Base, 3 , 1 52, 165

Bo ttom ash, 191

C

California bear ing rat io , 85 , 99

Coarse-grained mater ials , 252

Cohesive soil, 70, 224, 233

Compl iance , 176

Cone penetrat ion tes t , 233, 252

D

DarWIN, 224

DNER-ME 131194, 114

E

Elastic modulus, 191

E L S Y M 5 , 2 2 4

F

Fallin g w eight defle cto m eter test, 85, 191

Federal Highway Adminis trat ion , 30 , 41 ,

176

FHW A RD-96-176 , 4 I

F ield tes t ing, 3 , 152, 252

F lex ib le pavemen t , 3

Florida subgrade soils, 85

Fo und ry slag, 191

G

Gravel, 191

Industrial by-products, 191

K

KE N L A Y E R , ! 9 1

L

La borato ry tes t ing, 3 , 16, 1 14, 152, 165,

209, 252

repeatabi l i ty , 30

star tup procedures , 41

Large-scale model exper iment , 191

Layered e las t ic model , 224

Lime rock bear ing rat io , 85

Load ing per iod , 70

L o n g - Te r m P av em en t P e r f o r m an ce

Program, 30, 41, 209, 224

L o n g Te r m P av em en t P e r f o r m an ce P r o to co l

P46 , 16, 41, 129

M

Mo is tu re con ten t , 70

Motion contro l ler , 129

N

Non-coh es ive so i l, 224

P

Pavement design , 3 , 59 , 85 , 224

PID adaptive controller , 141

Po lyp rop yle ne f iber, 114

Pore water p ressu re , 70

Pro toty pe test, 191

Q

Quali ty contro l and assurance, 41 , 152, 209

R

Re pea ted-lo adin g tr iaxial test, 99, 1 14 , 165 ,

252

Resilient modulus, 3, 16, 30, 41, 59, 70,

85, 99, 114 , 129 , 152 , 191 ,2 09 ,

224, 233, 252

testing, 141, 165, 176

273




T