per mi ability

8/6/2019 Per Mi Ability

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APPENIDIX VII:PERMEABILITY TESTS

OF WATER THROUGH SOlL. The flow- ---water through a soil medium is assumed to follow Darcys law:

q= kiAwhere 4= rate of discharge through a soil of cross-sectional area A

k = coefficient of permeability

i = hydraulic gradient: the loss of hydraulic head per unitdistance of flow

The application of Darcys law to a specimen of soil in the laboratory is The coefficient c)f permeability, k (often term


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p e r m e a b i l i t y ) , i s d e f i n e d a s t h e r a t e o f d i s c h a r e o f wa t e r a t a t e r n -e r a tu r e o f 20 C under condi t ions of laminar f low through a un i t c r o s s -ect ional area of a soil medium under a un i t hydraul ic grad ien t , The

oefficient of permeabili ty has the dimensions of a velocity and is usually

x p r e s s e d i n c e n t i m e t e r s p e r s e c o n d . The permeabili ty of a soil de

rimarily on the s ize and shape of the soi l gra ins , the void ra t io of the

oi l , the shape and arrangement of the voids , and the de r ee o f s a t u r a t i o n .P e r m e a b i li t y c om p u t e d o n t h e b a s i s o f D a r c y s l a w i s l i m i t e d

ondit ions of laminar f low and complete sa tura t ion o t h e vo ids* n t u r b u -n t flow , the flow is no longer r opor t iona l t o the fir s t powe r o f the

y d r a u l ic g r a d i e n t . U n d er c on d i tion s of in c om p le te sa t u r a t ion , t h e f

n a t r a n s i e n t s t a t e a n d i s t i m e - d e p e n d e n t , T h e l a b o r a t o r y p r o c e d u r e s

r e s e n t e d h e r e i n fo r d e t e r m i n in t h e c oe ffi cie n t o f p e r m e a b i li t y a r e b a s en l l e s s o thexw i s e r e q u i r ec o m p l e t e s a t u r a t i o n

ons to s imula te

a tu r a l con on s i s s o m e t im e oweve r , the effects 0h o u l c l be r e co

nd taken in to cons ide ra t ion .

S O S A

ea d test . T h e s im p le st of a l l m e t h o d s fo r d e t e r m i n i n

ermeabil i ty is the constant-head type of test

s t i s pe r formed by measur ing the quant i ty oe soi l specimen, the length o t h e so i l s

and the elapsed t ime , t , T h e h e a d o f h e t e s t . F o r f ine- r a i n e d s o i l s , Q i s s m a l l a x e d m a y b e d ic2d.t t o m e a -u r e a c c u r a t e l y . The re fo r e9 t h e cons t a n t - h e a principally fo ro a r s e - g r a i n e d s o i l s ( c l e a n s a n s a n d grave l s ) w i t h k va lue s r e s t e r t habout A0 X 30- c m p e r s e c .

( 2 ) F a l l i n g -h e a d t e s t , h e p r i n c i p l e u a l l i n g - h e a d t e s t i l l u s t r a t e d i n i g u r e 2, This te s t i s conduc ted in the same manner as

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e c o n s t a n t - h e a d t e s t , e x c e p t t h a t t h e h e a d o f w a t e r i s n o t m a i n t a i n e d

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

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

om p u t a t ion . T h e fa l lin g -h e a d t e s t i s g en e r a l ly u s e d fo r le ss p e r v io u s

o i l s ( f i n e s an d s t o f a t c l ay s ) w i th k v a lu es l e s s t h an 10 X 10M4 cme r s e c .

b , T h e a p p a r a t u s u s e d f o r p e r m e a b i l i t y t e s t i n g m a ya ry co n s id e rab ly i n d e t a i l d ep en d in g p r im ar i l y o n t h e co n d i t i o n an d

h a r a c t e r o f t h e s a m p le t o b e t e st e d . Wh e t h e r t h e s a m p l e i s f in e -g r a i n e d

r co a r s e -g ra in ed , u n d i s tu rb ed , r em o ld ed , o r co m p ac t ed , s a tu ra t ed o r

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

as i c t y p es o f ap p a ra tu s , g ro u p ed acco rd in g t o t h e t y p e o f s p ec im en con -p e r m e a m e t e r ) , a r e a s fo l l ow s :

(1 ) P e r m e a m e t e r c y l i n d e r s

(2 ) S a m p l i n g t u b e s

(3 ) s u r e c y l i n d e r s( 4 ) C o n s 0 i d o m e t e r s

h e p e rm eab i l i t y o f r em o ld ed co h es io n l e s s s o i l s i s d e t e rm in ed i n

e r m e a m e t e r c y l in d e r s , w h i le t h e p e r m ea b ilit y of u n d is tu r b e d coh e sion -

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

b e a s a p e r m e a m e t e r . Th e p e rm eab i l i t y o f r em o ld ed co h es io n l e s s s o i l

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

ss so ils in a h o r izo n t a l d ir e c t io n . P r e ss u r e c yli n d e r s a n d conso l idomer s a r e u s e d f o r f i n e - g r a i n e d s o i l s i n t h e r e m o l d e d , u n d i s t u r b e d , o r

om p a c t e d s t a t e . F i n e - g r a i n e d s o i l s c a n b e t e s t e d w i t h t h e s p e c i m e nr i e n t e d t o o b t a i n t h e p e r m e a b i l i t y i n e i t h e r t h e v e r t i c a l o r h o r i z o n t a l d i -

c t i o n . T h e a b o v e - l i s t e d d e v i c e s a r e d e s c r i b e d i n d e t a i l u n d e r t h e.

d i v i d u a l t e s t p r o c e d u r e s . Pe rm eab i l i t y t e s t s u t i l i z i n g t h e d i f f e ren t t y p e

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

s cu s s ed i n t h e fo l l o win g p a rag rap h s .

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3. C O N S T AN T -H E AD P E R M E AB I L I T Y T E S T WI T H P E R M E AM E TE R

C Y L I N D E R . 2. U s e , Th e con st a n t-h e a d p er m e a bilit y t es t wit h th ep e r m e a m e t e r c y l i n d e r s h a l l i n g e n e r a l b e u s e d f o r d e t e r m i n i n g t h e p e r

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

s a n d s a n d g r a v e l s h a v i n g a p e r m e a b i l i t y g r e a t e r t h a n a b o u t 10 X 10N4 cp e r s e c .

b* Ap p a r a t u s . Th e a pp a ra tu s an d a ccessor y eq u ip m en t sh ou ldcons i s t o f the fo l lowing :

(1 ) A p e r m e a m e t e r c y l i n d e r s i m i l a r t o t h a t . s h o w n s c h e m a

ca l l y i n F ig u re 3a , T h e p e r m e a m e t e r c y l i n d e r s h o u l d b e c o n s t r u c t e d o f at r a n s p a r e n t p l a s t ic m a t e r i a l . T h e i n s i d e d i a m e t e r o f t h e c y l i n d e r s h o u l

b e n o t l e s s t h a n a b o u t 10 t i m e s t h e d i a m e t e r o f t h e l a r g e s t s o i l p a r t i c l ee x c e p t w h e n t h e s p e c i m e n i s e n c a s e d i n a r u b b e r m e m b r a n e a s i n t h e p e r m

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

d e r s h o u l d b e a t l e a s t s i x t im es t h e d i am e te r o f t h e l a rg es t s o i l p a r t i c l e s .O v t r h t w d L k n r t d Mrl l td W&r Sup&

Thcrmome fer -. p\ ,9 2 Munomtftr Bourd

/ Munomrfer Board

- Y-hermomtfrrF1lfer Moferlol

WIYP Sc rctn

(a) CONSTANT-HEAD APPARATUS (b) F AL LING-HEAD APPARATUS

Fig u re 3 . Sch em a t i c d i ag ram o f co n s t an t -h ead an d f a l l i n g -h eadp e r m e a b i li t y a p p a r a t u s

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ezometer taps a long the s ide of the permeameter wi thin l imits to be oupied by the sample a re advantageous in tha t the head loss wi thin the

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

on of hydraul ic gradient can be made .

bu o r a t e d m e t a l o r p l a s t i c d i s k s a n d c i r c u l a r w i r ereens, 35 to *100 mesh, cut for a c lose f i t inside the permeameter .

( 3 ) G l a s s t u b i n g , r u b b e r o r p l a s t i c t u b i n g , s t o p p e r s , s c r e w

am p s , e t c . , necessa ry to mak e conn ect ions a s shown in F igur e 3a .

(4 ) F i l t e r m a t e r i a l s s u c h a s O t t a w a s a n d , c o a r s e s a n d , a n d

r a v e l o f v a r i o u s g r a d a t i o n s .

(5 ) A device for maintaining a constant-head water supply.

(6) D e a i r e d d i s t i l l e d ? w a t e r . Tapwa t e r c o n t a i n s d i s s o l v e dr and gases which separa te from solut ion in the ini t ia l layers of a tes t

p ecim en of soil in t h e o r m o f s m a l l b u b b l e s . T h e s e b u b b l e s r e d u c e t h

ermeabil i ty of the soil by decreasing the void space available for the

ow of water . f o r r e m o v i n g d i s s o l v e d a i r

om water i s by i t a t r e d u c e d p r e s -

u r e s . e only with smal l quant i t ies of water .r e s h l y d i s t i l l e d w a t e r a l s o h a s a v e r y n e g l i g i b l e a m o u n t o f a i r , L a r g e

ua n t i t ie s 0 dea ired d is tilled wa ter may be p repa r ed and re t a ined fo rubsequent use by spraying di s t i l l ed water in a f ine s t ream into a con-

i n e r f r o m w h i c h t h e a i r h a s b e e n e v a c u a t e d ( s e e F i g . 4 ) . P e r m e a b i l i t y

s t s on sa tura ted spec imens should show no s igni f icant decrease in

r m e a b i l i t y w i t h t i m e i f p r o p e r l y d e a i r e d d i s t i l l e d w a t e r i s u s e d . H o w

ver, i f such a decrease in permeabi l i ty occurs during a test , then a p r eter , consis t ing of a layer of the same materia l as the test specimen,

ould be used be tween the dea i red di s t i l l ed water reservoi r and the tes

ecimen to remove the a i r remaining in solut ion.$lized water or t a p w to be r e la t ively fr1s may be used in p

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WATER SPRAY

S U P P L Y

DEAIRED DISTILLED- - - - - - W A T E R RESkRVOlR

- - - - - -- - - -- -

- - - - e- - - -

- - -- --

V A C U U M W A T E R T R A P

TO TEST SPECIMEN~ FROM VACUUM SU

-. D R A I N C O C K A N D V A CR E L E A S E

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

deaired dist i l led water

(7) a n o m e t e r b oa r d w it h t u b in g le a d in g fr om t h e p i ezom- . ..a LA

te r taps. I pieeometer taps are not provided, eq u i m e r i t t o measurehe d is tance between the constant -head source and ta i lwater i s requi re

device, a watch or clock with second hand,

ted cyl inder ) 100 -ml capacity.ade the rmomete r , r ange 0 to 50 C, accurate

o 0 .1 c ,k w a l ance , sensitive to 0.1 g .(12) Ove n {se e Ap p en d ix I, WA7cE CONTENT - G E N E

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(13) Scale, graduated in centimeters.

C, Placement and Saturation of Specimen. Placement and satura-Of the specimen shall be done in the following steps:

(1) Record all identifying information for the specimen, suc

as project, boring number, sample number, or other pertinent data, on a

data sheet (Plate VII-i is a suggested form),(2) Oven-dry the specimen. Allow it to cool and weigh to th

nearest 0.1 g. Record the oven-dry weight of material on the data sheetopposite W s. The amount of material should be sufficient to provide a

ecimen in the permeameter having a minimum length of about one to twimes the diameter of the specimen.

(3) lace a wire screen, with openings sm a l l e n o u g h t o r e t a ih e specimen, over a perforated disk near the bottom of the permeamete

above the inlet. The screen openings should be approximately equal to t

0 percent size of the specimen.

) Allow deaired distilled water to enter the water inlet of t

permeameter to a height of about 1/2 in. above the bottom of the screen,care that no air bubbles are trapped under the screen.

(5) Mix the material thoroughly and place in the permeamet

o avoid segregation. The material should be dropped just at the water

surface, keeping the water surface about a/2 in. above the top of the soilplacement. A funnel or a special spoon as shown in Figure 5 is

convenient for this purpose.

(6) The placement procedure outlined above will result in a

saturated specimen of uniform density although in a relatively loose condo produce a higher density in the specimen, the sides of the perm*tion.containing the soil sample are tapped uniformly along its circum

erence and length with a rubber mallet to produce an increase in density

however, extreme caution should be exercised so that fines are not put into

suspension and segregated within the sample. As an alternative to this pro

cedure, the specimen may be placed in the in the dry using a funnel Or

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7) After the speci-en has been placed, weigh the

xcess material, if any, and the

ontainer. The specimen weight is

he difference between the original

weight of sample and the weight ofDIPPF R -

he excess material. Care muste taken so that no material is lost C/t-----~c- fI -+,i

placement of the specimen.16

FRONT VIEW SIDE VIEW

there is evidence that material has

een lost, oven-dry the specimen

b J* t iJ+Ull LUf placing>hesionless soi lsnd weigh after the test as a check.

(8) Level the top of the specimen, cover with a wire screen

imilar to that used at the base, antd fill the remainder of the p e rme ame t ewith a filter material.

(9) Measure the length of the specimen and inside diameter

he permeameter to the nearest 0.1 cm and record on the data sheet as

nitial height and diameter of specimen.

(10) Test the specimen at the est ima.ted natural void ratio or

poon which permits the material

fall a constant height. The de-

red density may be achieved by

brating the specimen to obtain a

pecimen of predetermined height.

ompacting thenot recomme

ecimen in layersas a film ofmay be forme at the surface

y e r which mightty results .ly a vacuum

e specimen and per-enter the evacuated

ough the base of the

If_= ?

Ie nI*0 CONNECT.

WIRE

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at a ser ies of dif ferent void rat ios, produced by increasing the amount ofvibrat ion af ter each permeabil i ty determination. Measure and record the

length (height) of specimen in the permeameter pr ior to each determina-

t i o n . P e r m e a b i l i t y d e t e r m i n a t i o n s a t th ree d i f feren t vo id ra t ios are

usually sufficient to establish the relation of void ratio to permeability.

d . P r o c e d u r e . Th e p r oced u r e sh a ll con sist of t he follow in g st e(i ) M e a s u r e t h e d i s t a n c e , L1, between the cen ters of thepiezometer taps to the nearest 0 .01 cm and record on the data sheet .

(2) Adjust the he ight o f the constan t -head tank to ob ta in thedesir ed hydrau l ic g rad ien t , The hydrau li c g rad ien t shou ld be selected s

that the f low through the specimen is laminar . The range of laminar f low

condit ions can be determined by plot t ing d i s ch a r e v e r S u S h y d r a u 1 i c gramdient. A straight-line relation indicates laminar f low, while deviations

from the straight- l ine at high gradients indicate turbulent f low. Laminar

or f ine sands is l imited to hydraulic gradients less than approxi-

mately 0.3. It is usually not practicable to achieve laminar f low forc oa r se r soils , a n d t h e t e st s e n e r a lly sh ou ld b e r u n a t t h e h y d r a u lic

radient ant icipated in the f ield .

( 3 ) O p e n v a v e A b ee 3a) and record the ini t ia l p i eeom-eter read ings af te r the f low has become s tab le . xerc i se care in b u i l d i nup heads in the pe rmeamete r so tha t the s men is no t d is turbed .

) After allowing a few minu for equil ibr ium condit ions

to be reached, measure by means of a e the quanti ty of dischargecorresponding to a given t ime interval . e a su r e the piezometr ic headsand the wa te r t empera tu re in the pe rmeamete r ,

I ( 5 ) R e c o r d t h e q u a n t i t y o fflow* p i ezome te r r e ad i n g s*

w a t e r

t e m p e r a t u r e , a n d t h e t im e in t e r va l d u r i n g w h ic h t h e qu a n t it y of flow w a s

measured on the da ta sheet , P la te VII-$&.(6) Repeat steps (4) and (5) several t imes over a period of

about 1 hr, and compute the coefficient of permeability corresponding toeach se t o f measured da ta . I f there i s no substan t ia l change in the

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ermeability, then the computed permeability is probably reliable. If thermeability, then the computed permeability is probably reliable. If th

a slight decrease in the permeability, then the permeability computeda slight decrease in the permeability, then the permeability computed

om the initial.measurements, rather than the average, should be reporom the initial.measurements, rather than the average, should be reporo long as a plot of permeability versus time shows that the initial measo long as a plot of permeability versus time shows that the initial meas

ents are consistent with the subsequent measurements; a difference inents are consistent with the subsequent measurements; a difference in

ermeability may result from a change in density caused by inadvertentermeability may result from a change in density caused by inadvertent

arring of the specimen in the permeameter,arring of the specimen in the permeameter, If there is any substantial If there is any substantial

rease of the permeability with time, a prefilter should be used between trease of the permeability with time, a prefilter should be used between t

water reservoir and the permeameter (see paragraph 3b(6)). The criterwater reservoir and the permeameter (see paragraph 3b(6)). The criterr judginr judgin whether a change in the computed permeability is substant whether a change in the computed permeability is substant

epends on the desired accuracy of the coefficient of permeability.epends on the desired accuracy of the coefficient of permeability.

(7)(7) If desired, reduce the void ratio as previously describedIf desired, reduce the void ratio as previously describedeat the constant-head test,eat the constant-head test,

The computations consist of the followin The computations consist of the followinthe test void ratios in accordance with Appendithe test void ratios in accordance with Appendi

EE OF sE OF s Ained in accord-ned in accord-

nce with A

rmeability, k, by means o, by means oe followine followin

k20 =20 =QxLxRTxLxRT

h e r e kh e r e k2020

= coefficient of permeability, cm per set at 20 c= coefficient of permeability, cm per set at 20 C

over which head loss is measured,over which head loss is measured, cmcmtaps are used, L =taps are used, L =

ureure correction factor for viscosity of water ob-correction factor for viscosity of water ob-L, or difference in piezometerL, or difference in piezometer

A q cross-sectional area of specimen, sq cmA q cross-sectional area of specimen, sq cm

tt = elapsed time, see= elapsed time, see

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Table VII-1

Correction Factor, F&,, for Viscosity of Water at Various Temperatures

C 8A..-


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f. P r e s e n t a t i o n o f R e s u l t s . The coef f ic ien t o f pe rmeabi l i ty she r e po r t e d in un i t s w i th c oe f f i c i e n t s o f 1.0, 1 X 10v4, a n d 1 X 10d9 c m pe c . The vo id r a t io o f t he spe c ime n sha l l be r e po r t e d w i th a l l va lue s o f

he coef f ic ien t o f pe rmeabi l i ty , k , i s l oga r i thmic a l ly de pe nde n t upon t hoid ra t io of- the soi l . W h e r e k i s d e t e r m i n e d a t s e v e r a l v o i d r a t i o s , t h

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

igu r e 6 in wh ic h k i s p lo t t e d on t he a b s c i s s a I l o r ,a r i t h m i r sc;r~ l~b 2 n d t_ --- _-__ --------\--b------------ -1-1, w--v wo id r a t io i s p lo t t e d on the o r .____ __inate Iarithmetic srale).-.- -_------- -- -1-L

0.8 ,

0 . 4

1 10 1 0 0 1000

cc X F F I C I E N T OF P E R M E A B l L l f Y I N C M / S E C n : 1o-4

F i g u r e 6 . Re l t nd vo id r a t ioa t ion b e t w e e n p e r m e a b i l i t y 2f o r c o h e s i o n l e s s s o i l s

F AL L I N G -H E AD P E R M E AB I L I T Y T E S T R M E AM E T E R

Y L I N D E R , a . U s e , T h e f a l l i n g - h e a d t e s t w i t h t h e p e r m e a m e t e r

per mi ability

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