mcanoy cashman purvis(major piles)

8/6/2019 McAnoy Cashman Purvis(Major Piles)

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CYCLIC TENSILE TESTING OF A PILE IN GL ACIAL TILL

R.P.L. McAnoyA.C. Cashman

D. P u r v i s

T a y l o r W o o d r ow R e s e a r c h L a b o r a t o r i e s ,345 Ru is l ip Ro a d ,

Sout hall ,M i d d le s e xE n g la n d

RESUME

F o r o f f s h o re s t r u c t u r e s i n d e e p w a t e r , p i l e s a r e b ei n g d es ig n ed t o w i t h s t a n dc y c l i c t e n s i o n , d u e t o u p l i f t a n d w a v e l o a d in g , t h r o u g h o u t t h e i r d e s ig n l i fe .H o w e v e r t h e r e is a s c a r c i t y o f d a t a c o n c e r n i n g t h e l o a d l e v e l s w h ic h c a n b es a f e l y a p p l i e d i n t h i s m a n n e r . T h i s p a p e r r e p o r t s t e n s i l e tests on a h e a v i lyin s t ru me n te d 1 0 m e t re lo n g p i l e j a ck e d in to g la c ia l t il l. P re v io u s wo rk h a ds h o w n s a t i s f a c t o r y p i l e be h a v i o u r u n d e r c y c l i c t e n s i l e l o a d s p e a k i n g at u p to48% o f t h e u l t i m a t e t e n s i l e c a p a c i t y , a n d so t h i s w o r k w a s a i m e d ati n v e s t i g a t i n g pi l e r e s p o n se t o m o r e s e v e r e l o a d l e v el s , a p p r o a c h i ng f a i l u re .C y c l i c tests w e r e p e r f o r m e d w i t h v a r y i n g p e a k l o a d s u p t o 80% o f t h e i n i ti a ls t a t i c c a p a c i t y , a n d up t o 1 3, 50 0 c y c l e s w e r e a p p l ie d d e p e n d in g o n p i l ere s p o n s e. T h e p i l e s u s ta in e d e n c o u ra g in g ly h igh lo a d s w i th o u t s e r io u sd e f o r m a t i o n , b u t f a i l u r e di d o c c u r d u r in g t h e m o s t s e v e r e test, w h en t h e p e a klo a d wa s n o min a l ly 80% o f t h e u l t i m a t e t e n s i l e c a p a c i t y . P i l e r e s p o n sea n a l y s is p r o v id e d i n s i g h t i n t o c o m p r e s s io n p i le d e s i g n m e t h o d s w h e n a p p l i e d t ot e n s i o n pi le s. A l p h a a n d L a m b d a m e t h o d s , b u t n o t t h e B e t a m e t h o d, e s t i m a t e d

i u l t i m a t e t e n s i l e c a p a c i t y w e ll , w h i ls t s t i f f n e s s w a s g r e a t e r t h a n i m p l i e d bypublished T-Z curves .


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1.0 I NTRODUCTI ON

Th e oi l a nd a l t e r n a t i ve e ne r gy indus t r ie s , by the i r inc r e a s ing in t e r e s t inl a r g e s c a l e f lo a ti n g s t r u c tu r e s , h a v e s t i m u l a t e d r e s ea r c h i n t o t h eb e h a v i o u r of c o n v e n t i o n a l s t e e l p i p e p i l es as anchors .

A m a j o r d e v e l o p m e n t p r o g r a m m e h a s r e c e n t l y b e e n c o m p l e t e d f o r o n es uc h f loa t ing s y s te m, r e qu i r e d to p r ov ide a wor k ing p la t f o r m in the200 -400 m e t r e r a nge of w a te r de p th s ( Smi th a nd Ta y lo r 1980 ). Th es t r u c t u r e c o m p r i s e s a b u o y a n t c o l u m n , t e t h e r e d t o a f ounda t iona nc ho r a ge by a s e r i e s o f t e ndons. Due to t h e pos i t ive buoya nc y o f th ec o l u m n , t h e f l u c t u a t i n g l o a d s i m po s ed o n t h e f o u n d a ti o n are a l w a y stens i le .

T h e c h o i c e f o r t h e f o u n d a t i o n d es i gn w a s b e t w e e n a p i le d o r g r a v i tyb a se . M o st o f t h e f o u n d a ti o n d e v e l o p m e n t p r o g r a m m e w,as d i r e c t e dt o w a r d s a piled base.

A v a i l a b l e d e s ig n g u i d a n c e w a s c o n s id e r e d i n a d e q u a t e f o r b o t h t h eu l t i m a t e c a r r y i n g c a p a c i t y o f p i le s i n t e ns i o n a n d p i l e r e s p o n s e t ow o r k i n g l oa ds . F u r t h e r , t h e e f f e c t o n pi l e c a p a c i t y of t h e v e r t i c a l a n dl a t e r a l c y c l i c l o a d s t r a n s m i t t e d d u ri ng s e v e r e s t o r m s c o ul d o nl y b et e n t a t i v e l y q u a nt i fi e d. W i th t h i s l e v e l o f u n c e r t a i n t y t h e p r e l i m i n a ryd e s ig n m e t h o d h ad t o e n s u r e t h a t r e l a t i v e l y lo w s t r e s s l e v e l s w e r ea p p l i e d t o t h e p i l e s d u r i n g t h e 100 y e a r s t o r m . T o c h ec k t h e a d e qu a c yo f t h e d e s i g n a n e x p e r i m e n t a l p r o g r a m m e o f. l a b o r a t o r y a n d o n s h o r el a r g e s c a l e p i l e tests w a s u n d e r ta k e n . T h e s e tests s u b s t a n t i a t e d t h ed e s i g n a d o p t e d , e x a m i n e d t h e s t a b i l i t y o f a s o i l du r ing r e p r e s e n ta t ives t o r m l o ad i n gs a n d d e t e r m i n e d t h e r e l a t i v e e f f i c i e n c y of j ac k in g f o r c et o t e n s i l e c a p a c i t y . In t h e s e tests t h e b a s i c p il e p a r a m e t e r s a n d l o ad i n gr e g i m e s w e r e a p p l i c a b l e t o a j a c ke d p i l e a r r a nge me n t in a pr e l imina r yf ound a t ion de s ign.


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O n c o m p l e t i o n o f t h i s s e c t i o n o f t h e f i e l d test p r o g r a m m e i t w a s f e l tt h a t it w o u ld b e o f c o n s i d e r a b l e v a l u e t o d e t e r m i n e t h e be h a v i o u r of as in g le p i l e u n d e r mo re s e v e re lo a d in g s . T h u s a s ing le , heav i lyin s t ru me n te d , o p e n e n d e d 10.4m lo n g s t e e l p ip e p il e wa s t e s t e d u n d e r . as e r i e s o f hig h l e v e l t e n s i l e lo a d p a c ka g e s . T h e re s u l t s of th e s e tests a r ep r e s e n t e d i n t h i s p a p e r . F u r t h e r d e t a i l s of t h e l a b o r a t o r y a n d f ie l d testp r o g r a m m e h a v e b e e n r e p o r t e d b y G a r a s ( 1 97 9 ) a n d G a r a s a nd M c A n o y(1980).

DE S CRIP T ION OF FIELD %STS

2.1 TE ST SIT E

T a k i n g i n t o a c c o u n t l i k e l y N o r t h S e a l o c a t i o n s f o r a b u o y a n t c o l u m ns t r u c t u r e , t h e m o s t s u i t a b l e g r o un d c o n d i ti o n f o r a n o n s h o re test s i t ew a s c on s id e re d t o b e a c la y e y g la c ia l t i l l . T h e U K Build ing ResearchE s t a b l i s h m e n t ( B R E) ha d a l r e a d y e s t a b l i s h e d a test site o n t h eH o l d e r n e s s c o a s t at C o w d e n , 2 3 k m n o r t h east of Hul l , Humbers ide , toi n v e s t i g a t e t h e p r o p e r t i e s o f g l a c i a l t il l. A n a r e a of t h i s s i t e w a s m a d ea v a i l a b l e f o r t h e s e p i l e tests t o g e t h e r w i t h s i t e i n v es t i g at i o n d a t a ,i n c lu d i ng l a r g e s c a l e p l a t e tests a n d p r e s s u r e m e t e r r e su l ts .

T h e g r o u n d c o n s i s t s o f an e x p o s e d th ic k d e p o s i t of u n i fo rmo v e r c o n s o l i d a t e d , s a n d y s i l t y c l a y t i l l , w i t h i n t e r p o s e d l a y e r s o f s a n da n d g ra v el . B o r e h o l e s a nd c o n e p e n e t r o m e t e r r e s u l ts a d j a c e n t t o t h etest p o s i t io n i n d i c a t e z o n al w e a t h e r i n g o f t h e t i l l d o wn t o 4.5 m e t r e sa n d a d e n s e g r e y b l a c k s a n d a n d g r a v e l l a y e r at 10.5 me tre s . Mars landa n d P o we l l (1 9 8 0 ) g a v e a m o r e d e t a i l e d d e s c r i pt i o n o f t h e t i ll . Ac o m p a r i s o n o f t h e r e s i d u a l s t r e n g t h o f t h i s C o w d e n t i ll w i t h v a r i o u so t h e r c l a y t y p e s h a s b e e n p r e s e n t e d by L u p i ni et a1 (1981).

T a b l e 1 s ho w s t y p i c a l s o il s d a t a as a s s e s s e d f ro m in fo rma t io n p ro v id e dby t h e B R E, a n d f r o m t h e a b o v e r e f e re n c e s . F i g u r e 1 ( a ) s h o ws at y p i c a l b o r e ho l e lo g f o r t h e s i t e, a d j a c e n t t o t h e test p o s i t io n a n d ' l (b )t y p i c a l c o n e p e n e t r o m e t e r r ea di ng s.


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2.2 TEST PILE AND INS TRUME NT AT IONf

T h e t e s t p i le w a s o n e o f f o u r s t e e l p i pe p i l es ( 19 3 m m d i a m e t e r , 9 m m .wa l l th ic k n e s s b y 10.4m long) which w er e each jacked 9 .9m in t o theg r ou n d t o f o r m a s q u a r e g r o u p at 5 8 0 m m c e n t r e s . T h e y w e r e i n s t a l l e do p e n e n d e d w i th a c u t t i n g s h o e t o r e d u c e p lu gg in g. E x t e r n a l d u c t s w e r ew e ld e d t o t h e p il es t o p r o t e c t t h e i n s t r u m e n t s an d ca bl es . T h e l o c a ti o no f t h e i n s t r u m e n t s on t h e m o s t h e a v i l y i n s t r u m e n t e d p i le , us e d f o r t h e s es in g le p i l e tests, i s shown on F i gu re 2:

1T h e a x ia l lo a d a lo n g th e p i le wa s mo n i to re d by b r id g e we ld a b lee l e c t r i c a l r e s i s t a n c e s t r a i n g a u g e s , p o s i t i o n e d as pa irs , d i a m e t r i c a l l yo p p o s i t e e a c h o t h e r . T h e imp o s e d h e a d lo a d s we re mo n i to re d b y a loadc e l l b u i l t i n t o t h e l o ad in g s y s t e m . P o r e w a t e r a nd t o t a l l a t e r a l s oi lp r e s s u r e m e a s u r e m e n t s at t h e p i le /s o il i n t e r f a c e w e r e t a k e n bym i n i a t u r e e l e c t r i c a l t r a n s d u c e r s m o u n t e d in t h e d u c ts , f l us h w i t h t h eo u t e r f a c e .

P i l e h e a d v e r t i c a l a nd h o r i z o n t al d i sp l a c e m e n t s w e r e m e a s u r ed r e l a t i v et o a n i n d e p e n d e n t r e f e r e n c e b e a m b y l i n e a r d i s p l a c e m e n t t r a n s d u c e r s.P o r e p r e s s u r e s i n t h e s u r r o u n d i n g s o i l at 2, 6 and 12 rad ii and 3.5md e p t h w e r e m e a s u re d by h y d ra u l ic p i e z o m e t e r s o p e n t o t h e a t m o s p h e r e.

A l l i n s t r u m e n t s w e r e c a l i b r a t e d a nd c h e c k e d i n t h e l a b o r a t o r y , t oe n s u r e as f a r as p o s si b l e t h a t t h e y w o ul d p e r f o r m s a t i s f a c t o r i l y d u r in gt e s t i n g . W h e n e ve r p r a c t i c a l , t h e s a m e c a l i b r a t i o n p r o c e d u r e w a sr e p e a t e d on s i t e b e f o r e p i l e i n s t a ll a t i o n.

2.3 TEST P R O G R A M M E

T h e f o u r p i le s w e r e j a ck e d i n t o t h e g r o u nd o v e r an e i g h t d a y p e r i o d i nA p r i l 19 80 . A p i le w a s p it c h e d a n d t h e i n s t r u m e n t a t i o n c h e c k e d d u r i n go n e d a y , a n d t h e p i l e i n s t al l e d t h e n ex t . O n a v e r a g e i n s t a ll a t i on t o o k 6h o u r s t o r e a c h t h e f u l l e m b e d d e d l e n g t h o f 9.9 m e t r e s . . .


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O v e r a 4 1 d a y p e r io d f ro m th e e n d of j a c kin g , th e me a s u re d e x c e s s p o rep r e s s u r e at t h e p il e- so il i n t e r f a c e r e d u c e d t o w i t h i n 5 % of t h eh y d ro s ta t i c p re s s u re. Du r in g th i s p e r io d th e test f a c i l i t y w a sr e a r r an g e d t o a c c o m m o d a t e t h e lo a d a c t u a t i n g s y s t e m , a nd a r ig id s te ,e lp i l e c a p w a s w el d e d t o t h e h e a d o f t h e p i l es , l e a v i n g a c l e a r g a pb e t w e e n t h e p i le c a p a n d t h e g ro un d.

A s e r i e s o f c y c l i c l o ad tests, s u m m a r i s e d i n F i g u r e 3 , w e r e t h e n c a r r i e do u t on t h e p i le g r ou p . T h i s test wo rk , wh ic h is t o b e d i s cu s se d b yMc An o y et a1 (1982), iricluded a l o ad p a c k a g e e q u i v a l e n t t o t h es p e c t r u m o f a s e v e r e s t o r m , w i t h a p p l i e d l o a d s o f u p t o 4 8 % of t h ev e r t i c a l o r 6 % o f t h e h o r i z o nt a l e s t i m a t e d p u ll o u t c a p a c i t y (U ).tT h e e s t i m a t e o f U t w a s ba se d u p on t h e c a p a c i t y of a s ing le p i le o fi d e n t i c a l d i m e n s io n s i n s t a ll e d a n d t e s t e d o n t h e s a m e site a d j a c e n t t ot h e test p o s i t ion d u r in g th e s u mm e r o f 1 9 7 9 .

A t t h e c o n c lu s io n of t h e g r o u p tests i t w a s d e ci d e d t h a t i t w o ul d b e o fc o n s i d e r a b l e v a l u e t o d e t e r m i n e i n d iv i du al p i l e p e r f o r m a n c e u nd er e v e nm o r e d e m a n d i n g l o ad i n g c o n di t io n s . T h e p i le c a p w a s t h e r e f o r ed i s ma n t l e d , a n d t h e l o ad i n g s y s t e m p o s i ti o n ed o v e r o n e o f t h e f o u rpiles. A c o n s t a n t r a t e of e x t r a c t i o n test t o f a i l u r e w a s c a r ri e d o u t assoon as p o s s i b l e a f t e r t h e g r o u p tests t o d e t e r m i n e t h e u l t i m a t ec a p a c i t y of t h i s p il e. T h e v a l u e o b t a i n e d w a s t h e n u se d as t h e i n it i alc a p a c i t y o f the s in g le p i l e p rio r t o h igh l e v e l c y c l i c lo a d in g . Re s u l t sf r o m t h i s i n i t i al e x t r a c t i o n test a n d s u b s e q u e n t h ig h l e v e l c y c l i c lo a d in go f t h i s p i l e h a v e b e e n u s ed f o r t h e a n a l y si s p r e s e n te d . A s u m m a r y o ft h e test p r o g r a m m e c o n s i d e r e d i s s h o w n in F i g u r e 3(b).

E a c h of t h e t h r e e c y c l ic tests s h o wn wa s imm e d ia te ly fo l lo we d by ac o n s t a n t r a t e o f e x t r a c t i o n test t o d e t e r m i n e t h e u l t i m a t e p ul lo utc a p a c i t y . A r a t e o f d i s p la c e m e n t o f 0.75 mm /m in wa s u s e d, asr e c o m me n d e d b y Wh i ta k e r (19 6 3 ) fo r p i l es in c o h e s iv e so il s. T h e t e n s i l elo a d s a n d n u mb e rs o f c y c l e s ap p l i e d we r e n o min al ly :

M e a n C y c l i c C o m p o n e n t No. o f C y c l e s40 % UA - 20% UA 11,7754 0 % UB - 4 0 % UB 56430% Uc - 30% Uc 13,597


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fo r tests A, B a n d C r e s p e ct i v e l y, w h e r e U A i s t h e u l t i m a t e c a p a c i t yd e t e r m i n e d i m m e d i a t e ly b e f o r e test A , etc.

S in u s o id a l lo a d in g wa s p e r fo rme d at tw o f re q u e n c ie s (0.1 H a n dz1.OH ) t o m a i n t a i n s i m i l i t u d e of s t r a i n an d d r a i n a g e r e s p e c ti v e l y w i t hza p ro to ty p e pi le . P ro b le m s of s imi l i tu d e fo r s c a le d p i l e tests a r ed i s c u s se d b y Ga l l a g h e r a n d S t . J o h n (1 98 0) . T o e n s u re th a t v i s c o u sd a m p i n g di d n o t a f f e c t c y c l i c d i s p l a c e m e n t s w h e n d r a i n a g e w a s b e i n gm o d e ll e d, t e s t i n g w a s p e r f o r m e d u n d e r ' d i s p l ac e m e n t c o n t r o l f o r t h eh ig h e r f r e q u e n c y .

3.0 ANALYSIS OF FIELD TEST DATA

3.1 ULTIMATE TENSILE CA PA CI TY

3.1.1 Results

F i g u r e 4 s h o w s t h e s i x c o n s t a n t r a t e o f e x t r a c t i o n tests t o f a i l u r ep e r f o r m e d o n t h e p il e. T h e f i r s t t w o tests E l , E 2, w e r e c a r r i e d o u tb e f o r e t h e p i le h a d b e e n s u b j e c t e d t o hi gh l e v e l c y c l i n g an d w e r e u se dt o d e d u c e t h e u l t i m a t e t e n s i l e c a p ac i ty . T h e c h a n g e in t h e c a p a c i t ya f t e r a p p ly i n g t h e c y c l i c l oa d w a s a s s e ss e d by u s in g t h e c a p a c i t yr e c o r d e d o n e x t r a c t i o n tests E 3 t o E 6.T h e m a x i m u m l o a d f r o m test E l w a s 4 9 5k N , w h ic h w a s c o m p a r a b l e t o4 8 1 k N me a s u re d d u r in g test E 2. T h e f i r s t test, E l , w a s c a r r i e d o u t am o n t h a f t e r t h e c o m p l e t i o n of t h e g r ou p tests, a n d t h e s e c o n d test, E2,w a s p e r f o r m e d a m o n t h l a t er , o n e d a y b e f o r e t h e s t a r t o f t h e c y c l ictests. T h e s l o p e s of t h e l o a d d i s p l a c e m e n t c u r v e s a r e h o w e v e rc o n s i d er a b l y d i f f e r e n t . T h e f i r s t c u r v e w a s n o n- li n ea r o v e r t h em a j o r i t y o f i t s l e n g t h a n d p e ak c a p a c i t y w a s r e a c h e d at 5.2mmd i s p l a c e m e n t . T h e s e c o n d c u r v e w a s li n e a r u p t o o v e r 8 0 % o f t h eu l t i m a t e c a p a c i t y , w h i ch w a s r e a c h e d a t 3 .2mm disp lacement .

. .E x t r a c t i o n test E 3, p e r f o rm e d i m m e d i a t e ly a f t e r c y c l i c test A,i n d i c a t e d a d e c r e a s e i n u l t i m a t e l o a d c a p a c i t y , t o 4 57 kN . E x t r a c t i o ntest E 4 , a f t e r c y c l i c test B, i n d i c a t e d a f u r t h e r d e c r e a s e t o 4 00 kN . T h e


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l a s t t w o e x t r a c t i o n t e s t s , E 5 a n d E6 , s h o we d a s l ig h t in c re a s e ofu l t i m a t e c a p a c it y . T h e s h a p e of t h e l o ad - d is p la c em e n t c u r v e s a r el i n e a r o v e r 8 0 % o f t h e i r r an g e. T h e c o rr e s p o n d in g d i s p l a c e m e n tr e q u i r e d t o m o b i l i s e t h e s e v a l u e s w e r e r e a s o n a b l y c o n s i s t e n t at a b o u t2.5mm.

3.1.2 P re d ic t io n s o f U l t im a t e T e n s i l e Ca p a c i t y

T h r e e c o n v e n t i o na l m e t h o d s of p r e d i c t i n g u l t i m a t e p i le c a p a c i t y h a v eb e e n a s s e s s e d ; t h e A l p ha , B e t a , a n d L a m b d a m e t h od s . No n e o f th e s em e t h o d s d i s t in g u is h b e t w e e n t e n s i l e a n d c o m p r e s s i v e l oa d in g .

In u s in g th e m a n u mb e r o f a s s u m p t io n s h a v e b e e n ma d e b a s ed u po n s i t ei n v e s t i g a t i o n d a t a a n d e a r l i e r r e s u l t s o f p i l e l o a d d i st r ib u t io n . F i r s t l y i tis a s s u m e d t h a t t h e u p p e r m o s t 1 .0m o f t h e g ro u n d c o n t r i b u t e d n o t h i n gt o t h e s i d e r e s i s t a n ce , s i n c e s t r a i n g a u g e r e a d in g s i n d i c a te d t h a tr e s i s t a n c e w a s v e r y lo w i n t h i s r e gi on . S e c o n d l y t h e C u v s d e p t h p r o f i l e2c a n b e i d e a l i s e d to 170 kN/ m fo r de p t hs 1 .0m t o 4.5m and 1202k N/m fr om 4.5m to 10.0m de p th , as s u g g e s te d b y p re s s u re me te r testr e s u l t s (T a b le 1 ).

A lp h a Me th o dA P I R P 2 A ( 19 80 ) r e c o m m e n d s t h a t t h i s t o t a l s t r e s s m e t ho d i s t o b e u se df o r s o i ls o f m e d i u m t o l o w p l a s t i c i t y a n d c a n b e g e n e r a l l y a p p li e d t oo v e rc o n s o l id a te d c la y s . I t i s a s su m e d t h a t t h e u l t i m a t e s k in f r ic t i o n o nt h e p i le w a l l i s p r o p o r t io n a l t o t h e u nd r a in e d s h e a r s t r e n g t h , a c c o r d i n gt o t h e e q u at i on .

r s = a C uw h e r e 7 s = u l t i m a t e s h e a r s t r e s s o n pi l e w al lcx = 0.5 for t h e v a l u e s o f C u a s su m e d a b o v e .

T h e a l p h a m e t h o d p r e d i ct e d a s t a t i c t e n s i l e c a p a c i t y o f 4 10 kN .


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B e t a M e t h od'

A n u m b e r o f m e t h o d s h a v e r e c e n t l y b e e n d e v e l o pe d us in g t h e e f f e c t i v es t r e s s p a r a m e t e r s c', 9'. T h e s e m e t h o d s g e n e r a l l y r e q u i r e a n e s t i m a t eo f t h e r a d ia l s t r e s s o n t h e p i le s h a f t a f t e r set up. In hea vil yo v e r c o n so l i d a te d c l a y s t h i s i s d i f f i c u l t t o o b t a i n.T h e b a s i c e f f e c t i v e s t r e s s e q u a t i o n i n v o l v i n g P as s u g g e s te d b yBurland (1973) is ;

w h e r e P = K s t a n @ '@' = s o f t e n e d d r a i n e d a n g l e o f s h e a r r e s i s t e n c eK = c o e f f i c i e n t of l a t e r a l e a r t h p re s s u r e

S/Ov0 = i n si t u v e r t i c a l e f f e c t i v e s t r e s s

I t is a s su m e d t h r o u g h o u t t h a t c' = 0 d u e t o d i s t u r b a n c e o f t h e s oi l d u ri n gin s ta l l a t io n .

Me y e rh o f (1 9 7 6 ) h a s a n a ly s e d a l a rg e n u mb e r o f p i l e tests on bored andd r i v e n p i l e s t o d e r i v e P v a lu e s . He d e f in e d P a s a b o v e b u t f r o m h i sw o r k s t a t e s t h a t K s v a r i e s f r o m r o ug h ly K O t o 2 K O f o r d r i v e n pi le s, a n ds u g g e st s t h a t o n a v e r a g e K s m a y b e t a k e n as 1.5 KO in sti ff clays . A ne m p i r i c a l r e l a t io n s h ip b e t we e n th e o v erc on s ;l id a tion ra t io , p', and KO,is a l so sugges ted :-

KO = (l-sin@')@EiTw h e r e K O = c o e f f i c i e n t o f e a r t h p r e s s u r e at r e s t

OCR = o v e r c o n so l i d a t io n r a t i oH e n c e K s = 1.5 (1 - s i n@'){aM e y e r ho f 's f o r m u l a p r e d i c t e d a n u l t i m a t e p i l e c a p a c i t y of 2 70 kN .

L a m b d a M e t h od . .

T h e L a m b d a m e t h o d ( V i j a y v er g i ya & F o c h t , 1 9 7 2 ) h a s b e e n d e v e lo p e df r o m t h e s a m e p il e t e s t d a t a as t h e a l p ha m e t h o d , b u t i n c o r p o r a te s t h e


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e f f e c t o f p e n e t r a t i o n l e n g t h on u l t i m a t e s k i n f r i c t i o n , w h ic h isc a l c u l a t e d f r o m t h e e q u a ti o n

A = d ime n s io n le s s c o n s ta n t , wh ic h i s a f u n c t i o n o fp i l e p e n e t r a t i o n

A s = s u r f a c e a r e a o f p i le- = s i g n i fi e s a v e r a g e o v e r p i le l e n g t h

T h e L a m b d a m e t h o d p r e d i c te d a n u l t i m a t e p i l e c a p a c i t y of 4 30 kN.

3.1.3 D is cu s sio n o n U l t im a t e Ca p a c i t y

A s u m m a r y of m e a s u r e d a n d p r e d i c t e d u l t i m a t e c a p a c i t i e s i s g i v en i nT a b le 2 . T w o of t h e e x t r a c t i o n tests h a v e b e e n u s ed t o h i gh l ig h t t h em e a s u r e d c a p a c i t i e s b e f o r e a n d a f t e r f a i l u r e u n d e r c y c l i c lo a d in g ( T e s t sE l & E4 r e sp e c ti v e ly ) . I t i s p o s si b le t h a t t h e 1 9% c h a n g e i n m e a s u r e dc a p a c i t y d u r in g t h i s s e r i e s of tests w a s i n f lu e n c e d by t h e f o r m a t i o n o fc o n t i n u a u s s l i p s u r f a c e s , as 1 8 m m of c u m u l a t i v e d i s p l a c e m e n t w a sr e c o r d e d. T h e r e d u c t i o n i n c a p a c i t y w a s c l o s e t o t h a t w hi ch co u l d b ee x p e c t e d if t h e e f f e c t i v e an g l e o f f r i c t i o n of t h e s oi l r e du c ed t o t h eres idua l .T h e a l p h a a n d l a m b d a m e t h o d s p ro v i de d r e a s o na b l e e s t i m a t e s of t h eu l t i m a t e t e n s i l e c a p a c i t y , a n d c o m p a r e d p a r t i c u l a r l y w e l l w i t h t h em e a s u r e d c a p a c i t y a f t e r c y c l i c f a il u re . In o rd e r t o h a v e p r e d i ct e d t h em e a s u r e d c a p a c i t y b e f o r e c y c l i n g t h e a l p h a v a l u e s u se d w o u l d h a v e h a dto b e a p p ro x im a te ly 0.6. P re v i o u s case s t u d i e s i n d i c a te t h a t a l ph a i so f t e n h ig h e r t h a n t h e r e c o m m e n d e d v a lu e o f 0.5. F u r t h e r i t is g e n e r a l l ye x p e c t e d t h a t ja c ke d p i l es h a v e a g r e a t e r c a p a c i t y t h a n d r i v e n p i l e s .T h e g r e a t e r m e a s u r e d c a p a c i t y m a y also r e f l e c t t h e i n f lu e n c e of t h ei n s t a l l a t i o n of t h e a d j a c e n t t h r e e p i l e s d u e t o a c h a n g e of i n s i tu s t r e s s e sa c t i n g o n t h e p i le s h a f t .

T h e b e t a m e t h o d p r o v i d e d p o o r c o r r e l a t i o n b e t w e e n m e a s u r e d a n dp re d ic te d re s u l ts . Ho we v e r , M e y e rh o f (1 9 7 6 ) d o e s s h o w a w i d e s c a t t e rof p v a l u e s f r o m case r e c o rd s of p i l e s in s t i f f c la y s . I t h a s b e e n


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s ugge s te d th a t pa r t o f the r e a s on f o r th i s l i e s in th e va lue s of th ee f f e c t i v e s t r e s s e s a s s u m e d ( P a r ry & Swain, 19771, as i t is d i f f i c u l t t o ,a s s e ss t h e c o r r e c t v al ue s. T h i s u n c e r t a i n t y i s r e f l e c t e d i n t h e po orc o r r e l a t i o n no t e d a b o ve . H o w e v e r , g i v en a b e t t e r d e te r m i n a ti o n of t h ee f f e c t i v e s t r e s s e s to b e u s ed a n d t h e m a n n e r i n w hi ch t h e y c h a n g e d u et o i n s t a l l a t i o n a n d l o a di n g , t h e m e t h o d c o u ld i n p r i n c ip l e a ll o w f o r t h ee f f e c t s o f a d ja c e n t p il e s, me thod of in s ta l l a t ion a nd d i r e c t io n ofl oa d in g . B e t t e r c o r r e l a t i o n h a s b e e n a c h i e v e d i n s o f t c l a ys , i n w h i c he f f e c t i v e s t r e s s c a n b e m o r e a c c u r a t e l y a ss es se d .

D i f f i c u l t i e s w e r e e x p e r i e n c e d i n as s e s si n g t h e u nd r ai n e d s h e a r s t r e n g t hv a l u e s t o b e us ed i n t h e c a l c u l a t i o n s as t h e v a r i o u s i n si t u a n d l a b o r a t o r ytest m e t h o d s i n d i c a t e d v e r y d i f f e r e n t v a lu e s. M o st m e t h o d s i n d i c a t e dt h a t f o r 0-10 m e t r e d e p t h t h e t o p 4.5 m e t r e s of s o i l ha d a h ighe r Cuv a l u e t h a n t h e so i l b el ow . H o w e v e r , t h e m a g n i t u d e o f t h e d i f f e r e n c evar ied cons iderably .

RESPONSE DURING CY CLI C TESTS

D i s p l a c e m e n t s d u r i n g tests A, B and C a r e s ho w n i n F i g u r e s 5 a n d 6 .T e s t s A a n d C p r o d u c e d s u rp r is i ng l y s m a l l p e r m a n e n t d i s p l a c e m e n t s -0.12 and 0.14mm resp ecti vel y - a f t e r o v e r 1 1 , 00 0 c y c l e s d e s p i t e t h eh igh loa d l e ve l s a pp l i e d . A l ine a r r e la t ions h ip be tw e e n m e a nd i s p l a c e m e n t a n d l o g n u m b e r of c y c l e s i s e v i d e n t , w i t h t h e g r a d i e n t o ft h e l i n e b e i ng s l i g ht l y g r e a t e r f o r A t h a n f o r C , r e f l e c t i n g t h ed i f f e r e n c e in pe a k loa ds. Dur ing th e f i r s t 4b c y c l e s o r s o, t e s t Be xh ib i t e d a s i m i l a r l in e a r r e l a t i on s h i p , al t h o u g h t h e g r a d i e n t o f t h e l i n ew a s c on s id e ra b ly g r e a t e r t h a n f o r t h e o t h e r tests. Howe ve r , f r om 40c y c l e s o n w a rd s a n e n t i r e l y d i f f e r e n t r e s p o n se oc c u r re d . M e a nd i s p l a c e m e n t s i n c r e as e d d r a s t i c a l l y , a n d c o n t i nu e d t o d o s o up t o t h ep o i nt w h e r e t h e c h a n g e o f m e a n d i s p l ac e m e n t p e r c y c l e w a s i n c re a s i n gwi th e v e r y c yc le , ind ic a t ing p il e fa i lu r e. On c e th i s po int had be e nc l e a r l y p a s s e d test B w a s t e r m i n a t e d - only 564 c y c l e s h a d b e e nne c e s s a r y .


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N o c h a n g e i n c y c l i c d i s p l a c e m e n t o c c u r r e d w i t h i n a n y o f t h e t h r e etests, i n d ic a t in g th a t th e re wa s n o d e g ra d a t io n o f c y c l i c s o i l mo d u lu s ,c o n t r a r y t o t h e s u g ge s ti o n o f P o u l os ( 19 8 0) t h a t c y c l i c s h e a rd e g r a d a t i o n w a s a fu n c t i o n of s t r e s s l e v e l an d n u mb e r o f c y c le s . I t .i sp a r t i c u l a r l y s u r p r is i n g t h a t n o d e g r a d a t i o n i n c y c l i c s t i f f n e s s o c c u r r e ddur ing test B, e s p e c i a l l y w h e n t h e p i l e w a s f a i li n g as i s c l e a r ly s h o wn inF ig u re 6 (a ).

3.2.1 Ax ial Lo ad Di s tri but ion

F i g u r e 7 s h o w s t h e a x i a l l o a d do w n t h e p i l e un d e r c y c l i c an d s t a t i cload ing at t h e b e g in n in g a n d e n d of tests A , B a n d C. T h e re i s n os i g n i f i c a n t c h a n g e w i t h n u m b e r o f c y c l e s , i n d i c at i n g t h a t no l oa ds h ed d i ng o c c u r r e d du r in g cy c li n g. F u r t h e r m o r e t h e r e is n o c h a n g e int h e r e l a t i v e p r o p o r t i o n of l o ad t a k e n b y e a c h e l e m e n t du r i ng t h e s ec y c l i c tests a n d t h e u l t i m a t e v a l u e s g i v en b y e x t r a c t i o n test E3. It isc l e a r t h a t t h e a v e r a g e s h e a r s t r e ss , r e p r e s e n t e d by t h e r a t e of d e c r e a s eo f a x i a l l o ad w i t h d e p t h , v a r i e s c o n s i d er a b l y f r o m t h e 1 -3m d e p t h t o t h e3 -8 m d e p th , w h ic h is b ro a d ly c o n s i s t e n t w i th th e c h a n g e in s o il s t r e n g t hat a b o u t 4 -5 m b e lo w g ro u n d , as discu ssed in S ec ti on 3.1.2.

3.2.2 P o r e P r e s su r e s

Re a d in g s of e x c e s s p o re p re s s u re at t h e p i l e / s o i l i n t e r f a c e , t a k e n att h r e e d e p th s as s h o wn in F ig u re 2 during tests A, B a n d C s h ow e d t h a ti n i t i a l l o a d i n g g a v e r i s e t o a s m a l l e x c e s s p o r e p r e s s u r e . A m a x i m u m2i n c r e a s e o f 1 5 k N / m w a s m e a s u r e d at 3.15m leve l . For tests A a n dC, c y c l i c lo ad in g d id n o t l e a d to a n y b ui ld -u p in e x c e s s p o r e p re s s u r ea n d t h e i n i t i a l p r e s s u r e r ed u c ed . T h e r e w a s s o m e e v i d e n c e t o s ug g e s t as l i g h t i n c r e a s e i n e x c e s s p o r e p r e s s u r e d u ri n g t h e f i r s t 4 0 c y c l e s of test

20 t o a m a x i m u m o f 20 k N / m at th e 3 .15m leve l . A s pu l l-ou ti n c r e a s e d t h i s p r e s s u r e d i s s ip a t e d , a n d at t h e en d of a l l t h r e e testse x c e s s p o r e p r e s s u r e s w e r e c o n t i n u i n g t o d e cr e a s e . N o n e h a d q u i t er e t u r ne d t o z e ro , b u t t h e m a x i m u m v a lu e at t h e e n d o f c y c l in g wa s2d o wn t o a p p r o x im a t e l y 5 k N/m .


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3.2.3 P i le Head S t i f f ne ss and Ap par en t So il She ar Modulus

V a l u es o f p i le a n d s oi l s t i f f n e s s d e d u c e d f r o m t h e c y c l i c tests a r e s h ow ni n F i g u r e 8. T h e i n i t i a l s t a t i c s t i f f n e s s w a s r e a s o n a b l y c o n s i s t e n tb e t w e e n t e s t A , B a n d C , w h il s t t h e f i n a l s t i f f n e s s w a s s i m i l a r f o r t e s t sA a n d C b u t d ro p p ed b y 1 2 % in B. T h e e f f e c t i v e s t i f fn e s s r e du c e d ast h e p i l e g r a d u a l ly p u ll ed - ou t , t h e d r o p b e i n g d r a s t i c d u r in g test B.

T h e c y c l i c s t i f f n e s s e s r e m a i n c o n s t a n t t h r o u g h o u t e a c h test, b u t v a r yf r o m one test t o a n o th e r . F i g u r e 9 s h o w s a p lo t o f p i l e h e a d s t i f fn e s sv e s u s lo a d ra n g e (i.e. ma x imu m m in u s min imu m h e a d lo a d ) fo r th e th r e ec y c l i c tests. I t a p p e a r s t h a t l o ad r a n g e a n d h e n c e s t r e s s r a n ge , h a sb e e n t h e d o m i n a n t f a c t o r i n t e r m s of c y c l i c st i f f n e s s , r e f l e c t i n g t h en o n - lin ea r i ty o f th e s o i l s t r e s s - s t r a in c u rv e , p a r t i c u l a r ly at high loadlevels . M e a n l o a d l e v e l a n d r a t e o f test w ou ld a l s o b e e x p e c t e d t oi n f l u e n c e c y c l i c s t if f n e s s, b u t a r e n o t t h o u g h t t o b e s i g n i fi c a n t in t h i scase. F o r e x a m p l e , t h e h i g h e s t l o a d in g r a t e , w h ic h o c c u r r e d d u r in g testB , w ou ld b e e x p e c t e d t o p r o d u c e t h e h i g h es t c y c l i c s t i f f n e ss , w h e n i nf a c t test B e x h i b i t s t h e m o s t f l e x i b le r e s po n s e.

T h e a p p a r e n t s h e a r m o d ul us of t h e s o il at t h e pi le /s oi l i n t e r f a c e h a sb e e n d e r i v e d f o r a n e l e m e n t o f s o il at 4.5m d e p t h a n d e xh i b i t s t h e s a m et r e n d as p i le h e a d s t i f f n e s s ( F i g u r e 8). T h e a p p a r e n t s h e a r m o d u li2d e r i v e d , w h ic h r a n g e f r o m 50-76 MN/m , a r e 3 t o 7 t i m e s g r e a t e rt h a n v a l u e s d e t e r m i n e d f r o m p l a t e a n d p r e s s u r e m e t e r tests, T a b l e I .S i m i l a r b e h a v i o u r w a s o b se r v e d by G a l l a g h er & ' S t. J o h n f r o m p il e t e s t son t h e s a m e site. T h i s i s t o b e e x p e c t e d as t h e s h e a r s t r a i n d u ri ng t h etests wa s c o n s id e ra b ly lo we r th a n th o s e p ro du c e d b y mo s t in s i tu t e s t in g .

NUME RICAL ANAL YS IS OF LOAD-DISPLACEMENT BEHAVIOUR

O n e m e t h o d o f e s t i m a t i n g t h e l o a d - d is p l a c em e n t b e h a v i o u r o f a pi le i st o u s e a d i s c r e t e e l e m e n t t e ch n i qu e . T h e s o il is m o d e ll e d as a s e r i e s ofnon- l inear g round spr ings , ch ar ac te r ise d by IT-Z cur ves ' re la t ing p i led i s p l a c e m e n t t o m o b i l i s e d s h e a r s t r e s s . T h e p i l e i s d i v i d e d i n t o e l a s t i ce l e m e n ts a c te d o n by th e r e l e v a n t g ro u n d s p rin g. A b e a m-c o lu mnc o m p u t e r p r o g r am c a n t h e n b e u s ed t o d e t e r m i n e t h e p i le h e a d


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l o a d- d is p la c e m en t c u r v e . R e s u l t s f r o m t h e e x t r a c t i o n tests h a v e b e e na n a l y s ed t o d e r i v e e x p e r i m e n t a l T-Z c u r ve s . R e s u l t s f r o m e x t r a c t i o ntest E 4, w h ic h p r o d u ce d t h e l o w e s t u l t i m a t e c a p a c i t y , w e r e c o n s i d e re dt o b e of g r e a t e s t i n t e r e s t , a nd a r e p re s e n t ed h er e .

3.3.1 De r iva t ion o f T -Z Cur ve s f r o m Ex pe r im e n t a l D a t a

T h e p i le w a s d i vi d e d i n t o s e v e n e l e m e n t s as shown in F i gu re 10 . Us ingt h e m e a s u r e d d r o p i n a x i a l l o a d a c r o s s a g i v e n e l e m e n t , t h e a v e r a g es h e a r s t r e s s o n t h a t e l e m e n t w a s c o m p u t ed . D i s pl a ce m e n t, z, of ane l e m e n t w a s f ou n d f r o m t h e m e a s u r e d p il e h ea d d i s p l a c em e n t a nd t h ea x i a l l o a d d o w n t h e p i l e;

whe r e Q( x ) = a x i a l l o ad i n t h e p i l e at a n y d e p t h xA = s e c t i o n a l a r e a o f p i l eE = e l a s t i c m o d u l us of p i l e m a t e r i a l= = p i l e h e ad d i s p l a c e m e n t .

3.3.2 Re sul t s and Pr ed ic t io ns

F r o m e x t r a c t i o n test E 4 , t h e d e v e l o p m e n t o f s h e a r s t r e s s on e a c he l e m e n t f o r f o u r l o a d l e v e l s ( a ) - ( d ) a r e s hown on F ig u r e 11. Loa d l e ve l( d) r e p r e s e n t s t h e a p p r o x i m a t e u l t i m a t e c a p ac i t y . T h e co r r es p o nd i n gd i s p l a c e m e n t s of e a c h e l e m e n t a r e a l s o s ho w n . U s in g i n f o r m a t i o n oft h i s t y p e t h e T -Z c u r v e s fo r e l e m e n t s 3-6 h a v e b e e n p l o t t e d on F i g u r e12. A ls o s hown a r e ' p r e d ic te d ' c u r ve s , wh ic h ha ve be e n p r oduc e d f r omthe wor k by Coy le & Re e s e ( 1966 ) , who s ugge s te d a s e r i e s o f T -Z c u r v e sf o r p i l es in s t a ll e d i n c o h e s i v e s oi ls . T h r e e s t a n d a r d c u r v e s w e r ep r opos e d f o r va r y ing s oi l de p th s , e a c h be ing p r e s e n te d in t e r m s ofu n d r a i n e d s h e a r s t r e n g t h , a f t e r a c o r r e ct i o n t o t a k e i n t o a c co u n t t h eeffect o f p i l e i n st a l l at i o n . T h e p r e d i c t e d c u r v e s of F i g u r e 1 2 h a v e b e e np r oduc e d u sing t h e in -s itu und r a ine d s he a r s t r e n g th p r o f i l e a s s ume d inSec tion 3.1.2.


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Vij ayv er giy a (1 977) deve loped a d i f f e r e n t a p p r o a c h f r o m r e s u l t s o f l oa dt e s t s on compress ion p i les . I t w a s s u g g e st e d t h a t t h e e q ua t io n :

= T ( 2 \ IZ/ZcZ/Zc-l z c )m a x$ w h e r e T = a v e r a g e s h e a r s t r e s s on a n e l e m e n tT = u l t i m a t e a v e r a g e s h e a r s t r e s s on a n e l e m e n tm a xZ = v e r t i c a l d i s p l a c e m e n t of a n e l e m e n tZ c = c r i t i c a l d i s p l a c e m e n t o f a n e l e m e n t re q u ir e d t o

mo b i l i se T max .,

c o u l d b e u s e d t o d e f i n e T -Z c u r v e s f o r c o h e s i v e s o i l s u p t o f a i l ur e .F u r t h e r m o r e V i j a y v e rg i y a s u g g e s t e d t h a t T m a x s h ou l d b e d e r i v e du s i n g c o n v e n t i o n a l m e t h o d s f o r a x i a l c a p a c i t y , as d i scu ssed in S ec t io n3.1.3, an d t h a t 5-8mm is a t y p i c a l r a n g e o f Z fo r p i l e s o f 3 0 0 mmCd i a m e t e r a n d g r e a t e r . F i g u r e 1 3, p r o du c e d f r o m F i g u r e 1 2 s h ow s t h a tm e a s u r e d v a l u e s o f Z d e c r e a s e w i t h d e p t h f r o m a m a x i m u m o fCap p r o x im ate l y 1 .5 mm (0.8% o f p i l e d i am et e r ) t o 0 .4 mm. F ig u re 14s h o w s t h e d i f f e r e n c e i n s h a p e b e t w e e n n o r m a l i se d p l o t s o fV i j ayv erg iy a ' s eq u a t io n , m eas u red v a lu es , an d C o y le an d R eese ' s cu r v ef o r d e p t h s g r e a t e r t h a n 6 m e t r e s .

3.3.4 Discussion

I t i s c l e a r f r o m F i g u r e s 1 2 a n d 1 4 t h a t t h e T-Z c u r v e s e x h ib i t a bi l inearb e h a v i o u r , a n d t h a t t h e c u r v e s u g g e s t e d b y V i ja y v e rg i y a is i n a p p r o p r i a t ein th i s case. T h e c u r v e fo r e l e m e n t 3 i k l i c a t e s a s l i g h t l y s o f t e rr e sp o ns e t h a n t h e r e m a i n d e r, b u t t h i s i s c o n s id e r e d t o b e d u e t o t h ee x i s t e n c e o f a l ow r a d i a l s t r e s s o v e r t h e u p p e r p a r t o f t h i s e l e m e n t .E a c h c u r v e c a n b e d e s c r ib e d by t w o p a r a m e t e r s , T m a x a n d Zc.

T h e v a l u e s of T m a x p r e d i c t e d b y C o y l e & R e e s e f o r e l e m e n t 6 a g r e e sw i t h m e a s u r e m e n t s , b u t c u r v e s f o r e l e m e n t s 3, 4 an d 5 y i e ld g ro ssu n d e r e s t i m a t e s . I t w o u l d a p p e a r t h a t a meth o d o f p red ic t in g T m a xf r o m c o n e p e n e t r o m e t e r r e s u l t s i s d e si r a b l e , s i n c e s o m e c o rr e la t i. o n c a nb e o b s e r v e d b e t w e e n t h e s h a p e of t h e u l t i m a t e s h e a r s t r e s s d i st r ib u t io nof F i g u r e 1 ( a ) , a nd t h e s l e e v e f r ic t i o n m e a s u r e m e n t s o f F i g u r e l (b ).


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2. T h e l o w e s t U v a l ue o cc u r re d i m m e d i a t e l y a f t e r t h e test B, whe n r-tt h e p i l e f a i l e d u n d e r c y c l i c l o a di n g , a n d t h e r e d u c t i o n w a s p r o ba b l y 'd u e t o a c o m b i n a t i o n o f c y c l i c l o a di n g a n d c u m u l a t i v ed i s p l a c e m e n s.

A c c u r a c y o f C o m p r e s s i o n P i l e M e t h o d s f o r D e t e r m i n i n g U t

3. G o od c o r r e l a t i o n b e t w e e n m e a s u r e d a n d p r e d i c t e d U t v a l u e s w a sa c h i e v e d u si n g t h e a l p h a a n d l a m b d a m e t h o d s , w h i ch e r r e d by10- 20% on th e c on s e r v a t iv e s ide be f o r e c yc l ing , a nd we r e wi th in7% of t h e m e a s u r e d v a l u e a f t e r c y c l i c f a il u re .

4. T h e b e t a m e t h o d p r o v i d e d a g r o s s u n d e r e s t i m a t e b e f o r e a n d a f t e rcycling.

R e s p o n s e D u r i n g C y c l i n g

5. Th e p i l e s u s ta ine d e nc o u r a g ing ly high l e ve l s of c yc l i c loa d ing ,pe a k ing at up to 60% Ut, w i th pe r ma ne n t d i s p la c e m e n ts of on ly0 .14mm af te r 11,000 cyc les .

6 . A t a h ighe r loa d l e ve l , pe a k ing at nomina l ly 80% Ut , a d r a m a t i cc h a n g e in b e h av i o ur o c c u r r e d a f t e r a s m a l l n u m b e r of c y c l e s , a n df a i lu r e f o l lowe d .

7. T h e c y c l i c s t i f f n e s s of t h e p i l e di d n o t v a r y w i t h n u m b e r o f c y c l e sin any of the tests, e ve n du r ing f a i lu r e .

8. No s ign i f i c a n t bui ld -up o f po r e p r e s s u r e due to c yc l ing wa sobs e r ve d .

9 . No loa d s he dd ing down the p i l e oc c u r r e d du r ing c yc l ing , e ve n atf a i l u r e

. .


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T-Z Curves

10. The r e la tio r i sh ip be t we e n mob i li s ed s he a r s t r e s s ( T ) a ndd i s p l a c e m e n t (2) on a p il e e l e m e n t w as l in ea r f o r e Zc, t h e' c r it i c a l ' d i s p l a c e m e n t . F o r % Zc, T r e ma i ne d a pp r o x im a te lyc o n s t a n t .

11. U l t i m a te s he a r s t r e s s , Tma x , p r e d ic te d by th e T -Z me t hod o fC o y l e a n d R e e s e u n d e r e s t i m a t e d m e a s u r e d v a lu e s i n t h e u p p erl e v e l s of t h e p il e, a p a r t f r o m t h e t o p m e t r e , w h i ch t o ok nos ign i f i c a n t loa d.

12. The d i s t r ibu t ion o f Tma x wi th de p th s howe d s ome c o r r e la t ionw i t h c o r e p e n e t r o m e t e r s l e e v e f r i c t i o n r e su l ts .

13. The c r i t i c a l d i s p la c e me n t r e duc e d wi th de p th , poss ib ly due t o a ninc r e a s e in c on f in ing p r e ss u r e .

14. C r i t i c a l d i s p l a c e m e n t s w e r e c o n s i d e r ab l y l e s s t h a n t h e v a l u e ss u g g e s t e d by C o y l e a n d R e e s e . T h i s m a y b e p a r t l y d u e t o t h e testpi le be ing of a s m a l l e r d i a m e t e r t h a n t h o s e f r o m w h ic h t h e d es ig nc u r v e s w e r e d e r i v e d .

F u t u r e W orkT h i s i n v e s t i g a t i o n w a s l i m i t e d t o t h e t e n s i l e b e h a v i o ur o f j a ck ed p i le s in o n es o il type. Cons ide r a b ly mor e r e s e a r c h i s ne c e s s a r y be f o r e e f f i c ie n t de signm e th od s c a n be r e l i e d on f o r dyna mic a l ly loa de d t e ns ion p il es . Th i s r e s e a r c hs h ou l d c o n c e n t r a t e o n t h e lo a d t r a n s f e r m e c h a n i s m , c r e e p a n d s e n s i ti v i t y ofs o i l s t o d y n a m i c l o ad s .

Taylor Woodrow and th e U.K. Bu i lding Re s e a r c h E s ta b l i s h me n t ha v e p r opos e da n e x t e n s i v e d ev e l o p m e n t p r o g r a m m e t o m e a s u r e t h e p e r f o r m a n c e o f d i f f e r e n tt y p e s o f p i l e s u n de r r e p r e s e n t a t i v e t e n s i l e a x i a l a n d l a t e r a l l oa d i ng c o n di t i o n s. .a n d t o assess a p p r o p r i a t e d e si g n m et h o ds . T h i s w i ll i n c o r p o r a t e a n d e x t e n dbo th o r ga n i s a t ions ' p r e s e n t wor k in th i s a r e a . ( Ne g o t ia t io ns wi th po te n t i a ls pons o rs f o r th i s p r o je c t a r e we l l a dva nc e d , a l though f u r t he r s pons o r s h ip i ss t i l l be ing s ough t ).


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A c k n o w l e d g e m e n t sT h e A u t h o r s w o ul d l i k e t o t h a n k t h e D i r e c t o r s of T a y l o r W o od ro w f o r t h e i r 'p e rmis s io n to p u bl is h th e s e r e s u l t s , t h e U.K. Bu i ld in g Re s e a r c h E s ta b l i s h m e n tf o r t h e u s e of t h e i r test s i t e an d s i t e in v e s t ig a t io n re s u l t s , a n d a l l Re s e a rc hL a b o r a t o r y p e r s o n n el i n v o l ve d i n t h e p r o j e c t.

L IS T OF RE F E RE NCE SAndersen , K. "Be h a v io u r o f C la y S u b j e c te d t o Un d ra in e d C y c l i c L o ad in g" .P ro c . Co n f . Be h a v io u r o f Of f s h o re S t r u c t u re s , T ro n d h e im, Vol.1, 1 97 6.

Bu r la n d , J.B. "S h a f t F r i c t i o n o f P i l e s in C la y - A S i m p l e F u n d a m e n t a lApproach ", G roun d En gin eer ing , Vol. 6 ,3 , 1973.

Coyle, H.M. & Re ese , L .C. "Load Trans fe r fo r Axia l ly Loaded P i le s in Clay" .Jn l ASCE, SM2, March 1966 .

Ca ra s , F .K . "T h e Be h a v io u r of T en s ion P i l e s fo r Of f s h o re Ap p l i c a t io n s w i thR e f e r e n c e t o a P a r t i c u l a r T e t h e r e d B u o y a n t S t r u c t u r e " , 2nd Int. Conf. onBe h a v io u r o f Of f s h o re S t r u c t u re s , L on d o n, 1 9 7 9 .

Gar as , F .K. and McAnoy, R.P.L. "Of fshor e P i l ed Foun da t io ns wi th Pa r t icu la rRe fe re n c e t o Be h a v io u r Un d e r Cy c l i c T e ns io n ", In t . S ymp . o n Ma r in e S o i lMechanics , Mexico 1980 .

Idriss , I.M., Dob ry, R. and Singh, R.D. "Non-L inear B eha vio ur of S o ft C la ysDu r in g Cy c l i c L o ad in g" . J n l . Ge o t . E ng . D iv n , AS CE , ~ o l . 04, No. GT 12, 1978 .

Lee, K.L. & Focht , J .A. "S t re n g th o f C la y S u b je c te d T o Cy c l i c L o ad ing t1.M ari ne Ge ote chn olo gy, Vol. 1 , No. 3 , 1976.

Lupini, J .F. S kin ner , A.E. and Vaughan , P.R. " T he D r a i n e d R e s i d u a l S t r e n g t hof Co he siv e Soils" . Ge ot ec hn iq ue 31, No. 2 , 198 1.

Marsland, A. and Powell , J .J .M. " C y c l i c L o a d in g T e s t s on 8 6 5 m m D i a m e t e rP l a t e s in S t i f f C l a y Ti ll ", P ro c . Int . S y mp . o n S o i l s u n d e r C y c l i c a n d T ra n s ie n tLoading, Vol. 2 , Swansea, 1980.


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M at lo ck , H., M ey er , P.L. an d Ho lm qui st, D.V. "Ax col 3: A P r o g r a m f o rD i s c r e t e E l e m e n t S o l u t io n o f A x i al ly L o a d e d M e m b e r s w i t h L i n e a r o rN o n- Li ne ar S u pp o rt s" . R e p o r t t o t h e A m e r i c a n P e t r o l e u m I n s t i t u t e , A us t in ,Te xa s , Ma r c h 1976 .

Me ye r ho f , G.G . "Be a r ing Ca pa c i t y a nd Se t t l e m e n t of P i l e Founda t ions " , J n l .G eo t. Eng. Divn., AS CE, Vol. 102, GT 3, 1976.

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Poulos , H.G. "Cy cl ic Axia l Respo nse of S ingle P i le" Jn l . Geot . Eng . Divn .ASCE , Vol. 107 No. G T l, 1981.

Randolph , M.F. an d Wroth, C.P. "Analysis of De fo rm at io n of Ve rti call yLo ad ed Piles". Jnl. Geot.Eng.Divn, AS CE, Vol. 104, No. GT 12, 1978.

-- S m i t h J.R. a nd Ta y lo r R.S. "The De v e lopm e n t o f Ar t i c u la te d Buoya n t Co lumnS y s t e m s as an a i d t o E c o n o m i c O f f s h o r e P r o d u c ti o n " P a p e r 2 66 , E u r o p e c 1 98 0.

Vij ayver g iya , V.N. "Loa d - Move me n t Ch a r a c t e r i s t i c s of P i le s" . Po r t s '77Co nf e r e n c e , Long Be a c h , Ca l i f o r n ia , 1977.

Vijayverg iya , V.N. a n d F o c h t , J.A . "A N e w W ay t o P r e d i c t t h e C a p a c i t y o fP i l e s i n C l a y u , O f f s h o r e T e c h n o l o g y C o n f e r e n c e , H o u s to n , 1 9 72,

A P I R P ZA , P l a n n i n g , D es i gn i n g an d C o n s t r u c t i n g F i xe d O f f s h o r e P l a t f o r m s ,API Washin gton D.C. 1980.W h i t a k e r , T. "The C o n s t a n t R a t e of P e n e t r a t i o n T e s t f o r t h e D e te r m i n a t io nof t h e U l t i m a t e B e ar i ng C a p a c i t y o f a Pile", Proc. Inst. Civ. Eng. Vol. 26, 1963.. .W hita ke r , T. a nd Cooke , R .W. " I nve s tiga t ion o f Sh a f t a nd Ba s e Re s i s t a nc e ofLa r g e Bor e d P i l e s in London C lay" , P r oc . Sympos ium o f L a r ge Sc a l e P il e s.Inst . Civ. Engs. London 1966.


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T a b l e 1. T y p ic a l S o i l P ro p e r t i e s 0-10 .0 m De p th s

* C a l c u l a t e d f r o m t h e e qu a t io n C u = (PL - PH0)/6.18, whereP L = l i m i t i ng p r e s s u r e & P H O = o r i g i n a l h o r i z o n t a l s t r e s s i n t h e g r ou n d.

+ A v e r a g e G f o r 1% s t r a i n0 1S e c a n t m o d ul us o v e r r a n g e P v O t o P V O+ (qU - P VO) ,w h e r eq u = u l t i m a t e b a s e p r e s s u r e & P v o = o r i g i n a l v e r t i c a l s t r e s s in t h e '

g round .

P r o p e r t y -O v e r c o n s o l id a t i o n r a t i oD e p t h t o g r o un d w a t e r

I n d e x P r o p e r t i e s

W a t e r C o n t e n tP l a s t L i m i tL iq u id L imi t

S t r e n g t h - D e f o r m a t i on P r o p e r t i e sU n d r a i n e d S h e a r S t r e n g t h (C u )

0.0 - 4.'5m depths4.5 - 10.0m

E f f e c t i v e S t r e n g t h P a r a m e t e r :

C6'@r l

S h e a r M o d ul u s

Va lu e

51m

16%20%40 %

170 K N / ~ ~120 K N / ~ ~

o027'24 O1 2 MN/m21 7 M N / m 2

C o m m e n t

) P r e s s u r e m e t e r) resu l t*

) Un d ra in e d t r i a x ia l) test r e s u l tR i n g s h e a r r e s u l tP r e s s u r e m e t e r r e s u l tt8 6 5 m m P l a t e r e su l t0


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T a b l e 2. S u m m a r y of U l t i m a t e T e n si l e C a p a c i t y

T e s t No .

E lE 4

Me a s u re dValue (kN)

4 9 5400

P r e d i c t e d V a l u e s ( k N ) a n dP r e d i c t e d I M e a s u r e d V a l u e s (%)

A l p ha L a m b d a B e t akN

410410

%

8 3102

kN

430430

kN

270270

16

8710 7

%

5 467


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S l e e ve F r i c t i o n ( l o 3 k ~ l2 ) Cone Resistance ( l o 3 k N l m 10.3 0.2 0.1 2 4 6 8 1 0

Depth( m l O

2.0-3.0-

4 ' 0 -5 . 06.0-7.0-8.0-

9 . 0 -10.0-

FIGURE 1 ( a ) B o r e h o l e L o g (b) C o n e P e n e t r o m e t e r L o g

SOIL DESCRIPTIONTOP SOlLWEATHERED DARKBROWN CLAY TlLLWEATHERED DARKBROWN STIFFFISSURED TlLL

WEATHEREDBROWN FlRM TlLLUNWEATHEREDDARK GREY BROWNFlRM TlLL

O L L PL10 % 20 30 40

1

r q%

'10C LAY10 20 30 40


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Ground Level

Pore PressureTransducer FlushWith Cover PlateTota l PressureTransducer FlushWith Cover Plate

Cover Plate

Strain Gaugeon Pile Wall

Cover Plate J \pr ess ure Transducer

FIGURE 2 Pi le Instrumentation


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17-7-80 4.8 -80 5 -8.80 6 -8.80Da t e

FIGURE 3. Load History o f the Piles (a) PreviousLoading During Group Test ( b ) SinglePile Test.


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Cyc l i c Test A Cyc l ic Test 0 Cy c l i c Test C.

5 30 15C u m u l a t i v e D i s p l a c e m e n t ( m m )

FIGURE 4 . Constant R a t e o f Extraction TestsTo Failure, El - E 6


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Cyclic

I d

1.0-

Test A

-_Y- Peak0o. o f Cyclese - MeanFIGURE 5 . P i l e H e a d D i s p l a c e m e n t s D u r i n g

C y c l i cTes t 0

(1942 193kN)hEE 0.5-CCaJEaJ 0U I ' I r - I ' ' I . Imda

No. o f CyclesV)i3 1.5-

1.0-

0.5-8

0

. - Mean CyclicTes t C(123 2,122 k N

I " " I ' 9 ' 1 a , I10 100 1,000 10,000No. o f Cycles


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Cycl ic Test I3

- a Cyc l i c Tesa - - - - s

Cyc l i c Test

Number Of Cyc l e s

Cyc l i c Test B~~Y~~~~~ k N 1

100 I ,000Number Of Cyc les( b )

1.5-

hE 1.0-+ Cyc l i c T e s t Ac -(194 t 97 k N 1Ea

FIGURE 6 Pile Head Displacements(a) Cyclic Amplitude

U ImdnV).- 0.5:,Crgar:

a

Cyc l i c Test(123 2 122 kN


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I Pile / S t a t i c , I P e a k , 1 U l t i m a t e

A x i a lL o a d( k N )

H e a dLoadT e s t

FIGURE 7 Axial Load Distributions During Testing.

B e f o r e D u r i n g I D u r i n g 'Cyc l ing 1 C y c l i n g E x t r a c t i o nA , C B / C A 0 E3


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l n l n a iS t a t i c F i n a l

- - - - .---

(K ) - S t i f f n e s s , D e r i v e d F r o m C R E T e s t s Over S a m e L o a d R a n g eG - A p p a r e n t S h e a r M o d u lu s a t M i d - D e p t h o f P i l e (.MN l r n 2 )

D e s c r i p t i o n o f M o d u l u sI n i t i a l S t a t i c L o a d i n gC y c l i cE f f e c t i v e , l o t h Cyc le

I 1100 t hI I250 t h

I I500 th1,000 'h10,000 t h ,IF i n a l S t a t i c U n l o a d i n g

FIGURE 8 Variations in Pile Head Stiffness andApparent Soil Shear Modulus

P 17

K - P i l e H e a d S t i f f n e s s I k N l m m

T e s t AK

262(252)255

(215)249231

220217

G76

T e s t B

2 5 5

K262(252)226

(198)2 1119813 950

T e s t CG

77K

251(256)242

(233 12332 28

2171962510 1 2 2 8

/

G63

.50


31/36


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ElementNo. Depth t oCentre

( m )-0.25 - m+0.5 -

NoLoad

TensileLoad

FIGURE 10 ( a ) Division o f Pi le ~ n t o E l e m e n t s( b ) R e p r e s e n t a t i o n o f T - Z Curves


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Pile Head Load

Depth (m I

Shear Stress ( k ~ l r n ~ )

a b c d0 100 200 300 40

P i l e H e a d Load ( k N)( b )

FIGURE 11 ( a ) D i s t r i b u t i o n of A v e r a g e S h e a r S t r e s s &( b) C o r r e s p o n d i n g E l e m e n t a l D i s p l a c e m e n t sa t V a rio u s S ta g e s D u r in g E x t r a c t i o n E4


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- Element 3

After Cycling, Test A

Predicted - _ - -- -___-C. ---c---------/-+---

I I 1 I

After Cycl ing,/Test A Predicted----& -CC-

IDepths l- 3 m 1

Displacement Z ( mm )FIGURE 12 Comparison Between Measured and

Coyle & Reese T - Z Curves.


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C r i t i c a l V e r t i c a l D i s p l a c e m e n t , Z c , ( m m ) '0.5 1.0 1.5I I

FIGURE 13 C r i t i c a l V e r t i c a l D i s p la c e m e n tVersus D e p t h


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KEY-easured, Element 3Measured ,Element 4

x Measured ,Element 5A Measured ,Element 6 .- easured ,Elements 3 - 6

--- Coyle & Reese ,Curve C '-- i jayvergiyab

FIGURE 14 Normalised T -Z Curves

mcanoy cashman purvis(major piles)

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