hammer details pile drivability

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CHAPTER 23 P i l e D r i v e a b i l i t y A na ly si s

Car l W Fenske, P.E. , Sen ior Geotech nica l Consu l t an tMcCle l land Engin eers , In c . Houston, TexasT . J . H i r s c h , P h .D ., P . E ., P r o f e s s o r o f C i v i l E ng i ne er i ngTexas A M U n i v e r s i t y , C o l l e g e S t a t i o n , T ex as

INTRODUCTION

The p i l e p e n e t r a t i o n s r e q u ir e d t o s u pp o rt t h e d e s i gn l o ad s f o r o f f s h o r e

s t r u c t u r e s a r e u s u a l l y o b t a in e d f rom u l t i m a t e p i l e c a p a c i t y c u r v e s d ev e lo p edby c om pu ta t i ons ba se d on s o i l c ond i t i on s as de t e r m i ne d by a ge o t e c hn i c a li n v e s t i g a t i o n s e e C ha pt er 2 1 ) . When t h i s p ro c ed u re i n d i c a t e s l a r g e p i l e sa r e t o b e i n s t a l l e d t o s u b s t a n t i a l p e ne t ra t io n s o r t h e s o i l c on d it io ns a r es uc h t h a t t h e p i l e s w i l l h av e t o p e n e t r a t e d e n se sa nd l a y e r s o r o t h e rs t r o ng s o i l s , a q u e s t i on ca n a r i s e w he th er t h e p i l e s c a n b e i n s t a l l e d t ot h e r e q u i r e d p e n e t r a t i o n by d r i v i n g o n ly . I n fo r ma t io n t o a s s i s t i n a nsw er -i n g t h i s q u e s t i o n may b e de ve lo pe d by a p i l e d r i v a b i l i t y a n a l y s i s .

The a n a l y s i s of p i l e d r i v a b i l i t y c o n s i s t s of t h r e e p h a se s o r s t e p s . Thef i r s t s te p i s t o u s e a n a n a l y s i s ba s ed on t h e one- d i m e nsi ona l wave e qua t i ont o e s t i m a t e t h e r e s i s t a n c e t h a t c an b e ov er co me by t h e p a r t i c u l a r hammer-p i l e - s o i l s y s t e m . The second s t ep i s t o e v a l u a t e t h e s p e c i f i c s o i l con-d i t i o n s a t t h e l o c a t i o n t o e s t i a a t e t h e r e si s za n ce t h a t t h e s c i l w i l l o f f e rt o t h e f o rc e d p e n e t r a t i o n of t h e p i l e . The t h i r d s t e p i s t o c om pa r e t her e s i s t a n c e t h e h am m er -p il e- so il s y st e m c a n o ve rc om e w i t h t h e r e s i s t a n c e


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t h a t t h e s o i l c a n o f f e r i n o r d e r t o o b t a i n a n i n d i c a t i o n w he th er t h e p i l e c a nb e d r i v e n t o t h e d e s i r e d p e n e t r a t i o n . E n g in e er s sh o ul d b e a wa re t h a t ad r i v a b i l i t y a n a l y s i s d oe s no t n e c e s s a r i l y p r od uc e a d e f i n i t e a nswe r t o t h ep i l e d r i v a b i l i t y q u es ti on . Cons id e rab le eng inee r in g judgement i s r e q u ir e d f o ra l l t h r e e s t e p s o f a d r i v a b i l i t y a n a l y s i s , a nd e ve ry o ne making a d r i v a b i l i t ya n a l y s i s may n o t a r r i v e a t e x a c tl y t h e same c o n c l u s i o n s . A d r i v a b i l i t y a n a ly s i sshould be made f o r each sp ec i f i c combina t ion of hammer, p i l e a nd s o i l c o nd i ti o nsb e in g c o n si d e r ed f o r a p r o j e c t .

23.2 WAVE EQUATION ANALYSIS

Th e i mp ac t of a p i l e d r i v e r r a m on a p i l e c a n b e r e p re s e n te d f o r a n a l y t i c a lpu r pos e s by t h e c oa x i a l i m pac t of a s h o r t r od a nd a l ong r od as shown byF i g 2 3 . l ( a ) . T h i s r a m i mp ac t r e s u l t s i n a s t r e s s wave s t a r t i n g f ro m t h e p i l eh ea d and t r a v e l l i n g down t o t h e p i l e t i p w he re i t i s r e f l e c t e d u pw ar d. T h isp r o c es s co n t i nu e s u n t i l a l l e ne rg y i n t h e f o r c e p u l se i s d i s s i p a t e d . T h eenergy i s d i s s i p a t e d by p l a s t i c s o i l d e fo r m at i on , s o i l d am pin g, i n t e r n a lm a t e r i a l d am ping i n t h e p i l e , a nd o t h e r l o s s e s . The m o t io n of t h e s t r ss wavei s de sc r ib ed by t h e one-d imens iona l wave equ a t i on shown on F ig 23 . l ( b) .

The idea o a p p l y i n g t h e wave e q u a t i o n t o p i l e d r i v i ng p o ss i bl y was f i r s tsugges ted by D V I s a a c s i n 1931 ). A c l o s e d f or m a n a l y t i c a l s o l u t i o n oft h e one-d ' imens iona l wave equa t io n fo r a r e a l hammer-pi l e - so i l sys tem i s d i f f i -c u l t i f n o t i mp o ss i bl e . I n 1 93 8, a s o l u t i o n a t t r i b u t e d t o E N Fox w a sp u b l i sh e d b u t t h e s i m p l i f y i n g a s su m p ti o ns n e c e s s a r y t o a c h i e v e t h i ss o l u t i o n r ed u ce d t h e v a l u e of t h e s o l u t i o n f o r a r e a l p i l e d r i v i n g p ro blem .


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I n t h e 1 9 5 0 1 s, E. A . L ~ m i t h ( ~ ) ( ~ ) ( ~ )evelop ed and proposed a s tep-by-s t e p f i n i t e d i f f e r e nc e s o l u t io n t o t h e d i f f e r e n t i a l e q ua ti on t h a t

c o u l d b e u s e d w i t h t h e h ig h- sp ee d d i g i t a l c om p ut er s e me rg in g a t t h a t time.T h is s o l u t i o n and t h e r a p i d l y i n c r ea s i n g a v a i l a b i l i t y of h igh -s peed d i g i t a lc o mp u t er s h a s l e d t o t h e w i d e sp r ea d u se o f t h e o n e -d i m en s i on a l wave e q u a t i o nt o a n a l y ze p r a c t i c a l p i l e d r i v i n g p ro bl em s 6 ) 7 )

F or a wave e q ua t i o n a n a l y s i s , t h e p i l e d r i v e r r am, c u s h i o n, d r i v ec a p , p i l e a nd s o i l shown o n t h e l e f t s i d e o f F i g . 23-2 a r e m od el ed as shown ont h e r i g h t s i d e . The ram i s f r e q u e n t l y r e p r e s e n t e d by a c o n c e n t r a t e d m a ss , t h ec u s h i o n by a w e i g h t l e s s s p r i n g , a nd t h e d r - iv e c a p by a second p o i n t mass . Thep i l e i s d i v i d e d i n t o s e g me n ts , e a c h r e p r e s e n t e d by a p o i n t m ss e q u al t o t h emass o f t h e seg men t an d by a s p r i n g o f s t i f f n e s s e q u a l t o t h e s t i f f n e s s of t h esegment .

S o i l r e s i s t a n c e i s m od el ed by e l a s t i c - p l a s t i c s p r i n g s a nd d a s h p o t s a c t i n gi n p a r a l l e l w i th t h e p i l e s t i f f n e s s s p ri ng s . The l o c a t i o n an d u l t i m a t e r e s i s t a n c eo f e ac h o f t h e s o i l s p r i n g s i s s p e c i f i e d s o a s t o r e p r e s e n t t h e e s t im a te dd i s t r i b u t i o n and t o t a l v a l u e of t h e s o i l r e s i s t a nc e . The t o t a l s o i l r e s i s t a n ce ,RU i s by d e f i n i t i o n t h e u l t i m a t e s t a t i c s o i l r e s i s t a n c e f o r c e ac t i n g on t h ep i l e d ur i ng d r i v i n g o r i mm ed ia te ly a f t e r d r i v i n g i s s t o pp e d. T h i s u l t i m a t es t a t i c s o i l r e s i s t a nc e d u r i n g d r i v i n g c a n b e r e l a t e d t o l o ad b e a r i n g c a p a c i t yby c o n s i d er i n g s o i l s et-u p a f t e r d r i v i n g ceases. I n t h e c a s e of c o h e s i o n l e s ss o i l , l i t t l e . if a ny se t- up c an n or ma ll y b e a n t i c i p a t e d . I n t h e c a s e of c o he s iv es o i l , f a c t o r s of 2 o r 3 f o r s e t - u p a r e n o t uncommon. The set- up f a c t o r i sr e l a t e d t o s o i l s e n s i t i v i t y and d e g re e of r em ol di ng i n f r i c t i o n .


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The fo l l o wi n g p a rag rap h s p re s en t a b r i e f d e s c r i p t i o n of t h e st ep -b y-s t e p f i n i t e d i f f e r e n c e s o l u t i o n t o t h e o ne -d im en si on al wave e q u a t i o n p ro po se dby f o r s i n g l e - a c ti n g s t e a d a i r hammers.

v a l u e f o r t h e t o t a l s o i l r e s i s t an c e RU i s s e l ec t e d and t h i s r e s i s t -a n c e i s d i s t r i b u t e d o n t h e s i d e a nd t i p of t h e embedded p o r t i o n o f t h e p i l e .Ca lcu la t ion s beg in when t h e ram co n t ac t s t h e hammer cush ion . he r a m i sa s s i g n e d a n i n i t i a l i mp ac t v e l o c i t y wh i ch i s b as ed o n t h e r a t e d e n e r gy f o r t h ehammer t h e weigh t o f t h e r a m and h amme r e f fi c ie n cy ; a l l o t h er masses a r eu s u a l l y a ss i gn e d a n i n i t i a l v e l o c i t y of z e r o. t i m e i n t e r v a l f o r i t e r a t i v ec a l c u l a t i o n s i s s e l e c t e d . C a l c u l a t i o n s d e s c r i b i n g t h e m o ti o ns of t h e m as se sa n d t h e c o mp r es s io n s of t h e s p r i n g s a r e pe rf or me d a t t i m e s c o r r e s p on d i ng t ot h e s e l e c t e d t i me i n t e r v a l s d u ri n g t h e ram impact even t . The i n t e r v a l t o b eused must be small r e l a t i v e t o t h e s h o r t e s t n a t u r a l pe r io d of o s c i l l a t i o n ofa d j a c e n t s p ri n g-m as s co m b in a t i on s w i t h i n t h e s y s t em i n o rd e r t h a t t h e movementsof t h e s eg me nt s ca n b e p r e d i c t e d a c c u r a t e l y a nd that t h e c a l c u l a t i o n s r em ai nm a th e ma t ic a ll y s t a b l e ; f o r s t e e l p i l e s t h e ti m e i n t e r v a l i s f r e q u e n t l y o n t h eo r d e r o f 1 /5 00 0 s e c f o r a p i l e s eg ment l e n g t h of 8 t o 10 f t .

F or o n e t i m e i n t e r v a l a se t o f c a l c u l a t i o n s i s p e r fo rm ed fo r each masso r s e gm en t s t a r t i n g w i t h t h e ram a nd p r o c ee d i ng t o t h e p i l e t i p . The c a l -c u l a t i o n s f o r e ac h mass a r e a s f o l l ow s :

1 C a l c u l a t e t h e new p o s i t i o n of t h e mass by ad di ng t h e i n i t i a l

p o s i t i o n a t t h e b e gi n ni n s of t h e t i n e i n t e r v a l t o t h e c ha ng e i np o s i t i o n w hi ch i s t h e mass v e l o c i t y m u l t i p l i e d by t h e time i n t e r -v 2 l


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2 . C a l c u l a t e t h e c o m pr es si on a n d f o r c e s i n a l l a d ja c en t p i l e s p r i n g s ,s o i l s p r i n g s and d a s h po t s u s i n g t h e a p p r o p r i a t e s t i f f n e s s a ndd a m p i n g c o e f f i c i e n t s

3 C a l c u l a t e t h e n e t f o r c e on t h e mass4 C a l c u l a t e t h e a c c e l e r a t i o n of t h e mass a s t h e f o r c e d i v i de d by

t h e m as s.5 C a l c u l a t e t h e new v e l o c i t y f o r t h e mass by adding t h e produc t o f

t h e a c c e l e r a t i o n and time i n t e r v a l t o t h e l a s t v e l o ci t y d e te r -mined.

The c a l c u l a t i o n p ro c ee d s s e q u e n t i a l l y w i t h t h e c a l c u l a t e d m o ti on s a ndf o r c e s f o r t h e end o f o ne t im e i n t e r v a l b ecoming t h e s t a r t i n g p o i n t f o r t h ec a l c u l a t io n s i n t h e f o ll ow in g i n t e r v a l . The p r o c e s s c o n t i n u e s u n t i l t h eco mpu ted p i l e t i p d e f l e c t i o n r e a c h e s a maximum an d b e g i n s t o d e c r e a s e , a tw h ic h t i m e t h e wave e q u a t i o n a n a l y s i s f o r t h e a ssu med v a l u e o f t o t a l s o i lr e s i s t a n c e , RU i s u s u a l l y c o n s i d e r e d c o m p l e t e . Net p i l e p e n e tr a t io n i su s u a l l y c a l c u l a t e d as t h e maximum gr os s movement of th e p i l e t i p l e s s t h ee l a s t i c t i p d e f l e ct i on . N e t p i l e p e n e t r a t i o n i s u s u a l l y c o n s id e r e d as t h epermanent s e t o f t h e p i l e f o r t h e s i n g l e blow. The i n v e r s e of t h e se t p e rblow i s t h e p e n e t r a t i o n r a t e , u s u a l l y e x pr e ss e d i n blow s p e r i n c h , o rblows pe r f o o t , f o r t h e i n i t i a l l y s e l e c t ed v a l u e of u l t i m a t e s t a t i c s o i lr e s i s t a n c e , R I n n or ma l p r a c t i c e , t h e ab o ve c a l c u l a t i o n s a r e r e p e a te duf o r s e v e r a l v a l u es of R a nd t h e r e s u l t s a r e su mm arize d o n a p l o t o f Ry uv e r s u s P e n e t r a t i o n R a t e B lo ws P e r F o o t ) , c a l l e d a bear in g graph , a s showni n F ig . 23-3. F ig . 23-3 shows t h a t t h e maximum s o i l re s i s t an ce t h a t can beovercome by t h i s hammer-p il e - so il sys tem i s a bou t 29 k i p s a nd depe nds t o


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some e x t e n t o n t h e p i l e p e n e t r a t i o n . B ec au se o f t h e complex i n t e r r e l a t i o nbetween parameters , i t g e n e r a l l y i s n o t w i s e t o a t t e mp t t o e x t r a p o l a t e t h ee f f ec t s of v a r i a t i o n i n a p aram e te r f ro m o n e h am mer-pi le -s oi l s y s tem t oa n o t h e r . Consequen t ly, a wave equat ion an a l ys i s shou ld be per fo rmed f o r as p ec i f i c h am mer-pi le - so il s y s tem u s i n g s p e c i f i c v a l u es fo r a s many of t h ep a r a me t e r s a s p o s s i b l e . Knowledge o f t h e p a ram e t e r s fo r t h e wave eq u a t i o na n a l y s i s i s impor tan t whether one i s g oi ng t o m ake t h e a n a l y s i s o r o n l yf u r n i s h t h e s p e c i f i c p ar am et er i nf o rm a ti on f o r t h e a n a l y s i s .

T h e i n p u t p a ram e t e r s fo r a wave eq u a t i o n an a l y s i s can b e d i v i d ed i n t ot h r e e g r ou p s c or r e s po n d in g t o t h e t h r e e p a r t s o f t h e ha mm er -p il e- so ils ys te m. The f o l l o w i n g d i s c u s s i o n of t h e p r i n c i p a l p a r a me t e r s i s d i r e c t e dpr im ar i l y toward th e sys tem used p redominan te ly i n o f f s h o r e c o n s t r u c t i o n ,namely steam hammers an d s t e e l p i p e p i l e s .

Hammer Pa ram ete rs. The p i l e dr iv in g hammer i s descr ibed by (1) t h er a t e d hammer energy , (2 ) t h e weigh t o f t h e r a m o r s t r i k i n g p a r t s , 3 ) t h eef f i c i en cy o f t h e hammer, 4 ) t h e we ig ht o f t h e dr i ve h ea d o r p i l e c a p , (5)t h e c a p b l oc k s p r i n g c o n s t a n t , a nd 6 ) t h e c o e f f i c i e n t s of r e s t i t u t i o n f o rt h e r a m h i t t i n g t h e ca pb lo ck and f o r t h e p i l e c a p- p il e c o n t a c t . T h e r a t edenergy and t h e r am we i g h t r e es ta b l i s he d by t h e make and model o f t hehammer and may be ob ta ined f rom manuf ac tu rer s l i t e r a t u r e . In fo rmat i on fo rsome hammers u sed f o r o f f s h o r e p i l e d r i v i n g i s giv en i n Table 23-1. Thehammer e f f i c i e n c y , w hi ch r e l a t e s t h e a c t u a l e n er gy t o t h e r a t e d e ne rg y f o r t h ehammer, depends on th e cond i t io n of t h e hammer and t he op era t in g p rocedure a tt h e t i m e o f p i l e dr iv -i ng Hammer e f f ic ie nc y can va ry ov er a wide ran ge andc o n s i d e r a b l e e x p e r ie n c e o r e x p e r i m en t a l d a t a i s n eeded t o e s t i m a t e it S p e c i f i c


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in fo r mat i on on hammer e f f ic ie nc y usu a l ly i s no t av a i la b l e when a wave equa t iona n a l y s i s i s made but i t can be o b t a i n ed f ro m m easu rement s made i n t h e f i e l d .d u r i n g d r i v i n g ( s e e Ch a pt e r 25) . For hammers wi th a f ix ed ram s t r ok e , t h ee f f i c i e n c y p r o b a b l y i s n o t g re a t e r t h an ab o ut 9 0 p e rcen t even when i n ex ce l l e n tco n d i t i o n and o p e ra t ed p r o p e r l y and can be 30 p er ce nt o r l e s s i f t h e hammer i si n po or c o n d i t i o n o r n o t o p e r a t e d p r o p e r l y b ec a us e of i n s u f f i c i e n t s t e amp re s s u re a t t h e h ammer. E f f i c i e n c i e s o ve r 100 percen t have been measured fo rhammers having a v a r i a b l e s t r o k e o p er a te d a t le ss th an maximum st r ok e. Thiscan be a t t r i b u t ed fo r t h i s t y p e of hammer t o o v e r s t ro k e when o p e ra t ed a t al ow e r s t r o k e s e t t i n g . The h a m m e r e f f i c i e n c y e n t e r s t h e wave e q u a t i on a n a l y s i si n t h e c a l c u l a t i o n o f t h e v e l o c i t y of i mp ac t of t h e ram on t h e p i l e :

-

where h e f f e c t i v e r m s t r o k e ( f o r d ou bl e a c t i n g o r d i e s e lhammers t h e a c t u a 1 , p h y s i c a l s t r o k e i s n o t t h ee f f e c t i v e s t r o k e ) , L

e hammer e f f i c i e n c yg a c c e l e r a t i o n d ue t o g r a v i t y , L T ~

S i n c e t h e v e l o c i t y of i mp ac t f o r t h e ram i s a f u n c t i o n of t h e s q u ar e r o o t o ft h e hammer e f f i c i e n c y , t i s n o t s e n s i t i v e t o small c ha ng es i n e f f i c i e n c y .Most wave e quat i on an a ly ses a r e made us in g hammer e f f i c i e n c i e s of 6 t o 7 0p e r c e n t u n l e s s t h e r e i s s p e c i f i c k nowledge of a more r e a l i s t i c v a l u e f o r apar t icu la r hammer .

The dr i v e cap used w it h any t ype o r model hammer can vary depending ont h e t y p e and s i z e of p i l e t o be d r i v e n and o n c o n t r a c t o r p r e f e r e n c e s Con-s e q u e n t l y , i t i s p r e f e r ab l e t h a t a wave eq u a t i o n an a l y s i s b e made u s i n g s p e c i f i c


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n fo rm at io n f o r t h e p a r t i c u l a r d r i v e c ap t h a t i s t o b e u sed t o i n s t a l l t h ep i l e s . The c us h i on u s e d w i t h a g ive n hammer a l s o i s va r i a b l e . T he area andt h i c k n e s s of t h e cu s h i on an d t h e c u sh i o n m a t e r i a l u s ed i s a f unc t i on t o s om ee x t e n t o f t h e d r i v e c a p u se d b u t a l s o may d ep en d o n c o n t r a c t o r p r e f e r e n c e s .

The pr imary purpose of t h e cush ion ing mater ial i n t h e d r i v e c a p i s t ol i m i t i mp ac t s t r e s s e s i n t h e p i l e and i n t h e hammer. I n d o in g t h i s h ow ev era c e r t a i n a mount of t h e im pa ct e ne r gy i s absorbed in non l i ne a r de f o r m a t i on o ft h e c u s h i on mater ia l . I n t h e i d e a l i z a t i o n of t h e c us hi on material t h e l o a d-d e f o r ma t i o n b e h a v io r c a n b e r e p r e s e n t e d by two s t r a i g h t l i n e s w i th d i f f e r e n ts l o p e s a s s hown i n F i g . 23 4. The s l o p e o f t h e l o a d in g l i n e i s c a l l e d t h es p r i n g c o n s t a n t o f t h e c ap b l o c k w hi ch c a n be c a l c u l a t e d b y:

where 1k s p r i n g c o n s t a n t of c u s h i o n FL

c r o s s - s e c t i o n a l a r e a of c u s h io n L2

t t h i c k n e s s o f c u s h i o n L2E dynam ic m odul us o f e l a s t i c i t y of c us h i on mater ial FL

The s l o p e of t h e u n lo a d in g l i n e i s e q u a l t o t h e s p r i n g c o n s t a n t d i v i d e d by t h es q u a re of t h e c o e f f i c i e n t of r e s t i t u t i o n . I f t h e c us hi on i n t h e d r i v e ca pc o n s i s t s o f mo re t h a n o n e m a t e r i a l t h e n t h e s p r i n g c o n s t a n t of t h e c us h i o ni s obta ined by

w he r e n t h e num ber o f c us h i on i ng m a t e r i a l s i n t h e c a pb l o ck .


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The values of k e t c . a r e computed u s i n g t h e d yn am ic m od ul us of e l a s t i c i t y ,E , a nd t h e t h i c k n e s s , t f o r ea ch of t h e m a t e r i a l s i n t h e c u sh i on . As f o r . t h ed r i v e c a p we i g ht , t i s p r e f e r a b l e t h a t a wave e q u a t i o n a n a l y s i s b e made u s i n gi n fo r ma t io n f o r t h e s p e c i f i c c u sh io n t h a t w i l l b e us ed . The s p e c i f i c i n f o r m a t i onr e q u i r e d s t h e a r ea and th i ckn ess o f t h e cush ion and t h e dynamic modulus o fe l a s t i c i t y and c o e f f i c i e n t of r e s t i t u t i o n f o r t h e c u sh i on i ng m a t e r i a l . Dynamicmodulus of e l a s t i c i t y a nd c o e f f i c i e n t of r e s t i t u t i o n v a l u e s f o r some t y p i c a lc u s hi o n m a t e r i a l s a r e g i ve n n T a b le 23 .2 ; a d d i t i o n a l i n f o r m a t i o n o n t h e s ecu s h i o n p a ram e t e r s i s g iven i n Chap ter 25. For most o f f s h o r e p i l e s , t h e d r i v ec ap r e s t s d i r e c t l y on t h e to p of t h e p i l e . B ec au se n e i t h e r t h e d r i v e ca pn o r t h e p i l e t o p a r e p e r f e c t l y smooth, b ec au se t h e d r i v e ca p may n o t s ts q u a r e l y o n t h e p i l e t o p and b ec au se o f t h e d i s c o n t i n u i t y , t h e r e w i l l besome e ne r gy l o s s e s a t t h i s p o i n t d u r i n g d r i v i n g t h a t c a n be a p pr ox im at ed b yu s i n g a c o e f f i c i e n t of r e s t i t u t i o n of a bo ut 0 . 9 .

P i l e P a ra m et e rs . The fo l lowing inormat ion s r e q ui r e d t o d e f i n e a p i p ep i l e i n a wave e q u a ti o n a n a l y s i s : (1) p i l e d i am e te r ; 2 ) s ch ed u l e o f wa l lt h i c k n e s s v a r i a t i o n a nd l e n g t h of e a ch w a l l t h i c k n e s s ; 3 ) m od ul us of e l a s t i c i t ya nd u n i t w e ig ht of t h e p i l e m a t e r i a l ; and 4 ) l e ng th s of t h e i n i t i a l p i l es e c t i o n a nd e a ch add-on. F or t h e i d e a l i z e d p i l e as shown on Fi g. 23-2, t h ep i l e s d iv ide d in to segments which shou ld be approx imate ly t he s a m e l e n g t h .The segment l en g t h shou ld be on t h e o rd er o f 8 t o 1 0 f t f o r a s t e e l p i l e .T h i s means t h a t t h e number o f p i l e s ec t i o n s s p r o po r t io n al t o t h e p i l e l e n gt h .The s tep -b y -s t ep f i n i t e d i f f e re n c e s o l u t i o n of t h e wave eq u a t i o n may becomeu n s t a b le i f t h e s eg ment l e n g t h s made too lon g , w hi l e a s ho r t e r segmentle ng th j u s t adds to th e number o f segments and thereb y t o t he comput ing t ime.


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An o f f s h o r e p i l e u s u a l l y h a s a c o n s i d e r a bl e l e n g t h ab ov e t h e s o i l s u r f a c e .The p o s i t i o n o f t h e s o i l s u r f a c e s ho u ld be t a k e n i n t o a c c ou nt i n d i v i d i n g t h ep i l e i n t o s eg me nt s. The l e n g t h o f a n o f f s h o r e p i l e u s u a l l y s i n c r e a s e d i ns e c t i o n s , o r ad d-on s, as t s b e i ng d r i v e n . The p i l e f o r a wave e q u a t i o na n a l y s i s s ho ul d i n c l u d e t h os e s e c t i o n s t h a t w ould b e i n p l a c e f o r a g i v en p i l ep e n e t r a t i o n . The w e ig h t of t h e p i l e a nd t h e d i s t r i b u t i o n of w a l l t h i c k n e s s e scan h av e a v er y s i g n i f i c a n t e f f e c t in t h e maximum re s i s t an ce t h a t c an b eovercome by a gi ve n hammer-pile-soil syste m as determined by a wave equat ionan a l y s i s . C o n s eq u en t l y , t s i mp or ta nt f o r a d r i v a b i l i t y a n a l y s i s t h a t t h ep i l e u se d i n t h e wave e q u a t i o n a n a l y s i s s s i m i l a r i n make-up t o t h e a c t u a lp i l e t h a t w i l l b e dr i v en .

So i l Pa ram e t e r s . The p a ram e t e r s n a wave e q u at i o n a n a l y s i s t h a t a r er e l a t e d t o t h e s o i l i n c l u d e t h e f o l lo w i ng : 1 ) t h e e l a s t i c g ro un d c om pr es si on ,commonly r ef er re d t o as q u ak e , o n t h e s i d e s and a t t h e t i p of t h e p i l e ; 2 ) t h ed am pi ng co n s t an t o n t h e s i d e and a t t h e t i p of t h e p i l e ; 3 ) t h e t o t a l s t a t i c s o i lr e s i s t a n c e t o d r iv i ng f o r t h e p i l e ; and 4 ) t h e d i s t r i b u t i o n of t h e t o t a l s t a t i cs o i l r e s i s t a n c e t o d r i v i n g between t h e s i d e and t h e t i p of t h e p i l e . For t h ei d e a l i z e d p i l e shown o n F i g . 23-2, t h e f i r s t two p a ra m e te r s a r e r e p r e s e n t e d byt h e s p r i n g an d d as h p ot shown on t h e s i d e o f each e lem en t b el ow grou nd l i n e and a tt h e p i l e t i p . The l oa d- de fo rm at io n c h a r a c t e r i s t i c s of t h e id e a l i z e d s o i l s p r in gi s i l l u s t r a t e d i n Fig . 23-5 a ) . The sp r i ng can defo rm e l a s t i c a l l y to a maximumd efo rm a t i o n , 0 , a f t e r w hich t h e r e s no a d d i t i o n a l r e s i s t a n c e fr om c o n ti n u eddeformat ion . The va lu e o f Q s the quake which s t h e f i r s t s o i l p ar am et erg i v en ab ov e . The maximum s t a t i c r e s i s t a n c e fo r t h e s i d e o f each p i l e e lem en t and


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i t t h e p i l e t i p i s o b t a i n ed f ro m t h e l a s t two s o i l pa r a m et e r s l i s t e d a bo ve .W it h t h e maximum s t a t i c r e s i s t a n c e e s t a b l i s h e d , t h e s p r i n g c o n st a n t f o r t h es o i l s p r i n g a t t h e s i d e of e ac h p i l e e le me nt and a t t h e t i p i s g iven by :

where k = s o i l s p r in g c o n s ta n t , FL I

R = maximum s t a t i c s o i l r e s i s t a nc e a t s i d e ofp i l e e lement o r p i l e t i p ,

Q = s o i l q u a k e , L

The d a sh po t i n p a r a l l e l w i t h t h e s p r i n g a t t h e s i d e of e a ch el em en t a nd a t t h ep i l e t i p i s i n cl ud e d t o a cc o un t f o r t h e dy na mi c, o r v e l o c i t y - r e l a t e d , e f f e c t so n t h e s o i l c h a r a c t e r i s t i c s . The t o t a l r e s i s t a n c e of t h e s o i l s pr i n g anddashpot under dynamic load i s i l l u s t r a t e d on F i g. 2 1 - 5 b ) The r e s i s t a n c e oft h e d a sh p ot i s assumed t o b e d i r e c t l y p r o p o r t i o n a l t o t h e v e l o c i t y of t h eas s o c i a t e d s egm en t d u r i n g t h e di s p l acem en t . B ec au se of t h e d i r e c t p r o p o r t i o n a l i t yt o v e l oc i t y , t h i s r e s i s t an c e w i l l b e r e f e r r e d t o h e r e as l i n e a r v i s c o u s d am pin g.The r e l a t i o n b e tw ee n t h e dyn am ic s o i l r e s i s t a n c e a t t h e s i d e of a p i l e e l e m e n to r a t t h e p i l e t i p i s g iven by :

where Rd = dynamic s o i l r e s i s t a n c e ,

Rs = s t a t i c s o i l r e s is t a nc e , F1= s o i l damping co n s t a n t , TL

V = v e l o c i t y of t h e p i l e e l em en t, LT


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I n f or m a ti o n on t h e v a r i a t i o n of v a l u e s f o r s o i l q ua ke , Q and t h e s o i ldamping, J f o r v a r i o u s s o i l t y p e s a nd c o n d i t i on s i s n o t ex t e n s i v e and i ss t i l l t he su b j ec t of much s tudy . T h i s i n fo rm a t i o n i s g en e ra l l y o b t a i n ed b yf u l l - s c a l e p i l e l o a d t e s t s where t h e r e s i s t a n c e d ur i ng d r iv i n g i s measuredby o r e x t r a p o l a t e d fr om t h e l o a d t e s t r e s u l t s . Wave e q u a t i o n a n a l y s e s a r emade wi th vary ing va lue s f o r quake and damping t o de te rmine t hos e va l uesw hi ch g i v e t h e b e s t a gr ee me nt w i t h t h e m ea su re d r e s i s t a n c e t o d r i v i n g a ndt h e ob se rv ed r a t e of p e n e t r a t i on f o r t h e p i l e . h is torical summary ofquake and damping values i s g iven i n Ta b le 23-3 5) 8 ) 9 ) 10) 11) 12) . Values

o f damping p r e s e nt e d i n t h i s t a b l e a r e f o r l i n e a r v i s c o u s damping a s d e s cr i b edabove. Care must be used i n se le c t i ng val ue s of quake and damping fromsou rce s such a s those used f o r Tab le 23 .3. The quake and damping va lu esf ro m a g i v en s o u rce s h o u ld b e u s ed t o g e t h e r b ecaus e b o t h v a l u es p ro b ab l yw e re u s ed i n t h e i r d ev el op me nt f r o m f i e l d t e s t s . The values of quake andd am pi ng f o r each s o u rce on T ab l e 23 .3 d ep en d t o some ex t e n t o n t h e s o i l

an d p i l e co n d i t i o n f o r whi ch t h ey were d eve l o ped . For example , t h e va l uesof quake and damping deve lope d by Rouss el I 2) were f rom ana lyses o fd r i v i n g d a t a f o r l a r g e , h ig h -c a pa c it y o f f s h o r e p i p e p i l e s i n t h e Gulf ofMexico. B ec au se t h e t i p r e s i s t a n c e f o r t h e s e p i l e s i s small r e l a t i v e t ot h e s i d e r e s i s t a n c e , h a l vi n g o r d o ub l in g of t h e r e p o r t e d damping v a l u e s a tt h e t i p p ro ba b ly would n o t h av e s i g n i f i c a n t l y a f f e c t e d t h e c o r r e l a t i o n .Consequent ly , t h e va lu es f o r quake and damping proposed by Ro ussel mayn o t b e s u i t a b l e f o r s m a l l e r , s h o r t e r p i l e s , p a r t i c u l a r l y where t h e r e s i s -t a n c e i s p r i m a r i l y i n e nd b e a r i n g .

R es ea rc he rs a r e p ub l is h in g l a b o r a t or y t e s t r e s u l t s I 3 ) p r e s e nt i n g s o i ld am pi ng v a l u es b as ed o n n o n l i n ea r d amp in g n o t d i r ec t l y p ro p o r t i o n a l t o


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t o v e l oc i t y . C a re s h o ul d b e t ak e n i n u s i n g t h e s e v a l u es b ecau s e m os tcomputer programs would need mo di fi ca t i on t o hand le them prope rly . I nad d i t i o n , m o st o f t h e s e n o n l i n e a r v i s co u s damping v a l u es h av e n o t b eenc o r r e l a t ed w i t h l oa d t e s t r e s u l t s . E n g i n ee r i n g j u d g m en t s h o ul d b e u s ed t os e l e c t v a l u e s f o r qu ake and damping t h a t a r e most a p p r o p r i a t e f o r t h e p i l eand s o i l co n d i t i o n s b e i n g an a l y zed and t h e wave eq u a t i o n an a l y s i s com pu te rprogram being used.

23.3 RESISTANCE TO DRIVING OFFERED BY SOIL

The se co nd s t e p i n a d r i v a b i l i t y a n a l y s i s i s t o estimate t h e r e s i s t a n c e t h es o i l w i l l ov er co me when a p i l e i s fo r ced i n t o t h e g round by blows f rom t hed r i v i n g hammer. The s t a r t i n g p o i n t f o r t h e e s t i m a t i o n c a n b e a n u l t i m a t ep i l e c a p a c i t y c u r v e d ev el op ed f ro m a g e o t e c h n i c a l i n v e s t i g a t i o n . P ro ce -d u r e s f o r c om pu ti ng u l t i m a t e p i l e c a pa c i t y 1 4 ) 1 5 ) a l s o s e e Chap. 21 a r es e m i- e m p ir i c al i n n a t u r e an d a r e b as ed o n c o r r e l a t i o n s w i t h r e s u l t s f romp i l e l oa d t e s t s made s e v e r a l da ys a f t e r t h e p i l e s w ere i n s t a l l e d . For manys o i l s , p a r t i c u l a r l y c o h es i ve s o i l s , t h e u l t i m a t e p i l e c a pa c i ty s e v e r a l da ysa f t e r i n s t a l l a t i o n c a n b e s i g n i f i c a n t l y g r e a t e r t ha n t h e u l t i m a t e c ap ac i tyd u r i n g d r i v i n g a nd i mm ed ia te ly a f t e r d r i v i n g s t o p s . T h i s i s i l l u s t r a t e d byt h e lo ad t e s t r e s u l t s 16) shown on Fi g. 23-6 which show measured in cr ea se s i np i l e c a p ac i t y w i th t im e f o r s t e e l f r i c t i o n p i l e s i n c oh es iv e s o i l s . Theser e s u l t s s u gg e st th t t h e u l t i m a t e c a p a c i t y of a f r i c t i o n p i l e i n c l a y s i s n o t

o b ta i n ed u n t i l a month o r more a f t e r d r i v i n g . T he re a r e o t h e r s o i l s , g e n e r a l l yc o he s io nl e ss s o i l s , t h a t e x h i b i t r e l a t i v e l y l i t t l e change i n u l t i m a tec a p a c i t y w i t h ti m e a f t e r d r i v i n g . One method t o e s t i m a t e t h e r e s i s t a n c eo f f e r e d by t h e s o i l d u r i ng p i l e d r i v i n g f rom t h e u l t i m a t e p i l e c a p a c i tysome t i m e a f t e r d r i v i n g i s t o e v a l u a t e t h e e f f e c t s of d r i v i n g o n t h e com-p on en ts of t h e s t a t i c p i l e c ap a c it y which a r e t h e f r i c t i o n a l r e s i s t a n c e on t h e s i d ea nd t h e end b e a ri n g on t h e t i p of t h e p i l e .


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S i d e F r i c t i o n . The p i l e - s o i l s t a t i c f r i c t i o n a l r e s i s t a n c e c an c ha ng ed u r i n g d r i v i n g a nd a f t e r d r i v i n g h a s c e as e d . The magni tude of t h i s change .

d ep e nd s t o some e x t e n t on t h e t y p e o f t h e s o i l . For p i l e s i n s a nd , t h es t a t i c r e s i s t a n c e d u ri ng d r i v in g u s u a l ly i s assu med t o b e e q u a l t o t h es t a t i c r e s i s t a n c e s e v e r a l weeks a f t e r d r i v i n g. There i s some f i e l d e v i -de nc e o f t h i s be c aus e when t h e r e i s a s i g n i f i c a n t d el ay i n d r iv i n g a p i l e i ns a nd , t h e r a t e of p e n e tr a t io n f o r t h e p i l e f r e q u e nt l y i s a b o ut t h e same a f t e rt h e d e l a y as t was j u s t b e f o r e t h e d e l a y .

F or many c l a y s , t h e s t a t i c f r i c t i o n r e s i s t a n c e d ur i ng d r i v i n g may b es i g n i f i c a n t l y le ss t h a n t h e s t a t i c f r i c t i o n r e s i s t a n c e a f ew weeks o r some-t i m e s e ve n h o u rs , a f t e r d r i v i n g . To i l l u s t r a t e t h i s , c o n s id e r F i g. 23 7w hi ch shows t y p i c a l i n s i t u an d r em ol de d s t r e n g t h p r o f i l e s f o r a no rm a ll y-c o n s o l i d a t e d c l a y . D ur in g d r i v i n g o f a l o n g o f f s h o r e p i l e , t h e c l a y c a n ber em olde d a l m os t c om pl e t e l y du r i ng c on t i nuou s d r i v i ng . The r e d uc t on i nf r i c t i o n a l r e s i s t a n c e a t a g iv en d e p th p ro ba bl y i s a f u n c t i o n of t h e l e n g thof p i l e th t ha s pa s s e d th t d e p t h a s s u gg e st e d by t h e f r i c t i o n f a t i g u et he o r y p r opos ed by ~ ee re m a' '' ). H owever , u n t i l t h e r e a r e m et hods t oe v a lu a t e t h i s , t h e s t a t i c r e s i s t a n c e d u ri n g d r i v i n g of l on g o f f s h or e p i l e si n c l a y s c a n b e e s t i m a t e d by a ss um in g t h e c l a y s t o b e c o m p l et e l y re mo ld ed .A f t e r d r i v i n g ce a s es , t h e p i l e - s o i l f r i c t i o n a l r e s i s t a n c e f o r many c l a y si n cr e as e s u n t i l i t a pp ro ac he s, a f t e r a f ew w eeks, t h e s t a t i c r e s i s t a n c e a se s t i m a t e d by o ne o f t h e c o m p u t at i o n a l p r o c e du r e s f o r u l t i m a t e p i l e c a p a c i t y .T h is c a n pr o du ce t h e d i f f e r e n t p i l e c a p a c i t i e s s hown on F i g . 2 3 8 . Ther a t i o of t h e f i n a l c ap a ci t y t o t h e s o i l r e s i s t a n c e d u ri ng d r iv i n g i s c a l l e ds o i l s et -u p . I n f o r m a t i o n f ro m a l i m i t e d number of t e s t s o n f u l l - s c a l e


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p i l e s d r i v e n i n c l a y i n d i c a t e s t h a t t h e m a gn it ud e o f t h e s et -u p may b eo n t h e o r d e r of t h e r a t i o of t h e u n d i s tu r b e d t o t h e rem old ed s o i l s h e a rs t r e n g t h , r e f e r r e d t o a s t h e s e n s i t i v i t y o f t h e c l a y . T hi s l e n d s somec r e d e nc e t o t h e u s e of t h e rem old ed s h e a r s t r e n g t h o f c l a y s t o e s t i m a t e t h ef r i c t i o n r e s i s t a n c e d u r in g d ri v i n g i n c l a ys .

End Bearing. End b e a r i n g r e s i s t a n c e t o d r i v i n g of a p i l e p ro b ab ly i sr e l a t e d t o t h e u n d i s tu r b e d s h e a r s t r e n g t h of t h e s o i l , a nd u n i t e nd b e a ri n gr e s i s t a n c e c a n b e com pu ted on t h i s as s um p t io n . The p ri ma ry v a r i a b l e i n t h eend b e a ri n g r e s i s t a n c e i s t h e e f f e c t i v e end a r e a . For p i l e s w it h s o l i dc r o s s - s e c t io n s o r w i th end c l o s u r e s , t h e e f f e c t i v e end a r e a i s t h e g r o s send a r e a . Most o f f s h o r e p i l e s , h ow ev er , a r e s t e e l p i p e s d r i v e n w i t h o pe nends . I n t h e i n i t i a l d r i v i n g , t h i s p i l e t yp e u s ua l ly w i l l core t h e s o i lso t h a t t h e s o i l s u r f ac e i n s id e and o u t s i d e t h e p i l e a r e a t about t h e samel e v e l . The end b e a r i n g i n t h i s c a s e i s o n l y o n t h e c r o s s - s e c t i o n a l enda r e a of t h e p i p e wal ls . When t h e p i l e i s d r i v e n t o g r e a t e r p e n e t r a t i o n s o rposs ibly when i t e n c o u nt e r s a s t r o n g e r m a t e r i a l s u ch a s sa nd o r h ar d c l a y ,t h e p i l e m y plug s o t h a t t h e s o i l i n s i d e t h e p i l e moves w i th t h e p i l e a si t moves downward. Wi th t h e p r e s e n t s t a t e o f t he a r t , i t i s d i f f i c u l t t op r e d i c t when a p i l e w i l l p l u g , b u t i t pr oba b l y i s t r u e t h a t a d ee p-p e n e tr a t in g p i l e w i l l r e ac h r e f u s a l t o d r i v i n g wi t hi n a f ew f e e t a f t e r i tp l u g s . D u ri ng c o n t i n u o u s d r i v i n g i n c l a y , l a r g e di am et er p i p e p i l e s a r en o t l i k e l y t o p lu g. I f d r i v i n g c e a s e s f o r s e v e r a l ho u r s o r d a y s , h ow ev er ,a p l ug c a n o r m d u e t o s o i l s et -u p .

t c a n b e s e e n fr om t h e ab ov e d i s c u s s i o n t h a t t h e r e i s no uniquer e s i s t a n c e d u r in g d r i v i n g f o r a p i l e . We c a n, however, t a k e t h e s o i l


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i n f o r ma t i o n a nd d ev el op e s t im a t e d r e s i s t a n c e d u r in g d r i v i n g f o r s e v e r a lc o n d i t i o n s that c ou ld d ev el op du r i n g t h e i n s t a l l a t i o n . Curve 1 on Fig.23-9 i s t h e e s ti m a t ed r e s i s t a n c e d ur i n g c o nt i nu o us d r i v i n g . T h i s c u r ve i so b t a i n e d by co mp ut in g s i d e f r i c t i o n in c l a y s u s i n g r em ol de d s h e a r s t r e n g t h s ,s i d e f r i c t i o n i n s an ds us in g t h e s t a t i c s i d e f r i c t i o n , and t h e end b e ar in go n t h e p i l e w a l l end a r e a n o p l u g ) . There i s no r e l i a b l e way t o d i s t i n g u i s hbe tw een t h e f r i c t i o n o n t h e o u t s i d e of t h e p i l e f rom t h a t from t h e s o i lcolumn i n s i d e t h e p i l e . The p r oc e du r e f o r e s t i m a t i n g s i d e f r i c t i o n gi v e na bo ve u s i n g t h e o u t s i d e s u r f a c e a r e a of t h e p i l e i s c o ns i de r ed t o r e p r e s e n tt h e combined s i d e - f r i c t i o n a l r e s i s t a n c e f o r t h e p i l e d u ri n g c on ti nu o usdr iv in g . Curve 2 on F ig . 23-9 i s t h e e s ti m at e d r e s i s t a n c e d u ri n g d r i v i n gi f t h e p i l e p l u g s s o t h a t t h e s o i l i n s i d e t h e p i l e moves downward w i t h t h ep i l e . T h i s c u r v e i s o b ta i ne d by u s i ng t h e same s i d e f r i c t i o n a l r e s i s t a n c ea s f o r Cu rv e b u t w i th end b e ar i n g on t h e g r o s s end a r e a o f t h e p i l e .Curve on Fi g. 23-9 i s t h e computed u l t i m a t e c o m p re s si v e c a p a c i t y f o r t h ep i l e and i s a n e s t i m a te of t h e r e s i s t a n c e t o d r i v in g a f t e r a l on g de l ay i n t h ed r i v i ng . Cur ve s 1 a nd 3 o n F i g . 23-9, t h e r e f o r e , r e p r e s e n t t h e r a n g e ofe s t im a t e d r e s i s t a n c e t o d ri v 2n g t h a t m ig ht b e e nc ou nt er ed i n t h e i n s t a l -l a t i o n of a p i l e by d r i v i n g .

INTERPRETATION OF DRIV BILITY

The i n t e r p r e t a t i o n of d r i v a b i l i t y c o n s i s t s of comparing t h e r e s i s t a n c e t h a t

can be overcome by a given hammer-soi l -pi le s ys te m t o t h e r e s i s t a n c e t h a tt h e s o i l w l l o f f e r t o p i l e p e n e t r a t i o n . One method t o i n t e r p r e t d r i v a b i l i t yi s i l l u s t r a t e d o n F i g . 23-9. C ur ve s 1 , 2 an d 3 r e p r e s e n t t h e e s t i m a t e dr e s i s t an c e t h a t t h e s o i l w l l o f f e r t o p i l e d r i v i n g u nd er d i f f e r e n t c o n d it i o n s


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a nd c i r cu m st a nc e s t h a t m ig ht b e e n co u nt er ed d u r i n g t h e p i l e i n s t a l l a t i o n .I n f o r ma t i o n o n t h e r e s i s t a n c e that can be overcome by t h e hammer-pi le-soi lsys tem i s pr e s e n t e d on F i g . 23-3. Be c aus e o f da mage t o t h e p i l e - d r i v i n ghammer and o th er equipment wi t h har d d r iv in g , most hammer ma nu fac tu rer s andc on se qu en tl y p i l e i n s t a l l a t i o n c o n t r a c t o r s w i l l p l a c e a l i m i t t o t h e numbero f b lo ws p e r f o o t of p i l e p e n e t r a t i o n a t which they w i l l c o n t in u e t o o p e r a t ehammers f o r any gr ea t pe r io d of t ime . I f t h e a ss um p ti on i s made t h a t t h i sl i m i t i s 200 blows p e r f o o t , v a l u e s f o r t h e g r e a t e s t r e s i s t a n c e t h a t c a n b eovercome by t h e p a r t i c u la r hammer-p i le - so i l sys tem a t d i f f e r e n t d e p t h s ca nb e o b ta i ne d by t h e i n t e r s e c t i o n of t h e l i n e f o r 200 bl ow s p e r f o o t w i t h t h ec u r v e s o n F i g . 23-3. T he se v a l u e s a r e p l o t t e d a t t h e r e s p e c t i v e d e p t h s o nF i g . 23 9 and a r e u se d t o c o n s t r u c t t h e d as he d l i n e r ep r e s en t i ng t h e t r e n dw i t h p i l e p e n e t ra t i on f o r t h e r e s i s t a n c e t h a t c a n b e o ve rc om e by t h eha m me r -p i le - so i l s y s te m us e d f o r t h e wave e qua t i on a na l y s i s . T h i s t r e ndl i n e i n t e r s e c t s C urve a t a p e n e t r a t i o n o f a b o u t 210 f t a nd Cur ve 1 a t ap e n e t r a t i o n of a b o u t 330 f t . T h i s i m me d ia te ly i n d i c a t e s two f a c t o r s c o n c e rn i n gp i l e d r i v a b i l i ty . The f i r s t i s t h a t t h e r e s h ou ld b e no p ro bl em f o r t h i shammer t o d r i v e t h i s p i l e a t t h i s l o c a t i o n t o a p e n e t r a t i o n o f a bo ut 2 10f t The s ec ond f a c t i s t h a t e ve n u n d er t h e b e s t c i r c u m s t a nc e s t may notb e p o s s i b l e t o d r i v e t h i s p i l e w i t h t h i s hammer t o a p e n e r r a t i o n mo re t h a na b ou t 330 f t . F or p i l e p e n e t r a t i o n s be tw ee n 210 and 330 f t , p i l e d r i v a b i l i t yi s l e s s d e f i n i t e be ca us e t h e p e n e t r a t i o n t o w hich t h e p i l e c an be d r i v e nn a y d ep en d on f a c t o r s t h a t a r e no t e a s i l y p r e d ic t a bl e .

One f a c t o r t h a t i s n o t e a s i l y p r e d i c t a b l e i s p l ug g in g of t h e p i l e .There i s v er y l i t t l e i n fo rm at io n a v a i l a b l e a t t h i s t im e t o p r e d i c t w i th a ny


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c e r ta i n t y i f a p i l e w i l l p l ug d u r i n g d r i v i n g o r t h e d e p th a t w hic h tmight p lug . The t r e nd l i n e i n t e r s e c t s C ur ve 2 a t a p e n e t r a t i o n of a b o u t305 f t w hi ch i n d i c a t e s t h a t i t may n o t b e p o s s i b l e t o d r i v e a p i l e b el owt h i s p e n e t r a t i o n i f t h e p i l e s h ou ld p lu g. W hi le t h e e f f e c t of t h e p i l ep l u gg i n g on t h e p e n e t r a t i o n t o wh ic h t h e p i l e c an be d r i v e n i s r e l a t i v e l ym in or fo r t h e h amm er-p il e -s o il s y s tem o f F i g . 2 3-9 t h e e f f ec t i s mores i g n i f i c an t f o r t h e s y s tem shown on F i g . 23-10. The in fo rmat ion on F ig .23-10 would i n di c a t e t h a t t h e p i l e would r e a c h r e f u s a l a l m os t i m m ed ia te lyi f i t p lu g s a f t e r t h e t i p e n t e r s t h e s an d l a y e r f ound a t a p e n e t r a t i o n ofa b o ut 240 f t .

A s ec on d f a c t o r t h a t may n o t b e p r e d i c t a b l e i s t he number and le ng tho f any d e l ay s d ur in g t h e p i l e i n s t a l l a t i o n . I f t h e r e i s a d e l a y d u r i n gd r i vi n g p a r t i c u la r l y i f t h e p i l e i s b e i ng d r i v e n i n pr e do m in a te l y c l a y a st h e c a s e f o r Fi g . 23-9 t h e r e s i s t a n c e of t h e s o i l t o t h e p i l e p e ne t r at i onw i l l t en d t o i n c re a s e f ro m t h a t i n d i ca t ed by C urve 1 t ow ar ds t h e r e s i s t a n c ein d i ca te d by Curve 3 s t h e pe n e tr a t io n f o r t h e t re n d l i n e f o r t h e g r e a t e s tr e s i s t a n c e t h a t can be overcome by t h e hammer-p i le -so il sys tem in cr ea se sbelow t h e i n t e r s e c t i o n of t h e t r e n d l i n e a nd C ur ve 3 towards Curve 1 t h ep e n e t r a t i o n t o w hi ch t h e p i l e c a n b e d r i v e n becomes more s u s c e p t i b l e t o t h el e n g t h of a ny d e l a y d u r in g d r i v i n g . Long o f f s h o r e p i l e s a r e d r i v e n i ns e c t i o n s a nd t h e r e a r e d e l a y s i n d r i v i n g a s t h e s e c t i o n s a r e s ta bb ed a ndw el de d o n t o t h e d r i v e n p o r t i o n of t h e p i l e . T he se d e l a y s a r e n e c e s s a r y a ndwhi l e t h e number i s known t h e l e n g t h s a r e n o t . The i n f o r m a t i o n s u c h as t h a tp res en te d on F ig . 23-9 and 23-10 may be used t o p l an t h e lo ca t i on s o f t h ep i l e add-ons t o m in im iz e t h e e f f e c t s of t h e n e c e s s a r y d e l a y s . T hi s i n f o r -m a ti o n a l s o c a n b e u se d t o make a n e v a l u a t i o n o f t h e p o s s i b l e e f f e c t s o f


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unfor eseen de l ays due t o wea the r equipment breakdowns and o t he r cause s .s ec on d method t o i n t e r p r e t d r i v a b i l i t y i s i l l u s t r a t e d o n F i g . 23-11

w hi ch p r e s e n t s t h r e e c u r v e s o f e s t i m a t e d d r i v i n g r a t e i n b lo ws p e r f o o t ofp e n e t r a t i o n v e r s u s p i l e p e n e t r a t i o n . T he se c u r v e s w er e o b t a in e d fr om t h ee s t im a t e d r e s i s t a n c e t o d r i v i n g o f f e r e d by t h e s o i l g iv e n i n F i g . 23-9a nd t h e r e s i s t a n c e t h a t c a n be ove rc om e by t h e ha mm er - pi le -s oi l s y st e mgi ve n i n Fig . 23-3. The lower cu rv e on Fig . 23-11 w s developed by obta in-i n g v a l u e s f o r t h e e st im at ed r e s i s t a n c e o f f e r e d by t h e s o i l a t v a r i o u spe ne t r a t i ons f r om Cur ve 1 on F i g . 23-9 a nd u s i ng t he s e va l ue s t o ob t a i ne s t im a t e d d r i v i n g r a t e s a t t h e p e n e t r a t i o n s f ro m t h e c u r v e s on F i g . 23-3.The o th e r two cur ves on F ig . 23-11 were deve loped i n a similar manner us ingCurves 2 and 3 on Fig . 23-9.

he i n t e r p r e t a t i o n of d r i v a b i l i t y u s i n g i n f o rm a ti o n a s p r es e nt e d onFig. 23-11 i s s i m i l a r t o t h e i n t e r p r e t a t i o n u s in g i n fo r ma t io n a s p r es e nt e don Fig . 23-9. A ssum ing t ha t a d r i v i ng r a t e o f 200 bl ow s pe r f oo t r e p r e -s e n t s t h e d r i v i n g l i m i t i t may be seen on Fig . 23-11 t h a t t h e r e should beno p ro bl em t o d r i v e t h e p i l e t o a p e n e t r a t i o n o f a bo u t 210 f t . t a l s o c anb e s e e n t h a t i t may be d i f f i c u l t e ve n u nd e r t h e b e s t c o n d i t i o n s t o d r i v et h e p i l e t o a p e n e t r a t i o n much g r e a t e r t h a n ab o ut 3 30 f t . I n be tw ee n t h e s etwo d e p t h s t h e p e n e t r a t i o n t o wh ic h t h e p i l e ca n b e d r i v e n w i l l depend onw he th er t h e p i l e p l u g s o n t h e d u r a t i o n of a n y d e l a y s d u r i n g d r i v i n g an dt h e p e n e tr a t io n a t w hi c h t he y oc c u r a nd on o t h e r f a c t o r s that a r e n o te n t i r e l y p r e d ic t a bl e .

t should be e v i d e n t f ro m t h e i n f o r m a t i o n p r e se n t e d h e r e t h a t ad r i v a b i l i t y a n a l y s i s d o es n o t n e c e s s a r i l y p ro du c e a s i n g l e o r u n i qu e an sw er


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o t h e q u e s t io n ab ou t t h e a b i l i t y of a g i v e n hammer t o i n s t a l l a p a r t i c u l a rp i l e t o a s p e c i f i c p e n e t ra t io n a t a l o c a t io n . t should be recogn ized t ha tp r e c i s e s i n g u l a r r e s u l t s a r e n o t o b ta i ne d fr om e i t h e r t h e wave e qu a ti o nan a l y s i s t o o b t a i n t h e r e s i s t an ce t h a t c an b e o ve rcome by t h e hammer-pile-s o i l sy ste m o r t h e a n a l y si s t o e s t i m at e t h e r e s i s t a n c e t h a t t h e s o i l w l lo ff e r to d r iv ing . Because of t h i s con s ide rab le eng ineer ing judgment mus tb e use d w i th t h e s e r e s u l t s t o o b t a i n a n e v al u at i on of p i l e d r i v a b i l i t y . tu s u a l l y i s p o s s i b l e t o s e l e c t a p e n e t r a t i o n w he re i t i s a lm os t c e r t a i n ap i l e c a n b e d r i v e n and a l s o t o s e l e c t a p e n e t r a t i o n beyond w hi ch a p i l eprobab ly canno t be d r iven . This lea ve s a range of pe ne tr at io n which mayb e s i g n i f i c a n t l y l a r g e w he re t h e a c t u a l p e n e t r a t i o n t o which t h e p i l e canbe dr iv en may depend on f a c to r s th a t cannot be predetermined. However th er e s u l t s o f t h e d r i v a b i l i t y a n a l y s i s us ed w i t h e n g i ne e r in g judgm ent w l lp er mi t a b e t t e r e v a l u a ti o n of t h e p r o b a b i l i t y of i n s t a l l i n g a p i l e t o ag i v en p en e t r a t i o n w i t h a p a r t i cu l a r hammer t h an w i t h no i n fo rma t i o n a t a l l .T h i s i nf o rm a t io n a l s o h a s be en f ou nd t o b e u s e f u l t o e v a l u a t e t h e e f f e c t sof u n fo r s een ev en t s o ccu r r i n g d u ri n g p i l e d r i v i n g in a r r i v i n g a t d e c is i on stha t have to be made dur ing p i l e i n s t a l l a t i o n .


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REFERENCES

1. I s a a c s , D . V . , R e i n f o rc e d C o n c r e t e P i l e Fo rm u la , Transactions of theIn st i t ut io n of Engineers, Australia, V o l . 1 2 , p p . 3 1 2- 3 23 ( 1 9 3 1 ) .

2 . G l a n v i l l e , W .H ., G r i m e , G . , F o x , E .N ., a n d D a v i e s , W.W . , A n I n v e s t i -g a t i o n o f t h e S t r e s s e s i n R e i n f o r c e d C o n c r e t e P i l e s D u ri ng D r i v i n g ,Technical Paper No. 2 0 B r i t i s h B u i l d i n g R e s e a r c h B o a r d , 1 9 3 8 .

3 . S m i t h , E.A . L . , P i l e D r i v i n g I m p a c t , Proceedings, Industrial Camptation Seminar, S e p te m b e r 1 9 5 0 , I n t e r n a t i o n a l B u s i n e s s M a c hi ne s C o r p .,New York , N .Y . ( 1 9 5 1 )

. S m i th , E .A . L . , I m p a ct a n d L o n g i t u d i n a l W ave T r a n s m i s s i o n , I Transactions,ASME, p p . 9 6 3 - 9 7 3 , A u g u s t 1 9 5 5 .

5 . S m i t h , E .A .L ., P i l e D r i v i n g A n a l y s i s by t h e W ave E q u a t i o n , Transactions,ASCE, V o l. 1 2 7 , P a r t I p p 1 1 4 5 - 1 1 7 1 ( 1 9 6 2 ) .

6 . H i r s c h , T . J . , Carr L . a n d L o w e r y , L . L . , Pile Driving Analyses-WaveEquation User s Manual, T TI P r og r a m I m p l e m e n t a t i o n P a c k a g e , V o l . I11 111 a n d I V , 1 9 7 6 .

7 . G o b l e , G . G . a n d R a u s c h e , F. 2ave Epu ti on Analysis of PCZe D ~ v i n g ,W E D P r o g r a m I m p l e m e n t a t i o n P a c k a g e , V o l . I 11 111 a n d I V 1 9 7 6 .


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REFERENCES (co n t i n u ed)

8 Fore hand, P.W. and Ree se, J .L., J r . Pred i c t i o n of P i l e C apac i t y byt h e Wave Equat ion, Journal, soil Mechanics and Foundation Division,ASCE, Vol. 90, N O . SM2, pp. 1-25 (1964).

9. Lowery, L.L., H ir sc h, T . J . , Edwards, T.C., Coyle , H .M . and Sampson, C .H . , J r .Pi le Dr-iving Analy sis s t a t e of th e A r t Te xas T r a n s p o r t a t i o n I n s t i t u t e R e se a rc hRepor t 33-13, Texas A&M Un i v e r s i t y (1 9 6 9 ) .

10. Foye, R . , J r . Coyle, H.M. , Hir sch , T . J . , Bar tos kewi tz , R.E. and Mi lber ger , L . JWave Equation Analyses of FUZZ-Scale Test Piles Using Measured Field Data,T exas T ra n s p o r t a t i o n In s t i t u t e R es ea rch Rep or t 12 5-7, T ex as A&M U n i v e r s i t y ( 1 9 7

11 Hirsch, T . J . Lowery, L.L., Coy le, H.M. and Samson, C.H. , J r . Pi l e Dr i v i n gAnalysis by One-Dimensional Wave Theory: S t a t e o f t h e A r t , riighway ResearchRecord No. 333, Highway Re se ar ch Boa rd, pp. 33-54 (1970)

1 2 . Rousse l , H. J J r Pile Driving AnaZysis of Large Diameter li igh CapacityOffshcre ,Piles, Ph. D . Di s s e r t a t i o n , Dep ar tm en t of C i v i l E n g in ee r i n g,Tulane Un ive rs i ty (197 9)

13 . Heerema, E.P. Re la ti on sh ip s Between Wall Fric t ion , Disp iacernen t Veloc i tyand X o r i z o n t a l S t r e s s i n C la y an d i n S a nd , f o r P i l e D r i v e b i l i t y - An al ys is ,Growzz Zngineering, Vol. 1 2 No. 1 pp. 55-61, 65 (1 97 9) .


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REFERENCES (con t in ued)

14. A me ri ca n Pe t ro le u m I n s t i t u t e , Recornended Pra cti ce for Planning Designingand Co nstructi ng Fized 0 rfshore P2at fo ms AeI RP 2A, 12 th ed i t io n (1981) .

1 5 . Vi j ay v e rg i y a , V N and Focht , J . A . J r . A New Way t o Pr e d i c t t h e Capa ci tyo f P i l e s i n Cl ay, Offshore Teciinology Conference (1972) Vol. 2 pp. 865-874.

16 . Ve sic , A.S., Principles of Pile Foundation Design So i l M echani cs Se r i e sNo. 38, School of Engi neer ing, Duke Un iv er s i ty , (1975).

17. Heerema, E . P . P r e d ic t i ng P i l e D r i v a b i l i t y : H ea th er a s a n I l l u s t r a t i o no f t h e F r i c t i o n Fa t i g u e T heory, Boc eed ing s European Offshore Pe tr ol emConference and Exhibition Vol. 1 p p 413--422 (1978).


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T BLE 2 3 . 1 PR OPER TIES OF SOME H A t R S

H a m e rV u l c a n 6 3 0 0HBM 4 0 0 0N e n c k 1 2 5 0 0HBM 30 00 AM en ck 8 0 0 0V u l c a n 5 1 5 0Elenck 7000HBM 3 0 0 0V u l c a n 5 1 0 0M en ck 4 6 0 0HBM 1 5 0 0M en ck 3 0 0 0V u l c a n 3 1 0 0V u l c a n 5 6 0Kobe K-150Delmag D80-12V u l c a n 5 4 0M en ck 1 8 0 0V u l c a n 3 6 0MKT OS-60Delmag D62-02M i t s u b i s h i MB 7 0V u l c a n 5 3 0MKT OS-40V u l c a n 3 4 0Delmag D55Kobe K-60V u l c a n 4 0 0 CDelmag D46-02Kobe K-45M en ck 8 5 0V u l c a n 0 3 0Delmag D44Delmag D36-02Ko b e K-4 2HBM 5 0 0D e l m g D 3 0 - 0 2V u l c a n 0 2 0S T OS-20

R a t e d E n e r g yf t - l bW e i g h tRam

3 0 0 , 0 0 02 0 5 , 0 0 02 7 5 , 5 8 01 5 2 , 0 0 01 7 6 , 3 7 01 5 0 , 0 0 01 5 4 , 0 0 01 3 8 , 8 9 01 0 0 , 0 0 01 0 1 , 4 1 0

5 5 , 0 0 06 6 , 1 4 0

1 0 0 , 0 0 06 2 .5 0 03 3 , 1 0 01 9 , 5 0 04 0 . 0 0 03 8 , 5 8 06 0 , 0 0 06 0 , 0 0 01 4 , 0 0 01 5 , 8 4 03 0 , 0 0 04 0 , 0 0 04 0 , 0 0 01 2 , 1 0 01 3 , 2 0 04 0 , 0 0 01 0 , 1 2 0

9 , 9 0 01 8 , 9 6 03 0 , 0 0 0

9 , 5 0 07 , 9 0 09 , 2 0 09 , 4 8 06 , 6 0 0

2 0 . 0 0 02 0 , 0 0 0

W e i g h tI m p a c t B l o c k e i g h tD r i v e C a p3 ~ x p l o s i v eF o r c el b

' ~ n f o r m a t i o n t a k e n f ro m m a n u f a c t u r e r ' s p u b l i s he d data' o f f s h o r e d r i v e c a p o b t a i n e d f r o m m a n u f a c t ur e r w hen a v a i l a b l e ; o t h e r d r i v e c a p s m y b e u s e d .3X axim um e x p l o s i v e f o r c e o n p i l e .


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TABLE 2 3 2 TYPICAL PROPERTIES FOR COMMONLY-USED CAPBLOCK CUSHION MATERIALS

MaterialAluminum Pl a t e s

Dynamic Modulusof E l a s t i c i t y

12 C o ef f i c i en t o fk i p s / in R e s t i t u t i o n

Asbes tos 150 0.5

ConbestHardwood load

p a r a l l e l t o g r ai n )Micarta 450 0.8S t e e l P l a t e s

Va lu es fo r we l l- com p res sed , u s ed m a t e r i a l and t h e s h ea r l e v e l s ofo f f s h or e p i l e d r i v i n g.

2When t h e s e metal p l a t e s a r e u se d i n c om b in a ti o n w i t h a n o t h e rc us hi on m a t e r i a l t h e c o e f f i c i e n t o f r e s t i t u t i o n o f t h e o t he rm a t e r i a l s h o u l d be used.


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ul4

a

m


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Fig. 23-1Fig. 23-2Fig. 23-3Fig. 23-4Fig. 23-5Fig. 23-6Fig. 23-7

Fig. 23-8Fig. 23-9

Fig. 23-10

Fig. 23-11

C ha pt er 2 2 I l l u s t r a t i o n C ap ti o ns

One dim ens ion al wave equ at io nHammer-p il e -so il sys t em re pr es en ta t i onB e a r i n g g r a p h s f r o m wave e q u a t i o n a n a l y se sFo r ce - de f o rm a ti o n p r o p e r t i e s o f c a p b l o c kS o i l l oa d- de f or ma t i o n c h a r a c t e r i s t i c sP i l e c a p ac i ty g a in w i t h t im e f o r s t e e l p i l e s i n co he si ve s o i l sS t r e n g t h l o s s by r e m ol d in g f o r no r m al l y- c o ns o l id a te d c l a y s

P i l e c a p a c i t y g a i n w i t h s e t -u p .I n t e r p r e t a t i o n of p i l e d r i v e a b i l i t y r e s i s t a n c e t o d r i v i n gprocedure ExampleI n t e r p r e t a t i o n of p i l e d r i v e a b i l i t y r e s i s t a n c e t o d r i v i ngpro ced ure Example 2I n t e r p r e t a t i o n of p i l e d r i v e a b i l i t y r a t e o f p e n e t r a t i o np r o c e d u r e


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Pile

Disturbance

Material Properties nr

esistance

E Modulus o ElasticityMass ensity

p Stress Wave Velocity


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ide lized ile


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3000 ----

Vulcan 3100 Hammer48in .-Diam eter Pipe Pi le500--Symbol a t Tip. Pen., f t Max. Camp.-Stress ksi

0 10.5 210 20.9--- 10.5 321 21.310.5 366 21.700 50 100 150 200 250 300

Rate of Penetration, Blows Per Foot


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orce

eformation


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oadFQ

a) Static

b) ynamicA+- f f w 5 4 1 j 70


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Ult imate Pi le Capaci ty Kips


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1. Estimated Resistance to Driving Ru based onremolded side friction in clay static side frictionin sand and end bearing on pile wal l end area.

2 Estimated Resistance to Driving Ru , based onremolded side frict ion in clay static side frict ionin sand and end bearing on pile gross end area.3. computed Ultimate Compressive -- ile Capacity, Q


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f - Ultimate Static Pile Capacity Qu KipsResistance to Driving Ru Kips-1000 2000 3000 4000 5000 6000 7000

L

48-in.-Diameter Pipe Pile

1. Estimated Resistance to Driving R based onremolded side friction in clay static side frictionin sand and end bearing on pile wall end area.2. Estimated Resistance to Driving Ru based onremolded side friction in clay static side frictionin sand and end bearing on pile gross end area.3. Computed Ultimate Compressive Pile Capacity Q

hammer details pile drivability

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