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Effect of strain rate and structure on the development of cohesion and friction in a sensitive clay Gupta, Ramesh Chandra 1967

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E F F E C T O F S T R A I N R A T E A N D S T R U C T U R E O N T H E D E V E L O P M E N T O F C O H E S I O N A N D F R I C T I O N I N A S E N S I T I V E C L A Y b y R A M E S H C H A N D R A G U P T A B . S c . ( E n g g ) B a n a r a s H i n d u U n i v e r s i t y , I n d i a , I 9 6 0 . A T H E S I S S U B M I T T E D L N P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M . A . S c . • i n t h e D e p a r t m e n t o f C i v i l E n g i n e e r i n g v. W e a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d T H E U N I V E R S I T Y O F . B R I T I S H C O L U M B I A A p r i l , 1 9 6 7 . In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, Canada D a t e •+• S". £7 11 A B S T R A C T . T h e study was u n d e r t a k e n to i n v e s t i g a t e the e f f e c t s of rate of s t r a i n and s t r u c t u r e on the d e v e l o p m e n t of t r u e c o h e s i o n and t rue f r i c t i o n i n a s a t u r a t e d c o h e s i v e s o i l . T h e s o i l i n v e s t i -gated was a l o c a l l y a v a i l a b l e s e n s i t i v e c l a y . T h e v a r i o u s m e t h o d s p r o p o s e d b y d i f f e r e n t i n v e s t i g a t o r s to m e a s u r e t rue c o h e s i o n and t r u e f r i c t i o n a r e r e v i e w e d . A f t e r s o m e t r i a l s the m e t h o d adopted was that p r o p o s e d b y B i s h o p (1962) i n w h i c h o v e r - c o n s o l i d a t i o n i s u s e d to obta in s a m p l e s at the s a m e v o i d r a t i o / b u t d i f f e r e n t i n i t i a l e f f e c t i v e s t r e s s . A l l s a m p l e s w e r e t e s t e d i n u n d r a i n e d t r i a x i a l c o m p r e s s i o n . T o i n v e s t i g a t e the effec ts of ra te of s t r a i n on the d e v e l o p -ment of t rue c o h e s i o n and t rue f r i c t i o n , the r e s u l t s w e r e c o m -p a r e d f o r two i d e n t i c a l sets of s a m p l e s t e s t e d at two s i g n i f i c a n t l y d i f f e r e n t s t r a i n r a t e s . T o i n v e s t i g a t e the effects of s t r u c t u r e on the d e v e l o p m e n t of t rue cohe'sion and t r u e f r i c t i o n , a t e c h n i q u e was d e v e l o p e d to r e m o l d the s p e c i m e n s i n p l a c e at constant v o i d r a t i o af ter they had b e e n s h e a r e d i n the u n d i s t u r b e d s t a t e . R e m o l d i n g has the effect of b r e a k i n g - d o w n the s t r u c t u r e of a s e n s i t i v e u n d i s t u r b e d c l a y . T h e test r e s u l t s f r o m u n d i s t u r b e d and r e m o l d e d s a m p l e s w e r e c o m p a r e d . In g e n e r a l the i n v e s t i g a t i o n s h o w e d that i n the u n d i s t u r b e d I l l c l a y t h e s t r e n g t h i n t e r m s o f m a x i m u m (<rra$ d e c r e a s e d w i t h d e -c r e a s i n g s t r a i n r a t e , h o w e v e r , t h e s t r e n g t h i n t e r m s o f ( ^ / o p . ^ x w a s n o t s i g n i f i c a n t l y a f f e c t e d b y s t r a i n r a t e w h e n c o m p a r e d o n a n e f f e c t i v e s t r e s s b a s i s . In r e m o l d e d c l a y s t h e r e w a s a t e n d e n c y f o r t h e s t r e n g t h i n t e r m s ' o f m a x i m u m (o^-r^) t o i n c r e a s e w i t h i n c r e a s i n g t i m e to f a i l u r e . In t h e u n d i s t u r b e d c l a y t r u e c o h e s i o n d e v e l o p e d r a p i d l y at s m a l l s t r a i n s , a t t a i n e d a p e a k a n d d e c r e a s e d t o z e r o at l a r g e s t r a i n s . T r u e f r i c t i o n w a s m o b i l i z e d s l o w l y a n d a t t a i n e d a m a x i -m u m v a l u e at l a r g e s t r a i n s . A t s t r a i n s l e s s t h a n 8% b o t h t r u e f r i c t i o n a n d t r u e , c o h e s i o n i n c r e a s e d w i t h i n c r e a s i n g s t r a i n r a t e . H o w e v e r , at l a r g e s t r a i n s t r u e f r i c t i o n a n d t r u e c o h e s i o n w e r e n o t a f f e c t e d b y s t r a i n r a t e . In t h e r e m o l d e d c l a y t r u e c o h e s i o n d e v e l o p e d s i o w l y a t t a i n i n g a s m a l l b u t s i g n i f i c a n t v a l u e w h i c h r e m a i n e d c o n s t a n t w i t h s t r a i n . T h e m a x i m u m v a l u e o f t r u e c o h e s i o n i n t h e r e m o l d e d c l a y w a s v e r y m u c h l o w e r t h a n t h a t f o r t h e u n d i s t u r b e d c l a y . T h e d e v e l o p m e n t o f t r u e f r i c t i o n w i t h s t r a i n w a s e s s e n t i a l l y u n a f f e c t e d b y r e m o l d i n g a n d b o t h t h e u n d i s t u r b e d a n d r e m o l d e d c l a y d e v e l o p e d a b o u t t h e s a m e m a x i m u m v a l u e o f t r u e f r i c t i o n at l a r g e s t r a i n s . T h e o b s e r v e d b e h a v i o u r w a s e x p l a i n e d i n t e r m s o f c h a n g e s i n c l a y s t r u c t u r e w i t h s t r a i n r a t e a n d r e m o l d i n g . i v A C K N O W L E D G M E N T S T h e w r i t e r w i s h e s t o t h a n k m o s t s i n c e r e l y D r . R . G . C a m p a n e l l a , A s s i s t a n t P r o f e s s o r o f C i v i l E n g i n e e r i n g , f o r g u i d i n g h i s g r a d u a t e s t u d y p r o g r a m m e a n d f o r t h e a d v i c e r e -c e i v e d d u r i n g t h i s i n v e s t i g a t i o n . T h e f u n d s i n c l u d i n g t h e f i n a n c i a l s u p p o r t f o r t h e w r i t e r w e r e p r o v i d e d b y t h e N a t i o n a l R e s e a r c h C o u n c i l o f C a n a d a . G r a t e f u l a p p r e c i a t i o n i s e x p r e s s e d f o r t h i s a s s i s t a n c e w i t h o u t w h i c h t h e g r a d u a t e s t u d i e s a n d t h i s t h e s i s c o u l d n o t h a v e b e e n a c c o m p l i s h e d . T h e w r i t e r i s g r a t e f u l to P r o f e s s o r N . . D . N a t h a n , o f C i v i l E n g i n e e r i n g D e p a r t m e n t f o r h i s r e v i e w o f t h e m a n u s c r i p t a n d f o r h i s v a l u a b l e s u g g e s t i o n s . T h e w r i t e r i s i n d e b t e d t o D r . W . D . F i n n , H e a d o f t h e C i v i l E n g i n e e r i n g D e p a r t m e n t f o r t h e e n c o u r a g e m e n t r e c e i v e d f r o m t i m e to t i m e . T h e t e c h n i c a l a s s i s t a n c e s u p p l i e d b y t h e s t a f f o f t h e C i v i l E n g i n e e r i n g W o r k s h o p i s t h a n k f u l l y a c k n o w l e d g e d . V T A B L E O F C O N T E N T S P a g e C H A P T E R I C H A P T E R I I C H A P T E R I I I . 3 . 1 3 . 2 3 . 3 3 . 4 3 . 5 3 . 6 3 . 7 C H A P T E R I V C H A P T E R V 5 . 1 5 . 2 5 . 3 I n t r o d u c t i o n I n t r o d u c t i o n 1 P u r p o s e a n d S c o p e P u r p o s e , a n d S c o p e 3 L i t e r a t u r e R e v i e w G e n e r a l ' 4 P r i n c i p l e o f E f f e c t i v e S t r e s s 4 S h e a r S t r e n g t h a n d i t s C o m p o n e n t s 5 P h y s i c a l a n d P h y s i c o - c h e m i c a l E x p l a n a t i o n s f o r C o h e s i o n a n d F r i c t i o n 6 C l a y S t r u c t u r e a n d E f f e c t s o f S t r u c t u r e o n t h e S t r e n g t h 1 2 E f f e c t s o f R a t e o f S t r a i n o n t h e S t r e n g t h 1 5 M e t h o d s of D e t e r m i n i n g C o h e s i o n a n d F r i c t i o n 18 E q u i p m e n t E q u i p m e n t 2 8 F i e l d S a m p l i n g , S a m p l e P r e p a r a t i o n a n d P r o p e r t i e s o f C l a y T e s t e d F i e l d S a m p l i n g 3 3 S a m p l e P r e p a r a t i o n 3 3 P r o p e r t i e s o f C l a y T e s t e d 3 5 / v i P a g e C H A P T E R V I T e s t i n g P r o c e d u r e 6 .1 R a t e o f S t r a i n 4 0 6 . 2 S c h m e r t m a n n ' s T e c h n i q u e a n d D a t a o b t a i n e d 41 6 . 3 B i s h o p ' s M e t h o d 4 7 C H A P T E R V I I T e s t R e s u l t s , A n a l y s i s , a n d D i s c u s s i o n 7 .1 G e n e r a l 55 7 . 2 T e s t R e s u l t s a t F a s t e r S t r a i n R a t e 56 7 . 3 E f f e c t s o f S t r a i n R a t e o n U n d i s t u r b e d C l a y 66 7 . 4 . E f f e c t s of S t r u c t u r e 76 7 . 5 E f f e c t s o f S t r a i n R a t e o n R e m o l d e d C l a y 87 7 . 6 S h e a r i n g S t r e n g t h ••„ 89 7 . 7 D i s c u s s i o n o f t e s t r e s u l t s o n t h e b a s i s o f r a t e p r o c e s s t h e o r y 91 C H A P T E R V I I I S u m m a r y C o n c l u s i o n s a n d S u g g e s t i o n s f o r f u t u r e w o r k 8 .1 ' G e n e r a l 93 8 . 2 • E f f e c t s o f S t r a i n R a t e 9 4 8 . 3 E f f e c t s o f S t r u c t u r e 95 8 . 4 S u g g e s t i o n s f o r f u t u r e w o r k 96 A P P E N D I X A . S a m p l e P r e p a r a t i o n 97 A P P E N D L X B . R e m o l d i n g T e c h n i q u e 1 0 0 A P P E N D I X C . S a m p l e D a t a • 101 A P P E N D I X D . C a l c u l a t i o n s f o r t r u e c o h e s i o n a n d t r u e f r i c t i o n 110 L i s t o f R e f e r e n c e s \\Q v i i L i s t o f T a b l e s P a g e T a b l e I P h y s i c a l P r o p e r t i e s o f H a n e y C l a y 36 T a b l e I I C h e m i c a l P r o p e r t i e s o f H a n e y C l a y 37 T a b l e I I I S u m m a r y P r o c e d u r e f o r T e s t S a m p l e s 53 v i i i L I S T O F S Y M B O L S a - A p a r a m e t e r d e n o t i n g n u m b e r of i n t e r p a r t i c l e b o n d s S at <7^ =.o Au- / A - P o r e p r e s s u r e p a r a m e t e r /__"3 A - I n i t i a l a r e a o f c r o s s s e c t i o n o f a s a m p l e o A , - A r e a o f c r o s s s e c t i o n at s t r a i n 6 c b - A p a r a m e t e r r e l a t i n g c h a n g e i n S w i t h c h a n g e i n 05* B - P o r e p r e s s u r e p a r a m e t e r ^^/^.ci c v - C o e f f i c i e n t of C o n s o l i d a t i o n c e - T r u e c o h e s i o n c - R e p r e s e n t s s o i l c o m p o s i t i o n i n c l u d i n g s o l i d , l i q u i d a n d g a s e o u s p h a s e . C - U - C o n s o l i d a t e d u n d r a i n e d t e s t D - D e v i a t o r s t r e s s , a l s o b y e - V o i d r a t i o ' A F - A v e r a g e f r e e e n e r g y of a c t i v a t i o n r e q u i r e d t o r u p t u r e a b o n d _ 27 h - P l a n c k s c o n s t a n t 6 . 6 2 5 x 10" d y n e s - c m - s e c H - E q u i v a l e n t o f h i s t o r y _16 k - B o l t z m a n n ' s C o n s t a n t 1 . 3 8 x 10 d y n e - c m o r 1 „ 9 8 c a l / m o l e / o K o K N - A v o g a d r o ' s n u m b e r R - G a s c o n s t a n t S^ - S t a n d s f o r S o i l S t r u c t u r e S - N u m b e r o f i n t e r p a r t i c l e b o n d s p e r u n i t c r o s s s e c t i o n o v e r w h i c h t h e d e v i a t o r s t r e s s i s d i s t r i b u t e d I X T e s t d u r a t i o n c o r r e s p o n d i n g to 95%, p o r e p r e s s u r e e q u a l i z a t i o n T e m p e r a t u r e P o r e - w a t e r p r e s s u r e C h a n g e i n p o r e w a t e r p r e s s u r e W a t e r C o n t e n t i n % U n i t l e s s p a r a m e t e r r e l a t i n g f r e q u e n c y o f b o n d r u p t u r e t o a x i a l s t r a i n r a t e S t r a i n S t r a i n r a t e A v e r a g e d i s t a n c e b e t w e e n s u c c e s s i v e e q u i l i b r i u m p o s i t i o n s of a d j a c e n t a t o m i c v a l l e y s i n t h e d i r e c t i o n o f b o n d s h e a r i n g f o r c e S h e a r s t r e s s T r u e f r i c t i o n T o t a l n o r m a l s t r e s s C o n s o l i d a t i o n p r e s s u r e D e v i a t o r s t r e s s a l s o b y D . C h a n g e i n D e v i a t o r S t r e s s E f f e c t i v e N o r m a l S t r e s s P r i n c i p a l T o t a l S t r e s s e s P r i n c i p a l E f f e c t i v e S t r e s s e s / / / / ' X L i s t of F i g u r e s F i g u r e P a g e 1. M e t h o d o f o b t a i n i n g n o r m a l l y a n d o v e r - c o n s o l i -d a t e d s a m p l e s at s a m e w a t e r c o n t e n t . 20 2 . M o d i f i e d M o h r - C c u l o . m b d i a g r a m . 20 3 . S c h m e r t m a n n ' s C u r v e h o p p i n g - 1 22 4 . S c h m e r t m a n n ' s C u r v e h o p p i n g - 2 22. 5 . E v a l u a t i o n o f c o h e s i o n a n d f r i c t i o n f r o m m e t h o d 2 a t a n y s t r a i n . 24 6 . T r i a x i a l c e l l a n d c h a m b e r p r e s s u r e s y s t e m . 29 7 . D r a i n a g e s y s t e m . ~. 30 8 . T r i a x i a l c e l l w i t h s a m p l e c o n s o l i d a t i n g . 32 9 . T r i a x i a l e q u i p m e n t w i t h s t r a i n i n d i c a t o r s . 32 1 0 . T r i m m i n g e q u i p m e n t . 34 1 1. G r a i n s i z e d i s t r i b u t i o n o f H a n e y c l a y . 38 12. T y p i c a l s t a n d a r d c o n s o l i d a t i o n c u r v e f o r H a n e y c l a y . 39 1 3 . . D a t a f o r d e v e l o p m e n t o f c e a n d </>e f r o m S c h m e r t m a n n ' s m e t h o d . 4 3 14. G r a p h f o r e x t r a p o l a t i o n o f c o h e s i o n . 4 4 15. D e v e l o p m e n t of c g a n d c4 g f r o m S c h m e r t m a n n ' s m e t h o d . 45 16. D i a g r a m m a t i c : r e p r e s e n t a t i o n o f t h e p r o c e d u r e . 50 (a) U n d i s t u r b e d s a m p l e s . (b) R e m o l d e d s a m p l e s . 17. D i a g r a m m a t i c : : r e p r e s e n t a t i o n of p r o c e d u r e . 5 2 F i g u r e . / ? P a g e • / -18. D e v i a t o r s t r e s s e s a n d p o r e - p r e s s u r e i n u n d i s t u r b e d s t a t e at f a s t e r s t r a i n r a t e . 58 19. M i n o r p r i n c i p a l e f f e c t i v e s t r e s s 5^ i n u n d i s t u r b e d s a m p l e s at f a s t e r s t r a i n r a t e . 59 2 0 . /0$ f o r u n d i s t u r b e d s a m p l e s at f a s t e r s t r a i n r a t e . 61 6 2 21. P o r e - p r e s s u r e p a r a m e t e r A f o r u n d i s t u r b e d s a m p l e s at a f a s t e r s t r a i n r a t e . 2 2 . E f f e c t i v e s t r e s s p a t h s f o r u n d i s t u r b e d s t a t e at f a s t e r s t r a i n r a t e . 2 3 . D e v e l o p m e n t o f c e a n d <t>& w i t h s t r a i n i n u n d i s t u r b e d s t a t e at f a s t e r s t r a i n r a t e . 2 4 . E f f e c t o f s t r a i n r a t e o n d e v i a t o r s t r e s s e s i n u n d i s t u r b e d s t a t e . 64 65 67 2 5 . E f f e c t o f s t r a i n r a t e o n p o r e - p r e s s u r e s i n u n d i s t u r b e d s t a t e . 68 2 6 . . E f f e c t o f s t r a i n r a t e o n S k e m p t o n ' s p o r e - p r e s s u r e p a r a m e t e r A . 70 2 7 . E f f e c t o f s t r a i n r a t e o n 1 /2 (&7+5|, ) i n u n d i s t u r b e d s t a t e . "71 2 8 . (a) E f f e c t o f s t r a i n r a t e o n (07 _ ^ ) m a x i m u m . "72 (b) E f f e c t o f s t r a i n r a t e o n A f at ( 07 - ir_ ) m a x i m u m . 2 9 . E f f e c t o f r a t e o f s t r a i n o n °*I f o r u n d i s t u r b e d s a m p l e s . 73 3 0 . E f f e c t o f r a t e o f s t r a i n o n t h e d e v e l o p m e n t of c e a n d <£>e i n u n d i s t u r b e d s t a t e . 75 31. E f f e c t of s t r u c t u r e o n d e v i a t o r s t r e s s . 78 3 2 . E f f e c t o f s t r u c t u r e o n p o r e - p r e s s u r e s . ' 79 3 3 . E f f e c t o f s t r u c t u r e o n 81 3 4 . E f f e c t o f s t r u c t u r e o n p o r e - p r e s s u r e p a r a m e t e r A . 82 3 5 . E f f e c t o f s t r u c t u r e o n ^ I / < ^ S 3 X l l F i g u r e . P a g e 3 6 . E f f e c t of s t r u c t u r e o n t h e d e v e l o p m e n t o f cQ a n d <t>Q at t h e f a s t s t r a i n r a t e . 86 3 7 . E f f e c t o f s t r a i n r a t e o n d e v i a t o r s t r e s s e s i n r e m o l d e d s t a t e . 8 8 3 8 . E f f e c t o f s t r a i n r a t e o n p o r e - p r e s s u r e s i n r e m o l d e d s t a t e . 8 8 3 9 . E f f e c t o f r a t e o f s t r a i n o n t h e d e v e l o p m e n t o f c e a n d <t>Q i n r e m o l d e d s t a t e . 90 4 0 . E f f e c t i v e s t r e s s p a t h s f o r u n d i s t u r b e d s t a t e a t s l o w s t r a i n r a t e . 112 41 . D e v e l o p m e n t o f c e a n d $>& w i t h s t r a i n i n u n d i s t u r b e d s t a t e a t s l o w s t r a i n r a t e . 113 4 2 . E f f e c t i v e s t r e s s p a t h s f o r r e m o l d e d s t a t e a t f a s t s t r a i n r a t e . . 1 1 4 4 3 . D e v e l o p m e n t o f c e a n d <t>& w i t h s t r a i n i n r e m o l d e d s t a t e at f a s t s t r a i n r a t e . 115 4 4 . E f f e c t i v e s t r e s s p a t h s f o r r e m o l d e d s t a t e a t s l o w s t r a i n -r a t e . ' 1 16 4 5 . D e v e l o p m e n t of cQ a n d <fre w i t h s t r a i n i n r e m o l d e d s t a t e at s l o w s t r a i n r a t e . 117 H A P T E R / / / I n t r o d u c t i o n I n t r o d u c t i o n A n a c c u r a t e e v a l u a t i o n o f t h e s t r e n g t h o f a s o i l i s a p r e r e q u i s i t e f o r a s a f e d e s i g n w h e r e s o i l i s u s e d to s u p p o r t s t r u c t u r e s . I n d e c i d i n g u p o n s t r e n g t h s o m e f a i l u r e c r i t e r i o n s u c h a s m a x i m u m d e v i a t o r s t r e s s o r m a x i m u m p r i n c i p a l e f -f e c t i v e s t r e s s r a t i o i s c h o s e n . In d e s i g n t h e s t r e s s e s i m p o s e d o n t h e s o i l a r e u s u a l l y c o n s i d e r a b l y l e s s t h a n t h e f a i l u r e s t r e s s a n d t h e r e f o r e , a n u n d e r s t a n d i n g o f t h e d e v e l o p m e n t o f s h e a r i n g r e s i s t a n c e i n t h e s u b f a i l u r e r e g i o n i s i m p o r t a n t . T h e s h e a r i n g s t r e s s c a u s i n g f a i l u r e o n a n y p l a n e i s g i v e n b y M o h r - C o u l o m b t h e o r y a s : % £ = c + cr fccxrv . 1 - 1 / • w h e r e C " i s t h e t o t a l n o r m a l s t r e s s o n t h e p l a n e , c r e p r e s e n t s the . c o h e s i o n a n d ' <k> i s . t h e a n g l e o f f r i c t i o n . T e r z a g h i (1936) i n -t r o d u c e d t h e c o n c e p t o f e f f e c t i v e s t r e s s e s a n d H v o r s l e v ( 1 9 3 6 , 1 9 6 0 ) c o n s i d e r e d t h e / v o i d r a t i o at f a i l u r e . E q . 1-1 t h e n b e c o m e s : . / / X f = % + < r f ta/^^e^ / w h e r e u i s p o r e w a t e r p r e s s u r e , cr i s e f f e c t i v e n o r m a l s t r e s s , / / a n d f d e n o t e s v a l u e s o b t a i n e d at f a i l u r e of s p e c i m e n . / T h e p a r a m e t e r c g i s t e r m e d t h e " t r u e c o h e s i o n " a n d f o r a g i v e n s o i l i s d e p e n d e n t o n t h e v o i d r a t i o at f a i l u r e a n d <t>& i s t e r m e d t h e " t r u e a n g l e o f f r i c t i o n " a n d i s i n d e p e n d e n t o f v o i d r a t i o . 2 A n e v a l u a t i o n o r u n d e r s t a n d i n g o f t h e p a r t i c i p a t i o n o f t h e s e c o m p o n e n t s i n t e r m s o f p e r c e n t s t r a i n i n t h e d e v e l o p m e n t of s t r e n g t h , i . e . m o b i l i z a t i o n o f c e a n d </>e w i t h s t r a i n i s e v i -d e n t l y v i t a l . L a m b e (I960) p r e s e n t e d a c o n c e p t o f t h e d e v e l o p m e n t of c o h e s i o n a n d f r i c t i o n w i t h s t r a i n i n w h i c h t h e m a x i m u m c o h e s i o n i s d e v e l o p e d a t s m a l l s t r a i n s a n d m a x i m u m f r i c t i o n a t l a r g e s t r a i n s . S c h m e r t m a n n (I960) a n d (1963) , W u , D o u g l a s a n d G o u g h n o u r (1962) , a n d B e a (1963) p u b l i s h e d e x p e r i m e n t a l d a t a c o n c e r n i n g t h e d e v e l o p m e n t of c o h e s i o n a n d f r i c t i o n w i t h s t r a i n w h i c h s u p p o r t e d L a m b e ' s h y p o t h e s i s . It i s g e n e r a l l y a c c e p t e d t h a t s t r a i n r a t e a f f e c t s t h e s h e a r i n g r e s i s t a n c e o f c l a y s ( C a s a g r a h d e a n d W i l s o n , (1951), B j e r r u m et a l (1958) , C r a w f o r d ( 1 9 5 9 ) . H o w -e v e r , n o d a t a i s a v a i l a b l e to i n d i c a t e t h e e f f e c t o f s t r a i n r a t e o n the d e v e l o p m e n t o f c Q a n d d>e S t r u c t u r e h a s a p r o n o u n c e d e f f e c t o n t h e s t r e n g t h o f s e n s i -t i v e c l a y s . In t h e u n d i s t u r b e d s t a t e s e n s i t i v e c l a y s h a v e a f l o c c u - . l a t e d s t r u c t u r e . R e m o l d i n g o r d i s t u r b a n c e i n d u c e s s h e a r s t r a i n s , b r e a k s d o w n s t r u c t u r e a n d r e d u c e s i t s s t r e n g t h . T h u s t h e e f f e c t of c l a y s t r u c t u r e i s a n i m p o r t a n t v a r i a b l e a f f e c t i n g t h e s h e a r i n g r e s i s t a n c e of c l a y . T h e p r e s e n t i n v e s t i g a t i o n w a s c a r r i e d o u t t o s t u d y t h e e f f e c t s o f s t r a i n r a t e a n d s t r u c t u r e o n t h e d e v e l o p m e n t o f c e a n d <6 • i n a s a t u r a t e d c o h e s i v e s o i l . H A P T E R P u r p o s e a n d S c o p e 3 P u r p o s e and Scope T h e p r e s e n t i n v e s t i g a t i o n was c o n d u c t e d to s tudy the f o l l o w i n g : 1. T h e effect of ra te of s t r a i n on the d e v e l o p m e n t of t r u e c o h e s i o n and true f r i c t i o n d u r i n g d e f o r m a t i o n of a s a t u r a t e d c l a y i n the u n d i s t u r b e d s tate ,as e v i d e n c e d b y the c o m p a r i s o n of test r e s u l t s on i d e n t i c a l s a m p l e s at two s i g n i f i c a n t l y d i f f e r e n t s t r a i n r a t e s . ( T h e m a i n v a r i a b l e was s t r a i n r a t e ) . 2. T h e effect of s t r u c t u r e on the d e v e l o p m e n t of t r u e c o -h e s i o n and t rue f r i c t i o n d u r i n g d e f o r m a t i o n of a s a t u r a t e d c l a y as e v i d e n c e d by the c o m p a r i s o n of test r e s u l t s on u n d i s t u r b e d and r e m o l d e d s e n s i t i v e c l a y s a m p l e s at the s a m e v o i d r a t i o . ( T h e m a i n v a r i a b l e was s t r u c t u r e w h i c h i s v e r y d i f f e r e n t i n u n -d i s t u r b e d and r e m o l d e d c l a y s ) . T h e effect of ra te of s t r a i n and s t r u c t u r e on the d e v e l o p -ment of ( o j - c ~ j ) , p o r e - p r e s s u r e s , S k e m p t o n ' s p o r e p r e s s u r e p a r a m e t e r A , ( ^Vfl^) a n c ^ m i n o r p r i n c i p a l e f f e c t i v e s t r e s s w e r e a l s o i n v e s t i g a t e d . T h e s c o p e of the e x p e r i m e n t a l p r o g r a m m e i s l i m i t e d to an i n v e s t i g a t i o n of the b e h a v i o u r of u n d i s t u r b e d and r e m o l d e d s p e c i m e n s of a g i v e n s e n s i t i v e c l a y at a . g i v e n v o i d r a t i o . A l l s a m p l e s w e r e d e f o r m e d i n s t r a i n c o n t r o l l e d c o n s o l i d a t e d - u n -d r a i n e d t r i a x i a l c o m p r e s s i o n tests w i t h p o r e - p r e s s u r e m e a s u r e -m e n t s . T h e s t r a i n r a t e s u s e d w e r e 0 .89 p e r c e n t p e r h o u r and 0.079 p e r c e n t p e r h o u r ( i . e . 0 .025 i n c h p e r h o u r a n d 0 .0022 i n c h e s p e r h o u r f o r the 2 .8 i n c h l o n g s a m p l e s u s e d ) . C H A P T E R I L i t e r a t u r e R e v i e w A L i t e r a t u r e R e v i e w 3.1 G e n e r a l S t r e n g t h p r o p e r t i e s of s o i l s have b e e n a subjec t of i n -tens ive study f o r a long t i m e . In the g e n e r a l e n g i n e e r i n g f i e l d " r e s i s t a n c e to d e f o r m a t i o n u n d e r e x t e r n a l l o a d s " w o u l d be a sui table d e f i n i t i o n of s t r e n g t h . T h e m o r e w i d e l y e n c o u n t e r e d p h e n o m e n o n of f a i l u r e of c o h e s i v e s o i l s i s i n s h e a r , a n d t h e r e -f o r e , a f u n d a m e n t a l u n d e r s t a n d i n g of s h e a r i n g r e s i s t a n c e of s o i l i s i m p o r t a n t . S o i l s m a y be v i s u a l i z e d as a c o m p r e s s i b l e skele ton of s o l i d p a r t i c l e s e n c l o s i n g v o i d s , w h i c h i n s a t u r a t e d s o i l s a r e f i l l e d w i t h w a t e r . S h e a r s t r e s s e s a r e c a r r i e d b y the skele ton-of the s o l i d p a r t i c l e s o n l y . O n the other h a n d the n o r -m a l s t r e s s c o n s i s t s of two p a r t s - - o n e , the s t r e s s c a r r i e d b y s o l i d p a r t i c l e s and the o t h e r , the p r e s s u r e i n the f l u i d i n the v o i d s p a c e . S h e a r i n g r e s i s t a n c e w i l l d e p e n d on the c o m p o n e n t of the n o r m a l s t r e s s c a r r i e d b y the s o l i d p a r t i c l e s r a t h e r than on the total n o r m a l s t r e s s . 3 .2 P r i n c i p l e of E f f e c t i v e S t r e s s e s The concept of e f f e c t i v e s t r e s s as it s tands today w a s c o n c e i v e d by T e r z a g h i i n c o n n e c t i o n w i t h the c o n s o l i d a t i o n t h e o r y w h i c h he p r e s e n t e d i n 1923. S k e m p t o n (I960) w h i l e t r a n s l a t i n g f r o m T e r z a g h i 1 s o r i g i n a l w o r k s a y s , " B e f o r e a p p l i c a t i o n of the p r e s s u r e i n c r e m e n t the p r e s s u r e a c t i n g i n the s o l i d phase,, of c l a y at e a c h 5 point i n the l a y e r is p Q and the e x c e s s p o r e p r e s s u r e is z e r o . F o l l o w i n g an i n c r e a s e i n p r e s s u r e on the u p p e r s u r f a c e of the l a y e r f r o m p Q to p p the h y d r o s t a t i c e x c e s s p r e s s u r e at any point has a p o s i t i v e v a l u e u and at the s a m e point the p r e s s u r e ac t ing on the s o l i d p h a s e of the c l a y has a v a l u e p , w h e r e p<Pj and f r o m the e q u i l i b r i u m of the l a y e r p^ = p + u " . A s f a r as the r e s p o n s e of s o i l s to loads is c o n c e r n e d it i s g e n e r a l l y a c c e p t e d that the b e h a v i o u r u n d e r s t r e s s is g o v e r n e d b y the f o l l o w i n g equat ion: cf - c~ - u 3 - 1 w h e r e cr i s the so c a l l e d e f f e c t i v e s t r e s s and cr i s t o t a l n o r m a l s t r e s s . 3 . 3 . S h e a r s t r e n g t h and its c o m p o n e n t s . C o u l o m b is c r e d i t e d to be the f i r s t to g i v e an e x p r e s s i o n of the shear r e s i s t a n c e of a c o h e s i v e s o i l = c + cr£ tan <£> 3 - 2 T h e concept of e f f e c t i v e s t r e s s e s w i t h r e s p e c t to shear s t r e n g t h was i n t r o d u c e d b y T e r z a g h i (1936). It was a l s o r e a l i z e d that a v a r i e t y of v a l u e s of c and <k> c o u l d be o b t a i n e d f r o m C o u l o m b ' s a n a l y s i s f o r the s a m e s o i l d e p e n d i n g on " tes t c o n d i t i o n s " , B j e r r u m (I960, t r a n s l a t i o n s of T e r z a g h i 1 w o r k ) . T h e i m p a c t of s t r e s s h i s -t o r y on the shear s t r e n g t h was b r o u g h t to l ight b y t e s t i n g the s a m e s o i l u n d e r v a r y i n g c o n s o l i d a t i o n p r e s s u r e s p r i o r to s h e a r . H v o r s l e v (1936, I960) i n d i c a t e d that c i n E q . 3-2 d e p e n d s to a l a r g e extent on 6 t h e v o i d r a t i o o r m o i s t u r e c o n t e n t at t h e t i m e o f f a i l u r e . H e p r e -s e n t e d a m o r e g e n e r a l e x p r e s s i o n a p p l i c a b l e t o c o h e s i v e s o i l s a s % s f (e) + ( (T- u) t a n c 6 e f 3 - 3 w h e r e f(e) i s a f u n c t i o n o f v o i d r a t i o . T e r z a g h i i n d i c a t e d t h a t t h e c o m p r e s s i v e s t r e n g t h o f a c o m p l e t e l y u n l o a d e d c l a y w i t h t e n s i o n -f r e e p o r e w a t e r p r e s s u r e i n c r e a s e s p r o p o r t i o n a t e l y w i t h t h e s o c a l l e d e q u i v a l e n t c o n s o l i d a t i o n p r e s s u r e , w h i c h i s r e l a t e d t o t h e v o i d r a t i o . It w o u l d a p p e a r t h a t t h e f a c t o r f (e) s h o u l d b e a f u n c t i o n o f c o n s o l i d a t i o n p r e s s u r e a n d s h o u l d h a v e u n i t s o f s t r e s s . H v o r s l e v o n t h e b a s i s o f d i r e c t s h e a r t e s t s r e p r e s e n t e d f(e^ b y k o r w h e r e = c c o n s o l i d a t i o n p r e s s u r e . F o r a n o r m a l l y c o n s o l i d a t e d c l a y s u b j e c t e d to a c o n s o l i d a t e d u n d r a i n e d . t r i a x i a l t e s t t h e e q u a t i o n c a n b e w r i t t e n a s . Kcrc + t<r-v~)f tasns cj>€ 3 - 4 -T o m e a s u r e t h e s h e a r i n g r e s i s t a n c e e i t h e r t h e c o m p r e s s i v e s t r e n g t h d e f i n e d a s t h e d i f f e r e n c e ' b e t w e e n m a j o r a n d m i n o r p r i n c i p a l s t r e s s e s at f a i l u r e ( o~ - <^%)i» o r t h e c o m p r e s s i v e s t r e n g t h p e r u n i t o f e f -1 6 r 6=1- a f -fective m i n o r p r i n c i p a l s t r e s s at f a i l u r e ( == ) £ , w h i c h i s t h e s a m e a s ( ^ / t r j )^ - 1, m a y b e u s e d , L e o n a r d s (1962 ) . M a x i m u m d e v i a t o r s t r e s s ( < s ^ ~ ° ~ 3 ^ a n c * m a x i m u m p r i n c i p a l e f f e c t i v e s t r e s s r a t i o ( o r / t r ^ ) h o w e v e r m a y n o t o c c u r at t h e s a m e s t r a i n . F o r s p e c i f i c p u r p o s e s , h o w e v e r , w e m a y s p e c i f y f a i l u r e a t a c e r t a i n p e r c e n t s t r a i n . 3 . 4 P h y s i c a l a n d P h y s i c o - C h e m i c a l E x p l a n a t i o n s f o r C o h e s i o n a n d F r i c t i o n . B j e r r u m L . (1954) o n t h e b a s i s o f c l a s s i c a l B o w d e n - T a b o r 7 t h e o r y o f f r i c t i o n e x p l a i n s f r i c t i o n a l r e s i s t a n c e a s d u e t o m o l e c u l a r b o n d s / a t c o n t a c t p o i n t s b e t w e e n t h e m i n e r a l g r a i n s . T h e r e s i s -t a n c e i s s u p p o s e d to i n c r e a s e l i n e a r l y w i t h t h e t o t a l a r e a o f a l l c o n t a c t p o i n t s . T h i s a r e a i s , i n t u r n , b e l i e v e d to i n c r e a s e l i n -e a r l y w i t h t h e t r a n s m i t t e d s t r e s s e s , w h i c h i s t r u e i f a t e a c h c o n -t a c t p o i n t t h e m i n e r a l s a r e l o a d e d to t h e i r y i e l d s t r e s s . I n t h a t c a s e t h e t r u e a n g l e o f i n t e r n a l f r i c t i o n w i l l d e p e n d o n t h e p r o p e r -t i e s o f t h e c o n t a c t i n g m i n e r a l g r a i n s a n d o n t h e e x t e n t t o w h i c h the s t r e s s e s a r e t r a n s m i t t e d t h r o u g h g r a i n s i n d i r e c t c o n t a c t o r t h r o u g h t h e w a t e r s h e l l s w h i c h s u r r o u n d t h e c l a y p a r t i c l e s . H e c o n s i d e r e d t r u e c o h e s i o n a s d u e to a t t r a c t i v e f o r c e s b e t w e e n c l a y p a r t i c l e s w h i c h a r e n o t i n d i r e c t c o n t a c t a n d d u e t o t h e r e s i s t a n c e of w a t e r s h e l l s a r o u n d t h e c l a y p a r t i c l e s . R o w e (1957) d i v i d e d s h e a r i n g s t r e n g t h i n t o t w o p a r t s , o n e c o n t r i b u t i n g t o t r u e c o h e s i o n a n d t h e o t h e r to t r u e f r i c t i o n . H e a t t r i b u t e d t r u e c o h e s i o n t o L o n d o n 1 . V a n d e r W a a l s f o r c e s o f a t t r a c -t i o n a n d t r u e f r i c t i o n t o i n t e r p a r t i c l e c o n t a c t s . H e s u g g e s t e d t h a t s t r o n g e s t b o n d s c a r r y m o s t o f t h e l o a d w h i l e t h e o t h e r s w i l l f a i l a n d t r a n s f e r s t r e s s w h i c h l e a d s to a g r a d u a l t r a n s f e r o f s h e a r i n g r e s i s t a n c e f r o m t r u e c o h e s i o n t o t r u e f r i c t i o n . P r e s u m a b l y t h e n , c o h e s i o n c o m e s f r o m t h e w e a k e r V a n d e r W a a l s B o n d s . N o r e a s o n w a s g i v e n b y R o w e f o r t h e a s s u m p t i o n t h a t o n l y V a n d e r W a a l ' s f o r c e s o f a t t r a c t i o n c o n t r i b u t e t o ' t r u e c o h e s i o n . L a m b e (I960) d e f i n e d c o h e s i o n as the r e s i s t a n c e w h i c h c a n be m o b i l i z e d b e t w e e n two a d j a c e n t p a r t i c l e s on a c c o u n t of the l i n k a g e f r o m the f o r c e s a r i s i n g w i t h i n the p a r t i c l e s t h e m s e l v e s . C o h e s i o n m a y a r i s e due to c e m e n t a t i o n , edge to f a c e f l o c u l a t i o n , H - b o n d i n g , k - b o n d i n g , e t c . F r i c t i o n w a s c o n c e i v e d as a r i s i n g out of e l e c t r i c a l and p h y s i c a l i n t e r f e r e n c e b e t w e e n the a d j a c e n t / p a r t i c l e s d u r i n g s h e a r d i s p l a c e m e n t s . S e e d , M i t c h e l l a n d C h a n (I960) m e n t i o n e d s t r e n g t h i n t e r m s of p h y s i c a l ( f r i c t i o n a l ) a n d p h y s i c o - c h e m i c a l ( c o h e s i o n ) c o m p o n -e n t s . T h e p h y s i c a l c o m p o n e n t i s a t t r i b u t e d p r i m a r i l y to g r a n u l a r p a r t i c l e s a n d f o r a g i v e n c o m p o s i t i o n the m a g n i t u d e of t h i s c o m ? / ponent i s e s s e n t i a l l y d e p e n d e n t on the e f f e c t i v e n o r m a l p r e s s u r e b e t w e e n trie p a r t i c l e s . C o h e s i o n i s t a k e n to m e a n that p a r t of / s t r e n g t h ' w h i c h i s i n d e p e n d e n t of a n y a p p l i e d p r e s s u r e s , e i t h e r m e c h / a n i c a ^ o r c a p i l l a r y . It i s c o n s i d e r e d as a b o n d i n g of p a r t i c l e s w i t h i n a s o i l m a s s b y p h y s i c o - c h e m i c a l m e c h a n i s m s of a n i n t e r -a t o m i c , i n t e r m o l e c u l a r o r i n t e r p a r t i c l e n a t u r e . S o m e o f the v a r i a b l e s d i s c u s s e d b y t h e m a r e i n t e r p a r t i c l e a t t r a c t i v e . f o r c e s , i n t e r p a r t i c l e r e p l u s i v e f o r c e s , w a t e r , e x t e r n a l f o r c e s , s t r e s s h i s t o r y and c h e m i c a l f a c t o r s . T h e i n t e r p a r t i c l e a t t r a c t i v e f o r c e s s u g g e s t e d a r e V a n d e r "Waals f o r c e s , c o u l o m b i c a t t r a c t i o n b e t w e e n n e g a t i v e s u r f a c e s a n d p o s i t i v e e d g e s , p a r t i c l e - c a t i o n - p a r t i c l e l i n k a g e e t c . I n t e r p a r t i c l e r e p l u s i v e f o r c e s a r i s e out of the i n t e r -a c t i o n of d o u b l e l a y e r s s u r r o u n d i n g a d j a c e n t p a r t i c l e s a n d L a m b e ( 1958) has l i s t e d the f a c t o r s i n f l u e n c i n g the double l a y e r . L i t -e r a t u r e i s c o n t r o v e r s i a l about the p r e c i s e n a t u r e of a d s o r b e d water s t r u c t u r e and its m o b i l i t y . R o s e n q v i s t ( 1959) c o n c l u d e d that any c o n t r i b u t i o n to s h e a r s t r e n g t h r e s u l t i n g f r o m w a t e r v i s c o s i t y is n e g l i g i b l e i n c o m p a r i s o n w i t h the c o n t r i b u t i o n of i n t e r p a r t i c l e a t t rac t ive f o r c e s . A l t h o u g h the f a i l u r e p l a n e p a s -ses t h r o u g h the water s e p a r a t i n g p a r t i c l e s at p o i n t s of c l o s e s t a p p r o a c h , it a p p e a r s that the r e s i s t a n c e to s h e a r i s a t t r ibutable to the bond c a u s e d by a t t r a c t i v e f o r c e s o r i g i n a t i n g i n the p a r t i -c l e s t h e m s e l v e s and h o l d i n g t h e m i n p o s i t i o n . M i t c h e l l (1964) e x p r e s s e d the s t r e n g t h as a f u n c t i o n of the f o l l o w i n g S t r e n g t h - F (e, <k>, c , c , H , T , £ , _ , o j u , S]) and f o r a g iven s o i l at a g i v e n v o i d r a t i o D = ({£, e,. T , _ , tp , w h e r e D = D e v i a t o r s t r e s s 6= a p a r a m e t e r e x p r e s s i n g f r i c t i o n a l c h a r a c t e r i s t i c s of s o i l c - a p a r a m e t e r e x p r e s s i n g the i n t e r p a r t i c l e c o h e s i o n of s o i l c'= r e p r e s e n t s s o i l c o m p o s i t i o n i n c l u d i n g s o l i d l i q u i d and gaseous p h a s e s H = i s e q u i v a l e n t of s t r e s s h i s t o r y T is absolute t e m p e r a t u r e £ c o r r e s p o n d s to s t r a i n £ c o r r e s p o n d s to s t r a i n r a t e r e f e r s to a p p l i e d s t r e s s u. stands f o r p o r e p r e s s u r e 7 • / j f o r s o i l s t r u c t u r e . A c o m p r e h e n s i v e t r e a t m e n t of the d e v e l o p m e n t of an i n s t a n -/ taneous a x i a l strain- ra te equat ion on the b a s i s of r a t e p r o c e s s / t h e o r y was i n i t i a l l y g i v e n by M i t c h e l l (1964) and s u b s e q u e n t l y r e v i s e d by C a m p a n e l l a (1965). It r e l a t e s the r u p t u r e and r e -/ f o r m a t i o n of bonds on a m i c r o s c o p i c s c a l e to the ra te of d e -f o r m a t i o n on a m a c r o s c o p i c s c a l e and c a n be w r i t t e n as : i =X— e x p J e x P ( D * N ) 3 " 5 h R T ' 4 S R T w h e r e X ^ s a f u n c t i o n of both p the total n u m b e r of b o n d s p e r u n i t length i n the a x i a l d i r e c t i o n and the a v e r a g e a x i a l c o m p o n e n t of d i s p l a c e m e n t r e s u l t i n g f r o m a s i n g l e b o n d r u p t u r e at a g i v e n instant of t i m e . k = Boltzmann's C o n s t a n t h = P l a n c k ' s C o n s t a n t F = A v e r a g e f r e e e n e r g y of a c t i v a t i o n r e q u i r e d to r u p t u r e a b o n d . R = G a s C o n s t a n t A = d i s t a n c e between s u c c e s s i v e e q u i l i b r i u m p o s i t i o n s , N = A v o g a d r o ' s n u m b e r S = N u m b e r of i n t e r p a r t i c l e bonds p e r unit c r o s s s e c t i o n o v e r w h i c h the d e v i a t o r s t r e s s i s d i s -t r i b u t e d . D = a p p l i e d d e v i a t o r s t r e s s 11 P u t t i n g X ^ T = B and a s s u m i n g that S = a + b CTm and t a k i n g the l o g r i t h m of both the s i d e s i n E q . 3-5 it c a n be w r i t t e n as D = __I a ( ^ £ + m ( i - ) V U < n h | ' 4 R T b ( 4 H + m i _ )] 3 - 6 A N B V J " R T B . J A N \ R T w h e r e a = r e p r e s e n t s the n u m b e r of i n t e r p a r t i c l e bonds r e s i s t i n g d e f o r m a t i o n at z e r o m e a n n o r m a l e f f e c t i v e s t r e s s a n d a c c o u n t s f o r s o i l " c o h e s i o n " and b d e f i n e s the r e l a t i o n s h i p b e t w e e n S and ~ m ( m e a n n o r m a l e f f e c t i v e s t r e s s ) . If b i s p o s i t i v e S i n c r e a s e s wi th i n c r e a s i n g <J~m. It i s i m p o r t a n t to note that " a " is not constant and i s i n -f l u e n c e d by s t r e s s h i s t o r y and s t r u c t u r e . E q . 3 - 6 i s a n a l o g o u s to the g e n e r a l e q u a t i o n . ' t = C e -t- o~ t a n $ e 3-7 i n the sense that E q . 3 - 6 a l s o c o n s i s t s of two d i s t i n c t p a r t s -one dependent upon e f f e c t i v e s t r e s s and the o ther i n d e p e n d e n t of ef fec t ive s t r e s s . It m a y be n o t e d i n E q . 3 - 6 that s t r a i n r a t e affects both c e and <t>e. W h e n s t r a i n ra te i n c r e a s e s then c e a n d ^ <t>& i n c r e a s e , i f a l l o ther f a c t o r s r e m a i n c o n s t a n t . E f f e c t of s t r u c t u r e i s f o r the m o s t p a r t r e p r e s e n t e d t h r o u g h the t e r m S3 (S = a-f bo~ m ) ; " a " r e p r e s e n t s the n u m b e r of i n t e r p a r t i c l e b o n d s and accounts f o r s o i l c o h e s i o n . C h a n g e i n s t r u c t u r e w i l l change the n u m b e r of i n t e r p a r t i c l e bonds and the v a l u e of " a " w i l l be c h a n g e d . In E q . 3 - 6 a change i n the v a l u e of " a " w i l l a f fec t the v a l u e of the f i r s t t e r m . S t r u c t u r e i s l i k e l y to a f fec t c o h e s i o n s i g n i f i c a n t l y . I2 3. 5 C l a y S t r u c t u r e and E f f e c t s of S t r u c t u r e on S t r e n g t h . T e r z a g h i i n 1925 s u g g e s t e d v a r i o u s s i n g l e - g r a i n and h o n e y c o m b s t r u c t u r e s as an e x p l a n a t i o n of the g r e a t v a r i a t i o n s i n v o i d r a t i o and b e h a v i o u r of s o i l s . C a s a g r a n d e (1932) p r o -p o s e d a c o m p o u n d h o n e y c o m b s t r u c t u r e of s i l t g r a i n s and f l o c c u l a t e d c l a y p a r t i c l e s f o r s e n s i t i v e u n d i s t u r b e d c l a y s . L a m b e (1953, 1958) s u g g e s t e d that c l a y s w h i c h w e r e f l o c c u l a t e d d u r i n g s e d i m e n t a t i o n or c o m p a c t e d at w a t e r contents l e s s than o p t i m u m , have a r a n d o m o r i e n t a t i o n of c l a y p a r t i c l e s o r a ' t a r d h o u s e " type of s t r u c t u r e . O n the other h a n d c l a y s w h i c h w e r e d i s p e r s e d d u r i n g s e d i m e n t a t i o n , or c o m p a c t e d at a w a t e r content g r e a t e r than the o p t i m u m h a v e p a r a l l e l o r i e n t e d p a r t i c l e s . T h e f i n a l s o i l s t r u c t u r e is a r e s u l t of the i n t e r a c t i o n of a n u m b e r of v a r i a b l e s , L a m b e (1958). R o s e n q v i s t (1959) o b t a i n e d s t e r e o -p h o t o g r a p h s of the s t r u c t u r e of u n d i s t u r b e d c l a y s b y m e a n s of e l e c t r o n m i c r o s c o p e and found that the s t r u c t u r e of m a r i n e c l a y s / i n g e n e r a l is a r a n d o m o r i e n t a t i o n of p a r t i c l e s and r e s e m b l e s the c a r d h o u s e s t r u c t u r e s u g g e s t e d b y T a n (1957) and L a m b e (1958). B u e s s e m and N a g y (1953), S a l a s and S e r r a t o s a (1953) a n d . / M i t c h e l l (1956) u s e d x - r a y d i f f r a c t i o n or p o l a r i z e d l i g h t and / b i r e f r i n g e n t p r o p e r t i e s of c l a y c r y s t a l s to i n v e s t i g a t e the r e -l a t i v e o r i e n t a t i o n of c l a y p a r t i c l e s . P a r t i c l e s i n r e m o l d e d a n d u n i a x i a l l y r e c o n s o l i d a t e d c l a y s w e r e f o u n d o r i e n t e d p e r p e n d i -c u l a r l y to the d i r e c t i o n of p r i n c i p a l c o n s o l i d a t i n g s t r e s s . M i t c h e l l I I / 13 (1956) a l s o s t u d i e d t h e s t r u c t u r e o f m a n y u n d i s t u r b e d c l a y s w h i c h i n s o m e c a s e s h a d a c o m p l e t e l y r a n d o m o r i e n t a t i o n o f p a r t i c l e s w h e r e a s o t h e r s h a d v a r i o u s d e g r e e s o f p r e f e r r e d o r i e n t a t i o n . T h e r a t e p r o c e s s h y p o t h e s i s p r e s e n t e d b y E q . 3 - 6 d e m o n s t r a t e s tha t the m o s t i m p o r t a n t f a c t o r i n f l u e n c i n g s t r e n g t h m a y b e the t o t a l n u m b e r o f i n t e r p a r t i c l e b o n d s p e r u n i t a r e a o f s o i l c r o s s s e c t i o n . A f l o c c u l a t e d s t r u c t u r e w o u l d g i v e m o r e i n t e r p a r t i c l e b o n d s t h a n a d i s p e r s e d o n e . S h e a r i n g r e s i s t a n c e of f l o c c u l a t e d s t r u c t u r e s h o u l d , t h e r e f o r e , e x c e e d t h a t o f d i s -p e r s e d o n e s . T h e s e r e m a r k s c a n n o t b e i n t e r p r e t e d t o r e f l e c t s o l e l y t h e i n f l u e n c e o f t h e t e r m S , b e c a u s e at a g i v e n v o i d r a t i o d i f f e r e n t v a l u e s o f e f f e c t i v e s t r e s s e s m a y b e a s s o c i a t e d w i t h d i f f e r e n t s t r u c t u r e s . R e m o l d i n g i n d u c e s s h e a r s t r a i n s a n d d i s t u r b s t h e s t r u c t u r e o f t h e s o i l a n d i t m a y b e a s s u m e d t h a t t h e p a r t i c l e s a f t e r t h o r o u g h r e m o l d i n g h a v e a d i s p e r s e d s t r u c -t u r e w i t h c o n s i d e r a b l y l e s s i n t e r p a r t i c l e b o n d s . W u , D o u g l a s a n d G o u g h n o u r (1962) o n t h e b a s i s o f t h e i r t e s t r e s u l t s c o n c l u d e d t h a t : 1. R e m o l d e d c l a y s h o w e d a c o n t i n u o u s i n c r e a s e of t h e d e v i a t o r s t r e s s w i t h s t r a i n . P o r e w a t e r p r e s s u r e i n -c r e a s e d at a r a p i d r a t e d u r i n g t h e i n i t i a l p a r t o f t h e t e s t b u t a p p r o a c h e d a c o n s t a n t v a l u e a t l a r g e s t r a i n s . 2 . U n d i s t u r b e d c l a y b e h a v e d d i f f e r e n t l y . D e v i a t o r s t r e s s e s r e a c h e d a m a x i m u m v a l u e at a r e l a t i v e l y s m a l l s t r a i n 14 and d e c r e a s e d s l i g h t l y . P o r e w a t e r p r e s s u r e i n c r e a s e d p r o g r e s s i v e l y . 3. C o h e s i o n was m o b i l i z e d at a v e r y s m a l l s t r a i n w h e r e a s f r i c t i o n was d e v e l o p e d only af ter the m a t e r i a l d e f o r m e d to s t r a i n s of 0 .05 p e r cent or m o r e . L e o n a r d s and A l t a c h a e f f (1964) e x p l a i n e d the s t r e s s -s t r a i n r e s p o n s e of u n d i s t u r b e d and r e m o l d e d c l a y s . T h e y a s s u m e d a n o r m a l g a u s s i a n d i s t r i b u t i o n of the m a g n i t u d e of i n t e r p a r t i c l e bonds w i t h a s t a n d a r d d e v i a t i o n <C- a m e a s u r e of range i n b o n d s t r e n g t h . In r e m o l d e d c l a y s «C i s l a r g e a n d so s t r e s s - s t r a i n r e s p o n s e i s g r a d u a l . In u n d i s t u r b e d c l a y s <£ i s m u c h s m a l l e r . A f t e r a c r i t i c a l s t r e s s l e v e l is r e a c h e d a s m a l l i n c r e a s e i n s t r e s s b r e a k s a l a r g e n u m b e r of b o n d s a n d a m a r k e d change i n s t r e s s - s t r a i n r e s p o n s e is o b s e r v e d . O n c e a c r i t i c a l stage i s r e a c h e d s l i d i n g o c c u r s at m o s t of the c o n t a c t p o i n t s . T h i s c a n r e s u l t i n an i n c r e a s e or d e c r e a s e of b o n d s t r e n g t h s i n c e bonds m a y be b r o k e n at one point a n d r e f o r m e d at a n o t h e r . If the net effect i s t o w a r d s a d e c r e a s e i n b o n d strength' s h e a r f a i l u r e w i l l r e s u l t . & / / M i t c h e l l (1964) r e v i e w e d the data r e p o r t e d b y S c h m e r t m a n n •/ / and O s t e r b e r g (I960) i n the l i g h t of ra te p r o c e s s t h e o r y . T h e u n d i s t u r b e d s p e c i m e n s h o w e d an i n i t i a l p e a k i n c o h e s i o n at l o w / s t r a i n s as the n u m b e r of i n t e r p a r t i c l e b o n d s was l a r g e . F u r t h e r 15 deformation resulted in the destruction of undisturbed structure and increased dispersion, i.e. , the number of interparticle / bonds was, decreased which resulted in a gradual decrease of cohesion. Curves for remolded soils exhibited essentially constant cohesion beyond about 2% axial strain. Deformations were not likely to lead to appreciable structural change in these speci-/ mens 'as they were thoroughly reworked prior to shear. Thus the number of interparticle bonds remained almost constant as / j shear strains increased. 3.6 Effects of rate of strain on the strength. Vicat in 1833 and Collins in 1846 recognized that for a proper discussion of the strength of clay soils the effects of time should be considered. One of the most important ef-fects of time on strength is that of strain rate on the undrained shear strength of cohesive soils. This problem has been in-vestigated by many authors in relation to undisturbed, remolded and compacted clays. Hvorslev (1938) indicated the effect of rate of strain on shear strength in explicit terms. He indi-cated that rapid shear tests may give 10 to 20% higher values for strength than slow tests. He compared the test results on different batches of Little Belt clay and Vienna clay and sug-gested that the difference is due to structural viscosity. In (I960) he indicated that these results cannot be used to determin< 16 the s t r e n g t h d i f f e r e n c e due to t i m e as tests w e r e r u n on d i f f e r -end batches of c l a y . In this p a p e r w h i l e c o m p a r i n g r e s u l t s for V i e n n a c l a y he c o n c l u d e d that c o h e s i o n d e c r e a s e d w i t h i n -c r e a s e i n t i m e a s s u m i n g the f r i c t i o n a l c o m p o n e n t as c o n s t a n t . C a s a g r a n d e and W i l s o n (1951) s u g g e s t e d that the d e -c r e a s e i n s t r e n g t h w i t h d e c r e a s e i n s t r a i n r a t e m i g h t be c a u s e d by a change in the e x c e s s p o r e p r e s s u r e g e n e r a t e d d u r i n g the shear p r o c e s s . B j e r r u m et a l (1958) r e p o r t e d a d e c r e a s e i n (07 - 0 3 ) / 2 w i t h i n c r e a s i n g t i m e to f a i l u r e . T h e p o r e - p r e s s u r e p a r a m e t e r A at m a x i m u m v a l u e of - CTJ) i n c r e a s e d at s l o w e r r a t e s of s t r a i n . T h e y c o n c l u d e " the i n c r e a s e i n p o r e p r e s s u r e at f a i l u r e w i t h t i m e is not s u f f i c i e n t to a c c o u n t f o r the whole d e c r e a s e i n u n d r a i n e d s h e a r s t r e n g t h w i t h t i m e a n d t h e r e f o r e , a r e d u c t i o n i n t rue c o h e s i o n a n d / o r t r u e a n g l e of f r i c t i o n m u s t have t a k e n p l a c e as the ra te of l o a d i n g d e c r e a s e d . " A s i m i l a r t r e n d i n t e r m s of ( rr^ - <T^ ) m a x i m u m A | a n d p o r e p r e s s u r e s (h igher p o r e p r e s s u r e s at s l o w e r r a t e s of strain) "has; b e e n r e p o r t e d b y C r a w f o r d (1959). S e e d , M i t c h e l l and C h a n (I960) i n d i c a t e d that the effec ts of r e d u c t i o n i n the rate of l o a d i n g on the s t r e n g t h of c o m p a c t e d c l a y s m a y d e p e n d on the f o l l o w i n g f a c t o r s . 1. A t e n d e n c y f o r the s t r e n g t h to d e c r e a s e b e c a u s e of i n c r e a s e d t i m e a v a i l a b l e f o r c r e e p d e f o r m a t i o n s . - a l s o 17 L e o n a r d s a n d A l t a c h a e f f ( 1 9 6 4 ) . 2 . A t e n d e n c y f o r the s t r e n g t h t o i n c r e a s e d u e t o n o r m a l t h i x o t r o p i c s t r e n g t h i n c r e a s e s i n r e m o l d e d c l a y s . 3 . A t e n d e n c y f o r the s t r e n g t h t o i n c r e a s e b e c a u s e o f i n c r e a s e d t i m e a v a i l a b l e f o r r e g a i n o f t h i x o t r o p i c s t r e n g t h l o s t d u r i n g i n i t i a l d e f o r m a t i o n s u n d e r l o a d i n c r e m e n t s . 4 . A t e n d e n c y f o r t h e s t r e n g t h t o d e c r e a s e d u e t o a m a n i f e s t a t i o n o f the c r e e p s t r e n g t h p h e n o m e n o n s i m i l a r t o t h a t r e p o r t e d b y C a s a g r a n d e a n d W i l s o n (1951) f o r u n d i s t u r b e d c l a y s . A t t h e s l o w e s t l o a d i n g r a t e s , i n c r e a s e d b r i t t l e n e s s m a y b e b u i l t i n t o t h e s p e c i m e n a n d r e l a t i v e l y s u d d e n l o s s o f s t r e n g t h m a y t a k e p l a c e . T h e ' c o m p o n e n t s c g a n d 4>Q d o n o t r e a c h t h e i r m a x i m u m v a l u e s a t t h e s a m e s t r a i n . T h e c o n c e p t ' c o n c e r n i n g •; t h e d e v -e l o p m e n t o f c a n d <i> w i t h s t r a i n w a s p r e s e n t e d b y L a m b e e e ( I 9 6 0 ) . S c h m e r t m a n n ( I960) p u b l i s h e d e x p e r i m e n t a l d a t a c o n -/ c e r n i n g . t h e d e v e l o p m e n t of c o h e s i o n a n d f r i c t i o n , w h i c h h e / c a l l e d / c e a n d <£>Q ( c o h e s i o n a n d f r i c t i o n at a n y s t r a i n ) , w i t h s t r a i n . H i s i n v e s t i g a t i o n s a n d s u b s e q u e n t d i s c u s s i o n s ( I 9 6 0 , 196V, 1962)' , i n v e s t i g a t i o n s o f W u , D o u g l a s a n d G o u g h n e r (1962) / / a n d o f B e a (1963) a r e i n l i n e w i t h t h e c o n c e p t o f L a m b e a n d p o i n t o u t t h e f o l l o w i n g : 1. F u n d a m e n t a l c o h e s i o n a n d f r i c t i o n a r e f u n c t i o n s of s t r a i n . T h e y m a y n o t a t t a i n t h e i r m a x i m u m v a l u e s s i m u l -t a n e o u s l y . 18 2 . C o h e s i o n i s d e v e l o p e d t o a m a x i m u m v a l u e at a m u c h l o w e r s t r a i n a n d c a n h a v e a p e a k . 3 . C o h e s i o n a t a g i v e n w a t e r c o n t e n t i s n o t a c o n s t a n t b u t i s a f u n c t i o n g r e a t l y d e p e n d e n t o n s t r u c t u r e . 4 . F r i c t i o n d e v e l o p s s l o w l y a n d a t t a i n s i t s m a x i m u m at l a r g e r s t r a i n s . 5 . In t h e c a s e o f r e m o l d e d s a m p l e s f r i c t i o n d e v e l o p s f a s t e r w i t h s t r a i n w i t h the d e c r e a s e i n s t r a i n r a t e . C o h e s i o n o n t h e o t h e r h a n d h a s a t e n d e n c y to d e v e l o p s l o w l y a n d t o a t t a i n l e s s e r v a l u e s a t d e c r e a s e d s t r a i n r a t e . H o r n a n d D e e r e (1962) r e p o r t e d o n t h e b a s i s o f t e s t s o n P h l o g o p i t e t h a t a n i n c r e a s e i n 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 t a k e s p l a c e w i t h t h e i n c r e a s e i n t h e r a t e o f s l i d i n g ( p a r t i c l e s o f c l a y h a v e c r y s t a l s t r u c t u r e v e r y s i m i l a r t o m i c a s a n d o t h e r l a y e r e d l a t t i c e m i n e r a l s ) . 3 . 7 M e t h o d s of d e t e r m i n i n g t r u e c o h e s i o n a n d t r u e f r i c t i o n . T r u e c o h e s i o n (c ) a n d T r u e f r i c t i o n (c6 ) c a n b e d e t e r -e e m i n e d , u s i n g M o h r ' s c i r c l e s , f r o m t h e t e s t r e s u l t s f r o m t w o s a m p l e s h a v i n g s a m e v o i d r a t i o at f a i l u r e b u t s i g n i f i c a n t l y d i f -f e r e n t e f f e c t i v e s t r e s s e s . S o m e o f t h e r e c e n t m e t h o d s a r e p r e -s e n t e d h e r e . A c o m p r e h e n s i v e t r e a t m e n t o f e a r l i e r m e t h o d s h a s b e e n g i v e n b y B j e r r u m ( 1 9 5 4 ) . M o s t o f t h e e a r l i e r m e t h o d s w e r e f o r r e m o l d e d s a m p l e s a n d w e r e r u n u n d e r d r a i n e d c o n d i t i o n s F i r s t M e t h o d B i s h o p (1962) s u g g e s t e d t h a t c . a n d i c a n b e o b t a i n e d e e 19 r u n n i n g a s e r i e s of tests on n o r m a l l y and o v e r - c o n s o l i d a t e d s p e c i m e n s . H e obta ined two s a m p l e s at s a m e v o i d r a t i o b y u s i n g s l i g h t l y d i f f e r e n t i n i t i a l c o n s o l i d a t i o n p r e s s u r e . F i g . 1 shows one s a m p l e n o r m a l l y c o n s o l i d a t e d a l o n g the v i r g i n c o n -s o l i d a t i o n c u r v e to a c o n s o l i d a t i o n p r e s s u r e p^ at a w a t e r c o n -tent of w . A n o t h e r s a m p l e is c o n s o l i d a t e d a l o n g the v i r g i n c o n s o l i d a t i o n c u r v e to p r e s s u r e p , , , pas t the p r e s s u r e p^ a n d is s l o w l y r e b o u n d e d to the w a t e r content w . S a m p l e s 1 and 2 are at the s a m e water content but at d i f f e r e n t e f f e c t i v e s t r e s s e s . T h e y a r e then s h e a r e d to f a i l u r e u n d e r u n d r a i n e d c o n d i t i o n s . D a t a c a n be p l o t t e d w i t h l /2( '<r - ^%)^ a long the o r d i n a t e a n d 1/2(0^+5^ )^  a long the a b s c i s s a as s h o w n i n F i g . 2. If c g i s the i n t e r c e p t and *f the s lope t h e n : - sin(6 e = tan y> c e = Cs e T h i s plot has b e e n u s e d b y a n u m b e r of i n v e s t i g a t o r s and i s t e r m e d " M o d i f i e d M o h r - C o u l o m b d i a g r a m . " R e f e r e n c e is a v a i l a b l e i n O l s o n (1963) and C a m p a n e l l a (1965). T h e B i s h o p ' s m e t h o d c a n be u s e d f o r s e p a r a t i n g cQ a n d (6£ at any s t r a i n and has b e e n u s e d i n the p r e s e n t i n v e s t i g a t i o n w i t h three s a m p l e s . D e t a i l s a r e g i v e n i n S e c t i o n 6 . 3 . S e c o n d M e t h o d . S c h m e r t m a n n (I960), (1963) a r g u e s that s i n c e s o i l s t r u c -ture i s a f u n c t i o n of s t r a i n p f u n d a m e n t a l c o h e s i o n and f r i c t i o n a r e 20 P < o 2 I IS1 2 8 a r-< 7 Loo 1 c r^ METHCJ) <3P OBTAIM/MG NORMALLY A-f-JD O l / £ R -Co^SoUDATE . J> S A M P L E A T S A M E W.TER C O N T E N T —ccb /itwi^w f£ | lb" T Cs i JL CDS4>C =5"-MOD|P!£J> M O H R- C O U L O M B EH AG. R A M F I G . 2 21 also functions of strain. In the earlier work he uses the notation of C^. and to represent cohesion and friction at any strain and in the subsequent paper he refers to them as independent and dependent components (Schmertmann, 1963-b) . His con-tention is that C & = c e and ^ = $ e at large strains after 0~i/c% maximum. To separate the components with strain it is necessary to have two effective stress conditions with the soil at identi-cally the same structure and to do this at any strain. F o r ex-ample, in F i g . 3, specimen 2 is at a slightly reduced effective stress than specimen 1 and if both are sheared by the same method we can separate out c and <£> at any strain £ . The e e x y problem is that it is difficult to obtain two or morespecimens that are sufficiently identical to begin with. Schmertmann pre-sented his curve hopping technique using only one specimen with the idea to minimize structrual changes. The technique is ex-plained with the help of F i g . 4. Higher erf curve is followed by the specimen under controlled pore pressures up to the strain £ . At strain 6- the imposed effective stress is changed and the speci-men hops down to the lower eff curve. Schmertmann found that an .adequate hop between curves results in a void ratio change of less than 1% and that it is possible to make several such hops in either directions without greatly changing the position of stress-strain curves. The curves at two levels (high and low) of effective 22 FiG. -"3 L o w 5y e ' e 2 % e s PE-RCEJ^T STRA)M SCHMERTMANN ' 5 COfttfE HOPPING-_ PIG. 4 / 23 s t r e s s can then be d r a w n ( F i g . 4 ) . T h e s e p a r a t i o n of c o m p o n -ents c and (6 at any s t r a i n c a n be done as shown i n F i g . 5 . F r o m two c u r v e s v a l u e s of S 7 - tn, and 0^ , a r e i n t e r p o l a t e d f o r a g i v e n 2. " s t r a i n and are plot ted w i t h <?7 - c^alons; the y - a x i s and cH a l o n g the x - a x i s . c6 and c a r e obta ined f r o m the r e l a t i o n s s h o w n i n F i g . 5. T h e use of M o h r ' s c i r c l e s f o r s e p a r a t i o n of c o m p o n e n t s in the s u b f a i l u r e r e g i o n is s o u n d , S c h m e r t m a n n (1963-c). T h e concept of this technique i s d e v e l o p e d on the p r e m i s e that e i t h e r v e r y l i t t le s t r u c t u r a l change o c c u r s w i t h e a c h hop or the s h e a r r e s i s t a n c e effects of any change a r e a l m o s t r e c o v e r a b l e w i t h cont inued s t r a i n . The i m p o s e d change i n e f f e c t i v e s t r e s s that s t a r t s the c u r v e hop can be p e r f o r m e d i n a v a r i e t y of w a y , S c h m e r t m a n n (1963-b). T h e advantage of th is t e c h n i q u e i s that o n l y one s p e c i -m e n is r e q u i r e d and u n d i s t u r b e d s p e c i m e n s c a n be t e s t e d . It is a l s o c o n s i d e r e d that the c u r v e hop does not r e s u l t i n s i g n i -f i cant s t r u c t u r a l changes and h e n c e two s a m p l e s o b t a i n e d b y c u r v e hopping a r e " i d e n t i c a l " . T h e test h o w e v e r , r e q u i r e s a set up of t r i a x i a l e q u i p m e n t w h i c h i s not c o m m o n l y a v a i l a b l e and r e q u i r e s cont inuous a d j u s t m e n t s and s u p e r v i s i o n d u r i n g the t e s t . It m a y a l s o be noted that the v o l u m e c h a n g e s w h i c h take p l a c e b e c a u s e of the hop m a y b e c o m e s i g n i f i c a n t . T h i r d M e t h o d W u , D o u g l a s and G o u g h n o u r (1962) d e t e r m i n e d c o h e s i o n FIG. 5 25 and friction by first hydrostatically consolidating three samples under a given pressure. The pressure was reduced on two of the specimens by 0.25 kg. per sq. cm. and 0.50 kg per sq. cm-re-sulting in one normally consolidated and two slightly over-consolidated specimens. The three specimens were considered to have almost identical void ratio for all practical purposes and were sheared to failure in undrained condition. The investigators termed this method as a variation of Schmertmann's and Oster-berg's method and used it in studying the development of cohesion and friction with strain. It is felt however, that this method is very similar to,.the firs t method. In the fi r s t method a special effort is made to get the same void ratio by using slightly dif-ferent initial consolidation pressures and here it is assumed that they are the same if the final pressures are "nearly"the same. At any strain the three specimens are acted upon by three different effective stresses. Maximum shear stress and average normal stress are plotted against each other on the lines of F i g . 2. The plot is used for the entire region of test data rather than using it at failure. As the water content of the speci-mens are almost equal ;the difference in shear stress can only be attributed to friction and the differences in effective stresses. A line through these points represents the stresses in three speci-mens at a;given strain and cohesion and friction can be separated out (Fig. 2) . / / 26 F o u r t h M e t h o d . C r a w f o r d (1963) p r e s e n t e d a m e t h o d f o r d e t e r m i n i n g the s h e a r p a r a m e t e r s i n u n d i s t u r b e d s e n s i t i v e s o i l s . T r u e f r i c t i o n w a s f o u n d f r o m n o r m a l l y c o n s o l i d a t e d s p e c i m e n s b e c a u s e i t w a s a s s u m e d t h a t t h e r e w a s t h e n n o c o h e s i o n a n d " t r u e c o h e s i o n " w a s f o u n d at s u c h l o w n o r m a l s t r e s s e s o n o v e r c o n s o l i d a t e d s p e c i m e n s t h a t t h e r e w a s a s s u m e d to b e n o f r i c t i o n . T h e d e t e r m i n a t i o n w a s a t s t r e s s e s l o w e r t h a n at f a i l u r e . It w a s a s s u m e d t h a t w h e n o n e - h a l f o f t h e m a x i m u m s h e a r s t r e s s h a s b e e n a p p l i e d , 5 0 % o f t h e t r u e f r i c t i o n a l r e -s i s t a n c e i s m o b i l i z e d . T h e t r u e f r i c t i o n w a s o b t a i n e d b y d o u b l i n g t h e r a t i o o f s h e a r s t r e s s to n o r m a l s t r e s s a t t h i s (50%) s t a g e of l o a d i n g f r o m n o r m a l l y c o n s o l i d a t e d s a m p l e s . / It i s f u r t h e r p o i n t e d out t h a t the p r o c e d u r e c a n b e r e p e a t e d a t o t h e r / l o a d i n g s t a g e s to c o m p u t e f r i c t i o n a n g l e f o r a n y s t r a i n . C o h e s i o n w a s o b t a i n e d b y s h e a r i n g t h e s p e c i m e n at l o w e f f e c -t i v e s t r e s s - - s o l o w t h a t the d e v e l o p m e n t o f f r i c t i o n i s l i m i t e d b y l o w n o r m a l s t r e s s . T h e s a m p l e ( u n c o n f i n e d ) w a s i m m e r s e d i n w a t e r a n d w a s s h e a r e d s l o w l y . M o h r s c i r c l e w a s p l o t t e d f o r m a x i m u m (&] - cr j^nd a t a n g e n t to t h i s at t h e c o m p u t e d f r i c t i o n a n g l e d e f i n e d the c o h e s i o n . F i f t h M e t h o d . C a m p a n e l l a (1965) i n d i c a t e d a n o t h e r m e t h o d i n c o r p o r -a t i n g t e m p e r a t u r e c h a n g e s to i n d u c e o v e r c o n s o l i d a t i o n a n d 27 thereby to produce a set of samples at the same water content but different effective stresses. The method in principle is as follows: A' set of samples is consolidated to the same consoli-dation pressure at one temperature. Leaving one sample at this temperature, the temperature of the rest of the samples / is increased by different amounts under undrained conditions. In this way the pore pressures of the samples are changed by different amounts and a set of samples at the same water con-tent but different effective stresses are obtained. They can then be sheared and c and & determined. F i g . 2 can be e e used for the separation of c^and <t>Q . Sixth Method. Noorany and Seed (1965) proposed a method of obtaining samples at the same void ratio and almost the same structure but with differing effective stresses. The method involves anisotropic consolidation of two samples to the same void ratio after which time both samples are converted to undrained conditions. Then the deviator stress is removed from one sample which gives two samples at the same void ratio but dif-ferent effective stresses. The samples are then sheared at constant void ratio and separation of Mohr's cir c l e s at any strain allows the determination of friction and cohesion. Con-siderable separation was obtained for sensitive soils and hence they advocate the use for sensitive clays in particular. C H A P T E R I V E q u i p m e n t 28 E q u i p m e n t E q u i p m e n t ' F o r t h e p u r p o s e s o f t h i s i n v e s t i g a t i o n c o n s o l i d a t e d -u n d r a i n e d t r i a x i a l t e s t s w e r e r u n . T h e e q u i p m e n t u s e d i s s h o w n d i a g r a m a t i c a l l y i n F i g s . 6 a n d 7 . T h e a p p a r a t u s h a s b e e n d e s c r i b e d i n d e t a i l b y B y r n e (1966) a n d H i r s t (1966) a n d w a s m o d i f i e d a s f o l l o w s . (a) A F a i r c h i l d - S t r a t o s p r e c i s i o n a i r p r e s s u r e r e g u -l a t o r w a s c o n n e c t e d i n t o t h e l i n e to a d j u s t t h e b a c k p r e s s u r e s w h i c h a r e i n d i c a t e d b y a n e l e c t r o n i c p r e s s u r e t r a n s d u c e r . T h e r e g u l a t o r c o n t r o l l e d p r e s s u r e s t o b e t t e r t h a n i 0 . 0 2 l b s p e r s q . i n . (b) T h e t r i a x i a l c e l l w a t e r w a s c o n n e c t e d t o t h e t r a n s -d u c e r to f a c i l i t a t e t h e r e a d i n g o f c e l l p r e s s u r e s . R e a d i n g s o f c e l l p r e s s u r e s a n d p o r e p r e s s u r e s at e a c h s e t o f o b s e r v a t i o n w i t h the s a m e p r e s s u r e t r a n s d u c e r g a v e a v e r y a c c u r a t e r e a d i n g of the e f f e c t i v e s t r e s s e s . T h e e l e c t r i c a l t r a n s d u c e r ( D a t a S e n s o r s N o . P B 519A) h a d a r a n g e o f 0 - 1 5 0 l b s . p e r s q . i n . a b s o l u t e a n d a r a t e d c o m -p l i a n c e of 2 . 7 X 1 0 - ^ c u . i n . p e r l b s . p e r s q . i n . c h a n g e i n p r e s s u r e . T h e s y s t e m w a s c a l i b r a t e d a g a i n s t a d e a d l o a d t e s t e r . T h e c a l i b r a t i o n w a s f o u n d to b e l i n e a r w i t h p r e s s u r e , a n d p r e s -s u r e c h a n g e s o f 0 . 0 2 5 l b s . p e r s q . i n . c o u l d b e r e a d i l y m e a s u r e d . 29 To IVOLVn^Lgej, \l(XCuu,vr^ ft t # « | W 5/s o.b A L£G£>JJD {slow ih'i^) •TR/AXIAL CELL A N D C H A M B E R P e £ S S U R E M O T T ° 5 C M £ " S y s T E M FIG. <S 3 0 De- Aired. CorvruexitLOlKS Tr-ia~x.LcdL(aXX. 0 Ye, O . D . 10-c-c. buj/ctlEe. / 0 (6cu^c O-lcop*) / 1 ® LEGEKP X Hc#c S^m> VafcV NOT Tb ScTAi-E. S Y S T E M P I G . r A s t h e t r a n s d u c e r m e a s u r e d p r e s s u r e o n t h e a b s o l u t e s c a l e , b a r o m e t r i c r e a d i n g s w e r e t a k e n to r e f e r t h e p r e s s u r e t o g a u g e p r e s s u r e . T e s t s w e r e r u n i n a c o n s t a n t t e m p e r a t u r e r o o m i n w h i c h t e m p e r a t u r e w a s c o n t r o l l e d to 2 0 ° C ± 1° C. F i g s . 8 a n d 9 s h o w t h e t r i a x i a l c e l l w i t h s a m p l e , t r a n s d u c e r , a n d s t r a i n i n d i -c a t o r s . T h e w o o d e n f r a m e o f t h e c o n s t a n t t e m p e r a t u r e r o o m i s v i s i b l e i n t h e b a c k g r o u n d i n F i g . 9 . A l l t e s t s w e r e s t r a i n c o n t r o l l e d . T h e g e a r s y s t e m p e r m i t t e d t h i r t y d e f o r m a t i o n r a t e s f r o m 1 . 9 0 5 i n c h p e r h o u r to 0 . 0 0 0 1 4 6 i n c h p e r h o u r . A p r o v i n g r i n g w a s u s e d t o m e a s u r e t h e d e v i a t o r f o r c e i n t h e r a m . A s e a t i n g s t r e s s , n o t g r e a t e r t h a n 0 . 6 l b s . p e r s q . i n . w a s p l a c e d o n a l l s a m p l e s . T h e f o r c e d u e to u p l i f t a n d f r i c t i o n at t h e b u s h i n g w a s o b t a i n e d b y m o v i n g t h e l o a d i n g p l a t f o r m at the i n t e n d e d t e s t r a t e w i t h n o s a m p l e i n t h e c e l l . D e f o r m a t i o n s , ' i n t e r m s o f c h a n g e i n t h e s a m p l e l e n g t h , w e r e m e a s u r e d b y a 0 . 0 0 1 i n c h p e r d i v i s i o n d i a l g a u g e . T h e b a c k p r e s s u r e l i n e s w e r e d e a i r e d b y f l u s h i n g w i t h b o i l e d w a t e r at a b o u t 1 5 0 ° F . T h e s y s t e m w a s a l l o w e d t o c o o l a f t e r d e a i r i n g a n d c o n n e c t i o n s w e r e c h e c k e d f o r p o s s i b l e l e a k a g e . TRJAXIAL UWIT 1/vJITH SAMPLB C O N S O L I D A T I N G FIG S I Ay/At- EQUIPMENT W , T M 3TRA1W ,MD1CATOfLS C H A P T E R V F i e l d S a m p l i n g , S a m p l e P r e p a r a t i o n a n d P r o p e r t i e s o f C l a y T e s t e d F i e l d S a m p l i n g , S a m p l e P r e p a r a t i o n a n d P r o p e r t i e s o f C l a y T e s t e d 5 .1 F i e l d S a m p l i n g . B l o c k s a m p l e s w e r e o b t a i n e d f r o m t h e d e p o s i t o f t h e s e n s i t i v e c l a y at H a n e y , . B r i t i s h C o l u m b i a . A n o p e n p i t w a s h a n d d u g a n d h a d a n a r e a o f a b o u t 12 s q u a r e f e e t a n d a d e p t h o f 3 f e e t i n o r d e r to i s o l a t e a l a r g e b l o c k o f s o i l . T h e t o p 18 i n c h e s o r s o o f t h e u n d i s t u r b e d c l a y w a s r e m o v e d a n d b l o c k s a m p l e s w e r e c u t u s i n g f i n e p i a n o w i r e . T h e s e w e r e t r i m m e d t o r o u g h c u b e s h a v i n g 9 inch< s i d e s a n d w e r e c o a t e d w i t h w a x at t h e s i t e . B l o c k s w e r e c a r e f u l l y t r a n s f e r r e d t o t h e l a b o r a t o r y a n d w e r e g i v e n a -n o t h e r c o a t of w a x . T h e y w e r e s t o r e d i n a h u m i d r o o m u n t i l r e -q u i r e d . 5 . 2 S a m p l e P r e p a r a t i o n f o r t r i a x i a l t e s t i n g . S a m p l e p r e p a r a t i o n i s d e s c r i b e d i n d e t a i l i n A p p e n d i x A . A l l t e s t s w e r e r u n o n c y l i n d r i c a l s a m p l e s 2 . 8 i n c h e s l o n g a n d 1 . 4 i n c h e s i n d i a m e t e r . T r i m m i n g t o o l s a r e s h o w n i n F i g . 10 . B e -c a u s e o f t h e l a m i n a t e d n a t u r e o f t h e c l a y , w a t e r c o n t e n t s w e r e a v e r a g e d f r o m s i d e t r i m m i n g s o n l y . C o n t i n u o u s s l i t f i l t e r p a p e r s i d e d r a i n s w e r e u s e d a r o u n d to e x p e d i t e t h e s a m p l e / d r a i n a g e a n d p o r e - p r e s s u r e e q u a l i z a t i o n . F u r t h e r r e m a r k s a b o u t c o n t i n u o u s s l i t f i l t e r p a p e r s i d e d r a i n s a r e g i v e n i n S e c t i o n 6 . 1 . A s e a t i n g l o a d o f a b o u t 0 . 6 l b s . p e r s q . i n . w a s 3 4 TRIMMING EQUIPMENT FIG 10 35 c o n t i n u o u s l y m a i n t a i n e d o n t h e s a m p l e d u r i n g c o n s o l i d a t i o n . 5. 3 P r o p e r t i e s o f t h e c l a y t e s t e d T h e p r o p e r t i e s o f H a n e y c l a y h a v e b e e n s u m m a r i z e d / b y B y r n e (1966) a n d a r e r e p r o d u c e d h e r e i n b r i e f . T h e c l a y h a s a d a r k b l u e g r e y c o l o u r w h e n w e t a n d r e s e m b l e s t h e c o l o u r /' of n e a t c e m e n t w h e n d r y . In t h e p a r t i a l l y d r y s t a t e l i g h t a n d / . . d a r k l a m i n a t i o n s of v a r y i n g t h i c k n e s s e s a r e e v i d e n t . T h e p h y s i -/ * c a l p r o p e r t i e s of t h e c l a y t e s t e d a r e l i s t e d i n T a b l e I . C h e m i c a l • • / p r o p e r t i e s a r e a s i n T a b l e I I . G r a i n s i z e d i s t r i b u t i o n i s g i v e n / i n F i g . 11. A t y p i c a l c o n s o l i d a t i o n c u r v e i s g i v e n i n F i g . 12. 3 36 T A B L E I P h y s i c a l P r o p e r t i e s o f H a n e y C l a y S p e c i f i c G r a v i t y L i q u i d L i m i t P l a s t i c L i m i t P l a s t i c i t y I n d e x N a t u r a l W a t e r C o n t e n t P e r c e n t F i n e r T h a n 2 M i c r o n s A c t i v i t y ( P I - j - % < 2/*) U n d i s t u r b e d u n c o n f i n e d C o m p r e s s i v e S t r e n g t h R e m o l d e d U n c o n f i n e d C o m p r e s s i v e S t r e n g t h S e n s i t i v i t y M a x i m u m P a s t P r e s s u r e 2 . 8 0 44% 26% 18% 4 2 % ± 1% 46% 0 . 4 1550 l b s / s q . f t . 130 l b s / s q . f t . 12 5 5 0 0 l b s / s q . f t . ( 3 8 p s i ) 37 T A B L E II C h e m i c a l P r o p e r t i e s o f H a n e y C l a y . G r a i n S i z e M i n e r a l A m o u n t P r e s e n t S i l t F r a c t i o n ( G r e a t e r t h a n 2 m i c r o n s ) Q u a r t z F e l d s p a r C h l o r i t e M i c a A m p h i b o l e L a r g e L a r g e M o d e r a t e - S m a l l M o d e r a t e - S m a l l . S m a l l C l a y F r a c t i o n • ( l e s s t h a n 2 m i c r o n s ) C h l o r i t e F e l d s p a r M i c a / c h l o r i t e C h l o r i t e Q u a r t z M i c a A m p h i b o l e L a r g e M o d e r a t e - S m a l l M o d e r a t e - S m a l l S m a l l S m a l l S m a l l - q u e s t i o n a b l e 38 So 2 Z UJ Cs. VJ . I -T. <SAAIN £ / Z £ CJ-ASSI PIC AT/ON SUA CocxjrSJU Med-Ckxj 5 r ^ 005" 002. O O i OOo;5 0 002. OOO/ 0-0003 C^RAIM E>1AMEX£R, JM MM <S«AJM SVZE £HSTR( MOTION OP HAN£y F J 6 r . II CLAY FiCt. IZ H A P T E R V I T e s t i n g P r o c e d u r e 4 0 T e s t i n g P r o c e d u r e  6 .1 R a t e s of S t r a i n N o n - u n i f o r m s t r e s s e s a n d s t r a i n d u e t o e n d r e s t r a i n t l e a d to n o n - u n i f o r m p o r e p r e s s u r e s i n t h e u n d r a i n e d t e s t ( B i s h o p a n d H e n k e l , 1962 ) . U n d i s t u r b e d c l a y s , i n a d d i t i o n , a r e n o t l i k e l y to b e h o m o g e n e o u s a n d t h i s m a y a l s o l e a d to n o n - u n i f o r m p o r e p r e s s u r e s . T h e r a t e o f t e s t i n g s h o u l d b e c h o s e n s u c h t h a t p o r e - . i p r e s s u r e s t h r o u g h o u t t h e s a m p l e a r e c o n t i n u o u s l y e q u a l i z e d . / / B i s h o p a n d / H e n k e l (1962) a n d B l i g h t (1963) h a v e p r e s e n t e d d a t a j f o r d e t e r m i n i n g t h e r a t e o f s t r a i n f o r t r i a x i a l t e s t i n g . T o r e d u c e ; - • / / t h e t i m e ^ f o r p r i m a r y c o n s o l i d a t i o n a n d t o o b t a i n r a p i d p o r e p r e s -s u r e e q u a l i z a t i o n c o n t i n u o u s f i l t e r p a p e r ( W h a t m a n N o . 54) / / s i d e d r a i n s w i t h s l i t s w e r e u s e d i n a l l t h e t e s t s . T h e u s e o f s l i t f i l t e r p a p e r s i d e d r a i n s w a s s u g g e s t e d b y B i s h o p a n d G i b s o n ( 1 9 6 3 ) . C a m p a n e l l a (1965) f o u n d t h a t t h e u s e of s l i t f i l t e r p a p e r s i d e d r a i n s r e d u c e d t h e t i m e f o r 100 p e r c e n t p r i m a r y c o n s o l i d a t i o n b y a f a c t o r of a b o u t 5 . B l i g h t (1963) g a v e t h e r e l a t i o n : T = 0 . 0 7 h f o r t e s t s w i t h a l l r o u n d d r a i n s • c < r w h e r e T ^ = t e s t d u r a t i o n c o r r e s p o n d i n g t o 9 5 % p o r e p r e s s u r e e q u a l i z a t i o n . h = h a l f t h e s p e c i m e n h e i g h t = c o e f f i c i e n t o f c o n s o l i d a t i o n o f t h e s o i l f o r t h e t r i a x i a l s p e c i m e n b e i n g t e s t e d . 41 • / / ' If c o m p l e t e i n f o r m a t i o n o n t h e s t r e s s p a t h i s r e q u i r e d t h e d u r a t i o n / T ^ , w i l l b e . ' t h e p e r i o d b e t w e e n t h e s t a r t o f t e s t a n d t h e f i r s t s i g n i -f i c a n t s t r e s s m e a s u r e m e n t . F o r t h e c l a y t e s t e d Cr = 3 . 7 x 10 I N / / m i n a n d h = 1 . 4 i n c h . T h i s g a v e a t i m e o f a b o u t 4 m i n u t e s f o r T ^ . / T w o s t r a i n r a t e s w e r e c h o s e n f o r t h e t e s t i n g p r o g r a m . T h e " f a s t e r " s t r a i n r a t e w a s t a k e n a s 0 . 0 2 5 i n c h p e r h o u r f o r w h i c h i t t o o k a b o u t 3 1 /2 h o u r s t o r e a c h t h e p e a k d e v i a t o r s t r e s s a t a b o u t 3% s t r a i n . T h e s t r a i n a f t e r t h e i n i t i a l f o u r m i n u t e s w a s a b o u t 0 . 0 5 % . T h i s w a s j u d g e d to b e t h e f a s t e s t s t r a i n r a t e t h a t c o u l d r e l i a b l y b e u s e d to d e f o r m 1 . 4 i n c h d i a m e t e r s a m p l e s o f t h i s c l a y i f p o r e - p r e s s u r e m e a s u r e m e n t s a r e t o b e m e a n i n g f u l . T h e ' s l o w e r " s t r a i n r a t e w a s t a k e n a s 0 . 0 0 2 2 i n c h p e r h o u r o r a b o u t o n e t e n t h t h e f a s t e r r a t e o f s t r a i n . T o r e d u c e t h e e f f e c t s o f s e c o n d a r y c o n s o l i d a t i o n t h e s a m p l e s w e r e i n i t i a l l y c o n s o l i d a t e d f o r 36 h o u r s . B e f o r e s h e a r i n g , t h e s a m p l e w a s a l l o w e d t o s t a n d f o r a b o u t 24 h o u r s t o o b t a i n c o m p l e t e p o r e - p r e s s u r e e q u a l i z a t i o n . 6 . 2 S c h m e r t m a n n ' s T e c h n i q u e a n d D a t a O b t a i n e d . S c h m e r t m a n n ' s c u r v e h o p p i n g t e c h n i q u e w a s a t t e m p t e d i n t h i s i n v e s t i g a t i o n b y c o n t r o l l i n g t h e p o r e p r e s s u r e s a n d w o r k i n g w i t h t w o l e v e l s of <major p r i n c i p a l e f f e c t i v e s t r e s s . ••• T o r u n t h e s e t e s t s t h e e x i s t i n g e q u i p m e n t w a s m o d i f i e d s o t h a t t h e b a c k p r e s s u r e s c o u l d b e c o n t r o l l e d . A t a n y s t a g e d u r i n g t h e s t r a i n , c o n t r o l l e d t r i a x i a l t e s t 07= 034-05 -u,. / / / / • / • / T o k e e p a] c o n s t a n t w i t h i n c r e a s e i n s t r a i n t h e p o r e -p r e s s u r e u, w a s a d j u s t e d to m a t c h t h e v a l u e o f c r ^ a t t h a t s t r a i n . T h e p o r e - p r e s s u r e c h a n g e h o w e v e r , i s n o t c a r r i e d t h r o u g h o u t / the s a m p l e / i n s t a n t a n e o u s l y . T h e v a l u e of c r ^ a t a p a r t i c u l a r s t r a i n •i ' •' i s t h e r e f o r e to b e a n t i c i p a t e d i n a d v a n c e . K n o w i n g t h i s v a l u e o f . / ' cr^ a n d a l l o w i n g f o r t h e t i m e i n w h i c h t h e s p e c i m e n w i l l a t t a i n t h i s v a l u e ( the t i m e s h o u l d b e s u f f i c i e n t to g i v e p o r e - p r e s s u r e e q u a l i z a t i o n ) t h e p o r e p r e s s u r e w a s i n c r e a s e d b y a d j u s t i n g t h e b a c k p r e s s u r e . A l s o t h e p o r e p r e s s u r e c h a n g e s w i t h s t r a i n o n a c c o u n t of s h e a r i n g d u r i n g t h i s t i m e . P r e l i m i n a r y t e s t s w e r e r u n t o s t u d y t h e b e h a v i o u r o f d e v i a t o r s t r e s s a n d p o r e p r e s s u r e at a c o n s t a n t v a l u e of crj . C u r v e h o p p i n g w a s a t t e m p t e d i n t h e s u b s e q u e n t t e s t w h i c h w a s r u n at a r a t e o f 0 . 0 1 9 3 i n c h e s p e r h o u r . T h e h i g h v a l u e o f 07 w a s 5 5 . 0 l b s . p e r s q . i n r . a n d t h e l o w v a l u e w a s 4 6 . 0 l b s . p e r s q . i n ; : . T h e t e s t w a s i n i t i a l l y r u n u n d r a i n e d f o r 0 . 2 5 % s t r a i n at w h i c h t i m e 67 w a s at i t s h i g h v a l u e a n d c u r v e h o p p i n g to cc = 4 6 . 0 l b s . p e r s q . i n . w a s c o m m e n c e d . A t l e a s t ' t w o d i s t i n c t p o i n t s w e r e r e c o r d e d f o r e a c h l e v e l a t e a c h h o p . T h e p l o t o f d e v i a t o r s t r e s s a g a i n s t p e r c e n t s t r a i n i s s h o w n i n F i g . 13. W a t e r c o n t e n t . c h a n g e s w i t h s t r a i n a r e a l s o s h o w n o n F i g . 13. T h e d a t a h a s b e e n a n a l y s e d o n t h e l i n e s o f F i g . 5 ( S e e F i g . 14) . T h e v a r i a t i o n o f c o h e s i o n a n d f r i c t i o n w i t h s t r a i n i s p l o t t e d i n F i g . 15. T h e t e s t r e s u l t e d i n a t o t a l v o l u m e c h a n g e o f l.L'P c m 3 w h i c h r e p r e s e n t e d a w a t e r c o n t e n t c h a n g e o f 1.18% d u r i n g t h e t e s t . 43 44 45 F u r t h e r m o r e , i t w a s n o t p o s s i b l e t o a c c u r a t e l y s e p a r a t e o u t <T{ h i g h / a n d l o w c u r v e s f o r s t r a i n s l e s s t h a n 1%. T h i s m i g h t b e p o s s i b l e at v e r y s l o w s t r a i n r a t e s . T h e p u r p o s e o f t h i s i n v e s t i g a t i o n w a s t o i n v e s t i g a t e t h e e f f e c t o f r a t e o f s t r a i n o n t h e d e v e l o p m e n t o f c o -h e s i o n a n d f r i c t i o n . T h e d i f f i c u l t y i n r u n n i n g t h e t e s t s a t a r e l a -t i v e l y f a s t s t r a i n r a t e c o u p l e d w i t h r e l a t i v e l y l a r g e v o l u m e c h a n g e p o s e d a s e r i o u s l i m i t a t i o n . F u r t h e r m o r e , i n t h e r e d u c t i o n of d a t a t h e s l o p e a n d t h e i n t e r c e p t o f t h e l i n e s i n F i g . 14 d e p e n d o n t h e l o c a t i o n o f o n l y t w o . p o i n t s . T o l o c a t e a l i n e t h r e e p o i n t s , i f n o t m o r e , a r e p r e f e r a b l e . H o w e v e r , t w o p o i n t s s e p a r a t e d a g o o d d i s t a n c e a p a r t w i l l g i v e a n a c c u r a t e l o c a t i o n o f t h e l i n e b u t s h i f t i n g t h e p o i n t s f a r t h e r a p a r t w i l l m e a n l a r g e r v o l u m e c h a n g e s . D u e t o t h e a b o v e , a n d i n v i e w of t h e f a c t t h a t a c c u r a t e s e p a r a t i o n of c u r v e s w a s n o t p o s s i b l e at t h e f a s t s t r a i n r a t e f o r s t r a i n s l e s s t h a n 1%, t h i s t e c h n i q u e w a s n o t p u r s u e d f u r t h e r i n t h e i n v e s t i g a t i o n . It m a y a l s o b e n o t e d t h a t S c h m e r t m a n n ' s m e t h o d g a v e a v a l u e of & Q e q u a l to a b o u t 1 7 ° at 10% s t r a i n w h e r e a s t h e u s e o f B i s h o p ' s m e t h o d i n t h i s i n v e s t i g a t i o n g a v e a v a l u e o f <fc> e q u a l t o o a b o u t 32 at 10% s t r a i n . T h i s r a t h e r l a r g e d i s c r e p a n c y m a y b e d u e t o p o s s i b l e i n c o r r e c t s t r e s s p a t h s r e s u l t i n g f r o m t h e l a c k o f a c c u r a t e i n f o r m a t i o n c o n c e r n i n g p o r e - p r e s s u r e s w h e n u s i n g t h e S c h m e r t m a n n t e c h n i q u e . S c h m e r t m a n n (1962) a l s o r e m a r k s t h a t c u r v e h o p p i n g i s n o t s u i t a b l e f o r r e l a t i v e l y r a p i d s t r a i n r a t e t e s t i n g . 47 6 . 3 B i s h o p ' s M e t h o d T h e i n v e s t i g a t i o n r e p o r t e d h e r e i n m a d e u s e o f B i s h o p ' s m e t h o d of d e t e r m i n i n g t r u e c o h e s i o n a n d t r u e f r i c t i o n w h i c h w a s d e s c r i b e d i n g e n e r a l t e r m s p r e v i o u s l y a s F i r s t m e t h o d . H o w -e v e r , i n s t e a d o f u s i n g t h e m i n i m u m of t w o s a m p l e s , t h r e e s a m -p l e s w e r e u s e d to d e f i n e t h e M o h r e n v e l o p e at a g i v e n s t r a i n i n o r d e r to i m p r o v e t h e a c c u r a c y of t h e c-<£> d e t e r m i n a t i o n s . T h e t e s t s w e r e a l l of t h e c o n s o l i d a t e d - u n d r a i n e d t y p e a n d a x i a l l y d e f o r m e d t o a b o u t 18% s t r a i n i . e . , b e y o n d t h e p o i n t o f " " ^ m a x i m u m . T w o s t r a i n r a t e s w e r e s t u d i e d t o i n v e s t i g a t e t h e e f f e c t s of r a t e of s t r a i n o n t h e d e v e l o p m e n t o f c o h e s i o n a n d f r i c t i o n . T e s t s w e r e r u n o n u n d i s t u r b e d a n d r e m o l d e d s a m p l e s at e a c h s t r a i n r a t e a n d c o m p a r e d to s t u d y t h e i n f l u e n c e o f s t r u c t u r e . T e s t s o n t h e l i n e s o f t h i s m e t h o d c a n b e c l a s s i f i e d a s f o l l o w s : S e r i e s B U - F : C - U t e s t s o n u n d i s t u r b e d n o r m a l l y c o n -s o l i d a t e d o r s l i g h t l y o v e r - c o n s o l i d a t e d s a m p l e s at t h e f a s t e r s t r a i n r a t e . S e r i e s B R - F : C - U t e s t s o n s a m p l e s r e m o l d e d f r o m s e r i e s B U - F . T h e s e r e m o l d e d s a m p l e s w e r e t e s t e d at t h e s a m e w a t e r c o n t e n t t h e y h a d b e f o r e r e m o l d i n g a n d s h e a r e d at t h e f a s t e r s t r a i n r a t e . T h e p r o c e d u r e to o b t a i n t h i s c o n d i t i o n i s e x p l a i n e d s u b s e q u e n t l y . S e r i e s B U - S : C - U t e s t s o n u n d i s t u r b e d n o r m a l l y c o n s o l i -d a t e d v o r s l i g h t l y o v e r - c o n s o l i d a t e d s a m p l e s at the s l o w e r s t r a i n r a t e . S e r i e s B R - S : C - U t e s t s o n r e m o l d e d s a m p l e s f r o m s e r i e s B U - S at t h e s l o w e r s t r a i n r a t e . A d i a g r a m m a t i c r e p r e s e n t a t i o n o f t h e p r o c e s s i s s h o w n i n F i g . 16 (a) a n d (b) a n d r e l a t e s to o n e s t r a i n r a t e . U n d i s t u r b e d S a m p l e s . F i g . 16 (a) A s a m p l e w a s c o n s o l i d a t e d a l o n g "the v i r g i n c o n s o l i d a t i o n c u r v e to t h e d e s i r e d c o n s o l i d a t i o n p r e s s u r e p ^ . A f t e r e q u i l i b r i u m i t c o m e s to p o i n t 1. A n o t h e r s a m p l e w a s c o n s o l i d a t e d a l o n g t h e v i r g i n c o n s o l i d a t i o n c u r v e to t h e s a m e p r e s s u r e p-^ a n d i t s w a t e r c o n -t e n t n o t e d . A f t e r e q u i l i b r i u m o f p o r e - p r e s s u r e s i t w a s f u r t h e r c o n s o l i d a t e d to a p r e s s u r e p £ a n d a l l o w e d to r e b o u n d s l o w l y t o t h e w a t e r c o n t e n t i t h a d at p ^ . T h e s w e l l i n g p r o c e e d e d s l o w l y i n o r d e r to m a i n t a i n a u n i f o r m w a t e r c o n t e n t w i t h i n t h e s a m p l e . A f t e r e q u i l i b r i u m t h e s a m p l e c a m e to p o i n t 3. A t h i r d s a m p l e w a s s i m i l a r l y c o n s o l i d a t e d a l o n e t h e v i r g i n c o n s o l i d a t i o n c u r v e to t h e c o n s o l i d a t i o n p r e s s u r e p^ a n d i t s w a t e r c o n t e n t n o t e d . A f t e r p o r e - p r e s s u r e e q u i l i b r i u m i t w a s f u r t h e r c o n s o l i d a t e d t o a p r e s s u r e p ^ a n d a l l o w e d to r e b o u n d s l o w l y to t h e w a t e r c o n t e n t i t h a d at p ^ . A f t e r e q u i l i b r i u m t h i s s a m p l e c a m e t o p o i n t 5. S a m -p l e s 1, 3 a n d 5 t h u s o b t a i n e d a r e at d i f f e r e n t e f f e c t i v e s t r e s s e s b u t e s s e n t i a l l y s a m e v o i d r a t i o a n d s a m e s t r u c t u r e . It i s a s s u m e d t h a t s l i g h t o v e r - c o n s o l i d a t i o n d o e s n o t c h a n g e t h e s t r u c t u r e s i g n i -f i c a n t l y . It m a y a l s o b e n o t e d t h a t o n a c c o u n t o f p o s s i b l e v a r i a -t i o n s i n w a t e r c o n t e n t w i t h i n a b l o c k o f u n d i s t u r b e d s a m p l e s , 49 s a m p l e s 1, 3 a n d 5 m a y c o m e to s l i g h t l y d i f f e r e n t w a t e r c o n t e n t s at t h e s a m e c o n s o l i d a t i o n p r e s s u r e , ft . I n t h e p r o c e d u r e , s a m e c o n s o l i d a t i o n p r e s s u r e r a t h e r t h a n w a t e r c o n t e n t w a s u s e d a s i t i s c o n s i d e r e d t h a t s t r e n g t h i s p r i m a r i l y a f u n c t i o n o f c o n -s o l i d a t i o n p r e s s u r e . R e m o l d e d S a m p l e s . F i g . 16 (b) . S a m p l e N o . 1, i n F i g . 16 ( a ) , a f t e r s h e a r i n g w a s r e m o l d e d b y h a n d u s i n g a s t a n d a r d t e c h n i q u e at c o n s t a n t w a t e r c o n t e n t , i . e . , u n d e r u n d r a i n e d c o n d i t i o n s . A f t e r p o r e p r e s s u r e e q u a l i -z a t i o n t h i s s a m p l e c a m e t o p o i n t 2 . S a m p l e 3 a f t e r s h e a r i n g w a s a l l o w e d t o s w e l l , w a s t h e n r e m o l d e d b y t h e " s t a n d a r d " t e c h n i q u e a n d r e c o n s o l i d a t e d to t h e w a t e r c o n t e n t a t p ^ . A f t e r p o r e p r e s -s u r e s e q u a l i z a t i o n i t c a m e to p o i n t 4 . In a s i m i l a r f a s h i o n , s a m p l e 5 a f t e r s h e a r i n g w a s a l l o w e d to s w e l l t o a d i f f e r e n t w a t e r c o n t e n t , w a s t h e n r e m o l d e d b y t h e " s t a n d a r d " t e c h n i q u e a n d r e -c o n s o l i d a t e d t o t h e w a t e r c o n t e n t a t p . A f t e r p o r e p r e s s u r e / e q u a l i z a t i o n i t c a m e to 6. T h u s , t h r e e r e m o l d e d s a m p l e s a t t h e x / . A f t e r d r a i n i n g t h e c e l l w a t e r , t h e s a m p l e w a s r e m o l d e d i n p l a c e b y h a n d f o r 15 m i n u t e s . ( D e t a i l s a r e g i v e n i n A p p e n d i x B ) - . C a r e w a s t a k e n to m a i n t a i n i t s c y l i n d r i c a l s h a p e . W h e n t h e s a m p l e w a s ' b e i n g r e m o l d e d , p o r e - p r e s s u r e s w e r e a l s o r i s i n g , i n d i c a t -i n g t h a t t h e s t r u c t u r e w a s b r e a k i n g d o w n . T h e o v e r a l l l e n g t h o f t h e s a m p l e w a s n o t e d a n d t h e n e w s a m p l e h e i g h t d e t e r m i n e d . T h e o u t s i d e d i a m e t e r o f t h e r e m o l d e d s a m p l e w a s r e c o r d e d a t t o p , c e n t r e a n d b o t t o m . T h e c r o s s s e c t i o n a l a r e a o f t h e s a m p l e w a s o b t a i n e d a f t e r a l l o w i n g f o r t h e t h i c k n e s s e s o f f i l t e r p a p e r a n d t w o r u b b e r m e m b r a n e s . T h e t r i a x i a l c e l l w a s p u t i n p l a c e , f i l l e d w i t h w a t e r a n d t h e c h a m b e r p r e s s u r e r e a p p l i e d . 50 2 •ul Z o ri ul < 2 0 L O t S UNIDISTURB&P S A M P L E S - ^ \ 4 w ^ V - V ^ A _ ^ A A-REM0LJ>£J> A S S O C H LOG crc (b) REMOLDED SAMPLES D l A ^ P - A M M A T I d R E P R . E S £ N T A T I O f v j O F P R O C E D U R E P I C - f£> (P-J Q l d Cty 51 s a m e w a t e r c o n t e n t a n d e s s e n t i a l l y t h e s a m e d i s p e r s e d s t r u c -t u r e b u t d i f f e r e n t e f f e c t i v e s t r e s s w e r e r e a d y t o b e t e s t e d . A l l o d d n u m b e r s a m p l e s w e r e f o r t h e u n d i s t u r b e d c l a y a n d h a d p r e d o m i n a n t l y a f l o c c u l a t e d s t r u c t u r e . E v e n n u m b e r s a m p l e s h a d a p r e d o m i n a n t l y d i s p e r s e d s t r u c t u r e b e c a u s e o f l a r g e s h e a r s t r a i n s i n d u c e d d u r i n g r e m o l d i n g . T h e c o m p a r i -s o n o f t e s t r e s u l t s b e t w e e n u n d i s t u r b e d a n d r e m o l d e d s a m p l e s at t h e s a m e s t r a i n r a t e w i l l i n d i c a t e t h e e f f e c t s o f s t r u c t u r e . T o i n v e s t i g a t e the e f f e c t s o f s t r a i n r a t e s a m p l e s w e r e p r e p a r -e d i n t h e s a m e m a n n e r a s d e s c r i b e d a b o v e b u t s h e a r e d at a d i f f e r e n t s t r a i n r a t e a n d r e s u l t s c o m p a r e d . F i g . 17 g i v e s t h e e f f e c t i v e s t r e s s e s o f t h e s a m p l e s , t h e w a t e r c o n t e n t s a n d t h e d i a g r a m m a t i c s k e t c h o f t h e p r o -c e d u r e . T h e v a r i a t i o n i n w a t e r c o n t e n t s o f t h e s a m p l e s i s w i t h i n ± 1 °/o . T a b l e III d e s c r i b e s i n b r i e f t h e p r o c e d u r a l d e t a i l s a n d o t h e r p e r t i n e n t d a t a . B v a l u e s ( i ^ u - — _ \ w e r e Acr 3 m e a s u r e d b e f o r e c o n s o l i d a t i o n a n d b e f o r e s h e a r i n g t o c h e c k t h e d e g r e e o f s a t u r a t i o n . I n T a b l e III , t h e B v a l u e s g i v e n a r e t h o s e m e a s u r e d b e f o r e s h e a r i n g . B e f o r e r e m o v i n g t h e s a m p l e f o r a w a t e r c o n t e n t d e t e r -m i n a t i o n at t h e e n d o f t h e t e s t s t h e c e l l p r e s s u r e w a s l o w e r e d OZ 0 3 0 4 -5 "6 'T -8 -9 ( O 2.. 3 4 S' 6 r S 9 07J IM K G P E R 5<J C M D/AGRAY-IATIC: R E P R E S E N T A T I O N OF PROCEDURE P I G . I T T A B L E U l S u m m a r y P r o c e d u r e f o r A l l S a m p l e s S a m p l e N o . E f f e c t i v e S t r e s s P r o c e d u r a l D e t a i l s b e f o r e s h e a r i n g T e s t R a t e W / C B B U - F - 1 ( N . C ) B U - S - 7 ( N . C ) C o n s o l i d a t e d to cr: = 5 6 . 8 8 p s i ( 4 k g / c m ^ ) f o r 36 h r s a n d a l l o w e d to s t a n d f o r 24 h r s b e f o r e s h e a r i n g 3 . 6 k g / c m ^ 3 . 6 k g / c m 2 0 . 0 2 5 " / h r " 0 . 0 0 2 2 " / h r 35 . 60 3 5 . 4 5 1.01 1 . 0 0 B R - F - 2 ( R e m o l d e d f r o m B U -F - l a f t e r s h e a r ) B R - S - 8 ( R e m o l d e d f r o m B U -S - 7 a f t e r s h e a r ) A l l o w e d to s t a n d f o r 24 h r s . 0 . 0 3 9 k g / c m 2 0 . 0 6 k g / c m 2 0 . 0 2 5 " / h r 0 . 0 0 2 2 " / h r 35.60 3 5 . 4 5 0 . 9 9 1 .01 B U - F - 3 [ O C R - 1 .59) B U - S - 9 ( O C R = 1 .59) C o n s o l i d a t e d f i r s t t o c| = 5 6 - 8 8 p s i ( 4 k g / c m 2 ) f o r 36 h r s , a l l o w e d t o s t a n d f o r 2 4 h r s , c o n -s o l i d a t e d f u r t h e r to 3~c = 4 . 2 5 k g / c m 2 f o r 36 h r s , r e b o u n d e d a n d a l l o w e d to s t a n d f o r 24 h r s . 2 . 6 6 k g / c m 2 . 6 5 k g / c m ^ 0 . 0 2 5 " / h r 0 . 0 0 2 2 " / h r 3 4 . 70 3 4 . 75 1. 00 1. 00 B R - F - 4 ( R e m o l d e d f r o m B U F - 3 a f t e r s h e a r ) B R - S - 10 ( R e m o l d e d f r o m B U - S - 9 a f t e r s h e a r ) A l l o w e d t o s w e l l t a k i n g i n 2 c c o f w a t e r p r i o r t q r e m o l d i n g c o n s o l i d a t e d t o «> 0 . 1 5 4 k g / c m 2 a n d a l l o w e d to s t a n d f o r 24 h r s . 0 . 1 7 9 k g / c m 2 0 . 1 7 0 k g / c m 2 0 . 0 2 5 " / h r 0 . 0 0 2 2 " / h r 3 4 . 70 3 4 . 75 0 . 99 1. 00 B U - F - 5 ( O C R = 2 . 0 4 ) B U - S - 11 ( O C R = 2 .12) C o n s o l i d a t e d f i r s t t o crc - 5 6 . 8 8 p s i ( 4 k g / c m ) f o r 36 h r s a l l o w e d t o s t a n d f o r 2 4 h r s , c o n s o l i -d a t e d f u r t h e r to oz = 4 . 5 0 k g / c m f o r 36 h r s a n d r e b o u n d e d a n d a l l o w e d to s t a n d f o r 2 4 h r s . 2 . 2 0 k g / c m 2 2 . 1 1 k g / c m 2 0 . 0 2 5 " / h r 0 . 0 0 2 2 " / h r 3 5 . 1 5 34.60 1. 0 3 0 . 9 8 B R - F - 6 ( R e m o l d e d f r o m B U - F - 5 a f t e r s h e a r ) B R - S - 12 [ R e m o l d e d f r o m B U - S -11 a f t e r s h e a r ) A l l o w e d t o s w e l l t a k i n g i n 3 c c o f w a t e r p r i o r to r e m o l d i n g , c o n s o l i d a t e d t o = 1 2 . 8 p s i ( 0 . 9 k g / c m 2 ) a n d a l l o w e d t o s t a n d f o r 24 h r s . 0 . 1 9 3 k g / c m 2 0 . 1 9 3 k g / c m 2 0 . 0 2 5 " / h r 0 . 0 0 2 2 " / h r 3 5 . 1 5 3 4 . 6 0 0 . 9 9 t, 54 a p p r o x i m a t e l y 1 l b . p e r s q . i n . a b o v e t h e b a c k p r e s s u r e a n d t h e s a m p l e w a s a l l o w e d to s w e l l f o r a b o u t 10 h o u r s to d i s s i p a t e t h e n e g a t i v e p o r e p r e s s u r e s ( H e n k e l a n d S o w a , 1 9 6 3 ) . K n o w i n g t h e n e t a m o u n t of w a t e r d r a i n e d a n d the i n i t i a l w e i g h t o f t h e s a m p l e a c h e c k o n w a t e r c o n t e n t w a s o b t a i n e d . T h e w a t e r c o n t e n t c h e c k w a s f o u n d to b e a l w a y s w i t h i n + 0 . 4 % . T h i s v a l u e i n c l u d e s t h e s l o w e r s t r a i n r a t e t e s t s i n w h i c h t h e s a m p l e w a s i n t h e t r i a x i a l c h a m b e r f o r . a b o u t 22 d a y s . W a t e r c o n t e n t s o f s a m p l e s B U - S - 7 a n d B R - S - 8 a n d B U - S - 1 1 a n d B R S - 1 2 w e r e o b t a i n e d b y s l i c i n g t h e s a m p l e i n t o f o u r h o r i -z o n t a l l a y e r s to s t u d y t h e v a r i a t i o n of w a t e r c o n t e n t w i t h i n t h e s a m p l e . W a t e r c o n t e n t s i n t h e c e n t r e w e r e f o u n d t o b e s o m e w h a t l o w e r t h a n at t h e e n d s a n d t h e v a r i a t i o n w a s w i t h i n / / / C H A P T E R V I I T e s t R e s u l t s , A n a l y s e s a n d D i s c u s s i o n s /'• i l i I i i I I J i i 55 T e s t R e s u l t s , A n a l y s e s a n d D i s c u s s i o n s  7 . 1 G e n e r a l . T h e r e s u l t s a r e b a s e d o n t h e a n a l y s i s o f t w e l v e c o n s o l i -d a t e d u n d r a i n e d t r i a x i a l t e s t s . S i x t e s t s , t h r e e o n u n d i s t u r b e d ( n o r m a l l y a n d s l i g h t l y o v e r c o n s o l i d a t e d ) a n d t h r e e o n r e m o l d e d s a m p l e s w e r e r u n at the f a s t e r s t r a i n r a t e o f 0 . 0 2 5 i n c h p e r h o u r . T h e r e m a i n i n g s i x t e s t s , t h r e e o n u n d i s t u r b e d ( n o r m a l l y a n d s l i g h t l y o v e r c o n s o l i d a t e d ) a n d t h r e e o n r e m o l d e d s a m p l e s w e r e r u n at t h e s l o w e r s t r a i n r a t e o f 0 . 0 0 2 2 i n c h p e r h o u r . R e a d i n g s of c e l l p r e s s u r e s a n d p o r e - p r e s s u r e s w e r e t a k e n a t e a c h s e t o f o b s e r v a t i o n to g i v e a n a c c u r a t e r e a d i n g o f e f f e c t i v e s t r e s s . A l l s t r e s s - s t r a i n c u r v e s w e r e c o r r e c t e d f o r a r e a c h a n g e s ( ^ » ) , w h e r e A 0 = i n i t i a l a r e a o f c r o s s - s e c t i o n of t h e s a m p l e a n d Ak i s t h e a r e a at s t r a i n ^ - N o m e m b r a n e s o r f i l t e r p a p e r c o r r e c t i o n s w e r e m a d e . T y p i c a l t e s t r e a d i n g s f o r a t e s . t _ a r e s h o w n i n A p p e n d i x C . F o r s t u d y i n g t h e d e v e l o p m e n t o f c a n d (6 w i t h s t r a i n u s e i s m a d e o f " M o d i f i e d M o h r - C o u l o m b D i a g r a m " w i t h 1/2 (5^+ C3 ) a l o n g the a b s c i s s a a n d 1/2(^7 - ) a l o n g t h e o r d i n a t e , s e e F i g . 2 . C a l c u l a t i o n s f o r c e a n d (6 e a r e g i v e n i n A p p e n d i x D . T h e a n a l y s i s a n d c o m p a r i s o n of r e s u l t s a s s u m e s t h a t a l l t h e u n d i s t u r b e d s a m p l e s w e r e at e s s e n t i a l l y i d e n t i c a l s t r u c t u r e p r i o r to s h e a r i n g . T h e s a m e a s s u m p t i o n w a s n e c e s s a r y i n c o m p a r i n g t h e r e s u l t s o f a l l t h e r e -m o l d e d s a m p l e ' s . U n d i s t u r b e d s a m p l e s w e r e t e s t e d at o v e r - c o n s o l i d a t i o n r a t i o s f r o m 1 to 3 . T e s t r e s u l t s f r o m s a m p l e s w i t h o v e r - c o n s o l i -dation ratios greater than 3.0 were not continuous with the effec-tive stress path data of samples having over- consolidation ratios less than 3. This is possibly due to structural changes which may take place in a sensitive clay because of heavy oxer-consolidation. The results presented are limited to the experimental data from normally consolidated or slightly over-consolidated specimens, re For the/molded state the remolding was done by :hand. Assumption of equal structure depends therefore on the uniformity of this technique. Care was taken to ensure that the same procedure of remolding for a fixed time was performed on all the samples. 7.2 Test Results for Undisturbed State -- General Behaviour. Test results at faster and slower strain rates showed a similar pattern of behaviour; thus, only the data for the faster rate are shown in this section. Stress-strain curves for all the tests on undisturbed clay at the faster strain rate are shown in the upper part of F i g . 18. The deviator stress on all the samples reaches a maximum and then decreases. In the normally consoli-dated sample BUF-1 ( - ) maximum occurs at 3% strain. With increasing over-consolidation ratio the point of maximum deviator stress tends to occur at higher percent strain. The maximum deviator stress also reduces in value with increasing over-consoli-dation ratio. This decrease is not due to the differences in water content indicated in the figure since the sample with the highest water content had the highest strength. This suggests that consoli-dation history of clay is more important in determining its strength 57 p r o p e r t i e s . T h e p a t t e r n o f p o r e - p r e s s u r e s a n d t h e e f f e c t o f o v e r c o n s o l i d a t i o n o n p o r e - p r e s s u r e s i s p r e s e n t e d i n t h e l o w e r p a r t o f F i g . 1 8 . T h e s h a p e o f t h e c u r v e i n d i c a t e s t h a t r a t e o f c h a n g e of p o r e - p r e s s u r e s w a s h i g h e r at s m a l l e r s t r a i n s a n d t h e p o r e - p r e s s u r e s c o n t i n u e to r i s e e v e n a f t e r t h e m a x i m u m d e v i a t o r s t r e s s w a s r e a c h e d . T h e u n d i s t u r b e d s a m p l e s h a v e a f l o c c u l a t e d s t r u c t u r e w h i c h b r e a k s d o w n a s s h e a r s t r a i n s a r e i n d u c e d w h i c h c a u s e s p o r e - p r e s s u r e i n c r e a s e s . W i t h i n c r e a s i n g o v e r - c o n s o l i -d a t i o n r a t i o s h i g h e r p o r e - p r e s s u r e s a r e d e v e l o p e d b u t r a t e o f p o r e p r e s s u r e c h a n g e i s l e s s . T h e d i f f e r e n c e i s m u c h at s m a l l e r s t r a i n s , b e f o r e m a x i m u m d e v i a t o r s t r e s s , a s t h e s t r u c t u r e o f t h e s a m p l e c h a n g e s w i t h s t r a i n r a p i d l y i n t h i s r e g i o n . F i g . 19 s h o w s the m i n o r p r i n c i p a l e f f e c t i v e s t r e s s 6§, d e v e l -o p e d i n t h e u n d i s t u r b e d s a m p l e s . 5| d r o p s a p p r e c i a b l y u p t o 4 % t o 5% s t r a i n b e c a u s e p o r e - p r e s s u r e s a r e d e v e l o p e d f a s t i n t h i s r e g i o n . P o r e p r e s s u r e s c o n t i n u e to r i s e s l o w l y w i t h s t r a i n ( F i g . 18) a n d 03 c o n t i n u e s to d r o p w i t h s t r a i n ( F i g . 19) , t h e r e a f t e r . F i g . 20 g i v e s t h e d e v e l o p m e n t o f < 7 y£| w i t h s t r a i n . A m a x i m u m v a l u e o f 3.35 o c c u r s a t a b o u t 15.5% s t r a i n i n t h e n o r m a l l y c o n s o l i d a t e d s a m p l e w h e r e a s ( ^ - ^ ) m a x i m u m o c c u r s a t 3% s t r a i n ( F i g . 1 8 ) . T h e p h e n o m e n o n o f m a x i m u m d e v i a t o r s t r e s s o c c u r r i n g b e f o r e m a x i -m u m p r i n c i p a l e f f e c t i v e s t r e s s r a t i o a p p e a r s t o b e t y p i c a l o f s e n s i - . t i v e c l a y s a n d i s c a u s e d b y t h e c o n t i n u i n g r i s e i n p o r e p r e s s u r e s a f t e r t h e p o i n t of m a x i m u m d e v i a t o r s t r e s s . S i m i l a r r e s u l t s f r o m 58 2 0 L . z 4- <=> a 10 PERC.EMT ST-RAIM t X5E. VIATOR. S T R E S S E S A N D PORE PRESSURES STATE AT PASTER. STRAIN) RAT£ F / G . I S /2 IN UN0I5TOR.BED /4 59 A e a PEJLCENT STR-Afsl to MINOR, PRINCIPAL EFFECTIVE STRESS SAMPLES A T ' F A S T E R S T R A I N RATE IZ 14 IN UNDISTUR.&EJ) ; F / G . O I undrained tests on undisturbed sensitive clays have been reported earlier (Bjerrum and Simons I960) . It is also to be noted in F i g . 20 that 07/0^ developed, is significantly different for different samples particularly at small strains. However at large strains they have a tendency to merge into one curve. This suggests that at higher strains cohesion should drop to zero. The development of pore pressure parameter A( A-jr^. and reflects the change in pore pressure during a test as a proportion of the deviator stress ) is given in F i g . 21. Values decrease with • increasing overconsolidation ratio as reported by Henkel (1956). A p at failure, can be determined either at (07 - § 3 ) maximum or at ( /s\, ) maximum. The difference between A£ at ( 07 - 5 ^ ) maxi-mum and (<*? / " 3 ) maximum varies approximately with the sensi-tivity. For clays with small sensitivities these values are nearly equal but for very sensitive to quick clays A£ at 6 7 / ^  maximum is considerably larger than A f at ( o f - 5 ! ) maximum. Furthermore, 1 isotropically consolidated clays with small sensitivity are reported / to have values from 0.8 to 1.0 while the A f values are greater than /' • • ' unity for highly sensitive clays. (Ap will depend on how failure is defined - ( Sf _5j ) maximum or ( 07/<r| ) maximum) . F o r the clay investigated the normally consolidated sample had an A at ("Jf-^, ) maximum of 0.78 and 1.21 at ( ^ /0% ) maximum. The effective stress paths for undisturbed samples at the 61 62 FIG. Z I 63 f a s t e r s t r a i n r a t e a r e g i v e n i n F i g . 2 2 . A s p o i n t e d o u t e a r l i e r the s a m p l e s h a v e e s s e n t i a l l y t h e s a m e s t r u c t u r e p r i o r t o s h e a r i n g a n d h e n c e at a n y p a r t i c u l a r s t r a i n t h e s t r u c t u r e i s c o n s i d e r e d t o b e the s a m e . A l i n e j o i n i n g t h e p o i n t s a t t h e s a m e p e r c e n t s t r a i n w i l l t h u s d e f i n e c a n d c4„ at t h a t s t r a i n ( F i g . 2 ) . V a l u e s o f e e a n d - s o d e t e r m i n e d a r e p l o t t e d i n F i g . 2 3 . F r o m F i g . 2 3 t h e f o l l o w i n g c a n b e n o t e d . 1. C o h e s i o n d e v e l o p s at s m a l l e r s t r a i n s r e a c h e s a p e a k v a l u e a n d d e c r e a s e s at a f a s t r a t e . F o r t h e d a t a p r e s e n t e d c o h e s i o n a t t a i n e d a m a x i m u m of 5 . 3 6 l b s . p e r s q . i n . ( 7 7 0 l b s . p e r s q . f t . ) a t ' a s t r a i n o f 1% a n d d e c r e a s e d t o z e r o a t 6 % s t r a i n a n d r e m a i n e d z e r o t h e r e a f t e r . 2 . F r i c t i o n d e v e l o p s c o m p a r a t i v e l y s l o w l y a n d a t t a i n s a m a x i m u m at l a r g e r s t r a i n s . It a t t a i n e d a v a l u e o f a b o u t 3 3 ° at 12% s t r a i n . T h i s p a r t i c u l a r p a t t e r n of b e h a v i o u r f o r t h e d e v e l o p m e n t o f c o h e s i o n a n d f r i c t i o n w i t h s t r a i n w a s p o s t u l a t e d b y L a m b e ( I960) a n d h a s b e e n r e p o r t e d b y S c h m e r t m a n n ( I 9 6 0 ) , W u , D o u g l o u s a n d G o u g h n o u r (1962) a n d B e a (1963) a n d i s i n l i n e w i t h t h e c o n c e p t o f g r a d u a l t r a n s f e r of s t r e n g t h f r o m t r u e c o h e s i o n t o t r u e f r i c t i o n . F i g . 23 a l s o s u g g e s t s t h a t t h e r e a p p e a r s t o b e a f u n d a -m e n t a l d i f f e r e n c e b e t w e e n t h e m e c h a n i s m s c o n t r o l l i n g c o h e s i o n a n d f r i c t i o n . T h e d e v e l o p m e n t o f c o h e s i o n at s m a l l s t r a i n s s e e m s to b e r e a s o n a b l e a s i t i s g e n e r a l l y t h o u g h t t o b e b a s e d o n t h e 65 D E V E L O P M E N T O F C e A N D cf>e IA/ITH S T R A f M I N U N C X S T U R 6 E D S T A T E A T F A S T S T R A / ^ R A T E P I G . 2 3 66 e l e c t r i c a l a t t r a c t i v e f o r c e s b e t w e e n c l a y p a r t i c l e s a n d l a r g e s t r a i n s s h o u l d n o t b e r e q u i r e d t o a c t i v a t e t h e s e f o r c e s . F r i c t i o n on the o t h e r h a n d i s t h o u g h t to d e p e n d o n t h e i n t e r f e r e n c e b e t w e e n the p a r t i c l e s ( R o s e n q v i s t , 1959) a n d c o n s i d e r a b l e s t r a i n i s r e -q u i r e d to a c h i e v e m a x i m u m i n t e r f e r e n c e a n d h e n c e m a x i m u m f r i c t i o n . 7 . 3 E f f e c t s of S t r a i n R a t e o n U n d i s t u r b e d C l a y . T y p i c a l c u r v e s f o r d e v i a t o r s t r e s s at f a s t e r a n d s l o w e r s t r a i n r a t e s a r e p l o t t e d i n F i g . 2 4 . B U F - 1 i s s h e a r e d at t h e f a s t e r r a t e a n d B U - S - 7 at t h e s l o w e r r a t e ( b o t h a r e n o r m a l l y c o n -s o l i d a t e d ) . A r e d u c t i o n o f 1 1 . 0 % i n s t r e n g t h i n t e r m s o f ( " 7 - " 3 ) m a x i m u m t o o k p l a c e at t h e s l o w e r r a t e . R e s u l t s s h o w i n g d e c r e a s e i n s t r e n g t h ( i n t e r m s o f (<T - r 3 ) m a x i m u m ) f o r s e n s i t i v e c l a y s w i t h i n c r e a s i n g t i m e to f a i l u r e h a v e b e e n r e p o r t e d b y B j e r r u m , S i m o n s a n d T o r b l a a (1958) f o r a N o r w e g i a n c l a y o f s e n s i t i v i t y v a r y i n g f r o m 1 . 5 to 7 . 0 a n d b y C r a w f o r d (1959) f o r a ' C a n a d i a n c l a y f o r s e n s i t i v i t y g r e a t e r t h a n 2 0 . T y p i c a l p o r e - p r e s s u r e s at f a s t e r a n d s l o w e r r a t e s a r e s h o w n i n F i g . 2 5 . H i g h e r p o r e p r e s s u r e s a r e d e v e l o p e d at s l o w e r r a t e a n d m a y b e r e l a t e d t o s t r u c t u r a l b r e a k d o w n at t h e s l o w e r r a t e o n a c c o u n t o f m o r e t i m e a v a i l a b l e . S i m i l a r t r e n d i n p o r e -p r e s s u r e s f o r s e n s i t i v e c l a y s h a v e b e e n r e p o r t e d b y p r e v i o u s i n v e s t i g a t o r s . H i g h e r p o r e p r e s s u r e s a t t h e s l o w e r r a t e r e s u l t i n l o w e r d e v i a t o r s t r e s s at f a i l u r e . L e o n a r d s (1962) r e m a r k s t h a t 67. 68 28 4 <s a to iz. 14. • PERCENT STRAW EFFECT OP STRAW RATE O N P<3R6 - PR.E.SSXJR£S I'M U^rM5TURB£D S T A T E PIG. 2.5" as the r a t e of s l i d i n g i n c r e a s e s the v i s c o u s s h e a r s t r e s s e s i n the l i q u i d i n c r e a s e s . H e a l s o adds that the p h e n o m e n o n i s c o m p l i c a t e d b y t h e r m o d y n a m i c e f f e c t s due to h e a t e v o l v e d . E f f e c t of r a t e of s t r a i n on p o r e p r e s s u r e p a r a m e t e r A i s s h o w n i n F i g . 2 6 . H i g h e r v a l u e s at the s l o w e r r a t e a r e o b t a i n e d o n a c c o u n t of g r e a t e r t e n d e n c y f o r s t r u c t u r a l b r e a k d o w n , t h e r e f o r e , h i g h e r p o r e p r e s s u r e s a r e d e v e l o p e d at the s l o w e r r a t e w h e r e a s the d e v i a t o r s t r e s s e s d e v e l o p e d a r e l o w e r t h a n t h o s e at the f a s t e r r a t e . O t h e r i n v e s t i g a t o r s h a v e a l s o r e p o r t e d i n c r e a s i n g v a l u e s of A£ w i t h i n c r e a s i n g t i m e to f a i l u r e . A v e r a g e n o r m a l s t r e s s e s at t w o r a t e s of s t r a i n a r e p l o t t e d i n F i g . 2 7 . A t a g i v e n p e r c e n t s t r a i n the a v e r a g e n o r m a l s t r e s s i s l e s s at the s l o w e r s t r a i n r a t e b e c a u s e of h i g h e r p o r e p r e s s u r e s . V a l u e s of (cr-«3 ) m a x i m u m a n d A£ w e r e c o m p u t e d f o r the n o r m a l l y c o n s o l i d a t e d s a m p l e at f a s t e r a n d s l o w e r s t r a i n r a t e s and a r e p l o t t e d i n F i g . 28 a l o n g w i t h the r e s u l t s of B j e r r u m , S i m o n s and T o r b l a a (1958) a n d C r a w f o r d (19 5 9 ) . T h e r e s u l t s of t h i s i n v e s t i g a t i o n s h o w a s i m i l a r t r e n d . In F i g . 2 9 , v a l u e s of <T/o| f o r n o r m a l l y c o n s o l i d a t e d u n -d i s t u r b e d s a m p l e s at f a s t e r a n d s l o w e r r a t e a r e p l o t t e d . T h e p l o t s of a r e s i g n i f i c a n t l y d i f f e r e n t at s m a l l s t r a i n s w h e r e a s they m e r g e i n t o one at l a r g e s t r a i n s . T h i s i n d i c a t e s that the r a t e of s t r a i n h a s l i t t l e e f f e c t on the s t r e n g t h i n t e r m s of p r i n c i p a l e f f e c t i v e s t r e s s r a t i o at l a r g e s t r a i n s i . e . at m a x i m u m v a l u e E.FFE.CT OF- STRAfM RATE PARAMETER. A P A S . 71 EFFECT OF STRAIN H A T E yi<?i + 0$) IN UNJ>fSTUR&-££> STATE. FIG. zr i I i i i i i i I i i — i i i i i i L i i i i ' • ' ' i-O IO 'OO TIME T O F A I L U R E HRS D £ V I A T O R . S T R E S S AT F A I L U R E o-9 04 I 1 1 I 1 I I I 1 1—1—1 1 11 r ' A - ? ' ' ' ' ' " y / ^ _ - - -— "T 1 • l t . t r 1 1 1 1 1 1 > 1 T I M E TO F/.ILURE HRs S K E M P T O N J ' S A A T <P7-<7a) M A X . F/Gr. 22 73 o f Jc a n d f 4 e at t h e t w o s t r a i n r a t e s w e r e s e p a r a t e d a s f u n c t i o n of s t r a i n f r o m t h e p l o t s of s t r e s s p a t h s . S t r e s s p a t h s a n d d e v e l o p m e n t o f c „ a n d at t h e s l o w e r r a t e i s g i v e n i n A p p e n d i x C ( F i g s . 40 a n d 41). F i g . 30 s h o w s t h e d e v e l o p m e n t o f c a n d 6 at the f a s t e r a s w e l l a s s l o w e r s t r a i n r a t e . A e e s i g n i f i c a n t e f f e c t of s t r a i n r a t e i s e v i d e n t f o r s t r a i n s l e s s t h a n 8 % . F o r l a r g e s t r a i n s ( b e y o n d 8%) c> a n d <4 w e r e e s s e n t i a l l y e e i n d e p e n d e n t o f s t r a i n r a t e . C o h e s i o n . It d e v e l o p e d f a s t e r at t h e f a s t s t r a i n r a t e , a t t a i n e d a h i g h e r p e a k ( d e c r e a s e d b y 3 . 4 % a t 1% s t r a i n at s l o w e r r a t e ) a n d d e c r e a s e d at a f a s t e r r a t e . C o h e s i o n d e p e n d s o n t h e n u m b e r o f i n t e r p a r t i c l e b o n d s . A t t h e f a s t s t r a i n r a t e o n c e t h e c r i t i c a l s t a g e i s r e a c h e d s l i d i n g o c c u r s at m o s t of t h e c o n t a c t s a n d a l a r g e n u m b e r ' of i n t e r p a r t i c l e b o n d s a r e b r o k e n . T h i s r e s u l t s i n a f a s t d e c r e a s e i n c o h e s i o n a s t h e m a i n c o n t r i b u t i o n to i t i s t h r o u g h the i n t e r p a r t i c l e b o n d s . A t t h e s l o w e r s t r a i n r a t e , c o h e s i o n a g a i n d e v e l o p e d f a s t b u t r e a c h e d a l o w e r p e a k a n d d e c r e a s e d t o z e r o . A t l a r g e r s t r a i n s c o h e s i o n d e v e l o p e d i s h i g h e r at t h e s l o w e r r a t e p r o b a b l y o n a c c o u n t o f s o m e r e o r i e n t a t i o n o f p a r t i c l e s w i t h m o r e t i m e a v a i l a b l e . B e y o n d 8 % s t r a i n c o h e s i o n d r o p s t o z e r o at b o t h s t r a i n r a t e s . F r i c t i o n . It d e v e l o p e d f a s t e r at t h e f a s t e r s t r a i n r a t e a n d r e m a i n e d 75 35 30 25 20 U Q 2 <5 2 O h a 4- <a - * " • . . . ... E F F E C T O F R A T E O F S T R A W OM T H E DEVELOPMENT OF Ce. ArNTJ) d?£. I'M UND ISTUR,£>£J) 5 T A T E F/G. 30 h i g h e r t h a n t h a t at t h e s l o w e r r a t e . T h e a v e r a g e n o r m a l s t r e s s at t h e s l o w e r r a t e i s l e s s at a g i v e n p e r c e n t s t r a i n ( F i g . 27) a n d s m a l l e r f r i c t i o n a n g l e w o u l d b e e x p e c t e d . A n e x p l a n a t i o n i n t e r m s o f i n c r e a s e d r e p u l s i v e f o r c e s at t h e s l o w e r s t r a i n r a t e c a n a l s o b e a d v a n c e d . F o r e x a m p l e , i n a d d i t i o n t o h i g h e r p o r e p r e s s u r e s at t h e s l o w e r r a t e ( F i g . 25) t h e p a r t i c l e s a r e o r i e n t e d i n t o a m o r e p a r a l l e l c o n f i g u r a t i o n d u r i n g s h e a r ( W u , D o u g l a s a n d G o u g h n o u r , 1962) a n d t h e d o u b l e l a y e r r e p u l s i v e f o r c e s c o u l d b e d e v e l o p e d m o r e f u l l y . T h e d o u b l e l a y e r r e p u l s i v e f o r c e s a r e f l u i d p r e s s u r e s w h i c h a r e e x e r t e d b e t w e e n t h e f a c e s o f p a r a l l e l ( o r n e a r l y so ) c l a y p a r t i c l e s . T h e s e a r e i n a d d i t i o n t o t h e p o r e p r e s s u r e s a c t u a l l y m e a s u r e d . T h e y a p p e a r i n c a l c u l a t i o n s a s p a r t o f e f f e c t i v e s t r e s s a n d w i l l t h e r e f o r e c o n t r i b u t e to a v e r a g e n o r m a l s t r e s s b u t n o t t o s h e a r i n g s t r e n g t h a n d t h e r e f o r e r e d u c e f r i c t i o n ( O l s o n , 1 9 6 3 ) . 7 . 4 E f f e c t s o f S t r u c t u r e . T h e c l a y t e s t e d h a s a f l o c c u l a t e d s t r u c t u r e i n t h e u n d i s -t u r b e d s t a t e . T h e a d o p t e d r e m o l d i n g t e c h n i q u e g a v e a s a m p l e w i t h p r e d o m i n a n t l y d i s p e r s e d s t r u c t u r e at t h e s a m e w a t e r c o n t e n t . T o s t u d y t h e e f f e c t s o f s t r u c t u r e , o t h e r t h i n g s b e i n g e q u a l , t h e t e s t r e s u l t s o n u n d i s t u r b e d s a m p l e s a n d r e m o l d e d s a m p l e s c a n b e c o m p a r e d at o n e s t r a i n r a t e . D i s c u s s i o n h e r e r e l a t e s to t h e f a s t e r s t r a i n r a t e b u t a p p l i e s i n g e n e r a l to t h e s l o w e r r a t e a s w e l l . S t r e s s - s t r a i n c u r v e s f o r u n d i s t u r b e d a n d r e m o l d e d s a m p l e s a r e s h o w n i n F i g . 31. T h e 77 d e v i a t o r s t r e s s o n u n d i s t u r b e d s a m p l e s r a p i d l y r e a c h e d a m a x i -m u m a n d t h e n d e c r e a s e d w h e r e a s t h e d e v i a t o r s t r e s s ori r e m o l d e d s a m p l e s d e v e l o p t d g r a d u a l l y . T h e s i g n i f i c a n t d e c r e a s e i n s t r e n g t h f o r r e m o l d e d s p e c i m e n s i s a t t r i b u t e d t o t h e b r e a k d o w n i n s t r u c -t u r e d u r i n g r e m o l d i n g . B U F - 1 i s a n o r m a l l y c o n s o l i d a t e d s a m p l e a n d d e v e l o p e d a m a x i m u m d e v i a t o r s t r e s s o f 3 9 . 0 l b s . p e r s q . i n . a t 3% s t r a i n . T h e c o r r e s p o n d i n g r e m o l d e d s a m p l e B R - F - 2 d e v e l o p e d a d e v i a t o r s t r e s s o f 4 . 8 l b s . p e r s q . i n . a t 3% s t r a i n w h i c h i s o n e e i g h t o f t h e d e v i a t o r s t r e s s i n u n d i s t u r b e d s a m p l e s . P o r e p r e s s u r e s f o r f u n d i s t u r b e d a n d r e m o l d e d s a m p l e a r e s h o w n i n F i g . 3 2 . It i s t o b e / / n o t e d t h a t t h e r e m o l d e d s a m p l e s w e r e s h e a r e d at a l o w e r c e l l p r e s -/ ' , 1 s u r e ( a b o u t 14 l b s . p e r s q . i n . l o w e r ) . T h e s h a p e o f t h e s e c u r v e s i n d i c a t e t h a t t h e r a t e o f c h a n g e o f p o r e p r e s s u r e s i s h i g h e r i n u n d i s t u r b e d s a m p l e s p a r t i c u l a r l y at s m a l l e r s t r a i n s a s t h e s t r u c -/ / t u r e i s b r e a k i n g d o w n w i t h s t r a i n a n d d r a i n a g e i s p r e v e n t e d . I n t h e c a s e o f r e m o l d e d s a m p l e s t h e s t r u c t u r e i s a l r e a d y d i s p e r s e d to b e g i n w i t h a n d n o t m u c h i s h a p p e n i n g i n t e r m s o f s t r u c t u r a l b r e a k d o w n w i t h s t r a i n . P o r e p r e s s u r e s i n r e m o l d e d s a m p l e s c o n s e q u e n t l y d o n o t c h a n g e m u c h . It i s a l s o t o b e n o t e d t h a t r e m o l d -e d s a m p l e s d e v e l o p h i g h e r p o r e p r e s s u r e s o n a c c o u n t o f t h e i r d i s -p e r s e d s t r u c t u r e . In F i g . 33 t h e m i n o r p r i n c i p a l e f f e c t i v e s t r e s s e s d e v e l o p e d : a r e s h o w n . O n a c c o u n t o f h i g h e r p o r e p r e s s u r e s o n t h e r e m o l d e d s a m p l e s t h e 5| d e v e l o p e d i s v e r y l o w . It d o e s n o t c h a n g e m u c h oo a s t h e p o r e - p r e s s u r e s a r e n o t c h a n g i n g m u c h . O n t h e u n d i s -t u r b e d s a m p l e s d r o p s a p p r e c i a b l y at s m a l l e r s t r a i n s o n a c c o u n t o f r a p i d i n c r e a s e i n p o r e p r e s s u r e s . A t l a r g e s t r a i n s " ^ g r a d u a l l y d r o p s i n d i c a t i n g s l o w r i s e i n p o r e p r e s s u r e s . T h e r a p i d i n c r e a s e i n p o r e p r e s s u r e s a t s m a l l e r s t r a i n s i n u n d i s t u r b e d s e n s i t i v e c l a y s i s a s s o c i a t e d t o t h e r a p i d s t r u c t u r a l b r e a k d o w n i n t h a t r e g i o n . V a l u e s of t h e p o r e - p r e s s u r e p a r a m e t e r A , (^"o^ ) ^ o r u n d i s t u r b e d a n d r e m o l d e d s a m p l e s a r e s h o w n i n F i g . 34. T h e y a r e s i g n i f i c a n t l y a f f e c t e d b y s t r u c t u r e o f t h e s o i l a n d t h e d e v e l o p -m e n t i s i n l i n e w i t h t h e e s t a b l i s h e d p a t t e r n f o r u n d i s t u r b e d a n d r e m o l d e d s a m p l e s . It m a y b e n o t e d t h a t A v a l u e s b e c o m e n e g a t i v e i n t h e r e m o l d e d c a s e a n d s h o w t h e t e n d e n c y o f t h e s a m p l e t o d i l a t e . In F i g . 35 v a l u e s f o r b o t h u n d i s t u r b e d a n d r e m o l d e d s a m p l e s a r e p l o t t e d . H i g h e r v a l u e s o f o f / * ^ w e r e o b t a i n e d i n t h e c a s e o f r e m o l d e d s a m p l e s a s c o m p a r e d t o v a l u e s o b t a i n e d i n the c a s e o f u n d i s t u r b e d s a m p l e s . C u r v e s f o r r e m o l d e d s a m p l e s w e r e a l s o v e r y s i g n i f i c a n t l y d i f f e r e n t , m o r e s o f o r s m a l l e r s t r a i n s . It i s d i f f i c u l t to i n t e r p r e t i t i n p h y s i c a l t e r m s , b u t , s i n c e F i g . 33 s h o w s l o w 63 v a l u e s f o r t h e r e m o l d e d c a s e , t h e r a t i o w i l l b e q u i t e s e n s i t i v e to oj v a l u e s d e v e l o p e d . H o w e v e r , a t h i g h e r s t r a i n s t h e r e i s a t e n d e n c y f o r t h e 07/03 r a t i o t o a p p r o a c h t h e v a l u e s o b t a i n e d o n u n d i s t u r b e d s a m p l e s . S e e d , M i t c h e l l a n d C h a n (i960) w h i l e d i s c u s s i n g c o m p a c t e d c l a y s p r e s e n t e d c u r v e s w h i c h 81 SC, r 2. G £> <o fSr (4 PERCENT STRAIN EPPECT OM STRUCTURE, ONJ C%, 82 '•2 _0-4-l 1 1 1 1 1 1 1 2 4- & S IO 12- 14 P E R C E N T S T R A I N ^_ EFFECT OF STRUCTURE O N POOS.- PRES&OKE. PAFiAMETE.R. - A F I G . 3 4 EFFECT OF STRUCTuQ £. ON 07/d$ F-id 3 5 t h o u g h d i f f e r e n t i n i n i t i a l s t a g e s s h o w s a m e v a l u e s f o r <*T/oS a t 20% s t r a i n f o r s a m p l e s c o m p a c t e d b y s t a t i c a n d k n e a d i n g c o m -p a c t i o n . T h e s a m p l e s c o m p a c t e d b y k n e a d i n g c o m p a c t i o n h a s m o r e d i s p e r s e d s t r u c t u r e t h a n t h a t c o m p a c t e d b y s t a t i c c o m p a c -t i o n . A s i m i l a r p a t t e r n w a s s h o w n b y t h e m f o r t w o s p e c i m e n s , o n e h a v i n g a n i n i t i a l l y f l o c c u l a n t s t r u c t u r e a n d t h e o t h e r i n i t i a l l y d i s p e r s e d s t r u c t u r e . c g a n d « 5 e a t d i f f e r e n t s t r a i n s f o r r e m o l d e d s a m p l e s / w e r e d e t e r m i n e d f r o m t h e e f f e c t i v e s t r e s s p a t h s u s i n g t h e p r i n c i -p l e o f F i g . 2 . E f f e c t i v e s t r e s s p a t h s a n d t h e d e v e l o p m e n t o f c e a n d {£ i s g i v e n i n A p p e n d i x TJ. ( F i g . 4 2 a n d 4 3 ) . T o s t u d y t h e e f f e c t s o f s t r u c t u r e , t h e d e v e l o p m e n t o f a a n d <b i n u n d i s -e e t u r b e d s a m p l e s i s c o m p a r e d w i t h t h e i r d e v e l o p m e n t i n r e m o l d e d s a m p l e s ( s e e F i g . 3 6 ) . C o h e s i o n . A v e r y m a r k e d e f f e c t o n c o h e s i o n i s e v i d e n t . I n t h e u n -d i s t u r b e d s a m p l e t h e p e a k c o h e s i o n o c c u r e d a t 1% s t r a i n . C o h e s i o n at 1% s t r a i n i n t h e r e m o l d e d s a m p l e w a s a b o u t 1/8 o f t h e v a l u e f o r t h e u n d i s t u r b e d s a m p l e . T h e m a x i m u m c o h e s i o n o c c u r e d i n t h e r e m o l d e d s a m p l e at a b o u t 4% s t r a i n . C o h e s i o n i s c o n s i d e r e d a s a r i s i n g out of i n t e r p a r t i c l e b o n d s . In t h e u n d i s t u r b e d s t a t e t h e n u m b e r o f i n t e r p a r t i c l e b o n d s w a s l a r g e a n d a l a r g e a m o u n t o f c o h e s i o n w a s d e v e l o p e d . W i t h t h e b r e a k d o w n o f s t r u c t u r e t h e n u m b e r o f i n t e r p a r t i c l e b o n d s d e c r e a s e d s i g n i f i c a n t l y a n d t h e c o h e s i o n d e c r e a s e d . T h u s b o t h s a m p l e s g i v e w i d e l y d i f f e r e n t v a l u e s o f m a x i m u m c o h e s i o n . F u r t h e r m o r e , i n r e m o l d e d s o i l s e s s e n t i a l l y c o n s t a n t c o h e s i o n i s o b t a i n e d at l a r g e r s t r a i n s . L a r g e s h e a r s t r a i n s a r e n o t l i k e l y t o c h a n g e t h e o r i e n t a t i o n o f p a r t i c l e s , i . e . , t h e n u m b e r o f i n t e r p a r t i c l e b o n d s r e m a i n a l m o s t c o n s t a n t a s s h e a r s t r a i n s i n c r e a s e . T h u s , c o h e s i o n s t a y s a l m o s t c o n s t a n t . It i s i n t e r e s t i n g t h a t at l a r g e s t r a i n s t h e c o h e s i o n i n u n d i s t u r b e d s a m p l e s b e c o m e z e r o w h i l e t h e c o h e s i o n i n r e m o l d e d s a m p l e s a l w a y s m a i n t a i n e d a s m a l l b u t s i g n i f i c a n t r e s i d u a l v a l u e . T h i s c o n c l u s i o n w a s c o n s i s t e n t r e g a r d l e s s o f t h e s t r a i n r a t e u n d e r i n v e s t i g a t i o n . F r i c t i o n . -T h e e f f e c t o f s t r u c t u r e o n f r i c t i o n a l s o s h o w e d a s e t p a t t e r n w i t h h i g h e r v a l u e s f o r r e m o l d e d s t a t e , b u t t h e d i f f e r e n c e i s n o t a s m a r k e d a s i t w a s f o r c o h e s i o n . A t s m a l l s t r a i n s , <he f o r t h e r e m o l d e d s a m p l e w a s h i g h e r t h a n <t>e f o r t h e u n d i s t u r b e d s a m p l « m a i n l y b e c a u s e t h e r e l a t i v e l y l o w c g d e v e l o p e d i n t h e r e m o l d e d s a m p l e r e q u i r e d m o r e f r i c t i o n to b e d e v e l o p e d t o c a r r y t h e a p p l i e d s h e a r s t r e s s e s . It i s m o s t i n t e r e s t i n g , h o w e v e r , t h a t i n g e n e r a l i t c a n b e c o n c l u d e d t h a t a t l a r g e s t r a i n s « J e w a s e s s e n t i a l l y t h e s a m e v a l u e f o r u n d i s t u r b e d a n d r e m o l d e d s p e c i m e n s . H e n c e t h e p e a k f r i c t i o n d e v e l o p e d m a y b e i n d e p e n d e n t o f s t r u c t u r e . 86 EFFECT OF STRUCTURE. OW THE DEVELOPMENT OF C e AfHP <fc>e AT "n+E FAST STRAIN RATE CP025 /N/ffR) PICV 3 £ 87 7 . 5 E f f e c t s o f s t r a i n r a t e i n a R e m o l d e d C l a y . T h e r e s u l t s o f t e s t s o n r e m o l d e d s a m p l e s a t t w o s t r a i n r a t e s w e r e a v a i l a b l e a n d w e r e c o m p a r e d t o s t u d y t h e i n f l u e n c e o f s t r a i n r a t e i n t h e c a s e o f r e m o l d e d c l a y s . T y p i c a l c u r v e s f o r (^T-^TS ) a t t h e f a s t e r a n d s l o w e r s t r a i n r a t e s a r e p r e s e n t e d i n F i g . 3 7 . T h e r e i s a t e n d e n c y f o r t h e s t r e n g t h t o i n c r e a s e ( i n t e r m s o f ( < 3 T - ° 3 ) ) a t t h e s l o w e r r a t e s . T h i s m a y i n d i c a t e t h e t e n d e n c y f o r t h i x o t r o p i c s t r e n g t h g a i n i n r e m o l d e d s a m p l e s ( S e e d , M i t c h e l l a n d C h a n , I 9 6 0 ) . M i t c h e l l ( I960) c o n s i d e r e d t h e p o s s i b i l i t y o f g r a d u a l r e - o r i e n t a t i o n o f p a r t i c l e s a s a p o s s i -b l e r e a s o n f o r t h i x o t r o p i c g a i n a n d L e o n a r d s (1962) r e f e r r e d t o i t i n t e r m s o f n e w s t r u c t u r a l a r r a n g e m e n t o f o r i e n t e d w a t e r w i t h t i m e . F u r t h e r i n v e s t i g a t i o n s a r e n e e d e d t o e s t a b l i s h t h i s t r e n d . T y p i c a l p o r e p r e s s u r e s a r e p r e s e n t e d i n F i g . 3 8 . T h o u g h t h e c u r v e s a r e p r e t t y c l o s e t h e r e m a y b e t e n d e n c y f o r l o w e r p o r e -p r e s s u r e s at l a r g e s t r a i n s f o r t h e s l o w e r r a t e . T h i s m a y i n d i -c a t e t h e r e - o r i e n t a t i o n o f p a r t i c l e s w i t h t i m e . C u r v e s f o r t h e d e v e l o p m e n t o f c e a n d 4>e a t t h e t w o s t r a i n r a t e s a r e p r e s e n t e d i n F i g . 3 9 . T h e y i n d i c a t e t h e f o l l o w i n g : 88 6 PERCENT 3 IS. EFFECT STATE O F JSTRA/N R . A T E O N X>£l/)ATa«. S T R E S S I N R E M O t - f i E J ) C o h e s i o n N o t m u c h c o h e s i o n i s d e v e l o p e d at e i t h e r s t r a i n r a t e a s a l l s a m p l e s w e r e r e m o l d e d . T h e r e m a y , h o w e v e r , b e a t e n d -e n c y f o r c o h e s i o n to d e c r e a s e s l i g h t l y w i t h i n c r e a s i n g t i m e t o f a i l u r e at s m a l l e r s t r a i n s . A t l a r g e s t r a i n s t h e c o h e s i o n a t -t a i n e d a s m a l l b u t s i g n i f i c a n t r e s i d u a l v a l u e w h i c h w a s e s s e n t -i a l l y i n d e p e n d e n t o f s t r a i n r a t e . F r i c t i o n F r i c t i o n i s h i g h e r a t t h e s l o w e r r a t e s o f s t r a i n at s t r a i n s l e s s t h a n a b o u t 8%. H o w e v e r , a t l a r g e s t r a i n s f r i c t i o n a p p e a r s to b e i n d e p e n d e n t o f s t r a i n r a t e . I n g e n e r a l i t c a n b e c o n c l u d e d t h a t f o r r e m o l d e d c l a y s b o t h f r i c t i o n a n d c o h e s i o n at l a r g e s t r a i n s a r e i n d e p e n d e n t o f s t r a i n r a t e . 7 . 6 S h e a r i n g S t r e n g t h . T h e s h e a r i n g s t r e n g t h o f s o i l m a y b e d e f i n e d a s t h e s t r e n g t h at (<n -£3 ) m a x i m u m , ) m a x i m u m o r i t m a y b e r e l a t e d to a p a r t i c u l a r s t r a i n d e p e n d i n g o n t h e p r o b l e m b e i n g c o n s i d e r e d . It i s g e n e r a l l y a c c e p t e d t h a t (<T-^3 ) m a x i m u m a n d (*7/<*% ) m a x i m u m m a y n o t o c c u r a t t h e s a m e s t r a i n e s p e c i a l l y f o r s e n s i t i v e c l a y s . T h e c o m p o n e n t s o f s t r e n g t h , c o h e s i o n a n d f r i c t i o n , d e p e n d o n t h e s t r a i n a n d d o n o t a t t a i n t h e i r m a x i m u m v a l u e s s i m u l t a n e o u s l y a s r e v e a l e d b y t h i s i n v e s t i g a t i o n a n d a l -r e a d y p o i n t e d o u t b y L a m b e (I960) S c h m e r t m a n n (I960) a n d (1963) W u , D o u g l a s a n d G o u g h n o u r (1962) a n d B e a i ( 1 9 6 3 ) . e t c . F o r t h e TRUE CQHESIQM /N.' Psi o u c5 $ 8 TRUE FRfCrtQ-N IN DEGREES f 91 soil tested (07-03 ) maximum occure<4at about 3% strain and (o;/<^ ) ^ maximum at 15% strain for. the normally consolidated and slightly over-consolidated case. At 3% strain the cohesion at fast as well as slow strain rate has a tendency to decrease after having attained its maximum value whereas friction is not fully mobilized. Strength is partly.y due to the cohesional part and partly.; due to the frictional part. (At the faster strain rate at 3% strain c e developed was 1.78 lbs. per sq. in . and ^ e was 25° 46'). At 15% strain cohesion has dropped to zero and full friction is mobilized and contributes to the strength. (At the faster strain rate at 15% strain ^ e developed was 3 2 ° 5 3 ' ) . 7.7 Discussions of Test Results on the Basis of Rate Process  Theory. A reference to rate process theory was made in Section 3.5 and E q . 3-6 is reproduced below: 4RT A F A N a {^Y+ln(-J-)J+05hncrb ( -^-+ln -^r)\ 3-6 where symbols have the meaning as explained before. Effects of Rate of Strain. Strain rate £ appears in both the terms of E q . 3-6 given above in the numerator and it suggests that with an in-crease in the rate of strain both the terms should increase meaning thereby that with an increase in € , c and ^ should e e increase. In the present investigation in the undisturbed state higher values of (6e and a higher peak in c 'has been obtained at / /' / t h e f a s t e r s t r a i n r a t e a s c o m p a r e d t o «5 g a n d p e a k i n c e a t t h e s l o w e r r a t e . T h i s i s i n l i n e w i t h t h e b e h a v i o u r e x p e c t e d o n the b a s i s o f r a t e p r o c e s s t h e o r y . E f f e c t s o f S t r u c t u r e . T h e i n f l u e n c e o f s t r u c t u r e i n t h e E q . 3-6 i s t h r o u g h t h e t e r m S * co + b o ^ . T h e t e r m " a " r e p r e s e n t i n g t h e n u m b e r o f i n t e r p a r t i c l e b o n d s a p p e a r s i n t h e f i r s t b r a c k e t a n d t h i s s u g g e s t s t h a t t h e i n f l u e n c e o f s t r u c t u r e s h o u l d b e m a r k e d o n c o h e s i o n . In u n d i s t u r b e d c l a y h a v i n g a f l o c c u l a t e d s t r u c t u r e , t h e n u m b e r o f i n t e r p a r t i c l e c o n t a c t s i s m o r e t h a n i n a r e m o l d e d c l a y h a v i n g a d i s p e r s e d s t r u c t u r e . C o h e s i o n i s e x p e c t e d t o b e m o r e i n a n u n d i s t u r b e d c l a y . In a r e m o l d c l a y a t l a r g e r s t r a i n s n o t m u c h c h a n g e i n t h e s t r u c t u r e t a k e s p l a c e a n d h e n c e i n t e r -p a r t i c l e b o n d s d o n o t c h a n g e a n d c o h e s i o n : . ' s t a y s a l m o s t c o n s t a n t . t F r i c t i o n , o n t h e o t h e r h a n d , a p p e a r s t o b e l i t t l e a f f e c t e d b y s t r u c t u r e . In t h e p r e s e n t i n v e s t i g a t i o n c o h e s i o n i n r e m o l d e d c l a y d r o p p e d to a b o u t 1/8 i t s v a l u e i n a n u n d i s t u r b e d c l a y w h i c h i s a q u i t e s i g n i f i c a n t r e d u c t i o n . C o h e s i o n i n r e m o l d e d c l a y s a l s o m a i n t a i n e d a s m a l l , a l m o s t c o n s t a n t , v a l u e at l a r g e r s t r a i n s . F r i c t i o n o n t h e o t h e r h a n d i s n o t s i g n i f i c a n t l y a f f e c t e d b y s t r u c -t u r e . T e s t r e s u l t s a r e e x p l a i n a b l e ^ b y r a n d l a r g e o n t h e b a s i s o f r a t e p r o c e s s t h e o r y a n d t h e t h e o r y a p p e a r s t o b e a r e a s o n a b l e p o s t u l a t e . C H A P T E R V I I I S u m m a r y C o n c l u s i o n s a n d S u g g e s t i o n s F o r F u t u r e W o r k S u m m a r y , C o n c l u s i o n s a n d S u g g e s t i o n s / F o r F u t u r e W o r k  / 8 .1 G e n e r a l ' / T h e / e f f e c t o f s t r a i n r a t e a n d s t r u c t u r e o n t h e d e v e l o p m e n t o f s h e a r i n g r e s i s t a n c e d u r i n g d e f o r m a t i o n o f a s a t u r a t e d c o h e s i v e s o i l h a v e ^ b e e n s t u d i e d . T h e e f f e c t s o f s t r a i n r a t e w e r e e v a l u a t e d / b y c o m p a r i n g the t e s t r e s u l t s o f i d e n t i c a l u n d i s t u r b e d s a m p l e s a t / s i g n i f i c a n t l y d i f f e r e n t s t r a i n r a t e s ( t h u s b r i n g i n g i n s t r a i n r a t e a s a m a i n v a r i a b l e ) . T h e e f f e c t s o f s t r u c t u r e w e r e i n v e s t i g a t e d b y c o m p a r i n g t h e t e s t r e s u l t s o f u n d i s t u r b e d a n d r e m o l d e d s a m p l e s at s a m e v o i d r a t i o . R e m o l d i n g b r e a k s d o w n t h e s t r u c t u r e ( t h u s b r i n g i n g i n s t r u c t u r e a s t h e m a i n v a r i a b l e ) . T h e s t u d y h a s s h o w n t h a t i n t h e u n d i s t u r b e d s t a t e c o h e s i o n w a s d e v e l o p e d at s m a l l e r s t r a i n s , r e a c h e d a p e a k a n d t h e n d e -c r e a s e d to z e r o . F r i c t i o n w a s m o b i l i z e d s l o w l y a n d a t t a i n e d a m a x i m u m v a l u e at l a r g e s t r a i n s . T h i s p a t t e r n o f b e h a v i o u r f o r t h e d e v e l o p m e n t o f c o h e s i o n a n d f r i c t i o n w i t h s t r a i n i s i n l i n e w i t h t h e p o s t u l a t e o f L a m b e (I960) a n d s u g g e s t s a f u n d a m e n t a l d i f -f e r e n c e b e t w e e n t h e m e c h a n i s m c o n t r o l l i n g c o h e s i o n a n d f r i c t i o n . T h e s t u d y h a s r e v e a l e d t h a t t h e d e v e l o p m e n t o f t r u e c o -h e s i o n a n d t r u e f r i c t i o n i s i n f l u e n c e d b y r a t e o f s t r a i n a n d s t r u c -t u r e a n d t h e e f f e c t i s m o r e p r o n o u n c e d i n t h e s u b f a i l u r e r e g i o n . 9 4 T h e i n f l u e n c e i s b y a n d l a r g e e x p l a i n a b l e o n t h e l i n e s o f r a t e p r o c e s s t h e o r y p r e s e n t e d b y M i t c h e l l ( 1964 ) . 8 . 2 E f f e c t s o f r a t e o f S t r a i n . (a) U n d i s t u r b e d s e n s i t i v e c l a y . In t h e u n d i s t u r b e d s e n s i t i v e c l a y t e s t e d t h e r e w a s a t e n d -e n c y f o r t h e s t r e n g t h i n t e r m s o f m a x i m u m ( «7 - <5 ) t o d e c r e a s e w i t h d e c r e a s e i n s t r a i n r a t e . T h i s i s a t t r i b u t e d t o i n c r e a s e i n p o r e - p r e s s u r e s w i t h d e c r e a s e i n s t r a i n r a t e . ( C a s a g r a n d e a n d W i l s o n , 1951). A f ( S k e m p t o n ' s p o r e - p r e s s u r e p a r a m e t e r a t m a x i -m u m ( ) i n c r e a s e d w i t h d e c r e a s e i n s t r a i n r a t e a n d i s i n l i n e w i t h t e s t r e s u l t s o n s e n s i t i v e c l a y s r e p o r t e d b y B j e r r u m e t a l (1958) a n d C r a w f o r d (1959) . M a x i m u m p r i n c i p a l e f f e c t i v e s t r e s s r a t i o ^7/0% w a s , h o w e v e r , n o t s i g n i f i c a n t l y e f f e c t e d b y e i t h e r t h e J-s t r a i n r a t e o r s l i g h t o v e r - c o n s o l i d a t i o n . T r u e c o h e s i o n a n d t r u e f r i c t i o n b o t h s h o w e d a t e n d e n c y t o d e c r e a s e w i t h d e c r e a s e i n s t r a i n r a t e . T h e d e c r e a s e i n p e a k c o h e s i o n w i t h d e c r e a s e i n s t r a i n r a t e i s a t t r i b u t e d to a d e c r e a s e i n i n t e r p a r t i c l e b o n d s o n a c c o u n t o f m o r e t i m e a v a i l a b l e f o r r u p t u r e o f b o n d s at s l o w e r r a t e . (T-Kei d e c r e a s e i n f r i c t i o n w i t h t h e d e c r e a s e i n s t r a i n r a t e i s a t t r i b u t e d t o d e c r e a s e d a v e r a g e n o r m a l e f f e c t i v e s t r e s s e s a r i s i n g o u t o f h i g h e r p o r e - p r e s s u r e s a t d e c r e a s e r a t e o f s t r a i n . H i g h e r p o r e - p r e s s u r e s a l s o r e s u l t i n i n c r e a s e d p a r a l l e l i s m o f t h e p a r t i c l e s a n d i n c r e a s e d r e p u l s i v e f o r c e s a n d . h e n c e r e d u c e d «4 w i t h d e c r e a s e i n r a t e o f s t r a i n . 95 (b) Remolded C l a y s . In the case of r e m o l d e d c l a y the study has shown a tend-ency for the strength i n t e r m s of ( « 7 - « 3 ) t o i n c r e a s e with de-c r e a s e i n rate of s t r a i n and i s c o n s i d e r e d as due to t r i x o t r o p i c strength gain i n r e m o l d e d c l a y s , ( M i t c h e l l , (I960) and L e o n a r d s (1962). Cohesion i n r e m o l d e d c l a y s showed a tendency to de-c r e a s e with d e c r e a s e i n rate of s t r a i n whereas f r i c t i o n was not much affected. A t l a r g e r s t r a i n s , however, c o h e s i o n and f r i c t i o n a r e not s i g n i f i c a n t l y affected by s t r a i n rate i n u n d i s t u r b e d , as w e l l as r e m o l d e d c l a y s . 8.3 E f f e c t s of S t r u c t u r e . The u n d i s t u r b e d s e n s i t i v e c l a y has a p r e d o m i n a n t l y f l o c c u l a t e d s t r u c t u r e and the r e m o l d e d c l a y a p r e d o m i n a n t l y d i s p e r s e d s t r u c t u r e . In the r e m o l d e d c l a y s t r ength i n t e r m s of ) dropped a p p r e c i a b l y as c o m p a r e d to u n d i s t u r b e d c l a y on account of the breakdown of s t r u c t u r e d u r i n g r e m o l d i n g . Value of <ri/5% for r e m o l d e d c l a y showed a tendency to a p p r o a c h the values for u n d i s t u r b e d samples at l a r g e r s t r a i n s , i n d i c a t i n g thereby that at l a r g e s t r a i n s the s t r u c t u r e of both the u n d i s t u r b e d and r e m o l d e d samples a r e a l m o s t s i m i l a r . C o h e sion was m a r k e d l y affected by str u c t u r e . ' In u n d i s -turbed c l a y much higher c o h e s i o n as c o m p a r e d to r e m o l d e d c l a y ^ .' • • • / / 96 / i !• was obtained on account of l a r g e numbers of i n t e r p a r t i c l e bonds in undisturbed state. R e m o l d i n g r e s u l t e d i n breakdown of s t r u c -/ ture and the number of i n t e r p a r t i c l e bonds was r e d u c e d very-much and/cohesion dropped so s i g n i f i c a n t l y . It has a l s o been / noted tha( in u n d i s t u r b e d state c o h e s i o n always dropped to z e r o at l a r g e r s t r a i n s whereas on r e m o l d e d c l a y s a s m a l l r e s i d u a l , i almost constant, value of cohesion was obtained at l a r g e r s t r a i n s . F r i c t i o n does not appear to be dependent on s t r u c t u r e . 8.4 Suggestions for future work. 1. In the present i n v e s t i g a t i o n s only two s t r a i n r a t e s w e r e used. It might be of i n t e r e s t to study a set of s t r a i n r a t e s and to find i f a t h e o r e t i c a l c u r v e could be fi t t e d l i n k i n g s t r a i n p e r -cent, cohesion, f r i c t i o n and s t r a i n r a t e . 2. It might be of i n t e r e s t to study the t h i x o t r o p i c p r o p e r t i e s of r e m o l d e d c l a y s by allowing d i f f e r e n t s a m p l e s to stand f o r v a r y i n g p e r i o d s of time b e f o r e t e s t i n g . 3. M o s t of the s t a b i l i t y p r o b l e m s i n f i e l d r e s e m b l e plane s t r a i n conditions where there i s no change i n length along the axis of the s t r u c t u r e . The c o n c l u s i o n s of this i n v e s t i g a t i o n a r e based on r a d i a l l y s y m m e t r i c a l s t r e s s (case where 0^=03 ). It might be of i n t e r e s t to study the effects of rate of s t r a i n on the development of c e and 4> under plane s t r a i n c o n d i t i o n . 97 A P P E N D I X A S a m p l e p r e p a r a t i o n B e f o r e t r i m m i n g t h e s a m p l e t h e e q u i p m e n t w a s m a d e r e a d y . F o u r O - r i n g s o n r i n g e x p a n d e r s a n d o n e m e m b r a n e w e r e f e d o v e r the t o p l o a d i n g c a p d o w n t h e s p i r a l . A r o l l e d m e m b r a n e w a s a l s o p l a c e d d o w n t h e b o t t o m p e d e s t a l . P o r o u s s t o n e s a n d o n e c o n t i n u -o u s s l i t f i l t e r p a p e r w e r e b o i l e d f o r a b o u t 10 m i n u t e s i n w a t e r a n d a l l o w e d to c o o l . S i l i c o n g r e a s e w a s p l a c e d o n t h e s i d e s o f t h e b o t -t o m p e d e s t a l a n d t h e m e m b r a n e w a s r o l l e d h a l f w a y u p t h e b o t t o m p e d e s t a l . A s p o i n t e d i n t h e t e x t s e c t i o n 5 . 1 , b l o c k s a m p l e s f r o m t h e f i e l d w e r e s t o r e d i n a h u m i d r o o m . T e s t s w e r e c o n d u c t e d o n 2 . 8 i n c h e s l o n g 1 .4 i n c h d i a m e t e r c y l i n d r i c a l s a m p l e s . T h e y w e r e p r e p a r e d i n a m o i s t r o o m u s i n g t h e t r i m m i n g e q u i p m e n t s s h o w n i n F i g . 10. F o r w a t e r c o n t e n t d e t e r m i n a t i o n s i d e t r i m m i n g s c o r r e s p o n d -i n g to t h e a n t i c i p a t e d f i n a l l e n g t h o f t h e s a m p l e w e r e u s e d . T o p a n d b o t t o m t r i m m i n g s s h o w e d s i g n i f i c a n t d i f f e r e n c e s i n w a t e r c o n t e n t s d u e to t h e l a m i n a t e d n a t u r e o f t h e c l a y a n d w e r e n o t u s e d i n w a t e r c o n t e n t d e t e r m i n a t i o n s . T h r e e c i r c u m f e r e n t i a l m e a s u r e m e n t s ( t o p , c e n t r e a n d b o t t o m ) a n d f o u r l e n g t h m e a s u r e m e n t s w e r e t a k e n t o d e t e r m i n e s a m p l e d i m -e n s i o n s . S a m p l e s w e r e c a r r i e d i n r u b b e r s l i n g a b o u t 1 1 /2 i n c h e s w i d e to r e d u c e s t r e s s e s a n d w e r e h a n d l e d w i t h c a r e . T h e s a m p l e 97 A P P E N D I X A S a m p l e p r e p a r a t i o n B e f o r e t r i m m i n g t h e s a m p l e t h e e q u i p m e n t w a s m a d e r e a d y . F o u r 0 - r i n g s o n r i n g e x p a n d e r s a n d o n e m e m b r a n e w e r e f e d o v e r the t o p l o a d i n g c a p d o w n t h e s p i r a l . A r o l l e d m e m b r a n e w a s a l s o p l a c e d d o w n t h e b o t t o m p e d e s t a l . P o r o u s s t o n e s a n d o n e c o n t i n u -o u s s l i t f i l t e r p a p e r w e r e b o i l e d f o r a b o u t 10 m i n u t e s i n w a t e r a n d a l l o w e d to c o o l . S i l i c o n g r e a s e w a s p l a c e d o n t h e s i d e s o f t h e b o t -t o m p e d e s t a l a n d t h e m e m b r a n e w a s r o l l e d h a l f w a y u p t h e b o t t o m p e d e s t a l . / / • • A s p o i n t e d i n t h e t e x t s e c t i o n 5 . 1 , b l o c k s a m p l e s f r o m t h e • / • f i e l d w e r e s t o r e d i n a h u m i d r o o m . T e s t s w e r e c o n d u c t e d o n 2 . 8 , / i n c h e s l o n g 1 .4 i n c h d i a m e t e r c y l i n d r i c a l s a m p l e s . T h e y w e r e I / • • p r e p a r e d i n a m o i s t r o o m u s i n g t h e t r i m m i n g e q u i p m e n t s s h o w n i n F i g . 10. j ^ ' F o r w a t e r c o n t e n t d e t e r m i n a t i o n s i d e t r i m m i n g s c o r r e s p o n d -/ ' ' i n g to t h e a n t i c i p a t e d f i n a l l e n g t h o f t h e s a m p l e w e r e u s e d . T o p a n d b o t t o m t r i m m i n g s s h o w e d s i g n i f i c a n t d i f f e r e n c e s i n w a t e r c o n t e n t s d u e to t h e ' l a m i n a t e d n a t u r e o f t h e c l a y a n d w e r e n o t u s e d i n w a t e r c o n t e n t d e t e r m i n a t i o n s . T h r e e c i r c u m f e r e n t i a l m e a s u r e m e n t s ( t o p , c e n t r e a n d b o t t o m ) a n d f o u r l e n g t h m e a s u r e m e n t s w e r e t a k e n t o d e t e r m i n e s a m p l e d i m -e n s i o n s . S a m p l e s w e r e c a r r i e d i n r u b b e r s l i n g a b o u t 1 1 /2 i n c h e s w i d e to r e d u c e s t r e s s e s a n d w e r e h a n d l e d w i t h c a r e . T h e s a m p l e 98 a l o n g w i t h t h e r u b b e r w r a p was w e i g h e d t o d e t e r m i n e i t s i n i t i a l w e i g h t . T h e s a m p l e a n d t h e b o i l e d p o r o u s s t o n e s a n d f i l t e r p a p e r w e r e t a k e n i n to t h e c o n s t a n t t e m p e r a t i v e r o o m t o p l a c e t h e s a m p l e i n t h e c e l l . W a t e r w a s a l l o w e d to f l o w f r o m t h e b o t t o m d r a i n a g e l i n e to c o v e r t h e t o p o f t h e p e d e s t a l a n d f o r m a c o n v e x m e n i s c u s . B o t t o m s t o n e c o o l e d to r o o m t e m p e r a t u r e w a s s l i d i n t o p l a c e w i t h -o u t e n t r a p p i n g a n y air. A l i t t l e w a t e r w a s s p r e a d o n t h e e n d o f the s a m p l e a n d i t w a s s l o w l y r o t a t e d o v e r t h e p o r o u s s t o n e o n t h e ' / • ' ' • • p e d e s t a l . T h e t o p c a p w a s i n v e r t e d a n d w a t e r w a s a l l o w e d t o f o r m a m e n i s c u s . T o p p o r o u s s t o n e a n d t o p c a p w e r e r i g h t e d a n d s l i d / o n t h e t o p o f the ' s a m p l e . E x t r a w a t e r o f t h e s l i t f i l t e r p a p e r w a s s h a k e n o f f . I t^was g e n t l y p l a c e d a r o u n d t h e s a m p l e a n d c o v e r e d p a r t s of t o p a n d b o t t o m p o r o u s s t o n e s a s ' w e l l . A s m a l l a m o u n t o f w a t e r w a s a l l o w e d t o c o m e o u t t h r o u g h t h e b o t t o m p e d e s t a l s o a s to f o r m a r i n g o n t h e r o l l e d m e m b r a n e a t t h e b o t t o m p e d e s t a l . T h e m e m b r a n e w a s r o l l e d u p w i t h w a t e r t o f o r c e a n y a i r w h i c h m i g h t h a v e b e e n t r a p p e d . T h e m e m b r a n e w a s t a k e n o v e r t h e t o p c a p , w h i c h w a s a l s o p r e c o a t e d w i t h s i l i c o n g r e a s e . A f t e r p l a c i n g t h e f i r s t m e m b r a n e a l a y e r o f g r e a s e w a s s p r e a d o n i t a n d t h e s e c o n d m e m b r a n e w a s r o l l e d d o w n f r o m t h e t o p . T w o O - r i n g s w e r e p l a c e d o n t h e b o t t o m c a p a n d t w o o n t h e t o p c a p . T h e t o p o f t h e c e l l w a s t h e n p l a c e d i n p o s i t i o n a n d t h e a l i g n -m e n t o f t h e r a m w i t h t h e b a l l b e a r i n g o n t h e l o a d i n g c a p was a d j u s t e d i f n e c e s s a r y . T h e p l a t f o r m w a s r a i s e d u p a n d t h e r a m w a s a l i g n e d with the proving ring. Vertical dial gauge was adjusted if neces-sary. De-aired water was fed into the cell under gravity. A small cell pressure was applied to develope positive pore-pressures. A sample at this stage is considered as ready for B value measure-ments before consolidation. As pointed out earlier consolidation for 36 hours was permitted against a back pressure of 10 lbs. per sq. in. to ensure better saturation. A l l through the consolidation the ram was maintained in contact with the sample by cranking up the platform so as to keep a nominal seating load. 24 hours were permitted for pore-pressure adjustments after consolidations. Some of the samples were sheared thereafter and some were con-solidated further as detailed in the procedure. In either cases, . B values before shearing were obtained. , 100 A P P E N D I X B R e m o l d i n g T e c h n i q u e A f t e r d r a i n i n g t h e c e l l w a t e r t h e s a m p l e w a s r e m o l d e d i n p l a c e i n u n d r a i n e d c o n d i t i o n . T h e s a m p l e w a s g e n t l y r e m o l d e d b y o n e h a n d , to b e g i n w i t h , s q u e e z i n g i t f r o m a l r o u n d . I n a b o u t 5 m i n u t e s t i m e t h e s a m p l e s t a r t e d b e c o m i n g s o f t i n d i c a t i n g t h e s t a r t o f t h e c o l l a p s e o f t h e s t r u c t u r e . A t t h i s s t a g e t h e o t h e r h a n d w a s k e p t o n t h e t o p c a p a n d p r e s s u r e w a s a p p l i e d f r o m t o p d u r i n g a l r o u n d s q u e e z i n g . T h e r e m o l d i n g w a s d o n e s l o w l y a n d w i t h c a r e s o a s to m a i n t a i n t h e c y l i n d r i c a l s h a p e o f t h e s a m p l e . T h i s p r o -c e s s w a s c o n t i n u e d f o r 15 m i n u t e s a n d r e s u l t e d i n s u f f i c i e n t d i s -s a m p l e w a s b e i n g r e m o l d e d p o r e - p r e s s u r e s w e r e a l s o r i s i n g , i n d i -c a t i n g t h a t . t h e s t r u c t u r e w a s b r e a k i n g - d o w n . A P P E N D I X C / / / S a m p l e D a t a / • ' ( 101 Cot*J&OLiDATE-T> T d l A N A L TfeST SOIL SA-MPie. •  HAN£/ ^ A* TEST No W f - S f l w ^ W ' ' " 4 S P . S R A V I T Y _ Test type. 2.6 : PATC fob Is 1167 S - c P p g j E TEST W A T E R . 6 3 M T E N / T TESTED 6v R .c .6uf»&> S-F>£CJM£N LOCATION Si»E. SftDE. &4X>E. T O P BOTTOh/l &>NTAJN£R WUMfrfiR 1 Z 3 4- S C WT. CJNTAINER +• Wer J « L 5 S 7 0 42.ao 3 7 - 9 8 . . . . S * 6 q 4 a . 6 9 6 9 - 2 4 Mr. CONTAINER+ i>£y Soiu 44- 4& 3 4 . 6 9 3 / 8 9 4 3 . 7 ? S -4 .12 HT. WATER C*i H-2.2. 7-31 10 St »S-12 KJT. CONTAINER. GM< 1 7 4 0 17-19 1 7 4 0 I7-3S J7-5I 17-30 WT. XKIV GtAi 17-5X3 ( 4 4 9 26-4-4 17-6S 3 £ . S 2 WATCR CONTENT 41-40 41-70 4 2 - 0 O 41 00 4 3 . 6 o 4 I O O ClRJU)r4 (M CM. J)(A. C M . A f t E A To-P » a s 3 3 9 JO-M C £ * T £ £ C-2.8 3 S 9 10. II &OTT0N1 l'-28 3 (0 II Kit. Met Swf^qW/Wra/'a<33l9 ^ M 3. S O <SM Wi 1+ ur 9 I S O C M 3Z-<k> CM* 4 7 1 - 5 C M 3 3 8 - 9 0 6-» 3 1 1 9 A P T E E , TEST W A T E R C O N T E N T LOCATION hi HOLE CONTAINER tv/t, 1 Ur. OoNTAt^ER-t-W£T SOIL 198-85 NT- CoN TA<M&A J>n.y Son. <5M WT l^ATER c y ) 31-46 WT CONTAINER £tf 76-0? WT. J)RysoU- C M S>1-3o H A T E R . I N T E N T 3460 . ur . . 3 8 - o Q <SH 3 P&3R6E O F SATO RATION * » 9 8 V ^ /• Volu^vc c l a a * * / ^ g t u n x ^ C » > i A f U » o f c i w & 7 O O C M 3 W S _ i r l t34.fo «. O- f4crt A-l/" c 6-86 O r * 102 TRIAXIAL C O N S O L I D A T I O N T E S T W O E y u P 3 y By R. • C. <S. '66.89 tfSJ: INITIAL WATER. GaNTEh/rc 41-52% - »ooo P s i tor. W . A T T O W«</ A. C S S O O ^ M PATE. T I M E HU Mix* ELAPSED TiMfi /EXAP3EP v T I M E BORBTTB. VEfcTYCALPfM INC«65 'O • 42> b. O.<oo 9' oo T E M P «• 2oe± 0.04 8-6o O-. 15 0-5C? e zo 0: 34 0-75 7-61 ,1 :0o \oo T4» 1 : 34- -/2.-1S ISO / 3:04- 1-75 6.ir / A\0O 2 . 0 0 5-BO j 6:15 2.f0 SOS / 9:00 3 0 0 440 / I2;i5 5 50 -5 6:oo 4 - 0 0 2o-. 15 4.50 -/ Z5:oo 5oo -30.'5 &50 -36"Oo 6oo 3 oo 42: ;5 6-So --49:oo TOO 298 T-50 - : 64.06 &oo - . Z-oo o 66S1 ALPO-759* A?T£J^ CONSOLlJJATION ^  W r ^ WATER. » Ww - 2W • 31 O O WATtR. I N T E N T 1 1 33 9o CoMS6jJDATEJ> IjtNCTH Lc =• 2-7191 1M. CoNSoLipATfcJ) AR£A Ac ~ V"^V r ( . 4 5 103 TQ.IAXI/WL COMSOLI&ATION T E S T N O BUF -3 d W J f r f t F ' 4  TESTE-I) B V • ft.C,6, OtAH&£R PRESSURE = 70-4 Ps.T • IMiriAd. tVATE-g. CQNT&NT 4I-S2^f k/r. J>fty Soft, e 91 SO C M -DATE TiM£ HC.4 £.J-Ar»SEj)TlM£ / E L A P S E D v Tirte & y R e r T e , V£K.n<tAL JlAi. ie. 2 .67 11 OO Ay>v. (3<D : O O 0- Oo Zoo 0 - 8 S 5 1 0: OA O. 2 5 O: \S Oso fi^> « 29-So O: 3 4 O 15 |: Oo l o o 1-9 A I: 34 /•SO 3 :o4 I-7S f-91 -4:oo 2.00 — 6:iS 2 S O 9:oo 300 (2.-I5- 3.50 4 oo 1 8 9 e o : is- 4 s o ZS-oo 50O bO: IS s s o 36 : OO 6.oo AZ:\S G s O AS-.oo Too Sh : IS" 7 SO GA: OO 8-oo 19 .2. t7 /(•OO tfr~ . O - S787 A V = O 32 C M 3 A F T £ R . CONSO L IPA-TIOM 104 TRlA-itlAC CoMSoU D-ATI QN TEST NtQ J K J F - 3 CU~^V &fi'f^ T E S T E D by jZ.CO-tr~>\TlpH. h / A T E C C O N T E N T * 4*sz% H T . i > « - y S o n . • 91 S O C M h/Tt WAre.a. a 30.68 <TM T I M E Hfti MIN Gi-APSEpTiNfiE * T* M i & 0 £ E T T £ C M V E e r i c A t . 19- 2 ^ 7 (1 • o5>>^ c o o o oo O • 8 7 87 TBJ*U>m*ZO*C — i 0;o+ 0:15 0 so 0.-34- 0.75 1: 00 l<50 1:3* 1-25 2-IS I S O 3:04 1-75 1 90 4-.oo 2oo 6.-IS- 2 so 9:00 3.oo <94 12; Ii' 3-so Ifeoo Aoo 2o: IS* Aso 25: OO 5 O 0 bOWS 36: oo Coo 42 :iS 6so 49-<»o 7*> Sb:lS 7-SO QA-OO -2 .02 . .C7 A-Oo P*rJ Zoo O-8S0O AV= 0-32 C M A A L » O-OO14 •• 1 0 5 C O M S O U CVAT£<P QMI>PJMNEj) ~ fe . I A .X lM- TEST  C H A M f r E P . P « . £ S S D t t C =• 66-S 8 P .S - I . COM&OI-<&-AT£J) A R £ A = I -4S » * * C A M S Q t . I D r A . T E P . l E f j T H =. 2.719J IN O V U L A T I O N P A C T 6 a . 0 O t » / i > i v >ATE fcfc.gl. 67 JfeSTEJ By g.c.q-BA«OM£,TRI& Pg.ESt<jRE « 29-8X TE^ jpe-R.ATijae t 2 d ' c fob. I S * 'C.7 e> \><xL*iu> bcfr* Ceb. &\st % ? T/ME E> VAUJES Pone. PR-E S»U«£. 10 • 40 ls-s-6 f O - 4 2 221*4 2'6-< 6SS « 9 8 9 / 0 - 4 4 3o7j> 3of*S /I- 2.0 3 66S" ••• . 2<92 So* _ o 9 9 '/• 2-3 2»99JT 2 4 9 9 3(0 tz.5 - t o o M-asr 4l2X> 2 6 2 4 T I M E . 1 / t R . T t C A C I H . P C O V I N G Q . IN6V. £ f A-<-O • 000 i JrJ • TR. AMS f X J C E U . . C.EAJ) . C€.tL. PR-ESS. P b R £ . PtLBSS. B . P . • j z w r < ? » 4 K ^ , 1 n . 2 , - , 7 i—e * JO- 4 ? A n v 0 " Z - 9 7 10- 5X> O08 <2>I2 1 I S - 5 S - • • J 3 9 4 2 4 o o / 4 ' 7 l -S- 2 . 6 7 1437 |0 • ST5 *7n . 1 4 4 5 11 00 A n v £a*w)fi2ju> (Us 4 - 2 5 K^ /CM* 19- 2 . 6 7 io^^Jbuf ex! «jfc* t<"L = 2 - 7 0 D^ sjfcsv/ f o x Jo 10 JXJUUL) 2 o 2 . .67 f —1 f o l 4>m> Z1B V 2,1 • 2 - 6 7 II • 2 0 A " * « . II. Z.o CtJJj bYCKtfXA • v • /UUAt<t , a •a -si oa j»s t . 106 1 , TlMf ft-tA-C-pp_©v'N<s f U" < ! AU 6.P. CCiX. PS-£SS. Pro i/vrvA KMT\ se-s 21. 2 . 67 0 . 0 ^ 0 S S 2 4\e.o 2624- 29-8X •8 7 9S 71-O 4\ZO 2 6 7 0 -I1-7S- • 8790 86 -6 4 l 2 o 2728 -nsy •ST SO 1 03- ( 4 l 2 o 2 7 7 9 -J 2 o o •87fe2 4/2o 2 8 4 5 -12.25 •8T2S- JS2.2 4120 2 9 2 / -;2.5-0 •86S0 173-0 4ieo 2 9 6 9 -I2-7S /8S-7 4i2o 3011 -/3- 15 •SS4z 20 S O 4H7 3066 -•34 s o £ 1 5 - 4 4117 3<o7 - — / 4 - 3 o •8278 2259 4 I 2 0 3<9o 2 9 81 I S . 4 0 • 8 o 0 9 232-< 4 )19 3^72 -' S - 7 S •7 9 2 o 232-6 4116 329 S" -/&-6o • 7 7 0 8 233< 1 4 I 2 0 33 44 17- fO • 7571 233-1 4Hi 33S9 2 9 80 '8-20 •728o 2 3 2 - 0 4/17 34/2 2 9 7 9 I S - 8 S - •7'I9 230-9 4119 3 43S 22- SO -6233 2 2 6 9 4117 3*16 2 9 - T 6 2 3 - l o ' 6o27 22S>6> 4(18 3 S 3 z -24-00 224 i? 4M7 3S-46 --2S-30 2 2 4 0 4 M 9 3 S 6 4 £9-74 • 2 ? . e o 223-4 41IS - 35X-6 29-71 26- Z5 •52 39 222-6 4 H 6 3572 — 2 7 © o •So2>6 222- f 41 /3 3 S S o -2 7. 50 • 49o 4 2 2 / 4 4-l/sr 3S8 1 -29-oo •4771 220-s- 4 1 / 6 2>S84 •4-63S" 219-8 *M( S" 3 S 9 3 — /fcxJe-*-' tv^ 2 • 0 J i X . o£y oJ-t^tt-22.2- 67 £ = OIS4 107 TJZJ AxiArt- Ctt4SoU &AT/CN |MinA-c WAT&C CONTENT • 4 U 5 Z ? 0  Ur. D-fi.y Spit- t 9 /. s o 6>4 T;MC HAS M/*/I /EJ-APSEJ) ' TIME O f 3 VCATI CM. IN. &CMA<2.k£ 22. 2-C.7 •5 -IS" o-OO 6 0 0 0-0*<B 0 . 0 4 - 0-2S" 0.15 o s o 5- 9 0 CV-3 + / . O O l o o 1:3+ » -2 i -l-5o 2>.'C* I-7S- 5 - 7 9 4:00 ' 2 OO 6:15- Zso S . 6 9 9-O0 5 00 S- .6Z 1 a -. is- 3st ) (6 : OO 4 - 0 O 20 :IS" 4 - s o 2 j : o o . S-oe 5 - 6 o 3o; is* 5-SO - -36 :00 6 0 0 4i . - f .s- 6 s r > i i49:oo • 7- 0 0 /sfc: I? 7,S^> / £ 4 : 0 0 8 0 0 5-57 9- IO 4-72 /2. • J O * 6 o 15- 3 o / / •-/ 22. 2.67 zo- 3 0 A-OO O . 34-00 A L = 2 - 0 0 c x a O-OOlS -AFje-fS. C O N S O L I D A T I O N Hr, OP ^ A T^e. • 3 * <SM. / / 108 PRj0viN6 Oiuc TRANS^<jc£j^ . QEM • B.P C £ U . . PQ£&£ . Poos. PUMSS-22- 2. 67 -8- 30 • 3 46 O 9 • 10 f r " ' 34-55-23-2 T o o AP» 3 4 S O 7 2 S" 3s sz 3 4 S t > 1 ±£2- . 0 - 9 7 T 3 0 4014 3 S 9 0 432, ,. 0-99 7-3 S 3 5 T 8 3 4 - S S 22,.2-67 8- 17S* A7W. OJXJLJU • Provi* 8 - I7S- • 8 169 46>-l 3 S 7 S 3 ASS / 0 2 9 ^ 4 7 *? • 2 5 • 49-3 3 5 7 8 3 4 6 7 -8- 4 0 •5122 53.2 3S78 3483 -9-5TO ' 7857 61-9 3S78 3S1S -IO-To ' tSho 67-S 3 S T S 3 S 2 I II • 3 o ' 7 4 0 3 •71-0 3ST7 352-f 2 9 . 4 4 \Z-iO •Tf 9 9 V5-<3 3 5 7 6 3S17 -•6S 21 8 2 .9 3S 76, 3S-08 29-36 14- 7 o 8 7 S 3 S 7 7 S>SOo 29 31 I S i 4 5 " • 6 3 7 1 9 l O 3 5 7 6 3 4 9 o 2 9 3 0 (fcOo •615-1 9S--2 357 6 3 4 8 o -/fc-S-O • K o o 96 O 3 S 7 6 34 77 -17- JO • 5 * 4 9 9 9 O 3 S 7 6 3 4 7 o 29-26, 17-6.© •S82S - ><»1.7 3S77 3 4 6 3 — I9-2ST . • S-*2& 167-6 3 S 7 6 3 4 4 3 Zos-o • S W 0 7 (1/ • 8 3 S 7 6 3 4 2 8 2 9 - 2 o 2 2 . 2 s • 4 6 S 4 J I 7 - 0 3 S 7 7 3 4 0 7 — 2 2 . 4 0 • 4 6 1 9 ( '76 3 S 7 6 3 4 - O S .Sc ^ 4xU/ JiuuJb ' . 1 134-0 0 — — IZ-90 690 24.a.67 10. Ar* . 7-04-feaw enJbJ MA; {JL 1 APPENDIX D Calculations Calculations for the development of c e and 4>Q with s t r a i n i n undisturbed and remolded samples at both s t r a i n rate are given. The intercept on the Y-axis on the 1/2 ( " 3 ) Vs 1/2 ) plot i s termed as c s and ^ i s the slope of the line joining the points representing s t r e s s e s on the samples under consideration at same percent s t r a i n . (See F i g 2). Sin cpfe - tan y Cc = CVcoft<fce, 110 PASTEL R. S T R . A I M R A T E (ooa? incXe-» Uv\oUo t t n i i c l / U 4o ozs 3-70 9 0 O •/S8j8 9"6 5' •9-f739 9 1 1 a so 4-40 II S O •2o 345" H " 44 2.' •97908 450 (1-74 loo SZO U-40 •2S676 •966SD 1487 ISO A-40 1700 •30S73 17° 4 8 ' '952f 3 442 17-BO 2oo 3+0 I990 21* 133' ?32>9 2 . 1 22 23-5D •43481 Z S ° 4 * s ' •900SO 1-78 25-77 -4-oo <~6r> 2 5 ' 4 0 '47483 2 g ° 2 . | ' •&a 0 0 A 28-35 6 - 0 0 27-20 'SI 393 •SS7SS - 3o92 boo - 2g.ot> •5-H7-' 7 8 ' •84688 - 3 2 - 1 3 12-oo - 28-SO •S4296 -52° 53' - 3 7 - 8 © is-oo - 28-S-O •»397g -. 3 2 < 8 e \ 4** o-4A I3-2O •23424 •3° 33' •97217 •474 (3- S3 Oso 0 - 6 0 ! 14-SX) •2S84.0. / 4 e S 9 ' •96S96 642 14-9-J loo t <r>-63 ! 1 9 - S O 2o*f4' •9352© •674 2o-74 IS7J 0-64 ' 2 2 6 0 •4f62jfc 24°36' ' 9o924 • 7 0 S 246o 2 0 0 oe>s ' 2 4 « o 27" 3*' •8S6S8 '731 2752. 2) -oo 0 6 8 2 7-IO "5II73 3o* 4*7' • 7 5 ^ / 3o78 •400 0-82 27-3o •S16I4 ass 3 | 0 8 C 0 0 0-73 ! 2 S M © •2532. 33°ST,' » 2 - 9 g S •Sao 3 3 . 9 r lo-oo o-si I 3©.fc*> •*3/40 • » 0 6 3 3 •630 3 6 2 6 1 2 - 0 0 o s i •S?|40 36°iss ' *cT0633 •630 3 6 2 6 I l l SLONER STRAJKi RATE (00022 I n d w ^ ^ O < Cs. Ct, t«v ^ OZ.5 SZo 6" o o * • IOSIO 6 * 2 ' 3-22. 6\C3o OSO 3. BO I2-00 •2I2S6 / 2 ° / f c s ' •97708 389 I Z Z 7 5 \-00 SOO I 3 o o •23o87 13° 2 1 ' ' 9 7 a v « 5.14 ISO 4BZ (5-75 •2S 2o3 te"23' •95904 4 « 2 15.380 .Zoo A.CZ ll-oo •3oS73 1 7 ° 4 8 ' •952.13 4 « S n-Sao 2, Ao 2.0 zo 36793 2» * 35 s ' 929S2. 2 I & 9 0 4 o O 3 .40 Zi-Zo '3S7S7 •92169 3 6 8 22. s a c 6-00 2oo 2A.SO ' 4S973 27' 6 « ' •890'4 224 27toa 8 o'o Q-oA ze-zo •S3* 2© 3 2 * 6 s ' *«44«(? 0047 32-42o \2-oo - Z8AO 3 2 ° 2 S S ' •84<2o - • 32.750 is-oo 28-40 •^4o70 3Z.° 45' 64IZO ~~ - 32 7SO • \ 0» He^veleUJi TOMJUA \ T <>C d ^ . 4>£ o-zs 00s 19 73 •35904- 2 1 ° 2-3' • 93*33 2/f-041 oso 0-II 2 5 0 0 •46631 27°4ff' '88458 O 124- 27-8oo i-oo 0-22 2700 •50933 •Sfeo45 0-23S So-630 Zoo >27 ze-sv •53»-29^  3 2 ° sa* '8397g 0-322 J 2 . 8 8 0 3.00 0-3/ 2 9 S O •51,577 3 4 " 2 7 5 ' •81446 34 -454 4-oo 0-40 30-2VD •5920J '8-;wo 0-492 35 S90 \o-oo 0-4O 3o 7o S9b76 •S043S 0-492 36-424 \ZOO 0-40 3O70 S5376 36*255' '804&8 0 - 4 9 2 36-424 < 70 6o 50 •40 w a 7 o al I O 30 20 10 COHESION FRJCTION • » D EVELOPMENT O F Ce ANJD4>e WITH STRAIN / M REMOLPET) STATE A T FAST STRAIN RATE ' PIG- 4-5 1 2 3 4- 5 6 T 6 S IO E F F E C T I V E S T R E S S PATHS F O R REMOLDED STATE A T StOW S T R A I N R A T E 117 118 L I S T O F R E F E R E N C E S : ' ; 1. B e a , R . G . (1963) - D i s c u s s i o n s o f W u , D o u g l a s a n d G o u g h n o u r ( J u n e 1962 ) . J o u r n a l o f S o i l M e c h . a n d F o u n d . D i v i s i o n , A m e r i . S o c . o f C i v i l E n g . , F e b r u a r y , 1 9 6 3 . 2 . B i s h o p , A . W . , B l i g h t , G . E . , a n d D o n a l d , I . B . ( I 9 6 0 ) . - D i s c u s s i o n , P r o c . A m e r . S o c . o f C i v i l E n g i n e e r i n g . R e -s e a r c h C o n f . o n S h e a r S t r e n g t h o f C o h e s i v e • > S o i l s , B o u l d e r , C o l o r a d o , I 9 6 0 . 3 . B i s h o p , A . W . , a n d H e n k e l , D . J . (1962) . - " T h e M e a s u r e m e n t o f S o i l P r o p e r t i e s i n t h e T r i a x i a l T e s t s " , E d w a r d A r n o l d L t d . , 1962 , 2 n d E d i t i o n . 4 . B i s h o p , A . W . , a n d G i b s o n , R . E . ( 1963 ) . - " T h e I n f l u e n c e o f t h e P r o v i s i o n o f B o u n d a r y D r a i n a g e o n t h e S h e a r S t r e n g t h a n d C o n s o l i d a t i o n C h a r a c t e r i s t i c s o f S o i l M e a s u r e d i n t h e T r i a x i a l A p p a r a t u s " . A . S . T . M . S p e c i a l T e c h n i c a l P u b l i c a t i o n , N o . 361 , S e p t . 1 9 6 3 . 5 . B j e r r u m , L . ( 1 9 5 4 ) . - " T h e o r e t i c a l a n d E x p e r i m e n t a l I n v e s t i g a t i o n s o n t h e S h e a r S t r e n g t h o f S o i l s " , N o r w e g i a n G e p -t e c h n i c a l I n s t i t u t e P u b l i c a t i o n N o . 5 , 1 9 5 4 . 6 . B j e r r u m , L , S i m o n s , N a n d T o r b l a a , I . ( 1 9 5 8 ) . - " T h e E f f e c t o f T i m e - o n t h e S h e a r S t r e n g t h o f a S o f t M a r i n e C l a y " . P r o c . B r u s s e l s C o n f . o n E a r t h P r e s s u r e P r o -b l e m s , V o l . I , 1 9 5 8 . 7 . B j e r r u m , L . ( I 9 6 0 ) . - " T h e C o u l o m b ' s E q u a t i o n o f S h e a r S t r e n g t h o f C o h e s i v e S o i l s " T h e o r y t o P r a c t i c e i n S o i l M e c h a n i c s , I 9 6 0 . > 8 . B l i g h t , G . E . ( 1 9 6 3 ) . - " T h e E f f e c t o f N o n - U n i f o r m P o r e - P r e s s u r e s o n L a b o r a t o r y M e a s u r e m e n t s o f t h e S h e a r S t r e n g t h o f S o i l s " , A . S . T . M . s p e c i a l T e c h n i c a l P u b l i -c a t i o n , N o . 3 6 l , S e p t e m b e r 1 9 6 3 . 9 . B u e s s e m , W . R . a n d N a g y , B . ( 1953 ) . - " T h e M e c h a n i s m o f D e f o r m a -t i o n o f C l a y " . P r o c . S e c o n d . N a t . C o n f . o n c l a y s a n d c l a y M i n e r a l s , U n i v . o f M i s s o u r i , P u b l i c a t i o n N o . 3 2 7 , N a t i o n a l A c a d e m y o f S c i e n c e s W a s h i n g t o n , 1 9 5 4 . V % X 119 10. B y r n e , P . M . ( 1 9 6 6 ) . - " E f f e c t i v e S t r e s s P a t h s i n a S e n s i t i v e C l a y " . / M . A . S c . T h e s i s ' , U n i v e r s i t y o f B r i t i s h J C o l u m b i a , V a n c o u v e r , C a n a d a , 1 9 6 6 . 11. C a m p a n e l l a , R . G . (1965) . - " E f f e c t o f T e m p e r a t u r e a n d S t r e s s o n / t h e T i m e - D e f o r m a t i o n B e h a v i o u r o f S a t u r -. ' a t e d C l a y " . P h . D . t h e s i s , U n i v e r s i t y o f / C a l i f o r n i a , B e r k e l e y , 1 9 6 5 . 12. C a s a g r a n d e , / A . ( 1 9 3 2 ) . - " T h e S t r u c t u r e o f C l a y a n d i t s I m p o r t a n c e i n F o u n d a t i o n E n g i n e e r i n g " . J o u r . B o s t o n S o c . C i v i l E n g i n e e r i n g , V o l . 19 , 1 9 3 2 . 13. C a s a g r a n d e , A , a n d W i l s o n , S . D . (1951). - " E f f e c t o f R a t e o f L o a d r / i n g o n S t r e n g t h o f C l a y s a n d S h a l e s a t C o n -/ s t a n t W a t e r C o n t e n t " . G e o t e c h n i q u e , V o l . / I I , N o . 3 , J u n e , 1951. 14. C r a w f o r d , C . B . (1959) . - " T h e I n f l u e n c e o f R a t e o f S t r a i n o n E f f e c -t i v e S t r e s s e s i n S e n s i t i v e C l a y " . A . S . T . M . S p e c i a l T e c h n i c a l P u b l i c a t i o n , N o . 2 5 4 , 1 9 5 9 . . 15. C r a w f o r d , C . B . (1963) . - " C o h e s i o n i n a n U n d i s t u r b e d S e n s i t i v e C l a y " . G e o t e c h n i q u e , V o l . 13 , N o . 2 , J u n e 1 9 6 3 . -16. H e n k e l , D . J . (1956) - " T h e E f f e c t o f O v e r c o n s o l i d a t i o n cri t h e B e -h a v i o u r o f C l a y d u r i n g S h e a r " . G e o t e c h n i q u e 6 , 1 9 5 6 . . 17. H o r n , H . M . a n d D e e r e , D . U . (1962) - " F r i c t i o n a l C h a r a c t e r i s t i c s o f M i n e r a l s " G e o t e c h n i q u e N o . 4 , 1 9 6 2 . 18. H v o r s l e v , M . J . (1936) . - " C o n d i t i o n s o f F a i l u r e f o r R e m o l d e d C o -h e s i v e S o i l s " F i r s t I n t e r n a t i o n a l C o n f . o n S o i l M e c h a n i c s a n d F o u n d . E n g . C a m b r i d g e M a s s . V o l . I l l , 1 9 3 6 . 19. H v o r s l e v , M . J . ( I 9 6 0 ) . - " P h y s i c a l C o m p o n e n t s o f S h e a r S t r e n g t h o f S a t u r a t e d C l a y s " . R e s e a r c h C o n f . o n S h e a r S t r e n g t h o f C o h e s i v e S o i l s , B o u l d e r , C o l o r a d o , I 9 6 0 . 2 0 . L a m b e , T . W . ( 1 9 5 3 ) . - " T h e S t r u c t u r e o f I n o r g a n i c S o i l " . P r o c . A m e r S o c . o f C i v i l E n g . S e p a r a t e N o . 315 , 1 9 5 3 . \ 120 21. L a m b e , T . W . (1958). - " T h e S t r u c t u r e o f C o m p a c t e d C l a y " . J o u r n T o f S o i l M e c h . a n d F o u n d . D i v i s i o n , A m e r . , ; l s S o c . o f C i v i l E n g . M a y 1 9 5 8 . 2 2 . L a m b e , T . W . ( I960) . - " A M e c h a n i s t i c P i c t u r e o f S h e a r S t r e n g t h i n ' C l a y s " . R e s e a r c h C o n f . S h e a r S t r e n g t h o f C o h e s i v e S o i l s , B o u l d e r C o l o r a d o , I 9 6 0 . . ' 2 3 . L e o n a r d s , G . A . (1962) . - " E n g i n e e r i n g P r o p e r t i e s o f S o i l s " F o u n d -a t i o n E n g i n e e r i n g , M c G r a w - H i l l B o o k C o m p a n y , I n c . 1 9 6 2 . 2 4 . L e o n a r d s , G . A . a n d A l t a c h a e f f , A . G . ( 1 9 6 4 ) . - ' C o m p r e s s i b i l i t y o f C l a y s " J o u r n . o f S o i l M e c h . a n d F o u n d . D i v i s i o n , A m e r . S o c . o f C i v i l E n g . S e p t . 1 9 6 4 . : 2 5 . M i t c h e l l , J . K . ( 1 9 5 6 ) . - " T h e F a b r i c o f N a t u r a l C l a y s a n d i t s r e -l a t i o n t o E n g i n e e r i n g P r o p e r t i e s " . P r o c . H i g h -w a y R e s e a r c h B o a r d , V o l . 3 5 , 1 9 5 6 . '•i 2 6 . M i t c h e l l , J . K . (I960) - " F u n d a m e n t a l A s p e c t s o f T h i x o t r o p y i n S o | l s " . ' : J o u r n . o f S o i l M e c h . a n d F o u n d . D i v i s i o n , A m e r . S o c . o f C i v i l E n g . V o l . 8 6 , I 9 6 0 . 2 7 . M i t c h e l l , J . K . (1964) '.-"Shearing R e s i s t a n c e of S o i l s a s a R a t e P r o c e s s " . J o u r n . o f S o i l M e c h . a n d F o u n d . D i v i s i o n , A m e r . S o c . o f C i v i l E n g . J a n u a r y , 1 9 6 4 . 2 8 . N o o r a n y , I . a n d S e e d , H . B . ( 1965 ) . - " A N e w E x p e r i m e n t a l M e t h o d f o r t h e D e t e r m i n a t i o n o f H v o r s l e v S t r e n g t h P a r a . - - - , m e t e r s f o r S e n s i t i v e C l a y s " . P r o c . S i x t h I n t . C o n f . S o i l . M e c h . a n d F o u n d . E n g . C a n a d a 1 9 6 5 . 2 9 . O l s o n , R . E . ( 1 9 6 3 ) . - " S h e a r S t r e n g t h P r o p e r t i e s o f S o d i u m I l l i t e " . J o u r n . o f S o i l . M e c h . a n d F o u n d . D i v n . , A m e r . '• S o c . o f C i v i l E n g . F e b r u a r y 1 9 6 3 . 30. R o s e n q u i s t , J . T h . ( 1959 ) . - " P h y s i c o - c h e m i c a l P r o p e r t i e s o f S o i l s ; , S o i l - W a t e r S y s t e m s " . J o u r , o f S o i l M e c h . a n d i / F o u n d . D i v i s i o n , A m e r . S o c . o f C i v i l E n g . ' V o l . 8 5 , 1 9 5 9 . / • •. 31. R o w e , P . W . ( 1 9 5 7 ) . - " Q * o H y p o t h e s i s f o r N o r m a l l y L o a d e d C l a y s a t ! / E q u i l i b r i u m " . P r o c e e d i n g s , 4 t h I n t . C o n f . o n / S o i l M e c h . a n d F o u n d . E n g . V o l . I , 1 9 5 7 . s 121 3 2 . S a l a s , J . A . a n d S e r e a t o s a , J . M . (1953 ) . - " C o m p r e s s i b i l i t y o f C l a y s " . P r o c e . 3 r d I n t . C o n f . S o i l M e c h . a n d F o u n d . E n g . Z u r i c h , V o l . I, 1 9 5 3 . 3 3 . S c h m e r t m a n n , J . H . ( I 9 6 0 ) . - " A n E x p e r i m e n t a l S t u d y o f t h e D e v e l o p -m e n t o f C o h e s i o n a n d F r i c t i o n w i t h A x i a l S t r a i n i n S a t u r a t e d C o h e s i v e S o i l s " . R e s e a r c h C o n f . o n S h e a r S t r e n g t h o f C o h e s i v e S o i l s , ; B o u l d e r , C o l o r a d o , I 9 6 0 . 3 4 . S c h m e r t m a n n , J . H . a n d H a l l , R . J . J r . (1961). - " C o h e s i o n A f t e r N o n - . H y d r o - s t a t i c C o n s o l i d a t i o n " . J o u r , o f S o i l / M e c h . a n d F o u n d . D i v i s i o n A m e r . S o c . o f / C i v i l E n g . A u g u s t 1961. 3 5 . S c h m e r t m a n n , J . H . (1962) . - D i s c u s s i o n o f S c h m e r t m a n n , J . H . a n d j H a l l J . R . ( A u g u s t 1961), J o u r , o f S o i l M e c h . .' a n d F o u n d . D i v i s i o n , A m e r . S o c . o f C i v i l j E n g . A u g u s t 1 9 6 2 . 3 6 . S c h m e r t m a n n , J . H . (1963 ) . - D i s c u s s i o n o f W u , D o u g l a s a n d G o u g h n o u r ( J u n e 1 9 6 2 ) , J o u r , o f S o i l M e c h . . a n d F o u n d . D i v i s i o n , A m e r . S o c . o f C i v i l : E n g . F e b r u a r y 1 9 6 3 . 3 7 . S c h m e r t m a n n , J . H . (1963b) - " G e n e r a l i z i n g a n d M e a s u r i n g t h e / H v o r s l e v E f f e c t i v e C o m p o n e n t s o f S h e a r / R e s i s t a n c e " . A . S . T . M . S p e c i a l T e c h n i c a l ] j P u b l i c a t i o n . N o . 3 6 l „ S e p t e m b e r 1 9 6 3 . / 3 8 . S c h m e r t m a n n , J . H . (1963c) - D i s c u s s i o n o f S c h m e r t m a n n , J . H . (1963) A . S . T . M . S p e c i a l T e c h n i c a l P u b l i c a t i o n , N o . 361 , S e p t e m b e r 1 9 6 3 . 3 9 . S e e d , H . B . , M i t c h e l l , J . K . a n d C h a n , C . K . ( I 9 6 0 ) . - " T h e S t r e n g t h o f C o m p a c t e d C o h e s i v e S o i l s " . R e s e a r c h C o n f . S h e a r S t r e n g t h o f C o h e s i v e S o i l s , B o u l d e r , C o l o r a d o , I 9 6 0 . 4 0 . S k e m p t o n , A . W . ( I 9 6 0 ) . - " S i g n i f i c a n c e o f T e r z a g h i ' s C o n c e p t o f E f f e c t i v e S t r e s s " . F r o m T h e o r y t o P r a c t i c e i n S o i l M e c h a n i c s , I 9 6 0 . 41 . T a n , T . K . (1957) . - D i s c u s s i o n o n S t r u c t u r e a n d R h e o l o g i c a l P r o p e r t i e s o f S o i l s . P r o c e e d i n g s , 4 t h I n t . C o n f . S o i l M e c h . a n d F o u n d . E n g . L o n d o n , V o l . 1 .1957 . 4 2 . T e r z a g h i , K . ( 1 9 3 6 ) . - " T h e S h e a r i n g R e s i s t a n c e o f S a t u r a t e d S o i l s a n d t h e A n g l e B e t w e e n t h e P l a n e s o f S h e a r " . 1st Int . C o n f . o n S o i l M e c h a n i c s , V o l . I i 1 9 3 6 . 

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