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Effect of secondary compression on shear strength Lou, Jian-Kwei 1967

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THE EFFECT OF SECONDARY- COMPRESSION ON SHEAR STRENGTH  by JIAN-KWEI LOU B . S c , Cheng Kung U n i v e r s i t y , ,  1963  A THESIS SUBMITTED I N P A R T I A L FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Applied:  Science  i n the Department of Civil  Engineering'  We a c c e p t , t h i s t h e s i s required standard  as c o n f o r m i n g  to the  THE U N I V E R S I T Y OF B R I T I S H COLUMBIA June,  1967  In  presenting  for  an  that  advanced  the  Study.  thesis  a  t  e  freely  or  representatives.  of  of  this  thesis  July  for  permission.  Civil  24,  may  Engineering  1967.  Columbia  be  of  for  granted  It  is  financial  of  British  available  permission  purposes  b y h.i;s  fulfilment  University  it  that  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada D  the  make  agree  my w r i t t e n  Department  in p a r t i a l  scholarly  publication  without  at  shall  I further  for  thesis  degree  Library  Department  or  this  for  the  Columbia,  I  reference  and  extensive  by  the  requirements  copying  Head o f  understood  gain  shall  this  my  that  not  of  agree  be  copying  allowed  ABSTRACT  An 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 i n t o the e f f e c t of secondary  compression  on an u n d i s t u r b e d s e n s i t i v e c l a y i s  presented. The  t e s t s e r i e s c o n s i s t e d of t e 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 compression  t e s t s w h i c h were c a r r i e d  out a t c o n s t a n t s t r a i n r a t e on u n d i s t u r b e d s a t u r a t e d samples o f s e n s i t i v e Haney c l a y .  Each sample  was  n o r m a l l y and i s o t r o p i c a l l y c o n s o l i d a t e d f o r a d i f f e r e n t l e n g t h o f time.  B e f o r e each sample was  s h e a r i n g , the pore p r e s s u r e b u i l d - u p due compression  was  measured.  The  subjected to to  secondary  e f f e c t o f t h i s amount o f  pore p r e s s u r e b u i l d - u p on the shear s t r e n g t h c h a r a c t e r i s t i c s i s discussed. The  r e s u l t s of the i n v e s t i g a t i o n i n d i c a t e d t h a t  the secondary  compression  has an a p p r e c i a b l e i n f l u e n c e  on the pore p r e s s u r e s e t up f o r samples c o n s o l i d a t e d a s h o r t e r p e r i o d of t i m e . \  l o n g e r than one  For samples c o n s o l i d a t e d f o r  day, the e f f e c t of secondary  on pore p r e s s u r e can be n e g l e c t e d .  The  compression  s e n s i t i v i t y of  the c l a y , has a p r i m a r y importance  i n determining  behavior of s o i l , u n d e r l o a d .  "reverse t h i x o t r o p y "  e f f e c t due  The  the  to h i g h s e n s i t i v i t y i s b r i e f l y mentioned.  TABLE OF CONTENTS CHAPTER I.  II.  PAGE. 1  INTRODUCTION Purpose  1  Scope  2 3  HISTORICAL REVIEW  3  Secondary Compression S e n s i t i v i t y and S t r u c t u r e  III.  6  . . .  Failure Criteria  7  EXPERIMENTAL WORK  11  Description of S o i l  11  F i e l d S a m p l i n g and S t o r i n g  11  P r e l i m i n a r y Tests  .  11  D e s c r i p t i o n o f T e s t Equipment .  12  D i s c u s s i o n o f Test Procedures  l6  D i s c u s s i o n o f Non-uniform Pore P r e s s u r e i n Undrained Tests IV.  TEST RESULTS  24 26  Introduction  26  Pore P r e s s u r e B u i l d - u p b e f o r e S h e a r i n g . . .  26  The Secondary Compression E f f e c t on Pore Pressure/Strain Relationship  30  iv CHAPTER  PAGE The Secondary Compression E f f e c t on (6,'-cy )max  37  The Secondary Compression E f f e c t on (cV/6, )max 1  43  Summary  4-9  Suggestions f o r Further Research. . . . . .  50  LISTS OF REFERENCES  51  APPENDIX  54  LIST OF TABLES  TABLE I. II. III.  PAGE P h y s i c a l P r o p e r t i e s o f Haney C l a y  13  Summary o f T e s t R e s u l t s  28  Comparison Between T e s t s No. 1 and No. 8 .  . .  42  LIST OF FIGURES FIGURE  PAGE  1.  Types o f Secondary Compression C u r v e s . . . . .  2.  Schematic R e p r e s e n t a t i o n o f Secondary 4  Compression 3.  4  R e l a t i o n s h i p between the R a t i o o f Degree 9  o f M o b i l i z a t i o n .and S e n s i t i v i t y 4.  G r a i n S i z e D i s t r i b u t i o n o f Haney C l a y . . . . .  14  5.  T r i a x i a l C e l l and Chamber P r e s s u r e System. . .  17  6.  D r a i n a g e and Back P r e s s u r e System.  18  7.  Test Equipment  19  8.  Transducer  20  9.  Strain Indicator  20  10.  Trimming T o o l s and P r e p a r e d Sample  22  11.  Sample i n P l a c e on T r i a x i a l Base . •  22  12.  R e l a t i o n s h i p between Pore P r e s s u r e and 29  Time P r i o r t o S h e a r i n g . . 13-  C o n s o l i d a t i o n Curve by The Square Root o f 31  Time F i t t i n g Method 14.  C o n s o l i d a t i o n Curve by The L o g a r i t h m o f 31  Time F i t t i n g Method 15.  Pore P r e s s u r e v e r s u s S t r a i n Curve  16.  V a r i a t i o n s o f P.P.--at (6, -6^ )max. f o r  31  1  D i f f e r e n t C o n s o l i d a t i o n Time  33  . 1  vii FIGURE 17.  PAGE  R e l a t i o n s h i p between Water Content and Pore P r e s s u r e  34  P r i o r to Shearing  18.  R e l a t i o n s h i p between Skempton and A x i a l S t r a i n  36  19.  D e v i a t o r S t r e s s v e r s u s S t r a i n Curves  38  20.  E f f e c t o f C o n s o l i d a t i o n Time on (6, -6 ' )max. . .  21.  E f f e c t o f C o n s o l i d a t i o n and D i s p e r s i o n on  1  5  40  Shear S t r e n g t h 22.  E f f e c t o f Time on $6 and Pore l  at  Pressure  (6, ' - 6 ' ) max  44  5  23.  S t r a i n a t F a i l u r e versus" C o n s o l i d a t i o n Time. .  24.  R e l a t i o n s h i p between S t r a i n and P r i n c i p a l  45  46  Stress Ratio 25.  39  R e l a t i o n s h i p between C o n s o l i d a t i o n ,Time and Maximum P r i n c i p a l S t r e s s R a t i o  . . . . . . .  1  48  ACKNOWLEDGMENT  The  author i s i n d e b t e d  to the N a t i o n a l Research  C o u n c i l o f Canada f o r p r o v i d i n g the f i n a n c i a l  assistance  which made t h i s s t u d y p o s s i b l e . The  author a l s o g r a t e f u l l y  acknowledges t h e con-  t i n u o u s guidance and a d v i c e o f f e r e d b y Dr. W. D. L i a m F i n n and Dr. R. G. Campanella d u r i n g t h e r e s e a r c h program.  He  w i s h e s , t o o , t o thank h i s c o l l e a g u e s Mr. D. E. Snead, and Mr.  P. M. Byrne f o r t h e i r h e l p f u l d i s c u s s i o n d u r i n g t h e  course o f t h e work. The  t e c h n i c a l assistance supplied by the s t a f f o f  the C i v i l E n g i n e e r i n g Department workshop i s h e r e b y g r a t e f u l l y acknowledged as w e l l .  i  N O M E N C L A T U R E  A  Pore pressure parameter  £H±  B  Pore pressure parameter  _£u  C  C o e f f i c i e n t of con. o l i d a t i o n  C-U  Consolidated undrained t e s t  e  Void r a t i o  k  Pereability  t  Time  T  Time f a c t o r  u  Pore pressure Change i n pore pressure  U  Average degree of c o n s o l i d a t i o n  V  Volume of sample  w  Water content  E  Shear s t r a i n  cy  Deviator s t r e s s Change i n deviator  stress  6'  Effective  6/  E f f e c t i v e major p r i n c i p a l s t r e s s  6'  E f f e c t i v e minor p r i n c i p a l s t r e s s  6'  Effective consolidation  5  6, -6 l  3  l  stress  Effective-.deviator  pressure  stress  /6j E f f e c t i v e p r i n c i p a l s t r e s s r a t i o A  Newtonian dashpot  CHAPTER I INTRODUCTION Purpose T a y l o r (1940) p r o p o s e d the f i r s t t h e o r y t o a c c o u n t for  secondary c o m p r e s s i o n i n s o i l .  Since then, considerable  l i t e r a t u r e on secondary c o m p r e s s i o n ( L o , 1961 and Wahls, 1962) has been p r e s e n t e d , b u t i t appears t o l a c k i n v e s t i g a t i o n o f the  i n f l u e n c e o f the secondary c o m p r e s s i o n on t h e shear  s t r e n g t h and pore p r e s s u r e c h a r a c t e r i s t i c s o f s o i l . Recent r e s e a r c h ( B j e r r u m and Lo, 19&3) h a s , however, shown t h a t some c l a y s c o n s o l i d a t e d f o r d i f f e r e n t p e r i o d s o f time p r i o r t o s h e a r i n g may behave d i f f e r e n t l y d u r i n g t h e shear t e s t .  I t was a l s o shown t h a t c l a y s w h i c h e x h i b i t  secondary c o m p r e s s i o n w i l l g a i n i n shear s t r e n g t h w i t h t i m e consolidation.  However, t h i s i s n o t always t h e case f o r t h e  s t u d y p r e s e n t e d in' t h i s t h e s i s .  The pore p r e s s u r e w h i c h  b u i l d s up due t o secondary c o m p r e s s i o n may have g r e a t i n f l u e n c e on t h e s h e a r i n g r e s i s t a n c e i n t h e e a r l y s t a g e o f (deformation. 1  I t was t h e purpose o f t h i s t h e s i s t o i n v e s t i g a t e , e x p e r i m e n t a l l y , the e f f e c t o f s e c o n d a r y c o m p r e s s i o n on t h e pore p r e s s u r e and-shear s t r e n g t h c h a r a c t e r i s t i c s o f a normally consolidated undisturbed saturated clay; t o report  2  on the t e s t i n g p r o c e d u r e s u s e d i n the i n v e s t i g a t i o n , and the r e s u l t s of the s e r i e s of t e s t s are d e s c r i b e d h e r e i n . Scope A b r i e f r e v i e w of the l i t e r a t u r e on s e c o n d a r y  compression  and s e n s i t i v i t y i s p r e s e n t e d i n Chapter I I , - t o g e t h e r w i t h f a i l u r e c r i t e r i a which were adopted i n t h i s  the  thesis.  The t e s t s e r i e s c o n s i s t e d o f t e 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 c o m p r e s s i o n t e s t s which were c a r r i e d o u t a t  constant  s t r a i n r a t e on u n d i s t u r b e d - s a t u r a t e d samples of s e n s i t i v e  clay.  Each sample was n o r m a l l y and i s o t r o p i c a l l y c o n s o l i d a t e d f o r a d i f f e r e n t l e n g t h of t i m e .  The pore p r e s s u r e s ,  which b u i l d  up due t o secondary c o m p r e s s i o n , were c a r e f u l l y measured b e f o r e the samples were s u b j e c t e d  to s h e a r i n g .  Maximum  d e v i a t o r s t r e s s and maximum p r i n c i p a l s t r e s s r a t i o were o b t a i n e d d u r i n g each t e s t .  A d e s c r i p t i o n of t e s t i n g p r o -  cedures i s c o n t a i n e d i n Chapter The f i n a l t e s t r e s u l t s ,  III. along w i t h d i s c u s s i o n s of  e f f e c t of the secondary c o m p r e s s i o n on pore p r e s s u r e shear s t r e n g t h c h a r a c t e r i s t i c s , The " r e v e r s e  -  the  and  are i n c l u d e d i n Chapter I V .  t h i x o t r o p y e f f e c t " due t o the h i g h s e n s i t i v i t y  of the c l a y i s b r i e f l y m e n t i o n e d . f u r t h e r r e s e a r c h are a l s o  A few s u g g e s t i o n s  presented.  for  CHAPTER I I HISTORICAL REVIEW Secondary  Compression  The f i r s t t h e o r y t o account f o r s e c o n d a r y  compressions  was proposed b y T a y l o r and Merchant (1940), who assumed t h a t secondary c o m p r e s s i o n began a f t e r t h e p r i m a r y c e a s e d and t h e r a t e o f secondary c o m p r e s s i o n was p r o p o r t i o n a l t o t h e undeveloped secondary c o m p r e s s i o n .  Lo (1961) i n d i c a t e d  that  t h e r e a r e t h r e e t y p e s o f secondary c o m p r e s s i o n c u r v e s w h i c h can be c l a s s i f i e d a c c o r d i n g t o t h e i r c h a r a c t e r i s t i c s , as shown i n F i g u r e 1,  i n w h i c h c u r v e s f o r t h e whole c o n s o l i -  dation process are i l l u s t r a t e d .  Type I has a g e n t l e  c u r v a t u r e c o n c a v i n g upwards and t h e curve becomes h o r i z o n t a l where the u l t i m a t e c o m p r e s s i o n i s r e a c h e d .  The Haney c l a y  which was used i n t h i s t e s t s e r i e s b e l o n g s t o t h i s  group.  To d e s c r i b e secondary c o m p r e s s i o n b e h a v i o r , G i b s o n and Lo (1961) used a t h e o r e t i c a l model, as shown i n F i g u r e 2. When a time dependent e f f e c t i v e s t r e s s 6'(t) a c t s on t h e model, t h e Hookean s p r i n g compresses i n s t a n t a n e o u s l y , b u t the d e f o r m a t i o n o f K e l v i n element b-A to t h e Newtonian dashpot A . <5'(t)  i s r e t a r d e d owing  As t h e e f f e c t i v e  stress  i n c r e a s e s g r a d u a l l y w i t h time f r o m z e r o t o t h e f u l l  v a l u e o f the. a p p l i e d s t r e s s , t h e c o m p r e s s i o n o f t h e s p r i n g i s a l s o g r a d u a l and i s f u l l y a c c o m p l i s h e d o n l y when t h e  —  10  I  io  3  I0  Z  L0G t 10  FIGURE  I.  s  (MIN)  TYPES OF SECONDARY (AFTER  io  COMPRESSION  4  io  5  / CURVES '  LO , .1961) '  J6'(t)  FIGURE 2. SCHEMATIC REPRESENTATION ( AFTER  LO, I960.  OF SECONDARY COMPRESSION  '  io  6  a p p l i e d s t r e s s has r e a c h e d i t s f u l l v a l u e .  The g r a d u a l  compression o f s p r i n g "a" w i t h s t r e s s r e p r e s e n t s e l a s t i c deformations. dashpot A ,  I n i t i a l l y the l o a d i s t a k e n by the N e w t o n i a n  b u t i s p r o g r e s s i v e l y t r a n s f e r r e d t o the Hookean  s p r i n g "b" as c o m p r e s s i o n p r o c e e d s .  T h i s phenomenon o f  t r a n s f e r r e n c e c o r r e s p o n d s t o the p r o c e s s o f s e c o n d a r y compression o c c u r r i n g under s u s t a i n e d e f f e c t i v e A f t e r a p e r i o d of time has e l a p s e d , the f u l l  stress.  effective  s t r e s s w i l l be t a k e n by the s p r i n g "b" w i t h the dashpot s u s t a i n i n g no l o a d .  I t i s also clear, therefore,  that  secondary c o m p r e s s i o n i s c o n s i d e r e d t o o c c u r d u r i n g the range of p r i m a r y c o n s o l i d a t i o n . B j e r r u m and Lo (19&3) p e r f o r m e d a s e r i e s o f t e s t s i n which samples o f a n o r m a l l y c o n s o l i d a t e d  triaxial clay,  which shows secondary time e f f e c t s , were s h e a r e d a f t e r -' d i f f e r e n t p e r i o d s of t i m e . of  I t was  shown t h a t the b e h a v i o r  the c l a y when s h e a r e d depends on the "age" o f the  samples.  W i t h time the c l a y becomes more b r i t t l e  with  s m a l l e r a x i a l s t r a i n s a t f a i l u r e and the u n d r a i n e d shear s t r e n g t h shows a s l i g h t i n c r e a s e . the  Bjerrum concluded that  e f f e c t of time can be e x p l a i n e d by the g r o w i n g o f  c o h e s i v e bonds a t the c o n t a c t p o i n t s between the p a r t i c l e s . The growth o f c o h e s i v e bonds l e a d s t o a g r e a t e r r e s i s t a n c e a g a i n s t shear d e f o r m a t i o n , b u t t h e y are g r a d u a l l y d e s t r o y e d by i n c r e a s i n g  strain.  6  Sensitivity  and S t r u c t u r e  Terzaghi proposed that s e n s i t i v i t y undisturbed  i s the r a t i o of  peak s t r e n g t h t o remoulded peak s t r e n g t h .  c l a y has a s e n s i t i v i t y  12  which, according  Haney  t o Skempton  (1952),  i s c l a s s e d as an e x t r a - s e n s i t i v e c l a y . Thixotropy  i s a p r o c e s s o f s o f t e n i n g , caused b y  r e m o u l d i n g , f o l l o w e d b y a time-dependent r e t u r n t o t h e o r i g i n a l harder s t a t e .  T h i s e f f e c t c a n a c c o u n t f o r low o r  medium s e n s i t i v i t y , b u t n o t f o r h i g h Skempton and N o r t h e y of reducing  (1952)  the s a l t concentration  sensitivity.  i n d i c a t e d that the e f f e c t s i n t h e pore w a t e r o f a  c l a y b y l e a c h i n g a r e t h e main cause o f i n c r e a s i n g t h e s e n s i t i v i t y , but there  i s no r e a s o n t o assume t h a t  i s t h e s o l e cause o f h i g h s e n s i t i v i t y . w i l l be n e c e s s a r y b e f o r e  leaching  Much f u r t h e r  research  t h i s phenomenon c a n be f u l l y under-  stood. Some s o i l s d i s p l a y g r e a t e r others.  "structural"  influences  than  The magnitude o f s t r u c t u r a l e f f e c t s i n an u n d i s t u r b e d  c l a y i s r e f l e c t e d by i t s s e n s i t i v i t y .  Secondary c o m p r e s s i o n  i s assumed (Wahls, 1 9 6 2 ) t o be t h e v o i d - r a t i o change  that  r e s u l t s from v i s c o u s y i e l d i n g o f the g r a i n s t r u c t u r e . e f f e c t i v e pressure  t h a t the i n t e r g r a n u l a r s t r u c t u r e c a n .  support depends oh'-the p a r t i c l e void r a t i o .  The  Therefore,  o r i e n t a t i o n as w e l l as t h e  viscous r e o r i e n t a t i o n of the g r a i n s  g r a d u a l l y reduces t h e c a p a c i t y o f t h e i n t e r g r a n u l a r  skeleton  7 and produces a tendency f o r a s m a l l amount of the i n t e r g r a n u l a r p r e s s u r e t o be t r a n s f e r r e d t o the pore w a t e r . Wahls c o n s i d e r e d t h a t the term " s t r u c t u r e r e l a x a t i o n " i s d e s c r i p t i v e o f the cause of secondary c o m p r e s s i o n .  During  s h e a r , the r e m o u l d i n g o f the c l a y tends t o c r e a t e more dispersed structure ( p a r a l l e l p l a t y - l i k e p a r t i c l e s )  and  a f f e c t the shear s t r e n g t h and the s t r e s s - s t r a i n r e l a t i o n s h i p .  Failure  Criteria I n o r d e r t o i n v e s t i g a t e the secondary c o m p r e s s i o n  e f f e c t on shear s t r e n g t h , b o t h max.  d e v i a t o r s t r e s s and  p r i n c i p a l s t r e s s r a t i o have been u s e d as f a i l u r e  max.  criteria  f o r each t e s t . I n u n d r a i n e d t r i a x i a l t e s t s on n o r m a l l y c o n s o l i d a t e d c l a y , one o f the f o l l o w i n g two cases i n v a r i a b l y i s a p p l i c a b l e . (L. B j e r r u m , i 9 6 0 ) .  E i t h e r the pore p r e s s u r e and  max.  d e v i a t o r s t r e s s s i m u l t a n e o u s l y a t t a i n a maximum v a l u e and the two f a i l u r e c r i t e r i a c o i n c i d e ; or the pore p r e s s u r e c o n t i n u e s t o i n c r e a s e and o n l y r e a c h e s a maximum v a l u e upon further strain.  I f the d e v i a t o r s t r e s s i s c o n s t a n t or o n l y  decreases s l i g h t l y w i t h s t r a i n a f t e r  (d/ -d ' ) max.,  t h e n the  maximum 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 c c u r s a f t e r the 1  p o i n t of maximum-^deviator s t r e s s . For the Haney c l a y samples t e s t e d under u n d r a i n e d c o n d i t i o n s i n the n o r m a l l y c o n s o l i d a t e d s t a t e , the pore  8 pressure  was s t i l l i n c r e a s i n g when t h e d e v i a t o r s t r e s s r e a c h e d  a maximum.  I t was o b s e r v e d t h a t a f t e r 3% a x i a l s t r a i n , where  the maximum d e v i a t o r s t r e s s o c c u r r e d , was s t i l l a p p r e c i a b l e .  The v a l u e s  t h e r i s e i n pore  o f 0' c o r r e s p o n d i n g  pressure t o the  two f a i l u r e c r i t e r i a were 2 6 . 1 ° a t maximum d e v i a t o r s t r e s s and 31.3°  at maximum p r i n c i p a l s t r e s s r a t i o when samples were con-  s o l i d a t e d f o r one day p r i o r t o t e s t i n g . It  was suggested b y T. C. Kenney (1959) t h a t  this  phenomenon i s r e l a t e d t o t h e s e n s i t i v i t y o f t h e c l a y . The g r e a t e r the s e n s i t i v i t y , the g r e a t e r t h e d i f f e r e n c e between the v a l u e s o f jzP d e t e r m i n e d .according  t o t h e two f a i l u r e  c r i t e r i a , as shown i n F i g u r e 3> which i s a p l o t o f t h e degree o f m o b i l i z a t i o n ( r a t i o o f t a n ^' a t (d,-<5') max. t o 1  3  tan  1  a t (^d^ ) maxT] a g a i n s t t h e n a t u r a l The  Haney c l a y t e s t e d , r e p r e s e n t e d  dot i n F i g u r e  3>  w  a  s  sensitivity. by the t r i a n g l e  c l o s e t o t h e l i n e s u g g e s t e d b y Kenney.  B e s i d e s t h e s e n s i t i v i t y , t h e sample s i z e and t h e magnitude o f a x i a l s t r a i n a l s o have i n f l u e n c e s on t h e degree of m o b i l i z a t i o n . . F o r Drammen c l a y , (Simons, i960), t h e g r e a t e r the a x i a l s t r a i n a t which the d e v i a t o r s t r e s s a t t a i n e d a maximum i n t h e u n d r a i n e d t e s t s , t h e s m a l l e r t h e d i f f e r e n c e i n the v a l u e s o f ^' o b t a i n e d . b y t h e two c r i t e r i a . Two p o s s i b l e e x p l a n a t i o n s in  c a n be o f f e r e d f o r t h e g a i n  s h e a r i n g r e s i s t a n c e a f t e r the p o i n t o f maximum d e v i a t o r  s t r e s s has been r e a c h e d i n u n d r a i n e d t e s t s . all  F i r s t of a l l , not  the a v a i l a b l e s h e a r i n g r e s i s t a n c e i n t h e sample i s .  9  Z  .3  4  5-  10  20  30  49  50  SENSITIVITY  FIGURE  3. •  RELATIONSHIP TION  AND  BETWEEN SENSITIVITY  THE  DEGREE  (AFTER  L  OF  MOBILIZA-  BJERRUM,  I960)  10 m o b i l i z e d a t t h e low f a i l u r e s t r a i n a t w h i c h t h e d e v i a t o r s t r e s s i s a maximum, and hence even i f the e f f e c t i v e n o r m a l s t r e s s on t h e f a i l u r e p l a n e d e c r e a s e s w i t h f u r t h e r s t r a i n due to the r i s e i n pore p r e s s u r e ,  greater  angles of i n t e r n a l f r i c t i o n  can s t i l l be m o b i l i z e d , and t h e 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 increases.  Secondly, i t i s p o s s i b l e that a f t e r the p o i n t  of maximum d e v i a t o r s t r e s s i s r e a c h e d , t h e sample undergoes an i n t e r n a l p a r t i c l e rearrangement i n t h e f a i l u r e zone, and t h u s on f u r t h e r i n c r e a s e d s t r e s s , t h e 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 may i n c r e a s e .  CHAPTER I I I EXPERIMENTAL WORK D e s c r i p t i o n of S o i l The  c l a y d e p o s i t f r o m w h i c h the samples were o b t a i n e d  f o r t h i s t e s t program i s l o c a t e d a t Haney, B r i t i s h which i s about t h i r t y m i l e s e a s t o f Vancouver.  Columbia,  The  soil is  known l o c a l l y as Haney C l a y . Haney C l a y i s e x t r a - s e n s i t i v e and has c o l o r when wet,  and l i g h t g r e y when d r y .  a dark  The  blue-grey  clay contains  a p p r o x i m a t e l y h o r i z o n t a l l a m i n a t i o n s of medium t o f i n e and  silt  clay.  F i e l d Sampling and S t o r i n g B l o c k samples were o b t a i n e d by hand e x c a v a t i o n f r o m the c l a y d e p o s i t a t Haney near a b r i c k f a c t o r y . was a 12  dug and the d i s t u r b e d s u r f a c e m a t e r i a l was square f o o t a r e a .  The  i s o l a t e d b l o c k was  about 9 i n c h e s by 9 i n c h e s by w i r e saw w i t h a l a y e r o f wax.  A trench  removed f r o m trimmed t o  and i m m e d i a t e l y  coated  The b l o c k s were t r a n s p o r t e d c a r e f u l l y  t o the l a b o r a t o r y and g i v e n a f u r t h e r c o a t i n g o f wax  to  ensure t h a t t h e r e would be no change o f water c o n t e n t .  The  eaxed b l o c k s were^ t h e n s t o r e d i n a m o i s t room u n t i l u s e d . P r e l i m i n a r y Tests P r e l i m i n a r y i d e n t i f i c a t i o n t e s t s were p e r f o r m e d p r i o r t o the main s e r i e s o f t e s t s .  I t i n c l u d e d the  determination  12 of n a t u r a l water c o n t e n t , s p e c i f i c g r a v i t y , A t t e r b e r g l i m i t s , g r a i n s i z e a n a l y s i s , unconfined compression  strength, sensi-  t i v i t y , maximum p a s t p r e s s u r e and 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 . A l l o f these t e s t s were performed procedures  i n accordance  w i t h the  suggested b y Lambe (1958), and t h e r e s u l t s were 4.  shown i n Table I and F i g u r e  D e s c r i p t i o n o f T e s t Equipment The t e s t equipment u s e d i s shown i n F i g u r e s 5> 8 and 9.  A Clockhouse  of r e c e i v i n g 2.8  E n g i n e e r i n g T.10  i n c h e s b y 1.4  used f o r a l l t e s t s .  triaxial cell  inches diameter  6,  7,  capable  samples was  Drainage was p e r m i t t e d f r o m b o t h t h e t o p  and the bottom o f t h e sample, b u t t h e pore p r e s s u r e s were measured a t the base o f t h e sample o n l y b y means o f - a n electrical  transducer.  E s s e n t i a l l y no f r i c t i o n  existed  between t h e chamber and t h e s t a i n l e s s s t e e l ram w h i c h was greased b e f o r e each t e s t . as a chamber f l u i d .  D i s t i l l e d d e - a i r e d w a t e r was u s e d  The water was d e - a i r e d b y s p r a y i n g i t  i n t o a t a n k w h i l e under vacuum. The chamber p r e s s u r e was o b t a i n e d b y r e g u l a t i n g comp r e s s e d a i r from a house l i n e tank.  and a p p l y i n g i t t o t h e a i r - w a t e r  The c e l l p r e s s u r e was measured b y a 0 - 100  bourdon gauge g r a d u a t e d t o 0.5  lbs./sq. i n .  l b s . / s q . i n . The gauge was  * 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  v  = K(l-e)  Tw  13  TABLE I PHYSICAL PROPERTIES OF HANEY CLAY  2.8 '  SPECIFIC GRAVITY LIQUID LIMIT  50.8$  PLASTIC.LIMIT  29.6$  PLASTIC INDEX  21.2$  NATURAL WATER CONTENT  40.K%  UNDISTURBED UNCONFINED COMPRESSIVE STRENGTH  10.8 l b s . / s q . i n .  "PEAK" REMOLDED UNCONFINED COMPRESSIVE STRENGTH  12  SENSITIVITY ACTIVITY*  0.9 l b s . / s q . i n .  •  MAXIMUM PAST PRESSURE  0.44 50 l b s . / s q . i n .  *Activity:  The r a t i o o f t h e p l a s t i c i t y i n d e x t o . t h e p e r c e n t a g e b y w e i g h t of s o i l p a r t i c l e s o f diameter s m a l l e r than ... 2 m i c r o n s .  i  Q05  Q02  QOI  GRAIN  FIGURE 4 .  GRAIN  SIZE  .- Q005  DIAMETER  DISTRIBUTION  - Q002  (MMS)  OF- HA NAY CLAY  QPOI  Q0005  15 c a l i b r a t e d a g a i n s t a dead l o a d t e s t e r b e f o r e each  testing  series. A l l d r a i n a g e l i n e s were c o n s t r u c t e d o f s m a l l d i a m e t e r copper t u b i n g e x c e p t f o r the c o n n e c t i o n t o t h e d r a i n a g e b u r e t t e which was o f s a r a n t u b i n g .  The b u r e t t e was movable  and graduated t o 0.1 c u b i c c e n t i m e t e r s .  The l e v e l o f t h e  water i n t h e b u r e t t e was k e p t a t t h e same l e v e l as t h e m i d d l e o f the sample.  I n o r d e r t o o b t a i n complete s a t u r a t i o n , a  back p r e s s u r e o f 10 l b s . / s q . . i n . was a p p l i e d t o t h e sample pore water through t h e d r a i n a g e l i n e d u r i n g i n i t i a l solidation.  con-  The back p r e s s u r e was measured b y t h e t r a n s -  ducer . A l l pore water p r e s s u r e s were measured b y means o f an 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 manufactured b y D a t a Incorporated.  Sensors  The d r a i n a g e system was r i g i d and t h e t r a n s -  ducer was p l a c e d as c l o s e t o t h e c e l l as p o s s i b l e t o m i n i m i z e t r a n s m i s s i o n l i n e volume.  Thus, t h e system was e s s e n t i a l l y  a t c o n s t a n t volume d u r i n g u n d r a i n e d t e s t i n g . . The t r a n s d u c e r was used w i t h an e l e c t r i c a l r e a d - o u t d e v i c e ( s t r a i n  indicator)  and the system was c a l i b r a t e d a g a i n s t t h e dead l o a d  tester.  I t was f o u n d , however, t h a t t h e t r a n s d u c e r was g r e a t l y a f f e c t e d by s m a l l f l u c t u a t i o n s i n sample t e m p e r a t u r e d u r i n g undrained t e s t i n g .  These p r e s s u r e changes were due t o  d i f f e r e n t i a l volume changes between pore water and t h e conf i n i n g system.  I t was n o t e d t h a t a t e m p e r a t u r e  increase  16 r e s u l t e d i n a pore p r e s s u r e i n c r e a s e and a t e m p e r a t u r e d e c r e a s e r e s u l t e d i n a pore p r e s s u r e d e c r e a s e f o r u n d r a i n e d c o n d i t i o n s . Thus, i t i s e s s e n t i a l t o have f a i r l y a c c u r a t e t e m p e r a t u r e c o n t r o l during undrained t e s t i n g . The temperature c o n t r o l was a c c o m p l i s h e d b y cons t r u c t i n g an i n s u l a t e d room around t h e equipment i n w h i c h t h e temperature was k e p t a t 20°C b y an a i r - c o n d i t i o n i n g u n i t . I t was o b s e r v e d t h a t o n l y about 0.5°C v a r i a t i o n c o u l d be f o u n d i n s i d e the room.  T h i s f l u c t u a t i o n had n e g l i g i b l e e f f e c t s on  pore p r e s s u r e s as sample temperature f l u c t u a t i o n s were considerably less. D e - a i r i n g o f t h e d r a i n a g e system was a c c o m p l i s h e d b y p a s s i n g l a r g e q u a n t i t i e s o f b o i l e d d i s t i l l e d water t h r o u g h a l l t r a n s m i s s i o n l i n e s s e v e r a l t i m e s t o make sure t h a t no a i r was p r e s e n t i n t h e system.  Back p r e s s u r i n g t h r o u g h a  f i n e bore i n d i c a t i n g c a p i l l a r y tube was u s e d t o v e r i f y  that  the d r a i n a g e system was d e - a i r e d . A x i a l l o a d s were measured w i t h t h e u s e o f a p r o v i n g r i n g and a x i a l , d e f o r m a t i o n was i n d i c a t e d w i t h a .001  inch  d i a l gauge. D i s c u s s i o n o f T e s t i n g Procedures . The 2.8 i n c h e s l o n g b y 1.4 i n c h e s d i a m e t e r  samples  were trimmed i n a~"moist room on a p e r s p e x l a t h e and m i t e r box ( F i g u r e 10).  Because^of the v a r i a b l e nature o f c l a y ,  •  .  i  care was t a k e n t o ensure t h a t each sample came f r o m t h e  PlSnLUP ROViMG  RiN&  17  Di-AlHEO WATER  VACUUM  MACHINEO RAM  Oue-E  MA<«lNED  J-  BAIL BBARIHG LOAPING Cap  SATURATION SplML  O-RiiGS  SAMPLE  -DE-/HIRED  MEMBRANCS  WATER  fbRoUS STONE  TANK  REGULATORS  PRESSURE SuppLy  TUBING .  VACUUM  To  P^J^^_<  ? >  __  ( 5  SuppLy  yi To DRAINAGE SfSTEMl  •^r'o.D. COppER  ' '.—CONTROL  • yf 1  $ T « A I N f CONTROLLED A X I A L I DRIVB  PANEL  TUBiNft AMBER PRESSURE GAUG-E  1  ^4 O . D COppER TUBINI =*7  •f"o.o, FfelpTHELENe^  FIGURE 5  ^-STEEL. BALANCING TANK  TRMXIAL  CELL AND  CHAMBER  PRESSURE  SYSTEM  tx-mto W A T E R 3UPPLY  DISTILLED  To TRiAmAt CELL UPPER STONE  (J) L o w i * STONE  10 EX.  BURETTE  (ADJUSTABLE  HEIGHT)  MECURV  4'.MECURY  OVERFLOW  MANOMETER TO suppty 10 psi BACK PRESSURE  FIGURE  6.  £>RAIMGE  A N D ' BACK  PRESSURE  SYSTPM  FIGURE 7-  TEST EQUIPMENT.  FIGURE 9.  STRAIN INDICATOR  21 same v e r t i c a l e l e v a t i o n .  A l s o , due t o t h e l a m i n a t e d n a t u r e  of c l a y , i t , w a s n e c e s s a r y t o t r i m t h e sample so t h a t l a m i n a t i o n s were h o r i z o n t a l when p l a c e d i n t h e t r i a x i a l  cell.  I n s p i t e o f t h e s e p r e c a u t i o n s , t h e water c o n t e n t c a l c u l a t e d from t h e end t r i m m i n g s v a r i e d c o n s i d e r a b l y f r o m s i d e trimmings.  To ensure t h e s i d e t r i m m i n g s would  yield  r e p r e s e n t a t i v e average water c o n t e n t , f o u r t e s t s were performed b y Mr. H i r s t (1966)  i n w h i c h t h e average w a t e r  c o n t e n t o f f o u r s i d e t r i m m i n g s was compared w i t h t h e w a t e r c o n t e n t o f the whole sample.  I t was f o u n d t h a t t h e s i d e  samples method o f o b t a i n i n g t h e i n i t i a l water c o n t e n t o f the  specimen was s a t i s f a c t o r y .  Trimmings t a k e n f r o m t h e  top  and bottom o f t h e sample were n o t r e p r e s e n t a t i v e o f t h e  whole specimen because t h e y c o n t a i n e d a predominance lamination.  o f one  ,  The dimensions o f the trimmed sample were d e t e r m i n e d by measuring i t s l e n g t h i n f o u r p l a c e s , and i t s c i r c u m f e r e n c e a t the top', m i d d l e and bottom.  Samples were h a n d l e d w i t h :  care because of. t h e h i g h s e n s i t i v i t y o f the c l a y . ^  The porous s t o n e s were b o i l e d i n d i s t i l l e d w a t e r and  a l l o w e d t o c o o l b e f o r e t h e sample was assembled.  The sample  was p l a c e d i n t h e c e l l w i t h s t o n e s a t t o p and b o t t o m . F i g u r e 11 show's ^ p h o t o g r a p h y o f an i n s t a l l e d  sample .  The t o p o f the c e l l was t h e n p l a c e d i n p o s i t i o n and the  a l i g n m e n t o f t h e ram.with t h e sample was checked b y  FIGURE  1 1 .  SAMPLE  IN  PLACE  ON T R I A X I A L  BASE.  23 o b s e r v i n g whether t h e r e was a movement when t h e ram came i n c o n t a c t w i t h t h e b a l l b e a r i n g on t h e l o a d i n g c a p .  The sample  was p o s i t i o n e d m a n u a l l y u n t i l no movement c o u l d be d e t e c t e d , then, the v e r t i c a l d i a l s e t . fed  i n t o the chamber.  D i s t i l l e d d e - a i r e d w a t e r was  The chamber p r e s s u r e was a p p l i e d f r o m  10 l b s . / s q . i n . t o 100 l b s . / s q . i n . a t i n c r e m e n t s  of  10 l b s . / s q . i n . and a t i n t e r v a l s o f t h r e e t o f o u r m i n u t e s . The pore p r e s s u r e s were r e a d on t h e t r a n s d u c e r b e f o r e  each  increment was a p p l i e d , and t h e n t h e Skempton B p a r a m e t e r c o u l d be determined.  The B-parameter was d e t e r m i n e d p r i o r t o con-  solidation i n this test  series.  Samples were a l l o w e d t o c o n s o l i d a t e f o r t ^ o o * * two days, f o u r d a y s , and e i g h t days i n d i v i d u a l l y .  o  n  e  d a  y^  A back  p r e s s u r e o f 10 l b s . / s q . i n . was a p p l i e d t o t h e d r a i n a g e l i n e s d u r i n g c o n s o l i d a t i o n . B u r e t t e r e a d i n g s .were t a k e n and t^Q  3  tjoo  w  e  r  e  determined.  The c o n t a c t o f t h e ram and  the b a l l were a d j u s t e d m a n u a l l y t h r o u g h o u t t h e p e r i o d o f consolidation. Two days.were a l l o w e d t o o b s e r v e the pore build-up after consolidation. 1  pressure  I t was f o u n d t h a t t h e s h o r t e r  the c o n s o l i d a t i o n t i m e , t h e h i g h e r t h e pore p r e s s u r e b u i l d s up.  T h i s i s d i s c u s s e d i n Chapter I V . i  *t , time f o r p r i m a r y c o n s o l i d a t i o n , about 3 . 3 h o u r s in this test series. l o o  24 The sample was s h e a r e d i m m e d i a t e l y a f t e r the pore pressure build-up p e r i o d . program was 0.5$ p e r h o u r .  The s t r a i n r a t e adopted i n t h i s A t t h e end o f the s h e a r i n g . p r o c e s s ,  back d r a i n a g e was r e q u i r e d t o check on the water c o n t e n t . T h i s procedure was f i r s t s u g g e s t e d b y H e n k e l and Sowa (19&3), because the r e m o v a l o f h i g h chamber p r e s s u r e c a u s e s t e n s i o n s to  s e t up i n the pore w a t e r , w h i c h d r a i n s the w a t e r i n the  d r a i n a g e l i n e back i n t o the sample when i t i s removed.  Back  d r a i n a g e was done b y d r o p p i n g the chamber p r e s s u r e t o 12  l b s . / s q . i n . , w i t h a back p r e s s u r e o f 10 l b s . / s q . i n . and  removing the d e v i a t o r s t r e s s . for  Back d r a i n a g e was c o n t i n u e d  one day, t h e n the d r a i n a g e v a l v e s were c l o s e d .  The  sample was t h e n removed f r o m the c e l l , weighed and p l a c e d i n . the  oven f o r water c o n t e n t d e t e r m i n a t i o n . The d i f f e r e n c e o f the amount o f water . d r a i n i n g o u t and  back d r a i n e d c o u l d be c a l c u l a t e d .  The w a t e r c o n t e n t o f t h e  whole sample was t h e n d e t e r m i n e d b y back c a l c u l a t i o n f r o m the i n i t i a l water c o n t e n t and a l s o d i r e c t l y measured as a check. D i s c u s s i o n s o f Non-uniform Pore P r e s s u r e \ i n Undrained Tests  '  I t i s agreed b y most i n v e s t i g a t o r s  , (Whiteman, i960,  B i s h o p , 1957.,.,Blight, I963, and D o n a l d , 1942)  that f o r  n o r m a l l y c o n s o l i d a t e d and s e n s i t i v e m a t e r i a l s  during  u n d r a i n e d shear t e s t s , the-, pore p r e s s u r e a t the c e n t r e o f the  sample may be h i g h e r t h a n a t the ends, i f the r a t e o f  25 shearing  i s r e l a t i v e l y high.  These pore p r e s s u r e d i f f e r e n c e s  appear t o be caused m a i n l y by f r i c t i o n a l  r e s t r a i n t imposed  the ends o f the t r i a x i a l specimen by the r i g i d  loading  on  platens.  The s i m p l e s t way s u g g e s t e d by B l i g h t t o a v o i d  errors  due t o pore p r e s s u r e d i f f e r e n c e s i s t o use a r a t e o f  strain  which w i l l a l l o w the pore p r e s s u r e t o e q u a l i z e by i n t e r n a l r e d i s t r i b u t i o n of moisture.  He s u g g e s t e d t h a t the r e p r e -  s e n t a t i v e pore p r e s s u r e i n the f a i l u r e zone can be by a d j u s t i n g the t e s t d u r a t i o n t o a l l o w the r e q u i r e d  obtained degree  o f pore p r e s s u r e e q u a l i z a t i o n by t r a n s f e r o f m o i s t u r e .  A  t e s t d u r a t i o n w h i c h w i l l r e s u l t i n a d e s i r e d degree o f e q u a l i z a t i o n o f pore p r e s s u r e can be c a l c u l a t e d f r o m the c o e f f i c i e n t o f the c o n s o l i d a t i o n o f the s o i l , the d i m e n s i o n s of the t r i a x i a l specimen, and the c o n d i t i o n s o f d r a i n a g e /to be used i n the t e s t . The s t r a i n r a t e o f 0.5$  .. .  ,  p e r hour w h i c h was u s e d i n  t h i s t e s t s e r i e s has been c a r e f u l l y chosen and met B l i g h t s 1  criteria  \  quite w e l l .  CHAPTER I V TEST RESULTS Introduction The t e s t s e r i e s c o n s i s t e d o f t e n n o r m a l l y 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 on u n d i s t u r b e d samples o f Haney c l a y . A l l samples were i s o t r o p i c a l l y c o n s o l i d a t e d t o 75 l b s . / s q . i n . and deformed a t a c o n s t a n t a x i a l s t r a i n r a t e o f 0.5$ p e r h o u r . The specimens were c o n s o l i d a t e d f o r f i v e d i f f e r e n t p e r i o d s o f time (3.3  h o u r s , 1 day, 2 days, 4 days and 8 d a y s ) .  To check on the c o n s i s t e n c y and r e l i a b i l i t y o f t h e t e s t r e s u l t s , two t e s t s were p e r f o r m e d a t each time.  consolidation  T y p i c a l t e s t d a t a w e r e . r e c o r d e d as shown i n T a b l e I I  and Appendices I and I I . The r e s u l t s a r e p r e s e n t e d and d i s c u s s e d i n t h e f o l l o w i n order:  \ \  1.  Pore p r e s s u r e b u i l d - u p b e f o r e s h e a r i n g .  2.  The .secondary c o m p r e s s i o n e f f e c t on pore pressure/strain relationship.  3*  The secondary c o m p r e s s i o n e f f e c t on shear s t r e n g t h .  4.  Summary and c o n c l u s i o n s .  Pore P r e s s u r e B u i l d - u p B e f o r e S h e a r i n g To i n v e s t i g a t e the pore p r e s s u r e e q u i l i b r i u m  after  c o n s o l i d a t i o n , samples were a l l o w e d t o " s t a n d " f o r two days  27 p r i o r to shearing.  I t was o b s e r v e d t h a t a f t e r  consolidation,  pore p r e s s u r e s i n c r e a s e d w i t h o u t any a p p l i e d d e v i a t o r F i g u r e 12  shows the b u i l d - u p i n pore p r e s s u r e w i t h  stress.  logarithm  time f o r samples c o n s o l i d a t e d a t d i f f e r e n t p e r i o d s o f t i m e . The pore p r e s s u r e r i s e d e c r e a s e d w i t h i n c r e a s i n g time.  T h e . g r e a t e s t r e c o r d e d i n c r e a s e was  21.2  lbs./sq. i n . i n  two days a f t e r d r a i n a g e was c l o s e d f o r samples 3.3  hours and the s m a l l e s t was  consolidation  consolidated  2 l b s . / s q . i n . f o r samples  c o n s o l i d a t e d e i g h t days. There was. no l e a k i n the pore p r e s s u r e m e a s u r i n g because  system  a l l samples showed a d e c r e a s i n g r a t e o f pore p r e s s u r e  w i t h t i m e , thus i t cannot be a l e a k . u n l e s s i t i s g r a d u a l l y s e a l i n g i t s e l f , which i s u n l i k e l y . c o n s o l i d a t i o n t e s t s was the  The time f o r a l l the  l o n g e r t h a n the time r e q u i r e d f o r  p r i m a r y c o n s o l i d a t i o n as d e t e r m i n e d by the square time f i t t i n g method, ( T a y l o r , 1940).  of  root  Thus, the i n c r e a s e  i n pore p r e s s u r e was.not due t o i n c o m p l e t e p r i m a r y cons o l i d a t i o n , but to c o n t i n u i n g secondary compression  effect.  A t the end o f c o n s o l i d a t i o n , the d r a i n a g e v a l v e s were c l o s e d , thus the d r a i n a g e due t o s e c o n d a r y  compression  1  caused by f u r t h e r s t r u c t u r a l r e a d j u s t m e n t o f the c l a y p a r t i c l e s was p r e v e n t e d . >, T h e r e f o r e , the pore w a t e r the  sample was compressed  inside  and the pore p r e s s u r e b u i l t  The g r e a t e r the t e n d e n c y . t o d r a i n because  of  up.  structural  r e a d j u s t m e n t s , the h i g h e r the pore p r e s s u r e b u i l t - u p . '.  TABLE I I *TIME OF CONSOLIDATION .  t  100  WATER CONTENT  SUMMARY OP TEST RESULTS AT (d, -0 )max.  AT (<VAV )max.  <5,'/cV 2.59  26.4  14.4  31.1  3.26  B *P.P. 32.0 71.2 1.00  %  /•  o>d  - 1 9 6 mins. 40.7  33.1  3.66  0>d» 36.2  40.2  32.8  3.44  40.2  2.51  26.1  14.7  35.7  3.17  31.3  68.2  1.00  32.7  3.25  42.9  2/48  25.4  12.3  38.O  3.10  31.0  66.9  1.00  - 1 DAY • 2 DAYS  "  :  ' • '40 .2  /  \  3  • 4 DAYS  '40.2  32.5  2.92  41.7  2.46  25.0  14.8  36.0  3.06  30.4  67.6  1.00  . 8 DAYS  40.1  32.6  2.61  41.8  2.33  23.6  15.2  36.1  3.03  30.2  67.2  1.00  *Average o f two t e s t s . **Pore p r e s s u r e was a l l o w e d t o e q u a l i z e B =.AU  f o r two days a f t e r  consolidation.  (Measured p r i o r t o c o n s o l i d a t i o n ) .  ro co  29 i  1  81  I  I  10  100 TIME  FIGURE  12.'  U  (MIN)  RELATIONSHIP AND  TIME  ipoo  BETWEEN PORE PRESSURE  PRIOR TO SHEARING  30 F i g u r e 13 g i v e s the r e l a t i o n s h i p between volume o f water d r a i n e d d u r i n g c o n s o l i d a t i o n and the square r o o t o f time.  I t can be seen t h a t the time f o r p r i m a r y c o n s o l i d a t i o n  i s tioo  3*3 h o u r s (196 m i n s . ) .  =  u s i n g volume o f water vs. F i g u r e 14.  Another c u r v e p l o t t e d by  l o g a r i t h m o f time i s shown i n  The volume o f water d r a i n e d d e c r e a s e d w i t h t i m e .  S i n c e t h i s same l o g a r i t h m p l o t i s the same f o r a l l  samples,  the s h o r t e r c o n s o l i d a t i o n time r e s u l t s i n more w a t e r b e i n g prevented from d r a i n i n g .  C o n s e q u e n t l y , h i g h e r pore p r e s s u r e  was b u i l t - u p f o r . s h o r t e r c o n s o l i d a t i o n t e s t s . . T h i s amount o f pore p r e s s u r e r i s e t a k e s p l a c e i n the absence o f any  applied  d e v i a t o r s t r e s s , t h e r e f o r e a c e r t a i n amount o f the pore p r e s s u r e measured d u r i n g s h e a r i n g i s n o t due t o a p p l i e d d e v i a t o r s t r e s s b u t , secondary c o m p r e s s i o n .  '  _  The Secondary Compression E f f e c t on Pore P r e s s u r e / S t r a i n R e l a t i o n s h i p The change o f pore p r e s s u r e i n r e l a t i o n t o s t r a i n f o r a l l the samples are p l o t t e d i n F i g u r e 15.  I t shows t h a t i n  s p i t e o f the d i f f e r e n t p e r i o d s o f c o n s o l i d a t i o n a common r e l a t i o n s h i p appears t o e x i s t between pore p r e s s u r e and strain.  For e> 4$, the p o i n t s r e s u l t i n g f r o m f i v e  axial  different  p e r i o d s e x c e p t the.^3.3 h o u r s / c o n s o l i d a t i o n t e s t , f a l l v e r y c l o s e t o a s i n g l e c u r v e V ^ The r e a s o n the pore p r e s s u r e o f 3 . 3 hours c o n s o l i d a t i o n t e s t was h i g h e r t h a n o t h e r s i s  1  31b  31c  32  b e l i e v e d t o be due t o the s t r o n g e r s e c o n d a r y c o m p r e s s i o n e f f e c t (see F i g u r e 12). The c o n c l u s i o n may t h e r e f o r e be r e a c h e d t h a t f o r Haney c l a y , e x c e p t f o r the s h o r t e r t h a n one-day c o n s o l i d a t i o n t e s t , the secondary c o m p r e s s i o n has no e f f e c t on t h e pore p r e s s u r e / s t r a i n r e l a t i o n s h i p a f t e r e"^4$. From t h i s unique r e l a t i o n s h i p , i t w i l l be no p r o b l e m to e x p l a i n the c u r v e i n F i g u r e 16 w h i c h shows pore p r e s s u r e at maximum d e v i a t o r s t r e s s .  The l o n g e r the c o n s o l i d a t i o n  t i m e , the lower. the pore p r e s s u r e d e v e l o p e d a t due t o the s m a l l e r s t r a i n a t (6,'-d^) max. the  s t r a i n was l e s s a t  (d, -d^) max. 1  The r e a s o n why  (d, -d^) max. w i t h i n c r e a s i n g con1  s o l i d a t i o n time w i l l be d i s c u s s e d  later.  As mentioned b e f o r e , the pore p r e s s u r e b u i l d - u p was h i g h e r p r i o r t o s h e a r i n g f o r s h o r t e r p e r i o d s of c o n s o l i d a t i o n due t o secondary c o m p r e s s i o n .  T h i s can be shown i n F i g u r e 15,  which gave the r e l a t i o n s h i p s between pore p r e s s u r e and s t r a i n for at  d i f f e r e n t c o n s o l i d a t i o n time.  The h i g h e r pore p r e s s u r e  smaller s t r a i n f o r shorter c o n s o l i d a t i o n t e s t i s caused  by secondary c o m p r e s s i o n . F i g u r e 17 shows the r e l a t i o n s h i p between pore p r e s s u r e b u i l t up p r i o r t o s h e a r i n g and water c o n t e n t a f t e r c o n s o l i d a t i o n . "-The water c o n t e n t and pore p r e s s u r e b u i l t up were lower f o r l o n g e r c o n s o l i d a t e d samples.  Although there  was n o t much r e d u c t i o n i n water c o n t e n t (0.4$)  o f the •  33  64  CL  a-  54  521 0  1  1  I  2  FIGURE.  x  |  1 3  1  4  5  CONSOLIDATION  TIME  16..  OF  VARIATION  ""'MAXIMUM DIFFERENT  I '  PORE  DEVIATOR  6  7  8  (DAY)  PRESSURE STRESS  CONSOLIDATION  AT  "  . .  FOR TIME  •'  34  33  NOTE 1. EACH '  SAMPLE  INITIAL 2. P P  HAS  WATER  SAME  CONTENT.  EQUALIZED FOR  DAYS. PRIOR  TO  TWO SHEARING.  /  -'  <  /  ( ) | DAY <2 DAY  8 DAY  323  324 ' 32.5 WATER  3 2.6  CONTENT  \ '  FIGURE  4 DAY  (PER  17  32.7 AFTER  A N D PORE  32.9  330  331  CONSOLIDATION  CENT;  RELATIONSHIP .  328  BETWEEN  PRESSURE  WATER  PRIOR  TO  CONTENT, SHEARING-  35 samples d u r i n g t h e secondary c o m p r e s s i o n p e r i o d s , t h e pore pressure  r i s e was s t i l l a p p r e c i a b l e .  I t was mentioned  before  t h a t the r a t e o f secondary c o m p r e s s i o n was d e c r e a s i n g time.  F o r the l o n g e s t c o n s o l i d a t i o n t e s t , t h e water  with content  a f t e r c o n s o l i d a t i o n was l o w e s t , and the e f f e c t o f s e c o n d a r y compression on pore p r e s s u r e pressure  was s m a l l , thus the pore  r i s e due t o secondary c o m p r e s s i o n was n e a r l y  negligible. F i g u r e 18 shows the r e l a t i o n s h i p between Skempton pore p r e s s u r e  parameter A and s t r a i n .  The Skempton A v a l u e  i n c r e a s e d w i t h s t r a i n f o r a l l the t e s t s .  I t isinteresting  t o note t h a t the Skempton A v a l u e f o r t h e sample c o n s o l i d a t e d two days was lower t h a n the sample c o n s o l i d a t e d one day. For i s o t r o p i c u n d r a i n e d c o n s o l i d a t i o n t e s t s , t h e Skempton A v a l u e i s the r a t i o o f pore p r e s s u r e s t r e s s change.  change t o ,the d e v i a t o r  As mentioned b e f o r e , the pore p r e s s u r e  rise  p r i o r to shearing i s higher f o r shorter c o n s o l i d a t i o n samples pressure  (Figure 12),  and a l s o f r o m F i g u r e 15,  the pore  a f t e r 4$ s t r a i n i s n e a r l y t h e same f o r a l l t e s t s .  I t i s t h e r e f o r e b e l i e v e d t h a t the pore p r e s s u r e  increment  t  i S ' h i g h e r f o r t h e l o n g e r c o n s o l i d a t e d samples.  The r e a s o n  why the A - v a l u e o f two day c o n s o l i d a t e d sample i s l o w e r than one day "is-because  the i n c r e m e n t o f d e v i a t o r s t r e s s i s  h i g h e r f o r t h e two day' s. c o n s o l i d a t i o n t e s t .  37 The Secondary Compression  E f f e c t on  (c^ -<5') 1  Max.  F i g u r e s 1 9 and 2 0 show t h a t the u n d r a i n e d shear s t r e n g t h (di'-cy) max. i n c r e a s e d s i g n i f i c a n t l y w i t h c o n s o l i d a t i o n time t o a peak v a l u e a t two day's c o n s o l i d a t i o n .  (6^-6^)  max.,  then d e c r e a s e d s l i g h t l y and m a i n t a i n e d a c e r t a i n v a l u e f o r longer c o n s o l i d a t i o n p e r i o d s . There i s no t h e o r y so f a r t h a t can he u s e d t o e x p l a i n the b e h a v i o r shown i n F i g u r e 2 0 .  Therefore, the e x p l a n a t i o n  s t a t e d below i s proposed b y the a u t h o r : The c u r v e i n F i g u r e 2 1 was a c o m b i n a t i o n o f two e f f e c t s : 1.  The o r i g i n a l c l a y samples have a f l u c c u l a t e d  structure.  The h i g h e x t e r n a l c o n s o l i d a t i o n p r e s s u r e r e s u l t e d i n a d e c r e a s e i n s p a c i n g between t h e p a r t i c l e s due t o volume d e c r e a s e and thus the s t r e n g t h i n c r e a s e d .  As shown by h y p o t h e t i c a l  curve 1 i n F i g u r e 2 1 , the s t r e n g t h was i n c r e a s e d w i t h cons o l i d a t i o n time.  B e f o r e two days' c o n s o l i d a t i o n , t h e volume  decrease o f the samples was a p p r e c i a b l e , t h u s t h e s t r e n g t h increased r a p i d l y .  For l o n g e r . c o n s o l i d a t i o n time, the  volume decrease o f the samples was s m a l l , thus o n l y a s l i g h t i  i n c r e a s e o f s t r e n g t h can be seen i n curve 1 .  2.  I t i s u n d e r s t o o d that,, t h i x o t r o p y c a n o n l y a c c o u n t f o r  low o r medium s e n s i t i v i t y , b u t i t a p p e a r s . t o be u n a b l e t o account f o r h i g h s e n s i t i v i t y  (Skempton,  1952).  It is  !  38  40  a  x E  CL  LU < LU ac LU Q  vO  FIGURE  2I>EFFECT SION  OF ON  CONSOLIDATION SHEAR  STRENGTH  AND  D1SPER'  41 t e n t a t i v e l y proposed by the a u t h o r t h a t f o r e x t r a - s e n s i t i v e c l a y , t h e r e i s no t h i x o t r o p y e f f e c t b u t a tendency f o r the c l a y p a r t i c l e s t o become more d i s p e r s e d w i t h t i m e , under a c o n d i t i o n o f no volume change, thus the s t r e n g t h d e c r e a s e d . Curve 2 i n F i g u r e 21 i s the p r o p o s e d curve t o show the decrease i n shear s t r e n g t h a g a i n s t c o n s o l i d a t i o n time to d i s p e r s i o n e f f e c t f o r e x t r a - s e n s i t i v e c l a y .  due  The  d i s p e r s i o n e f f e c t i n c r e a s e d r a p i d l y a t an. e a r l y s t a g e  and  only s l i g h t l y increased f o r a longer p e r i o d of time. I t i s proposed t h a t the k i n k i n F i g u r e 20 was  due  to the c o m b i n a t i o n of these two e f f e c t s , as s t a t e d above. The curve 3 i n F i g u r e 21 i s the c o m b i n a t i o n of c u r v e s 1 and 2 and i s the same curve as shown i n F i g u r e 20. A l l the samples were a l l o w e d t o " s t a n d " f o r two days p r i o r t o s h e a r i n g d u r i n g which the d r a i n a g e prevented.  The e f f e c t o f curve 1 was  /  was  s t o p p e d whenever  the c o n s o l i d a t i o n was o v e r , and the e f f e c t o f c u r v e 2 w i l l keep on g o i n g u n t i l the end of the t e s t .  I t usually  t a k e s 2.3 days f o r the samples t o r e a c h t h e i r maximum d e v i a t o r s t r e s s a f t e r the c o n s o l i d a t i o n s t o p p e d . i  c o n v e n i e n c e , the a b s c i s s a o f curve 2 has 2.3  For  difference  from curve 1. Two  tests..were performed i n o r d e r t o check the  v a l i d i t y o f c u r v e s 1 and 2 as p r o p o s e d i n F i g u r e 20. The r e s u l t s o f these two t e s t s were l i s t e d i n T a b l e I I I .  42  TABLE I I I COMPARISON BETWEEN TESTS NO. 1 AND NO. 8  T e s t No.  Time o f C o n s o l i d a t i o n  (d, -d ' )max.  Time o f P.P.Rise Pr i o r She ar i n g  1  3 hours  1 day  8  3 hours  2 days  1  . 37.7 p s i J  36.2 p s i  B o t h t e s t s had t h e same c o n s o l i d a t i o n time b u t a d i f f e r e n t time f o r t h e pore p r e s s u r e r i s e p r i o r t o s h e a r i n g .  The con-  s o l i d a t i o n e f f e c t as r e p r e s e n t e d by c u r v e 1 was t h e same f o r b o t h t e s t s s i n c e t h e y have the same l e n g t h o f c o n s o l i d a t i o n time.  The e f f e c t o f d i s p e r s i o n on t h e s e two t e s t s was  different.  T e s t No. 8 has more d i s p e r s i o n e f f e c t  than  T e s t No. 1 because the time f o r t h e pore p r e s s u r e r i s e i n T e s t No. 8 was one day l o n g e r t h a n T e s t No. 1.  Thus, t h e  shear s t r e n g t h due t o d i s p e r s i o n s h o u l d be more i n T e s t No. 8. Prom T a b l e I I I , the (d,'-d ')max. was 37.7 p s i f o r T e s t No. 1 3  and 36.2 p s i f o r T e s t No. 8.  T h i s shows t h a t c u r v e s 1 and 2  b o t h e x i s t e d i n d e v e l o p i n g the shear s t r e n g t h i n t h e cons o l i d a t e d u n d r a i n e d t e s t on s e n s i t i v e c l a y , and i t i s r e a s o n a b l e t o employ t h e s e two c u r v e s t o e x p l a i n t h e k i n k i n F i g u r e 20.  43 Figure  22 shows the e f f e c t o f c o n s o l i d a t i o n time on  pore p r e s s u r e and angle o f s h e a r i n g r e s i s t a n c e ft* a t (<Y-Oj' )max.  W i t h i n c r e a s i n g time o f c o n s o l i d a t i o n , t h e  pore p r e s s u r e and angle o f s h e a r i n g r e s i s t a n c e a t (o '-oy )max. was d e c r e a s e d . (  The r e a s o n f o r the decrease i n pore p r e s s u r e a t (d ' -c3' )max. w i t h c o n s o l i d a t i o n time may he due t o t h e f a c t (  3  t h a t the s t r a i n a t (d ' -d^)max. d e c r e a s e d w i t h (  consolidation.  V/ith i n c r e a s i n g c o n s o l i d a t i o n t i m e , t h e sample becomes more b r i t t l e with smaller f a i l u r e s t r a i n . -a,' )max. was 3.65  the e# a t and  23,  f o r 3• 3-hour c o n s o l i d a t i o n  then d e c r e a s e d w i t h time t o 2.50  solidation test.  As shown i n F i g u r e  f o r an 8-day con-  S i n c e i t was shown t h a t the pore  p r e s s u r e / s t r a i n c u r v e s f o r a l l t h e t e s t s ( F i g u r e 15)  were  n e a r l y the same, i t f o l l o w s t h a t t h e pore pressure, was l e s s at  (07-d' )max. 3  w i t h i n c r e a s i n g c o n s o l i d a t i o n time because  the s t r a i n was l e s s . • The Secondary Compression E f f e c t on (d^/dj)max. Figure  24 shows t h e v a r i a t i o n s o f p r i n c i p a l e f f e c t i v e  •stress r a t i o w i t h s t r a i n f o r samples c o n s o l i d a t e d i n d i f f e r e n t periods lower f o r l o n g e r  of time.  A t any s t r a i n , t h e (d'/d"^) was  consolidation tests.  The maximum  p r i n c i p a l s t r e s s r a t i o f o r d i f f e r e n t c o n s o l i d a t i o n time  *0  X  i s evaluated  b y assuming C  ='0.  45  47 was p l o t t e d i n F i g u r e 2 5 .  The v a l u e o f (6'/o^ )max.  f o r 3.3 hours c o n s o l i d a t i o n t e s t and t h e n d e c r e a s e d  was 3-27 with  time t o 3.03 f o r e i g h t days c o n s o l i d a t i o n t e s t . The v a l u e o f ( d ' / c y )max. s e t up d u r i n g t h e t e s t .  depends on t h e pore p r e s s u r e  For i s o t r o p i c a l l y consolidated  samples, a t a g i v e n v a l u e o f d e v i a t o r s t r e s s , t h e h i g h e r t h e pore p r e s s u r e , the h i g h e r the v a l u e o f ( o ^ ' / d ) . 1  observed  t h a t secondary  compression  I t was  had a s t r o n g i n f l u e n c e on  the pore p r e s s u r e s e t up f o r t h e r e l a t i v e l y s h o r t e r consolidation periods.  Thus, t h e v a l u e o f ( d / ^ ) was h i g h e r . 1  1  For l o n g e r c o n s o l i d a t i o n p e r i o d s , t h e secondary e f f e c t on pore p r e s s u r e r i s e was s m a l l .  compression  Thus, t h e pore  p r e s s u r e / s t r a i n c u r v e s f o r those t e s t s c o n s o l i d a t e d l o n g e r than one day were c l o s e enough t o be r e p r e s e n t e d b y one s i n g l e curve which has been shown i n F i g u r e 15. I t was o b s e r v e d  t h a t i n t h i s t e s t s e r i e s , the  (d'/d^')max. always o c c u r r e d a t 14$ s t r a i n , and t h e v a l u e s o f d e v i a t o r s t r e s s and pore p r e s s u r e a t t h i s f a i l u r e  strain  were v e r y c l o s e f o r t e s t s l o n g e r than one-day c o n s o l i d a t i o n . From these f a c t s , i t i s t h e r e f o r e p o s t u l a t e d t h a t t h e v a l u e of (d'/<5j )max. (  f o r samples c o n s o l i d a t e d f o r l o n g p e r i o d s o f  time w i l l be v e r y c l o s e t o t h e v a l u e o f ( d ' ) m a x . a t (  8-days c o n s o l i d a t i o n t e s t w h i c h was i n c l u d e d i n t h i s which was i n c l u d e d i n t h i s t e s t program.  test  48  49  Summary I n t h e d e s c r i b e d t e s t s e r i e s , samples were n o r m a l l y , c o n s o l i d a t e d f o r d i f f e r e n t . p e r i o d s o f time b e f o r e t h e y were s u b j e c t e d t o u n d r a i n e d shear i n t h e t r i a x i a l a p p a r a t u s . The r e s u l t s c a n be summarized as f o l l o w s : 1.  Secondary c o m p r e s s i o n has an a p p r e c i a b l e i n f l u e n c e  on the pore p r e s s u r e s e t up a t s h o r t e r c o n s o l i d a t i o n  tests.  For c o n s o l i d a t i o n t e s t s l o n g e r t h a n one day, t h e e f f e c t o f secondary c o m p r e s s i o n on pore p r e s s u r e c a n be n e g l e c t e d . 2.  The maximum d e v i a t o r s t r e s s i n c r e a s e s w i t h t h e time •  o f c o n s o l i d a t i o n , i t r e a c h e s i t s h i g h e s t v a l u e s a t two days c o n s o l i d a t i o n , t h e n d e c r e a s e s s l i g h t l y f o r l o n g e r consolidation. 3.  F o r samples c o n s o l i d a t e d l o n g e r t h a n one day, t h e  pore p r e s s u r e / s t r a i n r e l a t i o n s h i p o b s e r v e d d u r i n g t h e shear t e s t s was independent o f t h e time o f c o n s o l i d a t i o n o f t h e samples. < . 4.  The e f f e c t i v e p r i n c i p a l s t r e s s r a t i o i n c r e a s e s more  r a p i d l y a t s m a l l s t r a i n s f o r t h e samples o f s h o r t e r  con-  s o l i d a t i o n and r e a c h e s i t s maximum v a l u e around 14$ s t r a i n . 5.  Due t o secondary c o m p r e s s i o n , t h e maximum e f f e c t i v e  p r i n c i p a l s t r e s s r a t i o was h i g h e r f o r s h o r t e r test. t o 3.03  The r a t i o ranges f r o m 3.25 f o r 8-day c o n s o l i d a t i o n .  consolidation  f o r 3.3-hour c o n s o l i d a t i o n  50  Suggestions f o r F u r t h e r Research 1.  I t was s u g g e s t e d i n t h i s t h e s i s t h a t s e n s i t i v i t y i s  an i m p o r t a n t f a c t o r i n d e t e r m i n i n g t h e shear s t r e n g t h o f Haney c l a y .  F u r t h e r s t u d i e s c a n be done on some c l a y  which has been remoulded 2.  so s e n s i t i v i t y i s l o w .  I t was d i s c u s s e d i n Chapter I V t h a t  secondary  compression has a d i r e c t i n f l u e n c e on t h e pore p r e s s u r e r i s e before shearing.  The pore p r e s s u r e r i s e depends on  the magnitude o f secondary c o m p r e s s i o n and t h e l e n g t h o f time f o r c o n s o l i d a t i o n .  I t might be i n t e r e s t i n g t o t e s t  c l a y samples which have d i f f e r e n t magnitude o f s e c o n d a r y compression and c o r r e l a t e t h e pore p r e s s u r e r i s e  with  magnitudes o f secondary c o m p r e s s i o n a t same c o n s o l i d a t i o n time. 3.  I n t e r e s t i n g comparison w i t h the r e s u l t s i n t h i s  t h e s i s can be done by r e p e a t i n g t h e s t u d y b u t s h e a r i n g immediately a f t e r c o n s o l i d a t i o n , which i s ' the p r e s e n t laboratory practice.  LIST OF REFERENCES B i o t , M.A., 1956. "Theory of D e f o r m a t i o n of A Porous V i s c o e l a s t i c A n i s o t r o p i c - S o l i d " . J o u r n a l of A p p l i e d P h y s i c s . May, 1956. B i s h o p , A.W. and D.J. H e n k e l . "The Measurement of S o i l P r o p e r t i e s i n the T r i a x i a l T e s t " . Edward A r n o l d (Publishers) Ltd. B j e r r u m , L a u r i t s and K.Y. Lo, 1963. " E f f e c t of Aging the Shear S t r e n g t h P r o p e r t i e s o f a N o r m a l l y Consolidated Clay." Geotechnique, June, 19&3-  on  B j e r r u m , L. and N.E. Simons, i 9 6 0 . "Comparison o f Shear Strength C h a r a c t e r i s t i c s of Normally Consolidated C l a y s . " R e s e a r c h Conference on Shear S t r e n g t h of Cohesive S o i l s , A.S.C.E., I960T B j e r r u m , L., 1961. "The E f f e c t i v e Shear S t r e n g t h Parameters o f S e n s i t i v e C l a y . " P r o c . F i f t h I n t . Conf. S o i l Mech., P a r i s . B l i g h t , G.E., 1963. "The E f f e c t of N o n - u n i f o r m Pore P r e s s u r e s on L a b o r a t o r y Measurements o f the Shear S t r e n g t h of S o i l s . " P r o c . NRC/ASTM Symposium on Shear T e s t i n g , Ottawa. B y r n e , P.M., 1966. " E f f e c t i v e S t r e s s Paths i n a S e n s i t i v e C l a y . " M.A.Sc. T h e s i s , U.B.C. Vancouver, B.C., Canada. Crawford, C a r l B., 1963. "Cohesion i n an S e n s i t i v e Clay." Geotechnique, June,  Undisturbed 1963.  Crawford, C a r l B., 1963. "Pore P r e s s u r e s W i t h i n S o i l '. Specimens i n T r i a x i a l Compression." 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 No. 361. x  Eden, W.J. and J.K. K u b o t a , 1961. "Some- O b s e r v a t i o n s the Measurement o f S e n s i t i v i t y of C l a y s . " P r o c . A.S.T.M., 1961.  on  y  H i r s t , T.J., 1966. " T r i a x i a l Compression T e s t s on an U n d i s t u r b e d S e n s i t i v e . C l a y . " M.A.Sc. T h e s i s , U . B . C , Vancouver, Canada.  52 Kenney, T.C., 1959. D i s c u s s i o n on C r a w f o r d , C.B. "The I n f l u e n c e o f Rate o f S t r a i n on 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. P r o c e e d i n g s , A n n u a l G e n e r a l Meeting. Lambe, T.W., 196a. "Compacted C l a y E n g i n e e r i n g B e h a v i o r . " T r a n s a c t i o n , J o u r n a l o f S o i l Mech. and F o u n d a t i o n Division. Leonards, G.A. and B.K. Bamiah, 1959"Time E f f e c t i n t h e C o n s o l i d a t i o n o f C l a y s . " S p e c i a l A.S.T.M. T e c h n i c a l P u b l i c a t i o n No. 254. Lo, K.Y., 196l. "Secondary Compression o f C l a y s . " A.S.C.E. J o u r n a l o f the S o i l Mechanics and F o u n d a t i o n E n g i n e e r i n g D i v i s i o n , August, 19SIT  Lowe, J . and T.C. Johnson, i960. "Use o f Back P r e s s u r e t o I n c r e a s e Degree o f S a t u r a t i o n o f T r i a x i a l T e s t Specimens." Research Conference on Shear S t r e n g t h o f C o h e s i v e S o i l s , A. S.C.E., I960.  Newland, P.L. and B.H. A l l e y , 1959-1960. "A Study o f t h e Consolidation C h a r a c t e r i s t i c s of a Clay." Geotechnique,  1959-1960.  R o s e n o v i s t , I.T., 1952. " C o n s o l i d a t i o n s on t h e S e n s i t i v i t y o f Norwegian Q u i c k - c l a y s . " G e o t e c h n i q u e , V o l . 3. S c o t t , R.F., 1962. " P r i n c i p l e s o f S o i l Mechanics." Addison-Wesley P u b l i s h i n g Company. Simons, N.E., i960. ."Comprehensive I n v e s t i g a t i o n s o f t h e Shear S t r e n g t h o f an U n d i s t u r b e d Drammen C l a y . " R e s e a r c h Conference on Shear S t r e n g t h o f Cohesive C l a y , A.S.C.E. Skempton, A.W.,- 1954. B. " Geotechnique.  "The. Pore P r e s s u r e C o e f f i c i e n t s A &  Skempton, A.W. and R.D. North'ey, 1952. ' C l a y s . " Geotechnique, V o l . 3.  "The S e n s i t i v i t y o f  T a y l o r , D.W. and W i l f r e d Merchant, 1940-1941. "A T h e o r y o f C l a y C o n s o l i d a t i o n A c c o u n t i n g f o r Secondary C o m p r e s s i o n . " J o u r n a l o f Mechanics and.-Physics. T a y l o r , D.W., 1948. "Fundamentals W i l e y & Sons, I n c . , London.  o f S o i l Mechanics."  John  53 Terzaghi, Karl. " T h e o r e t i c a l S o i l Mechanics." John Wiley & Sons, I n c . , London. W a h l s , H.E., 1962. " A n a l y s i s o f P r i m a r y and S e c o n d a r y Consolidation." A.S.C.E. J o u r n a l o f the _ S o i l M e c h a n i c s and F o u n d a t i o n s D i v i s i o n , December, 1964. Whitman, R.V., i960. "Some C o n s i d e r a t i o n s a n d D a t a R e g a r d i n g the S h e a r S t r e n g t h o f C l a y s . " R e s e a r c h Conference on 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 , A.S.C.E.  \  APPENDIX  TABLE  TIME TEST NO.  OF CONSOr Ll CATION  C^l  STRAIN  G  P - P.  «K  <PSO  f PsO  TESTS  RESULTS  c er,' / si )  j ) MAX.  *  RATE y. PER  -  OF  A*  1  .125  0.5  3.68  377  622  8  . 125  o.5  3.61  36.2  6?-3  .8* -84  TO  P- P  FAILURE C HR.)  Cpsi)  (psi)  TO  Af  B  FAILURE (HR)  2.65  783  14.73  31.2  irl.2  1.30  3.27  27.6  1.00  2.59  8.10  /4.4I  31.0  71-z  1.23  3.25  P9.o  1.00  8.75  |4.40  36.4  68.4  1.50  3.i9  26.6  1.00  7-70  15.00  35.0  67.9  1.48'  3.14  27.7  1.00  6.94  12.86  37.8  66.9  1.35  3.10  24.7  1.00  1. o  0.5  3.46  40.4  58.6  1. 11  2.53  6  1.0  0.5  3.42  39.9  58.0  1.03  2.43  4  2.0  0.5  3.22  43.1  j 56.3 |  10  2.0  ' 0.5  3.28  42.7  5  4. o  o.5  3.oo  7  4. o  0.5  II  8- o  0.5  12  8.0  " o.5  |  .93  2-4 7 j  56.9 |  .98  2.52  7 72  11-78  38.1  66.8  1.36  3.10  23. 1  1.00  41.4  55.9  1.02  2.42  9.8 3  1490  35.J  67. 5  1.49  3.o5  30.6  1.00  2. 8 4  42.0  5 5.7  1.0 1  2.50  a2o  |4.7o  36.4  67.6  1.46  3.o8  28.8  1.00  2. 5G  41. 9  54. 8  .95  2.30  5.50  15.20  36.1  67.2  1.50  3.o3  25.0  1.00  ?. 6 6  41.7  54.6  -96  2.36  6.o5  15.15  36.2  67.2  146  3.o3  28.1  1.00  |  * <5, - -  ,  TIME  TIME  %  3  T i ~  N<Av  MEASURED  PRIOR  TO  CONSOLIDATION  

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