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The effect of gradation and fines content on the undrained loading response of sand Kuerbis, Ralph H. 1989

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THE EFFECT OF GRADATION AND FINES CONTENT ON THE UNDRAINED LOADING RESPONSE OF SAND  by Ralph H. K u e r b i s B . A . S c , The U n i v e r s i t y  o f B r i t i s h Columbia, 1985  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE  in THE FACULTY OF GRADUATE STUDIES Department o f C i v i l  We a c c e p t t h i s  Engineering  t h e s i s as conforming  to the r e q u i r e d  standard  THE UNIVERSITY OF BRITISH COLUMBIA June 1989  ©  Ralph H. K u e r b i s  In presenting  this thesis in partial fulfilment of the  requirements for an  advanced  degree at the University of British Columbia, I agree that the Library shall make it freely available for reference  and  study. I further agree that permission for extensive  copying of this thesis for scholarly purposes may department  or  by  his or  her  representatives.  be  It is understood  publication of this thesis for financial gain shall not be permission.  Department of  Civil  Engineering  The University of British Columbia Vancouver, Canada Date  DE-6  (2/88)  July  5.  1989  granted by the head of that  copying  allowed without my  my or  written  ABSTRACT  A  systematic  gradation  and  undrained  loading  study  silt  of  content response  the  effect  of  on  t h e monotonic  of  sand  t h e behaviour  slurry  method  of f l u v i a l of  and h y d r a u l i c  deposition  is  size,  and  cyclic  i s presented.  o b j e c t i v e o f t h e study i s t o g a i n an improved of  grain  The  understanding  fill  sands.  developed  to  A  prepare  homogeneous specimens o f w e l l - g r a d e d and s i l t y sands, and t o simulate  hydraulic  Various s o i l slurry  fill  or  fluvial  deposition  g r a d a t i o n s c o n s o l i d a t e d from  deposition  compression  are  shown  to  have  processes.  loosest  state of  similar  triaxial  l o a d i n g behaviour, but q u i t e d i f f e r e n t  triaxial  e x t e n s i o n l o a d i n g behaviour.  Well-graded sands a r e shown t o  be  to soil  generally  silty  sands  regardless different ratio  effect  resistant  a r e shown t o possess of s i l t  void  is  behaviour  more  content,  ratios.  introduced of s i l t y  of s o i l  in  interpretation fabric  of  the  though  order  to  cyclic they  strengths  have  widely  skeleton void  explain  the  with varying f i n e s  observed  content. on  The  laboratory  Water p l u v i a t e d sand i s shown t o  fabric  and s t r e n g t h a n i s o t r o p y .  factors  which  contribute  and s t r e n g t h a n i s o t r o p y i s p r o v i d e d .  performance  Loose  o f sand  preparation technique  t e s t r e s u l t s i s discussed. have a c h a r a c t e r i s t i c  similar  The concept  sands  sample  even  liquefaction.  to  An sand  The p r a c t i c a l  o f water p l u v i a t e d sand i s d i s c u s s e d .  TABLE OF CONTENTS Page  ABSTRACT LIST OF  i i FIGURES  vii  LIST OF TABLES  XV  ..  NOTATIONS  xvi  ACKNOWLEDGEMENT  xvii  I.  INTRODUCTION .  1  II.  THE UNDRAINED BEHAVIOUR OF SAND - BACKGROUND CONCEPTS  5  2.1  Monotonic Loading Behaviour  6  2.1.1  C r i t i c a l Stress Ratio Line  9  2.1.2  Phase T r a n s f o r m a t i o n S t a t e  9  2.1.3  Steady-State Concepts  10  2.2  Soil 2.2.1  III.  Fabric  16  Rowe's S o i l  P a r t i c l e I n t e r a c t i o n Model  2.3  C y c l i c Loading Behaviour  2.4  E f f e c t of G r a d a t i o n and F i n e s Content on Undrained Loading Response of Sand  18 32  the  36  EXPERIMENTAL WORK  41  3.1  T e s t i n g Apparatus  41  3.1.1  Load C o n t r o l l e d T e s t i n g System  41  3.1.2  S t r a i n C o n t r o l l e d T e s t i n g System .....  44  3.1.3  Resolution  45  3.2  of Measurement  M a t e r i a l s Tested 3.2.1  45  General D e s c r i p t i o n o f Tested  -  iii  -  Materials 45  3.3  3.2.2  P h y s i c a l P r o p e r t i e s o f M a t e r i a l s T e s t e d 50  3.2.3  C r i t e r i a f o r Choosing T e s t S o i l s  Sample P r e p a r a t i o n - The S l u r r y D e p o s i t i o n Method Summary o f Sand Sample P r e p a r a t i o n Techniques  63  3.3.2  The S l u r r y D e p o s i t i o n Method  70  3.3.3  E v a l u a t i o n o f S l u r r y D e p o s i t i o n Method  79  3.3.4  Summary o f S l u r r y D e p o s i t i o n Method ..  90  Assembly o f T r i a x i a l T e s t Apparatus  3.5  U n i f o r m i t y o f Sample S t r a i n During and  IV.  V.  62  3.3.1  3.4  3.6  61  91 Monotonic  C y c l i c Loading  92  T e s t Program  93  TRIAXIAL TEST CONSOLIDATION RESULTS  97  4.0  Introduction  97  4.1 4.2  Accuracy o f C o n s o l i d a t i o n Data V o i d R a t i o and R e l a t i v e Density Consolidation  4.3  Volumetric  4.4  A x i a l and R a d i a l S t r a i n During  '.  97 During  S t r a i n During C o n s o l i d a t i o n  98 103  Consolidation  111  TRIAXIAL TEST UNDRAINED MONOTONIC LOADING RESULTS  116  5.0  Introduction  116  5.1  Uniqueness o f Undrained Response  117  5.2  Behaviour o f Clean Sands  119  5.2.1  S t r e s s - S t r a i n Response  119  5.2.2  E f f e c t i v e S t r e s s Path Response  125  5.2.3  Pore Pressure Response  126  -  iv -  5.3  5.4 VI.  5.2.4  E f f e c t of Consolidation Stress  5.2.5  E f f e c t of G r a i n S i z e and G r a d a t i o n  128 ...  129  M a t e r i a l Parameters  130  5.3.1  U l t i m a t e F a i l u r e Envelope  13 0  5.3.2  Angle o f Phase T r a n s f o r m a t i o n  13 3  5.3.3  C r i t i c a l Stress Ratio  134  5.3.4  Steady-State Concepts  136  E f f e c t of S i l t Content Upon Monotonic Loading Response  Undrained  138  CYCLIC TRIAXIAL TEST RESULTS  144  6.0  Introduction  144  6.1  General Response  149  6.2  S t r e s s - S t r a i n Response W i t h i n Loading C y c l e s  157  6.3  Pore P r e s s u r e G e n e r a t i o n During  Cyclic  Loading 6.3.1  E f f e c t of C y c l i c S t r e s s R a t i o  164  6.3.2  E f f e c t o f S i l t Content  168  6.3.3  E f f e c t of R e l a t i v e Density  173  6.3.4  Relationship and R e s i d u a l Relationship Pressure and  6.3.5 6.4  163  Between Induced S t r a i n Pore P r e s s u r e Between R e s i d u a l Pore H y s t e r e t i c Work  C y c l i c R e s i s t a n c e Data 6.4.1 6.4.2  176 182  C y c l i c R e s i s t a n c e Curves a t S i l t Content E f f e c t o f S i l t Content Resistance  - v  176  -  on  Constant  Cyclic  182 195  VIII.  DISCUSSION AND INTERPRETATION OF TEST RESULTS  212  7.1  Sand F a b r i c  215  7.2  I n t e r p r e t a t i o n o f F a c t o r s Which Produce and C o n t r o l Water P l u v i a t e d Sand F a b r i c  218  7.2.1  Sample P r e p a r a t i o n  219  7.2.2  Sample C o n s o l i d a t i o n  223  7.2.3  Compression Loading Response  231  7.2.4  Extension  233  7.2.5  Stress Reversal  237  7.2.6  The E f f e c t o f S t r e s s H i s t o r y Upon CSR  241  7.3  Loading Response  I n t e r p r e t a t i o n o f F a c t o r s Which Produce and C o n t r o l M o i s t Tamped Sand F a b r i c  242  V I I . PRACTICAL IMPLICATIONS  247  IX.  262  SUMMARY AND CONCLUSIONS  REFERENCES  270  APPENDIX A:  Membrane P e n e t r a t i o n  Correction  APPENDIX B:  C a l c u l a t i o n o f Membrane S t r e s s C o r r e c t i o n  - vi -  278 283  LIST OF FIGURES Figure 2.1(a)  Page C h a r a c t e r i s t i c monotonic undrained l o a d i n g s t r e s s - s t r a i n response of sandy s o i l s  7  C h a r a c t e r i s t i c monotonic undrained l o a d i n g e f f e c t i v e s t r e s s path response of sandy s o i l s (modified Mohr diagram)  8  Comparison o f undrained monotonic l o a d i n g e f f e c t i v e s t r e s s path response o f two d i f f e r e n t l o o s e sands  12  E f f e c t o f sample p r e - s t r a i n upon t r i a x i a l t e s t undrained monotonic l o a d i n g response ...  15  2.4  S t r e s s - s t r a i n mechanisms i n an i d e a l i z e d two dimensional s o i l s t r u c t u r e  19  2.5  Mohr's c i r c l e f o r s t r e s s e s r e q u i r e d t o cause s l i p on a p a r t i c l e c o n t a c t p l a n e  22  2.6  S t a b i l i t y contours f o r Rowe's p a r t i c u l a t e model as a f u n c t i o n of p a r t i c l e dimension f a c t o r and i n t e r p a r t i c l e c o n t a c t angle  26  Constant i n c r e m e n t a l s t r a i n r a t i o c o n t o u r s f o r Rowe's p a r t i c u l a t e model as a f u n c t i o n o f p a r t i c l e dimension f a c t o r and i n t e r p a r t i c l e c o n t a c t angle  27  Undrained c y c l i c l o a d i n g response of an a n 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 sandy s o i l subject to l i m i t e d l i q u e f a c t i o n  34  T y p i c a l undrained c y c l i c l o a d i n g response o f an 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 sandy s o i l t r i a x i a l t e s t sample  35  3.1  Schematic l a y o u t of l o a d c o n t r o l l e d c y c l i c t r i a x i a l t e s t i n g apparatus  42  3.2  G r a d a t i o n o f Ottawa C-109  47  3.3  G r a d a t i o n s o f Kamloops s i l t and v a r i o u s c l e a n Brenda t a i l i n g s sands t e s t e d  49  G r a d a t i o n s o f s i l t y 20/200 Brenda sands t e s t e d  51  2.1(b)  2.2  2.3  2.7  2.8  2.9  3.4  - vii-  sand  tailings  3.5  V a r i a t i o n o f maximum and minimum ASTM v o i d r a t i o s o f s i l t y 20/200 Brenda sand w i t h s i l t content  56  Comparison o f maximum v o i d r a t i o s o b t a i n e d by a i r p l u v i a t i o n and s l u r r y d e p o s i t i o n o f s i l t y 20/200 Brenda sand  59  Schematic drawing o f s l u r r y d e p o s i t i o n method f o r p r e p a r a t i o n o f t r i a x i a l t e s t sand specimens  72  G r a i n s i z e d i s t r i b u t i o n curves f o r h o r i z o n t a l l y q u a r t e r e d s e c t i o n s o f a water p l u v i a t e d sand sample  82  G r a i n s i z e d i s t r i b u t i o n curves f o r h o r i z o n t a l l y quartered sections of s l u r r y deposited sands  83  R e p e a t a b i l i t y o f s l u r r y d e p o s i t e d Brenda sand t e s t r e s u l t s  86  Comparison o f t e s t r e s u l t s f o r s l u r r y d e p o s i t e d and water p l u v i a t e d 20/40 Brenda sand  88  Comparison o f t e s t r e s u l t s f o r s l u r r y d e p o s i t e d and water p l u v i a t e d Ottawa C-109 sand  89  3.13  U n i f o r m i t y o f sample s t r a i n d u r i n g l o a d i n g ..  94  4.1  T r i a x i a l test isotropic consolidation r e s u l t s f o r l o o s e coarse g r a i n e d 20/40 Brenda t a i l i n g s sand  99  T r i a x i a l test isotropic consolidation results f o r l o o s e medium g r a i n e d 60/100 Brenda t a i l i n g s sand  100  T r i a x i a l test isotropic consolidation f o r l o o s e f i n e g r a i n e d 100/140 Brenda t a i l i n g s sand  101  3.6  3.7  3.8  3.9  3.10 3.11  3.12  4.2  4.3  4.4  4.5  results  T r i a x i a l test isotropic consolidation results f o r s i l t y w e l l - g r a d e d 20/200 Brenda t a i l i n g s sand  102  V o l u m e t r i c s t r a i n s o f v a r i o u s c l e a n sands d u r i n g i s o t r o p i c c o n s o l i d a t i o n from l o o s e s t state of s l u r r y deposition  104  - viii  -  4.6  V o l u m e t r i c s t r a i n s o f s i l t y 20/200 Brenda sand d u r i n g i s o t r o p i c c o n s o l i d a t i o n from loosest state of s l u r r y deposition  105  Bulk modulus o f v a r i o u s c l e a n Brenda sands d u r i n g i s o t r o p i c c o n s o l i d a t i o n from l o o s e s t state of s l u r r y deposition  107  Bulk modulus o f s i l t y 20/200 Brenda sands d u r i n g i s o t r o p i c c o n s o l i d a t i o n from l o o s e s t state of s l u r r y deposition  108  4.9  Summary o f c o m p r e s s i b i l i t y c h a r a c t e r i s t i c s o f s i l t y w e l l - g r a d e d 20/200 Brenda t a i l i n g s sand  109  4.10  Summary o f i n i t i a l c o m p r e s s i b i l i t y c h a r a c t e r i s t i c s o f s i l t y w e l l - g r a d e d 20/200 Brenda t a i l i n g s sand  110  S t r a i n paths o f v a r i o u s isotropic consolidation slurry deposition  112  4.7  4.8  4.11  4.12  5.1  c l e a n sands d u r i n g from l o o s e s t s t a t e o f  Incremental s t r a i n r a t i o s o f v a r i o u s sands d u r i n g i s o t r o p i c c o n s o l i d a t i o n loosest state of s l u r r y deposition  clean from  113  V e r i f i c a t i o n o f independence o f e f f e c t i v e s t r e s s path from t o t a l s t r e s s path i n undrained monotonic compression l o a d i n g o f Brenda 20/40 sand  118  5.2  Undrained monotonic t r i a x i a l t e s t r e s u l t s f o r 20/40 Brenda sand  120  5.3  Undrained monotonic t r i a x i a l t e s t r e s u l t s f o r 60/100 Brenda sand  121  5.4  Undrained monotonic t r i a x i a l t e s t r e s u l t s f o r 20/200 Brenda sand  122  5.5  Undrained monotonic t r i a x i a l t e s t r e s u l t s f o r v a r i o u s sand g r a d a t i o n s  123  5.6  P l o t o f Henkel's Pore P r e s s u r e Parameter 'a' Versus S t r a i n f o r V a r i o u s G r a d a t i o n s of Undrained Brenda Sand  127  Undrained monotonic t r i a x i a l t e s t r e s u l t s f o r s i l t y 20/200 Brenda sand  140  5.7  - ix -  5.8  V a r i a t i o n o f near l o o s e s t s t a t e s i l t y 20/2 00 sand undrained f r i c t i o n angles w i t h s i l t content  142  T y p i c a l undrained c y c l i c l o a d i n g response o f i s o t r o p i c a l l y consolidated s i l t y well-graded 20/200 Brenda sand  147  6.2  Development o f shear s t r a i n i n w e l l - g r a d e d 20/200 sand d u r i n g c y c l i c l o a d i n g  151  6.3  V a r i a t i o n o f boundary envelope f r i c t i o n during c y c l i c mobility loading  155  6.4  V a r i a t i o n o f maximum boundary envelope f r i c t i o n angle o f s i l t y w e l l - g r a d e d 20/200 Brenda sand w i t h s i l t content and sand skeleton r e l a t i v e density  156  6.5  C y c l i c l o a d i n g s t r e s s - s t r a i n response o f w e l l - g r a d e d sand a t low s t r a i n l e v e l  158  6.6  C y c l i c l o a d i n g s t r e s s - s t r a i n response o f w e l l - g r a d e d sand s u b j e c t t o l i m i t e d l i q u e f a c t i o n i n extension loading  159  6.1  6.7 6.8  6.9  6.10  6.11  6.12  6.13  angle  Development o f c y c l i c m o b i l i t y s t r a i n i n l o o s e s i l t y w e l l - g r a d e d 20/200 Brenda sand  ..  160  V a r i a t i o n o f pore p r e s s u r e g e n e r a t i o n i n l o o s e c l e a n 20/200 sand w i t h change i n c y c l i c stress ratio  165  V a r i a t i o n o f pore p r e s s u r e g e n e r a t i o n w i t h s i l t content i n 20/200 sand s u b j e c t t o limited liquefaction  169  V a r i a t i o n o f pore p r e s s u r e g e n e r a t i o n w i t h s i l t content i n 20/200 sand s u b j e c t t o limited liquefaction  170  V a r i a t i o n o f pore p r e s s u r e g e n e r a t i o n w i t h s i l t content i n 20/200 sand not s u b j e c t t o limited liquefaction  171  V a r i a t i o n o f pore p r e s s u r e g e n e r a t i o n w i t h s i l t content i n 20/200 sand not s u b j e c t t o limited liquefaction  172  V a r i a t i o n o f pore p r e s s u r e g e n e r a t i o n i n c l e a n w e l l - g r a d e d 20/200 sand w i t h change i n r e l a t i v e density  174  - x -  6.14  V a r i a t i o n o f pore p r e s s u r e g e n e r a t i o n i n c l e a n w e l l - g r a d e d 20/200 sand w i t h change i n r e l a t i v e density  175  V a r i a t i o n o f pore p r e s s u r e g e n e r a t i o n i n c l e a n 20/200 sand w i t h c y c l i c l o a d i n g shear strain level  177  C a l c u l a t i o n o f i r r e c o v e r a b l e work absorbed by a s o i l specimen from s t r e s s - s t r a i n response observed d u r i n g c y c l i c l o a d i n g  179  V a r i a t i o n o f pore p r e s s u r e g e n e r a t i o n i n l o o s e c l e a n 20/200 sand w i t h h y s t e r e t i c work absorbed d u r i n g c y c l i c l o a d i n g  180  V a r i a t i o n o f pore p r e s s u r e g e n e r a t i o n i n l o o s e t o dense c l e a n 20/200 sand w i t h h y s t e r e t i c work absorbed d u r i n g c y c l i c l o a d i n g ....  183  6.19  C y c l i c l o a d i n g l i q u e f a c t i o n r e s i s t a n c e curves o f c l e a n 20/200 Brenda sand  185  6.20  C y c l i c loading l i q u e f a c t i o n resistance curves o f s i l t y (4.3% s i l t ) 20/200 Brenda sand  186  C y c l i c loading l i q u e f a c t i o n resistance c u r v e s o f s i l t y (7.5% s i l t ) 20/200 Brenda sand  187  C y c l i c loading l i q u e f a c t i o n resistance curves o f s i l t y (13.5% s i l t ) 20/200 Brenda sand  188  C y c l i c loading l i q u e f a c t i o n resistance curves o f s i l t y 20/200 sand a t near l o o s e s t state of s l u r r y deposition  189  C y c l i c loading l i q u e f a c t i o n resistance curves o f c l e a n 20/200 Brenda sand  191  C y c l i c loading l i q u e f a c t i o n resistance curves o f s i l t y (4.3% s i l t ) 20/200 Brenda sand  192  C y c l i c loading l i q u e f a c t i o n resistance curves o f s i l t y (7.5% s i l t ) 20/200 Brenda sand  193  C y c l i c loading l i q u e f a c t i o n resistance curves o f s i l t y (13.5% s i l t ) 20/200 Brenda sand  194  6.15  6.16  6.17  6.18  6.21  6.22  6.23  6.24 6.25  6.26  6.27  - xi -  6.28  6.29  6.30  6.31  6.32  6.33  6.34  6.35  6.36  6.37  6.38  6.39  6.40  C y c l i c loading l i q u e f a c t i o n resistance curves o f s i l t y (4.3% s i l t ) 20/200 Brenda sand  196  C y c l i c loading l i q u e f a c t i o n resistance curves o f s i l t y (7.5% s i l t ) 20/200 Brenda sand  197  C y c l i c loading l i q u e f a c t i o n resistance curves o f s i l t y (13.5% s i l t ) 20/200 Brenda sand  198  V a r i a t i o n o f s i l t y 20/200 sand r e s i s t a n c e t o l i q u e f a c t i o n i n 10 l o a d c y c l e s w i t h c o n s o l i dation void r a t i o  199  V a r i a t i o n o f s i l t y 20/200 sand r e s i s t a n c e t o l i q u e f a c t i o n i n 20 l o a d c y c l e s w i t h c o n s o l i dation void r a t i o  200  V a r i a t i o n o f s i l t y 20/200 sand r e s i s t a n c e t o l i q u e f a c t i o n i n 50 l o a d c y c l e s w i t h c o n s o l i dation void r a t i o  201  V a r i a t i o n o f s i l t y 20/200 sand r e s i s t a n c e t o l i q u e f a c t i o n i n 100 l o a d c y c l e s w i t h consolidation void ratio  202  V a r i a t i o n o f s i l t y 20/200 sand r e s i s t a n c e t o l i q u e f a c t i o n i n 10 l o a d c y c l e s w i t h r e l a t i v e density  204  V a r i a t i o n o f s i l t y 20/200 sand r e s i s t a n c e t o l i q u e f a c t i o n i n 20 l o a d c y c l e s w i t h r e l a t i v e density  205  V a r i a t i o n o f s i l t y 20/200 sand r e s i s t a n c e t o l i q u e f a c t i o n i n 50 l o a d c y c l e s w i t h r e l a t i v e density  206  V a r i a t i o n o f s i l t y 20/200 sand r e s i s t a n c e t o l i q u e f a c t i o n i n 100 l o a d c y c l e s w i t h r e l a t i v e density  207  Summary o f t h e v a r i a t i o n o f s i l t y 20/200 sand c y c l i c s t r e n g t h w i t h v a r i a t i o n o f s i l t content a t c o n s t a n t sand s k e l e t o n r e l a t i v e density  209  V a r i a t i o n o f s i l t y 20/200 sand c y c l i c s t r e n g t h w i t h s i l t content a t c o n s t a n t c y c l i c stress ratio  211  - xii -  7.1  S t a b i l i t y contours f o r Rowe's p a r t i c u l a t e model as a f u n c t i o n o f p a r t i c l e dimension f a c t o r and i n t e r p a r t i c l e c o n t a c t angle  220  Constant incremental s t r a i n r a t i o c o n t o u r s f o r Rowe's p a r t i c u l a t e model as a f u n c t i o n of p a r t i c l e dimension f a c t o r and i n t e r p a r t i c l e c o n t a c t angle  222  7.3  Range o f s t a b l e p a r t i c l e c o n t a c t s a f t e r consolidation  224  7.4  Range o f s t a b l e p a r t i c l e c o n t a c t s a f t e r isotropic consolidation  7.5  Range o f p a r t i c l e c o n t a c t s which undergo Mode B s l i p i n t h e t r a n s f o r m a t i o n from K isotropic consolidation  7.2  7.6  K  Q  225  Q  to  226  Range o f p a r t i c l e c o n t a c t s which a r e subjected t o s l i p i n extension loading, a f t e r a K and i s o t r o p i c c o n s o l i d a t i o n s t r e s s history  234  Zone o f s t a b l e p a r t i c l e c o n t a c t s a t h i g h s t r e s s r a t i o d u r i n g compression l o a d i n g  238  Explanation of the large contractive s t r a i n s associated with p r i n c i p a l stress r e v e r s a l f o l l o w i n g l o a d i n g t o a h i g h s t r e s s r a t i o ....  240  Undrained l o a d i n g response o f Ottawa sand C109 a t v a r i o u s d e n s i t i e s  249  Change i n l a t e r a l t o t a l s t r e s s w i t h change in e f f e c t i v e stress state  260  U n i t membrane p e n e t r a t i o n o f v a r i o u s Brenda sand g r a d a t i o n s determined by t h e s i n g l e specimen method  280  S t r a i n i n v a r i o u s g r a d a t i o n s o f Brenda sand under v i r g i n i s o t r o p i c c o n s o l i d a t i o n and unloading  281  0  7.7 7.8  8.1 8.2 A.l  A.2  A. 3  S t r a i n i n Ottawa sand C109 d u r i n g i s o t r o p i c v i r g i n consolidation  and u n l o a d i n g  282  B. l  Rubber membrane s h e l l  285  B.2  Measurement o f membrane modulus a f t e r Bishop and Henkel (1962)  290  - xiii  -  C y l i n d r i c a l rubber membrane s t r e s s c o r r e c t i o n v e r i f i c a t i o n by t r i a x i a l t e s t c o n s t a n t r a t e o f s t r a i n l o a d i n g o f a Geotest membrane f i l l e d w i t h water  -  xiv -  LIST OF TABLES Table  Page  3.1  Brenda mine t a i l i n g s sand mineralogy  48  3.2  Physical properties of materials tested  52  5.1  Sand sample undrained f r i c t i o n angles  131  - xv -  NOTATIONS CSR  Critical  effective stress ratio  Dr  Relative  density  Dr D r  Relative density a f t e r consolidation  c  c(skel)  e e e  S a n c  * skeleton  Void  r e l a t i v e density a f t e r consolidation  ratio  Void r a t i o a f t e r consolidation  c  c(skel)  e.:,Dr^ J  S a n c  * skeleton void r a t i o a f t e r consolidation  I n i t i a l d e n s i t y a f t e r set-up and c o n s o l i d a t i o n t o 20 kPa  J  N  Number o f l o a d i n g  N-L  Number o f l o a d i n g c y c l e s t o i n i t i a l l i q u e f a c t i o n (2.5% s t r a i n )  U  Porewater p r e s s u r e  AU  Excess porewater p r e s s u r e  £ ,€ ,e a  r  v  cycles  A x i a l , r a d i a l and v o l u m e t r i c  strain  €^£3  S t r a i n s i n maximum and minimum s t r e s s d i r e c t i o n s  ^ult  Undrained l o a d i n g boundary envelope e f f e c t i v e f r i c t i o n angle  ^p  Effective friction  t  o' ,o' a  a' ,a 1  r  / 3  angle a t phase  A x i a l and r a d i a l e f f e c t i v e s t r e s s Maximum and minimum e f f e c t i v e s t r e s s  CT^  Deviator  a'  Effective isotropic consolidation  c  transformation  stress  a'2c  Effective confining  m  Membrane p e n e t r a t i o n  B  Bulk modulus d u r i n g  stress  stress f a c t o r (see Appendix A) consolidation  x v i  -  ACKNOWLEDGEMENTS  The Y.P.  author expresses  Vaid,  h i s thanks t o h i s s u p e r v i s o r , Dr.  f o r h i s guidance  during  this  research.  The  author a l s o wishes t o thank Dr. D. Negussey f o r h i s a d v i c e during Finn  t h e course  of the laboratory  f o r reviewing  the  work,  manuscript  and  and Dr. W.D.L. making  helpful  suggestions.  The h e l p f u l d i s c u s s i o n s w i t h my c o l l e a g u e s i n  the  Soil  Graduate  Mechanics  Laboratory  a t U.B.C. a r e a l s o  Engineering  Department Workshop  appreciated. The with  help  of the C i v i l  t h e development and c o n s t r u c t i o n o f t e s t  gratefully  acknowledged.  Mrs. K e l l y  Lamb  equipment i s  i s thanked f o r  p r e p a r a t i o n o f t h e manuscript. F i n a n c i a l support p r o v i d e d by t h e U n i v e r s i t y o f B r i t i s h Columbia  and t h e N a t u r a l  Science  and E n g i n e e r i n g  Research  C o u n c i l o f Canada i s acknowledged w i t h deep a p p r e c i a t i o n .  -  xvii  -  1  CHAPTER 1 INTRODUCTION  The  occurrence  during  rapid  soils  engineering  Extensive 1964  and  loading  has  been  research  damage due  earthquakes  sparked  o f sand l i q u e f a c t i o n or l o s s o f s t r e n g t h  to s o i l  in  the  in  focus  the  (Japan)  considerable  past  foundation  Niigata  of  fifty  f a i l u r e s during and  effort  has  loading gone  into  behaviour the  e v a l u a t i o n techniques, testing,  and  the  of  the  saturated  development  of  undrained  sand.  sand  Much  liquefaction  including laboratory testing,  development  dynamic l o a d i n g behaviour  of  the  (U.S.A.)  Alaska  c o n s i d e r a b l e i n t e r e s t i n understanding  dynamic  years.  in situ  p r e d i c t i v e models.  of sand has  The  been shown t o be  the  c r i t i c a l d e s i g n f a c t o r i n many g e o t e c h n i c a l p r o j e c t s . In  the  past,  an  understanding  sand l i q u e f a c t i o n behaviour t e s t s and  observations.  strength  properties  applicable  to  in  the  the  and  (2)  determined field  considered:  in  the  does  the  laboratory  problems,  (1)  two  i s the s o i l  laboratory  stability these  i n o p i n i o n about  evaluation  questions.  To  can  soil  sample t e s t e d  in situ  soil  testing  often  address  behaviour  be  these  are  fundamental  and  directly questions  being  technique  employed s i m u l a t e the l o a d i n g c o n d i t i o n s t h a t occur Differences  of  has been d e r i v e d from l a b o r a t o r y  l a b o r a t o r y r e p r e s e n t a t i v e of the  modelled;  fundamentals  To ensure t h a t fundamental m a t e r i a l  practical  q u e s t i o n s must be  of  in situ.  methods  of  a t t r i b u t e d to one  must  be  2  able  t o define  conditions.  representative  This  i s a very  i n situ difficult  soil  process,  properties  a r e dependent upon many d i f f e r e n t  addition,  the loading  element  are  conditions  difficult  to  on  any  quantify  and  loading as  soil  factors.  In  specific  because  soil  they  are  c o n t r o l l e d t o a l a r g e extent by t h e mechanical p r o p e r t i e s o f adjacent  soil  elements.  Material  changed d r a m a t i c a l l y by t h e process Most  fundamental  liquefaction performed  conducted  poorly-graded  may  studies  i n the past clean  sands,  of  sand  have  been  to  homogeneity and r e p e a t a b i l i t y o f s o i l samples f o r comparison  of  encountered  results.  Many  i n geotechnical  well-graded.  In  order  liquefaction susceptibility be  useful  gradation This  to identify upon  has been  natural  design to  problems  Some s i l t y the  past,  sample  and  contradictory conclusions and  sand  gradation  researchers. or  moist  content sand  as a major r e s e a r c h  laboratory  or the  and  samples.  o b j e c t i v e by  engineering.  methods test  employed i n evaluation,  as t o t h e e f f e c t s o f s i l t  have  are  sands have been t e s t e d i n  b u t due t o t h e d i f f e r e n t  preparation  which  sands, i t would  of laboratory  and well-graded  systematic  are s i l t y  of s i l t  the U.S. N.R.C. (1985) r e p o r t on earthquake  ensure  evaluate  o f such i n s i t u  the e f f e c t s  identified  sands  successfully  t h e behaviour  a l s o be  of loading.  laboratory  behaviour  using  properties  been  reported  by  content various  Samples have g e n e r a l l y been prepared i n a d r y  state.  Such  sample  preparation  methods  do not  3  simulate  the  natural water. to  depositional  fluvial  deposits,  A majority  are  of  deposited  hydraulic  sediment  practical by  a r t i f i c i a l hydraulic f i l l Previous  where  of  fill  settles  concern  natural  in  fluvial  deposition  of  laboratory  compression  or  placement.  l a b o r a t o r y t e s t i n g programs performed on  type  triaxial  prone  geotechnical  and w e l l - g r a d e d sand have a l s o g e n e r a l l y c o n c e n t r a t e d particular  or  through  o f l o o s e sandy m a t e r i a l s which are  l i q u e f a c t i o n and  designs  fabric  strength  loading,  even  test, though  silty on  one  such  as  numerous  l a b o r a t o r y t e s t r e s u l t s have shown sand s t r e n g t h  properties  t o be h i g h l y dependent upon d i r e c t i o n and  loading.  This sand  thesis  response,  understanding fluvial and  and  presents  with of  the  hydraulic  f i n e s content  on  the  a  systematic  objective  behaviour fill  and  sands.  study  of  The  by adding v a r i o u s p r o c e s s e d sand. gradations  Silty  i s ensured by use  improved  of  e f f e c t s of  natural gradation  investigated.  employed t o  sands were  percentages o f a c o h e s i o n l e s s Identical s o i l  undrained  an  performance  undrained behaviour are  w e l l - g r a d e d sands.  of  gaining  S e l e c t i v e s i e v i n g o f a t a i l i n g s sand was u n i f o r m and  type o f  mineralogy  obtain  simulated  silt  to  i n various  the soil  o f the same parent m a t e r i a l .  Fundamental s t u d i e s o f m a t e r i a l behaviour r e q u i r e t e s t s on  homogeneous  specimens.  Homogeneity  specimens i s mandatory i n o r d e r properties. developed  of  laboratory  test  t o determine elemental  soil  Consequently, a s l u r r y method o f d e p o s i t i o n  that  y i e l d s homogeneous specimens o f  was  well-graded  4 as w e l l  as s i l t y  simulates  well  hydraulic f i l l  sands.  the  T h i s method o f sample  placement  or f l u v i a l  sand  of  sand  through  preparation water  in a  deposit.  The b e h a v i o u r o f each m a t e r i a l a f t e r c o n s o l i d a t i o n from loosest  state  undrained extension effect  of  slurry  monotonic  deposition  loading  is  conditions.  studied Both  of loading  cyclic  determine  triaxial  and compression t e s t s a r e conducted t o e x p l o r e d i r e c t i o n upon m a t e r i a l  properties.  b e h a v i o u r o f s i l t y sand a t v a r i o u s d e n s i t i e s i s a l s o under  under  if  loading. there  is  Test a  results  systematic  behaviour w i t h change i n g r a d a t i o n  are  and s i l t c o n t e n t .  The  studied  evaluated  variation  the  in  to sand  5  CHAPTER 2 THE UNDRAINED BEHAVIOUR OF SAND - BACKGROUND CONCEPTS  S e v e r a l approaches have been developed f o r modeling evaluating  soil  conditions,  based  laboratory mechanical  and  behaviour upon  field  the  under observed  soils.  behaviour  undrained  The  modeling  behaviour  different  can  be  loading  of various  approaches  divided  groups: 1) l i m i t s t a t e models where a s o i l  and  to  into  two  i s deemed e i t h e r  s t a b l e when a p p l i e d shear s t r e s s i s below shear s t r e n g t h o r u n s t a b l e when shear s t r e s s  i s above shear s t r e n g t h ,  strain  where  soil  development  models  are d i r e c t l y  strains  related to stresses applied.  models have been developed s p e c i f i c a l l y of  failure,  similar  to  where that  soil  i s observed  a  viscous f l u i d .  of  models have been developed specifically to  f o r use  f o r denser s o i l s  flow f a i l u r e ,  undesirable  but  strains  applicability  of  cyclic  given  soil  i n the  field,  l o a d i n g which w i l l  and  in  a  manner  development analysis,  not be s u s c e p t a b l e be  model  conditions the  flow  subject  loading  the  exists  forms  may  soil  modeled,  f o r flow s l i d e  i n numerical  s t a b i l i t y problem  a  state  Strain  n e v e r t h e l e s s may  under  any  which  within  2)  Limit  to  method t o a s p e c i f i c being  induced  and  to  large  conditions.  The  or  soil  evaluation  i s determined by the  under  mechanism  be a p p l i e d t o the s o i l .  of  which  the  expected  soil field  6 2.1  MONOTONIC LOADING BEHAVIOUR  The  range o f undrained monotonic l o a d i n g  response 1969,  of  sand  is  shown  C a s t r o e t . a l . , 1982,  characteristic sand and  of  in  response  a  characteristic  sand and  1  and  behaviour.  In  behaviour has  dilative  2  Types 1 and exhibited  with  flow  response  confusion  Type  1  soils  with  resonse  liquefaction.  2 are  by  loose Type l  failure.  exhibited  Type 3  by  dense  undrained  this  uses of  henceforth  the be  strength  a t constant shear  strength ratio  Type  1969).  1 To  term " l i q u e f a c t i o n " called  steady-state  strength  the  which  shear and  i s considered of  at  sand,  effective  called t o be and  unlimited  the  uniquely is  be  (which may  be  preparation),  strain  history  called  limited  (Castro,  of  sample  1982).  liquefaction  "limited"  implies  that  softening  after  minimum  a  Type (Castro,  strain in  2  r e l a t e d to to  affected  method  confining  believed  structure  the  response 1969).  hardening undrained  shear  steady-state  independent o f f a c t o r s such as s o i l by  softening  manner,  l i q u e f a c t i o n (Castro,  other  shear  This  void  in  strain  In Type 1 response, sand u l t i m a t e l y reaches a  occur  stresses.  represent  responding  will  constant  s t r a i n may  response  been c a l l e d  avoid  the  Castro,  sand a t lower e f f e c t i v e c o n f i n i n g s t r e s s e s .  Type  minimum  (e.g.,  effective confining stress.  response i s g e n e r a l l y a s s o c i a t e d is  2.1.  Chern, 1985).  contractive  sand a t h i g h e r  Figure  stress-strain  or has The  prior been term  follows  strain  strength.  This  Figure 2.1(a)  Characteristic monotonic undrained loading s t r e s s strain response of sandy soils  Figure 2.1(b)  Characteristic monotonic undrained loading effective stress path response of sandy soils (modified Mohr diagram)  CD  9  s t r a i n hardening confining  t h a t i s accompanied by i n c r e a s i n g e f f e c t i v e  stress  and d e c r e a s i n g  pore  pressure  l i m i t s the  amount o f shear s t r a i n p o s s i b l e under c o n s t a n t shear  2.1.1  C r i t i c a l Stress Ratio Line Critical  principal either types  stress  steady-state i s triggered.  (Vaid  ratio  and  liquefaction  or  limited  s o f t e n i n g sand i n t r i a x i a l  Chem,  liquefaction  1985; Chung, in triaxial  compression l o a d i n g  1985) b u t dependent extension  Other r e s e a r c h e r s such as Sladen  Castro  t o the e f f e c t i v e  CSR has been shown t o be unique f o r a  deposition void ratio 1985).  (CSR) r e f e r s  s t r e s s r a t i o a t which c o n t r a c t i v e deformation o f  given s t r a i n  loading  (Chung,  (1982) however, show t e s t d a t a which i m p l i e s t h a t CSR  compression l o a d i n g . their  upon  e t . a l . (1985) and  v a r i e s as a f u n c t i o n o f c o n f i n i n g s t r e s s l e v e l  specimen p r e p a r a t i o n by moist  fabric  method.  is difficult Chung  in triaxial  These d i f f e r e n c e s may be a t t r i b u t e d t o tamping  p l u v i a t i o n by V a i d and C h e m and Chung. and  stress.  (1985)  as opposed t o  Specimen u n i f o r m i t y  t o c o n t r o l by t h e moist shows  that  triaxial  tamping  extension  CSR  v a l u e s a r e c o n s i d e r a b l y lower than compression CSR v a l u e s .  2.1.2  Phase T r a n s f o r m a t i o n The  point  increasing  a t which  and s t a r t s  State t h e induced  decreasing  pore  i n responses  l i q u e f a c t i o n o r d i l a t i v e type sand behaviour "phase t r a n s f o r m a t i o n  pressure of  stops limited  has been termed  s t a t e " ( I s h i h a r a e t . a l . , 1975).  In  10 the  former  effective  case, stress  this path  state  apears  diagram  as  an  (see F i g u r e  elbow  on an  2.1(b)).  The  f r i c t i o n angle a t phase t r a n s f o r m a t i o n s t a t e has been shown t o be unique f o r a g i v e n sand different (Negussey phase  sands  (Vaid and Chem, 1985) .  i t i s dependent  e t . a l . , 1988).  transformation  mobilized  a t steady  Under  angle state  Negussey  the  and under angle  e t a l . , 1988).  soil  undrained  equals  e q u a l s c o n s t a n t volume f r i c t i o n 1985;  upon  mineralogy loading, the  friction  drained  <f>  angle  loading i t  (Vaid  and Chem,  passing  t h e phase  cv  After  Among  t r a n s f o r m a t i o n s t a t e , t h e e f f e c t i v e s t r e s s path moves up t o and  f o l l o w s t h e undrained  failure  the l i n e o f maximum o b l i q u i t y  2.1.3  Steady-State If  t h e sand  undrained  steady-state 1982).  line. that  represents  ( I s h i h a r a e t . a l . 1975).  response  type  (or e f f e c t i v e  1, v o i d  confining  a r e assumed u n i q u e l y r e l a t e d  This relationship  pressure  that  Concepts shows  strength  envelope  between v o i d  ratio  pressure)  and at  (Castro e t a l . ,  ratio  and c o n f i n i n g  ( o r undrained s t r e n g t h ) i s c a l l e d t h e s t e a d y - s t a t e  The s t e a d y - s t a t e l i n e separates  initial  has been used  states  of  sand  as a boundary  into  regions of  c o n t r a c t i v e and d i l a t i v e behaviour. Steady-state drained ratio  triaxial  (Casagrande,  concepts tests  were  originally  and t h e concept  1975) .  developed  from  of c r i t i c a l  void  The a p p l i c a b i l i t y o f s t e a d y - s t a t e  concepts t o undrained l o a d i n g c o n d i t i o n s was p o s t u l a t e d f o r  11  several  years,  experimental undrained  until  evidence  in  dilative  concepts  c o n t r a c t i v e and behaviour  concepts.  from  one  have  be  transformation  a  soil  depending  explained  liquefaction  which stage  steady-state s t a t e as  to  slope  concepts  steady-state. stability  the  i s o n l y achieved  2.2).  dilation  of  limited  type  level.  of  stress  Most  have  soil strain  researchers  treated  phase  T h i s treatment  analyses  (1982) suggests  after a l l soil  very  large  dilation  undrained  Figure different  phase t r a n s f o r m a t i o n w e l l as s o i l d e n s i t y .  2.2 soils  also  based  on  adds  steadyto  ignored.  that  steady-state  i s complete, which  strength  shows  be  steady-state  if  a  s u b s t a n t i a l l y d i l a t i v e p a s t phase t r a n s f o r m a t i o n Figure  state  because the e f f e c t s o f s t r e n g t h g a i n due  contrast, Castro  at  either  The  o f the  d i l a t i o n a f t e r phase t r a n s f o r m a t i o n s t a t e are  be  is  on  using  d e f i n e d as s t e a d y - s t a t e .  s t a t e concepts,  may  extensive  depending upon s t r a i n  limited  must d e c i d e  used  conservatism  that  failure,  dilative,  the  i s indeed  In  first  response shows t h a t a s o i l may  cannot  For  response,  who  support  the  r e l a t i v e t o the s t e a d y - s t a t e l i n e .  l i q u e f a c t i o n type o f s o i l  curve  provided  Concepts  imply  or contractive to  the s o i l  Such  its  C r i t i q u e o f Steady-State  Steady-state  both  (1969)  compression t e s t s on s e v e r a l moist tamped sands.  2.1.3.1  of  Castro  that  which have been  the  soil  state degree  is (see of  s t r a i n e d past  s t a t e i s dependent upon s o i l A s o i l such as Ottawa C-109  type sand  as may  Figure 2.2  Comparison of undrained monotonic loading effective stress path response of two different loose sands  13 have a l i m i t e d a  l i q u e f a c t i o n type o f response y e t s t i l l  substantially  sand  such  h i g h e r u l t i m a t e undrained  as Brenda  sand,  which  does  have  s t r e n g t h than  not show  a  a  limited  l i q u e f a c t i o n type o f response. V a i d and C h e m and  (1985) t r e a t e d both l i m i t e d  steady-state  framework.  They  transformation unique  types  state  stress  compression  response  considered  relationship  confining  of  f o r limited between  (or  loading  stress  tests.  within  a  unified  conditions at  liquefaction  void  ratio  undrained  liquefaction  This l i n e  and found  and  strength)  phase a  effective  in  triaxial  a l s o encompassed t h e  s t e a d y - s t a t e data i f t h e t r u e s t e a d y - s t a t e type o f response was observed i n undrained l o a d i n g . Several  r e s e a r c h e r s have  shown t h a t  at a given  void  r a t i o and s t r e s s - s t a t e , undrained response o f sand may be a f u n c t i o n o f sample f a b r i c . t e c h n i q u e o f sample may  be a r e s u l t  (1982)  show  strain  response  through  there between  a i r , 2)  i s governed  f o r m a t i o n and any s t r a i n  of past  that  Sand f a b r i c  moist  s e i s m i c events. is a sands  large  tamping,  Miura  and  by 3)  I s h i h a r a and Okada (1978, 1982) and Chung undrained response (even  though  direction  opposite  to  to a  subsequent  C o n v e r s e l y , undrained response pre-straining  lower  that  and T o k i  i n stress-  1) moist  pluviation rodding.  (1985) show t h a t  i s s o f t e n e d i f t h e sand  reconsolidated  history  difference  prepared  by t h e  i s pre-strained  void  ratio)  undrained  i s strengthened by  i n t h e same d i r e c t i o n o f subsequent  in a  loading. initially undrained  14  reloading  (see F i g u r e  direction  opposite  initially  dilative  2.3).  A  large  pre-strain  t o subsequent s h e a r i n g sand  into  a  in a  may t r a n s f o r m  contractive  sand  an  (Chung,  1985). The  undrained  sensitive  to  consequence degree  of  soils  direction  of  loading.  of s o i l s  of this  fabric. sand  the  response  being  anisotropy  Chung  stress  loading.  state,  extension  weaker  contractive  This  related  undrained water  in triaxial  At a given  compression  initial  behaviour  could  (see F i g u r e  difference  undrained shown  between  loading  t o occur  extension softer research  triaxial  response.  void  to  soil  than i n  r a t i o and  be d i l a t i v e and  2.3).  Miura  extension  et.  al.  t e c h n i q u e upon and compression  The g r e a t e s t  difference i s Undrained  response i n a l l cases i s shown t o be  considerably  weaker  than  sand  The  specimens.  and  i n pluviated  is a  pluviated  extension  (1982) show t h e e f f e c t o f sample p r e p a r a t i o n the  particularly  anisotropic.  i s intimately  (1985) shows t h a t  i s considerably  compression  inherently  is  compression  response.  Recent  on t h e undrained behaviour o f water p l u v i a t e d  sand  u s i n g t h e h o l l o w c y l i n d e r d e v i c e shows s i m i l a r dependence o f undrained behaviour on t h e d i r e c t i o n o f l o a d i n g al., is  1985, Shibuya and Hight,  shown t o be l e a s t c o n t r a c t i v e  liquefaction and the  1987).  i n the t r i a x i a l  Water p l u v i a t e d  and l e a s t s u s c e p t a b l e  compression  most c o n t r a c t i v e o r most s u s c e p t a b l e triaxial  extension  mode  of  (Symes e t . sand to  mode o f l o a d i n g , to liquefaction i n  loading.  Directional  TRIAXIAL TEST COMPRESSION LOADING  ^  DIRECTION OF PRESTRAIN LOADING  vO^V^  ©  iti^ss'  /  L?J  ®  CD  V\  (3)  ^^\:  /  EFFECTIVE STRESS PATHS \  >  -  ®  X V  Figure 2.3  S  DEPOSITED  COMPRESSION  ;  © %  EXTENSION LOADING  A  /  \ TRIAXIAL TEST  EXTENSION  AFTER ISHIHARA ET. AL. (1 982) ^  ^ ^  A  \  \  N  D  CHUNG (1985)  \  Effect of sample pre—strain upon triaxial test undrained monotonic loading response  16  dependence  o f response  may  be q u a l i t a t i v e l y  explained i n  r e l a t i o n t o t h e f a b r i c o f sand.  2.2  SOIL FABRIC  Although  several  identified  the  anisotropy  in  researchers  effects  of  laboratory  s t r u c t u r e s and mechanisms  soil test  and  generally  only  i n practice,  macroscopic  qualitatively  derived  from  particles.  the  have  Home, 1965).  while  soil  reasons  neglected i s  as an  and  fabric  described  isotropic  anisotropy  interaction  of  Others  the  models t o r e l a t e  are  discrete  of  soil stress  1962,1971;  (Oda e t a l . , 1972,1974,1978,1985)  spacial  dependence o f o v e r a l l arrangement  of  methods  have  attempted t o  based on simple  soil  particles.  (1980), Matsuoka e t a l .  e t a l . (1982)  analytical  the effects  ( f o r example Rowe,  the s i g n i f i c a n t  upon  Mehrabadi  particles.  fabric  microscopic  Workers such as Nemat-Nasser  statistical  physical  The  relatively  attempted t o a n a l y z e  have r e c o g n i z e d  and  assessed.  been  upon an assembly o f p a r t i c l e s  properties  the  V a r i o u s workers i n t h e f i e l d o f p a r t i c u l a t e  mechanics have  and  resulting  inadequately  most models t r e a t  continuum,  and  which produce and c o n t r o l  have been r e l a t i v e l y  that,  and  results,  anisotropy  and a n i s o t r o p y  observed  fabric  and  fabric  have  (1980)  formulate  particulate  macroscopic behaviour t o t h e mechanics o f  17 Of past,  a l l the particulate the simplified  (1962,1971)  and Home  soil  models  physical  model  (1965)  provides  described  described  i n the by  perhaps  the best  p h y s i c a l d e s c r i p t i o n o f t h e f a c t o r s which c o n t r i b u t e fabric. basis  The p a r t i c u l a t e model d e s c r i b e d f o r h i s stress-dilatancy  representation  of the physical  a work f u n c t i o n  t o derive  t o sand  by Rowe forms t h e  theory.  A  mathematical  p a r t i c u l a t e model i s used i n  the stress-dilatancy  equation R =  KD, where R i 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 , constant  which  i s dependent  f r i c t i o n of the surface  Rowe  upon  the i n t r i n s i c  of individual s o i l  K i sa  angle o f  p a r t i c l e s , and D  i s t h e d i l a t a n c y produced by a p p l i c a t i o n o f t h e s t r e s s r a t i o R  (D = - 2 d e / d € 3  for triaxial  1  stress-dilatancy  equation  compression  has  been  loading).  shown  to  represent the mono-directional drained loading a  large  equation  number  of different  has a l s o  been  shown  fabric,  anisotropy,  1972b).  Although  the  of s o i l  fabric  independent  does n o t imply  that  stress  behaviour o f  materials.  stress  dilatancy test  The  of  direction  s t r e s s - s t r a i n behaviour  (Oda,  equation results,  soil  is this  i s independent  Drained s t r e s s - s t r a i n response has  anisotropy  of principal stress  direction  (Oda, 1972b,1981; A r t h u r and  Menzies, 1972; Negussey, 1984). the  adequately  independent  f o r drained  been shown t o be a f u n c t i o n soil  t o be  or p r i n c i p a l  of d i r e c t i o n o f l o a d i n g .  which i m p l i e s  particulate  The  This  apparent c o n f l i c t o f  non-dependence o f t h e s t r e s s d i l a t a n c y  equation y e t the  dependence o f s t r e s s - s t r a i n response upon s o i l a n i s o t r o p y i s  18 due  t o t h e f a c t t h a t t h e s t r e s s d i l a t a n c y e q u a t i o n i s based  upon  stress  and  strain  ratios,  not  the  magnitude  p r i n c i p a l s t r e s s e s and s t r a i n s .  Although i n c r e m e n t a l  magnitudes  at  ratio  different  under  incremental  a  given  stress  different  strain  ratio  may  directions  i s shown  be of  to  strain  considerably loading,  be  of  the  independent  of  d i r e c t i o n of loading. The  p h y s i c a l model which Rowe used t o d e r i v e t h e s t r e s s  d i l a t a n c y e q u a t i o n may be used t o e x p l a i n why s t r e s s - s t r a i n behaviour stress  i s dependent  direction,  upon  although  soil  anisotropy  t h e model  d e r i v e d nor employed t o e x p l a i n s o i l ideas  behind  section.  t h e model  The  mechanisms subsequently  model  was  used  to  which  control  soil  used  to explain  and  not  anisotropy.  a r e summarized is  and p r i n c i p a l  i n the  explain  originally The b a s i c following  factors  anisotropy, interpret  and  and  is  observed  test  results.  2.2.1  Rowe's S o i l P a r t i c l e I n t e r a c t i o n Model A  soil  uniformly shown (R)  sample  is  idealized  as  shaped p a r t i c l e s i n c o n t a c t  i n Figure  required  2.4.  an  with  assemblage  one another, as  The e x t e r n a l l y a p p l i e d  t o cause movement  on c o n t a c t  the  internal  Mohr's  stress  diagram  level  f o r stress  on  particle  conditions  stress  planes  s t r a i n i n t h e two dimensional model i s d e r i v e d dimensions o f t h e i d e a l i z e d s o i l s t r u c t u r e  ratio  and thus  from: (1) the  ( F i g u r e 2.4); (2)  contacts; on  of  a  and  contact  (3)  plane  19  CJ  v  G  a  (b) S i n g l e  (a)  Idealized  soil  structure  ( c )  Elemental  repetitive  free  body  CO.  |3 = I n t e r p a r t i c l e  contact angle  c-  hB  factor CT " P r i n c i p a l  stress  (1  5  °  Deformation  £  =  Strain  0  = I n t r i n s i c angle of  friction  0  = Mobilized  friction  angle  F i g u r e 2.4  Stress-strain  M  two  a  h  V  mechanisms i n an  dimensional  soil  structure  idealized  element  diagram  F i g u r e 2. 4 (d)  V a r i a t i o n of <=* and p  5  strain  level  parameters with  21  (Figure  2.5).  The  parameters; the p,  and  the  structure  inclination  may  o f the  be  defined  particle  by  contact  two  plane,  shape of a s i n g l e r e p e t i t i v e element, d e f i n e d  by  the s t r u c t u r e dimension f a c t o r a. The  model  may  f i r s t mode (Mode A) and  undergo was  slip  analyzed  in  only  two  by Rowe and  modes. other  The  workers,  i n v o l v e s movement i n the d i r e c t i o n o f maximum p r i n c i p a l  stress  ( F i g u r e 2.4c).  The  second mode o f movement (Mode B)  has not been p r e v i o u s l y i d e n t i f i e d ; t h i s i s p r o b a b l y because it  involves  of  maximum  external p r i n c i p a l stress.  Mode B movement i s o n l y  possible  for  particle  those  particle  movement  combinations contact  against  of  angle  0  the  direction  dimension  where  the  factor a  maximum  and  internal  p r i n c i p a l s t r e s s d i r e c t i o n at a contact plane i s opposite  to  the e x t e r n a l maximum p r i n c i p a l s t r e s s d i r e c t i o n . The required derived  mathematical to  cause  representation  strain  i n the  i n S e c t i o n 2.2.1.1.  two  of  the  stress  dimensional  ratio  model  is  22  2.2.1.1  Mathematical Representation of Stress—Strain Behaviour in Rowe's Two Dimensional Particulate Structure  From particle dimensions shown in Figure 2.4:  —  = tan  «  —  r5  =  tan  h  j  a L v  Oh  v  = —  t  n  =  —  v  cr  v *h  V  CT Q tan (JS) h  c  9  CT t a n ( « ) tan( fi)  v  h  MODE A DEFORMATION: and  5 t, v  r5hA  directions,  (see Figure 2.4)  Figure 2.5a  r 5 strain A v  in s a m e direction as CJ  Mohr's circle for stresses required to cause slip on a particle contact plane and produce MODE A deformation  °i  tan  =  Q-  (j  3  h  (P+0 )  tan (/3 )  M  =  Minimum stress ratio required to cause slip  23  CRITERION FOR MODE A DEFORMATION:  Cr  '  f  > CT  tan(0+&)  v  "fl^  CT  tan"(flf  <  CT  tan  CT  CT  V  V  h  h  CT CT  n 0 S  "P  +  tan(«) tan(jS)  CT If  —  < tan  +  tan ( « )  n  o  s  |j  p  E  q  n2  . 1  a  h  CT l f  > tan (0 + 1) tan ( « )  —  slip  Eqn. 2.1b  h  .  Sm  L  Z  =  v  £  h  77~7\  tan ( p + fl.) tancx + 1  m  g  tan (fi+fa)tan  .  -1 tanfJ tanoc  Eqn. 2.2  E c  ! - n  2  3  MODE B DEFORMATION:  and  (5VB (see  directions, C 5 « B strain against direction of CT  Figure  Figure 2.5b  2.4)  Mohr's circle for stresses required to cause slip on a particle contact plane and produce MODE B deformation  on contact plane to produce slip  °i  °h  CJ  CT  3  v  t  a  n  (/0  tan ( B - 0 J  Minimum stress ratio required to cause slip  CRITERION FOR MODE B DEFORMATION:  If  & - <  tan  h  no slip  tan(p-&)  a CT If  (p) ——  tan ( p ) ;  -z- £ (J  cr V  cr  h  — -  tan(p-i)  cr V  a t a n ( « ) tan(|3) h  slip  CT < cr V  25  cr If  —  > tan ( p - n p  tan ( « )  no slip  £  < tan  tan (tx)  slip  Eqn. 2.4b  q n  .  2.4a  0" If h  _ Sin  0 m  =  tan (  tan« - 1  tan ( P - 0 J  tan« + 1  ^ Eqn. 2.5  -1 tanp t a n «  E c  1 n  Z  6  Equations 2.1 and 2.4 are plotted as c o n s t a n t stress ratio c o n t o u r s in Figure 2.6.  The c o n t o u r s s e g r e g a t e an inner zone  of stable particle c o n t a c t population f r o m outer z o n e s of unstable particle c o n t a c t p o p u l a t i o n s .  Equation 2.6 which  defines the strain ratio derived f r o m slip under either MODE A or MODE B d e f o r m a t i o n is plotted in Figure 2.7.  Although strain  ratio is not a f u n c t i o n of m o d e of d e f o r m a t i o n (MODE A and MODE B), the degree of v o l u m e c h a n g e or dilatancy is a f u n c t i o n of m o d e of d e f o r m a t i o n .  When MODE A d e f o r m a t i o n is contractive,  MODE B d e f o r m a t i o n is dilative, and when MODE A d e f o r m a t i o n is dilative, MODE B d e f o r m a t i o n is c o n t r a c t i v e at a given strain ratio, unless strain ratio equals — 1 . 0 , in which c a s e no volume c h a n g e o c c u r s under any m o d e of d e f o r m a t i o n .  F i g u r e 2.6  S t a b i l i t y c o n t o u r s f o r Rowe's p a r t i c u l a t e model as a f u n c t i o n p a r t i c l e d i m e n s i o n f a c t o r « and i n t e r p a r t i c l e c o n t a c t a n g l e jS  I N T E R P A R T I C L E CONTACT ANGLE  JS  (DEGREES)  of  7  Constant  incremental  strain  ratio  contours  I N T E R P A R T I C L E CONTACT ANGLE  f o r Rowe's p a r t i c u l a t e  jS  (DEGREES)  model  28  D i s c u s s i o n o f Rowe a P a r t i c u l a t e Model  2.2.1.2  /  Equation ratio  2.1  required  respectively  and to  within  Equation cause the  2.4  Mode  show  A  model  that  and  the  stress  B  strain  Mode  particulate  structure  of  F i g u r e 2.4(a) i s a f u n c t i o n o f angle o f p a r t i c l e c o n t a c t fi, and  structure  model, a level.  is a  function  a.  factor of  spherical  the  idealized  dimensions  and  strain  i n nature (Rowe's o r i g i n a l in  Figure  p a r t i c l e c o n t a c t angle fi c o u l d a l s o v a r y w i t h  strain  level.  assumed  Within  particle  I f p a r t i c l e s were rounded  analysis 2.4d),  dimension  particles  S i n c e t h e developed  friction  as  shown  angle o f the  material  i s calculated  from the s t r e s s r a t i o r e q u i r e d t o cause  t h e developed  f r i c t i o n angle i s a l s o shown t o be a  slip,  function  o f p a r t i c l e c o n t a c t angle fi and s t r u c t u r e dimension f a c t o r a (see  Equation  friction strain  2.2  angle  and  i s also  Equation a f f e c t e d by  2.5).  Thus  developed  p a r t i c l e dimensions  level.  Figure  2.6  shows  that  the  external  stress  r e q u i r e d t o cause s l i p i n the i d e a l i z e d model may 1.0  (which  implies  slip  isotropic external stress, zero  degrees)  to  a  angle  friction  between p a r t i c l e s ,  fi.  separate  The  much  value  friction  and  and  stress  stable  from  along  or a developed of  stress  g r e a t e r than  ratio  contact  range  surfaces  from under  f r i c t i o n angle of  ratio  the  ratio  or  developed  intrinsic  angle  of  depending  upon the v a l u e s of a  contours  shown  unstable p a r t i c l e  at a p a r t i c u l a r stress r a t i o l e v e l .  in  Figure  2.6  contact populations  The middle zone between  29  two  similar  stress  respectively,  ratio  contours,  represents  a  stable  p o p u l a t i o n under t h e s p e c i f i e d outer  zone  particle  =  -  90, p =  90  population, with s t r a i n particle stress  contacts ratio.  structure under  with  no  strain  combination ratio.  type B.  stable  unstable  The o u t e r  a t an  zone  particle  model,  i f a  of a  combination  until  particle  to increasing the p a r t i c l e  that the s t r a i n  unstable  stress  ratio  and p stress contact  o f a and p i s s u b j e c t e d t o an u n s t a b l e  structure  The  function of external  i s subjected  F i g u r e 2.4(d) suggests  reduction  an  an u n s t a b l e  t o be a  i s induced  contact  The middle zone o f s t a b l e  the idealized  stress  A.  represents  a specific  isotropic  ratio,  the  In  type  strain  ratio.  0 represents  strain  i s shown  particle  external stress  p =  0,  population with  a  towards  a  towards  o f Mode A and B  stress  induced i n  may  cause  i n a and p v a l u e s , which may cause l a r g e  a  strains  o r a c o l l a p s e i n t h e s t r u c t u r e u n t i l a s t a b l e combination o f  a and p i s induced by s t r a i n . The volume  two dimensional model a l s o shows how d i l a t a n c y o r change  during  contact structure.  shear  may  The p r i n c i p a l  be  affected  by  particle  s t r a i n r a t i o f o r both Mode  A and Mode B s t r a i n may be c a l c u l a t e d u s i n g E q u a t i o n 2.3 o r 2.6.  I f the p r i n c i p a l  s t r a i n r a t i o equals -1.0, t h e r e i s no  change i n volume d u r i n g shear. than  -1.0, then  I f the s t r a i n r a t i o  the structure contacts  shear under Mode A s t r a i n , b u t d i l a t e s B strain.  When t h e s t r a i n  ratio  i n volume  i s less during  i n volume under Mode  i s g r e a t e r than  -1.0, t h e  30  structure  expands  contracts  under  i n volume  Mode  contours c a l c u l a t e d 2.7.  This  B  under  strain.  Mode  A  strain,  Constant  from E q u a t i o n  2.3  strain  a r e shown  but ratio  i n Figure  f i g u r e shows how both s t r a i n r a t i o and d i l a t a n c y  are a f u n c t i o n o f a and fi p o p u l a t i o n .  The s t r a i n induced by  a change i n s t r e s s r a t i o i s dependent upon t h e p o p u l a t i o n o f a and fi which was p r e v i o u s l y  within  the stable  zone but i s  now exposed t o an u n s t a b l e zone as s t r e s s r a t i o i s changed. In  order  increasing in  ratio  combinations may  be  shown  push  i n an  homogeneous  expected  in a  have  an  into  incremental  models  shown  variably  a  and  increase fi  value  the stable  zone.  fashion  i n t h e two  i n Figure  sized,  structures  anisotropic  or  d i r e c t i o n s of loading.  reversed  or  principal  2.4, but  variably  maximum  i n Figure variable  shaped  would  2.4  can be  response  to  I f stress d i r e c t i o n s are and  minimum  i n t e r c h a n g e d , t h e p r e v i o u s combination values  under  induced by an  unstable  different  contact  structure  such as sand.  two p a r t i c u l a t e  to  stable  of p a r t i c l e contacts  particulate material The  a  the s t r a i n  must  not o c c u r  structurally could  maintain  stress ratio,  stress  This  to  become a' =  stresses  are  o f a and fi p a r t i c l e  (90-a)  and fi' =  (90-fi) .  T h i s change i n a and fi v a l u e s f o r t h e same p a r t i c l e c o n t a c t configuration structure stable  would  considerably  structure  direction  tend  t o make a p r e v i o u s l y  less  considerably  of loading.  stable, more  or a stable  more  stable  previously under  the  less new  The s t r e s s - s t r a i n response observed  31  under  the  reversed  substantially  direction  different  from  observed under t h e p r e v i o u s  that  the  models  also  and show  of  a  not of  model  which  could  may  have  that  particulate  loading  material  under  response  loading.  is a  but  these  resistance  f a c t o r s may  Some key p o i n t s of  soil  The  function  shown i n F i g u r e  a l l t h e mechanisms which a f f e c t shear  behaviour.  friction  controls  of  level.  dimensional s t r u c t u r e  particulate soils,  how  been  2 . 4 a r e not a  shown i n F i g u r e  t h e model  does  contribute  provide  insight  resistance,  to d i r e c t i o n a l  t o consider  i s not o n l y  2 . 4 can  resistance  i n t o some o f t h e f a c t o r s which c o n t r o l s h e a r i n g and  be  conditions.  d i l a t a n c y behaviour  s t r e s s d i r e c t i o n and s t r a i n The two  loading  o f the s t r u c t u r e o f sand, they do show  structure  stress-strain  that  loading  Although t h e s t r u c t u r e s true representation  of  a r e : 1)  governed by  soil  frictional  the  intrinsic  angle o f the p a r t i c l e s which make up t h e s o i l ,  but  a l s o by t h e s p a c i a l r e l a t i o n s h i p between p a r t i c l e s which  may  be d e s c r i b e d  as s o i l  structure or s o i l  fabric;  2) a random  assemblage o f s o i l p a r t i c l e s may have a complex d i s t r i b u t i o n of  interparticle  contact  angles  and  soil  particle  o r i e n t a t i o n s ; 3) t h e f a c t o r s which make up c o h e s i o n l e s s fabric,  such  orientation, altered  by  as and  interparticle position  a change  of  contact  angle,  particles,  can  i n method o f placement  s t r a i n s ; 4 ) d i l a t a n c y i s governed by s o i l  soil  spacial  be  easily  o r by  induced  s t r u c t u r e ; and 5)  a s o i l may show d i f f e r e n t d i l a t a n c y response when  subjected  to d i f f e r e n t directions of loading. In  a  natural  distribution Slip  soil  o f contact  i s generally  particle respect which  contacts  slip  more  to  or  a  complex  orientations.  occur  on  particular  are p r e f e r e n t i a l l y oriented  loading  fabric that  is  and p a r t i c l e  likely  which  during  may  Particle  be r e o r i e n t e d  i s able  alternatively disturb  f a b r i c t o reduce  2.3  angles  there  t o the d i r e c t i o n of loading.  more s t a b l e load,  structure  contacts  t o develop  t o support g r e a t e r other  with  parts  a  applied  of the  soil  cyclic  and  strength.  CYCLIC LOADING BEHAVIOUR  There  are  many  monotonic l o a d i n g 1985;  behaviour  Chung, 1985).  ratio  lines  monotonic soil  are  subjected  independent Many  i s dilative  monotonic  (Castro,  1982; V a i d  of  mode  researchers  have  may  loading.  develop This  and Chem,  and c r i t i c a l  the  and develops  loading  to cyclic  between  Both s t e a d y - s t a t e  or c y c l i c .  which  under  simularities  only  of  stress loading,  found  that  limited  large  a  strain  strains  when  i s a consequence o f t h e  development o f c y c l i c m o b i l i t y . C y c l i c l o a d i n g l e a d s t o a gradual as pore p r e s s u r e low  shear s t r a i n  about  s o f t e n i n g o f response  and shear s t r a i n develop. occurs u n t i l  60% o f t h e i n i t i a l  In general,  a pore p r e s s u r e  effective stress  very  i n excess o f has  developed  (Seed, 1979).  S t r a i n development d u r i n g  be due t o : 1) s t e a d y - s t a t e together  1969; Seed,  1979).  The  m o b i l i t y s t r a i n i s represented diagram  by  movement  up  o r 2) c y c l i c development  Figure  2.9).  A  and down  transient  s t r e s s occurs a t the point The  magnitude  cyclic  of cyclic  loading  mobility  of  t h e undrained  contrast,  state  phases o f l o a d i n g o f zero  when t h e shear  mobility  strain  effective  stress  i s zero.  developed  i s governed by r e l a t i v e d e n s i t y .  mobility  a looser  strain,  loading. occurrence  even  sand  of  may  develop  very  i f i t i s dilative  Cyclic mobility limited  cyclic  friction  strain  may  large  under  develop  liquefaction,  or  during  I f a sand  i s dense i t may develop o n l y l i m i t e d c y c l i c m o b i l i t y In  may  on t h e e f f e c t i v e s t r e s s path  envelope i n both compression and e x t e n s i o n (see  loading  or l i m i t e d l i q u e f a c t i o n (classed  as c o n t r a c t i v e deformation),  (Castro,  cyclic  strain. cyclic  monotonic  without the  following  the  o c c u r r e n c e o f l i m i t e d l i q u e f a c t i o n (see F i g u r e 2.8). Due t o t h e v a r i o u s mechanisms which a r e r e s p o n s i b l e f o r s t r a i n development d u r i n g  cyclic  loading  ( i . e . steady-state  l i q u e f a c t i o n , l i m i t e d l i q u e f a c t i o n , o r c y c l i c m o b i l i t y ) , the r e s u l t s o f c y c l i c l o a d i n g a r e g e n e r a l l y a s s e s s e d i n terms o f a strain criterion.  The c y c l i c s t r e n g t h  or resistance of a  sample i s d e f i n e d as t h e c y c l i c s t r e s s amplitude r e q u i r e d t o cause a s p e c i f i e d l e v e l o f s t r a i n number o f l o a d c y c l e s .  (2, 5, o r 10%) i n a f i x e d  0 CYCLIC LOADING FROM A STATE OF ANISOTROPIC  CYCLIC MOBILITY LOADING  0  CONSOLIDATION  LIMITED LIQUEFACTION  ( L X + C T )/2 MONOTONIC LOADING  CYCLIC MOBILITY LOADING CYCLIC LOADING  AXIAL STRAIN £„ (%) Figure 2.8  Undrained cyclic loading response of an anisotropically consolidated sandy soil subject to limited liquefaction  35  Figure 2.9 Typical undrained cyclic loading response of an isotropically consolidated sandy soil triaxial test sample CYCUC MOBILITY LOADING  o  COMPRESSION  a.  CM  b  - 2 0 -  -60 -  w  100  200  (LT'<)/2  300  EXTENSION —i  400  (kPa)  150 - i SILTY 2 0 / 2 0 0 BRENDA SAND  ^—-  a 0_  "—'  100 50-  4.55% SILT CONTENT e = 0.673 c  Dr.= 4 6 %  0'd/ 0i2  to I  b°  0 -50-100  DEVELOPMENT OF CYCLIC MOBILITY STRAIN  -  -150- 115  -10  -5  AXIAL STRAIN  5  10  £.(%)  24  NUMBER OF LOAD CYCLES  N  26  36 2.4  THE EFFECT OF GRADATION AND FINES UNDRAINED LOADING RESPONSE OF SAND  Few of  and  fines  response o f sand. of preparing  This  laboratory  researchers  have  the  undrained  specimens  are  soil  studied  employed  t o the  specimens.  elemental  have  on  i s p r i m a r i l y due  soil  of who  sand  content  homogeneous t e s t  determination  silty  the  moist  for  or  air  specimens.  and  s i l t y sands found i n the f i e l d are fundamental  affect soil  deposited  and  and  Poulos  prepared  by  relative  density,  moist  (1976)  of  tamping.  studied  effect  upon  angularity.  rounded  or  grains  steady-state to  Ishihara undrained  When  gradation  mineralogy and  difficult  silty  does the method of sample p r e p a r a t i o n  the  effect  g r a d a t i o n upon s t e a d y - s t a t e behaviour o f sand u s i n g  lower  which  response.  Castro  magnitude  Many  question  must be addressed i n the e v a l u a t i o n o f w e l l - g r a d e d sand p r o p e r t i e s i s how  of  pluviation  well-graded  A  test  Most  properties  the  w i t h i n water.  the  properties.  for  settlement  loading  required  strength  of  effect  Homogeneous w e l l  tamping  preparation  THE  difficulty  techniques  by  ON  s t u d i e s have been conducted t o determine the  gradation  mixed  CONTENT  higher void  is  compared  shown  steady-state Sands w i t h C  u  show a  in  to  have  line  as  samples  terms the  of  same  changes  in  g e n e r a l l y more w e l l  general  ratios.  of  trend  Absolute  towards  trends  are  identify. et  cyclic  al.  (1980)  triaxial  present test  the  program  results  of  conducted  an to  i n v e s t i g a t e the  cyclic  t a i l i n g s sands and  resistance  slimes.  o f v a r i o u s types o f mine  Sand samples were a i r p l u v i a t e d  and e i t h e r tamped or v i b r a t e d t o the r e q u i r e d d e n s i t y b e f o r e saturation  with  from s l u r r y .  water.  Slimes  samples  were c o n s o l i d a t e d  When compared i n terms o f v o i d r a t i o , v a r i o u s  g r a d a t i o n s o f mine t a i l i n g s sands are shown t o have or s l i g h t l y  lower  cyclic  s t r e n g t h than  sands.  Slurry  reconstituted  to  cyclic  resistance  have  tailings  sands,  generally  while  greater  clean poorly-graded  c o h e s i o n l e s s s l i m e s are  similar  cohesive  cyclic  similar  to that  slimes  resistance  of cohesionless  are  than  shown  shown  to  either  have  tailings  sands o r non-cohesive s l i m e s . Lee and  Fitton  (1969) show t h a t w e l l - g r a d e d sands have  c y c l i c s t r e n g t h s s i m i l a r t o those o f p o o r l y - g r a d e d sands o f the  same r e l a t i v e  pluviation  in  density.  a i r and  in  Samples were prepared water.  The  by  undrained  both  loading  response o f w e l l - g r a d e d but non-homogeneous segregated water p l u v i a t e d sand  i s compared w i t h t h a t of l e s s segregated a i r  p l u v i a t e d sand. sand The  has  a higher  cyclic  (1969)  I t i s shown t h a t water p l u v i a t e d  is  cyclic  s t r e n g t h than  strength of s i l t y similar  to  segregated  unsegregated  sand.  sands t e s t e d by Lee and  that  of  clean  sands  at  Fitton  the  same  r e l a t i v e d e n s i t y , although the data s e t shown i s t o o l i m i t e d t o make broad  generalizations.  S l a d e n e t . a l . (1985) have a l s o used the moist t e c h n i q u e o f sample p r e p a r a t i o n t o determine silt  content  upon  steady-state  strength  tamping  the e f f e c t in  of  triaxial  38  compression the  loading.  failure  of  T e s t r e s u l t s were used t o  hydraulically  Nerlerk  berm  island  content  is  shown  i n the to  the  conclusion  reduce  that  susceptible to liquefaction Verdugo  Beaufort  in  silty  are  Silt  strength  l e a d i n g Sladen  sands  sands.  tamping.  et. a l .  always  c l e a n sands.  isotropically  r a t i o , Troncoso decreases  with  consolidated  and  cyclic  samples  at  more  Troncoso  T h e i r samples were a l s o prepared  From r e s u l t s o f s t a t i c  by  moist  triaxial the  silt  content;  2)  and  Chilean  tests  same  void  and Verdugo show: 1) d r a i n e d f r i c t i o n increasing  the  sea.  steady-state  ratio,  than  sand  (1985) d e r i v e s i m i l a r c o n c l u s i o n s f o r s i l t y  tailings  on  silty  Canadian  considerably at a given void to  placed  back-analyse  angle  higher  silt  c o n t e n t makes the sand l e s s d i l a t i v e d u r i n g d r a i n e d l o a d i n g ; 3) undrained level  decreases  pressure more  dynamic shear modulus as a f u n c t i o n o f with  increasing  generation during c y c l i c  easily  i n sands  with  a  silt  content;  undrained  higher  silt  strain  4)  loading content;  pore occurs  and  c y c l i c s t r e n g t h decreases s u b s t a n t i a l l y w i t h i n c r e a s i n g  5) silt  content. Many o f the c o n c l u s i o n s d e s c r i b e d above c o n c e r n i n g effect  of  g r a d a t i o n and  under s t a t i c be  due  types  to  and  the  tested;  preparation; comparison,  and  cyclic  fines  content  3)  behaviour  l o a d i n g are c o n f l i c t i n g .  following factors: 2)  upon s o i l  differences differences  1) in  This  differences method  i n method  of  the  in  may soil  of  sample  soil  density  f o r example c o n s t a n t v o i d r a t i o v e r s u s  constant  relative  density versus  constant  compactive  effort  applied  d u r i n g sample p r e p a r a t i o n . The method of sample p r e p a r a t i o n and the r e s u l t i n g fabric  have been shown t o  undrained  have a g r e a t  i n f l u e n c e upon  behaviour of sand (see S e c t i o n s 2.1  (1974) shows the extent technique  on  undrained prepared  by  compared.  strength  both  2.2).  of  well-graded  well-graded  p l u v i a t i o n i n a i r and  Sample  and  Ladd  preparation  method  sand. silty  moist  is  The sands  tamping  shown  to  was  have  l a r g e e f f e c t on c y c l i c s t r e n g t h a t a g i v e n v o i d r a t i o . pluviated  sand  is  comparable moist similar test In fines  the  shown  tamped  to  be  sand.  up  to  Mulilis  50%  et  i n t e r p r e t a t i o n of upon  soil  the  effect  behaviour  one  e f f e c t o f sample p r e p a r a t i o n technique.  of  gradation  and  must  recognize  the  If test results  to  be modelled must be sands  of  ensured.  interest  through deposits,  in  water, it  is  such  expected  range  of  density  the  This  can  only  expected method o f  be field  soil and  field  investigations  are  as  hydraulic  in  fill  or  reproduce  similar  I t i s a l s o important  t o know  and  to  stress  behaviour p o s s i b l e within a h y d r a u l i c f i l l deposit.  are  Since many w e l l - g r a d e d  imperative  f a b r i c i n l a b o r a t o r y samples. the  than  a l . (1977) show  be meaningful, s i m u l a t i o n o f the f a b r i c o f the f i e l d  fluvial  Air  weaker  to  deposited  a  results.  content  silty  the  o f the e f f e c t of sample p r e p a r a t i o n  the behaviour o f s i l t y  cyclic  soil  achieved  by  deposition  path  dependent  or f l u v i a l  simulating i n the  field  closely  preparation  of  laboratory  range  of  samples  loading  Unfortunately, thought water, Fitton,  simple  t o best results  systematic  a  paths water  simulate  They  laboratory tests.  anticipated pluviation  samples in  o f sand  well-graded  condition  o f element  the  o f sand,  for a  t o the field.  which i s  deposited i n  samples  can not be c o n s i d e r e d  necessary  assessment  subjecting  the f a b r i c  i n segregated  1969).  repeatable,  and by  (Lee and  homogeneous o r fundamental  properties  and  i n controlled  41  CHAPTER 3 EXPERIMENTAL WORK  This  chapter  undrained  describes  monotonic  materials  used  and  in  the  1)  the  apparatus  cyclic  triaxial  test  program,  p r e p a r a t i o n t e c h n i q u e developed specimens f o r t e s t i n g purposes,  used  loading, 3)  for  2)  the  the  sample  t o produce homogeneous and 4)  soil  the o b j e c t i v e s o f the  t e s t program.  3.1  TESTING APPARATUS  Triaxial 6.4  cm  specimens were approximately  i n diameter.  T e s t s were conducted  12.7  cm h i g h  u s i n g the  l o a d i n g system d e s c r i b e d by  Chern  triaxial  apparatus  and  schematic  diagram o f the equipment i s shown i n F i g u r e  (1985) .  A x i a l l o a d , c o n f i n i n g c e l l p r e s s u r e , pore p r e s s u r e and displacement coupled  to  were a  data  microcomputer.  3.1.1  measured  using  acquisition  electronic  system  and  A 3.1.  axial  transducers  interfaced  with  a  Volume changes were measured w i t h a p i p e t t e .  Load C o n t r o l l e d system  3.1.1.1  Consolidation  Samples increasing  were  cell  p r e s s u r e o f 100 Anisotropic  isotropically  pressure kPa  consolidated  i n reservoir  ( v a l v e s 1,  3 and  A  and  by using  6 open and  consolidation requires that  cell  stepwise a  back  7 closed) .  pressure  and  ///////s//////  M U I L E ACTING AIR LOAD  PISTON  CELL RATIO  LOAD C O K K E C T I W RIRS  RATIO  =«>=  TO RECORDER  RELAY  RELAY  LVDT '  XL  ELECTROPKEUMTIC TDANSDUCER  A1IAL  CYCLIC  LOAtlW  MOTORIZED PRESSURE REGULATOR  SYSTER  ANISOTROPIC  FUNCTION  CONSOLIDATION  SYSTER ARD STRESS  CONTROLLED  RONOTONIC LOADING  SYSTER  6ENERAT0R  PORE IERO PRESSURE  PRESSURE  TRANSDUCER  DATUX  2 LE6END  ©  PRESSURE  (g)  AIR SUPPLY PRESSURE  TO RECORDER  MUSE  RE6UIAT0R CELL  ®  VRLVE  SNITCH  ///)?>>/>>  PRESSURE  TRANSDUCER  '/ 1 I I I I ) ) 111 I I I  VALVE  Figure 3.1  Schematic  layout o f l o a d c o n t r o l l e d  monotonic  and  cyclic  -KB)  triaxial t e s t i n g  system  a x i a l s t r e s s be ratio.  increased simultaneously i n a  T h i s was  accomplished  predetermined  by f e e d i n g c e l l  p r e s s u r e as a  s i g n a l t o a r a t i o r e l a y and  the output  upper chamber o f the double  acting a i r piston  and  10  open  i n c r e a s e d by  and  6,  9  closed) .  the motorized  o f the r e l a y t o the  The  cell  regulator.  ( v a l v e s 7, pressure  Prior to  8 was  initiating  a n i s o t r o p i c c o n s o l i d a t i o n , both chambers o f the p i s t o n were pressurized difference  to  an  approximate  equal  base  pressure,  s e r v i n g t o compensate the u p l i f t  the  on t h e l o a d i n g  ram d u r i n g s e t t i n g up o f back p r e s s u r e .  3.1.1.2  Monotonic Loading System  Monotonic shear d e c r e a s i n g the double  a i r pressure  acting  regulator.  air  Vertical  compression  t e s t s were conducted  piston  i n one by  Cyclic  increasing  chambers o f  motorized  or the  pressure  l o a d i s i n c r e a s e d t o a c h i e v e monotonic  loading,  Cyclic  o f the the  or  decreased  extension loading at constant c e l l  3.1.1.3  by  to  achieve  monotonic  pressure.  Loading  loading  is  applied  by  means  of  an  e l e c t r o p n e u m a t i c t r a n s d u c e r d r i v e n by a f u n c t i o n g e n e r a t o r . A f t e r c o n s o l i d a t i o n , v a l v e 8 i s c l o s e d and v a l v e 9 opened t o the c y c l i c  l o a d i n g system i n which a p r e s s u r e equal t o  c u r r e n t p i s t o n p r e s s u r e i s p r e s e t by the D.C. function  generator.  electro-pneumatic  The  transducer  low  pressure  i s amplified  o f f s e t on  output by  from  a ratio  the the the  relay  before  admission  piston. Hz  t o one chamber  A sinusoidal cyclic  o f t h e double  load pulse  acting a i r  was a p p l i e d  a t 0.1  and c a l i b r a t e d p r i o r t o s e t t i n g up o f t h e t e s t specimen  by use o f a dummy r o d i n p l a c e o f t h e s o i l A 0.1 hz c y c l i c  loading  rate  sample.  i s generally  slower  a n t i c i p a t e d i n most earthquake l o a d i n g c o n d i t i o n s . the  slower  rate  of  loading  was  chosen  than  However,  for a  better  r e s o l u t i o n o f measurements w i t h t h e data a c q u i s i t i o n system. During  cyclic  loading,  cell  pressure  was  through r e s e r v o i r B r a t h e r than r e s e r v o i r A. a l a r g e bore c o n v e c t i o n any  maintained  This  provided  t o t h e c e l l water and thus prevented  f l u c t u a t i o n s i n c e l l pressure  due t o t h e displacement o f  water by t h e l o a d i n g ram moving i n and out o f t h e c e l l when l a r g e deformations developed.  3.1.2  S t r a i n C o n t r o l l e d T e s t i n g System  T h i s was done u s i n g a simple Wykeham F a r r a n c e Eng. L t d . (Slough, England) s t r a i n c o n t r o l l e d l o a d i n g machine. were conducted minute  to  pressures provide  a t an a x i a l  ensure  in silty  strain  confident  soil  tested  liquefaction. of  loading  pore  o f s t r e s s - s t r a i n and pore  i s subject  The undrained  due t o s o i l  of  to  pressure  tests, especiallyi f  limited  l i q u e f a c t i o n or  response may d i f f e r w i t h  creep.  (Chang e t . a l . , 1982; C a s t r o  water  Strain controlled tests  response than l o a d c o n t r o l l e d t r i a x i a l the  o f 0.5 p e r c e n t p e r  measurement  sand specimens.  a better record  rate  Tests  However,  several  e t . a l . , 1982; C h e m  rate  workers et.  al.,  1985)  report  that  undrained shear p r o p e r t i e s  r e l a t i v e l y unaffected  3.1.3  Resolution The  kPa.  loading  stresses  due  B,  to c e l l  sample  cap r o d area,  strain  direction  were g e n e r a l l y  corrected  Appendix  platen  are  to  0.4  by the r a t e o f l o a d i n g .  A x i a l s t r e s s was in  sand  o f Measurement  measured  described  of  3)  2)  accurate  f o r : 1) membrane l o a d s ,  uplift  pressure  friction  (see Appendix  force  on  the  as  upper  which does not a c t on  on the r o d , depending B) ,  4)  buoyant  weight  on of  l o a d i n g r o d and t o p cap, 5) LVDT s p r i n g f o r c e on sample, and 6)  1/2  total  pressure  and  weight axial  mid sample h e i g h t ,  of the  stress  pressure,  measurements were 3.1.  s t r a i n s was  pore  referenced  to  The r e s o l u t i o n  0.01%.  MATERIALS TE8TED  Ottawa sand  (ASTM-C-109) and Brenda mine t a i l i n g s  were used i n t h e t e s t i n g program. water p l u v i a t e d Chem  Cell  as shown i n F i g u r e  o f v e r t i c a l and v o l u m e t r i c  3.2  sample.  Ottawa  sand  The t r i a x i a l b e h a v i o u r o f  sand has p r e v i o u s l y  (1984), Chung (1985) and o t h e r s . The  been s t u d i e d triaxial  by  loading  b e h a v i o u r o f a p o o r l y - g r a d e d water p l u v i a t e d Brenda sand has been s t u d i e d  by C h e m  grain  and  sizes  (1984) .  gradations  of  In t h i s clean  study, v a r i o u s  Brenda  tailings  mean sand  were t e s t e d i n order t o i n v e s t i g a t e t h e e f f e c t o f g r a i n s i z e and g r a d a t i o n  upon undrained b e h a v i o u r .  Kamloops s i l t  was  mixed  with  examine  Brenda  the  sand  effect  monotonic  and  materials  tested  to  of  cyclic are  generate  silt  silty  content  loading fully  sands  on  response  described  the of  in  and  thus  undrained  sand.  The  the  following  (ASTM d e s i g n a t i o n C-109-69) i s a  subrounded  sections.  3.2.1  General D e s c r i p t i o n of M a t e r i a l s Tested  3.2.1.1  Ottawa Band ASTM-C-109  Ottawa sand  medium q u a r t z sand from Ottawa, I l l i n o i s .  The s t a n d a r d t e s t  sand i s used t o c a l i b r a t e both the t e s t i n g equipment sample p r e p a r a t i o n  t e c h n i q u e used  i n the t e s t  and the  program.  The  p a r t i c l e s i z e d i s t r i b u t i o n o f Ottawa sand i s shown i n F i g u r e 3.2.  3.2.1.2  Brenda T a i l i n g s Sand  Brenda  tailings  sand  copper and molybdenum British  Columbia  was  obtained  mine s i t u a t e d  (Soregaroli,  1974).  from  the  Brenda  i n the Okanogan a r e a , The  tailings  sand i s  c o a r s e t o v e r y f i n e g r a i n e d , s a l t and pepper c o l o r e d a n g u l a r sand  derived  from  g r a n o d i o r i t e rock. shown i n T a b l e  3.1.  mechanically  crushed  unweathered  The mineralogy o f the t a i l i n g s  sand i s  Figure 3.2  Gradation of Ottawa C - 1 0 9 sand  M.l.T GRAIN SIZE CLASSIFICATION SAND COARSE  SILT  MEDIUM  20  1  40  1  111 i i I i—r 1.0 0.5  FINE 60 l  100  i  140 l  COARSE 200 l  U.S.B.S.  i•i r 0.1 0.05 111  GRAIN SIZE  (mm)  MEDIUM SIEVE  FINE SIZE  111 i i | i—r 0.01 0.005  48  T a b l e 3.1  Mineralogy o f Brenda Mine T a i l i n g s Sand  (determined by examining g r a i n s p a s s i n g #20 and r e t a i n e d on #40 s i e v e s ) Plagioclase Feldspar Potassium F e l d s p a r Quartz B i o t i t e Mica Hornblende Heavy M i n e r a l s magnetite,pyrite In sand, set  41% 20% 27% 6% 4% 2%  o r d e r t o formulate a s p e c i f i c g r a d a t i o n o f t a i l i n g s oven d r i e d  o f U.S.  sieves  tailings  standard  f o r twenty  which had been s i e v e d through  #20,  #40,  #60,  minutes  were  taken  weighed t o 0.01 g accuracy, each sample.  #100, from  #140  and #200  storage  and independently  a  jars,  remixed f o r  Three types o f p o o r l y - g r a d e d sand samples were  prepared; t h e f i r s t o b t a i n e d from sand p a s s i n g t h e number 20 and r e t a i n e d on t h e number 40 s i e v e ( c a l l e d 20/40 sand), t h e second o b t a i n e d from sand p a s s i n g t h e number 60 and r e t a i n e d on t h e number 100 s i e v e obtained  from  sand  with  a grain  60/100 sand) and t h e t h i r d  p a s s i n g t h e number  t h e number 140 s i e v e sand  (called  (called  size  100 and r e t a i n e d on  100/140 sand).  distribution  g r a i n e d sand was a l s o prepared  from  A  well-graded  coarse  to  ( c a l l e d 20/200 sand).  fine Grain  s i z e d i s t r i b u t i o n s o f v a r i o u s Brenda sands t e s t e d a r e shown in  F i g u r e 3.3.  3.2.1.3  Kamloops s i l t  Kamloops s i l t was o b t a i n e d from an approximately year  old glacial  lake  deposit  which  occupies  the  10,000 valley  Figure  3.3  G r a d a t i o n s o f Kamloops s i l t t a i l i n g s sands t e s t e d  M.I.T.  GRAIN S I Z E  and v a r i o u s  20  1.0  MEDIUM 40  Brenda  CLASSIFICATION  SAND COARSE  clean  SILT FINE  COARSE  60 100 140 200  U.S. STANDARD SIEVE  0.1 GRAIN S I Z E  MEDIUM  0.01 (mm)  FINE SIZE  surrounding  the  Kamloops s i l t cohesive for  city  Kamloops,  British  Columbia.  i s brownish grey c o l o r e d medium g r a i n e d  inorganic  Kamloops s i l t  1951)  of  silt.  A  obtained  i s shown i n F i g u r e  p r e v i o u s l y used s i l t  grain  distribution  u s i n g the hydrometer t e s t 3.3.  was  size  During the  Various sand target  silt  21%  weight  by  (as  of  were mixed w i t h  described  contents  of  content  in  Section  3.3.2)  approximately 4.3%,  solids.  in  representative  of  The  hydraulic f i l l  grain  size  be  slurry.  homogeneous  silt  intermittent  deposition  particles.  Material  is  homogeneous  within of  sand,  coarser  properties  of  and  such  and  a  range o f probably  natural  been d e p o s i t e d  due  which  to  non-  produced  by  finer  grained  non-homogeneous  s o i l are d i f f i c u l t t o measure o r q u a n t i f y , as such s o i l stratified  3.2.2  the  3.2  presents  materials  is a  s o i l layers.  P h y s i c a l P r o p e r t i e s o f the M a t e r i a l s Table  of  assemblage of l e s s well-graded  and  rapidly  contents  s o i l s are probably  lenses  14%,  The  in  Higher average s i l t  found i n sandy f i e l d  obtain  d i s t r i b u t i o n s of  tested  found  20/200  to  7.5%,  sands  sands, where sand has  through a s i l t y may  silty that  oven d r i e d  Brenda  r e s u l t i n g s i l t y sands are shown i n F i g u r e 3.4. silt  derived  sample.  amounts o f s i l t  samples  (Lambe,  washed t o remove f i n e sand  soil  curve  t e s t i n g program,  from minor p a r t i c l e c r u s h i n g d u r i n g t e s t i n g , and b e f o r e reuse i n a new  non-  Tested  a summary o f the p h y s i c a l p r o p e r t i e s  tested.  The  physical properties  of  the  Figure  3.4  Gradations  of silty  M.l.T.  20/200 B r e n d a  GRAIN S I Z E  20  1.0  MEDIUM 40  sands  CLASSIFICATION  SAND COARSE  tailings  SILT FINE  60 100 140 200  COARSE  U . S . STANDARD S I E V E  0.1 GRAIN S I Z E  MEDIUM  0.01 (mm)  FINE SIZE  tested  TABLE 3.2  MATERIAL  OTTAWA C-109 SAND  Gs  2.67  Physical properties of materials  ASTM VOID RATIO (DRY) MAXIMUM MINIMUM  MAXIMUM SLURRY VOID RATIO DRY SATURATED  tested  GRAIN SIZE (mm) D50 D10  Cu  MEMBRANE PENETRATION FACTOR m (.cm) (see Appendix A)  0.760  0.50  0.770  0.770  0.4  0.25  1.64  0.0048  1,,1370  0..7734  1..1618  1..1576  0..7899 0..7765  1.,1977 1..2017  1..1323 1.,1504  0..8643  0..5180  0,,890  0..447 0..264 0..157 0..109 0..076 0..093  1,.41 1,.29 1,.29 1,.19 1 .20 3..44  0.00566  1..1850 1..1947  0,.595 0,.323 0..192 0..125 0,.088 0,.25  1,,447  0,.012  0..0043 3,.09  BRENDA TAILINGS SAND 20/40 40/60 60/100 100/140 140/200 20/200  2.68 2.68 2.689 2.705 2.705 2.689  KAMLOOPS SILT 2.67  2.,67  0 0 0 0.00078  0  m a t e r i a l s shown i n T a b l e  3.2 a r e d i s c u s s e d and compared i n  the f o l l o w i n g s e c t i o n s .  3.2.2.1  Specific Gravity  The s p e c i f i c g r a v i t y o f Brenda sand i s h i g h e r than t h a t of  Ottawa  sand  Brenda sand. constant,  due t o m a f i c  and minor  i t increases  slightly  g r a i n s i z e due t o a h i g h e r percentage  3.2.2.2  minerals i n  The s p e c i f i c g r a v i t y o f Brenda sand  although  as magnetite  heavy  with  i s fairly decreasing  o f heavy m i n e r a l s  such  i n f i n e r g r a i n e d Brenda sand.  ASTM Standard V o i d R a t i o s  ASTM standard maximum and minimum d r y v o i d r a t i o s were determined  f o r a l l sands  tested.  o b t a i n e d by s l u r r y d e p o s i t i o n method  Maximum  void  (see S e c t i o n 3.3) a r e  a l s o shown i n T a b l e 3.2 f o r comparison.  They a r e i n g e n e r a l  s l i g h t l y l a r g e r than t h e maximum ASTM v o i d r a t i o s . due  t o t h e lower  slurry  energy  deposition  essentially  zero  drop  inch  drop  height.  Grains  are  ratio  This i s using the  deposited  h e i g h t , when d e p o s i t e d  w h i l e ASTM maximum v o i d one  of deposition obtained  method.  ratios  in a  from  slurry,  samples a r e d e p o s i t e d from a  Maximum  simple water p l u v i a t i o n o f sand  void  ratios  achieved  a r e approximately  by  equal t o  those o b t a i n e d by t h e ASTM maximum v o i d r a t i o method. The v a r i o u s p o o r l y - g r a d e d Brenda sand g r a d a t i o n s t e s t e d have s i m i l a r maximum and minimum v o i d r a t i o s . and minimum v o i d r a t i o s o f w e l l - g r a d e d  ASTM maximum  20/200 sand  a r e much  lower  than  particles  those  o f p o o r l y - g r a d e d sands,  due t o  smaller  f i l l i n g v o i d space between l a r g e r p a r t i c l e s .  difference  between  maximum  and minimum  ASTM  void  o b t a i n e d f o r each sand g r a d a t i o n t e s t e d i s s i m i l a r .  The ratios  Rounded  Ottawa C-109 sand on t h e o t h e r hand has much lower maximum and minimum v o i d r a t i o s than a n g u l a r t a i l i n g s sand.  3.2.2.3  Maximum B i l t V o i d R a t i o  Kamloops s i l t  was p l u v i a t e d through both a i r and water  t o determine maximum d r y and s a t u r a t e d v o i d r a t i o s . dry  void  maximum expect  ratio water  was  found  pluviated  d r y maximum  dry  silt  ratio  unsegregated  thus  by s i f t i n g  state  maximum  water  tends  void  t o be  silt would  ratio;  t o segregate  smaller  f o r the following  silt  a  large void  deposition  difference  between  might  than  water  energy  of  must be s i f t e d t o segregate particles  which  t e n d t o produce  and 3) according  be a fundamental d i f f e r e n c e i n s i l t and water  One  r e a s o n s : 1)  higher  silt  to grain  a lower d r y  size,  which  interaction i n  which  d r y and s a t u r a t e d  through  Thus t h e r e must  particle  environments  remain  pluviated  would t e n d t o i n c r e a s e maximum v o i d r a t i o .  air  twice the  o f 1.447.  i n a i r with  2) oven d r i e d  particles,  2.67, almost  ratio  ratio  i s deposited  deposition; silt  void  void  p l u v i a t e d maximum v o i d  t o be  Maximum  produces t h e state  maximum  ratio. During  ratios  t h e d e t e r m i n a t i o n o f maximum  ASTM  dry  f o r f i n e sands i t was observed t h a t p a r t i c l e s  void  carry a  55  s t a t i c charge which i n some cases was l a r g e enough t o expel some h i g h l y charged p a r t i c l e s from t h e c o n t a i n e r they  were b e i n g  dry  maximum  the  repulsion  poured.  void  S i m i l a r l y , the excessively o f 2.67 o f s i l t  of e l e c t r i c a l l y  In t h e s a t u r a t e d neutralized  ratio  state,  by water,  i n t o which  charged  electrical  enabling  large  i s p r o b a b l y due t o dry s i l t  particles.  charges may be somewhat  particles to settle  into a  much denser s t r u c t u r e i n a manner s i m i l a r t o t h a t o f c o a r s e r grained  sand.  3.2.2.4  Maximum and Minimum V o i d R a t i o s  Figure ratios  o f S i l t y Sand  3.5 shows how maximum and minimum d r y ASTM v o i d  and maximum  s l u r r y deposition  void  ratios of  w e l l - g r a d e d 20/200 Brenda sand v a r y w i t h s i l t standard  ASTM  generally 12%  maximum  applicable  density  tests  with  The  a r e not than  f i n e s ( p a s s i n g t h e number 200 s i e v e ) . N e v e r t h e l e s s ,  ASTM  and minimum v o i d  to soils  content.  greater  maximum  considered  and minimum  silty  r a t i o s have been i n c l u d e d  t o show  the d i f f e r e n c e i n v o i d r a t i o s a t t a i n e d by a i r p l u v i a t i o n i n the d r y s t a t e and by p l u v i a t i o n through water. From F i g u r e  3.5 i t i s c l e a r t h a t  pluviation of s i l t y  sand through water y i e l d s a c o n s i d e r a b l y than p l u v i a t i o n through a i r . yields  much  higher  void  d i f f e r e n t material  A i r pluviation of s i l t y  ratios  than  pluviation  through  water, a l t h o u g h i n both cases p a r t i c l e s i z e s e g r e g a t i o n minimum.  The observed behaviour o f s i l t y  t h a t o f pure s i l t ,  sand  i sa  sand i s s i m i l a r t o  where t h e maximum v o i d r a t i o obtained  by  Fig. 3.5 1.0  C o m p a r i s o n of ASTM dry m a x i m u m a n d m i n i m u m v o i d r a t i o s a n d  s l u r r y d e p o s i t i o n m a x i m u m v o i d r a t i o s of silty 2 0 / 2 0 0 B r e n d a  1  i  0  sand  4  8  12  16  20  P E R C E N T A G E SILT CONTENT BY WEIGHT  24  28  pluviation  of s i l t  through  a i r (e = 2.67) i s much  than t h a t o b t a i n e d by p l u v i a t i o n through water  larger  (e = 1.447).  The mechanisms which c o n t r o l t h e l a r g e d i f f e r e n c e i n maximum void  ratios  o b t a i n e d by p l u v i a t i o n  s t a t e are probably s i m i l a r i n s i l t A  major  ratios sands  reason  o b t a i n e d by i s that  i n dry versus and s i l t y  f o r the difference a i r versus  water  through a s i l t y the  siurry  sands.  i n maximum  pluviation  sand has a much h i g h e r t e r m i n a l  s e t t l e m e n t through water than s i l t . slurry,  water  t h e sand  much f a s t e r  When sand  fraction  t h e same manner as through  clean  of  silty  i s deposited  settles  than t h e s i l t  void  velocity of  through  fraction.  c o u l d expect t h e sand t o p l u v i a t e through a s i l t y much  saturated  water,  One  slurry i n unless the  s l u r r y i s v e r y t h i c k and v i s c o u s w i t h a l a r g e f i n e s c o n t e n t . Consequently, one would expect t h e maximum v o i d r a t i o o f t h e sand f r a c t i o n o f a water p l u v i a t e d s i l t y sand t o v a r y with  increasing  fines  fraction  particles.  silt  content,  effectively  on  fills  Mechanical p r o p e r t i e s  the postulate void  space  o f water  little  that  between  pluviated  the sand silty  sand might a l s o be e s s e n t i a l l y c o n t r o l l e d by t h e d e n s i t y o f the  sand f r a c t i o n , o r sand s k e l e t o n v o i d r a t i o , which may be  c a l c u l a t e d u s i n g Eqn. 3.1:  •skeleton = tV G ) /(M-M T  s /  w  s i l t  )] - 1  where: V.p  = t o t a l volume o f t h e specimen  (3.1)  58  G  = s p e c i f i c g r a v i t y o f sand  s  = d e n s i t y o f water M  = t o t a l mass o f s o i l  M ^^^.  = mass o f s i l t  s  e  skeleton  Figure  =  s  3.5  a  n  ratio  20/200  sand  i s i n fact  content  by weight.  through  o f unsegregated  t h e sand  v i s c o u s , and a p p a r e n t l y  t o sand  skeleton  silt  slurry  essentially  u n t i l the s i l t  At large  which  respect  I t may be seen t h a t t h e maximum  void  increasing s i l t 20%  3.6.  skeleton  silty  ratio  i s r e p l o t t e d with  v o i d r a t i o as F i g u r e sand  i n t h e specimen  skeleton void  d  s o l i d s i n t h e specimen  constant  content  contents,  i s pluviating  deposited with  exceeds about  the s i l t y  i s very  slurry  thick  and  i n c r e a s e s maximum sand s k e l e t o n v o i d  ratio. Figure void  3.6  ratios  ratios. shows  also  shows t h e v a r i a t i o n o f sand  calculated  from  ASTM maximum  The ASTM maximum sand that  an  increase  structure  during  contrasts  radically  content  skeleton  in silt  content  a i r pluviation. with  only  minor  This  silty void  skeleton sand  ratio  bulks  curve  the  bulking  influence  void  sand  effect of  silt  upon sand s t r u c t u r e produced by p l u v i a t i o n o f s i l t y  sand through water. The  change i n ASTM minimum v o i d r a t i o w i t h s i l t  shown i n F i g u r e 3.5 i n d i c a t e s t h a t i t becomes more t o compact a d r y sand s k e l e t o n by v i b r a t i o n as s i l t i s increased.  In contrast, a s l u r r y deposited  content difficult content  sand w i t h 20%  F i g . 3.6  C o m p a r i s o n of m a x i m u m void r a t i o s o b t a i n e d by air p l u v i a t i o n slurry d e p o s i t i o n of silty 2 0 / 2 0 0 B r e n d a s a n d  i  0  MAXIMUM VOID RATIO i  4  i  i  8  i  i  12  i  i  16  i  ^  and  ^cB-n°a. i  20  P E R C E N T A G E SILT CONTENT BY WEIGHT  i  i  24  i  28 cn  silt  content  i s found t o have a 100% ASTM r e l a t i v e  density  when c o n s o l i d a t e d t o 350 kPa i s o t r o p i c e f f e c t i v e s t r e s s from an i n i t i a l l y l o o s e s t s t a t e o f s l u r r y d e p o s i t i o n . i s thus much more compressible  when d e p o s i t e d  S i l t y sand  i n a saturated  s t a t e than i n a d r y s t a t e . The 3.6  conclusion  is  that  t h a t may be drawn from F i g u r e s  ASTM  specifications  maximum  provide  a  and  rather  c l a s s i f i c a t i o n of hydraulic f i l l may  also  conclude t h a t  samples may  severely  minimum poor  silty  void  basis  soil  ratio  f o r the  sand b e h a v i o u r .  t h e method o f p r e p a r i n g  affect  3.5 and  fabric  One  silty  sand  and measured  soil  properties.  3.2.2.5  C o e f f i c i e n t of Uniformity  Table  3.2  uniformity of s i l t y content  provides  a  summary  o f t h e sands t e s t e d .  sand shows an abrupt increases  coefficient  of the c o e f f i c i e n t s  Coefficient of uniformity  jump from  from 7.5% t o 14.8%.  of uniformity provides  of  3.7 t o 19 as  This  silt  indicates that  a r a t h e r poor b a s i s f o r  the c l a s s i f i c a t i o n o f s i l t y sand g r a d a t i o n o r i t s behaviour.  3.2.2.6  Membrane P e n e t r a t i o n  Membrane p e n e t r a t i o n were  calculated  test results, Negussey  from  according  (1984).  Factors  corrections  load-unload  f o r t h e sands  isotropic  tested  consolidation  t o t h e method d e s c r i b e d by V a i d and  Membrane p e n e t r a t i o n  factor calculations  are summarized i n Appendix A and t h e c o r r e c t i o n f a c t o r s  'm'  61  at  loosest  density state  f o r t h e v a r i o u s sands t e s t e d a r e  shown i n T a b l e 3.2. Membrane  penetration effects  are small  f o r the w e l l -  graded  20/200 sand, zero f o r f i n e sands w i t h D50 l e s s  0.2 mm  ( g r a i n s i z e l e s s than approximately h a l f t h e membrane  t h i c k n e s s ) , and f a i r l y and Ottawa C-109  3.2.3  l a r g e f o r coarse g r a i n e d Brenda 20/40  sands.  C r i t e r i a f o r Choosing T e s t S o i l s Ottawa sand was chosen as a c o n t r o l  the  than  testing  produce  equipment  test  results  and  the  similar  sand  slurry  t o those  deposited obtained  p l u v i a t e d Ottawa sand by p r e v i o u s workers. Ottawa  sand  also  enabled  comparison  t o show t h a t sample  f o r water  T e s t s on rounded  with  t h e behaviour  of  a n g u l a r Brenda sand. Brenda sand was s e l e c t e d f o r t h e study o f t h e e f f e c t o f silt  content  generally  upon sand  have  behaviour  more  angular  because w e l l - g r a d e d particles,  soils  especially  in  s e i s m i c a l l y a c t i v e areas which a r e g e n e r a l l y mountainous and close  to  the  composition grain  source  o f Brenda  sizes.  of sand  The sand  well-graded i s fairly  i s made up  sediments.  uniform  of only  a  The  across a l l few common  m i n e r a l s such as q u a r t z , f e l d s p a r , and mica.  Since various  g r a d a t i o n s s e l e c t e d have t h e same mineralogy,  the e f f e c t of  gradation  upon  assessed.  Brenda sand i s from a t a i l i n g s dam, so t h e r e i s a  direct  material  applicability  of  behaviour  test  may  results  be s y s t e m a t i c a l l y  to  the  practical  problem  of  designing  hydraulic f i l l  dam  assessing  the  stability  of  a  composed o f w e l l - g r a d e d sand.  Kamloops s i l t of s i l t  and  was  selected  f o r the  study o f the e f f e c t  c o n t e n t upon s o i l behaviour because i t i s i n o r g a n i c ,  and  was  obtained  has  a s i m i l a r composition as Brenda sand o r Brenda  slimes.  The  commonly  from near the  silt  found  is  source o f  probably  within  Brenda sand.  representative  well-graded  fluvial  It  tailings of  fines  deposits  in  s e i s m i c a l l y a c t i v e areas.  3.3  SAMPLE PREPARATION - THE  Testing states studies  of  o f homogeneous (uniform) samples under uniform  stress  of  soil  necessary  SLURRY DEPOSITION METHOD  to  and  strain  property  be  able  is  required  use  to natural materials behaviour. must be  Each  to  precisely  and  considerably The fulfill  of r e c o n s t i t u t e d  reconstituted  the  ability  insitu  replicate  also  several  These requirements soils  cohesionless  to  for  This  in  preference  soil  makes the  r e p l i c a t e several  reconstituting  following c r i t e r i a :  l o o s e t o dense samples i n the an  is  soil  specimen  control  of  specimens  more d i f f i c u l t .  technique the  It  f o r fundamental i n v e s t i g a t i o n s of  i n d i v i d u a l l y prepared.  uniformity  fundamental  characterization.  homogeneous specimens f o r such s t u d i e s . have promoted the  for  soil  deposit;  2)  the  1)  the  density  sand  samples  must  method must produce range expected  samples must have a  within uniform  63 void  ratio  saturated, samples  throughout; particularly  should  segregation content;  be  5)  the  for  well  regardless  and  simulate  3)  samples  undrained  mixed  sample  the mode o f s o i l  be  without  fully 4)  testing;  of p a r t i c l e s i z e  the  must  the  particle  gradation  preparation  size  or  method  fines should  d e p o s i t i o n commonly found  in  the  s o i l d e p o s i t b e i n g modelled. Several  different  methods o f  sample p r e p a r a t i o n  have been used i n the p a s t are f i r s t d i s c u s s e d . deposition hydraulic above  method fill  criteria  proposed  sample  fluvial  is  method  determine the of  or  of  then  is  deposition described.  evaluated  homogeneity and  poorly-graded  preparation  and  by  a  The  slurry  which  models  and  which meets  the  The  success  the  series  of  of  tests  monotonic undrained  well-graded  which  sand  with  to  strength  and  without  fines. 3.3.1  Summary o f Techniques Used f o r Sand sample P r e p a r a t i o n S i n c e the f i r s t l a b o r a t o r y s t u d i e s of sand  behaviour has so  conducted  by  Casagrande  (1936),  been t o produce sand samples w i t h as  bulking  to  be  susceptible to  techniques  liquefaction literature.  designed  have The  most  sample  preparation  forces  between  Many  been  in  particles  preparation  a low  increase  described  effective a  a major  moist tend  techniques  Numerous  to  in  soil  where  expand specify  sand  susceptibility  sand b u l k i n g state  problem  enough d e n s i t y  liquefaction. to  liquefaction  the a  to  mechanics  technique  is  water  tension  soil  matrix.  minimum  of  d e p o s i t i o n a l energy t o achieve done by  reducing  through water. drawing  a  particle  Sand may  a loose s t a t e .  drop h e i g h t ,  a l s o be bulked  s i e v e mesh through  i t or  or  T h i s may  be  p l u v i a t i n g sand  a f t e r d e p o s i t i o n by  by  applying  an  upward  a  uniform  i n laboratory  studies  seepage g r a d i e n t s u f f i c i e n t t o induce and m a i n t a i n q u i c k sand c o n d i t i o n . An  important  i s whether the of  f a b r i c o f sand sample produced by the method  preparation  deposit soil  being  is  similar  modeled.  behaviour  preparation  factor to consider  that  Numerous  i s highly  technique  to  found  within  studies  dependent  upon  have  the  soil  shown  that  laboratory  ( f o r example M u l i l i s  et.  sample  al.,  1977,  and Miura e t . a l . , 1982).  3.3.1.1  M o i s t T»i"p-»Tiq  The  o l d e s t technique  f o r preparing  r e c o n s t i t u t e d sand  samples i n the l a b o r a t o r y i s moist or dry tamping o f s o i l i n layers  (Lambe,  consecutive  and  placed. fabric was  and  moist  rolled  originally The  technique  consists  of  each  layer f l a t  tamping  tamping  construction  before  method fills,  with  the  best  of  pouring  specified  next  f o r which  layer the  the  is soil  method  designed.  saturated  with  a  models  moist tamping method produces v e r y  partially uniform  tamping  frequency The  of  The  s o i l l a y e r s of s p e c i f i e d t h i c k n e s s i n t o a sample  former tube, force  1951).  samples  which  may  be  loose to somewhat  r e s p e c t t o d e n s i t y or p a r t i c l e s i z e  dense non-  gradation.  Several  s t u d i e s have been conducted t o a s s e s s the  o f samples prepared by moist tamping, conclusions  as  1969,1982).  success  uniformity  may  often with c o n f l i c t i n g  of  the  triaxial  (Castro,  samples prepared  I t i s shown t h a t a h i g h  be  method  e t . a l . , (1984) compare m i n i a t u r e cone  resistance within  methods.  results  the  Miura  penetration various  to  uniformity  degree  o f sample  a c h i e v e d by a i r p l u v i a t i o n w h i l e  i n considerable  n o n - u n i f o r m i t y i n cone  by  tamping  penetration  resistance. Due  to  water  tension  forces  between  grains,  samples p r e p a r e d by the moist tamping method may at  much  larger  saturated dumped  state. in  a  liquefaction capillary that  forces  moist  finer  ratios  to  a  sand  samples assembled  moist  material,  I t has  prepared  particularly structure  a  "bulked  by  thus f i n e r g r a i n e d  dry  that  or sand  prone  to  because  of  states  sand  been observed the  moist  that  fine  tamping  when  the s a t u r a t i o n p r o c e s s due  water  forces  similar  large strains  grains. i n moist  i s more coarse  grained  method  s t a t e t h a t they may  between  soil  f o r c e s than  s t r a i n s during  observed  a  Casagrande  by water t e n s i o n  i n such a l o o s e  tension  in  suggests  grains";  remains  be prepared  Water t e n s i o n f o r c e s between g r a i n s are l a r g e r  grained  sand.  is  "honeycomb  between  dumped  possible  (1976)  state  susceptible to bulking grained  than  Casagrande  moist due  saturated". in  void  sand  sand  may  be  undergo l a r g e  t o the removal  Other  workers  tamped s i l t y  of  have sands  d u r i n g t h e s a t u r a t i o n p r o c e s s (Marcuson e t . a l . , et.  a l . , 1982, Sladen e t . a l . , If  minor  a moist tamped s o i l induced  compressible pluviated  strain,  i t  1972, Chang  1985).  specimen is  can be s a t u r a t e d w i t h  often  considerably  during  consolidation  than  specimen,  and thus may  be c o n s o l i d a t e d  larger void ratios.  a  less  comparable  water  t o much  Such i n c o m p r e s s i b l e specimens a r e o f t e n  m e t a s t a b l e and more s u s c e p t a b l e t o l i q u e f a c t i o n i n monotonic loading.  3.3.1.2  A i r Pluviation  The major pluviated Negussey,  factors that  sands  are height  affect of  relative  particle  1986) and r a t e o f d e p o s i t i o n  density drop  (Vaid  a h i g h e r energy  specimen.  of deposition  Numerous workers  who  and thus have  and  (Miura e t . a l . 1982).  A h i g h e r drop h e i g h t o r a h i g h e r r a t e o f d e p o s i t i o n in  ofa i r  used  results  a denser  soil  a i r pluviation  have attempted t o r e s t r i c t drop h e i g h t and thus produce v e r y l o o s e sand samples. The specimens al.,  a i r pluviation depending  upon  t e c h n i q u e produces  fairly  t h e t e c h n i q u e used  1975, Miura e t . a l . , 1982, 1984).  uniform  (Mulilis et.  A i r pluviation  models t h e n a t u r a l d e p o s i t i o n p r o c e s s o f wind blown  best  aeolian  d e p o s i t s , which g e n e r a l l y c o n s i s t o f e i t h e r w e l l - s o r t e d sand or w e l l - s o r t e d Air  silt.  p l u v i a t i o n o f w e l l - g r a d e d sand i s not as s u c c e s s f u l  as a i r p l u v i a t i o n o f w e l l - s o r t e d sand.  Well-graded sand may  become segregated when d e p o s i t e d especially process  i f i t has  of  sample  a  by p l u v i a t i o n through a i r ,  considerable  saturation  f a b r i c , and produce some s o i l  may  fines  content.  disrupt  initial  The sand  s e g r e g a t i o n due t o washing out  o f f i n e s from t h e sample. Air  pluviated dry s i l t y  content extent silty  a r e prone t o b u l k i n g due t o t h e f i n e s c o n t e n t . of this  20/200  maximum v o i d unaltered void  sands which have a l a r g e f i n e s  method,  on  increases of s i l t y  i n Figure  3.6 for  The f i g u r e shows t h a t  t h e ASTM  i s illustrated  Brenda sand. r a t i o obtained  with  ratio  bulking  silt  by  the other  in silt  by a i r p l u v i a t i o n i s v i r t u a l l y  content  obtained  20%.  up t o about  the  hand,  proposed decreases  sand would n e i t h e r s i m u l a t e  The maximum  slurry  deposition  substantially  up t o about 20%.  content  The  with  A i r pluviation  the deposition  process  nor t h e range o f v o i d r a t i o s p o s s i b l e i n h y d r a u l i c f i l l s o r f l u v i a l d e p o s i t s which a r e o f t e n comprised o f s i l t y Figure void  ratio  3.6  also  of s i l t y  deposition  this  essentially  constant  decrease deposits it  shows t h e v a r i a t i o n o f sand sand  void  i n overall  sands.  i n the loosest state. ratio  with  be  increasing  void  through a s i l t y  may  ratio.  slurry  noted  silt This  skeleton By  slurry  to  content shows  remain despite  that  sand  i n much t h e same manner as  does through c l e a n water due t o t h e l a r g e d i f f e r e n c e i n  settlement water. increase  v e l o c i t y of finer  silt  and c o a r s e r  A i r p l u v i a t i o n on t h e o t h e r i n the void  ratio  of  sand  through  hand causes a  radical  the  sand  skeleton  with  68  increasing s i l t  content, thus demonstrating l a r g e b u l k i n g o f  the sand m a t r i x . Air be  pluviated s i l t y  metastable  those and  found  sand which i s bulked would tend t o  and undergo  i n moist  consolidation.  very  tamped Large  large  silty  strains  strains  sands  similar  during  to  saturation  induced w i t h i n  a  sample  d u r i n g t h e p r e p a r a t i o n stage impart a s t r a i n h i s t o r y t o t h e soil  that  natural water  i s much d i f f e r e n t  silty  sand  which  from  that  produced  i s invariably  and n o t a p p r e c i a b l y b u l k e d  by  i n a loose  deposited  silt  through  content.  Non-  s t a n d a r d i z a t i o n o f i n i t i a l s t r a i n d u r i n g sample p r e p a r a t i o n has been i d e n t i f i e d by Tatsuoka e t . a l . (1986) as one reason for  the v a r i a t i o n  various s o i l sands  in triaxial  laboratories.  bulked  susceptible  by to  silt  Very  content  liquefaction  behaviour  of  sand  loose a i r pluviated would  under  tend  to  monotonic  be  or  studies  have  been  conducted  silty more cyclic  l o a d i n g than c l e a n w e l l - s o r t e d sands a t t h e same v o i d Numerous  among  ratio.  t o explore the  e f f e c t o f sample p r e p a r a t i o n t e c h n i q u e and t h e i n f l u e n c e o f sand  fabric  upon  undrained  behaviour.  Laboratory  tests  conducted by Miura and T o k i (1982) i n d i c a t e t h a t t h e r e i s a large  difference  pluviation rodding. and  i n behaviour  through Tatsuoka  a i r and  of clean by  moist  e t . a l . (1986) r e p o r t  sands  prepared  tamping similar  or  moist  results,  f i n d t h a t a i r p l u v i a t e d and water p l u v i a t e d c l e a n  have f a i r l y  by  s i m i l a r c y c l i c s t r e n g t h which i s g e n e r a l l y  sands lower  than  the c y c l i c  strength  o f comparable  v i b r a t e d sand a t t h e same v o i d  3.3.1.3  Water  Sample  moist  tamped  or  ratio.  Pluviation  preparation  by t h e water  p l u v i a t i o n technique  has been d e s c r i b e d by s e v e r a l r e s e a r c h e r s , i n c l u d i n g Lee and Seed  (1967), F i n n e t . a l . (1971), Chaney e t . a l . (1978), and  Vaid  and Negussey  (1984).  ensures  sample  falling  through water  through a i r .  saturation.  The water p l u v i a t i o n t e c h n i q u e The t e r m i n a l  velocity  i s lower than t h a t  o f sand  o f sand falling  T h i s l e a d s t o a lower energy o f d e p o s i t i o n i n  water p l u v i a t e d samples and hence a l o o s e r d e p o s i t , as l o n g as s e d i m e n t a t i o n c u r r e n t s a r e not s e t up w i t h i n t h e water i n the d e p o s i t i o n mold. The water p l u v i a t i o n t e c h n i q u e s i m u l a t e s t h e d e p o s i t i o n o f sand through water found i n many n a t u r a l environments and mechanically  placed  hydraulic  fills.  Oda e t . a l . (1978)  r e p o r t t h a t n a t u r a l a l l u v i a l sands and water p l u v i a t e d sands have  similar  fabric  and  thus  similar  stress-strain  and  strength behaviour. The water p l u v i a t i o n t e c h n i q u e produces u n i f o r m samples of  poorly-graded  particle  size  sand  (Vaid  segregation  and  Negussey,  i s a problem  of well-graded or s i l t y  sands.  as  a r e designed  the t r i a x i a l  test  c o n d i t i o n s which e x i s t samples  but  pluviation  S i n c e l a b o r a t o r y t e s t s such  at a point  t o ensure uniform  i n water  1984),  stresses  t o model  the  and thus r e q u i r e and s t r a i n s ,  stress uniform  t h e water  70  pluviation  technique  graded sands. size  should  only  When a well-graded  segregation  during  be used soil  to test  i s subjected  pluviation,  poorlyto grain  t h e segregated  soil  g e n e r a l l y has a l a r g e r average maximum v o i d r a t i o than t h a t o f t h e unsegregated s o i l , and i t s mechanical p r o p e r t i e s a r e s i m i l a r t o t h a t o f a more poorly-graded The a given  soil.  maximum p o s s i b l e v o i d r a t i o a f t e r c o n s o l i d a t i o n t o s t r e s s s t a t e o f a water p l u v i a t e d sand i s g e n e r a l l y  lower than t h a t o f d r y o r moist tamped sand. the  e f f e c t s of bulking  tension are  forces  generally  o f f i n e s i n t h e d r y s t a t e o r water  i n t h e moist more  state.  compressible  Water p l u v i a t e d  during  moist tamped sands due t o t h e h i g h e r o f water p l u v i a t e d sand f a b r i c  3.3.2  sands  consolidation  than  radial compressibility  (see S e c t i o n 4.1.4).  The S l u r r y D e p o s i t i o n Method To  overcome  preparing 3.3.1  inherent  reconstituted  problems  sand  samples  ( e s p e c i a l l y t h e problem  poorly-graded the  T h i s i s due t o  slurry  or s i l t y deposition  of  described  of p a r t i c l e  segregation  in  slurry  3.3.2.1  P r e p a r a t i o n o f Sand  preparation  i n Section  method  specimens i s d e s c r i b e d  of test  of  called  triaxial  mass  methods  sand samples) a new t e c h n i q u e was  developed.  d e p o s i t i o n method used i n t h e p r e p a r a t i o n  A  the  sand  The  o f 63 mm  diameter  i n t h e f o l l o w i n g paragraphs.  sufficient  mold a t minimum d e n s i t y  to f i l l  i s poured  t h e sample into a flask  with  sufficient  water  (see  f i f t e e n minutes t o d e - a i r  Figure  the  mixture.  d e - a i r e d water i s added t o the If  the  test  separate water  sample  flask  is  is  to  filled  approximately  contain  of  the  final  sample  cylindrical  tube  diameter and a  clay  and  a  fines,  a  volume  allowed to  of The  cool.  sample P r e p a r a t i o n M i x i n g Tube  The  has  more  sample volume.  f i n e s s l u r r y i s a l s o b o i l e d t o d e - a i r and  3.3.2.2  for  i t completely.  or  fines  boiled  cooling,  fill  silt  the  and  After  flask to  with  60%  3.7(a))  preparation (see  tube  is  clear  F i g u r e 3.7(b)) 22.5  with walls  5 mm  thick.  rubber membrane gasket s e a l  number 11.5  a  cm  The  plexiglass  long,  6 cm  preparation  glued to  one  rubber stopper which i s used t o  end,  seal  in  tube and  the  a  other  end. The  fines  fraction  p r e p a r a t i o n tube and to  flush  clean  within  the  bottom  of  the  topped up fines  preparation the  tube  sample i s p l u v i a t e d  slurry  is  w i t h the  slurry  tube  before i n t o the  poured  is  flask.  sand  tube.  the  preparation  tube i s simply  The  sand f l a s k opening i s c o n s t r i c t e d  s t o p p e r which a i d s from  the  flask  saturation Some s l u r r y  to  in pluviation the  i s maintained fines  which  of  For  may  to  fines  slurry  settle  clean  of  to  the  sand  the soil  samples water.  with a tapered  rubber  sand through water  tube.  Thus  a l l stages o f  move up  sample  with de-aired  the  preparation during  The  fraction  filled  the  d e - a i r e d water used  allowed  the  into  into  the  sample  preparation. sand  flask  (b)  (<0  SILT SLURRY OR CLAY SLURRY OR NAIER POURED INTO TRANSPARENT PLASTIC R U I N S TUBE; SAND PLUVIATED INTO R U I N S TUBE; SILT OR CLAY SLURRY LOST DURING SAND PLUVIATION IS COLLECTED TO BE NEISHED  SAND BOILED IN WATER TO DE-AIR; SILT OR CLAY SLURRY BOILED SEPARATELY  RUBBER HEHBRANE SEAL BLUED TO  ONTO BASE PLATEN OF TRIAXIAL TEST APPARATUS  FIGURE 3.1 SCHEMATIC DRAWING OF SLURRY DEPOSITION METHOD FOR PREPARATION OF WELL GRADED SILTY OR CLAYEY WELL MIXED SATURATED LOOSE TRIAXIAL TEST SAND SPECIMENS  FIGURE 3.1 (continued) SCHEMATIC DRAWING OF SLURRY DEPOSITION METHOD FOR PREPARATION OF WELL GRADED SILTY OR CLAYEY WELL MIXED SATURATED LOOSE TRIAXIAL TEST SAND SPECIMENS  (h)  0)  TOP CAP APPLIED CAREFULLY TO TOP OF SAMPLE; OVERSIZE CYLINDRICAL RING PLACED AROUND TOP CAP OHIO TOP OF FORHER TUBE. SAMPLE MEMBRANE PULLED UP OVER CYLINDRICAL RING; RUBBER 0-RIN6 ROLLED OVER RUBBER HEHBRANE AND CYLINDRICAL RING. EICESS RUBBER MEMBRANE ROLLED DONN TO O-RINfi TO ALLON REIOVAL CF CYLINDRICAL RING AND ACHIEVE UNDISTURBED SEALING OF TOP CAP NITH O-RINS  FIGURE 3.T (continued) SCHEMATIC DRAWING OF SLURRY DEPOSITION METHOD FOR PREPARATION OF WELL GRADED SILTY OR CLAYEY WELL MIXED SATURATED LOOSE TRIAXIAL TEST SAND SPECIMENS  (j) RECONSTITUTED SOIL SAMPLE MAINTAINED UNDER VACUUM AFTER REMOVAL OF SPLIT SAMPLE FORMER TUBE  75  during  pluviation  are retained  and weighed  when  a d j u s t t h e weight o f f i n e s r e t a i n e d w i t h i n t h e sand  3.3.2.3  dry to sample.  S e a l i n g o f Sample P r e p a r a t i o n M i x i n g Tube  To  mix t h e sand  slurry  within  t h e sample p r e p a r a t i o n  m i x i n g tube, t h e tube i s s e a l e d i n t h e f o l l o w i n g manner. A thin  2  inch  diameter  rubber  membrane  i s rolled  onto t h e  o u t s i d e o f t h e open end o f t h e mixing tube and t h e tube i s placed  i n a water bath as shown i n F i g u r e 3 . 7 ( c ) . A b o i l e d  and d e - a i r e d porous d i s k , which triaxial be  i s t h e bottom  platen of the  t e s t apparatus upon which t h e f i n i s h e d sample  will  s e a t e d , i s p l a c e d upon t h e open end o f t h e mixing  tube  w i t h i n t h e water bath, m a i n t a i n i n g s a t u r a t i o n o f t h e porous d i s k w i t h i n t h e water bath. The is pulled of  the  rubber membrane around over t h e porous disk  t h e end o f t h e m i x i n g  d i s k assembly,  assembly.  A  thin  sealing the sides  round  metal  approximately t h e same diameter as t h e porous d i s k i s p l a c e d upon t h e d i s k assembly  tube  plate assembly  and rubber membrane  which  s e a l s i t , thus completely s e a l i n g t h e end d i s k assembly and sample m i x i n g tube. The m i x i n g tube  i s then withdrawn from t h e water  while maintaining a firm assembly  t o keep  bath  f i n g e r p r e s s u r e upon t h e end d i s k  i t sealed.  The s l u r r y  within  t h e sample  m i x i n g tube i s then mixed by v i g o r o u s l y r o t a t i n g t h e mixing tube  (see F i g u r e 3 . 7 ( d ) ) .  The p r o g r e s s o f sample mixing may  be observed through t h e c l e a r p l a s t i c tube.  Twenty  minutes  76 of  mixing  was  homogeneous  3.3.2.4  found  sufficient  to  obtain  completely  samples.  Placement  o f M i x i n g Tube Onto T r i a x i a l Base P l a t e n  Before t h e sand sample i s prepared i n t h e m i x i n g the  triaxial  bath  as  test  shown  base in  ( g e n e r a l l y 0.3 mm is  rolled  sealed  onto  platen  Figure  thickness,  t h e base  i s assembled  3.7(e).  A  i n t h e mixing  discussed  in  the  of the t e s t  has  previous  been  section,  is  sedimented plate  allowed to  to  settle.  i t s loosest  the  i s removed  from  the d i s k  s i d e s o f t h e porous d i s k which t h e membrane  on  the sides  thoroughly tube  the  state,  is  as  held  slurry  the basal  assembly  membrane which h o l d s t h e d i s k assembly  and  downwards, and t h e  After  stable  apparatus  Once t h e sand  mixed  v e r t i c a l l y w i t h t h e porous d i s k assembly slurry  membrane  59 mm diameter and 20 cm long)  platen  tube  a water  rubber  t o t h e p l a t e n w i t h a rubber o - r i n g .  slurry  and  within  tube,  and  has metal  the  rubber  i s p u l l e d back t o t h e  i s now h e l d by water o f t h e porous  tension  disk.  The  porous d i s k end o f t h e mixing tube i s then c a r e f u l l y  placed  upon  Figure  the  triaxial  test  base  platen  3.7(e). The rubber membrane which  as  shown  in  s e a l s t h e porous  disk i s  now r o l l e d up o f f t h e mixing tube. The platen  sample rubber membrane i s r o l l e d and  o-ring  seal  which  retains  up from  one  end,  t h e base over  the  porous d i s k and mixing tube towards t h e rubber s t o p p e r which s e a l s t h e upper end o f t h e mixing tube.  The mixing tube i s  thus s e a l e d t o t h e base p l a t e n and t h e whole apparatus may be removed from t h e water bath and taken t o t h e f i n a l assembly  station.  3.3.2.5  Deposition of  A split  «»mpi«  sample former tube i s assembled around t h e base  p l a t e n and sample mixing tube (see F i g u r e 3 . 7 ( f ) ) . rubber membrane i s p u l l e d r a d i a l l y outwards the  sample  former.  sample  mixing  tube  and  folded  At t h i s point the s p l i t  over  The s o i l  from t h e t o p o f the top of the  former c o m p l e t e l y s e a l s t h e  o u t s i d e o f t h e sample membrane. A c y l i n d r i c a l rubber membrane (75 mm diameter by 100 mm h e i g h t , see F i g u r e 3.7(f)) i s s t r e t c h e d over t h e t o p o f t h e split  sample  former  Water  i s poured  and t h e t o p o f t h e sample  into  the c y l i n d r i c a l  water bath above t h e s p l i t inside  former.  o f t h e former withdraws  former w a l l s  and a l s o  water bath above.  membrane  membrane. t o form  a  A vacuum a p p l i e d t o t h e  t h e sample membrane t o t h e  draws water  down  from  t h e membrane  The i n s i d e o f t h e sample membrane i s now  ready t o a c c e p t t h e sand s l u r r y . The  rubber s t o p p e r which  m i x i n g tube withdrawn are  Excess s l u r r y  fines  o r water a r e  from w i t h i n t h e t o p o f t h e sample mixing tube and  weighed  content  i s removed.  p l u g s t h e end o f t h e sample  l a t e r when oven d r y t o determine t h e e x a c t f i n e s  i n t h e sand  sample.  c a r e f u l l y and s t e a d i l y withdrawn  The  mixing  tube  i s then  t o d e p o s i t t h e sand  slurry  78  w i t h i n t h e membrane i n a v e r y l o o s e , homogeneous  saturated  state. The  t o p o f t h e sample  i s carefully  f i n e s s l u r r y o r water a r e withdrawn bath  ( t o be weighed  removed  from  leveled,  excess  from t h e membrane water  dry) and t h e water  t h e t o p o f t h e sample  bath  former  membrane i s tube  (Figure  3.7(g)).  3.3.2.6  A p p l i c a t i o n o f «»mpie T O P Cap  The upper  triaxial  test  platen  i s c a r e f u l l y p l a c e d on A s m a l l c i r c u l a r bubble  t h e t o p s u r f a c e o f t h e sand sample.  l e v e l p l a c e d upon t h e t o p o f t h e p l a t e n i s used t o keep i t l e v e l a t a l l times d u r i n g The  slightest  placement.  p r e s s u r e upon o r v i b r a t i o n  o f t h e upper  p l a t e n causes s e t t l e m e n t o f t h e l o o s e sample.  Therefore a  special  upper  platen  was  slightly  larger  than  technique  developed. the  diameter  upon  for  sealing  A cylindrical  copper r i n g  of the platen  t h e t o p o f t h e sample  applied  the  (see F i g u r e former.  t o t h e t o p o f t h e copper  ring  3.7(h)) While t o hold  i s placed  pressure i s t h e sample  membrane i n p l a c e a g a i n s t t h e t o p o f t h e former, t h e f o l d e d portion  o f t h e membrane  i s pulled  up o f f t h e s p l i t  and onto t h e s i d e s o f t h e copper r i n g . rolled  former. tube  A rubber o - r i n g i s  downwards over t h e rubber membrane which  copper tube u n t i l  former  c o v e r s the  t h e o - r i n g touches t h e t o p o f t h e sample  The excess rubber membrane which c o v e r s t h e copper  i s rolled  down on t o p o f t h e o - r i n g ,  and h e l d  down  f i r m l y w h i l e the copper r i n g i s withdrawn. onto the  top  platen  the sample w i t h no The t o be  top  very  cap  and  over the  disturbance. placement method d e s c r i b e d  effective  sealed  applied  t o the  specimen. split  in  o - r i n g snaps  sample membrane, s e a l i n g  i n the  assembly o f  specimens o f i n i t i a l l y l o o s e s t d e n s i t y . been  The  i t s rubber  membrane,  pore p r e s s u r e  line  has  as  been  found  deposited  sand  Once the sample a  20  kPa  i n order  to  has  vacuum confine  is the  A f t e r c o n s o l i d a t i o n under the a p p l i e d vaccuum the  former  is  dismantled,  and  triaxial  cell  assembly  completed i n the manner d e s c r i b e d i n S e c t i o n 3 . 4 .  3.3.2.7  P r e p a r a t i o n of D e n s i f i e d Band Samples  D e n s i f i e d sand samples are prepared  by p l a c i n g the  top  p l a t e n upon the s o i l sample, a p p l y i n g a s l i g h t p r e s s u r e upon the p l a t e n , and v i b r a t i n g the base o f the t r i a x i a l c e l l a  mechanical  vibrator  or  soft  r e l a t i v e density i s attained.  hammer  until  the  with  desired  Excess pore p r e s s u r e s  caused  by v i b r a t i o n are allowed t o d i s s i p a t e through top and  bottom  drainage density soil  lines.  This  throughout  samples  are  technique  (Vaid finally  and  yields  Negussey,  sealed  and  samples  of  1986).  confined  uniform  Densified i n the  same  manner as l o o s e samples (see S e c t i o n 3.3.2.6).  3.3.3  E v a l u a t i o n o f S l u r r y D e p o s i t i o n Method The  are  as  a t t r a c t i v e f e a t u r e s o f the s l u r r y d e p o s i t i o n method follows:  1)  a  sand  sample  remains  fully  saturated  80  within  de-aired  water  p r e p a r a t i o n i s normally  during  excess  particle  pore  drop  through  during samples  water  4)  the  (poorly-graded  deposited  mechanical  gradation, the  as  to  vibration;  method  forms  i s generally  5)  respect  be  the  test  samples  to  void  method models the  the  method. a  uniformity  deposition  20/200  u s i n g the  under  segregation  by  denser  than by  exceptionally  and  particle  f i n e s content;  soil  simple  densified  are  ratio  loose  fabric  found  size  and  6)  within  fills.  «*mpHomogeneity  slurry  graded  slightly  of thus  initially  uniformly  n a t u r a l f l u v i a l deposits or h y d r a u l i c  To  and  3)  with  height  deposition  r e g a r d l e s s o f g r a d a t i o n and  deposition  3.3.3.1  minimize  during  sand) which may  homogeneous w i t h  hours;  unsegregated sand o b t a i n e d  p l u v i a t i o n through water slurry  so  c u r r e n t s and p a r t i c l e s i z e  deposition;  sample  as a l e a n s a t u r a t e d s l u r r y  water  c o n t r o l sedimentation  2)  completed w i t h i n about 1.5  a sample i s mixed thoroughly little  preparation;  Brenda  method, sand  identical  were prepared  samples were  set  c o n f i n i n g pressure by  membrane was horizontal  samples prepared  s l u r r y d e p o s i t i o n method and The  described  o f sand  Emery  et.al.,  removed  slices.  of  and  Grain  in a 20  kPa  1973).  the  sample  samples in a  using  of  well-  loose  state  the water p l u v i a t i o n 2.5%  gelatin  (using When cut  size distribution  the  solution procedure  solidified,  the  into  four  equal  and  void  ratio  81  o f each s l i c e was then measured.  The t e s t r e s u l t s a r e shown  i n F i g u r e 3.8 and F i g u r e 3.9. The  slurry  homogeneous w i t h 3.9).  In  deposited  may  be  seen  to  respect t o p a r t i c l e s i z e gradation  contrast,  considerable p a r t i c l e water  sample  pluviated  the size  and  water  segregation  slurry  v i s u a l l y q u i t e uniform,  pluviated  (Figure  sample  shows  ( F i g u r e 3.8).  deposited  samples  be  Both  appeared  although water p l u v i a t e d samples may  have v i s i b l e  layers of f i n e r  and c o a r s e r  insufficient  care  to  homogeneity.  V o i d r a t i o d i s t r i b u t i o n w i t h sample h e i g h t o f  is  taken  maintain  both water p l u v i a t e d and s l u r r y d e p o s i t e d uniform,  although  uniformity water  may  a  tendency  be noted  pluviated  toward  i n slurry  specimen  grained visual  a  at  sample  samples i s f a i r l y slightly  deposited  deposited  soil i f  a  better  samples.  slightly  The  looser  s t a t e due t o p a r t i c l e s e g r e g a t i o n d u r i n g d e p o s i t i o n (compare void  ratios  i n F i g u r e s 3.8 and 3.9).  In c o n t r a s t , p o o r l y -  graded sand, which by d e f i n i t i o n cannot segregate,  was  found  t o be s l i g h t l y denser when d e p o s i t e d by p l u v i a t i o n than when d e p o s i t e d by s l u r r y d e p o s i t i o n . The uniformity  results  of  a  of a slurry  similar  test  to  determine  the  deposited  silty  sand  specimen  with  14%  s i l t c o n t e n t a r e a l s o i l l u s t r a t e d i n F i g u r e 3.9.  be  noted  that  the  silty  sand  specimen  is  I t may  remarkably  homogeneous w i t h r e s p e c t t o p a r t i c l e s i z e g r a d a t i o n over i t s e n t i r e h e i g h t , even though i t has p r e v i o u s l y been d e n s i f i e d and c y c l i c a l l y loaded t o i n i t i a l  liquefaction.  Figure  3.8  Grain s i z e d i s t r i b u t i o n curves f o r h o r i z o n t a l l y q u a r t e r e d s e c t i o n s o f a water p l u v i a t e d sand sample  M.l.T.  GRAIN  SIZE CLASSIFICATION  SAND COARSE  100 LD  i—i UJ  90  MEDIUM 40 _j  SILT FINE  MEDIUM  COARSE  60 100 140 2 0 0 i i i  U.S. STANDARD SIEVE  VOID RATIO (BRENDA  80  SECTION  >CD  70  1  m  60  LU  40 30  UJ LJ  20  UJ  10  rr  SIZE  DISTRIBUTION  20/200  SAND)  VOID  O • A  RATIO  0. 893 0. 892 0. 908 0. 924  50 UJ LD  FINE  TOTAL  CLEAN  0. 904  WELL-GRADED  PLUVIATED SAND  20/200 BRENDA  (LOOSEST  Gc =  WATER  STATE)  20 k P a  0  -i—r  0. 01 (mm)  00  ]ure 3.9  Grain s i z e d i s t r i b u t i o n curves f o r h o r i z o n t a l l y quartered s e c t i o n s o f s l u r r y d e p o s i t e d sands  M. I. T. GRAIN S I Z E  CLASSIFICATION  SAND COARSE  MEDIUM  20  FINE  COARSE  BO 100 140 2 0 0 I  I  I  (BRENDA  \  70  -  \ y  W  Yv  40  CLEAN _  LT' = 20 k P a C  0  I Ii i i i  1. 0  i  i  i  VOID  RATIO  1  0. 788  2  0. 780  3  0. 787  4  0. 800  (AFTER  SAND\\  (LOOSEST STATE)  SAND)  0.798  20/200 SAND + 1 3 . 5 % S I L T  WELL GRADED \ \  20/200 BRENDA  SIEVE SIZE  20/200  TOTAL  30 20 ~  FINE  DISTRIBUTION  SECTION  50  10  U . S . STANDARD  VOID RATIO  \  80  MEDIUM  I  \  90  60  40  i  00  SILT  95%  CYCLIC  RELATIVE  \  LOADING, DENSITY) CT  r  = 350 k P a  \  i n M i l  i  11 i i i i  0. 01  0. 1  GRAIN S I Z E  i  (mm)  i  i  84  A major that  advantage o f  regardless  of  the  size  slurry  gradation,  homogeneous w e l l mixed samples. The obtained  in  homogeneity the  skill  that  the  sample  and  the  experience  slurry  of  method  tube  researcher.  method  mixing sample  be c o n t r o l l e d I t was  produces  samples w i t h r e p e a t a b l e r e s u l t s i f the sand for  produces  controls  T h i s may  the  deposition  the  e x t e n t o f sample  mixing  (see F i g u r e 3.7(d)).  d e p o s i t i o n method i s  found  homogeneous  slurry  i s mixed  a t l e a s t twenty minutes f o r the sample s i z e used.  homogeneity  of  controlled  silty  because  completely  mixed  sand  the  specimens  well-graded  before  a  uniform  was  more  material slurry  by  The easily  had  to  be  consistency  and  c o l o r were o b t a i n e d . Four slurry  factors  deposition  dimensions tube  affect  at  the  diameter  diameter  homogeniety  the of  choice of  method  mixing  loosest  state  should  of  the  be  only  completed  the  soil  dimensions  tube: of  1)  i n the  soil  smaller  specimen  original  the  specimen  d e p o s i t i o n , 2)  slightly soil  for  mixing  than  to  the  maintain  w e l l mixed  state  d u r i n g the t r a n s f e r p r o c e s s , 3) the s l u r r y w i t h i n the mixing tube  should  mixing,  and  have 4)  the  a  high  enough  water  slurry  should  have  content a  low  to  allow  enough  water  c o n t e n t such t h a t p a r t i c l e s e t t l e m e n t d i s t a n c e i s kept t o a minimum and sedimentation c u r r e n t s do not segregate the during 10%  sedimentation.  A mixing  tube  volume which  l a r g e r than the volume o f sand d e p o s i t e d i n the  s t a t e was  found t o be most e f f e c t i v e .  The dimensions  soil  is 5  to  loosest o f the  85  s l u r r y mixing tube used f o r t h i s study are 3.7(b).  A  longer  graded  sand  with  higher  viscosity  mixing 20  tube  percent  and  was  used  silt  shown i n  to  content  Figure  deposit because  wellof  l a r g e r segregated volume o f the  the silty  sand. Better grained  sample  homogeneity  samples might be  mixed  directly  within  d i r e c t l y w i t h i n the transfer  from  attained the  perhaps  i f the  sample  looser  sand  former  mixing  tube.  d e n s i f i c a t i o n or segregation  may  This occur  is  and  were  deposited need f o r a  because  during  fine  slurry  sample membrane without the  the  the mixing tube.  and  slight  t r a n s f e r from  Such a method would r e q u i r e  construction  o f a s p e c i a l i z e d mixing apparatus.  3.3.3.2  Replication  The able  degree t o which the  to  replicate  illustrated  i n Figure  s l u r r y d e p o s i t i o n technique i s  specimens 3.10.  at  Results  compression response o f two  a  desired  Excellent  is  o f monotonic undrained  identical  specimens o f  20/40 Brenda sand 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 shown.  density  r e p e a t a b i l i t y may  be  t o 200  noted  uniform kPa  are  i n the  test  possible  with  For a g i v e n  silty  results. Similar  replication  s i l t y sands u s i n g up t o 20% sand,  the  following specimens  same slurry was  loosest  of  silt  by  was  content.  state  deposition. insured  specimens  void Since  the  ratio the  was  obtained  uniformity  deposition  of  technique,  HALF DEVIATOR STRESS, CT /2 PORE PRESSURE A U (kPa) d  98  87  r e p l i c a t i o n o f specimens was e a s i l y a t t a i n e d a t any t a r g e t e d density.  3.3.3.3  Sand F a b r i c  S i n c e water p l u v i a t e d sands have been shown t o possess fabric  similar  necessary  to  also gives  to natural evaluate  rise  fluvial  i f the  to a similar  sands  slurry  (Oda,  1978),  deposition  fabric.  This  i t is  technique  evaluation  was  done by comparing undrained monotonic response o f specimens of  Brenda 20/40 sand a t i d e n t i c a l  water  pluviation  technique.  the  other  by  state  and s l u r r y possible  deposited  response.  by  water  This  i s typical  (Miura and T o k i ,  A  sands  pluviation  (near t h e  and  slurry  monotonic  loading  1982)  compression than i n e x t e n s i o n  o f a i r o r water p l u v i a t e d  and u n d i s t u r b e d n a t u r a l sands  sands (Miura  1984).  similar  deposited  deposition  Both d e p o s i t i o n methods produce c o n s i d e r a b l y more  d i l a t i v e response i n t r i a x i a l  and T o k i ,  slurry  loose  d e p o s i t i o n methods) have s i m i l a r t r i a x i a l  loading.  one p r e p a r e d by  The r e s u l t s i l l u s t r a t e d i n F i g u r e 3.11 show t h a t  water p l u v i a t e d loosest  and  density,  comparison  ASTM Ottawa  C-109  of  water  sand  pluviated  and  i s shown i n F i g u r e  slurry 3.12.  Sample p r e p a r a t i o n t e c h n i q u e may be seen t o a f f e c t behaviour of  Ottawa C-109  sand shown i n F i g u r e 3.12  more than t h a t o f  p o o r l y - g r a d e d Brenda 20/40 sand i l l u s t r a t e d The g r e a t e r degree o f v a r i a t i o n t h a t Ottawa  i n Figure  3.11.  i s p r o b a b l y due t o t h e f a c t  sand, though c o n s i d e r e d uniform  (Cu = 1 . 5 ) , i s  Figure 3.11  Comparison of test results for slurry deposited and wate pluviated 20/40 Brenda sand  140 EXTENSION  120o  100-  Q_  80-  CM  60-  COMPRESSION c  -c(X)  1  1.011  35  1.009  35  2  0.995  39  1.009  35  40ID  200 -20 -40  H 0  40  80  120  160  (aVa;)/2 (kPa)  140 n 120 -  CM TD  20 -  1  SAMPLE PREPARATION  80 60 40 -  240  2  100 o Q_  200  METHOD 1  SLURRY DEPOSITION  2  WATER PLUVIATION  o -  -20 - • -40 -10  2 1  1  "*VJ T  -5  5  0  AXIAL STRAIN  (%)  10  89  Fig. 3.12  C o m p a r i s o n of undrained r e s p o n s e of slurry deposited and  water pluviated Ottawa C — 1 0 9  sand  o  o_ CM  100  200 (a; + LT;)/2  SAMPLE PREPARATION METHOD  300  400  (KPa)  EXTENSION Dr  c(*)  COMPRESSION Dr„  c  'cW  1 SLURRY DEPOSITION 0.689 27 0.707 21 2 WATER PLUVIATION 0.691 26 0.705 21  1.0  O  0.8  a: LU  OC  o  D  \ fi  LU  \ ZJ  in in  t-,  0.6 -  ~  0.4 -  °- <  0.2 -  cc LU DC  o a.  a  120 80  LO  §  COMPRESSION  0  tn C;  ac 2  EXTENSION  CM  ^  i  40 0 1  % b° -40 •15  -10  -5 0 AXIAL STRAIN  5 (%)  10  15  more w e l l - g r a d e d  than  Brenda  20/40 sand  and  thus  i s more  s u b j e c t t o s i z e s e g r e g a t i o n d u r i n g p l u v i a t i o n through water than Brenda 20/40 sand. observed  on  G r a i n s i z e s e g r e g a t i o n was  water p l u v i a t i o n  of  Ottawa  sand.  visually  Apparently,  g r a i n s i z e s e g r e g a t i o n produced by p l u v i a t i o n through water makes  a  more  well-graded  sand  initially  stiffer  or  more  d i l a t i v e a t low s t r a i n l e v e l , such t h a t i t behaves as i f i t were a more p o o r l y - g r a d e d  material  (see  Section  5.2).  c o n t r a s t , a t l a r g e r s t r a i n l e v e l , water p l u v i a t e d sand i s a p p a r e n t l y  l e s s d i l a t i v e than  In  segregated  s l u r r y deposited  well  mixed sand.  3.3.4  Rumfflwry  To  o f s l u r r y D e p o s i t i o n Method  overcome  inherent  problems  sample p r e p a r a t i o n methods a new d e p o s i t i o n method has been  of  reconstituted  technique  c a l l e d the  state  saturation. slurry  within  Samples  with  little  slurry  developed.  S l u r r y d e p o s i t i o n sand samples are prepared saturated  sand  de-aired  are  mixed  excess  water  to  thoroughly  pore  water  so  in a  fully  ensure  full  as  a  as  to  saturated minimize  h e i g h t o f sand p a r t i c l e drop through water d u r i n g d e p o s i t i o n and  thus  c o n t r o l sedimentation  segregation initially generally  during  loose  deposition.  s t a t e with  larger  than  an  that  currents Samples initial obtained  unsegregated water p l u v i a t e d sand.  and are  void in  Initially  particle formed ratio a  size in  an  which i s comparable  loose  samples  may  be u n i f o r m l y  a desired void  d e n s i f i e d by mechanical v i b r a t i o n t o  ratio.  S l u r r y deposited with  respect  to  of  deposition  method  a  samples are  void  regardless  within  obtain  ratio  gradation  natural  and  and  particle  fines  simulates fluvial  e x c e p t i o n a l l y homogeneous  well  or  size  content. the  soil  hydraulic  fill  gradation, The  slurry  fabric  found  deposit,  yet  c r e a t e s homogeneous samples t h a t can be e a s i l y r e p l i c a t e d as required  in  material  3.4  tests  for  fundamental  of  ASSEMBLY OF TRIAXIAL TEST APPARATUS  the  former and is  sample  has  been  deposited  the top p l a t e n p o s i t i o n e d ,  recorded  ratio.  to  determine  Sample h e i g h t  sealed  w i t h the  removed and  maximum  i s again  the  void  w i t h sample h e i g h t sample  the  split  sample  height  deposition  once the top The  former,  to  and  void platen  former vacuum  vacuum i s a p p l i e d t o the pore  c o n s o l i d a t i o n under t h i s 20 kPa together  initial  recorded  sample membrane.  a 20 kPa  within  slurry  l i n e t o c o n f i n e the s o i l specimen.  of  studies  behaviour.  Once  is  laboratory  is  pressure  The volume change d u r i n g  effective stress i s  recorded  c i r c u m f e r e n c e a f t e r removal  determine  initial  dimensions  and  ratio. The  reaction  triaxial bar  F i g u r e 3.1)  cell  bolted  to  is  then  the  top  b e f o r e the f i n a l  assembled platen  sample h e i g h t  and  an  LVDT  loading  rod  (see  and volume change  data are recorded and  the pore p r e s s u r e l i n e c l o s e d t o  the c o n s o l i d a t i o n vacuum.  The  triaxial  cell  seal  is filled  with  d e - a i r e d water and t r a n s f e r e d t o the l o a d i n g frame. Transducers pressure, c e l l to  their  f o r the  determination  p r e s s u r e , and  initial  zero  of a x i a l  a x i a l deformation  levels,  and  data  load,  pore  are then  zeros  for a l l  t r a n s d u c e r s are recorded by s t r i p c h a r t or computerized acquisition  data  system.  The c e l l p r e s s u r e l i n e i s a t t a c h e d t o the t r i a x i a l and  cell  pore  pressure  pressure  to  attached  to  undrained  i n 25 kPa  pressure  is  saturation. to  the  the  20  zero.  The  pore  and  the  sample,  The  anisotropically of  increased to  increments  recorded  desired  pressure  set  was  consolidation  increment  minutes  order  in  to  cell  was  state  during  c o n s o l i d a t i o n t o be completed  now  applied  check  for  isotropically 3.1.1.1.  A  consolidation.  maintained  allow  is  I n c r e a s e i n pore thus  i n Section  used  line  pressure  and  sample  consolidated incrementally  stress  described  kPa  pressure  evaluate  effective  t o b r i n g the  t o 120 kPa.  sample i s then  as  100  to  kPa  cell  most  for of  ten the  (Negussey, 1984;  to  or back Each  twenty  secondary  Mejia et a l . ,  1988). 3.5  UNIFORMITY OF SAMPLE STRAIN DURING MONOTONIC AND LOADING  Strain extension  during loading  undrained was  observed  triaxial to  be  compression uniform  for  CYCLIC  and axial  93  s t r a i n l e v e l s below 10 t o 15%, strain  levels  g r e a t e r than  10  to  by  the development  strain.  Samples loaded i n e x t e n s i o n developed t h i n n i n g  l e d to  the  better  maintained  Only  test  to  in  from  in this  of  conjugate  shear  in  section large of  sample,  planes  and  O f t e n sample s t r a i n u n i f o r m i t y i s extension  reduced  results  been i n c l u d e d  mid  o f shear p l a n e s a t v e r y  evolution  sample n e c k i n g .  due  the  area a t a random h e i g h t w i t h i n the  radical  loading  at  loaded  followed  which  bulge  samples  developed  x-sectional  uniform  15%,  At  compression  the  a  as shown i n F i g u r e 3.13.  loading  than  compression  end  effects  i n extension  the  uniform  region  thesis.  of  R e s u l t s from  loading.  strain  have  the r e g i o n  of  loading behaviour  of  l a r g e non-uniform s t r a i n have been excluded.  3.6  TEST PROGRAM  The several  range  o f undrained monotonic  Brenda  confining extension  sand  types was  stresses. tests  Both  were  determined  over  monotonic  compression  conducted.  Several  a  range  of and  poorly-graded  sands, a w e l l - g r a d e d sand, a p o o r l y - g r a d e d s i l t y sand, and a well-graded  silty  consolidated  from  sand  were  loosest  tested.  state  of  All  slurry  samples  were  deposition,  to  determine the range o f maximum c o n t r a c t i v e response f o r the v a r i o u s sands  tested.  s l u r r y d e p o s i t i o n was provide  a  method  of  Consolidation  from  loosest  state  of  a l s o chosen as a r e f e r e n c e d e n s i t y t o comparing  different  sand  properties  94  S A M P L E S H A P E UP TO 10 TO 1 5 % STRAIN  COMPRESSION  EXTENSION  "7" / / /  D E V E L O P M E N T OF NON-UNIFORM  STRAIN AT  LARGE STRAIN L E V E L > 1 5 %  Figure 3.13  Uniformity of s a m p l e strain during  loading  95  which The  takes  into  concept  account  of relative  the o r i g i n density  of the s o i l  attempts  deposit.  to classify  soil  d e n s i t y as a s t a t e between extremes o f l o o s e s t and densest s t a t e obtained  by standard  may not r e f l e c t When  test  laboratory t e s t techniques.  t h e mechanism o f placement o f f i e l d  results  are  consolidation  after  automatically  considered:  compared  slurry  at  loosest  deposition, (1)  two  various  This soils.  state  factors  soil  of are  gradations  undergo t h e same d e p o s i t i o n and l o a d i n g h i s t o r y as would be expected and  t o occur  (2) because  deposited  in a fluvial samples  or hydraulic  are at  loosest  deposit;  possible  slurry  s t a t e , t h e maximum p o s s i b l e c o n t r a c t i v e behaviour  o f sand d e p o s i t e d w i t h i n water can be In  fill  summary,  the objectives  assessed.  o f t h e monotonic  loading  t e s t program a r e as f o l l o w s : (1)  To determine t h e e f f e c t content  have  upon  which s o i l  t h e undrained  gradation loading  and  response  silt of  Brenda sand c o n s o l i d a t e d from l o o s e s t s l u r r y d e p o s i t i o n state; (2)  To determine t h e e f f e c t content  which s o i l  gradation  and  silt  have upon t h e d i f f e r e n c e between e x t e n s i o n and  compression l o a d i n g response; (3)  To determine t h e e f f e c t content  which s o i l  gradation  have upon t h e v a r i a t i o n o f undrained  with c o n s o l i d a t i o n s t r e s s l e v e l .  and  silt  response  C o n s o l i d a t i o n data  from a l l t e s t s was  the  e f f e c t which s o i l  the  range  of  void  r e l a t i v e density,  gradation  ratio, and  and  compiled t o determine silt  relative  content  density,  have upon  sand  skeleton  c o n s o l i d a t i o n s t r a i n s obtained  during  c o n s o l i d a t i o n from l o o s e s t s t a t e o f s l u r r y d e p o s i t i o n .  A  series  conducted  on  poorly-graded Silty  sand  of  undrained  isotropically silty  sand;  cyclic  triaxial  consolidated  and  (2)  samples were prepared  tests  samples  well-graded i n a very  of:  silty  loose  were  to  (1) sand. dense  state.  C y c l i c t e s t s were conducted t o determine the  effect  of s i l t  content  cyclic  loading  behaviour:  upon the (1)  following features stress-strain  pressure  generation;  (3)  constant  void  relative  ratio,  r e l a t i v e d e n s i t y ; and  v a r i a t i o n of density,  of  sand  response; cyclic and  (2)  strength  sand  pore at  skeleton  ( 4 ) v a r i a t i o n of c y c l i c strength a f t e r  c o n s o l i d a t i o n from l o o s e s t s t a t e o f s l u r r y d e p o s i t i o n .  97  CHAPTER 4 TRIAXIAL TEST CONSOLIDATION RESULTS  4.0  INTRODUCTION  The  f o l l o w i n g sections present  isotropic consolidation  data f o r t h e v a r i o u s sand m a t e r i a l s t e s t e d .  D i f f e r e n c e s and  similarities  are  including  in  consolidation  1) v o i d r a t i o s  behaviour  and r e l a t i v e  discussed,  densities at loosest  s t a t e o f s l u r r y d e p o s i t i o n and subsequent c o n s o l i d a t i o n , 2) compressibility  and b u l k  modulus  during  c o n s o l i d a t i o n , 3)  s t r a i n paths d u r i n g c o n s o l i d a t i o n , and 4) i n c r e m e n t a l ratios  t o demonstrate  inherent  anisotropy  during  strain  isotropic  consolidation.  4.1  ACCURACY OF CONSOLIDATION DATA  Inaccuracies mainly  i n calculated volumetric  from membrane p e n e t r a t i o n  chnages  were  therefore  corrected  effects.  strains  result  Measured  volume  f o r membrane  penetration  a c c o r d i n g t o method 2 d e s c r i b e d by V a i d and Negussey  (1984)  (see Appendix A ) . Two sands no  membrane  changes.  (Brenda 60/100, 100/140 g r a d a t i o n s ) penetration  This  was  correction  consistent  with  to  required  measured  the c r i t e r i o n  volume that  membrane p e n e t r a t i o n e f f e c t s a r e minimal i f average p a r t i c l e s i z e i s l e s s than h a l f t h e membrane t h i c k n e s s .  Well-graded  98  20/200  sand  coarse  grained  required  samples  required  a  Brenda  sand  20/40  relatively  large  small  correction,  and  membrane  Ottawa  while  C-109  penetration  sand  corrections  (see T a b l e 3.2). Although t h e c o n s o l i d a t i o n data p r e s e n t e d i s c o n s i d e r e d reliable, state  samples  were  generally  consolidation density  consolidated subject  response.  between  The  directly  complementary compression sand  at  identical  4.2  to  as  deposited  greater  difference  comparable  and e x t e n s i o n  consolidation  minimum, and was g e n e r a l l y relative  from  loosest  variation in  in  consolidated  tests,  such  as  t e s t s , on t h e same  stress  was  l e s s than 0.01 v o i d  kept  to  a  ratio  o r 2%  density.  VOID RATIO AND RELATIVE DENSITY DURING CONSOLIDATION  Figure  4.1  t o Figure  4.4  display  consolidation  (void r a t i o versus logarithm  of e f f e c t i v e confining  f o r the various  and s i l t y  Brenda c l e a n  sands.  data  stress)  As shown i n  t h e s e diagrams, t h e v o i d r a t i o a t t a i n e d by c l e a n sands a f t e r slurry  deposition  and a f t e r  (nominal c o n s o l i d a t i o n equal  density  deposited  tests  sands  although there among  stress  t o t h e maximum v o i d  minimum  various  placement of  ratio  attained  similar  by ASTM  3.2).  gradations,  standard  A l l loosest  consolidation  i s a large v a r i a t i o n i n absolute sand  platen  1 kPa) i s approximately  (see T a b l e  possess  of the top  especially  curves  void between  ratio the  FIGURE  4.1  TRIAXIAL TEST ISOTROPIC  CONSOLIDATION RESULTS  LOOSE COARSE GRAINED 2 0 / 4 0 BRENDA TAILINGS  FOR  SAND  FIGURE  1.20  4.2  TRIAXIAL TEST ISOTROPIC C O N S O L I D A T I O N R E S U L T S F O R L O O S E MEDIUM GRAINED 6 0 / 1 0 0 B R E N D A TAILINGS S A N D  -i  r °  1.10 -A 1.00  -  0.90  -  -20 40 60 80  0.80  <  0.70  z LU o  120  LU  140  LU  on  o >  0.60  -  160 0.50 0.40  -  CO  100  > 1—  rr  <  180 "I  1—l—l  l l I I| 10  EFFECTIVE ISOTROPIC  T  1  1—I  I I I I|  T  10  CONSOLIDATION STRESS  0\  1  1—I  (kPa)  I I I I  10 o o  FIGURE  4.3  TRIAXIAL T E S T UNIFORM  ISOTROPIC  FINE  GRAINED  CONSOLIDATION RESULTS 100/140  FOR  B R E N D A TAILINGS  LOOSE  SAND  103  u n i f o r m sands graded sand ratio  (Figure  (Figure  4.4).  The r e l a t i v e l y  o f the well-graded  result  of  finer  4 . 3 ) and t h e w e l l -  4.1 through F i g u r e  sand  particles  low maximum  i s interpreted  filling  voids  void  t o be t h e  between  coarser  p a r t i c l e s i n t h e w e l l mixed w e l l - g r a d e d sand.  4.3  VOLUMETRIC STRAIN DURING CONSOLIDATION  Figure  4.5 d i s p l a y s how v o l u m e t r i c s t r a i n changes w i t h  confining  stress  consolidated interesting show  i n gradation  absolute  void  compressibility sand may loose  may  the  slurry deposition  4.2, t h e r e ratios.  size,  of t h e i r  state.  It is  sands  even  tested  in  as  i n their  volumetric  gradations similar  with  though,  difference  similarity  the various  sands  compressibility  i s a large This  clean  Brenda  i n volumetric  o r mean g r a i n  between  various  the various  be a consequence  of  Brenda  fabric  i n the  state. The  in  that  difference  noted i n S e c t i o n  for  loosest  t o note  little  change  from  level  compressibility  Figure  4.5  of loose  Ottawa sand i s a l s o  f o r comparison purposes.  be seen t o be c o n s i d e r a b l y  less  This  shown  rounded  compressible  sand  than t h e  a n g u l a r t a i l i n g s sand, even though both sands were i n i t i a l l y at t h e i r loosest s l u r r y deposition Figure sand. little  The  4.6  state.  shows c o m p r e s s i b i l i t y o f l o o s e s i l t y  test  results  indicate  that  silt  20/200  content  has  e f f e c t on t h e c o m p r e s s i b i l i t y o f sand prepared a t the  Figure 4.5  Volumetric strains of various clean sands during isotropic consolidation from loosest state of slurry deposition  0.05 ISOTROPIC CONSOLIDATION  CHARACTERISTICS  F R O M L O O S E S T STATE O F S L U R R Y  DEPOSITION  0.04  POORLY GRADED 6 0 / 1 0 0 BRENDA  > CO  POORLY GRADED 2 0 / 4 0 0.03  BRENDA SAND  -  <  — I Ul  S A N D ^  WELL GRADED 2 0 / 2 0 0 BRENDA SAND  0.02  -  0.01  -  O LU  3 _J  OTTAWA C - 1 0 9 SAND, NORMAL PREPARATION  O >  -0.01 200  400  EFFECTIVE CONFINING STRESS  600  O"'  (kPa)  o  Figure 4.6  0.04  Volumetric strains of silty 2 0 / 2 0 0 Brenda sand during isotropic consolidation from loosest state of slurry deposition  106  loosest  state  of s l u r r y  d e p o s i t i o n , even  though  absolute  v o i d r a t i o undergoes a d r a s t i c r e d u c t i o n w i t h an i n c r e a s e i n silt  content  as  shown  i n Figure  4.4.  This  i s clearly  consequence o f e s s e n t i a l l y c o n s t a n t sand s k e l e t o n v o i d regardless of s i l t  a  ratio  content.  F i g u r e 4 . 7 d i s p l a y s t h e v a r i a t i o n o f b u l k modulus w i t h isotropic sands.  consolidation stress Bulk  modulus  confining stress  f o r various  i s seen  to  clean  increase  linearly  f o r each g r a d a t i o n o f sand  square of  root of confining stress.  was  found  for silty  deposition relative  The i n i t i a l b u l k  = 4 . 5 MPa.  Q  well-graded  densities  20/200  sand  with s i l t  content and sand  how  the  parameters  expression B = B  Q  sand, void  although ratio.  and  Q  K  B  several  A  summary  2 0 / 2 0 0 sand  skeleton  i n the  B  + K a ' vary with  silt  relative  The f i g u r e s bulk  content  modulus sand  The t e s t r e s u l t s show t h a t  silt  e f f e c t upon the c o m p r e s s i b i l i t y  silt  and  and  3  skeleton r e l a t i v e density. c o n t e n t has l i t t l e  B  level  at  (see F i g u r e 4 . 8 ) .  d e n s i t y i s shown i n F i g u r e 4 . 9 and F i g u r e 4 . 1 0 . show  modulus  i n b u l k modulus w i t h s t r e s s  compressibility c h a r a c t e r i s t i c s of s i l t y  its variation  This i s i n  l i n e a r v a r i a t i o n with  each sand i s approximately t h e same w i t h B A similar variation  of  quoted  with  t e s t e d , with a  s l i g h t v a r i a t i o n i n s l o p e f o r each type o f sand. c o n t r a s t w i t h t h e more commonly  tailings  content  drastically  The b u l k modulus o f v e r y  reduces  silty  sand  of s i l t y absolute or  silty  sand a t l a r g e r sand s k e l e t o n r e l a t i v e d e n s i t y may be seen t o increase s l i g h t l y with increasing s i l t  content.  Figure 4.7  Bulk modulus of various clean Brenda sands during isotropic consolidation from loosest state of slurry deposition  ISOTROPIC CONSOLIDATION  CHARACTERISTICS  FROM L O O S E S T STATE O F S L U R R Y  1 0  1  1 200  1  DEPOSITION  1 400  EFFECTIVE CONFINING STRESS  1  CT^  (kPa)  1 600  Figure 4.8  Bulk modulus of silty 2 0 / 2 0 0 Brenda sands during isotropic consolidation from loosest state of slurry deposition  13.33±.15% SILT e = 0.442+.002 c  = 94.910.6% c (skel) = 57.510.1% 13.67±.14% SILT e = 0.4881.001 c  Dr = 8 3 . 1 1 0.3% c  13.94±.13% SILT  e  c  = 0.5341 .007  Dr = 71.012% c  D r  200  ISOTROPIC CONSOLIDATION  c(skel)=  2 0  400  STRESS  -°  ± 2 %  600  LT'  FIGURE  4.9  S U M M A R Y O F COMPRESSIBILITY SILTY W E L L - G R A D E D  CHARACTERISTICS O F  20/200  B R E N D A TAILINGS  INITIAL SAND SKELETON VOID RATIO 0.86  130  0.82  0.78  0.74  e ( {  ske  |)  0.70 0.66  0.62  D  120  BULK MODULUS B  100-  ACT3  cri + Bo  +  i (skel). i (skel) taken at 20 kPa effective stress after sample preparation. e  D  r  80 BY  X  60  -10  0  % SILT WEIGHT *0 * 4.3 + 7.5 • 14 A 21  X  30  SAND  10  20  30  40  INITIAL SAND SKELETON RELATIVE DENSITY  50 Drj (  60 ske  |)  70  FIGURE 4 . 1 0  SUMMARY OF INITIAL COMPRESSIBILITY CHARACTERISTICS OF SILTY WELL-GRADED 2 0 / 2 0 0 BRENDA TAILINGS SAND INITIAL SAND SKELETON VOID RATIO 0.86  0.82  0.78  0.74  e; ( k | ) s  e  0.70  J—i—i—I—i—i—i—I—l—i i I i i i I i i i I  12  0.66 0.62 ' ' ' I ' l l  11 10 BULK MODULUS  9  B =  =  K CT3 + 0  Bo  8 7 6 •  5  % SILT BY WEIGHT  A-  * 0 * 4.3 + 7.5 • 14 A 21  3 2 1 • 0J  1 -10  e  i  (skel)-  Drj (skel)  t a k e n at 2 0 k P a e f f e c t i v e  stress after sample preparation.  r—1 0  i  1 10  1  1 20  1  1 30  1  1 40  1  1  1—r  50  60  INITIAL SAND SKELETON RELATIVE DENSITY Drj ( |) ske  70  Ill  4.4  AXIAL AND  RADIAL STRAIN DURING CONSOLIDATION  Although  the  magnitude  consolidation  is  similar  tailings  sands  distribution  tested,  the  is  various  a  large  than  consolidation.  This  techniques  rise  give  compressible  in  direction.  This  strain  indicates  that  to  and  has  a  fabric  the  horizontal  type  of  ratio,  see  radial  strain  incremental  a  strain  ratio  sand would  the  be  sand  as  would  is  not  may  be equal  been  a  anisotropic.  would  If  1.0, is  Okada  for  the  (incremental an  indicator vertical  strain  equals  consolidation, be  1.0 If  the  and  the  the sand  incremental  compressibility  important  by  (1969).  and  axial  isotropic.  It  vertical  method  radial  more  observed  used as  isotropic  to  isotropic  the  El-Sohby  be  sample.  ratio  greater  inherently  in  has  as  slurry  (1984), I s h i h a r a and  between  during  compressibility strain  in  reconstitution  c o n s o l i d a t i o n s t r a i n path  F i g u r e 4.12)  of  is  than  suggested  difference  compressibility  these  behaviour  Negussey  been  s l o p e of the  the  clean  variation  during  that  measurement o f i n h e r e n t a n i s o t r o p y by  of  loose  t e c h n i q u e show much  axial  o t h e r workers i n c l u d i n g  strain  during  A l l sands prepared u s i n g the  water p l u v i a t i o n  strain  The  strain  of a x i a l v e r s u s r a d i a l s t r a i n f o r each sand,  d e p o s i t i o n or  (1982),  volumetric  for  there  shown i n F i g u r e 4.11.  radial  of  to  note  of  that  Figure 4.11  0  0.002  Strain paths of various clean sands during isotropic consolidation from loosest state of slurry deposition  0.004  0.006  0.008  0.01  AXIAL STRAIN  0.012  £  a  0.014  0.016  0.018  Figure 4.12  Incremental strain ratios of various clean sands during isotropic consolidation from loosest state of slurry deposition WELL GRADED 2 0 / 2 0 0 BRENDA SAND  1 0  1  1 200  1  1  1  400  EFFECTIVE CONFINING STRESS  1 600  &'  c  (kPa)  114 isotropic loading  strain  incremental  shown  to  be  consolidation (1984).  isotropic  strain  ratio  monotonic  essentially  stress,  as  o f l o o s e Ottawa  constant  was  also  with  observed  variation  consolidation incremental  stress.  strain  compressibility  incremental  strain  ratio  i s low, i n d i c a t i n g than  radial  consolidation stress,  increases  Negussey  sand  show a  ratio  A t low c o n s o l i d a t i o n s t e s s  i s much lower  increasing  Apparently,  of  sand i s  increasing by  Various gradations of clean t a i l i n g s  consistent  ratio  do n o t ensure  response.  The  With  ratios  to  an  the process  levels, vertical  compressibility.  incremental  strain  constant  value.  essentially  of i s o t r o p i c  that  with  consolidation alters  the a n i s o t r o p i c c o m p r e s s i b i l i t y p r o p e r t i e s o f t a i l i n g s  sand  samples, when c o n s o l i d a t e d from a v e r y l o o s e s t a t e . F i g u r e 4.12 shows t h a t f i n e p o o r l y graded t a i l i n g s (100/140  gradation)  compressibility,  has  while  the  greatest  well-graded  sand  anisotropy  tailings  sand  in  (20/200  g r a d a t i o n ) shows t h e l e a s t a n i s o t r o p y i n c o m p r e s s i b i l i t y . A occurs  large only  difference during  isotropically consolidation, strain  =  radial  between  virgin  unloaded  strain)  and r a d i a l  consolidation. and  the s t r a i n  axial  path  below  strains  I f t h e sand i s  reloaded  after  virgin  reflects  isotropy  (axial  t h e maximum  past  pressure.  T h i s f e a t u r e has been used t o estimate membrane p e n e t r a t i o n correction  (Vaid and Negussey, 1984, Method 2 ) .  who use d r y o r moist tamping t o prepare sand  Researchers  samples, which  115 must  be  saturated  essentially following been  after  generally  i s o t r o p i c behaviour d u r i n g  saturation  observed  deposition  deposition,  (Miura  that  are  much  virgin  and T o k i ,  sands less  which  sands which a r e prepared  must  be  resaturated  display  I t has  saturated  compressible  c o n s o l i d a t i o n than water p l u v i a t e d sands. that  consolidation  1982). are  observe  also after  during  virgin  One may  conclude  i n a moist o r d r y s t a t e and a  form  of  overconsolidation  behaviour. Consolidation  strain  paths  dependent upon many f a c t o r s , level, perhaps  strain most  shown  including  i n Figure void  4.11  ratio,  stress  h i s t o r y , time dependent creep behaviour, importantly  the  The  that  strain  results paths  and from  sample  preparation  Figure  4.11 a r e average r e s u l t s f o r s e v e r a l t e s t s performed  on each sand t y p e .  technique.  fabric  are  shown i n  116  CHAPTER 5 UNDRAINED MONOTONIC LOADING BEHAVIOUR  5.0  INTRODUCTION  The clean  results  on  different  sand  20/40,  (20/200) w i t h a D  graded  sand,  and  sands  tests  T e s t s were conducted on p o o r l y - g r a d e d sands w i t h (gradations  Brenda  loading  compared.  50  silty  undrained monotonic  a r e p r e s e n t e d and  D  and  of  60/100 and  w e l l - g r a d e d 20/200  distributions).  Samples  soil  sand  which  contained  (see S e c t i o n 3.2.1.2 f o r g r a i n of  each  loosest state of s l u r r y deposition. yields  a well-graded  s i m i l a r t o t h a t o f 60/100 p o o r l y -  5 0  v a r i o u s amounts o f s i l t  state  100/140),  which  displays  sand  were  size  prepared  at  C o n s o l i d a t i o n from t h i s the  most  contractive  undrained l o a d i n g response expected f o r each water d e p o s i t e d material. triaxial  Samples were  isotropically  Both  compression and e x t e n s i o n t e s t were performed over  a range o f c o n f i n i n g s t r e s s e s . initial  consolidated.  state  emphasize  of  isotropic  t h e e f f e c t s which  Samples were t e s t e d from an consolidation  in  order  to  d i r e c t i o n o f l o a d i n g have upon  s o i l behaviour.  The e f f e c t s o f i n h e r e n t a n i s o t r o p y i n water  pluviated  sand  are  properties  specific  and  discussed,  and  identified  in  test  t o water p l u v i a t e d various  c a t e g o r i z a t i o n are assessed.  methods  results.  sand of  Soil  are  identified  sand  behaviour  117 5.1  UNIQUENESS OF UNDRAINED RESPONSE  For s a t u r a t e d s o i l a t a g i v e n c o n s o l i d a t i o n and d e n s i t y state,  t h e undrained  s t r e s s path  stress-strain  response  and  a r e unique r e g a r d l e s s o f t h e t o t a l  effective  s t r e s s path,  as l o n g as t h e d i r e c t i o n o f major p r i n c i p a l s t r e s s e s remains the  same  in  relation  to  the  sand  deposition  (Bishop and Wesley, 1973; V a i d e t a l . , 1988). in  Figure  5.1  f o r coarse-grained  compression  loading  (denoted  and  A  compression t e s t active t r i a x i a l shown.  by  B).  two  different  Results  of  test  Essentially  identical  extension  c o n f i n i n g pressure,  membrane  stress  a l . , 1975;  paths  and an  s t r e s s constant) a r e response  f o r t h e two t e s t s . although  penetration,  but i t may  and  (3)  and The the  i s i n general not i d e n t i c a l  undrained  Ishihara  in  triaxial  s t r e s s constant)  effective  et  At a  stress  path  a l s o be a f f e c t e d a t t h e  same v o i d r a t i o by (1) p r e s t r a i n h i s t o r y et  sand  as d i s c u s s e d i n S e c t i o n 2.1.3.1.  depends on v o i d r a t i o ,  Seed  total  i s a l s o unique,  e x t e n s i o n e f f e c t i v e s t r e s s path compression path,  20/40  stress-strain  undrained  response  T h i s i s shown  conventional  (with a x i a l t o t a l  s t r e s s path may be noted  given  a  (with r a d i a l t o t a l  effective  to  Brenda  direction  (Finn e t a l . , 1970;  a l . , 1978,  sample  1982),  preparation  (2)  method  ( M u l i l i s e t a l . , 1975; Marcuson and Townsend, 1974; Tatsuoka et  a l . , 1986). Uniqueness o f e f f e c t i v e s t r e s s path f o r a g i v e n l o a d i n g  mode r e q u i r e s t h a t pore p r e s s u r e generated  during  undrained  Figure  5.1  Verification in u n d r a i n e d  of  independence  monotonic  of  effective  compression  stress  loading  of  path  from  Brenda  total  20/40  stress sand  path  119 l o a d i n g be dependent for  upon t o t a l  s t r e s s path.  compression t e s t A and B i n F i g u r e 5.1.  p r e s s u r e response i s c l e a r l y not unique.  T h i s i s shown A b s o l u t e pore  The f a c t t h a t pore  p r e s s u r e response i s not unique makes i t a r a t h e r poor index property  f o r the  comparison  of  soil  behaviour  subject  to  d i f f e r e n t modes o f l o a d i n g .  5.2  BEHAVIOUR OF CLEAN SANDS  Figure  5.2  through  F i g u r e 5.4  l o a d i n g behaviour o f v a r i o u s c l e a n The  sands  were  consolidated  from  display Brenda  loosest  the  monotonic  sand g r a d a t i o n s . state  of  slurry  deposition, t o various l e v e l s of consolidation s t r e s s .  For  comparison purposes, the response o f c l e a n sands a t 200  kPa  c o n s o l i d a t i o n s t r e s s has been summarized i n F i g u r e 5.5.  5.2.1  S t r e s s - S t r a i n Response The  typical All  results undrained  p r e s e n t e d i n F i g u r e 5.2 stress-strain  response  of  5.5  Brenda  show sand.  g r a d a t i o n s show a c o n s i d e r a b l e d i f f e r e n c e o r a n i s o t r o p y  between e x t e n s i o n and  compression  sort of anisotropy i n s o i l natural  and  loading  reconstituted  sands  by  several  This  a n i s o t r o p y i n undrained  response  workers,  Chang e t a l . (1982),  Miura and T o k i (1982), and Chung (1985).  g r a i n s i z e and g r a d a t i o n .  response.  behaviour has been observed f o r  i n c l u d i n g I s h i h a r a e t a l . (1978,1982),  that  through  T e s t r e s u l t s show  i s affected  by  both  P o o r l y - g r a d e d g r a d a t i o n s o f sand  120  Figure 5.2  Undrained monotonic triaxial test results for 2 0 / 4 0 Brenda sand  1 00 —I—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—i—r 0  100  200  (LTj < 1  o  300 )/2  400  (kPa)  .  0.8 -  AXIAL STRAIN £  0  (%)  500  600  121  Figure 5.3  Undrained monotonic triaxial test results for 6 0 / 1 0 0 Brenda sand  0  100  200  K  <  300 )/2  400  (kPa)  AXIAL STRAIN  £  a  (%)  500  600  122  Figure 5.4  Undrained monotonic triaxial test results for 20/200 Brenda sand  0  100  200  300  (C7>LT;)/2  400  500  5  10  600  (kPa)  1 _  o  -15  -10  -5  0  AXIAL STRAIN  £  0  (%)  15  123  Figure 5.5  Undrained monotonic triaxial test results for various sand gradations  (LTj+CT'Vz  (kPa)  AXIAL STRAIN  £  o  (%)  (20/40,  60/100  anisotropy uniform soil  100/140)  60/100  and  100/140  20/200  extension  sand  has  loading,  transformation  sands  i n compression  l i q u e f a c t i o n response  graded  exhibit  considerably  than t h e w e l l - g r a d e d 20/200 sand.  response  state  and  state  loading,  than  typically  grained dilative  y e t almost  i n extension  limited  with  have  Finer  more  steady-  loading.  Well-  l i q u e f a c t i o n response  larger observed  strength  at  i n any o f t h e  in  phase poorly-  graded sands. The from  various  loosest  behaviour  in  Brenda sands which have been  state  of  slurry  compression  behaviour i n extension  deposition  loading  loading.  but  consolidated show  rather  similar different  These r e s u l t s suggest  although t h e behaviour o f d i f f e r e n t s o i l s  that  i n one p a r t i c u l a r  mode o f l o a d i n g may be s i m i l a r , t h i s does not ensure s i m i l a r behaviour suggest  i n other  that  soils  modes o f l o a d i n g . with  loading  test  each s o i l was d e p o s i t e d The  density  through capacity  water  of  results  d i f f e r e n t f a b r i c s may  d i f f e r e n t or s i m i l a r s o i l properties. compression  These  have  either  I t i s suggested  r e s u l t s are s i m i l a r only  deposited  i s governed  of the material  by  by  vertical  the v e r t i c a l  a t low s t r e s s  state.  settlement  load  level.  that  because  at loosest slurry deposition  sands  also  bearing  Apparently  the l o o s e s t s t a t e v e r t i c a l c o m p r e s s i b i l i t y p r o p e r t i e s o f t h e various  soil  gradations  being maintained a t higher  i s s i m i l a r , with  this  similarity  consolidation stress level.  125  5.2.2  E f f e c t i v e S t r e s s Path Response The  various  effective  Figures  5.2  through  5.5  loading  on  undrained  stress  path  emphasize  behaviour.  responses  shown i n  the e f f e c t  o f mode o f  Figure  shows  5.5  that  u n i f o r m f i n e g r a i n e d sands (60/100 and 100/140) have s i m i l a r behaviour,  which  i s considerably  different  from  that  of  e i t h e r coarse g r a i n e d 20/40 sand o r w e l l - g r a d e d 20/200 sand. The  effective  probably  stress  affected  p e n e t r a t i o n causes response  due  path by  of coarse  membrane  induced  20/40 sand i s  penetration.  a characteristic  t o lower  grained  stiffening  pore  p e n e t r a t i o n e f f e c t s d u r i n g undrained  Membrane o f undrained  pressures.  Membrane  loading are believed to  be minor f o r t h e f i n e r g r a i n e d sands t e s t e d (see T a b l e 3.2). A peculiar  f e a t u r e o f t h e compression  of t h e w e l l - g r a d e d at  low  deviator  20/200 sand stress  slightly  softer  than  deviator  stress  and  and  strain  level,  this  sand  sand,  yet  at  level,  well-graded  s l i g h t l y s t i f f e r than p o o r l y - g r a d e d sand. probably  a result  response  shown i n F i g u r e 5.5 i s t h a t  poorly-graded strain  loading  of the difference  sand  is high is  T h i s behaviour i s  i n fabric within well-  graded and p o o r l y - g r a d e d w a t e r - p l u v i a t e d sands. Effective  stress  well-graded  sand  graded  behaviour.  sand  path  behaviour  plots  show  quite  clearly  that  i s l e s s a n i s o t r o p i c than p o o r l y -  126  5.2.3  Pore P r e s s u r e Response As d e s c r i b e d i n S e c t i o n 5.1, pore p r e s s u r e response i s  not  unique,  but dependent  upon  total  stress  path.  Pore  p r e s s u r e d a t a shown i n F i g u r e s 5.2 through 5.5 r e f l e c t s t h e influence of t o t a l comparison  s t r e s s path and mode o f l o a d i n g .  o f pore  p r e s s u r e s generated  e x t e n s i o n l o a d i n g may to  the  difference  compression  i n compression  lead to u n r e a l i s t i c in  total  Direct and  c o n c l u s i o n s , due  confining  stress  between  and e x t e n s i o n modes o f l o a d i n g .  To s e p a r a t e shear induced pore p r e s s u r e from changes i n pore p r e s s u r e induced by changes i n mean normal pressure  data  has been p l o t t e d  p r e s s u r e parameter clearly  that  extension  loading  induced are  Fine  grained uniform  anisotropy  pressures  anisotropy  response,  isotropic towards  consolidation in  larger  isotropic  'a'  'a'  while well-graded  stress.  stress.  parameters  parameters  consolidation  than  in  those tested.  sand i s  response.  'a' curves a r e n o r m a l i z e d w i t h  response  consolidation  larger  smaller  soil  generated  a r e shown t o have t h e g r e a t e s t  Pore p r e s s u r e parameter to  pore  F i g u r e 5.6 shows  shown t o have t h e l e a s t a n i s o t r o p y i n l o a d i n g  respect  (1960)  l o a d i n g f o r a l l sand types  sands  i n loading  pore  considerably  generated i n compression  pore  u s i n g Henkel's  'a' (see F i g u r e 5.6).  shear  stress,  The  is  reduced  There  There  show  by  that  increasing  i s a general trend  i n compression  i n extension stress.  curves  loading  loading, i s also  at  and  higher  a general  127  Figure 5.6  P l o t of Henkel's pore pressure parameter ' a ' versus s t r a i n f o r various gradations of undrained Brenda sand  16 15  AU = A CF_ + a 3 ( A T )  14  oct  13 AL7  12  b  - (ALTJ +Acr  z  +Acr  3  )/3  ?oct- CCLT,-0^).(0^-LT)»cCr3-flri)]/3  11  3  10 9  6 0 / 1 0 0 BRENDA  8  ( S E E F I G U R E 5.3)  SAND  7 6 oc LU  s: < OC  <  a.  oc CO  to  LU OC Q_ LU CC O  a. co LU  5 4 3 2 1 0 54  2 0 / 4 0 BRENDA  3  SAND  ( S E E F I G U R E 5.2)  2 1 0 54  2 0 / 2 0 0 BRENDA  3  SAND  ( S E E FIGURE 5.4)  2 1 0 -1 -15  -5  0  AXIAL STRAIN  5 £  (%)  10  15  128 trend  toward  smaller  variation  in  'a'  parameter  with  v a r i a t i o n i n s t r a i n l e v e l at higher consolidation s t r e s s .  5.2.4  E f f e c t of Consolidation An  increase  extension  Stress  i n isotropic consolidation  stress  affects  and compression l o a d i n g response d i f f e r e n t l y . A l l  sand t y p e s show a tendency toward more c o n t r a c t i v e  response  i n compression l o a d i n g a t h i g h e r c o n s o l i d a t i o n s t r e s s .  This  contrasts  s i g n i f i c a n t l y w i t h a tendency toward more d i l a t i v e  response  in  extension  There  is a  stress.  between compression consolidation of inherent stress.  trend  at  anisotropy  higher  towards  and e x t e n s i o n  stress.  The  loading  This  lessening  difference  response w i t h  implies  tendency  increasing  a change i n t h e nature  w i t h changing l e v e l  observed  consolidation  of consolidation  towards  more  isotropic  behaviour a t h i g h e r c o n s o l i d a t i o n s t r e s s i s s i m i l a r t o t h a t observed  i n consolidation  Consolidation  stress  strain  level  observed i n c r e a s e  response w i t h i n c r e a s i n g only  of  water  behaviour stress,  may or  conditions.  gradation.  i n d i l a t a n c y of extension isotropic consolidation stress  sand, due t o t h e h i g h l y  pluviated be  sand  observed  under  after at  anisotropic  Anisotropic  loading  s t r e s s may  range behaviour o f anisotropic  deposition.  much  4.4).  t o have l e s s o f an  than s o i l  be c h a r a c t e r i s t i c o f lower  water p l u v i a t e d  (see S e c t i o n  i s observed  e f f e c t upon sample a n i s o t r o p y The  data  larger  nature  Different consolidation  consolidation  consolidation with v e r t i c a l  stress stress  129 l a r g e r than h o r i z o n t a l s t r e s s has been observed t o decrease d i l a t a n c y and s t r e n g t h i n e x t e n s i o n  5.2.5  E f f e c t o f G r a i n S i z e and G r a d a t i o n For  loading  loosest state slurry response  extension upon  loading.  i s s i m i l a r regardless  loading  response  gradation.  behaviour  c o u l d be e x p l a i n e d  loading  r a t i o w i t h i n more well-graded  difference various slurry  in  sands t e s t e d .  densities,  compression  of gradation, quite  toward  i n more  dependent  more  dilative  well-graded  This explanation  i t cannot  loading  explain  response  Consolidation  a l l sands  sand  from  void  i s not  the small  between  the  loosest state of  i s observed t o produce v a r i a b l e  although  while  toward lower a b s o l u t e  sand.  because  compression  deposition  trend  by t h e t r e n d  convincing  sands,  i s apparently  The observed  i n extension  completely  deposited  consolidated  relative  from  loosest  s l u r r y d e p o s i t i o n s t a t e have s i m i l a r b u l k modulus o r volume change c h a r a c t e r i s t i c s (see S e c t i o n appear  t o be  density  of s o i l  differences can  be  inherent soil  a  simple  and i t s undrained  explained  anisotropy  gradation.  loading  as d i f f e r e n c e s  well-graded  dilative  relative  response. soil  The  gradations fabric  and  of differences i n  Uniform sands show t h e g r e a t e s t  while  more  the  in soil  which a r e t h e r e s u l t  more i s o t r o p i c behaviour. slightly  There does not  r e l a t i o n s h i p between  between responses o f d i f f e r e n t  best  anisotropy,  4.3).  degree o f  sands show a tendency  toward  Coarse g r a i n e d 20/40 sand shows a  response  than  other  uniform  sands,  130 which  could  effects.  be  a  consequence  Membrane p e n e t r a t i o n  of  membrane  effects  penetration  are believed  t o be  as c r i t i c a l  stress  n e g l i g i b l e f o r o t h e r sands t e s t e d .  5.3  MATERIAL PARAMETERS  Various ratio, (or  material  parameters,  phase t r a n s f o r m a t i o n  friction  angle  such  angle,  ultimate  a t maximum o b l i q u i t y ) ,  friction  and s t e a d y - s t a t e  concepts have been used by v a r i o u s r e s e a r c h e r s 2.0)  to  characterize  undrained  (see S e c t i o n  behaviour,  with  assumption t h a t t h e m a t e r i a l parameters a r e c o n s t a n t s p e c i f i c type o f sand. indicate  that  sand  indeed  and  s t r e s s paths,  stress  fairly  ratio  applicable.  material  parameters  such  fora  while  other  parameters  and s t e a d y - s t a t e  concepts  5.1 p r e s e n t s  as  phase  angle a t maximum o b l i q u i t y  c o n s i s t e n t between v a r i o u s  Table  the  T e s t r e s u l t s o f Brenda t a i l i n g s sand  t r a n s f o r m a t i o n angle and f r i c t i o n are  angle  such  test  samples  as c r i t i c a l  are not generally  a summary o f t h e m a t e r i a l  properties.  5.3.1  U l t i m a t e F a i l u r e Envelope F r i c t i o n angle  1975),  o r boundary  1982),  has been  types  o f sands  a t maximum o b l i q u i t y surface  shown tested  friction  t o be f a i r l y using  (Ishihara et. a l . ,  angle  (Chang e t .  constant  t h e undrained  al.,  f o r various  triaxial  test.  T h i s angle has a g e n e r a l dependence upon s o i l mineralogy and  131  Table 5.1  Sand s a m p l e undrained friction  angles  Undrained friction angle (Degrees) Compression 0 .t  tt  0CSR  U  Brenda  Extension  0CSR  Sand  Gradation 20/40  WP  37.5  35.2  20/40  SD  35.6  34.2  36.0  34.0  35.3  33.0  SD  36.0  33.9  (Chem,  1985)  38.2  36.5  25.1  Ottawa  C - 1 0 9 Sand  60/100  SD  100/140 20/200  SD  C-109  37.5  34.5  18  26.4  33.0  31.7  17.0  26.4  36.0  34.0  16.1 12.0  34.0  SD  30.6  29.5  20.0  WP  30.9  30.1  21.5  (Chern,  1985)  31.5  29.5  23.5  (Chung,  1985)  31.5  29.5  23.0  WP = Loosest state water pluviated  sand  SD = L o o s e s t state slurry deposited sand  31.4  19.0  9.1 31.5  29.5  10.7  31.5  29.5  13.5  the  intrinsic  angle  Some r e s e a r c h e r s for  a  single  variation with  1982, in  o f sand  stress  increasing  transformation  1982),  material  1982),  and  and  angle a t v e r y 2.2), (2)  density  tests (4)  shown  then  (Chang some  results,  tested  increasing  decreasing  to  some i n c r e a s e  w i t h an  increase  triaxial  with  5.1, a  not  varying  from  36  as  Toki,  preparation  angle  consistent  at  maximum  f o r a l l Brenda  loading.  consistent  degrees  and  and  1982).  friction  i n compression  and T o k i ,  extension  sample  (Miura and T o k i ,  are  phase  et.a l . ,  e t . a l . , 1982, Miura  results  (1) some  (Castro  variation  i n Table  gradations  first  angle  large s t r a i n  o b l i q u i t y o f 36 degrees i s f a i r l y  loading  grains.  as f o l l o w s :  (Chang e t . a l . , 1982, Miura  t e c h n i q u e o r sand f a b r i c As  mineral  level,  (3) some v a r i a t i o n between  compression  sand  between  and s t r a i n  strain  see F i g u r e  relative  friction  have found s l i g h t v a r i a t i o n s i n t h i s  type  with  of  Extension  as  compression  f o r 60/100  sand  t o 34  degrees f o r 20/200 sand and 33 degrees f o r 20/40 sand. slight  variations  obliquity  could  following: extension much  i n extension  be due t o s e v e r a l  (1) v a r i a t i o n w i t h loading  lower  stress  effective  l o a d i n g s t r e s s paths, properties different  friction  between sand  angles  factors,  a t maximum  i n c l u d i n g the  effective stress  paths  confining  reach  ultimate  stress  The  than  level,  as  failure  at  compression  (2) some n a t u r a l v a r i a t i o n i n m a t e r i a l  extension  gradations,  and compression (3) incomplete  loading f o r  development  of  133 ultimate  friction  angle  i n the stress  and s t r a i n  range  tested. Some e x t e n s i o n maximum than  obliquity  10  to  extension strains  test  results  friction  15%)  due  failure  angle  to  planes.  i n extension  show a marked decrease i n at large  t h e development The development  test  strain  results  of  (greater conjugate  o f non-uniform  can be e a s i l y  identified  by t h i s marked decrease  i n boundary envelope f r i c t i o n  The  from  test  data  derived  representative  of  strain  elemental  ranges  soil  which  behaviour  angle.  a r e non-  have  been  omitted. I t may be t h a t f r i c t i o n angles v a r i o u s sand g r a d a t i o n s because  stress-strain  similar  (see F i g u r e  a t maximum o b l i q u i t y o f  i n compression  behaviour 5.5).  loading are similar  i n compression Stress-strain  extension loading i s considerably d i f f e r e n t g r a d a t i o n s o f l o o s e sands t e s t e d . produce  the  extension ultimate 2.1  variation  tests friction  may  also  angles  behaviour  in  f o r the various  Sand f a b r i c e f f e c t s which  stress-strain  account  behaviour  in  f o r the variation  i n extension  loading  in  (see S e c t i o n  and 2.2).  5.3.2  Angle o f Phase Phase  slurry  angles  Transformation  transformation  t e s t e d a r e summarized by  of  loading i s  deposition  angles  i n Table have  as samples prepared  f o r the various  5.1.  similar  Sand samples phase  sands  prepared  transformation  by water p l u v i a t i o n .  Extension  phase t r a n s f o r m a t i o n angles g e n e r a l l y show g r e a t e r v a r i a t i o n with  sand  gradation  transformation than  than  angles  t h e angles  compression  angles.  Phase  a r e c o n s i s t e n t l y 1 t o 2 degrees  o f maximum  obliquity.  As w i t h  less  ultimate  f r i c t i o n angles d e s c r i b e d i n t h e p r e v i o u s s e c t i o n , e x t e n s i o n phase  transformation  between  different  angles  may  gradations  due  be  slightly  different  to differences  i n sand  fabrics.  5.3.3  C r i t i c a l Stress Ratio Critical  stress  ratios  of  Brenda  sand  (see S e c t i o n  2.1.1) a r e q u i t e v a r i a b l e between compression and e x t e n s i o n loading  (Table 5.1), thus CSR v a l u e s may be assumed t o be a  function  o f mode  friction  angle  stress  only)  density before as  sample  stress ratio  initial  when  deposition  Extension  CSR  CSR-  consolidation  a t 26  degrees.  lower and have been  sample p r e p a r a t i o n  technique  2.1).  Table  i n extension  relative  i s used  as  for a  density  a  5.1  from soil  specific a r e found  c o n f i n i n g s t r e s s over  or  sample  strain  indicates  that  l o a d i n g a l s o v a r i e s with  consolidation  values  preparation  increasing  constant  a r e much  preparation  critical  gradation  i n higher  loading  c o n s o l i d a t i o n (Chung, 1985), and (2) f a c t o r s  (see S e c t i o n  slurry  are f a i r l y  (1) i n i t i a l  history  soil  Compression  (obtained  l o a d i n g CSR v a l u e s  shown t o v a r y w i t h  such  loading.  values  samples  Extension  of  loosest density  sand  state of reference.  gradation  t o be c o n s t a n t  and with  the c o n s o l i d a t i o n s t r e s s  135 range t e s t e d , as has been found f o r Ottawa C-109 is the  isotropically same  sand  which  consolidated to various stress levels  initial  preparation  g e n e r a l i z a t i o n , one may  density  (Chung,  1985).  s t a t e t h a t more a n i s o t r o p i c  graded sands a r e more l i k e l y  t o have lower CSR  from As  a  poorly-  v a l u e s than  w e l l - g r a d e d sands. From t e s t r e s u l t s ,  one may  conclude t h a t a  compression  l o a d i n g C S R - f r i c t i o n angle v a l u e o f 26 degrees i s a maximum value  f o r Brenda  sand,  because  i t i s observed  in  samples  which have o n l y minor l i m i t e d l i q u e f a c t i o n b e h a v i o u r and a r e generally d i l a t i v e CSR  values  are  d e s c r i b e d above. design  CSR  in triaxial possible  and  Thus i t may  value  based  compression depend  loading.  upon  the  Lower factors  be u n c o n s e r v a t i v e t o assume a  upon  compression  loading  r e s u l t s , as lower CSR v a l u e s a r e p o s s i b l e and indeed i n some f i e l d l o a d i n g c o n d i t i o n s .  Sand m i c r o - f a b r i c  test likely  factors  which determine CSR v a l u e s i n undrained l o a d i n g a r e p r o b a b l y different 2.2  i n compression and e x t e n s i o n l o a d i n g  and S e c t i o n 7 . 0 ) . G e n e r a l i z a t i o n s made about compression  loading  CSR  values  (Castro,  Mohamad and Dobry, 1986) CSR  (see S e c t i o n  values,  other  than  determined  CSR the from  may  1982,  samples  et.  a l . , 1985,  not a p p l y t o e x t e n s i o n l o a d i n g  v a l u e s determined triaxial  Sladen  from  compression which  loading  test,  are prepared  or  conditions CSR  in a  values  different  manner o r have a s t r a i n h i s t o r y which d i f f e r s from t h a t used i n t h e t e s t s e r i e s upon which the g e n e r a l i z a t i o n s a r e based.  136 5.3.4  S t e a d y - S t a t e Concepts The  state  triaxial  concepts  undrained  test  results  (Castro  loading  show  clearly  e t a l . , 1982)  response  of  do  Brenda  that  not  apply t o  sand.  Steady  concepts imply t h a t undrained s t r e n g t h i s s o l e l y a of s o i l void r a t i o ,  and  i s not dependent  steady the  state  function  upon the d i r e c t i o n  o f l o a d i n g o r the type o f t e s t performed.  Undrained  tests  performed on water p l u v i a t e d Brenda sands c l e a r l y do not these  criteria  (Chung,  undrained  strength  pluviated  Ottawa  results  up  considered,  upon  C109  to  600  Brenda  liquefaction  1985  or  shows a  direction  sand). kPa  sand  low  and  dilatancy would  and  stress  undrained  water  If  to liquefaction, Such  strength  on  are  extension highly  especially  dependence o f  direction  i n the use  concepts o f d e s i g n (Castro e t a l . ,  test  stress  sand i s found t o be  levels.  of  non-susceptible to  liquefaction.  have s e r i o u s i m p l i c a t i o n s  in  compression  confining  i s found t o be  susceptible  dependence  loading  only  effective  limited  consolidation  of  If  behaviour i s c o n s i d e r e d , Brenda contractive  similar  fit  1982),  of  soil  loading  o f steady wherein  at  a  state unique  steady s t a t e l i n e o b t a i n e d from compression t e s t s i s the key assumption.  I t would be n e g l i g e n t not t o c o n s i d e r  extension t e s t  results  i n an a n a l y s i s  o f sand  triaxial  liquefaction  resistance. The  difference  in  the  e x t e n s i o n response o f water  observed pluviated  compression sand  is a  versus  reflection  o f t h e i n h e r e n t a n i s o t r o p y o f the m a t e r i a l w i t h r e s p e c t  to  137 the  d i r e c t i o n o f maximum p r i n c i p a l s t r e s s o f l o a d i n g .  angle  between  deposition a.  the  maximum  and  the  i s designated  mode corresponds t o a=0° w h i l e t h e e x t e n s i o n  mode corresponds t o a=90°.  4.4)  stress  d i r e c t i o n ( v e r t i c a l under g r a v i t y )  Compression  loading  principal  The  S o f t e r response under h o r i z o n t a l  (as a l s o noted i n c o n s o l i d a t i o n s t r a i n d a t a , S e c t i o n  i s mainly  extension similar  responsible  f o r contractive  behaviour i n  b u t d i l a t i v e behaviour i n compression difference  undrained  response  1971;  Miura  1982;  Chung,  in triaxial has been  and T o k i ,  compression  reported  1982; Hanzawa,  1985).  Recent  by  loading.  and  extension  others  (Bishop,  1980; Chang  undrained  testing  A  eta l . ,  using the  hollow c y l i n d e r t e s t apparatus which may induce a f u l l  range  o f v a r i a t i o n o f maximum p r i n c i p a l s t r e s s d i r e c t i o n from Q=0 to  a=90 degrees  systematic  shows t h a t  pluviated  extension  pluviated  sand  undergoes  weakening under i n c r e a s i n g a (Symes e t a l . , 1985;  Shibuya and H i g h t , 1987). water  water  sand  These t e s t r e s u l t s i n d i c a t e t h a t  i s most c o n t r a c t i v e  mode o f l o a d i n g ,  and l e a s t  under  a  triaxial  contractive  o r most  d i l a t i v e under a t r i a x i a l compression mode o f l o a d i n g . The  nature  of  inherent  specimens  appears  pronounced  as t h a t i n water d e p o s i t e d  This  could  be  to  be  anisotropy  attributed  similar  to  but  i n moist  tamped  possibly  sands  n o t as  (Hedberg,  one-dimensional  1977).  vertical  compression i n t h e forming mold s i m i l a r t o t h a t which o c c u r s during  water  deposition.  Consequently,  moist  tamped  m a t e r i a l s would a l s o show d i r e c t i o n a l v a r i a t i o n i n undrained  138 behaviour.  I t i s s u r p r i s i n g t h a t r e s e a r c h e r s engaged i n t h e  development  and a p p l i c a t i o n  remained  o f steady  state  concepts  o b l i v i o u s t o path dependence o f undrained  have  response,  when such a dependence i n c l a y has been r o u t i n e l y c o n s i d e r e d s i n c e t h e p i o n e e r i n g work o f Bjerrum Although  the  (1972).  undrained  strengths  t r a n s f o r m a t i o n o r steady s t a t e i n compression are d i f f e r e n t ,  the f r i c t i o n  at  phase  and e x t e n s i o n  angle i s e s s e n t i a l l y  identical.  T h e r e f o r e , t h e phase t r a n s f o r m a t i o n o r steady s t a t e l i n e f o r contractive Chem,  response  1985)  is  not  essentially  unique  differences  in  transformation  i n void  in  unique,  undrained  strength  horizontal  compressibility.  large variation a  simple  soil  though  extension  loading  embankment  these  lines  space.  mainly on  on  could  foundation.  expect  a  assessment o f s o i l  i t is  s t r e n g t h be structures.  EFFECT OF SILT CONTENT UPON UNDRAINED MONOTONIC LOADING RESPONSE  The response sand  pore  greater  Thus  important t h a t a d i r e c t i o n a l dependence o f s o i l  5.4  phase  larger  account  one  These  or  to  are  s t r e s s d i r e c t i o n s , even w i t h i n or  considered i n the s t a b i l i t y  (Vaid and  state  conditions,  i n principal  space  stress  steady  a r e due  induced  field  in  stress  effective  pressures  Under  ratio  undrained  effective  of monotonically  samples  deposited  s t r e s s paths and s t r e s s - s t r a i n  loaded  at  silty  loosest  well-graded  state  by  the  20/200 slurry  d e p o s i t i o n method and i s o t r o p i c a l l y  consolidated  e f f e c t i v e s t r e s s a r e shown i n F i g u r e 5.7. state  void  ratio  obtained  by  Since the loosest  slurry deposition  s u b s t a n t i a l l y with increasing s i l t  content  the response shown i n F i g u r e 5.7 r e p r e s e n t s void  ratios.  loosest  The ASTM standard  state  samples  with increasing s i l t silt  content  to  relative  98%  at  22.3%  o f sand s k e l e t o n  l e s s with increasing s i l t  4.4)  a l a r g e range o f d e n s i t i e s of the substantially  (Figure 5.7), from 29% a t zero silt  s k e l e t o n v o i d r a t i o o f t h e samples a definition  decreases  (see F i g u r e  a r e shown t o i n c r e a s e  content  t o 350 kPa  content.  (see S e c t i o n  The  sand  3.2.2.4 f o r  v o i d r a t i o ) i s shown t o v a r y  content  ( F i g u r e 5.7).  F i g u r e 5.7 shows t h a t t h e compression l o a d i n g behaviour of  the s i l t y  increasing  20/200 sand  dilatancy  as  behaviour i n e x t e n s i o n  i s dilative silt  with  content  loading  a trend  towards  i s increased.  The  i s contractive with l i m i t e d  l i q u e f a c t i o n , and a t r e n d towards l e s s c o n t r a c t i v e behaviour as  silt  content  i s increased.  The compression  behaviour  appears t o be more g r e a t l y a f f e c t e d by an i n c r e a s e c o n t e n t than t h e e x t e n s i o n Ishihara  in silt  behaviour.  e t . a l . (1980) suggest t h a t  relative  density  i s n o t a s u i t a b l e index f o r c h a r a c t e r i z i n g t h e behaviour o f s i l t y sands.  Instead  they suggest t h e use o f v o i d r a t i o f o r  comparing t h e behaviour o f s i l t y  sands. The v o i d  r a t i o and  r e l a t i v e d e n s i t y data shown i n F i g u r e 5.7 suggests t h a t both relative  density  characterizing  and  void  t h e behaviour  ratio  are  of s i l t y  poor  sands,  indices because  for both  140  Figure 5.7  0  Undrained monotonic triaxial test results for silty 2 0 / 2 0 0 sand  T i i i  i i i i i i i i i i i i i — i i i i—i—i 100 200 300 400  0J ' a  <  )/2  (kPa)  0.8 -  A X I A L STRAIN  E  a  (%)  i i — i — i i—r 500 600  141 density  parameters v a r y  content, yet s o i l  s u b s t a n t i a l l y with  behaviour i s not observed t o v a r y a  amount w i t h i n c r e a s i n g s i l t The silt may  minor  content be  changes  soil the  instructive  to  behaviour  silt  occupying sand s k e l e t o n  with  within  the  v o i d space and  e f f e c t upon s o i l  the e f f e c t o f s i l t  silt large  content.  in  suggest t h a t  p a r t have l i t t l e  increasing  behaviour. To  increasing silty  sands  f o r the  most  investigate  content upon s i l t y sand behaviour, i t i s  ignore  the  silt  f r a c t i o n of  the  soil  compare s o i l p r o p e r t i e s i n terms o f sand s k e l e t o n v o i d  and ratio  (see S e c t i o n 3.2.2.4), as a l l s i l t y 20/200 sands t e s t e d have the same g r a d a t i o n  and  thus s i m i l a r sand s k e l e t o n s .  It  may  be seen t h a t c o n s o l i d a t i o n o f s i l t y 20/200 sand from l o o s e s t state  of  slurry  deposition  produces  samples  s i m i l a r sand s k e l e t o n v o i d r a t i o s ( F i g . 5.7), t o t a l v o i d r a t i o s which v a r y c o n s i d e r a b l y This  may  explain  the  observation  that  does not change much as s i l t c o n t e n t i s F i g u r e 5.8  increasing  silt  when  undrained  silt  they may  also  sand  and  to  content. behaviour  increased.  (up t o  Effective  and  angle o f  2 degrees)  friction  angles  with of  compression l o a d i n g a l s o become  i s added.  friction  w i t h d e n s i t y and  slightly  content.  20/200 sand i n e x t e n s i o n equal  with s i l t the  have  i n contrast  shows t h a t phase t r a n s f o r m a t i o n  maximum o b l i q u i t y i n c r e a s e  which  As  described  in  Section  angles have been found t o v a r y  5.3,  slightly  sand f a b r i c , thus i t i s not unexpected t h a t  vary  with  silt  content.  Rowe  (1962,  shows t e s t r e s u l t s which i n d i c a t e t h a t the f r i c t i o n  1971)  angle of  Figure 5.8  Variation of near loosest state silty 2 0 / 2 0 0 friction angles with silt content  sand undrained  403938-^~-~-^  3736  B r  ~^^  MAXIMUM OBLIQUITY A N G L E  /  J  /  P H A S E TRANSFORMATION A N G L E  35- /  B  34-t  ^  —  &—  /  4  33-  / /  32-  _  31 300  TRIAXIAL C O M P R E S S I O N  B  i  i  i  i  1 5 SILT  i  i  i  i  TRIAXIAL E X T E N S I O N l i 10  i  i  C O N T E N T B Y WEIGHT  i  i i 15 (%)  i  TEST  TEST i  r~i—i—i—i—i— 20 25  143 a material account  for  i n c r e a s e s with the  increase  s i l t y 20/200 sand w i t h  decreasing in  grain  effective  increasing s i l t  size,  friction content.  which  may  angles  of  144 CHAPTER 6 CYCLIC TRIAXIAL TEST RESULTS  6.0  INTRODUCTION  Cyclic silty of  triaxial  tests  Brenda 20/40 and  silt  content  liquefaction.  conducted  the  resistance  poorly-graded  showed s i m i l a r v a r i a t i o n i n c y c l i c silt  content.  Thus only  20/200 sand i s d i s c u s s e d are i n g e n e r a l Triaxial t o 350 is  kPa  within  deposits rather  the  cyclic  1975,  C a s t r o and  and  strength  in detail,  as  silty  of  effect  sand  well-graded  behavior of  samples were  to  sands  w i t h change i n  silty  well-graded  natural  silty  isotropically  The  sands  of  sample  test  Seed, 1967,  Seed, 1983, Poulos,  Castro,  1977,  and  is  Lee  1969,  upon and  reported  e t . a l . 1975, 1975,  for  the  i s simpler,  complex  views  soil  consolidation  chosen  consolidation  conflicting  and  was  preparation  results  in situ  Isotropic  consolidation  anisotropic  with (Lee  (1)  consolidated  c o n s o l i d a t i o n s t r e s s used  encountered.  anisotropic  triaxial  literature  of  range i n which l i q u e f a c t i o n o f  reasons:  understood,  al.  test  i s generally  effect  samples  more w e l l - g r a d e d .  the  following  the  effective stress.  than  on  20/200 sand t o determine the  upon Both  were  (2)  undrained not  well  in  the  Seed  et.  Casagrande,  1976,  C a s t r o e t . a l . 1982), and  most c o r r e l a t i o n s between f i e l d  and  laboratory  behaviour  (3) of  145 soils  are  based  upon  isotropically  consolidated  test  samples. Anisotropic susceptibility  consolidation of  a  triaxial  depending upon many f a c t o r s consolidation, Mohamad and sand  be  density,  of  and  various  the  liquefaction, anisotropic Chem,  1983,  f a c t o r s which a f f e c t  specimen p r e p a r a t i o n .  consolidation  consolidation  to  sand type (Vaid and  has  a f u n c t i o n o f method o f l o a d i n g .  anisotropic  o r decrease  i n c l u d i n g degree o f  method o f  anisotropic  increase  specimen  Dobry, 1986), and  f a b r i c , such as  effect  may  also  Seed  The  been shown  to  (1979) shows t h a t  a f f e c t s simple shear and  triaxial  test results differently. The  cyclic triaxial  s p e c i f i c form o f f i e l d soil  subject  partly  to  (from  d i r e c t i o n s of properties one  question,  of  simple  may  An  model a  element o f  have p a r t l y  shear a  soil  to  plane  field  stress  s t r a i n ) , and  and  the  The  triaxial  which  can  of  model  i f soil  q u e s t i o n then a r i s e s as t e s t t o determine  f o r c o r r e l a t i o n purposes. To  behavior  variable  f a c t o r which i s important  i t i s i n s t r u c t i v e to consider  conditions.  sand  using  the  full  recent the  spectrum  cyclic  address  this  research  hollow of  to  on  cylinder loading  U s i n g the hollow c y l i n d e r t e s t equipment, Symes  e t . a l . (1985) and water  loading.  loading  anisotropic.  b e s t use  undrained  device,  cyclic  loading,  are  may  strength  the  cyclic  i n general,  s t r a i n c o n t r o l l e d boundaries, v a r i a b l e mechanisms o f  loading  how  t e s t does not,  pluviated  Shibuya and sand  is  Hight  least  (1987) have shown t h a t contractive  and  least  146 susceptable  to liquefaction i n a triaxial  compression mode  t o t a l s t r e s s path, y e t most c o n t r a c t i v e and most s u s c e p t i b l e to  liquefaction i n a triaxial  path.  extension  mode t o t a l  These t e s t r e s u l t s i n d i c a t e t h a t  isotropically  consolidated  triaxial  cyclic  stress  t e s t i n g of  specimens  in  both  extension  and compression phases w i l l  resistant  and l e a s t r e s i s t a n t l o a d i n g  such t h a t  one might hope t o a t t a i n an average e s t i m a t e o f  susceptibility  to  liquefaction  ensure t h a t both most phases a r e i n c l u d e d ,  which  is  useful  for  c o r r e l a t i o n purposes. A  factor  t o consider  i n the s e l e c t i o n  o f a, c y c l i c  l o a d i n g t e s t t e c h n i q u e i s s t r e s s and s t r a i n r e v e r s a l , which occurs  in triaxial  extension by  phases.  several  Mohamad  workers  of  reorganization  the  directional response  compression  and  fluctuation  (see F i g u r e  a  to  The  the  profound  extent  t o which  occur  in field  may  loading of  pore  softening  of  associated 6.1).  1983,  mechanical  centrifuge studies  field  i s generally  Chem,  e s p e c i a l l y during the  mobility  and  and  t o have  due  particles.  but r e c e n t  hardening  reversal  mobility  indicate  cyclic  which  behavior,  and c y c l i c  i s disputed,  induce  strain  of s o i l  1988)  Vaid  1986, and others)  cyclic  reversal  Schofield,  between  ( f o r example  e f f e c t upon s o i l  development  loading  loading  S t r e s s and s t r a i n r e v e r s a l has been shown  and Dobry,  softening  stress  test  Thus  (Lee and  conditions  may  pressure  and  stress-strain  with  stress  and  for correlation  147  Figure 6.1a  D  Q_  60-  4 0 -—  Typical undrained cyclic loading response of isotropically consolidated silty well-graded 2 0 / 2 0 0 Brenda sand  CYCLIC MOBILnY LOADING  COMPRESSION  20-  —  0-  \ 1  1  -20-40-60-  EXTENSION C  100  200  (0"^<)/2 150-i D  D.  100 500  300  (kPa)  SILTY 20/200 BRENDA SAND 4.55% SILT CONTENT e = 0.673 Dr = 46%  c(**r  0 V 2 0 % = 0.167  c  c  e  °-  7 5 4  Dr  c(*..)=  3 2  %  -50-  DEVELOPMENT OF CYCLIC MOBILITY STRAIN  -100-150 -15  400  -10  -5  AXIAL STRAIN  0  10  £„(%)  NUMBER OF LOAD CYCLES  N  148  Fig. 6.1b  Comparison of the typical undrained cyclic loading response of poorly—graded 2 0 / 4 0 and well—graded 2 0 / 2 0 0 Brenda  sand  (both samples prepared at loosest state)  POORLY-GRADED 20/40 SAND (analog data recorded on strip chart)  <G'+(j')/2 CkPa) a  r  149 purposes  it  is  prudent  l o a d i n g w i t h s t r e s s and For  the  to  strain  consolidated  symmetrically  loaded  the  most  general c o r r e l a t i o n For  the  2.5%  single  strain  effects  of  cyclic  i t i s believed  triaxial  cyclic  specimens and  that  which  compression  triaxial  test  are  phases  data  for  purposes. of  this  research,  l o a d i n g i s d e f i n e d as  amplitude  between  above,  extension  useful  purposes  undrained t r i a x i a l  in  the  reversal.  reasons d e s c r i b e d  isotropically  provide  observe  axial  extension  strain  and  (5%  liquefaction  the  development  peak t o  compression  in  peak  loading  axial  phases).  I f s t e a d y - s t a t e l i q u e f a c t i o n or l i m i t e d l i q u e f a c t i o n are induced by  c y c l i c loading,  as  of c y c l i c t e s t s performed on 2.5%  i s the  case f o r the  20/200 sand, the  s t r a i n g e n e r a l l y corresponds t o the  of a t r a n s i e n t cycles  100%  required to  pore p r e s s u r e r a t i o . induce l i q u e f a c t i o n  not  majority  development of  initial The  of  occurrence  number of  i s d e f i n e d as  load  N^.  A  r e p r e s e n t a t i v e example of data o b t a i n e d from a s i n g l e c y c l i c t r i a x i a l t e s t on The  s i l t y 20/200 sand i s shown i n F i g u r e  following  cyclic triaxial over a  large  number  of  sections  present  t e s t s performed on  range of  cycles  to  densities,  pore  pressure  g e n e r a t i o n , and  generation resistance  obtained  from  80  s i l t y 20/200 Brenda sand c y c l i c stress  liquefaction.  c o n t e n t upon e f f e c t i v e s t r e s s  data  6.1.  The  ratios,  effects  path, s t r e s s - s t r a i n  characteristics, t o l i q u e f a c t i o n are  of  and silt  response,  shear  strain  discussed.  150 6.1  GENERAL RESPONSE  Two cyclic  different  loading:  initiation  pressure  (1)  of  liquefaction,  types  o f response  cyclic  loading  steady-state  with  a  and shear  and  (2) c y c l i c  in  pore p r e s s u r e  very  strain  pore  below  pressure  during c y c l i c  loading  few  pore ratio,  increase  may  after  a  achieved.  liquefaction  In addition,  s t r e s s must exceed  cycles  only  may  only  l o a d i n g i f i t i s p o s s i b l e under  of large c y c l i c  loading  100% pore p r e s s u r e  or limited  ( i n e i t h e r extension  development  limited  o f both  o f 100% has been  conditions.  and c y c l i c  strength  or  mobility strains  ratio  be  static  t o the  and s t r a i n w i t h each l o a d c y c l e , w i t h t h e  liquefaction  monotonic  generation  under  leads  l o a d i n g which produces a s y s t e m a t i c  Steady-state initiated  which  liquefaction  rapid  development o f l a r g e c y c l i c transient  a r e observed  phase  o r compression mobility strain  follow  t h e sum  of  transformation phases).  The  in relatively  t h e occurrence  of  limited  liquefaction. The  c y c l i c l o a d i n g response o f s i l t y 20/200 Brenda sand  shown i n F i g u r e 6.1 i s g e n e r a l l y c h a r a c t e r i s t i c o f t h e w e l l graded c l e a n and s i l t y of  the e f f e c t i v e  sands t e s t e d .  stress  path  The g e n e r a l  o f well-graded  character  sand  under  c y c l i c l o a d i n g does not show a g r e a t d e a l o f v a r i a t i o n  with  relative  does  density,  not o c c u r . only  provided  that  limited  liquefaction  Limited l i q u e f a c t i o n i n the well-graded  observed  t o occur  i n the extension  phase  sand was of  cyclic  loading  (as observed i n monotonic t e s t r e s u l t s ) and o n l y i n  v e r y l o o s e w e l l - g r a d e d sand samples which r e q u i r e d 10  cycles  t o achieve  samples which  2.5%  strain.  l e s s than  For the majority  f a i l e d by t h e development  of c y c l i c  of  mobility  s t r a i n , t h e d i f f e r e n c e i n l o a d i n g response between l o o s e and dense  sands  required and  i s mainly  t o induce 2.5% s t r a i n  the  ease  developed  once  has  t h e magnitude  with  which  a transient  occurred.  Axial  of deviator  i n a given  cyclic state  strains  number o f c y c l e s ,  mobility  o f zero much  strains  are  effective stress  less  than  g e n e r a l l y observed d u r i n g pore p r e s s u r e g e n e r a t i o n pore p r e s s u r e r a t i o .  stress  1%  were  up t o 60%  A x i a l s t r a i n s l a r g e r than 1%  occurred  w i t h t h e development o f l i m i t e d l i q u e f a c t i o n and/or w i t h t h e development o f c y c l i c m o b i l i t y . generally of  15%  Loose t o medium dense sands  developed l a r g e c y c l i c m o b i l i t y very  development  quickly  of i n i t i a l  within zero  a  few  s t r a i n s i n excess  load  cycles  effective stress,  after  even when a  l a r g e number o f l o a d c y c l e s were r e q u i r e d t o a c h i e v e zero  effective  required  stress  a greater  (see F i g u r e  number o f l o a d  6.2).  cycles  initial  Denser  sands  t o achieve  c y c l i c m o b i l i t y s t r a i n s a f t e r t h e occurrence o f i n i t i a l effective  stress  state,  with  limited c y c l i c mobility strain  very  dense  development  except  after  cycles  i n denser  a  was  large  observed number  sands,  zero  reaching  a  l e v e l b e f o r e t h e development  o f conjugate shear planes i n t h e e x t e n s i o n Strain  sands  large  phase o f l o a d i n g .  t o be u n i f o r m  of  cyclic  as a r u l e ,  mobility  o r t h e development  of  loading conjugate  Figure 6.2  Development of shear strain in w e l l - g r a d e d 2 0 / 2 0 0 s a n d during cyclic loading  0  0.2  0.4  0.6  0.8  1  1.2  NORMALIZED NUMBER OF LOAD CYCLES  1.4  N/N,  shear p l a n e s  i n extension loading a f t e r  large extension s t r a i n s . shear  planes  data,  as e f f e c t i v e  deviates  in a  from  soil  t h e development o f  The development o f e x t e n s i o n phase may  stress  be e a s i l y  path  identified  i n test  on a m o d i f i e d Mohr diagram  t h e boundary envelope  during c y c l i c  mobility  loading. The major d i f f e r e n c e i n c y c l i c l o a d i n g response between well-graded gradation  and has  liquefaction  poorly-graded  upon  sands  steady-state  response.  As  i s the e f f e c t  liquefaction  observed  or  which limited  i n monotonic  test  r e s u l t s , p o o r l y - g r a d e d sands a r e more s u s c e p t i b l e t o l i m i t e d liquefaction  than  well-graded  sand.  Thus w e l l - g r a d e d  sand  i s more l i k e l y t o f a i l by t h e development o f c y c l i c m o b i l i t y strain  than  poorly-graded  sand.  The  range  of  cyclic  s t r e n g t h s o f w e l l - g r a d e d and p o o r l y - g r a d e d sands i s s i m i l a r , and w i t h i n t h e range o f c y c l i c s t r e n g t h s p r e v i o u s l y r e p o r t e d for  other  graded  sands.  sands a r e l e s s  both w e l l - g r a d e d pore  This  pressure  indicates  t h a t although  susceptible to limited  and p o o r l y - g r a d e d  and c y c l i c m o b i l i t y  more  well-  liquefaction,  sands a r e s u s c e p t i b l e t o strain  development  under  c y c l i c loading. Well-graded difference  and  poorly-graded  i n the e f f e c t i v e  i n t e r m e d i a t e stages o f c y c l i c loading range  cycles, from  20%  with to  stress  of  path  loading.  development 60%  sands  a  produced  During  o f pore  initial  show  by the  intermediate  pressure  effective  marked  i n the  stress,  e f f e c t i v e s t r e s s path o f w e l l - g r a d e d sand appears  the  t o be more  154 symmetric on  the  between compression  modified  Mohr  e f f e c t i v e s t r e s s path Mohr diagram.  This  and  diagram  extension (see  loading  Figure  i s closer to v e r t i c a l i n c r e a s e d symmetry  phases  6.1b).  on the  The  modified  in effective  path response i s s i m i l a r t o t h a t observed  stress  between monotonic  compression and e x t e n s i o n l o a d i n g . The e f f e c t i v e s t r e s s path d u r i n g i n t e r m e d i a t e c y c l e s o f l o a d i n g c o u l d be c o n s i d e r e d t o r e p r e s e n t e s s e n t i a l l y soil  response.  The  recoverable  d u r i n g l o a d i n g are due and  changes  with  stress.  response d u r i n g  gradation  i n pore  e s s e n t i a l l y to e l a s t i c  i n mean normal  pore p r e s s u r e  changes  implies that  this  The stage  soil  elastic pressure response  observation  that  of loading v a r i e s  pore p r e s s u r e  response  is  not  o n l y a f u n c t i o n of change i n mean normal s t r e s s , but a l s o a function  of  the  loading.  The  elastic  elastic  volume  changes  s t r e s s - s t r a i n behaviour  thus shown t o be a f u n c t i o n o f g r a d a t i o n . sand  i s shown t o  strains  in  have  variation similar  in  to  that  anisotropy  loading  and  More  loading  observed  results),  response  in plastic  dilative  with  elastic elastic  sand.  This  gradation  loading  response  where more w e l l - g r a d e d  i n d i l a t a n c y behaviour  well-graded  contractive  more  during  o f a sand i s  l o a d i n g than p o o r l y - g r a d e d  elastic  monotonic t e s t less  g e n e r a l l y more  compression  s t r a i n s i n extension  induced  between  sand  is (in  shows  compression  and e x t e n s i o n l o a d i n g . The boundary s u r f a c e f a i l u r e envelopes i n e x t e n s i o n compression  loading  phases were  found  to  have  and  essentially  155 t h e same f r i c t i o n a n g l e s , although w i t h some v a r i a t i o n or  minus  1  (Section change  degree)  as  5.3.1).  observed  These  slightly  with  i n monotonic  friction  axial  angles  strain  test  were  level,  with  compression  l o a d i n g phases  envelope trends  larger  friction in  angles  cyclic  development  of  a  strain,  generally  mobility  angles.  and  larger  mobility  friction  developed  compression  strains,  shown  compression larger soil  in  strains  The  larger  and  to  vary  6.4  friction  softer  with  development.  residual  phase  The  extension  boundary  observed  phase  majority  larger  friction  compression  to coincide  extension  phase  of  extension  generally  angles.  The  with  boundary  test  samples  strains  are  i n the e x t e n s i o n phase  a n i s o t r o p y and  Failure  thus e x t e n s i o n phase boundary  Figure  phase  was  smaller  angles.  generally  angles  extension  observed t o c o i n c i d e w i t h  strain  and  first then  the development o f r e s i d u a l  compression  envelope  observed  strain  s m a l l e r compression  Similarly,  phase c y c l i c  also  towards  c y c l i c m o b i l i t y s t r a i n was extension  in  than  friction  larger  than  development  is partially  extension loading  to  and  as shown i n F i g u r e 6.3. were  trend  both  results  observed  increasing with increasing c y c l i c m o b i l i t y s t r a i n , decreasing  (plus  due  response,  of to and  p a r t i a l l y due t o the f a c t t h a t s o i l samples were t e s t e d i n a l o a d c o n t r o l l e d r a t h e r than a s t r e s s c o n t r o l l e d manner,  and  thus  and  changes  i n sample  s m a l l e r compression observed v a r i a t i o n  area produced  larger  extension  maximum s t r e s s e s a t l a r g e s t r a i n s . i n f a i l u r e envelope  The  f r i c t i o n angles with  156  Figure 6.3  Variation of boundary envelope friction angle during cyclic mobility loading  50  40  COMPRESSION  SILTY 2 0 / 2 0 0 BRENDA  30  SAND WITH 4.35%  -  SILT BY WEIGHT  TOTAL  20  5 9 . 7 0.627  SAND 47.1 0 . 7 0 1 SKELETON q&/20$ c  0.251  0" ' = 3 5 0 k P a  10 f-  c  Ni = 5 CYCLES  0  T  -5  0  AXIAL STRAIN  -15  COMPRESSION  5  40  A  15  EXTENSION  n  n  50  10  (%)  \  30  ^ 5 a  y  LU  I—I  Q_ O  £  20 ^  10 0  ~~i  0  i  2  i  i  4  i  "—i  6  1  1 8  N U M B E R O F LOAD C Y C L E S  1  1 10 N  1  1—'—r  12  14  Figure  6.4  V a r i a t i o n of m a x i m u m b o u n d a r y e n v e l o p e f r i c t i o n a n g l e of silty 2 0 / 2 0 0 B r e n d a s a n d with silt c o n t e n t a n d s a n d s k e l e t o n r e l a t i v e d e n s i t y  158 c y c l i c mobility  s t r a i n development may be an i n d i c a t i o n o f  change  i n sand  strain  amplitude.  envelope strain the  fabric  The  friction  level  with  a  change  observed  angles  with  which  control  variations  direction  may be q u a l i t a t i v e l y  structures  in cyclic  mobility  i n boundary  of  l o a d i n g and  e x p l a i n e d by c o n s i d e r i n g  soil  fabric,  as d e s c r i b e d i n  S e c t i o n 2.2. Maximum  obliquity  friction  i n c r e a s e w i t h i n c r e a s i n g sand  angles  were  observed  to  s k e l e t o n r e l a t i v e d e n s i t y , as  shown i n F i g u r e 6.4. The f r i c t i o n angles shown i n F i g u r e 6.4 generally  have a s c a t t e r  o f p l u s o r minus  1 degree.  The  s c a t t e r i n maximum o b l i q u i t y f r i c t i o n angles i s p r o b a b l y due to  the v a r i a t i o n  of f r i c t i o n  s t r a i n development. maximum  with  cyclic  mobility  F i g u r e 6.4 a l s o shows t h e v a r i a t i o n o f  obliquity  content.  angle  friction  The f r i c t i o n  angles  angles  with  increasing  o f l o o s e sand  silt  (with a  sand  s k e l e t o n r e l a t i v e d e n s i t y l e s s than 50 percent) was observed to  i n c r e a s e somewhat w i t h  observed  in  monotonic  contrast,  maximum  increasing s i l t  test  obliquity  results friction  content, as a l s o  (Section angles  of  5.4). I n moderately  dense t o dense sands (with a sand s k e l e t o n r e l a t i v e d e n s i t y greater  than  50 percent)  with increasing s i l t  were  content.  observed  t o change  little  159 6.2  STRESS-STRAIN RESPONSE WITHIN LOADING CYCLES  Figure  6.5,  Figure  6.6,  and F i g u r e  6.7  show  typical  s t r e s s v e r s u s s t r a i n loops o b t a i n e d d u r i n g c y c l i c l o a d i n g o f clean  and  researchers types  silty  well-graded  have  reported  ( f o r example  Seed  20/200  similar and  sands.  results  Lee,  1966,  Several  f o r other Ishihara  sand 1978).  There a r e i n g e n e r a l t h r e e c h a r a c t e r i s t i c types o f undrained cyclic  l o a d i n g s t r e s s - s t r a i n response:  response a t low induced as  shown  i n Figure  steady-state  (1)  pre-liquefaction  s t r a i n and pore p r e s s u r e  6.5,  liquefaction  level  (2) c o n t r a c t i v e response or limited  shown  i n Figure  6.6,  and  (3) c y c l i c  shown  i n Figure  6.7,  which  develops  liquefaction  as  m o b i l i t y response  as  with  stress reversal  In  type  (1)  there  is a  (1) and ( 3 ) . general  flattening  h y s t e r e s i s loops w i t h i n c r e a s i n g l o a d c y c l e s . only  in cyclic  loading  monotonic l o a d i n g , and o n l y transformation  strength.  t h i s i s g e n e r a l l y observed l o o s e sand, Type  effective  A s i n g l e s o i l sample may undergo a l l t h r e e types o f  s t r a i n development, o r j u s t types  occur  of the  types  f o l l o w i n g r e a l i z a t i o n o f t r a n s i e n t s t a t e s o f zero stress.  such  i f cyclic  Type (2) w i l l  i s contractive i n  s t r e s s exceeds phase  In t h e well-graded  sands t e s t e d ,  o n l y i n moderately l o o s e t o v e r y  or a t higher e f f e c t i v e  (1) and  (2) s t r e s s - s t r a i n  governed by (a) t h e i n i t i a l s o i l loading.  i f sand  of the  confining stress  responses  level.  are i n general  f a b r i c , and (b) t h e mode o f  Figure 6.5  Typical cyclic loading stress—strain response at low strain level  140 120  WELL-GRADED 2 0 / 2 0 0 BRENDA  rod  Dr = c  o  D_ TO  tn LU  10  kPa CYCLES  CT /2CT^ =  40  d  c  0.1786  20 0 -20  on  -40  Lu  N, =  60  a: \tn  o  45%  CTj = 3 5 0  80  SAND  FIFTH LOAD  CYCLE  -60 -80 -100 -120 -140  -0.20  -0.15  -0.10  -0.05  AXIAL STRAIN  (PERCENT)  0  0.05  0.10 o  Figure 6.6  Cyclic loading s t r e s s — s t r a i n response of well—graded sand subject to limited liquefaction in extension loading  STRAIN  WELL GRADED 2 0 / 2 0 0 BRENDA SAND 80-  Dr = 22% c  CTj = 3 5 0 k P a  60-  N| = 6 C Y C L E S  40  O /2LJi d  c  =0.147  20-1 0  LIMITED LIQUEFACTION IN FIFTH LOAD C Y C L E  -8  -7  •5  -4  "i  -- 3 3  i  -2 2 -  AXIAL STRAIN  r~  -1 -1  0  (PERCENT)  HARDENING  F i g u r e 6.7  D e v e l o p m e n t of c y c l i c m o b i l i t y s t r a i n in l o o s e silty w e l l — g r a d e d 2 0 / 2 0 0 Brenda sand  -8  -6  -  4  -  A X I A L STRAIN  2  0  (PERCENT)  2 CTi  Type strain  ( 3 ) response  reversal  rather  i s governed  mainly  than  level.  stress  by  stress  When  s t r e s s i s i n c r e a s e d toward compression o r e x t e n s i o n single  phase  of  loading,  the  occur,  may  c y c l i c mobility  quickly  reversal  reach  does  relatively  a  few l o a d  very  small  If cyclic  strains  may  is  in  number o f  low d e v i a t o r s t r e s s  t o a c h i e v e an i n i t i a l  and  stress  occur  even though a l a r g e  c y c l e s o f t h e same r e l a t i v e l y were r e q u i r e d  value.  large  cycles,  during a  I f s t r e s s r e v e r s a l does  s t r a i n s are generally  limiting  occur,  applied  s t r e s s - s t r a i n response  c h a r a c t e r i z e d by s t r a i n hardening. not  and  amplitude  t r a n s i e n t s t a t e o f zero  effective stress. The in  development o f s t r a i n  each  consecutive  phase  hardening which  of mono-directional  i s observed loading  is  i n d i c a t i v e o f a changing f a b r i c w i t h i n t h e sample d u r i n g t h e development  of  cyclic  mobility  strain.  Sample  fabric  becomes more d i l a t i v e under i n c r e a s i n g s t r e s s , which causes the  material  The  s t i f f e n i n g o f response i n t h e d i r e c t i o n o f a p p l i e d  i s contrasted  to stiffen  i n the d i r e c t i o n of applied  T h i s i n d i c a t e s t h a t t h e d i l a t i v e and  s t a b l e f a b r i c established during highly  principal mobility between  contractive  stress strain  soil  load  by a s o f t e n i n g o f t h e response when p r i n c i p a l  stresses are reversed.  also  load.  and  reversal.  l o a d i n g i n one d i r e c t i o n i s  unstable The  with  t h e onset  development  of  of  cyclic  o c c u r s as a consequence o f t h e f l u c t u a t i o n  f a b r i c s which a r e s t a b l e under each phase o f  compression and e x t e n s i o n  loading.  The c h a r a c t e r  of s t r e s s -  164 s t r a i n c u r v e s i n both phases o f l o a d i n g indicates each  that  a s i m i l a r type  d i r e c t i o n of loading.  a r e s i m i l a r , which  of fabric  i s established i n  The s t a b l e  axis  of the s o i l  f a b r i c developed i n each phase o f l o a d i n g i s p a r a l l e l t o the direction  of  (boundary  envelope)  phase  loading  of  maximum  principal  friction  stress.  angle  i s essentially  The  mobilized the  i n d i c a t e s a s i m i l a r i t y i n developed s o i l  effective  during  each  which  also  same,  f a b r i c between each  mode o f l o a d i n g . Incremental cycles  are  generated  s t r e s s - s t r a i n loops  similar,  although  i s significantly  fact  suggests t h a t  load  cycles  i n progressive  t h e magnitude  larger with  each  of  strains  cycle.  t h e major d i f f e r e n c e between  i s t h e amount o f induced  load  strain  This  successive  required  to  i n i t i a t e d i l a t a n t and hence s t r a i n hardening response. Type  (3)  recoverable This the  stress-strain  strain  means a g r e a t soil  during deal  unloading  i n each c y c l e o f l o a d i n g .  the  show of  only  deviator  small stress.  o f h y s t e r e t i c work i s absorbed by  work absorbed by t h e s o i l quantify  loops  directional  during soil  Perhaps t h e h y s t e r e t i c loading  could  be used t o  fabric  produced  by  the  loading.  6.3  PORE PRESSURE GENERATION DURING CYCLIC LOADING  As pressure  i n monotonic generation  loading  during  results  undrained  (Section cyclic  5.1)  loading  pore is a  165 function are  of t o t a l s t r e s s path.  generally  changing  mean  fluctuations cyclic  large  fluctuations  normal  is  stress  t o t a l s t r e s s path i f the constant. total  This  stress  pressure level  induced  which  The  equivalent  to  definition  of  conditions  i n the  after  cyclic  correspond  cyclic  remains  completed.  the  the  each  The  independent  of  For  not  because the  in  the  initial  field  total  the  pore  at  stress  may  residual  cycle  samples  this thesis. pressure at all  samples  stress.  i s adopted f o r the  were  states  initially  of  point  is This  loading  total  ceased  stress  may  not  conditions.  presentation  The  laboratory  of  R e s i d u a l pore p r e s s u r e i s d e f i n e d transient  been  conditions.  s t a n d a r d d e f i n i t i o n of r e s i d u a l pore p r e s s u r e i n test  has  this  residual  stress  pore  pressure  model c y c l i c  has  pore  testing  the  loading  upon  of  laboratory  as  remain  pressure  interpretation  level  total  stress  field,  these  path.  pore  defined  stress  initial  residual  the  induced  loading  after  total  loading  to  of  workers have by  stress  with  of  principal stress directions  c y c l i c loading.  previous  magnitude  total  there  pressure  i s , however,  complicates  p r e s s u r e induced by purposes,  path  shows t h a t  pore  The  upon  dependence  path  in  stress.  dependent  effective  F i g u r e 6.1  results as the  pore  isotropic t o t a l stress,  consolidated  under  in  as  isotropic  166 6.3.1  E f f e c t of C y c l i c Stress Ratio Figure  response change  6.8  shows  of clean in  how  20/200  cyclic  the  sand  stress  residual  (without  pore  silt)  ratio.  The  pressure  varies  with  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 350 kPa e f f e c t i v e s t r e s s , w i t h a r e l a t i v e d e n s i t y o f 45% a f t e r v i b r a t o r y d e n s i f i c a t i o n and consolidation. The  number  o f c y c l e s r e q u i r e d t o induce  increases with decreasing c y c l i c s t r e s s r a t i o ,  liquefaction as  expected.  R e s i d u a l pore p r e s s u r e g e n e r a t i o n curves i n F i g u r e 6.8 have been  normalized  with  required t o achieve  respect  to  liquefaction,  the  number  of  cycles  i n o r d e r t o determine i f  the c h a r a c t e r o f normalized pore p r e s s u r e g e n e r a t i o n is  similar,  as suggested  curves a r e o f t e n used in  situ.  by  De  Alba  t o estimate  (1976).  curves  Normalized  pore p r e s s u r e  generation  T h i s r e q u i r e s t h a t t h e normalized curves have t h e  same g e n e r a l shape. Figure  6.8  shows  g e n e r a t i o n curves clear with  trend  ratio, ratio.  pore  do not have t h e same shape.  cyclic  stress  o f pore ratio.  pore  during  pressure initial  up  to  and r e l a t i v e l y more q u i c k l y a f t e r At higher  liquefaction,  cyclic  normalized  stress  curves  ratio  liquefaction,  pore  70% pore o r few  a r e almost  stress  relatively  30%  is a  generation  A t low c y c l i c  apparently b u i l d s loading  pressure  There  pressure  o r a l a r g e number o f c y c l e s t o i n i t i a l  normalized quickly  t h e normalized  i n the v a r i a t i o n  changing  ratio,  that  linear  more  pressure pressure cycles to over t h e  Figure 6 . 8 a  1  0  V a r i a t i o n of p o r e p r e s s u r e g e n e r a t i o n in l o o s e c l e a n 2 0 / 2 0 0 with c h a n g e in c y c l i c s t r e s s r a t i o  1  1  0.2  1  1  0.4  1  1  0.6  1  1  1  0.8  NORMALIZED N U M B E R OF LOAD C Y C L E S  i  1.0 N/N|  1  sand  1  1.2  F i g u r e 6.8b  V a r i a t i o n of p o r e p r e s s u r e g e n e r a t i o n in l o o s e c l e a n 2 0 / 2 0 0 s a n d with c h a n g e in c y c l i c s t r e s s r a t i o  NUMBER OF LOAD CYCLES  N  oo  169  range  of  loading  liquefaction  was  cycles. not  Steady-state  observed  in  45%  or  limited  relative  density  samples, r e g a r d l e s s of the c y c l i c s t r e s s l e v e l .  6.3.2  E f f e c t of s i l t Figure  6.9  and  water p r e s s u r e  at  Figure  6.10  generated by  sand v a r i e s w i t h prepared  Content show how  cyclic  change i n s i l t  near  loosest  of  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 350  relatively  large  cyclic  The  loading  The  slurry  kPa,  r e s i d u a l pore  in silty  content.  state  sand s k e l e t o n v o i d r a t i o s .  the  20/200  samples were  deposition  and thus have s i m i l a r  samples were s u b j e c t e d  stress  ratio  and  and  thus  to a  required  a  s m a l l number o f c y c l e s t o achieve l i q u e f a c t i o n . Residual essentially  pore  the  pressure  response  same f o r sand w i t h  These samples a l l developed l i m i t e d sixth  load  content the  cycle.  required  occurrence  skeleton  void  Apparently limited  a  In  9  of  contrast,  cycles  to  limited  ratio  was  large s i l t  may  0 to  be 15%  the  develop  bulked content  by  sand  pore p r e s s u r e  generated  sand v a r i e s w i t h samples  were  Figure  change  prepared  by  6.12  20%  retards  the  with  in s i l t at  near  content.  20%  the silt  sand  content.  development  loading.  loading  the  silt  T h i s was  of  also  5.4)  a l s o show how  cyclic  be  l i q u e f a c t i o n without  the  cyclic  to  l i q u e f a c t i o n during  observed i n monotonic t e s t r e s u l t s ( S e c t i o n and  silt  l i q u e f a c t i o n , although  l i q u e f a c t i o n during  F i g u r e 6.11  noted  the r e s i d u a l  in silty  content.  As  loosest  state  20/200  before, of  the  slurry  Figure 6.9  Variation of pore pressure generation with silt content in 2 0 / 2 0 0 s a n d subject to limited liquefaction  D_  — 0.1 H  0  r~  1  2  1  1  1  1  1  1  4 6 8 NUMBER OF LOAD CYCLES  1  1  10 N  1  12  Figure 6.10  Variation of pore pressure generation with silt content in 20/200 sand subject to limited liquefaction  — 0.1 -i 0  1  1  0.2  1  1  0.4  1  1  0.6  1  1  1  0.8  NORMALIZED NUMBER OF LOAD CYCLES  1  1  N/N |  1  1.2  Figure 6.11  Variation of pore pressure generation with silt content in 2 0 / 2 0 0 sand not subject to limited liquefaction  NUMBER OF LOAD CYCLES  N  P O R E P R E S S U R E RATIO  AU/CX  o o o o o o o o o o ^ O - ^ b u ^ u l C D N j O O C D  CZ.T  174  deposition thus  and  isotropically  have s i m i l a r  sand  consolidated to  skeleton void  350  ratios.  kPa,  The  and  samples  were s u b j e c t e d t o a r e l a t i v e l y low c y c l i c s t r e s s r a t i o , thus  required  a  larger  number  of  cycles  to  and  achieve  liquefaction. Figure  6.11  liquefaction reduced also  by  indicates  and  any  generation  addition  indicates  that  of  the  that  silt  content.  with increasing s i l t In  residual  pore  silt  t o the  sand.  The  figure  degree  of  increase  in  cyclic  The  i s not a d i r e c t variation  the  normalized  generation  curves  of  c l e a n sand  normalized  curves  of  silty  little sand  variation normalized  stress ratio represent  magnitude silt  6.3.3  with  sand  are  strength  complex.  pore  i n Figure  pressure 6.8,  shown i n F i g u r e 6.12 silt  content.  representative of  one  curves of  cyclic  stress  appears  to  stress  ratios. be  ratio  more  and  less  The  the show  The  (0.113) w h i l e the c l e a n sand n o r m a l i z e d cyclic  is  f u n c t i o n of  of c y c l i c  residual  shown  increasing  curves  variable  normalized  pressure  content appears t o be f a i r l y  contrast to  to  of  strength with a d d i t i o n of s i l t percentage  susceptibility  silty cyclic curves  shape  dependent  of  upon  dependent  upon  residual  pore  content.  E f f e c t of R e l a t i v e Density Figures  pressure  6.13  generated  and in  6.14 clean  show  how  20/200  loading v a r i e s with r e l a t i v e density.  the sand  during  There appears  cyclic to  be  Figure 6.13  Variation of pore pressure development in clean well—graded 2 0 / 2 0 0 sand with change in relative density  0 -0.1 H  0  1  1 20  1  1 40  1  1——i  60  1 80  1  1  1  100  NUMBER OF LOAD C Y C L E S  1 120 N  1  1 140  1  1 160  1 1 180  Figure 6 . 1 4  —0.1  H 0  V a r i a t i o n of p o r e p r e s s u r e g e n e r a t i o n in c l e a n w e l l — g r a d e d 2 0 / 2 0 0 s a n d with c h a n g e in relative d e n s i t y  \  1 0.2  1  1 0.4  1  1 0.6  1  1 0.8  NORMALIZED N U M B E R OF LOAD C Y C L E S  1  1 1 N/N|  1 1.2  177  little  variation  i n normalized  curves  r e l a t i v e density between 45% and 60%. 22%  relative  extension initial lower  density  loading part  of  pore  suffered  during the  The  limited  curve  generation  dense sample  sands with  a  The loosest sample at  s i x t h load  normalized  pressure  liquefaction.  the  for  liquefaction cycle,  at  81%  shows a response which i s considerably  thus  suggests  before  in the  relatively  the  onset  relative  of  density  d i f f e r e n t than that  of looser samples, because the dense material i s generally A great deal of c y c l i c mobility s t r a i n must  dilative.  developed before  an i n i t i a l  be  state of zero e f f e c t i v e stress  i s achieved. 6.3.4  R e l a t i o n s h i p Between Induced S t r a i n and Pressure  Figure  6.15  shows  how  the  residual  Residual  pore  Pore  pressure  generated i n clean 20/200 sand during c y c l i c loading varies with the development of shear s t r a i n . which i s varied  i n the  The  figure i s c y c l i c  only parameter  stress r a t i o  and  hence the number of cycles required to achieve l i q u e f a c t i o n . Strain  level  extension  and  cycle.  The  i s defined  difference  between  peak  peak compression s t r a i n during  a given  load  figure  as  shows  the  that  there  is  no  direct  r e l a t i o n s h i p between residual pore pressure and shear s t r a i n l e v e l induced by c y c l i c loading.  In fact, estimates of pore  pressure based upon s t r a i n l e v e l may  be o f f by 60% depending  upon the magnitude of c y c l i c stress r a t i o .  Figure  6.15  V a r i a t i o n of p o r e p r e s s u r e  g e n e r a t i o n in c l e a n  with s h e a r s t r a i n level d u r i n g c y c l i c  loading  20/200  sand  179  6.3.5  Relationship Between H y s t e r e t i c Work  Residual  Pore  Pressure  and  Some r e s e a r c h e r s have attempted t o r e l a t e r e s i d u a l pore pressure  to  damage induced  loading  (Finn and  a soil  specimen may  absorbed by may  be  the  Bhatia, be  in a  loading  within  by  the  irrecoverable  calculated  stress-strain  per  been  correlate well  damage induced  quantified  unit  from  (Figure  volume  by  shown by  with  the  of  hysteretic  work absorbed  has  The  loading.  cumulative area w i t h i n hysteretic  cyclic  specimen d u r i n g c y c l i c  easily  absorbed  sample d u r i n g  1981).  observed d u r i n g c y c l i c l o a d i n g work  soil  a  work loops  Irrecoverable  is  equal  to  the  s t r e s s - s t r a i n loops.  sand  specimen d u r i n g  Towhata  induced  This  6.16).  soil  work  and  residual  Ishihara  The  cyclic  (1985)  pore p r e s s u r e .  Their  hollow c y l i n d e r t e s t r e s u l t s f o r Toyoura sand show t h a t correlation  between  pressure  valid  is  hysteretic  regardless  work  of  and  stress  residual  path  and  to  the pore  mode  of  loading. The 20/200  development sand  during  irrecoverable A good for  cycles. a  possibly area  which  The  require  cyclic  undergo  number of  pore  loading the  i s observed  correlation  large  due  residual  work absorbed by  correlation  samples  of  proportionally  is  soil  (see  liquefaction  i s not  as  cycles  good  to  stress-strain  t o the number of l o a d i n g  two  6.17).  parameters  in  less  for  samples  i n the  clean versus  Figure  achieve  loops,  in  plotted  between the  t o accumulation of e r r o r  within  pressure  than  60  which  liquefaction, calculation  which cycles.  of  increases  Figure 6.16 140 120  C a l c u l a t i o n of i r r e c o v e r a b l e w o r k a b s o r b e d by a s o i l s p e c i m e n stress—strain response observed during cyclic loading  A P P R O X I M A T I O N OF HYSTERETIC WORK WITHIN S T R E S S - S T R A I N L O O P  100 80 D CL  60  Dr = 45% c  CT = 3 5 0 k P a c  N, = 10  40 to  tn tn  LU cr j—  tn 01  CYCLES  20 0 -20 -40  o  -60  Lu  -80  Q  from  THIRD LOAD C Y C L E STRESS-STRAIN LOOP  -100  WELL GRADED 2 0 / 2 0 0 BRENDA SAND  -120 -140  l .10  1  1  -.08  1  1—  -.06  i -.04  1  r  1  -.02  AXIAL STRAIN  —i  0  (PERCENT)  1  0.02  1  1  0.04  1  1  0.06  1—  0.08 co o  Figure  6.17  Variation sand  of p o r e  with  pressure  hysteretic  generation  work  absorbed  in l o o s e  clean  20/200  during cyclic  loading  1.0 0.9  -  0.8  -  o  b ZD  0.7 O h<  LY.  LU Cri ZD  CO  =  oV  3 5 0 kPa  0.6 0.5  -  0.4  TEST N  Ul  LU  A B C D E F G  m o_  LU  a: o  0.0  i — i  10  -2  i  11111  10  "1  -1  1  I I I I 111  1  1  L  233 54 43 16 10 7 4 1  I I II ! l |  10  cT /2o-3 d  C  0.1 1 14 0.1314 0.1386 0.1620 0.1786 0.1929 0.2214 1  IRRECOVERABLE SHEAR WORK ABSORBED PER UNIT VOLUME OF SOIL (kN/rn )  1  I I I I  11  10 CO  182  Figure  6.18  development  of  shows  residual  the pore  relationship pressure  between  and  the  irrecoverable  h y s t e r e t i c work i n c l e a n sand a t v a r i o u s r e l a t i v e d e n s i t i e s . Again  there  parameters,  is  a  good  correlation  between  the  two  even though r e l a t i v e d e n s i t y , which c o n t r o l s the  mode o f f a i l u r e o f the v a r i o u s samples under c y c l i c l o a d i n g , i s v a r i e d from 20 t o  80%.  H y s t e r e t i c work c o u l d p r o v i d e an the p r e d i c t i o n  of residual  behaviour  be  can  pore  modelled  efficient  pressure,  sufficiently  method f o r  i f stress-strain well  to  predict  h y s t e r e t i c damping.  6.4  CYCLIC RESISTANCE DATA  C y c l i c t r i a x i a l t e s t s were conducted well-graded  Brenda  e f f e c t of s i l t in  20/200  sand  samples  to  content upon c y c l i c s t r e n g t h .  silty  determine  the  To show t r e n d s  c y c l i c r e s i s t a n c e , raw t e s t data from a s e r i e s o f samples  with  constant  interpolation  silt of  content curves  d i f f e r e n t methods o f 6.4.1  c o n t e n t and with  and  into  density different  is  processed  forms  samples  density.  number o f  were  prepared  cycles to  6.4.1.1.  allow  by  Content  controlling  silt  Thus the v a r i a t i o n o f c y c l i c s t r e n g t h liquefaction  c o n t o u r s can be d i r e c t l y observed Section  to  by  comparison.  C y c l i c R e s i s t a n c e Curves a t Constant S i l t Triaxial  in  on c l e a n and  To  further  on  constant  density  from t e s t data, as p l o t t e d reduce  c y c l i c resistance  Figure  6.18  0.0  Variation 20/200  of p o r e  sand  pressure  with h y s t e r e t i c  H 1—i i i 1111|  10 "  2  generation  10 ~  1—i 1  i i 11111 1  work  1—i  in l o o s e t o  dense  absorbed  during cyclic  i i 1111|  1—i  10  I R R E C O V E R A B L E S H E A R WORK A B S O R B E D P E R UNIT V O L U M E OF SOIL (kN/m ) 2  i i 1111 10  2  clean  loading  184  data  such  that  c o n t e n t may  the  effects  of  be b e t t e r understood, raw  6.4.1.1 i s i n t e r p o l a t e d t o number  relative  of  cycles  to  contours  on  Raw  T e s t Data  Figures versus  i n S e c t i o n 6.4.1.2.  silty  densities. stress  The  ratio  moderately  with  range  from  dense  of  0.08  to  sands  and  show  each  cyclic  Contours  number o f c y c l e s t o l i q u e f a c t i o n f o r c l e a n and sand,  6.23  ratio  ratio  Brenda  through  constant  stress  - constant Density  piumtiwry  silt  stress  20/200  6.19  of  cyclic  v e r s u s r e l a t i v e d e n s i t y p l o t s presented  6.4.1.1  and  t e s t data from S e c t i o n  determine  liquefaction  density  sand  cyclic  at  various  strengths  shown  0.30)  is typical  silty  sands  workers ( f o r example Seed and Lee,  1966,  relative  of  reported  (cyclic loose by  to  other  I s h i h a r a , 1980).  In g e n e r a l , c y c l i c r e s i s t a n c e curves a r e concave upward or  straight  cyclic  i f the  mobility  presented),  and  development  mechanism  (as  is  by  case  limited  Only  subjected  to  developed  limited  a  for  development  most  very  liquefaction loose  relatively  sand  large  liquefaction  of  is  the  curves  steady-state  samples  cyclic  strain  which  stress  extension  were ratio as  content  of  near l o o s e s t s t a t e of s l u r r y d e p o s i t i o n  and  variation  in  or  by  loading,  described i n Section  samples prepared  the  strain  concave downward i f the mechanism o f  liquefaction.  The  is  of  6.1.  of c y c l i c  i s o t r o p i c c o n s o l i d a t i o n t o 350 A t near l o o s e s t s t a t e , any  strength with  kPa  silt  i s shown i n F i g u r e  increase i n s i l t  content  6.23. may  be  Figure 6.19  1  i  1  Cyclic loading liquefaction resistance curves of clean 20/200 Brenda sand  i  i  i  i  i i i |  1  10 NUMBER  O F C Y C L E S TO LIQUEFACTION  1  1 — i — i i i i |  1  1  1—i—i  i i i |  10 * ( 2 . 5 % S I N G L E A M P L I T U D E STRAIN)  10 N|  5  i-  1  ™  Figure 6.20  0.28  i  0.26  -  0.24  -  Cyclic loading liquefaction resistance curves of silty (4.3%  CT - 350 kPa  b  4.341.1 5% SILT 0.22  -  0.20  -  e  c  = 0.6251 .002  0.18  c  H  e  cn P£  cn  D r  0.14  = 0.674+ .003  c ( s k e l e t o n ) = ^2.31 0.5%  H e =  0.7101.008  c  0.12  -  0.10  -  Dr = 3 5 . 0 1 2 . 1 % c  Dr  'c  u  / ,  , i  \ = 22.612.2%  (skeleton)  4.5 1.21% SILT  4.0 1.20% SILT 0.08  Q  Dr. = 46.0± 0.5%  0.16  o  >o  LIMITED LIQUEFACTION  (skeleton) = 47.5+0.5%  CO  LU  ©  Dr_ = 60.0± 0.5% D r  K  sand  SILTY 20/200 BRENDA SAND  \5> CM  silt) 2 0 / 2 0 0 Brenda  n  1—i—i  i i i  i  10  NUMBER OF CYCLES TO LIQUEFACTION  1—i—i—i t i 10  i—i  i i r~i 10  1  (2.5% SINGLE AMPLITUDE STRAIN)  N|  3  CO  Figure 6.21  Cyclic loading liquefaction resistance curves of silty (7.5% silt) 20/200 Brenda s a n d  SILTY 20/200 BRENDA SAND  CT = 350 kPa  7.6 ±.30% SILT e  C  = 0.605-+- .005  c  _  7.3 ±.15% SILT  D r = 61.0± 1.0% c  D r  (skel)  c  =  e  36.6±0.5%  = 0.5571 .003  c  Dr = 74.5±0.7% c  D r  c (skeleton) =  5  3  ®  2  ±  1  -  0  %  LIMITED LIQUEFACTION  7.76±.30% SILT e  = 0.655+ .006  c  7.71 ± . 1 0 % SILT  Dr = 47.2± 1.5%  e  c  D r  c  = 0.643± .006  Dr = 50.1 ± 1.0%  c (skeleton) = 2 0 . 0 1 1 . 5 %  Drc ke.r - ± 2 3  5  1  5 %  ( s  1  1  1—i—i i i i~|  1  1  10 NUMBER OF CYCLES TO LIQUEFACTION  1—i—i—i i i |  1  1  1—i—i i i i |  10* (2.5% SINGLE AMPLITUDE STRAIN)  10  N|  cn  Figure 6.22 Cyclic loading liquefaction resistance curves of silty (13.5% silt) 20/200 Brenda sand  0.28  - i  SILTY 20/200 BRENDA SAND  0.26 -  0" ' = 350 kPa c  0.24 «N  0.22  ©  13.33±.15% SILT  LIMITED LIQUEFACTION  0.4421 .002 D r = 94.9±0.6%  T3  b o  c  (skeleton) =  0.20 -  5 7  -5±0.1%  I—  cr 0.18 to to  UJ  £  to  0.16  13.67±.14% SILT e = 0.488± .001  CJ  rj 0.14 H  c  LI  Dr = 83.110.3% c  0.12 D r  0.10 0.08  c  (skeleton) "i  Dr / i i i \ = 40.010.5% c (skeleton)  >±2%  1—i—i i i i 10  NUMBER OF CYCLES TO LIQUEFACTION  l  1—i—i i i i |— 10  7  i  i—i—i  (2.5% SINGLE AMPLITUDE STRAIN)  N|  i i i | 10  3  03 OO  Figure 6.23  Cyclic loading liquefaction resistance curves of silty 20/200 sand at near loosest state of slurry deposition  0.28  0.26  PERCENTAGE SILT CONTENT BY WEIGHT  5  0.24 -  D *  CM  0.22 -  \ v. -a  b  0.20  -  0.18  -  0.16  -  SILTY 2 0 / 2 0 0 BRENDA SAND  0 4.3 7.5 13.5 21  CT' = 3 5 0 k P a  rRESS RATI  o  to  CYCLl  o  21 ±1.6% SILT e = 0.4461 .006 c  Dr = 9 6 1 2 . 5 % c 0.14 -  D r  c (skel)"  8  (  _  1  - '° 5  , 4  -  6 ) %  0.12  0.10  0.08  "i  1—i—r i i i | 10  NUMBER OF CYCLES TO LIQUEFACTION  T  1  1 1 I I I  "1  1  1—I—I  ( 2 . 5 % SINGLE AMPLITUDE STRAIN)  I'll  10  10 '  N|  3  00  190 seen t o i n c r e a s e t h e c y c l i c r e s i s t a n c e o f t h e sand. cases,  a  small  increase  in silt  content  may  I n some  apparently  i n c r e a s e c y c l i c s t r e n g t h more than a l a r g e r i n c r e a s e i n s i l t content. 6.4.1.2  Comparison o f C y c l i c S t r e n g t h Cycles to Liquefaction  Figures versus  6.24  standard  number  of  through  relative  cycles  to  6.27  show  density  liquefaction.  Although t h e range o f c y c l i c silt  content,  standard  increase s u b s t a n t i a l l y with compared small  i n terms  to  observation 3.2.2.4, 1980,  drastically leads  Section  and ASTM  reduce  resistance deposition.  5.4  or  would  density  were  i s shown t o  content.  density silt  When  (for  the  content i s  strength.  This  made  i n Section  researchers  (Ishihara,  t h e standard  ASTM  relative  a r e l a t i v e l y poor b a s i s f o r t h e comparison sand.  6.26 one can see t h a t  o f f r a p i d l y near  d e n s i t i e s could  tend  loosest  state  sand samples w i t h be prepared  d r y p l u v i a t i o n , as d e s c r i b e d  samples  curves  does n o t change  overlap),  and by o t h e r  Bulked s i l t y  ASTM r e l a t i v e  fixed  one t o t h e c o n c l u s i o n  6.25 and F i g u r e  drops  f o r several  strength  cyclic  o f mechanical p r o p e r t i e s o f s i l t y In F i g u r e  ratio  The  relative  D-2049-69) t h a t  density provides  stress  increase i n s i l t  o f standard  Number o f  i n S e c t i o n 6.4.1.1.  relative  range i n which some curves  shown  cyclic  curves  i n t e r p o l a t e d from raw data presented  with  i n Fixed  t o be  metastable  of slurry  lower  standard  by moist  i n Section under  cyclic  tamping  3.3.1. monotonic  Such or  Figure 6.24  0  10  Cyclic loading liquefaction resistance curves of clean 2 0 / 2 0 0 Brenda  20  30  40  50  ASTM STANDARD RELATIVE DENSITY  60 Dr  c  70 (*)  80  sand  90  100  Figure 6.25  Cyclic loading liquefaction resistance curves of silty ( 4 . 3 % silt) 2 0 / 2 0 0 Brenda  sand  0.28  SILTY 2 0 / 2 0 0 B R E N D A S A N D  0.26  4 . 3 % SILT C O N T E N T B Y WEIGHT 0  C  *  N| = N U M B E R O F C Y C L E S TO LIQUEFACTION  CN  b  0.20  2  0.18  a: m m  0.16  !<  in  = 350 kPa  10  ( 2 . 5 % S I N G L E A M P L I T U D E STRAIN)  20 -  N| = 5 0 N  l  = 100  0.14  a 0.12 _i o 0.10  -  0.08 10  20  30  40  50  ASTM STANDARD RELATIVE DENSITY  T  60 Dr  c  70 (*)  80  90  100  Figure 6.26 Cyclic loading liquefaction resistance curves of silty (7.5% silt) 20/200 Brenda sand  0.28  100 ASTM STANDARD RELATIVE DENSITY  Dr (s) c  Figure 6.27  Cyclic loading liquefaction resistance curves of silty ( 1 3 . 5 %  silt) 2 0 / 2 0 0 Brenda  sand  0.28 0.26  -  J"o 0.24  -  SILTY 2 0 / 2 0 0 B R E N D A S A N D 1 3 . 5 % SILT C O N T E N T B Y WEIGHT  G' = 3 5 0 . k P a c  A  0.22  H  cj  0-20  H  o  0.18  -  N, = N U M B E R O F C Y C L E S TO LIQUEFACTION ( 2 . 5 % S I N G L E A M P L I T U D E STRAIN)  <  cc cn cn  0-16  £ cn  0.14  § o  0.12  °  0.10  UJ  N, N,  N, -  Ni  0.08 10  n 20  1  1  30  1  1  40  1  1  1  50  ASTM STANDARD RELATIVE DENSITY  1  1  60 Dr  c  r 70  (*)  80  90  100  195 c y c l i c l o a d i n g and would be s u b j e c t t o v e r y low s t e a d y - s t a t e liquefaction  strength  Unsegregated  water  as  described  pluviated  clean  by  and  Castro  silty  (1969).  20/200  sand  samples a r e p o s s i b l e o n l y i n t h e range o f r e l a t i v e d e n s i t i e s shown. The  data  replotted shown  shown  i n terms  i n Figures  skeleton  similar.  6.24  skeleton  through  density  curves This  Figures  o f sand 6.28  relative  resistance  in  through  relative  6.30.  In  i t i s observed  for different  indicates that  silt  cyclic  6.27  density,  terms  that  of  the  contents strength  is as  sand  cyclic  are  very  i s governed  m a i n l y by t h e sand p o r t i o n o f s i l t y sand f o r up t o about 20% homogeneous s i l t  content.  Silt  content  tends  to  increase  c y c l i c s t r e n g t h somewhat when sand s k e l e t o n r e l a t i v e  density  i s chosen as t h e b a s i s f o r comparison. 6.4.2  E f f e c t o f S i l t Content on C y c l i c Data p r e s e n t e d  form a s e t o f curves on  the c y c l i c  curves  6.4.2.1  i n S e c t i o n 6.4.1 may be i n t e r p o l a t e d t o which show t h e e f f e c t  strength  a r e presented  Resistance  of s i l t y  of s i l t  20/200 Brenda  content  sand.  Such  i n the following s e c t i o n s .  V a r i a t i o n o f C y c l i c S t r e n g t h With V o i d  Ratio  I s h i h a r a e t a l . (1980) have suggested t h a t i n t h e case of s i l t y  sands, v o i d r a t i o might be a b e t t e r b a s i s  comparison o f c y c l i c 6.34  show  such  strength.  variation  Figure  of c y c l i c  number o f l o a d c y c l e s t o l i q u e f a c t i o n  f o r the  6.31 through  strength  for a  Figure given  (10, 20, 50, and 100  Figure 6.28  Cyclic loading liquefaction resistance curves of silty (4.3% silt) 20/200 Brenda sand  0.28 0.26 u 0.24  *  SILTY 2 0 / 2 0 0 B R E N D A S A N D 4.3%  SILT C O N T E N T B Y  WEIGHT  0c = 350 kPa  0.22  y  N,=  10  CM \  0.20  b  o < ir tn cn 111 cc icn u _i o >o t  .  s  N = 20 (  ^  0.18  N| = 5 0 N, = 1 0 0  0.16 0.14 0.12  N, = N U M B E R O F C Y C L E S TO LIQUEFACTION (2.5%  0.10  SINGLE AMPLITUDE  STRAIN)  0.08 10  20  30  40  50  S A N D S K E L E T O N RELATIVE DENSITY  60 Dr  70 c  ( s k e l e t o n )  80 (%)  90  100  Figure 6.29  Cyclic loading liquefaction resistance curves of silty ( 7 . 5 % silt) 2 0 / 2 0 0 Brenda s a n d  0.28 SILTY 2 0 / 2 0 0 B R E N D A  0.26  SAND  7 . 5 % SILT C O N T E N T B Y WEIGHT  CT  *  C  ,  = 350 kPa  CM  b°  0.20  2  0.18  N.= 1  X  N,=  y ^  -  ^  cc  ^S ? 3  10  20  N, = 5 0 N, =  ^  100  CO CO  CO  o _J  N, = N U M B E R  CO  O F C Y C L E S TO  LIQUEFACTION  ( 2 . 5 % SINGLE AMPLITUDE 0.08  0  10  20  30  SAND SKELETON  40  50  RELATIVE DENSITY  60 Dr  c  (  s k e  70 |  e t o n  )  (%)  STRAIN) 80  90  100  Figure 6.30  Cyclic loading liquefaction resistance curves of silty (13.5% silt) 20/200 Brenda s a n d  0.28 0.26  -  0  10  20  30  40  50  S A N D S K E L E T O N RELATIVE DENSITY  60 Dr ( c  s k e  70  | ton) e  ( ) %  80  90  100  Figure 6.31 Variation of silty 2 0 / 2 0 0 sand resistance to liquefaction in 10 load cycles with consolidation void ratio  0.28  co LU _l CM  \  Q  fc)  O  O O — I *-  2 z CO CO LU  CO  0  0.26  P E R C E N T A G E SILT C O N T E N T B Y WEIGHT  0.24 SILTY 2 0 / 2 0 0 B R E N D A  0.22  0' = 3 5 0 c  0.20  SAND  kPa  0.18  o 0.16 o 0.14  O LU  0.12 33 > o- _i0.10  o or  0.08  Loosest State  0.40  I 0.45  I 0.50  I 0.55  VOID RATIO  0.60  0.65  0.70  0.75  0.80  0.85  0.90  Figure 6.32  Variation of silty 2 0 / 2 0 0 sand resistance to liquefaction in 20 load cycles with consolidation void ratio  0.28 UJ  0.26  H  0  I  P E R C E N T A G E SILT C O N T E N T B Y WEIGHT  SILTY 2 0 / 2 0 0 B R E N D A  SAND  (j' = 3 5 0 k P a c  LY.  o  Loosest State  0.10 H  0.08  0.40  1 0.45  1 0.50  r— 0.55 VOID RATIO  0.60  0.65  0.70  0.75  0.80  0.85  0.90  Figure 6.33  Variation of silty 20/200 sand resistance to liquefaction in 50 load cycles with consolidation void ratio  0.28 CO LU  o  0  CY  fc)  0.26  1  0.24  OA  CJ  0.22  CN \ Q  J  PERCENTAGE SILT CONTENT BY WEIGHT  SILTY 20/200 BRENDA SAND  _i  O 1—  <  o m  0.20  G  c  = 350 kPa  0.18  on \—  CO  o  _i  o  >o  O  CT  LJ  CO z  <  LU-  LU  0.16 0.14  ZD  O  _l  0.12  cn 0.10 o  Loosest State  Lu  0.08 0.40  0.45  0.50  0.55 VOID RATIO  0.60  0.65  0.70  0.75  0.80  0.85  0.90  Figure 6.34  Variation of silty 20/200 sand resistance to liquefaction in 100 load cycles with consolidation void ratio  0.28  in  H  0.26  -  0.40  0.45  0.50  0.55 VOID RATIO  0.60 e  c  0.65  0.70  0.75  0.80  0.85  0.90  203  load  cycles)  for silty  20/200 sand.  near l o o s e s t s t a t e o f d e p o s i t i o n each c u r v e ) , s i l t y regardless  of  difference to  shift  content  The f i g u r e s show  (the lowest  data  p o i n t on  20/200 sands have s i m i l a r c y c l i c  silt  content,  i n void ratios.  although  strength  is a  The r e s i s t a n c e curves  h o r i z o n t a l l y toward  increases.  there  lower  A t each s i l t  void  content  that  large  a r e seen  ratios  as  silt  t h e r e appears t o be  an a p p r o x i m a t e l y s i m i l a r i n c r e a s e i n c y c l i c r e s i s t a n c e f o r a g i v e n decrease i n v o i d r a t i o . ratio, s i l t  content  I f compared a t c o n s t a n t  void  i s shown t o decrease s e v e r e l y t h e c y c l i c  s t r e n g t h o f a sand m a t e r i a l , as observed i n t h e v a r i a t i o n o f cyclic  strength  discussed higher  with  i n Section  void  ratios  standard  ASTM  6.4.1.2. may  be  As  relative  discussed  attained  would tend  t o have v e r y  low c y c l i c  previously,  i f silty  p r e p a r e d by m o i s t tamping o r a i r p l u v i a t i o n .  and monotonic  6.35 through F i g u r e  6.38 show how  a f f e c t s the c y c l i c  strength  of s i l t y  skeleton  density  as  described sand  relative density  i s used  i n Section  i s considered  density,  strength, sand.  silt  i n terms  content  c y c l i c strength.  opposed  to  i s shown  ASTM to  silt  content  ASTM  standard  f o r comparison.  i f cyclic of  Density  20/200 sand when sand  as t h e b a s i s  6.4.1.2,  are  samples  V a r i a t i o n o f C y c l i c S t r e n g t h With R e l a t i v e  Figure  relative  sands  Such  which i s u n c h a r a c t e r i s t i c o f water p l u v i a t e d s i l t y  6.4.2.2  density  strength standard  of  As silty  relative  substantially  reduce  In c o n t r a s t , i f compared i n terms o f sand  Figure 6.35  Variation of silty 2 0 / 2 0 0 sand resistance to liquefaction in 10 load cycles with relative density  0.28  co UJ  _j  0.24  CN  \  0.26  a  -o < fc> O  0.22  o o  0.20  2 s  0.18  — I  CO  *-  2  0.16 CO O  < Lu LU  Z i =>  o  g or o  0.14 -  PERCENTAGE SILT CONTENT BY WEIGHT  0 4.3 7.5 13.5 21  21  4- SAND SKELETON RELATIVE DENSITY • ASTM RELATIVE DENSITY  LT  C  = 350 kPa  21  21  0.12  SILTY 2 0 / 2 0 0 B R E N D A  (7 = 3 5 0 k P a  Loosest State  0.10  SAND  C  0.08 10  20  30  40 RELATIVE  50 DENSITY  70  60 Dr  c  (%)  80  90  100  Figure 6.36 Variation of silty 20/200 sand resistance to liquefaction in 20 load cycles with relative density  1 0  I  |  10  i  |  20  I  |  30  l  |  l  |  l  40 50 RELATIVE DENSITY  |  I  60 Dr (*) c  |  70  l  |  80  I  |  90  i  |  100  Figure 6 . 3 7  Variation of silty 2 0 / 2 0 0 sand resistance to liquefaction in 50 load cycles with relative density  CO Ld  CN  0.28  PERCENTAGE SILT CONTENT BY WEIGHT  0.26  0 4.3 7.5 13.5 21  U  0.24  o o P m  0.22  SILTY 20/200 BRENDA SAND  0'  c  21  0.20  + SAND SKELETON RELATIVE DENSITY • ASTM RELATIVE DENSITY  2 Ld O  0.18  CT = 350 kPa  <  0.16  £ z  CO  Lu O Ld  •  a g >- —i ° c o  = 350 kPa  C  Loosest State  0.14 0.12 0.10  11  ^  21  0.08 10  20  ~r 30  40 RELATIVE  50 DENSITY  70  60 Dr.  (*)  80  90  100  Figure 6.38  Variation of silty 20/200 sand resistance to liquefaction in 100 load cycles with relative density  0.28  tn LU  PERCENTAGE SILT CONTENT BY WEIGHT  0.26  4.3 7.5 13.5 21  0.24  o O  §O  <  LY tn  2  tn < O  LL. UJ  ci O  °  °-  2 0  —  SAND  Oi = 3 5 0 k P a  — 21  0.18 -  4- SAND SKELETON RELATIVE DENSITY • ASTM RELATIVE DENSITY  0.16  (T = 3 5 0 k P a c  0.14  Loosest State  0.12  LY. 0.10  O  u.  -  SILTY 2 0 / 2 0 0 B R E N D A  0.08  21  21  — r  10  20  30  40 RELATIVE  50 DENSITY  60 Dr  c  70 (*)  80  90  100  208  skeleton little  relative effect  upon  increase c y c l i c space  density,  within  silt  cyclic  strength.  t h e sand  content  strength, The s i l t  without  i s shown  t o have  infact  slightly  or  essentially  causing  a  fills  large  void  change i n  c y c l i c strength properties. 6.4.2.3  V a r i a t i o n o f C y c l i c S t r e n g t h With S i l t Content a t Constant Sand S k e l e t o n R e l a t i v e D e n s i t y  Interpolation curves  yields  strength  of  of  Figure silty  increase  in silt  skeleton  relative  Section 6.39,  sand  which  cyclic  shows  i s increased  content,  A small  up  that  the  absolute  in silt  content  any sand  density  indicates  produced  by  reason  increasing s i l t  an  f o r an  content a t  sand s k e l e t o n r e l a t i v e d e n s i t y .  Test strength  This  i s not t h e o n l y  increase i n c y c l i c strength with constant  by  i n c r e a s e c y c l i c s t r e n g t h more than a (13.5% by weight).  increase  15%  cyclic  a d d i t i o n o f s i l t (4.3%  addition of s i l t in  to  the  a t constant  large  increase  resistance  that  when c o n s i d e r e d  density.  by weight) may i n f a c t  6.4.2.2  results  i n F i g . 6.39  of hydraulic f i l l  been d e p o s i t e d deposition  or f l u v i a l  silty  through water s u f f i c i e n t l y segregated  silt  that  cyclic  sand which has  quickly t o avoid estimated  c o n s e r v a t i v e l y by t e s t s on c l e a n sand o f s i m i l a r  gradation  sand s k e l e t o n v o i d r a t i o .  loading  behavior  of clean  layers  the  be  and  of  indicate  may  The major d i f f e r e n c e i n f i e l d and  silty  sands  would  e x t e n t o f d r a i n a g e p o s s i b l e d u r i n g and a f t e r c y c l i c a  factor  which  i s not c o n s i d e r e d  i n elemental  be the loading,  undrained  Figure 6.39  S u m m a r y of the variation of silty 2 0 / 2 0 0 s a n d cyclic strength with variation of silt content at constant sand skeleton relative density  0.26  6° "  P E R C E N T A G E SILT B Y WEIGHT  0.24 -  0  0.22 -  XI  b 5  0.20 0.18  -  4.3 - 7.5 13.5  =  350 kPa SAND S K E L E T O N RELATIVE DENSITY (PERCENT)  or  co  co 0 . 1 6  UJ CO LY. O  ^ o  0.14  55  -  0.12  40  0.10  25  0.08 1 NUMBER  i  i  i  i  i i i  10  OF C Y C L E S TO LIQUEFACTION  T  1  1—I  I I I  1 0  1  1  1  1—I  2  ( 2 . 5 * SINGLE AMPLITUDE  STRAIN)  N,  I I I  10  210 laboratory  testing,  because  undrained s t a t e throughout  6.4.2.4  6.40  d e r i v e d from Section  resistance  has  6.4,  been  drawn  to  show  from  interpolated  the v a r i a t i o n  a t constant applied  interpolated  cyclic  of  stress  liquefaction ratio,  of the i n t e r p o l a t e d data.  plots  i s checked  case.  form  by p l o t t i n g  in cyclic  resistance  and t o  The v a l i d i t y interpolated  a s e t o f smooth curves, as i s observed  The same t r e n d s  data  presented  data from a l l o t h e r p l o t s on F i g u r e 6.40 t o determine data  i n an  testing.  a l l previous c y c l i c resistance p l o t s  check t h e v a l i d i t y of  a r e maintained  Consistency o f Interpolations  Figure  in  samples  t o be the  data  been p r e v i o u s l y d e s c r i b e d a r e seen i n F i g u r e 6.40.  i f the  as have  211 Figure 6.40  Variation of silty 2 0 / 2 0 0 sand cyclic strength with silt content at constant cyclic stress ratio  10 PERCENTAGE SILT CONTENT BY WEIGHT  0 4.3 7.5 13.5  <  — I  co UJ Q  + SAND SKELETON RELATIVE DENSITY  •  0 =  <  Ld _J O  ASTM RELATIVE DENSITY  C  10  350 kPa  O-J20L  =0.16  CO  in  CN  CJ  If UJ  o 10  -  CO UJ  o  UJ  m  n 10  i  i  20  30  i  40  i  50  1 60  RELATIVE D E N S I T Y  i  70  Dr  c  1  1  80  90  (%)  1 100  1  212 CHAPTER 7 DISCUSSION AMD  The cyclic  following  INTERPRETATION OF TEST RESULTS  features  o f t h e observed  l o a d i n g behaviour o f c l e a n and s i l t y  monotonic and  sands  deposited  through water m e r i t f u r t h e r d i s c u s s i o n : 1)  The monotonic compression  loading  behaviour  o f Brenda  sand a f t e r c o n s o l i d a t i o n from l o o s e s t s t a t e i s observed t o be g e n e r a l l y d i l a t i v e liquefaction  ( i . e . steady-state  i s not observed  during  or limited  shear).  This i s  t r u e f o r both c l e a n and s i l t y sands r e g a r d l e s s o f t h e i r average g r a i n s i z e , g r a d a t i o n and s i l t 2)  For  samples  compression  prepared  at  loosest  behaviour  is  dilative,  behaviour i s c o n t r a c t i v e liquefaction regardless silt  content  confining stress. is  shown  to  during  gradation,  behave  state,  monotonic  yet  extension  ( i . e . steady-state  i s observed  of t h e i r  content.  in this  or limited  shear).  A l l sands  average g r a i n manner  over  a  s i z e and range  The same sand a t a g i v e n v o i d  be  either  contractive  or  of  ratio  dilative,  depending upon d i r e c t i o n o f l o a d i n g . 3)  A l l sands effective until  a  effective  tested confining  unique  display stress  phase  friction  an  initial  under  undrained  transformation  angle  decrease  i s mobilized.  or  in  loading,  steady-state Once  state, the materials  sheared  past  phase t r a n s f o r m a t i o n  dilate  with  consequent i n c r e a s i n g e f f e c t i v e c o n f i n i n g s t r e s s .  An e s s e n t i a l l y c o n s t a n t e f f e c t i v e angle o f f r i c t i o n i s maintained w i t h i n behaviour loading  the material during d i l a t i o n .  i s observed  regardless  and t h e magnitude  of  o f maximum  This  direction positive  of pore  p r e s s u r e developed.  Some o f these a s p e c t s o f m a t e r i a l behaviour p r e s e n t departures undrained  from  the generally  behaviour  o f sands.  may l i e i n t h e sand the  water  water  ideas  Causes o f these  m a t e r i a l s used  deposited  Ottawa  i n this  Figure  i n both 3.12  extension below  or  C109  sand  kPa.  liquefaction response  from  compression  response.  t o be  at  liquefaction l o a d i n g (see  Brenda  sand  isotropic  consolidation  Ottawa  sand  i n compression considerably  o f water  in  stress limited  extension  contractive  This anisotropy i n loading  characteristic  shows  only  shows  loading,  more  For  loosest  response  Although  still  while  f a b r i c of  liquefaction an  response  is  and compression  1985),  limited  loading  500  appears  extension  and Chung,  steady-state  departures  study.  d e p o s i t i o n s t a t e shows s t e a d y - s t a t e o r l i m i t e d response  regarding  type and t h e c h a r a c t e r i s t i c  deposited  example,  accepted  radical  than  response  deposited  sands,  r e g a r d l e s s o f sand type. Chung  (1985)  has shown t h a t  t h e a n i s o t r o p y o f water  d e p o s i t e d sand may be r a d i c a l l y a l t e r e d by s t r e s s and s t r a i n history  (see F i g u r e  2.3).  Thus  d e p o s i t i o n must impart a s p e c i f i c  the process  fabric  of  to the s o i l  soil which  214 may o n l y be a l t e r e d soil  i s shown  consolidation  by induced s t r a i n .  t o be o n l y stress  small s t r a i n ) .  slightly  changed  (which  generally  level  observed  t o be  confining  stress.  increasing  only  induces  (which may induce l a r g e r s t r a i n ) and i s  essentially  research  independent  on t h e undrained  e s p e c i a l l y w e l l - g r a d e d and s i l t y u s i n g moist  by  S o i l f a b r i c i s observed t o be dependent upon  stress ratio history  Most  The a n i s o t r o p y o f  tamped  samples.  behaviour  sands,  of  has been  of  sands,  conducted  These samples may possess an  entirely  different  samples.  R a d i c a l d i f f e r e n c e s i n t h e undrained behaviour o f  the  two d i f f e r e n t  expected  fabric  o f magnitude  types  than  that  o f water  of reconstituted  due t o d i f f e r e n c e s  i n fabric.  pluviated  samples  may be  In addition,  most  r e s e a r c h has been c o n c e n t r a t e d on t h e study o f s o i l s t r e n g t h behaviour under a s i n g l e mode o f l o a d i n g , commonly  triaxial  compression  triaxial  loading  and  less  commonly  e x t e n s i o n o r simple shear l o a d i n g . identify been  anisotropy  missed.  tacitly  i n undrained  The undrained  assumed  tamped  sands  extension testing triaxial strain  response  behaviour  (Castro,  techniques,  o f sands  Some  often  has been  researchers  f o r not conducting  1975).  As  t h e development  samples i n v a r i a b l y produces conditions  has most  have  s t r a i n s i n e x t e n s i o n l o a d i n g o f moist  as t h e reason  tests  Thus t h e o p p o r t u n i t y t o  t o be i s o t r o p i c .  i d e n t i f i e d non-uniform  under  (either  in  triaxial  i n most  laboratory  of larger  strain i n  non-uniform  s t r e s s and  compression  or  extension  loading strain  directions) . behaviour  uniform  observed  strains  consider  is  at  the  due  samples  not mean t h a t  before the  invalid.  what  point  The does  to  of  sample  maintain  important  may  non-uniformity. uniformity  the  soil  test  results  practical  7.1  strength i s valid  behaviour in  the  factor  to  behaviour  in  extension  Water  pluviated  well  past  phase  (see F i g u r e  o b t a i n e d from  strain  non-  be p r e d i s p o s e d  strains  transformation state i n extension loading Thus  stressof  stress-strain  non-uniform  strain  the  development  M o i s t tamped specimens  development  loading  does  is  become i n v a l i d ? to  This  range  3.13).  extension  which  is  of  significance.  BAND FABRIC  Moist  tamped  sand  samples  have  been  shown  to  have  s t e a d y - s t a t e o r l i m i t e d l i q u e f a c t i o n response i n compression loading  over a range o f v o i d  ratios  (Castro e t a l . ,  1985)  r e g a r d l e s s o f g r a d a t i o n , s i l t c o n t e n t , sand t y p e o r p a r t i c l e shape.  C a s t r o e t a l . (1982) p r e s e n t t e s t r e s u l t s f o r Lornex  t a i l i n g s sand which has a s i m i l a r mineralogy and as Brenda t a i l i n g s sand.  angularity  M o i s t tamped Lornex sand i s shown  t o be h i g h l y c o n t r a c t i v e i n compression l o a d i n g over a range of v o i d r a t i o s . tested  in this  loading, tamping  even  S i n c e a l l the water d e p o s i t e d a n g u l a r sands study are g e n e r a l l y i n the  t e c h n i q u e must  loosest be  dilative  deposition  imparting  a  i n compression  state,  fabric  the  t o the  moist sand  216  which  promotes  contractive  behaviour.  Conversely,  p l u v i a t i o n o f sand through water must be i m p a r t i n g a f a b r i c that  promotes  compression When  dilative  sand  i n a bulked  zero p e r c e n t .  density.  behaviour,  at  least  Casagrande  i s placed  before  state  a relative  with  Tamping i s used  A moist sand  densification  due  tamping,  to  capillary  honeycomb s t r u c t u r e " which between moist g r a i n s " .  t o a c h i e v e any d e s i r e d  tensions moist  between  to  greater  i s induced  bulking  "metastable  by " c a p i l l a r y  The magnitude o f c a p i l l a r y  capillary  an  forces  tensions  Finer grained  t e n s i o n s and thus  and  grains.  dumped sands t o be  v a r i e s with grain s i z e .  larger  less  i s i n i t i a l l y bulked and r e s i s t a n t t o  (1976) has i d e n t i f i e d  within a s o i l  i t is  density  p a r t i c u l a r l y prone t o l i q u e f a c t i o n due t o t h e i r  generate  under  loading. moist  generally than  more  increased  soils  may be s u b j e c t resistance  to  d e n s i f i c a t i o n by tamping. At  low  particle  stress  interaction  level,  capillary  w i t h i n a moist  c a p i l l a r y f o r c e s upon s o i l  tensions  soil.  control  The e f f e c t s o f  f a b r i c may be expected t o p e r s i s t  i n some form even a f t e r tamping t o d e n s i t i e s h i g h e r than t h e ASTM minimum.  T h i s i s suggested by some l a b o r a t o r y s t u d i e s ,  where l o o s e moist have  been  saturation  shown  to  process,  consolidation Sladen  tamped  vacuum  specimens o f f i n e r  experience even  while  (Marcuson,  e t a l . , 1985).  This  grained  large  strains  being  maintained  1972; Chang  collapsing  soils  d u r i n g the under  a  e t a l . , 1982;  characteristic  on  217 mere removal o f c a p i l l a r y is  metastable.  This  tensions fabric  c o n t r a c t i v e behaviour d u r i n g In sands  contrast  are  forces  and  is  likely  to  tamped  deposited  under  g r a v i t a t i o n a l forces  through  sands,  water.  i n t e r a c t i o n i s governed by  water  Upon  expected water,  to  the  yield  by  ratios  grained  a  and  drag  deposition,  interparticle  coarse  sand  deposition,  in  friction.  Table  a i r versus  give  rise  to  as  friction,  This  slurry  3.2.  In  water  The  with  i s indicated  by  contrast fine as  sands i s due silt  in  silt  content  i n dry  tension moist  grains  the  in  the  dry  sand  in  much  state.  the  f o r c e s i n moist sand.  tamped  samples may  accessible  deposited  to and  soils.  range  of  indicated and  In  the be  manner  duplicate ratios  by  Figure ratio silty  as  dry  state,  considered capillary  Thus both a i r p l u v i a t e d  neither void  silty  f o r c e s between  g r a i n s may same  coarse  a i r pluviated  t o the pronounced e l e c t r o s t a t i c  e l e c t r o - s t a t i c f o r c e s between s i l t bulk  maximum  l a r g e i n c r e a s e i n maximum sand s k e l e t o n v o i d  increase  fine  through  deposition  fabrics,  be  is  the l o o s e s t s t a t e v o i d r a t i o s shown i n F i g u r e 3.5 3.6.  could  interaction  pluviated  different  air  deposition  particle  between ASTM and  shown  through  similar fabric  upon  sands,  sands may  dry  interparticle  similarity  void  of  because  governed  the  pluviated  not c a p i l l a r y t e n s i o n f o r c e s . Deposition  to  in  shear.  moist  settlement  which  result  to  during  particle  suggests a f a b r i c  the  possible  fabric in  and nor  water  218  7.2  INTERPRETATION OF FACTORS WHICH FABRIC OF WATER PLUVIATED SAND  Water p l u v i a t e d strength  sands  PRODUCE  AND  CONTROL  show a c h a r a c t e r i s t i c t r e n d i n  behaviour and a n i s o t r o p y .  Thus t h e f a b r i c o f water  p l u v i a t e d sand must have s p e c i f i c f e a t u r e s which a r e d e r i v e d from  the process  of pluviation  through  water.  For the  purposes o f e x p l a i n i n g and p o s s i b l y p r e d i c t i n g t h e behaviour of  water  pluviated  sands,  i t i s important t o i d e n t i f y t h e  f a c t o r s which produce and c o n t r o l t h e i r f a b r i c . Much reported  o f t h e behaviour can be e x p l a i n e d  observed  be used  response  t o show t h a t  of  a  a.  Dilatancy  loading  material  simply  between  level  (see S e c t i o n  a and fi o f Rowe's model  an  Rowe's  particles population  assemblage model  i s that of  controlled  is  controlled  and  of a  2.2).  by  factor  natural  angles  t o the  manner because  particles.  p a r t i c l e contact  The p h y s i c a l  are applicable  The  sand  difference  assemblage  a sand has a s t a t i s t i c a l  dimension f a c t o r s (a). is  and s t r e s s - s t r a i n  angle fi and p a r t i c l e dimension  d e s c r i p t i o n o f sand f a b r i c i n a g e n e r a l is  Rowe's model  i s a l s o shown t o be a f u n c t i o n o f d i r e c t i o n o f  and s t r a i n  parameters  2.2.  i n Section  the dilatancy  particulate  i n t e r p a r t i c l e contact  results  i n terms o f Rowe's two d i m e n s i o n a l  p a r t i c u l a t e model as d e s c r i b e d can  i n the t e s t  of  sand  d i s t r i b u t i o n or  (fi) and  structure  As l o n g as t h e d e f o r m a t i o n i n a sand  mainly by t h e f r i c t i o n a l  resistance  between  219 particles,  Rowe's  reasonable  model  may  be  expected  s i m u l a t i o n of deformation  Strain  behaviour  produce  between p a r t i c l e F i g u r e 7.1  0  sand  of  increased.  and  a  combinations slip  a  in  which  to  a  behaviour. is  are  controlled  rendered  contacts  as  by  the  unstable  and  stress ratio  is  shows the range of s t a b l e p o p u l a t i o n  o f a and 0 f o r v a r i o u s l e v e l s o f s t r e s s r a t i o . o f F i g u r e 7.1a  provide  and F i g u r e 7.1b  shows how  A  comparison  the i n t r i n s i c  angle  o f f r i c t i o n on p a r t i c l e s u r f a c e s a f f e c t s the range o f s t a b l e population of p a r t i c l e contacts.  The  and  within  0  within  a  depending upon  sand  may  vary  stress-strain  a c t u a l population of a the  h i s t o r y and  stable  method  zone,  of  sample  p r e p a r a t i o n , as d e s c r i b e d i n the f o l l o w i n g paragraphs.  7.2.1  Sample P r e p a r a t i o n During  subjected  p l u v i a t i o n through  to gravitational  f o r c e s and  F l a t t e r shaped p a r t i c l e s may their axis  longer i n the  axes  vertical  deposition  addition  to  tend  sand  particles  viscous  direction,  due  having  with  this  particle  and  t o water drag  the p a r t i c l e s would tend  plane  drag  preferred  preferably oriented c l o s e r to v e r t i c a l  i n order  concentration  of  particle  contact  f a c t o r s would tend  lower a v a l u e s population.  and Thus  higher the  shortest forces.  orientation, in  normals  Both of these  with  t o s e t t l e upon  contact  self-weight.  are  forces.  t o o r i e n t themselves  in a horizontal direction,  Upon sedimentation, the  water,  which to  are  support  t o induce  0 values particle  in  a  the  contact  F i g u r e 7.1a  S t a b i l i t y c o n t o u r s f o r Rowe's p a r t i c u l a t e model as a f u n c t i o n o f p a r t i c l e d i m e n s i o n f a c t o r « and i n t e r p a r t i c l e c o n t a c t a n g l e JS  INTERPARTICLE  CONTACT A N G L E  ft  (DEGREES)  F i g u r e 7.1b  S t a b i l i t y c o n t o u r s f o r Rowe's p a r t i c u l a t e model as a f u n c t i o n o f p a r t i c l e d i m e n s i o n f a c t o r « and i n t e r p a r t i c l e c o n t a c t a n g l e j8  INTERPARTICLE  CONTACT A N G L E  H  (DEGREES)  Fig.  7.2  C o n s t a n t i n c r e m e n t a l s t r a i n r a t i o c o n t o u r s f o r Rowe's p a r t i c u l a t e model as a f u n c t i o n o f p a r t i c l e d i m e n s i o n f a c t o r « and i n t e r p a r t i c l e c o n t a c t a n g l e |8  INTERPARTICLE  CONTACT A N G L E  j8  (DEGREES)  223  p o p u l a t i o n would tend t o be c o n c e n t r a t e d hand c o r n e r o f F i g u r e 7.1 and F i g u r e  7.2.2  i n t h e lower r i g h t  7.3.  Sample C o n s o l i d a t i o n Following  the settlement  consolidation material.  i s e s t a b l i s h e d under  This  approximately  of p a r t i c l e s ,  produces and  a  self-weight  maintains  a  from  deposited  contacts 7.4.  from K  samples K  Q  Q  isotropically  are  range  of  consolidated particle  shown i n F i g u r e  induced  during  the  transformation  c o n s o l i d a t i o n t o i s o t r o p i c c o n s o l i d a t i o n , because a  s t r a i n unstable implies  slip  principal  i s exposed t o t h e mode B  zone, as shown i n F i g u r e 7.5. against  stress  the  direction  (see S e c t i o n  specimen,  h e i g h t when r a d i a l vertical  the  i m p l i e s t h a t mode B c o n t r a c t i v e  zone o f p r e v i o u s l y s t a b l e c o n t a c t s  triaxial  D  7.3.  of stable  t o the p o p u l a t i o n  The p a r t i c u l a t e model strains  are  s t a t e , the  i s transformed  volumetric  K  2.0 w i t h i n the m a t e r i a l , which i m p l i e s a range  laboratory  as  within  stress ratio  o f s t a b l e p a r t i c l e c o n t a c t s as shown i n F i g u r e As  state of  this  would  of  2.2). imply  external  In a K an  Mode B s t r a i n  Q  maximum  consolidated  increase  in  sample  s t r e s s i s i n c r e a s e d t o t h e magnitude  s t r e s s i n o r d e r t o induce  of  isotropic consolidation.  T h i s form o f s t r a i n development was observed and v e r i f i e d a t low c o n f i n i n g s t r e s s d u r i n g the p r e p a r a t i o n o f t a i l i n g s sand samples.  Saturated  deposition  by  samples  maintaining  an  were 80  K  Q  kPa  consolidated vacuum  between  after the  former tube and t h e o u t s i d e s u r f a c e o f t h e sample membrane,  Figure  0  7.3  Range  10  20  of  stable  particle  30  40  INTERPARTICLE  contacts  50  CONTACT A N G L E  after  50  jS  Ko  consolidation  70  (DEGREES)  80  90  Figure 7.4  Range of stable p a r t i c l e contacts after  INTERPARTICLE  CONTACT  ANGLE  jS  isotropic consolidation  (DEGREES)  F i g u r e 7.5  0  Range o f p a r t i c l e c o n t a c t s w h i c h u n d e r g o Mode B s l i p t r a n s f o r m a t i o n f r o m Ko t o i s o t r o p i c c o n s o l i d a t i o n  10  20  30  INTERPARTICLE  40  50  CONTACT  ANGLE  60 |8  70 (DEGREES)  i n the  80  90  227  while  a  20  sample. and  kPa vacuum  was  applied  i n increments  t o the  Thus t h e v e r t i c a l s t r e s s on t h e sample was 20 kPa,  radial  stress  a  lower  amount  corresponding  to  K  Q  c o n s o l i d a t i o n , because zero r a d i a l s t r a i n was imposed on the sample. kPa  Now, without d i s t u r b i n g t h e sample, t h e e x t e r n a l 80  vacuum  released,  on  the  so t h a t  outside  surface  of  the  sample  t h e sample would be transformed  was  from  K  Q  c o n s o l i d a t i o n t o i s o t r o p i c c o n s o l i d a t i o n without a change i n vertical while  stress.  large  contractive  occurrence predicted  Sample h e i g h t  of  large  range  o f incremental  i n population  change  i n stress ratio the  is  considerably observed confirm  strain  from  t o increase, i n d i c a t e d the  strains.  ratio  contacts  K  from  t o be g r e a t e r larger  radial  than  test  -0.4,  axial  i s predicted  which  Test  mode B s t r a i n s a r e indeed  results  possible  particle  material  contacts.  completely r i g i d .  may  only  be  thus  within  a  effectively  observed behaviour.  Rowe's p a r t i c u l a t e model assumes t h a t particulate  a  as has been  sand, and t h a t Rowe's p a r t i c u l a t e model can be used t o e x p l a i n otherwise u n e x p l a i n a b l e  ratio  indicates  strain,  results.  7.2.  isotropic  to horizontal strain  than  by a  due t o a  Figure  to  Q  The  induced  c o n t r a c t i v e mode B deformation  in triaxial that  radial  can be determined  Incremental v e r t i c a l  estimated  strains  of stable p a r t i c l e  transformation  consolidation, t o occur.  volumetric  compressive  change  During  was observed  induced  strain by s l i p  within  a  between  I n d i v i d u a l p a r t i c l e s a r e assumed t o be The r e s u l t o f these assumptions  i s that  228  s t r a i n i s o n l y p r e d i c t e d t o be induced r a t i o , and  not by  by a change i n s t r e s s  a change i n the magnitude o f s t r e s s .  The  model suggests t h a t when a p a r t i c u l a t e m a t e r i a l i s s t a b l e a t one magnitude o f c o n s o l i d a t i o n s t r e s s , i t w i l l remain s t a b l e under slip  i n c r e a s i n g or at p a r t i c l e  stress  ratio  reasonable  contacts  is  for  decreasing  held  consolidation stress (i.e.  will  not  be  induced) as  constant.  completely  rigid  This  long  as  contention  particles  whose  is  intrinsic  angle o f s u r f a c e f r i c t i o n i s not a f u n c t i o n o f normal s t r e s s level.  The  relatively  small  amount  of  sand d u r i n g c o n s o l i d a t i o n a t constant be due  consolidation  is  expected  crushing  the  elastic  These  and  two  considered by  these  in  a  mechanisms  two  induce  slip  contact  crushing  elastic The crush  due  strain  of  to  of  strain  non-rigid  slip  during  particles.  The  contacts. isotropic  contacts  and  are  not  strain  induced  unstable  changes  which The  could  in  magnitude  of  consolidation  is  t o the magnitude of s t r a i n  particle  contact  development  populations,  at p a r t i c l e  coupled  at  contact  isotropic  particle  mechanisms c o u l d a l s o induce  expected t o be by  be  in  particles.  i n sand d u r i n g  i n Rowe's p a r t i c u l a t e model.  and fi p a r t i c l e  particle  to  induced  s t r e s s r a t i o must then  t o f a c t o r s o t h e r than s l i p between r i g i d  The m a j o r i t y o f s t r a i n induced  turn,  strain  the  developed  magnitude  of  strain. relatively  resistant  substantially  s m a l l c o n s o l i d a t i o n s t r a i n s observed i n  Ottawa C109  larger  sand  strains  (see  observed  Figure in  4.5)  angular  and  the  Brenda  sand,  which  crushing, factor  i s considerably  confirm  in  the  that  less  particle  development  resistant  crushing  of  strain  to  i s an  particle important  during  isotropic  or e l a s t i c  strain i n  consolidation. The  proportion  loosest  state  of recoverable  Ottawa  sand  after  virgin  isotropic  c o n s o l i d a t i o n from 50 kPa t o 550 kPa and u n l o a d i n g a g a i n t o 50  kPa (see F i g u r e A.3) i s approximately  and  51% r a d i a l  strain,  while  less  a t 36 t o 32% a x i a l  (see  Figure  A.2).  consolidation  o f Brenda  correlation  sand  and a h i g h  percentage  c o u p l e d s t r a i n development under i s o t r o p i c strains  consolidation axial  and  observed  a r e always  radial  under  compressive  directions  indicates  that  the strains  crushing  and  elastic  of recoverable  o r mode B p a r t i c l e  combination  of  both  components  which  compressive  result  in a  Figure  2.4).  The e l a s t i c  during  virgin  consolidation  strains  induced  during  slip  by  and  component  isotropic  be  i n both  4.11).  This  particle  contact  predominate  during  induced by mode  require that  negative  may  isotropic  or positive  deformation  contact  mechanism o f  virgin  i s o t r o p i c c o n s o l i d a t i o n , because t h e s t r a i n s A  particle  consolidation.  (see F i g u r e induced  strain  lower magnitude o f  e l a s t i c s t r a i n tends t o support t h e i n t e r p r e t e d  The  i s much  of greater  i n Ottawa sand w i t h  strain  strain  s t r a i n and 21 t o 23% r a d i a l  This  crushing resistance  that  97% a x i a l  t h e r e be a  extensional strain  r a t i o (see  of strains estimated  unloading.  strain  induced from  The  the  strains  230  recovered  during  isotropic  unloading  are  essentially  i s o t r o p i c and e l a s t i c  (see S e c t i o n 4.4, Appendix A, and V a i d  and  When t h e e l a s t i c component o f s t r a i n  Negussey, 1984).  i s s u b t r a c t e d from v i r g i n s t r a i n , t h e remaining irrecoverable considerably of  axial less  strain  compressive  irrecoverable radial  component induced  must  is  still  strain.  crushing  strain  remaining  strain  elastic  and  crushing  i s assumed  to  preparation  to isotropic  crushing  during v i r g i n i s o t r o p i c particle  particle (a  contact  virgin contact  stability  become  isotropic  contacts  which  strains  the  slip i s observed  switching  from  Since  K  Q  induced  are r e l a t i v e l y  i n Figure  during  slip  be  small  Thus  expected only  i s close to s l i p 7.4) c o u l d  isotropic  the  failure  be expected t o  consolidation.  The  during v i r g i n c o n s o l i d a t i o n i s  implies that  become  a and p may  consolidation.  p o p u l a t i o n which  t h e Mode B type  contact  consolidation.  population  boundary  unstable  then  c o n s o l i d a t i o n , o n l y s m a l l changes i n  inference that p a r t i c l e of  and  particle  similar t o that  when  and e l a s t i c  If  isotropic,  component due t o p a r t i c l e  sample  consolidation  during  strain  crushing,  strain.  be  i n f e r r e d t o be o f t h e mode B type,  the  component  The i r r e c o v e r a b l e contact  but  s l i p between p a r t i c l e c o n t a c t s which have been made by  particle  compressive  than t h e remaining  be due t o p a r t i c l e  unstable  during  component o f  unstable  the majority during  of particle  virgin  isotropic  c o n s o l i d a t i o n a r e c l o s e t h e mode B s t a b i l i t y boundary shown in  Figure  7.4.  This  might  be  expected  because  of the  231 previous stress  K  consolidation  Q  history  stress  has i n s u r e d  that  history. stable  This  previous  particle  contacts  have never been f a i l e d c l o s e t o t h e node B s t r a i n boundary, while  t h e mode A  shifted not  strain  a large  population  c l o s e t o t h i s boundary  of stable  recently  been  may  also  particle  contacts  (between t h e s t r e s s r a t i o o f 1.0 and  c o n t o u r s as shown i n F i g u r e  model  has o n l y  i n t o a p r e v i o u s l y u n s t a b l e zone, and thus one would  expect  2.0  boundary  be used  7.5).  to explain  Thus t h e p a r t i c u l a t e the r e l a t i v e l y  larger  i r r e c o v e r a b l e h o r i z o n t a l s t r a i n component o f water p l u v i a t e d sand under v i r g i n i s o t r o p i c c o n s o l i d a t i o n .  7.2.3  Compression Loading Response After  isotropic  consolidation,  expected t o have a p o p u l a t i o n in  t h e middle  increased  compression  p a r t i c l e contacts  after  Because  sample  7.5.  loading,  of the K  consolidation  Q  (see S e c t i o n  d e f i c i e n c y o f stable p a r t i c l e contacts  below  a  stress  Thus only  7.5,  concentrated with  zone  ratio  o f 2.0.  i n t h e bottom  h i g h e r fi v a l u e  7.2.2)  of  stable  7.5 o r 7.1, t o mode A history  there  is a  below t h e 2.0 s t r e s s i s generated  In a d d i t i o n ,  because o f  of p a r t i c l e  r i g h t hand  and  as shown  stress  minor mode A s t r a i n  s e t t l e m e n t through water, t h e m a j o r i t y is  the  is  stress i s  stable p a r t i c l e contacts  preparation  r a t i o contour.  sample  As v e r t i c a l  s h i f t s t o the r i g h t of Figure  thus exposing p r e v i o u s l y strain.  test  of p a r t i c l e contacts  zone o f F i g u r e  in  a  lower  corner a  value.  contacts  of Figure Under  232 compression large  loading,  stress  predict  ratio  fairly  incremental increase  this  zone  remains  (see F i g u r e  7.1) thus  s m a l l mode A s t r a i n s .  strain  ratio  stable  and  up t o v e r y  one c o u l d  A prediction  dilatancy  again o f the  induced  by  an  i n s t r e s s r a t i o may be made from F i g u r e 7.2.  Under i n i t i a l  increases  i n stress  r a t i o from 1.0, t h e  model i n d i c a t e s t h a t v e r t i c a l s t r a i n i s g r e a t e r i n magnitude than h o r i z o n t a l be  contractive  confining all  s t r a i n , thus induced s t r a i n i s p r e d i c t e d t o  soil  ratio  (e.g.,  stress tests  i n t h e low s t r e s s  response  response. directly stress  The s t r e s s determined  ratio  will  be  from  (Figure  model  transformed  7.1)  water  7.2).  Strains  t o the previous K sands,  contacts  which  Q  consolidation  that  dilatant  model,  as one  by  several  induced by an  the s o i l . stress history i n  and t h e r e s u l t i n g may s l i p  below  response i s n o t expected below a s t r e s s  of  into  deficiency  a stress  the t r i g g e r i n g of steady-state or l i m i t e d  undrained  stress  i n s t r e s s r a t i o a r e governed by t h e p o p u l a t i o n o f a  pluviated  particle  As  predicts  i s crossed  p p a r t i c l e c o n t a c t s which e x i s t w i t h i n Due  as observed i n  r a t i o range.  the p a r t i c u l a t e  s t r a i n r a t i o contours  2.0,  loading),  i n effective  r a t i o a t which t h i s o c c u r s cannot be  (Figure  and  reduction  the p a r t i c u l a t e  contour  increase  a  d u r i n g undrained  i s increased,  contractant  t o show  loading  steady-state  contractive  o f water p l u v i a t e d  or limited  range o f l o a d i n g  in  r a t i o of  liquefaction  r a t i o o f 2.0.  In  sands, t h e t r i g g e r i n g  l i q u e f a c t i o n i s expected  i n the  response from a s t r e s s r a t i o o f  233  2.0  to  the  phase  transformation  state.  This  is  indeed  observed i n the undrained  loading response of Ottawa sand,  which has  of approximately  a constant 20  friction  angle  of  correlate  well  with  contact  slip  CSR  degrees) .  the  Thus  initiation  predicted  in  water  of  2.0  CSR  (mobilized  is  shown  increased  pluviated  to  particle  sand  by  the  p a r t i c u l a t e model. The  essentially  maintained to  constant  on the undrained  represent  particle  the  contacts  increasing  state is  strain.  ultimate  friction  angle  f a i l u r e envelope i s interpreted where  both  Such  a  similar  created  and  a mechanism  population destroyed  could  of  under  explain  the  observed increase i n ultimate f r i c t i o n angle with increasing sand density greater  (see Figure 6 . 4 ) ,  because one  resistance to p a r t i c l e  could expect a  rearrangement  in a  denser  sand.  7.2.4  Extension  Loading Response  I f the p a r t i c l e contact population which i s interpreted to  exist  pluviated previous  within sand  an  (the  section)  isotropically  same sand  as  that  i s subjected  to  extension  values of a and fi must be transformed 90-/9.  This  consolidated  transformation  accounts  described  to a'  in  the  loading,  the  = 90-a  for the  water  and fi' =  reversal  p r i n c i p a l stress d i r e c t i o n i n loading (see Figure 2 . 4 ) .  of The  r e s u l t i n g i n i t i a l population of p a r t i c l e contacts i s shown i n Figure  7.6.  Figure  7.6  Range o f loading,  p a r t i c l e c o n t a c t s which a r e s u b j e c t e d t o s l i p a f t e r a Ka and i s o t r o p i c c o n s o l i d a t i o n s t r e s s  90  ZONE OF MODE B SLIP WHEN LT /LT< t a n ( ] 8 ( i ) * t an (°< )  in  1  UJ LU  cr  LD LU  a  8 cr o i— CJ  < a  in extension history  h  80  70  ZONE OF PROBABLE PARTICLE CONTACT POPULATION DUE TO THE Ko STRESS HISTORY AND ISOTROPIC CONSOLIDATION  PARTICLE CONTACT POPULATION WHICH BECOMES STABLE UNDER ISOTROPIC CONSOLIDATION. BUT WHICH IS RELATIVELY DEPLETED DUE TO Ko STRESS HISTORY  60  50  1.0  40  i—i LO LU  30  UJ  20  REVERSED STRESS DIRECTION: LX>LT  cr  ZD I— C_)  10  ZD  cr i— LO  n v  «' = 90 - °<  jS' = so -  J3  ZONE OF MODE A S L I P WHEN LT /LT> t a n C P + ^ m a n C o * ' ) h  0 10  20  30  INTERPARTICLE  40  50  CONTACT A N G L E  60  fT  70  (DEGREES)  80  90 to CO  Due  to  the  sample  preparation  and  isotropic  consolidation s t r e s s h i s t o r y , there i s a large population of particle  contacts  extension contrasts  which  loading with  as  a r e exposed  stress  t h e sparse  ratio  of contacts  i s increased i n extension  to slip  during  during  reasonable  critical  explanation  stress ratio  compression  loading  i s believed  contacts stress  which  ratio,  history.  to slip  (1.0 t o 2.0) have never been Thus a l a r g e  i s induced  loading.  even a t low  This difference i n  and compression l o a d i n g o f f e r s  f o r t h e observed  differences i n  (CSR) behaviour between e x t e n s i o n and (see S e c t i o n s  observed t o be e s s e n t i a l l y constant which  contacts  The p o p u l a t i o n  sample p r e p a r a t i o n .  extension  in This  l o a d i n g which a r e s u b j e c t  s o i l f a b r i c between e x t e n s i o n a  slip  i n compression l o a d i n g as  amount o f p l a s t i c c o n t r a c t i v e s t r a i n stress ratio  of p a r t i c l e  from 1.0 t o 2.0.  i n t h e same s t r e s s r a t i o range subjected  A  i s increased.  population  which a r e exposed t o mode A s l i p stress ratio  t o mode  2.1 and 5.3).  CSR i s  i n compression  loading,  t o be due t o t h e s p a r c i t y o f p a r t i c l e  may  undergo  slip  below  due t o t h e p r e v i o u s  K  Q  a K  Q  consolidation  consolidation  stress  P a r t i c l e c o n t a c t s which a r e s u b j e c t t o s l i p by an  i n c r e a s e o f s t r e s s r a t i o above 2.0 have never been caused t o slip  by p r e v i o u s  s t r e s s h i s t o r y , thus when s t r e s s r a t i o i s  increased  close  to  induced.  I f these  2.0,  large  contractive  contractive  s t r a i n s are s u f f i c i e n t to  produce a r e d u c t i o n i n sand s t r e n g t h , is  observed.  In  contrast  to  s t r a i n s are  a CSR o f c l o s e t o 2.0  compression  loading  CSR,  extension  loading  CSR  deposition void ratio  i s observed  to  (Chung, 1985).  be  function  of  CSR i s g e n e r a l l y much  lower than observed i n compression l o a d i n g w i t h l o o s e s t s t a t e samples having  a  (see T a b l e 5.1),  t h e lowest CSR, and denser  samples showing a gradual  i n c r e a s e i n CSR.  CSR  can be a t t r i b u t e d t o t h e reduced  i n extension  contractive Although  behaviour  there  sand d u r i n g  diminished  with  is  with  for a  density.  toward volume c o n t r a c t i o n o f  t h e magnitude  increasing density.  with  with  sufficient  increasing  increasing  stress  of  stress  contraction  I n undrained  amount  ratio is  loading,  o f pore  pressure  ratio  sand  density,  history  density, unless  thus  CSR  is  i t i s fixed  by  as observed  i n compression  results. Greater  contraction  i s observed  because a l a r g e r number o f p a r t i c l e to  increasing  to t r i g g e r liquefaction or limited l i q u e f a c t i o n  reduced  previous test  density,  potential  increased  sand  shear up t o phase t r a n s f o r m a t i o n of  generation  of  i s a tendency  regardless  the  loading  The behaviour o f  contractive  population  slip  of contacts  under  extension contacts 7.2.1) values.  extension  i s the i n i t i a l  results  When  these  This  contractive strain i n  concentration  i n generally values  are  they  stress history.  produced by d e p o s i t i o n through water which  are subjected  loading.  by p r e v i o u s  f a c t o r which y i e l d s g r e a t e r loading  contacts  loading  e x i s t s w i t h i n t h e sand because  have not been rendered u n s t a b l e A second  i n extension  lower  a  of p a r t i c l e (see S e c t i o n  and  transformed  h i g h e r fi to  their  equivalent higher  a'  i n the extension and  loading  lower fi' v a l u e s  concentration  of p a r t i c l e  through water  i s i n t h e upper  7.6.  This  zone  under e x t e n s i o n subject  under  Thus  produced  left  hand  contacts  loading, while  to slip  result.  contacts  of p a r t i c l e  direction,  generally t h e major  by d e p o s i t i o n  corner  of Figure  i s subject  to  slip  t h e same p o p u l a t i o n was n o t  compression  loading.  Due  to  this  c o n c e n t r a t i o n o f p a r t i c l e c o n t a c t s produced by p l u v i a t i o n o f p a r t i c l e s through water, more c o n t r a c t i v e s t r a i n s a r e a g a i n predicted i n extension loading.  7.2.5  Stress Reversal  As  stress  ratio  i s increased  loading,  t h e s t a b l e zone o f p a r t i c l e  shifted,  as shown i n F i g u r e  i n one  direction  of  contact population i s  7 . 7 f o r compression  loading.  A l l newly e s t a b l i s h e d p a r t i c l e c o n t a c t s which a r e induced by s t r a i n must e x i s t w i t h i n t h e new s t a b l e zone, i n o r d e r f o r the  particulate  ratio  m a t e r i a l t o remain s t a b l e .  i s achieved  boundary  strain  stable  zone  can no l o n g e r be pushed t o a h i g h e r  stress  ratio  contour.  In  other  when  t h e mode  words,  p o p u l a t i o n produced by s l i p  A  A peak s t r e s s  the stable  particle  contact  i s t h e same as t h a t b e f o r e  slip  occurred. If of  stress ratio  stable particle  expect exposed  mode  B  i s reduced f o l l o w i n g l o a d i n g , t h e zone contacts  strains  i s shifted  again.  as t h e p r e v i o u s l y  t o t h e mode B s t r a i n  unstable  One  stable  zone.  could  zone i s  Because the  STRUCTURE DIMENSION  FACTOR  cx  (DEGREES)  mode  B strain  ratio  stable  contour  increasing  has  stress  concentration  zone  only  recently  ratio,  one  loading  could  made  stable  not expect  within  stress  this  by  a  large  zone.  Thus  s t r a i n s t o be s m a l l i n comparison  The mode B s t r a i n s which do o c c u r on  strains.  unloading  the 1 . 0  above been  o f p a r t i c l e contacts  one c o u l d expect u n l o a d i n g to  boundary  are predicted  by  the p a r t i c u l a t e  model  t o be  c o n t r a c t i v e , as observed i n c y c l i c l o a d i n g t e s t r e s u l t s (see 6.0).  Section stress ratio  In contrast,  which  generally  i n undrained  unloading  should  observed  accompanies  loading be  the reduction  i n t h e unloading  a reduction  implies  dilative.  o f mean normal  that The  i n stress  elastic  s t r a i n s on  contractive  o f undrained  test  strains  samples  thus  i n d i c a t e s t h a t t h e mode B s t r a i n s induced by a r e d u c t i o n o f s t r e s s r a t i o a r e l a r g e r than t h e e l a s t i c s t r a i n s induced by the r e d u c t i o n o f mean normal s t r e s s . 7.8  Figure  displays  reversal.  Compression  transformed  t o extension  of  the  compression l o a d i n g unstable  zone  predict  large  reversal  happens  to  the  stable  shown i n F i g u r e 7 . 7 w i t h t h e o c c u r r e n c e o f s t r e s s  population  majority  what  loading  a  loading  previously  and fi v a l u e s  extension  contractive  and e x t e n s i o n  stable  zone  The  produced  by  i n t o t h e mode A s t r a i n  loading.  strains  loading.  been  a' and fi' v a l u e s .  i s shown t o f a l l  under  have  Thus  t o occur  This  one  upon  behaviour  would stress  i s indeed  observed i n undrained t e s t s , and l e a d s t o t h e development o f large c y c l i c  m o b i l i t y s t r a i n s i n sands which a r e g e n e r a l l y  7. 8  gur e  Explanation of the large contractive s t r a i n s associated with principal stress reversal following loading t o a high stress  ZONE OF MODE B S L I P  ratio  WHEN  0~ /LT < t a n (jS ft,)* t a n («') 1  h  80  THE PARTICLE CONTACT POPULATION WHICH WAS PREVIOUSLY STABLE AT A STRESS RATIO OF 4.0 (SEE PREVIOUS FIGURE) SUBJECT TO UNLOADING AND REVERSAL OF PRINCIPAL STRESS DIRECTION. THE PARTICLE CONTACT DISTRIBUTION IS VERY UNSTABLE UNDER THE NEW DIRECTION OF LOADING. AND LARGE CONTRACTIVE STRAINS OCCUR UNTIL A MORE STABLE MATERIAL FABRIC IS REESTABLISHED.  70  60 H  50  ORIGINAL STRESS DIRECTION:  40  LT >CT v h  30  -I  REVERSED  or >LT h  20 -  ZONE OF MODE A S L I P  v  ( 0" /CT )max = 4.0 v h STRESS DIRECTION: cx' = 9Q  |B'  - ex.  - 90 -  J8  WHEN  ( J / 0 " > t a n (]3+ft,)* t a n («')  0  10  20  T  T  30  40  50  INTERPARTICLE CONTACT ANGLE  60  JS'  70  (DEGREES)  80  90  241  d i l a t i v e under m o n o d i r e c t i o n a l cyclic  mobility  fluctuation different  strain  fabric  directions  of  of  contraction  sand  between  fabric,  must be produced  i n each  effective  and s o i l  to  With  the  Thus load  be  extremes  loading.  i s increased.  stress  The development o f  i s considered  o f sand  fluctuation  loading.  due  generated i n each  tendency  greater  cycle  strength  to the  extreme  for  dilative  i n order to carry  volume strains  to  increase  the  applied  load.  7.2.6 A stress  The E f f e c t o f S t r e s s H i s t o r y Upon CSR K  Q  consolidation  ratio  of  2.0  stress  during  history  sample  which  induces  preparation  has  a  been  i n t e r p r e t e d as t h e reason why water p l u v i a t e d sand has a CSR of  2.0  i n compression  7.2.4).  loading  sand t o t h i s  limited  7.2.3  and  T h i s i n t e r p r e t a t i o n i m p l i e s t h a t CSR may be changed  t o a g i v e n s t r e s s r a t i o by simply  (1985)  (see S e c t i o n s  on  given  stress ratio.  the e f f e c t s  o f sample  l i q u e f a c t i o n response  increased equivalent  to  a  specific  stress  prestraining a contractive  prestrain  show t h a t  value  ratio  Data p r e s e n t e d  value.  by  by Chung  upon  CSR may  CSR indeed  prestraining As  long  as  to  and be an  limited  l i q u e f a c t i o n behaviour i s maintained a f t e r p r e s t r a i n i n g and reconsolidation, reloading  and  are the  the  same,  direction t h e CSR  of  value  preloading obtained  r e l o a d i n g i s v e r y c l o s e t o t h e maximum s t r e s s r a t i o during  preloading.  This  i s true  i n both  and during  achieved  compression and  242  extension  loading  prestrain  effect  i s consistent  interpretation of factors  INTERPRETATION OF FACTORS MOIST TAMPED SAND FABRIC  At  which  of  with the  contribute  sand  sample  between g r a i n s .  expect  within  soil  i s because  l a r g e r than  PRODUCE  AND  to  CONTROL  because  structure  by c a p i l l a r y  capillary  self-weight  p a r t i c l e contacts  t h e sample,  control  i s controlled  This  considerably  could  WHICH  low c o n f i n i n g s t r e s s , t h e i n t e r n a l s t r u c t u r e  moist  are  observed  f a b r i c and behaviour o f water p l u v i a t e d sands.  7.3  a  The  upon measured CSR v a l u e s  particulate the  directions.  tensions  tension  forces.  t o be  within  Thus one  essentially  t h e water t e n s i o n  a r e independent  forces  random  forces  which  of direction.  The  p r o c e s s o f compaction by tamping may tend t o induce a l e s s random  structure  samples,  i n higher  t h e random  density  samples.  may  a  structure  have  In  loose  and /3 p a r t i c l e  c o n t a c t v a l u e s which a r e unbounded by s t r e s s r a t i o c o n t o u r s , because water t e n s i o n between One  forces  p a r t i c l e s maintain  could  thus  expect  and n o t f r i c t i o n a l  t h e sample  relatively  interparticle One  might  capillary  also  expect  tensions large  p r o c e s s , as c a p i l l a r y t e n s i o n the  sample.  while  Such  t h e moist  large  sand  i n a stable  large  s t r a i n s i n a moist sand as an e x t e r n a l  resistance  and  state.  contractive  s t r e s s which exceeds  i s applied  t o t h e sample.  s t r a i n s during  the saturation  f o r c e s a r e removed from w i t h i n  strains  induced  i s maintained  during  under  a  saturation  consolidation  243 vacuum have been r e p o r t e d et  by Marcuson e t a l . (1972),  a l . (1982) and Sladen e t a l . (1985). The  initial  stress  history  applied  to a  moist  sample c o u l d be expected t o e s t a b l i s h t h e i n i t i a l anisotropic conditions,  character  of  population  within  the  sample.  an i s o t r o p i c s t r e s s  vacuum w i t h i n t h e sample. a  the stress  which  ratio  stress  has been  =  1.0  contours  Section  unlike  subjected  a f t e r preparation  a  Figure  7.1.  c o u l d be expected o f water  pluviated  consolidation  consolidation  Q  exists  s t a t e (see  7.2.).  during  initial  stresses  application  induced  et a l .  employed  by  preparation  within  (1969,  himself o f moist  allowed  of  a  vertically  radially  may  1982) d e s c r i b e s and  many  tamped  supported  encases  i n the moist  confining  t h e sample  soil  by  the  n o t be i s o t r o p i c .  researchers  specimens.  method f o r the  This  method  on each end o f t h e sample  the s p l i t  t h e sample.  sample  vacuum,  t h e standard  other  requires that the loading platens be  that  which  of  to isotropic  at a K  Depending upon t h e s t r a i n  Castro  by c r e a t i n g  p a r t i c l e contacts  be e s s e n t i a l l y random,  sand  normal  T h i s might be expected t o c r e a t e  and p  of a  sand  f a b r i c and  Under  i s applied  W i t h i n t h e s t a b l e zone, p a r t i c l e c o n t a c t s to  Chang  As  an  former initial  tube  which  vacuum i s  a p p l i e d t o t h e i n s i d e o f t h e sample, t h e rubber membrane on the  s i d e s o f t h e sample i s drawn i n , and t h e sample i s f r e e  to contract on  i n the r a d i a l d i r e c t i o n .  Thus t h e r a d i a l  t h e sample equals t h e vacuum p r e s s u r e .  stress  But because the  l o a d i n g p l a t e n s a t e i t h e r end o f the sample a r e s e p a r a t e d by the r i g i d  former tube, e s s e n t i a l l y z e r o s t r a i n may  the a x i a l d i r e c t i o n .  occur i n  The r e a c t i o n due t o t h e vacuum on the  end p l a t e n s i s c a r r i e d by t h e former tube, and o n l y t h e K  Q  component o f s t r e s s generated i n t h e a x i a l d i r e c t i o n o f the sample  due  equivalent  to to  the K  higher  radial  consolidation  Q  stress.  in  the  As  this  ground  but  is with  r e v e r s e d d i r e c t i o n s o f p r i n c i p a l s t r e s s , the a x i a l s t r e s s on the  sample  could  be  expected  t o be  only  half  the  radial  s t r e s s , u n t i l t h e s p l i t former tube i s removed. Upon removal o f t h e former tube, a s t a t e o f s t r e s s would be e s t a b l i s h e d w i t h i n the sample. h i s t o r y would  result  i n a f a b r i c which  This  be  predicted  strains to  be  induced by e x t e n s i o n  relatively  small  in  direction.  loading  to  the  p l u v i a t e d sands If  the  consolidated expect  shear  trend  predicted  and  would  comparison  subsequent s t r a i n s induced by compression l o a d i n g . opposite  stress  i s p r e l o a d e d i n the  r a d i a l d i r e c t i o n , but not p r e l o a d e d i n the a x i a l Thus subsequent  isotropic  observed  to  This i s in  water  (see S e c t i o n 7.2).  moist during  tamped  sand  initial  induced  pore  were  sample  truely  isotropically  preparation,  pressures  under  one  could  subsequent  u n d r a i n e d l o a d i n g t o be e s s e n t i a l l y independent o f d i r e c t i o n of  loading.  In comparison  t o water  pluviated  sands,  one  c o u l d a g a i n p r e d i c t g r e a t e r shear induced pore p r e s s u r e s i n t h e compression l o a d i n g response o f moist tamped sand.  245  The  predicted  pluviated  and  explanation types.  d i f f e r e n c e s i n sand f a b r i c between water  moist  tamped  sands  In water  pluviated  i n extension  5.3). to  a  reasonable  f o r d i f f e r e n c e s i n CSR behaviour o f t h e two sand sands,  c o n s t a n t i n compression l o a d i n g , lower  offers  loading  CSR  i s observed  t o be  but v a r i a b l e and g e n e r a l l y  (see S e c t i o n  2.1  and  Section  CSR behaviour i n water p l u v i a t e d sand i s i n t e r p r e t e d  be  a  consequence  of  the  soil  fabric  produced  by  s e t t l e m e n t o f p a r t i c l e s through water (see S e c t i o n 7.2.3 and 7.2.4).  In compression  interpreted  loading,  t o have a CSR equal  approximately  2.0  because  water  t o the K  the  K  h i s t o r y f o l l o w i n g sand d e p o s i t i o n a  deficit  of p a r t i c l e  contractive extension the  deformation  loading,  particle  contacts below  pluviated Q  stress r a t i o of  consolidation  Q  loading  which  may  a stress  slip  ratio  slip  behaviour  and  induced  of  moist  has been d e s c r i b e d  variable,  contraction  tamped  by C a s t r o  generally  increasing  sand  Thus t h e CSR behaviour  compression pluviated  cause  o f 2.0.  which  loading  i s more  sand under e x t e n s i o n  like  in  In thus  triggers  values. compression  (1982), Sladen e t a l . CSR has been shown t o  with  increasing  Very low CSR v a l u e s have a l s o been r e p o r t e d loading.  and  no such s t r e s s h i s t o r y has o c c u r r e d ,  (1985) and Mohamad and Dobry (1986). be  stress  has ensured t h a t t h e r e i s  l i q u e f a c t i o n may occur a t lower and v a r i a b l e CSR CSR  sand i s  o f moist that  loading.  density.  i n compression tamped  observed This  sand i n i n water  i s explained  by t h e d i f f e r e n c e i n i n t e r p r e t e d sand f a b r i c between t h e two  246  sand  types.  Moist  tamped  sand  compression s t r e s s h i s t o r y o n l y during  sample  preparation,  population  which  controlled  by  relatively  loose  the  c o n t a c t s which may may  may  fail degree  sands,  is due  thus under and  there  t o the the  compression  no  of  have  a  tamping h i s t o r y  particle  method is  to  contact  loading  is  tamping.  deficit  of  In  particle  f a i l d u r i n g compression l o a d i n g , thus  CSR  be low and tend t o i n c r e a s e w i t h i n c r e a s i n g d e n s i t y . In g e n e r a l ,  could  be  more  compression  one  could  contractive  loading,  and  p r e d i c t t h a t moist tamped than  behaviour o f the two  water  possibly  water p l u v i a t e d sands i n e x t e n s i o n in  interpreted  pluviated  less  sand types i s due  f a b r i c produced by sample p r e p a r a t i o n .  sands  contractive  loading.  The  sands in  than  difference  to differences i n  247  CHAPTER 8 PRACTICAL IMPLICATIONS  The strain  mechanism o f  history  imparts  of  principal premise  strength  strength  stress of  of  a  i n v a r i a b l y induces an  anisotropic  variation  placement  is  the  sand  and  inherent  properties  to  i t s stressf a b r i c which  the  sand.  properties  with d i r e c t i o n of  in  conflict  direct  steady-state  basic  states  void  ratio.  r e s u l t s presented i n t h i s t h e s i s i n d i c a t e  that  given  contractive principal state  consolidation or  dilative,  stresses  theory  unconservative  a  sand  shear.  lead  estimates  to  of  Thus the either  soil  order  to  determine  strength,  c h a r a c t e r i s t i c s of n a t u r a l we  must  from  an  either  obtain  in situ  the  fluvial  deposit,  or  either  orientation use  of  or upon  strength. undrained  strength fill  undisturbed  i f t h i s i s not  sands, samples  possible,  deposition  p r o c e s s and  s t r e s s h i s t o r y expected i n the  must  simulated  in  be  of  steady-  depending  or h y d r a u l i c  representative  be  conservative  the procedure employed t o determine s o i l In  may  depending upon the  during  may  state,  dependent  that  upon  a  solely  the  soil  at  is  which  maximum  steady-state Test  strength  theory,  with  The  reconstituted  laboratory  the field test  specimens. Water  pluviated  under l o a d i n g ; vertical  i t has  loading  and  sand  has  a  relatively relatively  c h a r a c t e r i s t i c behaviour low  compressibility  under  high  compressiblity  under  248  horizontal  loading.  This  anisotropy  i n compressibility  r e s u l t s i n an undrained l o a d i n g response which i s dependent on  the i n c l i n a t i o n  the in  deposition  a o f t h e maximum p r i n c i p a l s t r e s s An a v a l u e  direction.  relatively  less  contractive  o f 0 degrees r e s u l t s  response  compression l o a d i n g ) , w h i l e an a v a l u e in  relatively  extension Symes  more  contractive  loading).  et a l .  systematic  Hollow  (1985)  weakening  reduction  in  phase  pluviated  sand  with  (as i n  tests  and H i g h t  (increasing  extremes  pluviated is  of  (1987)  sand.  strength)  i n a from  tested, type. have  t h e degree  have  in  0 t o 90  in  water  degrees,  tests  a  and  provide  given  water  i n inherent  anisotropy  sands which  have  been  i s dependent  upon  sand  pluviated  of anisotropy  show a  F o r example, water p l u v i a t e d Ottawa sand i s shown t o l i m i t e d l i q u e f a c t i o n behaviour  compression l o a d i n g the  possible  Although t h e t r e n d  s i m i l a r f o r a l l water  same  stress  limited  loading.  when loaded  range,  angular  liquefaction  Figure  8.1  i n both  at loosest tailings  behaviour  shows t h a t  extension  sand  only  although  range  of void  substantial  ratios,  dilation  transformation  state.  the material  once  i t  is  The c o n t r a s t  and  state, while i n i s shown t o in  extension  Ottawa  sand i s  s u b j e c t t o l i m i t e d l i q u e f a c t i o n i n compression l o a d i n g a  by  contractiveness  transformation  behaviour  triaxial  performed  which suggests t h a t compression and e x t e n s i o n the  triaxial  o f 90 degrees r e s u l t s  cylinder  increase  (as i n  response  and Shibuya  with  is still strained  over  subject past  to  phase  i n l o a d i n g behaviour o f  Fig. 8.1  U n d r a i n e d loading r e s p o n s e of water d e p o s i t e d Ottawa  Sand  C 1 0 9 at v a r i o u s  2.5  densities  r  /  + +  "  = 2.0 k g f / c m  Cr " 3  c  1  2  c  -  • SAMPLE SET  • A O O +  1.0  Drj(%)  1 2 3 4 5  o P  J  O  /  o  / A  /  F //  K = 1.0 1.5  /*  ®  Dr (*)  n  O A  7  c  32.5 36 36.0 40.5 39.0 43.0 43.5 46.5 60 62.5  >  ! 1 <])  t  \  < >  < >  O-O-COO^g 0.5  cr  ,  +  1.0 / + I  1.5 -  7  I -  l 5  -  l 3  I AXIAL  I 1 STRAIN  £  1  1  1  3 tt)  1  1  1 5  1 7  250  Ottawa sand and Brenda sand i n d i c a t e s t h a t i t i s w e l l w h i l e t o conduct l a b o r a t o r y t e s t s on r e p r e s e n t a t i v e  worth  samples  o f a g i v e n sand i n order t o c h a r a c t e r i z e i t s p r o p e r t i e s . The a n i s o t r o p i c p r o p e r t i e s o f water p l u v i a t e d sands may lead  to  modes  failure  in a  difficult  failure  soil  mass  to predict  methods. lateral  of  Soil  facilities  which  such  mechanisms o f t r i g g e r i n g  which  using  masses  loading,  and  a r e both  presently  which  as i n o f f s h o r e  may be h i g h l y s u s c e p t a b l e  and  available analytical  are subject  are subject  unexpected  t o any  islands  of  and harbour  t o i c e , wave o r boat  to liquefaction.  form  loading,  In contrast,  a  s o i l mass which i s s u b j e c t t o mainly v e r t i c a l l o a d i n g may be relatively resistant to liquefaction. methods  of evaluation  arise  Problems w i t h c u r r e n t  i n the majority  cases where a s o i l mass may be s u b j e c t e d loading  conditions.  identify water  The  following  sand  fabric  paragraphs  and  should  embankment  of  conditions,  compressibility pluviated  sand  (1967) s t a t e stable,  and under  that  due high  to  upon  vertical  "A c l e a n  sand  a l t h o u g h i t may be l o o s e ,  into  stable  the  pluviated  positions.  because a  static  of  Terzaghi  deposited  In  sand  relatively strength  loading.  the  embankment.  water  undrained  to  implications of  be r e l a t i v e l y r e s i s t a n t t o l i q u e f a c t i o n under  loading  down  constructed  attempt  properties  performance o f a common s t r u c t u r e , a s o i l An  practical  t o a combination o f  and e x p l a i n some o f t h e p r a c t i c a l  pluviated  of  under  low water  and  water i s  the grains  sand  Peck  capable  roll of  251  spontaneous this  l i q u e f a c t i o n , some  process".  liquefaction static most  The  of  relatively  failures  loading  tends  embankments  must  small  of hydraulic  conditions  these  agent  interfere  number  fill  of  reported  embankments  t o support  are r e s i s t a n t  with  under  the idea  that  to liquefaction  under normal c o n d i t i o n s . The  f a c t t h a t some h y d r a u l i c f i l l  observed  to fail  under  specific  features  o f e i t h e r t h e sand used o r t h e method o f  construction presented loosest degrees  resulted  in this state of  loading. and  has  thesis  after  failure.  indicate that  to  sand  may  i s more under  some  results  d i f f e r e n t sands a t  liquefaction  of i n t r i n s i c  susceptable  vertical  have  varying  under  vertical  rounded quartz friction  on  particle  t o t h e development  loading  than  angular  sand  of  flow  felsic  sand  angle o f i n t r i n s i c f r i c t i o n on  surfaces.  The  amount  sand  may  also  sand  fabric  deposited  o f a i r entrapped  i n t e r f e r e with  during  within  a hydraulic  t h e development  deposition.  A  sand  of a  slurry  fill stable  which i s  below water l e v e l may be expected t o have a small  percentage  o f entrapped  a i r , which would  have v e r y  e f f e c t on water p l u v i a t e d sand f a b r i c due t o s m a l l tension  that  Test  indeed  suggests t h a t  which has on average a h i g h e r particle  in  suggests  A comparison o f t h e p r o p e r t i e s o f Ottawa C109 sand  which has a lower angle  failure  loading  deposition  resistance  Brenda t a i l i n g s  surfaces  static  embankments have been  forces.  A sand which i s d e p o s i t e d  little  capillary  i n t o water  may  252  contain r e l a t i v e l y  more entrapped a i r , w h i l e a sand  which i s d e p o s i t e d above water may entrapped a i r ,  c o n t a i n a l a r g e amount o f  and thus develop a f a b r i c which i s more  entrapped a i r i s g e n e r a l l y more u n s t a b l e under  l o a d i n g than sand which  i s deposited  vertical  i n a saturated  due t o t h e b u l k i n g e f f e c t and i n f l u e n c e o f c a p i l l a r y f o r c e s between g r a i n s . water  is  re-graded  compaction, further  mechanism  important  be  without  which  state, tension  i s deposited  b u l k e d and  above  significant  i t s fabric  altered  i s considerably  less  loading.  of hydraulic  affect to  bulldozer  a material  s t a b l e under v e r t i c a l  significant  a  t h e sand may  t o produce  The  I f a sand which  by  like  A sand which has a l a r g e content  t h a t o f m o i s t tamped sand. of  slurry  upon  specify  fill  placement  i t s performance,  and  control  the  thus  may  have  a  i t i s very  mechanism  of  fill  placement. The saturated  mechanism state  of hydraulic  may  also  m a t e r i a l performance. test  specimens  thus  and  elemental  f l u v i a l and h y d r a u l i c f i l l  the  silty  may  be  in  sand  material  situ  in a  assessed  performed on Ottawa sand C109  from  fully  fabric  and  deposited  a r e homogeneous  properties.  and  Natural  sands, i n p r a c t i c e , w i l l  some degree o f p a r t i c l e s e g r e g a t i o n . segregation  placement  L a b o r a t o r y prepared s l u r r y  o f sand  represent  affect  fill  undergo  The e f f e c t o f p a r t i c l e the  results  (see F i g u r e 3.12).  of  tests  One s e t o f  compression and e x t e n s i o n t e s t s was performed on homogeneous slurry  deposited  sand  specimens  (with  no  s e g r e g a t i o n ) and  another s e t o f t e s t s was specimens 1.5).  (some v i s i b l e  conducted  at  increase  both  similar  s e g r e g a t i o n - Ottawa sand has  the  density.  peak  transformation  strength  though  a  smaller  The  effect  to  loading.  undrained compression gradation Figure  upon  When  p o o r l y - g r a d e d sand  as  well  i n compression. extent, of  is  response  is as  The  observed  particle  compression  5.5).  Segregation  strength  size  same  compared  at  at  o r unsegregated sand  segregated sands lower  density  graded sand may  extension  i n Brenda loosest  sands state  and segregated sand  large  strain  level  ( F i g u r e 3.12).  state  (see F i g u r e 3.8,  conclude  segregation  from  tends  to  loading  after  response  slurry  after  (Figure  or  level  than  the  (Figure  In a d d i t i o n ,  both  a r e shown t o have  unsegregated  observations an  otherwise  i s compared  deposition,  or  well-  at  at  that  One  particle  well-graded  sand  T h i s would be t r u e  either  constant  loosest  density.  state Since  p o o r l y - g r a d e d sands a r e more s u s c e p t i b l e t o l i q u e f a c t i o n limited  liquefaction  of  (see  F i g u r e 3.9 and T a b l e 3.2).  these make  than  behave as i f i t were more p o o r l y - g r a d e d . if  to  s e g r e g a t i o n upon  and p o o r l y - g r a d e d sands  at loosest  state  effect,  compression response o f homogeneous w e l l - g r a d e d sand 5.5)  =  l o a d i n g response o f homogeneous  ( F i g u r e 5.5)  softer  u  phase  i s shown t o be i n i t i a l l y s t i f f e r a t s m a l l s t r a i n somewhat  C  shown the  in  sand  i s s i m i l a r t o the e f f e c t  response  d e p o s i t i o n , t h e compression  and  pluviated  A l l t e s t s were conducted on e s s e n t i a l l y l o o s e s t  specimens  3.12)  on water  i n extension loading  or  than w e l l - g r a d e d  sands,  when  consolidated  from  loosest  state  after  d e p o s i t i o n , some segregated sands c o u l d a l s o be expected t o be more c o n t r a c t i v e than unsegregated sands under  extension  loading at loosest state. In  situ  particle more and  size  sands  which  segregation  susceptible  i n v a r i a b l y have could  some  be expected  t o l i q u e f a c t i o n under  degree  t o be  of  slightly  horizontal  loading  s l i g h t l y l e s s s u s c e p t i b l e t o l i q u e f a c t i o n under v e r t i c a l  loading  than  unsegregated  samples  of equivalent  gradation  which a r e a l s o c o n s o l i d a t e d from l o o s e s t s t a t e . In  laboratory  water occurs  studies, the deposition  i n the v e r t i c a l  direction,  o f sand  with  settlement  p a r t i c l e s upon a h o r i z o n t a l d e p o s i t i o n p l a n e . in  the v e r t i c a l  loading  least  d i r e c t i o n having  deposited  contractive  response  on  may  a  slope  shift  d i r e c t i o n normal t o t h e s l o p e . e f f e c t of decreasing potential  failure  in a  the l e a s t  technique  hydraulic  of  fill  vertical  surface  i f the  slope  was  An o p p o s i t e  sand  towards  a  shell  towards  construction  e f f e c t of f i n e r grained  by f i l l i n g  also  occur  on a s l o p e  the c e n t r a l  could  constructed  effect,  i n resistance t o l i q u e f a c t i o n could  the outer  The a x i s  t h e r e s i s t a n c e t o l i q u e f a c t i o n along a  embankment was c o n s t r u c t e d from  and  T h i s c o u l d have t h e damaging  outwards from t h e c e n t r a l c o r e . increase  from  of  This r e s u l t s  h o r i z o n t a l l o a d i n g t h e most c o n t r a c t i v e response. of  through  limit  core.  o r an i f the  that  dips  Such  a  t h e damaging  o r s i l t y beds and l e n s e s w i t h i n the  embankment s l o p e , because these l e s s permeable beds would be  d i p p i n g downwards towards t h e c e n t r a l core, o p p o s i t e of  t h e embankment  This  and a p o t e n t i a l  orientation of f i n e r  dissipation and  slope  grained  o f pore p r e s s u r e s  failure  beds would  from  the d i p  within  surface.  cause  faster  t h e embankment,  would a l s o l i m i t t h e e f f e c t which any p a r t i c u l a r weaker  o r impermeable bedding l a y e r might have upon t h e o r i e n t a t i o n of a f a i l u r e The  r e s u l t s presented  deposited  silty  liquefaction sands,  than  under  undrained  clean  sand.  decreases  field  loading  i n clean  i n this  study  sands c o u l d be s l i g h t l y  however,  Thus,  than  surface.  sands,  with  occur which  that  increase a  water  l e s s susceptable t o  The p e r m e a b i l i t y  conditions, could  show  of  in silt  condition  content.  of  strictly  more r e a d i l y i n s i l t y could  make  silty  silty  sands  sands  more  vulnerable t o l i q u e f a c t i o n . The  stress  conditions  on a p o t e n t i a l f a i l u r e  through an embankment v a r y maximum  principal  embankment, the  crest  a t and below  t h e embankment.  stress  towards  undergoes  the crest  The  direction  continuous  a  Factor  of Safety  important  t o determine  this  with d i r e c t i o n of loading. the s t a b i l i t y  because h y d r a u l i c f i l l  for a  given  variability  of the  stress at of  rotation  t h e t o e o f t h e embankment.  calculate  analyzing  from t h e c o n d i t i o n o f a v e r t i c a l  towards h o r i z o n t a l maximum p r i n c i p a l  toe of  principal  stress  surface  maximum  from t h e  In order slope,  of s o i l  to  i ti s strength  T h i s i s e s p e c i a l l y important i n of  hydraulic  fill  embankments,  properties are highly anisotropic.  A  consequence o f fill  sand  the  with  toward the  relatively  the  lower  r o t a t i o n of  horizontal direction  strength  maximum  of  hydraulic  principal  i s t h a t one  stress  c o u l d expect  a  r e l a t i v e l y deep seated f a i l u r e s u r f a c e w i t h i n an embankment. A major p o r t i o n o f the f a i l u r e s u r f a c e would be p r e d i c t e d t o be f a i r l y f l a t , as observed i n the f a i l u r e zone o f the lower San  Fernando h y d r a u l i c f i l l  e t a l . , 1975). lower  San  which  the  Fernando  correspond friction  On  to  at  Dam,  the  undrained  necessary  principal  apply  measured t r i a x i a l order  to  reported  by  samples  taken  et  from  overestimate  of  effects  probably  dependence magnitude  of of  in  thesis.  transformation  reduction  =  the  dam  situ  be  strength  factor  suitable  from the  at  the  strength i n  blamed  for  strength, a  and  most  of of  reported  of  a the  extension  extension 10%  an its  neglect  results has  but  estimate  compression  C109  to  sand  be  at  20  D e n s i f i c a t i o n of  An  is  of  (as  strength.  sand  a  failure  to  that  vertical  not  could  between  63°,  i t would probably  due  Loose Ottawa  a = a  If  the  the  steady-state  obtained  than  is  s  in  strength  overstated  anisotropy  37°,  steady-state  a l . , 1985).  steady-state  l o a d i n g modes may this  a  back-analysed  Castro  are  s  the  would  s t r e n g t h were used  compression t e s t  obtain  ^  stress.  of steady-state  to  strength  s  With  Seed  zone of  + <j> /2, where ^  45  a n a l y s i s o f the s t a b i l i t y of the dam, be  failure  a horizontal direction  maximum  dependent v a l u e s  a =  flat  steady-state.  i s closer to of  (Castro e t a l . , 1985;  relatively  loading with  angle  direction  dam  in  phase  that  in  257  compression tailings  (Figure  sands  compression The  enough  to  show  of  may  8.1),  a  pluviated  role  hydraulic  strain  low s t r e n g t h .  behaviour i n  sands  under  i n the i n i t i a t i o n  fill  embankment.  embankment  softening,  of  Once  are  large  the toe region  may  The development o f low s t r e n g t h  t h e t o e o f t h e embankment  i s essentially  t h e t o e o f t h e embankment.  unloading  angular  5.4).  a t t h e t o e o f an  initiate  while  contractive  water  play  in a  stresses  unloading in  strength  flow  develop v e r y at  do not even  loading  contractive lateral  Figure  ( F i g u r e 5.2 through F i g u r e  low  horizontal  3.12,  equivalent t o  As would be observed  t h e t o e o f any embankment,  this  reduction of  s o i l s t r e n g t h a t t h e t o e would cause a r e d i s t r i b u t i o n o f t h e d r i v i n g s t r e s s e s deeper w i t h i n t h e embankment, which may be s u f f i c i e n t t o i n i t i a t e progressive  or e n t i r e f a i l u r e of the  embankment.  contribute  lateral  Any  loading  factors  which  to  o f t h e t o e o f t h e embankment  increased may  cause  i n i t i a t i o n o f t o e f a i l u r e and subsequent p r o g r e s s i v e  failure  of the e n t i r e slope.  induced  by  external  increase either  cyclic  static pore  pressure  Increased  pore  which  l o a d may be  due t o s e i s m i c under  loading. may  induce  the  loading,  o r an  conditions  The mechanism an i n c r e a s e  of  whereby  i n lateral  i n the f o l l o w i n g paragraphs. pressure  by r a p i d r a t e s  embankment  lateral  pressure  of c y c l i c  stress i s described  an  loading  i n porewater  increased  induced  Increased  within  an embankment  of construction,  retains  water,  by  by seepage  may  be  through  the i n i t i a t i o n  of  258  s t r a i n softening  c o n t r a c t i v e response, o r by c y c l i c  Beneath t h e c r e s t  o f an embankment, v e r t i c a l  distribution  function  within  is a  t h e embankment.  of s o i l  may  only  Vertical  be a l t e r e d  effective  effective stresses the  mobilized  weight  stress  and depth total  i s e s s e n t i a l l y constant,  by a change i n embankment  stress  porewater p r e s s u r e .  total  The d i s t r i b u t i o n o f v e r t i c a l  s t r e s s below t h e embankment c r e s t and  unit  loading.  i s i n addition  a  height.  function  of  In contrast,  both h o r i z o n t a l t o t a l and  are a function  o f porewater p r e s s u r e and  angle  of f r i c t i o n  within  each  soil  element.  Assuming t h a t v e r t i c a l t o t a l s t r e s s d i s t r i b u t i o n i s c o n s t a n t (i.e.  that  derive  t h e embankment  Equation  horizontal total .of  an  8.3  which  with  i s not changed)  relates  s t r e s s on a s o i l  embankment  mobilized  height  the  one may  variation  of  element beneath t h e c r e s t  the mobilized  friction  (effective  s t r e s s r a t i o R) and pore p r e s s u r e w i t h i n  the s o i l  element. Equation within  a soil  would p r o b a b l y stress.  8.3  shows t h a t  element also  Horizontal  an i n c r e a s e  beneath  the crest  induce an i n c r e a s e total  i n pore  pressure  o f an embankment  i n horizontal  stress within  these s o i l  total  elements  c o u l d be expected t o v a r y from a minimum c o r r e s p o n d i n g t o K consolidation  state,  horizontal  total  effective  stress.  within  these  up  stress  soil  to are  a  maximum equal  The h o r i z o n t a l elements  embankment must be t r a n s f e r e d  when  at  a  total  beneath  vertical  state stress  the  of  Q  and zero  generated  crest  of  and c a r r i e d by a d j a c e n t  an soil  elements  within  t h e embankment  slope.  This  spreading  of  l a t e r a l s t r e s s would tend t o r o t a t e t h e d i r e c t i o n o f maximum principal  s t r e s s away from v e r t i c a l  within s o i l elements, the  elements i n t h e embankment s l o p e .  horizontal total  magnitude  crest  of i n i t i a l  f a c t exceed i n i t i a l extension  s t r e s s would vertical  o f t h e embankment.  triaxial  and towards h o r i z o n t a l Within  these  n o t be l i m i t e d  by  s t r e s s , as beneath t h e  Horizontal  total  s t r e s s may i n  vertical total stress, giving rise to a type  o f l o a d i n g towards t h e t o e o f t h e  embankment s l o p e . If  pore  pressure  i s increased  t h i s may a l s o l e a d t o a s p r e a d i n g  within  of l a t e r a l t o t a l stress i n  the embankment, which c o u l d t r i g g e r s t r a i n toe o f t h e embankment. t h i s would s i m u l a t e progressive  softening a t the  I f s t r e n g t h a t t h e t o e i s reduced,  unloading  o r complete of triggering  flow  relevant  to  fill  hydraulic  o f t h e t o e , which may produce  failure  mechanism  characteristic  an embankment,  o f t h e embankment.  deformation  is  embankments,  This  particularly due  to  the  s t r e n g t h a n i s o t r o p y o f water p l u v i a t e d sand.  For a s o i l element beneath t h e embankment c r e s t :  R  = (o  w  - U)/(a  n  - U)  (8.1)  where  R  effective  mobilized p r i n c i p a l  a.V  v e r t i c a l total stress  stress ratio  260  a  h  U  =  horizontal total  stress  =  porewater p r e s s u r e  Then  o  =  h  U  +  ( a  v  -  (8.2)  U)/R  D i f f e r e n t i a t i n g Equation  da da Aa  when a  v  Aa  h  h  h  h  +  d(a /R)  (8.2):  =  dU  = =  dU + d a / R - <7 dR/R - dU/R + U d R / R (1-1/Ri) ( U - U ) + ( a -a )/R +(U -a )  v  -  d(U/R) 2  v  2  v  2  1  v  2  v  l  1  2  2  Aa  U  2  n  2  ( l / R j - l / R ^  = constant:  =  (1-1/Ri) ( U - U ) + ( U - a ) ( l / R ^ l / R j ) 2  1  2  v  where:  R  v  =  i n i t i a l mobilized stress  =  f i n a l mobilized stress  =  change i n h o r i z o n t a l t o t a l  =  i n i t i a l pore p r e s s u r e  =  f i n a l pore p r e s s u r e (see F i g u r e  ratio  ratio stress  8.2)  (8.3)  F i g . 8.2  C h a n g e in l a t e r a l t o t a l s t r e s s with c h a n g e in e f f e c t i v e s t r e s s s t a t e for a soil e l e m e n t b e n e a t h the c r e s t of an e m b a n k m e n t  262 CHAPTER 9 SUMMARY AND CONCLUSIONS  In t h e p a s t , liquefaction  our knowledge o f t h e fundamentals o f sand  behaviour  has  t e s t s and o b s e r v a t i o n s . strength  determined  applicable to practical  (2)  and  in  laboratory  the  does  laboratory  problems, two b a s i c  of  sample  the  in  questions  tested  i n the  soil  being  situ  the laboratory  are  testing  technique  s t u d i e s have shown t h a t sand l i q u e f a c t i o n behaviour  preparation  majority  designs  i s controlled  and mode o f s o i l  liquefaction  of loose  and  of  hydraulic  well-graded  by both  sandy  by fill  with  method  o f sample  testing. soils  practical  are deposited  artificial often  from  the loading conditions that occur i n s i t u .  the laboratory  A  in  i s the s o i l  representative  employed s i m u l a t e Previous  field  (1)  must be c o n s i d e r e d :  modelled,  derived  To ensure t h a t fundamental m a t e r i a l  properties  laboratory  been  concern  natural  a r e prone t o  in  fluvial  placement.  some f i n e s  which  geotechnical  deposition  These  content.  deposits  or are  A majority  of  l a b o r a t o r y t e s t i n g i n t h e p a s t has been conducted on p o o r l y graded sands i n order required  i n most  elemental s o i l and  sands  limited. field,  t o ensure sample u n i f o r m i t y ,  laboratory  properties.  tests  The study  i n order  some  fines  content  Since  these  sands  are r e l a t i v e l y  of the e f f e c t  to  measure  of well-graded  with  t h e study  which i s  has  been  relatively  common  of gradation  sands  and  i n the fines  263 content upon sand behaviour has been research  objective  by  the  earthquake e n g i n e e r i n g .  U.S.  Most  identified  N.R.C.  as a major  (1985)  report  sands which have been  tested  i n t h e p a s t have been r e c o n s t i t u t e d i n the l a b o r a t o r y the  m o i s t tamping  preparation.  or dry p l u v i a t i o n  These t e c h n i q u e s may  techniques  on  of  using sample  not s i m u l a t e e i t h e r  the  d e n s i t y range o r s t r e n g t h behaviour p o s s i b l e i n a sand which is  pluviated  fill  through water,  as  in a  fluvial  or  hydraulic  sand d e p o s i t . In  order  hydraulic  to  fill  model  sands  the in  behaviour  the  of  fluvial  laboratory,  the  and slurry  d e p o s i t i o n method o f sample p r e p a r a t i o n has been developed. This  method  fluvial  simulates  t h e mechanism  of h y d r a u l i c  fill  or  sand d e p o s i t i o n through water v e r y w e l l , y e t y i e l d s  homogeneous  well-mixed  samples  which  are  essentially  unsegregated, r e g a r d l e s s o f g r a d a t i o n and f i n e s c o n t e n t . comparison o f the s o i l  strength properties of poorly-graded  water p l u v i a t e d and s l u r r y d e p o s i t e d sand samples t h a t both sample  A  preparation  techniques y i e l d  indicates  similar  test  gradation  and  results. In  order  to  observe t h e  effect  which  f i n e s c o n t e n t have upon the p r o p e r t i e s o f sands which  have  been p l u v i a t e d through water, a s e r i e s o f u n d r a i n e d t r i a x i a l t e s t s have been conducted on samples o f p o o r l y - g r a d e d , w e l l graded  and  silty  Brenda  Mine,  angular  British  tailings  Columbia.  sands This  derived tailings  from sand  the is  r e p r e s e n t a t i v e o f g e n e r a l l y more w e l l - g r a d e d and s i l t y sands  found i n s e i s m i c a l l y a c t i v e mountainous a r e a s , and sands  which  tailings  are  sand  derived  derived  from  from  mineralogy i s e s s e n t i a l l y triaxial order  compression  to  show  and  the  granitic  rock.  tailings  The  use  crushed r o c k ensures t h a t  independent  of grain  size.  of  sand Both  e x t e n s i o n t e s t s were employed, i n  effect  of  direction  of  loading  upon  s t r e n g t h behaviour. The  f a b r i c o f water p l u v i a t e d sand i s shown t o produce  a characteristic Water p l u v i a t e d loaded  under  anisotropy  i n undrained l o a d i n g  response.  sand i s s u b s t a n t i a l l y more c o n t r a c t i v e when  a  horizontal  maximum  principal  stress,  and  s u b s t a n t i a l l y l e s s c o n t r a c t i v e when loaded under a v e r t i c a l maximum  principal  stress.  The  substantial  directional  dependence o f sand s t r e n g t h a t c o n s t a n t v o i d r a t i o  conflicts  w i t h the main premise o f s t e a d y - s t a t e concepts, which that  the  ultimate  undrained  strength  of  sand  states  i s only  a  f u n c t i o n o f s o i l v o i d r a t i o , and independent o f f a c t o r s such as  soil  state.  fabric, The  compression  direction  use  test  of  loading  steady-state  results  water p l u v i a t e d sand would strength.  of  and  concepts  to characterize result  consolidation and  triaxial  the b e h a v i o u r  of  i n h i g h e s t i m a t e s o f sand  The use o f such e s t i m a t e s i n d e s i g n c o u l d  result  i n d e s i g n s which are h i g h l y u n c o n s e r v a t i v e . In state fill  water  pluviated  of deposition,  sands  as might  consolidated be  expected  from in a  loosest hydraulic  d e p o s i t , t r i a x i a l compression s t r e s s - s t r a i n response i s  essentially  the  same  for various  gradations of  sand.  In  265 contrast, upon  triaxial  soil  e x t e n s i o n response  gradation.  substantially extension  less  Well-graded  contractive  loading.  anisotropy,  or less  sand  than  Well-graded  i s highly  dependent  i s shown  poorly-graded sand  of a difference  thus  be  sand i n  shows  less  between e x t e n s i o n and  compression t e s t response than p o o r l y - g r a d e d sand.  One may  conclude t h a t w e l l - g r a d e d sand i s i n g e n e r a l more to  to  resistant  l i q u e f a c t i o n than p o o r l y - g r a d e d sand. In  poorly-graded  produce  slightly  sand,  more  smaller grain  dilative  size  response  in  tends  to  compression  l o a d i n g , y e t more c o n t r a c t i v e response i n e x t e n s i o n l o a d i n g . Strength  anisotropy of i s o t r o p i c a l l y  shown t o be g r e a t e s t at  high  a t low c o n s o l i d a t i o n  consolidation  consolidation  i s thus  anisotropy, or s o i l  consolidated  stress. observed  The  stress  process  to slightly  sand i s and l e a s t  of  alter  isotropic strength  fabric.  G r a d a t i o n g e n e r a l l y has a g r e a t e r e f f e c t upon m a t e r i a l properties especially  of  sand  i f t h e sand  increase i n s i l t deposited  than  20/200  non-cohesive  portion  fines  i s coarser grained.  content up t o 20% i n l o o s e s t sand  makes  behaviour  somewhat  more  behaviour  somewhat  less  content,  monotonic  dilative  and  contractive.  state  An  slurry  compression  loading  extension  loading  The  rather  small  change i n l o a d i n g behaviour w i t h i n c r e a s i n g s i l t  c o n t e n t can  be  void  e x p l a i n e d by  remains  virtually  the fact unaltered  that with  sand  skeleton  increasing  silt  ratio  content.  S i l t e s s e n t i a l l y f i l l s sand s k e l e t o n v o i d space and does not  greatly  affect  soil  behaviour.  On  the other  hand,  silty  sands need not have a l a r g e v o i d r a t i o t o be s u s c e p t i b l e t o liquefaction,  as long  as sand s k e l e t o n  void  ratio  and  silt  p o r t i o n v o i d r a t i o are high. S i l t y 2 0 / 2 0 0 sands a t l o o s e s t s t a t e show o n l y increase despite  in cyclic  strength  a large reduction  c o n s t a n t sand s k e l e t o n  with  increasing  i n void ratio.  lenses, soil  f r a c t i o n of a s o i l  as o f t e n  deposits,  expected  lower  (when c o n s i d e r e d because  size  segregated  i s segregated i n t o s i l t y  than  of  fill  or  fluvial  the material  i f the material  o f t h e segregated  gradation  soil  liquefaction,  may  i s well  soil  a r e more  be  mixed simply poorly-  would  because  and v o i d tend  to  ratio be  a r e compared, t h e  more  i t i s effectively  resistant  to  more p o o r l y - g r a d e d  thus a t an e f f e c t i v e l y denser s t a t e . For  silt  content.  I f a segregated sand and a w e l l mixed sand w i t h t h e  same g r a i n  and  strength  i s shown  at loosest state of consolidation),  elements  graded.  When compared a t  i s t h e case i n h y d r a u l i c cyclic  t o be  content,  void r a t i o , c y c l i c strength  to increase s l i g h t l y with increasing s i l t If the s i l t  silt  a slight  practical  content  considering pluviated laboratory  in  purposes a  undrained  i t i s conservative  hydraulic soil  reconstituted has a s i m i l a r  fill  strength,  silt sand  free  silty as long  material  gradation  to sand,  when  as t h e water tested  and sand  v o i d r a t i o as t h e s i l t y sand b e i n g modelled.  ignore  i n the skeleton  267  The  conclusion  laboratory s o i l compared void  at  silt  content  generally  makes  a  sample more r e s i s t a n t t o l i q u e f a c t i o n (when  both  or  constant  take  into  account  o f porewater as may  occur  ratio)  migration  that  loosest  does  not  state  sand  skeleton  drainage  in a field  and  embankment.  In g e n e r a l , a s i l t y sand embankment of s i m i l a r sand  skeleton  d e n s i t y and g r a d a t i o n as a c l e a n sand embankment may  be more  susceptible  greater  to  strain  development  r e t e n s i o n o f pore p r e s s u r e and b u i l d - u p The water  pluviated  mechanics of during  of  stress ratio  interpreted to  stress  ratio  derived  by  anisotropy  considering  the  a  function  soil  loading,  f a b r i c o f a sand  sample p r e p a r a t i o n fabric  and  and  properties  method s e l e c t e d f o r s o i l placement i n the f i e l d  may  influence of  the  of  and  are  considering  method  The  of  which  by  specific  be  particles,  d i r e c t i o n of  level.  function of The  to  rigid  slip  (the s p a c i a l d i s t r i b u t i o n  contacts),  strain a  shown  of  of  be  a c t i v e during  method  migration  may  explained  a  assembly  fabric  and be  response and  explained  is  history.  from  The  an  particle  level  (2)  resistance to p a r t i c l e contact  loading  s t r u c t u r e or  orientation  be  For  during  particle  may  (1)  at s i l t y layer b a r r i e r s .  loading  frictional  loading.  dilatancy  is  sand  to:  d u r i n g l o a d i n g , and  o f pore p r e s s u r e  characteristic  due  physical  deposition processes  deposition.  the soil  stability  of  deposition  a has  soil been  mass c o n s i d e r a b l y . shown t o  have  a  The large  e f f e c t upon: (1) the range of v o i d r a t i o s p o s s i b l e w i t h i n a  268  soil  (2)  deposit, (3)  possible,  t h e range, o f undrained  loading  t h e range o f s o i l a n i s o t r o p y  response  p o s s i b l e , and  the magnitude o f s o i l s t r e n g t h a t a g i v e n v o i d r a t i o .  (4)  Moist  o r d r y s o i l may be prepared a t much l a r g e r v o i d r a t i o s than possible  i n s i m i l a r water p l u v i a t e d  strengths  may be obtained  sand, simply  or  stronger  than  depending upon s o i l Laboratory  observations  r a t i o s are possible.  or  moist  upon  concerning  and perhaps d e s i g n i n g  soil  The h y d r a u l i c  tamped  long  of  the f i l l  fairly  good  as t h e h y d r a u l i c  relatively  properties  fill  i n that  better  may field  form  be  used  material.  fill In  depositional  l e s s compressible  t e c h n i q u e ensures addition,  would  characteristic properties  result  in  characteristic  is void  effort,  saturation  hydraulic  under v e r t i c a l  in  construction  of construction  lower  i s o f t e n b e n e f i c i a l under f i e l d l o a d i n g The  sand,  the e f f e c t of s o i l  r a t i o s can g e n e r a l l y be a t t a i n e d w i t h no compactive as  of a  f a b r i c and d i r e c t i o n o r mode o f l o a d i n g .  evaluating  t o be  void  a i r pluviated  method  shown  lower  water p l u v i a t e d sand may be weaker  deposition  techniques.  Thus much  by moist o r d r y p r e p a r a t i o n  because much h i g h e r  At t h e same v o i d r a t i o ,  soil.  fill  loading,  is  which  conditions.  o f water p l u v i a t e d modes  of  failure  sand and  t r i g g e r i n g f a i l u r e w i t h i n a s o i l mass which may be d i f f i c u l t to  predict.  direction The be  The  variation  of loading  should  method o f s t a b i l i t y able  t o account  of material be c o n s i d e r e d  a n a l y s i s employed  properties during i n design  f o r t h e v a r i a t i o n o f undrained  with  design. should strength  2 6 9  with the i n c l i n a t i o n deposition  direction.  pluviated to  o f maximum p r i n c i p a l The r e l a t i v e l y  sand under  induce a deep  lateral  seated  loading  failure  stress t o the f i l l  low s t r e n g t h conditions  surface  o f water  would  tend  i n an embankment.  In a d d i t i o n , undrained f a i l u r e o f an embankment i s l i k e l y t o be  triggered  which  is  by i n i t i a l  induced  embankment. principal  by  liquefaction failure increased  s t r e s s which i s c l o s e t o h o r i z o n t a l would  simulate  t h e embankment  t o e , which  progressive  or  Liquefaction  a t t h e t o e may be t r i g g e r e d  which  induces  embankment  complete  t h e t o e under  i n the maximum  of  at  stress  toe,  a  unloading  Liquefaction  lateral  a t the  an  slope,  increase  failure  in  of  could the  loading  i n pore p r e s s u r e w i t h i n t h e embankment.  to  embankment.  by any mechanism  lateral  i n c l u d i n g dynamic  lead  stress o r an  i n the increase  270  REFERENCES ASTM D2049-69 "Standard T e s t Method f o r R e l a t i v e D e n s i t y o f C o h e s i o n l e s s S o i l s , " Annual Book o f ASTM Stadards, 1983, S e c t i o n 4, S o i l and Rock; B u i l d i n g Stones. 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" C y c l i c Undrained T r i a x i a l and T o r s i o n a l Shear S t r e n g t h o f Sands f o r D i f f e r e n t Sample P r e p a r a t i o n Methods," S o i l s and Foundations, V o l . 26, No. 3, pp. 23-41. Tatsuoka, F., T o k i , S., Miura, S., Kato, H., Okamoto, M., Yamada, S., Yasuda, S., and Tanizawa, F. (1986). "Some F a c t o r s A f f e c t i n g C y c l i c Undrained T r i a x i a l S t r e n g t h o f Sand," S o i l s and Foundations, V o l . 26, No. 3, pp. 99-116. T e r z a g h i , K. and Peck, R.B. (1967). " S o i l mechanics E n g i n e e r i n g P r a c t i c e , " John Wiley & Sons, New York.  in  Towhata, I . and I s h i h a r a , K. (1985). "Shear Work and Pore Water P r e s s u r e i n Undrained Shear," S o i l s and Foundations, V o l . 25, No. 3, pp. 73-84. Troncoso, J.H., and Verdugo, R. (1985). " S i l t Content and Dynamic Behaviour o f T a i l i n g s Sands," Proc. o f the E l e v e n t h I n t e r n a t i o n a l Conference on S o i l Mechanics and Foundation E n g i n e e r i n g , V o l . 3, San F r a n c i s c o .  277  V a i d , Y.P. and Chem, J.C. (1983). " E f f e c t o f S t a t i c Shear on R e s i s t a n c e t o Liquefaction," Soils and Foundations 23(1):47-60. V a i d , Y.P. and Chem, J.C. (1985). " C y c l i c and Monotonic Undrained Response o f S a t u r a t e d Sands," Advances i n t h e A r t o f T e s t i n g S o i l s Under C y c l i c C o n d i t i o n s , ASCE Convention, D e t r o i t , pp. 120-147. V a i d , Y.P. and Negussey, D. (1984). "Relative Density of P l u v i a t e d Sand Samples," U.B.C. S o i l Mechanics S e r i e s No. 82, The U n i v e r s i t y o f B r i t i s h Columbia. V a i d , Y.P. and Negussey, D. (1984). "A C r i t i c a l Assessment o f Membrane P e n e t r a t i o n i n t h e T r i a x i a l T e s t , " G e o t e c h n i c a l T e s t i n g J o u r n a l , V o l . 7, No. 2, pp. 70-76. Vaid, Y.P. and Negussey, D. (1986). "Preparation of R e c o n s t i t u t e d Sand Specimens," U.B.C. S o i l Mechanics S e r i e s No. 98, The U n i v e r s i t y o f B r i t i s h Columbia, 26p. V a i d , Y.P., Negussey, D. and Zergoun, M. (1988). "A S t r e s s and S t r a i n - C o n t r o l l e d Monotonic and C y c l i c Loading System," ASTM STP 977.  278  Appendix A:  Membrane Penetration Correction  Volumetric and radial strains during consolidation have been corrected for membrane penetration errors using Method 2 described by Vaid and Negussey (1984).  Method 2 membrane penetration corrections are determined by conducting  an isotropic consolidation load and unload test on a single soil sample.  In  isotropic consolidation loading, soil specimen strains need not be isotropic due to soil anisotropy, but in isotropic consolidation unloading, soil specimen strains have been found to be isotropic.  The deviation of triaxial test soil  specimen unloading strain from isotropy with respect to axial strain is shown to be due to membrane penetration effects in the radial direction of loading. The correction to radial strain required to maintain isotropic unloading strain is the correction required to account for membrane penetration effects. unit membrane penetration correction £  ^v = £ tu  Where:  £  cT  m  Vtu  A m  S  A>+ ^ o u  m  The  is calculated as shown in Equation A.1:  Eqn. A.1  = unit membrane penetration correction or membrane penetration volume per unit surface area of membrane = total volumetric strain measured in an unloading step  cl au = axial strain measured in an unloading step  3cT  ou  = true volumetric strain in the unloading step if there is no membrane penetration (top and bottom platens must be rigid)  A V  s  0  = surface area of soil sample covered with rubber membrane = initial volume of soil sample within membrane  Equation A.1 may be rewritten in terms of soil sample diameter, Equation A.2: £ Where:  =  m  £v  t u  -3c:  a u  )D /4 e  D = soil sample diameter 0  Eqn.  A.2  279  Unit membrane penetration £  m  varies approximately linearly with logarithm  of effective consolidation stress (see Figure A.1, after Vaid and Negussey, 1984).  The slope (m, Equation A.3) of unit membrane penetration with logarithm  of effective stress is essentially constant, and may be used in Equation A.4 to calculate true volumetric strain within a soil specimen whose m value is known.  m  Eqn. A . 3 Eqn. A.4  Where:  m  membrane penetration function slope (see Figure A.1) consolidation effective stress on membrane initial consolidation effective stress on membrane true volumetric strain corrected for membrane penetration  FIGURE A.1  0.007 - i  Unit m e m b r a n e  penetration of various Brenda  sand  gradations determined by the single s p e c i m e n After Vaid and Negussey  (1984)  method ,  281  Figure A.2 Strain in V a r i o u s G r a d a t i o n s of B r e n d a S a n d Under Virgin Isotropic C o n s o l i d a t i o n a n d Unloading  AXIAL STRAIN  £  q  (%)  282  Figure A.3  Strain in Ottawa sand C 1 0 9 during isotropic virgin consolidation and unloading  283  Appendix B:  Calculation of Membrane Stress Correction  Various methods for calculating the stresses applied to a soil sample by its confining rubber membrane have been described in soil mechanics literature. These corrections are based on a number of assumptions which may or may not be true, depending upon test conditions.  There are three general types of  membrane correction assumptions as follows (from Fukushima and Tatsuoka, 1984): Method 1) the membrane is assumed to maintain the shape of a thin wall cyclindrical shell, such that elastic thin shell compression theory can be used; Method 2) it is assumed that axial deformation occurs independently of radial and circumferential deformations; and Method 3)  it is assumed that the  resistance of a membrane against axial deformation is negligible due to membrane buckling, and only membrane "hoop stresses" are applied to the soil sample. theory.  Method 2 is thought to be unreliable because it neglects elastic Method 3 is useful for compression test corrections at larger strain  level if buckling can be visually observed, especially in the testing of soft clay samples which are prone to large consolidation strains and are generally tested with very thin membranes.  Method 1 is generally preferable to the other  methods of correction at smaller strain levels as long as membrane buckling is not observed and if soil samples are tested in both compression and extension loading.  Method 1 is particularly useful for testing sandy materials for  susceptability to liquefaction, as low stress levels are encountered, larger membrane thicknesses which are less susceptable to buckling are used to overcome membrane penetration and damage problems, consolidation strains which may increase susceptability to buckling are small, and samples may be loaded in both extension and compression directions.  Method 1 type corrections have been  derived and used by numerous workers, for example Henkel and Gilbert (1952), Duncan and Seed (1967). Berre (1982), Ponce and Bell (1971), Molenkamp and Luger (1981) and DeGroff et. al. (1988).  Although the same general method of  evaluation has been used, different researchers have used different formulations which may or may not take into account the following factors which should be considered: 1 ) stress and strain induced in the membrane during sample preparation, 2) change in soil membrane thickness during strain, 3)  284  change in membrane modulus with strain level, 4) change in membrane stress and strain during sample saturation and consolidation, and 5) change in membrane stress with axial and radial strain during loading; it is important to note that according to elasticity theory, axial and radial membrane strains have an effect upon both axial and radial stresses, depending upon Poisson's ratio.  In  addition to theoretical formulation of membrane stress corrections, experimental verification of corrections should be undertaken to validate their reliability. A formal derivation of Method 1 corrections which takes into account all of the factors described above and which simplifies the calculation of membrane stress correction is presented in the following pages.  Experimental  verification of the derived membrane stress correction factors is provided by a strain controlled undrained extension and compression test upon a triaxial test sample membrane filled with water.  Calculation of membrane stress correction by Method 1 (elastic shell theory): The elastic strains in an elastic membrane cylindrical shell are as follows:  ^MO= ( ^ . - V O ^ - V O J / E £MC=  (-^a+^c-^U/  £ t=  (-VOJ-VLJ^+GJ/  M  Where:  ^u = a  £ £ E  U c  Eqn. 1  M  E  Eqn. 2  M  E  M  axial strain in cylindrical membrane  = circumferential strain in cylindrical membrane = radial strain, or strain in thickness of the cylindrical membrane  u t  = Young's modulus of membrane rubber  u  1/ = Poisson's ratio of membrane rubber 0 y = axial stress in membrane a  tT = circumferential stress in membrane Uc  Oy ==LT «= radial stress in cylindrical membrane t  r  Eqn. 3  285  From the cylindrical dimensions of the membrane and radial stress upon the inside of the membrane, a relationship between LT and 0" Uc  Figure B.1  ul  may be determined:  Rubber membrane shell  H  D * H * a = t X *2*t*H r  MC  i  ff =t7 *2*t/D r  Me  If t << D (for a thin cylindrical elastic shell) assume that  CT <<  (J,  thus one can  0, and may be ignored; from Equations 1 and 2:  CT = (J = Ui  'Ma  (OMa-^  'Mc  (-^ 4-CT  M c  a  )/E M c  M  )/E  M  Eqn.  4  Eqn.  5  Hence:  CLo=  (^  0  +^^  C  )*EM/(I-T/  2  °M = ( V E ^ > E / ( 1 - V ) c  M  M  M  a  )  Eqn. 6 Eqn. 7  Corrected stresses on a cylindrical soil sample within a confining membrane are  O a ^ O a ' ff>  4  * ^ ) * ^  q ' - 2 * ( t / D ) * o ;Mc  Eqn. 8 Eqn. 9  286  Where:  CT = corrected axial stress on soil sample GT  = corrected radial stress on soil sample  CT  = axial stress on soil sample  CT  = radial stress on soil sample  t  = present membrane thickness  D = present sample diameter Thus membrane corrected sample stresses are:  (6) +(8)  a >CT'-4*(t/D)*E *(cT a  (7) +(9) .  u  Eqn. 10  + VEj/O-V ) 2  M Q  = j/-2*(t/D)*E *(VE tE M  M  M B  )/(1-vy ) a  Eqn. 11  (Compression stress and strain is positive) With a membrane rubber Poisson's ratio of V = 0.5 as is commonly measured (which implies that the membrane rubber undergoes zero volume change when strained): from  (10) a > a ; - 8 < t / D ) * E < 2 £  from  (11)  M  a  a l = CT'-4*(t/D)*E rr  M  M a  +ci  * ( £ +2 £ Mo  With no volume change in rubber during strain ( V  Where:  M o  M c  )/3  E q n . 12  )/3  Eqn. 13  = 0.5):  = volumetric strain in rubber  Considering circumferential strain in membrane: S  AS  =7TD  =7TAD  Eqn.  15  287  Where:  S = circumference of cylindrical membrane S = nominal unstretched membrane circumference 0  D = diameter of cylindrical membrane D0 = nominal unstretched membrane diameter  E  Uc  £  Where:  £  =AS/5 =7TAD/7rD = A D / D = 6  0  =  (DL - D ) / D  D =  ( 1 - E )*D  r  0  £  E q n . 16  r  e  r  Eqn. 17  o  = radial strain of cylindrical membrane dimensions referenced  r  to initial unstretched membrane diameter Considering radial strain in membrane (or change in membrane thickness):  = ( t o " 0/t = - ( £ + £ o  r  Ma  Eqn. 18  )  t = t.(1+ ci + E ) Where:  Eqn. 19  r  Ma  t = nominal undisturbed membrane thickness 0  Considering volume contained within membrane:  ^v  = (V - V ) / V =  ^  =  R  from (21) + (17)  e  Where:  ( ^ V - ^ M O  D =  V  0  2  M o  +2E  r  )  Eqn. 20  Eqn.  )/2  D (2+ £  =7TD H  (£  M  a  -  £  v  )/2  E  q  n  >  21  2  2  /4  V = nominal volume within unstretched cylindrical membrane 0  H = nominal height of unstretched membrane which contains sample q  cT = volumetric strain of volume within the stretched membrane referenced to unstretched membrane volume v  288  Considering axial stress on soil sample:  C  a  >CT;-8<t/D)*E <2£ M  CT = C T ' - S * ^ / D ) * E  (12)+(19)  +  T  m  M  M o  +ci  M c  £ +£  *(1 +  r  CT^ = G T ' - 2 * a / D ) * E *(2+ £ + £  (2D  M  , , CT = CT  +(22)  v  E q n . 12  )/3  Ma  )(2 £ + £  Mq  )( £ + E  M o  3  Ma  4*t *E (24-£ + e )(3 £ + £ ) — — ^—^ ^ lJ. 0  M  v  Uo  M a  r  )/3  v  )/3  v  E  a  03  n  Considering radial stress on soil sample:  <L = L T ' - 4 * ( t / D ) * E * ( £ M  +2ci  M a  M c  E q n . 13  )/3  from (l3) + (l9) + (22) + ( 2 l )  CT =  8*E *t (i+e M  a  o  M a  4-£ )£ r  3*D (2- £ + 0  O  v  3*D (2-£ 0  v  v +  O  ^  E  2  4  Thus soil stresses corrected for axial and radial membrane loading are:  n  ff  -  ^  ""  ^  4«t *E (2+£ + £ J(3£ „+£ ) 0  u  v  3*0.(2- £  u  v+  £  u  U o  )  v  ^  E  2  3  (2+ £„ + £ „ „ ) £ „ a  Note:  -  =  C  f -  3*D„(2- £  v +  £„„)  E  q  n  -  2  4  All strains are measured with respect to nominal unstretched membrane dimensions.  289  Determination of membrane Young's modulus E  M  :  In the previous derivation of membrane stress corrections, present membrane thickness and dimensions are used in the calculation of membrane stresses.  The experimental technique for the determination of membrane Young's  modulus described by Bishop and Henkel (1962), which requires that a strip of rubber membrane be hung between two glass rods and loaded with known mass to measure induced deformation in the membrane, is adequate for the determination of membrane Young's modulus as long as stretched membrane area is used in the calculation of induced membrane stress and thus Young's modulus.  The original  method of Young's modulus calculation described by Bishop and Henkel does not account for changes in stretched membrane dimensions. If stretched membrane area is used in the calculation of membrane stress. Young's modulus is found to be constant from 0 to 2 5 % extension loading strain (see Table B.1).  If initial membrane area is used to calculate induced stress  and thus Young's modulus, Young's modulus is shown to decrease up to 2 5 % with 25% extension strain.  Thus the calculation of Young's modulus using present  induced membrane stress is also preferable because calculated modulus is found to be constant with changing stress and strain level.  Poisson's ratio  can also be verified to be 0.5 when Bishop and Henkel's experimental method is used to determine Young's modulus, by simply measuring the width and thus lateral strain in the test membrane as load is applied. Calculation of membrane stress corrections: To use Equations 23 and 24 to calculate membrane stresses on a soil sample, the following procedure is employed during sample preparation: 1)  Initial membrane unstretched thickness t  and nominal diameter D„ are  determined. 2)  Horizontal lines 10 cm apart are drawn with a marker pen on the unstretched membrane, so that initial axial sample preparation strain in the membrane may be determined by measuring the distance between  290  Determination of membrane Young's modulus E  u  for a Geotest membrane (2.36"  diameter by 0.012" thick by 8" high):  Figure B.2  Measurement of membrane modulus after Bishop and Henkel (1962):  I — length between marks on membrane W = load on membrane E  u  = Young's Modulus by Bishop and Henkel method of calculation, using initial dimensions of sample membrane.  E = u  Young's Modulus using loaded thickness and width of membrane to calculate stress on membrane.  f  W  Table B.1 Load W  Length I  Calculation of a Geotest membrane modulus  £,  Width  (kg)  (cm)  (cm)  0  7.85  5.05  0.25  8.26  E  EL  u  (kg/cm )  (kg/cm )  0.0522  15.46  16.31  2  0  2  0  0.5  8.70  0.1083  14.91  16.66  0.75  9.26  0.1796  13.48  16.28  1.0  9.92  12.25  16.25  V  4.38  0.2637  = 0.1327/0.2637 = 0.503  Use E = u  Note:  16.3 k g / c m  2  0.1327  (used to calculate membrane area and stress)  = 1600 kPa  One should use present membrane dimensions to calculate stress in membrane and thus membrane modulus.  291  pen marks after sample preparation has been completed. 3)  The length of membrane which covers the sample after sample preparation has been completed is adjusted for axial strain induced in the membrane during sample preparation to determine the unstretched height H  0  which  covers the soil sample. 4)  The unstretched volume of membrane which contains the sample is determined from H  5)  0  and D,. . 0  The axial and volumetric strains used in Equation 23 and 24 are calculated from unstretched membrane dimensions, and updated every time the soil sample within the membrane undergoes axial or volumetric strain. It should be noted that the probability of membrane buckling can be  reduced or completely avoided by prestretching the membrane during sample preparation.  If a membrane is axially prestretched 5 to 10% during sample  preparation, which is not uncommon if the membrane is initially of smaller diameter than the soil sample and stretched to the sides of a sample former tube by an external vacuum, then the membrane will be under axial tension up to 5 to 10% soil sample compression strain and maintain an unbuckled shape at higher compression strain level.  The initial load on the soil sample due to  the sample membrane is not a problem as it may be accurately calculated using Equations 23 and 24. Equations 23 and 24 have been validated by assembling a rubber membrane within a triaxial test cell with only de—aired water filling it to its initial cylindrical sample shape.  The water filled membrane was loaded undrained in a  strain controlled testing apparatus, to determine the load—strain response of the membrane experimentally as shown in Figure B.3.  The predicted load—strain  response calculated using Equation 23, as also shown in Figure B.3, provides a good estimate of membrane load—strain response.  The membrane does not  buckle until compression strain is greater than 5%; buckling resistance is better in a soil test because membrane shape is maintained by the soil sample within the membrane.  .3  Cylindrical rubber m e m b r a n e stress correction verification by triaxial test c o n s t a n t rate of strain loading of a Geotest m e m b r a n e filled with water Geotest membrane  Unstretched membrane  specifications  2.36" Dia. x 0.012" x 8"  H  E  t  u  = 1600 kPa = 16.3 kg/cm  Membrane state before loading: •= 413.8 cm  13.00 cm £  Ma,  = 0.008  Cy,"  -0-119  1  = 13.104 cm 0  V  = 0.0305 cm  dimensions:  = 369.77 cm  3  0  Rod area = 0.3167 cm Cap buoyant weight = 0.2412 kg Cell pressure = 142 kPa  Compression  Predicted load versus strain using elastic shell theory  Friction on rod = 0.22  kg Extension Measured undrained load versus strain response of a rubber membrane filled with water (corrected for LVDT spring)  S a m p l e axial strain  £ =  H, — H  0 (percent)  5  10  

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