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Undrained time dependent behavior of a lightly overconsolidated natural clay Zergoun, Mustapha 1982

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UNDRAINED OF  TIME  DEPENDENT  A LIGHTLY  BEHAVIOR  OVERCONSOLIDATED  NATURAL  CLAY  by  Mustapha B.Sc.A.  A  Civil  THESIS THE  Engineering,  SUBMITTED  Zergoun  Laval  U n i v e r s i t y , Quebec,  IN P A R T I A L  REQUIREMENTS  FOR  THE  F U L F I L M E N T OF DEGREE  OF  M.A.Sc . in  the Department of  Civil  We  accept  this  Engineering  thesis  required  THE  UNIVERSITY  OF  August,  as c o n f o r m i n g  to the  standard  BRITISH 1982  COLUMBIA  1976  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the  requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t  the L i b r a r y s h a l l make  it  and study.  f r e e l y a v a i l a b l e f o r reference  I further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by t h e head o f my department o r by h i s o r her r e p r e s e n t a t i v e s .  It i s  understood t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l n o t be allowed without my  permission.  Department o f  CIVIL ENGINEERING  The U n i v e r s i t y o f B r i t i s h 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date  r->T7'  a  I ~> /na  \  M)6A>ST M |  Wis  Columbia  written  ABSTRACT  Time  dependence  characteristics have  been  time  loading  of a s e n s i t i v e ,  i n v e s t i g a t e d under histories  under  a given  speed  of t e s t i n g  and a  higher  among  strain-rate.  does  with  behavior.  showed  with  tests  significant  of  supported  t h e same  causes  rupture  was  strain. the v a l i d i t y strain  i n i t s time  of  and  destructured  destructuration  change  response  or load  stress, clay  Various  increase i n  In a l l t e s t s ,  relating  that  that  stress  level  clay  compression,  stress-strain  critical  uniquely  Comparison  any  time.  intact  conditions.  sustained  the various  strength  triaxial  history,  that  c o n s o l i d a t i o n showed  not cause  undrained  in stiffer  t h e same  equation-of-state  normal  and  of strength  at about  Correlation the  results  and  overconsolidated,  i n undrained  consolidation  strength,  reduction  triggered  of s t r e s s - s t r a i n  on  of the c l a y dependent  TABLE  OF  CONTENTS  Page  CHAPTER  1  INTRODUCTION  CHAPTER  2  REVIEW  OF  KNOWLEDGE AT  SOME OF  CONSTANT  2.1.  1  Effect  CONTRIBUTIONS  TIME  CHAPTER  CHAPTER  3  4  5  CLAYS 5  of r a t e  General  of t e s t i n g  strength  Undrained  behavior CHAPTER  ON  THE  VOLUME  undrained 2.2.  EFFECTS  TO  on t h e  of c l a y s  . . . . .  5  stress-strain-time  of c l a y s  8  EXPERIMENTATION  15  3.1.  Material  15  3.2.  Apparatus  3.3.  Experimental  TESTS  tested . . . . '.  18  procedure  23  RESULTS  27  4.1.  Constant  rate  of s t r a i n  4.2.  Constant  stress  4.3.  Constant  rate  of l o a d i n g  4.4.  Constant  load  creep  CORRELATIONS  OF  VARIOUS  LOADING  TIME  . . . .  creep shear  . . .  44 48  TESTS  WITH  HISTORIES  5.1Stress-Strain-Strain  27 34  R E S U L T S FROM  ship  shear  rate  55 relation55  i i i  Page  CHAPTER  5  (cont'd) 5.2.  Comparison normally  5.3.  Stress  6  LIST  REFERENCES  OF  the behavior  consolidated  conditions  effective CHAPTER  with  stress  CONCLUSION  Haney  of clay  . .  61  a t maximum ratio  . . . . . . .  68 70 72  iv  LIST  OF  TABLES  Page  1.  P r o p e r t i e s o f Haney  clay  16  2.  Results  of c o n s t a n t  rate  3.  Results  of c o n s t a n t  stress  4.  Results  of constant  rate  of l o a d i n g  5.  Results  of c o n s t a n t  load  creep  of  v  strain  shear  28  creep  35  shear  . . . .  45  49  LIST  OF  FIGURES  Page  1.  Distribution vertical  2.  of n a t u r a l  samples  Components  Pore  4.  a  c  0.5  Influence  7.  Axial stress  8.  Axial  due  to the a r r e s t 38  strain  of  strain  hrs  of  consolidation  on  undrained  stressclay  in  shear  pore  29  pressure  O.C.  Haney  with  clay  axial  i n constant  shear  31  of undrained  strength  rate  versus  of  time  with  strain  rate  shear  relationship  of . . . .  in  strain  36  rate  stress  pressure  with  time  33  constant  creep  Pore  Haney  of  i n constant  constant  9.  system f o r  o f o v e r c o n s o l i d a t e d Haney  strain  strain  seal  24  of e x c e s s  Variation strain  17  20  after  f o r undrained  of  clay  2  rate  rate  Variation strain  6.  of  behavior  constant  rate  generated  kg/cm  along  cell  compression  =  strain  5.  triaxial  pressure  secondary at  o f Haney  content  of the h y d r o s t a t i c  frictionless  3.  water  versus  time  relationship  in  creep  response  i n constant  38  at  the base  stress  clay  creep  of on  the  sample  O.C. 40  vi  LIST  OF  FIGURES  (cont'd) Page  10.  Time  dependence  stress  11.  Variation  rate  rate  of  Axial  of  on  43  undrained  stress-  o f o v e r c o n s o l i d a t e d Haney  of  loading  rate  with  rate  creep  loading  clay  of  clay  in  shear  46  s t r e n g t h of  loading  O.C.  i n constant  Haney  rate  of  shear  strain  47  versus  time  relationship  in  constant  creep  Axial  50  strain  Initial  rate  load  Initial strain  time  stress  versus  stress  load  in  time  • 53  minimum  i n constant  strain  rate  dependence  strength  i n constant  rate  of  constant  stress  creep  to f a i l u r e  creep  versus  relationship  Comparison of  relationship  52  i n constant  deviator rate  versus  creep  deviator  relationship  18.  stress  of u n d r a i n e d  constant  17.  strength with  Variation  load  16.  of  behavior  loading  15.  of undrained  Influence  constant  14.  i n constant 42  i n constant  strain  13.  strength  creep  strain  12.  of u n d r a i n e d  strain  axial  load  of  creep  54  undrained  shear  and 57  vii  LIST  19.  OF  FIGURES  Deviator  stress  strain  level  strain  shear,  rate  20.  of  versus  constant  triaxial  using  Variation strain  various  rate  of undrained  stress  and  time  rate  f o r O.C.,  of  load  relationship  strength  equal  constant  constant  on  at  rate  creep,  loading  strain  creep  rate  i n constant  compression  i n constant  constant  strain  stress  shear,  Stress-strain-strain  clay  axial  relationship  loading  undrained  21.  (cont'd)  O.C.  creep  for Haney  histories  . . .  with  of  rate  shear and  and N.C.  Haney  clay  22.  Time and  23.  dependence N.C.  Stress O.C.  Haney  of undrained clay  conditions  Haney  clay  strength  i n constant  for a l ltests i n the M o d i f i e d  vi i i  stress  of  O.C.  creep  (0,/oJ on 1 3 max Mohr d i a g r a m at  LIST  Skempton s 1  pore  OF  SYMBOLS  pressure  parameter  =  Excess pore pressure Deviator stress intercept  of  ln  e  versus  shear  stress  level,  slope  of  e  time  ln  elapsed  rupture slope  at  t  =  t^  ^ ±~ 2^^ i~°3^f a  versus  since  D,  ln  the  t,  a  a  at  initiation  a of  fixed  D  creep  life  of  ln  axial  strain  axial  strain  minimum  axial  e  versus  at  rate strain  principal  effective  deviator  stress  effective  D,  stress  rate stresses  ratio  ix  any  fixed  time  ACKNOWLEDGEMENTS  Grateful Research study.  Council  adviser,  the d i f f i c u l t  experimental Civil  o f Canada  The a u t h o r ' s  research in  acknowledgement  felt  D r . Y.P. V a i d ,  data.  Engineering  Columbia  for financial  deeply  task  f o r their  i s expressed  Workshop highly  support  g r a t i t u d e goes  wishes  his guidance  and  to thank  the s t a f f  professional  x  to  reliable  of the U n i v e r s i t y of  assistance.  of the  f o r h i s constant  of obtaining  He a l s o  to the N a t i o n a l  technical  accurate of the  British  1  CHAPTER  1  INTRODUCTION  Time shear  i s one  strength  materials. difficult minor a  to  importance.  analysis effects  and on  other  with  hand,  stability  with  general  the  s h e a r i n g of  varying  constant time  the  of  factors  for  traditional  have  clays,  of  affect  both  a l l geological  time or  is  has  time  been  i n the  a  (undrained  to  either a  relatively  effects  The  dependence between  on  two  may  have  of  types  whether  conditions). of  clays  one  The  of the  or  strain time  strength is  with  and  time.  has  knowledge a  and  on  tests  to  aspect  and  of  the  concerned  second  the During  are  the  i s considered The  in  problems,  effects  volume  time  hand,  phenomenon  strength,  stress,  deformation  mechanics,  shear  clays.  conditions)  behavior  of  first  of  between  settlement  application  clay,  (drained  in soil  c o n s i d e r e d , on  tests  problems.  time  separation  analysis  oedometer  depending  dependent  effect  other  However,  relationship  encountered is  from  stability  of  the  volumetric deformations  deals  the  soils  behavior  that  influence.  clays  application  various variables  deformation  isolate  Following  slope  and  the  In most  considerable  the  of  to of  considerable  material be undrained practical  2,  importance  in  deformations  the and  prediction stability  of  of  end  of  earth  construction  structures  involving  such  materials.  Undrained  time  characteristics researchers the  conventional in  pronounced time  clays  have  tests  strength with in clays are  with  speed a  observed  the  life  rupture  time of  and  loading  to  behavior  or  behavior (32),  no  correlate  results  Furthermore, clay  of  i n 1977  investigators test  testing  creep  as  the  with  most have  clays.  Similar  limited  (15,31,33),  of  of  level  been  studies even  In  clay  of  an  attempt  was  index.  the  to  clay  restricted  to  time  such  of  by  the  study Vaid  and  previous  behavior histories.  dependent  normally consolidated  overconsolidated clays  though  stress-  the  the  deformation of  and  stress  function  by  the  Similar  stresses,  Prior  the  where  stress-strain-strength time  using  more  general,  made  that  testing;  creep  undisturbed  investigations  on  of  is a  deformation.  different  the  a  of  loading,  applied  several  found  being  plasticity  constant  strength response  dependent  Campanella  from  decreases  been  speed  strength  by  laboratory  the  (9,10,15,21,25,28,32,31).  history  time  of  during  i n c r e a s e s under  I t has  on  higher  and  investigated  i n the  depends  deformation  strain  stress-strain  been  s t r e n g t h measured shear  effects  increases  of  (1,2,3,8,10,14,24,32).  undrained  increase  of  dependence  clays  have  a  are wide  very  3  spread  occurrence.  during  their  that  were  melted, or  geological  later  (6,7).  i s important  The t i m e  foundations,  and t u n n e l  Since  their  natural  the  apparent  this  intact. clay  pressure  i s defined  one-dimensional distinguished  overconsolidated laboratory  stress. to  undergo  where  t h e maximum  laboratory.  consolidation  from  This  i n most  then  i s then stress  of a  higher  than that  to shear maintained of the  apparent the incremental  d e f i n i t i o n i s t o be  studies  the samples  consolidation,  The o v e r c o n s o l i d a t i o n  state  the overconsolidation  test.  is  change i n  prior  to the i n - s i t u  t h e one u s e d  i t  i t i s necessary  i s t o be  as e s t i m a t e d  consolidation  normal  clays,  stresses  exceeded  of the clay  respect  clays  these  construction  a radical  pressure,  i s never  pressure  from  of  cuttings,  of s e n s i t i v e  investigation, with  of  at consolidation  i f the s t r u c t u r e In t h i s  to weather,  behavior  t h e end o f  later  the o v e r c o n s o l i d a t i o n  preconsolidation  preconsolidation  to  study  clays  structure  limiting  testing  dependent  exposure  strata  openings.  clearly  sensitive  of s o i l  of i c e that  the s t a b i l i t y  the e x p e r i m e n t a l  clay.  overconsolidated  by t h e w e i g h t  i n predicting  to define  be  due t o t e m p o r a r y  or assessing  important  may  by t h e w e i g h t  deformations  In  clays  history  eroded,  by d e s s i c a t i o n  by a g i n g  soils  Natural  on  are f i r s t rebounded  defined  applied  with  i n the  subjected to a  lower  respect  4  In  the present  deformation strain  and l o a d i n g  studied.  sensitive, A variety  identical  conventional creep, among  on t h e u n d r a i n e d  (32,33).  attempted.  of s t a t e  clay  types  used  clay i s  These  shear,  constant load  stress  creep  of the c l a y i s  of t e s t s  using  i n metal  creep  the r e s u l t s  i n the normally  the concept  and a l s o  deformation  to  include  behavior  dependent with  stress-  of l o a d i n g a r e used  samples.  of s t r a i n  of  undisturbed,  o f l o a d i n g , and c o n s t a n t  to the time  t h e same  test  rate  various  Comparisons  o f an  histories  The d e f o r m a t i o n  among  equation  of time  rate  of r a t e  o v e r c o n s o l i d a t e d , marine  constant  others.  applicable  on  history  triaxial  constant  correlated the  the i n f l u e n c e  and s t r e n g t h c h a r a c t e r i s t i c s  saturated,  shear  study,  of  of  found  clays  of the s i m i l a r  consolidated state  study  are also  5  CHAPTER  REVIEW  OF  SOME  KNOWLEDGE  In  the l a s t  contributions undrained  behavior  two g r o u p s .  of  undrained  variation  the f i e l d .  between  of t e s t i n g  will  have  been  effects  studies  with  on t h e  may  be  the time  classified dependence  by t h e e f f e c t o f  the  i n c l u d i n g the  as creep  of c l a y s .  hereafter  and a l s o  general  and time  as w e l l  behavior  several  i n the l a b o r a t o r y  strain  be r e p o r t e d  CLAYS  as e v i d e n c e d  deals  stress,  ON  concerns  of t e s t i n g  and s t r e n g t h  contributions  o f time These  of clays  TO THE  VOLUME  there  group  The s e c o n d ,  of rate  deformation  decades,  The f i r s t  i n the speed  influence  CONSTANT  of clays.  strength  relationship  EFFECTS  to the knowledge  in  in  three  CONTRIBUTIONS  OF TIME  AT  2  effects Some  following  of  on t h e these  this  distinction.  2.1.  Effect  of Rate  of Testing  on t h e U n d r a i n e d  Strength  of  Clays The the  influence  measurement  laboratory  of rate  of testing  of the undrained  as w e l l  has been  strength  as i n the f i e l d .  recognized  of clays  in  i nthe  In t h e l a b o r a t o r y , the^  6  effect  of rate  compression earliest 1943  of  has  undrained  The  strength with  Numerous  studies  clay  tested  attention.  subject  was  made  of remoulded  followed  Boston  Blue  of the a x i a l  then  the e f f e c t  on v a r i o u s of r a t e  of  established  a  minimum  strength  In  value  1950,  on  i n rate  of rate  remains  experimental loading  increase  essentially  Casagrande study  and  partly  the s t r e n g t h  clay  shales  at constant  were  used:  creep-strength  quickly and  and m a i n t a i n e d  long-time  specimens  were  elapsed  time  tests.  As  subjected  between  the pore  Wilson  tests  with  the e f f e c t  saturated  to  10%  there  is  undrained  until  tests  of load  were  of rate  types  loads  clays of  were  the specimen  to i n c r e m e n t a l  increments  an  brittle  Two  i n which  compression  pressures  5  the  (10) r e p o r t e d  content.  constant  unconfined  by  constant.  fully  water  the  However,  which  value  cohesion  that  increases  below  dealing  of  apparent  of s t r a i n .  of s t r a i n  rate.  the  well  a 10-fold  increases  on  I t i s now  clays  the  strain  (3,8,14,23,24).  saturated  that  in  clays i n  termed  for  Taylor  of  also  of  by  of the  types  strength,  strength  undrained One  Clay  strain  the undrained  undrained  in  o f h i s i n v e s t i g a t i o n showed  the l o g a r i t h m  to determine  samples  considerable  to t h a t  results  linearly  of  on  received  contributions  (30).  order  strain  tests built  up  the  loading,  varying  and  failed;  i n which  axial  of  the  for different  not measured, the  effect  7.  of  the  test  duration was  was  strength  ratio  strength  corresponding  creep-strength used,  and  for  minutes. the  In  strength  percent  of  tests  to a  in  clearly  a  days  indicate increases  decreases  under  the  demonstrating  of  shear  strength  being  discrepancy field the  vane  rate  and  failure  the the  in  in  of  rate  an  the  shear  of  long-time saturated  from  its  These  loading  of and  loads.  field  studies  for  computing  then  of  built  The of  observed  strength  on  incorrect  estimation  strength  10  40  strength  analysis.  He  and  fully  40%  of  was  content  For  embankment  because the  80  loading.  several used  1 minute  water  of  about  In  loading  days.  undrained  testing.  was  30  sustained  of  of  between  time  undrained  cases  time  A  compressive  of  constant  of  the  mainly  of  failure  of  reported  errors  between  reported  of  introduced  the  to  strength  the  stability  such  tests  total  procedures  unsatisfactory  causing  strength  (5)  the  construction  were  factor  that  loading.  about  with  effect  Bjerrum  of  at  the  that  clays  rate  decrease  of  saturated  1972,  in  tests,  showed 30  to  value  compression  the  normal  values  reduced  value  clay  a  stresses.  of  time  tests  total  ratio  normal  was  normal  of  the  tests  clay  end  a  to  creep-strength  City  In  as  normal  long-time  Mexico  results  defined  i t s normal  unconfined  related  soft  values  dominant  the  shear  that  measured  the  in  back-calculated  essentially  the  dependent  on  the from the  8  plasticity the  clay,  field  of  mobilized  measured which  i n a vane  introduced  carefully  factor gain  of  2.2  The time  on  will  Undrained of  the  and  He  established the  correction multiplied  This the of  to  then  the  such  values  before  correction  clay.  He  the a  factor  with i t is  factor  further  proposed  correction  c o n d i t i o n s where  t h e c o n s t r u c t i o n due  conducted  creep  on  above  be  were  the  to a  essentially  the undrained  behavior aspect  of  They of  do  such  time  s t r e n g t h of not  effects  any  with on  presented.  relationship clays  through  samples.  give  clays  Stress-Strain-Time Behavior  of  essentially  clay  the vane  stressing.  that  now  i n the behavior  tests  of  the d e f o r m a t i o n  study  between  be  of  discussed  the v a r i a t i o n  clays  plastic  consolidation.  the d u r a t i o n of  General  index  t h e more  a  analysis.  increases after  C o n t r i b u t i o n s on  undrained  should  that  s t r e n g t h and  proposed  strength i s limited  with  with  and  shear  the v a l i d i t y  contributions  indication time.  that  safety  concerned  field  strength  i n s t r e n g t h by  The  clays  the  the p l a s t i c i t y  undrained  out  strength.  stability  stated  pointed  the d i s c r e p a n c y  test  shear  in a  with  He  undrained  between  a vane  varied  clay.  the l a r g e r  correlation  of  the  between  at constant  of  stress, volume  Clays  strain  and  was  the e x p e r i m e n t a l  o b s e r v a t i o n of  The  of  accumulation  strain  with  9  time  in  constant  manifestation behavior  of  based  the  of  on  metals  creep  the  time The  of  to  Two  assume  either:  a)  the  response  state  adopted  of  the  used  the  was  been  proposed  description  the  creep  leading  and  is time.  are to  describe  two  time  changes.  depends  by  of  strain  effects  stress  creep  (16,18,34).  temperature  to  largely  a n a l y s i s of  have  three  material  clays  the  assumptions  the  on  I t may  the  be  present  explicitly,  the  material  history.  past  assumption formulation, theory.  most  present  leads while The  researchers  experience and  the  remembers  its  application  for  arbitrary  to  successful  in  stress,  been  responds  by  the that  have  under  that  memory  of  Generally,  fundamental  assumed  called  clays.  f u n c t i o n of  response  state  accumulated  (17,21,25,29)  dependent  of  creep  models  approaches  first  of  clear  stress-strain  rheological  different  The  study  of  and/or  a  or,  dependence  materials  i s customary  b)  constitutes a  engineering  deformation as  tests  other  researchers  separable.  creep  experience  and  expressed It  of  clays.  Mathematical various  stress  with  to  in  what  the  this  understanding.  explicitly  a manner  that  i s known  second  equation for  i t s past  of  as  results state  practical  reflects  the in  and  equation the  so-  approach  was  reasons  of  theory,  and  Various  expressions  past  simplicity of  in its the  10  equation  of  stress,  time,  effect the  state  of  most  and  were  temperature.  temperature known  proposed  to  relate  In  a l l these  i s i n c o r p o r a t e d as  expressions  i s the  creep  a  strain,  expressions  constant.  so-called  creep the  One  of  Bailey-Norton  law:  e  where:  e =  creep  strain  a  =  creep  stress  t  =  time  A,m,n  =  constants  Other  more  Generally,  the  gives  to  rise  two  differentiated hardening be  by  and  the  the  so-called  strain these  time  rate  i s of  respect  to  have  hardening  and,  hardening  strain  rate  fundamental  for  were the  the  and  the  creep  time,  the  so-called  Another  between  the  This  strain  constants,  considerations, using  characterization  the  is  time  formulation equation  procedure  current  temperature.  of  can state  leads  f o r m u l a t i o n i n which on  use.  analysis  the  depends  developed  found  If  expression.  strain  through  relationships  time  also  interest  possibilities.  with  temperature.  expressions  eliminating  creep  techniques  of  /i \ (1)  formulation i s obtained.  derived  current  function  complex strain  . m n Ao t  =  to  the  stress, Based  on  phenomenological empirical of  creep  curve-fitting of  soils.  11  In  1968,  approach an  and  f o r the case  apparently  stress  Singh  and  general  time  Mitchell  (28) used  of constant function  i n the  stress  relating  the  time  creep, creep  hardening  and  proposed  rate,  creep  form:  e  A  -  1  e X  t p(aD)(- i)  (2)  m  E  where :  • e  = axial  rate  of  strain  t  =  elapsed  time  under  t^  =  elapsed  time  at which  shear  a  stress  the constant  -a A ^ is  defined D  =  (o^-o^)^  shear  stress  level a  o  <  i s obtained  from  deformation  undrained  1  t f  - o  l  _ 0  3  3 f )  constant  rate  triaxial  of compression  te st m  =  slope  of l n £ vs  I n t a t any  of l n e vs  D a t any  fixed  value  of  D a  This  phenomenological  limitations. while  = slope  creep  The  relationship  creep  deformation  stress  suffers  i s assumed  i s taking  fixed  from to  p l a c e , and  time  some  remain  t.  serious constant  the e x p r e s s i o n  12  proposed  i s not  stressing. to  a  It  variable  relationship the  rules  of  experimental only  A  the  data  do  not the  and  fail of  of  has  state  creep  obtained  a  agreement  good  clays  extensive  but  a  clear  state  did of  clay,  on  of  this  of  function  the  creep  rupture  Vaid  The  empirical  take  the  into  in  curve-  account  the  process.  models  models the  achieved using  between data.  with  observed  developed real  the  are  stress-  In  time and  1952,  In  of to  Campanella  of  application  strain  hardening  the  a  behavior  of  (22) the  Burn  and  correlation i t . of  In  equation  compression  an  an  presented  the  and  Marin  results  support  (32)  and  rate  Coates,  such  supporting triaxial  strain  Pao  1963,  dependent  evidence  results  data  the  constant  validity any  by  the  in correlating  have  the  and  these  Plexiglass.  not  experimental  theory.  test  suggested  study  undisturbed  of  duplicate  been  correlation  tests  from  theory  stress  for  the  (12)  form  end  clays.  constant  McRostie  the  or  apply  deformation  that  to  to  of  to  necessarily  indicated  success  equation  types  and  models  creep  approach  two  beginning  possibility  prediction  response  greater  the  the  rheological  approximate  strain-time  the  situation,  out  governing  Comparisons  at  tests.  techniques  mechanisms  of  stress  general,  fitting  either  is therefore d i f f i c u l t  laboratory In  valid  in  1977  of  tests  on  13  normally  consolidated  increase  in  and  strain  thixotropic  stress-strain on  the  response  the  instantaneous strain the  rate  test  rate  shown  that  clay  tested  was  of  the  quick  of  and  The  similarity  at  deviator  peak  defined  supported which 1963  the  rupture (12).  evidence  for  responsible Leonards (33) .  at  any  A  found a  between  loadings.  in  magnitude  the  minimum  strain  existence  of  a  occurs  suggested  for  of  the  triggering Campanella  of  by  a  Vaid  has (9),  for  the  to  The  the  study  was rate  shear  the  axial  strain  at  in  creep  tests,  and  rate  Coates  critical  was  effects.  strain  shear  supported  It  overconsolidated  strain  failure, and  rate  critical  suggestion,  existence  of  past  together  envelope  applicable  constant  creep  constant  the  the  tied  time  heavily  in  a  of  histories.  failure of  Based  (or  satisfactory correlation  clay  as  only  loading  aging,  undrained  independent  kind  stress  Such  (19),  is  of  strain  function  time  of  of  that  strength.  correlations  similarly  behavior  stress  -  a  and  by  stiffer  level  effective stress  this  failure  is  in  showed  length  undrained  given  various  (33).  for  constant  a  successful  was  rate  clay  established  at  clay  loading,  higher  unaffected  state  strain Leda  the  of  strain,  from  Haney  a l l result  stress  of  history,  also  rate  and  that  shear  results  equation  rate,  hardening  assumption  structure),  undisturbed  by  strain and  and  -  level  at  McRostie  in  experimental  level also  shear  of  been Vaid  strain made et  al.  by  14  In  the  behavior be  of  studied  behavior  state  the  lightly  the  on  and  same  in  obtain  subject.  The  its strain  in  basic  available in  comparisons  clay  the  time  overconsolidated,  to  data  that  theory  presented .  investigation,  i n order  considered, with  a  as  deficient of  present  the  of  dependent  sensitive  information  the  literature  applicability  hardening the  normally  of  clay  on  general  form  consolidated  such  is  still  the  formulation of  will  equation will  be  behavior  state  will  be  15  CHAPTER  3  EXPERIMENTATION  3.1  Material A  clay) been  local was  block  used  for  sampled to  obtained  silty  clay clay  typical  an  sample.  noticeable may  be  rupture  very  low  Some Table  test to  test  axial  layers did  clay  samples from  was  least  physical properties It  of  is a  about  Figure  grey  0.5  1  cm  shows  along  water  content  not  to  blocks  the  1.  were  have  were  content  of  to  subjected  The  ensured  water  and  interest  compression  This  values  These  the  unconfined at  higher  later  cm  material.  initial  a l l samples  of  7.5  samples.  organic  of  on  x  Haney  is believed  and  horizontal layers  layers.  effect  clay  (called  a l l test  outlined in  grey  The  cm  horizon.  are  clay  infiltration.  p i t and  $> 3.5  uniform  dark  in  open  same  Haney  surface  of  stiff  environment  individual  with  encountered  It  the  organic  study.  to  distribution  vertical the  due  tested  of  medium  a marine  cylinders  among  thickness  the  from  from  variation the  in  leaching  trimmed  to  undisturbed  deposited  partial  of  Tested  in a  a are  due  regularly  seem  to  have  any  results. report  the  that  samples  strain.  The  during  the  exhibited  a  failure  planes  brittle formed  16  TABLE  Natural  water  of s a t u r a t i o n  Liquid  limit  OF  HANEY  CLAY  63  Liquidity  89% 35%  index  54%  index gravity  0.52 of s o l i d s  Clay  fraction  ( d < 0.002  Silt  fraction  (0.002  mm  0.70  mm) < d < 0.06  85% mm)  13% 0.64  past  Unconfined (e  to  2.80  Activity Maximum  to 73% 100%  limit  Plasticity  Specific  PROPERTIES  conent  Degree  Plastic  1  =  Sensitivity  pressure  compression 1.1%/min, e  strength f  =  3.5  kg/cm  2  1.4  kg/cm  2  1.4%) 6 t o 10  17  FIG. 1  DISTRIBUTION OF NATURAL WATER CONTENT ALONG VERTICAL SAMPLES OF HANEY CLAY.  18  a  wedge  cone  close  to  the  top  of  vertically  to  the  bottom.  regardless  of  the  d i r e c t i o n of  bedding  3 .2  type  of  loading  and  failure with  extended  occurred  respect  to  the  Apparatus  small  kg/cm  strength  confining  deviator 2  and  for  alone  of  of  standard  around  the  friction  loading  the  the  It ram  and  due  accurate  is  cumbersome  a  by  any  methods  any  available  friction  effects  triaxial  cell,  on  the  the  i  with  the  shear, the is  samples.  developed  The  amount  of of  value  deformation  or  the  rate  of  the  amount  bending  top of  cap  the  reduction axial  seal  load  system  of  of  Among of  with  a  of  sample.  generated the  error  outside  the  the  the  friction  questionable.  2  accurate  strength  seal.  0.5  kg/cm  the  measured  hydrostatic  1.0 The  in  friction  of  on  the  for  about  shear.  to  occasional  case  is  at  maximum  depends  tilting of  7  clay  pressure  undrained  0-ring  of on  measurement in  The  confidence  loading  rate  of  applied  the  depends  and  of  great  load  during  to  low.  strain  apparatus,  ram  the  also  of  variation  axial  generated  ratio  rate  requires  loading  The  several  relatively  Haney  effective confining  triaxial  cell-pressure loading.  is  constant  thus  measurement a  an  overconsolidated  overconsolidation  conventional  time  of  pressure  stress  determination  In  specimens  layers.  Undrained  in  This  the  due  to  the continuous  19  air-leakage  around  satisfactory. continuously  the  Figure  loading 2  shows  air-leaking  ram  has  the  proven  components  system  originally  design  of  to of  be  quite  the  proposed  by  Chan  (11). A  slightly  modified  incorporated  in  program.  using  such  by  equal  In  counteracted of  the  cell.  leaking the  develop  only  the  represent no  of  the  the  friction  can  be 2  i s not  The  only  application  generation  through cell  the  water level  the of  seal  to  the  the  must  contact  of  the  loading  An  such  attempt then,  develop  since  cause  increase be  The  in  sealing  applied  between  is a the air  to  between  the  measure  that  loading  ram  used  ram (2.5  friction.  during  slight  delay  chamber pressure  water  to  small  pressure in  may  found  simultaneously  a i r and  top  the  the  encountered  pressure  pressure  be  cell  the  believed  with  of  may  and made  is  of  is  friction  i t was  magnitude  that  tolerance  ram  It  was  continuously  was  bending  any  through  that  and  force.  pressure  air  The  seal  testing  water  is  involved  same  system.  this  ram  gram  confining  pressure of  ram.  will  difficulty  of  loading  10  in  applied  film  of  hydrostatic  cell  a  generated  The  likely  the  forms  loading  loads  disregarded.  kg/cm )  the  axial  used  pressure  bushing.  additional friction of  air  contact  ball  cell  seal,  the  approximately  magnitude  the  at  a  system  and  steel  amount  triaxial  around  ring  stainless  an  This  upward  fixed  the  this  will  the in  and and so be  the that kept  20  FIG. 12'-  COMPONENTS OF THE HYDROSTATIC SEAL SYSTEM FOR LOW FRICTION TRIAXIAL CELL.  21  above may  the  be  top  done  of  by  the  and  pressure  regulator  the  confining is  for  outside  the  a  to  be  for  strain  the  tests  clay  compression,  at  effective  confining pressure  the  ratio  stress. clay  of  During  showed  a  major  volume  are  conditions.  therefore  change  very  measurements  electronic  of  of 7,  Volume  small. must  differential  the  bore  chamber,  to  the  clay,  of  the  i s almost this  has  stress  a  over  about after  changes  Both be  pore  accurate  pressure  0.5% 24  and  the contact  cell  0.3  water  cm  system.  the  pore  air  reservoir  measurement  is critical.  conventional  excess  same  tube  small  spiral  This  water  air-water  in  and  to  of For  constant  pressure equal  to  the  tremendous minor  r e c o n s o l i d a t i o n , samples  change  ratio  the  the  tested  stress  cell  water  shearing  effective  isotropic  overconsolidation drainage  deviator  input.  application of  on  the  during  the  generated  on  peak  of  leak  large  diffusion  generated Haney  level  switched  tube  for  plexiglass  top  be  air  system  a  initial  the  triaxial  pressure  seal  providing  the  may  the  a i r supply  temporary  saran  overconsolidated of  by  above  undrained  below  leaking  When  connection  pore  rate  and  chamber  diameter  In  air  pressure.  ensured  pressure  the  between  triaxial  and  coupling.the  pressure  connection  cell  for  hours  effect  effective of  Haney  an under  double  during reconsolidation pressure and  and  volume  reliable.  transducer  was  used  An for  22  volume  change  monitored  with  capacity rated  compliance  o f 0.0044  diffusion  loops  pressure  cm  The r e l i a b i l i t y system  water  a sensitivity  2  measuring  Pore  an e l e c t r o n i c  of 7 kg/cm ,  pressure. the  measurements.  with  o f 0.005  ensured  thoroughly 1 metre  also  having  kg/cm ,  a  and a  2  change i n  2  by f u l l  deaired long  were  saturation of  water  o f 0.3  cm  spiral  outside  saran  tube  pressure  glass  p i p e t t e , and t h e c e l l - p r e s s u r e p l e x i g l a s s  detection  The s p i r a l  tubing  between to  and t h e chamber  the a i r pressure  saran  minimize  having  by a L i n e a r  displacement extension  o f 1.5  3.0  cm.  chamber.  the pressure of d i f f u s e d a i r  as s h o r t  diameter  as p o s s i b l e  and the e l e c t r i c a l  Displacement  x 10  - 1 +  cm  measured  by t h e d i s p l a c e m e n t  rods  The v e r t i c a l  stainless  kept  the v i s u a l  cm o u t s i d e  of the t r i a x i a l  o f one o f t h e t h r e e  cm  T h e 0.3  transducers  steel  was  Transducer  placed  retaining  sample  of a r i g i d loading  sample  DCDT  f o r a maximum  T h e L . V . D . T . was  triaxial  <(> 0.635  allowed  the presence  were  Variable  of  the back-  of the system.  deformation  an a c c u r a c y  from  apparatus  the compliance  axial  measured  lines  loops  and p r o t e c t e d  supply.  drainage  the t r i a x i a l  The  diffusion  of any a i r b u b b l e s  transducers from  the transducers,  and  diameter  reservoir.  between  transducer  f o r 7 kg/cm  3  was  of at least  pressures  on an  the top of the  deformation  was  bar clamped  ram.  Since  the  on t h e cell  23  pressure  was  constant  displacement occur  throughout  due t o s t r a i n i n g  to a l t e r  the test  program,  of the pressurized  t h e r e f e r e n c e on w h i c h  no  chamber  t h e L.V.D.T.  will  was  mounted.  3.3  Experimental All  test  all-round and  24  samples  effective  was  3.5  equal 2  In  of  Double  i n one i n c r e m e n t  of approximately  2.0 k g / c m . 2  The  a maximum  drainage  was  0.5  t o an  kg/cm  2  overconsolidation in-situ  allowed  past  pressure  f o r a period  of  for a l l tests. a preliminary  effective pressure  pressure generated  consolidation observed.  3 shows  The  fluctuation noise  variations. pressures  2  c o n f i n e d under  f o r 38 h o u r s ,  t h e amount  an u n d r a i n e d  of  and p a r t l y  Nevertheless, A  stable  of about  conditions  (10,000  sufficient  to i n f l u e n c e  time  minutes),  a n d i t was  Hence,  2000  minutes.  be d u e p a r t l y  to  temperature  i n these of  was  pressure  pore  0.04 k g / c m  of r e l i a b i l i t y  the measurement  process.  may  to s m a l l  maximum  and t h e pore  period,  of pore  the changes  f o r the longest  the shear  period  an  secondary  i n t h e measurement  effects  are small.  anticipated  kg/cm  was  a t t h e end o f t h e d r a i n a g e  Figure  electronic  a sample  due t o t h e a r r e s t  during  small  test,  o f 0.5  developed  during  subjected  to 7 assuming  kg/cm .  hours  were  pressure  a back-pressure  ratio of  Procedure  of  2  was  undrained  c o n s i d e r e d not of pore  pressure  f o r the remaining  tests  the  24  CN  6 o 60  400  800  1200  1600  2000  TIME (min)  FIG. 3 PORE PRESSURE GENERATED DUE TO THE ARREST OF SECONDARY COMPRESSION AFTER 38 HRS CONSOLIDATION AT a =0.5 kg/cm . 2  25  shear  loading  period.  followed  This  preliminary  leakage  will  through  the  coat  of  high  In  a l l tests,  confining pore  take two  thin  machine.  The  In  the  the  air  loading  regulator. sample of  of  piston.  stress  the in  ensured the  membranes  that  no  sample  separated  capacity  for  of  creep by  by  a  tests  were  creep  tests  loading  <j> 3.81  cm  area  the  rate  by  piston  as  while  was  air a  dead the  with  specimen.  Farrance used  to  and  the  axial  The  tests  were  loading  choose  the  rates  compression  of  tests.  force  was  frictionless pressure precision  was  frame,  constant  conditions  the  Wykeham  constant  with  compression  the  a  shot  of  tests,  metallic  constant  compression  the  rate  from  lead  constant  base  strain  these  loading  undrained  controlled  rigid  small  in  the  of  The  was  load  corresponding  loaded  tonne  stress  a  consolidation  and  compression  at  rate  levels  The  discrete  In  1  piston  also cell  rubber  imposed  constant  through  vertical the  was  instantaneously  Bellofram  the  the  grease.  results  constant  applied  the  a  stress in  sealing  constant  using  of  between  measurement  performed  after  observation  vertical  pressure  conventional  loading  place  vacuum  pressure  range  immediately  supply  Fairchild  transferred allowing  weights sample  to  was  for  the keep  to  the  addition the  compressing  and  increasing. of  under  loading a  tests,  continuously  the  samples  increasing  were  axial  26  force.  A  used  apply  to  <|> 5.08  cm  the  loading  p i s t o n was  coupled  to  a  This  system  with  time  the  load  on  the  controlled  precision ensured  a  resulting  sample. by  Fairchild linear  in  a  Bellofram The  air piston  a i r supply  a v a r i a b l e speed a i r pressure  increase  constant  of  rate  for  ' the  servo-motor  regulator.  a i r pressure  of  was  vertical  supply  loading  of  sample. The  to  frictionless  the  constant  constant  load  creep  tests  stress  creep  tests.  instantaneously  applied  pressure  acting  supply  Bellofram  piston.  horizontal  area  continuously All  order  to  eliminate  <f> 5.08  sample creep  performed  was  was  in a  measurements  were  carried  tape  using  a  high  speed  Vidar  a  was  controlled  air  frictionless taking  constant  variation  i n f l u e n c e of  automatically  by  load  place,  the  increasing, resulting  pressure  were  axial  similarly  in  a  stress.  temperature  the  The  cm  pore  data  rates  a  performed  constant  and  test  System.  were  kept  compression  the  (maximum  deformation All  of  in  decreasing  tests  environment  As  and  were  temperature of  ±  temperature  0.25°C)  in  on  measurement. out  recorded Digital  electronically on  a  Data  digital  and  the  cassette  Acquisition  27  CHAPTER  TEST  4.1.  Constant Table  rate  of  2  Rate  strain  to  strain  on  the  in  for  the  of  rate  of  -  defined  stiffer  with  as  peak  deviator  strain  rate  variation note  and  rate  of  axial  in  the  can  be  seen  constant response  that  the  Haney  rate of  of  the  clay  clay  is  dependent  stress  becomes  constant  stress of  that  1.2  peak  deviator  as  about the  rate  high 3  axial  1.5%.  deviator  overconsolidated  as  -  strain.  30%  orders  independent to  of  may  of  of  rate  The stress clay.  sharp is  to  noted  magnitude. at  peak of  typical in  for It  is  deviator strain  decrease  Straining  on  Differences  be  strain the  is  stress-strain  peak  range  sensitive  constant  of  from  the  the  the  parameter  prior  was  past  end  response  essentially  strength  the  stress-strain  was  of  at  constant  The  stress in  stresses  varying  the  overconsolidated  the  to  only in  conventional  the  stress-strain  increasing  interesting  the  variation  It  strain.  failure  Since  of  loading.  4.  the  results  difference  resulting  Figure  Shear  tests.  shear  the  the  similar,  influence  relation  in  is  during  strain shown  are  test  The  shear  RESULTS  Strain  summarizes  consolidation test  of  4  of  and  in a  the  post  a  TABLE 2  Test  RESULTS OF UNDRAINED CONSTANT RATE OF STRAIN SHEAR FOR OVERCONSOLIDATED  Number  A x i a l S t r a i n Rate (%/min) Void R a t i o :  Before c o n s o l i d a t i o n After consolidation  Consolidaton Stresses:  o^(kg/cm ) 5 (kg/cm ) 2  T  2  3  D e v i a t o r i c S t r e s s (a-j-Og) (kg/cm ): at e = 0.8% at e = 1.0% a t e = 1.2%  HANEY CLAY  6-80  2-80  29-80  4-80  1.03-x 10°  1.37 x 10-1  1.40 x 1 0 "  2.025 2.015  2.037 2.020  1.967 1.962  1.953 1.948  1.967 1.967  0.54 0.50 1.07  0.57 0.49 1.17  0.50 0.41 1.20  0.47 0.46 1.04  0.62 0.50 1.23  1.24 1.28 1.31 1.32  1.08 1.18 1.21 1.21  0.93 1.00 1.06 1.18  0.92 1.01 1.06 1.07  0.88 0.94 0.95 0.95  2  2.59 x 10"  8-80 3  8.72 x 1 0 ^  2  Maximum S t r e s s R a t i o Axial Strain a  t  a  t  a^/a-j  195.9  OO  7.9  15.4  9.0  e (%):  (il-^max ( l/°3>max a  1.41 1.41  1.15 1.15  1.54 1.54  1.15 1.15  1.50 0.93  0.38 0.38  0.40 0.40  0.35 0.35  0.36 0.36  0.39 0.42  P.P. Parameter A : a  t  a  t  (£l-°3>max ( l/ 3>max a  a  -29,  AXIAL STRAIN e ( % )  FIG.,4.'  INFLUENCE OF RATE OF STRAIN ON UNDRAINED STRESSSTRAIN BEHAVIOR OF OVERCONSOLIDATED HANEY CLAY IN CONSTANT RATE OF STRAIN SHEAR.  30  peak  region  collapse strain  of a s e n s i t i v e  of the structure  softening  appears  for  other  (32),  clays  Figure  et a l  5 shows  increase  i n pore  the i n i t i a l  pressure  water  pressure  occurs  strain  of pore rate  However,  i t appears  pressure  parameter  strain pore  rate  water  associated deviator The effective the  peak  Vaid  have  and  this  Similar been  made  Campanella  Table  This  among  with  t o a maximum  value  pressure,  prior  followed  T h e maximum  time  of about  would  the i n f l u e n c e  value.  Skempton s  pore  1  n o t show a n y c l e a r  imply  tests  t o 1.5%.  strain i s  to the peak  does  by a  deviator  1.0  axial  close  pore  as t h e peak  with  2 that A^  pressure sharp  level  various  water i s a  pressure  dependent from  There  value.  strain  water  dependence.  solely  stable  at failure  pressure  tested  level  of pore  reaching  a t t h e same  and a t a c o n s t a n t  clearly  et a l . (12),  effective confining t o a more  variation  consequence,  of s t r a i n .  strain  of the sample.  decrease  The  As a  (33).  rapid  stress  level  the v a r i a t i o n  a t the base  with the  and f o r t h e c l a y  a critical  by C o a t e s  measured  to  of the m a t e r i a l .  at a c r i t i c a l  regarding  and V a i d  i s associated  i s initiated,  to t r i g g e r  observations  clay  that  (Figure  of s t r a i n  differences i n 5) a r e rate  on  stresses. results stress deviator  on T a b l e ratio  2 also  i s reached  stress  indicate a t about  f o r a l l constant  that  t h e maximum  t h e same rate  of  strain  strain  as  31  i  i  2  4  i .  6  i  r  i  L  8  10  AXIAL STRAIN (%) FIG. 5 VARIATION OF EXCESS PORE PRESSURE WITH AXIAL STRAIN FOR UNDRAINED O.C. HANEY CLAY IN CONSTANT RATE OF STRAIN SHEAR.  32  shear  tests.  consequence which,  The e x t r e m e l y of very  i n turn,  generated reported Norwegian occurred test,  strain study  early  2% a x i a l  stress  depending  lateral apparent lower  preconsolidation  consolidation  structure  of the clay.  contrasting  deviator  stress  an  small  nature  the of  later  level  a t an a x i a l  was  obtained  a possible clay  effective  of the  rebounding previously  them t o this  sensitive explanation  f o r which stress  by  o f no  i n excess  of the natural  may  For that  both  ratio  be t h e u n a l t e r e d  for  maximum  occur at sensitive  structure.  strain  rate  clay  tested  i s better  increase  As n o t e d  o f Haney  of s t r a i n  o f maximum  the c o n d i t i o n s  then  ratio  compression  ratio.  largely  Therefore,  The  6.  under  pressure,  stress  triaxial  of the clay  stress  a n d maximum  of the clay  Figure  effective  i n the test  state  i n a collapse  behavior  sensitive  and t h e p o i n t  stresses.  results  equal  ( 2 7 ) have  on t h e p r e c o n s o l i d a t i o n  procedure  the  investigators  i n an u n d r a i n e d  t o a same  stress  pressures  a l l the samples,  strain,  are a  pore  o f maximum  reached  ratio  effective  overconsolidated  the overconsolidated  consolidating  of t h i s  to the high  strain,  was  values  of minor  Other  the point  fairly  deviator  time.  for lightly  clays  about  low v a l u e s  are related  at that that  high  dependence  The r e s u l t s  i n undrained  shown  of the undrained  i n the semi-logarithmic  of these  strength  strength  with  tests  indicate  the logarithm  of plot  a linear of a x i a l  34  strain  rate  of the order  increases  ranging  rate  reported  were  clays,  both  o f 8%  between by  normally  per l o g c y c l e .  5 and  Similar  10% p e r l o g c y c l e  several other  researchers  of  strain  f o r other  c o n s o l i d a t e d and o v e r c o n s o l i d a t e d  (1,2,3,5,8,12,14,23,24,30,32,33).  4.2.  Constant The  Table  results  3.  Since  essentially the  The  level rate  Creep  of t h i s  deviator  development  of creep of  0.83  was  series  the only stress  stress kg/cm  observed  until  It i s believed  develop For  with  time  the higher  strained Figure  7 that  sample) creep  with  under  strength under  stress time  a  that value  time was  this and  levels,  is  various  For a  stress  deformation  of r e l i a b i l i t y  terminated  stress that  to test  no  level  (10,000 approaches  failure  than  of  will  this  value.  the samples p r o g r e s s i v e l y  eventual  of f a i l u r e  sustained  7.  at  decreasing  stresses smaller  until  the time  the test  test  time  i n Figure  t h e maximum  minutes).  yield  in  loading.  with  a continuously  2  from  creep  strain  i s shown  c o n d i t i o n s when  upper  a r e summarized  variable  during  of a x i a l  undrained  the  of t e s t s  t h e end o f c o n s o l i d a t i o n c o n d i t i o n s a r e  identical,  constant  levels  Stress  stress  rupture. (total  It i s clear  c o l l a p s e of the  decreases  with  from clay  increasing  stress. For  change  the t e s t  i n creep  at a stress  stress  was  level  suddenly  of  0.70  applied  kg/cm , 2  after  an  a  step  elapsed  TABLE 3  RESULTS OF UNDRAINED CONSTANT STRESS CREEP FOR OVERCONSOLIDATED HANEY CLAY  19 80  21-80  51-81  45-81  27-80  24-80  28-80  18-80  31-81  1.15  1.13  1.06  1.01  0.98  0.95  0.93  0.83  0.70 1.08  Void R a t i o : Before c o n s o l i d a t i o n After consolidation  1.878 1.876  1.822 1.822  1.845 1.852  1.774 1.771  1.883 1.888  1.768 1.811  1.952 1.996  1.755 1.774  1.891 1.927  Consolidation stresses: a (kg/cm ) 0 3 (kg/cm ) O1/O3  0.52 0.51 1.02  0.50 0.48 1.05  0.52 0.49 1.05  0.53 0.50 1.06  0.49 0.49 1.00  0.51 0.50 1.02  Test Number Deviatoric  r  Stress Level (kg/cm ) 2  2  1  2  A x i a l S t r a i n Rate e(%/min): at "e = 0.8% a t e = 1.0% a t e = 1.2% • e . min • Time a t j[ (minutes)  x  2  X  2  2  x  2  X  3  6.5 10~ 9.4xl0 2.7 10~ 2.0 10~ X  2  - 3  X  3  X  3  0.51 0.49 . 1.04  1.7 10 3.1xl0 1.0 10 4.8 10 X  - 2  - 3  X  - 3  x  -lt  6.4 10 l.lxIO 5.0 10 2.5 10 X  -3 - 3  x  _lt  x  _tt  3.5 10": 2.4xl0 .  6.7 10 1.2X10-  1.4 10 1.2 10  8.3 10  X  3  _it  x  _tf  x  -lf  x  X  -lt 11  - 5  2.7 10~ 9.0xl0X  8.5 10 X  160  800  .1000  1300*  2100  8000  (%)  1.42  1.30  1.45  1.55  1.55  1.60  1.10  1.00  A at £ • mm  0.39  0.35  0.36  • 0.29  0.28  0.45  0.38  0.29  Axial Strain at e  m  i  n  • m  5  6  46  n  P.P. Parameter  2.2xl0 2.1 10~ 1.5 10~  _1  0.51 0.50 1.02  19  e  m  1.4 10 2.5xl0~ l.l 10~ 9.6 10~ X  - 2  . 0.57 0.51 1.11  - 6  no rupture  37  i time  of  about  kg/cm .  As  2  a  intermediate levels  of  level  1.08  the  between 1.06  2  and  The  existence  loading  in  For  time  tests by  initially  sample  at  time  the  is  It the  at  identical  be  such  is  assumed  used  to  bring  relationship  for  of  deformation  illustrated  the  stress if  stress,  independent  clay  the  in  Figure  8.  strain-time  eventually until  rates  to  clay  failed,  of  rupture. tested  the  acceleration  leading  to  other  termed  rate  with  researchers secondary  stress  to  level, strain  between axial  1.0  note the rate and  strain  of  was  is  a  was  stress  was  Figure  7.  rate  reached  rupture.  level, time  plot  deformation  value  stress  constant  curves  minimum  yield  in  This  a  the  stress  current  and  the  at  5.  minimum  to  unique  1.08  anticipated  r e l a t i o n s h i p between  a  interesting  ranging  tests  would  result  to  time  a  e s s e n t i a l l y constant  creep  defined level  is  in  a  Such  2  history  upper  by  rupture  at  straddle  deformation  out  of  occurred  level  which  rate  which  region,  strain  time  stress  kg/cm ,  the  decreased  decreasing pointed  failure  differentiating  subsequent  the  1.13  history  is  samples  its  of  Chapter  The  derived  that  strain  time  creep  and  bringing  the the  kg/cm .  the  shown  minutes,  result,  hypothesis  strain,  of  80  For  before the  continuously observed.  As  (4,9,15,17,21,25,28,29,32)  creep, does on  over not  Table  failure -  at  seem 3 of  occurred  1.6%. peak  which  This  the  to  at  irrespective  clay an  samples  axial  strain  deviator  of  exist.  that, the  rate  a  level  stress  -  strain is in  the  ,•-38 .  1.15  1.13  1.07  1.01 0.98  10=- i  0.95 y 0.93  L  -2  10 •H  -3 10 53 H  H  3 -4  10  o -a ±  3  (kg/cm ) =  -5  10  10  100  1000  ELAPSED TIME t (min) FIG. 8.  AXIAL STRAIN RATE VERSUS TIME RELATIONSHIP IN CONSTANT STRESS CREEP.  39  constant  rate  of s t r a i n result  described  i n the  i s a further indication  of the  section.  This  existence  of a c r i t i c a l  structure  of t h i s  shear  tests  strain  particular  level  clay  beyond  which  c o l l a p s e s and  previous  the  failure  ensues. The the  variation  base  of the sample,  Essentially, application until  there  arrows  very  rapidly  on t h e p l o t  tests,  the pore  indication pressure  to take  place.  reaching  a stable  change  0.70 value  decreasing  test  pressure missing  i n creep  shows  strain  failure  does  kg/cm ,  not give  slowly  following  stress.  until  to a higher  occurred.  the sudden  at the a p p l i c a t i o n  initial  of creep  of the remaining  stress  In  The  creep  pore  rupture i s  starting  water  the i n i t i a l  Consequently,  failure  indicate  any  when  test  pressure  vertical  reached.  the pore  2  decrease  time  of the sample.  decreasing  up  The  versus  was  at the  the pore  value.  pressure  behavior  brought  clearly  i n the p l o t  stable  at  9.  pressure  by a s l o w  when  For the step-creep  'instantaneously'  started this  of  followed  measured  i n Figure  of pore  occurred,  small  steadily  pressure,  i s shown  rise  stress,  of a x i a l  of impending  stress  step  time  of the pore  pressure  is still  water  sudden  to a  rate  constant  was  a  of the a x i a l  t h e minimum  about  was  with  c o l l a p s e of the sample  dropped  when  of the pore  with  pressure  rise value  was  when i t due t o t h e  the pore  pressure  The c u r v e f o r rise  of  pore  as t h i s  constant  a  stress  part  was  creep  10  100  1000  ELAPSED TIME (min) FIG. 9 PORE PRESSURE RESPONSE AT THE BASE OF THE SAMPLE WITH TIME IN CONSTANT STRESS CREEP ON O.C. HANEY CLAY. ^  O  41  tests of  because  i s also  effective time  as  maximum the  stress  beginning  pore  time  10  from  creep  stress  represents,  be  start  increase with  relationship rates  with  be d i s c u s s e d  a t t h e same  later.  time  strain  until  that  The  life  final  a given  plot  (time collapse)  level  f o r more  than  of a  of F i g u r e  rates  levels. rate  level.  fixed 10  strength  shows  are  with  essentially  Comparison  strain  plotted  The v a r i a t i o n  of undrained  constant  as  stress.  of rupture  strain  stress  stress  from  total  clay.  the v a r i a t i o n  of deformation  with  i s at the very  the c l a y  11, t h e minimum  the corresponding  the  Hence, the  the r e d u c t i o n of undrained  l o g a r i t h m o f minimum  linear  seen  collapse.  particular  Figure  be  s u s t a i n e d by  i n fact,  and m i n o r  of the creep  of creep  tests,  variation  shear.  occur  that  the v a r i a t i o n  I t may  major  during  will  i n these  similar  both  pressure,  undergoing  for this  against  shows  stress.  cannot  In  ratio  the i n i t i a t i o n  without  time  water  since  constant  stress  that,  has a  of the a p p l i c a t i o n  Figure  with  pressure  effective  to note  a /a^  ratio  are maintained  maximum  elapsed  interesting  the pore  stresses  will  of r e c o r d i n g at the  loading. It  the  of the low frequency  of  a  this  strength  rate  of  shear  with tests  I io"  I 5  io  I - 4  io  I - 3  io"  I io  2  MINIMUM AXIAL STRAIN RATE e .  I - 1  I  10°  (%/min)  mm  FIG. 11. VARIATION OF UNDRAINED STRENGTH WITH MINIMUM RATE OF STRAIN IN CONSTANT STRESS CREEP. OJ  44  4.3.  Constant In  this  Rate serie.8  linearly  increasing  of  tests  these  conditions end  rate  the a x i a l  force  of the samples  during  samples only  relation study,  shear on  i n Figure  Since  was  the samples  a r e summarized  of loading  shown  12.  loading slight  constant results range  rate.  testing The  be  effect  i n Figure  undrained  As  was  This  before,  the  at the  varying The e f f e c t  and t h e s t r e s s - s t r a i n  tests,  f o r some  with  behavior  increase  speed  of  of shear.  to r e a c h  A  a  discrepancy  In s p i t e  of loading,  i n this  the v a r i a b l e  i n the system  strength  of  deformation.  on a t t h e s t a r t  rates.  i n the  of the narrow a  tendency  increasing  t o an  speed  of  behavior,  as  noted. of rate  of loading  13, i n d i c a t e s  strength  with  on  the c l a y  a definite increase  increasing  of  of the c l a y i s the rupture  of  the continuous  i n the rate and  results  of the post-peak  of these  account  loading  rate  by  of p a r t i c u l a r i n t e r e s t  turned  may  of tests,  stress  measurement  experienced  in stiffness may  were  to r e g u l a t e  of v a r i a t i o n  4.  The  of l o a d i n g .  large  deviator  I n some  at various  increase  shown  was  time.  and t h e o n l y  type  at a very  air-pressure delay  period,  to f a i l u r e  used  loaded  are e s s e n t i a l l y i d e n t i c a l  For t h i s  the continuous  servo-motor  i n Table  i s the rate  t h e maximum  not r e c o r d e d .  with  were  the s t r e s s - s t r a i n response  occurred  prior  Shear  of tests,  of the c o n s o l i d a t i o n  parameter  the  of Loading  logarithm  in  of the  loading  TABLE 4  Test  RESULTS OF UNDRAINED CONSTANT RATE OF LOADING SHEAR FOR OVERCONSOLIDATED HANEY CLAY  13-80  Number  2.54X10  Loading Rate (kg/min) Void  9-80  12-80 1  2.74x10°  2.6xl0  10-80  44-81 _ 1  1.6xl0  1.4xl0  _ 1  46-81 _ 1  4.9xl0  - 2  14-80.  52-81  1.6xl0  8.3xl0  - 2  -3  Ratio: Before c o n s o l i d a t i o n After consolidation  Consolidation stresses: Oj_ (kg/cm ) a (kg/cm ) 2  2  3  a /a 1  3  D e v i a t o r i c S t r e s s o^-a.j(kg/cm ) a t e = 0.8% a t e = 1.0% a t e = 1.2%  1.963 1.966  1.997 1.984  1.990 1.996  1.804 1.939  1.998 2.002  1.763 1.878  1.986 1.975  2.054 1.987  0.50 0.42 1.21  0.48 0.46 1.06  0.54 0.43 1.25  0.52 0.50 1.04  0.44 0.41 1.06  0.52 0.50 1.04  0.53 0.54 0.98  0.53 0.51 1.03  1.45  1.37 1.40  1.10 1.16 1.19 1.24  0.95 1.04 1.10 1.14  0.99 1.09 1.16 1.22  1.02 1.12 1.14 1.15  1.08  0.90 1.01 1.07 1.02  2  ( l- 3>max 0  Axial at at at  a  S t r a i n Rate e (%/min): e = 0.8% e = 1.0% e = 1.2%  -  .1.52  '  -  1.40  6.4X10  1  —  l.OxlO —  1  6.5X10" 9.0xl0" 1.5*10  2 2  -1  3.6X10"  2.9*10  4.8X10"  3.8X10"  2  2  6.5><10~  2  5.0 10 X  -2 2  - 2  -  1.12  4.7X10" 1.5X10" 5.0 10"  3  X  2  2  6.0 10 X  -  -  -3  1.6*10 2.2X10 4.2 10 X  Maximum S t r e s s R a t i o (o-^/o^) max  21.06  10.37  13.73  50.00  11.23  33.22  10.87  23.66  A x i a l S t r a i n (%): a t (°r°$)maK a t (a /a ) 1 3 max  0.96 0.96  1.06 1.06  1.60 1.60  1.52 1.52  1.44 1.44  1.33 1.17  0.89 0.89  1.02 1.59  P.P. Parameter A: a t (21-^3) max at max  0.23 0.23  0.29 0.29  0.28 0.28  0.41 0.41  0.31 0.31  0.40 0.40  0.37 0.37  0.45 0.39  _3 -3  -3  46  0.4  0.8  1.2  1.6  2.0  AXIAL STRAIN (%) FIG. 12  EFFECT OF RATE OF LOADING ON THE STRESS-STRAIN RESPONSE OF O.C. HANEY CLAY IN CONSTANT RATE OF LOADING SHEAR.  10  2  10  1  10°  io  1  RATE OF AXIAL LOADING (kg/min) FIG. 13  VARIATION OF UNDRAINED STRENGTH OF O.C. HANEY CLAY' WITH.RATE OF LOADING IN CONSTANT RATE OF LOADING SHEAR.  48  rate.  This  8%  log  per  similar  increase cycle  to  the  in rate  loading.  observations  reported  s a t u r a t e d Mexico  on  normally  Samples loaded  with  time.  As  creep  Load in  under  5  In  behavior  this  series  and  clay  of  Casagrande by  Vaid  is and  and  Wilson  Campanella  (32).  tests  loads  deformation  were  which  in a  instantaneously  were  progressed,  resulting  summarizes  Figure  with  at  14  time  constant  strain  It  under  the  held  constant  sample  continuous  level  collapse  of  sample  allowed.  This  already was  axial  terminated; strain  undergoing  of  failure.  be  that  seen  (Figure 7).  Due  stress  with  area  decrease  that  0.92  kg/cm  had  in and  in  about  i s based excess  1.2  on  of  shown to  the  to  to  level  the  time  1.0%  creep  for  axial  would  at  a  that  was  the  result  fact  earlier,  1.5%  low  test  will  the  creep  deformation  during  2  load  is similar  the  sufficient  as  constant  decrease  likely  of  argument  strained  of  load  i s most  stress  results  constant  the  deviator  the  the  i t can  stress  failure,  significant.  of  by  behavior  stress .  tests.  test  (10)  This  approximately  Creep  thereby  Table  had  clay  predetermined  the  increased,  City  c o n s o l i d a t e d Haney  Constant  strength i s  of  on  4.4.  i n undrained  in  in  sample  when  critical  result  a been  the  strain  not  initial  creep  that  of  the  level sample  TABLE 5  Test  RESULTS OF UNDRAINED CONSTANT LOAD CREEP FOR OVERCONSOLIDATED  Number  I n i t i a l Deviatoric (kg/cm ) Void  Stress  Level  Ratio: Before c o n s o l i d a t i o n After consolidation  Consolidation stresses: 6^ (kg/cm ) 0 3 (kg/cm ) 2  2  D e v i a t o r i c S t r e s s 0-^-0^(kg/cm at e = 0.8% at e = 1.0% at e = 1.2% A x i a l S t r a i n Rate e (%/min): at e = 0.8% at e = 1.0% at e =1.2%  •  e  41-81  39-81  42-81  43-81  25-80  26-80  17-80  1.20  1.18  1.14  1.10  1.02  0.92  0.88 1.01  1.907 2.033  1.991 2.160  1.860 2.016  1.825 1.814  1.941 1.940  1.989 1.993  1.806 1.814  0.49 . 0.48 1.02  0.51 0.49 1.02  0.49 0.48 1.03  0.54 0.49 1.11  0.52 0.50 1.04  0.49 0.50 0.97  0.51 0.50 1.02  1.20 1.20  1.17 1.17  1.14 1.14 1.14  1.10 1.10 1.10  1.02 1.02 1.02  S t r a i n a t e . (%) min ' v  • P.P. Parameter A a t  e min  '  )  3.8xl0 8.0 10 2.1xl0 l.lxlO X  -1  _1  - 1  2.8 10 l.lxlO 6.0xl0 X  min  Time a t e .„ (minutes) min ^ ' Axial  2  HANEY CLAY  3  6  _1  - 1  - 2  _1  5.0 10~ l.OxlO" l.OxlO X  2  2  - 2  l.lxlO  - 1  9.0 10 9.5xl0 6.0xlO X  20  70  -3  -3  -3  0.92 0.92  3.3xl0  - 2  5.6 10 1.5xl0 1.3xl0  -3  X  5.4X10- * 1  9.0 10  - 5  8.4xl0  - 5  X  - 3  - 3  215  2900 1.00  1.40  • 1.50  1.30  1.50  1.40  0.35  0.33  0.33  0.33  0.35  0.38 no rupture  1 10  1 100  I  I  1000  ELAPSED TIME t (min) FIG. 14. AXIAL STRAIN VERSUS TIME RELATIONSHIP IN CONSTANT LOAD CREEP. '  | ' °  51  By time  differentiating  history  deformation before  of  Figure  16  very  also  similar  In against  Figure  Results  similar  stresses  a minimum  and  until  then  final  seen  the  life  this  stress  failure.  (time  collapse)  strain  of  eventual  that  from  value  of the a x i a l under  The  of  to the l i k e l i h o o d  of rupture  17, t h e minimum levels  16  strain  elapsed with  relationship  constant  o f minimum with  of a x i a l  are  stress  strain  17  stress  would creep,  accumulation.  The  rates i s  stress  excessively i n constant strain  plotted  of shear.  initial  and F i g u r e  f o r constant  d i d not vary  rates  at the s t a r t  increase  i n Figure  to those  low l e v e l s  rate,  15.  the onset  relationship  to the r e s u l t s  a linear  shown  the shape  I t c a n be  of the l o g a r i t h m  essentially  until  14, t h e  10.  the s t r e s s  variation  of Figure  i n Figure  signaling  point  of creep  stress.  i n Figure  that  does creep  obtained  thus  of time  2  curves  decreased  the v a r i a t i o n  the i n i t i a t i o n  is  to  kg/cm  shows  creep  be  noted  t h e minimum  initial  creep  be  time  was  initially  logarithm  0.92  reaching  rates  increasing,  I t may  versus  level  from  rates  finally  failure. rate  of creep  strain  be  levels. expected  since load  to  creep  creep  due  I 10 FIG. 15.  .  I  100 ELAPSED TIME t (min)  1 1000  AXIAL STRAIN RATE VERSUS TIME RELATIONSHIP IN CONSTANT LOAD CREEP.  FIG. 16.' INITIAL DEVIATOR STRESS VERSUS TIME TO FAILURE RELATIONSHIP IN CONSTANT LOAD CREEP.  1.2  0.8  0.4  MINIMUM AXIAL STRAIN RATE e . (%/min) min  FIG. 17. INITIAL DEVIATOR STRESS VERSUS MINIMUM AXIAL STRAIN RATE RELATIONSHIP IN CONSTANT LOAD CREEP.  55  CHAPTER  5.1.  CORRELATIONS  OF  WITH  TIME  LOADING H I S T O R I E S  Rate  Relationship  VARIOUS  Stress-Strain-Strain In  tests this  order  with  to e s t a b l i s h  the d i f f e r e n t  investigation,  variable  among  time  the various  between  at  any g i v e n  level  is  identical  to assuming  in i t sstrain  R E S U L T S FROM  correlations  the rate  relationship  state  5  TESTS  of r e s u l t s  loading  histories  of s t r a i n  i s used  tests. stress  and c u r r e n t  of s t r a i n  during  shear  the v a l i d i t y  hardening  e  the  considered as a  The u n i q u e n e s s  current  from  in  unifying  of the  strain  i s assumed.  of the equation  rate This of  formulation:  = f(o,e)  (3)  where: e  =  creep  rate  or a x i a l  e  =  creep  deformation  0  =  creep  stress  In  this  expression,  the  of  both  the  stress  current  strain  or a x i a l  or d e v i a t o r  current and  rate strain  rate strain stress  of s t r a i n  is a  function  and i s i n d e p e n d e n t  of  56  the  past  strain  established strain  Since  at  strain  between  constant  strength  versus  correlation. between  by  other  axial  strain  from  tests  essentially  rate  strain with  may  be  rate  i s shear  undrained  seen  have  such  to  of t e s t s .  as w e l l  and  first  of s t a t e  illustrates  normally  may  a  exist  As  been  obtained  consolidated  and  as f o r o t h e r  be a t t e m p t e d  i n terms  i n Figures  level,  a variety  i t may o f time  curve,  of state.  be  a l l the stress  of s t r a i n  prior  1 9 a , 19b  and 19c  0.8,  and 1.2%.  noted  loading  thus  among  of deviator  levels  of r e s p e c t i v e l y  o n t h e same  the equation  shear  the  strain of  results  at fixed  a r e shown  levels  the  (16,22).  investigation strain  18  types  (15,32,33)  correlation  These  chosen  clays  materials  similar  each  of  two  f o r both  failure. chosen  of these  investigators  in this  versus  agreement  comparable  engineering  tests  excellent  Figure  creep,  equation  i n terms  previously,  overconsolidated  A  rate.  that  t h e same a t  of s t r a i n  of constant  tests  be  values.  stress  of the proposed  creep  the r e s u l t s  mentioned  i n constant  strain  An  to given  rate  may  provided  i s essentially  the r e s u l t s  stress  relationship  stress  i n constant  rate  of the v a l i d i t y  and  fixed  level  stress  A direct  rate  i s maintained  deviator  attempted and  strain  the s t r a i n  minimum  proof  history.  between  level  maximum  rate  1.0 that  supporting  A l l the c o r r e l a t i o n s  f o r the  the data  histories the are  to  For point  fall validity  10  5  10  4  10  3  10  2  10  1  10°  AXIAL STRAIN RATE e (%/min) FIG. 18.  COMPARISON OF STRAIN RATE DEPENDENCE OF UNDRAINED STRENGTH IN CONSTANT RATE OF STRAIN SHEAR AND CONSTANT STRESS CREEP.  Ln  1 io"  5  1 io"  4  I i o  -  J 3  i o  -  2  I io"  I 1  J  10°  AXIAL STRAIN RATE e (%/min) FIG.I9a--.,  DEVIATOR STRESS VERSUS AXIAL STRAIN RATE AT EQUAL STRAIN LEVEL RELATIONSHIP IN CONSTANT RATE OF STRAIN SHEAR, CONSTANT STRESS CREEP, CONSTANT RATE OF LOADING SHEAR, AND CONSTANT LOAD CREEP.  . co  Ui  i  1  r  AXIAL STRAIN RATE e (%/min) FIG. 19b.-, DEVIATOR STRESS VERSUS AXIAL STRAIN RATE AT EQUAL STRAIN LEVEL RELATIONSHIP IN CONSTANT RATE OF STRAIN SHEAR, CONSTANT STRESS CREEP, CONSTANT RATE OF LOADING SHEAR, AND CONSTANT LOAD CREEP.  10  -5  10  -4  ,-3 10 "  1  .-2 10  10  -1  10  AXIAL STRAIN RATE e (%/min) FIG. 19c.  DEVIATOR STRESS VERSUS AXIAL STRAIN RATE AT EQUAL STRAIN LEVEL RELATIONSHIP IN CONSTANT RATE OF STRAIN SHEAR, CONSTANT STRESS CREEP, CONSTANT RATE OF LOADING SHEAR, AND CONSTANT LOAD CREEP.  ov, o  61  summarized  i n Figure  essentially stress  of a x i a l  variation  similar a  plot  plastic  constant shows  presented  from  rate  that  the rate  an i n c r e a s e  strain  history  rate,  t h e same  by B e r r e  and B j e r r u m  (2).'  of shear  tests  strain  i n the shear  used  to shear  with  the Behavior  rate.  that  study  A of  was  conventional  diagram  essentially  increases exponentially  stress  and t h i s  as  i n a study  using  This  fixed  slope  log strain  However,  only.  deviator  a t each  with  tests  is insignificant,  loading  between  strain  compression  of s t r a i n  that the  strength  Drammen  to t r i a x i a l  seen  has a p p r o x i m a t e l y  of undrained was  be  obtained  of the a x i a l  strain,  clay  restricted  with  relationship  and l o g a r i t h m  level the  linear  2 0 , a n d i t may  provided  the change i n  independently  the clay  of the  i n undrained  time  triaxial  compression.  5.2.  Comparison Haney The  were state to  and s t r e n g t h  previously investigated  compare  results  and C a m p a n e l l a  the data  obtained  on o v e r c o n s o l i d a t e d  important  because  Consolidation  Consolidated  clay.  stress-strain  by V a i d  of Normally  preconsolidation  pressure  o f Haney  clay  i n the normally  consolidated  (32).  be  from Haney  of the s e n s i t i v e  of a s e n s i t i v e  behavior  clay  into  I t would  that  study  clay.  past  with  This  nature  interesting the present  i s particularly  of the clay  the  the normally  used.  apparent consolidated  T  FIG." 20  STRESS-STRAIN-STRAIN RATE RELATIONSHIP FOR UNDRAINED TRIAXIAL COMPRESSION ON O.C. HANEY CLAY USING VARIOUS TIME LOADING HISTORIES.  63  region Thus  i s associated  the behavior  state  may,  after the  a radical  of the u n a l t e r e d  characteristics  i t has been  may  be  qualitative batches and  upon  pointed  because  of the c l a y  Campanella  out t h a t  structure,  reflect  different  normal  such  time  from  those  consolidation in  difference  used  and  study.  in this  The  content  plastic  limit  o f 26%, and a c l a y  presented study,  higher  a s shown  uniform  thin  a further  different The Haney  indication than  i n constant  same  sharp  was  observed  decrease  on  more  that  this  t h e one  rate  i n behavior  than  0.002  i n the  Vaid  and  of  clay  a  Campanella.  d i d not  consolidated  4.  as i t The  samples  deviator due  exhibit  value  in Figure  is essentially  from  clay  consolidated  the peak  t h e maximum  mm)  present  obtained  shear  past  o f 44%, a  i n the present  was by  of s t r a i n  limit  had a  The o c c u r r e n c e  of normally  i n stress  past  1.  tested  behavior  i n Vaid  properties  tested  clay  the o v e r c o n s o l i d a t e d  gradually  difference  physical  be  i n the  used  (less  materials  s o f t e n i n g of the normally  occurred  content  Table  of organic  stress-strain  the  This  layers  can only  consolidated clay  f o r the clay  p r e v i o u s l y on  that  40%, a l i q u i d  A l l these  values  horizon  clay  strain  o f about  50%.  study  normally  water  approximately  a comparison  of the s i g n i f i c a n t  natural  is  i n i t soverconsolidated  significantly  destructured  in i t s structure.  laboratory. It  of  change  of the n a t u r a l clay  because  dependent  with  stress .  to the  64  destructuration prior  to shear  effective  of the normally loading  confining  preconsolidation  when  stress  i n the behavior  states.  The  the  of  rate  stress  was  the c l a y higher  pressure.  observed  strain  consolidated  a t an  the  normally  for  the o v e r c o n s o l i d a t e d  was  cases  axial  consolidated  state  similarities  independent  the peak  of about  as compared  were  consolidation  essentially  strain  t o an  apparent  i n both  although  occurring  subjected  the  some  of the c l a y  i n both  reached  than  However,  at f a i l u r e  strain  was  clay  2.5  t o 1.2  of  deviator t o 3.0% to  in  1.5%  clay.  o  The strain creep  v a r i a t i o n of undrained  rate  i s shown  presented 8%  from  constant  i n Figure  a regular  per l o g c y c l e  clay  exhibited  rates  (less  of s t r a i n  no  than  change 5 x  10~  of about  speed  deformation.  The with  Figure a  from  22.  similar  larger  9%  comparison  time  consolidated  clay  strain  While  %/min),  seen  stress that  of  f o r short  strength  of  stress  strain  at low  rate  tests of  states.  failures  about  strain  pronounced  of undrained  observed  of  clay  consolidated  the behavior  were  time  constant  a more  creep  consolidation  of strength  and  strength  then  of the r e d u c t i o n  be  logarithm  the normally  i n undrained 3  with  the o v e r c o n s o l i d a t e d  i n undrained  per l o g c y c l e  i n both  reductions  of  rate,  the constant  I t may trend  21.  increase  increase of  rate  strength  for  strength  i s shown  in  the c l a y  has  However,  i n the  (less  higher  than  normally 100  °  Constant S t r a i n Rate Shear at (°1-°3) max Constant Stress Creep at e  •  n  0  •  10  5  10  4  10  3  10  2  10  1  I  mm  10°  AXIAL STRAIN RATE (%/min) FIG. 21 VARIATION OF UNDRAINED STRENGTH WITH RATE OF STRAIN IN CONSTANT STRAIN RATE SHEAR AND CONSTANT STRESS CREEP FOR O.C. AND N.C. HANEY CLAY.  ON  Ln  NORMALLY CONSOLIDATED (Destructured) 3.4  2.4  1.6 OVERCONSOLIDATED (Intact structure) 0.8  ±  -L  10  0  io  J  ±  ± 10  10  10  10"  TOTAL RUPTURE LIFE (min) FIG. 22  TIME DEPENDENCE OF UNDRAINED STRENGTH OF O.C. AND N.C. HANEY CLAY IN CONSTANT STRESS CREEP,  67  minutes  in total  Since proved  f o r both  essentially  and  life).  the v a l i d i t y  relationship  shear  rupture  of the equation  clays,  between  which  stress,  independent  the c l a y ,  constant  the r e s u l t s  load  creep  shear  the constant  From  will  the  same  state  with  but  caused  rate  that  on  load.  with  time  tests.  to shear  will of  strain  Therefore,  a clay  such  a  structured  and  apparent  change  preconsolidation  variation  with  In both  clays,  the c u r r e n t  the current  strain  rate  i n the magnitude may  increasing  noted,  remains  rate  stress  of  strain  i n undrained  of s u s t a i n e d  a t any g i v e n  be  e s s e n t i a l l y t h e same  reduction  the e f f e c t  has  dependent  behavior  showed  t h e same  of the clay  strength  dependent  clays  been  overconsolidated  i n the time  A minor  strength  under  has  i n t h e l a b o r a t o r y „and  the undrained  and  that  the d e s t r u c t u r a t i o n  Both  i n undrained of loading,  strength  rate  to the i n - s i t u  t h e same.  used  of loading  as t h e c o n s t a n t  consolidation  the c h a r a c t e r i s t i c time  increase  to  effects  rate  clays  between  any s i g n i f i c a n t  the time  history  necessary.  of the m a t e r i a l .  basically  or  respect  been  rate i s  f o r t h e two  in i t sintact,  i t appears  behavior of  by n o r m a l  clay  pressure, not  n o t be  and s t r a i n loading  creep  has  the unique  of constant  stress  the comparison  destructured  strain,  tests  be a s c o m p a r a b l e  comparison  that  of the time  certainly and  means  of state  was level  stress  uniquely  or  related  of s t r a i n  prior  68  to  failure,  during  5.3.  Mohr  regardless  Conditions  Figure  23 s h o w s  plot  =  time the  This  results  failure  history  diagram  conditions stress  used  of a l l the v a r i o u s  for a l l tests data  a n d t h e 45 d e g r e e  consolidated tests  envelope line  were  clay  lined  of the  indicating tests (o^  evidence  I t i s however  on  points are  i n the t r i a x i a l  n o t show a n y c l e a r  of the normally  Ratio  i n the modified  the f a i l u r e  conditions  does  Stress  ratio  A l l the test  of the r e s u l t s .  envelope.  Effective  between  clay  of the stress  dependence  points  clay.  range  consolidated  limit  0).  effective  Haney  i n a narrow  normally  a t Maximum  the s t r e s s  a t maximum  overconsolidated  the  loading  shear.  Stress  located  of the time  of a  different where  up a l o n g  the a  from data  unique  69  1 T—  O • A A + x  '  71  . Constant s t r a i n rate shear Constant s t r e s s creep Constant loading rate shear ' Constant load creep Step change constant s t r e s s creep Step change constant load creep  FIG. 23. STRESS CONDITIONS FOR ALL TESTS AT (•o-/cO ON O.C. HANEY CLAY. 1 3 max  70  6  CHAPTER  CONCLUSION  The  time  deformation  dependence  behavior  overconsolidated, compression, variety  strength strain in  natural  clay  have  histories.  rate  sensitive, been  The  history, tests  in  triaxial  under  a  showed  that  result  s t r e s s - s t r a i n response  and h i g h e r  undrained  investigated.  to t r i g g e r  study.  rupture  A critical  A c o r r e l a t i o n among  of the e q u a t i o n  hardening  formulation,  that  prior  to the c u r r e n t  to f a i l u r e ,  stress  regardless  of  performed  tests  of s t a t e  i s , the current  stiffer  low l e v e l  the v a r i o u s  the v a l i d i t y  related  in  i n a l l the tests  supported  strain  examined  of loading  appears  uniquely  and  and r a t e  f o r the c l a y  this  saturated,  strength  consolidation  loading  in strain  undrained  of a  f o r a given  of time  increase  of undrained  in i t s strain  strain  rate i s  a t any g i v e n  of the time  level  of  loading  history. A study  q u a l i t a t i v e comparison o f t h e same  laboratory  normal  destructuration change  clay,  consolidation,  of the clay  i n i t s time  observed  sensitive  with  dependent  and r e l a t e d  the r e s u l t s  of a  destructured indicated  has not caused behavior.  to the n a t u r a l  similar  upon  that  the  any s i g n i f i c a n t  The o n l y  structure  differences  of the  71  overconsolidated obtained  from  the  stress  all  tests  clay  conventional  conditions plotted  overconsolidated  clay  at failure,  effective  stress  regardless  i n the s t r e s s - s t r a i n  response  constant  tests,  a t maximum  on a m o d i f i e d  structure  ratio,  were  exhibited  strain  effective Mohr  a pronounced  envelope  o f the time  stress  diagram.  a n d i t d i d n o t show  failure  rate  loading  history  r a t i o of  The collapse  any w e l l  a t maximum  and i n  i t s  defined  effective of  of  stress  shearing.  72  LIST  Alberro, Mexico  J.A.  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