Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Plane strain creep rupture of a saturated undisturbed clay Mallawaratchie, Dayalal Pandula 1970

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1970_A7 M34.pdf [ 5.41MB ]
Metadata
JSON: 831-1.0050564.json
JSON-LD: 831-1.0050564-ld.json
RDF/XML (Pretty): 831-1.0050564-rdf.xml
RDF/JSON: 831-1.0050564-rdf.json
Turtle: 831-1.0050564-turtle.txt
N-Triples: 831-1.0050564-rdf-ntriples.txt
Original Record: 831-1.0050564-source.json
Full Text
831-1.0050564-fulltext.txt
Citation
831-1.0050564.ris

Full Text

PLANE  STRAIN  C R E E P RUPTURE UNDISTURBED  OF A  SATURATED  CLAY  by DAYALAL B.Sc.  A  PANDULA  (ENG),  University  THESIS  SUBMITTED  THE  REQUIREMENTS MASTER  in  MALLAWARATCHIE of Ceylon,  IN PARTIAL FOR  F U L F I L M E N T OF  THE DEGREE  OF A P P L I E D  1965  OF  SCIENCE  the Department of  Civil  We  accept  required  THE  this  Engineering  thesis  as conforming  standard  UNIVERSITY  OF  June,  BRITISH 197 0  COLUMBIA  to the  In presenting this thesis i n p a r t i a l fulfilment of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t freely available for reference and study.  I further  agree that permission for extensive copying of  this  thesis for scholarly purposes may be granted by the Head of my Department or by his representatives.  It  understood that copying or publication of this thesis for  f i n a n c i a l gain s h a l l not be allowed without my  written permission.  Department of C i v i l Engineering The University of B r i t i s h Columbia Vancouver 8 , Canada  is  ABSTRACT  Undrained tests  constant stress  have b e e n p e r f o r m e d under K  consolidated  level  creep  on an u n d i s t u r b e d ,  conditions,  sensitive  rupture  normally clay  in a  o rectangular The  ( 1 " x 4" x 2^-" h i g h )  behaviour  increasing  (keeping  (keeping creep  resulting  constant)  ditions  and t h e n  creasing  a2'  loaded  Snead t e s t e d  c o n s o l i d a t e d under  conditions rate versus  comparison  shows t h a t  i n which  time  and t r i a x i a l  isotropic  are essentially stress  minimum s t r a i n  paths,  rupture  r e p o r t e d by  but  stress  initially  and  axially  apparatus,  the l i n e strain  under p l a n e  o f minimum  a t minimum  the d e v i a t o r stresses  ^  strain  strain  strain  t h e same f o r i n c r e a s i n g  rates are different.  con-  q  as d e -  creep  those  o f creep r e s u l t s  and t h e a x i a l  triaxial  a^, as w e l l  t h e same c l a y  although  undrained  c o n s o l i d a t e d under K  i n the conventional t r i a x i a l The  paths o f  Several  l o a d e d by i n c r e a s i n g strain  apparatus.  and d e c r e a s i n g  was c o m p a r e d .  The p l a n e  (1970) .  normally  ing  constant)  normally  strain  stress  r e s u l t s w e r e compared a l o n g w i t h  Snead  rate  total  t e s t s have a l s o been performed  s p e c i m e n s were f i r s t  test  from  plane  and d e c r e a s a  i ~  a  ^  v  e  r  s  u  s  The crepancies and  i n the  triaxial  initially seen  comparison of  K  q  i f the  creep  rupture  c o n d i t i o n are  the  slope  failure.  that both the  lines  t h a n do  the  so  long  as  the  test  data  dis-  strain  clay i s  Of  particular and  i n t e r e s t was  decreasing  time to  slope  consolidated  compared  p r e d i c t i o n of  the  observation  plane  failure.  t e s t s p r e d i c t much s h o r t e r  are  consolidated.  were  a v a i l a b l e methods f o r t h e  isotropically  the  isotropically  of  increasing  strain  b e h a v i o u r under plane  samples are  same p r e d i c t i o n o f  plane  shows t h a t t h e  However, l a r g e d i s c r e p a n c i e s  In a d d i t i o n , a l l of along  results  slight,  consolidated. triaxial  test  strain However  times to triaxial  give the  failure tests.  iv  TABLE OF CONTENTS Chapter  I II  Page  INTRODUCTION LITERATURE  REVIEW  Field  Observation  Creep  and C r e e p  Summary III  . . . . . . . . . . . . . . . . . . . . . . . . . . . o f Creep  Rupture  Description  o f the A p p a r a t u s Used i n  Study  Tested  . . . .  of S o i l  . . . . . . . .  30 30 32  . . . . . . . . . . . . . . . .  33  D i s c u s s i o n o f T e s t i n g Procedure (Plane S t r a i n Tests) . . . . . . . . . . . . . .  40  RESULTS  Tests  OF  PLANE STRAIN  i n Which  Was  CREEP RUPTURE  Increased  . . . . .  47  Comparison o f " a ^ I n c r e a s e d " and " c ^ D e c r e a s e d " Types o f c r e e p tests . . . . . . . . .  63  S \intITlcl  33  o  a  s  COMPARISON OF  S  VI  Programme  7 28  . . . . . . . . . . . .  Description  This  V  . . . . . .  . . . . . . . . . . . . . . . . .  LABORATORY TESTING  5  Creep  Studies  Development o f a T e s t i n g  IV  and  1  UHTlTll cl3T y  o  PREDICTION Summary  »  OF  o  o  o  o  o  a  o  o  D  PLANE STRAIN AND  e  o  »  SLOPE  t  >  o  o  o  FAILURE  o  o  a  o  a  a  TRIAXIAL  o  o  o  o  o  o  Q  95  . . . . . . .  -97  . . . . . . . . . . . . . . . . . .  106  V Chapter VII  APPENDIX  Page SUMMARY AND CONCLUSIONS  I - EXPERIMENTAL II III  . . . . . . . . . .  PROCEDURE  . . . . . . .  - CALCULATION OF STRAIN RATES  . . . .  - WATER CONTENT, STRESSES AT THE END OF CONSOLIDATION AND DURING CREEP . . . . . . . . . . . . . . .  108  117 119  121  vi  LIST  OF  TABLES  Table I II  Page P h y s i c a l p r o p e r t i e s o f Haney c l a y Some r e s u l t s creep  III  a  D  test  -  V  plane  plane  strain  55  F i g u r e 4.4, tests  increased . . . . . . . . . . Some r e s u l t s o f u n d r a i n e d p l a n e s t r a i n creep t e s t s decreased . . . . . . . . . a a t t h e same e and e f r o m F i g u r e 4.9, for undrained plane s t r a i n t e s t s D  34  strain  increased . . . . . . . . . .  a t t h e same e and e f r o m  for undrained IV  o f undrained  . . . . . .  62 70  vii  L I S T OF  FIGURES  Figure  Page  2.1  A t y p i c a l creep rupture curve c o n c r e t e and p l a s t i c s . ( A f t e r  2.2  A t y p i c a l s t r a i n - t i m e curve f o r normally consolidated Haney c l a y u n d e r sustained d e v i a t o r s t r e s s ( A f t e r S n e a d , 1970) . . . . .  11  Logarithm of a x i a l s t r a i n rate versus e l a p s e d time f o r n o r m a l l y consolidated u n d r a i n e d c r e e p t e s t s on Haney c l a y ( A f t e r S n e a d , 1970) . . . . . . . . . . . . . .  13  Log s t r a i n r a t e v e r s u s l o g t i m e f o r s a t u r a t e d i l l i t e ( A f t e r C a m p a n e l l a , 1965)  15  2.3  2.4 2.5  2.6  2.7  2.8  2.9A  for metals Garofalo,  R e l a t i o n s h i p between c r e e p r u p t u r e l i f e s t r a i n r a t e ( A f t e r S a i t o and Uezawa,  . . and  19 6 J_ )  o  Total tests  rupture l i f e of laboratory creep ( A f t e r S n e a d , 1970) . . . . . . . . . . .  a  o  o  o  o  o  o  o  o  o  o  o  o  o  o  o  o  o  o  1 7  19  R e l a t i o n s h i p b e t w e e n t i m e t o r u p t u r e and c u r r e n t s t r a i n r a t e ( A f t e r S n e a d , 1970) . . .  21  A x i a l s t r a i n rate versus a x i a l s t r a i n curves for normally consolidated Haney c l a y u s i n g conventional t r i a x i a l apparatus (After S n e a d , 1970) . . . . . . . . . . . . . . . .  23  A n a l y s i s o f y i e l d v a l u e on t h e b a s i s o f e f f e c t i v e s t r e s s a p p l i c a t i o n of the y i e l d v a l u e ( A f t e r S h i b a t a and K a r u b e , 1969) . . .  27  2.9B  I n f l u e n c e of r a t e of s t r e s s a p p l i c a t i o n of t h e y i e l d v a l u e ( A f t e r S h i b a t a and K a r u b e ,  3.1  Sample u n d e r p l a n e d e f o r m a t i o n s  3.2  Schematic diagram of f o r the p l a n e s t r a i n  the l o a d i n g apparatus  . . . . . . < , equipment . . . . .  36  37  viii Figure  3.3  Page  Schematic layout of plane s t r a i n apparatus w i t h apparatus t o measure volume changes and p r e s s u r e s . . . . . . . . . . . . . . . .  39  4.1  Typical plot of axial strain versus time for undrained plane s t r a i n creep tests  4.2  Logarithm of a x i a l strain rate versus logarithm of time f o r undrained plane s t r a i n creep t e s t s increased (Haney c l a y ) . . . . . . . . .  4.3A  Pore water pressure versus a x i a l s t r a i n f o r undrained plane s t r a i n creep tests -  4.3B  S k e m p t o n "A" plane s t r a i n  50  versus axial strain f o r undrained creep tests increased . . .  57  4.3C  Effective stress ratio versus axial strain for undrained plane s t r a i n creep tests  4.4  Log a x i a l s t r a i n rate versus a x i a l strain for undrained plane s t r a i n creep tests increased ( u n d i s t u r b e d Haney c l a y ) .  60  Comparison o f a versus e f o r undrained plane s t r a i n incremental loading tests u n d i s t u r b e d Haney c l a y . . . . . . . . . . .  64  4.5  4.6  D  Comparison o f deformation behaviour o f undrained plane s t r a i n creep test f o rthe cases o f "a^ i n c r e a s e d " and "o^ d. 6 G JC G ci S GCil a o o s o o a i o o a a a a o a  o  66  o  4.7  Logarithm of axial strain rate versus logarithm of time f o r undrained plane s t r a i n creep t e s t s  4.8  Lines  4.9  Log a x i a l s t r a i n rate versus a x i a l strain for undrained plane s t r a i n creep tests  4.10A  a  D  versus  plane 4.10B  o f minimum  strain  minimum  strain  creep  strain tests  rates-plane  rate  strain.  .  69  f o r undrained  . . . . . . . . . .  T/O* a t e versus e f o r undrained plane , m. m , . m s t r a i n creep tests . . . . . . . . . . . . .  74  1  A  74  N  IX  Figure  4„11A  4.11B  4.12  Page  T/O' m plane  5.1  5.2  axial  strain  strain  creep  tests  for  undrained  . . . . . . . . . .  76  Pore pressure versus a x i a l s t r a i n f o r undrained plane s t r a i n creep tests . . . . .  76  Variations for  4.13  versus  of  Henkel  undrained  plane  "a" and  79  Octahedral stress paths f o r undrained plane s t r a i n creep tests (Undisturbed Haney c l a y ) . . . . . . . . . . . . . . . .  81  Comparison rates  89  lines  creep  strain . . .  of  strain  axial  o f minimum  tests  strain  x  ./(a* .) a t minimum s t r a i n r a t e oct oct c ^oct'm ^ ^ r a i n e d c r e e p t e s t s on o  C  lcL^  •  «  r  o  versus Haney  u n c  a  o  o  »  o  *  a  »  a  »  a  o  o  a  a  5.3  . / ( a ' ,) a t minimum s t r a i n rate oct' oct c versus t f o r undrained creep tests on  5.4  x j / a ' ^ a t (Y ^) ' o_„t' c t .. o c t o oc ctt mm undrained creep tests  6.1  6.2  6.3  o  9  3>  T  (y ,) for ogcett . m.. clay . . . . .  94  R e l a t i o n between t o t a l time t o r u p t u r e and minimum s t r a i n r a t e f o r u n d r a i n e d plane s t r a i n creep tests . . . . . . . . . . . .  98  R e l a t i o n between t o t a l time t o r u p t u r e and minimum s t r a i n r a t e . . . . . . . . . . . .  100  7  1  versus -  Haney  R e l a t i o n between c u r r e n t s t r a i n r a t e and time t o r u p t u r e f o r undrained plane strain C JT" 6 G  6.4  o  16  S t S  •  o  R e l a t i o n between time t o r u p t u r e  e  a  »  o  t  t  t  t  O  0  o  o  *  o  o  0  c u r r e n t s t r a i n r a t e and . . . . . . . . . . . . . .  1 0  4  105  X  LIST  a  l,2,3  a' K  0  '  Principal  total  stresses  effective  Deviator  Q  t  Elapsed  t  SYMBOLS  Coefficient  o  a  Principal  OF  of earth pressure at rest  stress  (a^ -  Time t o minimum s t r a i n  m  Total  tt  Time t o r u p t u r e  e  Secondary  s  rupture  creep  Minimum  x  Shear  a'  Effective  t^  Time t o f a i l u r e  H  Half  strain  strain rate  stress  the height of  of  specimen  consolidation  u  Pore  A & B  Skempton s  a  Henkel pore pressure  a' m  Mean n o r m a l e f f e c t i v e  x  Octahedral  shear  Octahedral  effective  . oct . oct  rate  stress  Coefficient  v  rate  life  e m  0'  a^)  time  t  c  stresses  pressure 1  pore pressure  parameters  parameters stress  stress normal  stress  XI  Y , 'oct  O c t a h e d r a l shear  strain  Y , .' o c t  O c t a h e d r a l shear  strain  s, (a  Principal strains  0  1  rate  .) oct c  Mean n o r m a l e f f e c t i v e s t r e s s  a t t h e end o f  consolidation (Y  .) oct m  Minimum o c t a h e d r a l s h e a r  strain  rate  xii  ACKNOWLEDGEMENTS  The  w r i t e r w i s h e s t o e x p r e s s h i s most g r a t e f u l  thanks t o h i s r e s e a r c h for  the continuous  research. to  s u p e r v i s o r , D r . R.G. C a m p a n e l l a  quidance during  D r . W.D.L. F i n n  The  a n d D r . P.M. B y r n e f o r r e v i e w i n g t h e  tinued  i n S o i l M e c h a n i c s a t U.B.C. f o r t h e i r  during  interest  gratefully  author  given  In p a r t i c u l a r ,  the con-  b y Mr. Y.P. V a i d i s  i s indebted  t o t h e governments o f  f o r a Commonwealth s c h o l a r s h i p w h i c h  him d u r i n g  The Civil  research.  and a d v i c e  Canada and C e y l o n  the  this  appreciated. The  supported  suggestions.  w r i t e r a l s o wishes t o express h i s thanks t o  colleagues  assistance  of this  He f u r t h e r w i s h e s t o e x p r e s s h i s a p p r e c i a t i o n  m a n u s c r i p t and making v a l u a b l e  his  the course  this  research.  technical assistance  Engineering  Department  s u p p l i e d by t h e s t a f f o f  i s gratefully  acknowledged.  1  CHAPTER I INTRODUCTION  Creep o r continuous ations of earth to sustained Haefeli Suklje  time-dependent  structures, slopes  and f o u n d a t i o n s ,  (1957), S a i t o  (1969).  d e f o r m a t i o n s have g i v e n  (1953), Henkel  long  These time-dependent  shearing  t h e e n g i n e e r many d i f f i c u l t i e s  i n the design  need  term b e h a v i o u r .  f o r research  of slopes,  Therefore,  foundations  no  there  and e a r t h  lateral yield.  laboratory  samples  This  initially  a r e more r e p r e s e n t a t i v e hydrostatically  i s termed K  consolidated  o f many t y p e s o f f o u n d a t i o n walls,  long  frequently  structures  f o o t i n g s , as w e l l take place  under K  conditions  samples.  as c u t s ,  under c o n d i t i o n s  sedimen-  consolidation  consolidation.  consolidated  of field  of clays.  d e p o s i t i o n most  c l a y s t r a t a have undergone v e r t i c a l  reliably  i s an i m m e d i a t e  on c r e e p and c r e e p r u p t u r e  Due t o t h e n a t u r e o f t h e i r tary  reporters.  (1957),  s t r u c t u r e s o f c l a y s o i l s , a s he i s u n a b l e t o p r e d i c t the  deformsubjected  s t r e s s e s , have been o b s e r v e d by s e v e r a l  ( 1 9 5 3 ) , H a e f e l i and S h a e r e r  particularly  shearing  q  with Thus,  conditions  than the u s u a l  Furthermore,  failures  such as r e t a i n i n g fills  and s l o p e s ,  of plane  strain.  2 Thus, the  particular  soil  under the  (1)  (2)  behind  can  b e s t be  K  q  a long  cases centre  simulated  creep  no  rupture  reasons  r u p t u r e was  of a s t r i p  an  sheared  i n the  the  long-term  the  stress  the  stresses)  under  t h a t the  sustained shearing  strain  present  conditions.  study  stability  on  change which  stress. this axial  pressure The  type  of  stress  a b o u t by  leads  has  It i s for strain  problems the  to f a i l u r e  creep  stress  i s another  However, i n  retaining  walls,  i n the  a  minor closely  field  test  c o n d i t i o n i s a creep  i s kept  reducing  aspect  (fills  l a b o r a t o r y t e s t w h i c h most  decreasing  a b o u t by  loading  i s primarily  or a decrease  constant  the  lateral  brought  the  of creep  and  failure  is  At  present  i n which creep  rupture  lateral  stress.  in  stress.  r u p t u r e w h i c h was  Therefore considered  study.  Thus, the effect  plane  o f c u t s , s l o p e s and  is  this  apparatus.  (failure  i n v e s t i g a t i o n s have b e e n r e p o r t e d  in  of  i n which  no  this  use  i n v e s t i g a t i o n s have been r e p o r t e d  in lateral  reproduces  pressure,  strain  s t r u c t u r e s p l a c e d on w e a k e r s o i l s ) .  principal  brought  the  plane  i n c r e a s e i n the major p r i n c i p a l  other  which  earth  and  undertaken.  and  decrease  foundation,  laboratory with  I n many l o n g r a n g e s t a b i l i t y involves  condition of  w a l l under a c t i v e  i n the  been performed under p l a n e these  stress-strain  line  retaining  c o n s o l i d a t e d samples  At present  of  of  (1)  K  investigation  consolidation  herein considers (2)  plane  strain  the condition  3 (3)  total  stress  major p r i n c i p a l a^)  stress  on  paths  of  stress  a^,  the  creep  creep of  and  rupture  i t s simplicity  and  i s the  solidated  and  then  of  is axially  Usually  the  problems  anisotropic  and  are d i f f e r e n t . results  of  answer t o t h i s be can  considered be  rupture  really i n the  symmetric and  actual i n i t i a l  tests  question before  con-  creep  the  meaningful  results  and  equal).  applied to  field  consolidation i s often three p r i n c i p a l to apply  condition?  A  of  stresses  the  definite  i s unknown a t t h e p r e s e n t ,  the  state  intermediate  justification  to f i e l d  but  laboratory t r i a x i a l  as a means o f p r e d i c t i n g  should tests  creep  field.  creep  in this  rupture  same c l a y  used  apparatus  have been r e p o r t e d  rupture  isotropically  always  are  o c c u r s when t h e  I s t h e r e any  S t u d i e s on  investigation  test  because test  During  are  study  "triaxial"  (where t h e  of t r i a x i a l  creep  triaxial  is first  to  apparatus,  In a  loaded.  stresses  where t h e  undrained  apparatus  "triaxial"  soil  axially  results  test  availability.  specimen of  minor p r i n c i p a l  of  principal  clay.  a cylindrical  stress  of i n c r e a s i n g  the minor  behaviour  most commonly u s e d  creep  (comparison  to d e c r e a s i n g  rupture  specimens of a s e n s i t i v e The  loading  reported  tests obtained  study)  i n the by  herein, from  of a s e n s i t i v e conventional  Snead the  triaxial  (1970).  results  In  clay  triaxial the  of Snead s  s a m p l e s have  (the  1  been  creep  4 compared w i t h ever  those  i n a l l of  isotropically  obtained  Snead's t e s t s  a^,  relatively  triaxial  c o n d i t i o n and  s l o p e s and  rupture  possible  time  to p r e d i c t  movements and  thus  the  rupture  specimen then  How-  was  =  by  o"^.  h a v e shown t h a t  foundations  occur  movements.  i s understood,  to f a i l u r e  allow remedial  tests  loaded  with  long p e r i o d of continuous  the mechanisms o f c r e e p  tests.  J  observation of creep  earth structures,  strain  Thus some c r e e p  o as w e l l as d e c r e a s i n g  Field of  plane  s a m p l e s were i n i t i a l l y  i n which the  c o n s o l i d a t e d under K  increasing  the  consolidated.  were a l s o p e r f o r m e d first  from  and  during  failures  after  a  Therefore i f i t should  be  pre-failure  s a f e t y measures  to  be  taken a c c o r d i n g l y .  The of  possibility  slope f a i l u r e  (Saito, ered  1965;  in this  strain  i n the  of p r e d i c t i n g  field  u s i n g the  S n e a d , 1970), w i t h study.  d a t a was  The  time  available  of  occurrence  methods  l a b o r a t o r y d a t a , was  p r e d i c t e d times  compared w i t h  the  those  from  consid-  obtained  from  triaxial  data.  plane  5  CHAPTER 2  LITERATURE  This information emphasized  literature  REVIEW  review w i l l  present the pertinent  on c r e e p and c r e e p r u p t u r e . that  I t h a s t o be  no i n f o r m a t i o n i s a v a i l a b l e  a t p r e s e n t on  c r e e p and c r e e p r u p t u r e b e h a v i o u r  of K  which deformed under p l a n e  conditions with the creep  deviator  stress  decreasing is  .  being applied As t h e need  d e m o n s t r a t e d by f a i l u r e s  observation of creep review w i l l  1.  by e i t h e r  of creep  o f f o u n d a t i o n s and s l o p e s ,  field  and  and c r e e p  literature  failures.  studies.  O b s e r v a t i o n o f C r e e p and Creep  Failures  observations of creep  i c e were r e p o r t e d b y H a e f e l i  Shaerer  The  i n s e c t i o n s as f o l l o w s s -  observation of creep  Many f i e l d  or  f o r better understanding  2. C r e e p a n d c r e e p r u p t u r e  Field  increasing  a l s o h a s t o be d i s c u s s e d .  be p r e s e n t e d  Field  strain  c o n s o l i d a t e d samples  q  (1953).  (1953) h a s d e s c r i b e d i n d e t a i l  i n soils,  snow  H a e f e l i and  the e f f e c t  on  an abutment  of a bridge.  in  a reinforced  c o n c r e t e b r i d g e , were c a u s e d  of creep  S e v e r a l cracks which by s o i l  appeared creep  which r e s u l t e d horizontal ment.  stiffening  o f one o f t h e a b u t m e n t s .  beam was b u i l t  to r e s i s t  A measuring d e v i c e , which permitted  creep  p r e s s u r e was  observed with  i n movements  time  fitted  that the creep from  beam.  continuously  1944 t o 1950, e x c e p t  for  move-  the recording of  to the s t i f f e n i n g  pressure  this  A  I t was  increased  some  seasonal  fluctuations.  Long  term f a i l u r e s  of a retaining  w a l l and a c u t -  ting  i n L o n d o n c l a y were d e s c r i b e d by H e n k e l  site  of the c u t t i n g  he r e p o r t e d t h a t s u b s t a n t i a l  as w e l l as t e n s i o n c r a c k s observed site  wall,  a few months b e f o r e  failure  along  described  by S u k l j e  failure  the  a discontinuous  slide  over  the Gradot Ridge (1956).  a l e n g t h of about  before to  failure  the lower  have s u b s i d e d  weeks b e f o r e  20 cm.  failure.  A t the  Along  series  30 y e a r s  after  long  term  creep  i n 1956  was  the upper boundary o f  o f d e e p c r a c k s were Cracks  before  of over  failure.  subsidence  formed  30 f t i n One  b o u n d a r y o f t h e c r a c k s was Further  was  occurred.  i n Macedonia  270 m e t r e s .  d e p t h had been measured  occurred.  were  3 f t movement o f t h e w a l l  A l a n d s l i d e which o c c u r r e d movements  At the  movements  near the top o f the slope  s e v e r a l months b e f o r e  of the r e t a i n i n g  observed  (1957).  year  observed  appeared  some  7 Saito  and  Uezawa  many l a n d s l i d e s a l o n g Measurements o f the  top  of  several they  the  days b e f o r e  It that of  failure  time.  plane  of  by  failure  i s evident often  be  used  may  be  less  pression and  ments a t  described  be  mechanisms o f attempted  long  period  plane  by  strain  and  creep,  the  remedial  There-  prediction  and  safety  Studies  by  Casagrande  and  Wilson  undisturbed  deform under  strength  test.  For  applied  short  above.  approximated  sustained  i n d i c a t e d by  the the  sustained deviator  load,  intervals  common i n t e r v a l .  After  of the  time,  load  and  and  clay  that  appreciably  a normal undrained  loading  load  (1951) h a v e  clays  u l t i m a t e l y o c c u r s under a s u s t a i n e d  Wilson  measurements  t h e s e c r e e p movements.  some t y p e s o f b r i t t l e  than the  Uezawa  accordingly.  continuously  failure  at  failure.  laboratory  study  the  Investigations  shales  and  cracks  From t h e s e  time to  The to  Creep Rupture  shown t h a t  Saito  occurred.  t h e s e movements c a n  time to f a i l u r e  C r e e p and  by  of  tracks.  the  o c c u r s a f t e r movements o v e r a  understanding  measures taken  occurrence  Japanese r a i l w a y  from o b s e r v a t i o n s  conditions.  apparatus could fore,  on  were r e c o r d e d  to p r e d i c t the  Most o f  strain  cuttings  the  t i m e d e p e n d e n d e n t movements o f slopes  attempted  (1961) r e p o r t e d  case,  i n four  Casagrande  to eight  1 minute being  d e v i a t o r i c l o a d was  com-  the  incremost  applied  to  8 the  sample  i t deformed w i t h  means t h a t time. tion  the  stress  F a i l u r e was i n the  deformation  on  the  a t an  increasing  they d e f i n e d time  tion  i n the  they in  (1)  l o a d , and  the  (2)  t o the  the  plastics  into  with  inflec-  Shear c r a c k s i n the the p o i n t of place.  the  For  inflection these  reasons,  e l a p s e d time between  increment curve.  and  this  point of  For Mexico C i t y  to f a i l u r e  increased with  time  the inflec-  clay,  decrease  t o f a i l u r e was  linearly  stress.  s t r a i n - t i m e curve  f o r metals,  i s shown i n F i g u r e 2.1.  I t has  concrete  been s u b d i v i d e d  s t a g e s by many r e s e a r c h e r s .  These  stages  follows:-  1.  Instantaneous  deformation  2.  Primary  stage  Creep  3. Secondary creep 4.  Tertiary The  elastic t o as  continuous  l o g of the  applied  four separate  a r e as  f o l l o w e d by  as  This  slightly  a p o i n t of  took  load  time  i t s area.  by  after  curve  final  A typical and  shortly  time-deformation  found:  related  preceded  rate.  to f a i l u r e  o f the  increasing  sample d e c r e a s e d  Strain-Time curve  time-deformation  application  the  invariably  s a m p l e s were o b s e r v e d in  time,  and  the  creep  from  stage stage  0 to e . o t  from from  to t ^ .  Q  t ^ to t . 2  t  2  to t .  instantaneous deformation  plastic  initial  deformations  elastic  r  consists  although  deformation.  of  both  i t i s often  Primary  creep  referred i s the  9  FIGURE  21  A  TYPICAL FOR CAFTER  CREEP  METALS,  RUPTURE  CONCRETE  CURVE AND  GAROBALO, 1965".)  PLASTICS.  "";  10 stage  during  while  the  rate  the  strain  secondary creep  i s nearly  stage ing  which  during  to creep  constant.  which  the  rupture.  have b e e n o b s e r v e d  rate  i s continuously  i s that during The  strain  tertiary rate  which the  creep  S a i t o and  increases  Uezawa  strain  i s the  final  gradually  S i m i l a r s t r a i n - t i m e curves  by  decreasing  (1961) f o r  lead-  for clays triaxial  tests.  Vialov of  creep  and  i n frozen  Skibitsky  soils  been f r o z e n  i n the  deformation  initially  gradually  to  Skibitsky  showed  defined not  as  cause  failure,  the  the  f a i l u r e with  that  consolidated the  the then,  not  find  concluded  strain  a stage  have o c c u r r e d .  creep  undisturbed  then  Vialov  of increased and  strength  s t r e s s which would  t e s t s on  i s given  triaxial i n Figure  confirmed  the  called  2.2.  He  rate  failure  existence  observed  He  could  constant.  i s reached, can  A  a minimum,  to rupture.  r a t e remained  and  undrained  apparatus.  decreased, reached  strain  rupture  a  sensitive clay,  conventional  when t h e  He  2.1.  shearing  gradually proceeding  eventually  and  o f a upper y i e l d  t h a t , o n c e a minimum s t r a i n  sample w i l l  rate  had  time.  rate i n i t i a l l y  increased  t h a t the  shown i n F i g u r e  effect  rods which  to a constant  existence  s t r a i n - t i m e curve  and  to  decreased as  shear along  They o b s e r v e d  (1970) p e r f o r m e d  Haney c l a y , u s i n g typical  b a s e d on  maximum s u s t a i n e d  Snead normally  soil.  (1957) i n v e s t i g a t e d t h e  be of  He  the  considered an  upper  O I O  " SOO  1  1  1  ISOO  IOOO  —  2000  1  25*00  ELAPSED TIME  FIGURE2-2  A TYPICAL  STRAIN - TIME  CONSOLIDATED .DEVMTOR  HANEY  CURVE CLAY  STRESS. C A F T E R  FOR NORMALLY  UNDER  S N E A D , 1970.)  SUSTAINED  12 yield  strength  strength This ing by  f o r Haney c l a y w h i c h was a b o u t  obtained  indicates that  samples c o u l d  stresses appreciably a standard  rate  tests with  43.4  o f 75 P S I .  reached  to rupture. be  deviator  it  was o b s e r v e d  on  this  rate  stress. that  the locus  versus  failure  shearing  hydrostatic  stresses greater  initially  the s t r a i n  increased stages  r a t e deproceeding  o f creep  can not  increases  with  and t h e  the decrease  results  of a l l points  having  obtained a minimum  s t r e s s l i e on a s t r a i g h t  log t plot.  than  rapidly  The t i m e t o f a i l u r e  rate  a series  apparatus. A l l  From t h e e x p e r i m e n t a l  f o r a given  log  was f o u n d  plot.  minimum s t r a i n  in  strain  that  creep  P r i m a r y and s e c o n d a r y  time t o reach  sustained  t o an e f f e c t i v e  a minimum t h e n  d i s t i n g u i s h e d on t h i s  shear-  indicated  2.3 b y p e r f o r m i n g  triaxial  For deviator  P S I , i t was o b s e r v e d  creased,  the strength  varying  the conventional  s a m p l e s were c o n s o l i d a t e d pressure  under s u s t a i n e d  test.  the l o g - l o g p l o t of s t r a i n  and t i m e , a s shown i n F i g u r e  stresses using  fail  loading  test.  (1970) o b t a i n e d  creep rupture  incremental  l e s s than  laboratory  Snead  of  from a s p e c i f i e d  82% o f t h e  The E q u a t i o n  of this  line line  to be:-  log  where t  1 Q  =  t = - .142 - 1.15  elapsed in  log  time u n t i l  minutes.  1 Q  e  m  ± .116  . . .  t h e minimum s t r a i n  2.1  rate  13  -f-  'o°  POINTS  DENOTES  io'  O F  MINIMUM STRAIN RATES  zo  a  ELAPSED  FIGURE  TIME  LOGARITHM  2 3  /o*  i d  (M/N)  OF AXIAL  STRAIN  RATE  VFRSUS t  LOG  Hl^PSED  ^DRAINED  TIM£  CREEP  FOft  TESTS  NORMALLY ON  HANEY  CONSOLIDATED CLAY. (AFTER SNEAD, 117$  em - minimum s t r a i n obtained  o f minimum  stress the  strain  strain  rate-time  rates  curves  imposed  parallel  consolidated  rates  below t h e l i n e  towards t h i s  line i f  b u t changes  deviator  that  t h e sample s h o u l d  never  towards  i t s c o u r s e and  t o t h e l i n e o f minimum s t r a i n  stresses illite,  below t h e upper y i e l d  Campanella  rates.  fail  Thus  under the  were r e p r e s e n t e d of strain  straight  lines  Mitchell  (1968)  minimum s t r a i n  plot  f o r stresses  S i n g h and M i t c h e l l  straight  lines  lines  on a l o g - l o g 2.4.  long  and  i n creep rupture  the slope  "m"  that  of these  times, whether t h e s t r a i n  increasing  rates  eventually  result-  (m <_ 1) .  I t was o b s e r v e d investigators  till  above upper  almost cease, continue a t ever decreasing start  Parallel  by S i n g h a n d  f o r stresses  (1969) u s e d  strain  of the t e s t ,  below t h e upper y i e l d  to predict after  (m > 1) o r i n some c a s e s  strain  were p r e d i c t e d  r a t e was r e a c h e d  yield.  r a t e s may  straight  and t i m e a s shown i n F i g u r e  on t h i s  that  f o r the duration  by p a r a l l e l  rate  strength f o r  (1965) o b s e r v e d  r a t e was c o n t i n u a l l y d e c r e a s i n g  the  start  stresses.  For  ing  considered.  o f 42.8 P S I t h e c u r v e a p p e a r s t o be p r o c e e d i n g  was p r e d i c t e d  plot  are  F o r t h e sample w i t h a  l i n e o f minimum s t r a i n  and  p f e r m i n u t e and ± .116 was  and p r o c e e d  i s t o take p l a c e .  continues it  i n tpercent  when 95% o f t h e d a t a p o i n t s  All  failure  rate  by S n e a d  (1970) a n d s e v e r a l  o n c e t h e minimum s t r a i n  r a t e began t o i n c r e a s e  r a t e was  other  reached,  and t h e sample was bound t o  15  .ooooi l  •2  l  I  I  I  l  I  S  I  2  «5  10  20  ELAPSED  FIGURE  24  LOG SATURATED  STRAIN  I  I  100  I  I  200  TIME-fM/N.)  RATE  I LL/TE  VERSUS (AFTER  LOG  TIME  CAMPANELLA,  J  '  FOR  0  0  °  fail.  Snead u s e d  a failure  t h e e x i s t e n c e o f a minimum  r a t e as  criterion.  Saito  and Uezawa  (1961) p r o p o s e d  ship' between t h e l o g o f s e c o n d a r y of  strain  the t o t a l  compression  time  to rupture.  tests  relation-  r a t e and t h e l o g  They performed  on f o u r J a p a n e s e  soils  triaxial  and t h e i r  those  Figure  T h i s F i g u r e shows t h e e r r o r b a n d c a l l e d  confidence equation Saito  limits  investigators,  results  together with 2.5.  of other  strain  a linear  e n c l o s i n g 95% o f a l l d a t a  of the s t r a i g h t  line  a r e shown i n  points.  95% The  i n F i g u r e 2.5 was o b t a i n e d b y  and Uezawa t o be  log  1 Q  t  r  = 2.33 - .916 l O 9 "  £ 1 0  s  . . . »  2.2  -4 e t  secondary  g  total  r  It obtained  from  solidation  rupture  different  history  r a t e expressed  i n 10  per minute  life.  i s important  Equation equation  strain  t o note  types  that Equation  of s o i l s ,  stress  2.2 h a s b e e n levels,  con-  and d r a i n a g e c o n d i t i o n s . 2.2 was  simplified  2.3 b y a p p r o x i m a t i n g  by S a i t o and Uezawa t o  .916 l o g ^ g  e  g  as e q u a l t o  9  log,,, e . ^ 10 s  t  Thus,  r  The natural  • e  s  = 216  Equation  s l o p e s and f u l l  . . . .  2.3 was scale  a p p l i e d by S a i t o experiments  during  (1965') t o secondary  2.3  17  FIGURE  2S  RELATIONSHIP LIFE  AND  STRAIN  8E-TWEEN  RATE  CREEP  RUPTURE  (AFTER 3AITO <S.UEZAWA,\%l)  18 creep of  stage.  occurrence  w o n d e r s why  predicted with  of  slope f a i l u r e  S a i t o was  occurrence triaxial  He  of  conditions.  by  from  t e s t s w h i c h do  e  was  possible  c a n c e l l i n g - o u t of opposing  g  empirical relationships  cation.  I n any  could  a n s w e r e d by  be  event  measured  hoped  the r e s u l t s  One  the u s u a l  of  field  limits  or  Perhaps  theoretical  t h a t some o f  of  field;  inaccuracies?  of the  time  conventional  i n the  hold without  i t was  of  time  2.3.  the wide c o n f i d e n c e  t h e way  the  i n which  simulate  ± 500%;  the  a c c u r a t e l y the  the r e s u l t s  not  Is i t because of  accuracy  using Equation  able to p r e d i c t  slope f a i l u r e  creep  reasonable  these  investigation  justifiquestions reported  herein.  Snead not  exist  strain equal  r a t e m e a s u r e d by  observed  2.6.  and  of the  total  lines  line  by  between the rupture  life  shown i n F i g u r e 2.6.  straight  line  i n F i g u r e 2.6  t  total  rupture  e  minimum s t r a i n  log, ^10  m  n  life  Snead  logarithm as  shown i n  relationship with  also  - .92  in  ±  did  secondary  him.  are  .751  stage  approximately  rate calculated  the  creep  t h a t the  Uezawa was  relationship  r a t e and  log,„ t = ^10 r where  suggested  Uezawa's s t r a i g h t  confidence  equation  t h a t a secondary  S a i t o and  a linear  minimum s t r a i n  Figure 95%  f o r Haney c l a y ,  t o t h e minimum s t r a i n  (19 70) of  (1970) f o u n d  Snead's  i s given  .272  the  by  . . . .  minutes.  r a t e percent per  minute.  2.4  19  fo°  io -  10'  3  TOTAL  FIGURE  2.6  TOTAL  CREEP  TESTS  RUPTURE  /o  LIFE  R U P T U R E LIFE (AFTER  /o*  3  SNEAD,  (MIN-)  OF  LABORATORY  19 70.)  20 The  95%  those  confidence  obtained  suggested "e "  is  s  for  by  by  limits  S a i t o and  Snead  similar  a l l soils  as  before  to slope tertiary  (1970) t h a t t h e soils  suggested  by  failure creep.  a method o f p r e d i c t i n g for as  tertiary the  and  creep  elapsed  obtained  rupture 2.7.  Snead  .23  time  instant  "t "  occurrence  other  time  a  constant.  hand  proposed  "time  to  till  failure rupture"  failure  l o g o f time  e, a s  to  shown i n F i g u r e  below  . . . .  2.5  i n minutes rate i n percent  a was  to t t  stages  to slope  - a log-^Q £  current strain  and  unique  the  considered  rate,  to rupture  reduced  of  between  i s given  e  equation  the  Snead d e f i n e d the  relationship  =  was  between  necessary  than  Uezawa.  (1970) on  the o c c u r r e n c e  obtained  tt  where t t  Thus, the  not  S a i t o and  current strain  equation  0  therefore i t  relation  but  smaller  been a p p l i e d f o r c r e e p  from the  a linear  log^  has  stage.  time  " t t " and  The  are  (1965) method o f p r e d i c t i n g  1  time  Uezawa and  for other  Saito s of  f o r Haney c l a y  found  t o be  per  minute  =1.  17 = —^—  . . . .  2.6  e  Saito slope  failure  (1969) a l s o p r o p o s e d  during  tertiary  assumed a r e l a t i o n s h i p b e t w e e n Equation  2.6,  t o o b t a i n an  creep.  a method  predicting  I n t h i s method  " t t " and  expression  for  "e"  similar  for strain  by  he to  mathematical  21  IO |  10°  I  1  1  10' TIME  FIGURE  2-1  RELATIONSHIP CURRENT  STRAIN  1 10* TO  1  1  'o  1  3  RUPTURE  BETWEEN RATE  - MINAS  1  io*  TIME To  (AFTER  1  RUPTURE  SNEAD, 1970.)  I  so*  AND  22 integration.  He  found  dicted  and  observed  Stress  - Strain  gation  of available  and  strain rate  independent written  time  Rate  (1961) s u g g e s t e d  - Strain Relationship  that  a relation exists  f o r metals  form  stress  e  current  strain  e  current  strain  1.  the  over  This  strain  which i s  r e l a t i o n can  be  t h i s concept  to s o i l s ,  but  conditions:-  same c o n s o l i d a t i o n  history  and  consolidated.  Undrained.  3. C o n t i n u a l l y 4. C o n s t a n t investigated  relation strain  stress,  temperature  t o the f o l l o w i n g  not h e a v i l y  Snead  between  Felgar  rate.  (1970) e x t e n d e d  Sample h a v i n g  2.  history.  at constant  current  i t s use  Upon i n v e s t i -  of  s  Snead  -  pre-  failure.  at constant temperature  s t r a i n rate  s = f ( e , e)  restricted  of occurrence of slope  r e s e a r c h on m e t a l s , L u b a h n and  of the  i n the  r e a s o n a b l e agreement between the  by  as  compressive  axial  strains.  temperature. the v a l i d i t y  plotting  controlled  Haney c l a y  increasing  of the a p p l i c a t i o n  the d a t a of the  tests  on  2.8.  this  incremental loading  normally consolidated  shown i n F i g u r e  of  Along  and  undrained  the c u r v e s o f  strain  23  2  2  13  I  I I h Q? J X  - 4  - 6  /  A X I A L  FIGURE  2.8 FOR  AXIAL  STRAIN  NORMALLY  CONVENTIONAL  2  -4  STRAIN  RATE  TRIAX/A L  PERCENT  VERSUS  ODNASOLIDATED  20  IO  6  AXIAL  HAMEY  STRAIN  CLAY  APPARATUS. C ^ T E R  CURVES USING  SNE^^TQ)  controlled stress  a  creep  and  strain  Figure  incremental  at that strain  D  the  tests.  and  tests  r a t e are given, while  independent  a g r e e m e n t was  This concept  and  strain  the v a l u e s of d e v i a t o r  the constant d e v i a t o r s t r e s s  A reasonable  histories  and  r a t e s h o u l d be  2 . 8 .  loading tests  found  t o be  was  of the  checked  t h a t the c o n s o l i d a t i o n h i s t o r i e s  of  tests  namely c r e e p  Snead accuracy and  the  Snead a  functional  but  (1)  f o r any  dated  performed  was  is this  one  by  (2)  o f one  hypothesis  by  of the  f o r plane  ( 3 ) when t h e  and  increasing reasons  undertaken.  using data  why  type  of path  strain  shear  0  rate from  attempt  between, s t r e s s  consolidation stress  samples  triaxial  is  But  three  should types  loading test,  for strain  d i d n o t make an  relationship  of the  It  strain  p o s s i b l e to p r e d i c t with  curve  loading tests  p r e d i c t e d the behaviour  another.  incremental  showed i t was  (1970)  shown i n  same.  stress-strain  incremental  as  agreement.  noted  t e s t s were t h e  him  of  f o r other c o n s o l i d a t i o n  be  controlled  strain  three types  o b t a i n e d by  i n reasonable  tests,  a t any  for  Q  and  =  as  based  rate, upon  valid  for K  q  consoli-  c o n d i t i o n s as w e l l  tests  and  creep  tests  as w e l l as d e c r e a s i n g 0 ^ ? this  tests.  evaluate  strain  f ( e , e)  such  controlled creep  to  of t e s t  reasonable  investigation  on  creep  as are This  rupture  25 Analysis  of  Creep  i n Terms o f  data obtained  from u n d r a i n e d  not  generally  been a n a l y z e d  for  the  1.  The  following  and  sentative  of  restraints  Creep  stress controlled tests i n terms o f  in obtaining  the  of  have  effective stresses,  accurate  and  reliable  hence e f f e c t i v e s t r e s s e s which are e n t i r e sample.  the  loading  uniform pore pressures just  -  reasons:  difficulty  pressures  E f f e c t i v e Stresses  platens  also questionable,  and  may  since  cause c o r r e s p o n d i n g l y  pore pressures  the  example,  often  throughout  p r i o r to creep rupture  are  For  the  cause  the  high  non-  rates  rates  giving non-equalization  Also  pore  strain  of  of  repre-  end  sample.  recorded  pore  pressures are  large  change  in  pore  pressures.  2.  I t has  been  pressures often  in  which  strain  decrease,  rate  should of  sustained  shearing  the  same sample has  not  be  hardening explained  pore  stresses  in effective  cause a l o s s i n s t r e n g t h .  this  which can  been found  and by  Yet to  a possible  gain  considering  stresses.  When an consolidated  investigators that  r e s u l t i n g i n a decrease  indicating strain  strength  effective  several  i n a sample u n d e r  increase,  stresses, the  f o u n d by  undrained  triaxial  s e n s i t i v e c l a y was  specimen of  subjected  to  normally  sustained  shear-  26 ing in  s t r e s s e s , i t e x h i b i t e d a steady pore p r e s s u r e .  (1969) a n a l y z e d  Snead  this  time-dependent  (1970), Walker  behaviour  increase  (1969).  Walker  i n t e r m s o f an e f f e c t i v e  stress-strain  relationship.  the  s t r e s s s t a t e i n t h e sample c h a n g e d w i t h  effective  towards t h e f a i l u r e  Shibata special  drained  envelope  and Karube  creep  was  practically  and  overconsolidated  water content. and data the  Undrained  on u p p e r y i e l d  Figure  (1969) p e r f o r m e d during  s t r e s s concept.  value  strength  1  The  and a n a l y z e d The " y i e l d  on  value"  t e s t was f o u n d  shearing  resistance obtained  lines  with  ' a s shown i n  slope parameter Y  ' measured by  t e s t was s e e n t o be a v a r i a b l e from t h e f i r s t  m e a s u r e d by t h e d r a i n e d  strength  increment t o creep  t o be c l o s e t o t h e maximum a n g l e o f  Walker  from normal compression  (1969), S h i b a t a  h a v e made an a t t e m p t t o s t u d y terms o f e f f e c t i v e  consolidated  c o n s o l i d a t e d c l a y p l o t t e d on x - a'  The s l o p e Y^  Therefore  initial  on n o r m a l l y  s t r e n g t h were p r e s e n t e d  The y i e l d creep  consolidated  t h e same  o f c ' c o t y ' on t h e a x i s a n d s l o p e Y  undrained  last.  tests  content  c l a y s a m p l e s were a l s o p e r f o r m e d .  d e p e n d i n g on t h e t i m e o f l o a d i n g the  on n o r m a l l y  s y s t e m was a p p r o x i m a t e d b y s t r a i g h t  2.9.  time  a series of  which t h e water  constant,  creep  b a s i s o f an e f f e c t i v e  intercept  creep  f o r the c l a y .  c l a y samples h a v i n g  envelopes o f normally  the  tests,  maintained  overconsolidated  co-ordinate  He showed t h a t d u r i n g  stresses.  the r e s u l t s  and Karube of creep  tests.  (1969)  tests i n  27  oa  O-f  2 9A  FIGURE  THE  0-6  0-2  FIGURE  OF  I  04  29 B  I  12. 1-4-  OF  16  YiELD  EFFECTIVE  SHIBATA  CAFTER  O  »0  A/VMLYVS/S  e^SlS  J  0-8  I  0-6 0 8  STRESS  AND  1  '0  (AFTER  CONCEPT.  KARUBE,  1  1  1-2  I-+  INFLUENCE APPLICATION  ON  VALUE  iq&)  L  IC  OF OF  SHl&AT/\  RATE  THE ANX>  YIELD  OF  STRESS VALUE.  KARUBE,  28 Summary  1. A t p r e s e n t no i n v e s t i g a t i o n taking  into  (b) p l a n e loading  account  strain  the e f f e c t  condition  (comparison  and  that  (a) K  of  (c) t o t a l  of increasing  type o f creep t e s t s ) . review  o f c r e e p r u p t u r e has been q  done  consolidation  stress  paths o f  and d e c r e a s i n g  I t was d i s c u s s e d i n t h e l i t e r a t u r e  t h e above c o n d i t i o n s a r e o b t a i n e d i n t h e f i e l d  c a n be s i m u l a t e d i n t h e l a b o r a t o r y b y u s i n g a p l a n e  strain  apparatus.  above t h a t  I t i s because  t h e s t u d y on p l a n e  o f the reasons  strain  outlined  c r e e p r u p t u r e was  undertaken.  2.  In a v a i l a b l e ment t h a t the time tained  3.  literature  to failure  shearing  sensitive  shearing indicated  tests  there i s agree-  f o r samples under s u s t a i n e d s h e a r i n g increases with the decrease  by s e v e r a l  o r remoulded  stresses  clays  investigators failed  appreciably less  by a s t a n d a r d l a b o r a t o r y  investigators  stresses, i n sus-  stresses.  I t has been o b s e r v e d of  on t r i a x i a l  that  under s u s t a i n e d  than shear  the strength test.  These  h a v e showed t h e e x i s t e n c e o f a u p p e r  o r maximum c r e e p  s t r e s s which w i l l  samples  n o t cause  yield  failure  with,  time.  4. The e x i s t e n c e o f a minimum s t r a i n (1970) a s a f a i l u r e  criterion.  r a t e was u s e d  by S n e a d  5.  Snead  (1970) o b s e r v e d  strain  rates  undrained  the existence  f o r normally  i n the t r i a x i a l  minimum s t r a i n  rates  was  of a l i n e  o f minimum  consolidated  samples  apparatus.  This  used  tested  line  by S n e a d a s a  of  failure  criterion. 6. Snead  (1970) h y p o t h e s i z e d  s a m p l e s o f Haney  clay with  that  = f ( e , e) f o r t r i a x i a l  t h e same i n i t i a l  f o r d i f f e r e n t types of t e s t s  (i.e.,  mental  rate  loading  tests).  tests, strain  creep  conditions  tests,  controlled  A l l s a m p l e s s h o u l d be t e s t e d for continually  shear  undrained  stant  temperature  axial  s t r a i n s , and t h e s a m p l e s n o t h e a v i l y  incre-  increasing  at  con-  compressive  overcon-  solidated.  7. S a i t o ' s creep  (1965) method  and S n e a d ' s  tertiary  creep  f o r creep  (1970) and S a i t o ' s  s t a g e were  the p r e d i c t i o n o f the time shearing  8. A l t h o u g h  of  total  the only to slope  tertiary  (1969) methods f o r  methods failure  available for under  sustained  stresses.  a few i n v e s t i g a t o r s h a v e a t t e m p t e d  the r e s u l t s o f creep studies  stage before  i n terms o f e f f e c t i v e  o f c r e e p has been m a i n l y stresses.  to  study  stresses,  investigated  i n terms  30  CHAPTER  3  LABORATORY TESTING  Development o f a T e s t i n g  Programme  This  restricted  undisturbed K  o  o  Haney c l a y .  c o n d i t i o n was  laboratory K  s t u d y was  about  The p r e c o n s o l i d a t i o n p r e s s u r e 60 P S I as d e t e r m i n e d  consolidation  test.  consolidated to a v e r t i c a l  the  testing  programme  to normally consolidated  Therefore effective  i n order  by a •*  standard  a l l s a m p l e s were  stress  t o ensure  under  o f 75 P S I i n  that the c l a y  was  normally consolidated. The following  testing  series  1. K , n o r m a l l y  (major  increment, This  type  was  2. K  q  principal  while  creep  will  t o include the  rupture  tests?  samples, wherein stress  the l a t e r a l  of test  a^)  was  the v e r t i c a l  i n c r e a s e d i n one  p r e s s u r e was k e p t  be c a l l e d  a creep  test  constant. i n which  increased.  , normally  stress  of undrained  consolidated  q  stress  programme was p l a n n e d  (minor  increment  c o n s o l i d a t e d samples, wherein principal  while  stress  the v e r t i c a l  a^) was  the l a t e r a l  reduced  s t r e s s was k e p t  i n one  constant.  This type of test w i l l be c a l l e d a creep test i n which a.j was decreased. The above l i s t e d undrained creep tests i n the laboratory can have p r a c t i c a l significance situations.  i n several  field  If a thick layer of clay having low permeability  and a long drainage path was subjected to sustained  shear-  ing stresses, the drainage would be very small even over a considerable period of time.  This condition can be simulated  in the laboratory by performing undrained creep t e s t s . most f i e l d conditions,however,  In  there i s p a r t i a l or f u l l  drainage after a considerable period of time.  These conditions  can only be handled i n the laboratory by considering both undrained and drained states.  But t h i s investigation on creep  rupture was r e s t r i c t e d to only the undrained drainage c o n d i t i o n . increased and rj^ decreased types  Further, a comparison of  of creep test could be done only i f both types of tests are run under undrained conditions.  Temperature  -  Temperature fluctuations during undrained  tests on saturated samples has a marked effect on observed pore pressures  (Campanella  and M i t c h e l l , 1 9 6 8 ) .  These pore  pressure variations may cause s i g n i f i c a n t v a r i a t i o n of the strength of the samples. Campanella and M i t c h e l l  M i t c h e l l and Campanella ( 1 9 6 3 ) , (1968),  M i t c h e l l , Singh and  Campanella (1969) have also i l l u s t r a t e d the influence of  32 temperature  on s o i l  creep.  temperature  Therefore  in  a constant  by  means o f an a i r c o n d i t i o n e r .  Reference  Tests  -  undrained  incremental  enclosure, maintained  I t was  necessary  loading test  s t r e s s which would cause c r e e p samples. thesis load  An i n c r e m e n t a l  as a shear  test  i s maintained  takes  place  decreased  loading test  the "incremental  failure  place  takes  Description  of Soil  The  clay  this  clay  a piano  0.5  in  consolidated  i s defined i n this  For the case  loading test" PSI e v e r y  4^- t o 5  so t h a t  failure  when  is  i s performed  10 m i n u t e s  so t h a t  hours.  used  in this  testing  programme was  Columbia.  Block  o f about  3 feet  square  ^- c u b i c  an  by 2 f e e t  undisturbed  depth.  and in  given a moist  of 1 f t . length, 5 i n . width  5 o r 6 c o a t i n g s o f wax. room u n t i l  required.  Blocks  f o o t i n s i z e were c u t w i t h  T h e s e b l o c k were w r a p p e d i n t h e f i e l d  smaller blocks  obtained  samples  s a r a n wrap, t r a n s p o r t e d t o t h e l a b o r a t o r y where t h e y into  by  Tested  of approximately wire.  standard  the d e v i a t o r i c  c l a y were c u t , by d i g g i n g a p i t a r o u n d  volume o f c l a y of  q  10 m i n u t e s  f r o m an o p e n p i t i n Haney, B r i t i s h of  of K  a  i n which the r a t e o f a p p l i c a t i o n o f  i n 4— t o 5 h o u r s .  by a b o u t  to estimate  performed  a t 21°C ± .5°C  to perform  rupture  a t 1 K G every  decreasing  a l l t e s t s were  with were c u t  4 i n . height  The b l o c k s were  stored  33 This been used  (1966),  Snead  (1970).  Gupta  Snead  a sensitive  of  I t has  about  I n d e x = 18%. and  has  obtained  60  PSI.  The  in  Table  I.  Description  of  the  important  the  plane  will  be  structure.  46%  clay  liquid  (%  The  and  limit  o f about  f r o m a one  12.  of  Byrne  and  44%  apparatus  details  tests,  designed The  will  K  q  triaxial  main  a  explained.  Plasticity state  consolidometer  in This  are  used  in this  the  K  summarized  study  (196 8 ) .  Only  using  (Campanella q  was  In a d d i t i o n t o  were p e r f o r m e d  apparatus  was  Study  discussed here.  features of  and  The p r e c o n s o l i d a t i o n  d e s c r i b e d by V a i d  four tests  the  (1966)  undisturbed  diminensional  be  rain  a n a t u r a l water  and  i n the  by  in a  p r o p e r t i e s of  by  has  (1966),  (1968)  leached  > 2y)  main p i e c e o f apparatus  strain  also  Byrne  Vaid  subsequently  the A p p a r a t u s Used  strain  19 7 0 ) .  Haney c l a y  p h y s i c a l p r o p e r t i e s o f Haney c l a y  The  specially  (1967),  I t i s medium s t i f f  pressure  Vaid,  41%,  a sensitivity  the plane  Lou  a t TJ.B.C.  have been d e s c r i b e d i n d e t a i l  (1970) .  content  (1967),  e n v i r o n m e n t and  water causing tests  others  known as  I t i s b e l i e v e d t o have been d e p o s i t e d  glacial  clay  which i s l o c a l l y  f o r r e s e a r c h by  Hirst  post  clay,  triaxial  a  and apparatus  34  TABLE  PHYSICAL  Specific Liquid  PROPERTIES  OF  HANEY  I  CLAY  Gravity  2 . 8 0  Limit  Plastic  44%  Limit  Plasticity  26%  Index  18%  Natural  Water  Content  Percent  Finer  than  2  4 1 . 5  Microns  Activity  1%  46%  0 . 4 %  Undisturbed Strength  Unconfined  PSI  Compressive  Sensitivity Past  Compressive 1 0 . 8  Remolded U n c o n f i n e d Strength  Maximum  ±  0 . 9  PSI  1 2  Pressure  6 0  PSI  35 Plane this of  study  soil  in. it  S t r a i n Apparatus was  (Figure  height to  a  4  plates  thick  of  tudinal plates  and and  lateral  was  plane  the in  lateral  layout  of  Figure  3.2.  through  steel  and  by  load  equipment from  the  loading  yoke,  load  rectangular  loading  cap.  The  diaphragm  load  K  q  and  and  to  yield  in  perspex  through  by  2~  principal water  chamber. in  rigid  prevented  to  subject  measured  consolidation  were  2  flexible  not  applied  lateral  diaphragms  loading The  The  using  in  specimen  lateral  backed  constant  independently  pressure  motion  yield  The  was  During  the  vertical  i n . width  lateral  by  used  end  both the  volume  of  water  stresses  on  the  this  longend  in  the  diaphragms.  vertical  the  (no  stress  a  1  apparatus  rectangular  lateral  sample a  a  shear.  deformations  maintaining  controlled  no  strain  perspex.  pressure  The  of  during  to  strain  length,  automatically  lateral by  plane  in.  longitudinal principal but  the  consolidate  diaphragms  apparatus  were  of  applied  rubber  to  of  direction)  was  The  conditions  condition  stress  The  3.1)  under  longitudinal  filled  designed  -  by  two  vertical cell  means  of  i s given  cell,  rod  load  measured  fully  is  active  by  and  schematic (1968)  transmitted rod  was  ball  The  in Vaid  loading  linear  a  as  air piston  Thompson  having  air piston  respectively.  loading  was  an  sample  and  guided  the in i t s  bushings.  a  beryllium  strain  gauge  copper bridge.  36  FIGURE  3-1  SAMPLE  UNDER  PLANE  DEFORMATIONS.  37  L o a i cell  Ant iroiadioh.  4  guide  Bracket f o r dial Thompson linear ball busKinds -Top  11  circulA.Tr  Loading  LoaAi'ng  ja/ate  TOL C&.f>  Up r/^kt rods Bottom . Space r  Loading  0'rCu/a.r  p/ate  feet  P ktforin  IT  A I T ^i"sto«x -Yoke  -Cross  FIGURE 32  SCHEMATIC FOR  THE  OF PLANE STRAIN  THE  ka.rs  LOADiMG EQUIPMENT  APPARATUS.  38 Vertical rod  by  deformation  means o f  vertical  .0001  deformations  ment t r a n s f o r m e r )  A  and  schematic  of  the  inch d i a l  a chart  from the  bottom of  d e v i c e w h i c h has c h a n g e s and pressure.  The  I n a few  the  3.3.  a LVDT  Drainage  leads  lateral  pressure  was  measured w i t h  same t r a n s d u c e r .  pressure  was  a p p l i e d through  to prevent  the  device.  A  similar  pressure  when r e q u i r e d .  At  diffusion  the  of a i r into  of K o  a deviator stress For  the  t o be was or  occurrence  i n c r e a s e d by  done by as  the  determined sustained  using case  saran  a r r a n g e m e n t was  end  rupture  increasing a t h r e e way may  be  a i r pressure. s t r e s s was  by  and  the The  the p r e s s u r e  used  maintained  connected  to apply  and  the  diaphragm  sample was ^  rapidly  .  slightly  under  occur.  deviator stress  had  This  changing a  c o n d i t i o n of constant by  used  measuring  s w i t c h i n g the v a l v e to The  back  r u p t u r e does not this  water  diaphragm  t u b i n g w h i c h was  or decreasing valve  volume  pipette  c o n s o l i d a t i o n , the '  under which creep of creep  device  the graduated  O.D.  this  pressure  to t h i s  of  to  f o r measuring pore  from the  the  pressure  lines  p i p e t t e f o r measuring  d i a p h r a g m s were a l s o c o n n e c t e d  to a 6 f t . long c o i l  the  (displace-  sample were c o n n e c t e d  gauge t r a n s d u c e r  drainage  using  tests  t h e v o l u m e c h a n g e and  i n Figure  a calibrated  a strain  gauge.  the p i s t o n  recorder.  layout of  i s given  and  m e a s u r e d on  were m e a s u r e d by  measuring device top  sample was  preyertical  i n c r e a s i n g the  ®  Wondi'splacehieKt valve GTAaaat&d  RtsSefUoirv  LoaamoJ  -wVJatai-  Wafer-  TJ  9  T6f> drainage  Plane Strain-  Ap-pajredus ^ft  Laieral cLtykrag*  LateraJ d  Soil Sao»f>le  D  FIG 3.3  SCHEMATIC MEASURE  cfrajnage leads I  TL  LAYOUT VOLUME  IL  Saraji tubfn<3  U  Ll  OF  PLANE  CHANGES  AND  STRAIN  APPARATUS  PRESSURES.  W/7~H  APPARATUS  To  a i r pressure in the a i r piston as the sample compressed and i t s area increased s l i g h t l y . of the increasing  The experimental procedure  and decreasing  type of undrained  creep tests in the plane s t r a i n apparatus i s given i n Appendix I .  K  q  T r i a x i a l Apparatus  -  The important features of the K  t r i a x i a l apparatus w i l l be discussed here. essentially  Q  This apparatus i s  a t r i a x i a l apparatus with a special arrangement  to consolidate c y l i n d r i c a l specimens of s o i l under K  q  condition  or v e r t i c a l deformation only.  During creep the state of  stress i s a x i a l l y symmetric  - o^).  The measurement of  stresses, sample pore pressures, v e r t i c a l deformation and the application of the creep deviator stress was done i n the same way as the undrained plane s t r a i n creep rupture t e s t s .  Discussion of Testing Procedure (Plane Strain Tests) The following items w i l l be discussed i n t h i s section:  (1) K  q  consolidation,  diaphragm and sample,  (2) f r i c t i o n between l a t e r a l  (3) measurement of  e f f e c t i v e p r i n c i p a l s t r e s s ) , and  (intermediate  (4) errors i n the measure-  ment of pore water pressure. 1. K Consolidation —o  -  During K consolidation the l a t e r a l ^ o  deformation of the sample was prevented by maintaining a constant volume of water i n the l a t e r a l pressure diaphragms.  Before on  t h e sample were s e t a t 90 P S I .  the to  c o n s o l i d a t i o n the v e r t i c a l  pressure  i n the l a t e r a l  an a v e r a g e v a l u e  compliance  strain Vaid  q  .002.  condition.  Friction  between  -  from  their  90 P S I t o 55.0 P S I .  i n t h e diaphragm would  However, p r e v i o u s small  strain  study  Since  lateral  c a u s e d an 4% f r o m t h e  compliance  the a x i a l  s t r e s s e s on t h e s a m p l e  on t h e l o a d i n g r o d a n d t h e f r i c t i o n d i a p h r a g m membranes, s h o u l d  s e a l s on t h e l o a d i n g  negligible.  b e t w e e n t h e s a m p l e , and l a t e r a l  d i a p h r a g m s and end p l a t e s was m e a s u r e d b y V a i d was f o u n d  correction as  t o be q u i t e a p p r e c i a b l e .  f o r the v e r t i c a l  6% o f t h e v e r t i c a l  correct Vaid  be  shaft arenot  t h e f r i c t i o n on t h e l o a d i n g r o d was  f r i c t i o n a l drag  and  have  r e s e a r c h by  o f about o n l y  Thus, i n t h i s  In estimating  considered.  this  pressure  sample and l a t e r a l  required,  reduced  neglected.  f r i c t i o n a l drag  The  water  i n the l a t e r a l  c o r r e c t i o n was  the  reduced  (1968) i n d i c a t e d t h a t  true K  Because o f  i n t o t h e sample g i v i n g a c o m p r e s s i v e  o f about  error  diaphragms  t h e diaphragms undergo volume d e c r e a s e o f  "incompressible"  squeezed  pressures  After consolidation  pressure  o f 55.2 P S I .  0.3 c c , when t h e p r e s s u r e The  and l a t e r a l  The f r i c t i o n  s t r e s s was f o u n d  stress at failure.  f o r f r i c t i o n were d e r i v e d  (1970) and a r e a s f o l l o w s : -  a t U.B.C.  t o be  high  Formulae t o  from data  obtained  by  For  the type o f creep t e s t  = 0.100  For  the  C  type o f creep t e s t  = 0.096 x I n i t i a l  2  Where  and  t o t h e end  creep  C  relatively tests  M e a s u r e m e n t o f al, As  a2  i s required  it  was  Vaid's  In t h i s  stress  c o n s t a n t s from since  total  s h o r t term  with  two  the  time  (less  i n PSI. begin-  of  than  weeks) V a i d  7 days) (1970)  time.  study  f o r the c a l c u l a t i o n  2  =  K(a' +  was  not  measured.  of c e r t a i n  parameter  a formula d e r i v e d  from  K =  Pressures  ol)  0.34.  -  During  a l l undrained  w a t e r p r e s s u r e s were m e a s u r e d  main  decreased  (1970) d a t a .  Where  using  for vertical  d e c i d e d t o e s t i m a t e i t by  o  Pore  -  was  pressure  (more t h a n  increase in f r i c t i o n  increased  pressure  lateral  of creep t e s t s  In v e r y l o n g term  was  i n which  were t a k e n as  2  l o a d i n g was  observed  lateral  = correction  and ning  x Initial  i n which  an  electrical  sources of  tests,  the  a t the base o f the  pressure transducer.  There  i n a c c u r a c y i n t h e measurement o f  water p r e s s u r e i n the sample.  There  h a v e t o be  pore  samples are  two  pore taken  43 into  consideration  sample, to  b e f o r e the pore p r e s s u r e s w i t h i n the  as i n d i c a t e d  by t h e m e a s u r i n g  be r e p r e s e n t a t i v e  are  due t o :  (a)  The t i m e - l a g due  o f t h e sample.  to non-uniform  The  stress  the pore water  pore water  to record  p r e s s u r e change would  Side  In  friction  pore  of stresses  on t h e sample  the d i s t r i b u t i o n  when t h e sample pressures.  This  f cr p i e z o m e t e r s minutes  pressure rises  on t h e sample  c r e e p and a f u n c t i o n  reality  9 5% o f t h e a p p l i e d  rapidly  of the this  significant.  friction  uniform d i s t r i b u t i o n  during  F o r the measuring  Therefore except f o r i n i t i a l  s h o u l d n o t be  over  be a b o u t one m i n u t e .  on a r e l a t i o n s h i p  c r e e p t e s t s when t h e p o r e w a t e r  is a  the per-  and t h e a r e a o f t h e sample  the time r e q u i r e d  (Penman, 1 9 6 0 ) .  t h e sample  system  system,  p r e s s u r e i s measured.  c o m p u t a t i o n was b a s e d  side  system  conditions.  response time o f the measuring  o f t h e sample  system used  the  pressure within  o f compliance o f the measuring  meability  error  inaccuracies  to i t s compliance.  due  which  These  are taken  i n the response o f the measuring  (b) The n o n - u n i f o r m p o r e w a t e r  function  system,  may r e s u l t  i n t h e sample. was assumed  o f the i n i t i a l of side  rise  However,  t o be c o n s t a n t lateral  friction  i s loaded thus g i v i n g  i n a non-  might  pressure. change  t o non u n i f o r m  Frictional in  non-uniform  specimen  tests.  axial  pressures Because  axial  stresses  thus g i v i n g  undrained uniform  restraints  rise  also  to s t r a i n  of t h i s  due  to bulging  to non-uniform  Furthermore,  strains  due  a t the l o a d i n g  rise  dependent  of the  clays  different  to non-uniform  structural  t h e p o r e p r e s s u r e i n t h e end  from  that  t o measure r e p r e s e n t a t i v e pressures  to equalize  moisture. for  Blight  the time  within  a specimen  at mid-height.  zones  The  (where may  be  simplest  way  pore p r e s s u r e s i s to a l l o w the  (1963) p r o p o s e d f o r 95%  of s o i l  pore  breakdown.  t h r o u g h o u t t h e sample by  required  test  non-  t h e p o r e p r e s s u r e s were m e a s u r e d ) i n t h e s p e c i m e n quite  result  pore p r e s s u r e s i n  in sensitive  give  platens  transfer  the f o l l o w i n g  equalization  subjected  pore of  equation  of pore pressure  to a constant rate  to  loading.  tj-  =  1.6  H —  2  . . . .  3.1  v  Where  t^  time  to f a i l u r e  o r time a t which  p r e s s u r e measurements a r e of H c This equalization may  be  two  reasons.  the  half v  representative  sample  the h e i g h t o f the  coefficient equation gives  of  extremely conservative,  specimen  consolidation  a t i m e o f 150  of pore p r e s s u r e .  Firstly,  pore  This  t i m e o f 150  i.e.,  the v a l u e o f  minutes  f o r 95%  minutes  f a r too l a r g e , f o r  "c " d u r i n g  undrained  45 loading  is difficult  obtained  during drainage  samples. test  to evaluate since  to obtain normally consolidated v  many t i m e s Secondly,  larger  than  the time  than  applied  the value  Thus t h e a c t u a l v a l u e o f " c " f o r t h e u n d r a i n e d  ( i n which e f f e c t i v e  tests  one u s e s  i n load  stresses  a r e d e c r e a s i n g ) may be  t h a t measured d u r i n g  for equalization control  i n a short period  tests o f time  consolidation.  s h o u l d be l e s s  because rather  i n creep  the load i s than  a t a constant  rate. Strain on  controlled  t h e same c l a y  pore  tests  pore  equalization 60  of  a sensitive  pore  that  t h e sample con-  o f 60  minutes.  i s applied  required  almost  t o o b t a i n 95%  p r e s s u r e s s h o u l d be c o n s i d e r a b l y l e s s  minutes.  i s no known method o f e s t i m a t i n g t h e t i m e f o r  equalization  of Vaid  indicate  Hence f o r s t r a i n  an e l a p s e d t i m e  t h e e l a p s e d time  of pore  There 95%  after  i n t h e c r e e p t e s t where t h e l o a d  instantaneously,  (1970)  p r e s s u r e s measured a t t h e base o f t h e  sample a r e r e l i a b l e Again  uniform within  an e l a p s e d t i m e o f 60 m i n u t e s .  trolled  by V a i d  and u s i n g t h e same a p p a r a t u s  pressures are e s s e n t i a l l y  after  than  t e s t s performed  o f pore  clay.  pressures f o r undrained  T h e r e f o r e on t h e b a s i s  creep  tests  of the r e s u l t s  (1970) i t may be r e a s o n a b l e t o assume t h a t a n y  p r e s s u r e s m e a s u r e d b e f o r e 60 m i n u t e s  may be i n a c c u r a t e .  46  For the type of creep tests i n which  was decreased  the time to 9 5 % equalization of pore pressures should be very small because the c o e f f i c i e n t  of consolidation i s very  much greater during rebound or decreasing effective  stresses  than during i n i t i a l consolidation. Pore pressures recorded at the end of a creep t e s t are also questionable since at f a i l u r e the s t r a i n rate and the rate of change of pore pressures are high g i v i n g nonequalization of pore pressures.  47  CHAPTER 4  RESULTS OF  K  During 3 6 hours.  for  s a m p l e s was was side  After  variation  compliance.  b u i l d - u p was or was  i n sample  in  secondary  Tests  At  t h e end  tests strain  on  q  stress. (1966)  ,  s a m p l e s as due  Was  after  correcting v a l u e may  temperature  period  an a v e r a g e This rise Lou  a  samples of  pore  pore-pressure  and  3 . 2 PSI,  pressure  Snead  (1970)  to the p r e v e n t i o n of c o n t i n u e d  the d r a i n a g e  lines  were  closed.  Increased  this  K  n o r m a l l y c o n s o l i d a t e d Haney c l a y  apparatus  to  volume  the  i n pore  (1967)  due  value of  In q  be  and  completed  value  Q  f o r sample  for equalization  of t h i s  w h i c h had  Byrne  compression  i n Which  size,  f o r 1 2 hours  4 % of c o n s o l i d a t i o n  the t r i a x i a l  in K  c o n s o l i d a t i o n was  observed  e x p l a i n e d by  . 0 1 ,after  This deviation  were k e p t u n d r a i n e d water p r e s s u r e s .  the water content of a l l  3 4 . 4 ± 0 . 4 % , w h i l e the K  0 . 5 7±  After  a l l s a m p l e s were d r a i n e d  consolidation  t o be  t o be  friction.  slight  consolidation  o  found  measured  PLANE STRAIN CREEP RUPTURE TESTS  section  when a,  the r e s u l t s  was  of a l l undrained  increased, w i l l  i n the  creep  plane  be d i s c u s s e d .  All  s t r e s s e s were c o r r e c t e d  was  taken  test  f o r sample  as c o n s t a n t w i t h t i m e .  g a v e a maximum d e v i a t o r  43.2 P S I a t an a x i a l deviator  stress  performed 39.5,  strain  39.0 and 38.2 P S I .  tents  stress,  (a,  -  which  loading  aO  of  o f 1.05 p e r c e n t .  Using  this  stresses  o f 44.5, 41.8, 40.7,  The s t r e s s e s  on t h e s a m p l e s  after con-  are g i v e n i n Appendix I I I .  rupture  strain-time  f o r the undrained  shown i n F i g u r e 4.1. then reached curve  tertiary  a minimum  tests  c o u l d be d i v i d e d  f o r plane  i n which rate  and g r a d u a l l y  i s seen  strain  rate  i s obtained.  Figure  4.2  l o g elapsed time,  the  strain  and  finally  rupture. constant.  rate  initially  the s t r a i n  t.  till  then  and  stage the  the  reached  increased rapidly  Therefore a secondary tested  creep  minimum  rate,  F o r t h e samples which  A t no s t a g e o f t h e c r e e p  f o r Haney c l a y  secondary,  of l o g s t r a i n  decreased,  rate  decreased,  increased to rupture.  slightly  shows t h e p l o t  creep  increased i s  initially  i n t o primary,  to decrease  strain  was  creep, although d u r i n g secondary  rate  against  curve  The s t r a i n  strain  exist  The i n c r e m e n t a l  and d u r i n g c r e e p , and t h e sample w a t e r  A typical  This  friction  a s t h e r e f e r e n c e s t r e n g t h , t e s t s were  a t creep deviator  consolidation  side  failed,  a minimum  leading to  t e s t s was t h e s t r a i n  stage  under p l a n e  e  rate  f o r c r e e p does n o t strain  condition.  AXIAL  C X)  STRAIN - P E R C E N T  m  ? -<H"0 m  2  co r  $  "D  2  O  o  O 71  H  r CO  1  m  (0  H  2 2  R fc?  1 o •n  \  ^  S S  NO.  0)  < m  2  JM 6TR/<U/\  8  2 (6  o  TEST  $  A  PS 1 i  2  8  m  •n o  to  c g  2 2  tn O  8 2 O in  a? H  -0  Q <^  —  n o  a  50 <TE<"fO-7RSZ  /0  FIGURE 4 . 2  LOGARITHM  LOGARITHM  OF  TIME  CREEP  TESTS  FOR  AXIAL UNDRAINED  - 0 7 INCREASED  M  W/c s3*2  19 ooo  I OOO  'OO  OR  94-5%<5K  STRAIN  RATE  VERSUS  PLANE:  STRAIN  (HANEY  CLAY)  It  i s p o s s i b l e , however, t o i d e n t i f y  approximately line  between p o i n t s  Figure to  constant  4.1.  stage of  r a t e by d r a w i n g a  straight  B and C f o r t h e s t r a i n - t i m e p l o t i n  The s l o p e  t h e minimum s t r a i n  lower the d e v i a t o r  strain  a creep  of l i n e rate.  BC i s a p p r o x i m a t e l y  Figure  4.2  s t r e s s the smaller  equal  shows t h a t t h e  t h e minimum  strain  rate.  The the on  points  experimental  o f minimum s t r a i n  the l o g - l o g p l o t  was a l s o t h e c a s e for  conventional  The  equation  is  given  data  of Figure  rate f a l l  of strain  creep  of the s t r a i g h t  Where t m  =  rupture  line  (1970) ,  t e s t s on Haney c l a y .  obtained  time u n t i l  from F i g u r e  4.2  triaxial  fail.  samples.  rate could  . . . .  minimum s t r a i n  rate  i n percent  4.1  rate  per minute  r a t e o f a sample p a s s e s t h r o u g h a  i t has been c o n s i s t a n t l y o b s e r v e d  eventually  example  This  minutes  Once t h e s t r a i n  strain  line  time.  by Snead  n  minimum s t r a i n  for  reported  - .74-1.16 log, e ^10 m  elapsed * in  will  on a s t r a i g h t  that  by  log, _ t ^10 m  minimum  suggests  r a t e and e l a p s e d  f o r the r e s u l t s triaxial  4.2  that  t h e sample  T h i s was a l s o o b s e r v e d by Snead He s a i d  be u s e d  that the existence  as a f a i l u r e  f o r the p o i n t A i n Figure  criterion.  (1970)  o f a minimum For  4.2, t h e s a m p l e u n d e r  these  c o n d i t i o n s has reached was  bound  kept a  to fail  constant.  minimum  indicated Thus, the  left  towards  the other  rate,  by p o i n t  curves  B  like  moved  but  gradually  the  line  changed  o f minimum  intersect  the line  f r i c t i o n along  for  such  behaviour.  and  the side  stress  with  T h i s would  time.  particular  rate-log fail.  any  elapsed  i n these  longer  cause  time  curve  i twill  time,  the behaviour  not possible  i s small.  to  never  fail.  could  account  due t o membrane  then the  but would  f o r the samples  experiments.  consequence,  parallel  t h e sample  constant  fail  rates,  and never  membranes,  from  d i d not  a reduction i n strain  explaining  fail.  strain  boundaries  decrease rate  at  of log strain which  d i d not  t o measure  side  However, i t i s b e l i e v e d  the existence of a varying side large  rate  between  diaphragm  U n f o r t u n a t e l y , i t was  friction that  i s no  time,  which  Presumably  strain  rate  and moved  and proceeded  rates.  grease  not  were  reaches  strain  rates,  o f minimum  t h e sample  pressure  never  started  f r i c t i o n increases with  "sustained"  any  the line  out of silicone  the l a t e r a l  failed  sample  sample  t h e sample  sample  strain  The  o f minimum  side  squeezing  i t .  strain  on  i t should  which  i t scourse  The  If  4.2,  o f minimum  towards  i f a  and t h e  the instantaneous  o f a l l the samples  and i n t e r s e c t e d  rate,  stresses  hand  i n Figure  of the line  initially  strain  i f the applied  On  strain  a minimum  f r i c t i o n with  First  of a l l ,  time  similar  of  53 behaviour observed  f o r the by  Snead  w h i c h t h e r e was tests  by  Vaid  apparatus constant an  curves  test  affect  Figure  4.2  failure will  d u r a t i o n s o f a few  strain  the  with  side  time  for  friction  strain  essentially  days.  Therefore  f o r creep  rupture  c o n d i t i o n should  s t r a i n - t i m e curves  upper y i e l d w o u l d be  will  not  o f an  occur  occur  be  small  of  and  upto a p e r i o d  upper y i e l d  Snead  exists  upper y i e l d 88.7  cuts 4.2).  Shibata  the  plot  The  and  curve of  strain  PSI.  than  of  PSI.  ( 1 9 6 1 ) , V i a l o v and  That i s ,  The  percent  the  loading  hypotheses  in Figure  (1957)  strength not  4.2  strength  occur. corresponds  obtained  test.  corresponding  log e versus rate-time  but  Skibitsky  rupture w i l l  of the  PSI  observance  s t a t e t h a t a upper y i e l d  90.6  shown i n  39.0  i s i n agreement w i t h  strength for results and  results  39.0  38.2  below which c r e e p  incremental  The  38.2  at stresses greater  stress  for soils,  from the  between  (1970) w h i c h  t o between  s t r e n g t h f o r the  a t a s t r e s s below  o f Murayama and  The  was  was  samples  of plane  side f r i c t i o n  fail  days d u r a t i o n . An  and  Secondly,  same t y p e  side f r i c t i o n  samples under p l a n e  4-7  the  showed t h a t t h e  not  tested t r i a x i a l  side f r i c t i o n .  (1970) on  f o r the  samples which d i d not  ( 1 9 7 0 ) , who  no  increase of  should  of  to the upper y i e l d  log t into  c o n d i t i o n of  two  parts  a l l the  strength (Figure  samples  54 which  failed  strain fail  are plotted  r a t e - t i m e c o n d i t i o n s o f t h e samples which d i d n o t  are plotted  plot.  the s t r a i n  stresses.  i t would If this  fail  and i f p l o t t e d  sample would n o t f a i l . stresses,  l o g e versus  representing  fail  l o g t would enable  o r n o t , under  particular  failure  time  tests.  increased  From t h i s  with  strain  i n time  be s e e n  3.0 t i m e s  during  f o r the d e v i a t o r  stress as a  the time  tertiary  -  creep  time  i n deviator stress. the s t r a i n  time  the elapsed  that the  to rupture With the  t o minimum From T a b l e  to rupture  t o minimum s t r a i n  two-thirds  of the creep  i t c o u l d be s e e n  to increase s l i g h t l y .  that the t o t a l  Pore Pressures pressure  f o r constant applied  r a t e and t h e t o t a l  to failure,  w o r d s , more t h a n spent  p a r t a t "B" t h e  s t r e n g t h c o u l d be u s e d  table  the decrease  r a t e was o b s e r v e d could  t h e sample  I I g i v e s some o f t h e r e s u l t s  t o minimum  increase  log t plot  i s plotted  criterion. Table  rupture  Therefore  us  constant  condition  i n the lower  the upper y i e l d  log t  r a t e - t i m e c o n d i t i o n o f any  t h e u p p e r p a r t a t "C" i n F i g u r e 4.2 t h e n  would  to  part of l o g e versus  on t h e l o g e v e r s u s  p r e d i c t whether  applied in  i n the lower  Therefore  sample p l o t t e d to  i n t h e upper p a r t whereas t h e  II i t  i s about  rate. time  strain  2.4  In other to rupture  was  stage.  I t was d i s c u s s e d i n C h a p t e r  o f samples measured b e f o r e a time  3, t h a t  pore  o f 60 m i n u t e s  55  TABLE  H  SOME CREEP  Test N o . Dev/a.for  OF  RESULTS -  TEST  UNDRAINED  cr,  Straj'h. rSe SfrajA ra+<? •PerCetdlmi* -fti-cmt  PSI-CI F S 1 - C 2  41-8  9 7 - 3  •Q23  •>56  2 6  0070  £7  SO  84 154  90  2J4  3 9 - 5  9 / 7  •OOS4  •60  v39-0  9 0 6  •0O22  •62  EXPERIMENT <H>M  000035  3 3 - 2  PARAMETERS  - MAXIMUM  INCREMENTAL  raie - frrxt'n. - fni'v  vS^raj^  3  -Gf  *  MC/IV»  •54  94-S  "RSI-C6  to  mini  •o9o  4 0 7  Psi - C s  TVfv^e  /Q32  PSI - C 3 Psi  MEASURED WAS DEVIATOR L.QADING  STRAIN  INCREASED.  PferCeKt 0/ Mm/niuni Axial Strain  <  PLANE  •44  AT  THE  P2v5 —  TIME  8  69,5 -4300  WHEN  THE  STOPPED. STRESS TEST.  OBTAINED  FROM  AN  56 and  a t t h e end  o f t h e c r e e p t e s t may  be  considered  inaccurate.  Figure axial  strain  Figure  stress  by  level,  observed  to develop  strain.  T h i s may  structural  For  and the  be  undrained  similar  Au  in  "Au"  "Aa^"  soil  3  + A  axial  (2) t h e t e s t  with  p r e s s u r e f o r the time  soil  same  available  for  structure.  specimens the change i n pore condition  c a n be  e x p r e s s e d by  (1954) f o r t r i a x i a l  (La  "A"  ~ Aa )  1  i s the increment  "B"  that:  an  conditions.  1962)  and-"Aa^".  soil  pore  sensitive  1  the  seen  to the a d d i t i o n a l  to:Skempton s  B[Ao  =  m e t e r known as ated  largest  strain  Henkel,  reported i n  increase i n  (1970) and  versus  therefore longest duration, i s  due  p r e s s u r e under p l a n e  Where  Snead  breakdown o f the  ( B i s h o p and  i t c o u l d be  pressure increased with  as o b s e r v e d  equation  o f the creep t e s t s  From F i g u r e 4.3A  (1) t h e p o r e  lowest  shows t h e p o r e w a t e r p r e s s u r e  for several  4.2.  strain,  4.3A  3  i n pore  ]  p r e s s u r e due  i s an e m p i r i c a l  Skempton's  = 1, w h i c h was  "A"  value.  the case  pore  to  increments  pressure para-  For a f u l l y  i n the creep  satur-  tests  performed.  Figure axial  strain.  4.3B  shows t h e Skempton  From F i g u r e 4.3B  "A"  i t c a n be  parameter  seen  that  versus  for  any  57  OS AFTER CONSOLIDAT ION = £<?-6 PSI AFTER C.ONSQL IDA"lON= SS-1 PSt /03-? % 0 S VJ/C ^^4-7  44-5 PSI 03-  6~3 AXIAL FIGURE  43A  PORE UNDRAINED  -  TIME  PRESSURE;  PLANE  STRAIN  6 AXIAL  FIGURE 4 3 8  SKEMPTON UNDRAINED  AXIAL  FIGURE 43CEFFECT/V£  UNDRAINED  STRAIN  Kjfc  M  = 34 2 T} = \S4 M X O i M W/c = 34-2 T = 4300 MIN TO FAILURE  Tl 2^4" PERCENT  STRAIN W A T E R  % C73  PSi H7t  T)  Tf--8S<*)in  M  VERSUS  AXIAL  TESTS -<T/  CREEP  ? 4  VERSUS  PLANE  STRAIN  -  INCREASING  STRAIN  CREEP  FOR  TESTS-C:  INCREASED.  PERCENT  STRESS PLAME  AXIAL  STRAIN  FOR  3-z  PERCENT  A  STRAIN  RATIO  STRAIN  VERSUS CREEP  AXIAL  TESTS  STRAIN  < - 7T  FOR.  INCREASED.  IN  58  p a r t i c u l a r a x i a l s t r a i n the lower the deviator s t r e s s , higher was the value of Skempton "A".  the  This i s s i m i l a r to  the conclusions of Crawford (1959), that "A" value at f a i l u r e i s dependent on time to f a i l u r e . Figure 4.3C shows the v a r i a t i o n of e f f e c t i v e r a t i o "o^/o^" versus a x i a l s t r a i n for tests.  The effective  stress  several of the creep  stress r a t i o increases with a x i a l  s t r a i n , mainly due to increase i n pore pressure with a x i a l strain.  For the samples which f a i l e d ,  "a^/a^"  even after the minimum s t r a i n rate i s reached.  increases Therefore,  based on a al/ol f a i l u r e c r i t e r i o n ,' a sample, 1' 3 max * ' whose s t r a i n rate i s beginning to increase, would not be considered on the verge of f a i l u r e , but on the basis of minimum s t r a i n rate i t i s on the verge of f a i l u r e .  This p a r t i c u l a r disagree-  ment concerning f a i l u r e c r i t e r i o n need c l a r i f i c a t i o n through additional research. For "a|/a^"  tests 0.45  the sample which did not f a i l the increase i n  with a x i a l s t r a i n i s smaller than that for the other  (Figure 4.3C).  This test was stopped at a s t r a i n of  percent when the "a^/o^" r a t i o was s t i l l increasing -5  and  s t r a i n rate of 3.5 x 10  percent/min.was s t i l l decreasing.  The decision to stop the test was taken because of the probable undetected increase in side f r i c t i o n after about a week or more of sustained load (Vaid, 1970).  59 Stress-Strain-Strain the p l o t creep  of  and  log strain  incremental  marked a l o n g stresses loading failed and it  a t the test  the  of about  strain  axial  the  the  strain,  of  slightly  the  but  the  For  while  the  for  incremental  samples  which  reaches  strain.  the  axial  a minimum However, strain  compressive  sample w h i c h d i d n o t  a t an  ever  fail  decreasing rate  with  never  reached  incremental  test,  l o a d s were a d d e d a t  I t was just  evaluated  after  The from  strain-time obtained  observed the  strain  strain  before  decreased  i n Figure  drawn t h r o u g h  the next  inter-  rate  a d d e d and  rates plotted  a smooth c u r v e  just  0.6%.  t h a t the  l o a d was  is  the d e v i a t o r  t h a t a t t h e minimum  u n d e r g o n e an  both  strain  thereafter.  l o a d was  curve,  For  for  shows  deviator stress  r a t e decreases,  interesting  the  strain  The  increase of a x i a l  0.6%.  F i g u r e 4.4  increment  indicated.  s a m p l e s had  slightly  were t h o s e  stress  strain  10 m i n u t e s .  increased  the  r a t e decreased  For vals  of  -  axial  loading tests.  also  is particularly  strain  of  end  are  i n creep  a l l of  rate versus  the a p p r o p r i a t e creep  increases with  rate  Rate R e l a t i o n s h i p  increment  4.4  points of  added.  It  s h o u l d be  recalled  t h a t a t the  end  of K  consolio  dation, -  the  a^)  When t h i s the  s a m p l e s were u n d e r a d e v i a t o r i c  of about  29.6  deviatoric  samples  failed  PSI,  (also  s t r e s s was  i n creep  indicated  stress  i n Figure 4 . 4 ) .  i n c r e a s e d beyond  rupture.  (i.e.,  Therefore  34.0  PSI  there are  two  go  <7*'4 ISPs I 03 AFTER CONSOL IDATION -29G PSI 0£ AFTER CONSOLIDATION*55-1 <=$r_  CREEP  TESTS  w / c =347.  <Tj> =44 5 RSI  Oo = 418 0SI OB *40-7flSI  w/c =34-a  C i » 39 O RSX  0-4  05 > 38 2 BSr  SS-7% <£„  INCREMENTAL  LOADING  " T 2  STRAIN AXIAL FIGURE 4 4 LOG AXIAL STRAIN UNDRAINED  PLANE  CUNDISTURSED  RATE  STRAIN  HANEY  FS ~ PERCE VERSUS  CREEP  T&Sr W/^34-2  ^ZT  "3*  NT  AXIAL TESTS-cr,  CLAY.)  1  STRAIN FOR INCREASED  i n c r e m e n t s o f d e v i a t o r s t r e s s w h i c h c o u l d be The  f i r s t one b e i n g  considered.  t h e " a d d i t i o n a l " d e v i a t o r s t r e s s added  a t t h e end o f c o n s o l i d a t i o n .  The o t h e r  i s the " t o t a l "  d e v i a t o r s t r e s s on t h e sample d u r i n g c r e e p , as g i v e n i n F i g u r e 4.4. value  The " a d d i t i o n a l " d e v i a t o r s t r e s s may be o f  s i n c e i t i n d i c a t e s t h e a d d i t i o n a l l o a d t h a t can be  a p p l i e d i n t h e f i e l d t o s t r a t a i n i t i a l l y under K tion.  q  consolida-  The " t o t a l " d e v i a t o r s t r e s s on t h e o t h e r hand i s a  more fundamental parameter and hence has been used i n t h i s study. Snead's (1970) h y p o t h e s i s  namely a  Q  = f ( e , e) o r  t h a t a t t h e same s t r a i n and s t r a i n r a t e t h e d e v i a t o r should  be t h e same f o r b o t h c r e e p and i n c r e m e n t a l  t e s t s , c o u l d be e v a l u a t e d  stresses  loading  from t h e r e s u l t s o f F i g u r e  4.4.  I n v e s t i g a t i o n o f r e s u l t s i n d i c a t e r e a s o n a b l y good agreement between t h e c r e e p and i n c r e m e n t a l  l o a d i n g t e s t s i n terms o f  " t o t a l " d e v i a t o r s t r e s s on t h e sample as g i v e n i n T a b l e I I I . But i n terms o f t h e " a d d i t i o n a l " d e v i a t o r s t r e s s e s added a f t e r c o n s o l i d a t i o n , e r r o r s o f t h e o r d e r o f 20% and h i g h e r , e x i s t as g i v e n i n T a b l e I I I . comparing i n c r e m e n t a l the a  Q  w i t h c r e e p t e s t s a t t h e same e and e  i n the incremental  t h a n from c r e e p t e s t s . decreasing incremental  Note i n F i g u r e 4.4 t h a t when  l o a d i n g t e s t was always  higher  In a l a t e r section t e s t data f o r  s t r e s s p a t h s w i l l be e v a l u a t e d and creep, l o a d i n g w i t h r e s p e c t  s t r a i n , stress behaviour.  f o r both  to s t r a i n r a t e ,  62  TABLE  7H  OS  AT  F/GUftE STRAIM  "TOTAL"  THE 4.4,  SAME FOP  TESTS  PSI  07  C  AMD  UNDRAINED -  07  /NORE^SE-D.  ADDITIONAL"  Oi - PSI  INCREMENT/*]  CREEP  INCREMENT/U  CREEP  LOADING TEST  TEST  loABlMG T£ST  TEST  361  v38 2  6-A*  8£  39 O  9 a  9-6  42-0  v39S  12-4  [Ql  42-3  407  J2 7  11 1  43 Q,  4'8  13-4  '2-4  39  T  £  FROM P U N £  COMPARISON CREEP  OF  I N C R E A S E D " AND  which  "g^ the  this  was  results  variations  of  The  consolidated  samples  section,  decreased"  increased".  to  same  i n water to  temperature  and  volume  fully  undrained For  and  principal  show  e  that  constant  be  "g^  the  test  and  the g^  tests,  increased  same  similar of  the  g^  OF  type  i t may  results  of  of  "g^  in  was  of  tests  The  stresses  were  slight on  the  sample  as  the  shear  same  constant tests  size,  and  results test  tests  tests  creep  that test  with as  intermediate  obtained of  g^  the  g^ "g^  be  tests,  is  should  give  kept  increased"  considered  comparable  i n plane  by  versus  decreasing  where  the  i s increased.  loading  may  are  test  the  were  g^  tests  for  g^  results  and  that  results  (with  Therefore  concluded  undrained  reported  incremental  shear  i f shear be  tests  comparison  types  triaxial  constant  i s increased.  Thus,  type  shear  f o r the  with  decreased"  analogous.  creep  o^)  ( F i g u r e 4.5)  in  in soil,  have  give  i s kept  Comparison  approximately  and  g^  ^  two  initial  undrained  strain  stress  creep  conditions.  (1962)  decreasing  where  the  i n which  variations  Henkel  plane  (1968).  strain  g^  tests  undrained  Vaid  TYPES  compliance.  saturated clays,  constant  tests  and  of  discussed  initial  slight  and  be  f o r these  content  due  results  creep  samples  the  Bishop  the will  the  are  g^  "a., D E C R E A S E D "  TESTS  In  with  "g  with  strain give  to  the  the  g^  same  64  0  0  cr, INCREASING  » y.  CTj J)ECR£AS/NG  9 46 a L  "ft  42 40  38  —  /  36 h  64  TO  a 32  <  > So UJ Q  28 O  6-2.  0-4  Ax'AL, FIGURE  4S  0-4  0-8  vSTRA/N - 6  COMPARISON PLANE  IO  STRAIN  -UNDISTURBED  |2.  1-4  1-6  1-8  PERCENT O F  OD. VERSUS  INCREMENTAL  HANEY  € LOADING  CLAY.  POR  UNDRAINED TESTS.  behaviour  as  the  The  decreased  type  incremental loading test  g a v e a maximum d e v i a t o r s t r e s s of  1.45  percent.  strength, 42.5  and  creep 41.3  anticipated the  tests  PSI.  test  curve  f o r creep  istics  4.6  42.5  and  two  and  curves  4.7  the  strain  reference  44.8,  42.6,  and  and during  yield  about  89%  The  increased.  I t could  are  upper y i e l d was  a  rate versus  tests. tests  and  i n which  93.5  value  tests  of the r e f e r e n c e s t r e n g t h . between the upper y i e l d and  f o r the tests  between  percent of  a^"  are  was  strength f o r creep  "increasing  increasing  log  These curves  rates exists  (c^ - a^)  96.2  be  similar.  log strain  f o r creep  In the  a marked d i f f e r e n c e a,  typical  strain-time character-  creep  which are  strength.  from  the  for  along with a  o f minimum s t r a i n  decreased  PSI  s t r a i n - t i m e curve  was  that  shows t h e  obtained  case.  41.3  determined  a t 46.1,  axial  of c o n s o l i d a t i o n  types of curves  reference  was  i n which  a line  was  was  as  decreased  Sample w a t e r c o n t e n t s  decreased  for decreasing  decreasing i n which  friction.  was  two  to those  increased,  a t an  deviator stress  shows a t y p i c a l  test  these  f o r the  similar  PSI  was  A l l s t r e s s e s were c o r r e c t e d f o r t h e  i n which  curves  i n which  44.1  s a m p l e s a t t h e end  Figure time  test.  are given i n Appendix I I I .  creep  from  this  sample s i d e  Figure  seen  Using  of  t e s t s were p e r f o r m e d  stresses of  creep  of creep  the  the  upper  Thus,  there  strength  a-, d e c r e a s i n g t y p e  of  POINT OF  MINIMUM STRAIN RATE  CT/ INCREASED TEST Na flSJ-GS  s320  COMPARISON PLANE  OF  STRAIN  INCREASED  "  DEFORMATION CREEP  AND  v560  MINUTES TEST  UNDRAINED  BEHAVIOR FOR  THE  640  CASES  OF  DECREASED."  CTv  cn  BSE %-2 %  Oi--  T/M£ LOGARITHM  LOGARITHM  OF TIME  CREEP  TESTS  -  OF FOR  03  10,000  JOO  io  FIGURE4.7  W/C»34-4  MINUTES  AXIAL UNDRAINED  DECREASED.  STRAIN  RATE  PLANE  VERSUS STRAIN  68 creep will  rupture  tests.  be d i s c u s s e d i n t h e l a t t e r  Figure minimum can  be  strain seen  other.  4.8  shows  rates  these  line.  two  state  lines  purposes  they  4.8  i s t h e same  of this  types  straight  Figure  i n upper  the comparison  suggest  the sustained shearing  initial  part  f o r t h e two  For practical  straight how  This difference  stress  chapter.  of creep very  c o u l d be that  strength  of the lines  fall  close  i t does  o f '.  tests.  taken  i s applied  and t h a t  yield  As  to  each  as one  not  matter  so long  as t h e  i s f o r compressive  strains.  Table plane  IV g i v e s  strain  could  be  seen  total  time  that  With  minimum  strain  at  percent  observed which the that the were  rate  t o minimum  increased with  was  From  observed  f o r a l l samples  was  stopped.  to  obtained  time  minimum  From  to failure,  which  to rupture strain  was  for increasing  and t h e i n deviator  the strain  strain  2.6  of creep  constant  sample  o f 1.77  before  also  seen  t o 3.2  Similar  at  behaviour  However, t h e  i s about  a, type  rate  t h e same  IV i t c o u l d  rate  table i t  approximately  axial  Table  this  the decrease  t o be  had a p e r c e n t  of the decreasing  strain  f o r the " a ^ increased" tests.  the t o t a l time  tests.  the i n c r e a s e i n time  d i d not f a i l  test  of the results  rupture  the time  to rupture  stress.  0.56  creep  some  be  times  values tests.  69  INCLEASED  DECREASE!  01  100  IO  TIME FIGURE  4.8  LINES -PLANE  OF  MINS  MINIMUM STRAIN  /OOO  STRAIN  RATES  10,000  70  TABLE.SOME  RESULTS CREEP  Test No.  OF UNDRAINED  TESTS  PLANE  - G£ DECREASED.  Thne to T o t a l W rnir\i fv»u*n *o /ai'/uve Strain rate at Hinirnutri vStraiK rat* Stw'n raie Ru-Cfcrit/Mi'h - rniVx - Percent - m iV\  Percent of Mini tnmtvt Creep-PSI  RS3- Cl  461  /o4a  •034  SS  /o  2?  PS3-C2  44>8  /OJ-7  •o/a  56  30  82  PS3-C3  42-6  96 3  •0O37  56  IOO  32/  PS3-C4 *PS3-G5  425  962  •0029  •55  125  41-3  R35  •oooo?  *  STRAIN  PARAMETERS EKPERIMENT  3DM AN  MEASURED WAS  MAXIMUM INCREMENTAL  117  AT  35/ 7200  —  THE  WHEN T H E  TIME  STOPPED.  DEV/ATOR  STRESS  LOADING  OBTAINED  TEST  -  (<r - a-,)  FROM  71 Stress-Strain-Strain the p l o t creep  of l o g of s t r a i n  test  similar  Rate R e l a t i o n s h i p  i n which  rate versus  was d e c r e a s e d .  to that obtained  f o r creep  -  F i g u r e 4 . 9 shows  axial  strain  f o r the  The b e h a v i o u r i s  tests  i n which  was  increased.  The Figure The  4.9 f o r both  hypothesis  results  loading sample  order Figure  the as  i n T a b l e V. added a f t e r  4 . 9 , comparing e and  lower  results  than obtained  incremental  deviator stress  consolidation,  as g i v e n  the from  and  indicate  on t h e  But i n terms o f t h e " a d d i t i o n a l "  incremental  e  test.  i n T a b l e V. loading with  i n incremental creep  errors  tests.  for increasing  of the  Note t h a t i n creep  tests  loading test i s  This i s opposite to type  o f creep  tests  shown i n F i g u r e 4 . 4 .  Figure  4 . 1 0 A shows t h e o b s e r v e d  versus  l o g minimum  decreasing  yield the  I n v e s t i g a t i o n of the r e s u l t s  o f 2 0 % was o b t a i n e d  stresses and  stress  loading  = f ( e , e) c a n be e v a l u a t e d w i t h t h e  Q  i n terms o f t h e " t o t a l "  as g i v e n  t h e same  always  that a  good a g r e e m e n t b e t w e e n t h e c r e e p  tests  deviator  ( c ^ - a^) a r e i n d i c a t e d i n  c r e e p t e s t s and i n c r e m e n t a l  of Figure 4.9.  reasonably  at  deviator stresses  value  plot  type  i s also  of a  n  strain  of creep  indicated  v e r s u s minimum  behaviour  of deviator  rate f o r increasing  tests.  i n this  An a p p r o x i m a t e plot.  upper  The c u r v e s  e can not c u t the s t r a i g h t  on  72  426 est 0 5 42 s PSI s  CT2 AFTER CONSOLIDATION - 3 0 J FBI C77 = S 4 - 6 ASI „ CTj, = 4<Sl PSX I04-2%G3M Vt/c =340 A <a 03 * 44 8 Psx ro/-7 % Oh* w/e = S4-6 • • 0i=42-6Rsx ?6-3%CTS W/c=J4€ O i = 42-5 BSI 96-2% C J > M W/C ^V£*4 cn, - 4 i - 3 PSI 03-5% cri>M IA//C =v?4-5» v  M  © ©  *SH£AR TEST  O3  J>EC/?S4S/MC_ W/c--34£  C77 = 8 4 - 6 ftsx CXi COMSOL = 301 PSI  g5> = 41-3 PS£ J)iD NOT  C-4 FIGURE 4-9  LOG A X / A L  FOR -O3  I •2 STRAIN -  0-8  AXIAL  STRAIN  UNDRAINED DECREASING.  PLANE  20  1-6 PERCENT  RATE  VERSUS  STRAIN  FAIL.  AXIAL.  CREEP  STRAIN  TESTS  73  TABLE 2  OF  AT  " T H E SAME  FIGURE  4 - . 9 , FOR  TESTS  ~ O3  'TOTAL"  <5  'INCREMENTAL  LOADING T£Sr  39- 0  £  AND  UNDRAINED  PLANE  DECREASED.  - PSI  ADDITIONAL  03  CREEP TEST  INCREMENTAl  CREEP TEST  4/3  LOADING TEST  89  - PSI  W-4  42 5  IO-2  126  411  426  H-2  127  A3  44-8  f3  14-9  0  £  1  FROM STRAIN  o  <T7  \NCRE\S2D.  + 03 J)£CRi:A6£D.  ar  3  D E C R E A S E D  V  2 •50  07 '*'CREAS£I>  •-4S  to MINIMUM FIGURE  10 "  JO °  STRAIN  RATE as  4.10A  FOR  -  VERSUS  MINIMUM  TESTS.  PLANE  STRAIN  STRAIN!  IO'*  RATE  PERCENT/MINUTE  UNDRAINED  CREEP  10"  IO"  RATE  FIGURE 4 1 0 8  Vcr^' A T  FOR UNDRAINED STRAIN  CREEP  IO"  ~ 6^ VERSUS PLANE TESTS.  lines  r e p r e s e n t i n g t h e upper y i e l d  a minimum not  strain  fail.  r a t e does n o t e x i s t  t h e upper y i e l d  any p a r t i c u l a r  v a l u e a s shown i n F i g u r e 4.10A.  v a l u e o f minimum  decreasing  type o f creep  increasing  type o f creep t e s t .  although minimum for  a  D  different  total  (increasing  7* f (e) a t e ^ .  imately equal creep can  tests.  The (where T =  comparison  1  2  creep  total  with  tests  m  or e = A t  m  compressive  was f o u n d  stress  t o be a p p r o x and d e c r e a s i n g  t h a t OJ-J = f ( e , e) paths  of loading.  stress  ratio  a s shown i n F i g u r e 4.10B. i n the stress showing  a r e s t r o n g e r than  comparison  axial  show t h a t  T  / ^ a  r  terms o f e f f e c t i v e  T/O'  f o r the  a n d a' i s t h e mean n o r m a l e f f e c t i v e m + a I)) a t e f o r t h e i n c r e a s i n g a, a n d 3' m 1  two t y p e s o f c r e e p t e s t s ,  The  l o g time  of the e f f e c t i v e  these  tests  Q  representing the  f o r increasing  i s a marked d i f f e r e n c e  in  curve  of axial  at e  there  decreasing  a  c r ^ when compared t o d e c r e a s i n g a^)  for different  2  D  These r e s u l t s  Therefore the hypothesis  = 4(0"-! + ol  decreasing  paths  The s t r a i n  ^  3  stress  o" f o r the  rate,  i s g r e a t e r than  of l o g e versus  t o 0.6 p e r c e n t  not apply  stress  test  strain  t h e r e seems t o be a u n i q u e i or a plot  loading  f o r s a m p l e s w h i c h do  T h e r e f o r e t h e two c u r v e s must a s y m p t o t i c a l l y  approach For  v a l u e , as t h e o r e t i c a l l y  strain  ratio  Again  at e . for m  t h a t samples o f  increasing  tests  stresses., of the effective  stress  i s g i v e n i n F i g u r e 4.11A.  ratio F o r any  76 1  DECREASING CQ T y P £ OP C R E E P T E S T S  J  CPEC P TESTS - <T3 DECREASED CT, = <84 6 RSI O i COMSOL *30 • I RSI  „ +  lOll°/ Gj>M  T/- » 86 M / M <5, 44 8 R S I  ^.A  4 2 6 Psi  TV,321M/NJ  0  4 T/.1300MIM 0 i « 4 / - 3  W/C*&4-C  a  PSX  <?C v3 % O w  \*ljc-34<  'tesT^CGiwj  Uj/c ,34-8  CREEP TEST -CT, INCREASED Tf . TT»vi e 6^4  FIGURE  OU  Ta  r e To  AX/AL  STRAINI  4MA  V/c^f  UNDRAINED  -  /<a,i" /u>*c. 3,2  PERCENT  VERSUS  PLANE  fo  £4  AXIAL  STRAIN  FOR  STRAIN  CREEP  TYPICAL  TESTS.  TEST  FOR INCREASING  TYPE OF CREEP TESTS  DECREASING crj  OF CREEP  _  TYPE  TESTS  _ AVERAGE. _POPE PRESSURE AT THE BEGINNING OF CR£EP T E S T * 18-2 PSL  O  0-4  OS  AXIAL. FIGURE  STRAIN  4-118 PORE FOR.  1-6  12  20  *8  S-2  PERCENT  PRESSURE:  UNDRAINED  2-4  VERSUS  PLANE  STRAIN  AXIAL CREEP  STRAIN TESTS  particular compared  strain,  to the  T  / ° ^ i s h i g h e r f o r the d e c r e a s i n g  increasing  the p r o c e e d i n g d i s c u s s i o n tests  lie  type of creep i t c a n be  have a h i g h e r s t r e s s  strain  rate.  A possible  i n the comparison  stress  paths,  and  -  ratio  of pore  p r e s s u r e f o r the i n c r e a s i n g  t h e s e two  was  decreased  while 2_  a  The  Although  a  decreasing  increase i n strain  i n p o r e w a t e r was  under 1960;  in total  due  stress tests, increasing  type of  normal  Gupta  1968).  t h e sample w h i c h d i d n o t failed.  w h e t h e r a sample w o u l d pressure versus a x i a l  fail  The  However  strain  as  pore  (Crawford  1959;  shape o f t h e c u r v e s f o r  is similar  or not  the  soil  to those  Therefore i t i s d i f f i c u l t fail  with  stress  under s u s t a i n e d s t r e s s  shearing strains.  creep  associated  t o breakdown o f s e n s i t i v e  increasing  of  types  of increase i n shearing s t r e s s e s .  p r e s s u r e r i s e was  may  beginning  i n c r e a s e d i n the  For the d e c r e a s i n g  decrease  and  behaviour  i n c r e a s e d a t the  influence of decrease  samples which  strain  shows t h e c o m p a r i s o n and  was  D  s t r e s s was  with  Hirschfield  Y  type of creep  to that  structure  a n  i n the decreasing  compared the  r  t h e mean n o r m a l  initial  the dominant  that decreasing  types of creep t e s t s  t h e mean n o r m a l  the  f°  From  be d i s c u s s e d .  F i g u r e 4.11B  type of creep t e s t s .  tests  a  hence t h e s e w i l l  pore  of  / ^  tests.  p r e s s u r e s and o c t a h e d r a l  Pressures  creep t e s t s .  T  seen  explanation of t h i s  Pore  of  when  x  from  the p l o t s  of to of  the determine pore  shown i n F i g u r e 4.11B.  78 Pore sensitive is  p r e s s u r e parameter  t o change i n t o t a l  e v e n more p r o n o u n c e d  (Henkel  1960;  the changes expressed shearing  i n pore  stress  been  path.  found  This  states  of stresses  p r e s s u r e s have been  to  be  sensitivity 7*  However, f o r u n d r a i n e d  i n terms of changes stresses  has  i f s h e a r o c c u r s when  V a i d 1968).  under non-symmetrical  "A"  shear  (i.e.,  7*  shown t o be  i n o c t a h e d r a l normal  as g i v e n i n E q u a t i o n 4.2  o^)  better and  (Henkel  and  Wade  1966) .  A  Aa,-fAa^ + Aa., = —-—y - + |  u  Where Au  , ^ (Aa -Aa ) +(Aa -Aa ) +(Aa -Aa ) 2  1  a  2  was  fore  e s t i m a t e d as p r e v i o u s l y  decreasing  Henkel in  of Henkel  are  similar.  did  not  fail.  The  The  curves  upper  two  in o  this  test  F o r each  Q  1  p r e s s u r e due  and  Aa  pressure  "a" parameter  versus a x i a l f o r t h e two  a t any and  parameter.  for be  strain  3.  There-  increasing done.  i s given  types of creep  r e p r e s e n t samples particular  strain  i n c r e a s e i n time  the parameter  to  3  discussed i n Chapter  curves  "a" parameter  ased w i t h the decrease strain.  2  3  type of creep t e s t s w i l l  "a" parameter  F i g u r e 4.12.  pore  Aa  . .  2  3  of pore  o f Aa^,  i s the Henkel  the comparison  and  2  i s the increment increments  a  2  2  to  tests  which increreach  "a" i n c r e a s e d  4.2  79  Ar denotes  poi^S Nor  F4U.  —  CTi, 40-7  7/.3.21  MIN  9<Jh 44S P&I s  44-8 tex Tf * 86 M I N  qj =  ^2x461 Rsr T  S  Ci*  d~S  O  AXIAL FIGURE  4.12  Q  ^  +  F6~ STRAIN  VARIATION FOR  0  UNDRAINED  ' 29  M I N S  A4S(>st  PLANE  STRA  N- err  INCREASED  P L A N E s r ^ i N - 0 5 J)ircR£/4S£D  2-4  32  PERCENT OF  HENKEL PLANE  "a" STRAIN  AND  AXIAL CREEP  STRAIN TESTS.  80 with  increase i n axial  d e p e n d e n t on a x i a l a t minimum  strain  stress  octahedral  tests  stress  paths  stresses.  The " a " v a l u e s  in a  Q  f o r both  ( F i g u r e 4.12).  the intermediate p r i n c i p a l  the minor p r i n c i p a l  the "a" value i s  time.  the decrease  and d e c r e a s i n g  As  effective  Therefore  and e l a p s e d  e increased with  increasing  to  strain.  stress  f o r plane  i s not equal  strain  may be b e t t e r e x p r e s s e d The o c t a h e d r a l s h e a r  t e s t s , the  i n terms o f  stress  "x  " and oct  oct"  T  oct = I  a'  (a -a ) 1  = a  oct  principal  slight ^  variation  form  paths  i n a^ as  (a -a ) 3  n  by  2  1  i n t e r m e d i a t e and minor  o f creep  paths i n  strain  creep  a t h i g h normal e f f e c t i v e pore  stress  pressures.  in T . i s due t o t h e e s t i m a t e d oct  that  a  are kept  '  a o  c  t  t  ^  f°  constant during r  creep.  t h e d e c r e a s i n g o"  that of increasing  paths  test  plane  due t o i n c r e a s i n g  and  than  The s t r e s s  start  creep  variations  a r e lower  e  +  f o r the undrained  with  s h o u l d be n o t e d  tyP  2  3  e  4.13 shows t h e o c t a h e d r a l s t r e s s  A l l stress  tests.  2  v  stresses.  which decrease  tests  (a -a )  i  , o'^ a r e e f f e c t i v e m a j o r ,  dimensionless  It  +  9  e  =  1  Figure  The  2  r  m  Where a | ,  tests.  2  a  3  type  o f creep  i n F i g u r e 4.13 f o r t h e i n c r e a s i n g  have been r e l a t i v e l y  d i s p l a c e d more  •44  y DENOTES POINTS OF MINIMUM STRAIN RATES  AFTER CONSOLIDATION CREEP TESTS - 0 7 INCREASED +. CREEP TESTS - <r DECREASED  Q  0  +  ^ A  s  INCREMENTAL INCREMENTAL  X  A  LOADING LOADING  TEST TEST  - 0 7 INCREASING -<§ DECREASING  •2c  Go  FIGURE 413  •68  OCTAHEDRAL CREEP  TESTS.  •72  STRESS  •76  PATHS  (UNDISTUR8ED  80  84  FOR  UNDRAlN'ED  HANEY  •95  •88  PLANE  9T  /•Oo  STRAIN  CLAY) CO  towards t h e a creep  tests.  which  failed  for  oct T  a x i s when compared  oct  when  at  failure  Strength  ence i n t h e upper decreasing  o r a t minimum e f o r s a m p l e s  was d e c r e a s e d  -  Possible  yield  plane  was g r e a t e r t h a n  that  when o^ was i n c r e a s e d .  samples which f a i l e d  Upper Y i e l d  t o the other type of  explanations of the d i f f e r  strength f o r the i n c r e a s i n g  strain  creep tests  and  may be due t o t h e  following:  1. H i g h e r a  3  increase i n f r i c t i o n  type o f creep t e s t s ,  friction  the  2.  f o r the decreasing  when compared  to the increase i n  f o r the other type of creep t e s t s .  difficult obtained  w i t h time  to understand f o r the  friction  It is  why a h i g h e r f r i c t i o n  d e c r e a s i n g type o f creep  c o u l d be tests,  should decrease with the decrease  Instantaneous  loading  o f t h e samples g i v i n g  an  in  as .  "impulse"  w o u l d be s m a l l e r i n t h e c a s e o f " u n l o a d i n g " f o r " a ^ decreased"  tests.  Further the t r a n s i e n t  pore  would d e c r e a s e  the strength o f the increasing  of  because  creep t e s t ,  stresses  decreased  3. H i g h e r because  stress  a r e i n c r e a s e d a t t h e same t i m e , w h i l e  decreasing is  b o t h mean n o r m a l  type o f creep but the shear  tests,  mean n o r m a l  stresses  due t o l o w e r  type and s h e a r i nthe stress  are increased.  strength f o r the decreasing of prestressing  pressures  type o f creep a  1  .. oct  tests  83 Summary  1. F o r b o t h plane  the i n c r e a s i n g  strain  creep  rupture tests,  initially  decreased  gradually  until  does n o t e x i s t  reached  failure.  and  constant applied  failure  of  rate  strain  type  the s t r a i n  a minimum and t h e n i n c r e a s e d  strain rate  rate  strain  creep rupture  i s reached,  stresses w i l l  rate  tests.  t h e sample  inevitably  rupture  c a n be c o n s i d e r e d t o o c c u r .  3. E x p e r i m e n t a l strain  types o f  Secondary creep  f o r plane  2. When t h e minimum s t r a i n under  and d e c r e a s i n g  data fall  rate  of creep  suggest  that  on a s t r a i g h t  t h e p o i n t s o f minimum line  and e l a p s e d t i m e , tests.  on t h e l o g - l o g  plot  f o r increasing  This straight  line  be a l m o s t t h e same f o r t h e d e c r e a s i n g  was f o u n d t o type  of creep  tests.  4. The c u r v e  o f a sample h a v i n g  approximately log  e versus  whether  l o g t p l o t w o u l d g i v e an sample w o u l d  condition  curve would creep,  equal t o the upper y i e l d  any o t h e r  rate-time  a deviator stress of  indication  or not.  o f a sample p l o t t e d  indicate  and b e l o w  fail  strength i n the  this  that  above  t h e sample w o u l d  curve  that  A  strainthis  fail in  i t would n o t f a i l .  Snead's  (1970)  agreement  h y p o t h e s i s namely  i n terms o f " t o t a l "  incremental "additional"  loading a  Q  tests  errors  S n e a d ' s h y p o t h e s i s was total  The ing  stress  paths  strain-time  of  t o be s i m i l a r . minimum s t r a i n different.  =  f(e,  e ) was  found  i n good  stresses for  tests.  In terms o f  o f t h e o r d e r o f 2 0 % were t o be n o t v a l i d  observed.  for different  loading.  rate-time behaviour  of  increas-  t y p e s o f c r e e p t e s t s were • f o u n d  But the upper y i e l d rate  Q  deviator  and c r e e p  and s t r a i n  and d e c r e a s i n g  a  b e h a v i o u r were  s t r e n g t h and found  t o be  quite  -  85  CHAPTER 5  COMPARISON OF  This strain  and  PLANE STRAIN AND  chapter  strain  discusses  c o n d i t i o n s on  for  strain,  plane  apparatus.  The  were o b t a i n e d pically with  a  2  dates  conventional  results  °3  the  •  N  E  K  q  samples under  dimensional  conditions.  of  samples t e s t e d  K  and  q  conventional  loaded  (no  comparison  triaxial  (1970) and  triaxial  RESULTS  stress, under  c o n s o l i d a t e d Haney c l a y  from the  f r o m Snead  T  of  normally  c o n s o l i d a t e d samples =  the  rate behaviour  undrained  TRIAXIAL  apparatus lateral  Four K  triaxial  considers in axial  triaxial  only  compression  initially  y i e l d ) and  triaxial  isotro-  creep  consolione  tests  were  o performed, three a^  was  will 1.  decreased.  be  Creep t e s t s  Creep t e s t s by  3.  was  increased  The. f o l l o w i n g t y p e s  of  and  one  creep  i n which tests  compared. performed  apparatus with  2.  i n which  increasing  performed  increasing  Creep t e s t s increasing  i n the  and  performed a . and  by  i n the by  conventional  triaxial  plane  apparatus  .  decreasing  i n the  K  Q  decreasing  strain .  triaxial a_.  apparatus  by  After triaxial  consolidation  samples  (K  the  plane  consolidation)  s t r a i n and  K o deviator  were u n d e r a  o stress  while  static  consolidation)  Thus t h e  the  conventional  for K  and  q  During triaxial while no  samples  the  plane  equal  to  application different parison  of  a t t e m p t e d by a'  .; oct  Y  o  c  =  t  ^oct  =  The as all  behaviour of  the  the  shear  stress,  modes  and  tests.  octahedral  .; oct  shear  2  1  ( y  £3  oct  2  2  2  3  was of are  However, a com-  i n creep w i l l  shear y 'oct  strain rate, '  .  1  be  stress  octahedral  .  .  .  . . . .  )  are  with  strains  2  3  3  sample and  stresses  T  a  Q  laterally  creep the  samples  K  and ~  o c t a h e d r a l normal e f f e c t i v e  the  existence  parameters of  comparison purposes at  principal  of  a failure criterion. the  triaxial  ^(e -e ) +(e -e ) +(e -e )  dt ,  Where e^,  of  d i f f e r e n t types of  and  |  axis  are  samples.  l a t e r a l l y with  v a r i a t i o n , cc t h e  using  y ,; 'oct  consolidated  Therefore during  the  stress.  consolidation  conventional  longitudinal  octahedral  strain,  hydrostatic  (hydro-  deviator  s t r a i n samples would deform  and  the  u n d e r any  would deform  o^.  for  samples  paths during  c r e e p the  s t r a i n i n the  not  were n o t  effective stress  different  triaxial  5.2  strains.  a minimum s t r a i n r a t e Hence i t may  stresses,strains the  5.1  be  desirable  and  minimum s t r a i n  can  be to  used take  s t r a i n rates rate.  for  Since  t h e mean n o r m a l e f f e c t i v e  stress  a t t h e end o  consolidation  (Y , ) i s n o t t h e same f o r d i f f e r e n t t y p e s o f 'oct c * creep t e s t s , the dimensionless r a t i o s x ./(a .) and oct OCt Q ' 4-/(0' , ) w i l l be u s e d f o r c o m p a r i s o n p u r p o s e s . The oct OCt Q J  1  a  effective  stress  ratio, x ,/o . a t t h e minimum s t r a i n ' oct' oct a l s o be c o n s i d e r e d f o r c o m p a r i s o n p u r p o s e s .  rate w i l l  1  Comparison o f Creep T e s t s of  t h e samples  to  be s i m i l a r  reached is  i n the three  The s t r a i n types  i n that the s t r a i n  rate-time  of creep  behaviour  t e s t s were  rate i n i t i a l l y  rupture  life,  t o note  that the r a t i o  t o the time  2.5 t o 3 f o r p l a n e 4 to 5 f o r K  of the t o t a l  t o minimum s t r a i n  strain, triaxial  It  creep  r a t e i s about  3 to 4 f o r conventional tests.  found  decreased  a minimum and i n c r e a s e d g r a d u a l l y t o f a i l u r e .  interesting  and  -  triaxial  T h i s means t h a t most o f  o the  creep  i.e.,  rupture  life  i s spent  shear  strains  7.65 p e r c e n t compared for  tertiary  creep  stage,  at progressively increasing rates. From t h e c r e e p  dral  during  K  q  t o 0.9 p e r c e n t  that Vaid  rates vary  f o r plane  strain  The c o r r e s p o n d i n g  and 0.3% f o r K  that the octahefrom  i n conventional t r i a x i a l  2.4 t o 5.4% f o r c o n v e n t i o n a l strain  i t was f o u n d  a t minimum s t r a i n  f o r samples  triaxial.  tests  triaxial,  triaxial. o (1970) o b t a i n e d s i m i l a r  and 0.45  axial  3.4 t o  tests percent  strains are  0.6% f o r p l a n e  I t i s i n t e r e s t i n g t o note ^ values f o r strains a t  88 failure  (maximum  triaxial, at  plane ^  constant  strain  rate  strains three  strain  strain  o  a^).  tests  lines  Figure  are  triaxial  almost p a r a l l e l . this  probably p a r a l l e l The  that and  conventional  8 times  that  triaxial  rate  seen  a s shown i n F i g u r e  and p l a n e ,  lines  triaxial  tests  and d e c r e a s i n g  would  K  Q  from 5.1.  rates f o r  strain  tests  triaxial  rates  strain  rates.  rate f o r  i s about plane  tests  i s also  o f minimum s t r a i n  minimum  that  to conventional  i s clearly  l i n e o f minimum s t r a i n  f o r increasing about  strain  The i n c r e a s i n g  t i m e t o r e a c h any p a r t i c u l a r  increasing  o f minimum s t r a i n  triaxial  to the other  increases  to conventional  a^). This rates  the s t r a i n  t h e l i n e o f minimum s t r a i n  conventional  that  f o r the  i t m i g h t be e x p e c t e d  to plane ^  (increasing  5.1 shows t h a t  indicate  different  rate  strain  value  o f minimum s t r a i n  increasing  o f minimum  Therefore the  are quite  Therefore  t i m e t o any p a r t i c u l a r  triaxial  (run  tests.  o  the  rate  t r i a x i a l , to plane ' ^  from K  shear t e s t s  to the values  t h e same minimum s t r a i n  (increasing  increase  triaxial  similar  a t minimum s t r a i n  from the K  o  f o r conventional  from c r e e p t e s t s ) .  types o f creep  tests  and K  rate  obtained  For  the  failure criterion)  3.5  strain  times tests,  for increasing  a,, K triaxial tests. 1 o Therefore the s t r a i n rate-time behaviour of the i n c r e a s i n g a, c o n v e n t i o n a l t r i a x i a l , p l a n e s t r a i n and K triaxial tests 1 ^ o r  are  quite  different.  As t h e e x i s t e n c e  o f a minimum  strain  r<  —  1  Oi FIGURE  —  '  1  IO S.L  COMPARISON  1  1  /OO  IO OF  TIME LINES  1  1  IN OF  MINUTE MINIMUM  1  /Ooo STRAIN  1  |  10,000  RATES CO  rate be  c o u l d be  used  as a f a i l u r e  to correlate  ventional  triaxial  Comparison the  used  the results  tests  creep  tests,  Figure  5.1  con-  conditions.  - . To compare the stress  the results  ratio,  T  ./(a OC L  may  be  compared  may  of the increasing  to field  of Stress Ratios  different  criterion,  a t any p a r t i c u l a r  minimum  of ,)  1  OCtl  octahedral  c  shear  strain rate (Y ^.) as shown i n F i g u r e 5.2. Note t h a t (a' .) r e f e r s t o mean n o r m a l e f f e c t i v e s t r e s s a t w h i c h oct oc  c  the  sample  was  differences  i n the stress  decreasing Chapter stress  4.  to  plane  creep  be n o t e d  creep  test  increasing  tests  that  i n the stress  5.2  there  were  ing An  the decrease rate  upper  f o r 10 yield  fold  tests.  strain  i n minimum  s t r e n g t h i n terms  of T  for different  increasing tests,  plane  the curve  considerably  types  strain  (Figure  higher  than  of creep  ./(cr . ) oct oct c 1  but at a strain  ./(a' O C "C  defined  strain  Fora l l  i n T  rate,  tests.  rate.  .)  OCt  decreas-  may  be  Q  When  comparing  and c o n v e n t i o n a l t r i a x i a l  5.2)  f o r plane  Q  compared  f o r plane  i s a decrease  decrease  i n  i n the  s m a l l when  ratio creep  i n minimum  and  and d e c r e a s i n g a^, K  3  with  f o rthe  suggested  differences  seems t o be q u i t e  and d e c r e a s i n g  i n Figure  reasons  f o r the increasing  f o r the increasing  the differences  curves  The p o s s i b l e  ratio  strain  I t should  ratio  triaxial  consolidated.  strain  conventional triaxial  tests  creep are  tests,  •45r  T  k  0  0  a © CONVENTIONAL PLANE STRAIN  TR IAXIAL INCREASING CT, - INCREASINGsn.  4- + P I A NE STRAIN  DECREASING f\NCREASING C7 - $ECREA\S IN6 03  TRIAXIAL TRIAXIAL  X X  •2o  S\l6  FIGURE  lO-i MINIMUM  -a  3  S.2.  10  OCTAHEDRAL  Foci/jfcr^ct} UNDRAINED  c  AT  SHEAR  MINIMUM  CREEP  TESTS  STRAIN  STRAIN ON  RATE RATE  HANEY  -(Xoct)^  VERSUS CLAY.  PERCENT/MINUTE  (abet)*,  FOR  indicating  that plane  considerably  stiffer  than  From F i g u r e T  4-/(0'  elapsed  , )  per  Hvorslev may  f o r a l l the types like  (1960)  Figure ratio  x  and u s e d by B i s h o p f o r creep  rupture  types  of creep  . are evaluated oct  the  i n c r e a s i n g a. c o n v e n t i o n a l ^ 1 slightly,  are  obtained  strain  with  value  tests  versus  the type  increases rapidly  (Y , ) 'oct m  strain tests  of  ./a , oct oct 1  of test.  a t (y  .)  Therefore  can not i n i t s p r e s e n t  rupture.  Considerably  a failure  For  o f f as t h e  (Figure  5.4)  plane curves i n this  criteria  f o r m be u s e d  more r e s e a r c h  e x p l a n a t i o n c a n be g i v e n  ^  ./a' . oct' oct  p a r a m e t e r b a s e d on a  condition  T  a t low region  varies considerably  OCt  stress  x  and d e c r e a s i n g of these  for  rate.  and l e v e l s  S i m i l a r curves  but the behaviour  f o r m o f an e f f e c t i v e  rational  (1969)  Note t h a t both  triaxial  for increasing  of x  i n strength  clay.  (Y O_) i s n o t known a s d a t a was n o t o b t a i n e d 'oct m The  Therefore  a s p o s t u l a t e d by  o f Haney  a t t h e minimum  rate decreases.  creep  tests.  and L o v e n b u r y  tests.  a'  strain  increased  5.4 shows t h e c o m p a r i s o n o f t h e e f f e c t i v e  and  log  specimens.  decrease  to failure  . / a ' , a t (Y .) oct' oct 'oct m  the d i f f e r e n t  decreases  triaxial  of creep  a constant  i n c r e a s e i n time  n o t be v a l i d  stress  conventional  5.3 i t c a n be s e e n t h a t l o s s i n  relationship  10 f o l d  s p e c i m e n s a r e s t r o n g e r and  becomes g r a d u a l l y s m a l l e r w i t h  times,  a simple  strain  critical  f o r creep  i s needed b e f o r e  f o r the data  i n the  a  i n Figure  5.4  TIME FIGURE S.3  Toot //tr'ocOc  UNDRAINED  / 4 T  ~ MINIMUM  CREEP  TESTS  TO MINIMUM STRAIN  RATE  O M HANEY  'OOO  STRAIN  RATE  VERSUS  U,  CLAY  - t  i q o o o  K  FOR  MINUTES  /cr  FIGURE  MINIMUM £.4  OCTAHEDRAL  Tact/(Tod -HANEY  IO FT  10-2  AT  SHEAR  (Zoct)^ VERSUS CLAY.  STRAIN  C^ocOm  RATE FOR  - (Xoct )^  UNDRAINED  / » - c W / W W e CREEP  TESTS  Stress-Strain-Strain investigation that  Rate  Relationship  compared w i t h S n e a d ' s  Snead's h y p o t h e s i s o f a  increasing strain noted  a^, K  creep that  triaxial,  q  tests  taken  R e s u l t s from  (1970) r e s u l t s ,  this  show  = f ( e , e) i s n o t v a l i d f o r  Q  conventional t r i a x i a l  together.  the hypothesis o f a  1. When t h e i n i t i a l  -  and p l a n e  T h e r e f o r e i t s h o u l d be  = f ( e , e) i s n o t v a l i d ,  Q  conditions are different  (i.e.,  consolidation). 2. When t r i a x i a l  and p l a n e  even though  the i n i t i a l  K  and p l a n e *  triaxial  o  strain  deformation  a r e compared  c o n d i t i o n s a r e t h e same,  strain  (i.e.,  tests),  Summary  From t h e c o m p a r i s o n t e s t s with those o f plane it  c a n be s e e n  clay  strain  clay.  and K  behaviour  q  i n the f i e l d  conventional indication  from  q  creep tests because  creep  triaxial of K  q  of increasing c a n be u s e d  of their  i t c a n be c o n c l u d e d  triaxial  conventional creep  tests  o f creep behaviour  tests  consolidated  that of i s o t r o p i c a l l y  I f the r e s u l t s  triaxial  conditions,  and K  strain  the creep behaviour  i s quite different  solidated  field  that  of increasing  con-  plane to predict  reproduction of K  that  Q  increasing  do n o t g i v e a g o o d  under  field  c o n d i t i o n s namely  because of the be  results  the of  initial the  conventional  r e p r e s e n t a t i v e of  correlation tests  of  i s made.  isotropic  creep  the data  consolidation. triaxial  rupture  from the  Therefore  apparatus  i n the  different  field, types  may  not  unless  a  of  creep  97  CHAPTER 6  PREDICTION OF  In the  field  stage will  strain  apparatus.  be compared w i t h  The d a t a  rupture i n creep  (1970) f o r t e r t i a r y the data  obtained  the t r i a x i a l  obtained  from  this  may from  to t r i a x i a l .  using  the r e s u l t s  Hence from  be c o n s i d e r e d t o be more a c c u r a t e the t r i a x i a l  Saito's  t r , versus  strain  -  minimum s t r a i n  increasing  The p l o t  of t o t a l 3  and d e c r e a s i n g  tests.  I t was  relationship  exists  between  6.1  than  con-  the p r e d i c t i o n  plane  r a t e em i s g i v e n  creep  Equation  strain  strain  that  tests  obtained  tests.  (1965) M e t h o d  both  apparatus  should g i v e the b e t t e r s i m u l a t i o n of f i e l d  slope f a i l u r e  from  study.  s h o u l d be p o i n t e d o u t t h a t t h e l a b o r a t o r y p l a n e  when compared  creep  r e p o r t e d by S a i t o and  (1970) f r o m  the data  of creep  (1965) f o r s e c o n d a r y  Snead's method  (1961) and by Snead  ditions  for  the p r e d i c t i o n  u s i n g S a i t o ' s method  apparatus  of  FAILURE  be d i s c u s s e d and e v a l u a t e d w i t h  Uezawa  It  chapter  and by u s i n g  plane  will  this  SLOPE  observed log t  rupture  i n F i g u r e- 6.1. o r  types  of  plane  that a straight  and l o g  life,  line  as g i v e n  by  TOTAL  TIME  TO  RUPTURE  -MINUTES  log  t  1 Q  Where t r  total  This Snead  and  - 1.20  time  straight  log  line  Uezawa's 95% c o n f i d e n c e  ^  . . . .  m  i n minutes c  i s compared  with  the  lines,  of the four undrained  given  criticized  Saito's  known method before in  triaxial  taken  of time  order  o f 100% may  Saito  and Uezawa's s e c o n d a r y  equal  t o t h e minimum s t r a i n From  may  i s the only  to slope  failure  I t was  discussed,  that i f a  when e r r o r s  Therefore  assumed  Equation  6.2  and E q u a t i o n  6.3.  of the  t o be  i n t h e same  seen  t h a t a l l the  95% c o n f i d e n c e o f 1100%.  (1961) and Snead's  rate.  in this discussion  r a t e was  i t c a n be  d e v i a t i o n s i n excess  S a i t o and Uezawa's  be  the e r r o r of  l i e w i t h i n S a i t o and Uezawa's 95% c o n f i d e n c e  represent gross  "secondary  that i t could  r a t e and g i v e n  figure  (1970)  t o t h e minimum s t r a i n  strain  s h o u l d be p o i n t e d o u t t h a t t h e s e  of  clay  be n e g l i g i b l e  be t o l e r a t e d .  this  Snead  to slope f a i l u r e ,  this  data  assumption  equal  using  6.2.  i s reached.  i s r e q u i r e d f o r Haney  In the p r e d i c t i o n  time  6.2.  creep t e s t s ^  t h i s method  t h e h e l p o f F i g u r e 4.1  t o be a p p r o x i m a t e l y  Figure  Although  to predict  stage  Saito  a s shown i n F i g u r e K  (1965) method,  creep  4 with  rate"  figure.  at present  tertiary  Chapter  strain  i n this  results  (1961) a l o n g w i t h  o are a l s o  6.1  . -4 rate i n l o per minute,  (1968) , S a i t o and Uezawa  The r e s u l t s  1 Q  to rupture  . . . minimum s t r a i n  m  of  = 2.00  lines.  It  limits The  equations  (1970) a r e g i v e n  by  100  SHEAD FOR TRI CREEP TESTS. Olio)  \  FROM  THIS  PLANE ON  STUDY  FOfi  STRAIN  HANEY  CREEP  CL>4Y  ^°Sk>^" * 2 0 0 -/-20 /o° ^>»» (0  6^ _ m i n i  10  To"  fv»oLtv\  >d.fe  5ii-a.r"*v  /O"  2  MINIMUM  F-IGURE6.Z  AND  4  T1  n  to  'O  c  STRAIN  RELATION  /6" /* '  -  RATE  IO~ /MIN  BETWEEN  TOTAL  MINIMUM  4  STRAIN  TIME  RATE.  TO  RUPTURE  101  log t = 2.33 ^ r  - 0.916  log ^10  log t = 2.59 ^ r  - 0.92  log... e ^10 m  Where t e e  from  time  secondary  g  straight  strain  lines  lines  s t u d y on K  in this  plot.  the e s t i m a t e d time times  that  for K  Q  triaxial F o r any  to f a i l u r e triaxial  s  rate  rate  on  6.3  per  and  on  minute  minute  c  Uezawa,  and  Haney c l a y  and  parallel  particular  . . . .  per  Saito  creep tests fall  6.2  -4  -4 10  in  . . . .  minutes  i n 10  o b t a i n e d by  for conventional t r i a x i a l this  e  to rupture i n ^  minimum s t r a i n  m  The Snead  total  r  i n  straight  value of  strain  rates  f o r Snead's d a t a w o u l d be  results  and  3 times  that  6  for Saito  o and  Uezawa's d a t a .  The  triaxial  creep  tests  straight  lines  with d i f f e r e n t  low  and  d a t a f o r Haney c l a y from  plane  strain  times.  Therefore, for predicted  failure  of less  than  apparatus of are  may  be  3 to 6 times  the d a t a  times  from  o b t a i n e d from  plane  of  the  u n c o n s e r v a t i v e as p r e d i c t e d that  tests  higher predicted  elapsed  days,  creep  give  slopes which are f a r a p a r t a t  elapsed times but converge.at  10  for conventional  total slope  triaxial  times  strain  to  failure  condition  indicated. Saito  simple  relation  (1965) a p p r o x i m a t e d between t o t a l  time  t h e e q u a t i o n 6.2 to f a i l u r e  and  to  a  secondary  102 strain  rate given  t  He  found  fairly may  • e  r  by  =  s  216  . . . . 6 . 4  that h i s prediction  accurate,  be b e c a u s e  f o r times  the s t r a i g h t  o f time  of the order lines  from t h i s  study  the  o f few d a y s as shown  order  to slope  failure  o f few d a y s .  relationship  and S a i t o and Uezawa  converges  i n Figure  from the time of  secondary  actual failure  ascertained. was  rate  f o r plane  4 i t was  b e t w e e n 2.4 t o 3.2 strain  creep  f o r times  times  rupture found  life  to  failure  rupture  test.  t o minimum  o f 30%.  may  to  with  s m a l l as t h e p r e d i c t i o n  the a v a i l a b l e  Therefore strain for  creep  tests  prediction  is  reached  of  creep.  o f time  methods c a n n o t be c o n s i d e r e d  even p r e d i c t i o n w i t h  errors of less  than  of slope  failure  before  strain  This  failure to give  100%.  S a i t o ' s method by u s i n g d a t a c o u l d be u s e d w i t h  rupture  T h i s means t h a t  S a i t o ' s a s s u m p t i o n g i v e s an e r r o r o f t h e o r d e r considered  time  h a s t o be  that the t o t a l  the time  of  Further the  r a t e was m e a s u r e d t o t h e  t o be t h e t o t a l  In Chapter  life  strain  This  obtained  6.2.  .error i n S a i t o ' s assumption o f t a k i n g the time  was  from the plane  reasonable tertiary  as b e t t e r methods a r e n o t a v a i l a b l e  accuracy creep  stage  for this  stage  i  Snead's  (1970) M e t h o d  (1970) methods w i l l proposed  linear  and  to rupture  time  creep  tests,  -  For tertiary  be d i s c u s s e d .  for results  " was d e f i n e d by Snead  the  time  the s t r a i n  straight  line  Where  tertiary  t t  r  stage.  =  creep  Snead s 1  shows t h e rate  plane  strain  Time t o r u p t u r e  (1970) a s t h e t i m e  r a t e was m e a s u r e d  i n Figure  log^Q  6.3  from undrained  creep  "tt  during  Figure  stage,  r e l a t i o n s h i p between c u r r e n t s t r a i n  for tertiary  failure,  creep  elapsed  from  t o t h e time o f  stage.  The e q u a t i o n  o f the  6.3 i s g i v e n by  - .37 - 1.05 l o g ^ Q  tt r  time  to rupture ^  e  current tertiary  . . . .  e  6  i n minutes strain  rate i n percent/  min. Equation field,  6.5 c o u l d be u s e d  to predict  i f the c u r r e n t s t r a i n  noted  that creep  tests  i n which  times  to failure.  The  tests  r a t e i s known.  i n which  was  was d e c r e a s e d  straight  line  and l o g c u r r e n t s t r a i n  from plane  strain  conventional For  triaxial  current strain  creep  K  q  test  r a t e s o f 10  i n the  I t should  i n c r e a s e d and  relationships  tests  failure  be  creep  g i v e s t h e same p r e d i c t e d  to rupture  creep  slope  -3  between  rate f o r data triaxial  creep  are given percent  l o g time obtained t e s t s and  i n F i g u r e 6.4.  p e r minute  the pre  DATA  -fi  * x  2  FROM ALL TESTS k-0 TRMXWL - V,  PLOTTED.  INCREASED  ^-O T R M X M L - CTi .DECREASED.  A 4  h  ARE  U AXIAL  iu u  or tty - t i m e  UJ  £  xy  -  fo ru.f>tufe  Current  - mr»%  StfcAlA Tdite.  ^Ce^t/m,'^  UJ FROM  s  FOR  h  X  PLANE  TESTS  "  THIS  loo  ON  J10  tb  STUDY  STRAIN  CREEP  HANEY  SNEAD (/970)  &  CRE£ P  CLAY  = ->37 - /OS  J  lo0£  lo  '°  9(o  FOR TR/AX/AL TESTS  tt,.. 3 2  OM  -  HANEY CLAY  lo  Q /  /  z  m  a a :> u  /o' TIME: FIGURE  6.1 RELATION TO  io TO  RUPTURE  BETWEEN RUPTURE.  37  JO  it*'  CURRENT  MINS  STRAIN  RATE  AND  TIME  106 dieted both of  time  plane  to slope f a i l u r e strain  2.3 t i m e s  tests. but  and K  q  i s predicted  F o r g r e a t e r times  a t a slow r a t e .  creep tests  i s approximately  triaxial  creep t e s t s ,  to rupture this  o f times to that  strain  Plane  creep rupture t e s t s . time  take p l a c e under plane Equation  failures.  strain  the world,  decreases triaxial  Most  slope  give  failures  Therefore  laboratory  creep  s h o u l d be u s e d  on v a r i o u s s o i l s  plane  creep t e s t s  T h i s must be c o n f i r m e d b y  programmes c o n d u c t e d throughout  strain  creep  o b t a i n e d from  condition.  6.5 o b t a i n e d b y p e r f o r m i n g  time  t o rupture which a r e  to failure.  strain  under c o n d i t i o n s o f plane slope  error  Therefore the conventional  give prediction  lowest p r e d i c t e d  but a  by c o n v e n t i o n a l t r i a x i a l  u n c o n s e r v a t i v e when compared  the  t h e same f o r  tests  to predict  testing  under v a r i o u s c o n d i t i o n s  and b y a p p l i c a t i o n  of results  to f i e l d  conditions.  Summary  Saito's s t a g e and S n e a d ' s  (1965) method (1970) method  were d i s c u s s e d and f o u n d application suggested from slope  plane  f o r creep before the t e r t i a r y f o r the t e r t i a r y  t o be s a t i s f a c t o r y  according to the creep  that  to predict  strain  failures  stage.  slope f a i l u r e  creep tests  creep  stage  f o r the range o f However, i t i s  the r e s u l t s  s h o u l d be u s e d  obtained  b e c a u s e most .  take p l a c e under c o n d i t i o n s o f p l a n e  strain  and  because p r e d i c t e d  ventional  triaxial  found  S a i t o ' s method stage reaches  o b t a i n e d from p l a n e  prediction  o f time  creep  to failure  a , and d e c r e a s i n g a w e r e  results  strain  of  creep  tests.  c r e e p by  accurately  as t h e c r e e p  s t a g e by S n e a d ' s m e t h o d . f o r t h e two c a s e s o f found  con-  c o u l d be r o u g h l y  stage before t e r t i a r y  and e s t i m a t e d f a i r l y tertiary  from  t o be u n c o n s e r v a t i v e  of occurrence of slope f a i l u r e  estimated during creep  ing  of f a i l u r e  t e s t s were  when compared t o t h a t The t i m e  times  t o be t h e same.  The  increas-  108  CHAPTER 7  SUMMARY AND  The  following  the a n a l y s i s  CONCLUSIONS  is a list  of conclusions derived  of data:  1. F o r v a r i o u s t y p e s o f c r e e p r u p t u r e t e s t s strain then  rate,  decreased,  rate d i d not e x i s t  confirmed rate  initially  increased gradually  strain  until  studied the  reached  failure.  f o r these  a minimum and Secondary  tests.  This  t h e h y p o t h e s i s t h a t when t h e minimum  i s reached,  stresses w i l l considered  rate  inevitably  to occur.  r u p t u r e and f a i l u r e  The t i m e  and e l a p s e d t i m e  dition found  3. The c u r v e the upper  was  rate  stresses.  b e t w e e n minimum  samples under u n d r a i n e d  t o be a l m o s t  c a n be  strain  f o r creep rupture of normally  when a.^ was i n c r e a s e d .  which  study  strain  t o minimum s t r a i n  r e l a t i o n s h i p was o b s e r v e d  consolidated  creep  t h e sample u n d e r s u s t a i n e d s h e a r i n g  increased with decreasing sustained shearing  2. A l i n e a r  from  plane  strain  This relationship  conwas  t h e same f o r t h e t y p e o f t e s t s i n  decreased.  o f a sample h a v i n g yield  a deviator  strength i n the s t r a i n  stress rate  just  elapsed  below time  109  p l o t w o u l d g i v e an i n d i c a t i o n under  t h e same c o n s o l i d a t i o n  sustained  history with  s h e a r i n g s t r e s s e s would  particular  strain  above  c u r v e would  fail  w h e t h e r any o t h e r  this  fail  rate-time condition indicate  i n c r e e p and b e l o w t h i s  that  curve  sample  different  or not.  A  o f a sample t h e sample  that  plotted  would  i t would n o t  fail.  4. S n e a d ' s  (1970) h y p o t h e s i s namely  agreement  i n terms o f " t o t a l "  incremental a of  D  errors  tests  a  = f ( e , e) was i n g o o d  deviator  and c r e e p t e s t s .  stresses f o r  I n terms o f " a d d i t i o n a l "  o f t h e o r d e r o f 20% was o b s e r v e d .  Up = f (e, e) was f o u n d (a) When t h e i n i t i a l  t o be n o t v a l i d  The h y p o t h e s i s  -  c o n d i t i o n s o f sample a r e  different. (b) F o r t h e i n c r e a s i n g creep t e s t s (c)  the  types of plane  together. strain  deformations are  even though t h e i n i t i a l  and s t r a i n strain  decreasing  stress-strain different.  and p l a n e  types o f  c o n d i t i o n s were  same.  5. The s t r a i n - t i m e  and  when t a k e n  When t r i a x i a l compared  and d e c r e a s i n g  rate-time behaviour  creep t e s t s were a l m o s t  rate-strain  performed t h e same.  of the  by i n c r e a s i n g Butthe  b e h a v i o u r was f o u n d  t o be q u i t e  6.  The  found  t o be  quite different  consolidated  7.  of K  creep rupture behaviour  Saito's  from  consolidated clay that of  isotropically  method  Snead's  f o r creep  stage before  tertiary  method  for tertiary  creep  (1970)  s t a g e were d i s c u s s e d and  found  the range o f a p p l i c a t i o n  a c c o r d i n g to the creep  The  time  of occurrence of  estimated  during creep  S a i t o ' s method and  stage.  The  data  found  o b t a i n e d from  decreased.  plane  The  the  plane  strain  predicted  from  triaxial  time  using results  from  samples w i t h  time of  incre-  from p l a n e  is a list  strain  from  with  failure  specimens gave s e v e r a l  Following  tertiary  to f a i l u r e  samples,  by  by  same f o r t h a t p r e d i c t e d strain  roughly  creep  accurately  o f time  for  stage.  c o u l d be  stage reaches  prediction  t o be  satisfactory  stage before t e r t i a r y  estimated f a i r l y  d a t a o b t a i n e d from a s e d was  t o be  slope f a i l u r e  S n e a d ' s method as t h e c r e e p creep  was  clay.  (1965)  c r e e p and  q  times  using  results  the  predicted  apparatus.  of suggested  topics  for  future research: 1.  The  study of creep r u p t u r e under p l a n e  w i t h measurement o f so t h a t  the  and  the  sample  sustained shearing stress  strain side  condition  friction,  i s kept  constant  Ill with  the  i n c r e a s e of time.  creep rupture tests which  The  c r e e p r u p t u r e c o u l d be ratios,  study o f comparison of  2.  study  i n which  i s increased.  consolidation  The  extension  i s decreased s t u d y on  repeated and  of  over-  conditions.  from  in  strain  for different  drainage  of r e s u l t s  plane  and  different  The types  tests.  Similar  studies of creep  r u p t u r e i n the K  triaxial o  apparatus. and t o be  The  strengths of  types of undrained these  compared w i t h  increasing creep the  results.  on  of time the  of  line  l o a d i n g o f the creep d e v i a t o r  o f minimum s t r a i n  of creep r u p t u r e i n terms o f e f f e c t i v e  in  attempt  The  d a t a on  basis  to o b t a i n  i n the  of e f f e c t i v e  6. An  soils  attempt  time  time  criteria  s t r e n g t h t o be concept,  S h i b a t a and  under d i f f e r e n t  to f a i l u r e  failure.  failure  stresses  done by  to f i n d  to  stresses,  f o r creep  field.  upper y i e l d  investigations other  total  upper  Study  used  and  rates,  strength  an  tests  plane  yield  t o be  5.  decreasing  effect  stress  4.  upper y i e l d  compared, and  strain 3.  The  analyzed  similar  Karube  to  on  the  the  (1969) f o r  conditions.  a b e t t e r method f o r p r e d i c t i n g  d u r i n g the  creep  stage before  tertiary  creep  stage.  Snead's(1970) method  and S a i t o s 1  method o f p r e d i c t i n g t i m e t o s l o p e tertiary different  creep types  stage  t o be compared  of s o i l  The p r e d i c t i o n o f s l o p e field (1970)  failure  during  and s t u d i e d f o r  under d i f f e r e n t  c o n d i t i o n s by u s i n g methods.  failure  (1969)  conditions.  t o be c h e c k e d f o r  Saito's  (1969) and  Snead's  113  REFERENCES  1.  B i s h o p , A.W., H e n k e l , D . J . (1962), "The measurement of s o i l p r o p e r t i e s i n t h e t r i a x i a l t e s t , " Edward A r n o l d , Second E d i t i o n .  2.  B i s h o p , A.W., and L o v e n b u r y , H.T. ( 1 9 6 9 ) , " C r e e p c h a r a c t e r i s t i c s o f two u n d i s t u r b e d c l a y s " , P r o c , 7 t h I n t . C o n f . on S.M.F.E., M e x i c o , V o l . 1, pp. 29-38.  3.  B j e r r u m , L . , Simmons, N. and T o r b l a a , I ( 1 9 5 8 ) , "The e f f e c t o f t i m e on t h e s h e a r s t r e n g t h o f a M a r i n e c l a y " , P r o c . B r u s s e l s c o n f . on E a r t h P r e s s u r e P r o b l e m s , V o l . 1, 1958.  4.  B l i g h t , G.E. ( 1 9 6 3 ) , "The e f f e c t o f n o n - u n i f o r m p o r e p r e s s u r e s on l a b o r a t o r y m e a s u r e m e n t s o f t h e s h e a r strength of s o i l s . " Symposium, l a b o r a t o r y s h e a r t e s t i n g o f s o i l s , O t t a w a , ASTM, STP. 361.  5.  B y r n e , P.M. sitive  6.  Campanella ( 1 9 6 5 ) , " E f f e c t o f t e m p e r a t u r e and s t r e s s on t h e t i m e - d e f o r m a t i o n b e h a v i o u r o f s a t u r a t e d clay". Ph.D. T h e s i s , U n i v e r s i t y o f C a l i f o r n i a , Berkeley.  7.  C a m p a n e l l a and M i t c h e l l (1968), " I n f l u e n c e o f tempera t u r e v a r i a t i o n s on s o i l b e h a v i o u r " . Journal of s o i l m e c h a n i c s and f o u n d a t i o n d i v . , ASCE, V o l . 94, No. SM. 3.  8.  C a m p a n e l l a and V a i d ( 1 9 7 0 ) , "K t r i a x i a l • apparatus". S o i l M e c h a n i c s s e r i e s , No. 15, U.B.C.  9.  C a s a g r a n d e , A. and W i l s o n , S. ( 1 9 5 1 ) , " E f f e c t o f r a t e o f l o a d i n g on s t r e n g t h o f c l a y s and s h a l e s a t c o n s t a n t water c o n t e n t " . G e o t e c h n i q u e , V o l . I I , No. 3, J u n e 1951.  (1966), " E f f e c t i v e s t r e s s p a t h s c l a y " , M.A. S c . T h e s i s , U.B.C.  i n a sen-  10.  C r a w f o r d ( 1 9 5 9 ) , "The i n f l u e n c e o f r a t e o f s t r a i n o n effective stresses i n a sensitive clay". Papers on s o i l s , ASTM, STP. No. 254.  11.  C r a w f o r d ( 1 9 6 3 ) , " D i s c u s s i o n " , Symposium on l a b o r a t o r y s h e a r t e s t i n g o f s o i l s , ASTM, STP No. 361, p p . 184-185.  114  12.  G o l d s t e i n , M. a n d T e r - S t e p a n i a n , G. ( 1 9 5 7 ) , "The l o n g t e r m s t r e n g t h o f c l a y s and d e p t h o f c r e e p o f slopes". P r o c e e d i n g s , 4 t h I n t . C o n f . o n SM & F . E . V o l . I I , pp. 311, 1957.  13.  Gupa,  14.  H a e f e l i , R. ice".  R.C. (1967), " E f f e c t o f s t r a i n r a t e and s t r u c t u r e on t h e d e v e l o p m e n t o f c o h e s i o n and f r i c t i o n i n a s e n s i t i v e c l a y . " M.A.Sc. U.B.C.  and  ( 1 9 5 3 ) , " C r e e p p r o b l e m s i n s o i l s , snow a n d P r o c e e d i n g s , 3rd I n t . C o n f . on s o i l . Mech.  Found. Eng., V o l . I l l , pp.  238-251,  1953.  15.  H a e f e l i , R. a n d S c h a e r e r , (1953), " B e h a v i o u r under the influence of s o i l creep pressure of a concrete bridge in Switzerland". P r o c , 3rd I n t . Conf. on S.M. & F.E., V o l . I I , p. 175, 1953.  16.  Henkel, D.J. ( 1 9 5 7 ) , " I n v e s t i g a t i o n o f two l o n g t e r m f a i l u r e s i n L o n d o n c l a y s l o p e s a t Wood a n d N o r t h o l t " , P r o c e e d i n g s 4 t h I n t . C o n f . o n S.M. and Found Eng., V o l . I I , p. 315, 1957.  17.  Henkel, D.J. remolded strength  ( 1 9 6 0 ) , "The  shear strength of saturated c l a y s " , ASCE, R e s e a r c h c o n f e r e n c e on s h e a r of cohesive s o i l s , Boulder, Colorado,  pp. 533-554. 18.  Henkel, on  D . J . a n d W a d e , N.H. a s a t u r a t e d remolded  Found.  (1966), "Plane s t r a i n clay",  D i v . , ASCE, V o l . 92,  Jour,  S.M.  6,  of  pp.  S.M.  tests and  67-80.  19.  H i r s c h f i e l d , R.C. ( 1 9 6 0 ) , " D i s c u s s i o n , S e s s i o n 4", A S C E , R e s e a r c h c o n f e r e n c e on s h e a r s t r e n g t h o f c o h e s i v e s o i l s , B o u l d e r , C o l o r a d o , pp. 1073-1079.  20.  H i r s t , T . J . (1966), " T r i a x i a l Compression t e s t s on an undisturbed sensitive clay". M.A. Sc. T h e s i s , U.B.C.  21.  H v o r s e l e v , M.J. (1960), " P h y s i c a l components o f t h e shear strength of saturated c l a y s . " Proc. ASCE, Res. C o n f . Shear s t r e n g t h o f c o h e s i v e s o i l s , B o u l d e r , pp. 437-501.  22.  Lou,  23.  L u b a h n , J.D., creep of York, p.  J.K. ( 1 9 6 7 ) , "The e f f e c t o f s e c o n d a r y c o m p r e s s i o n on s h e a r s t r e n g t h . " M.A.Sc. T h e s i s , U.B.C. a n d F e l g a r , R.P. (1961), metals", John W i l e y and 600.  "Plasticity Sons I n c . ,  and New  115  24.  M i t c h e l l , J . K . a n d C a m p a n e l l a , R.G. (1963), "Creep studies on s a t u r a t e d c l a y s , " Symposium on L a b o r a t o r y s h e a r t e s t i n g s o i l s , ASTM-NRC, O t t a w a , C a n a d a , ASTM s p e c i a l T e c h n i c a l P u b l i c a t i o n s , No. 361.  25.  M i t c h e l l , J . K . , C a m p a n e l l a , R.G., a n d S i n g h , A. (1968) " S o i l c r e e p as a r a t e p r o c e s s . " J o u r , o f S.M. and F o u n d D i v . A S C E , V o l . 9 4 , S.M. 1, p p . 231-254.  26.  M i t c h e l l , J.K., S i n g h , A . , C a m p a n e l l a , R.G., (1969) "Bonding, E f f e c t i v e s t r e s s e s , and s t r e n g t h o f soils," J o u r , o f S.M. and Found D i v . ASCE, V o l . S.M. 5, p p . 1 2 1 9 - 1 2 4 6 .  95,  27.  M u r a y a m a , S. a n d S h i b a t a , T . (1961), " R h e o l o g i c a l properties of c l a y s " , Proc. 5th I n t . conf. soil Mech. and Found Eng., pp. 269-273, 1961.  28.  Pao,  29.  P e n m a n , A.D.M. ( 1 9 6 0 ) , "A s t u d y o f t h e r e s p o n s e t i m e various types of Piezometer," C o n f . on p o r e p r e s s u r e and s u c t i o n i n s o i l s , London, B u t t e r worths, 1961.  30.  S a i t o , M. a n d U e z a w a , H. (1961), " F a i l u r e of creep, Proceeding of the 5th I n t . Conf. F.E., P a r i s , V o l . I , pp. 315-318.  31.  S a i t o , M. (1965), " F o r e c a s t i n g the time o f o c c u r r e n c e o f a slope failure," P r o c . 6 t h I n t . C o n f . o n S.M. & F.E., M o n t r e a l , V o l . I I , pp. 537-541.  32.  S a i t o , M. (1969), " F o r e c a s t i n g time of s l o p e f a i l u r e by tertiary creep," P r o c . 7 t h I n t . C o n f . o n S.M. & F.E., M e x i c o , V o l . I I , pp. 677-683.  33.  S i n g h , A and M i t c h e l l , J.K. (1968), "General s t r a i n time f u n c t i o n f o r s o i l s " . Jour, & Found D i v . ASCE, J a n u a r y 1968.  34.  S i n g h , A . and M i t c h e l l , J.K. (1969), "Creep potential and c r e e p r u p t u r e o f s o i l s , " Proc. 7th I n t . Conf. o n S.M. and F.E., M e x i c o , pp. 379-384.  35.  S h i b a t a , T. a n d K a r u b e , D. (1969), "Creep r a t e s t r e n g t h or, c l a y s , " Proc. 7th I n t . Conf. & F.E., M e x i c o , pp. 379-384.  Y.H. and M a r i n , J . curves from s t r e s s 1952, V o l . 52, pp.  (1952), " P r e d i c t i o n o f c r e e p strain data," P r o c . ASTM, 951-957. of  s o i l due t o o n S.M. &  stressof S.M.  and of  creep S.M.  116  36.  S h e r i f , M.A. ( 1 9 6 5 ) , "Flow and F r a c t u r e P r o p e r t i e s o f S e a t t l e C l a y s " , R e s e a r c h s e r i e s No. 1, U n i v e r s i t y o f W a s h i n g t o n S o i l E n g i n e e r i n g , J a n u a r y 1965.  37.  S n e a d , D. ( 1 9 7 0 ) , " C r e e p s t u d i e s on an u n d i s t u r b e d sensitive clay," F o r t h c o m i n g Ph.D. T h e s i s , U.B.C.  38.  S u k l j e ( 1 9 6 1 ) , "A l a n d s l i d e due t o l o n g t e r m c r e e p , " P r o c e e d i n g s 5 t h I n t . C o n f . on S.M. & F o u n d . E n g . V o l . I I , p . 727, 1 9 6 1 .  39.  V a i d , Y.P. (196 8), " A p l a n e s t r a i n M.A. S c . T h e s i s , U.B.C.  40.  V a i d , Y.P.  41.  V i a l o v , S. and S k i b i t s k y , A . ( 1 9 5 7 ) , " R h e o l o g i c a l p r o c e s s e s i n f r o z e n s o i l s and d e n s e c l a y , " P r o c . 4th I n t . C o n f . on S.M. & F . E . , V o l . I , p . 121, 1957.  42.  W a l k e r , L.K. ( 1 9 6 9 ) , " U n d r a i n e d c r e e p o f a clay," G e o t e c h n i q u e , December 1969.  (1970), F o r t h c o m i n g  apparatus  Ph.D. T h e s i s ,  for soils," U.B.C.  sensitive  117  APPENDIX I EXPERIMENTAL PROCEDURE  The preparation and setting up of the sample i n the plane s t r a i n apparatus was done i n the same way as i n Vaid  (1970).  Once the apparatus with the sample was  set  up i n the loading frame, the v e r t i c a l and l a t e r a l stresses on the samples were gradually increased with the same increments to 90 PSI.  The "B" value was estimated and found  to be varying between 94% and 100%.  To further increase  the degree of saturation the samples were l e f t undrained under the applied v e r t i c a l and l a t e r a l stress of 90 PSI for  about 12 hours before the s t a r t of the  process.  The samples were K  q  consolidation  consolidated for 3 6 hours,  followed by a period of 12 hours during which the  samples  were l e f t undrained. The deviator stress required for creep rupture was obtained by using a three-way valve as described i n Chapter 3.  Once this creep deviator stress was applied to the  sample the v e r t i c a l deformations and pore pressures were measured t i l l of time  f a i l u r e of the sample, at d i f f e r e n t  intervals  (in order to plot a smooth s t r a i n log time curve  to  calculate  strain  r a t e s Appendix  constant  vertical  slightly  i n c r e a s i n g the a i r pressure  the  sample  sustained  II).  compressed  and  s t r e s s was  i t s area  The  condition of  maintained  by  i n t h e a i r p i s t o n as  increased  slightly.  (Chapter 3 ) .  The w a t e r c o n t e n t at  t h e end o f c r e e p  rupture  o f t h e s a m p l e s were d e t e r m i n e d tests.  119  A P P E N D I X  C A L C U L A T I O N  OF  II  S T R A I N  R A T E S  The s t r a i n r a t e s were computed by u s i n g the s t r a i n log  time p l o t  as shown i n F i g u r e A l .  drawn through the s t r a i n - l o g "raw" d a t a .  A smooth curve was  time p o i n t s p l o t t e d  from the  The technique t o c a l c u l a t e s t r a i n r a t e s assumes  a l i n e a r change i n s t r a i n  f o r f i n i t e time i n t e r v a l s .  The  s t r a i n r a t e a t a g i v e n time " t " was determined by s u b s t r a c t ing  the v a l u e of the s t r a i n a t (t - At) from the v a l u e a t  t + At and d i v i d e d by time i n t e r v a l At (Figure A l ) .  That  i s the s t r a i n a t B (Figure Al) was taken t o bes Strain  ordinate at C - strain ordinate at A time AC  (natural  scale).  lat'At!  EQUAL T / M E INTERVALS  (SMALL)  it  LOG F/GURE/d  CALCULATION  T/ME OF  STRAIN  RATES.  121  APPENDIX WATER CONTENT, CONSOLIDATION A.  STRESSES AND  UNTRAINED  Test No.Devlaiar  445  PetCeri qqB After  PSI -C2  4/8  RSJ.-C3 RS1-C4 PS1-C5  407  39-5 39 0  PS1-C&  38-2  8-  - PSI  103a Q7-3 94-5 9/7 906 £8 7  UNDRAINED  AT  DURING  PLANE  Stress duriij Creep - fiSl  PSl-Cl  111  2.9-4  290 29-8 29-8 29-8  29-6  THE  OF  CREEP.  STRAIN  CREEP TESTS-01 INCREASED  OS After , Creep ConSol'ckli'a - PSI - PSI  34-8 550 5S3 54$ 55-8 54i  PLANE STRAIN  END  993  <Jj cLun'Kg C*eef>  . Psi 54 8  Waiter Content - Percent 34-7 342  Q7$ $5-2 94 3 94-8  v5v5-8  93-J  <54-S  54-9  CREEP TESTS-  34-2 342 340 342  DECREASED.  I  Test No. Dc.via.tor Percent 05, After eg A-fter CJ7d.Uri"np ConSoli<Uii<ii\ SirfiBBdurig of , Creep CansoliAadui CJj J M - PSL G-eeP-fel -Rsl -PSI  Water Creep -PSI  Content -Percent.  P S 3 - C 1  4 6 - 1  1 0 4 2  3 0 2  S4-4  84 Q  38S  3 4  P S 3 - C 1  4 4  / 0 I - 7  S 0 4  542  8 4 - 6  39 g  34 £  PS3-C3  4 2 - 6  9 6 - 3  3 0 - 1  542  84q  421  34 6  PS3-C4  4 2 5  9<S2  v 3 0 0  542  S4-2  9 3 - 5  3 0 0  548  84 B  41-G 43-6  34 434-8  PS3-C5  •§  4 / - 3  0  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0050564/manifest

Comment

Related Items