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Ground surface motions in the Fraser delta due to earthquakes Wallis, Douglas Montague 1979

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GROUND SURFACE MOTIONS IN THE FRASER DELTA DUE TO EARTHQUAKES BY DOUGLAS MONTAGUE WALLIS BiAi  S C . , U N I V E R S I T Y OF B R I T I S H C O L U M B I A ,  1975  A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L L M E N T OF THE R E Q U I R E M E N T S FOR THE D E G R E E OF MASTER OF A P P L I E D S C I E N C E  US  THE FACULTY OF GRADUATE STUDIES (Department of C i v i l Engineering)  We a c c e p t to  this  thesis  the required  as  standard  THE U N I V E R S I T Y OF B R I T I S H April,  conforming  COLUMBIA  1979  <c) DOUGLAS MONTAGUE WALLIS, 1979  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r  an advanced d e g r e e a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e - f o r r e f e r e n c e and I f u r t h e r agree that permission f o r s c h o l a r l y p u r p o s e s may by h i s r e p r e s e n t a t i v e s .  for extensive  study.  copying of this thesis  be g r a n t e d by the Head o f my Department o r It i s understood that copying or p u b l i c a t i o n  o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my written  permission.  Department The U n i v e r s i t y o f B r i t i s h Columbia 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5 Date  • E-6  BP  75-51  I E  dPc*  2  7?  ABSTRACT  The purpose o f t h i s t h e s i s i s to i n v e s t i g a t e the p o t e n t i a l ground s u r f a c e motions i n the F r a s e r D e l t a due to earthquakes. The g e o l o g i c a l h i s t o r y o f the area i s reviewed and i n f o r m a t i o n concerning the nature o f the t h i c k s o i l d e p o s i t s t h a t form the  Delta i s presented.  soils for  a r e c a l c u l a t e d and a model o f the d e p o s i t i s developed  use w i t h e x i s t i n g computer a n a l y s i s based on wave  propagation theory. the  The dynamic p r o p e r t i e s o f the D e l t a  The computer a n a l y s i s method i n v o l v e s  computation o f the ground motions as a v e r t i c a l l y  propagating shear wave passes from bedrock, through l a y e r s , to the s u r f a c e . at  soil  The accuracy o f the model was checked  t h r e e s i t e s by comparison o f the s u r f a c e motions  computed  u s i n g a recorded bedrock o b j e c t motion w i t h the ground  surface  motion recorded d u r i n g the same earthquake.  correlation  The c l o s e  between the computed and recorded motions confirms the v a l i d i t y of  the a n a l y s i s method and the s o i l model. The s u r f a c e motions r e s u l t i n g from l a r g e r , maximum p r o b a b l e ,  earthquakes a r e computed.  I t was found t h a t the t h i c k  d e p o s i t s o f the D e l t a a f f e c t both the ground  accelerations  and the p e r i o d o f the peak s t r u c t u r a l a c c e l e r a t i o n s . the  soil  Under  i n f l u e n c e o f low magnitude earthquakes the maximum a c c e l e r a -  t i o n i s l a r g e r on the s u r f a c e o f the deep s o i l d e p o s i t s than i t i s on nearby bedrock o u t c r o p s , w h i l e f o r l a r g e magnitude earthquakes the  reverse i s true.  During l a r g e magnitude earthquakes, s h o r t  b u i l d i n g s with p e r i o d s o f 0.25 s e c . w i l l  experience greater  a c c e l e r a t i o n s i f they a r e founded on bedrock than they w i l l i f  founded on the  thick  buildings  periods  far  with  greater  deposits  than  with  magnitude  they would  the  6 or  empirical  of  the  9 meter  deposits  of  a b o u t one if if  they  are  depth.  Taller experience  Test  is  sand d e p o s i t s ,  soil  bedrock.  indicates  liquefaction  Delta.  founded on deep  founded on  relations  Delta  the  second w i l l  Standard Penetration  earthquakes  few meters  of  accelerations  Comparison o f Delta  soil  data that  likely but  is  in  the  Fraser  under  large  in.the  upper  unlikely  below  -ivTABLE OF CONTENTS PURPOSE AND SCOPE  1  CHAPTER 1  INTRODUCTION TO THE AREA OF STUDY  3  Physical Setting Pre P l e i s t o c e n e H i s t o r y Pleistocene History Post G l a c i a l H i s t o r y  3 6 7 10  1-1 1-2 1-3 1- 4 CHAPTER 2 2- 1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 2- 11 CHAPTER 3 3- 1 3-2 3-3 3- 4 CHAPTER 4 4- 1 4-2 CHAPTER 5 CHAPTER 6 6-1 6-2  SOIL CHARACTERISTICS OF THE FRASER DELTA,. .  12  S o i l Type and Extent S o i l Data requirements S o i l Data Source and Accuracy Water Content Atterberg Limits Compression Index Undrained Shear Strength Dry Density o f Sand Standard P e n e t r a t i o n Test R e l a t i v e Density o f Sands F r i c t i o n Angle o f Sands  12 17 18 20 21 24 25 27 28 39 48  DYNAMIC ANALYSIS  51  Type o f A n a l y s i s S o i l P r o f i l e s and Dynamic P r o p e r t i e s Pender I s l a n d Earthquake C o r r e l a t i o n S e i s m i c i t y and the Design Earthquake  51 56 68 73  RESULTS  81  Pender I s l a n d Earthquake C o r r e l a t i o n A n a l y s i s Using the Design Earthquake  81 87  COMMENT ON THE LIQUEFACTION POTENTIAL OF THE FRASER DELTA  95  CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH  99  Conclusions Suggestions f o r F u r t h e r  LIST OF REFERENCES  Research  99 101 190  -vAPPENDIX  1  19 5  APPENDIX  2  196  APPENDIX  3  19 8  -viLIST OF TABLES  R e l a t i v e Density Data  -vii• LIST OF FIGURES Figure  Page  1-1- 1  Index Map o f F r a s e r Lowland  103  1-1- 2  P h y s i o g r a p h i c Regions  104  1-1-•3  Recent . S u r f i c i a l  Deposits  105  1-1- 4  Depth to G l a c i a l  Till  106  1-1- 5  Depth to Bedrock  107  1-2- 6  Geolog i c Time S c a l e  108  2-1- 1  D i s t r i b u t i o n of S u r f i c i a l S o i l  2-1- 2  Surficial Soil  2-4- 1  Clay:  Water Content vs Depth  111  2-4- 2  Silt:  Water Content vs Depth  112  2-4- 3  Peat:  M o i s t u r e Content vs depth  113  2-5- 1  Clay:  L i q u i d L i m i t and P l a s t i c L i m i t vs Depth  114  2-5- 2  Silt:  L i q u i d L i m i t and P l a s t i c L i m i t vs Depth  115  2-5- 3  Silt:  Plasticity  Index vs Depth  116  2-5- 4  Clay:  Plasticity  Index vs Depth  117  2-5- 5  Plasticity  2-6-•1  Silt:  Compression Index vs Depth  119  2-6- 2  Clay:  Compression Index vs Depth  120  2-7-•1  Clay:  Undrained Shear S t r e n g t h vs Depth  121  2-7- 2  Silt:  Undrained Shear S t r e n g t h vs Depth  122  2-8- 1  Sand:  Dry D e n s i t y vs Depth  123  2-9- 1  Blow Count vs Depth i n Sand  Types  Profiles  109 110  Chart  118  (Typical)  124  -viiiFigure 2-9-2  Page  ;  C o e f f i c i e n t o f R e l a t i v e Curve Smoothness Depth f o r SPT i n sand:  Comparison  vs  125  between  Blow counted from 0 to 0.3m. and from 0.15m -0.4 5m on each sample. 2-9-3  Data from 3 s i t e s .  C o e f f i c i e n t o f R e l a t i v e Curve Smoothness Depth f o r SPT i n Sand:  Comparison  vs  126.  between  Blows Counted from 0 - 0.3m and from 0.3 0.6m on each Sample, 2-9-4  Data from 3 s i t e s .  Comparison o f SPT Blow Counts Recorded i n f i r s t  127  0.3m w i t h those r e c o r d e d from 0.15m - 0.4 5m on Sample o f sand, Data from 3 s i t e s . 2-9-5  Comparisons o f SPT Blow Counts Recorded i n  128  F i r s t 0.3m w i t h those recorded from 0.3 t o 0.6m. on Same Sample o f Sand, Data from 3 sites. 2-9-6  Comparison o f SPT Blow Counts Recorded i n the  129  F i r s t 0.3m w i t h those recorded a t o t h e r p o s i t i o n s on the same sample o f sand. 2-9-7  Comparison s i t e :  Blow Count vs Depth i n Sand.  130  Blow Counts Recorded f o r P e n e t r a t i o n from 0 0.3m. 2-9-8  Comparison S i t e :  Blow Count vs Depth i n Sand.  131  Blow Counts Recorded f o r P e n e t r a t i o n from 0.150.45m. 2-9-9  Comparison S i t e :  2-9-10  Roberts Bank:  Blow Count vs Depth i n Sand  Blow Count vs Depth i n Sand  132 133  -ixFigure  Page  2-9-11  Sturgeon Bank:  Blow Count vs Depth i n Sand  2-9-12  Tilbury Island:  2-9-13  Sea I s l a n d :  2-9-14  Ladner:  2-9-15  Annacis I s l a n d :  Blow Count vs depth i n Sand  138  2-9-16  Annacis I s l a n d :  Blow Count vs Depth i n Sand  139  2-9-17  Richmond:  2-9-18  Head o f D e l t a , Blow Count vs Depth i n Sand  141  2-9-19  Byrne Rd:  14 2  2-9-20  Lulu Island:  2-9-21  North Richmond:  2-9-22  Summary, Blow Count vs Depth i n Sand  145  2-10-1  Blow C o u n t - R e l a t i v e  Density  Relationships  14 7  2-10-2  Blow C o u n t - R e l a t i v e  Density R e l a t i o n s h i p s  148  2-10-3  G r a i n S i z e Curves f o r the S o i l s Used to Develop  Blow Count vs Depth i n Sand  Blow Count vs Depth i n Sand  Blow Count vs Depth i n Sand  Blow Count vs Depth i n Sand  Blow Count vs Depth i n Sand Blow Count vs Depth i n Sand Blow Count vs Depth i n Sand  the Blow C o u n t - R e l a t i v e  Density  134 135 136 137  140  143 144  149  Relationships  2-10-4  G r a i n S i z e Curves f o r T y p i c a l F r a s e r D e l t a S o i l s  150  2-10-5  R e l a t i o n Between R e l a t i v e D e n s i t y and Blow Count  151  w i t h Depth a t a P a r t i c u l a r  Site  2-11-1  Sand:  F r i c t i o n Angle vs Dry D e n s i t y  2- 11-2  V a r i a t i o n o f Blow Count with Depth and F r i c t i o n  153  3- 1-1  H y s t e r e t i c S t r e s s - S t r a i n Path  154  3-1-2  D e f i n i t i o n o f Shear Modulus and Damping  154  3-2-1  S i t e s Chosen f o r Dynamic A n a l y s i s  155  3-2-2  Roberts Bank:  156  3-2-3  Annacis I s l a n d :  3-2-4  Brighouse:  S o i l P r o f i l e and S o i l Model S o i l P r o f i l e and S o i l Model  S o i l P r o f i l e and S o i l Model  152  157 158  -x-  Figure  Page  3-2-5  Roberts Bank:  Maximum Shear Modulus  159  3-2-6  Annacis I s l a n d :  3-2-7  Brighouse:  3-2-8  Roberts Bank:  3-2-9  Annacis I s l a n d :  3-2-10  B r i g h o u s e Maximum Damping R a t i o  16 4  3-2-11  Modulus Reduction Curves  165  3-2-12  Damping Reduction Curves  166  3-4-1  D i s t r i b u t i o n o f Earthquakes i n S t r a i t o f  167  Maximum Shear Modulus  160  Maximum Shear Modulus  161  Maximum Damping R a t i o  16 2  Maximum Damping R a t i o  163  Georgia-Puget Sound Area from M i l n e e t a l (1978) 3-4-2  Major F a u l t s and L i t h o s p h e r i c Boundaries i n  16 8  Western B.C. 3-4-3  S t r a i n Release vs Time i n C o n t i n e n t a l A r e a  168  3-4-4  Magnitude vs Time R e l a t i o n f o r G e o r g i a S t r a i t -  169  Puget Sound Area, from M i l n e e t ajL (1978) . 3-4-5  Predominant  P e r i o d s f o r A c c e l e r a t i o n i n Rock  169  from Seed, I d r i s s and K i e f e r 1969. 3- 4-6  Average Values o f Maximum A c c e l e r a t i o n i n Rock  170  from Schnabel and Seed 1972 4- 1-1  Annacis I s l a n d :  Response  S p e c t r a o f Computed  171  and Recorded S u r f a c e Motions Due to Pender I s l a n d Earthquake 4-1-2  Brighouse:  Response  S p e c t r a o f Computed and  Recorded S u r f a c e Motions due t o Pender  172  Island  Earthquake 4-1-3  Roberts Bank:  Response  S p e c t r a o f Computed and  Recorded S u r f a c e Motions due t o Pender Earthquake  Island  173  -xiFigure 4-1-4  Page Annacis Island:-  Response S p e c t r a o f Motions  174  Computed w i t h i n the S o i l P r o f i l e due to Pender Island 4-2-1  Earthquake  Response S p e c t r a o f Design Earthquake s c a l e d  175  to Maximum A c c e l e r a t i o n o f 0.25g. 4-2-2  Annacis Island:  Response S p e c t r a o f S u r f a c e  176  Motions f o r Design Earthquake s c a l e d t o A  4-2-3  max=  0 . 1 6 g .  Annacis I s l a n d :  Response S p e c t r a f o r S u r f a c e  177  Motion f o r Design Earthquakes s c a l e d to A  4-2-4  max - ° ' 9 2 5  Annacis Island:  Response S p e c t r a o f S u r f a c e  178  Motions f o r Design Earthquakes S c a l e d to A  4-2-5  max ' 9= 0  3 3  Brighouse:  Response S p e c t r a o f S u r f a c e Motions  179  f o r Design Earthquake S c a l e d t o ^ ^ = 0 . 16g. 4-2-6  Brighouse:  Response S p e c t r a o f S u r f a c e Motion  to Design Earthquake S c a l e d to A 4-2-7  Brighouse:  4-2-8  Brighouse:  =0.25g.  Response S p e c t r a o f S u r f a c e Motions  f o r Design Earthquake S c a l e d to A  max  Mean o f the Response S p e c t r a f o r  Annacis I s l a n d :  181  =0.33g.  Three Design Earthquakes o f a P a r t i c u l a r 4-2-9  180  A  182  m a x  Mean o f the Response S p e c t r a  183  f o r Three Design Earthquakes o f a P a r t i c u l a r ^nax  4-2-10  Brighouse:  Response S p e c t r a o f S u r f a c e Motions  f o r Desiqn Earthquake S c a l e d t o A =0.25g. and ^ max O b j e c t Motion a p p l i e d to Top o f G l a c i a l T i l l 3  J  184  -xiiFigure 4-2-11  Page Annacis I s l a n d :  Response S p e c t r a  of Surface  185  Motions f o r Design Earthquake S c a l e d to A . =0.25g. and O b j e c t Motion a p p l i e d to max . J  Top 4-2-12  of G l a c i a l T i l l .  Annacis I s l a n d :  Mean Response S p e c t r a - O b j e c t  Motion and S u r f a c e Motion f o r A  =0.25g max  4- 2-13  186  2  Maximum A c c e l e r a t i o n on Rock vs Maximum  187  A c c e l e r a t i o n a t Ground S u r f a c e 5- 1  Blow Count - L i q u e f a c t i o n P o t e n t i a l R e l a t i o n s  188  5-2  L i q u e f a c t i o n P o t e n t i a l s o f the F r a s e r  189  Delta  -xiii-  ACKNOWLEDGEMENTS The W r i t e r wishes to express h i s thanks t o h i s research during  s u p e r v i s o r Dr. P.M. Byrne f o r h i s guidance  t h i s research.  He f u r t h e r wishes to express  h i s a p p r e c i a t i o n to Dr. R.G. Campanella f o r h i s valuable  suggestions.  Data on the s o i l p r o p e r t i e s i n the F r a s e r D e l t a were k i n d l y made a v a i l a b l e by Cook, P i c k e r i n g and Doyle L i m i t e d , MacLeod G e o t e c h n i c a l  L i m i t e d , B r i t i s h Columbia  Hydro, and the Vancouver o f f i c e o f the G e o l o g i c a l Survey of Canada.  Time h i s t o r i e s o f l o c a l earthquake motions  were provided  by Dr. W.G. Milne o f the P a c i f i c  Geoscience  Centre/Department o f Energy, Mines and Resources. The W r i t e r would a l s o l i k e to express h i s a p p r e c i a t i o n to the N a t i o n a l Research C o u n c i l o f Canada and Golder Brawner and A s s o c i a t e s who provided investigation.  f i n a n c i a l support  for this  -1PURPOSE AND The  SCOPE  F r a s e r R i v e r D e l t a i s an area  to meet i n d u s t r i a l and  t h a t i s growing r a p i d l y  r e s i d e n t i a l demands.  It is a  r e g i o n i n the most s e i s m i c l y a c t i v e zone i n Canada. engineering  s t r u c t u r e s should  earthquakes.  Design o f  i n c o r p o r a t e the e f f e c t s o f p o s s i b l e  An earthquake can produce a d d i t i o n a l f o r c e s which  must be r e s i s t e d by the s t r u c t u r a l members and can  populated  a l s o reduce the s t r e n g t h o f the foundation  foundation. s o i l by  It  processes  such as l i q u e f a c t i o n . To assess  the e f f e c t s of the earthquake induced  f o r c e s on  the s t r u c t u r e , the c h a r a c t e r i s t i c s of the earthquake must be known.  These c h a r a c t e r i s t i c s can be expressed i n terms o f a  response s p e c t r a .  I t i s w e l l documented t h a t the ground  surface  motions i n areas of deep s o i l d e p o s i t s are g r e a t l y a f f e c t e d by the type and e x t e n t o f the s o i l s p r e s e n t .  Mathematical methods  are i n e x i s t a n c e which a l l o w the ground motion c h a r a c t e r i s t i c s i n deep s o i l d e p o s i t s earthquake.  to be modelled under the i n f l u e n c e of  These m o d e l l i n g  .techniques  an  r e q u i r e knowledge of  the  dynamic p r o p e r t i e s o f the - s o i l . T h i s study i s developed i n three stages.  In the f i r s t  stage,  a v a i l a b l e data d e s c r i b i n g the extent of the s o i l d e p o s i t s and  their  engineering  soil  p r o p e r t i e s were c o l l e c t e d and  analyzed  to produce  p r o f i l e s d e s c r i b i n g the dynamic s o i l p r o p e r t i e s of three i n the F r a s e r D e l t a .  The  sites  second stage i n v o l v e d using e x i s t i n g  methods o f dynamic a n a l y s i s to f i n d the degree o f accuracy  with  which the a n a l y s i s method, using the p r o p e r t i e s determined i n stage one,  agreed with  the observed behaviour i n s i t u a t i o n s where  -2the  s u r f a c e response was known.  In the t h i r d stage the model  was  used to p r e d i c t the ground response to l a r g e r , maximum probable, earthquakes.  -3CHAPTER 1 INTRODUCTION TO THE AREA OF STUDY 1-1 P h y s i c a l S e t t i n g The F r a s e r R i v e r D e l t a occupies  an area i n the southwest  corner o f mainland B r i t i s h Columbia t h a t s t r e t c h e s eastward from the S t r a i t o f Georgia  a d i s t a n c e o f 23 k i l o m e t e r s , and  northward from Boundary Bay a d i s t a n c e o f 16 k i l o m e t e r s 1-1-1).  (figure  The most dominant geomorphological f e a t u r e o f the d e l t a  area i s the F r a s e r R i v e r , which emerges onto the d e l t a a t New Westminster through a narrow gap i n P l e i s t o c e n e sediments, and s p l i t s i n t o two major channels. gently sloping t i d a l  f l a t s extend westward 6 k i l o m e t e r s i n t o  the S t r a i t o f Georgia, slopes a r e s t e e p e r .  On the e a s t e r n d e l t a f r o n t ,  to the d e l t a f o r e - s l o p e , where the  On the southern  f r o n t , to the east o f the  P o i n t Roberts upland, the t i d a l f l a t s extend southward i n t o Boundary Bay. The  F r a s e r D e l t a forms the western p a r t o f the F r a s e r Lowland,  which s t r e t c h e s eastward from Vancouver, and north-eastward from Bellingham, 105  Washington to d e f i n e a t r i a n g u l a r area with i t s apex  k i l o m e t e r s e a s t o f the S t r a i t o f Georgia.  The F r a s e r Lowland  i s bounded on the north by the Coast Mountains and on the east by the Cascade Mountains ( f i g u r e 1-1-2). p a r t o f a major p h y s i o g r a p h i c The Georgia  I t forms the e a s t e r n  r e g i o n , the Georgia  Depression.  Depression  i s part of a linear structural  depression  which runs from A l a s k a  through Hecate S t r a i t , Georgia  Strait,  and  the Willamette-Puget Lowland to the Great V a l l e y o f C a l i f o r n i a .  -4The s u r f i c i a l d e p o s i t s o f the F r a s e r Lowland  consist of  l a t e g l a c i a l and p o s t - g l a c i a l d e p o s i t s , o v e r l y i n g o l d e r rock formations o f i r r e g u l a r topography.  These o l d e r formations  outcrop a t s e v e r a l l o c a t i o n s i n ;bhe lowland. area o f low r e l i e f silts,  The d e l t a i s an  and low e l e v a t i o n where p o s t - g l a c i a l  and c l a y s , to depths o f up to 210 meters  sands,  overlie  P l e i s t o c e n e d e p o s i t s e x i s t i n g to depths o f over 800  meters  (700 meters a t Boundary Bay). F i g u r e 1-1-3  shows the l o c a t i o n o f the s u r f i c i a l  silt,  sand and g r a v e l d e p o s i t s i n the western Fraser^Lowland. of  Areas  peat d e p o s i t s have not been marked s i n c e these are g e n e r a l l y  l e s s than 8 meters t h i c k .  A more d e t a i l e d breakdown o f the  s u r f i c i a l d e p o s i t s can be seen on maps by Johnston (1956,1957,1960).  F i g u r e 1-1-4  (1923), Armstrong  shows areas o f t i l l outcrop,  and approximate contours o f the b u r i e d c o n t a c t between the upper till  s u r f a c e and the o v e r - l y i n g  , more r e c e n t d e p o s i t s .  The  bed-  rock outcrops and the approximate bedrock contours are shown i n f i g u r e 1-1-5.  F i g u r e s 1-1-3, 1-1-4, and 1-1-5  from unpublished maps compiled by A.  have been adapted  Jerkevics.  The remainder o f the lowland c o n s i s t s o f low,  flat-topped  h i l l s or uplands separated by wide, f l a t - b o t t o m e d v a l l e y s ,  Most  of  these uplands are composed o f P l e i s t o c e n e d e p o s i t s o f g l a c i a l  or  Glaciomarine o r i g i n ;  though some, such as C a p i t o l H i l l  Burnaby Mountain have bedrock cores and a few are r a i s e d delta  (Armstrong  1957).  and marine  -5The  r e c e n t and P l e i s t o c e n e d e p o s i t s o v e r l i e T e r t i a r y  and  Cretaceous rocks which extend to depths of up to 4600 meters (Holland 1976).  To the e a s t of the lowland  the T e r t i a r y  Cretaceous rocks are reduced i n t h i c k n e s s and o v e r l i e T e r t i a r y metamorphics with u l t r a b a s i c formations.  Pre-  i n t r u s i o n s , a n d paleocene  In the south,, the c o n t a c t between the o l d e r  younger rocks i s obscure and probably (Hopkins 1966) .  and  involves a f a u l t  and  relationship  The western boundary of the bas-in i s open to  S t r a i t of Georgia.  To the n o r t h the T e r t i a r y and  the  Cretaceous  rocks reduce i n t h i c k n e s s and o v e r l i e C r y s t a l l i n e Complex.  The  Coast C r y s t a l l i n e Complex i s the g r a n i t i c u n i t which forms the mountains t h a t r i s e a b r u p t l y north of Vancouver to between and  2100  (1965).  meters.  1500  I t has been d e s c r i b e d e x t e n s i v e l y by Roddick  T h i s same u n i t u n d e r l i e s the P a l e o z o i c and  s t r a t a t h a t bound the F r a s e r Lowland to the south  Mesozoic  and  east  (McTaggert 1977). The F r a s e r D e l t a i s p r e s e n t l y growing due of r i v e r sediments on the d e l t a f r o n t .  to the  accumulation  The F r a s e r River i s the  l a r g e s t r i v e r i n B r i t i s h Columbia, with an outflow v a r y i n g from 800 m /s  to 10,000 m /s  drainage  area  3  3  (Hoos and  Packman 1974), drawn from a  o f 270,000 square k i l o m e t e r s .  20 m i l l i o n c u b i c meters of sediment per year. are d e p o s i t e d 1 to 3.5  to form t i d a l f l a t s having  The  river carries  These sediments  s l o p e s v a r y i n g from  degrees (Mathews and Shepard 1962).  A critical  t i o n of the growth p a t t e r n s o f the present d e l t a i s s i n c e i t may  examina-  important,  r e v e a l p a t t e r n s of sediment d i s t r i b u t i o n t h a t w i l l  -6-  a i d the i n t e r p r e t a t i o n o f the s o i l types and the v a r i a b i l i t y i n the b u r i e d d e l t a d e p o s i t s . I n f i l l i n g o f abandoned channels, g u l l e y formation by a c t i v e channels and slumping a r e three mechanisms t h a t d i s r u p t the uniform  d e p o s i t i o n o f the sediments.  i s r e l a t i v e l y protected  The S t r a i t o f Georgia  from the waters o f the P a c i f i c Ocean,  but i t s r e s t r i c t e d passages and the t i d a l nature r e s u l t i n c u r r e n t s which c o n t r i b u t e to the shaping o f the d e l t a .  The  i r r e g u l a r i t y o f these shaping f o r c e s and the p o s s i b l e nonu n i f o r m i t y o f i s o s t a t i c rebound w i t h i n the F r a s e r Lowland  area  (Mathews, F y l e s and Nasmith 1970),, i n d i c a t e the p r o b a b i l i t y o f a complex growth p a t t e r n .  Scotton  (1977) suggests t h a t t h i s i s  q u i t e l i k e l y , even though he found no d i f f e r e n c e i n t h e . e n g i n e e r i n g p r o p e r t i e s o f samples o f a p a r t i c u l a r s o i l type b u t o f p o s s i b l e age  difference.  T h i s suggests t h a t o n c e " c l a s s i f i e d by type, the  p r o p e r t i e s o f the d e l t a s o i l d e p o s i t s w i l l be w e l l bounded. 1-2  Pre P l e i s t o c e n e H i s t o r y In Lower Cretaceous times  (see appendix 1 f o r g e o l o g i c  time  scale) the area which i s now the F r a s e r Lowland was a marine b a s i n having  v o l c a n i c i s l a n d s ( f i g u r e 1-2-5).  the formation i n nature.  o f bedrock which was both v o l c a n i c and sedimentary  Magma rose from depths w i t h i n the e a r t h and s o l i d i f i e d  to form coarse  crystalline,  igeneous rocks, composed mainly o f  quartz d i o r i t e and g r a n o d i o r i t e . s t r a t a were i n c o r p o r a t e d inclusions.  This r e s u l t e d i n .  The o l d e r v o l c a n i c and sedimentary  i n t o the magma as r o o f pendants and  During t h i s process  some r e c r y s t a l i z a t i o n  occurred,  -7forming metamorphic r o c k s . the rock mass allowed  As c o o l i n g took p l a c e , c r a c k i n g o f  the u n d e r l y i n g magma to r i s e i n t o  c r y s t a l i z e d rocks to form dykes and  sills.  the  T h i s complex  s t r u c t u r e i s c a l l e d the Coast C r y s t a l l i n e Complex  (Formerly  known as the Coast Range B a t h o l y t h ) . In Upper Cretaceous C r y s t a l l i n e Complex was period started. P a c i f i c Ocean.  The  and Lower T e r t i a r y times  the  Coast  e l e v a t e d above sea l e v e l and an e r o s i o n a l  eroded m a t e r i a l was  By Lower T e r t i a r y times  washed towards the these sediments had  become cemented by groundwater, and compressed to form conglomerate, sandstone, s i l t s t o n e and  shale.  During  this period, volcanic  a c t i v i t y r e s u l t e d i n the formation of dykes and B u r r a r d and K i t s i l a n o Formations,  sills.  which outcrop on the B u r r a r d  P e n i n s u l a , north of the present F r a s e r D e l t a , are two sedimentary formations. two  formations, was  Johnston  not convinced  break between the two them a s i n g l e u n i t .  formations,  The  (1923), who  such  f i r s t defined  t h a t there was and Roddick  these  a prolonged  (1965) now  time  considers  S i m i l a r formations, with t h i c k n e s s e s of  over a thousand meters, underly the present  delta.  In Late T e r t i a r y times, u p l i f t of the b a s i n o c c u r r e d and sedimentary sheets were eroded i n the north to form a p e n e p l a i n s l o p i n g down to what i s now 1-3  the d e l t a  the  broad  area.  Pleistocene History The F r a s e r Lowland has  one minor i c e advance  undergone a t l e a s t three major and  (figure 6 ) .  These advances can be d i s t i n g u i s h e d  by the sequence.of s o i l d e p o s i t s l a y e d down d u r i n g and a f t e r each g l a c i a l advance.  In the Pre-Olympia p e r i o d , the Semour and Semiamu  Groups are the o n l y r e c o g n i z a b l e P l e i s t o c e n e d e p o s i t s .  They  may  -8o v e r l i e g l a c i a l and i n t e r g l a c i a l sequences non-glacial Pliocene deposits. produced two o f the three t i l l the  The Semour and the Semiamu advances l a y e r s t h a t are found u n d e r l y i n g  present F r a s e r D e l t a , and which can be seen on exposed  banks and sea c l i f f s the  (Danner 1968), o r  term ' t i l l '  river  i n the. F r a s e r Lowland.. . Throughout t h i s work  i s used as a s h o r t e r v e r s i o n o f ' g l a c i a l  till',  which i s a very compact, unsorted mixture o f sand, s i l t ,  clay  and stones, d e p o s i t e d d i r e c t l y beneath the g l a c i e r i c e .  This  excludes from the ' t i l l ' of  c l a s s i f i c a t i o n as used h e r e i n , m a t e r i a l  the same composition which has been d e p o s i t e d through water  from f l o a t i n g i c e , and which i s sometimes c a l l e d g l a c i o - m a r i n e  till.  The Olympia I n t e r g l a c i a t i o n , which s t a r t e d about 50,000 years ago, and f o l l o w e d the Semour and Semaimu advances i s the p e r i o d when the major p a r t o f the p r e s e n t l y e x i s t i n g n o n - g l a c i a l sediments were l a y e d down. time (Armstrong 19 56),  Quadra  The P o i n t Grey c l i f f s date to t h i s  and a r e p a r t o f a f l o o d p l a i n t h a t may  have extended to Vancouver I s l a n d .  The l a t e r phases o f the Olympia  I n t e r g l a c i a t i o n were p e r i o d s o f e r o s i o n f o r many areas. Much o f the  topography o f the B u r r a r d P e n i n s u l a and o f o t h e r areas o f the  F r a s e r Lowland were then shaped c l o s e to t h e i r p r e s e n t c o n f i g u r a t i o n . The Olympia I n t e r g l a c i a t i o n was f o l l o w e d by the F r a s e r t i o n , which s t a r t e d about 18,000 years ago. the  Glacia-  The f i r s t advance o f  g l a c i e r , the Vashon Stade, was the t h i r d o f the major i c e  advances t h a t shaped the topography o f the F r a s e r Lowland. d i s t r i b u t e d outwash, t i l l sediments.  Surrey T i l l  It  and g l a c i o - m a r i n e d r i f t over the Quadra"  and Newton Stoney Clay are two such d e p o s i t s  t h a t are present i n Surrey to depths o f 9 meters  (Armstrong 1956).  The r e t r e a t o f the i c e o c c u r r e d predominantly through w a s t i n g .  The  -9i c e thinned and f l o a t e d , l a y i n g down the g l a c i o - m a r i n e d e p o s i t s . As i n the Semour g l a c i a t i o n , the l a n d was depressed by the weight of the 2100 meters o f i c e . The Vashon Stade was f o l l o w e d by the Everson I n t e r s t a d e , which s t a r t e d about 13,000 years ago, and subdued the topography by infilling.  Mathews e t a l (19 70), s u b d i v i d e d the Everson I n t e r -  stade i n t o Post Vashon Emergence and the Pre-Sumas Subsidence. During the Post-Vashon Emergence, which marked the removal o f the weight o f i c e , the sand and g r a v e l d e p o s i t s o f the C a p i l l a n o Group were l a y e d down.  During the Pre-Sumas Subsidence the g l a c i o -  marine Watcom d e p o s i t s were l a y e d down. The Everson I n t e r s t a d e was f o l l o w e d by the Sumas Stade, which was a minor advance  i n which the i c e approached to w i t h i n  40 k i l o m e t e r s o f Vancouver.  I t s t a r t e d about 11,500 years ago,  and l a s t e d f o r about 1,500 y e a r s .  I t has been e s t i m a t e d t h a t a t  t h i s time , the land under p r e s e n t day Richmond was depressed by about 210 meters  (Blunden 1973), so t h a t Sumas d e p o s i t s were l a y e d  down as g l a c i o - m a r i n e l a y e r s o f sand, s i l t , material.  c l a y and unsorted  I t should be noted t h a t e s t i m a t e s both o f the times o f  the g l a c i a l p e r i o d s and o f the p o s i t i o n o f the l a n d s u r f a c e r e l a t i v e to the ocean, w i l l depend on the methods by which these v a l u e s were o b t a i n e d . 1-4  Post G l a c i a l  (Recent) H i s t o r y  A f t e r the Sumas G l a c i a t i o n , which ended between 10,000 and 8,000 years -ago, came a p e r i o d o f i s o s t a t i c adjustment: Emergence.  the Sumas  T h i s u p l i f t o f about 150 meters produced the t e r r a c e s  -10and beaches on the present day Vancouver North Shore, and  subjected  the former deep-water d e p o s i t s of the F r a s e r R i v e r to wave e r o s i o n . By 7000 BP its to  (Before Present)  the mouth of the F r a s e r advanced  e n d - o f - P l e i s t o c e n e p o s i t i o n a t present-day the p o s i t i o n now  occupied by Twigg I s l a n d .  New  Westminster  By t h i s  time,  the southward flow of the F r a s e r to Boundary Bay had stopped 1973).  from  (Blunden  A t 2500 BP the land rose about 3 meters r e l a t i v e to the  ocean, u p l i f t i n g the s a l t marshes o f f L u l u I s l a n d to form  Sea  Island. The s u r f a c e of the present d e l t a i s composed of sand and  silt  d e p o s i t s w i t h some c l a y , and l a r g e areas of peat, the l a t t e r up to 8 meters deep.  Due  to the method of growth of the d e l t a there  e x i s t abandoned r i v e r channels which have become i n f i l l e d  with  sand and  present  s i l t and covered with more r e c e n t d e p o s i t s .  The  channels are being kept s t a b l e by dredging, dyking and u s i n g to  jetties  c o n t r o l the c u r r e n t s . The present d e l t a f r o n t i s growing due  the r i v e r sediments.  Johnston  (19 23)  to the d e p o s i t i o n of  estimated the r a t e o f d e l t a  e x t e n s i o n to be 3 meters per year, w h i l e Mathews and Shepard, in  a more e x t e n s i v e survey o f f Main Channel,  to  vary on average  to  8.5 meters per year a t the 90-meter depth.  (1962)  found the r a t e there  from 2.3 meters per year a t the 6-meter depth This increased  growth r a t e a t depth means t h a t the slope of the d e l t a f r o n t i s more shallow now  than i t was  i n d i c a t e t h a t t h i s may  be due  30 years ago. to the reduced  Mathews and  Shepard  amount o f s a n d - s i z e  sediment d e p o s i t e d , as a r e s u l t of man's dredging a c t i v i t i e s i n the  -11r i v e r channels.  Luternauer  (1975) has  p o i n t e d out. t h a t the  underwater topography and r a t e o f growth at any p a r t i c u l a r on the d e l t a f r o n t i s h i g h l y v a r i a b l e .  spot  Some p a r t s are advancing  a t v a r i o u s r a t e s while o t h e r p a r t s are s t a b l e .  CHAPTER 2 SOIL CHARACTERISTICS OF THE  ;  2-1  FRASER DELTA •  S o i l Type arid Extent The p r e s e n t d e l t a c o n s i s t s predominantly  o f l o o s e sand  s i l t and c l a y d e p o s i t s r e s t i n g i n a deep b a s i n formed o f P l e i s t o d e n e d e p o s i t s o v e r l y i n g bedrock.  S u r f i c i a l deposits  can be i d e n t i f i e d by c a r e f u l mapping, however the v a r i a t i o n of  the s o i l s with depth i s more d i f f i c u l t to determine.  mentally p i c t u r i n g the d e l t a as being composed of an number of elements i n three dimensional  space, one  infinite  can  t h a t e x t e n s i v e s u r f i c i a l mapping w i l l o n l y r e v e a l the of  the elements on one plane i n t h i s space.  t h i r d dimension  see nature  Knowledge of the  can o n l y be o b t a i n e d by probing  T h i s can be done u s i n g d i r e c t d r i l l i n g and  By  vertically.  sampling  methods,  or i n d i r e c t g e o p h y s i c a l methods. If  undisturbed samples c o u l d be recovered from the  total  l e n g t h o f the d r i l l h o l e , the nature of a s i n g l e l i n e o f elements in  t h i s three dimensional  procedure  for a relatively  space would be known.  T h i s i s an  small amount of i n f o r m a t i o n .  expensive  For  reasons of c o s t , most d r i l l i n g w i l l be done with the aim of r e c o v e r i n g r e l a t i v e l y u n d i s t u r b e d samples every 1.5  or 3 meters,  and n o t i n g i n t e r m e d i a t e changes i n the s o i l s by watching c u t t i n g s being brought to the s u r f a c e w i t h the d r i l l i n g  the fluid.  T h i s method o b v i o u s l y cannot i d e n t i f y a l l the elements on a particular  line.  G e o p h y s i c a l surveys g e n e r a l l y i n v o l v e making t r a v e r s e s along the ground s u r f a c e :  hence the examination i s o f s o i l  d e f i n i n g p a r t o f a v e r t i c a l plane.  elements  U n f o r t u n a t e l y these g e o p h y s i c a l  methods are capable o n l y o f r e c o g n i z i n g major changes  in specific  s o i l p r o p e r t i e s , and then o n l y i f the surveys are r e l a t e d to borehole d a t a .  In terms o f the model o f elements i n space, t h i s means  t h a t we know something about the elements on the top plane, but very l i t t l e about elements on o t h e r p l a n e s , p a r t i c u l a r l y those near the bottom o f the space.  Knowledge o f the processes by  which these d e l t a d e p o s i t s were l a y e d down and the p r o c e s s e s which have s i n c e shaped them w i l l prove i n v a l u a b l e when t r y i n g to deduce the nature o f the d e l t a d e p o s i t s from the small amount o f data available. The depth o f bedrock i s not w e l l known.  Figure  1-1-5  i n d i c a t e s t h a t bedrock l i e s a t depths g e n e r a l l y over 300 throughout-most of the d e l t a .  meters  In the n o r t h e r n p a r t o f the d e l t a ,  where the sedimentary rocks s l o p e up to form the B u r r a r d P e n i n s u l a , the depths are s l i g h t l y l e s s , probably i n the 210 o r 240 meter depth range.  A remarkable f e a t u r e i s the i r r e g u l a r i t y o f the b u r i e d  c o n t a c t between the bedrock and the P l e i s t o c e n e d e p o s i t s .  This  can be seen both from the i n d i v i d u a l p o i n t s t h a t were o b t a i n e d from bore h o l e s , r a n g i n g from 250 to 700 meters, and from the more d e t a i l e d contours to the e a s t o f the d e l t a . were o b t a i n e d by c o n s u l t a n t s who work w i t h borehole d a t a .  These contours  correlated detailed  geophysical  The i r r e g u l a r bedrock topography would  be. the r e s u l t of e r o s i o n t h a t took p l a c e d u r i n g the u p l i f t i n  -14Oliogocene and Miocene ages, and  the g l a c i a t i o n i n the  Pleistocene  Age. Above the bedrock l i e the P l e i s t o c e n e d e p o s i t s .  Figure  shows t h a t the depth to the top of these d e p o s i t s i s l i k e l y be over 120  meters, and  i s probably  about 210  1-4 to  meters throughout  most of the d e l t a .  The  c o n t a c t between the P l e i s t o c e n e  the r e c e n t d e p o s i t s  slopes upward i n the north, u n t i l  and  the  P l e i s t o c e n e d e p o s i t s reach the s u r f a c e on the southern p a r t of the B u r r a r d i n Surrey  Peninsula.  They a l s o reach  and White Rock, and  the s u r f a c e to the  east  the south on the P o i n t Roberts  Upland, which must have been an i s l a n d i n e a r l y P l e i s t o c e n e Despite New  the f a c t t h a t Annacis I s l a n d i s c l o s e to both the  Westminster and  Surrey  times.  high  areas of P l e i s t o c e n e d e p o s i t s , the  top  of the P l e i s t o c e n e d e p o s i t s i s s e v e r a l hundred f e e t below ground surface there. Fraser  T h i s i s because a channel had been eroded by  the  River.  I t i s e v i d e n t from the d i s c u s s i o n o f g l a c i a l h i s t o r y  that  these P l e i s t o c e n e d e p o s i t s c o u l d c o n s i s t o f up to t h r e e l a y e r s of g l a c i a l t i l l , sands, s i l t s ,  and  p o s s i b l y separated clays.  of a complete p r o f i l e with  A t any  by i n t e r g l a c i a l d e p o s i t s  p a r t i c u l a r l o c a t i o n , the  of  existence  l a y e r s of each d e p o s i t type i s u n l i k e l y ,  because of the e f f e c t s of e r o s i o n . Above the P l e i s t o c e n e sediments l i e the r e c e n t  deposits.  To o b t a i n an understanding of the sequencing of the beds i t i s important to c o n s i d e r  the stages  A t the end o f P l e i s t o c e n e times,  i n (the growth o f the  delta.  the waters of the F r a s e r  River  -15emerging  from t h e i r narrow channel a t New Westminster,  slowed  as they spread o u t i n t o what was then a p a r t o f the S t r a i t o f Georgia. to  The heavy s a n d - s i z e p a r t i c l e s would q u i c k l y be dropped  form the n e a r - h o r i z o n t a l t o p - s e t beds as the v e l o c i t y and  sediment c a r r y i n g c a p a c i t y were reduced.  As the v e l o c i t y was  f u r t h e r reduced with d i s t a n c e from the r i v e r mouth,  silt-size  p a r t i c l e s were l a y e d down w i t h the s m a l l e r sand s i z e s .  A t some  d i s t a n c e from the mouth, an i n c r e a s e i n s l o p e would occur as i n c r e a s i n g l y f i n e r g r a i n e d s o i l s were d e p o s i t e d i n the r e l a t i v e l y s t i l l waters  to form the n e a r - h o r i z o n t a l bottom-set beds.  method o f development would l e a d one to expect a s o i l  This  profile  i n the d e l t a t h a t c o n s i s t s o f sands near the s u r f a c e , g r a d i n g down to s i l t s i n the middle l a y e r s , and c l a y s a t depth. T h i s g e n e r a l i z e d p r o f i l e would be a f f e c t e d by any p e r t u r b a t i o n s to such a uniform, i d e a l i z e d system.  The flow v e l o c i t y  and volume o f the F r a s e r was not c o n s t a n t , so the amount o f sediment a v a i l a b l e to be added to the d e l t a and the d i s t a n c e from the mouth to the spot where a p a r t i c u l a r p a r t i c l e - s i z e would vary w i t h time.  drop  Seasonal v a r i a t i o n s o f t h i s type r e s u l t i n  the varves t h a t have been observed i n d r i l l h o l e s on the d e l t a . V a r i a t i o n s i n bottom topography  and ocean c u r r e n t s would modify  the shape o f the advancing d e l t a .  I s o t a t i c rebound  and e u s t a t i c  s h i f t s would change the flow p a t t e r n s o f the r i v e r , and r e s u l t i n a l t e r a t i o n i n the model p a t t e r n s by e r o s i o n .  Abandoned r i v e r  channels would f i l l w i t h m a t e r i a l t h a t was o f a d i f f e r e n t nature than t h a t found i n the surrounding l a n d s .  An example o f t h i s i s  the o l d channel t h a t e x i s t s on L u l u l s l a n d to the north-west o f  -16Annacis I s l a n d and the p r e s e n t southern channel.(Armstrong 1956) I t i s from 0.8 to 1.6 k i l o m e t e r s wide and about 6 k i l o m e t e r s long. the  I t can be seen on maps o f the s u r f i c i a l d e p o s i t s because  channel was a c t i v e 'recently enough to be covered by a small  thickness of f l o o d p l a i n s i l t  i n s t e a d o f peat.  The major p a r t o f the r e c e n t d e l t a d e p o s i t s conform g e n e r a l l y to  the b a s i c p r o f i l e d e s c r i b e d , and i s thus e x p l i c a b l e on the  b a s i s o f the d e l t a ' s growth mechanism.  There a r e s u r f i c i a l  flood-  p l a i n and swamp d e p o s i t s to shallow depths, u s u a l l y l e s s than 8 meters, u n d e r l a i n g e n e r a l l y by sands to depths o f about 30 meters. a t depth. the  Under the sand there i s s i l t , which i s u n d e r l a i n by c l a y s In the P o i n t Roberts area the t i l l  surface.  l a y e r s r i s e up to  The surrounding d e p o s i t s c o n s i s t o f sands and s i l t s ,  presumably because the c l a y s s e t t l e d i n the deep water surrounded t h i s one-time  that  island.  The s u r f i c i a l d e p o s i t s o f the d e l t a area have been d e s c r i b e d by Armstrong  (1956), and those o f Richmond have been  i n more d e t a i l by Blunden  (1973) .  described  Since the d e s c r i p t i o n o f  s u r f i c i a l d e p o s i t s i s p e r i p h e r a l to the c e n t r a l purpose o f t h i s paper, o n l y b r i e f and g e n e r a l i z e d r e f e r e n c e w i l l be made to t h e i r distribution.  The western h a l f o f the d e l t a has s u r f i c i a l  deposits  which c o n s i s t o f m a t e r i a l r a n g i n g from c l a y s to sandy s i l t s , to depths o f up to 4.5 meters, o v e r l y i n g sand o r s i l t y  sand.  Generally  t h i s top l a y e r i s graded, w i t h the f i n e r m a t e r i a l b e i n g found further inland.  The western h a l f o f the d e l t a i s covered to a  l a r g e degree by s u r f i c i a l peat l a y e r s .  These peat l a y e r s may be  up to 8 meters deep and g e n e r a l l y o v e r l i e sand s i l t y  sand.  Some  -17of the t h i n n e r peat l a y e r s o v e r l y a t h i n c l a y e y - s i l t l a y e r which r e s t s on the t h i c k sand or s i l t y sand l a y e r . found i n l a y e r s of other m a t e r i a l w i t h i n 4.5 Blunden (19 73)  Peat seams are meters of the  i n d i c a t e d t h a t i n some areas tlie v a r i a b l e  often  surface.  surficial  l a y e r o v e r l i e s c l a y r a t h e r than the sand or s i l t y sand u s u a l l y found.  Figures  2-1-1  and  1-1-2  of the s u r f i c i a l d e p o s i t s ,  and  shows g e n e r a l i z e d  soil  profiles  their d i s t r i b u t i o n within  the  delta. 2-2  S o i l Data Requirements To model the behaviour of a s o i l d e p o s i t under the  of dynamic e x c i t a t i o n the s t r e s s - s t r a i n behaviour of the under the p r e v a i l i n g f i e l d c o n d i t i o n s must be known. t e s t i n g i n the l a b o r a t o r y has general  provided  influence soil  Cyclic  an understanding of  the  type o f behaviour t h a t can be expected over a range of  conditions incorporate  for various  soil  types.  The  mathematical a n a l y s i s must  a model of these s t r e s s - s t r a i n c h a r a c t e r i s t i c s t h a t  s u c c e s s f u l l y d u p l i c a t e s the behaviour of the s o i l over the  stress  range a n t i c i p a t e d , to a degree of accuracy c o n s i s t e n t w i t h  the  type o f a n a l y s i s . The  possession  of a r e a l i s t i c  s t r e s s - s t a i n law,  and  a method  o f a n a l y s i s w i t h which i t can be used does not i n i t s e l f  allow  a n a l y s i s of a f i e l d problem.  soil  The  c h a r a c t e r i s t i c s )df the  p r o f i l e must be known w e l l enough t h a t the s o i l s t r e s s - s t r a i n law can be determined.  This c o u l d be done by d i r e c t l a b o r a t o r y  t e s t i n g of the s o i l , or e m p i r i c a l l y , through a knowledge o f more easily obtainable  properties.  Unless the problem i n v o l v e s a c r i t i c a l  i n s t a l l a t i o n i n a s p e c i f i c area, d i r e c t l a b o r a t o r y t e s t i n g f o r s t r e s s - s t r a i n r e l a t i o n s i s not p r a c t i c a l because o f the  difficulty  i n o b t a i n i n g r e p r e s e n t a t i v e undisturbed samples and the e x t e n s i v e and c o s t l y t e s t i n g procedure.  The c a l c u l a t i o n of the  c h a r a c t e r i s t i c s , g e n e r a l l y expressed  stress-strain  i n terms of shear modulus  and damping a t v a r i o u s s t r a i n l e v e l s from other more e a s i l y o b t a i n a b l e p r o p e r t i e s , i s the method t h a t was  used i n t h i s  study.  T h i s method i s p a r t i c u l a r l y s u i t e d becasue o f the l a r g e a r e a l extent of the d e l t a , and  the e x i s t e n c e o f s o i l data from e n g i n e e r i n g  projects. 2-3  S o i l Data Source and  Accuracy  The development of s o i l p r o f i l e s , which presented c h a r a c t e r i s t i c s of the s o i l l a y e r s adequately was  undertaken i n three stages.  c o l l e c t i o n o f e x i s t i n g data.. borehole l o g s and  The  the  f o r a dynamic a n a l y s i s ,  f i r s t stage i n v o l v e d the  These data c o n s i s t e d mainly of the  the r e s u l t s of l a b o r a t o r y t e s t s which had been  undertaken by l o c a l g e o t e c h n i c a l c o n s u l t a n t s as p a r t o f  site  i n v e s t i g a t i o n s f o r e n g i n e e r i n g p r o j e c t s , and were made a v a i l a b l e through  the g e n e r o s i t y o f these f i r m s .  Where data was  not  a v a i l a b l e , e i t h e r because the e n g i n e e r i n g p r o p e r t y was  not  which was  one  commonly t e s t e d f o r , or because the t e s t s were not  performed i n the p a r t i c u l a r area where the i n f o r m a t i o n was a r e a l i s t i c estimate of the d e s i r e d p r o p e r t y had to be T h i s o p e r a t i o n c o n s t i t u t e d the second.stage. were estimated  needed,  obtained.  These p r o p e r t i e s  through an i n t e r p r e t a t i o n of the a v a i l a b l e  and a knowledge o f the o r i g i n s o f the d e p o s i t s .  The  third  data stage  -19i n v o l v e d the use o f the standard e n g i n e e r i n g p r o p e r t i e s t h a t had been obtained i n the f i r s t two stages to develop p r o f i l e s o f the s o i l which c h a r a c t e r i z e d t h e i r dynamic behaviour.  Essentially,  t h i s e n t a i l e d determining the shear modulus and damping r a t i o o f the s o i l l a y e r s when s u b j e c t e d to a range o f shear s t r a i n s . two  f u n c t i o n s d e s c r i b e the s t r e s s - s t r a i n behaviour o f the s o i l i n a  way t h a t enables mathematical to  These  earthquake-induced  ground  m o d e l l i n g o f the s o i l when s u b j e c t motions.  The e n g i n e e r i n g p r o p e r t i e s which are presented here range from fundamental s o i l p r o p e r t i e s such as f r i c t i o n  angle, to index  p r o p e r t i e s such as A t t e r b e r g l i m i t s o r blow count from the Standard P e n e t r a t i o n t e s t which have been c o r r e l a t e d e m p i r i c a l l y with the more fundamental p r o p e r t i e s . The data t h a t i s p o r t r a y e d on the borehole l o g s has been subjected to s e v e r a l p o t e n t i a l sources o f e r r o r b e f o r e being developed of  i n t o t h i s p r e s e n t a b l e form.  the s o i l should be c o n s i d e r e d .  The l a t e r a l  variability  The l o g o b t a i n e d from one  d r i l l h o l e i s assumed to be r e p r e s e n t a t i v e o f the immediately surrounding a r e a .  While  this i s likely  to be t r u e when c o n s i d e r i n g  the g e n e r a l form and p r o p e r t i e s o f the s o i l , i t may not be t r u e when l o o k i n g a t d e t a i l s o f the p r o f i l e because o f the s o i l v a r i a t i o n r e s u l t i n g from the i r r e g u l a r d e l t a growth. Normal d r i l l i n g  procedures  do not p r o v i d e the observer with  a complete r e p r e s e n t a t i o n o f the s o i l , even a t the p a r t i c u l a r being t e s t e d .  site  Samples o f the s o i l a r e u s u a l l y taken a t i n t e r v a l s  g r e a t e r than one meter.  The v a r i a t i o n o f the s o i l between the p o i n t s  -20of sampling i s i n t e r p r e t e d by  the d r i l l e r by q u a l i t a t i v e l y  noting  the r a t e of advance o f the b i t and  the type o f m a t e r i a l  returned as c u t t i n g s .  not be r e p r e s e n t a t i v e of  Samples may  being the  l a y e r w i t h i n which they l i e , and are d i s t u r b e d to v a r y i n g degrees, depending on the sampling procedure and care e x e r c i s e d by the  the degree o f  driller.  In the t e s t i n g o f the samples there i s o p p o r t u n i t y  to  introduce  e r r o r through improper h a n d l i n g o r the use of non-standard procedure. In s i t u t e s t i n g e l i m i n a t e s the problems of t r y i n g to procure an undisturbed  sample, but adverse f i e l d c o n d i t i o n s make i t d i f f i c u l t  to o b t a i n h i g h q u a l i t y r e s u l t s . obtained  there may  Even i f c r e d i b l e r e s u l t s are  be doubt as to whether the t e s t i t s e l f i s meaningful*  Having the d r i l l e r s l o g s , the l a b o r a t o r y c l a s s i f i c a t i o n of samples, and  the r e s u l t s of any  f i e l d or l a b o r a t o r y t e s t s performed,  the engineer must use h i s experience  and  knowledge o f the  to prepare h i s i n t e r p r e t a t i o n of the s o i l p r o f i l e . the a v a i l a b l e data had  the  area  Similarly,  to be i n t e r p r e t e d f o r the r e s e a r c h  purposes  of t h i s p r o j e c t . 2-4  Water Content Water content data  i s r e l a t i v e l y easy to o b t a i n f o r p l a s t i c  s o i l s s i n c e i t i n v o l v e s measuring the wet sample, which may Water content procedure. where 100%  and  dry weight o f a  be d i s t u r b e d so long as i t i s not allowed  i s a u s e f u l parameter to check i n the  In f i n e - g r a i n e d samples procured  to d r a i n .  classification  below the water t a b l e  s a t u r a t i o n can be assumed i t g i v e s the v o i d r a t i o of  the  -21s o i l , when m u l t i p l i e d by the s p e c i f i c g r a v i t y o f the s o l i d s . In cases where the c o n s o l i d a t i o n c h a r a c t e r i s t i c s o f the s o i l can be determined, comparison w i t h the a c t u a l change i n v o i d ratio  determined from the f i e l d water c o n t e n t w i l l  whether  indicate  the s o i l type and the method o f d e p o s i t i o n are c o n s t a n t  w i t h depth. The v a r i a t i o n o f water c o n t e n t w i t h depth f o r the c l a y s o i l s i s shown i n F i g u r e 2-4-1.  The water c o n t e n t v a r i e s  l i n e a r l y from 45% a t the s u r f a c e to 29% a t a depth o f 30 meters. Samples w i t h o r g a n i c c o n t e n t have water contents g r e a t e r than the mean.  T h i s , and the p o s s i b i l i t y t h a t water t a b l e f l u c t u a t i o n has  produced an o v e r - c o n s o l i d a t e d d e s i c c a t e d l a y e r , accounts f o r the l a r g e r v a r i a t i o n of the moisture c o n t e n t a t the s u r f a c e o f the deposit.  The water c o n t e n t p r o f i l e i n the s i l t  s o i l s has the  same form as the c l a y p r o f i l e , v a r y i n g from an average o f 41% a t the s u r f a c e to 26% a t a depth o f 60 meters as shown i n f i g u r e 2-4-2.  The presence of o r g a n i c m a t e r i a l and c l a y s near the  ground s u r f a c e , r e s u l t s i n the l a r g e r s c a t t e r i n g o f the near s u r f a c e samples towards h i g h e r water c o n t e n t s .  The water c o n t e n t  o f the peat s o i l s i s h i g h l y v a r i a b l e , as shown i n f i g u r e 2-4-3. G e n e r a l l y , seams l e s s than 0.3 meters t h i c k have water c o n t e n t s v a r y i n g from 100 to 250%.  Seams from 0.3  water contents v a r y i n g from 250% to 600%.  to 1.0 meters t h i c k have The l a r g e r l a y e r s have  moisture c o n t e n t s . v a r y i n g from 600% to 1150%. 2-5  Atterberg Limits The l i q u i d l i m i t and p l a s t i c l i m i t are u s e f u l parameters i n  the c l a s s i f i c a t i o n o f f i n e - g r a i n e d s o i l s , p a r t i c u l a r l y c l a y s .  As  -22p a r t o f the t e s t procedure  the samples a r e remolded, so the  d i s t u r b e d samples recovered d u r i n g the Standard P e n e t r a t i o n Test a r e s u i t a b l e f o r a n a l y s i s . directly  The t e s t s do not y i e l d  results  i n terms o f fundamental s o i l p r o p e r t i e s , b u t experience  has l e d to r e l a t i o n s which i n d i c a t e the g e n e r a l c h a r a c t e r i s t i c s of  the s o i l . F i g u r e 2-5-1 shows the l i q u i d and p l a s t i c  s o i l s under study p l o t t e d a g a i n s t depth. depth,  limits  f o r the c l a y  Both a r e c o n s t a n t with  the l i q u i d l i m i t having a mean v a l u e o f 34% and the p l a s t i c  l i m i t a mean value o f 22%. w i t h depth f o r the s i l t examination  A p l o t o f the l i q u i d and p l a s t i c  s o i l s i s shown i n f i g u r e 2-5-2.  A close  o f the p l o t r e v e a l s t h a t the p o i n t s a r e b e t t e r  c h a r a c t e r i z e d by d i s c o n t i n u o u s v e r t i c a l continuous  limits  sloping l i n e .  of a t l e a s t two d i s t i n c t  l i n e s r a t h e r than by a  T h i s f e a t u r e p o i n t s to the e x i s t e n c e silt  types.  The data p l o t t e d above the  d i s c o n t i n u i t y i n the mean l i n e were o b t a i n e d i n g e n e r a l from a d i f f e r e n t l o c a t i o n i n the d e l t a than the data p l o t t e d below the d i s c o n t i n u i t y so t h i s phenomina i s u n l i k e l y to be the r e s u l t o f a sudden change i n the composition o f the F r a s e r R i v e r The mean l i q u i d l i m i t i s about 40% i n the upper s i l t the lower s i l t . and  The mean p l a s t i c  23% i n the lower The p l a s t i c i t y  sediments.  and 33% i n  l i m i t i s 30% i n the upper  silt  silt. index i s d e f i n e d as the d i f f e r e n c e between the  l i q u i d l i m i t and the p l a s t i c  l i m i t , and i s i n d i c a t i v e o f the range  i n water contents over which the s o i l r e t a i n s i t s p l a s t i c i t y . 2-5-3 shows a p l o t o f the p l a s t i c i t y index i n the s i l t  Figure  soils, i t i s  constant w i t h depth., v a r y i n g from 5% to 15%, w i t h a mean o f 9%.  -23F i g u r e 2 - 5 - 4 presents soils.  a p l o t o f the p l a s t i c i t y  index i n the c l a y  I t v a r i e s from 8% to 1 7 % and has a mean o f 1 1 % . The  p l a s t i c i t y index can be p l o t t e d . a g a i n s t the l i q u i d l i m i t o f the s o i l s on the p l a s t i c i t y c h a r t , as shown i n f i g u r e 2 - 5 - 5 . to t h e i r  According  p l o t t e d p o s i t i o n on the p l a s t i c i t y c h a r t , the c l a y would  be c l a s s i f i e d as an i n o r g a n i c c l a y o f medium p l a s t i c i t y , and the s i l t s as i n o r g a n i c s i l t s o f medium c o m p r e s s i b i l i t y . soils, classified their  principally  classification  the mean values  on the b a s i s o f g r a i n s i z e , r e t a i n  when examined i n terms o f p l a s t i c i t y .  Though  f o r the s o i l s p l o t q u i t e d i s t i n c t l y on the p l a s t i c i t y  c h a r t , when the range o f values overlap s u b s t a n t i a l l y . the lower s i l t ,  These  i s considered,  This i s p a r t i c u l a r l y  the areas d e f i n e d  t r u e i n the case o f  which can almost be c l a s s i f i e d  i n these terms as a  clay. The  l i q u i d i t y index i s d e f i n e d as the d i f f e r e n c e between the  n a t u r a l water content plasticity soil  index.  and the p l a s t i c  I t provides  l i m i t , d i v i d e d by the  a measure o f the s o f t n e s s o f the  i n i t s remolded s t a t e by showing how c l o s e the moisture  of the s o i l i n i t s n a t u r a l s t a t e i s to the l i q u i d l i m i t .  content  Using  the s t r a i g h t l i n e mean r e l a t i o n s h i p s developed f o r the l i m i t s and  i n d i c e s , the l i q u i d i t y index o f the c l a y i s c a l c u l a t e d to range  from a p r o j e c t e d average o f 2 . 0 a t s u r f a c e to 0 . 6 4 a t a depth o f 50 meters.  The l i q u i d i t y index o f the upper s i l t v a r i e s from 1 . 3  a t the s u r f a c e to 0 . 5 5 a t a depth o f 2 5 meters and the l i q u i d i t y index o f the lower s i l t v a r i e s from 1 . 3 a t 2 5 meters to 0 . 3 3 a t 6 0 meters.  Each d e p o s i t shows the same t r e n d , changing from a very  consistency  i n the upper regions  to a s t i f f e r one with depth.  soft  -24-  2-6  Compression  Index  The compression index i s the slope o f the p l o t o f v o i d r a t i o versus the l o g e r i t h u m o f c o n f i n i n g p r e s s u r e o b t a i n e d from a consolidation test.  As such i t i s i n d i c a t i v e o f the amount o f  settlement t h a t can be expected to occur as the r e s u l t o f a known i n c r e a s e i n e f f e c t i v e normal p r e s s u r e .  Figure 2 - 6 - 1 i s a  p l o t o f compression index a g a i n s t depth f o r the s i l t s . presence o f two d i s t i n c t s i l t  The  types i s a g a i n r e v e a l e d by a  d i s c o n t i n u i t y i n the compression index v a l u e s w i t h depth.  The  upper s i l t has c o n s t a n t compression index w i t h depth, v a r y i n g from 0.20  to 0 . 4 0 about a mean o f 0 . 3 1 . The p l o t shows the compression  index o f the lower s i l t of  to be c o n s t a n t w i t h depth a t a mean v a l u e  0 . 2 1 , w i t h data p o i n t s i n the range from 0 . 1 5 to 0 . 2 6 .  The  data p o i n t s from the sandy s i l t s p l o t g e n e r a l l y i n the lower end of  the t h i s range, w h i l e those from the c l a y e y s i l t s p l o t i n the  upper end.  The l i m i t e d data o b t a i n e d i n d i c a t e s the compression  index o f the sand to be almost an order o f magnitude l e s s than t h a t o f the s i l t ,  w i t h a v a l u e o f about 0 . 0 6 .  The compression index o f the c l a y i s c o n s t a n t w i t h depth, v a r y i n g from 0 . 3 3 to 0 . 4 8 w i t h a mean value o f 0 . 4 2 as shown i n figure 2 - 6 - 2 .  The compression index o f c l a y s can a l s o be  estimated from the l i q u i d l i m i t u s i n g Skempton-'sr-. equation C  c  34%,  = 0.009  (liquid limit - 1 0 ) .  Using the mean l i q u i d l i m i t o f  t h i s e q u a t i o n p r e d i c t s a v a l u e o f compression index o f 0 . 2 2 .  This p r e d i c a t e d v a l u e i s l e s s than the measured v a l u e s .  The  reason may be t h a t t h i s c l a y i s more s e n s i t i v e than those used by  Skempton to d e f i n e h i s r e l a t i o n s h i p between the compression index of  remolded and u n d i s t u r b e d c l a y s . The change i n v o i d r a t i o t h a t would  d a t i o n of a homogenous s o i l d e p o s i t was to  c a l c u l a t e d and compared  the a c t u a l v o i d r a t i o change w i t h depth, based on the water  content. the  r e s u l t from the c o n s o l i -  The v o i d r a t i o i n c l a y c a l c u l a t e d a t 50 meters below  s u r f a c e from the c o n s o l i d a t i o n c h a r a c t e r i s t i c s d i f f e r s  3% from t h a t deduced  from the measured water content.  only  T h i s good  c o r r e l a t i o n confirms the h y p o t h e s i s t h a t the c l a y d e p o s i t s are normally c o n s o l i d a t e d and uniform i n s t r u c t u r e and components w i t h depth. of  constitutive  A s i m i l a r analysis gives a v a r i a t i o n  11% i n the v o i d r a t i o s a t the 30 meter depth i n the upper  and an v a r i a t i o n o f 20% a t the 50 meter depth i n the lower T h i s l a r g e r v a r i a t i o n may  silt,  silt.  be i n p a r t the r e s u l t of having used  a s i n g l e s t r a i g h t l i n e to c h a r a c t e r i z e the water content w i t h depth instead of f i t t i n g  separate l i n e s f o r the upper and lower  silts.  An examination o f the lower s i l t data r e v e a l s t h a t the water content may  change l e s s w i t h depth than i s i n d i c a t e d by the s i n g l e  straight line f i t . 2-7  Undrained Shear S t r e n g t h The undrained shear s t r e n g t h o f s o i l s may  be determined by  performing a vane shear t e s t or an unconfined compression t e s t on an u n d i s t u r b e d sample.  The torvane and pocket penetrometer can a l s o  be used to g i v e q u i c k r e s u l t s on small specimens, but are not as accurate. of  F i g u r e 2-7-1  i s a p l o t o f the undrained shear s t r e n g t h  c l a y w i t h depth as determined by these methods.  Below the 6  -26meter depth the data can be c h a r a c t e r i z e d by a s t r a i g h t p a s s i n g through  the o r i g i n .  weight of the s o i l ,  By assuming a v a l u e f o r the u n i t  the slope o f t h i s l i n e can be expressed  terms o f a r a t i o o f the undrained e f f e c t i v e overburden pressure of  0.19.  The C/P  equation, C/P  in  shear s t r e n g t h (C) to the  (P).  T h i s c l a y has a C/P  r a t i o can a l s o be estimated  = 0.10  value of 0.14.  line  ratio  from Skempton's  + 0.004 ( p l a s t i c i t y i n d e x ) , which g i v e s a  These two  estimates o f the C/P  r a t i o are i n good  agreement c o n s i d e r i n g the s m a l l number of data p o i n t s a t depth and  t h a t Skempton's equation i s g e n e r a l i z e d f o r a l l c l a y s .  Samples  o b t a i n e d i n the top 6 meters o f the d e p o s i t d e v i a t e s u b s t a n t i a l l y from the s t r a i g h t l i n e C/P  r e l a t i o n s h i p due  t i o n e f f e c t of s u r f a c e d e s s i c a t i o n . upper l a y e r range up to 105 The undrained  The  to the o v e r c o n s o l i d a -  shear s t r e n g t h s i n t h i s  kPa.  shear s t r e n g t h data f o r the s i l t s are shown  p l o t t e d a g a i n s t depth i n f i g u r e 2-7-2..  As with the c l a y , a  d i s t i n c t d e s s i c a t e d l a y e r i s p r e s e n t above the 6 meter Below the 6 meter depth,  the data are w i d e l y s c a t t e r e d .  s h a l l o w l y s l o p i n g l i n e having a C/P to  data determined  depth.  r a t i o of 0.30  i n one area u s i n g a pocket  while the s t e e p l y s l o p i n g l i n e having a C/P  The  is fitted  penetrometer,  r a t i o of 0.11  is  f i t t e d to data gathered over a s l i g h t l y l a r g e r area u s i n g v a r i o u s techniques.  The  l a r g e r v a r i a t i o n i n the r e s u l t s of the t e s t s c o u l d  be due both to the f a c t t h a t the samples were from d i f f e r e n t of  the d e l t a and  to the d i f f e r e n t t e s t s and  t e s t techniques  areas used.  -27-  The h a n d l i n g o f the sample and the r a t e o f t e s t i n g w i l l the  affect  r e s u l t s because completely undrained c o n d i t i o n s may n o t  e x i s t i n the s i l t - s i z e  sample.  Though Skempton's. e q u a t i o n was  developed f o r c l a y s , i t may be a p p l i c a b l e to a c e r t a i n e x t e n t to  these s i l t s because, as can be seen from the p l a s t i c i t y  chart  (figures  2-5-5),  the s i l t s can have a h i g h c l a y c o n t e n t .  The C/P r a t i o determined from Skempton's e q u a t i o n i s 0 . 1 4 , which between those d e f i n e d by the two s t r a i g h t 2-8  lies  lines.  Dry D e n s i t y o f Sand To measure the d e n s i t y o f a s o i l a r e p r e s e n t a t i v e sample must  be o b t a i n e d i n such a way t h a t the o r i g i n a l volume o f the sample can be measured o r c a l c u l a t e d .  The volume o f a f i n e g r a i n e d  s o i l sample can be measured as i t i s e x t r a c t e d from the ground by the sampling t o o l , o r i t can be c a l c u l a t e d i n the l a b o r a t o r y by measuring the water content i f the s p e c i f i c g r a v i t y i s known, and the s o i l the  i s saturated.  The water content o f sand and t h e r e f o r e  volume cannot be determined from f i e l d samples handled u s i n g  normal methods because the pore spaces are too l a r g e to prevent drainage o f the sample b e f o r e the wet weight can be determined. T h i s means t h a t the volume o f sample must be measured d i r e c t l y i n the f i e l d d u r i n g the sampling procedure. are  difficult  to o b t a i n a c c u r a t e l y .  d e n s i t y o f sand samples  These measurements  F i g u r e 2 - 8 - 1 shows the dry  taken from v a r i o u s l o c a t i o n s i n the d e l t a .  There i s no d i s c e r n a b l e trend w i t h depth, the v a l u e s ranging from 1 4 kN/m  3  t o 1 6 . 5 kN/m , around a mean v a l u e o f 1 5 kN/m . 3  3  -28-  The  v o i d r a t i o i s r e l a t e d to the dry d e n s i t y by  the  equation: e  = JfwGs  -1  yd Here e i s the v o i d r a t i o , Jfw i s the u n i t weight o f water, JTd i s the dry d e n s i t y of the s o i l , and gravity. values  Gs  i s the  Using a s p e c i f i c g r a v i t y of 2.8, and  specific  the dry  density  shown i n f i g u r e 2 - 8 - 1 , the v o i d r a t i o o f the sand  c a l c u l a t e d to range from 0.68  to 0.96  was  about a mean of 0.84  for  those sands sampled. 2-9  Standard P e n e t r a t i o n The  standard  penetration  of blows of a standard standard  Test t e s t i n v o l v e s counting  the number  weight t h a t are r e q u i r e d to d r i v e a  sampler i n t o the.bottom o f a d r i l l h o l e .  I t gives  r e s u l t s i n terms o f blow counts, which are dependent on more fundamental p r o p e r t i e s of the s o i l . the many v a r i a b l e s and procedure and  because of  sources of e r r o r i n v o l v e d i n the t e s t i n g  the absence of complete t h e o r e t i c a l understanding  of the mechanism o f s o i l - s a m p l e r between the blow counts and i s not w e l l developed.  r a t h e r than f i e l d  i n t e r a c t i o n , the r e l a t i o n s h i p  these more fundamental  properties  E x i s t i n g c o r r e l a t i o n s were developed  using p a r t i c u l a r s o i l s and  accurate  Unfortunately,  procedures and o f t e n under l a b o r a t o r y  c o n d i t i o n s , so t h a t even i f the r e l a t i o n i s  under those p a r t i c u l a r c o n d i t i o n s , i t i s u n l i k e l y to  universally representative. these c o r r e l a t i o n s should  This means t h a t the trends  be r e p r e s e n t a t i v e but  t h a t the  be  shown i n actual  -29magnitudes  cannot be found without s p e c i f i c s i t e t e s t i n g to a d j u s t  the c r i t e r i a f o r s p e c i f i c  soils.  Despite these disadvantages, the Standard P e n e t r a t i o n T e s t (SPT) i s w i d e l y used f o r s i t e i n v e s t i g a t i o n o f deep s o i l  deposits  because i t can be e a s i l y be performed u s i n g a standard d r i l l f i g and i t a l l o w s r e c o v e r y o f samples.  These samples a r e d i s t u r b e d  but a r e s u i t a b l e f o r use i n some t e s t s and f o r c l a s s i f i c a t i o n . T h i s l a b o r a t o r y i n f o r m a t i o n , o b t a i n e d from from the SPT sample, when used w i t h the blow count i n f o r m a t i o n , a l l o w s i n d e n t i f i c a t i o n o f the s o i l l a y e r s and i n d i c a t e s the v a r i a t i o n w i t h i n each l a y e r of those p r o p e r t i e s which i n f l u e n c e the blow count. S o i l p r o p e r t i e s determined from the blow counts o f two standard p e n e t r a t i o n t e s t s can d i f f e r because o f the d i f f e r e n c e i n the s t a t e o f the s o i l between the two t e s t s , because o f a v a r i a t i o n i n procedure between the two t e s t s , o r because o f i n a c c u r a c i e s i n the f u n c t i o n used to c o r r e l a t e the blow count w i t h those p r o p e r t i e s .  T h e - f i r s t - i s the d i f f e r e n c e t h a t we wish  to observe, w h i l e the second and t h i r d must be regarded as e r r o r s , to be minimized. The s t a t e o f the s o i l , as i t i n f l u e n c e s the SPT can be thought o f i n terms o f the s t r e s s regime, the s t r e n g t h c h a r a c t e r i s t i c s and the f a i l u r e mechanism.  In i t s u n d i s t u r b e d form, the s t r e s s  state  of the s o i l can be d e s c r i b e d i n terms o f an overburden p r e s s u r e and a l a t e r a l pressure.  T h i s i n d i c a t e s the importance o f the over  c o n s o l i d a t i o n r a t i o , which i n f l u e n c e s the l a t e r a l p r e s s u r e and i s e f f e c t e d by the method o f d e p o s i t i o n o f the s o i l and i t s s t r e s s  -30-  history.  T h i s s t r e s s s t a t e w i l l be a l t e r e d l o c a l l y by the  presence o f the bore h o l e , but the magnitude and e x t e n t o f t h i s l o c a l v a r i a t i o n i s d i f f i c u l t to determine.  The s o i l s t r e n g t h  i s g e n e r a l l y expressed i n terms o f a cohesion and a f r i c t i o n angle, the v a l u e s o f which w i l l depend on the v o i d r a t i o o f the soil.  The f a i l u r e mechanism which must occur i f the sampler i s  to - p e n e t r a t e i n t o the s o i l , w i l l vary to some degree with properties. important.  soil  P a r t i c l e s i z e , shape, g r a d a t i o n and o r i e n t a t i o n are In s i l t - s i z e s o i l s below the water t a b l e the s m a l l  pore spaces i n h i b i t the flow o f pore f l u i d , r e s u l t i n g i n p a r t i a l l i q u e f a c t i o n o f the s o i l surrounding the sampler with each blow, so t h a t the p e n e t r a t i o n r e s i s t a n c e i s g r e a t l y reduced observed i n the more f r e e d r a i n i n g sand samples. became s i g n i f i c a n t i n the data reviewed was composed o f more than 20 percent  from  that  This reduction  f o r t h i s work when the s o i l  silt.  In a t e s t such as the SPT, e n t a i l i n g an a r b i t r a r y  procedure,  v a r i a t i o n s i n the p r e s c r i b e d procedure can be c o n s i d e r e d e r r o r s o n l y i n the sense t h a t they w i l l prevent data o b t a i n e d i n a nonstandard way from b e i n g compared with the standard d a t a . M o d i f i c a t i o n s t o the t e s t procedure may w e l l r e s u l t i n data which are more meaningful required.  i n the p a r t i c u l a r sense f o r which t h a t data i s  In order to assess the accuracy w i t h which any two data  s e t s may be compared, i t i s important to have an understanding o f those elements  o f procedure which can a f f e c t the r e s u l t s o f the t e s t .  Kovacs, Evans, and G r i f f i t h  (19 77) undertook.a  study to assess  the e f f e c t o f some o f these v a r i a b l e s on the measured blow counts. They found t h a t the number o f t u r n s o f rope around  the cathead changed  -31-  the  f r i c t i o n between rope and cathead, which i n t u r n a f f e c t e d the  speed a t which the weight c o u l d f a l l , of  and so; i n f l u e n c e d , the amount  energy imparted to the top o f the d r i l l  string.  A larger  number o f wraps o f the rope around the cathead reduces the energy imparted and i n c r e a s e s the blow count f o r one f o o t o f p e n e t r a t i o n . They found t h a t new, s t i f f e r ropes, when r e l e a s e d from the cathead, formed loops w i t h a l a r g e r r a d i u s o f c u r v a t u r e than o l d e r ropes, r e d u c i n g f r i c t i o n and i n c r e a s i n g the energy imparted.  The cathead  speed and the mechanism by which the o p e r a t o r r e l e a s e d the rope were a l s o found to have an e f f e c t on the energy imparted. These a r e o n l y some o f the sources o f v a r i a t i o n i n -the amount o f energy imparted to the top o f the d r i l l  string.  Though the e f f e c t s  of  these v a r i a t i o n s c o u l d be l i m i t e d b y - c a l l i b r a t i n g each  drill  rig  to a standard impact energy, t h i s does n o t h e l p when  old  t e s t r e s u l t s , and w i l l not a i d i n s o l u t i o n o f some o f the o t h e r  comparing  problems which have t h e i r o r i g i n below the ground. Rod l e n g t h w i l l i n f l u e n c e blow count.  Gibbs and H o l t z (1957)  found t h a t the blow count was i n c r e a s e d when u s i n g a long r o d i n a deep h o l e through loose sands because o f the weight o f the r o d , but of  was decreased when u s i n g a long r o d i n dense sands  because  the energy l o s t due to the f l e x u r e and whipping o f the rods.  The types o f rods used and t h e i r p h y s i c a l c o n d i t i o n w i l l  also  i n f l u e n c e the blow count because o f the v a r i a t i o n i n weight, and the  d i f f e r e n c e s i n s t i f f n e s s and s i z e  of.eccentricities.  The blow count i n the STP i s g e n e r a l l y recorded over three increments o f 0.15 meters, making the t o t a l p e n e t r a t i o n o f the sampler 0.45 meters.  I f the d r i l l e r does not e x e r c i s e care i n  -32c l e a n i n g out the bottom o f the h o l e , the l o o s e d i s t u r b e d found there w i l l  r e s u l t i n low  c h a r a c t e r i z e the s o i l . may  soil  i n i t i a l blow counts which do  U n c h a r a c t e r i s t i c a l l y h i g h blow counts  occur near the end of the 0.45  meter p e n e t r a t i o n i f the  sampler i s o v e r - d r i v e n or i f o p e r a t i o n becomes o b s t r u c t e d s o i l w i t h i n the tube or c a s i n g .  meter increment should be c o n s i d e r e d  Not a l l f i r m s use  t h i s procedure.  0.15  as a s e a t i n g d r i v e , and  number of blows r e q u i r e d f o r the second and meters should be c o n s i d e r e d  by  The ASTM d e s i g n a t i o n D1586-67  d e s c r i b i n g the p e n e t r a t i o n t e s t i n d i c a t e s t h a t the f i r s t  0.15  not  the  t h i r d increments of  the p e n e t r a t i o n r e s i s t a n c e . Schnable (1971) suggests t h a t a  more l o g i c a l procedure would be to s e a t the sampler with a  few  l i g h t taps, and  0.3  then to r e c o r d the blow count on the f i r s t  meters o f p e n e t r a t i o n . skillful  driller,  o f the t e s t w i l l and experienced  He p o i n t s out t h a t t h i s method r e q u i r e s a  however the whole method i s such t h a t the  results  o n l y be s i g n i f i c a n t i f i t i s performed by a driller.  Schnable must be assuming t h a t the  of s o i l a f f e c t e d by the s t r e s s r e l i e f  i n the bottom of the  skillful bulb  drill  hole i s small enough i n e x t e n t and magnitude t h a t the blow count measured there i s not a f f e c t e d by t h i s phenomenon any more t h a t i t i s i n the deeper two to be supported a  'friction  0.15  meter increments.  T h i s assumption seems  by the data shown by Schmertmann (1971).  cone SPT  formula*  He  with data c o l l e c t e d from cone  used 1  . .... .  penetration t e s t s i n the form of the f r i c t i o n a l and end b e a r i n g components o f r e s i s t a n c e to p r e d i c t the blow counts i n each o f the three meter increments t h a t would be expected from a SPT  0.15  i n the same s o i l .  These values were compared with the a c t u a l blow count values  that  -33were o b t a i n e d from a c a r e f u l l y executed SPT i n an a d j a c e n t h o l e . The r a t i o o f the blow counts i n the f i r s t  increment to those  i n the t h i r d increment, and those i n the second increment to those i n the t h i r d increment i n l o o s e to medium sands r e s p e c t i v e l y 0.61 0.81  and 0.80  was  f o r the p r e d i c t e d v a l u e s , and 0.63  f o r the observed v a l u e s .  and  The e x c e l l e n t agreement o f both  s e t s o f r a t i o s not o n l y i n d i c a t e s the v i a b i l i t y o f Schmertmann s 1  ' f r i c t i o n cone SPT formula' but a l s o shows t h a t under t e s t i n g procedure used, the blow counts i n the f i r s t increment were not abnormally low.  the c o n t r o l l e d 0.15  The i n c r e a s e i n the blow count  over the three increments i s more probably due to the way the of  meter  that  sampler m o b i l i z e s the p e n e t r a t i o n r e s i s t a n c e i n a combination s i d e f r i c t i o n and end b e a r i n g , r a t h e r .than due to a change i n  s o i l s t r e n g t h w i t h depth. Much o f the SPT data c o l l e c t e d f o r t h i s study i n c l u d e d blow counts r e p o r t e d over the f i r s t 0.3 meters o f p e n e t r a t i o n . data presented i n t h i s way  Though  i s v a l i d i t cannot be compared d i r e c t l y  with data recorded over the 0.15  to 0.4 5 meter p e n e t r a t i o n range.  To f a c i l i t a t e data comparison and to permit the use o f r e l a t i o n s h i p s which have been developed to c o r r e l a t e the blow counts i n the to 0.4 5 meter range w i t h more fundamental  0.15  s o i l properties, a relation-  s h i p was developed to a l l o w the blow counts recorded over the  first  0.3 meters o f p e n e t r a t i o n to be expressed as e q u i v a l e n t blow counts i n the 0.15  to 0.45  meter p e n e t r a t i o n  range.  A t y p i c a l p l o t o f blow count v e r s u s depth f o r a sand l a y e r i s shown i n f i g u r e 2-9-1.  One  curve shows the v a r i a t i o n o f blow  count recorded over the f i r s t 0.3 meters o f p e n e t r a t i o n w h i l e the other i s a p l o t o f the blow count recorded from 0.15  to 0.45  meters  -34on the same sample.  These two curves are r o u g h l y p a r a l l e l .  To assess the degree o f correspondence between the two curves, a method of comparison was  needed which would not compare the  two curves w i t h an a r t i f i c i a l curve o f some a r b i t r a r y shape, but w i t h each o t h e r .  The change i n blow count between s u c c e s s i v e  t e s t s was used as a method o f comparing the c u r v e s . assumed t h a t the v a r i a t i o n o f the blow count would be  I t was linerally  p r o p o r t i o n a l to the magnitude o f the blow count, so the change i n blow counts between two s u c c e s s i v e t e s t s was d i v i d i n g - i t by the average o f the two v a l u e s . these normalized d i f f e r e n c e s was r e l a t i v e curve smoothness  1  normalized by The r a t i o o f  c a l l e d the ' c o e f f i c i e n t o f  and was p l o t t e d a g a i n s t depth.  This  c o e f f i c i e n t , developed from blow counts recorded from 0 to 0.3 and those from 0.15  meters  to 0.4 5 meters, i s shown i n f i g u r e 2-9-2,  and the c o e f f i c i e n t from those r e c o r d e d from 0 to 0.3 meters those recorded from 0.3  and  to 0.6 meters i s shown on f i g u r e 2-9-3.  The p o i n t s are s c a t t e r e d , but evenly d i s t r i b u t e d around the a x i s where the c o e f f i c i e n t o f r e l a t i v e curve smoothness  i s equal to 1.  T h i s suggests the v a l i d i t y o f the n o r m a l i z i n g procedure.  Points  p l o t t i n g to the l e f t o f the a x i s show t h a t the blow count curve for  p e n e t r a t i o n from 0 to 0.3 meters i s smoother  p e n e t r a t i o n from 0.15 loose s o i l  to 0.4 5 meters.  than t h a t f o r  T h i s could be due to  i n the bottom o f the d r i l l h o l e which would g i v e a  reduced but c o n s t a n t number o f blows i n the f i r s t few inches which would not show i n the 0.15  to 0.45 meter r e a d i n g .  I t could  a l s o be due to the jamming of the sampler i n the l a s t few i n c h e s ,  -35which would r e s u l t i n an abnormally h i g h blow count i n the 0.15  to 0.45  meter r e a d i n g .  When the p o i n t s p l o t to the r i g h t  of the a x i s , i t i n d i c a t e s t h a t the blow count f o r curve p e n e t r a t i o n from 0.15  to 0.45  t i o n from 0 to 0.3 meters.  i s smoother  than t h a t f o r p e n e t r a -  T h i s c o u l d be due to i r r e g u l a r o r  improper c l e a n i n g o f the d r i l l h o l e b e f o r e the sampler was which i s i n d i c a t i v e of poor d r i l l i n g technique.  placed,  Because o f the  crudeness o f the a n a l y s i s , the v a r i a t i o n i n the p o i n t s away from the a x i s would be s i g n i f i c a n t o n l y when s e v e r a l c o n s e c u t i v e p o i n t s e x h i b i t e d the same t r e n d s . shown i n f i g u r e 2-9-3  With the e x c e p t i o n o f one s e t o f data  t h i s i s not the c a s e .  The p o i n t s l i e s c a t t e r e d  about the a x i s , i n d i c a t i n g t h a t a simple r e l a t i o n s h i p between the blow count asecorded when p e n e t r a t i n g from 0 to 0.3 meters and from 0.15  to 0.4 5 meters should e x i s t . To r e v e a l t h i s r e l a t i o n s h i p , the d i f f e r e n c e between the blow  count recorded d u r i n g p e n e t r a t i o n from 0 to 0.3 meters and recorded from 0.15  to 0.45  meters was  that  c a l c u l a t e d and normalized  by d i v i d i n g i t by the blow count from 0 to 0.3 meters.  Expressed  as a percentage t h i s d i f f e r e n c e was p l o t t e d a g a i n s t depth i n f i g u r e 2-9-4.  F i g u r e 2-9-5  shows the r e s u l t s o f the same procedure  a p p l i e d to the d i f f e r e n c e i n blow counts recorded from 0 to and 0.3  to 0.6 meters.  The b e s t f i t  0.3  straight line characterizing  each data s e t was determined and r e p l o t t e d f o r convenience i n f i g u r e 2-9-6. from 0.15  The i n c r e a s e i n blow count recorded f o r p e n e t r a t i o n  to 0.45  meters p e n e t r a t i o n over t h a t recorded from 0 to  0.3 meters v a r i e d from 49% a t the s u r f a c e o f the sand d e p o s i t to 37% a t a depth of 30 meters. from 0.3  The i n c r e a s e d blow count measured  to 0.6 meters p e n e t r a t i o n over t h a t measured from 0 to  -360.3  meters ranged from 66%  a t the s u r f a c e to 53% a t a depth  o f 30 meters. This decrease i n the  'per cent d i f f e r e n c e  1  with depth means  t h a t the f i r s t blow count increment, from 0 to 0.15  meters c o n t r i b u t e s  p r o p o r t i o n a t e l y more to the t o t a l reading, with depth, than does the l a s t increment from 0.3 cannot be due  to 0.45  meters.  T h i s phenomenon  to the presence of an i n i t i a l d i s t u r b e d l a y e r a t  the bottom of the d r i l l hole as t h i s would produce the e f f e c t , the u n i f o r m l y and  i n c r e a s i n g the  i s more reasonably  loose l a y e r g i v i n g n e a r l y constant blow count  'per cent d i f f e r e n c e ' with depth.  The  r e l a t e d to the mechanism by which the  tion resistance i s mobilized. formula'  opposite  Using  the  ' f r i c t i o n cone  developed by Schmertmann (1971), the t o t a l  trend penetraSPT  penetration  r e s i s t a n c e developed a t a p a r t i c u l a r depth o f sampler embedment can be subdivided due  i n t o the percentage due  to s i d e f r i c t i o n ,  (appendix 2).  p r e d i c t s t h a t approximately 72% be provided  by end b e a r i n g  to end b e a r i n g ,  For sands, t h i s  a t the 0.15  i s more dominant i n the f i r s t 0.15  meter p e n e t r a t i o n  level,  component would be bearing  meter increment o f each t e s t ,  'percent d i f f e r e n c e ' values with depth below  the ground s u r f a c e c o u l d be due in  relation  Because the r e s i s t a n c e developed by end  the r e d u c t i o n i n the  to a d i s p r o p o r t i o n a t e  the r e s i s t a n c e generated through end b e a r i n g .  As  increase the  sampler  i s d r i v e n , a compacted plug of s o i l i s formed ahead o f i t . end  b e a r i n g r e s i s t a n c e i s a f f e c t e d by the i n c r e a s e d  pressure  that  of the p e n e t r a t i o n r e s i s t a n c e would  while a t the 0.4 5 meter l e v e l the end b e a r i n g reduced to 46%.  and  The  confining  a t depth and a l s o by the i n c r e a s e d energy r e q u i r e d to  -37compact the s o i l a t depth. To check the u s e f u l n e s s o f the r e l a t i o n developed  between  the blow count recorded from 0 to 0.3 meters and t h a t recorded from 0.15  to 0.45  meters, data from one d r i l l e r d e s c r i b i n g  blow count from 0.15  to 0.45  meters was  the  compared to data o b t a i n e d  by another d r i l l e r and i n the same area recorded from 0 to  0.3  meters but m o d i f i e d to g i v e the equivalent.0.15 to 0.45  meter  readings u s i n g the curve i n f i g u r e 2-9-6.  shows  the curve developed for  F i g u r e 2-9-7  from the blow count recorded by one  p e n e t r a t i o n from 0 to 0.3 meters i n each t e s t .  d e s c r i b i n g the blow count data Recorded 0.15  to 0.45  curve  d u r i n g p e n e t r a t i o n from  meters i s d e p i c t e d i n f i g u r e 2-9-8.  i s a comparison  The  driller  Figure  2-9-9  of these two curves and the curve m o d i f i e d from  the 0 to 0.3 meter p e n e t r a t i o n curve to g i v e the e q u i v a l e n t blow count f o r the 0.15  to 0.45  meter p e n e t r a t i o n .  The  comparison  between the measured and m o d i f i e d curves showing the blow count for  the 0.15  to 0.45  meter penetrations' good, p a r t i c u l a r l y s  c o n s i d e r i n g t h a t the two drillers, of  t e s t s e t s were performed  each u s i n g t h e i r own  the f a c t t h a t the d r i l l  by  different  technique and equipment, and i n view  h o l e s were not i n the same spot, even  though c l o s e i n l o c a t i o n . A d d i t i o n a l blow count i n f o r m a t i o n from d r i l l  holes i n the  F r a s e r D e l t a i s shown p l o t t e d a g a i n s t depth i n f i g u r e s 2-9-10 to  2-9-21.  A curve has been f i t t e d  to each data s e t , and where  necessary the c o n v e r s i o n shown i n f i g u r e 2-9-6 to  has been a p p l i e d  t h i s curve express the data i n terms o f the e q u i v a l e n t  blow count from 0.15  to 0.45  meters o f p e n e t r a t i o n on each  sample.  -38The data i n each f i g u r e are w i d e l y spread from the mean due to irregularities  i n the s o i l i t s e l f , and i n the t e s t i n g procedure.  In f i g u r e 2-9-12 data o b t a i n e d by two d r i l l e r s i n the same a r e a are  plotted together.  One data s e t p r e d i c t s h i g h e r blow counts  w i t h depth than does the o t h e r , p o i n t i n g to a v a r i a t i o n i n the d r i l l i n g technique and equipment. vertical  F i g u r e 2-9-15 i s composed o f  l i n e s i n d i c a t i n g average blow counts over the depths  d e f i n e d by each l i n e , r a t h e r than p o i n t s i n d i c a t i n g the measured blow count a t a s p e c i f i c depth.  Because o f t h i s p r e s e n t a t i o n  of averaged data, the curve f i t t i n g gives r e s u l t s which are l e s s i n d i c a t i v e o f the s o i l s p r e s e n t .  F i g u r e 2-9-11 shows a p l o t o f  blow count from d r i l l h o l e s i n the Sturgeon Bank Sea I s l a n d a r e a . Those samples c l o s e r to Sea I s l a n d g e n e r a l l y show h i g h e r blow counts than those f a r t h e r out on the banks, though a s i n g l e curve i s used to c h a r a c t e r i z e a l l the d a t a . The curves r e p r e s e n t i n g the blow count f o r p e n e t r a t i o n from 0.15  to 0.45  meters are summarized i n f i g u r e 2-9-22.  These are  the  curves t h a t w i l l be u s e d to determine s o i l p r o p e r t i e s ,  the  c o r r e l a t i o n s between s o i l p r o p e r t i e s and the SPT have been  developed u s i n g sampler p e n e t r a t i o n from 0.15  since  to 0.4 5 meters.  The  curves are grouped together i n two major c o n c e n t r a t i o n s , w i t h some lone curves i n d i c a t i n g lower blow counts.  The f i r s t  i s composed o f curves which run roughly i n a s t r a i g h t l i n e a blow count  (N) o f 14 a t 6 meters  group from  to an N o f 62 a t 18 meters.  This  group i s composed o f data from bore h o l e s along the n o r t h e r n p a r t of  the d e l t a , one s i t e on Sea I s l a n d , one south o f Sea I s l a n d on  Number Three Road, one near the head o f the d e l t a , and one south o f  the  Oak  Street Bridge.  The second group i s composed o f curves  which run i n a s t r a i g h t l i n e from an N o f 15 a t 6 meters to an N o f 3 5 a t 18 meters.  Below 18 meters  the N v a l u e remains almost  c o n s t a n t to the l i m i t o f the data a t 40 meters.  This group i s  composed o f d a t a from s i t e s throughout the c e n t r a l p o r t i o n o f the  delta.  There are s i t e s on Annacis I s l a n d , on South E a s t e r n  L u l u I s l a n d , i n Ladner, and i n the Sturgeon Bank-Sea I s l a n d a r e a . The curve c h a r a c t e r i z i n g the s o i l i n the Brighouse area of Richmond resembles the curves o f group 2 to a depth o f 12 meters, where the  s l o p e changes and N remains c o n s t a n t , o r decreases s l i g h t l y  with depth. of  The T i l b u r y I s l a n d curve shows a low N u n t i l a depth  27 meters i s reached, where i t j o i n s the second group o f c u r v e s .  The Roberts Bank curve d e p i c t s a very low N, r a n g i n g from 11 a t a depth o f 6 meters to 41 a t a depth o f 30 meters. Despite the trends t h a t may the  seem to be apparent r e g a r d i n g  d i s t r i b u t i o n o f the s o i l p r o f i l e types, i t would be a mistake  to make g e n e r a l i z a t i o n s , o t h e r than t h a t the N v a l u e appears to be l e s s on the banks than throughout the r e s t o f the d e l t a . so because t h i s data was the  This i s  c o l l e c t e d f o r the purpose o f understanding  s o i l p r o f i l e a t three p a r t i c u l a r l o c a t i o n s r a t h e r than every-  where i n the d e l t a .  I t may  however, on the b a s i s o f the wide  d i s t r i b u t i o n o f data, be reasonable to assume t h a t the sand types shown here a r e t y p i c a l and r e p r e s e n t a t i v e of these throughout the delta. 2-10  R e l a t i v e D e n s i t y o f Sands The r e l a t i v e d e n s i t y o f a s o i l  i s a measure o f the d e n s i t y  -40of the s o i l r e l a t i v e to i t s most dense and most loose i s defined  as  = e e  max max  -e —e  min  where Dr = R e l a t i v e Density e = i n - s i t u void r a t i o e v o i d r a t i o of sample i n i t s l o o s e s t max -  Accordingly,  It  follows: Dr  e  states.  . min  = v o i d r a t i o o f sample i n i t s densest  the l a r g e r the value of r e l a t i v e d e n s i t y  dense the sample. i n ASTM Designation  state state the more  A standard procedure f o r the t e s t i s presented D2049-69, however many firms use  non-standard  techniques. The  errors inherent  i n the r e l a t i v e d e n s i t y  i n v e s t i g a t e d by Tavenas, Ladd, and to the e r r o r s introduced  by  LaRochelle  t e s t were  (1972).  In a d d i t i o n  the use of non-standard technique,  and  the e r r o r i n determining the i n - s i t u v o i d r a t i o from f i e l d volume measurements, they found t h a t the f o r m u l a t i o n r e l a t i v e d e n s i t y magnified l a b o r a t o r y were w i t h i n reasonable bounds. of the r e l a t i v e d e n s i t y was and  o f the equation f o r  e r r o r s which i n themselves  They found t h a t the v a r i a b i l i t y  u s u a l l y 10  times t h a t of the maximum  minimum d e n s i t i e s , g i v i n g e r r o r s i n the r e l a t i v e d e n s i t y  the order of p l u s or minus 30 to  47%.  Because of the d i f f i c u l t y i n determining the r e l a t i v e and  the l a r g e amount o f data a v a i l a b l e from the SPT,  have been developed between the N v a l u e and this increases  dramatically  in  density  correlations  r e l a t i v e density.  the amount of r e l a t i v e d e n s i t y  Although  information  -41t h a t i s a v a i l a b l e , i t decreases the accuracy o f such data.  To  develop the r e l a t i o n s h i p , the r e l a t i v e d e n s i t y must be determined for  s o i l s o f known N v a l u e , k n o v n p r o p e r t i e s and known s t a t e o f  stress.  Such a complete r e l a t i o n s h i p would be d i f f i c u l t to  formulate and i m p r a c t i c a l f o r f i e l d a p p l i c a t i o n where the important parameters a f f e c t i n g the r e l a t i v e d e n s i t y a r e n o t any  b e t t e r known than the r e l a t i v e d e n s i t y i t s e l f .  For t h i s  reason the r e l a t i v e d e n s i t y and N value a r e g e n e r a l l y c o r r e l a t e d with the v e r t i c a l e f f e c t i v e s t r e s s o n l y ,  though S a i t o  (197 7)  p o i n t s o u t t h a t the mean e f f e c t i v e p r i n c i p a l s t r e s s would be b e t t e r , and de Mello  (1971) i n h i s e x t e n s i v e  s t a t e o f the a r t  r e p o r t on the SPT i n d i c a t e d t h a t important e f f e c t o f the f r i c t i o n angle.  Other e r r o r s a r e i n c o r p o r a t e d  laboratory determination tion.  i n the r e l a t i o n through the  o f the r e l a t i v e d e n s i t y f o r the c o r r e l a -  The m a j o r i t y o f the r e l a t i o n s i n e x i s t e n c e were developed  by s i m u l a t i n g  f i e l d c o n d i t i o n s i n the l a b o r a t o r y .  i s not exact,  so a d d i t i o n a l e r r o r s are i n t r o d u c e d  This  simulation  at this  In a d d i t i o n to t h i s , there a r e a l l the e r r o r s i n h e r e n t  point.  i n the  SPT. Despite  the problems i n v o l v e d i n the a p p l i c a t i o n o f such  e m p i r i c a l c o r r e l a t i o n s , they continue to be used because they g i v e l a r g e volumes o f inexpensive  information.  When using  these  c o r r e l a t i o n s i t must be remembered that they were developed by t e s t i n g a s p e c i f i c s o i l i n a p a r t i c u l a r f a s h i o n , so they  should  o n l y be used q u a l i t a t i v e l y u n t i l the c r i t e r i a can be adjusted by local testing. using  De Mello  (1971) warns o f the danger i n h e r e n t i n  these c o r r e l a t i o n s b l i n d l y when he says ' i f any sand i s not  -42c l o s e l y s i m i l a r to the (tested) sands, the chances of adequately r e p r e s e n t i n g the behaviour by analogy w i t h the (test)  results  w i l l be v e r y s m a l l . ' Many r e s e a r c h e r s have developed r e l a t i o n s h i p s between the blow count o f the SPT and overburden p r e s s u r e a t v a r i o u s v a l u e s of  r e l a t i v e density.  In the F r a s e r River D e l t a , the water  table  i s g e n e r a l l y w i t h i n a few f e e t o f the ground s u r f a c e , and the sand d e p o s i t s q u i t e uniform. shown i n f i g u r e 2-8-1  The dry d e n s i t y o f the sand i s 3 to be i n the range from 14.3 kN/m to  15.5 kN/m , which suggests t h a t a reasonable assumption f o r the 3  3  s a t u r a t e d u n i t weight would be 19.2  kN/m  .  Using t h i s v a l u e , the  s o i l p r o f i l e can be i d e a l i z e d as one having buoyant u n i t weight 3  of  9.4  kN/m  , c o n s t a n t with depth.  T h i s allows the blow count-  r e l a t i v e d e n s i t y i n f o r m a t i o n to be p l o t t e d a g a i n s t depth as w e l l as overburden p r e s s u r e . relations.  F i g u r e s 2-10-1 and 2-10-2 show f i v e such  Though the curves are s i m i l a r i n trend there can be  a 50% d i f f e r e n c e between the r e l a t i v e d e n s i t y v a l u e s p r e d i c t e d for  a sample a t a p a r t i c u l a r depth and w i t h a p a r t i c u l a r N v a l u e . I f the SPT data i s to be used to advantage,  i t i s important  to determine which o f these r e l a t i o n s h i p s b e s t d e s c r i b e s the sands p r e s e n t i n the d e l t a .  To t h i s end, these r e l a t i o n s h i p s can be  examined on the b a s i s o f v a r i o u s c r i t e r i a .  The experimental methods  used to determine the r e l a t i o n s h i p s can be examined.  The g r a i n  curves o f the t e s t s o i l s can be compared to those o f .samples the  field.  from  D i r e c t measurements o f the r e l a t i v e d e n s i t y determined  from f i e l d samples can be compared to p r e d i c t e d v a l u e s . of  size  The  variation  r e l a t i v e d e n s i t y w i t h depth can be checked f o r c o n f o r m i t y w i t h  -43-  the r e l a t i o n s p r e d i c t e d from a knowledge o f the h i s t o r y o f the deposit. The  Bazaraa curves  i n the f i e l d ,  were developed from data, obtained  (1967)  and would t h e r e f o r e be s u b j e c t to the e r r o r s i n  blow count and r e l a t i v e d e n s i t y measurement o u t l i n e d p r e v i o u s l y . The other r e s e a r c h e r s laboratory.  t r i e d to simulate  Though t h i s allowed  f i e l d c o n d i t i o n s i n the  c a r e f u l measurements to be  taken i n a c o n t r o l l e d environment, i t would n o t e l i m i n a t e a l l the sources o f e r r o r present other The  i n the f i e l d and c o u l d  e r r o r s through i n a c c u r a t e m o d e l l i n g  introduce  o f the f i e l d  conditions.  l a b o r a t o r y procedures i n v o l v e d d r i v i n g the sampler i n t o a l a r g e  c o n t a i n e r o f s o i l which had been placed a t some known r e l a t i v e d e n s i t y , and which c o u l d be s u b j e c t e d by l o a d i n g the p l a t e c o v e r i n g  to a known v e r t i c a l s t r e s s  the s u r f a c e o f the c o n t a i n e r .  However, the c o n t a i n e r used to hold the s o i l c o u l d n o t produce p r e c i s e l y the same boundary c o n d i t i o n s as those i n the f i e l d . Marcuson and Bieganousky  (1977)  improved an e a r l i e r method by  u s i n g a c o n t a i n e r formed o f a l t e r n a t i n g s t e e l and rubber r i n g s stacked  to the r e q u i r e d h e i g h t ,  so t h a t the c o n t a i n e r  could  deform s l i g h t l y i n the v e r t i c a l d i r e c t i o n when the top p l a t e was loaded,  thereby reducing  the e f f e c t s o f the s i d e f r i c t i o n .  placement o f the s o i l a t uniform is difficult.  The  d e n s i t y throughout the c o n t a i n e r  The method o f o b t a i n i n g a known r e l a t i v e  density  v a r i e d between r e s e a r c h e r s , b u t i n some cases the d e n s i t y c o n t r o l was not good.  In the l a b o r a t o r y , the e f f e c t s o f the f r i c t i o n  between the r o d and the h o l e o r c a s i n g were not reproduced, and the r o d l e n g t h ; though v a r i e d to a c e r t a i n extent i n the t e s t i n g  -44programs,  would not correspond e x a c t l y  to the f i e l d  situation.  The m a j o r i t y o f the t e s t s were performed on a i r d r i e d Gibbs and H o l t z  samples.  (1957) performed a s e r i e s o f t e s t s on submerged  samples, but were u n s a t i s f i e d w i t h t h e i r r e s u l t s , and recommended t h a t the curves developed f o r the a i r d r i e d sand be used f o r the submerged s i t u a t i o n .  Marcuson and Bieganousky  (19 77)  performed  t h e i r s e r i e s o f t e s t s on submerged samples, but d i d not a c h i e v e complete s a t u r a t i o n .  One o f the problems encountered i n t e s t i n g  the  i s that within  submerged samples  the small t e s t i n g tank, the  pore p r e s s u r e response system r e s u l t i n g from the dynamic would not d u p l i c a t e The g r a i n  that  found i n the  loading  field.  s i z e d i s t r i b u t i o n o f the sands t e s t e d  to develop  the r e l a t i v e d e n s i t y - b l o w count r e l a t i o n s h i p are shown i n f i g u r e 2-10-3 and the g r a i n  s i z e d i s t r i b u t i o n o f sand samples o b t a i n e d  from the F r a s e r D e l t a are shown i n f i g u r e 2-10-4. were procured from the western p a r t of the d e l t a may  The  samples  so these curves  not be r e p r e s e n t a t i v e o f the t o t a l d e l t a sand d e p o s i t s .  sands used by Gibbs and H o l t z  (1957) and S c h u l t z e and Melzer (1965)  compare p o o r l y w i t h the s o i l s i n the d e l t a . grain  s i z e and more w e l l  They are l a r g e r i n  graded than the d e l t a s o i l s .  used by S h u l t z e and Menzenbach (19 61)  The  size.  The sands used by  Marcuson and Bieganousky  (1977) are c l o s e s t i n g r a i n  samples  they a r e s i m i l a r . i n u n i f o r m i t y ,  they l i e i n the upper range o f a c t u a l  sand  compares more f a v o u r a b l y ,  being more uniform and s m a l l e r i n g r a i n  from the d e l t a :  The  grain  s i z e to the though  size.  With knowledge o f the s o i l c h a r a c t e r i s t i c s and the v a r i a b i l i t y of the d e p o s i t i o n a l  environment,  the shape o f the curves r e l a t i n g  -45blow count to e f f e c t i v e overburden p r e s s u r e f o r v a r i o u s v a l u e s o f r e l a t i v e d e n s i t y can be p r e d i c t e d .  I t was  found i n s e c t i o n  2-6  t h a t the change i n v o i d r a t i o w i t h depth determined from the water content v a l u e s i n the s i l t and c l a y s o i l s c o u l d be accounted f o r by the c o n s o l i d a t i o n o f the s o i l under the weight o f the overburden. T h i s i n d i c a t e s t h a t the d e p o s i t i o n a l environment has been c o n s t a n t throughout the time when these d e p o s i t s were l a y e d down.  Accordingly,  one would expect the sand d e p o s i t s to d i f f e r i n d e n s i t y w i t h depth i n a manner p r e s c r i b e d by the c o n s o l i d a t i o n c h a r a c t e r i s t i c s o f the soil.  The v a l u e s of r e l a t i v e d e n s i t y and dry d e n s i t y w i t h depth  which are shown i n t a b l e 2-9-1  were used w i t h an assumed s p e c i f i c  g r a v i t y i n the s o l u t i o n o f simultaneous equations to y i e l d  average  v a l u e s o f maximum and minimum v o i d r a t i o f o r the sand d e p o s i t . The a n a l y s i s y i e l d e d an average maximum v o i d r a t i o o f 1.2 average minimum v o i d r a t i o o f 0.66. the  and an  These v a l u e s were used w i t h  compression index o f the sand to p r e d i c t the change i n r e l a t i v e  d e n s i t y t h a t would occur w i t h depth as a r e s u l t o f the d e p o s i t s c o n s o l i d a t i n g under i t s own  weight.  Over a change i n depth o f  one l o g a r i t h m i c increment, say from 3 to 30 meters, the r e l a t i v e d e n s i t y was  found to i n c r e a s e by an increment o f 10.1%.  The v a r i o u s r e l a t i v e d e n s i t y r e l a t i o n s shown i n f i g u r e s 2-10-1 and 2-10-2 were checked to see whether they s a t i s f i e d t h i s  criterion,  by o v e r l a y i n g them on the average blow count curves shown i n f i g u r e 2-9-22.  R e c a l l t h a t t h e r e were two g e n e r a l curve shapes,  one where the N v a l u e i n c r e a s e d l i n e a r l y to a depth o f 18  meters  and then remained almost c o n s t a n t w i t h depth, and another where the  -46N value i n c r e a s e d l i n e a r l y to a l a r g e r value a t a g r e a t e r The  former group of curves was  examined f i r s t .  The  depth.  Schultze  and Menzenback and the Bazaraa  curves correspond most c l o s e l y  to the p r e d i c t e d curve shape.  These were f o l l o w e d , i n order  of best f i t by the Marcuson and Bieganouski, and  the S c h u l t z e and Mel.zer curves.  the Gibbs and H o l t z ,  When the theory d e s c r i b i n g  the i n c r e a s e i n r e l a t i v e d e n s i t y w i t h depth was the l a t t e r group of curves poor correspondence with the r e l a t i v e d e n s i t y r e l a t i o n s .  a p p l i e d to was  achieved  The S c h u l t z e and  curves provided a b e t t e r f i t than the o t h e r s , but one not p a r t i c u l a r l y c l o s e .  This suggests  Melzer that  was  t h a t the l a t t e r curve  group r e p r e s e n t s p r o f i l e s where the s o i l s o r the d e p o s i t i o n a l environment were not uniform w i t h depth,  so t h a t the r e l a t i v e  d e n s i t y i n c r e a s e s with depth more than c o u l d be expected the c o n s o l i d a t i o n o f the d e p o s i t under i t s own  weight.  from This  phenomina c o u l d a l s o be e x p l a i n e d i f the sands i n t h i s l a t t e r group had a very h i g h s i l t content so t h a t the c o n s o l i d a t i o n characteristics silts,  would resemble those o f the more compressable  p r e d i c t i n g a much l a r g e r i n c r e a s e i n r e l a t i v e d e n s i t y  w i t h depth.  However, an examination  of the d r i l l  l o g s does not  lend support to t h i s h y p o t h e s i s . A c t u a l f i e l d measurement of r e l a t i v e d e n s i t i e s are in  critical  the s e l e c t i o n o f the r e l a t i v e d e n s i t y r e l a t i o n which b e s t  d e s c r i b e s the s o i l s o f the d e l t a .  The values o f r e l a t i v e d e n s i t y  from t a b l e 2-10.-1 are shown a t the a p p r o p r i a t e depths along w i t h the p l o t of N a g a i n s t depth f o r the d r i l l h o l e s i n t h a t area,  from f i g u r e 2-9-22.  The l a r g e v a r i a b i l i t y i n the r e l a t i v e  d e n s i t y measurements i s more l i k e l y due  to e r r o r s i n the measure-  ment than to a c t u a l v a r i a b i l i t y i n the s o i l . d e n s i t y measurement i s 63%,  so i t was  The average  relative  assumed, from the knowledge  o f the shape of the curve, t h a t the r e l a t i v e d e n s i t y would i n c r e a s e q u i c k l y from a v a l u e of 58% a t a depth o f 3 meters, to a value o f 68% a t a depth of 30 meters. and  On  the b a s i s of these v a l u e s ,  the r a t i o o f the change i n r e l a t i v e d e n s i t y to the r e s u l t i n g  change i n N value a t v a r i o u s depths, as observed d e n s i t y r e l a t i o n s i n f i g u r e s 2-10-1 and  from the  relative  2-10-2, the approximate  l i n e s showing the change i n N value with depth f o r r e l a t i v e d e n s i t i e s of 60% and 80% were c o n s t r u c t e d i n f i g u r e 2-10-5. l i n e s were compared with the r e l a t i v e d e n s i t y c u r v e s . c o r r e l a t i o n w i t h the S c h u l t z e and Menzenbach curves was  These  The very good.  The Gibbs and H o l t z curves gave a reasonable p r e d i c t i o n , but other r e l a t i o n s were l e s s Scotton  the  satisfactory.  (1977) performed  a s e r i e s of c a r e f u l l y  controlled  r e l a t i v e d e n s i t y measurements on the n e a r - s u r f a c e s o i l s a t Sturgeon Bank. he concluded  Using these and N v a l u e s from nearby d r i l l h o l e s ,  t h a t the Bazaraa  relative density relations better  d e s c r i b e d these s o i l s than the Gibbs and H o l t z r e l a t i o n s .  This  i s c o n s i s t e n t with the o b s e r v a t i o n t h a t the Gibbs and H o l t z r e l a t i o n over-estimates the r e l a t i v e d e n s i t y c a l c u l a t e d on b a s i s of the curve shape determined  from the c o n s o l i d a t i o n  c h a r a c t e r i s t i c s , though the d i f f e r e n c e c o u l d be due t e s t s being performed  the  on a d i f f e r e n t s o i l  i n p a r t to the  type.  On the b a s i s of these d i s c u s s i o n s , the S c h u l t z e and Menzenbach r e l a t i o n s were s e l e c t e d as b e s t d e s c r i b i n g the r e l a t i v e d e n s i t y  -48c h a r a c t e r i s t i c s o f the d e l t a sands.  T h i s r e l a t i o n i s much c l o s e r  i n form to the Gibbs and H o l t z than to the Bazaraa r e l a t i o n .  At  depths l e s s than 4.5 meters, where the S c h u l t z e and Menzenback r e l a t i o n i s not d e f i n e d , the r e l a t i v e d e n s i t y may  be b e t t e r  d e s c r i b e d by the Bazaraa than the Gibbs and H o l t z r e l a t i o n s .  It  i s importaat to remember t h a t t h i s c h o i c e of a r e l a t i v e d e n s i t y r e l a t i o n was based on a s m a l l number o f r e l a t i v e d e n s i t y measurements and t h a t the c h o i c e o f t h i s r e l a t i o n does not mean t h a t it  i s the r e s u l t o f the most a c c u r a t e t e s t i n g program.  Rather,  i t b e s t d e s c r i b e s the p a r t i c u l a r s o i l s i n the F r a s e r D e l t a . 2-11  F r i c t i o n Angle o f Sands The angle o f i n t e r n a l f r i c t i o n depends p r i m a r i l y on the  r e l a t i v e d e n s i t y o r v o i d r a t i o of the s o i l , d i s t r i b u t i o n and the g r a i n shape.  the g r a i n  size  I t s d i r e c t dependence on  the s t r e s s s t a t e of the s o i l i s s m a l l .  The f r a c t i o n angle i s  g e n e r a l l y determined u s i n g the data from t r i a x i a l or shear t e s t s to d e f i n e the f a i l u r e envelope of the s o i l .  F i g u r e 2-11-1 i s a  p l o t o f f r i c t i o n angle a g a i n s t dry d e n s i t y f o r two One  sand t y p e s .  i s a f i n e to medium sand, and the o t h e r i s a s i l t y  Both s o i l types show the expected trend of i n c r e a s i n g angle with i n c r e a s i n g dry d e n s i t y .  sand. friction  The s i l t y sand had a f r i c t i o n  angle 5 o r 6 degrees g r e a t e r than the c l e a n sand a t the same dry density. De M e l l o (1971) suggests t h a t the apparent f r i c t i o n angle may  be more fundamental  and more s i g n i f i c a n t parameter...to use i n  c o r r e l a t i o n s w i t h the blow count o f the SPT than the r e l a t i v e  -49density.  I t may  be p o s s i b l e to develop a s i n g l e r e l a t i o n s h i p  between the N v a l u e and f r i c t i o n angle w i t h c o n f i n i n g p r e s s u r e which i s a p p l i c a b l e to a l l sand types.  Once the f r i c t i o n angle  had been determined, the r e l a t i o n between i t and the r e l a t i v e d e n s i t y c o u l d be developed f o r each s o i l type. The curves developed by De M e l l o are shown i n f i g u r e 2-11-2 i n a form r e l a t i n g the N v a l u e and the depth -below s u r f a c e f o r v a r i o u s v a l u e s of f r i c t i o n angle.  T h i s was  v a l u e f o r the s p e c i f i c g r a v i t y and assuming saturated.  done u s i n g an average the s o i l to be  De M e l l o ' s curves d e s c r i b i n g the f i n e sand, and the  average o f the f i n e and coarse sands are shown.  The r e l a t i o n s are  i n the form o f s t r a i g h t l i n e s because o f the form of a n a l y s i s used.  statistical  Shown w i t h these r e l a t i o n s are the p l o t s o f N  value a g a i n s t depth f o r the s i t e s where the samples used to determine the f r i c t i o n angles shown i n f i g u r e 2-11-1. 3 Using the mean dry d e n s i t y from f i g u r e 2-8-1  o f 14.9  f i g u r e 2-11-1 indicates- t h a t the f i n e to medium sand has a angle o f 38.5 degrees. the  kN/m  ,  friction  Using De M e l l o ' s r e l a t i o n w i t h the mean o f  f i n e and medium curves i n f i g u r e 2-11-2 r e s u l t s i n a p r e d i c t e d  f r i c t i o n angle o f 41 degrees f o r the p e n e t r a t i o n p r o f i l e shown. T h i s i s a reasonable c o r r e l a t i o n .  The s i l t y sand samples were  taken from Roberts Bank, where no separate measurements o f dry d e n s i t y were o b t a i n e d , so the average dry d e n s i t y achieved i n the t e s t s was  used to g i v e an a n t i c i p a t e d f r i c t i o n angle o f 37 degrees,  from f i g u r e 2-11-1.  Using the s e t o f curves d e s c r i b i n g the f i n e  sand i n f i g u r e 2-11-2 and the N p r o f i l e f o r the Roberts Bank a r e a , a f r i c t i o n angle o f 36 degrees was  predicted.  T h i s i s a good  c o r r e l a t i o n , which tends to c o n f i r m t h a t the N v a l u e can be r e l a t e d  -50-  more s u c c e s s f u l l y  to the f r i c t i o n angle than to. the r e l a t i v e  d e n s i t y f o r a l a r g e range of s o i l types.  CHAPTER 3  DYNAMIC ANALYSIS  3-1  Type o f A n a l y s i s In areas o f s e i s m i c  activity,  s t r u c t u r e s should i n c o r p o r a t e  the d e s i g n o f  engineering  some method o f c o n s i d e r i n g the  e f f e c t s o f p o s s i b l e earthquakes.  The method used to assess  these e f f e c t s w i l l depend on the type and the purpose o f the s t r u c t u r e and the problems a s s o c i a t e d w i t h i t s p o t e n t i a l Various c r i t e r i a a r e considered  failure.  when attempting to c h a r a c t e r i z e  the e f f e c t s o f an earthquake on a p a r t i c u l a r s t r u c t u r e .  The  maximum a c c e l e r a t i o n and the frequency content o f the motion a r e important. The  frequency content i s o f p a r t i c u l a r i n t e r e s t as s t r u c t u r e s  having a predominant p e r i o d c l o s e to t h a t o f the earthquake w i l l expeience l a r g e d e f l e c t i o n s .  Most b u i l d i n g s are designed to  absorb the energy o f the earthquake through the d u c t i l i t y members.  of their  For such designs, the d u r a t i o n o f the s t r o n g motion and  the d u r a t i o n o f any l a r g e a c c e l e r a t i o n pulses  a r e important, as the  energy-absorbing c a p a c i t y o f the s t r u c t u r e i s f i n i t e . To analyze the e f f e c t s o f an earthquake on a s t r u c t u r e , whether i t be a b u i l d i n g , an e a r t h s t r u c t u r e , or a b u r i e d  s t r u c t u r e ; the  changing c h a r a c t e r i s t i c s o f the motion and t h e i r e f f e c t s , c a n be followed  from the source to the bedrock a t the s i t e ,  through the  s o i l l a y e r s to the s u r f a c e , and through the b u i l d i n g as a whole,  -52-  to i n d i v i d u a l members. process,  T h i s procedure i n v o l v e s a  which becomes i n c r e a s i n g l y d i f f i c u l t and  stages are i n c l u d e d .  At some stage,  modelling c o s t l y as more  a break i s made from  a t i o n o f the earthquake's dynamic e f f e c t s to c o n s i d e r a t i o n the s t r u c t u r a l behavior i n terms of standard The  seismic  r i s k and  divided  used to c a l c u l a t e e q u i v a l e n t h o r i z o n t a l i n e r t i a l  The  loads  the  defines  ground a c c e l e r a t i o n on rock or deep s o i l d e p o s i t s  loads are i n c l u d e d w i t h other  i n the d e s i g n  the  t h a t may loading.  be These  of the members.  e f f e c t s of a p a r t i c u l a r earthquake on a s e r i e s of  can be examined u s i n g a response spectrum.  of  design methods.  N a t i o n a l B u i l d i n g Code of Canada has  country i n t o zones of v a r y i n g  consider-  structures  A response spectrum  shows the r e l a t i v e magnitude of the v a r i o u s uniform harmonic waves that combine to g i v e the complex motion o f an earthquake r e c o r d and  can be thought of as a p l o t of v e l o c i t y , displacement, or  a c c e l e r a t i o n response of a single-degree-of-freedom of v a r y i n g n a t u r a l frequency and to a s p e c i f i c earthquake. and  the s t r u c t u r e .  is likely o f other  The  a p a r t i c u l a r amount of damping  I t i s a f u n c t i o n both o f the  T h i s form of p r e s e n t a t i o n  most s t r u c t u r e s can be roughly and damping.  structure  earthquake  i s valuable  because  c h a r a c t e r i z e d by a n a t u r a l  frequency  response spectrum i n d i c a t e s whether the  structure  to undergo a l a r g e response r e l a t i v e to s i m i l a r s t r u c t u r e s periods  and  g i v e s an i n d i c a t i o n of the magnitude o f  the  response f o r a p a r t i c u l a r earthquake. Methods e x i s t whereby the response s p e c t r a of p o t e n t i a l e a r t h quakes can be p r e d i c t e d from the s p e c t r a of recordcJearthquakes. Housner produced a s e t of curves which r e p r e s e n t s  the average  response s p e c t r a o f s e v e r a l recorded earthquakes percentages o f c r i t i c a l damping.  f o r various  The curves can be s c a l e d  a c c o r d i n g to the magnitude o f the earthquake  that i s anticipated.  Newmark developed a method where s p e c t r a a r e produced s t r u c t u r e by a p p l y i n g to the ground  for a  s p e c t r a and m u l t i p l i c a t i o n  f a c t o r which i s r e l a t e d to the s t r u c t u r a l damping.  The ground  s p e c t r a i s a curve drawn f o r convenience to r e p r e s e n t the maximum a n t i c i p a t e d ground v e l o c i t y a c c e l e r a t i o n s and displacement; He found t h a t the v e l o c i t y , which i s r e l a t e d absorbed;  to the energy  the a c c e l e r a t i o n , which i s r e l a t e d to the f o r c e s  experienced, and the displacement, which i s r e l a t e d to the d i s t o r t i o n ; were c r i t i c a l d e s i g n parameters  i n different  p e r i o d ranges.  a d e s i g n curve t h a t i s  The Newmark method produces  structural  an envelope o f analyzed cases. The next stage i n complexity i n v o l v e s m o d e l l i n g the s i t e to a n a l y t i c a l l y produce a spectrum which t y p i f i e s the b u i l d i n g  response.  Using an earthquake r e c o r d t h a t i s r e p r e s e n t a t i v e o f the motion on bedrock and a model d e s c r i b i n g the dynamic "properties o f the soil,  the r e s u l t i n g ground  s u r f a c e motions  can be mathematically  determined and the s u r f a c e response c a l c u l a t e d .  If carefully  executed, t h i s procedure should y i e l d a response spectrum  that i s  more t y p i c a l o f the l o c a l s i t e c o n d i t i o n s than the methods previously described. The f i n a l stage i n complexity i n v o l v e s l i n k i n g the s t r u c t u r e and s o i l together through the use o f f i n i t e elements  and m o d e l l i n g  the whole system to f i n d the a c t u a l response o f the s t r u c t u r e to a • p a r t i c u l a r earthquake on bedrock.  The attempt o f t h i s method i s to  - 5 4 -  i n c o r p o r a t e the e f f e c t s of s o i l  structure interaction.  This i s  d e s i r a b l e because the f r e e - f i e l d response o f s o i l i s not the. same as the response o f s o i l which u n d e r l i e s a b u i l d i n g .  Finite  element  a n a l y s i s i s a l s o s u i t e d to problems where the s o i l cannot be modelled as s e m i - i n f i n i t e h o r i z o n t a l l a y e r s . of  However, t h i s method  a n a l y s i s i s c o s t l y , and f o r g e n e r a l problems may  not y i e l d  r e s u l t s which are any more r e l i a b l e than those o b t a i n e d f o r the one-dimensional a n a l y s i s . A good combination of p r a c t i c a l i t y and accuracy i s p r o v i d e d by the dynamic the  a n a l y s i s o f methods t h a t use the p r o p e r t i e s o f  s o i l d e p o s i t s to produce a response spectrum on s u r f a c e from  an assumed earthquake motion a t bedrock.  Because o f t h e i r complexity  when a p p l i e d to r e a l problems, these methods g e n e r a l l y r e q u i r e the use o f a computer.  There are two g e n e r a l c l a s s e s o f  programs;  those which use a lumped mass model and those which p r o v i d e a s o l u t i o n to the wave e q u a t i o n .  The lumped-mass method uses a  s o i l model c o n s i s t i n g o f d i s c r e t e masses connected by  stiffness  elements which c h a r a c t e r i z e the p r o p e r t i e s o f the v a r i o u s layers.  The wave equation methods are based on the theory o f  one-dimensional wave p r o p a g a t i o n i n a continuous medium. of  soil  Both  these c l a s s e s o f a n a l y s i s are based on the assumption t h a t the  earthquake can be r e s p r e s e n t e d by a shear wave p r o p a g a t i n g v e r t i c a l l y through h o r i z o n t a l s o i l l a y e r s .  T h i s assumption i s more v a l i d f o r  deep than f o r shallow earthquakes. Computer programs based on the wave-equation methods use a f o u r r i e r t r a n s f o r m to develop the f o u r r i e r spectrum. f u n c t i o n s which i n c o r p o r a t e the dynamic  Transfer  e f f e c t o f the s o i l  deposit  -55-  are  developed to produce a f o u r r i e r  the ground-surface motion  spectrum which d e s c r i b e s  i n the frequency domain., Because the  f o u r r r i e r spectrum c o n t a i n s a l l the i n f o r m a t i o n d e s c r i b i n g the ground motion,  i t i s p o s s i b l e to produce  the p r e d i c t e d  ground  s u r f a c e r e c o r d i n the time domain i n the form o f an a c c e l e r a t i o n record. In t h i s study, a wave p r o p a g a t i o n s o l u t i o n was employed to p r e d i c t the s u r f a c e motion c h a r a c t e r i s t i c s .  The SHAKE  program developed i n B e r k l e y (Schnabel, Lysmer, and Seed, 19 72) was used, w i t h a minor m o d i f i c a t i o n to allow the use o f a g r e a t e r range o f dynamic s o i l p r o p e r t i e s .  SHAKE uses an i t e r a t i v e v i s c o -  e l a s t i c method o f a n a l y s i s to s o l v e a n o n - l i n e a r problem.  When  s o i l i s deformed i t f o l l o w s a h y s t e r i t i c s t r e s s s t r a i n path, the shape o f which i s dependent on the s t r e s s s t r a i n amplitude, as d e p i c t e d i n f i g . 3-1-1.  The SHAKE program approximates  this  behaviour through the use o f a secant shear modulus, and a damping ratio.  As shown.in f i g u r e 3-1-2, the shear modulus i s d e f i n e d by  a straight  l i n e through the end p o i n t s o f the s t r e s s l o o p , and the  damping r a t i o i s r e l a t e d to the r a t i o o f the area o f the h y s t e r e s i s loop and the area o f a t r i a n g u l a r area d e f i n e d by the shear modulus and the end-point o f the l o o p .  The SHAKE program uses t h i s e q u i v a l e n t  l i n e a r modulus and a v i s c o u s damping r a t i o to determine  the s t r a i n  amplitude which w i l l d e f i n e a new modulus and damping r a t i o . i t e r a t i o n continues u n t i l the s o l u t i o n s t a b i l i z e s .  The  I t i s assumed  t h a t the average s t r a i n amplitude i s 65% o f the peak experienced from the t o t a l earthquake  amplitude r e c o r d .  The SHAKE program has  -56th e same l i m i t a t i o n s as o t h e r s i m i l a r dynamic  analysis i n  t h a t i t performs a one-dimensional a n a l y s i s o f h o r i z o n t a l semii n f i n i t e beds and uses an approximate mathematical s o l u t i o n . The i n p u t to the SHAKE program c o n s i s t s o f a d e s c r i p t i o n of the s o i l p r o f i l e a t the s i t e and an a c c e l e r a t i o n r e c o r d to be used as the o b j e c t motion on bedrock. in  terms o f l a y e r s with s i m i l a r dynamic  thickness  The s o i l i s d e s c r i b e d properties, varying i n  from l e s s than 2 meters near the s u r f a c e to up to 50  meters a t depth.  The dynamic  p r o p e r t i e s a r e presented i n terms  of the maximum shear modulus determined a t low s t r a i n amplitude; a t t e n u a t i o n curves d e s c r i b i n g the r e d u c t i o n i n modulus experienced as the s t r a i n l e v e l i n c r e a s e s , and the maximum damping r a t i o and i t s v a r i a t i o n w i t h s t r a i n amplitude. 3-2  S o i l P r o f i l e s and Dynamic P r o p e r t i e s The dynamic  stages.  a n a l y s i s i n t h i s study was undertaken i n two  In the f i r s t  stage o f the a n a l y s i s , the SHAKE program  was used to p r e d i c t the s u r f a c e motions o f s e v e r a l s i t e s i n the Fraser Delta.  The 19 76 Pender I s l a n d earthquake was used as  the bedrock i n p u t , and the dynamic  p r o p e r t i e s a t the s i t e s were  c a l c u l a t e d from the i n f o r m a t i o n gained i n the examination o f the delta s o i l s .  These motions were compared w i t h the a c t u a l motions  recorded f o r the 1 9 7 6 Pender I s l a n d earthquake a t those s i t e s , to form an e s t i m a t i o n o f the accuracy o f the m o d e l l i n g procedure and i n p u t parameters.  With t h i s knowledge,  the second stage o f  a n a l y s i s c o u l d be undertaken.  T h i s i n v o l v e d s u b j e c t i n g the  p r o f i l e developed i n the f i r s t  stage to data r e p r e s e n t i n g  earthquakes  -57of v a r i o u s magnitudes to assess the e f f e c t of l a r g e motions on the  sites. Because of the n e c e s s i t y of comparison between the  predicted  and measured earthquake i n the f i r s t stage,  the s i t e s were l i m i t e d  to those where s u r f a c e records  Pender I s l a n d  quake had been o b t a i n e d . They c o n s i s t o f one one  f o r the 1976  Three s i t e s s a t i s f i e d  a t Roberts Bank, one  criterion.  on Annacis I s l a n d  and  i n the Brighouse area of Richmond, as shown i n f i g u r e 3-2-1.  These s i t e s are widely spaced across and  this  earth-  the area of the r e c e n t d e l t a ,  t h e i r p r o f i l e s are r e p r e s e n t a t i v e o f the s o i l s found through-  out the d e l t a . The  three p r o f i l e s t h a t were developed and  the s o i l models  t h a t were used f o r the computer a n a l y s i s are shown i n f i g u r e s 3-2-2, 3-2-3 deposits  and  3-2-4.  Generally,  i s w e l l known from d r i l l  the nature o f the  holes  near-surface  i n the v i c i n i t y of the  Below depths o f 45 meters to 60 meters, the nature of the and  t h e i r p r o p e r t i e s have been gleaned from a few  and  a knowledge of the h i s t o r y of the d e l t a formation.  deposits,  deep d r i l l The  a i d s i n the e x t r a p o l a t i o n of known s o i l c h a r a c t e r i s t i c s near to those a t depth.  Depths to the top o f the t i l l  estimated by p r o j e c t i o n of the t i l l drill few  surface  holes which i n t e r c e p t e d the t i l l ,  i s o l a t e d deep h o l e s .  a few deep d r i l l  The  h o l e s , and  site.  holes later surface  d e p o s i t s were  slopes as i n d i c a t e d by  and by c o r r e l a t i o n with a  depth to bedrock was  vibro-seismic p r o f i l e s .  estimated from Figure  1-1-5  shows the l a r g e i r r e g u l a r i t y i n the bedrock s u r f a c e , i n d i c a t i n g t h a t the bedrock depths estimated c o u l d e a s i l y vary by from the true depth.  30 meters  -58The Brighouse p r o f i l e s c o n s i s t o f 3.7 meters o f c l a y e y s i l t o v e r l y i n g sand to about 45 meters.  Below t h a t i s s i l t  grading downwards to c l a y .  Till  i s estimated to be §t 19 8 meters  and bedrock a t 305 meters.  Because o f the sequence o f  g l a c i a t i o n t h a t e f f e c t e d the p r e s e n t F r a s e r D e l t a area, there i s a p o s s i b i l i t y t h a t the t i l l  could contain layers of i n t e r -  g l a c i a l d e p o s i t s o f sand, c l a y o r s i l t ,  though because o f t h e i r  l a c k o f r e s i s t a n c e to a b r a s i o n and e r r o s i o n , these d e p o s i t s  may  have been completely e l i m i n a t e d . The Roberts Bank p r o f i l e c o n s i s t s o f 9.1 meters o f sandy silt  fill  and s i l t o v e r l y i n g sand w i t h some s i l t  about 60 meters. where t i l l of  Below t h i s , s i l t  l a y e r s to  i s expected to 107 meters,  i s e s t i m a t e d to o c c u r , a g a i n w i t h the p o s s i b i l i t y  i n t e r g l a c i a l deposits.  Bedrock i s estimated to be a t 228  meters. The Annacis I s l a n d p r o f i l e i s s i m i l a r to the Roberts Bank profile.  I t c o n s i s t s o f 6 meters o f sandy s i l t o v e r l y i n g sand  to  about 37 meters w i t h sandy s i l t  to about 91 meters, where  is  estimated to occur, p o s s i b l y w i t h some i n t e r g l a c i a l  till  deposits.  Bedrock i s estimated to be a t 220 meters. The s o i l model c o n s i s t s o f s o i l l a y e r s r a n g i n g from a few f e e t i n t h i c k n e s s a t the s u r f a c e , to 30 meters i n t h i c k n e s s a t depth.  This approach i s taken s i n c e a s i n g l e v a l u e o f each  dynamic  parameter must be s e l e c t e d to be r e p r e s e n t a t i v e of a l l  the  s o i l i n each l a y e r .  The l a y e r s are shown c l a s s i f i e d by the  major s o i l - t y p e they r e p r e s e n t , as t h i s w i l l determine the method used to d e r i v e the dynamic  p r o p e r t i e s o f the l a y e r .  The dynamic p r o p e r t i e s o f the s o i l s shown i n the p r o f i l e are  i n p u t i n terms o f a maximum shear modulus, maximum damping  r a t i o , and r e d u c t i o n curves which show the r e l a t i o n s h i p between these maximum v a l u e s and the s t r a i n l e v e l . c h a r a c t e r i s t i c s have been determined  The dynamic  from r e l a t i o n s  by o t h e r s u s i n g both l a b o r a t o r y and f i e l d  tests.  soil  developed  In the  l a b o r a t o r y , the m a t e r i a l b e i n g t e s t e d i s w e l l known b u t i t i s difficult  t o apply t e s t c o n d i t i o n s t h a t a r e r e p r e s e n t a t i v e o f  the s i t u a t i o n found i n the f i e l d , w h i l e i n f i e l d reverse i s true.  Both l a b o r a t o r y and f i e l d  d i v i d e d i n t o two groups;  t e s t i n g the  t e s t s can be sub-  those which attempt to measure the  response o f the s o i l system to dynamic e x c i t a t i o n , and those which measure the shear wave v e l o c i t y to the s o i l , from the modulus can be c a l c u l a t e d . for  which'  Common l a b o r a t o r y techniques  the measurement o f the s o i l s t r e s s s t r a i n p r o p e r t i e s  include  the resonant column t e s t , u l t r a s o n i c p u l s e t e s t s , shake t a b l e t e s t s and c y c l i c  tests.  The c y c l i c t e s t s may be e i t h e r  simple shear, o r t o r s i o n a l . stress or strain controlled.  triaxial,  These c y c l i c t e s t s can be e i t h e r Common f i e l d  tests are seismic  r e f r a c t i o n survey, c r o s s h o l e survey, down h o l e survey, o r surface-save techniques.  These g i v e the modulus i n d i r e c t l y  through measurement o f the shear wave v e l o c i t y .  Vibro-seismic  methods can a l s o be used, as can the c y l i n d r i c a l i n s i t u  test  developed by B r a t t o n and H i g g i n s (1978), i n which accelerometers on a s u r f a c e g r i d measure the response o f the s o i l to an e x p l o s i o n and an i t e r a t i v e procedure i s used to determine  the s o i l  properties.  Because o f the l a c k o f knowledge o f the m a t e r i a l being t e s t e d  -60i n the f i e l d , most modulus and damping r e l a t i o n s have been developed from l a b o r a t o r y  data.  I t i s important,  therefore,  to e s t a b l i s h a c o r r e l a t i o n between the f i e l d and l a b o r a t o r y data, which o f t e n d i f f e r because o f the v a r y i n g a t which the t e s t s were  strain levels  performed.  The maximum shear modulus has been c a l c u l a t e d  f o r the  s o i l l a y e r s i n the t h r e e p r o f i l e s from s e v e r a l r e l a t i o n s and i s shown i n f i g u r e s  3-2-5, 3-2-6, and 3-2-7.  Hardin and Black  (1968) developed the r e l a t i o n s h i p f o r cohesive and c o h e s i o n l e s s soils: Gmdx  =1230(2.973-e)  2  —(OCR)  k  CT.* ( p s i )  1 + e where the f a c t o r K depends on the p l a s t i c i t y index o f the s o i l as f o l l o w s : P l a s t i c i t y Index  K  0  0  20  .18  40  .30  60  .41  80  .48  100 o r g r e a t e r  .50  The above equation r e l a t e s the maximum shear modulus (G,.-,v)  to the v o i d r a t i o (e) , the over c o n s o l i d a t i o n  r a t i o (OCR) ,  a f a c t o r r e l a t e d to the p l a s t i c i t y index (K). and the mean normal effective stress  (<r„).  Seed and I d r i s s (1970) developed separate  r e l a t i o n s f o r sand and f o r c l a y . G max  =1000 (K,). * max  ( V  a  )  For sand they use the r e l a t i o n s h i p : h  (psf)  -61-  Here W i s the mean normal  e f f e c t i v e s t r e s s and (K_) i s a factor 2 max which depends upon the r e l a t i v e d e n s i t y o f the sand. For clay 0  s o i l s the f o l l o w i n g r e l a t i o n s h i p was developed: G Max  =Su (K)  (psf) c i  Here, Su i s the undrained s t r e n g t h , and K i s a c o n s t a n t which ranges from 1100 to 4000 w i t h an average o f 2200. Iwasaki  Ohsaki and  (1973) bypass the steps r e q u i r e d to a s c e r t a i n the  r e l a t i v e d e n s i t y by u s i n g the folowing f o r m u l a t i o n : G  Max  =  1  2  0  0  ( N )  *  (t/m )  8  2  They r e l a t e the maximum shear modulus d i r e c t l y to the standard p e n e t r a t i o n t e s t blow count  (N), Murphy e t a l (1978) have  developed a g r a p h i c a l r e l a t i o n s h i p f o r the g l a c i a l t i l l  used  i n t h e i r study which r e l a t e s the maximum shear modulus to the mean c o n s o l i d a t i o n s t r e s s and maximum p a s t p r e s s u r e . The maximum shear modulae o f the v a r i o u s l a y e r s i n the p r o f i l e s were c a l c u l a t e d from these equations u s i n g the s o i l presented i n Chapter  2.  The p l a s t i c i t y  index was read d i r e c t l y  from the p l o t s shown i n Chapter 2, as was the undrained s t r e n g t h , though  data  shear  the l a c k o f i n f o r m a t i o n a t depth made i t i m p o s s i b l e  to o b t a i n a measure o f the c r a t i o , - a c c u r a t e l y enough to e x t r a p o l a t e P  the s i l t d a t a .  The blow count data was taken d i r e c t l y from the  curves o f blow count f o r 0.15 to 0.45 meter p e n e t r a t i o n f o r the s i t e area i n q u e s t i o n , as shown i n Chapter  2.  The r e l a t i v e  density  v a l u e s were computed from the blow count curves u s i n g the S c h u l t z e and Menzenback r e l a t i o n s h i p .  The v o i d r a t i o s were.computed from the  water content o f the c l a y s and s i l t s ,  and the r e l a t i v e d e n s i t i e s o f  the  sands.  The v o i d r a t i o data was e x t r a p o l a t e d to depth by-  assuming t h a t the change i n v o i d r a t i o was due o n l y to c o n s o l i d a t i o n o f the m a t e r i a l under the weight o f the overburden, an assumption  t h a t was supported by the data c o l l e c t e d i n Chapter 2.  This allowed the v o i d r a t i o to be computed u s i n g the c o e f f i c i e n t of  consolidation.  In cases where the s o i l had been over c o n s o l i d a t e d  by g l a c i a t i o n , the rebound o f the s o i l was c o n s i d e r e d . p r i n c i p l e e f f e c t i v e s t r e s s was computed from the v o i d  The mean ratio,  s p e c i f i c g r a v i t y and u s i n g an assumed v a l u e o f the c o e f f i c i e n t of  l a t e r a l pressure which v a r i e d from 0.6 f o r the s o f t c l a y s to  0.4 f o r the t i l l s . the  The o v e r c o n s o l i d a t i o n r a t i o was determined a t  s u r f a c e from the p l o t s o f undrained shear s t r e n g t h versus depth,  and the c r a t i o . P  A t depth the o v e r c o n s o l i d a t i o n r a t i o was determined  from a knowledge o f the g l a c i a l h i s t o r y . of  the t i l l s  The e n g i n e e r i n g p r o p e r t i e s  were taken from the v a l u e s presented by Klohn  (1965),  Radhakrishna and Klym (1974), C l a r k e (1966) and Murphy e t a l (1978). for  The p r o p e r t i e s o f the rocks a r e based on average v a l u e s  the rock type a n t i c i p a t e d , as presented by C l a r k  (19 66).  The v a l u e s o f maximum shear modulus computed u s i n g these methods are shown f o r the t h r e e s o i l p r o f i l e s i n f i g u r e s 3-2-5, 3-2-6, and 3-2-7.  I t can be seen t h a t d e s p i t e the change i n s o i l  type between l a y e r s , the modulus p r e d i c t e d by each method i n c r e a s e s smoothly w i t h depth, t h e r e b e i n g no major d i s c o n t i n u i t i e s , where the t i l l  and rock l a y e r s a r e encountered.  except  In f i g u r e 3-2-7,  for  the Brighouse p r o f i l e the range o f the maximum shear modulus  was  shown.  T h i s range was based on the maximum range a n t i c i p a t e d i n  those parameters which a r e used to c a l c u l a t e the modulus. The range,  though l a r g e i s s t i l l  s m a l l e r than the range  between the modulus values determined which suggests  by d i f f e r e n t methods,  t h a t e f f o r t s should be made to make a c h o i c e  between the a n a l y s i s methods used r a t h e r than c o n c e n t r a t i n g on the p o s s i b l e e r r o r s i n the d a t a .  The p l o t s show t h a t the  Ohsaki and Iwasaki method g e n e r a l l y p r e d i c t e d the h i g h e s t modulus, and the Hardin and Black method the lowest, w i t h the Seed and I d r i s s method l y i n g i n between.  This i s i n keeping  w i t h the f i n d i n g s o f Anderson e t a l (1978) , who compared these methods w i t h values measured i n the f i e l d . t h a t the Hardin and Black method underestimated  They  found  the f i e l d  value by a f a c t o r o f 1.8, t h a t the Seed and I d r i s s method underestimated  the f i e l d value by 1.6 and the Ohsaki and  Iwasaki method overestimated the f i e l d value by a f a c t o r o f 1.4.  The trends seen i n the p r o f i l e s c a l c u l a t e d f o r the  F r a s e r D e l t a s i t e s a r e s i m i l a r to those found by Anderson et  a l , but the magnitude o f the v a r i a t i o n i s not as g r e a t . In  the t i l l  l a y e r , the use o f the r e l a t i o n s h i p  formulated  by Murphy e t a l gave v a l u e s o f shear modulus i n c r e a s i n g w i t h depth.  F o r the Brighouse p r o f i l e , values o f shear modulus  were a l s o c a l c u l a t e d u s i n g the Harden and Black f o r m u l a t i o n for  till,  and f o r l a y e r s o f c l a y and sand interbedded between  till  layers.  till  was about 80% o f t h a t p r e d i c t e d f o r t i l l  method.  The modulus p r e d i c t e d f o r the i n t e r g l a c i a l c l a y and  The modulus o f the i n t e r - g l a c i a l sand was l e s s  50% o f the value f o r t i l l of  by Murphy's than  p r e d i c t e d by Murphy's method, because  the l a c k o f any cohesion o r o v e r - c o n s o l i d a t i o n e f f e c t .  -64For  the computer  a n a l y s i s , the Harden and B l a c k mean  curves were used i n the sediments above the t i l l gave v a l u e s o f the modulus i n a l l s o i l l a y e r s .  because they The data  a v a i l a b l e was not s u f f i c i e n t to permit a c c u r a t e use o f the Seed and I d r i s s formula i n deep s i l t  layers.  The Ohsaki and  Iwasaki method c o u l d not be used i n s i l t because i t was not designed f o r t h a t , and c o u l d not be used i n c l a y because o f lack of data. in t i l l  The modulus p r e d i c t e d by Murphy e t a l was used  layers.  The maximum damping r a t i o i s an important i n p u t parameter for of  the dynamic  analysis.  Seed and I d r i s s  (1970) show p l o t s  damping r a t i o versus s t r a i n f o r sands and c l a y s from a  l a r g e number o f t e s t s by v a r i o u s r e s e a r c h e r s .  They show the  maximum damping r a t i o i n sands to be from 21% to 28%, and t h a t of  c l a y from 26% to 32%.  Hardin and Drnevich (1972) developed  r e l a t i o n s h i p s from experiments on v a r i o u s s o i l  types.  They  •found t h a t f o r s a t u r a t e d sands: D  For  Max  =  2  8  "  saturated  1  ,  5  (  l  o  g  n  )  silts:  D., = 26 - 4 f * Max o  + .If*  - 1.5 ( l o g n) ^  and f o r c l a y s : D„ = 31 - (3 + . 0 3 f ) v " ' ^ Max o Here T ' Q  f.is  + L S f * - 1.5 ( l o g n) 3  i s the mean e f f e c t i v e p r i n c i p a l s t r e s s i n kg/cc,  the frequency i n c y c l e s / s e c o n d and n i s the number o f c y c l e s . A v a r i a t i o n w i t h i n a reasonable range o f n and f does not  have a l a r g e e f f e c t on v a l u e s o f maximum damping r a t i o .  These  two parameters form p a r t o f the e q u a t i o n because the l a b o r a t o r y  -65samples which were t e s t e d  to form the r e l a t i o n s h i p were  subject  to c y c l e s o f complete s t r e s s r e v e r s a l a t a c e r t a i n frequency. The  s t r e s s - s t r a i n c h a r a c t e r i s t i c s could  particular cycle.  be determined f o r any  For t h i s computer a n a l y s i s , v a l u e s f o r n and  f must be s e l e c t e d which are r e p r e s e n t a t i v e  o f the i r r e g u l a r  motion o f the s i g n i f i c a n t p a r t o f the earthquake. and  Kiefer  Seed,Idriss  (1969) present a r e l a t i o n s h i p which c o r r e l a t e s the  earthquake magnitude with the d i s t a n c e energy r e l e a s e  from the source o f  and the predominant p e r i o d .  For the nearby  earthquakes analyzed i n t h i s study a frequency o f 3.3 c y c l e s per second was chosen u s i n g t h e i r r e l a t i o n s h i p .  The true  value  w i l l vary with the earthquake used f o r the o b j e c t motion and the  s o i l layer considered.  Idriss,MaRdisi  Methods have been developed  and Banerjee  (1975) whereby an i r r e g u l a r s t r e s s -  s t r a i n h i s t o r y can be represented by a uniform s t r e s s however because the i n p u t  (Seed,  series,  to the computer program c o n s i s t s o f  the average damping over s e v e r a l  s o i l layers experiencing a  range o f o f earthquake motions, t h i s a n a l y s i s would n o t be o f benefit, The  so a mean value o f 15 was  selected.  maximum damping r a t i o s computed u s i n g  these  r e l a t i o n s h i p s a r e shown f o r the three p r o f i l e s i n f i g u r e s 3-2-8, 3-2-9, and 3-2-10.  The .damping r a t i o f o r the t i l l  s o i l s was taken from the average o f those presented by Murphy et a l .  I n s u f f i c i e n t data .was a v a i l a b l e to attempt to  characterize till. and  a change i n damping r a t i o w i t h depth i n the  The damping r a t i o a n t i c i p a t e d  i n l a y e r s o f sand, c l a y  s i l t which might be p r e s e n t as i n t e r g l a c i a l d e p o s i t s  between t i l l  layers  i s shown i n the Brighouse p r o f i l e .  i n t e r g l a c i a l sand and c l a y would have h i g h e r damping than the t i l l , damping.  The  ratios  w h i l e the i n t e r g l a c i a l s i l t would have lower  The damping c h a r a c t e r i s t i c s o f the rock were o b t a i n e d  from average v a l u e s presented by Schnabel, Lysmer and Seed (1972) , Both the shear modulus and damping r a t i o vary with the s t r a i n amplitude.  Seed and I d r i s s  (1970) p r e s e n t damping  r e d u c t i o n curves f o r c l a y and sand, "however,. they i n d i c a t e a range o f v a l u e s with an average  f o r each s o i l  type.  only  Hardin  and Drnevich  (1972) present a method o f c a l c u l a t i n g the  relationship  between the maximum shear modulus, and the shear  modulus a t any given s t r a i n l e v e l .  I t has the f o l l o w i n g  formulation: G  = 1  G Max  where  1 + X. h  =  y  1 + a exp (- frb)  Xr  ttr  Here: X G  = strain level =the shear modulus a t s t r a i n l e v e l  G Max  =the maximum shear modulus  a  =a c y c l e  b  =a s o i l  w  y  f a c t o r which depends on the s o i l  type  coefficient  =the r e f e r e n c e s t r a i n  The r e f e r e n c e s t r a i n can be thought o f the s t r a i n t h a t would experience i f i t had a c o n s t a n t shear modulus o f was s t r a i n e d  to f a i l u r e .  p l o t o f the s o i l  stress  I t can be computed from G state.  M a x  the s o i l G  a M  a  x  ^d  and a Mohr  -67The modulus r e d u c t i o n for  the sands,  The r e d u c t i o n  silts,  curves were computed by t h i s method  c l a y s and the t i l l  l a y e r s i n the p r o f i l e s .  curves f o r a l l the s i l t and c l a y l a y e r s were  v i r t u a l l y i d e n t i c a l , as were a l l the curves o f the sand and of the t i l l in  layers.  layers  The mean o f each curve s e t i s p l o t t e d  f i g u r e 3-2-11 along with the r e l a t i o n f o r rock o b t a i n e d  from Schnabel e t a l (19 72) . . i.n3. u i y th -  and another curve f o r t i l l  This a d d i t i o n a l t i l l laboratory  from Murphy e t a l (1978).  curve was o b t a i n e d by r e p l o t t i n g the  data developed by Murphy e t a l without  arbitrarily  f o r c i n g the curve to go through an end-point t h a t was by g e o p h y s i c a l methods. reduction  determined  This a d d i t i o n a l curve p r e d i c t e d a greater  i n modulus a t a p a r t i c u l a r s t r a i n l e v e l than d i d the  Hardin and Drnevich curves. Hardin and Drnevich a l s o proposed  the f o l l o w i n g r e l a t i o n -  s h i p d e s c r i b i n g the dependence of the damping r a t i o on the s t r a i n level: D_ D„ Max  = 1  -_G G  Max  Here D i s the damping r a t i o a t s t r a i n l e v e l 2f , and D maximum damping r a t i o . in  M a x  i s the  This r e l a t i o n , a p p l i e d to the curves  f i g u r e 3-2-11 y i e l d s the r e l a t i o n s h i p f o r sands, c l a y s and  silts  and t i l l  shown i n f i g u r e 3-2-12.  The damping  reduction  curve f o r rock was o b t a i n e d from Schnabel e t 'al (1972) . For the computer a n a l y s i s the Hardin and Drnevich damping reduction  curves were used f o r the sands, s i l t s ,  and the Schnabel e t a l curves were used f o r rock.  c l a y s and . . t i l l s , The Seed and  -68I d r i s s r e d u c t i o n curves f o r s o i l were too g e n e r a l and  the  Murphy e t al. curve d i d not f o l l o w the p a t t e r n s e t by the Hardin and Drnevich curves.  Anderson  (1976) found t h a t the Hardin  Drnevich curves were more r e p r e s e n t a t i v e o f sample than the Seed and  I d r i s s curves.  behaviour  Arango e t a l (19 78)  present  data which a l s o i n d i c a t e s t h a t the Hardin and Drnevich are s u p e r i o r to those of Seed and 3-3  and  equations  Idriss.  Pender I s l a n d Earthquake C o r r e l a t i o n Ground s u r f a c e a c c e l e r a t i o n r e c o r d s were o b t a i n e d f o r the  1976  Pender I s l a n d earthquake,  in Victoria.  The o b j e c t was  from the P a c i f i c Geoscience  Centre  to compare the s u r f a c e motions  recorded a t the three s i t e s a t which p r o f i l e s had been  developed,  w i t h the s u r f a c e r e c o r d s obtained by dynamic a n a l y s i s , u s i n g the SHAKE program and the motions recorded on rock f o r the same earthquake  a t the Lake Cowichan S a t e l l i t e S t a t i o n as the base  i n p u t motion.  The  s o i l p r o p e r t i e s developed  were used i n the a n a l y s i s .  i n Section  3-2  V a r i a t i o n s were made i n these  p r o p e r t i e s and p r o f i l e s to.determine  the e x t e n t to which  i n a c c u r a t e data would e f f e c t the a n a l y s i s  results.  The q u e s t i o n as to whether s c a l i n g of the i n p u t earthquake was  motion (Lake Cowichan record) would be  examined.  necessary  T h i s s c a l i n g c o u l d be necessary because o f a  d i f f e r e n c e i n the d i s t a n c e from the earthquake  source to the  Lake Cowichan s i t e and the F r a s e r D e l t a s i t e s , or a d i f f e r e n c e i n the rock type through which the s e i s m i c waves passed.  Scaling  c o u l d a l s o be necessary because the motions recorded a t the  -69-  s u r f a c e rock outcrop would be d i f f e r e n t than those  experienced  by a b u r i e d rock s u r f a c e , even i f both s i t e s were c l o s e together.  In examining these problems i t was necessary  i n mind the accuracy  o f our knowledge o f the dynamic  to keep  soil  p r o p e r t i e s a t the s i t e s and the p o t e n t i a l magnitude o f e r r o r s t h a t c o u l d be induced  by an i n v a l i d assumption r e g a r d i n g the  scaling required. The  e p i c e n t r a l d i s t a n c e o f the Lake Cowichan s i t e i s 54km,  while the e p i c e n t r e d i s t a n c e o f the F r a s e r D e l t a s i t e s ranges from 37 km to 52km.  F i g u r e s presented  by Schnabel and Seed (1972)  g i v e a r e l a t i o n s h i p between the maximum a c c e l e r a t i o n , the magnitude o f the earthquake, and the d i s t a n c e from the source of energy r e l e a s e .  T h i s r e l a t i o n s h i p compares w e l l with  s i m i l a r r e l a t i o n s h i p s , as shown by T r i f u n a c and Brady  other  (1975), who  found t h a t f o r d i s t a n c e s g r e a t e r than 30km the a c c e l e r a t i o n amplitude v a r i e d i n v e r s e l y with the square o f the d i s t a n c e to the source.  F o r a small earthquake, such as the Pender I s l a n d  earthquake w i t h a magnitude i n the order o f 5 to 5.5, these r e l a t i o n s h i p s show t h a t the d i f f e r e n c e i n maximum a c c e l e r a t i o n s f o r these s i t e s would be s m a l l .  The earthquake was not s c a l e d  on the b a s i s o f d i s t a n c e from the source  s i n c e other f a c t o r s  which c o u l d not be accounted f o r , such as bedrock topography, would have a g r e a t e r e f f e c t on the maximum a c c e l e r a t i o n s . The bedrock u n d e r l y i n g the three F r a s e r D e l t a c o n s i s t s o f r e l a t i v e l y low shear wave v e l o c i t y  sandstone,  conglomerate, and s h a l e , o v e r l y i n g higher v e l o c i t y rocks.  sites  Since the low v e l o c i t y rocks a r e present  granitic  i n thicker  s t r a t a a t the F r a s e r D e l t a s i t e s than a t the Lake Cowichan site,  i t i s p o s s i b l e t h a t s e i s m i c waves t r a v e l l i n g , to. the  d e l t a s i t e s would experience more damping than those t r a v e l l i n g to  the Lake Cowichan s i t e .  Because o f the d i f f i c u l t y  i n assessing  the  magnitude o f these e f f e c t s no attempt was made to compensate  for  them by s c a l i n g .  T h i s e f f e c t may  compensate to'some  degree f o r the d i f f e r e n c e from the e p i c e n t r e to the Lake Cowichan and F r a s e r D e l t a  sites.  The theory o f shear wave p r o p a g a t i o n i n a one-dimensional system i s d e s c r i b e d by Schnabel, Lysmer, and Seed  (1972).  They  p o i n t out t h a t the h o r i z o n t a l displacements a t any l a y e r i n the system are caused by two components o f the shear wave.  One  component i s due to the i n c i d e n t wave t r a v e l l i n g upwards the  towards  s u r f a c e and the o t h e r i s caused by the r e f l e c t e d wave  t r a v e l l i n g back i n t o the e a r t h .  A t the f r e e s u r f a c e , the  magnitude o f the i n c i d e n t and r e f l e c t e d waves are the same. I t i s reasonable to assume t h a t the i n c i d e n t waves a t the rock outcrop w i l l be o f the same amplitude as the i n c i d e n t waves a t a nearby b u r i e d rock l a y e r , s i n c e the i n c i d e n t waves are not e f f e c t e d by the o v e r l y i n g s o i l s .  However, w h i l e the r e f l e c t e d  wave a t the rock outcrop i s equal to the i n c i d e n t wave, the r e l e c t e d wave amplitude a t the b u r i e d rock s u r f a c e w i l l be than the i n c i d e n t wave amplitude because o f the damping q u a l i t i e s of the o v e r l y i n g s o i l l a y e r s .  From t h i s i t can  be seen t h a t the amplitude o f the b u r i e d base rock motion w i l l be between 50% and 100% o f the amplitude o f the rock outcrop motion.  I t would be 50% i f the wave p r o p a g a t i n g up  from the b u r i e d rock s u r f a c e and r e f l e c t e d back had been  less  -71completely absorbed  b e f o r e i t reached  the rock s u r f a c e a g a i n .  I t would be 100% i f the wave had not changed i n c h a r a c t e r on i t s r e t u r n to the b u r i e d rock l a y e r .  The a c t u a l r a t i o o f  amplitudes would depend on the damping i n the d e p o s i t , the impedence r a t i o between the d e p o s i t and the rock, and the frequency d i s t r i b u t i o n o f the wave energy  i n the rock  relative  to the resonant frequency o f the d e p o s i t (Schnabel, Lysmer, Seed, 1972).  T h i s means t h a t the d i f f e r e n c e i n the response s p e c t r a  f o r a p r o f i l e which had been computed u s i n g the t r u e motion on the b u r i e d rock l a y e r and the response  s p e c t r a f o r the same  p r o f i l e which had been computed u s i n g a nearby measured rock outcrop motion would be g r e a t e s t a t the p e r i o d s where the l a r g e s t a m p l i f i c a t i o n had taken p l a c e between the rock motion and the s u r f a c e motion. Lysmer, Seed, and Schnabel  (1971) performed  a series of  analyses on p r o f i l e s c o n s i s t i n g o f up to 90 meters o f sand and c l a y over rock, and found  t h a t the maximum a c c e l e r a t i o n i n the  b u r i e d rock l a y e r s was between 85% and 92% o f the maximum a c c e l e r a t i o n oh nearby rock o u t c r o p s , f o r rock having a shear wave v e l o c i t y o f 1800 m/s, and between 80% and 85% o f the maximum a c c e l e r a t i o n f o r rocks having a shear wave v e l o c i t y of 1200 m/s.  The t h r e e s i t e s i n the F r a s e r D e l t a were  analyzed u s i n g a base rock modulus o f 16,000 MPa, which corresponds  to a shear wave v e l o c i t y o f l e s s than 2400 m/s.  Lysmer e t a l (1971) a l s o found t h a t the response  s p e c t r a f o r the  s u r f a c e motions were e s s e n t i a l l y the same i n shape whether computed u s i n g the rock outcrop motion o r the a c t u a l motion on  -72-  the b u r i e d rock as the o b j e c t motion. Because there was l i t t l e d i f f e r e n c e i n the response s p e c t r a , and the d i f f e r e n c e i n the rock outcrop motion and b u r i e d motion was dependant on the p r o p e r t i e s o f the o v e r l y i n g soil  and not e a s i l y s c a l e d , i t was decided  a n a l y s i s u s i n g the unsealed records  to perform the  obtained  from the Lake  Cowichan s i t e rock outcrop, which we a r e assuming would have s i m i l a r motion to a rock outcrop i n the F r a s e r D e l t a , i f such an outcrop e x i s t e d .  The r e s u l t s o f the a n a l y s i s c o u l d be  examined i n the l i g h t o f the known e f f e c t s t h a t t h i s v a r i a t i o n from r e a l i t y would produce. Comparison o f the computed motions and recorded for  motions  the three s i t e s was made u s i n g a c c e l e r a t i o n response s p e c t r a .  T h i s was done because the ground s u r f a c e a c c e l e r a t i o n s a r e r e l a t e d to the maximum f o r c e s experienced by s t r u c t u r e s a t the s i t e , and because the s p e c t r a presents  the a c c e l e r a t i o n t h a t would be  experienced by s t r u c t u r e s o f v a r y i n g  fundamental p e r i o d s .  The  a c c e l e r a t i o n response s p e c t r a were produced f o r s i n g l e degree o f freedom s t r u c t u r e s having 5% o f c r i t i c a l  damping.  to the amount o f damping t h a t would be present  T h i s corresponds  i n most b u i l d i n g s  when the s t r u c t u r e had reached y i e l d , where most o f the energy of the earthquake would be absorbed.  Response s p e c t r a were  produced f o r the l a y e r s t h a t marked the d i v i s i o n between s o i l s o f d i f f e r e n t types to permit an assessment o f the r e l a t i v e e f f e c t s o f each s o i l , type on the. ground motion.  The response  spectrum t h a t was used f o r comparison w i t h the a c t u a l recorded  surface  spectrum was one which was computed a t a 1.5  meter depth below the s o i l s u r f a c e .  This was  account f o r the f a c t t h a t the accelerographs concrete  done to t r y to were on  rigid  f l o o r s l a b s i n b u i l d i n g s , which added a normal l o a d .  In the case of the Brighouse r e c o r d i n g , the a c c e l e r o g r a p h  was  i n a basement. 3-4  S e i s m i c i t y and  the Design Earthquake  The F r a s e r R i v e r D e l t a l i e s i n one a c t i v e zones i n Canada. set  of the most s e i s m i c a l l y  A network of accelerographs  has  been  up by the E a r t h P h y s i c s Branch of the Department of Energy,  Mines and area.  Resources, to monitor earthquake a c t i v i t y i n t h i s  Through i n f o r m a t i o n obtained  from ot he rs  from these r e c o r d e r s  i n the United S t a t e s , an understanding  magnitude and  frequency  of  and  the  of the earthquakes i n t h i s area,  and  the c a u s i t i v e mechanism as r e l a t e d to p l a t e t e c t o n i c s , has The  emerged.  records magnify the ground motions to g i v e p l o t s o f  the earthquake motions i n three c o o r d i n a t e d i r e c t i o n s .  By  examining the phases of the records produced by the a r r i v a l of body and and  s u r f a c e waves, i t i s p o s s i b l e to estimate  asimuth to the e p i c e n t r e and  accelerograph to  records  the  distance  the depth to the focus.  All  t h a t show the p a r t i c u l a r event can be used  l o c a t e the e p i c e n t r e .  Inaccuracies  i n the l o c a t i o n can  result  from i n a c c u r a t e a c c e l e r a t i o n r e c o r d s , or a poor knowledge of the time a t each of the r e c o r d i n g s t a t i o n s .  The  velocity  c h a r a c t e r i s t i c s of the e a r t h ' s c r u s t must a l s o be modelled, so the s o l u t i o n cannot be expected to be The  accuracy  earthquake and  exact.  of l o c a t i o n w i l l vary with the s i z e of  the  the l o c a t i o n o f the r e c o r d i n g s t a t i o n s , so t h a t  -74both s c a t t e r i n g and  systematic e r r o r s are i n t r o d u c e d .  Earth-  quakes of s m a l l magnitude, o r those a t a l a r g e d i s t a n c e from r e c o r d i n g c e n t r e s may map  not be d e t e c t e d .  A relatively  of e p i c e n t r e s can be produced by e l i m i n a t i n g the  unbiased low  magnitude earthquakes, which are d e t e c t e d o n l y i n areas where there are nearby seismographs.  Bias due  to the l o c a t i o n s o f  the r e c o r d i n g s t a t i o n s i s a p a r t i c u l a r problem with h i s t o r i c a l l y o l d earthquakes, which may  have o c c u r r e d a t a time when there  were very few r e c o r d i n g s t a t i o n s . if  They would be d e t e c t e d  only  they were l a r g e and near an i n h a b i t e d area and c o u l d not  so a c c u r a t e l y l o c a t e d . distribution  F i g u r e 3-4-1  be  from M i l n e e t a l (1978) shows  of earthquakes g r e a t e r than magnitude 2 i n the Puget  Sound - S t r a i t of Georgia  area.  The earthquakes which are of a  magnitude which i s s u b j e c t to r e g i o n a l b i a s because of distribution  o f accelerographs  the  are marked with an"X", w h i l e  others are graded by magnitude. On a r e g i o n a l s c a l e , the boundaries lithosperic  between the major  p l a t e s (Figure 3-4-2) correspond  to areas o f h i g h  seismic a c t i v i t y .  Milne e t al.(1978) have d e s c r i b e d  relationship.  Queen C h a r l o t t e - F a i r w e a t h e r  The  fault,  northern e q u i v a l e n t of the San Andreas f a u l t , marks a between the P a c i f i c and America p l a t e s . r e l a t i v e motion o f about 5 cm/year. latitude,  this the division  These p l a t e s have a  South o f 51 degrees  the r i d g e f r a c t u r e . zone between the Juan de Fuca  and E x p l o r e r p l a t e s marks the area of i n t e r a c t i o n between two  small p l a t e s and  the P a c i f i c p l a t e .  these  In the c o n t i n e n t a l  area the E x p l o r e r and Juan de Fuca p l a t e s are subducting  under  -75the /America p l a t e a t a r a t e o f 2^ cm/year.  M i l e e t a l (1978)  found t h a t the s e i s m i c r e c o r d s i n d i c a t e t h a t the i n t e r a c t i o n between the two o c e a n i c p l a t e s and the America p l a t e i s i n the form o f a s t r i k e s l i p f a u l t . r a t h e r than the t h r u s t f a u l t normally expected i n areas o f subduction. convergence o f the p l a t e s .  T h i s i s due to the o b l i q u e  Rogers and Hasegawa (1978) p o i n t  out t h a t the m a j o r i t y o f l a r g e r earthquakes i n t h i s  continental  r e g i o n occur a t depth, w i t h i n the c o n t i n e n t a l c r u s t .  The  t e c t o n i c f o r c e s c a u s i n g these earthquakes probably r e s u l t  from  the motion o f the upper p l a t e s i n the subduction zone. An assessment o f the maximum probable earthquake motion to occur i n the F r a s e r D e l t a can be made on the b a s i s o f s e v e r a l c r i t e r i a , which must c o n s i d e r both the magnitude o f the earthquake, and i t s h o r i z o n t a l d i s t a n c e and depth from the site,  s i n c e the earthquake c h a r a c t e r i s t i c s change as the waves  propogate through the l i t h o s p h e r e .  These c r i t e r i a a r e the s t r a i n  r e l e a s e versus time r e l a t i o n s , magnitude versus time r e l a t i o n s and the a n t i c i p a t e d mechanism. S t r a i n r e l e a s e i s a measure o f the t o t a l energy r e l e a s e d by an earthquake, and i s r e l a t e d to i t s magnitude.  By p l o t t i n g  s t r a i n r e l e a s e a g a i n s t time and assuming a c o n s t a n t r a t e o f p o t e n t i a l s t r a i n accumulation, e s t i m a t e s can be made o f the maximum expected earthquake on a p a r t i c u l a r f a u l t system.  In  f i g u r e 3-4-3 M i l n e e t aL (1978) show the p o s s i b i l i t y o f a s i g n i f i c a n t earthquake,, g r e a t e r than magnitude 7, i n the Georgia S t r a i t - Puget Sound a r e a . V a r i o u s methods o f examination o f a c c e l e r o g r a p h r e c o r d s are used to determine the magnitude o f an earthquake.  These  -76methods may g i v e r e s u l t s which vary by one u n i t . p o s s i b l e to f i n d e m p i r i c a l r e l a t i o n s h i p s between  It is earthquake  magnitude and r e t u r n p e r i o d f o r a p a r t i c u l a r a r e a .  These  r e l a t i o n s h i p s a r e d i f f i c u l t to determine a c c u r a t e l y because o f the b i a s i n magnitude e s t i m a t e s .  A t low magnitudes,  events may  go undetected, and a t h i g h magnitudes events may be q u i t e r a r e . M i l n e e t a l (1978) have analyzed the data f o r the Georgia S t r a i t - Puget Sound area and have formed a r e l a t i o n s h i p which can be represented as shown i n f i g u r e 3-4-4. p r e d i c t s t h a t a one-hundred-year earthquake  This r e l a t i o n i n the F r a s e r D e l t a  area would have a magnitude o f about 7.4 The maximum magnitude o f an event i s l i m i t e d by the mechanism and by the e x t e n t o f the f a u l t i n g .  Milne e t a l  (1978) estimate t h a t the maximum magnitude earthquake  i n the  Puget Sound - Georgia S t r a i t area would be g r e a t e r than 8 f o r t h r u s t f a u l t i n g , which i s the most common f a u l t type found i n subduetion zones. to  However, the earthquakes  e x h i b i t s t r i k e s l i p o r normal  maximum magnitude i s l i k e l y  i n t h i s area appear  f a u l t i n g mechanisms so the  to be l e s s than 8.  The d i s t a n c e from the F r a s e r D e l t a s i t e s to the source o f energy r e l e a s e i s an important f a c t o r i n a s s e s s i n g the earthquake motion s i n c e i t e f f e c t s the predominant experienced.  p e r i o d and the a c c e l e r a t i o n s  Large magnitude events, due to the t e c t o n i c  developed i n the subduetion p r o c e s s , a r e l i k e l y depths o f up to 60km w i t h i n the c o n t i n e n t a l (personal communication G. Rogers).  forces  to occur a t  lithosphere  These events would probably  not cause s u r f a c e r u p t u r e , so they would n o t n e c e s s a r i l y be  -77a s s o c i a t e d w i t h the presence o f s u r f a c e f a u l t s .  Such  earth-  quakes c o u l d reasonably be expected to have a source o f energy r e l e a s e 20 o r 30km w i t h i n the e a r t h ' s c r u s t . An earthquake w i t h a hypocentre c l o s e r to the e a r t h s u r f a c e has a g r e a t e r l i k e l i h o o d o f being r e l a t e d to an e x i s t i n g with surface expression.  fault  Rogers and Hasegawa (1978) p o i n t out  t h a t the magnitude 7.2 B r i t i s h Columbia Earthquake o f 1946  may  have r e s u l t e d from r u p t u r e along the p r o j e c t i o n o f an e x i s t i n g fault.  Some g e o l o g i c a l i n t e r p r e t a t i o n s have i n f e r r e d t h a t t h e r e  i s a f a u l t e x i s t i n g i n the S t r a i t o f Georgia. this interpretation, while others,  Muller  (1977) shows  (Jackson and Seraphin (19 76)),  do not i n d i c a t e the presence o f a f a u l t .  The e x i s t a n c e o r  otherwise o f a f a u l t . i n the S t r a i t o f G e o r g i a , where s u r f a c e rock exposures cannot be mapped, i s d i f f i c u l t  to v e r i f y  would be open to the i n t e r p r e t a t i o n o f i n d i v i d u a l  geologists,  based on an understanding o f the r e g i o n a l geology and patterns.  and  seismic  Because the presence o f a f a u l t i s not g e n e r a l l y ,  accepted, the assumption i s made i n t h i s study t h a t i f such a f a u l t e x i s t s i n the S t r a i t o f Georgia, and i f i t c o u l d undergo movements due to an earthquake, t h a t the source o f energy r e l e a s e d would be no c l o s e r to the F r a s e r D e l t a s i t e s than the 20 o r 30km expected from the deep earthquake. For the purposes o f t h i s work earthquakes o f s e v e r a l magnitudes  were s t u d i e d .  On the b a s i s o f the i n f o r m a t i o n  o u t l i n e d , an earthquake o f magnitude 7.4 was  just  a t a d i s t a n c e o f 30km  s e l e c t e d as the maximum probably earthquake.  In o r d e r to  assess the e f f e c t o f earthquake i n t e n s i t y on the s o i l s ,  earthquake  -78of magnitude 8.0,  p o s s i b l e i f there was  faulting in  a thrust  mechanism, and o f magnitude 6.5 were a l s o s e l e c t e d f o r a n a l y s i s . S e v e r a l d e s i g n earthquakes were used i n an attempt to observe the e f f e c t s of earthquakes i n g e n e r a l , s i n c e i t i s u n l i k e l y t h a t the a c t u a l earthquake o c c u r r i n g a t the s i t e resemble completely any p a r t i c u l a r d e s i g n earthquake.  would  Ideally,  the d e s i g n earthquakes should have the same c h a r a c t e r i s t i c s as the p o t e n t i a l earthquake.  They should be caused by the same  mechanism, have the same magnitude,  and have the same d i s t a n c e  to the hypocentre through s i m i l a r g e o l o g i c f o r m a t i o n s .  Because  o f the form o f the a n a l y s i s used,the i n p u t must be an e a r t h quake recorded on rock. 1949  The Western Washington  earthquake o f  and the Puget Sound Earthquake would be the i d e a l d e s i g n  earthquakes i f r e c o r d i n g s had been o b t a i n e d on rock, s i n c e they s a t i s f y the above c r i t e r i a .  I t would be p o s s i b l e to perform an  a n a l y s i s s i m i l a r to t h a t now b e i n g undertaken, to o b t a i n a base rock motion a t the r e c o r d i n g s i t e s o f these two  earthquakes  u s i n g the s u r f a c e r e c o r d , i f the s o i l s d e p o s i t s a t the s i t e were w e l l known.  T h i s was  not done, because the data were not r e a d i l y  a v a i l a b l e and such a n . a n a l y s i s would  introduce a d d i t i o n a l  errors  i n t o the F r a s e r D e l t a a n a l y s i s . Recordings made on rock outcrops o f earthquakes o f s i m i l a r magnitude and d i s t a n c e from source to s i t e were used i n the computer a n a l y s i s .  T h i s e l i m i n a t e d the need to s c a l e the p e r i o d ,  which as can be seen from F i g u r e 3-4-5 accurate procedure.  i s not a w e l l d e f i n e d or  The earthquakes chosen were the  component o f the magnitude 7.6  N21E  Kern County earthquake o f 19 52  -79-  as recorded 56km from the source a t T a f t , the S69E component o f magnitude 6.6 San Fernando  earthquake as recorded 26km from the  source a t Lake Hughes S t a t i o n #4, and the N21E component o f the magnitude 6.6 San Fernando  earthquake as recorded 21km from the  source a t Lake Hughes s t a t i o n #12.  The Kern County  earthquake  i s o f a l a r g e r magnitude b u t w i t h a source a t g r e a t e r d i s t a n c e than the p r i n c i p l e d e s i g n earthquake f o r the F r a s e r D e l t a w h i l e the two San Fernando  sites,  earthquakes a r e o f a s m a l l e r  magnitude b u t a s h o r t e r d i s t a n c e .  F i g u r e 3-4-5 shows t h a t i t  i s l i k e l y t h a t a l l three r e c o r d i n g s would have a predominant p e r i o d s i m i l a r to the a n t i c i p a t e d earthquake.  The San  Fernando earthquake e x h i b i t s predominately l a t e r a l s l i p  motion,  which i s the type o f motion most l i k e l y to occur i n the F r a s e r Delta area. The a n a l y s i s used i n the SHAKE program  i s based on the  assumption, t h a t the earthquake r e c o r d i n p u t as the e x c i t a t i o n motion repeats i t s e l f to produce a continuous r e c o r d .  The  r e c o r d s used i n the a n a l y s i s were the f i r s t 16 seconds o f recorded motions o f the s e l e c t e d earthquakes.  This t i m e - p e r i o d c o n t a i n s  the major p a r t o f the strong motions. The t h r e e d e s i g n earthquakes were s c a l e d a c c o r d i n g to the r e l a t i o n developed by Schnabel and Seed i n f i g u r e 3-4-6.  (1972) and reproduced  This r e l a t i o n s h i p was developed from e a r t h -  quakes which o c c u r r e d i n C a l i f o r n i a , b u t N u t t l i  (1973) s t a t e d  t h a t " t h e r e i s no evidence f o r a marked c o n t r a s t i n a t t e n u a t i o n p r o p e r t i e s o f the e a r t h as observed i n C a l i f o r n i a and i n Western North America".  A t a d i s t a n c e o f 30km from the source, o f energy  r e l e a s e t h i s r e l a t i o n g i v e s the maximum a c c e l e r a t i o n due t o magnitude  -808.0, 7^4, and 6.5 earthquakes as 0.33g, 0.25g, and 0.16g respectively.  The earthquake r e c o r d i n g s were not s c a l e d i n  any other way, to f a c i l i t a t e comparison o f the r e s u l t s on the b a s i s o f o n l y one changing parameter.  -81CHAPTER 4 RESULTS 4-1  Pender I s l a n d Earthquake C o r r e l a t i o n The  r e s u l t s of the dynamic a n a l y s i s u s i n g the  developed i n S e c t i o n 3 and  the Lake Cowichan earthquake as  o b j e c t motion, are presented response s p e c t r a .  profiles  i n the form of a c c e l e r a t i o n  They are compared to the s p e c t r a of  a c t u a l s u r f a c e motion as recorded  the  a t the three s i t e s .  The  degree o f correspondence between the recorded.and computed curves i s examined and  the s i g n i f i c a n c e o f . t h e curve shape  as a f u n c t i o n o f v a r y i n g s o i l p r o p e r t i e s i s i n v e s t i g a t e d . The  a c c e l e r a t i o n response s p e c t r a f o r a  freedom s t r u c t u r e with  single-degree-of  5% of c r i t i c a l damping produced when the  Lake Cowichan r e c o r d of the Pender I s l a n d Earthquake was  used  as the o b j e c t motion on the p r o f i l e s d e v e l o p e d . i n S e c t i o n  3,  are shown with  the s p e c t r e of the a c t u a l s u r f a c e r e c o r d f o r  the same earthquake i n f i g u r e 4-4-1, 4-1-2 s p e c t r a of the ground motions recorded perpendicular  and  on two  4-4-3.  The  mutually  component axes are shown f o r both the recorded  the computed motions.  I t w i l l be n o t i c e d t h a t the a b s c i s s a a x i s  has been p l o t t e d u s i n g a v a r i a b l e s c a l e , to show the  important  d e t a i l a t low p e r i o d s while a l l o w i n g a f u l l range of p e r i o d s be presented.  The  curve to r e p r e s e n t  to  curves were not smoothed to develop a s i n g l e the c h a r a c t e r i s t i c s of each o f the  and computed motions.  T h i s was  between the s p e c t r a o f two and  and  because producing  done to show the  recorded  variability  components o f the same earthquake,  a smooth curve from such a data  base.  -82could be m i s l e a d i n g . F i g u r e 4-1-1, shows the s p e c t r a o f the recorded and computed motions a t the Annacis .Island s i t e . sets compare very f a v o r a b l y . s p e c t r a a t a p e r i o d o f 0.25 0.14g  There i s a major peak i n the . seconds to a magnitude o f about  and a minor peak a t a p e r i o d o f 0.8  of 0.08g.  The two curve  seconds to magnitude  The s p e c t r a o f the computed motion shows a peak i n  the h i g h p e r i o d range, where none was observed i n the s p e c t r a of the recorded motion.  T h i s i s probably the r e s u l t o f the  mechanics o f the a n a l y s i s and w i l l be d i s c u s s e d  later.  The s p e c t r a developed from the computed and r e c o r d e d motions a t the Brighouse s i t e are shown i n f i g u r e 4-1-2.  A  major peak to an a c c e l e r a t i o n o f O . l l g i s p r e s e n t a t a p e r i o d o f 0.2  seconds.  The curves are s i m i l a r i n shape, though the  s p e c t r a developed from the computed motions do e x h i b i t minor peaks i n the h i g h p e r i o d range, which are not obvious i n the s p e c t r a o f the recorded motions. The s p e c t r a developed f o r the Roberts Bank motion are shown i n f i g u r e 4-1-2.  The general shape o f the computed and  recorded s p e c t r a i s the same. p e r i o d o f 0.2 of 0.5  The major e x c i t a t i o n i s a t a  seconds w i t h s m a l l e r peaks i n the p e r i o d  seconds to 0.8  range  seconds, but the magnitude o f the  a c c e l e r a t i o n s shown i n the s p e c t r a o f the computed motions i s larger.  As a t the other two s i t e s ,  the s p e c t r a developed from  the computed motions are l e s s smooth than those developed from the recorded motions and show l a r g e r peaks i n the h i g h p e r i o d range.  -83G e n e r a l l y , the s p e c t r a o f the recorded and computed compared w e l l .  motions  The major peaks o c c u r r e d a t the same p e r i o d s and  w i t h the e x c e p t i o n o f the Roberts Bank s i t e , showed the same acceleration.  The c h i e f d i f f e r e n c e between the s p e c t r a was  that  those developed from the computed motion were l e s s smooth and show small a c c e l e r a t i o n peaks a t h i g h p e r i o d s where they were l e s s e v i d e n t i n the s p e c t r a developed from the recorded motions. The b e t t e r agreement between s p e c t r a a t the Brighouse and Annacis I s l a n d s i t e s than.at the Roberts Bank s i t e  suggests  t h a t the method o f a n a l y s i s used i s a p p r o p r i a t e but the parameters used a t Roberts Bank were l e s s r e p r e s e n t a t i v e o f the a c t u a l s i t u a t i o n than those used a t the other s i t e s . u n l i k e l y t h a t the dynamic s o i l p r o f i l e developed was  It is less .  a c c u r a t e a t the Roberts Bank s i t e because reasonable s o i l data was  a v a i l a b l e i n that area.  the  o b j e c t motion used f o r the a n a l y s i s a t the Roberts Bank  s i t e was was of  A more probable e x p l a n a t i o n i s t h a t  not as r e p r e s e n t a t i v e o f the t r u e o b j e c t motion as i t  a t the o t h e r two s i t e s .  T h i s c o u l d be due to the e f f e c t  b u r i e d bedrock topography on the earthquake waves.  I t may  a l s o be due to the p o s i t i o n s of the s i t e r e l a t i v e to the e a r t h quake source and the u n d e r l y i n g geology. was  The o b j e c t motion  the s u r f a c e bedrock motion recorded a t Lake Cowichan.  waves t r a v e l l i n g from the source a t Pender  used Seismic  I s l a n d to Lake Cowichan  would t r a v e l p r i m a r i l y through igneous and metamorphic rock which have a h i g h shear wave v e l o c i t y . the  s u r f a c e rocks are sedementary,  To the e a s t o f Pender  Island  w i t h lower shear wave  v e l o c i t y and h i g h e r damping than the g r a n i t i c r o c k s .  Because the  Roberts Bank s i t e i s c l o s e r to the e p i c e n t r e than the Annacis I s l a n d  -84s i t e , which has  a similar soil profile,  the Roberts Bank s i t e may  s e i s m i c waves r e a c h i n g  have t r a v e l l e d more through the  shear wave v e l o c i t y upper l a y e r sedementary r o c k s , and  low  may  t h e r e f o r e have been more s u b j e c t to damping than those waves reaching  the Annacis I s l a n d s i t e .  recorded  motion being  T h i s c o u l d account f o r the  l e s s severe than the computed motion a t  the Roberts Bank s i t e . The a n a l y s i s i n v o l v e s the d i v i s i o n of the s o i l i n t o d i s c r e e t l a y e r s which can be represented properties.  The  number of l a y e r s t h a t may  by  profile  specific  soil  be used i s l i m i t e d  by the c o s t of a d d i t i o n a l computing time.  Obviously  such a  model u s i n g l a y e r s of s o i l with d i s c r e e t d i v i s i o n s where dynamic p r o p e r t i e s change i s not completely  accurate.  Each o f  these small sublayers used i n the a n a l y s i s w i l l have a predominant p e r i o d which can be estimated by the  n  n  = 4H_ V (2n-l) s  eq'n  4-1-1  i s the n a t u r a l p e r i o d , H i s the l a y e r t h i c k n e s s , V  the shear wave v e l o c i t y of t h a t m a t e r i a l , and The  range  equation: T  Here T  i n the e l a s t i c  is  s  n i s the mode.  r e s u l t o f t h i s i s t h a t every sublayer w i l l be e x c i t e d a t  s l i g h t l y d i f f e r e n t p e r i o d s of motion. e x c i t a t i o n s w i l l be m o d i f i e d surrounding  Although these  by the e f f e c t s o f the  other  l a y e r s , the response spectrum w i l l m i r r o r  small e x c i t a t i o n s as small, p e r t u r b a t i o n s . a c t u a l recorded  The  these  spectra of  the  motions are smooth because the p r o p e r t i e s of  s o i l type w i l l change g r a d u a l l y with depth, so the s p e c t r a not be i n f l u e n c e d by the resonance o f a r t i f i c i a l l a y e r s .  any  will  -85Where major l a y e r s o f s o i l w i t h g r e a t l y d i f f e r e n t  dynamic  p r o p e r t i e s e x i s t i n the same p r o f i l e , : major peaks i n the response s p e c t r a can be observed.  Each peak r e f l e c t s the  c h a r a c t e r i s t i c s o f a p a r t i c u l a r s o i l group.  These a c c e l e r a t i o n  peaks a r e a t p e r i o d s which correspond roughly to the n a t u r a l p e r i o d range c a l c u l a t e d f o r the major s o i l group u s i n g e q u a t i o n 4-1-1, s i n c e a t the low l e v e l o f e x c i t a t i o n o f the Pender I s l a n d earthquake, the s o i l s a r e near t h e i r e l a s t i c response range.  Changing the p r o p e r t i e s o f a p a r t i c u l a r s o i l  (Rock, t i l l ,  o r s o f t sediment) w i l l  group  have a primary e f f e c t on the  peak i n the response s p e c t r a caused by the resonance o f t h a t p a r t i c u l a r s o i l group and secondary e f f e c t on the g e n e r a l shape o f the s p e c t r a .  The i n t e r a c t i o n o f the v a r i o u s  soil  groups i n the development o f the earthquake motions from t h a t c a u s i n g the e x c i t a t i o n a t the base o f a s o i l d e p o s i t to the r e s u l t i n g s u r f a c e motion can be seen i n f i g u r e 4-1-4.  This  f i g u r e shows p l o t s o f the response s p e c t r a o f the motion a t v a r i o u s l e v e l s i n the s o i l d e p o s i t f o r the Annacis I s l a n d  profile,  with the Pender I s l a n d earthquake recorded a t Lake Cowichan as o b j e c t motion.  The o b j e c t motion i s shown to have a predominant  p e r i o d o f 0.2 seconds w i t h very l i t t l e periods.  e x c i t a t i o n a t high  The motion a t the top o f the t i l l  l a y e r shows one peak  i n a c c e l e r a t i o n a t the same p e r i o d as seen i n the o b j e c t motion. I t a l s o shows another a t a p e r i o d o f 0.8 5 seconds which i s c l o s e to  the n a t u r a l p e r i o d o f 0.7 seconds c a l c u l a t e d f o r the t i l l  l a y e r s u s i n g e q u a t i o n 4-1-1.  ;  The response spectrum o f the s u r f a c e  motion shows these two peaks i n approximately the same p o s i t i o n , along w i t h a new area o f i n c r e a s e d e x c i t a t i o n a t l a r g e r p e r i o d s  -86-  caused by the s o f t sediments o v e r l y i n g the g l a c i a l The modified  till.  c h a r a c t e r i s t i c s o f any response spectrum w i l l be s l i g h t l y by minor changes i n the dynamic p r o p e r t i e s  o f any s o i l l a y e r and by changes i n the c o n f i g u r a t i o n o f the soil profile.  In any r e a l s i t u a t i o n , i t i s n o t p o s s i b l e to  s e l e c t p a r t i c u l a r values  f o r the dynamic p r o p e r t i e s o f the  s o i l with complete confidence,, have complete confidence  nor i s i t always p o s s i b l e to  i n the t h i c k n e s s o f the v a r i o u s  l a y e r s which make up the p r o f i l e .  soil  F i e l d i n v e s t i g a t i o n and  l a b o r a t o r y a n a l y s i s y i e l d a range o f values  t h a t may  represent  the f i e l d s i t u a t i o n . For the three s i t e s examined, changing the i n p u t parameters w i t h i n t h e i r probable range d i d not g r e a t l y e f f e c t the general  shape o f the response s p e c t r a .  a c c e l e r a t i o n occurred  The peaks i n  a t the same p e r i o d s , b u t the magnitude  of the peak c o u l d change by up.to 50%. The most important parameter i n determing the shape o f the response s p e c t r a i s the depth to bedrock, f o l l o w e d t h i c k n e s s o f the o v e r l y i n g t i l l  layer.  by the  T h i s i s what one would  expect s i n c e the shear modulus and damping d i f f e r by orders o f magnitude between the rock, g l a c i a l t i l l  and s o f t sediments.  By comparison, the d i f f e r e n c e i n dynamic p r o p e r t i e s between sand, silt,  and c l a y , and the range i n p r o p e r t i e s l i k e l y f o r any given  layer are small. Because o f the i n t e r a c t i o n between l a y e r s i n the p r o f i l e , seen mathematically as an i n t e r r e l a t i o n s h i p between the . s t r a i n dependant damping r a t i o and shear modulus, i t - i s not p o s s i b l e to make meaningful comment on the s p e c i f i c e f f e c t s o f changes i n  the  parameters.  modulus  s t r a i n  expect,  a  those  o t h e r  p e r i o d s .  l a y e r  produced  4-2  observed  and  the  the  3-4,.  Using  s i t e s  same  response  a t  program  w i t h  to  three  g i v e  caused  dynamic  of  d i f f e r e n t s p e c t r a  were  compared  w i t h  developed r e s u l t s  to  The as are  the  by  t h i s  shown  i n  to  and  l e s s e r  a  one  the  s t i f f e n  and would  s p e c t r a e f f e c t  a  a t  p a r t i c u l a r  p e r i o d s ,  as  would  the  Pender  I s l a n d  computed  motion  a t  the  same  was  s i t e s  as  chosen  s i t e . and  a t  determine  the  A n n a c i s  and i n  The  and  the  s e c t i o n  s u r f a c e  u s i n g  motions  the  SHAKE  s c a l e d  This  response  g e n e r a l  Lake  p r o f i l e s  bedrock.  These  the  and  d e s c r i b e d  o b j e c t  w i t h  u s i n g  p r o f i l e s ,  computed  of  E a r t h q u a k e ,  s o i l  performed.  a c c e l e r a t i o n s  other  the  s o i l  was  s p e c t r a  B r i g h o u s e  of  earthquakes  each  response  produced  s p e c t r a  r e l a t i o n s h i p s  s i g n i f i c a n c e  of  the  a r e a .  response  o b j e c t  each  o t h e r s ,  the  three  a t  of  g i v e n  the  s u i t a b i l i t y  two  the  response  the  a n a l y s i s  the  as  range  to  at  had',  damping  Earthquake  motion  l a r g e r  n i n e  modulus  the  l a y e r .  of  Using  each  p e r i o d  e x c i t a t i o n  by  method.  of  s o i l  between  the  each  l a y e r s  Design  o b j e c t  f o r  for the  the  c o n f i r m s  motions  the  of  s p e c t r a as  c h a n g i n g  the  c o r r e l a t i o n  r e c o r d  however,  a c c e l e r a t i o n s  the  motion  a n a l y s i s  o b j e c t  l a r g e r  response  Cowichan I s l a n d  I n c r e a s i n g  c l o s e  the  i n  produced  damping  A n a l y s i s  The  e f f e c t  l a y e r s  the  g e n e r a l ,  r e l a t i o n s h i p s  primary  where  r e d u c i n g  In  s p e c t r a  m o t i o n s , f i g u r e  of  s c a l e d  4 - 2 - 1 .  the  three  d e s i g n  to  0.25g  maximum  F i g u r e  4-2-2  shows  earthquakes,  used  a c c e l e r a t i o n , the  response  ,  -88s p e c t r a developed from the t h r e e s e t s o f s u r f a c e motion a t the Annacis I s l a n d s i t e ,  t h a t were computed from these t h r e e  i n p u t earthquakes s c a l e d to a maximum a c c e l e r a t i o n o f 0.16g. These three curves e x h i b i t the same general, c h a r a c t e r i s t i c s , w i t h a peak i n the s u r f a c e a c c e l e r a t i o n f o r p e r i o d s o f about one second.  The response s p e c t r a developed from s u r f a c e  motions due to an o b j e c t motion s c a l e d to 0.25g and 0.33g a r e shown i n f i g u r e s 4-2-3 and 4-2-4 r e s p e c t i v e l y .  The same  s e r i e s o f curves f o r the Brighouse s i t e a r e presented i n f i g u r e s 4-2-5, 4-2-6, 4-2-7.  The s p e c t r a produced a t a  given s i t e u s i n g the three d i f f e r e n t o b j e c t motions,  scaled  to the same v a l u e o f maximum a c c e l e r a t i o n , a r e s i m i l a r i n form and i n magnitude i n every case. For ease i n comparison, the t h r e e response s p e c t r a curves shown on each o f the aforementioned f i g u r e s have been f i t t e d with a smooth curve so t h a t the s p e c t r a developed a t three d i f f e r e n t a c c e l e r a t i o n l e v e l s may be summarized f o r each s i t e on one page.  The response s p e c t r a o f the s u r f a c e motion caused by a  base l a y e r e x c i t a t i o n by earthquakes o f three d i f f e r e n t  magnitudes  are shown f o r the Brighouse s i t e i n f i g u r e - 4-2-8, and f o r the Annacis I s l a n d s i t e i n f i g u r e 4-2-9.  The most s t r i k i n g  c h a r a c t e r i s t i c o f these curves i s t h a t changing the maximum a c c e l e r a t i o n on bedrock by over 100% produces v e r y l i t t l e d i f f e r e n c e i n the s p e c t r a o f the s u r f a c e motions.  For these  three r e l a t i v e l y l a r g e magnitude earthquakes, i n c r e a s i n g the a c c e l e r a t i o n o f the o b j e c t motion r e s u l t s i n a .very small i n c r e a s e i n the a c c e l e r a t i o n a t the ground s u r f a c e .  When c o n s i d e r i n g  -89the p o t e n t i a l -damage to b u i l d i n g s i t i s important to remember t h a t the a c c e l e r a t i o n s experienced a r e o n l y one of the f a c t o r s i n v o l v e d .  The d u r a t i o n o f these strong  a c c e l e r a t i o n s i s a l s o important, s i n c e the c a p a c i t y o f a s t r u c t u r e to absorb the energy o f the earthquake i s f i n i t e . Larger magnitude  earthquakes would be o f longer  duration.  The predominant p e r i o d o f the s u r f a c e motion, as shown by the peak i n the s u r f a c e a c c e l e r a t i o n response s p e c t r a , is  a l s o important because b u i l d i n g s which have a predominant  p e r i o d s i m i l a r to t h a t o f the earthquake w i l l e x p e r i e n c e much l a r g e r a c c e l e r a t i o n s than those which do not. The p e r i o d o f peak a c c e l e r a t i o n f o r the three design  earth-  quakes has changed d r a m a t i c a l l y from the predominant periods  f o r the rock motion and the low magnitude  I s l a n d earthquake s u r f a c e motion.  Pender  However, d i f f e r e n c e s i n  the predominant p e r i o d o f the s u r f a c e a c c e l e r a t i o n caused by a s i n g l e o b j e c t motion s c a l e d to the three d i f f e r e n t  large  a c c e l e r a t i o n s cannot be s i g n i f i c a n t l y observed w i t h the database used. The t i l l greater  l a y e r s have a shear modulus which i s s u b s t a n t i a l l y  than t h a t o f the o v e r l y i n g s o f t sediments, b u t i s s t i l l  s i g n i f i c a n t l y l e s s than t h a t o f the u n d e r l y i n g  bedrock.  a n a l y s i s which a p p l i e d an o b j e c t motion to the g l a c i a l  I f an till  s u r f a c e would y i e l d s i m i l a r r e s u l t s to an a n a l y s i s which a p p l i e d the same motion to the bedrock s u r f a c e , modelling dynamic  the s i t e f o r  a n a l y s i s would be s i m p l i f i e d , because data on t i l l  p r o p e r t i e s and the depth to bedrock would not be r e q u i r e d . F i g u r e 4-2-10 and 4-2-11 show the response s p e c t r a f o r the three design  earthquakes s c a l e d to .25g and a p p l i e d as o b j e c t motions  -90to  the  top of  Island  sites.  show t h e object thick the  the  spectra  layer  spectra  and  has  the  to  that  at  larger  above the  the  Island  this  means  with  periods  large  for  the  that  so  of  motions  has the  about  0.8  the  response  accelerations Comparison o f  at the  and t h o s e d e v e l o p e d  of  Island  at  the  the Annacis spectra  i t  from the  of  1.0  be  spectra  soft  the  sediments  The p e r i o d  at  the Annacis of  the  Island  physical  used,  which  results,  structures susceptible  Brighouse  Generally,  buildings,  Brighouse  site  as  were  to  site,  seconds w o u l d be  site.  computed  can  are  terms  developed  dynamic  the  for  Island  motion  surface  less.  of  object  may b e b e c a u s e  damage a t about  the  t h e maximum  earthquakes  acceleration  spectra,  This  In  of  If  and t h e  sites  thickness  resulting  the Annacis  the  two  larger  the  analysis.  both  is  which  the  shape  the  bedrock  peak on  site.  periods  the  on t h e  the  site  is  that  seconds w o u l d be most  susceptible  by  the  design  with  and  for  damping  and s t r u c t u r e s  accelerations  in  less  occurs  the  and t h e  at  the  site.  with  acceleration.  for  Island  Brighouse  for  of  acceleration  peak a c c e l e r a t i o n than  spectra  profile  performed  effect  the  Annacis  4-2-6 a n d 4 - 2 - 3 ,  be m e a n i n g f u l ,  surface  Brighouse  the bedrock,  site  to  accounted  and t h e  than at  Annacis  are  of  and  demonstrates  a significant  the  Brighouse  figures  bedrock,  the Annacis  acceleration  the  same a n a l y s i s  to  the  t i l l  When c o m p a r i n g seen  the  an a n a l y s i s  of  at  the magnitude  m u s t be a p p l i e d effects  for  applied  t i l l  of  layer  Comparison w i t h  motion  results  t i l l  most  groundrepresented less  than  site. from  the  surface  object  motions  motion shows  the  s h i f t i n predominant p e r i o d of the motion from about seconds f o r the earthquakes recorded motion, to 0.8  seconds or 1.0  on rock and  0.25  used as  seconds f o r the earthquake motions  computed a t the s u r f a c e of the deep s o i l d e p o s i t s .  This  o b s e r v a t i o n o f an i n c r e a s e i n the predominant p e r i o d of earthquake motion recorded over t h a t recorded  a t the s u r f a c e of deep s o i l  on rock i s i n accordance w i t h  observed by o t h e r s ,  object  (Seed, Ugas, Lysmer 1976).  the  general the  deposits  trends  F i g u r e 4-2-12  i s a p l o t of the mean response s p e c t r a of the o b j e c t motions s c a l e d to 0.25g, with a p l o t o f the r e s u l t i n g s u r f a c e motions a t the Annacis I s l a n d s i t e . curves i s t y p i c a l of what was  The  r e l a t i o n s h i p between the  found a t both s i t e s u s i n g  three l a r g e magnitude earthquakes.  the  These reponse s p e c t r a  can be thought of as p l o t s of the a c c e l e r a t i o n t h a t a s i n g l e degree o f freedom s t r u c t u r e with experience,  as i t s p e r i o d was  5% o f c r i t i c a l damping would  changed.  F i g u r e 4-2-12 shows  t h a t the r e l a t i o n between the peak i n a c c e l e r a t i o n and  the  b u i l d i n g p e r i o d i s more important than the ground a c c e l e r a t i o n i n determining  the behaviour o f the s t r u c t u r e d u r i n g an  earth-  quake . Using equal  to 0.1  the approximation t h a t the p e r i o d of a s t r u c t u r e i s times the number o f s t o r i e s , the F i g u r e 4-2-12  shows t h a t a b u i l d i n g of 2 o r 3 s t o r i e s with a predominant p e r i o d of about 0.25  sec. would experience  a c c e l e r a t i o n s i f b u i l t on bedrock, while i n the F r a s e r D e l t a would experience  very  large  an i d e n t i c a l b u i l d i n g  much s m a l l e r a c c e l e r a t i o n s .  A 10 s t o r e y b u i l d i n g , with a p e r i o d i n the order of 1.0  sec. would  -92-  experience g r e a t e r a c c e l e r a t i o n s i n the d e l t a area than i t would i f c o n s t r u c t e d on bedrock. for of  the l a r g e magnitude  These o b s e r v a t i o n s apply  earthquakes a n a l y z e d .  The a n a l y s i s  the Pender I s l a n d Earthquake i n d i c a t e d t h a t the maximum  b u i l d i n g a c c e l e r a t i o n due to s m a l l e r magnitude o c c u r r e d a t small p e r i o d s whether rock o r a deep s o i l  earthquakes  the s t r u c t u r e was on  deposit.  The r e l a t i o n between the maximum a c c e l e r a t i o n recorded on rock and the maximum a c c e l e r a t i o n recorded a t the ground i s shown i n f i g u r e 4-2-13. are  The data developed i n t h i s  analysis  shown w i t h the average curves produced from recorded data by  Seed, Murarka, Lysmer and I d r i s s the  surface,  (1976).  The g e n e r a l shape o f  curve developed from the data produced i n t h i s study i s  s i m i l a r to the curve f o r o t h e r deep s o i l d e p o s i t s developed by Seed e t a l (1976).  Low magnitude  earthquakes produce  l a r g e r a c c e l e r a t i o n s on the s u r f a c e o f deep s o i l than they do on rock, w h i l e l a r g e r magnitude  deposits  earthquakes produce  smaller a c c e l e r a t i o n s on the s u r f a c e o f deep s o i l d e p o s i t s than they do on rock.  Low magnitude  earthquakes e x c i t e the s o i l  d e p o s i t s and cause them to s t r a i n o n l y s l i g h t l y so the s o i l s remain c l o s e to t h e i r e l a s t i c s t r e s s s t r a i n range, and damping i s small even though the s o i l i s b e i n g d i s p l a c e d by the e a r t h quake. the  Large magnitude  earthquakes cause l a r g e r movement o f  s o i l p a r t i c l e s , which s t r a i n g r e a t l y and f o l l o w  their  h y s t e r i t i c s t r e s s s t r a i n path to produce l a r g e amounts o f damping, which reduce the a c c e l e r a t i o n o f the s o i l .  The c o r r e l a t i o n between the data developed i n t h i s a n a l y s i s and the average curve shown i n f i g u r e 4-2-13 i s good. The curve shape i s s i m i l a r , though  the curve developed f o r the  Fraser Delta s o i l deposits predicts smaller surface accelerat i o n s f o r the same rock a c c e l e r a t i o n than do the average of  Seed e t a l (1976) .  curves  The data from t h i s a n a l y s i s should not  be expected to f a l l c l o s e to the Seed e t a l (1976) curve because  t h e i r curve shows the average r e s u l t s from many  d i f f e r e n t s i t e s , none of which w i l l be i d e n t i c a l to the s i t e s analyzed i n t h i s study.  The curve developed from the  data i n t h i s study i n d i c a t e s t h a t as the magnitude of the earthquake  i n c r e a s e s , the s u r f a c e a c c e l e r a t i o n o f a deep s o i l  d e p o s i t becomes an i n c r e a s i n g l y s m a l l e r percentage of the rock acceleration. and Brady  T h i s i s i n keeping with the f i n d i n g s o f T r i f u n i c  (19 75),  who  noted t h a t the maximum a c c e l e r a t i o n s  were reached by earthquakes o f magnitude 6.5 for  to 7.0,  which  the area and c o n f i g u r a t i o n t h a t we are d e a l i n g w i t h ,  corresponds to a maximum a c c e l e r a t i o n of about 0.2g.  Larger  magnitude earthquakes do not produce a n o t i c e a b l e i n c r e a s e i n maximum a c c e l e r a t i o n , though  the d u r a t i o n w i l l be  larger.  The curves from Seed e t a l (1976) e x h i b i t t h i s t r e n d , but not as markedly T h i s may  as the curve f o r the data developed i n t h i s study.  be i n p a r t because  e x t r a p o l a t e d beyond.the 0.3g  the Seed e t a l curves have been acceleration.  The s p e c i f i c r e s u l t s of t h i s a n a l y s i s can be compared w i t h the recommendations o f the N a t i o n a l B u i l d i n g Code.  The N a t i o n a l  B u i l d i n g Code recommends t h a t d e s i g n i n ttie F r a s e r D e l t a area  incorporate  the e f f e c t s o f a c c e l e r a t i o n due to an earthquake  of 0.08g on f i r m ground and 0.12g on s o f t sediments. r e s u l t s o f t h i s work a r e somewhat.different. study o f the s e i s m i c i t y o f t h i s area,  a design  The  Based on the earthquake  o f magnitude 7.4 i s expected, which c o u l d r e s u l t i n an a c c e l e r a t i o n o f 0.25g on rock.  The dynamic a n a l y s i s has  p r e d i c t e d t h a t the maximum a c c e l e r a t i o n on the s u r f a c e o f the deep s o i l d e p o s i t s due to such an earthquake would be i n the order o f 0.16g.  The maximum a c c e l e r a t i o n s p r e d i c t e d by  t h i s a n a l y s i s a r e more severe than those p r e d i c t e d by the N a t i o n a l B u i l d i n g Code, though Byrne (1977) has p o i n t e d o u t t h a t the d u c t i l i t y o f most b u i l d i n g s i s such t h a t i f designed according  to the N a t i o n a l B u i l d i n g Code c r i t e r i a ,  they c o u l d  a c t u a l l y r e s i s t greater  a c c e l e r a t i o n s than the code would  predict.  also incorporate  Design should  the e f f e c t s o f the  s h i f t o f predominant p e r i o d o f the earthquake t h a t i s observed where l a r g e magnitude earthquakes occur i n areas o f deep deposits.  soil  The s h i f t i n predominant p e r i o d r e s u l t s i n b u i l d i n g s  on deep s o i l d e p o s i t s e x p e r i e n c i n g  greatly different accelera-  t i o n s from b u i l d i n g s on bedrock, q u i t e a p a r t from what the ground a c c e l e r a t i o n s might be.  CHAPTER 5 COMMENT ON THE  LIQUEFACTION.POTENTIAL OF THE  FRASER.DELTA  A d e t a i l e d d e s c r i p t i o n o f the mechanics o f l i q u e f a c t i o n and  a study of the f a c t o r s i n v o l v e d and  s i t e s being  t h e i r r e l a t i o n to  the  i n v e s t i g a t e d i s beyond the scope o f t h i s work.  E m p i r i c a l methods o f e s t i m a t i n g been developed through f i e l d  l i q u e f a c t i o n p o t e n t i a l have  i n v e s t i g a t i o n of many s i t e s .  These methods were a p p l i e d to the F r a s e r D e l t a s i t e s u s i n g s o i l s data presented i n Chapter 2 to provide  the  a simple measure  of the l i q u e f a c t i o n p o t e n t i a l a t these s i t e s .  Refinements on  the r e s u l t s presented here c o u l d be made u s i n g  the more com-  p l i c a t e d a n a l y t i c a l procedures t h a t are i n Areas of s a t u r a t e d  s o i l subjected  to c y c l i c  such as those caused by an earthquake, may pore p r e s s u r e s .  I f these pore pressures  are equal to the overburden p r e s s u r e , the s o i l w i l l become zero.  existence. shear  experience  stresses increased  increase u n t i l  they  the e f f e c t i v e s t r e s s i n  S o i l i n t h i s s t a t e i s s a i d to have  l i q u e f i e d , s i n c e i t cannot r e s i s t shear s t r e s s e s and i t s behavior resembles t h a t of a dense  fluid.  A l i q u e f i e d s o i l can pose a t h r e a t to man  i n s e v e r a l ways.  L i q u e f i e d s o i l cannot r e s i s t shear s t r e s s e s , so h o r i z o n t a l f o r c e s a p p l i e d to the s o i l cannot be r e s i s t e d , and.large d e f l e c t i o n s result.  The  like a fluid,  other major problem i s t h a t l i q u e f i e d s o i l behaves so s t r u c t u r e s i n o r on the s o i l w i l l change  e l e v a t i o n u n t i l t h e i r buoyant f o r c e i s equal to the weight of the d i s p l a c e d f l u i d .  B u i l d i n g s c o u l d s i n k i n t o the s o i l  and  -96-  b u r i e d s t r u c t u r e s such as storage to  tanks o r sewers c o u l d  rise  the s u r f a c e . The  f a c t o r s i n f l u e n c i n g the earthquake induced  liquefaction  p o t e n t i a l o f a s i t e a r e r e l a t e d both to the c h a r a c t e r i s t i c s o f the s o i l and the c h a r a c t e r i s t i c s o f the earthquake motion. These f a c t o r s have been i n v e s t i g a t e d i n the l a b o r a t o r y under w e l l known c o n d i t i o n s , and i n the f i e l d where g e n e r a l l y the l i q u e f a c t i o n p o t e n t i a l has been c o r r e l a t e d to Standard P e n e t r a t i o n Test d a t a .  The data developed from the l a b o r a t o r y  a n a l y s i s i s e x t e n s i v e enough t h a t the process o f l i q u e f a c t i o n can be m o d e l l e d - a n a l y t i c a l l y (Finn, Byrne and M a r t i n  1976).  However, there may be d i f f i c u l t y i n a p p l y i n g the r e s u l t s o f these analyses  to f i e l d  s i t u a t i o n s because the c o r r e l a t i o n  between the l a b o r a t o r y and f i e l d s o i l p r o p e r t i e s must be done u s i n g Standard P e n e t r a t i o n Test r e s u l t s i f i t i s to be done on a wide b a s i s using e x i s t i n g data.  The problems i n v o l v e d i n  o b t a i n i n g a r e p r e s e n t a t i v e c o r r e l a t i o n between the r e s u l t s o f the Standard P e n e t r a t i o n t e s t and other s o i l p r o p e r t i e s have been o u t l i n e d in. Chapter 2. The  f i e l d data was developed u s i n g the Standard  Test v a l u e s d i r e c t l y ,  so the problem o f choosing  correlation i s eliminated.  Penetration  a suitable  However, the r e s u l t s o f these  e m p i r i c a l r e l a t i o n s are not s p e c i f i c s i n c e the s o i l p r o p e r t i e s have been considered  through a s i n g l e parameter o n l y .  These  e m p i r i c a l r e l a t i o n s do provide a simple method o f e s t i m a t i n g the liquefaction potential of a site. Oshaki  (1970)  proposed the c r i t e r i a t h a t i f the blow  count a t some depth from the standard  penetration tests i s  -97equal  to  occur.  two  times  Kishida  the blow count methods  the  depth  (1969) of  consider  the the  meters,  proposed Standard  Penetration  properties  attempt  consider  the  effects  ratio  the  relative  stress  Gibbs this  and H o l t z relation  blow count  earthquake.  of  of  the  to  criteria  at  and I d r i s s  (1976)  relates  the  ratio  can a l s o depth,  be e x p r e s s e d  as  These  for  define  blow  The Seed e t  developed  than  group of  the  values  occupies  Curves  relationship  with  three  tion  in  this  study  used  in  the  analysis  as  0.18g  for  Figure  an upper  are  limit  earthquakes  4-2-13.  of  relating from  the  between  Seed,  a method  site, the  Murarki,  which  blow count.  not,  design  O.lg for  the  This and  are  have  These  more  the  earthquakes 5-2  magnitude greater  7.4  within  Seed e t under  .  may  finely  a mean p o s i t i o n using  The 6.5  figure  relations  liquefaction is  been  shown i n  the magnitude  magnitude  These c u r v e s  are  which  figure  for  that  30 k m .  obtained  shown i n  are  by  a particular  3.  soils  where  relationship,  others,  the  have  earthquake.at  count  al  (1975)  between blow count  separate  that  curves.  0.16g  developed  two  3.  from those  a band o f  For  on  the  determined  appendix  a normalized  which  7.4  but.not  a relationship  as a r e l a t i o n  relations  liquefy  to  These  earthquake  not  based  and S w i g e r  sites.  as  have  the  will  also  Test.  soil  density  field  appendix  a magnitude  occur.  the  shown i n four  known t o 5-1  stress  of  shown i n  Lysmer,  the  Christian  can be e x p r e s s e d  and d e p t h as  liquefaction  a relationship  properties to  the  in  al  considera-  accelerations earthquake,  earthquake,  than  8,  shown s u p e r i m p o s e d  as  and  shown  on the  in curves  -98p r e s e n t i n g the r e l a t i o n s between blow count and depth f o r v a r i o u s areas i n the F r a s e r D e l t a . figure indicates  An examination o f t h i s  t h a t when sand s o i l s  meter depth, l i q u e f a c t i o n  i s likely  e x i s t above the 6  to occur i n most areas  of the d e l t a when subjected to a magnitude 7.9 earthquake a t 30km, w h i l e below the 6 meter depth, most sand areas a r e unlikely  to l i q u e f y when subjected.to the same earthquake.  Under the i n f l u e n c e  o f a l a r g e r earthquake, o f magnitude  g r e a t e r than 8, l i q u e f a c t i o n  i s l i k e l y a t depths l e s s than  9 meters, w h i l e f o r a magnitude 6.5 earthquake,  liquefaction  i s u n l i k e l y a t any depth.  figures  also reveals that  there a r e p r o f i l e s that do not conform  to t h i s g e n e r a l i z a t i o n , application the  Examination o f these  and more i m p o r t a n t l y that the  of d i f f e r e n t c r i t e r i a give d i f f e r e n t r e s u l t s f o r  same s i t e . These e m p i r i c a l  methods g i v e a g e n e r a l idea o f the l i q u e -  f a c t i o n p o t e n t i o n 6 f the F r a s e r D e l t a . results at a particular To make t h i s a n a l y s i s  F o r more s p e c i f i c  s i t e , more r i g o r o u s a n a l y s i s  useful,  between f i e l d and l a b o r a t o r y  close  correlation  conditions.  i s needed.  i s needed  -99CHAPTER 6 CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH 6-1  Conclusions 1)  recorded  The c o r r e l a t i o n developed between the blow count 0 to 12 inches p e n e t r a t i o n and t h a t recorded  to 18 inches p e n e t r a t i o n i n the Standard P e n e t r a t i o n g i v e s meaningful r e s u l t s , and allows data recorded manners to be used 2)  for 6 Test  i n both  together.  The r e l a t i o n s h i p between r e l a t i v e d e n s i t y and the blow  count o f the Standard P e n e t r a t i o n Test developed by S c h u l t z e and Menzenbach b e s t t y p i f i e s the behavior  o f the sands found  i n the F r a s e r D e l t a . 3) and  The c o r r e l a t i o n between the f r i c t i o n angle o f sands  the blow count o f the Standard P e n e t r a t i o n T e s t developed  by de M e l l o g i v e s reasonable 4)  r e s u l t s i n the F r a s e r D e l t a  soils.  The dynamic a n a l y s i s used i n the SHAKE computer program  g i v e s e f f e c t i v e r e p r e s e n t a t i o n o f the s u r f a c e motions r e s u l t i n g from an o b j e c t motion a c t i n g a t the base o f a s o i l p r o f i l e , the dynamic p r o p e r t i e s o f which have been determined from more readily available s o i l 5)  information.  In the dynamic a n a l y s i s , the most c r i t i c a l  parameters  of the s o i l p r o f i l e a r e the depth to bedrock and the t h i c k n e s s o f the g l a c i a l t i l l  e x i s t i n g above the bedrock.  The d i f f e r e n c e  i n dynamic p r o p e r t i e s between c l a y , s i l t and sand l a y e r s i s not as  significant.  (100) 6)  A s u i t a b l e d e s i g n earthquake f o r dynamic  i n the F r a s e r  Delta  analysis  i s one o f magnitude o f 7.4 a t a d i s t a n c e  of 30km, which produces a bedrock a c c e l e r a t i o n o f about 0.25g. However, the p o s s i b i l i t y o f l a r g e r earthquakes o f magnitude greater  than 8 should not be r u l e d o u t .  7)  Use o f the dynamic  o f magnitudes  a n a l y s i s w i t h d e s i g n earthquakes  6.5, 7.4 and 8.0 a t two s i t e s i n the d e l t a  yielded surface  motions w i t h a predominant p e r i o d o f 0.8 to  1.0 seconds, and a maximum ground a c c e l e r a t i o n o f about 0.16g. For  the l a r g e magnitude  magnitude  earthquakes used, an i n c r e a s e  i n the  o f the o b j e c t motion d i d not g r e a t l y a f f e c t the  predominant p e r i o d o r the maximum a c c e l e r a t i o n a t the ground surface.  The maximum ground a c c e l e r a t i o n a t these magnitudes  was much l e s s than the bedrock a c c e l e r a t i o n .  The predominant  p e r i o d o f the s u r f a c e motion under the l a r g e magnitude quakes had i n c r e a s e d  g r e a t l y from the predominant  of both the bedrock motion under l a r g e magnitude and the s u r f a c e 8)  motion under small magnitude  The dynamic  e f f e c t s o f the t i l l  and must be modelled w i t h the o t h e r s o i l 9)  earth-  period earthquakes,  earthquakes.  l a y e r a r e important layers.  The l i q u e f a c t i o n p o t e n t i a l estimated from empiracal  r e l a t i o n s h i p s suggests t h a t f o r an earthquake o f magnitude 7.4 l i q u e f a c t i o n i s l i k e l y i n the upper 6 meters o f sand sediments, but l e s s l i k e l y below the 6 meter depth. severe earthquake o f magnitude  greater  Under a  than 8, l i q u e f a c t i o n i s  u n l i k e l y to occur i n sands below the 9 meter depth.  (101) 6-2  Suggestions for- F u r t h e r 1  1)  For l a b o r a t o r y data to be a p p l i e d to f i e l d s i t u a t i o n s  a r e l i a b l e method i s needed density. for  Research  to determine the f i e l d  Research which develops accurate  relative  f i e l d technique  determining the r e l a t i v e d e n s i t y and r e l a t i n g i t to the  Standard P e n e t r a t i o n Tests would be v a l u a b l e . 2)  The l i q u e f a c t i o n p o t e n t i a l o f the F r a s e r D e l t a  could  be i n v e s t i g a t e d u s i n g r i g o r o u s a n a l y t i c a l methods as w e l l as the e m p i r i c a l methods used i n t h i s study. 3) soils.  The F r a s e r D e l t a c o n t a i n s  a large proportion of  silt  Because of the problems i n v o l v e d i n sampling and t e s t i n g  these s o i l s where p e r m e a b i l i t y i s i n a mid range between t h a t of c l a y and sand, l i t t l e  f i e l d or laboratory i n v e s t i g a t i o n of  dynamic p r o p e r t i e s has been done. dynamic p r o p e r t i e s o f s i l t , p r o p e r t i e s by simple f i e l d 4)  An i n v e s t i g a t i o n i n t o the  and a method o f d e f i n i n g i t s t e s t s would be v a l u a b l e .  The Western Washington  Earthquake o f 1949 and the  Puget Sound Earthquake of 19 65 a r e large-magnitude earthquakes which would probably resemble the type o f earthquakes t h a t would e f f e c t the F r a s e r D e l t a a r e a .  An a n a l y s i s s i m i l a r to  the one performed i n t h i s study c o u l d be undertaken to produce the bedrock motion of these earthquakes from the motion recorded  a t ground s u r f a c e .  These bedrock motions c o u l d then  be used as the o b j e c t motions f o r a n a l y s i s i n the F r a s e r area.  Delta  (102) Suggestions 5)  f o r F u r t h e r Research cont'd  The a n a l y s i s performed i n t h i s study has  ignored  the  e f f e c t s t h a t a b u i l d i n g would have on the u n d e r l y i n g s o i l s . 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S)A/£>  7/2./.  0.7  0.6 1  OA  -I—1—I—1—I—I—I—  —I  A  .i  O ./  . 2  .3  1  1  .6  1  1—'—I  .7  .8  1—>  .9  1  1  /o  1  1—I  /.z.  1  '—I—I  /.£,  1  /4  1—I—I—I  AO  7.5  1  1—I—I—  30  3.f  -185-  Efdj  4-Z-//  /^1 O 7/OA/S /f/VO  03JSCT  •'  AMNAC/S  /=•<=>/?  iRe  ISZ/*A/D  }  O/ZS/tS/V /WO 7~/£/sV  £r/3/?7A/e? si Pp/.  /££  S/2OASS<F  US/A'**  Tip yi5>>=  j/>^r/p/<i J*CS9/./F/? os*  SCSS°F/)<£  S~<£? /  <$£/0£-//3/L  + x  4  *  7~//./.  7-/>/*T /V tS&/V/£S  &/2  0.2  £  J  -186-  /Ro£Ae  7^70 7/OAS  /AAA£> OP  5OXrACS  —  /War'OAS  —  —  —  /7&MAJ  3  A^OS*  or  AMAy  J - ^ V S W / F -<?  /Ze-sroA/ss  ro  A)****  s cA?r/9  •*= 7  KOCA- - 0.2  ro*  _- o. z S~j  ez/*iss*e>  /Vo  ro  £j  /ir,^  r  O.z-fj  /.z •  /.O •  o.e -  /  J  Ob •  i V I  '  \  '  \  '  \  I  \  /  OA •  \  ;  /^~X  \  D.Z •  \  o  \  \ \  i i i 1 i i 1 i i ' 1 1 r i • 1 1 i 1 1 i 1 •-• 1 r — i — - i  J  .£  .3  .+  .S  .6  -7  .8  .1  AO  /.Z  /.+  /.A  /.e  1 1 1 * r——i 1 i — £JO  3o  JiS  -/87-  *t-2-/£  ••  S f/9it/+rt>Af'  St dcC^i.  t  £A*s+ 7/OfV  GAS /9oc/(  i/S.  Af/9X/t^f(//-l  1 I  V  -I—  ./  — I  .5  .a r-oc<4'  'PSCAV  *ft<i/ Curve  Sorter's  ef cvC/oy>ce/  ?*Ar *  ,  ®  f  e/oAa  eft***  A  <9rjA  *Acjo tj f  /j)  -189P/&  5-2  :  L/Q U/FA CT/O/V Po r£AJ T//)i\ OJC T/VJf pMAS£/Z /Oz/.rs>  -190-  REFERENCES Anderson, A.M., Espana, C , McLamore, V.R., 1978, E s t i m a t i n g I n - S i t u Shear Moduli a t Competent S i t e s " , Earthquake E n g i n e e r i n g and S o i l Dynamics S p e c i a l t y Conference, Pasadena, 181-197. Arango, I., Moriwaki, Y., Brown, F., 1978, "In S i t u and L a b o r a t o r y Shear V e l o c i t y and Modulus." Earthquake E n g i n e e r i n g and S o i l Dynamics S p e c i a l t y Conference, Pasadena, pp. 198-212. Armstrong, J.E., 1956, " S u r f i c i a l Geology of Vancouver Area, B.C." G.S.C. Paper 5 5-4 0. Armstrong, J.E., 1957, " S u r f i c i a l Geology o f New Map Area, B.C." G.S.C. Paper 5 7-5.  Westminster  Armstrong, J.E., 1960, " S u r f i c i a l Geology o f Sumas, Westminster, B.C." 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F i n n , W.D.L., Byrne, P.M., M a r t i n , G.R., 1976, "Seismic Reponse and L i q u e f a c t i o n o f Sands." ASCE Jour. G e o t e c h n i c a l E n g i n e e r i n g D i v i s i o n , V o l . 102, pp. 841-856. Gibbs, H.J., H o l t z , W.G., 1957^ "Research on Determining the Density o f Sands by Spoon P e n e t r a t i o n T e s t i n g . " Proceeding, 4th I n t . Conf. S o i l Mechanics and Foundation E n g i n e e r i n g , London, V o l . 1, pp.35-39. Hardin, B.O., Black, W.L., 1968, " V i b r a t i o n Modulus o f Normally C o n s o l i d a t e d C l a y . " ASCE Jour, o f S o i l Mechanics and Foundations D i v i s i o n , V o l . 94, pp. 453-464. Hardin, B.O., Drnevich, V.P., 1972, "Shear Modulus and Damping i n S o i l s : Measurement and Parameter E f f e c t s . " ASCE Jour. S o i l Mechanics and Foundations D i v i s i o n , V o l . 98, pp. 603-624. Holland, S.S., 1976, "Landforms o f B r i t i s h Columbia: A P h y s i o g r a p h i c O u t l i n e . " B.C. Dept. Mines and Petroleum Resources, B u l l e t i n 4B. Hoos, L.M., Packman, G.A., 1974, "The F r a s e r R i v e r E s t u a r y , Status of Environmental Knowledge to 1974." Report o f the Estuary Working Group, Department o f Environment, Regional Board., P a c i f i c Region. Hopkins, W.S., 1966, "Palyntology of T e r t i a r y Rocks of Whatcom B a s i n , Southwestern B.C. and Northern Washington" Ph.D. D i s s e r t a t i o n , U n i v e r s i t y of B r i t i s h Columbia. Jackson, E.V., Seraphin, R.H., 1976, Map: " F a u l t s , Porphyry Deposits and Showings and T e c t o n i c B e l t s o f the Canadian Cordillera." C.I.M.M. S p e c i a l Volume 15. Johnston, Area."  W.A., 1923, "Geology o f the F r a s e r R i v e r D e l t a G.S.C. Memoir 135.  Map  K i s h i d a , H. 1969, " C h a r a c t e r i s t i c s o f L i q u e f i e d Sands During Mino-Owari, Tohnankai, and Fukui Earthquakes." S o i l s and Foundations, V o l . 9, pp. 75-9 2.  -192Klohn, E . J . , 1965, "The E l a s t i c P r o p e r t i e s of a Dense G l a c i a l T i l l Deposit." Cdn. G e o t e c h n i c a l J o u r n a l , Vol. 11, pp. 116-140. Kovacs, W.D., Evans, J.C., G r i f f i t h , A.M., 1977, "Towards a more Standardized Standard P e n e t r a t i o n T e s t . " Proceedings o f the 9th I n t e r n a t i o n a l Conference on S o i l Mechanics and Foundation E n g i n e e r i n g V o l . IT. Luternauer, J . , Murray, J . , 1973, Sedimentation on the Western D e l t a F r o n t of the F r a s e r R i v e r , B.C." Cdn. Jour, of E a r t h Sciences V o l . 10 #11, pp.1642-1663. Lysmer, J . , Seed, H.B., Schnabel, P . B . , 1971, "The I n f l u e n c e of Base Rock C h a r a c t e r i s t i c s on Ground Response". Marcusson, W.F., Bieganousky, W.A., 1977, "Laboratory Standard P e n e t r a t i o n Tests on F i n e Sand" Jour. Of S o i l Mechanics and Foundation Div. A.S.C.E. V o l . 10 3 pp. 565-588. Mathews, W.H., F y l e s , J.G., Nasmith, H.W., 1970, " P o s t g l a c i a l C r u s t a l Movements i n Southwestern B.C. and Adjacent Washington S t a t e . " Cdn. Jour. E a r t h Sciences Vol. 7, pp. 690-702. Mathews, W.H., Shepard, F.P., 1962, "Sedimentation of the F r a s e r D e l t a , B.C." B u i . o f the Am. Assoc. o f Petroleum G e o l o g i s t s , V o l . 46, pp. 1416-1438. McTaggart, K.C., E x c u r s i o n #11  Dolmage, V., 1977 "Vancouver G e o l o g y - F i e l d Guide Book." G.S.C.  Milne, W.G., Rogers, G.C., Riddihou, R.P., McMechan, G.A., Hyndman, P.D., 19 78, " S e i s m i c i t y o f Western Canada." Cdn. Jour, of E a r t h Sciences V o l . 15, pp. 1170-1193. M u l l e r , J.E., 1977, " E v o l u t i o n o f the P a c i f i c Margin, Vancouver I s l a n d and Adjacent Regions." Cdn. Jour. E a r t h Sciences, V o l . 14, pp. 2062-2085. Murphy, D.J., K o u t s o f t a s , D., Covey, J.N., F i s c h e r , J.A., 1978, "Dynamic P r o p e r t i e s of Hard G l a c i a l T i l l . " Earthquake E n g i n e e r i n g and S o i l Dynamics S p e c i a l t y Conference, Pasadena. N u t t l i , O.W., 1973, "Seismic Wave A t t e n u a t i o n s and Magnitude R e l a t i o n s f o r E a s t e r n North America." S.Geophys. Res. Vol. 78, pp. 876-885. Ohsaki, Y., 1970, " E f f e c t s of Sand Compaction on L i q u e f a c t i o n d u r i n g the T o k a c h i a k i Earthquake." S o i l s and Foundations, Vol. 10, No. 2  -193Ohsaki,.Y., Iwasaki, Poissons Ratio o f Foundations, Vol. Radhakrishna, H.S., o f Dense G l a c i a l pp. 396-408. Roddick, J . A . , 1965, Map A r e a s , B . C . . " Rogers, G.C., Earthquake Society of  R. , 1973, " O n D y n a m i c S h e a r M o d u l i a n d Soil Deposits." S o i l Mechanics and 13, No. 4, pp. 6 1 - 7 3 . K l y m , T.W. , 1 9 7 4 , " G e o t e c h n i c a l Till". Cdn. G e o t e c h n i c a l J o u r .  "Vancouver N o r t h , Coquitlam, G.S.C. memoir 335.  Properties Vol. 11,  and P i t t  Lake  H a s e g a w a , 1 9 7 8 , "A S e c o n d L o o k a t t h e B . C . o f 23 J u n e , 19 4 6 . " Bulletin of Seimological America, V o l . 68, pp. 653-675.  S a i t o , A . , 19 7 7 , " C h a r a c t e r i s t i c s o f P e n e t r a t i o n R e s i s t a n c e o f a R e c l a i m e d Sandy D e p o s i t a n d t h e i r Change t h r o u g h Vibratory Compaction." S o i l s a n d F o u n d a t i o n s V o l . 17 #4, pp. 31-43. Schmertman, J . H . , 1 9 7 1 , D i s c u s s i o n on Paper by V. d e M e l l o , 4 t h Pan A m e r i c a n C o n f e r e n c e o n S o i l M e c h a n i c s and F o u n d a t i o n Engineering, pp. 91-98. S c h n a b e l , J . , 1 9 7 1 , D i s c u s s i o n on Paper by V. de M e l l o , 4 t h Pan A m e r i c a n C o n f e r e n c e o n S o i l M e c h a n i c s a n d F o u n d a t i o n Engineering, pp. 89-98. Schnabel, P . B . , Lysmer, J . , Seed, H . B . , 1972, "SHAKE-A C o m p u t e r Program f o r E a r t h q u a k e Response A n a l y s i s o f H o r i z o n t a l l y L a y e r e d S i t e s . " EERC 7 2 - 1 2 E a r t h q u a k e E n g i n e e r i n g R e s e a r c h Centre, University of C a l i f o r n i a , Berkeley. S c h n a b e l , P . B . , S e e d , H . B . , 1 9 7 2 , " A c c e l e r a t i o n s i n Rock f o r Earthquakes i n the Western United S t a t e s . " Report N o . EERC 7 2 - 2 , E a r t h q u a k e E n g i n e e r i n g R e s e a r c h C e n t r e , University of California, Berkeley. S c h u l t z e , E . , M e l z e r , K . J . , 1965, "The D e t e r m i n a t i o n o f t h e D e n s i t y and Modulus o f C o m p r e s s i b i l i t y o f Non-Cohesive S o i l s by S o u n d i n g s . " Proceedings 6th I n t . Conf. Soil Mechanics and F o u n d a t i o n E n g i n e e r i n g , M o n t r e a l , V o l . 1 pp. 517-521. S c h u l t z e , E., Menzenbach, E . , 1 9 6 1 , "Standard P e n e t r a t i o n T e s t and C o m p r e s s i b i l i t y o f S o i l . " 5th I n t . Conf. Soil Mechanics and F o u n d a t i o n E n g i n e e r i n g , V o l . 1 , p p . 5 2 7 - 5 3 1 . S c o t t o n , 1977, "The O u t e r Banks o f t h e F r a s e r R i v e r D e l t a , " E n g i n e e r i n g P r o p e r t i e s and S t a b i l i t y C o n s i d e r a t i o n s . " M.A.Sc. t h e s i s , U.B.C.  -194Seed. H.B., I d r i s s , I.M., 1970, " S o i l Moduli and Damping F a c t o r s f o r Dynamic Response A n a l y s i s . " EERC Report No. 70-10, Earthquake E n g i n e e r i n g Research Centre, U n i v e r s i t y o f C a l i f o r n i a , Berkeley. Seed, H.B., I d r i s s , I.M, 1971, " S i m p l i f i e d procedure f o r Evaluating S o i l Liquefaction Potential." Journal of S o i l Mechanics and Foundation D i v i s i o n , ASCE, V o l . 97, No. 5 pp. 1249-1273. Seed, H.B., I d r i s s , I.M.,Keifer, F.W., 1969, " C h a r a c t e r i s t i c s o f Rock Motions During Earthquakes." Jour. S o i l Mechanics and Foundations Div. ASCE, V o l . 95, No. 5, pp.1199-1218. Seed, H.B., I d r i s s , I.M. Makdise, F., Banerjee, N., 1975, "Representation o f I r r e g u l a r S t r e s s Time H i s t o r i e s by E q u i v a l e n t Uniform S t r e s s S e r i e s i n L i q u e f a c t i o n A n a l y s e s . " EERC 75-29, Earthquake E n g i n e e r i n g Research Centre, University of C a l i f o r n i a , Berkeley. Seed, H.B., M o r i , K., Chan, C.K., 1977, " I n f l u e n c e o f Seismic H i s t o r y on the L i q u e f a c t i o n o f Sands." Jour, o f G e o t e c h n i c a l E n g i n e e r i n g D i v i s i o n , ASCE, V o l . 103, No. G74, pp. 257-270. Seed, H.B., Murarka, R., Lysmer, J . , I d r i s s , I.M., 1976, " R e l a t i o n s h i p s o f Maximum A c c e l e r a t i o n , Maximum V e l o c i t y , D i s t a n c e from Source, and L o c a l S i t e C o n d i t i o n s f o r Moderately Strong Earthquakes." B u l l e t i n o f S e i s m o l o g i c a l S o c i e t y o f America, V o l . 66 No. 4, pp. 1323-1342. Seed, H.B., Vgas, C , Lysmer, J . , 1976, " S i t e Dependent S p e c t r a f o r Earthquake R e s i s t a n t Design." B u l l e t i n o f S e i s m o l o g i c a l S o c i e t y o f America, V o l . 66 No. 4, pp. 221-24 3. Tavenas, F.A.,Ladd, R.S., La R o c h e l l e , P., 1972, "The Accuracy of R e l a t i v e D e n s i t y Measurements: R e s u l t s o f a Comparative T e s t Program." Department de Genie C i v i l , U n i v e r s i t e L a v a l . T r i f u n a c , M.D., Brady, A.G., 1975, " C o r r e l a t i o n s o f Peak A c c e l e r a t i o n V e l o c i t y and Displacement w i t h Earthquake Magnitude D i s t a n c e , and S i t e C o n d i t i o n s .  -195APPENDIX 1 GEOLOGIC TIME SCALE ERA  PERIOD  APPROXIMATE NUMBER OF YEARS AGO*  Quaternary Recent Pleistocene  Last  10,000  1 0 , 0 0 0 to 1 , 0 0 0 , 0 0 0 (Ice Age)  Cenozoic  Tertiary Pliocene Miocene Oligocene Eocene Paleocene  Mesozoic  Cretaceous Jurassic Triassic  6 3 to 1 3 5 1 3 5 to 1 8 1 1 8 1 to 2 3 0  Palaeozoic  Permian Pennsylvanian and Mississippian Devonian Silurian Ordovician Cambrian  2 3 0 to 2 8 0  Proterozoic  Keweenawan Huronian  Archaean  Temiskaming Keewatin  •Science, A p r i l 1 4 , 1 9 6 1 , p . 1 1 1 1  (Millions) to 13 to 25 to 36 to 58 to 63  1 13 25 36 58  280 345 405 425 500  to to to to to  345 405 425 500 600  6 0 0 to 2 , 0 0 0  2 , 0 0 0 to 4 , 8 0 0  -196APPENDIX 2 USE OF FRICTION CONE S.P.T. FORMULA TO SEPARATE PENETRATION RESISTANCE DUE TO END BEARING AND FRICTION  From Schmertmann (1971) we have F  = Fe + Fs  Fe  = Ae* qc  Fs  = TT (Di + Do) L-fs  FR  fs/qc  where F Fe Fs Ae qc  = = = = =  Di Do L fs FR  = = = = =  to sampler r e s i s t a n c e to advance end b e a r i n g component o f r e s i s t a n c e f r i c t i o n a l component o f r e s i s t a n c e h o r i z o n t a l l y p r o j e c t e d end area o f SPT sampler" end bearing r e s i s t a n c e , a t same depth from s t a t i c cone t e s t i n s i d e diameter o f sampler o u t s i d e diameter o f sampler l e n g t h o f sampler imbedded i n s o i l l o c a l f r i c t i o n from s t a t i c cone p e n e t r a t i o n t e s t F r i c t i o n r a t i o , a f u n c t i o n o f s o i l type  Take the r a t i o o f end b e a r i n g Fe Fs f o r Ae Di Do FR We g e t  Ae  • qc (Di + Do) L . f s  —  and f r i c t i o n a l = Ae  components:  (Di + Do)L . FR  10.7cm — 1.375 i n - 2in = 1% (Loose to med. sands, Schmertmann 1971) 2  Fe Fs  = 39.7 L  -197-  FOR VARIOUS LENGTHS OF SAMPLER IMBEDMENT THIS GIVES:  DEPTH OF SAMPLER IMBEDMENT  Fe Fs  (in)  Resistance From End Bearing %  Resistance From Friction %  6  2.60  72%  28%  12  1.30  56%  44%  18  0.868  46%  59%  24  0.651  39%  61%  -198APPENDIX 3 LIQUEFACTION POTENTIAL RELATIONSHIPS CHRISTIAN & SWIGER (1975) A =  dT *S '  where A = \T = QV = a =  0  s t r e s s r a t i o a t some depth overburden p r e s s u r e a t t h a t depth e f f e c t i v e s t r e s s a t t h a t depth maximum ground a c c e l e r a t i o n  f o r a water t a b l e a t the s u r f a c e Fraser  cr  Delta:  a t the s o i l , as i n the  J» r r '  /\  f o r design earthquake o f 17 = 7.4, F i g . 4-2-12 p r e d i c t s maximum ground s u r f a c e So:  a c c e l e r a t i o n o f 0.16g.  A = 2 (.16) = .32g  The r e l a t i o n developed by C h r i s t i a n & Swiger presented by Byrne  (19 7 5) and  (1977) p r e d i c t s t h a t f o r A = .32g  l i q u e f a c t i o n i s u n l i k e l y to occur i n sands w i t h a R e l a t i v e Density g r e a t e r  than 71% as determined from the  Gibbs and H o l t z r e l a t i o n s .  The Gibbs and H o l t z r e l a t i o n  f o r Nvs. DR = 71% was p l o t t e d i n f i g . 5-2. SEED, MURARKI, LYSMER, IDRISS (19 76) A = 0.65 where  a  (To.  A = c y c l i c s t r e s s r a t i o o f some depth c a u s i n g liquefaction a = maximum ground a c c e l e r a t i o n g = a c c e l e r a t i o n due to g r a v i t y \u» = t o t a l overburden s t r e s s CTa = e f f e c t i v e overburden s t r e s s r = stress reduction d  factor  -199-  f o r - water t a b l e a t the s u r f a c e - t o t a l u u n i t weight o f 122 p c f -d o f 0.16g A - .65  ft).16g\ 122 (depth) • r d I g J (122- 62.4) (depth)  A = .21rd Seed and I d r i s s  (1971) produced r e l a t i o n s between r d  and depth so the s t r e s s r a t i o can be determined with depth. The s t r e s s r a t i o c a u s i n g l i q u e f a c t i o n can be empirically  to the p e n e t r a t i o n r e s i s t a n c e ,  related  so from  data presented by Seed, Arango and Chan 19 75, the blow count i n sands u n l i k e l y to l i q u e f y may  be  determined f o r the v a r i o u s s t r e s s r a t i o s c a l c u l a t e d . blow count g i v e n i s one c o r r e c t e d  to a standard overburden  p r e s s u r e so from i t the a c t u a l blow count r e q u i r e d each depth may  The  at  be determined from the r e l a t i o n .  CN = 1-1.25 l o g V~ ' where N = Ni CN 0  here CN = c o r r e c t i o n f a c t o r N = true blow count N = blow count normalized to standard p r e s s u r e . In t h i s way required  a r e l a t i o n s h i p •.between the blow count  to reduce the p o s s i b i l i t y o f l i q u e f a c t i o n  a p a r t i c u l a r earthquake, and depth may This r e l a t i o n i s p l o t t e d  i n f i g . 5-1.  under  be developed.  

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