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UBC Theses and Dissertations

Sources and receivers with the seismic cone test Laing, Nancy Louise 1985

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SOURCES AND RECEIVERS WITH THE SEISMIC CONE TEST  by  NANCY LOUISE LAING B.A.Sc,  The U n i v e r s i t y o f B r i t i s h Columbia, 1983  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE  in THE FACULTY OF GRADUATE STUDIES Department o f C i v i l  Engineering  We a c c e p t t h i s t h e s i s as conforming to the r e q u i r e d s t a n d a r d  THE UNIVERSITY OF BRITISH COLUMBIA June 1985  ©  Nancy L o u i s e L a i n g , 1985  DE-6  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 of  requirements f o r an advanced degree a t the  the  University  o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r reference  and  study.  I further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may department o r by h i s o r her  be granted by the head o f representatives.  my  It is  understood t h a t 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 gain  s h a l l not be  allowed without my  permission.  Department o f  I ^'A-ge^/^ C  The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date  (3/81)  M  /  written  ii ABSTRACT  D i f f e r e n t types o f s o u r c e s and r e c e i v e r s used w i t h the s e i s m i c  cone  p e n e t r a t i o n t e s t were i n v e s t i g a t e d . The s o u r c e s i n v e s t i g a t e d were mechanical shear and compression wave s o u r c e s c o n s i s t i n g o f a hammer-and-weighted-plank s o u r c e ; an on-shore B u f f a l o gun source u t i l i z i n g  shotgun s h e l l s ; an o f f - s h o r e  s e i s m i c cap source; and an o f f - s h o r e embedded b l a d e w i t h s e i s m i c cap s o u r c e . The r e c e i v e r s i n v e s t i g a t e d were h o r i z o n t a l  and v e r t i c a l  geophones and  accelerometers. The hammer shear source used p r e v i o u s l y w i t h the s e i s m i c cone  (Rice,  1984), was used as a s t a n d a r d f o r c o m p a r i s o n . The hammer P-wave source was not used s u c c e s s f u l l y w i t h the s e i s m i c c o n e , because the v e r t i c a l used i n the cone do not r e p r e s e n t the s o i l  receivers  response and thus can not be used  with any s o u r c e , and because the a m p l i t u d e o f the P-waves produced by the source was not l a r g e enough t o d e t e c t on the h o r i z o n t a l  receivers.  B u f f a l o gun source d i d not g i v e r e p e a t a b l e or a c c u r a t e shear wave  The velocities  f o r depths l e s s than 12 m e t e r s , but d i d appear r e p e a t a b l e and a c c u r a t e  below  12 m e t e r s . The s e i s m i c cap sources i n c l u d i n g the embedded b l a d e source were found t o g i v e reasonable wave v e l o c i t i e s  if  shear wave v e l o c i t i e s  and reasonable  compression  the depth at which the s e i s m i c cap was f i r e d was kept  constant. Both h o r i z o n t a l shear wave v e l o c i t i e s  geophones and a c c e l e r o m e t e r s were found t o g i v e  similar  f o r the hammer shear s o u r c e , but f o r the B u f f a l o gun  source the a c c e l e r o m e t e r s g i v e d i f f e r i n g r e s u l t s from the geophones because o f a v a r i a b l e phase s h i f t a s s o c i a t e d w i t h the f i l t e r i n g o f accelerometer. V e r t i c a l  probably the  r e c e i v e r s were not s u c c e s s f u l l y used w i t h the  cone because they do not g i v e a response r e p r e s e n t a t i v e o f the s o i l  seismic  response,  because o f the v e r t i c a l  s t i f f n e s s o f the cone and r o d s .  The use of compression and shear wave v e l o c i t i e s t o determine P o i s s o n ' r a t i o gave reasonable r e s u l t s i f  the s t r a i n l e v e l  and type o f compression  wave were taken i n t o a c c o u n t . A p r e l i m i n a r y d e t e r m i n a t i o n o f the m a t e r i a l damping r a t i o gave r e s u l t s whtich were h i g h e r than e x p e c t e d ,  probably  i n d i c a t i n g the s e i s m i c wave r e c e i v e r s were responding t o the  cone-soil  system, r a t h e r than t o the s o i l  alone.  iv TABLE OF CONTENTS  1.  Abstract  ii  Table of Contents  1v  L i s t of Figures  vii  Acknowledgements  x  Introduction  1  2. S e i s m i c Wave Theory and C o n v e n t i o n a l 2.1  In S i t u M e t h o d s . .  Introduction  3 ....3  2.2 Types o f S e i s m i c Waves and T h e i r C h a r a c t e r i s t i c s  3  2.3 Seismic Wave V e l o c i t i e s and the E l a s t i c Moduli  8  2.3.1  Development o f E l a s t i c Moduli  8  2.3.2  C a l c u l a t i n g S e i s m i c Wave V e l o c i t i e s  11  2.4 Conventional  In S i t u Methods f o r S e i s m i c Measurement  3 . Equipment and Procedures 3.1  Introduction  13  16 16  3.2 The Seismic Cone P e n e t r o m e t e r . . .  16  3.3 Seismic Wave Sources and R e l a t e d T r i g g e r i n g Systems  19  3.3.1  Introduction  19  3.3.2 3.3.3 3.3.4 3.3.5 3.3.6 3.3.7  Mechanical Sources T r i g g e r i n g System f o r the Mechanical Sources On-Shore E x p l o s i v e Source T r i g g e r i n g System f o r the On-Shore E x p l o s i v e Source O f f - S h o r e E x p l o s i v e Sources T r i g g e r i n g System f o r the O f f - S h o r e E x p l o s i v e Sources  21 22 22 25 27 29  3.4 Seismic Wave D e t e c t i o n and R e c o r d i n g 3.4.1 Introduction 3 . 4 . 2 Geophones 3.4.3 Accelerometers 3.4.4 Signal F i l t e r i n g 3 . 4 . 5 Recording O s c i l l o s c o p e 3.5 F i e l d Procedures  29 29 32 ..34 37 43 44  V  4. F i e l d I n v e s t i g a t i o n s  48  4.1 McDonalds Farm S i t e  48  4.2 Beaufort Sea S i t e s  49  4.2.1  Schoolhouse S i t e  49  4 . 2 . 2 Swimming P o i n t S i t e 4 . 2 . 3 Richards I s l a n d S i t e 4 . 2 . 4 TuktOyaktuk Harbour S i t e  51 51 52  5. E v a l u a t i o n of D i f f e r e n t Sources  53  5.1 E v a l u a t i o n of the Mechanical  Sources  53  5.1.1  Hammer Shear Wave Source  53  5.1.2  Hammer P-wave Source  53  5.2 On-Shore E x p l o s i v e Source  56  5.3 O f f - S h o r e E x p l o s i v e Sources  ..62  5.3.1  Seismic Cap Source  62  5.3.2  Embedded Blade w i t h S e i s m i c Cap Source  64  5.4 Comparison of D i f f e r e n t Sources  .....68  5.4.1  B u f f a l o Gun Source v e r s u s Hammer Shear Wave Source  68  5.4.2 5.4.3  Seismic Cap Source v e r s u s Hammer Shear Wave Source Embedded Blade Source v e r s u s S e i s m i c Cap Source  72 ..72  6. Evaluation of D i f f e r e n t Seismic Receivers  76  6.1 Geophones versus A c c e l e r o m e t e r s  76  6.2 H o r i z o n t a l  81  versus V e r t i c a l  Receivers  7. E v a l u a t i o n o f Compression Wave Data  85  8 . E v a l u a t i o n o f Damping C h a r a c t e r i s t i c s  89  8.1  Introduction  8.2 Accelerometers t o o b t a i n S o i l  89 Damping  8.3 Waveform A n a l y s i s t o determine S o i l 8.3.1  Damping  R e s u l t s o f Manual Waveform A n a l y s i s  89 92 93  vi  9. Conclusions  96  References  99  Appendix A  102  vii  LIST OF FIGURES  2.1 C h a r a c t e r i s t i c s o f a Compression Wave  5  2.2 C h a r a c t e r i s t i c s o f a Shear Wave  6  2.3 P a r t i t i o n of E l a s t i c Wave a t I n t e r f a c e between Two E l a s t i c Media  7  2.4 Schematic View o f the R a d i a t i o n P a t t e r n o f a V e r t i c a l S u r f a c e P o i n t Source  9  and H o r i z o n t a l  2.5 Determination of S e i s m i c Wave V e l o c i t y  12  2.6 Conventional  14  In S i t u Methods f o r S e i s m i c Measurement..  3.1 15 s q . cm Seismic Cone Penetrometer  17  3.2 10 s q . cm Seismic Cone Penetrometer  ..18  3.3 CPT Seismic Equipment Layout f o r Mechanical 3.4 E l e c t r i c a l  Step T r i g g e r C i r c u i t  Sources....  20  f o r Hammer Source  ...23  3.5 B u f f a l o Gun and i t s O p e r a t i o n  24  3.6 T r i g g e r i n g Systems f o r B u f f a l o Gun Source  26  3.7 Geophone T r i g g e r Response t o B u f f a l o Gun Source  28  3.8 Operation of S e i s m i c Cap Source  30  3.9 Schematic of M a s s - s p r i n g Type o f V i b r a t i o n - m e a s u r i n g T r a n s d u c e r  31  3.10 Schematic of Geophone  33  3.11 Geophone S p e c i f i c a t i o n s  35  3.12 Schematic of S t r a i n - g a g e A c c l e r o m e t e r  36  3.13 U n a m p l i f i e d and A m p l i f i e d A c c e l e r o m e t e r Responses  38  3.14 F i l t e r e d and U n f i l t e r e d A c c e l e r o m e t e r Responses  39  3.15 A t t e n u a t i o n and Phase S h i f t C h a r a c t e r i s t i c s  o f the Low Pass  Filters..41  3.16 E f f e c t o f D i f f e r e n t F i l t e r C u t - o f f F r e q u e n c i e s on A c c e l e r o m e t e r Response  42  3.17 Schematic of the E l e c t r o n i c s S e t - u p f o r S e i s m i c T e s t i n g  45  4.1 L o c a t i o n Map f o r B e a u f o r t Sea S i t e s  50  vi i i 5.1 H o r i z o n t a l 5.2 V e r t i c a l  Geophone Response P r o f i l e  f o r Hammer Shear Source  54  A c c e l e r o m e t e r Response t o Hammer P-Wave S o u r c e . . . .  55  5.3 H o r i z o n t a l  A c c e l e r o m e t e r Response t o Hammer P-Wave Source  57  5.4 H o r i z o n t a l  Accelerometer-Response P r o f i l e  58  f o r B u f f a l o Gun  5.5 V a r i a t i o n o f A c c e l e r o m e t e r Response w i t h P o s i t i o n o f B u f f a l o Gun Source 5.6 Comparison of Shear Wave V e l o c i t y P r o f i l e s 5.7 Comparison between True and Pseudo I n t e r v a l 5.8 H o r i z o n t a l  Geophone P r o f i l e  60  from B u f f a l o Gun S o u r c e . . . . 6 1 Measurement  Response f o r S e i s m i c Cap Source  63 fired  j u s t below Ice  65  5.9 Comparison o f Shear Wave V e l o c i t y P r o f i l e s f o r the S e i s m i c Cap Source f i r e d j u s t below Ice a t Swimming P o i n t S i t e 66 5.10 H o r i z o n t a l Mudline  Geophone Response P r o f i l e  5.11 H o r i z o n t a l  Geophone Response P r o f i l e  f o r S e i s m i c Cap Source f i r e d  at 67  f o r Embedded Blade Source  69  5.12 Shear Wave V e l o c i t y P r o f i l e s from the H o r i z o n t a l Hammer and B u f f a l o Bun Sources  Accelerometer  for  5.13 Shear Wave V e l o c i t y P r o f i l e s from the H o r i z o n t a l and B u f f a l o Gun Sources  Geophone f o r Hammer  70  71  5.14 Shear Wave V e l o c i t y P r o f i l e s f o r Hammer and Seismic Cap Sources 5.15 Shear Wave V e l o c i t y P r o f i l e s f o r S e i s m i c Cap Source f i r e d j u s t Ice and a t Mudline  73 below 74  5.16 S e i s m i c Wave V e l o c i t y P r o f i l e s f o r Embedded Blade and S e i s m i c Cap Sources  75  6.1 H o r i z o n t a l Source  Geophone and A c c e l e r o m e t e r Responses t o Hammer Shear 77  6.2 H o r i z o n t a l Source  Geophone and A c c e l e r o m e t e r Responses t o the B u f f a l o Gun 79  6.3 Shear Wave V e l o c i t y P r o f i l e s from the H o r i z o n t a l Geophone and A c c e l e r o m e t e r f o r the Hammer and B u f f a l o Gun Sources 6.4 H o r i z o n t a l below Ice 6.5 V e r t i c a l  Geophone Response t o the S e i s m i c Cap Source f i r e d  Geophone Response P r o f i l e  80 just 82  f o r S e i s m i c Cap Source  84  ix 7.1 C a l c u l a t e d P o l s s o n ' s R a t i o s f o r School house a) Depth 0 t o 15 meters b) Depth 15 t o 30 meters  Site 86 87  7.2 C a l c u l a t e d P o i s s o n ' s R a t i o s f o r Tuktoyaktuk Harbour S i t e 8.1 D e f i n i t i o n o f Log Decrement from H o r i z o n t a l Hammer Shear Source  A c c e l e r o m e t e r Response  88 to 90  8.2 Damping R a t i o s from A c c e l e r o m e t e r Response v e r s u s Depth  91  8.3 Geophone Waveforms d e f i n i n g Q u a n t i t i e s  94  8.4 Damping R a t i o s from Manual  f o r Damping C a l c u l a t i o n  Waveform A n a l y s i s v e r s u s Depth  95  x  ACKNOWLEDGEMENTS  I would l i k e support, thanks,  s u g g e s t i o n s and g u i d a n c e also,  invaluable. help  t o e x p r e s s my s i n c e r e  to Dr. Special  i n the f i e l d  thanks to Dr.  throughout  Campanella f o r  the course of  this  study.  R o b e r t s o n , whose a s s i s t a n c e and s u g g e s t i o n s thanks to Mr.  Don G i l l e s p i e and M r .  and w i t h a n a l y s i s a n d f o r  their  his Many  were  J o h n Howie f o r  critical  their  comments on  the  text. The p r o j e c t w o u l d n o t have been p o s s i b l e w i t h o u t  the f i n e  s u p p o r t and w o r k m a n s h i p o f M e s s e r s A r t  Brookes, Glenn J o l l y ,  Postgate.  Brown, Mr.  Davies  The a s s i s t a n c e o f M r .  i n the f i e l d  help with  appreciated.  to thank the G e o l o g i c a l  Head, S e i s m i c Method  Section, for  Group a t U . B . C . w i t h the o p p o r t u n i t y shore.  The h e l p o f  G.S.C. while  Bruce O ' N e i l l  thanks to Mr.  Dick and M r .  Mike  Jim Greig f o r  Dr.  P.J.  K u r f u r s t , Mr.  support from Natural  his  and h e l p w i t h  very special  C a n a d a and D r .  providing  the  In S i t u  N i x o n , and M r .  Testing  B. Gagne o f  S c i e n c e s and E n g i n e e r i n g R e s e a r c h Canada i s  gratefully  t h a n k s go t o my h u s b a n d , D o u g , f o r  presentation.  J.A.  offthe  appreciated.  Canada and E n e r g y , M i n e s and R e s o u r c e s , Lastly,  Survey of  t o p e r f o r m s e i s m i c cone t e s t i n g  i n t h e B e a u f o r t was g r e a t l y  Financial of  Special  and  computers.  I would l i k e Hunter,  is  Peter  technical  his  Council  acknowledged. support  1 1.  INTRODUCTION  In r e c e n t y e a r s , the study o f s o i l  dynamics has been assuming an  Increasingly important r o l e in geotechnical Soil  engineering s i t e  investigations.  dynamics i s used t o analyze and design f o r dynamic l o a d i n g o f  soils,  which i n c l u d e e a r t h q u a k e s , ocean waves, and v i b r a t i n g m a c h i n e r y . As dynamic a n a l y s i s o f s o i l s becomes more complex, more a c c u r a t e dynamic s o i l  parameters  are n e c e s s a r y . Small s t r a i n dynamic e l a s t i c moduli o f a s o i l d e n s i t y and compression and shear wave v e l o c i t i e s  can be determined i f i n the s o i l  soil  are known. A t  p r e s e n t , the downhole and c r o s s h o l e s e i s m i c t e s t i n g methods are u s e d , most commonly, f o r d e t e r m i n i n g i n s i t u compression and shear wave v e l o c i t i e s . These methods may be c o s t l y and time consuming, because they i n v o l v e  the  d r i l l i n g and c a s i n g o f one o r more b o r e h o l e s . The s e i s m i c cone p e n e t r a t i o n t e s t i s a r e l a t i v e l y new t e c h n i q u e determining i n s i t u compression and shear wave v e l o c i t i e s . being i n v e s t i g a t e d a t U . B . C . , a n d was f i r s t  This technique  r e s e a r c h e d by Rice  is  ( 1 9 8 4 ) . Rice  found t h a t the s e i s m i c cone p e n e t r a t i o n t e s t "can p r o v i d e a r a p i d , assessment o f shear moduli  for  accurate  at s i t e s where cone p e n e t r a t i o n can be c a r r i e d  o u t . " Rice a l s o found the s e i s m i c cone p e n e t r a t i o n t e s t t o have  distinct  advantages o v e r the downhole and c r o s s h o l e t e s t methods, because i t was f a s t e r and needed o n l y one uncased t e s t h o l e . The main o b j e c t i v e o f t h i s t h e s i s was t o e v a l u a t e the use o f  different  sources and r e c e i v e r s o f s e i s m i c body waves w i t h the s e i s m i c cone penetrometer. S i m i l a r s t u d i e s have been done f o r the downhole and c r o s s h o l e techniques  ( P a t e l , 1981; W a r r i c k ,  1974; Stokoe and Hoar, 1978).  o f s o u r c e s and r e c e i v e r s was c a r r i e d out both on and o f f - s h o r e , mechanical  Investigation with  and e x p l o s i v e s o u r c e s . The r e c e i v e r types i n v e s t i g a t e d were  2 horizontal  and v e r t i c a l  geophones and a c c e l e r o m e t e r s .  Secondary o b j e c t i v e s o f t h i s t h e s i s were, f i r s t t o determine P o i s s o n ' s r a t i o u s i n g the compression and shear wave v e l o c i t i e s t e s t i n g , and second, t o take an i n i t i a l u s i n g the s e i s m i c cone penetrometer The t h e s i s w i l l  o b t a i n e d from the  look a t damping r a t i o f o r the  soil  data.  begin with a b r i e f  review o f s e i s m i c wave  c h a r a c t e r i s t i c s , e l a s t i c moduli d e t e r m i n a t i o n ,  and c o n v e n t i o n a l  in  situ  s e i s m i c t e s t i n g methods. Then, the equipment used d u r i n g the r e s e a r c h , including sources, t r i g g e r s ,  r e c e i v e r s and r e c o r d i n g i n s t r u m e n t s , w i l l  d e s c r i b e d i n d e t a i l , f o l l o w e d by a b r i e f  d e s c r i p t i o n o f each t e s t  The r e s u l t s o f the e v a l u a t i o n of d i f f e r e n t sources w i l l Each source w i l l  site.  be p r e s e n t e d .  be e v a l u a t e d a l o n e , and then compared t o o t h e r  sources,  where p o s s i b l e . A f t e r t h i s f o l l o w s a comparison o f the d i f f e r e n t  seismic  r e c e i v e r types u s e d . D e t e r m i n a t i o n o f P o i s s o n ' s r a t i o and damping r a t i o then p r e s e n t e d . F i n a l l y , summarized.  be  the major c o n c l u s i o n s o f the t h e s i s w i l l  be  are  3 2. SEISMIC WAVE THEORY AND CONVENTIONAL IN SITU TESTING METHODS  2.1  Introduction  This chapter w i l l  briefly  review the r e l e v a n t theory a s s o c i a t e d w i t h  s e i s m i c wave types and w a v e - p r o p a g a t i o n .  It will  then o u t l i n e the  o f e l a s t i c c o n s t a n t s as r e l a t e d t o s e i s m i c wave v e l o c i t i e s . conventional briefly  development  Finally,  methods f o r d e t e r m i n i n g s e i s m i c wave v e l o c i t i e s w i l l  the  be very  reviewed.  R i c h a r t e t al  (1970), Mooney (1974) and Borm (1977) have w r i t t e n  d i s c u s s i o n s on s e i s m i c waves, t h e i r c h a r a c t e r i s t i c s ,  ample  and the r e l a t i o n  of  s e i s m i c wave v e l o c i t i e s t o dynamic e l a s t i c m o d u l i . These r e f e r e n c e s were used extensively i n preparing Sections 2.2.  and 2 . 3 .  L i t e r a t u r e reviews o f c r o s s h o l e and downhole s e i s m i c t e s t i n g methods have been c a r r i e d out by P a t e l  (1981) and R i c e  (1984) and w i l l  not be  repeated h e r e . I n s t e a d , the r e l e v a n t c h a r a c t e r i s t i c s and procedures f o r each test will  be b r i e f l y o u t l i n e d , w i t h an emphasis on s o u r c e s and r e c e i v e r s  used.  2.2 Types o f Seismic Waves and T h e i r  Characteristics  Seismic waves observed i n e n g i n e e r i n g s t u d i e s f a l l body waves and s u r f a c e waves. Body waves t r a v e l  i n t o two c a t e g o r i e s ;  i n t o the I n t e r i o r o f  the  e a r t h i n the form o f compression waves and shear waves. S u r f a c e waves propagate o n l y near the s u r f a c e and do not extend t o any g r e a t d e p t h . The two forms o f s u r f a c e waves are R a y l e i g h and Love waves. Although R a y l e l g h waves have been used i n e n g i n e e r i n g s e i s m i c s t u d i e s , r e s e a r c h and so n e i t h e r t h e y ,  they were not used i n  nor Love waves w i l l  Compression waves ( a l s o known as d i l a t a t i o n a l o r primary waves ( P - w a v e s ) ) . c a u s e p a r t i c l e s  be d e s c r i b e d  this  further.  waves, l o n g i t u d i n a l  t o move p a r a l l e l  t o the ray  waves, path  4 o f the wave, i n the d i r e c t i o n of wave p r o p a g a t i o n Compression waves can t r a v e l  (see F i g u r e  2.1).  through both sol Ids and f l u i d s .  In o r d e r t o d e t e c t compression waves, a r e c e i v e r must be a l i g n e d parallel  t o the d i r e c t i o n of wave p r o p a g a t i o n ,  this direction  (see F i g u r e 2 . 1 ) . T h e r e f o r e ,  s i n c e p a r t i c l e motion i s  f o r a source which generates  v e r t i c a l l y p r o p a g a t i n g compression waves, a v e r t i c a l Shear waves ( a l s o known as d i s t o r t i o n a l secondary waves ( S - w a v e s ) ) , cause p a r t i c l e s  in  d e t e c t o r must be u s e d .  waves, t r a n s v e r s e waves or t o move i n a plane  t o the ray path o f the wave. The d i r e c t i o n o f motion w i t h i n  perpendicular  this  p e r p e n d i c u l a r p l a n e depends mainly on the d i r e c t i o n o f the s e i s m i c  source.  For convenience shear waves can be r e s o l v e d i n t o two components. The shear wave component i s denoted SV when both p a r t i c l e motion and wave p r o p a g a t i o n are i n the same p l a n e , g e n e r a l l y a v e r t i c a l wave component i s denoted SH i f  p l a n e (see F i g u r e 2 . 2 ) . The shear  p a r t i c l e motion i s i n a plane t r a n s v e r s e  the plane d e f i n i n g the SV component,  generally a horizontal  2 . 2 ) . S i n c e f l u i d s can not develop a s h e a r i n g r e s i s t a n c e , travel  through f l u i d s . T h e r e f o r e ,  plane  to  (see F i g u r e  shear waves can not  shear waves can only t r a v e l  through  solids.  For d e t e c t i o n of both SV and SH-waves, a r e c e i v e r must be a l i g n e d i n the plane p e r p e n d i c u l a r t o the d i r e c t i o n o f wave p r o p a g a t i o n . Thus, as can be seen from F i g u r e 2 . 2 ,  f o r a v e r t i c a l l y p r o p a g a t i n g shear wave,  horizontal  r e c e i v e r s must be u s e d . Each type o f body wave behaves d i f f e r e n t l y when i t  strikes a geologic  boundary. As can be seen from F i g u r e 2 . 3 a , when a compression wave s t r i k e s a boundary between two mediums w i t h d i f f e r e n t P-wave v e l o c i t i e s ,  P and SV-waves  are r e f l e c t e d and r e f r a c t e d . No SH-waves a r e g e n e r a t e d . S i m i l a r l y , when a SVwave s t r i k e s a boundary, SV and P-waves a r e r e f l e c t e d and r e f r a c t e d  (see  F i g u r e 2 . 3 b ) . A g a i n , no SH-waves a r e g e n e r a t e d . However, when an SH-wave  5  F i g u r e 2.1 C h a r a c t e r i s t i c s  of a Compression Wave  coordinate axes  a) SV-wave j  ^ v e r t i c a l plane (not n e c e s s a r i l y i n xz-plane)  d i r e c t i o n of SV-wave p a r t i c l e motion p e r p e n d i c u l a r to d i r e c t i o n of wave propagation d i r e c t i o n of S-wave propagation  d e t e c t o r a l i g n e d with the d i r e c t i o n of p a r t i c l e motion  coordinate axes  b)SH-wave ^ h o r i z o n t a l plane (not n e c e s s a r i l y * p e r p e n d i c u l a r t o d i r e c t i o n of wave propagation) — d i r e c t i o n of SH-wave p a r t i c l e motion p e r p e n d i c u l a r to d i r e c t i o n of wave propagation  r T  d i r e c t i o n of S-wave propagation  detector aligned p a r t i c l e motion  F i g u r e 2.2  with d i r e c t i o n of  Characteristics  of a Shear Wave  7  P-Pl  p  /  P-SV1  ^  //^  Medium 1  \ \^  Medium 2  *Y  SV-SV1  sv  ^  SH-SH1 \  Pl,Vpl,Vsl VS.  \  p2,Vp2,Vs2  \  SV-P2  SH-SH2  SV-SV2  P-SV2  F i g u r e 2.3 P a r t i t i o n Media  SV-P1  \  P-P2  a) I n c i d e n t P-wave  SH  b)Incident  SV-wave  c) I n c i d e n t SH-wave  o f E l a s t i c Wave a t I n t e r f a c e between two E l a s t i c  8  s t r i k e s a boundary only SH-waves a r e r e f l e c t e d and r e f r a c t e d . No P o r SVwaves a r e g e n e r a t e d . (See F i g u r e  2.3c).  A s i m i l a r phenomenon o c c u r s w i t h s o u r c e s . A source e i t h e r predominantly P and SV-waves w i t h no SH-wave component, predominantly SH-waves w i t h l i t t l e  the complete l a c k  s u r f a c e p o i n t s o u r c e , and the l a c k o f a v e r t i c a l waves f o r the h o r i z o n t a l  and v e r t i c a l  shows  surface  o f SH-waves f o r a v e r t i c a l component f o r the P and SV-  s u r f a c e p o i n t s o u r c e . T h i s phenomenon i s an  i m p o r t a n t c o n s i d e r a t i o n when d e s i g n i n g a s e i s m i c Characteristically,  generates  P and SV-wave components. F i g u r e 2.4  s c h e m a t i c a l l y the r a d i a t i o n p a t t e r n s o f a h o r i z o n t a l point source. This i l l u s t r a t e s  or i t  generates  source.  compression waves a r e f a s t e r than shear waves. The  shear wave v e l o c i t y can be up t o 70% Compression wave v e l o c i t i e s  o f the compression wave v e l o c i t y .  a l s o t e n d t o have a h i g h e r frequency then  shear  waves. A f u r t h e r comment about SH-wave s o u r c e s i s needed. Sources which produce SH-waves u s u a l l y have the a b i l i t y  t o r e v e r s e the p o l a r i t y  o f the SH-wave.  P o l a r i z a t i o n of the SH-wave i s o b t a i n e d by r e v e r s i n g the d i r e c t i o n o f energy impulse which generates the SH-waves. T h i s energy r e v e r s a l  the  gives  r e c e i v e r responses t o the SH-wave, which are o p p o s i t e i n s i g n . However, waves generated by these sources w i l l g r e a t l y a i d s shear wave (SH) a r r i v a l  not show p o l a r i z a t i o n . T h i s  Development o f E l a s t i c  property  interpretation.  2.3 S e i s m i c Wave V e l o c i t i e s and the E l a s t i c  2.3.1  P-  Moduli  Moduli  I t has been found t h a t one e q u a t i o n can d e s c r i b e the b e h a v i o u r o f many v i b r a t i n g physical  systems. That e q u a t i o n i s known as the wave e q u a t i o n . The  development o f t h i s e q u a t i o n can be found i n many t e x t s , al,  1970, and w i l l  not be i n c l u d e d h e r e .  including Richart  et  9  1  1  —  .  P  / - V — •  "  sv  1  —1  No S H rr  V e r t i c a l Source  Figure  SH  H o r i z o n t a l Source  2.4 Schematic View of the R a d i a t i o n P a t t e r n of a V e r t i c a l and H o r i z o n t a l S u r f a c e P o i n t Source (From K a h l e r and M e i s s n e r , 1983)  Assuming i s o t r o p i c  and homogeneous e l a s t i c i t y  o f the ground, the  s o l u t i o n s to the wave e q u a t i o n u s i n g Hooke's l a w s , g i v e the  following  e x p r e s s i o n s f o r the v e l o c i t i e s o f compression and shear waves: Vp Vs  2  2  = (X + 2G)/p = G/p  where Vp = compression wave v e l o c i t y Vs = shear wave v e l o c i t y \ = Lame's  constant  G = shear modulus and P = d e n s i t y o f p r o p a g a t i o n medium. Thus, i f  the v e l o c i t y o f the shear wave p r o p a g a t i n g through the s o i l  d e n s i t y o f the s o i l  and the  i s known, the shear modulus o f the s o i l may be  determined. I f the compression wave v e l o c i t y through the s o i l  i s a l s o known,  then Lame's c o n s t a n t can be d e t e r m i n e d . Knowing the shear modulus and Lame's constant allows a l l  o t h e r e l a s t i c moduli t o be determined f o r a g i v e n  The e l a s t i c moduli o b t a i n e d u s i n g the f i e l d methods o u t l i n e d i n t h e s i s are small  s t r a i n moduli  ( s t r a i n s l e s s than .0001 p e r c e n t ) .  e l a s t i c moduli are s t r a i n dependent, comparison o f moduli  this  Since  determined u s i n g  d i f f e r e n t t e s t i n g p r o c e d u r e s , must take I n t o account the s t r a i n l e v e l which the t e s t s were performed. T h u s , shear moduli s e i s m i c cone p e n e t r a t i o n t e s t ,  at  determined u s i n g the  a r e maximum o r dynamic shear m o d u l i ,  Gmax because they are determined a t very small  soil.  strains  denoted  (Seed and I d r i s s ,  1970). One o t h e r important e l a s t i c c o n s t a n t which w i l l  be used i n t h i s  i s P o i s s o n ' s r a t i o . P o i s s o n ' s r a t i o can be determined d i r e c t l y wave v e l o c i t i e s as f o l l o w s :  thesis  from the two  v  = ((VP/Vs)  2((Vp/Vs) where v = P o i s s o n ' s and Vp and Vs a r e as d e f i n e d  - 2) .  2  -1)  2  ratio  previously.  The assumption of an i s o t r o p i c ,  homogeneous, e l a s t i c medium f o r s o i l  o n l y a f i r s t a p p r o x i m a t i o n , and moduli determined u s i n g t h i s  1s  assumption  s h o u l d be used w i t h c a u t i o n . A l s o the compression wave v e l o c i t y s o i l may not be the t r u e compression wave v e l o c i t y o f the s o i l  in  saturated  and may 1n  f a c t be the v e l o c i t y o f the compression wave through the pore f l u i d  (see  R i c h a r t e t a l , 1970). Thus, the P o i s s o n ' s r a t i o determined u s i n g Vp s h o u l d be used w i t h c a u t i o n and a g a i n , o n l y as a f i r s t 2.3.2  approximation.  C a l c u l a t i n g Seismic Wave V e l o c i t i e s The t e c h n i q u e used f o r c a l c u l a t i n g v e l o c i t i e s o f s e i s m i c waves from the  s e i s m i c cone p e n e t r a t i o n t e s t i s the pseudo i n t e r v a l d e p t h , the a r r i v a l  t e c h n i q u e . A t each  time o f the s e i s m i c wave (compression or shear) 1s  recorded. This arrival  time i s assumed t o be the time f o r the wave t o  the path ATP shown i n F i g u r e 2 . 5 .  Each a r r i v a l  as shown, t o the time taken to t r a v e l source were l o c a t e d d i r e c t l y F o r the pseudo i n t e r v a l between t e s t d e p t h s , AT,  time i s c o r r e c t e d  a vertical  a d j a c e n t t o the technique,  path, Tcorr,  the time t o t r a v e l  time AT,  1s taken t o r e p r e s e n t the average v e l o c i t y The s t r a i g h t l i n e t r a v e l a p p r o x i m a t i o n . However, R i c e  as i f  the  the  interval  f o r t h a t depth  travel  the depth  and the c a l c u l a t e d  velocity  interval.  path o f the wave from source t o r e c e i v e r 1s an (1984), found t h a t t h i s assumption 1s  s a t i s f a c t o r y f o r c a l c u l a t i o n of the s e i s m i c v e l o c i t i e s , pseudo i n t e r v a l  vectorially,  i s c a l c u l a t e d by s u b t r a c t i n g the c o r r e c t e d  i s d i v i d e d by the i n t e r v a l  travel  testhole.  times f o r two a d j a c e n t t e s t depths. To c a l c u l a t e the v e l o c i t y , i n t e r v a l AZ  test  especially i f  t e c h n i q u e i s used and the a n g l e o f the t r a v e l  the  p a t h , o> (see  12  Signal  Source  |<  Offset,  Xn  ATPn+1, Tmeas,n+1  >exsmometers  ATPn Tcorr Velocity =  F i g u r e 2.5  = Tmeas(  ATP ,n )  A Z _ (Zn+1 - Zn) AT (Tcorr,n+1 - T c o r r , n )  D e t e r m i n a t i o n of S e i s m i c Wave V e l o c i t y  Figure 2 . 5 ) , cancel  i s g r e a t e r than 45 d e g r e e s . The i n t e r v a l  t e c h n i q u e tends  out e r r o r s a s s o c i a t e d w i t h equipment and t r a v e l  steep t r a v e l along s o i l  to  path assumptions. The  path angle minimizes the e r r o r due t o r e f r a c t i o n o f the waves  boundaries.  2.4 Conventional  In S i t u Methods f o r S e i s m i c Measurement  There are t h r e e c o n v e n t i o n a l  methods o f measuring s e i s m i c wave  v e l o c i t i e s . These methods a r e : the s e i s m i c r e f r a c t i o n s u r v e y , the c r o s s h o l e s e i s m i c method, and the downhole s e i s m i c method. The e s s e n t i a l each o f these methods w i l l  be o u t l i n e d i n the f o l l o w i n g  elements  of  paragraghs.  The s e i s m i c r e f r a c t i o n survey c o n s i s t s o f a s t r i n g o f r e c e i v e r s s e t out i n a s t r a i g h t l i n e from a source l o c a t i o n . The source e m i t s body waves which are r e f r a c t e d by boundaries between s o i l s o f d i f f e r e n t d e t e c t e d by the r e c e i v e r s arrival  velocities,  (see F i g u r e 2 . 6 a ) . The r e l a t i o n s h i p between the  time and the o f f s e t d i s t a n c e o f the r e c e i v e r from the source  i n d i c a t e s l a y e r v e l o c i t i e s and t h i c k n e s s e s as shown i n F i g u r e I f compression wave v e l o c i t i e s  2.6a.  are d e s i r e d , then v e r t i c a l  used and sources which emit s t r o n g P-waves, used.  and  receivers  such as e x p l o s i v e s o u r c e s ,  I f shear wave v e l o c i t i e s are d e s i r e d , then h o r i z o n t a l  receivers  are  are are  used and sources which emit predominantly shear waves, such as a hammer and weighted plank s o u r c e , are u s e d . The c r o s s h o l e method, i l l u s t r a t e d i n F i g u r e 2 . 6 b ,  c o n s i s t s of  several  b o r e h o l e s i n which r e c e i v e r s are p l a c e d a t the same e l e v a t i o n . Another borehole i s d r i l l e d f o r the s o u r c e . When the source i s a t the same e l e v a t i o n as the r e c e i v e r s , i t  i s a c t i v a t e d and the time f o r the body waves t o  between the source and r e c e i v e r s i s r e c o r d e d . Knowing t h i s t r a v e l the t r a v e l  d i s t a n c e s , the v e l o c i t y o f the l a y e r can be determined.  procedure i s repeated at s u c c e s s i v e depths t o o b t a i n a v e l o c i t y  travel  time and This  profile.  TIME  [msec!  ~m^~-— T-  Gf  r- R t c a i v t r iBorehoto  12II ( 3 . 7 m l — 4 — 1 2 I I ( 3 . 7 m ) — 4 — 7 1 1 (2.1 m ) - ^  0 . - P L A H VIEW  Vertical Velocity  a-PLAN VIEW  i x  |COl  -Vtrlicol  r£o2  .  .x  OFFSET  (ra]  GEOPHONE  SOURCE  T  ^-3-0 Velocity |N Transducer Wedged m Pk>ct  w^V^^,,...  1  .i/C. (Not lo S c o n ) (Not lo S c o l a )  v*!  cSOOm/sec,  vjsZv^,  V3 = 3 v i ,  hi  =7.5rn,  = 2hi  b.-CROSS-SECTIONAL b.-CROSS-SECTIONAL  s)  Three-ltyer r t f r t c t l o n  time/distance »nd n y path d i i g r u  (from Borm,1977)  b)  VIEW  VIEW  Crosshole  seismic  method.  (from Stokoe and Hoar,1977)  c) Downhole seismic method. (from Stokoe and Hoar,1977)  F i g u r e 2.6 Conventional In S i t u Methods f o r S e i s m i c Measurement  For compression wave v e l o c i t i e s ,  e x p l o s i v e s o u r c e s are u s e d ,  p o s s i b l e , because they generate s h a r p e r , l a r g e r i n i t i a l mechanical  sources are a l s o used i f  the t r a v e l  P-waves.  if However,  path between source and  receiver i s relatively  s h o r t (Stokoe and Hoar, 1 9 7 8 ) . F o r shear wave  v e l o c i t i e s , mechanical  sources are g e n e r a l l y u s e d . These sources can be  impulse sources or t o r s i o n a l  sources and are g e n e r a l l y r e v e r s i b l e so t h a t  p o l a r i z a t i o n of the shear wave can be o b t a i n e d . The down-hole method, i l l u s t r a t e d i n F i g u r e 2 . 6 c ,  c o n s i s t s of a s i n g l e  borehole with the r e c e i v e r i n the b o r e h o l e and the source a t the s u r f a c e a s h o r t d i s t a n c e from the b o r e h o l e . When the r e c e i v e r i s a t the t e s t depth, source i s a c t i v a t e d , and the a r r i v a l  the  time o f the body waves i s r e c o r d e d . The  r e c e i v e r i s moved t o the next t e s t d e p t h , and the procedure i s r e p e a t e d . The pseudo i n t e r v a l  technique,  described in Section 2.3.2,  i s g e n e r a l l y used t o  determine s e i s m i c wave v e l o c i t i e s . The s e i s m i c cone p e n e t r a t i o n described in t h i s thesis i s ,  essentially,  For compression wave v e l o c i t i e s  test  a downhole s e i s m i c t e s t method.  determined from the downhole t e s t ,  the  same type o f sources are used as f o r the c r o s s h o l e method. For shear wave v e l o c i t i e s , a r e v e r s i b l e , m e c h a n i c a l , impulse source i s g e n e r a l l y u s e d , such as a hammer and weighted  plank.  Generally a t r i a x i a l  package o f r e c e i v e r s i s used f o r both the c r o s s h o l e  and downhole methods. In the c r o s s h o l e method, a v e r t i c a l  r e c e i v e r i s used t o  d e t e c t shear waves from an impulse source such as t h a t shown i n F i g u r e A transverse horizontal  r e c e i v e r i s used f o r a t o r s i o n a l  source.  Horizontal  r e c e i v e r s are used f o r the hammer and weighted plank source used f o r downhole method. G e n e r a l l y , both methods.  P-waves a r e d e t e c t e d on v e r t i c a l  2.6b.  the  receivers  for  16 3. EQUIPMENT AND PROCEDURES  3.1  Introduction  This chapter w i l l  o u t l i n e and d e s c r i b e the equipment and procedures used  f o r t h i s t h e s i s . The c h a p t e r w i l l  begin w i t h a d e s c r i p t i o n o f the  cone, i n c l u d i n g i t s c a p a b i l i t i e s as a s t a n d a r d cone f o r cone tests,  and i t s a d d i t i o n a l  capabilities  U.B.C.  In S i t u T e s t i n g v e h i c l e w i l l  The f o l l o w i n g s e c t i o n s w i l l  seismic  penetration  f o r d e t e c t i n g s e i s m i c waves. The  then be b r i e f l y  go on t o d e s c r i b e ,  described. sequentially,  the  equipment i n v o l v e d i n the s e i s m i c t e s t i n g , i n c l u d i n g the s e i s m i c s o u r c e s , t r i g g e r s f o r the r e c o r d i n g i n s t r u m e n t s , r e c o r d i n g instruments The f i n a l  the s e i s m i c wave d e t e c t o r s ,  and the  themselves.  section will  outline typical  f i e l d t e s t i n g procedures.  the r a t i o n a l e behind the procedures and the m o d i f i c a t i o n s procedures w i l l  the  t o the  Both  initial  be d i s c u s s e d when n e c e s s a r y .  3.2 The Seismic Cone Penetrometer  The s e i s m i c cone penetrometers used f o r t h i s study had e i t h e r a 15 s q . cm o r a 10 s q . cm base a r e a . These cones a r e d e p i c t e d i n F i g u r e 3.1 and 3 . 2 . A l l UBC cones are capable o f measuring b e a r i n g r e s i s t a n c e ,  friction  r e s i s t a n c e , and pore p r e s s u r e , i n a d d i t i o n t o temperature and i n c l i n a t i o n . These c a p a b i l i t i e s are d e s c r i b e d i n f u l l  detail  i n Campanella and Robertson  (1981). The 15 s q . cm s e i s m i c cone was i n s t r u m e n t e d w i t h a t r i a x i a l s e i s m i c wave r e c e i v e r s . These r e c e i v e r s were e i t h e r geophones  package  of  or  a c c e l e r o m e t e r s . The two o t h e r s e i s m i c cones used (denoted UBC#6 and UBC#8) were 10 s q . cm c o n e s , and each was i n s t r u m e n t e d w i t h a s i n g l e ,  horizontally  17 To  16 c o n d u c t o r c a b l e  amplifier  board  1  - t r i a x i a l geophone or a c c e l e r o m e t e r package ( i n s t a l l e d at d i f f e r e n t times)  -slope  sensor  •Quad r i n g  2 q u a l end a r e a f r i c t i o n sleeve ( 225 sq. cm area)  s t r a i n gages f o r f r i c t i o n load c e l l  ft pressure  transducer -  porous p l a s t i c -  small  F i g u r e 3.1  cavity-  • s t r a i n gages f o r cone bearing load c e l l  -rxngs -Quad r i n g -60* cone 43.7 mm  15 sq. cm S e i s m i c Cone Penetrometer  O.D.  -•wage fitting to lock 14 c o n d u c t o r c a b l e  wires s p l i c e d to c a b l e Inside tube  - seismometer  -•lope sensor  -Quad ring  strain gages f o r friction load cell  -equal end area friction sleeve ( 1 5 0 c m ' area)  temperature sensor -  pressure transducer -  -•train gages for cone bearing load cell  -O-rlngs -Quad ring porous plastic -  •mall cavity —'  F i g u r e 3.2  60'cone 35.68mm O.D.  10 s q . cm S e i s m i c  Cone Penetrometer  19 oriented,  s e i s m i c wave r e c e i v e r . The UBC#6 cone was Instrumented w i t h a  geophone, and the UBC#8 cone with an a c c e l e r o m e t e r . The cones were connected to the s u r f a c e w i t h a 16 c o n d u c t o r  carrier  c a b l e which was threaded through one meter l e n g t h s o f s t a n d a r d 20T Dutch cone r o d s . The conductor c a b l e f e d the analog data i n t o a data a q u i s i t i o n manufactured by Hogentogler & C o . I n c . and m o d i f i e d a t U . B . C . The  system  signals  from the cone were a m p l i f i e d i n the cone, but d i g i t i z a t i o n o f the b e a r i n g , friction,  and pore p r e s s u r e was done a t the s u r f a c e by the Hogentogler  data  a q u i s i t i o n system. F o r the 15 s q . cm cone instrumented w i t h a c c e l e r o m e t e r s ,  the  amplifiers  f o r the temperature and i n c l i n a t i o n were used i n the cone to a m p l i f y  the  a c c e l e r o m e t e r o u t p u t . The a c c e l e r o m e t e r output was not d i g i t i z e d by the Hogentogler data a q u i s t i o n system, but came out o f the system as an analog signal  which went i n t o a r e c o r d i n g o s c i l l o s c o p e  The cone was advanced i n t o the s o i l vehicle  ( t r u c k ) . The t r u c k  (see S e c t i o n 3 . 4 . 5 ) .  u s i n g the U . B . C .  In S i t u  Testing  shown i n F i g u r e 3.3 weighs approximately  11 t o n s ,  and has two h y d r a u l i c c y l i n d e r s with which the cone i s pushed i n t o the To p r o v i d e the r e a c t i o n f o r c e needed t o push the c o n e , the t r u c k two h y d r a u l i c pads as shown i n the f i g u r e . F u r t h e r d e t a i l s  soil.  i s r a i s e d on  about the  design  o f the t r u c k are g i v e n i n Campanella and Robertson ( 1 9 8 1 ) .  3.3 S e i s m i c Wave Sources and R e l a t e d T r i g g e r i n g Systems  3.3.1  Introduction Several  d i f f e r e n t types o f sources were I n v e s t i g a t e d f o r t h i s s t u d y .  s o u r c e s can be d i v i d e d i n t o three c a t e g o r i e s : mechanical e x p l o s i v e s o u r c e s , and o f f - s h o r e e x p l o s i v e s o u r c e s .  sources,  discussed.  on-shore  In the f o l l o w i n g  these t h r e e c a t e g o r i e s and t h e i r r e l a t e d t r i g g e r i n g systems w i l l  The  be  sections  20  F i g u r e 3.3  CPT S e i s m i c Equipment Layout f o r Mechanical Sources (after Rice,  1984)  21 The reason f o r I n v e s t i g a t i n g d i f f e r e n t e x p l o s i v e sources o f waves stems from the a p p l i c a t i o n of the cone t o o f f - s h o r e  seismic  investigations.  E x p l o s i v e sources are used o f f - s h o r e t o a v o i d employing a c o s t l y  mechanical  seabed d e v i c e . The e x p l o s i v e s o u r c e s used o n - s h o r e were researched f o r two reasons. F i r s t ,  f a m i l i a r i t y with i n t e r p r e t i n g e x p l o s i v e sources was d e s i r e d  b e f o r e o f f - s h o r e work was u n d e r t a k e n . Second, because e x p l o s i v e sources  input  a l a r g e r amount o f energy i n t o the g r o u n d , the use o f these sources f o r deep on-shore cone work was i n v e s t i g a t e d . 3 . 3 . 2 Mechanical  Sources  For t h i s s t u d y , the g e n e r a t i o n o f both P and S waves was d e s i r e d . As d i s c u s s e d i n Chapter 2, compression wave s o u r c e s a l s o generate shear waves. The a r r i v a l  o f the shear wave from t h i s t y p e o f source i s o f t e n d i f f i c u l t  i n t e r p r e t because o f the a d d i t i o n of the two wave t y p e s . Thus, t o accurate a r r i v a l  time e s t i m a t e s , two d i f f e r e n t mechanical  - one t o generate SH-waves, and one t o g e n e r a t e A good mechanical with l i t t l e  to  allow  sources were  tried  P-waves.  source f o r g e n e r a t i n g l a r g e amplitude shear (SH) waves  or no compressional wave component c o n s i s t s o f a plank  weighted  to the ground and impacted on one end (Mooney, 1 9 7 4 ) . T h i s type o f mechanical shear source (hammer shear source) was used f o r t h i s  study.  The r e a r h y d r a u l i c pad o f the UBC In S i t u T e s t i n g v e h i c l e was used as the weighted plank f o r the hammer shear s o u r c e  (see F i g u r e 3 . 3 ) . S i n c e the  t r u c k i s r a i s e d on i t s two h y d r a u l i c pads d u r i n g t e s t i n g , the pads are  in  good mechanical c o n t a c t with the ground. To p r e v e n t damage t o the pads,  one  i n c h t h i c k metal  pad.  p l a t e s were welded onto the ends o f the r e a r h y d r a u l i c  These p l a t e s were struck h o r i z o n t a l l y w i t h a 7 kg s l e d g e hammer. P o l a r i z e d shear waves were e a s i l y generated by s t r i k i n g o p p o s i t e ends o f the pad. The use o f the r e a r pad e l i m i n a t e d the n e c e s s i t y o f h a v i n g a second v e h i c l e on  22 s i t e t o weigh down a p l a n k . A s i m i l a r system, u s i n g the r e a r h y d r a u l i c pad o f the t r u c k and a s l e d g e hammer, was used to generate P-waves. A s t e e l  plate,  2.5 cm t h i c k ,  wide and 1.2 m l o n g , was p l a c e d p a r t way under one s i d e o f the r e a r pad and the pad was lowered on top o f i t  0.45 m hydraulic  (see F i g u r e 3 . 3 ) . Approximately  0.5  meters o f the p l a t e p r o t r u d e d out beyond the end of the pad and t h i s was s t r u c k w i t h a blow, d i r e c t e d v e r t i c a l l y  downward, from the 7 kg sledge  hammer. The r e s u l t s o b t a i n e d from these mechanical  sources w i l l  be d i s c u s s e d  in  Chapter 5 . 3.3.3  T r i g g e r i n g System f o r the Mechanical An a c c u r a t e ,  reliable  Different triggers U.B.C.  trigger is essential  f o r the mechanical  for.any  seismic t e s t i n g .  source used i n c o n j u n c t i o n w i t h the  s e i s m i c cone have been i n v e s t i g a t e d p r e v i o u s l y by Rice  found an e l e c t r i c a l  step t r i g g e r ,  ( 1 9 8 4 ) . Rice  recommended by Hoar and Stokoe (1978) t o be  the most a c c u r a t e . The t r i g g e r c i r c u i t signal  Sources  i s shown i n F i g u r e 3 . 4 .  I t has a  r i s e time o f l e s s than 1 m i c r o s e c o n d .  3 . 3 . 4 On-Shore E x p l o s i v e  Source  The on-shore e x p l o s i v e source used f o r t h i s study was a " B u f f a l o gun" o r i g i n a l l y designed by the G e o l o g i c a l  Survey o f Canada f o r  s u r f a c e s e i s m i c surveys ( P u l l a n and MacAulay,  engineering  1984). The 12-gauge B u f f a l o  gun  c o n s i s t s o f a 1.0 t o 1.5 meter l e n g t h o f s t a n d a r d 3/4 i n c h water pipe and f i t t i n g s as shown i n F i g u r e 3 . 5 a . Winchester 12-gauge AA T r a p l o a d s h e l l s  with  a 7/8 o z . l o a d were u s e d . The s h e l l s f i t t e d snugly between the n i p p l e and the c o u p l e r and d i d not move when the shot was f i r e d . A handle was a t t a c h e d  to  the top o f the pipe as shown, t o a i d i n p l a c i n g the gun 1n the ground. A 1 1/4 i n c h diameter auger was used t o d r i l l  a h o l e f o r the  gun. The gun was then lowered i n t o t h i s h o l e , w i t h the s h e l l  Buffalo  end down,  until  23 Volts  = 6V R i s e Time =0.1 us Hammer Impulse .Time 1=1.1(R)(C) a) T r i g g e r  Signal  A 5 - 14 V o l t s D.C.  LM555 I.C  to o c i l l o s c o p e t r i g g e r input  b) C i r c u i t Diagram  Figure  3.4  E l e c t r i c a l Step T r i g g e r C i r c u i t  f o r Hammer Source  r^n ci m S T E E L DROP ROD  ~ m r>—PND CAP  ^TEE^^NIPPLE  Drop Rod  —  Buffalo  3/4" PIPE  Trigger and F l a n g e  Prebored Hole \ ^ FIRING  PIN  Q*-N  12 G A U G E  SHELL  Shell  Ready to F i r e a) Schematic of B u f f a l o  Figure  b) O p e r a t i o n o f B u f f a l o  Gun  (from P u l l a n and MacAulay,  Detonated Gun  1984)  3.5 B u f f a l o Gun and i t s O p e r a t i o n  ro  I t was f i r m l y  s e a t e d p a s t the end o f the augered hole  ( g e n e r a l l y , 0.75 meters  d e e p ) . The f i r i n g rod ( o r drop r o d ) , with p i n end down, was then lowered down the c e n t e r o f the gun u n t i l  i t was approximately 0.3 meters above the  The f i r i n g rod was then r e l e a s e d and the s h e l l  shell.  detonated (see F i g u r e 3 . 5 b ) .  A f t e r the s h e l l was d e t o n a t e d , the gun was p u l l e d out o f the ground, and r e l o a d e d , a new h o l e was dug, and the procedure r e p e a t e d with the cone a t next t e s t d e p t h . R e s u l t s o b t a i n e d from t h i s source w i l l  the  be d i s c u s s e d i n  Chapter 5 . 3.3.5  T r i g g e r i n g System f o r the On-Shore E x p l o s i v e  Source  Two t r i g g e r i n g systems were used w i t h the B u f f a l o gun. The f i r s t  system  c o n s i s t e d o f a geophone. The second system c o n s i s t e d o f a hammer s w i t c h . These systems w i l l  be d e s c r i b e d below.  A geophone, i d e n t i c a l  t o those d e s c r i b e d i n d e t a i l  in Section  3.4.2  below, was used t o t r i g g e r the r e c o r d i n g i n s t r u m e n t s . The geophone was o r i g i n a l l y a t t a c h e d t o the gun u s i n g a hose clamp (see F i g u r e 3 . 6 a ) .  This  method f o r a t t a c h i n g the geophone was found t o be inadequate because  the  l e a d s coming from the geophone were not rugged enough t o be exposed i n  this  manner. The geophone was then mounted on a f l a n g e t h a t was a t t a c h e d t o the rods (see F i g u r e 3 . 6 b ) . T h i s f l a n g e was dual mount f o r the geophone, and second, i t  purpose. F i r s t ,  it  served as a  prevented any d e b r i s from s h o o t i n g out  o f the h o l e and i n j u r i n g the o p e r a t o r when the s h e l l  was d e t o n a t e d . The  f l a n g e was r i g i d l y a t t a c h e d t o the gun w i t h a s e t - s c r e w as shown i n 3.6b and t h i s p r o v i d e d good mechanical  coupling  Figure  between the gun and the  geophone. The geophone i t s e l f was e x c i t e d by the compression wave t r a v e l l i n g back up the gun a f t e r the s h e l l  e x p l o d e d . T h i s compression wave t r a v e l l e d up the  gun a t a speed of approximately 5100 meters per s e c o n d , p r o v i d i n g a f a i r l y  Buffalo  Gun  Geophone Hose Clamp  a)Geophone w i t h Hose Clamp  Buffalo  Gun .Geophone Case  Set  Screw— Flange  c  ' O I—'*• i  -Geophone i n Case  I.L  b; Geophone w i t h F l a n g e  Figure  3.6  T r i g g e r i n g Systems f o r B u f f a l o Gun  Source  consistent trigger  (see F i g u r e 3 . 7 ) . P r e t r i g g e r i n g d i d o c c u r however, when  the f i r i n g rod was lowered i n t o the gun, o r when the f i r i n g rod was through the gun b e f o r e i t  h i t and detonated the s h e l l .  The  falling  first  p r e t r i g g e r i n g problem was e a s i l y remedied. The gun o p e r a t o r would simply check w i t h the r e c o r d i n g o p e r a t o r to ensure the t r i g g e r was ready b e f o r e dropping the f i r i n g p i n the f i n a l  0.3 m and d e t o n a t i n g the s h e l l .  The second  p r e t r i g g e r i n g problem was mostly overcome by d e c r e a s i n g the s e n s i t i v i t y the t r i g g e r  of  circuit.  The second system c o n s i s t e d o f a hammer s w i t c h manufactured by EG & G G e o m e t r i e s . The hammer switch was a c t i v a t e d by the compression wave t r a v e l l i n g up the gun a f t e r the s h e l l  e x p l o d e d . The s w i t c h c i r c u i t r y  created  a s t e p - l i k e i n c r e a s e i n v o l t a g e over a p e r i o d o f l e s s than one m i c r o s e c o n d , but a d e l a y o c c u r r e d between the d e t o n a t i o n o f the shotgun s h e l l t r i g g e r i n g o f the r e c o r d i n g i n s t r u m e n t . T h i s d e l a y was v a r i a b l e Thus, t h i s t r i g g e r was found t o be i n a d e q u a t e . with the hammer shear source and found i t 3.3.6  Off-Shore Explosive  Rice  and the and unknown.  (1984) used t h i s  trigger  inconsistent.  Sources  The e x p l o s i v e sources used f o r t h i s study were S e i s m l c a p Mark II c a p s , which were detonated with a Geometrix b l a s t e r  seismic  box.  The s e i s m i c caps were used i n a v a r i e t y o f ways 1n an attempt  to  generate a wave t r a i n from which both P and S waves c o u l d be e a s i l y i n t e r p r e t e d . The s e i s m i c caps were i n i t i a l l y Next, they  lowered t o tnudline and f i r e d .  were lowered to a p o s i t i o n j u s t below the i c e and f i r e d  S e c t i o n 4.2 f o r s i t e d e s c r i p t i o n ) . When f i r e d j u s t below the i c e ,  (see  the  caps were e i t h e r weighted w i t h a c h a i n o r a t t a c h e d t o a p o l e o f f i x e d  seismic length  b e f o r e b e i n g l o w e r e d . T h i r d , the s e i s m i c caps were f i x e d t o the s i d e o f a b l a d e and t h i s b l a d e was subsequently embedded i n the sea f l o o r with the s e i s m i c cap f a c i n g away from the cone and r o d s . Once the b l a d e was embedded,  111 ^ Time of Detonation-  V Response of G e o p h o n e — T r i g g e r to B u f f a l o Gun Source  \  McDonalds Farm -30  •20  •10  0 Time  F i g u r e 3.7  10  i  i  20  30  (milliseconds)  Geophone T r i g g e r Response to B u f f a l o Gun  Source  40  29 the s e i s m i c cap was d e t o n a t e d . F i g u r e 3.8 i l l u s t r a t e s  the d i f f e r e n t  seismic  cap s o u r c e s . R e s u l t s o b t a i n e d from these s o u r c e s w i l l  be d i s c u s s e d i n  Chapter 5 . 3.3.7  T r i g g e r i n g System f o r the O f f - S h o r e E x p l o s i v e  Sources  The Geometrix b l a s t e r box was used t o t r i g g e r the r e c o r d i n g  instrument.  The b l a s t e r box detonated the s e i s m i c cap by sending a 5 V o l t s t e p s i g n a l the c a p . T h i s same 5 V o l t  step s i g n a l  was used t o t r i g g e r the  i n s t r u m e n t . The r i s e time f o r the s t e p s i g n a l  to  recording  was much l e s s than 10  m i c r o s e c o n d s . T h i s t r i g g e r i n g system was found t o be v e r y r e l i a b l e  and  accurate.  3.4 Seismic Wave D e t e c t i o n and Recording  3.4.1  Introduction Two d i f f e r e n t types o f t r a n s d u c e r s were used f o r t h i s t h e s i s t o  s e i s m i c waves - geophones and a c c e l e r o m e t e r s .  Geophones are  detect  velocity  t r a n s d u c e r s and a c c e l e r o m e t e r s are a c c e l e r a t i o n t r a n s d u c e r s . The theory d e s c r i b i n g how the t r a n s d u c e r s work i s , of t h i s t h e o r y  however, the same and a b r i e f  review  follows.  Both v e l o c i t y  and a c c e l e r a t i o n t r a n s d u c e r s can be modelled by the mass-  s p r i n g system i l l u s t r a t e d  in Figure 3 . 9 .  (The system may o r may not be  damped). The mass 1s a t t a c h e d t o the t r a n s d u c e r case by the s p r i n g . The t r a n s d u c e r case moves w i t h the s t r u c t u r e t o which i t  i s a t t a c h e d and motion  1s i n f e r r e d by the r e l a t i v e motion between the mass and the c a s e . The t r a n s d u c e r s c o n v e r t t h i s mechanical motion i n t o an e l e c t r i c a l can be I n t e r p r e t e d by the e l e c t r i c a l Depending on the n a t u r a l  recording  signal  which  instrument.  frequency o f the m a s s - s p r i n g system and the  frequency o f the e x c i t a t i o n s i g n a l , the r e l a t i v e motion between the mass and  To In s i t u T e s t i n g  Figure  3.8  Vehicle  O p e r a t i o n of S e i s m i c Cap  Source  31  t r a n s d u c e r case.  spring  r e l a t i v e motion between mass and case 'motion to be measured  mass  v i s c o u s damper  „  /;///////;///  MOVING PART  F i g u r e 3.9 Schematic o f M a s s - s p r i n g Transducer  Type o f V i b r a t i o n - m e a s u r i n g  the s t r u c t u r e w i l l  be p r o p o r t i o n a l  a c c e l e r a t i o n . The undamped n a t u r a l  to e i t h e r d i s p l a c e m e n t ,  velocity  or  frequency o f a system i s g i v e n by:  2 UJ  = (k/m)  where w=the n a t u r a l k=the s p r i n g  frequency stiffness  and m=the mass. Systems w i t h a low n a t u r a l  frequency w i t h r e s p e c t t o the e x c i t a t i o n  (low s p r i n g s t i f f n e s s and high mass), a high natural  are v e l o c i t y  This section will  required w i l l  (high s p r i n g  d e s c r i b e the geophones and a c c e l e r o m e t e r s used f o r i n c l u d e d where n e c e s s a r y . The  a l s o be o u t l i n e d and the p e r t i n e n t i n f o r m a t i o n  the r e c o r d i n g o s c i l l o s c o p e 3.4.2  signal  transducers.  t h i s t h e s i s . F u r t h e r t r a n s d u c e r theory w i l l . b e filtering  t r a n s d u c e r s . Systems w i t h  frequency w i t h r e s p e c t to the e x c i t a t i o n  s t i f f n e s s and low mass), are a c c e l e r a t i o n  signal  about  reviewed.  Geophones Geophones were i n s t a l l e d i n both the 10 and 15 s q . cm c o n e s . The 15 s q .  cm cone was instrumented w i t h a t r i a x i a l  package o f geophones, w h i l e the 10  s q . cm cone (UBC#6) had a s i n g l e h o r i z o n t a l  geophone. The o r i e n t a t i o n o f  this  geophone was marked on the o u t s i d e o f the UBC#6 c o n e , and a s i m i l a r marking was made f o r one o f the h o r i z o n t a l  geophones i n the 15 s q . cm c o n e . The  purpose o f these markings was t o enable the geophone to be f a v o u r a b l y o r i e n t e d f o r a d i r e c t e d shear wave s o u r c e . The geophones c o n s i s t e d of a permanent magnet w i t h a w i r e c o i l from l e a f  s p r i n g s as shown i n F i g u r e 3 . 1 0 . An e l e c t r i c c u r r e n t i s  i n the c o i l  the l e a f  generated  when r e l a t i v e movement e x i s t s between the magnet and the  Thus, the magnet i s a c t i n g as the t r a n s d u c e r c a s e , the c o i l  i n the c o i l  coll.  as the mass, and  s p r i n g as the s p r i n g d e s c r i b e d i n t h e m a s s - s p r i n g system o f  3 . 4 . 1 . The output v o l t a g e c r e a t e d by the c u r r e n t  suspended  Is  Section  directly  33  F i g u r e 3.10  Schematic of Geophone  proportional  t o the s o i l  particle  velocity.  The geophones were GSC-14-L3 m i n i a t u r e v e l o c i t y by Geospace C o r p o r a t i o n . The m a n u f a c t u r e r ' s  transducers  specifications  manufactured  are shown i n  F i g u r e 3 . 1 1 . The geophones were 1.7 cm i n d i a m e t e r , 2.0 cm h i g h , and weighed 19 grams. T h e i r n a t u r a l  frequency was a p p r o x i m a t e l y 28 Hz. They were s m a l l ,  rugged and operated i n any o r i e n t a t i o n . A m p l i f i c a t i o n of the geophone was not necessary f o r shallow o n - s h o r e t e s t i n g . However, f o r t e s t i n g the geophone s i g n a l  signal  off-shore  was a m p l i f i e d a t the s u r f a c e i n some c a s e s . The  a m p l i f i e r used was the model AD521 manufactured by Analog D e v i c e s . The response o f the geophones w i l l 3.4.3  be d i s c u s s e d i n  Chapter 6 .  Accelerometers  A c c e l e r o m e t e r s were i n s t a l l e d i n both 10 and 15 s q . cm c o n e s . Geophones and a c c e l e r o m e t e r s were i n s t a l l e d a t d i f f e r e n t times i n the 15 s q . cm c o n e . The 10 s q . cm cone (UBC#8) had a s i n g l e , h o r i z o n t a l l y As mentioned above, the o r i e n t a t i o n o f  the h o r i z o n t a l  oriented  accelerometer.  a c c e l e r o m e t e r s was  marked on the o u t s i d e o f the cone so t h a t the a c c e l e r o m e t e r c o u l d be f a v o u r a b l y o r i e n t e d . D u r i n g most o f the r e s e a r c h , o n l y the marked h o r i z o n t a l and the v e r t i c a l  a c c e l e r o m e t e r s i n the 15 s q . cm. cone were c o n n e c t e d ,  because o n l y two a m p l i f i e r s were a v a i l a b a l e . A m p l i f i e r s were necessary reasons o u t l i n e d  for  below.  The a c c e l e r o m e t e r s used f o r t h i s study were o f the s t r a i n gage type shown i n F i g u r e 3 . 1 2 . The a c c e l e r o m e t e r s were model TGY-155-10 manufactured by K u l i t e Semiconductor P r o d u c t s I n c . The n a t u r a l  frequency o f  the  a c c e l e r o m e t e r s was a p p r o x i m a t e l y 550 Hz. The theory f o r the m a s s - s p r i n g t r a n s d u c e r can be a p p l i e d t o the s t r a i n gage t r a n s d u c e r . The w i r e s o f s t r a i n gage a r e e l o n g a t e d or r e l a x e d i n response t o the r e l a t i v e  the  displacement  between the w i r e and the t r a n s d u c e r c a s e . As the w i r e changes l e n g t h ,  the  GSC-1U-L3 SEISMOMETER The GSC-Ht-13 Is a very small, extremely rugged seismometer. It Is designed • nd built to maintain performance characteristics even after being subjected to high shock forces. Principal applications Include intrusion detection, military use and vibration monitoring. Standard natural frequency Is 28 Hz, with t i l t angle of operation up to 180°. SPECIFICATIONS Standard Natural Frequency  28 Hz t 5 Hz  Standard Coll Resistance P 25°C  570 Ohms t 5%  Intrinsic Voltage  .29 V/in/sec t 15%  Sensitivity  .012 / T c " (V/ In/ sec)  Normalized Transduction Constant T i l t Angle of Operation  180°  Open Circuit Damping  18 of C r i t i c a l 1 .04  Moving Mass  2.15 g  -30°F to +160°F  Operating Temperature Dimensions: Diameter  .66 in (1.7 cm)  Height  .70 In (1.8 cm)  Height With Terminals  .80 In (2.0 cm)  Weight  19 9 20  21  SO  40  ISO  SO CO  200 250 3O0  DAM PMC  SHUNT  l*%l  _0_PEN  .30 .25  4QQ SOO  laooo.  I30-J  9200, .19  .12}  3 O  l_J_J|_S SEISMIC OSO  1  .040  !  .OJO  .on  1  1 •  10  IS  1  20  FREQUENCY (Hi)  1  ) e=_)l_r—  01: T E C T O R OUT PUT VS  RESPONSE FREOUENCY  CURVE  0SC-I4 L3 DE TECTON. HOOEL TYPE NATU »»L UNDAMPED FREQUENCY 2> HI STO OMUS A T 2 5* C COIL RESISTANCE Heir Ifktil ivllr 7» V/IN/SEC 1* X OF CNITICAL OPEN CIOCUIT OAMPING  23 30  F i g u r e 3.11 Geophone S p e c i f i c a t i o n s  ( a f t e r Geo Space Corp.)  36  resistors  v i s c o u s damper Ar = change i n resistance « 6  6 = r e l a t i v e motion between mass and case t r a n s d u c e r case  resistors  F i g u r e 3.12  Schematic o f S t r a i n - g a g e A c c e l e r o m e t e r  r e s i s t a n c e o f the w i r e changes. The change 1n r e s i s t a n c e i s p r o p o r t i o n a l the s o i l  particle  to  acceleration.  The change i n r e s i s t a n c e o f the s t r a i n gage w i r e 1s i n v e r s e l y proportional  t o the square of the n a t u r a l  f r e q u e n c y . S i n c e the  natural  frequency o f the a c c e l e r o m e t e r s i s h i g h , the change i n r e s i s t a n c e upon e x c i t a t i o n i s v e r y small signal  must be a m p l i f i e d .  unamplifled signal  and the output s i g n a l  i s very s m a l l . Thus the  output  The d i f f e r e n c e between the a m p l i f i e d and  i s shown i n F i g u r e 3 . 1 3 . A m p l i f i c a t i o n o f  a c c e l e r o m e t e r s i g n a l s was done u s i n g AD522 p r e c i s i o n IC  the  instrumentation  a m p l i f i e r s , manufactured by Analog D e v i c e s . Because the n a t u r a l frequency s i g n a l s w i l l a considerable  frequency o f the a c c e l e r o m e t e r i s h i g h ,  cause the a c c e l e r o m e t e r to r e s o n a t e . I t was found  f i l t e r i n g o f the s i g n a l  i n the f o l l o w i n g  difficult.  Signal  In o r d e r t o reduce  was employed. T h i s f i l t e r i n g w i l l  this  be d e s c r i b e d  section.  The response o f the a c c e l e r o m e t e r w i l l 3.4.4  that  amount o f high frequency n o i s e was accompanying the wave  s i g n a l . T h i s n o i s e made i n t e r p r e t a t i o n noise,  high  be d i s c u s s e d i n Chapter  6.  Filtering  Although s i g n a l  filtering  velocity investigations,  i s not recommended t o be used f o r s e i s m i c wave  (Stokoe and Hoar,  1977), f i l t e r i n g o f  the  a c c e l e r o m e t e r s i g n a l s was n e c e s s a r y f o r i n t e r p r e t a t i o n . F i l t e r e d and u n f i l t e r e d a c c e l e r o m e t e r responses t o the mechanical in Figure  hammer source are shown  3.14.  One of the reasons s i g n a l  filtering  i s not recommended, 1s because  f i l t e r i n g causes a phase s h i f t . A phase s h i f t 1s a s h i f t 1n time o f output s i g n a l  the  w i t h r e s p e c t to the Input s i g n a l . The amount o f phase s h i f t due  to f i l t e r i n g depends on the frequency o f the i n p u t s i g n a l , the frequency o f the f i l t e r ,  and the f i l t e r  characteristics.  cut-off  +.025.  )»—WWNAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA -.025.  Unamplified  + +1.0-  Response  +  ,1  \A AAAAAAA A % l i r -1.0.  McDonalds Farm Depth 2.0 meters U n f i l t e r e d Responses  ill!'  Amplified . .i  10  20  30 Time  Figure  3.13  Unamplified  40  50  60  Response i  70  80  (milliseconds)  and A m p l i f i e d  A c c e l e r o m e t e r Responses  CO CO  F i l t e r e d Signal Low pass f i l t e r w i t h 300 Hz c u t - o f f frequency  •Unfiltered  20  40  80  60 Time  F i g u r e 3.14  100  120  140  Signal  -4 McDonalds Farm Depth = 8.0 m A m p l i f i e d Response  160  (milliseconds)  F i l t e r e d and U n f i l t e r e d A c c e l e r o m e t e r  Responses  CO  40 D i f f e r e n t analog f i l t e r s were used on and o f f - s h o r e . The f i l t e r shore was the model 1022F Dual Hi/Lo f i l t e r , Laboratories, a signal  manufactured by Rockland  I n c . A low-pass f i l t e r was u s e d . T h i s means a l l  p a s s i n g through the f i l t e r  above a s e t c u t - o f f  a t t e n u a t e d by the f i l t e r ,  but a l l  passed through the f i l t e r  unattenuated.  frequency  are shown i n  f r e q u e n c i e s was t r i e d w i t h  this  and the r e s u l t s a r e shown i n F i g u r e 3 . 1 6 . The phase s h i f t caused by  the d i f f e r e n t c u t - o f f off  of  frequency were  The a t t e n u a t i o n c h a r a c t e r i s t i c s o f the o n - s h o r e f i l t e r  filter  frequencies  f r e q u e n c i e s below the s e t c u t - o f f  F i g u r e 3 . 1 5 . A range o f d i f f e r e n t c u t - o f f  used on-  f r e q u e n c i e s can be c l e a r l y  seen i n t h i s  figure. A cut-  frequency o f 100 Hz was used f o r most of the data c o l l e c t i o n . The f i l t e r  used o f f - s h o r e was the model 2B31J manufactured by Analog  D e v i c e s . The c u t - o f f  frequency o f t h i s f i l t e r was 100 Hz. The  c h a r a c t e r i s t i c s of t h i s  filter  attenuation  are a l s o shown i n F i g u r e 3 . 1 5 . As can be seen  i n the f i g u r e , the a t t e n u a t i o n c h a r a c t e r i s t i c s o f the o f f - s h o r e f i l t e r s m a l l e r than those o f the o n - s h o r e f i l t e r .  In f a c t ,  a t t e n u a t e d high frequency amplitudes by only h a l f filter.  the o f f - s h o r e  were  filter  as much as the o n - s h o r e  The r e s u l t s o b t a i n e d by the two d i f f e r e n t f i l t e r s w i l l  be d i s c u s s e d  i n Chapters 5 and 6. The a c c e l e r o m e t e r response can a l s o be d i g i t a l l y  filtered.  Digital  f i l t e r i n g i n v o l v e s t r a n s f o r m i n g the d i g i t i z e d response from the time domain t o the frequency domain u s i n g a F o u r i e r t r a n s f o r m , e l i m i n a t i n g  selected  f r e q u e n c i e s w i t h i n the r e s p o n s e , and t r a n s f o r m i n g the a l t e r e d response back t o the time domain. The r e c o r d i n g o s c i l l o s c o p e used f o r t h i s study capable of d i g i t a l l y  (see S e c t i o n 3 . 4 . 5 )  1s  f i l t e r i n g a p o r t i o n o f a d i g i t i z e d response s t o r e d  in  i t s memory. A d i g i t i z e d  response s t o r e d i n the o s c i l l o s c o p e has e i t h e r 15872,  41  NORMALIZED  FREQUENCY  -  f/t  c  Figure 3.15 Attenuation and Phase Shift Characteristics of the Low Pass F i l t e r s (after Rockland Laboratories, Inc., 1969)  Low Pass F i l t e r McDonalds Farm 8.0 m Depth  shear wave  arrivals"  ( d e l a y due t o phase  Cut-off  4  frequency = 20 Hz 30 Hz  shift)j  1  40 Hz  in  w -P  o >  <u T3 3  •P •H r-l  'W-/\A~./v>  VUVwWVyW-. 600 Hz  -~v~v-^nMA/vVv^^  0  20  40  60 Time  30  100  120  140  (milliseconds)  F i g u r e 3.16 E f f e c t o f D i f f e r e n t F i l t e r C u t - o f f F r e q u e n c i e s on A c c e l e r o m e t e r Response  7936, o r 3968 data p o i n t s  (see S e c t i o n 3 . 4 . 5 ) . The d i g i t a l  filter  program f o r  the o s c i l l o s c o p e can only operate on 1024 d a t a p o i n t s a t one t i m e . Thus, f i l t e r can only f i l t e r  a small window o f the s i g n a l , and not the  r e s p o n s e . T h i s type of f i l t e r i n g c o u l d o n l y be used i f arrival  entire  approximate  time was a l r e a d y known.  The c a p a b i l i t y typical  the  the  to d i g i t a l l y  filter  the l a r g e number o f data p o i n t s i n a  a c c e l e r o m e t e r response r e q u i r e s a l a r g e amount o f computer  s p a c e . Thus, i n o r d e r to d i g i t a l l y  filter  storage  an a c c e l e r o m e t e r response from the  o s c i l l o s c o p e , the response must f i r s t be t r a n s f e r r e d t o a computer w i t h k i n d o f memory c a p a c i t y .  Once t r a n s f e r r e d , d i g i t a l  this  f i l t e r i n g can be  performed. The computer system needed f o r t h i s type o f f i l t e r i n g  is  still  under i n v e s t i g a t i o n a t U . B . C . 3.4.5.  Recording O s c i l l o s c o p e  The responses o f the geophones and a c c e l e r o m e t e r s t o the s e i s m i c wave e x c i t a t i o n were d i s p l a y e d and r e c o r d e d u s i n g a N i c o l e t 4094  digital  o s c i l l o s c o p e with a CRT s c r e e n and a f l o p p y d i s k s t o r a g e c a p a b i l i t y . A complete d e s c r i p t i o n of t h i s o s c i l l o s c o p e  i s g i v e n by R i c e  the p e r t a i n e n t c h a r a c t e r i s t i c s o f the o s c i l l o s c o p e , study, w i l l  (1984), and o n l y  as they r e l a t e t o  this  be summarized h e r e .  The o s c i l l o s c o p e was an analog t o d i g i t a l a s i n g l e input signal  r e c o r d e r , capable o f  recording  t o the n e a r e s t 10 m i c r o s e c o n d s , and two simultaneous  i n p u t s i g n a l s t o the n e a r e s t 20 m i c r o s e c o n d s . The d o u b l e - s i d e d  double-density  f l o p p y d i s k s used f o r data s t o r a g e i n c o n j u n c t i o n w i t h the o s c i l l o s c o p e , d i v i d e d i n t o 20 s e c t o r s . A s i n g l e  signal  c o u l d be s t o r e d i n f u l l ,  q u a r t e r s e c t o r s , which c o u l d h o l d 15872, 7936, and 3968 d a t a respectively.  half  were  or  points  (Two s i m u l t a n e o u s l y r e c o r d e d s i g n a l s c o u l d o n l y be s t o r e d  in  h a l f o r q u a r t e r s e c t o r s ) . Known t r i g g e r d e l a y s c o u l d be p r e s e t on the o s c i l l o s c o p e . By u s i n g known t r i g g e r d e l a y s and maximum s t o r a g e c a p a c i t y ,  the  maximum sampling r a t e c o u l d be used t o g r e a t e r d e p t h s . The data c o u l d be a m p l i f i e d on the s c r e e n and a d d i t i o n or s u b t r a c t i o n o f s i g n a l s c o u l d be performed. Disk programming packages used with the o s c i l l o s c o p e signal  smoothing, d i g i t a l  filtering  (see S e c t i o n 3 . 4 . 4 ) ,  allowed  and o t h e r  operations.  3.5 F i e l d Procedures  An i m p o r t a n t element f o r o b t a i n i n g a c c u r a t e r e p e a t a b l e  s e i s m i c d a t a 1s a  s t a n d a r d f i e l d procedure performed by w e l l - t r a i n e d p e r s o n n e l . T h i s will  o u t l i n e the b a s i c  section  f i e l d procedures used w i t h the s e i s m i c cone f o r  t h e s i s . Most o f these procedures have been o u t l i n e d p r e v i o u s l y by R i c e and w i l l  be o n l y b r i e f l y  reviewed h e r e . S p e c i a l  (1984)  p r o c e d u r e s , t o be used w i t h  s p e c i f i c sources or r e c e i v e r s , have been o u t l i n e d p r e v i o u s l y i n t h i s or w i l l  this  chapter  be i n c l u d e d i n Chapters 5 and 6 .  The f i e l d procedure I n v o l v e d s e v e r a l begin. F i r s t ,  steps b e f o r e s e i s m i c t e s t i n g  the t r u c k was r a i s e d and l e v e l l e d on i t s h y d r a u l i c pads,  c r e a t i n g the plank f o r the mechanical  could thus  shear wave s o u r c e . I f a mechanical  compression wave source was t o be u s e d , the s t e e l  p l a t e was p o s i t i o n e d  under  the r e a r h y d r a u l i c pad b e f o r e the pads were l o w e r e d . Second, the i n i t i a l  set-  up o f the e l e c t r o n i c s and r e c o r d i n g systems was made. T h i s s e t - u p i s shown s c h e m a t i c a l l y i n F i g u r e 3 . 1 7 . T h i r d , the cone was s a t u r a t e d and the a q u i s i t i o n system i n i t i a l i z e d cone, with s e i s m i c t r a n s d u c e r s soil  t o the f i r s t  test  data  (see Campanella and R o b e r t s o n , 1981). Next, f a v o u r a b l y o r i e n t e d , was advanced i n t o  the  the  depth.  At each t e s t depth a s i m i l a r procedure f o r s e i s m i c t e s t i n g was f o l l o w e d . T h i s procedure c o n s i s t e d  of:  - s e t t i n g the o s c i l l o s c o p e to the c o r r e c t  sampling r a t e s , maximum  voltages,  Seismic Cap Source  Blaster Box Cone Data T to D.A.S.  Power Supply to Cone Accelerometers or Geophones  Trigger  Conditioni Box^  Seismic Cap  Hammer Source Switch 'Low Pass F i l t e r and/or Amplifier Vertical Input  Trigger Input Truck Pad  r/  Geophones  v>  si—  Sledge Hammer  B u f f a l o Gun Source  I  <  h.  Geophone HF  V Cone  Shotgun Shell  F i g u r e 3.17 Schematic of the E l e c t r o n i c s Set-up f o r S e i s m i c T e s t i n g en  and t r i g g e r  delays;  -removing the l o a d from the cone and rods and t u r n i n g the t r u c k engine if  off  necessary;  - c h e c k i n g t h a t the t r i g g e r i s working and a c t i v a t i n g  it;  - i n d u c i n g a s e i s m i c wave i n t o the ground w i t h e i t h e r a mechanical  or  explosive source; - s t o r i n g the wave s i g n a l  on the o s c i l l o s c o p e f l o p p y d i s k r e c o r d e r and n o t i n g  the t e s t i n f o r m a t i o n an a data - p o l a r i z i n g the s i g n a l , i f  sheet;  u s i n g a hammer shear s o u r c e ;  - a d v a n c i n g the cone t o the next t e s t depth and r e p e a t i n g the  procedure;  A few notes should be made about some o f the t e s t s t e p s . When u s i n g the on-shore e x p l o s i v e s o u r c e , t o a v o i d unnecessary r e p e t i t i o n of the t e s t due t o p o o r l y chosen s c a l e s ,  i t was found u s e f u l  t o use the hammer source as an  i n d i c a t o r o f the time and v o l t a g e s c a l e s needed b e f o r e d e t o n a t i n g the s o u r c e . T h i s t e c h n i q u e c o u l d not be used f o r the o f f - s h o r e e x p l o s i v e However, c a r e f u l  study o f the p r e v i o u s s i g n a l  distance  sources.  c o u l d , with experience,  with s e l e c t i o n of a p p r o p r i a t e s c a l e s , although d i f f i c u l t i e s t e s t depths were a c o n s i d e r a b l e  point  help  did arise i f  the  apart.  Checking the t r i g g e r b e f o r e f i r i n g the o n - s h o r e e x p l o s i v e s o u r c e , mentioned i n S e c t i o n 3 . 3 . 5 , was e s p e c i a l l y i m p o r t a n t , c o n s i d e r a b l y more time t o repeat than the mechanical  s i n c e the t e s t source t e s t s ,  as  takes  and many  r e p e t i t i o n s c o u l d be c o s t l y due t o the shotgun s h e l l s needed. The a u g e r i n g o f the h o l e and l o a d i n g o f the B u f f a l o gun was done w h i l e the cone was b e i n g advanced, 1n o r d e r t o save t i m e . To reduce the amount o f n o i s e t r a v e l l i n g down the rods from the In t e s t i n g v e h i c l e , a t each t e s t depth the rods were uncoupled from the  situ  truck.  T h i s u n c o u p l i n g was accomplished by removing the l o a d from the rods and a l l o w i n g the rods t o stand f r e e In the r o d w e l l . I f e x c e s s n o i s e i n the wave  signal  was encountered a f t e r the u n c o u p l i n g o f the r o d s , then the  engine was s h u t o f f while the wave s i g n a l The use of a f r i c t i o n  truck  was t r a v e l l i n g through the  soil.  r e d u c e r with the s e i s m i c cone (see Campanella and  Robertson, 1981) t o reduce f r i c t i o n  along the r o d s , a l s o helped  excess n o i s e from t r a v e l l i n g i n the  rods.  prevent  48 4. FIELD  INVESTIGATIONS  The data c o n t a i n e d i n t h i s t h e s i s was o b t a i n e d from two s i t e s . The s i t e was McDonalds Farm l o c a t e d i n the F r a s e r R i v e r D e l t a , B.C.  first  near Vancouver,  The second s i t e , c a l l e d the B e a u f o r t Sea s i t e , c o n s i s t e d o f f o u r sub-  sites,  all  l o c a t e d near Tuktoyaktuk,  N . W . T . , 1n the McKenzie R i v e r D e l t a ,  the B e a u f o r t S e a . These s i t e s are d e s c r i b e d i n d e t a i l penetration p r o f i l e s for a l l  below. T y p i c a l  and  cone  the s i t e s can be found i n Appendix A .  4.1 McDonalds Farm S i t e  The McDonalds Farm s i t e was an abandoned farm l o c a t e d on the n o r t h o f Sea I s l a n d , near the Vancouver I n t e r n a t i o n a l  A i r p o r t . Sea I s l a n d  l o c a t e d between the North Arm and M i d d l e Arm o f the F r a s e r R i v e r ,  side  is  on the  n o r t h s i d e o f the main F r a s e r R i v e r D e l t a . The s i t e ,  from s u r f a c e t o a depth of 2 m e t e r s , c o n s i s t e d o f  c o m p r e s s i b l e c l a y s and s i l t s . The sand from  soft,  2 meters t o 13 meters was a  medium t o coarse g r a i n s i z e w i t h t h i n l a y e r s o f medium t o f i n e g r a i n  size.  The sand g e n e r a l l y i n c r e a s e d i n d e n s i t y with d e p t h . A t h i n t r a n s i t i o n o f f i n e sand w i t h some s i l t u n d e r l a i n by a t h i c k  layer  e x i s t e d from 13 t o 15 m e t e r s . The sand was  d e p o s i t of s o f t ,  normally c o n s o l i d a t e d , c l a y e y s i l t .  The  groundwater t a b l e was a p p r o x i m a t e l y 1 meter below the ground s u r f a c e and p r e s s u r e s were approximately h y d r o s t a t i c .  (Campanella e t a l . , 1982).  Seismic cone p e n e t r a t i o n t e s t s were performed a t McDonalds Farm w i t h both the 10 and 15 s q . cm c o n e s . The 10 s q . cm cones were Instrumented w i t h either a single, horizontal  geophone (UBC#6) o r a c c e l e r o m e t e r (UBC#8). The 15  s q . cm cone was Instrumented at d i f f e r e n t times w i t h a t r i a x i a l geophones and a c c e l e r o m e t e r s . The o n - s h o r e f i l t e r was used i n c o n j u n c t i o n w i t h the a c c e l e r o m e t e r s .  package  described in section Both the mechanical  of 3.4.4  hammer  49 and B u f f a l o gun s o u r c e s were used a t the  site.  4.2 B e a u f o r t Sea S i t e s  The l o c a t i o n s of the B e a u f o r t Sea s i t e s are shown i n F i g u r e 4 . 1 . The f o u r s u b - s i t e s are c a l l e d the School house s i t e , Richards Island s i t e ,  the Swimming P o i n t s i t e ,  and the Tuktoyaktuk Harbour s i t e . T e s t i n g a t  s i t e s was performed i n l a t e March ( 1 9 8 5 ) . Ice was p r e s e n t a t a l l and was approximately 2 meters t h i c k .  These s i t e s w i l l  these  the  sites  be d e s c r i b e d below.  The s i t e d e s c r i p t i o n s are summarized from Campanella e t a l . 4 . 2 . 1 School house  the  (1985).  Site  The School house s i t e was l o c a t e d i n the near o f f s h o r e area west o f Tuktoyaktuk  (see F i g u r e 4 . 1 ) . Depth of water and s e a - i c e  (depth t o mudline)  a t the s i t e v a r i e d from 2.5 t o 4.25 m e t e r s , and was g e n e r a l l y i n c r e a s i n g w i t h i n c r e a s i n g d i s t a n c e from the s h o r e l i n e . The s o i l c o n s i s t e d o f medium dense t o dense, s i l t y ,  a t Schoolhouse  site  f i n e sand, g e n e r a l l y ending  in  p e r m a f r o s t . The d e n s i t y of the sand and depth to p e r m a f r o s t appeared t o i n c r e a s e with I n c r e a s i n g d i s t a n c e from the  shoreline.  S e i s m i c cone p e n e t r a t i o n t e s t s were performed u s i n g both the 10 and 15 s q . cm c o n e s . Both the UBC#6 and the UBC#8 cones were u s e d . The 15 s q . cm cone was instrumented a t d i f f e r e n t times w i t h a b i a x i a l  package o f  and a c c e l e r o m e t e r s . U n f o r t u n a t e l y ,  described in  the o f f - s h o r e f i l t e r  geophones section  3 . 4 . 4 d i d not adequately a t t e n u a t e the unwanted f r e q u e n c i e s from the a c c e l e r o m e t e r r e s p o n s e s . T h u s , the s i g n a l s from the a c c e l e r o m e t e r s were not adequately f i l t e r e d , and c o u l d not be u s e d . The s e i s m i c cap source was used e x c l u s i v e l y a t the Schoolhouse s i t e . three d i f f e r e n t c o n f i g u r a t i o n s  d e s c r i b e d i n S e c t i o n 3 . 3 . 6 were a l l  t h a t 1 s , the s e i s m i c cap was lowered on a p o l e below the i c e ,  The  tried;  the s e i s m i c cap  135°  2C  3C  •in  r=bo:  E A  u  f  5C rrfr-r  134°  o ;R  >P""* Vj'lsland  133  c  2C  50  r-r+rr  70°  T  ( A R C T I C  723  3C  4C  S E A O C E A N J  n  < '225' Hoooer' " Island ;  BELUGA  BAY  K U G M i \ L L I T  SITE 3 RICHARDS ISL.  fa  ^ C ! ^I^V'.-.. Summer  A Y  A Y •>• -  " ."" * •  j'jrtendrickson "V  -JA--...•>•'Bay  Topk.k Pt^- ^  •^••IsJand  TuktoyaktukoJ•'•-> •  • •  -  -Umiak' . V  f r _ ..•  Kittigazuit  SITE 1 SCHOOLHOUSE  -Denis  -• Fisn  - •  •225. ,  Ut  - .  i - •  SITE 2 SWIMMING POINT l ' -  F i g u r e 4.1 L o c a t i o n Map f o r B e a u f o r t  Sea S i t e s  was lowered f r e e l y t o below the i c e and t o the m u d l i n e ,  and the s e i s m i c cap  was a t t a c h e d t o a blade and embedded below t h e m u d l i n e . U n f o r t u n a t e l y , soil  a t the s i t e s u r f a c e was too dense t o a l l o w the b l a d e w i t h the  the  seismic  cap t o be embedded. Thus, no data was o b t a i n e d from t h i s source a t t h i s 4.2.2  Swimming P o i n t  Site  The Swimming P o i n t s i t e was l o c a t e d i n the e a s t channel River,  site.  approximately 65 km south west o f Tuktoyaktuk  o f the McKenzie  as shown i n F i g u r e 4 . 1 .  The depth t o mudline v a r i e d from 1.75 meters t o 11.0 meters depending on the d i s t a n c e from s h o r e . C l o s e t o s h o r e , where the depth t o mudline was l e s s  than  2 m e t e r s , the i c e extended t o the m u d l i n e . The upper s o i l s a t the s i t e c o n s i s t e d o f predominantly  soft,  organic  s i l t w i t h l a y e r s t h a t were more c l a y e y o r sandy. The c l a y e y l a y e r s were s l i g h t l y o v e r c o n s o l i d a t e d . U n d e r l y i n g these s o f t s o i l s was a g r a v e l The t h i c k n e s s o f the s o f t s o i l s i n c r e a s e d towards  layer.  shore.  S e i s m i c cone p e n e t r a t i o n t e s t s were performed w i t h both the UBC#6 and 15 s q . cm c o n e s .  The 15 s q . cm cone was i n s t r u m e n t e d w i t h a b i a x i a l  geophones. The UBC#8 cone site,  the f i l t e r i n g  was used a t t h i s s i t e ,  but,  as a t the  package  of  Schoolhouse  was i n a d e q u a t e .  Both the mechanical  hammer source and the s e i s m i c cap source were used  a t the Swimming P o i n t s i t e . The hammer source was used where the 1ce extended to m u d l i n e . The s e i s m i c cap source was used where t h e r e was both water and i c e . The s e i s m i c cap source was used w i t h the s e i s m i c cap lowered f r e e l y j u s t below the i c e or lowered to m u d l i n e . 4.2.3  Richards Island S i t e The R i c h a r d s I s l a n d s i t e was l o c a t e d i n Beluga Bay, west o f  Point,  North  R i c h a r d s I s l a n d (see F i g u r e 4 . 1 ) . The i c e extended t o mudline  R i c h a r d s I s l a n d and was 1.9 meters t h i c k . through the Ice d u r i n g p e n e t r a t i o n .  at  Water d i d f l o w I n t o the h o l e  to  The s o i l s a t the R i c h a r d s I s l a n d s i t e c o n s i s t e d mainly o f s i l t y  clay  with a l a y e r o f dense sand between 4 meters and 8 m e t e r s . The c l a y e y  soils  were s l i g h t l y o v e r c o n s o l i d a t e d . P e r m a f r o s t was encountered a t a depth o f  13.5  meters. The UBC#6 cone was u s e d . The mechanical  hammer source p r o v i d e d the  source f o r s e i s m i c waves. The s e i s m i c cap source was not used a t t h i s 4 . 2 . 4 Tuktoyaktuk Harbour  site.  Site  The Tuktoyaktuk Harbour s i t e was l o c a t e d w i t h i n the harbour near the hamlet o f T u k t o y a k t u k .  (see F i g u r e 4 . 1 ) . The depth t o mudline was 6.6 m e t e r s .  The s o i l s a t Tuktoyaktuk Harbour c o n s i s t e d o f medium dense t o dense f i n e with some t h i n l e n s e s o f s i l t y  sand  sand. The d e n s i t y of the sand appeared t o  decrease w i t h d e p t h . The UBC#6 cone was u s e d . The s e i s m i c cap source g e n e r a t e d the  seismic  waves. The s e i s m i c caps were e i t h e r lowered on a p o l e t o below the i c e , a t t a c h e d t o a b l a d e and embedded j u s t below the m u d l i n e . The s o i l s u r f a c e o f t h i s s i t e was s o f t ,  at  the  a l l o w i n g the b l a d e t o be e a s i l y embedded.  or  53 5. EVALUATION OF DIFFERENT SOURCES  The main c r i t e r i a upon which a s e i s m i c source i s e v a l u a t e d , are the source's r e p e a t a b i l i t y , This chapter w i l l  s t r e n g t h and d i r e c t i o n a l i t y  (Stokoe and Hoar,  e v a l u a t e the use o f t h r e e c a t e g o r i e s  o f sources w i t h the  s e i s m i c cone penetrometer. These c a t e g o r i e s o f s o u r c e s , as o u t l i n e d Chapter 3, a r e mechanical  be compared w i t h each  5.1 E v a l u a t i o n o f the Mechanical  5.1.1  in  s o u r c e s , on-shore e x p l o s i v e s o u r c e s , and o f f - s h o r e  e x p l o s i v e s o u r c e s . Each o f the source types w i l l and then they w i l l  1978).  be l o o k e d a t  individually,  other.  Sources  Hammer Shear.Wave Source The hammer shear wave source employed f o r t h i s study produced, as  expected, s t r o n g , d i r e c t i o n a l , polarized horizontal  repeatable  shear waves. F i g u r e 5.1  geophone response p r o f i l e s  shows  from the hammer shear wave  s o u r c e . E v a l u a t i o n o f the use o f t h i s source w i t h the s e i s m i c cone penetrometer has been p r e s e n t e d p r e v i o u s l y  (Rice,  1984), and w i l l  not be  repeated h e r e . The main advantages o f t h i s s o u r c e a r e i t s ease o f u s e , polarizing capabilities,  and i t s a b i l i t y  waves. These c h a r a c t e r i s t i c s make i t  t o generate predominantly  its  shear  a s t a n d a r d t o which o t h e r sources may be  compared. 5.1.2  Hammer P-wave Source The hammer P-wave source was not s u c c e s s f u l l y used w i t h the  cone. The hammer P-wave source g e n e r a t e d a compression wave t h a t s component was l a r g e r than i t s h o r i z o n t a l d e t e c t e d by a v e r t i c a l Typical  vertical  seismic vertical  component, and thus was b e s t  receiver. a c c e l e r o m e t e r responses from the hammer P-wave source  at two s u c c e s s i v e depths are shown i n F i g u r e 5 . 2 . As can be seen from the  54  Time  F i g u r e 5.1  (milliseconds)  H o r i z o n t a l Geophone Response P r o f i l e f o r Hammer Shear Source  V e r t i c a l Accelerometer Hammer P-wave Source McDonalds Farm  (Low Pass F i l t e r C u t - o f f Frequency  Time Interval  Time = 0.16 msec ===^ V e l o c i t y  = 100 Hz)  (milliseconds)  = 6250 m/s, a p p r o x i m a t e l y Vp i n s t e e l  F i g u r e 5.2 V e r t i c a l Accelerometer Response to Hammer P-wave Source  f i g u r e , the wave forms a r e not s e p a r a t e d i n time as e x p e c t e d . F o r a v e l o c i t y o f 1600 m/s, an average expected P-wave v e l o c i t y interval  for this soil  time would be 0.625 m i l l i s e c o n d s . The i n t e r v a l  wave forms shown i s o n l y 0.16 m i l l i s e c o n d s ,  type,  the  time between the two  i n d i c a t i n g a v e l o c i t y o f 6250  m/s, which i s approximately the speed o f a compression wave i n s t e e l . A l s o , the d i r e c t a r r i v a l  v e l o c i t y u s i n g the d i r e c t a r r i v a l  time f o r 10 meters  depth, g i v e s a v e l o c i t y o f 1086 m/s, a slower v e l o c i t y than expected saturated, inorganic  soil.  The reasons f o r the response o f the  r e c e i v e r not r e p r e s e n t i n g the s o i l Horizontal  response w i l l  vertical  be d i s c u s s e d i n Chapter  a c c e l e r o m e t e r s were a l s o used t o d e t e c t the wave s i g n a l  the hammer P-wave s o u r c e . F i g u r e 5.3 shows the h o r i z o n t a l  amplitude o f the i n i t i a l  P-wave a r r i v a l  that i f  i s very s m a l l , making  Thus, because i n t e r p r e t a t i o n o f the f i r s t a r r i v a l  large errors in interval  times and thus v e l o c i t i e s ,  several horizontal  6. from  accelerometer  responses a t two s u c c e s s i v e d e p t h s . As can be seen from the f i g u r e ,  difficult.  for  the  interpretation is  can o c c u r .  difficult, It is  possible  a c c e l e r o m e t e r responses from the hammer P-wave  source were added t o g e t h e r ,  the a r r i v a l  time o f the P-wave c o u l d be p i c k e d  with more c o n f i d e n c e .  5.2 On-shore E x p l o s i v e  Source  The B u f f a l o Gun, the on-shore e x p l o s i v e s o u r c e , was found t o be a s t r o n g source o f compression and shear waves. However, the B u f f a l o gun c o u l d not be p o l a r i z e d , and was not r e p e a t a b l e at s h a l l o w depths m e t e r s ) . These a t t r i b u t e s  o f the B u f f a l o gun w i l l  (depths l e s s than 12  be d i s c u s s e d below.  The B u f f a l o gun produced s t r o n g compression and shear waves. F i g u r e shows a t y p i c a l (Vertical  horizontal  a c c e l e r o m e t e r response p r o f i l e  f o r the B u f f a l o  5.4 gun  r e c e i v e r s c o u l d not be u s e d . See C h a p t e r 6 ) . The compression wave  57  Hammer P-wave Source McDonalds Farm H o r i z o n t a l Accelerometer Low Pass F i l t e r w i t h C u t - o f f Frequency = 100 Hz  20  40 Time  F i g u r e 5.3  60  (milliseconds)  H o r i z o n t a l A c c e l e r o m e t e r Responses to Hammer P-wave Source  ure 5.4 Horizontal Accelerometer Response P r o f i l e f o r Buffalo Gun  arrival  i s e a s i l y p i c k e d as the f i r s t wave t o a r r i v e . The shear waves are the  s t r o n g , lower frequency waves with a much slower a r r i v a l  time than the  compression waves. A t depths g r e a t e r than about 10 m e t e r s ,  it  is f a i r l y  easy  t o p i c k the shear wave a r r i v a l s , although the compression wave i s more d i f f i c u l t to p i c k ,  because i t  is highly attenuated.  F o r depths l e s s than 10  m e t e r s , d i s t i n g u i s h i n g between the compression and shear wave i s  difficult  because o f the a d d i t i o n of the two waves. E x p l o s i v e s o u r c e s are not d i r e c t i o n a l  and thus can not be p o l a r i z e d .  However, the amplitude and s i g n o f the waveform r e c e i v e d from the B u f f a l o gun was a f f e c t e d by the alignment o f the source and r e c e i v e r . The  largest  amplitude s i g n a l s were o b t a i n e d when the B u f f a l o gun was on the l i n e o f o r i e n t a t i o n o f the h o r i z o n t a l  receiver,  and the s m a l l e s t amplitude  the  signals  when the B u f f a l o gun was i n a l i n e p e r p e n d i c u l a r t o the o r i e n t a t i o n o f  the  r e c e i v e r (see F i g u r e 5 . 5 ) . Because a h o r i z o n t a l  sign  r e c e i v e r was u s e d , the  o f the B u f f a l o gun response depended on which s i d e o f the t r u c k the gun was fired.  The combined e f f e c t s o f source and r e c e i v e r alignment and the  wave source made i n t e r p r e t a t i o n  multiple  difficult.  The r e p e a t a b i l i t y o f the B u f f a l o gun was o n l y good below approximately 12 meters (see F i g u r e 5 . 6 ) . Above 12 m e t e r s ,  the r e s u l t s v a r i e d , a t some  depths by as much as 50 p e r c e n t . Some o f t h i s v a r i a b i l i t y was due t o d i f f e r e n t types o f r e c e i v e r s and t h i s w i l l  be d i s c u s s e d i n Chapter  the  6.  However, the v a r i a b i l i t y was mainly due t o t r i g g e r i n g problems and/or t r a v e l path problems. These two f a c t o r s w i l l  be d i s c u s s e d below.  N e i t h e r o f the t r i g g e r i n g systems used w i t h the B u f f a l o Gun were particularly  s u c c e s s f u l . T h i s was because the t r i g g e r was a c t i v a t e d by the  wave t r a v e l l i n g through the gun, and t h i s wave was not c o n s i s t e n t . the geophone t r i g g e r was used with some s u c c e s s , wave a r r i v a l  it  Although  d i d not a l l o w compression  times t o be p i c k e d c o n s i s t e n t l y w i t h c o n f i d e n c e . The a r r i v a l  of  Time 40  60  60  (milliseconds) 80  100  120  160  (LI  00  O >  4-1  3  Cu  •u  r0  3  O  cu co CO  4J  C  - H  O  O  co 6  Ph  LlOO  (-1  <D  4-1 CU  B  O J-l  0J i H  0) O O  <:  Location of B u f f a l o Gun • Shotholes  McDonalds Farm Depth 10.5 meters B u f f a l o Gun O f f s e t 4.5 meters Shothole Depth .75 meters Horizontal Accelerometer Low Pass F i l t e r C u t - o f f Frequency = 100 Hz  Orientation of/ H o r i z o n t a l Accelerometer  F i g u r e 5.5  V a r i a t i o n of A c c e l e r o m e t e r Response w i t h P o s i t i o n of B u f f a l o Gun Source  61 S - Wava V e l o c i t y (m/e) B u f f a l o Gun S o u r c e 0 0-J  100 I  200  300  400 I  500  LEGEND Caophonae Acca1sramatari  O  s-  10  a. a a  O  I  15-  AO  A O McDonalds Farm 20  _1_  F i g u r e 5.6 Comparison o f Shear Wave V e l o c i t y P r o f i l e s  from B u f f a l o Gun Source  62 the slower shear wave was l e s s a f f e c t e d by the t r i g g e r i n g problems. c a l c u l a t e d compression wave a r r i v a l shear wave a r r i v a l  times were sometimes used t o c o r r e c t  the  times f o r the t r i g g e r i n g e r r o r . T h i s c o r r e c t i o n was,  t i m e s , as much as 2.5  at  milliseconds.  The c a l c u l a t i o n o f t r a v e l  path l e n g t h f o r the B u f f a l o gun has t o  i n t o account not only a h o r i z o n t a l vertical  However,  take  o f f s e t from the cone r o d s , but a l s o a  o f f s e t from ground s u r f a c e . Both o f these o f f s e t s were v a r i a b l e .  e l i m i n a t e some o f t h i s v a r i a b i l i t y and thus ease i n t e r p r e t a t i o n , decided t o f i x the v e r t i c a l  offset.  To  i t was  T h i s meant f i r i n g o n l y one shot per h o l e ,  s i n c e the gun c o u l d not be l o d g e d f i r m l y a t the same depth a second t i m e . L i m i t i n g the use o f the B u f f a l o gun t o one shot per h o l e made the B u f f a l o gun a l a b o r i o u s and r e l a t i v e l y slow t e c h n i q u e t o u s e . At depths l e s s than 6 m e t e r s ,  the t r a v e l  path angle f o r the B u f f a l o gun  can be l e s s than 60 d e g r e e s . R e f r a c t i o n of the wave s i g n a l may i n c r e a s e the e r r o r t r a v e l velocity  path l e n g t h and thus the v a r i a b i l i t y  in  technique was u s e d , i n s t e a d o f the pseudo i n t e r v a l technique  ( i n v e s t i g a t e d by R i c e ,  would e l i m i n a t e t r i g g e r i n g and t r a v e l  a true  interval  t e c h n i q u e . The t r u e  1984), i l l u s t r a t e d i n F i g u r e  5.7,  path problems, a l l o w i n g both  compression and shear a r r i v a l s t o be p i c k e d w i t h g r e a t e r  5.3 O f f - s h o r e E x p l o s i v e  the  interpretation.  The B u f f a l o gun c o u l d be c o n s i d e r a b l y improved i f  5.3.1  boundaries  (see S e c t i o n 2 . 3 . 2 ) . A l s o , r e f r a c t e d waves may be adding t o  d i r e c t waves, c o n f u s i n g  interval  on s o i l  confidence.  Sources  Seismic Cap Source The s e i s m i c cap source was found t o be a s t r o n g , r e p e a t a b l e  source  compression and shear waves. The s e i s m i c cap source was f i r e d e i t h e r  of  just  63  T r a v e l t i m e c a l c u l a t e d by m o n i t o r i n g s h e a r wave a r r i v a l from s e p a r a t e energy impulses.  f  O  T r a v e l t i m e c a l c u l a t e d by simultaneously monitoring two s h e a r wave a r r i v a l s from a s i n g l e energy impulse.  s  f  V  P S E U D O I N T E R V A L  T R U E I N T E R V A L  s  o  Ol  V  V a)  F i g u r e 5.7  S  [Ol  b)  Comparison between True and Pseudo I n t e r v a l Measurement (from R i c e , 1984)  below the i c e o r a t the m u d l i n e . These two methods o f f i r i n g the s e i s m i c cap will  be c o n s i d e r e d  separately.  F i g u r e 5.8 shows a t y p i c a l  horizontal  s e i s m i c cap f i r e d j u s t below the i c e  geophone response p r o f i l e  the  (lowered on a p o l e t o a f i x e d d e p t h ) .  The compression waves are d i s t i n g u i s h e d by b e i n g the f i r s t wave t o The shear waves are the l a t e r ,  for  lower frequency waves w i t h f a i r l y  a m p l i t u d e s . I n t e r p r e t a t i o n o f the shear wave a r r i v a l the B u f f a l o gun, use of the t r u e i n t e r v a l  arrive.  high  is difficult.  As w i t h  t e c h n i q u e would help g r e a t l y  with  i n t e r p r e t a t i o n , because the same waveform c o u l d be compared at two s u c c e s s i v e d e p t h s . However, the s e i s m i c cap source was found t o be f a i r l y seen i n F i g u r e  repeatable,  5.9.  I t was found t h a t i n o r d e r t o use the compression wave a r r i v a l s , depth o f the s e i s m i c cap below the i c e had t o be c o n s i s t e n t .  Several  the seismic  cone p e n e t r a t i o n soundings were done w i t h o u t p r o p e r l y c o n t r o l l i n g t h i s and the compression wave v e l o c i t i e s c o u l d not be d e t e r m i n e d . Some o f v a r i a b i l i t y o f the S-wave v e l o c i t y  depth,  the  shown i n F i g u r e 5.8 c o u l d be from t h i s  v a r i a b l e depth problem. T h i s depth c o n t r o l true interval  as  would not have been necessary i f  a  t e c h n i q u e were u s e d .  F i g u r e 5.10 shows a t y p i c a l  horizontal  geophone response p r o f i l e  for  the  s e i s m i c cap f i r e d at the m u d l i n e . T h i s t e c h n i q u e d i d not have the same s e p a r a t i o n i n time o f the compression and shear waves as the technique f i r i n g the s e i s m i c cap j u s t below the i c e ,  because o f the t r a v e l  I n t e r p r e t a t i o n o f the shear wave a r r i v a l s was d i f f i c u l t ,  but not  of  path l e n g t h . appreciably  more d i f f i c u l t than t h a t f o r f i r i n g t h e s e i s m i c cap j u s t below the  ice.  Moreover, compression wave v e l o c i t i e s c o u l d always be determined from t h i s technique because the p o s i t i o n of the s e i s m i c cap was c o n s i s t e n t . 5 . 3 . 2 . Embedded Blade w i t h S e i s m i c Cap Source Although the embedded blade w i t h s e i s m i c cap source was only used once  F i g u r e 5.8 H o r i z o n t a l Geophone Response P r o f i l e f o r S e i s m i c Cap f i r e d j u s t below Ice (Campanella e t a l , 1985)  Source  66  S - Wove V e l o c i t y <m/«> Seismic Cap Source 100 1  0 o-  200 1  300 I  400 I  500  LEGEND o  GSC#5 GSC06 GSDV8A  o A  A  i\ A  15Swimming P o i n t S i t e - B e a u f o r t  Sea  F i g u r e 5 . 9 Comparison of Shear Wave V e l o c i t y P r o f i l e s f o r the S e i s m i c Source f i r e d j u s t below I c e a t Swimming P o i n t S i t e  Cap  F i g u r e 5.10  H o r i z o n t a l Geophone Response P r o f i l e f o r S e i s m i c Source f i r e d a t Mudline  Cap  t o o b t a i n a s e i s m i c cone pentrometer p r o f i l e , semi-directional  1t appeared t o be a s t r o n g ,  s o u r c e . F i g u r e 5.11 shows the geophone response p r o f i l e  for  the embedded b l a d e s o u r c e . T h i s source not only g i v e s a s t r o n g compression wave a r r i v a l , but a l s o shows a s t r o n g e r shear wave then the s e i s m i c cap  alone  showed. The reason the embedded blade shows s t r o n g e r shear waves c o u l d be because o f i t s asymmetry. Mooney (1980) s t a t e s t h a t t h e o r e t i c a l l y must be u n b a l a n c e d , d i r e c t i o n a l ,  and asymmetric t o generate shear waves. The  embedded blade source i s a r e l a t i v e l y  slow t e c h n i q u e t o use s i n c e the blade  must be l i f t e d up from mudline a f t e r each  5.4 Comparison o f D i f f e r e n t  5.4.1  a source  test.  Sources  B u f f a l o Gun Source v e r s u s Hammer Shear Wave Source F i g u r e s 5.12 and 5.13 show shear wave v e l o c i t y p r o f i l e s  B u f f a l o gun and hammer s o u r c e . The p r o f i l e s o b t a i n e d from the  f o r both the accelerometer  show s i m i l a r r e s u l t s f o r both methods below 12 m e t e r s , but above 12 meters the v e l o c i t i e s o b t a i n e d from the two s o u r c e s , vary by as much as 50 p e r c e n t . The p r o f i l e o b t a i n e d by the geophone shows the B u f f a l o gun t o g i v e  velocities  which are g e n e r a l l y s m a l l e r than those g i v e n by the hammer. Thus the gun g i v e s reasonable analysis,  Buffalo  r e s u l t s f o r depths g r e a t e r than 12 m e t e r s . A s t a t i s t i c a l  such as the one c a r r i e d out by Rice  (1984) f o r the hammer shear  s o u r c e , s h o u l d be performed w i t h the B u f f a l o gun i n o r d e r t o a s c e r t a i n reliability.  Chapter 6 w i l l  its  compare the geophone and a c c e l e r o m e t e r r e s p o n s e s .  F o r use o n - s h o r e , the hammer i s very much s i m p l e r than the B u f f a l o gun t o use and t o i n t e r p r e t ,  because i t  1s a wave g e n e r a t o r which can be e a s i l y  p o l a r i z e d . However, the hammer does not produce s t r o n g compression waves which can be d e t e c t e d by h o r i z o n t a l  receivers,  and thus P o i s s o n ' s r a t i o  Chapter 7) can not be determined u s i n g the hammer source a l o n e . I f an  (see  F i g u r e 5.11 H o r i z o n t a l Geophone Response P r o f i l e f o r Embedded Source  Blade  F i g u r e 5.12 Shear Wave V e l o c i t y P r o f i l e s from the H o r i z o n t a l A c c e l e r o m e t e r f o r the Hammer and B u f f a l o Gun Sources  o  200  McDonalds Farm  F i g u r e 5.13 Shear Wave V e l o c i t y P r o f i l e s from the H o r i z o n t a l Geophone f o r Hammer and B u f f a l o Gun Sources  a c c u r a t e t r i g g e r i n g c i r c u i t can be developed f o r the B u f f a l o gun, o r i f true i n t e r v a l  a  t e c h n i q u e i s used w i t h the B u f f a l o gun, then i t would be a good  source f o r compression waves f o r depths l e s s than 10 m e t e r s . As can be seen from F i g u r e 5 . 4 ,  the compression wave does a t t e n u a t e f a i r l y  depth. T h i s problem c o u l d be a l l e v i a t e d by adding s e v e r a l depth.  rapidly  with  signals together  I n t e r p r e t a t i o n of shear waves produced by the B u f f a l o gun i s  difficult  at  not  a t depth because o f the s e p a r a t i o n o f the compression and shear  waves. Thus i f  very deep on-shore cone t e s t i n g i s n e c e s s a r y (depths  greater  than 40 m e t e r s ) , the B u f f a l o gun c o u l d be employed f o r depths below 10 meters. 5.4.2  Seismic Cap Source v e r s u s Hammer Shear Wave Source F i g u r e 5.14 shows shear wave v e l o c i t y p r o f i l e s  f o r the s e i s m i c cap  source and hammer s o u r c e . Both these sources show s i m i l a r r e s u l t s f o r wave v e l o c i t y . T h i s i n d i c a t e s  t h a t the s e i s m i c cap s o u r c e , although  t o i n t e r p r e t g i v e s reasonable  results.  shear  difficult  The p o s i t i o n a t which the s e i s m i c cap i s f i r e d , e i t h e r j u s t below the i c e o r a t the m u d l i n e , does not a f f e c t  the r e s u l t s o f the shear wave  velocity  c a l c u l a t i o n as can be seen from F i g u r e 5 . 1 5 . Although both p o s i t i o n s similar results,  f i r i n g , t h e cap j u s t below the i c e g i v e s a g r e a t e r  between the P and S-wave, thus a i d i n g i n 5.4.3  give  separation  interpretation.  Embedded Blade Source v e r s u s S e i s m i c Cap Source F i g u r e 5.16  shows the P and S-wave v e l o c i t y p r o f i l e s o b t a i n e d from both  the embedded blade and s e i s m i c cap s o u r c e s . The f i g u r e  shows t h a t  very  s i m i l a r r e s u l t s a r e o b t a i n e d from both sources f o r P-wave v e l o c i t i e s .  The  shear wave v e l o c i t i e s o b t a i n e d from the s e i s m i c cap source a r e c o n s i s t e n t l y s m a l l e r than those o b t a i n e d from the embedded blade s o u r c e . F u r t h e r Is necessary t o a s c e r t a i n i f two s o u r c e s .  research  t h i s i s a c o n s i s t e n t r e l a t i o n s h i p between the  S - Wove V e l o c i t y (m/s) Hammer S o u r c e  S - Wove V e l o c i t y (m/s) S e i s m i c Cap S o u r c o 200  COME BEARING 0c (bar)  Swimming P o i n t S i t e - CPT GSC//8A F i g u r e 5.14 Shear Wave V e l o c i t y P r o f i l e s f o r Hammer and S e i s m i c  Cap Sources  250  S - Wave V e l o c i t y (m/s) S e i s m i c Cop a t m u d l i n e  S - V e l o c i t y (m/s) S e i s m i c Cop below i c e 100  200  I  I  300 i  400 L_  500  0 04  100 I  3D0 I  .400 I  500  CONC BEARING 0c (bar)  LEGEND  LEGEND O  200 I  Shot-hole 1 Shot-hole 2  Shot-hole 1 Shot-hole 2  (>A  Ok OA  iO  10'  15-  Swimming P o i n t S i t e - CPT GSC//7 F i g u r e 5.15 Shear Wave V e l o c i t y P r o f i l e s f o r S e i s m i c Cap source f i r e d below Ice and a t Mudline  just  Wove V a l o c l t y 1000  1500  F i g u r e 5.16  (m/«0 2000  S - Wave V e l o c i t y 2500  0  100  200  300  (m/«) 400  CONE BEARING Bo (bar) 500  0  Tuktoyaktuk Harbour S i t e - "CPT GSC//12 Seismic Wave V e l o c i t y P r o f i l e s f o r Embedded Blade and S e i s m i c Cap Sources  76 6. EVALUATION OF DIFFERENT SEISMIC  This chapter w i l l  p r e s e n t the r e s u l t s o f a comparison between  r e c e i v e r s . As mentioned i n c h a p t e r 3 , horizontal  and v e r t i c a l  RECEIVERS  different  the types of r e c e i v e r s used were  geophones and a c c e l e r o m e t e r s .  6.1 Geophones v e r s u s A c c e l e r o m e t e r s  Geophones and a c c e l e r o m e t e r s w i l l  be examined i n t h i s s e c t i o n with the  o b j e c t i v e o f d e t e r m i n i n g t h e i r r e l a t i v e advantages and d i s a d v a n t a g e s . The important c h a r a c t e r i s t i c s o f each r e c e i v e r type w i l l compared, and c o n c l u s i o n s w i l l specific  be o u t l i n e d and  be drawn about the a p p r o p r i a t e n e s s o f each t o  applications.  Geophones are rugged, r e l a t i v e l y  i n e x p e n s i v e s e i s m i c wave r e c e i v e r s  which do not need t o be a m p l i f i e d or f i l t e r e d . When used w i t h the mechanical hammer s o u r c e , they produce c l e a r s i g n a l s as shown i n F i g u r e  6.1.  Accelerometers are l e s s rugged, and more expensive then geophones. They must be a m p l i f i e d and f i l t e r e d b e f o r e wave s i g n a l s can be d i s t i n g u i s h e d . However, once a m p l i f i c a t i o n and f i l t e r i n g i s done, the a c c e l e r o m e t e r s i g n a l when used w i t h the hammer source (see F i g u r e 6 . 1 ) , the hammer source t o a c o n s i d e r a b l y g r e a t e r depth than the  produces a c l e a r  and i t can  detect  unamplified  geophone. Geophones can be a m p l i f i e d . T h i s i n c r e a s e s t h e i r expense and complexity,  but a l l o w s d e t e c t i o n o f s e i s m i c waves t o g r e a t e r  The r a t i o n a l e  depths.  behind the i n v e s t i g a t i o n of the use o f a c c e l e r o m e t e r s  the cone p e n e t r a t i o n t e s t ,  with  stemmed from the a p p l i c a t i o n o f the s e i s m i c cone  to o f f - s h o r e I n v e s t i g a t i o n s . E x p l o s i v e sources are g e n e r a l l y used o f f - s h o r e , and these sources produce predominantly P and SV-waves. Thus, the wave s i g n a l s r e c e i v e d a r e a c o m b i n a t i o n of both P and SV-waves, and p i c k i n g arrival  time o f the SV-wave can o f t e n be  difficult.  the  77  T  1  1  1  1  r  SH  Geophone  Hammer Shear Source McDonalds Farm Depth = 10.0 m Accelerometer *(C.O.F. = 100Hz)  20  40  60 Time  80  100  120  140  *Low pass f i l t e r c u t - o f f frequency = 100 Hz  160  (milliseconds)  F i g u r e 6.1 H o r i z o n t a l Geophone and A c c e l e r o m e t e r Responses to Hammer Shear Source  Because the n a t u r a l  frequency o f the geophones used i n t h i s study was  c l o s e t o the frequency o f the shear waves i n the s o i l , geophone i s c l o s e t o resonance, and the i n t e r n a l  damping o f the  a f f e c t s i t s response t o a l a r g e d e g r e e . The n a t u r a l a c c e l e r o m e t e r s used i n t h i s  the response o f  frequency o f shear waves i n s o i l ,  the  above the  and the a c c e l e r o m e t e r s were undamped. Thus,  the a c c e l e r o m e t e r s tend to show a response which more c l o s e l y response o f the  geophone  frequency o f  s t u d y , on the o t h e r hand, was w e l l  represents  the  soil.  In c o n v e n t i o n a l  s e i s m i c t e s t i n g methods, geophones a r e g e n e r a l l y u s e d .  However, these geophones g e n e r a l l y have a very low n a t u r a l  frequency  Hz) and t h u s , a r e not e x c i t e d near r e s o n a n c e . Such low n a t u r a l  geophone was too b i g t o f i t  (5 to 15  frequencies  r e q u i r e a l a r g e r mass, and t h u s , g e n e r a l l y a l a r g e r s i z e . T h i s type  F i g u r e 6.2  the  of  i n a 10 o r 15 s q . cm c o n e .  shows a comparison o f h o r i z o n t a l  responses t o the B u f f a l o gun.  geophone and  accelerometer  Although i n t e r p r e t a t i o n o f the f i r s t  o f the shear wave i s d i f f i c u l t w i t h t h i s source from both the and geophone, the a c c e l e r o m e t e r tends t o show more d e t a i l  arrival  accelerometer  o f the  soil  response. F i g u r e 6.3 compares the shear wave v e l o c i t y p r o f i l e s o f the hammer and B u f f a l o gun o b t a i n e d u s i n g both geophones and a c c e l e r o m e t e r s . The geophone and a c c e l e r o m e t e r show good agreement o f shear wave v e l o c i t i e s o b t a i n e d the hammer shear s o u r c e . V a r i a t i o n between the two can be mainly f o r by a change i n b e a r i n g r e s i s t a n c e between the two soundings  accounted (compare  F i g u r e s 5.12 and 5 . 1 3 ) . T h u s , f i l t e r i n g o f the a c c e l e r o m e t e r s i g n a l t o have a n e g l i g i b l e  appears  a f f e c t on the v e l o c i t y c a l c u l a t i o n f o r the hammer shear  s o u r c e . T h i s i s as e x p e c t e d i f  a source r e p e a t e d l y produces shear waves o f  the same f r e q u e n c y , because the phase s h i f t w i l l the p s e u d o - I n t e r v a l  from  be a c o n s t a n t . The use o f  t e c h n i q u e f o r c a l c u l a t i n g wave v e l o c i t i e s e l i m i n a t e s  the  79  F i g u r e 6.2  H o r i z o n t a l Geophone and A c c e l e r o m e t e r Responses to the B u f f a l o Gun Source  S  Wave V e l o c i t y <m/e> Hammar S o u r c e 100 I  200 L_  300 I  400 L_  5C0  0  0  - Wave V e l o c i t y (m/e) B u f f a l o Gun S o u r c e 200 i  100 1_  30G i  400 I  LEGEND  LEGEND Geophone Acce1erometer  -  10-  .  CONE BEARING 0c (bar)  500  10-  a.  A  Gaophone  O  Accelerometer  10  AO  a  D  AO  A  20-  20-  30-  O  X  30-  McDonalds Farm - CPT//21 F i g u r e 6.3 Shear Wave V e l o c i t y P r o f i l e s from the H o r i z o n t a l Geophone and Accelerometer f o r the Hammer and B u f f a l o Gun Sources  200  e f f e c t o f the c o n s t a n t phase  shift.  For the B u f f a l o gun s o u r c e , the geophone and a c c e l e r o m e t e r do not  give  as s i m i l a r r e s u l t s as f o r the hammer. T h i s v a r i a t i o n c o u l d be due t o a combination of changes i n b e a r i n g r e s i s t a n c e between s o u n d i n g s ,  trigger  i n c o n s i s t e n c i e s , and v a r i a t i o n i n phase s h i f t o f the a c c e l e r o m e t e r  response  due to a d d i t i o n of compression and shear waves. The a d d i t i o n o f compression and shear waves causes a frequency change i n the s i g n a l phase s h i f t . As can be seen from F i g u r e 6 . 3 ,  and thus a change  the v a r i a b i l i t y between the two  r e c e i v e r s i s g r e a t e r a t the s h a l l o w e r depths where the a r r i v a l s compression and shear waves a r e c l o s e r  in  of  together.  Geophones were used with the s e i s m i c caps o f f - s h o r e . As w i t h the  Buffalo  gun, the s e i s m i c cap produces predominantly P and SV-waves. I n t e r p r e t a t i o n the geophone response t o the s e i s m i c cap was d i f f i c u l t . that i f  However,  i t was found  the s e i s m i c cap was f i r e d from a p o s i t i o n j u s t below the i c e ,  s e p a r a t i o n o c c u r r e d between the P and SV-wave s i g n a l s made the i n t e r p r e t a t i o n of the f i r s t  6.2 H o r i z o n t a l  versus V e r t i c a l  In c o n v e n t i o n a l  arrival  greater  (see F i g u r e 6 . 4 ) .  Receivers  s e i s m i c t e s t i n g , both v e r t i c a l  wedged i n the b o r e h o l e i n such a way, i n both the v e r t i c a l Both h o r i z o n t a l seismic  and h o r i z o n t a l  receivers  and v e r t i c a l  directions.  d e t e c t o r s were i n s t a l l e d i n the 15 s q . cm  cone p e n e t r o m e t e r . The h o r i z o n t a l  sources. Typical  are  so t h a t the r e c e i v e r s move w i t h the  and h o r i z o n t a l  SH-waves from the mechanical  This  o f the SV-wave somewhat e a s i e r .  are used t o d e t e c t compression and shear waves. These r e c e i v e r packages  soil  of  receivers  successfully  s o u r c e , and P and SV-waves from the  responses o f the h o r i z o n t a l  source types are shown i n F i g u r e s 6 . 1 , 6 . 2 ,  detected explosive  r e c e i v e r s from each o f the and 6 . 4 .  three  S e i s m i c Cap Source Schoolhouse S i t e - B e a u f o r t Depth = 6.0 m  F i g u r e 6.4  Sea  H o r i z o n t a l Geophone Response to the S e i s m i c Cap Source f i r e d below the I c e .  just  The use o f v e r t i c a l  r e c e i v e r s i n the s e i s m i c cone d i d not meet w i t h  s u c c e s s . The r e c e i v e r response d i d not change a p p r e c i a b l y w i t h d e p t h . 6.5  shows the response with depth of a v e r t i c a l  geophone. As can be s e e n ,  n e i t h e r compression nor shear wave a r r i v a l s can be c o n s i s t e n t l y A p o s s i b l e e x p l a n a t i o n f o r the response o f the v e r t i c a l do w i t h the v e r t i c a l  and because i t  r e c e i v e r has  i s made o f a very  material  i n comparison with the s o i l ,  vertical  s o i l motion as i t can to h o r i z o n t a l  vertical  r e c e i v e r does not r e p r e s e n t the response o f the s o i l  waves p a s s i n g through  picked.  s t i f f n e s s of the cone and r o d s . Because the cone  weighted down by the rods above i t ,  it.  Figure  to  is stiff  the cone can not respond as e a s i l y s o i l motion. Consequently,  to the  t o the body  84  0 r  50 i  100 1  J  F i g u r e 6.5 V e r t i c a l  I  Time ( m i l l i s e c o n d s ) 150 200 250 300 350 400 1  1  I  1  I  • 1  1  •  •  L  Geophone Response P r o f i l e f o r S e i s m i c Cap Source  85 7. EVALUATION OF COMPRESSION WAVE DATA  The a b i l i t y  t o generate and d e t e c t not only shear waves, but  also  compression waves, a l l o w s the c a l c u l a t i o n of P o i s s o n ' s r a t i o f o r the For example, both Beeston and M c E v i l l y  (1977) and Warrick  (1974) have used i n  s i t u body waves to o b t a i n P o i s s o n ' s r a t i o . T h i s c h a p t e r w i l l the r e s u l t s o b t a i n e d u s i n g the o f f - s h o r e e x p l o s i v e s o u r c e s t o Poisson's  soil.  briefly  outline  obtain  ratio.  The e x p l o s i v e s o u r c e s d e s c r i b e d i n Chapter 5,  generate both compression  and shear waves, and these waves can be d e t e c t e d and i n t e r p r e t e d w i t h s e i s m i c cone. Using the e q u a t i o n g i v e n i n Chapter 2,  the  P o i s s o n ' s r a t i o was  c a l c u l a t e d f o r the Schoolhouse and Tuktoyaktuk Harbour s i t e s . F i g u r e s 7.1 7.2 show the P and S-wave v e l o c i t y r a t i o s f o r these  and  p r o f i l e s w i t h the c a l c u l a t e d P o i s s o n ' s  sites.  The c a l c u l a t e d P o i s s o n ' s r a t i o s vary between 0.33 and 0.46 a t the two s i t e s . P o i s s o n ' s r a t i o o b t a i n e d f o r sand from c o n v e n t i o n a l  t e s t i n g methods  is  g e n e r a l l y around 0 . 3 3 . Thus, the r e s u l t s o b t a i n e d from the s e i s m i c cone seem t o be h i g h . There are two f a c t o r s which may e x p l a i n t h i s d i s c r e p a n c y .  First,  the compression wave i s probably t r a v e l l i n g through the water i n the s o i l , which case i t s v e l o c i t y the s o i l  1s only p a r t i a l l y  a f f e c t e d by the c o m p r e s s i b i l i t y  s k e l e t o n . Second, P o i s s o n ' s r a t i o 1s a f f e c t e d by s t r a i n l e v e l  o n l y those v a l u e s o b t a i n e d at the same s t r a i n l e v e l  1n of  and  s h o u l d be compared. The  r e s u l t s o b t a i n e d u s i n g the s e i s m i c cone p e n e t r a t i o n t e s t are s i m i l a r  to  r e s u l t s o b t a i n e d by Beeston and M c E v i l l y  downhole  seismic t e s t in s i m i l a r  soils.  (1977) u s i n g a c o n v e n t i o n a l  F i g u r e 7.1  Schoolhouse S i t e - CPT GSC//3 C a l c u l a t e d Poisson's R a t i o f o r Schoolhouse S i t e a) 0 to 15  meters  P  - Wave V e l o c i t y (m/s) S e i s m i c Cap Source  S  - Wave V e l o c i t y (m/s) S e i s m i c Cop S o u r c e 500  H  CONE BEARING Oc (bar) 15  20  2S  30  •  Schoolhouse S i t e - CPT GSC#3 F i g u r e 7.1 C a l c u l a t e d P o i s s o n ' s  R a t i o f o r Schoolhouse S i t e b) 15 to 30 meters  250  Tuktoyaktuk Harbour  S i t e - CPT GSC//12  F i g u r e 7.2 C a l c u l a t e d Poisson's R a t i o f o r Tuktoyaktuk Harbour  Site co Co  89 8. EVALUATION OF DAMPING CHARACTERISTICS  8.1  Introduction  The d e t e r m i n a t i o n of 1n s i t u m a t e r i a l  damping g r e a t l y enhances the  dynamic a n a l y s i s o f s o i l s . Two d i f f e r e n t methods o f o b t a i n i n g m a t e r i a l damping u s i n g the s e i s m i c cone were b r i e f l y e v a l u a t e d f o r t h i s s t u d y .  First,  undamped a c c e l e r o m e t e r s were used i n an attempt t o o b t a i n the t r u e  response  o f the s o i l  data  and t h u s , s o i l  ( o b t a i n e d by R i c e ,  damping. Second, t r u e i n t e r v a l  geophone  1984) was used i n c o n j u n c t i o n with a waveform a n a l y s i s  suggested by Hoar and Stokoe ( 1 9 8 4 ) , i n an attempt t o o b t a i n m a t e r i a l damping. These methods w i l l  be d i s c u s s e d below.  8.2 A c c e l e r o m e t e r s to o b t a i n S o i l  Damping  As d i s c u s s e d i n C h a p t e r 6 , a c c e l e r o m e t e r s tend t o show a response which more c l o s e l y r e p r e s e n t s the response o f the s o i l . c h a r a c t e r i s t i c s of s o i l  Thus,  damping  s h o u l d t h e o r e t i c a l l y be a t t a i n a b l e  from a c c e l e r o m e t e r  r e s p o n s e s . U s i n g a c c e l e r o m e t e r responses from the hammer shear s o u r c e ,  the  l o g decrement and thus damping r a t i o o f the response were determined. The l o g decrement o f a c y c l i c  response i s the n a t u r a l  r a t i o o f the amplitude o f two s u c c e s s i v e peaks  logarithm of  the  (see F i g u r e 8 . 1 ) . The damping  r a t i o , D, can be determined from the l o g decrement u s i n g the  following  equation: D-  6  /(<5  where Typically,  2  +  4(TT) )  & = log  2  decrement.  s o i l s have a damping r a t i o , D, o f approximately  . 0 5 . Damping  r a t i o s determined u s i n g the a c c e l e r o m e t e r responses are p l o t t e d i n 8 . 2 . The average v a l u e D i s 0 . 1 9 6 ,  Figure  a p p r o x i m a t e l y 4 times the v a l u e e x p e c t e d .  Typical  H o r i z o n t a l A c c e l e r o m e t e r Response to Hammer Shear Source  Time A  Log Decrement 6 = In 1 A  2  F i g u r e 8.1 D e f i n i t i o n of Log Decrement from H o r i z o n t a l A c c e l e r o m e t e r Response to Hammer Shear Source  Damping  .05 I  .1  L  Ratio  . 15  25  2  A A  r a. o a  5-  A  ~  McDonalds Farm Hammer Shear Source  Damping r a t i o s c a l c u l a t e d a c c e l e r o m e t e r response.  from l o g decrement of h o r i z o n t a l  F i g u r e 8.2 Damping R a t i o s From A c c e l e r o m e t e r Response v e r s u s Depth  A p o s s i b l e e x p l a n a t i o n f o r the high damping r a t i o v a l u e s o b t a i n e d  from  the a c c e l e r o m e t e r s i s t h a t the a c c e l e r o m e t e r s are not responding t o the  soil  a l o n e . The a c c e l e r o m e t e r i s f i r m l y a t t a c h e d t o the s e i s m i c cone penetrometer which i s i t s e l f c o u p l e d t o the s o i l .  The s e i s m i c cone penetrometer has  its  own response c h a r a c t e r i s t i c s t o wave e x c i t a t i o n . Thus, the a c c e l e r o m e t e r response r e p r e s e n t s a c o m b i n a t i o n o f the cone and s o i l the s o i l  response  responses, rather  alone.  In o r d e r to determine the response o f the s o i l  a l o n e , the response  the cone t o s p e c i f i c wave e x c i t a t i o n must be d e t e r m i n e d , and then from the t o t a l  than  response o f the c o n e - s o i l  8.3 Waveform A n a l y s i s t o determine S o i l  Determination of i n s i t u m a t e r i a l  system seen by the  of  subtracted  accelerometer.  Damping  damping has been attempted by Hoar and  Stokoe, 1984, u s i n g the c r o s s h o l e s e i s m i c t e s t i n g method. Hoar and Stokoe s t a t e t h a t o t h e r s e i s m i c f i e l d methods, such as downhole t e s t i n g , c o u l d be used t o o b t a i n i n s i t u m a t e r i a l  damping, as l o n g as two shear wave a r r i v a l s  are monitored from a s i n g l e energy i m p u l s e . That i s ,  the t r u e  technique must be u s e d , as opposed t o the pseudo i n t e r v a l Rice (1984) used the t r u e I n t e r v a l  Interval  technique.  t e c h n i q u e t o o b t a i n much o f the  data  f o r h i s r e s e a r c h . U s i n g some o f t h i s d a t a , the manual waveform a n a l y s i s suggested by Hoar and S t o k o e ,  1984, was performed t o o b t a i n i n s i t u  r a t i o s . The F o u r i e r waveform a n a l y s i s suggested by Hoar and S t o k o e , not performed, because the computer f a c i l i t i e s  damping 1984, was  t o perform t h i s a n a l y s i s were  unavailable. This section w i l l  briefly  o b t a i n i n g damping r a t i o s  summarize the r e s u l t s o f t h i s i n i t i a l  from the s e i s m i c cone  penetrometer.  look  at  8.3.1  R e s u l t s o f Manual  Waveform A n a l y s i s  The decay o f amplitudes o f body waves as they propagate through the 1s a combination of g e o m e t r i c a l  and m a t e r i a l  dampings. The m a t e r i a l  soil  component  f o r body waves ( a l s o known as the v i s c o u s damping component) i s g i v e n by the following equation: D =  1n(Al-Rl/A2-R2)  where D = damping and a l l  ratio  other v a r i a b l e s are defined in Figure  F i g u r e 8.4 15 m e t e r s , the value of 0.08.  8.3.  shows the r e s u l t s o f t h i s data a n a l y s i s .  In the sands above  damping r a t i o s ranged from 0.023 t o 0 . 1 3 8 , w i t h an average In the c l a y e y s i l t s below 15 m e t e r s , the damping r a t i o s  ranged  from 0.057 t o 0 . 1 5 5 , w i t h an average v a l u e of 0 . 1 0 5 . These damping r a t i o s g r e a t e r than those o b t a i n e d by Hoar and S t o k o e . A l s o , Seed and I d r i s s show s l i g h t l y h i g h e r damping r a t i o s  i n sand then i n c l a y , whereas  o p p o s i t e i s seen h e r e . These d e v i a t i o n s  (1970)  the  from the e x p e c t e d values may be due  t o the way i n which the s e i s m i c cone penetrometer i n t e r a c t s w i t h the  soil.  More r e s e a r c h o f t h i s t e c h n i q u e i s needed b e f o r e c o n c l u s i v e r e s u l t s can be obtained.  are  Top H o r i z o n t a l Geophone I Rj - Straight-line travel path length from source to r e c e i v e r  CD XI  3  a.  Z\ McDonalds Farm Hammer Shear Source Depth 10.6 meters (Data from d i s k s AR-82-24 t h r u 30)  Straight-line travel path length from source to r e c e i v e r  10  20  30 Time  40 50 (milliseconds)  F i g u r e 8.3 Geophone Waveforms d e f i n i n g Q u a n t i t i e s  _L  60  70  f o r Damping C a l c u l a t i o n  80  Damping  0 04-  05 _L_  Ratio  15 _L_  1  .2  10-  r.  •p a. a  •  20-  A  McDonalds Farm Hammer Shear Source Data from Rice,1984 d i s k s AR-82-24 t h r u 30 30 Damping R a t i o C a l c u l a t e d (Hoar and Stokoe, 1984)  Figure  8.4  _L from Manual Waveform A n a l y s i s  Damping R a t i o s from Manual Waveform A n a l y s i s  versus  9.  96  CONCLUSIONS  D i f f e r e n t types o f sources and r e c e i v e r s used with the s e i s m i c cone p e n e t r a t i o n t e s t were i n v e s t i g a t e d f o r t h i s t h e s i s . The sources were mechanical  investigated  shear and compression wave sources c o n s i s t i n g o f a hammer-  and-weighted-plank  s o u r c e ; a B u f f a l o gun s o u r c e ; a s e i s m i c cap s o u r c e ; and an  embedded blade w i t h s e i s m i c cap s o u r c e . The r e c e i v e r s i n v e s t i g a t e d were horizontal  well  and v e r t i c a l  geophones and a c c e l e r o m e t e r s .  The hammer shear s o u r c e , p r e v i o u s l y i n v e s t i g a t e d by R i c e ,  1984, worked  and was used as a s t a n d a r d f o r comparison. The mechanical  compression  wave source was not used s u c c e s s f u l l y w i t h the s e i s m i c cone p e n e t r a t i o n because the v e r t i c a l  receivers,  test,  needed t o d e t e c t t h i s s o u r c e , d i d not give a  response r e p r e s e n t a t i v e o f the s o i l  r e s p o n s e . Rather,  the v e r t i c a l  probably responded t o waves t r a v e l l i n g i n the cone and r o d s .  receivers  Horizontal  r e c e i v e r s used w i t h the hammer P-wave source d i d not produce a m p l i t u d e s enough t o i n t e r p r e t a c c u r a t e l y . A d d i t i o n of s e v e r a l i n t e r p r e t a i o n and s h o u l d be r e s e a r c h e d  large  s i g n a l s may improve the  further.  The B u f f a l o gun source gave shear wave v e l o c i t i e s which compared r e l a t i v e l y well w i t h the shear wave v e l o c i t i e s o b t a i n e d u s i n g the hammer o n l y a t depths g r e a t e r than 12 m e t e r s . A t depths l e s s than 12 meters the two sources d i f f e r e d by as much as 50 p e r c e n t . However, the B u f f a l o gun was difficult  t o i n t e r p r e t because o f the a d d i t i o n of the P and SV-waves,  e s p e c i a l l y a t shallow d e p t h s . The t r i g g e r i n g system used w i t h the B u f f a l o gun was not c o n s i s t e n t enough t o a l l o w a c c u r a t e compression wave v e l o c i t y p r o f i l e s t o be d e t e r m i n e d . Thus, e i t h e r a more c o n s i s t e n t t r i g g e r i n g s h o u l d be found f o r the B u f f a l o gun, o r a t r u e i n t e r v a l  circuit  t e c h n i q u e should be  u s e d , where the energy impulse i s d e t e c t e d s i m u l t a n e o u s l y by two r e c e i v e r s , one meter a p a r t .  The s e i s m i c cap s o u r c e s , used o f f - s h o r e , were found t o g i v e shear wave v e l o c i t y d e t e r m i n a t i o n s .  In a d d i t i o n ,  v e l o c i t y d e t e r m i n a t i o n s were f o u n d , i f fired,  remained c o n s t a n t .  reasonable  reasonable compression wave  the depth at which the s e i s m i c cap was  I n t e r p r e t a t i o n o f the waves r e c e i v e d from the  s e i s m i c caps was d i f f i c u l t ,  because o f the a d d i t i o n o f c o m p r e s s i o n ,  shear,  and r e f l e c t e d waves. I n t e r p r e t a t i o n o f the s e i s m i c cap source s i g n a l easier i f  the t r u e i n t e r v a l  technique,  would be  d e s c r i b e d f o r the B u f f a l o gun, was  u s e d . Use o f t h i s t e c h n i q u e would a l s o e l i m i n a t e the n e c e s s i t y of  controlling  the f i r i n g depth o f the s e i s m i c c a p . The embedded blade source appears to g i v e a more well then the s e i s m i c cap a l o n e . a l o n e , because the s o i l  I t i s more d i f f i c u l t  d e f i n e d SV-wave  t o use than the s e i s m i c cap  a t mudline must be s o f t enough t o allow the b l a d e  be embedded, and because the blade must be l i f t e d a s e i s m i c cap a f t e r each t e s t .  However,  from the mudline to  to  attach  s i n c e the embedded blade source was  used only once t o o b t a i n a s e i s m i c wave p r o f i l e ,  further investigation  of  t h i s source s h o u l d be c a r r i e d out b e f o r e f u r t h e r c o n c l u s i o n s can be made. Both geophones and a c c e l e r o m e t e r s were found t o g i v e s i m i l a r shear wave v e l o c i t i e s f o r the hammer shear s o u r c e . L e s s s i m i l a r i t y was seen f o r  the  B u f f a l o gun s o u r c e . T h i s c o u l d be a r e s u l t o f a v a r i a b l e phase s h i f t o f f i l t e r e d a c c e l e r o m e t e r . S i n c e compression and shear waves from the gun add t o g e t h e r ,  the frequency o f t h e s i g n a l  may v a r y ,  the  Buffalo  and t h u s , the phase  s h i f t due t o the f i l t e r may a l s o vary^ Although geophones were s u c c e s s f u l l y used with the e x p l o s i v e o f f - s h o r e  s o u r c e s , the use o f adequately  filtered  a c c e l e r o m e t e r s w i t h o f f - s h o r e e x p l o s i v e s o u r c e s s h o u l d be I n v e s t i g a t e d i n  the  f u t u r e . A c c e l e r o m e t e r s may prove e a s i e r t o i n t e r p r e t and more a c c u r a t e . Since geophones are cheaper and e a s i e r t o u s e , and g i v e  reasonable  r e s u l t s with e x p l o s i v e s o u r c e s , they are p r o b a b l y the b e s t r e c e i v e r t o u s e . A c c e l e r o m e t e r s , because they are a m p l i f i e d and can d e t e c t s i g n a l s t o a  98 g r e a t e r depth, can be used f o r deep p e n e t r a t i o n work with mechanical s o u r c e s . However, a m p l i f i c a t i o n of the geophone s i g n a l  shear  may be c h e a p e r ,  and  thus geophones c o u l d a l s o be used f o r deep p e n e t r a t i o n work. As mentioned above, v e r t i c a l cone penetrometer,  r e c e i v e r s can not be used i n the  seismic  because they do not g i v e a r e p r e s e n t a t i v e response o f  the  soil. The use o f compression and shear wave v e l o c i t i e s r a t i o gave reasonable r e s u l t s i f  the s t r a i n l e v e l  t o determine P o i s s o n ' s  and type o f  compression  wave were taken i n t o a c c o u n t . The p r e l i m i n a r y d e t e r m i n a t i o n o f the m a t e r i a l damping r a t i o gave r e s u l t s which were h i g h e r than e x p e c t e d . These  results  probably i n d i c a t e the a c c e l e r o m e t e r i s responding t o the s o i l - c o n e system, r a t h e r than to the s o i l  a l o n e . Thus, f u r t h e r r e s e a r c h s h o u l d be undertaken  i n v e s t i g a t e the response o f the a c c e l e r o m e t e r t o the cone a l o n e .  to  This  response c o u l d then be s u b t r a c t e d from the response t o the combined c o n e - s o i l system, and thus the s o i l  response c o u l d p o s s i b l y be e x t r a c t e d .  As b e t t e r computer f a c i l i t e s become a v a i l a b l e ,  greater analysis of  the  data o b t a i n e d from the s e i s m i c cone c o u l d be p e r f o r m e d . F o r example,  digital  f i l t e r i n g o f the a c c e l e r o m e t e r responses c o u l d be c a r r i e d o u t . A l s o ,  a  F o u r i e r waveform a n a l y s i s t o o b t a i n m a t e r i a l from t r u e I n t e r v a l  damping (Hoar and S t o k o e ,  responses c o u l d be a t t e m p t e d . Both d i g i t a l  filtering  F o u r i e r a n a l y s i s r e q u i r e computer storage space and communication between the r e c o r d i n g o s c i l l o s c o p e and the computer, which are u n a v a i l a b l e , but which a r e b e i n g r e s e a r c h e d a t U . B . C .  1984)  lines  currently  and  99 REFERENCES  A l l e n , F . N . , R i c h a r t , F . E . J r . , and Woods, R . D . , 1980, " F l u i d Wave P r o p a g a t i o n i n S a t u r a t e d and N e a r l y S a t u r a t e d S a n d s " , J o u r n a l 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 . 106, No. GT3, March, pp.235-254. B a l l a r d , R . F . J r . and McLean, F . 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E . , 1974, " S e i s m i c I n v e s t i g a t i o n o f a San F r a n s i c o Mud Bay S i t e " , B u l l e t i n o f the S e i s m o l o g i c a l S o c i e t y o f A m e r i c a , V o l . 6 4 , No. 2, A p r i l , pp.375-38"5T Whitman, R . V . , 1965, " A n a l y s i s o f Foundation V i b r a t i o n s " , from V i b r a t i o n s C i v i l E n g i n e e r i n g , e d i t e d by B.O. S k i p p , B u t t e r w o r t h s & C o . L t d . , pp. 1597179":  in  W i l s o n , R . C . , W a r r i c k , R . E . , and B e n n e t t , M . J . , 1978, " S e i s m i c V e l o c i t i e s o f San F r a n s i c o Bayshore Sediments", Proceedings ASCE 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 S p e c i a l t y Conference on Earthquake E n g i n e e r i n g and S o i l Dynamics, Pasadena, C a l i f o r n i a , pp.1007-1023.  102  APPENDIX A  UBC Sito On  Location! Site  Loci  IN  SITU  MCDONALD'S FARM CPT-21  PORE PRESSURE  SLEEVE FRICTION  U ta. o f «at«r)  <ba->  TESTING  CPT D a t a . 05/14/85 NL MD JH Cono U s e d i CONE BEARING Oc  (bor)  UBC#B STD T I P F R I C T I O N RATIO Rf  Pago Noi Commontsi  1 / 1 CMAX  DIFFERENTIAL P . P .  CO  RATIO  AU/Qc  INTERPRETED PROFILE  Soft SILT  Coarse SAND  Fine SAND  Soft clayey SILT  Oopth I n c r s n a n t >  .025 m  Max D e p t h i  20.525 m  O  UBC  I M  Si to Locations  Schoolhouse  On  GSC#3  Si to  Loci  PORE PRESSURE  Site  SLEEVE FRICTION  Dopth Incramont t  SIT  CPT D a t a i Cona Uaadi CONE BEARING  .025 m  U  rES" r i M  G  1  Page Noi  03/22/85 14i 51  Commantsi  UBCiCB BT t h i n F R I C T I O N RATIO  Max  1 / 2  295cm  DIFFERENTIAL P.P.  Oapth i  18.45 m  lco*wator INTERPRETED  UBC SI t o L o c o t l o n i  I M Schoolhouaa  Sits  On S i t o L o c i GSCIV3 SLEEVE FRICTION PORE PRESSURE (bar) U (n. of *atar) 2.5 0 100 0 15 15  SITU  TESTING  CPT Oato i  03/22/85  Const Usadi  UBC#6 BT t h i n  CONE BEARING 0c (bar)  14i51  Pago Noi  Commontai  2 / 2  295cm  Ic«+«atsr  INTERPRETED FRICTION RATIO DIFFERENTIAL P.P. PROFILE Rf «> RATIO AU/Oc Generalized 250 0 5 -.2 0 .8 15i5-tr- — —'— —I 15 J  1  1  SAND  1  4  thin gravelly l a y p r  maximum b e a r i n g of 387 b a r  20-  20-  20  25  25-  • 25  30-  30-  (3 I S . '  20  s t o p p e d on frozen 20- ground  25  25  L (V •P 01 E  0_ LU O  25  30-  30  30 Dopth Incronant i  . 025 m  Max D o p t h i  18.45 m O  UBC  I  M  SIX  Site Locatloni  SWIMMING POINT  CPT D a t o i  On  GSC #8 ON SHORE  Cong Usadi  SLEEVE FRICTION  CONE BEARING  Site  Loci  PORE PRESSURE  Depth Increment •  i 025 m  U  T E S "r i  03/27/85 PKR DC  Pago Not  UBC8 STDSBEHINO  Conmontei  FRICTION RATIO  MG  1/1  ICE DPTH-1.5m  DIFFERENTIAL P.P.  Max D e p t h i  14.3  INTERPRETED  • O  UBC  Si to Location! On  Site  IN  Richards  Is.-Tutt  L o c i ' GSC#9  PORE PRESSURE SLEEVE FRICTION U (*. of voter) (bar) 0 100 _0 . . . . 2.5  SITU  TESTING  CPT O a t a i  03/28/85 12i 51  Cone Usodi  UBC#6 S t d T i p BT FRICTION RATIO Rf (X)  CONE BEARING 0c (bar) 'frozen at surface  Pago Noi  Commantai  1 / 1  190 cm l c a / 0 H20 INTERPRETED PROFILE generalized  DIFFERENTIAL P.P. RATIO iU/Oc -.2 0 .B 0  sandy  SILT  SAND t o s i l t y SAND  c l a y e y SILT to s i l t y CLAY  W L  Dense SAND  01  •P  0)  J QL LU  a  ir>  10  C l a y e y SILT to s i l t y CLAY  refusal 15-  15 Oapth  Increment i  . 025 m  Max D e p t h i  13. 7 m O  UBC Site Location! On S i t o Loci PORE PRESSURE  IN Tuk H a r b o u r S i t s GSC#12 SLEEVE FRICTION  Dopth Increment i  SITU CPT D a t o i Cono Uaedi CONE BEARING  .025 m  TESTING  03/30/8S 12i 10 UBC#6 S t d T i p BT FRICTION RATIO  P a g o Noi Commentei  1 / 1 660cm I c a + w a t o r  DIFFERENTIAL P.P.  Max D e p t h i  14.775 m  INTERPRETED  

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