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The seismic cone penetrometer Rice, Anthony Henry 1984

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THE SEISMIC CONE  PENETROMETER  by ANTHONY HENRY RICE B.A.S.c.,the  U n i v e r s i t y Of B r i t i s h  C o l u m b i a , 1980  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED  SCIENCE  in THE FACULTY OF GRADUATE Department  We a c c e p t to  Of C i v i l  this  standard  OF BRITISH COLUMBIA  December  ©  Engineering  t h e s i s as c o n f o r m i n g  the required  THE UNIVERSITY  STUDIES  1984  A n t h o n y Henry R i c e ,  1984  In  presenting  requirements  this f o r an  Columbia,  I  available  for  permission p u r p o s e s may or  her  be  of  shall  reference  and  study.  I  extensive granted  by  this thesis written  Civil  10  December  copying the  Head of  It for  is  this thesis my  Columbia  gain  the  of  British  it  freely  agree for  Department  understood  permission.  make  further  financial  Engineering  1984  of  of  University  Library  The U n i v e r s i t y of B r i t i s h 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5  Date:  the  the  a l l o w e d w i t h o u t my  Department of  partial ' fulfilment  that  representatives.  publication  in  advanced degree at  agree  for  thesis  that  that  scholarly  or  by  copying  shall  not  his or be  0  •  11  ABSTRACT A static small  cone p e n e t r o m e t e r  diameter  evaluated selected B.C.  by  triaxial  obtaining  the  assess  on  of  determining  geophone p a c k a g e was  a practical  incorporate  in-situ  added t o t h e  wave v e l o c i t y  a was  profiles  the F r a s e r R i v e r D e l t a near  the a c c u r a c y of shear  determine  to  geophone p a c k a g e . T h i s i n s t r u m e n t  purpose  m o d u l i . A second  modified  downhole s h e a r wave v e l o c i t y  research sites  for  was  at  Vancouver  dynamic  shear  instrument  to  measurements, and  instrument c o n f i g u r a t i o n  for routine  to  field  use. Shear  wave  repeatability energy  and  source  rational  characteristics,  and  testing  exclusively  signal  amplitude  were  Plank  found  c o n v e n i e n t . Geophone r e s p o n s e excellent of  and  40 m e t r e s .  and  The  shear  Down r o d s i g n a l  testing results  penetrometer r a p i d and velocity  procedures of t h i s  s u r v e y . The  soil  orientation. pore  to  and  both  receiver  indicate  to s o i l  that  single  i t minimizes  receiver  to develop  and  c o u p l i n g were to  depths  repeatability  coupling from  a  static  allows  wave  superior  disturbance, provides  and  controlled  t h e cone b e a r i n g ,  measurement e l e m e n t s ,  cone  provide a  out a downhole s h e a r  soil  by  techniques.  geophone can  procedure  a  used  satisfactory  interpretation  a  the  n o i s e l e v e l s were overcome  testing  Combined w i t h d a t a  pressure  be  for carrying  cone  signal  s o u r c e s were  transmission, signal  just  a c c u r a t e method  signal  and  waves were o b t a i n e d  study  containing  wave r e c o r d s s i n c e  excellent  and  to  problems with h i g h background  selective  shear  identifiable  response,  type  and  velocities,  were s t u d i e d , t o e v a l u a t e  downhole r e c e i v e r  procedure.  and  downhole  the  receiver friction  interpretation  of  in-situ hole,  static  and dynamic  is greatly  enhanced.  soil  properties,  using  a single  test  ii ii  TABLE OF  CONTENTS PAGE i i  ABSTRACT TABLE OF L I S T OF  CONTENTS FIGURES  ACKNOWLEDGEMENTS  ii ii vi viii  1.0  INTRODUCTION 1.1 R a t i o n a l e f o r S e i s m i c Cone Development 1.2 S h e a r Modulus as a G e o t e c h n i c a l P a r a m e t e r 1.3 T h e s i s O r g a n i z a t i o n  1 1 2 6  2.0  IN-SITU SHEAR MODULUS DETERMINATION 2.1 S e i s m i c Wave Phenomenon 2.1.1 T y p e s o f S e i s m i c Waves 2.1.2 S h e a r Wave C h a r a c t e r i s t i c s 2.2 D e t e r m i n a t i o n o f E l a s t i c P a r a m e t e r s 2.3 C o n v e n t i o n a l I n - S i t u S e i s m i c Measurement 2.3.1 C o n v e n t i o n a l C r o s s h o l e T e s t i n g 2.3.2 C o n v e n t i o n a l Downhole T e s t i n g  8 8 8 10 12 17 18 19  3.0  CPT 3.1 3.2 3.3  DOWNHOLE SEISMIC EQUIPMENT AND PROCEDURES Introduction S e i s m i c Cone P e n e t r o m e t e r S h e a r Wave G e n e r a t i o n 3.3.1 S i g n a l S o u r c e 3.3.2 S o u r c e L o c a t i o n 3.4 S h e a r Wave D e t e c t i o n 3.4.1 Geophone Response 3.4.2 S i g n a l F i l t e r i n g 3.4.3 O s c i l l o s c o p e R e s o l u t i o n 3.5 T r i g g e r i n g Systems 3.6 F i e l d P r o c e d u r e 3.7 Summary  25 25 27 30 30 31 34 35 40 41 44 45 48  4.0  DATA INTERPRETATION AND ANALYSIS 4.1 I n t r o d u c t i o n 4.2 A r r i v a l Time Measurement 4.2.1 S h e a r Wave I n t e r p r e t a t i o n 4.2.2 S t a t i s t i c a l E r r o r A s s e s s m e n t 4.3 S h e a r Wave V e l o c i t y D e t e r m i n a t i o n 4.3.1 T r a v e l Time E f f e c t s 4.3.2 T r a v e l P a t h E f f e c t s 4.4 Dynamic S h e a r Modulus C a l c u l a t i o n 4.5 Summary  50 50 50 51 54 62 63 65 69 74  V  PAGE 5.0  DYNAMIC SHEAR MODULUS F I E L D MEASUREMENTS 5.1 I n t r o d u c t i o n 5.2 CPT S e i s m i c F i e l d T e s t i n g C a p a b i l i t y 5.2.1 M c D o n a l d s Farm S i t e 5.2.2 F o r t L a n g l e y Freeway S i t e 5.2.3 A n n a c i s N o r t h P i e r S i t e 5.3 C o m p a r i s o n o f I n - S i t u M o d u l i Measurements 5.3.1 S e l f - B o r i n g P r e s s u r e m e t e r M o d u l i 5.3.2 CPT Cone B e a r i n g C o r r e l a t i o n s 5.3.3 C o n v e n t i o n a l C r o s s h o l e T e s t i n g 5.4 C o n v e n t i o n a l E m p i r i c a l R e l a t i o n s h i p s 5.5 Summary  6.0  CONCLUSIONS 6.1 Summary o f R e s e a r c h F i n d i n g s 6.2 F u r t h e r R e s e a r c h 6.3 C o n s i d e r a t i o n s for Practical REFERENCES  Application  76 76 76 79 81 83 85 85 87 87 92 97 98 98 101 103 106  v\  L I S T OF FIGURES FIGURE  PAGE  1  Stress,  2  V a r i a t i o n o f Shear Modulus  3  T y p e s o f S e i s m i c Waves  4  S h e a r Wave C h a r a c t e r i s t i c s  5  Variation  6  Conventional Crosshole Testing  20  7  C o n v e n t i o n a l Downhole T e s t i n g  22  8  CPT S e i s m i c  26  9  15 cm  10  Signal  11  Geophone C o n s t r u c t i o n  36  12  Geophone S p e c i f i c a t i o n s  37  13  O b s e r v e d Shear Wave T r a c e s from a S i n g l e  2  S t r a i n and S h e a r Modulus  in Stress  Relationship  w i t h Shear S t r a i n  5 9 1 1  Across a Small S o i l  Equipment  Element  Layout  28  S t r e n g t h V e r s u s Depth  33  Hammer 38  14  E f f e c t s of S i g n a l  15  Electrical  16  P o l a r i z e d Shear Wave T r a c e s from T r a n s v e r s e Geophones C o m p a r i s o n Between T r u e a n d Pseudo Measurement  18 19 20  14  S e i s m i c Cone  Impulse  17  3  Enhancement  Step T r i g g e r  43  Circuit  46  52 Interval 55  C o m p a r i s o n Between T r u e and Pseudo T i m e s f o r Unmatched Geophones  Interval  C o m p a r i s o n Between T r u e and Pseudo Times f o r Matched Geophones  Interval  Travel 60 Travel 61  V e l o c i t y Measurement A c c u r a c y a s a F u n c t i o n o f Measurement P r e c i s i o n and Geophone S e p a r a t i o n  21  E f f e c t s of Signal  Refraction  on Wave T r a v e l  Path  22  C o m p a r i s o n Between C o n v e n t i o n a l a n d I t e r a t i v e Velocity Calculations  64 66  70  v i i  FIGURE  PAGE  23  Sand D e n s i t y  24  Research S i t e Location  25  M c D o n a l d s Farm Cone  26  Fort  27  Annacis North Pier  28  C o m p a r i s o n Between CPT S e i s m i c and P r e s s u r e m e t e r , M c D o n a l d s Farm  29 30 31 32  - Cone B e a r i n g  L a n g l e y Cone  Correlation  73  Map  78  Profile  80  Profile Cone  82  Profile  C o m p a r i s o n Between CPT S e i s m i c P r e d i c t i o n , McDonalds Farm  84 Self-Boring  and CPT  86 Bearing 88  C o m p a r i s o n Between CPT S e i s m i c and CPT P r e d i c t i o n , Annacis North P i e r  Bearing  C o m p a r i s o n Between Downhole and C r o s s h o l e Measurements, A n n a c i s N o r t h P i e r C o m p a r i s o n Between CPT S e i s m i c S h e a r M o d u l u s , McDonalds Farm  89 Velocity  and E m p i r i c a l  91 Dynamic 94  33 C o m p a r i s o n Between CPT S e i s m i c a n d E m p i r i c a l Shear M o d u l u s , F o r t L a n g l e y  Dynamic  34 C o m p a r i s o n Between CPT S e i s m i c and E m p i r i c a l Shear Modulus, A n n a c i s North P i e r  Dynamic  95 96  vi i i  ACKNOWLEDGEMENTS  The and of  writer  critical this  Peter  Information  seismic  extremely  t o acknowledge the support,  provided  equipment  by  research  Ertec  K. R o b e r t s o n  a l s o proved  possible  without  and  provided  the  fine  technical  by M e s s e r s A r t B r o o k e s , G a r y  K i r s c h , Dick  Postgate,  a n d Don Smythe.  a s s i s t a n c e o f Mr. Andy N i c h o l s , Mr. Tsang,  Cook d u r i n g  the  Steve  Mr. J i m G r e i g , Ms. Nancy L a i n g , data  CPT was  by D r .  i n v a l u a b l e . The p r o j e c t would n o t  provided  Clifford  on  development  workmanship  The  the course  Western  u s e f u l . The a s s i s t a n c e and s u g g e s t i o n s  have been  suggestions  comments from D r . R.G. C a m p a n e l l a d u r i n g  study.  downhole  wisher  aquisition  phase  of  support  B u r l o c k , Guy  Brown,  a n d Ms.  the  and  Mr.  Tricia  project  was  appreciated. The  cooperation  Transportation for also  access  of  the  British  a n d Highways, a n d G o l d e r  t o and i n f o r m a t i o n  Columbia Associates,  on t h e A n n a c i s  Ministry  of  Vancouver,  N o r t h P i e r S i t e was  appreciated. Special  thanks  also  go  t o Ms. T r i c i a  Cook who t y p e d t h e  thesis. Financial Engineering  support  was p r o v i d e d  by t h e N a t u r a l  R e s e a r c h C o u n c i l o f Canada.  Science  and  1  1 .0 INTRODUCTION  1.1 R a t i o n a l e f o r S e i s m i c Cone D e v e l o p m e n t  Accurate essential  component  structures response of  assessment of  subjected  analysis  t h e most  of  dynamic  foundation to  properties  design  oscillatory  of ground  for  vibration  s u b j e c t e d t o earthquake  i m p o r t a n t dynamic  modulus, G. The s i m p l e  soil  soil  properties  is  an  machines and  and  in  the  s h a k i n g . One  i s the s o i l  shear  relationship  TVs G = pVs  2  2  =  1 g  from  elastic  density,  theory  p (total  acceleration  relates  unit  weight  due t o g r a v i t y ,  s h e a r wave v e l o c i t y ,  two  determining  most  soil  c r o s s h o l e methods conventional the  use  expensive The the  of  g) m u l t i p l i e d  by t h e s q u a r e  wave  velocity  using i n - s i t u  wave  used  special  special  the  of the  hence  shear  s e i s m i c methods f o r  are  ( S t o k o e and A b d e l - r a z z a k ,  techniques require  and  by  s e i s m i c methods.  in-situ  velocity  divided  the 1975).  testhole  downhole However  and these  p r e p a r a t i o n and  e q u i p m e n t . They c a n be t i m e c o n s u m i n g a n d  to perform. recent acceptance  premier  deposits  7,  commonly  shear  s h e a r modulus G t o t h e s o i l  of the s o i l ,  V s . Shear  modulus c a n be d e t e r m i n e d The  the  logging  tool  (Campanella  of t h e s t a t i c  for in-situ and  cone  penetrometer  investigations  Robertson,  1982)  as  in soft  soil  makes  the  2  incorporation extremely  o f dynamic  attractive.  research carried penetrometer. cylindrical modified depth  This  By  cavities  penetrometer. velocity  A  the  results  velocity  cone  t i p and  shear  cone  static  of cone  transducers  in  performing  wave v e l o c i t y  o f t h e r e s e a r c h were t o m o d i f y  testholes. the  the  a  versus  determined.  rational  testing  rapid,  s h e a r modulus p r o f i l e s  enhance  within  instrumented  survey,  t e c h n i q u e s so t h a t  penetration to  the  seismic  objectives  thus  presents  geophone  behind  e q u i p m e n t , and t o d e v e l o p  and  thesis  placing  p r o f i l e s were  analysis  capability  o u t u s i n g a geophone  downhole  The  testing  stratigraphic technique  be  and  obtained  cone data  velocity  from  cone  i t was c o n s i d e r e d d e s i r a b l e  logging  was  procedures  a c c u r a t e s h e a r wave  could  In p a r t i c u l a r  existing  capability  developed  whereby  and s h e a r modulus c o u l d be measured o v e r  of. t h e c o n e shear  wave  1 metre  depth  increments. An  important  aspect of  the  repeatability  and  accuracy  the advantages  and l i m i t a t i o n s  deformation  modulus to  is  shear  a  to  o f the s e i s m i c cone wave v e l o c i t y  Modulus as a G e o t e c h n i c a l  Shear  was  assess  the  o f t h e measurements and t o compare  c o n v e n t i o n a l methods o f s h e a r  1.2 Shear  research  soil  loading  with  measurement.  Parameter  parameter as  method  shown  which r e l a t e s in  Figure  1a.  shear The  relationship T  = Gy  2  FIG.  1.  S T R E S S , S T R A I N AND MODULUS  SHEAR  RELATIONSHIP  4  where 7  r i s t h e a p p l i e d shear  i s the  resulting  modulus o f determine  a  among  soil  the  principal  strain,  i s a familiar  i s , however,  precisely.  and D r n e v i c h  shear  s t r e s s , G i s t h e shear modulus, and  not  an  o n e . The s h e a r  easy  parameter  I t i s d e p e n d e n t on numerous f a c t o r s .  (1972) c l a s s i f i e d most i m p o r t a n t  these  s t r e s s , v o i d r a t i o , and degree of s o i l  of  disturbance  particularly  on  a  duplication  of  during  saturation.  in-situ  void  soils  i t may  saturation  levels  i n laboratory  modulus  most  important  i s the strain  most s o i l s h a v e a  be  soil  The  Likewise to  accurate for  maintain  partly in-situ  samples.  the  four factors a f f e c t i n g  l e v e l a t which  curvilinear  proposition.  complicate  ratios.  difficult  of  s t r e s s e s on  s a m p l i n g , h a n d l i n g and t e s t i n g  cohesionless  saturated  The  that  were s t r a i n a m p l i t u d e , e f f e c t i v e mean  samples i n t h e l a b o r a t o r y i s a d i f f i c u l t  effects  Hardin  f a c t o r s and determined  D u p l i c a t i o n o f i n - s i t u e f f e c t i v e mean p r i n c i p a l soil  to  the s o i l  stress  shear  i s t e s t e d . Because  strain  relationship  as  shown i n F i g u r e 1b, t h e s h e a r m o d u l u s , shown a s t h e s l o p e o f t h e secant  line,  level.  A  study  quantitatively In  Figure  increasing  2a  The  by  Seed  and  and  At  2b,  strain  the  dynamic shear  Idriss  reduction  i s shown  strains  of 10-  i s a maximum a n d l i t t l e  maximum  reduction with increasing (1970)  the e f f e c t s of s t r a i n amplitude  shear  respectively. modulus  shows s i g n i f i c a n t  shear  modulus  U  of  for  strain  presented  on s h e a r  modulus.  shear modulus sands  and  with clays  % or l e s s however, t h e shear  affected  by  strain  amplitude.  i s g e n e r a l l y known a s Gmax o r t h e  modulus.  The s e n s i t i v i t y  of t h e shear modulus p a r a m e t e r t o t h e above  a)  SANDS  0  1  1  I0  -  5  ICT  4  SHEAR  F I G . 2.  r  1  KT  3  STRAIN  KT  %  VARIATION OF WITH SHEAR  2  1  1  r  KD  I  10  -1  -PERCENT  SHEAR STRAIN  MODULUS  6  factors  i s the primary  strain  seismic  reason  waves  that  in-situ  i s preferred  over  testing  using  laboratory  low  testing for  t h e d e t e r m i n a t i o n o f Gmax.  1.3 T h e s i s O r g a n i z a t i o n  This cone  thesis  d i s c u s s e s t h e d e v e l o p m e n t and u s e o f a  penetrometer. Presented a r e d e t a i l s  e q u i p m e n t , an o u t l i n e discussion accurate  of  of  rational  i n - s i t u s h e a r wave  of t h e i n - s i t u  testing  the i n t e r p r e t a t i o n  testing  procedures,  techniques required  velocity  seismic  measurement  and  a  to permit  and  dynamic  s h e a r modulus d e t e r m i n a t i o n . Chapter  2  presents  a  brief  discussion  phenomenom a n d c o n v e n t i o n a l methods o f velocity  in-situ.  The  advantages  on s e i s m i c wave  determining  and  shear  disadvantages  c o n v e n t i o n a l methods a r e a s s e s s e d . A b r i e f  wave  of these  l i t e r a t u r e review  is  included. Chapter equipment study.  3 d i s c u s s e s development  and  the  Emphasis  limitations  rational  is  of  placed  the  of the s e i s m i c cone  testing on  procedures  identifying  available  equipment  used  the and  testing in this  technical measurement  techniques. Chapter techniques velocity In  4  discusses  required  to  the  interpretation  permit  accurate  d e t e r m i n a t i o n and dynamic  particular  quantitatively  an e f f o r t the  in-situ modulus  analysis shear  wave  calculations.  i s made t o a s s e s s b o t h q u a l i t a t i v e l y and  magnitude  moduli d e t e r m i n a t i o n s .  shear  and  of e r r o r  associated  with  dynamic  7  5 presents  Chapter the  seismic  cone  determinations sites  i n the  between  River  values  data  for  measurements  Dynamic  soils  at  B.C.  calculated  from  different  in-situ  out  moduli of  other  are  compared  research  Comparisons  in-situ  complementary  Columbia,  also  from  moduli  selected  Vancouver  and  using  shear  near  British is  field  Delta  arising of  of  penetrometer.  measurements  University  results  presented  Fraser  correlations  cone  are  moduli  velocity  the  seismic  measurement  research  also  presented.  with  existing  at  The  the  seismic  empirical  relationships. 6  Chapter important  aspects  potential penetrometer discussion equipment.  concludes of  the  additional is of  also  the  thesis  seismic research  presented.  cone  with  review  research. A  utilizing The  a  the  chapter  considerations for practical  of  the  most  discussion seismic closes  application  of cone  with of  a  this  8  2.0  2.1  Seismic  Since integral brief  Wave Phenomenon  t h e measurement of component  review Mooney  on  IN-SITU SHEAR MODULUS DETERMINATION  of  in-situ  wave  (1974) and  Borm  been  used  velocities  is  an  dynamic modulus d e t e r m i n a t i o n ,  of wave phenomenon i s p r o v i d e d (1977) p r o v i d e  s e i s m i c wave p r o p e r t i e s  have  seismic  and  in this  in  chapter.  extensive discussions  characteristics.  extensively  a  preparing  Their the  papers  following  discussion.  2.1.1  T y p e s of S e i s m i c  Four  types  Compressional first  two  of  s e i s m i c waves p r o p a g a t e  (P),  are  Waves  Shear  (S),  Rayleigh  body waves w h i c h p e n e t r a t e  through (R)  into  and the  soil Love  media: ( L ) . The  interior  of  r  the  earth  and  the  last  p r o p a g a t e w i t h i n one  or  on  the  the  layering  propagation  of  in  two  two  are  s u r f a c e waves w h i c h  w a v e l e n g t h s of  system  (See  body waves t h a t  the  Figure  i s important  surface 3).  typically depending  It  in i n - s i t u  is  the  modulus  determinat ion. The  compression  vibration  which l i e s  direction  of p a r t i c l e  direction  of  as  the  longitudinal  (P) waves parallel vibration  are to the  ray path  i s uniquely  ray. Compression or  characterized  irrotational  by  particle  f o r t h e wave.  determined  by  (P) waves a r e a l s o r e f e r r e d waves  and  propagate  The the to  through  FIG. 3. TYPES OF SEISMIC WAVES  10  s o l i d s and f l u i d s .  They p r o p a g a t e  at  a  higher  velocity  than  s h e a r waves. The  shear  (S) waves a r e c h a r a c t e r i z e d  perpendicular may  t o t h e r a y p a t h . The d i r e c t i o n  l i e anywhere  depending The  the  waves  and  also  are  compression  soil  voids at the v e l o c i t y  waves  travel  geotechnical near  only  For  soil  measurements  resolved  into  component  i n the v e r t i c a l  Seismic  sources  SV  the  or  a  S  If  through  or  fluids.  saturated  soil,  t h r o u g h t h e p o r e water  i n the  soil  waves i n w a t e r .  Shear  skeleton. Therefore for  at sites  where t h e water  table  which  the s u r f a c e of the e a r t h ,  particle  component  for  are often  an  SH  vibration parallel  direction  shear  is  can  be  i n Figure  4a.  designed to generate e i t h e r  dominantly  waves.  behavior wave  generation  (SH) and a  engineering  SH  wave  conveniently  to the surface  (SV) a s shown  the true  in  dominantly  fundamentally d i f f e r e n t boundary.  of the  properties.  near  of  and  source.  Characteristics  direction  P  ray,  transverse  i t i s t h e s h e a r wave measurement  in assessing  investigations  as  fully  of c o m p r e s s i o n  e n g i n e e r i n g purposes  Shear Wave  to  in a  the  the  a t t h e wave  unable t o propagate  through  to  motion  by t h e d i r e c t i o n  referred  (P) waves t r a v e l  the s u r f a c e ,  important  2.1.2  of motion  vibration  of p a r t i c l e  perpendicular  e t a l . (1980) h a s shown t h a t  the  is  plane  i s not u n i q u e l y determined  (S) waves a r e  rotational Allen  in  m a i n l y on t h e d i r e c t i o n  direction  r a y . Shear  by p a r t i c l e  of  strikes  The SV  reason and  a  SH  lies waves  horizontal  i n the at  a  geologic  INCIDENT S-WAVE  O)  COMPONENTS OF SHEAR WAVE MOTION  b)  SHEAR WAVE POLARIZATION  FIG. 4 . S H E A R W A V E  CHARACTERISTICS  12  discontinuity, part  is  t h e SH  of the energy  reflected  back, but  t y p e . In c o n t r a s t ,  geologic P;  part  discontinuity  reflected  and  discontinuity seismic  will  also  substantial  P  waves. Thus  the  complicated  sequence  type  seismic  wave  arrivals. Shear  for  waves  P and  SV  of  the  directional  signal  obtained.  not  usually displayed  seismic  P  a unique  waves of  form  careful the  waves. also  (Schwarz and the  energy  the  direct  and  an  SH  of o t h e r  allows  wave  types,  Musser, impulse  illustrated  a  which  other  1972). at  By  a  bi-  s h e a r waves  can  i n F i g u r e 4b,  by c o m p r e s s i o n a l waves, and that  produce  d e s i g n of  polarized  Most  include  interference  from  a  also detect P  of  characteristic  and  striking  may  consisting  identification  horizontal  wave  outgoing  wave  should minimize  This characteristic,  reasons  a  SV waves w i l l  source, oppositely  be  a  most SV d e t e c t o r s w i l l  direction  and  o u t g o i n g waves; SV  four  arrivals  compressional  through  striking  four  waves. I n c o n t r a s t ,  source  reversing  fundamental  produce  to produce  observed  accurate  particularly  wave  produce  and  waves d i s p l a y  their  SV  transmitted. Similarly  sources designed  converted  transmitted  b o t h o f t h e o u t g o i n g waves a r e of  an  will  is  i s one  of  s e i s m i c s h e a r wave s u r v e y  is the  i s so  useful.  2.2  Determination of E l a s t i c  The can  e q u a t i o n s of motion  be d e v e l o p e d  small  Parameters  o f body waves i n an  by c o n s i d e r i n g  rectangular parallelepiped  the v a r i a t i o n as a s t r e s s  elastic  media  in stress across a wave p a s s e s  through  13  it  (Kolsky, As  can  parallel in  1963). be  to each  seen  daxx  i s equal  \ 5x)6y5z /  dx  which s i m p l i f i e s (  six  separate forces act  The  resultant  force  acting  drxy +  5y|5x5z - r x y  5x6z  dz  to daxx  Newtons  5,  to  / Sy5z + [ r x y \  - axx  drxy  +  dx  By  Figure  of the t h r e e a x e s .  the x - d i r e c t i o n  [ffxx +  in  +  drxz  dy  second  law  f o r c e s ) the e q u a t i o n  of  j 6x5y5z  dz  motion  ( neglecting  gravitational  equals  )  d -u u a 2  p[5x5ySz  V  where p i s t h e d e n s i t y in  the  / dd tt  2  2  of the element  and  u i s the  displacement  x-direction.  Therefore d u 2  o  dt Similarly  i n t h e y and  =  d v  dryx  dt  dx  dy  drzx  drzy  2  2  +  dayy  drxz  6  dz  +  dryz dz dazz  "t*  P dt  strains  +  dy  directions  dw  calculate  drxy  z  P  the  +  dx  2  2  Assuming  daxx  material  dx  2  dy  is isotropic,  using the  relations  dz  Hookes Law  may  be  used  to  V A R I A T I O N IN S T R E S S A S M A L L SOIL  ACROSS  ELEMENT  15  where  axx  = Xev + 2Gexx  r x y = r y x = G7xy  9a  ayy  = Xev + 2Geyy  r y z = r z y = G7yz  9b  azz = Xev + 2Gezz  r z x = r x z = G7ZX  9c  X I s known a s Lame's c o n s t a n t and G i s o f t e n  as t h e modulus o f r i g i d i t y and ratio  to  o r t h e s h e a r m o d u l u s . Lame's c o n s t a n t  t h e s h e a r modulus a r e o f t e n v,  referred  expressed  i n terms o f P o i s s o n ' s  and Young's modulus E, where i>E  7 =  10 (\+v)(\-2v)  E G =  1 1 2(1+*)  S t r a i n s and r o t a t i o n s i n t h e m a t e r i a l  are determined  du exx  eyy  dv  =  7xy =  12a  dx  dv  dw dv 7yz = — + dy dz  dy dw  dy  dv  ezz =  =  7ZX  dz  ev = exx + eyy + ezz dw 2coxx  = —  dv  1 4a  1 4b  du -  dx  13  dz  dv dw 2wyy = — - — dz dx  =  12c dx  dv - —  dy  2CJZZ  12b  dw +  dz  follows  du +  dx =  as  1 4c  dy  16  Using  the L a p l a c i a n operator d V  dy  2  15 dz  2  of motion s i m p l i f y t o dev  2  p  = 7 + G dt d v  = 7 + G dt  describes  = 7 + G  the  + GV w  18  dev  2  2  dz  2  above e q u a t i o n s  17  dy  dw dt  + GV v 2  2  p  16  dx dev  2  p  + GV u 2  2  which  2  +  2  d u  The  d  2  + dx  the equations  d  2  =  2  may be s o l v e d i n t e r m s o f  propagation  an  o f an i r r o t i o n a l  wave, and i n  t e r m s o f an e q u a t i o n w h i c h d e s c r i b e s t h e p r o p a g a t i o n rotation equations  wave. The f i r s t 16,  respectively,  17,  solution  and  18  and a d d i n g  equation  of  a  pure  i s o b t a i n e d by d i f f e r e n t i a t i n g  with  respect  the expressions  to  x,  y,  together. This  and  z,  gives  d ev 2  p  = 7 + 2G V ev  19  2  dt  which  i s known a s t h e  dilation  wave  or compression  equation.  2  =  The equation and  then  other 17 w i t h  E( 1-j>) =  P  where B i s t h e b u l k  indicates  that  a  wave p r o p a g a t e s w i t h a v e l o c i t y 7 + 2G  Vc  This  p(1+f)(1-2f)  B = — p  20  modulus.  solution  can  be  obtained  r e s p e c t t o z and e q u a t i o n  eliminating  by d i f f e r e n t i a t i n g  18 w i t h  respect to  y  ev by s u b t r a c t i n g t h e two e x p r e s s i o n s t o  17  give d wxx 2  p  = GV GL>XX  21  2  dt  Similar  e x p r e s s i o n s c a n be  equations a  indicate  obtained  f o r coyy  that a r o t a t i o n a l  shear  and  uzz.  These  wave p r o p a g a t e s  with  velocity G  Vs  =  2  22  —  P  which  i s equivalent to equation The  related  compression  wave and  1. the  shear  wave  velocities  by t h e e q u a t i o n Vc  1 -v  2  =2 Vs  except the  in  the  relationship  2.3 C o n v e n t i o n a l  situ a  published  on  comprehensive the of  c o n d i t i o n when  In-Situ  Seismic  thesis.  t o 0.5 and  fifteen  y e a r s a good d e a l o f  concerning  literature  the g e o t e c h n i c a l a p p l i c a t i o n s measurement. R e c e n t l y  conventional literature  Measurement  downhole  review  s u b j e c t . H i s work was a u s e f u l this  v i s equal  i s indeterminent.  s e i s m i c wave v e l o c i t y  thesis  23 1-2*  2  undrained  Over t h e l a s t been  are  Patel  testing  of  has in-  (1981) i n  prepared  a  a n d e x t e n s i v e b i b l i o g r a p h y on reference i n the  preparation  18  As m e n t i o n e d for  i n Chapter  d e t e r m i n i n g shear  crosshole  wave v e l o c i t y  of  shear  distances  through  generated  by hammer  wave  wave soil  travel media.  addressed  1978).  Large  as a r e s e a r c h t o p i c the following  the advantages  2.3.1  Stokoe  induced velocity  strain  in this  the  are  levels  strain  in-situ  been p o s s i b l e  (Wilson  in-situ testing  was  not  thesis. of the c o n v e n t i o n a l t e s t i s provided  and  Testing  comprehensive  studies  aspects of c r o s s h o l e seismic t e s t i n g a n d Woods  low s t r a i n  level  shear  isolated  s i t e s . Wilson  et  al  test  (1978)  waves  hammer  and  detectors located  a  the  prepared  per cent. A v i b r a t o r y  shear  wave  modified  test  crosshole impulse  i n c l o s e proximity to the source,  crosshole signal  deep  measure  designed mechanical  was measured a t s t r a i n  and  was  and a t t h r e e f i e l d  introduced  technique. Using a s p e c i a l l y  (1976)  to  facility  testing  wave v e l o c i t y  into  ( 1 9 7 2 ) . They r e p o r t e d on t h e u s e o f hammer  an  Ballard  waves  strain  l i t e r a t u r e review  earlier  in  shear  travel  and d i s a d v a n t a g e s o f e a c h method a r e p r e s e n t e d .  of  geotechnical  have  known  these  a t shear  s u b s e c t i o n s each  Conventional Crosshole  One  3  over  Generally  measurements  methods i s d e s c r i b e d . A b r i e f  by  times  blows and propagate  velocity  Brown and Schwarz,  In  methods  i n - s i t u are the conventional  10-" p e r c e n t o r l e s s . R e c e n t l y however, l a r g e  shear  used  and downhole m e t h o d s . B o t h o f t h e methods r e q u i r e t h e  measurement  of  1, t h e most f r e q u e n t l y  crosshole  levels  of 10-  1  t o 10-  s o u r c e was d i s c u s s e d by  production  testing  was  19  discussed  by  The method  Auld  (1977).  conventional  is illustrated  crosshole  shear  i n F i g u r e 6.  The  wave  velocity  survey  testing  procedure  usually  entails  the placement of  t h r e e o r more b o r e h o l e s  shown.  The  cased  holes  transmission that is  and  are  they are  and  grouted  surveyed  for  t h e d i s t a n c e between t h e h o l e s  struck v e r t i c a l l y  borehole.  These  oppositely  polarized  upward  impulse  between a d j a c e n t  a r e d e t e c t e d a t two  on  wave can  the  be  signal  a  to ensure  generate  SV  line  signal  to  ensure  signal  source.  r e c e i v e r h o l e s a r e used  by  source  waves i n  or more a d j a c e n t  obtained  as  good  verticallity  i s known. The  to p r e f e r e n t i a l l y  SV  in  holes.  An  with  an  pulling  Interval  travel  to determine  one  times  shear  wave  velocity. The need  most s e r i o u s s h o r t c o m i n g s  to prepare  spacing, generate The be  polarized method has and  without  use  of  Subsequently work  with  SV  the c r o s s h o l e t e s t  the u n c e r t a i n t y  for specialized  are  about  the hole  in-hole signal  sources  in that strain  level  to  waves.  s e v e r a l advantages t e s t s can  problems with  Conventional  S c h w a r z and the  multiple boreholes,  t h e need  controlled  usually  2.3.2  and  of  be  performed  signal  to considerable  a t t e n u a t i o n and  can depth  refraction.  Downhole T e s t i n g  Musser  polarized  (1972) were among t h e shear  waves  numerous i n v e s t i g a t o r s  in  first  downhole  have r e p o r t e d t h e  t h e c o n v e n t i o n a l downhole t e c h n i q u e .  notable c o n t r i b u t i o n s to  the  to report  literature  are  on  testing. results  of  Some o f  t h e more  Warrick  (1974),  20  Receiver Boreholes  12 ft (3.7m)  Source Borehole  7ft(2.lm)-*-  a.-PLAN VIEW Vertical Velocity Transducer^.  --Vertical j Impulse  Generation of Body Waves  (Not to Scale) b.-CROSS-SECTIONAL  VIEW  FIG. 6. C O N V E N T I O N A L C R O S S H O L E T E S T I N G  21  Ballard  and  (1977),  McLean  and W i l s o n  types of s i g n a l documented  (1975),  sources  discussion  the  Society Hoar,  downhole  of  (1981)  and M c E v i l l e y  tested  various  and p r e s e n t s a w e l l  h i s f i n d i n g s . Hoar and S t o k o e  o f recommended  and  they  Beeston  f o r downhole t e s t i n g  testing  (1978)  procedures  for  c r o s s h o l e t e c h n i q u e s , f o r the American  for Testing Materials. 1978)  (1977),  e t a l . (1978). P a t e l  have p r e p a r e d an o u t l i n e both  Auld  In a s e p a r a t e p a p e r ,  (Stokoe  have p r e p a r e d an e x t e n s i v e d i s c u s s i o n  v a r i a b l e s which can a f f e c t  the a c c u r a c y of i n - s i t u  and  on t h e  seismic  wave  measurement. The  conventional  illustrated A triaxial and  a  downhole  shear  wave  in Figure 7 involves d r i l l i n g  and c a s i n g a  geophone d e t e c t o r p a c k a g e i s l o w e r e d  shear  wave  the  signal  wave s i g n a l  a  sledge  generate  a polarized  device consisting  particle the  The  parallel  shear  geophone of a  at  The v e r t i c a l l y  The p l a n k  a  used  firmly  on  shear to the  i s impacted  transverse  generate  an  the a x i s of s i g n a l geophone  and  and  electric  a moving c o i l  horizontal  oriented  wave  with  end and t h e n a t t h e o t h e r t o  to  D e t e c t i o n o f SH waves i s most is  shear  d e t e c t o r package i s a t h r e e  radial,  geophones  geophone to  one  hole,  wave.  a c c e l a r a t i o n s cause  geophone.  detector  first  it.  testhole. the  commonly  o f a wooden p l a n k h e l d onto  survey  recording device  i s s t o r e d . The most  a vehicle  hammer,  The t r i a x i a l  geophone.  trace  source c o n s i s t s  g r o u n d by d r i v i n g  into  i s g e n e r a t e d a t t h e s u r f a c e . The  g e n e r a t i o n p r o c e s s t r i g g e r s an o s c i l l o s c o p e which  velocity  i s intended  a  vertical  current  oscillate effective  oriented  s o u r c e hammer  component  with impacts  to  when within  when t h e its  axis  a s shown.  preferentially  Receiver Borehole  (0.6m) 2ft  Cost-tn-PlaceConcrete Block  1  2ft (0.6m) 20 ft (6.1m)  -PLAN VIEW Oscilloscope  •Embedded Angle Iron Electrica  Hammer  Trigger  Generation of Body Waves  3-D Velocity Transducer Wedged in Place  -CROSS-SECTIONAL  (Not to Scale)  VIEW  FIG. 7. CONVENTIONAL DOWNHOLE TESTING  23  detect at  compression  the s i g n a l There  waves g e n e r a t e d  a r e two  fundamental  in  measuring  the increment  methods o f o b t a i n i n g  a downhole t e s t . The  travel  time  t i m e method. The  pseudo  interval  advancing  a single  measuring  the t r a v e l  energy  impulses.  simultaneously a  single  energy  Section  t h e h o l e . The  interval  the t r a v e l  methods a r e  by  either  interval carried  a  travel out  by  in a testhole  and  between d e p t h s  downhole  from  separate  method  time  involves separation  interval  discussed  seismic  p r o c e s s of d r i l l i n g expensive.  triaxial  flexible  The  from  further  and  survey casing  drilling  geophone p a c k a g e  cables though  so  geophone  wedges o r  the package t o the c a s i n g ,  through  the  effective The less  required and  by  geophones w i t h a known  calculating  conventional  m a i n t a i n e d . Even  is  time  is  c o n s i d e r a b l e d i s t u r b a n c e to the s o i l  using  the  true  i m p u l s e . These  t i m e c o n s u m i n g and  hold  interval  The  and  s h o r t c o m i n g s . The  to  time  wave  be d e t e r m i n e d  method o r a t r u e method  shear  a in  4.2.  The  cause  may  geophone t o v a r i o u s d e p t h s  m o n i t o r i n g two  testhole  velocity  o f s h e a r wave t r a v e l  interval  in  impacts  source.  velocity  pseudo  f r o m v e r t i c a l hammer  casing survey  i s easier  process  can  immediately is  several  t h e h o l e can  also  lowered  cannot  i n f l a t a b l e p a c k e r s a r e used good  shear  wave  T h i s can  be  adjacent  commonly  orientation  i s not g u a r a n t e e d .  be to  transmission severely  limit  depth.  main a d v a n t a g e s expensive  has  o f t h e downhole t e c h n i q u e a r e  than  t h e c r o s s h o l e method and  to o p e r a t e . A l s o the  d e t e c t e d d u r i n g the  test  shear  are v e r t i c a l l y  the  waves  that  it  equipment generated  propagating,  similar  24  to  t h o s e c a u s e d by a deep The  is  CPT s e i s m i c  primarily  development. Campanella on  cone  It  is  a  and R o b e r t s o n ,  and development  carried  out  recognizing  i n an e f f o r t  shortcomings  discussed  r e l a t i v e l y new d e v e l o p m e n t 1982),  seismic  work the  thesis  stage  of  (Ertec,l98l,  however much o f t h e  literature  methods i s p e r t a i n e n t . The  described advantages  in  this  of  t o the conventional  thesis  downhole  t o d e v e l o p an i n s t r u m e n t f r e e  inherent  in this  instrument at i t s present  geotechnical  research  the  penetrometer  a downhole t e s t  conventional  testing  earthquake.  test  of  was  seismic some  methods.  of  25  3.0 CPT DOWNHOLE SEISMIC EQUIPMENT AND  3.1  PROCEDURES  Introduction  The  impetus  f o r development  equipment a t t h e U n i v e r s i t y o f research  and  development  (1981) i n C a l i f o r n i a . using Hz.  a  triaxial  velocity very  their  research  coupled  out  perform  seismic  came  out of  by E r t e c  i n v e s t i g a t i o n s by  package  to  Columbia  carried  Preliminary  transducers  were  British  work  geophone  o f t h e CPT downhole  containing downhole  Western  that  group  miniature  seismic  surveys  s u c c e s s f u l . Among t h e r e c o m m e n d a t i o n s r e s u l t i n g were t h a t  the t r i a x i a l  t o a cone p e n e t r o m e t e r  reliability  of v e l o c i t y  evaluated.  These  from  geophone p a c k a g e s h o u l d  t i p , and t h a t  the  measurements made u s i n g  recommendations  28  formed  accuracy  this  the  be and  e q u i m e n t be  basis  for this  study. During  the  determined integral  that part  operational in  testing  study  a  this  certain in  a plank  research  study  field  measurement  field  testing  i s shown i n F i g u r e  4094 d i g i t a l  the  accuracy  and  15  cm  course  of  equipment  2  static  the  developed  8. The equipment c o n s i s t e d  o s c i l l o s c o p e with  s i g n a l source  p l a y e d an  method.  of  cone p e n e t r o m e t e r , a  15 b i t  (100  r e s o l u t i o n and f l o p p y d i s k c a p a b i l i t y .  type  i t was  Equipment m o d i f i c a t i o n s a n d v a r i a t i o n s  o f t h e CPT downhole s e i s m i c  instrumented  project  characteristics  p r o c e d u r e s were r e q u i r e d d u r i n g  layout  digital  this  equipment  assessing  limitations.  geophone  Nicolet to  of  t o d e v e l o p an optimum The  for  progress  KHz)  analog  A 7 Kg hammer,  a n d an e l e c t r o n i c t r i g g e r  switch  were  26  U.B.C. IN-SITU TESTING  VEHICLE  OSCILLOSCOPE a TRIGGER  S  "7  olGNAL SOURCE HAMMER IMPULSE  GROUND SURFACE •  A S S U M E D SHEAR WAVE TRAVEL PATH  •CONE PUSHING RODS  -4- RADIAL ^TRANSVERSEf^VORABLY, ADDITIONAL TRIAXIAL GEOPHONE PACKAGE (FOR T R U E INTERVAL MEASUREMENT}  VERTICAL  T R I A X I A L G BO PHONE PACKAGE ° | — T R I A X I A L GEOPHONE PACKAGE  I5cm^  FIG. 8.  CPT  SEISMIC EQUIPMENT  CONE  LAYOUT  27  used. This  chapter  which d i r e c t l y dynamic the  obtain  3.2  Seismic  cones  in  testing  long.  The  conductor transmit the  cm.  The  bearing  shear  9.  wave v e l o c i t y  chapter  w h i c h were d e v e l o p e d  downhole s e i s m i c  response  also in  and  details  order  to  data.  Penetrometer  i n t h e downhole s e i s m i c  It  was  very  at  the  1981). The  are hollow hollow  (16 mm  cable  I.D.  20T X  through from  to the  B.C.  i s shown 5  channel  (Campanella  u s i n g t h e U.B.C.  the  O.D.)  and  1.0  installation  the  pushing  rod  &  in-situ  c a p a c i t y D u t c h Cone  36 mm  permits  signals  of  advanced  standard  investigaion  in design  University  design  electrical  similar  c o n e was  using  carrier  c o n e was  sectional  an  larger area  cone t i p  developing pushing  of  of e q u i p m e n t  rods. metres  of  a  anulus  14 to  t h e cone t o r e c o r d i n g equipment  surface.  The cross  Cone  vehicle  These rods  the a c c u r a c y  procedures  service  Robertson,  at  field  cone used  Figure  aspects  modulus d e t e r m i n a t i o n s . The  a c c u r a t e CPT  The in  affected  shear  rational  d i s c u s s e s those  (44 mm  provided  resistance  equal  end  sensor  and  area  through  cell,  sleeve  geophone  an  automatic  load c e l l  friction  a triaxial  O.D.), and  freely.  load  friction  c o n v e n t i o n a l cones having  an  oversize hole  rods c o u l d pass  transducer, a  than  The  friction  which the  cone  a  overall  was  pore  15  cm  2  package.  reducer  by  equipped  diameter with  a  measurement  surface area), a The  2  50  t o measure r e s i s t a n c e a l o n g (225  cm  l e n g t h of  smaller  pressure  a  geophone  an  slope  package  28  14 CONDUCTOR ELECTRICAL CABLE  ADDITIONAL 28Hz TRIAXIAL GEOPHONE PACKAGE  (For true interval measurement)  -~o  :  -28Hz TRIAXIAL GEOPHONE PACKAGE  FRICTION LOAO CELL SLOPE SENSOR EQUAL END AREA 225m FRICTION SLEEVE 2  BEARING LOAD CELL PORE PRESSURE TRANSDUCER  POROUS PLASTIC DISK 60° CONE TIP, (43.7mm o.d.)  FIG. 9.  15 c m  2  C P T SEISMIC CONE  29  contained  one  vertically  oriented  and  horizontally  o r i e n t e d GSC-14-L3 m i n i a t u r e  which  have  a  orientation  of  exterior Geo  of  19  the  the  were o r i e n t e d  geophone was  cone  geophone and for  c o n e . The  placed  was  testing  placed  marked  transducers, in diameter,  Hz.  The  on  the  manufactured 20  cm  high,  by and  transverse  by  be  true the  geophone  and  the  acted  as  a  radial  transverse  r e o r i e n t e d . The provided  a snug  method of  and  the  seating  advancing  firm  the  mechanical  surrounding  transmission.  c o n t r o l l e d and  design  In  soil.  addition,  extremely  accurate  obtained.  worked  arose  arrivals  continuous  signal  transverse  s h e a r wave a r r i v a l s i f  was  geophone c a r r i e r  The  (parallel  c o n f i g u r a t i o n . The  and  provided  surveys  address t h i s question triaxial  SV  geophone p a c k a g e . The  questions a  wave  geophone c a r r i e r  for excellent  using  to d e t e c t  s i g n a l source  the  instrument  progressed,  shear  convenience  the  velocity  SH  s i g n a l source.  in crosshole  orientation could  This  second  28  and  d e p t h measurements c o u l d  obtained  clearly  of  (perpendicular)  placed  cone o r  between  This allowed  interval  order  h o r i z o n t a l geophones  cone p e n e t r o m e t e r  geophone  the  transducers  the  used  for  triaxial  contact  cm  velocity  procedure  to d e t e c t  t o be  c o n s t r u c t i o n of  static  1.7  o r i e n t a t i o n to the  i f the  the  velocity  were  in r a d i a l  geophone was  phone was  in  geophone p a c k a g e was  field  favorable)  vertical  frequency  perpendicular  grams.  During  the  the  Space C o r p o r a t i o n ,  weighed  or  resonant  two  well (see  for  Section  whether  carrying  better survey  cone was  modified The  pseudo  as  research  2.2.2) but  interval  package.  out  results method. to  might  be  In o r d e r  to  incorporate  a  geophone p a c k a g e s were  30  similarly metres and  aligned  from  with the a x i s of each  geophone  i t s c o u n t e r p a r t . The r e s u l t i n g  true i n t e r v a l  survey data  exactly  comparison  1.000  of pseudo  i s d i s c u s s e d i n S e c t i o n 4.2.  3.3 Shear Wave G e n e r a t i o n  As d i s c u s s e d i n C h a p t e r signal shear The  source  source  different  types  investigators indicate  that  consists  of  should of  (See  s l e d g e hammer.  The  Patel,  directional  have  positioned testhole  A number o f  been  evaluated  downhole s e i s m i c  force used  by  other  of t h e i r  studies  shear  wave  source  t o t h e g r o u n d and s t r u c k w i t h a exclusively  in  this  study.  Source  signal  to  source  p r o v i d e a good  on l e v e l and  wave component.  portable.  1981). The r e s u l t s  weighted  amplitude  reversible,  Such a s o u r c e was u t i l i z e d  seismic  plate  large  seismic  and  consisted  l a m i n a t e d wood p l a n k . The ends o f t h e p l a n k steel  downhole  generate  relatively  sources  plank,  downhole s e i s m i c  3.3.1 S i g n a l  be  an e x c e l l e n t a  suitable  o r no c o m p r e s s i o n a l  s h o u l d be r e p e a t a b l e ,  the  CPT  a  preferentially  (SH) waves w i t h l i t t l e  signals  and  should  2,  a  mineral  vehicle  t o h o l d the plank  soil  striking  of  a 3 metre  long  were  covered  with  s u r f a c e . The p l a n k  w i t h ends e q u i d i s t a n t  was d r i v e n o n t o  from  was the  i t to p r o v i d e a normal  i n p l a c e . A 7 k i l o g r a m s l e d g e hammer was  t o induce a p o l a r i z e d  shear  wave by s t r i k i n g  opposite  ends  31  of  the  p l a n k w i t h a m o d e r a t e blow. The  approximately  t h e same h e i g h t  plank  s o u r c e was  it  difficult  was  waves o f p o o r Since signals  the  seismic  condition plates  these e f f e c t s .  noted  that  of t h e s t e e l  became  steel  3.3.2  metre  long  i n c o n v e n i e n t t o use lower  energy  as S  were  generated  manually,  the  However  procedural  and  dented  striking  The  portability  to out-weigh  the  these  signal quality  striking and  to produce.  To  4.2  was  simplicity  affected  by  of  the  e x t e n s i v e use,  repeatable signal  ensure  were  shortcomings.  plates. After  c h i p p e d , and  and  and  good  signal  the  traces  quality,  p l a t e s were r e p l a c e d when worn.  Source L o c a t i o n  The was  from  1  t e c h n i q u e s d i s c u s s e d i n S e c t i o n s 3.6  were more d i f f i c u l t the  A  produced  repeatable.  source appeared  was  found  and  waves  were not e n t i r e l y  signal  i t was  to hold s t i l l ,  the  t o reduce  It  but  impulse.  dropped  quality.  interpretation used  tested  f o r each  hammer was  distance  from  placed (signal  factor.  It  preferential when  signal  been  strength  angle  of (Ertec,  source  too  t r a n s m i s s i o n may  1981)  close  by  normalized  incidence  to  Patel  for  the  an (1981)  He  has  travel  the  ground that  testhole,  occur. T h i s p o s s i b i l i t y  may  source  important that  shown  a  that  path length,  waves t r a v e l l i n g  have s u g g e s t e d to  the plank  considered  window e x i s t s .  i s r e c o r d e d f o r SH  investigators is  is  at which  was  suggested  wave r a d i a t i o n  maximum a m p l i t u d e degree  source o f f s e t )  has SH  the t e s t h o l e  at  surface.  a  45  Other  if  the  signal  down  rod  signal  exist  if  the  rods  32  come  in  contact  verticallity, indicate  with  hole  that  the  side  squeezing  down  rod  of  or  the  hole  caving.  Our  signal transmission  due  to  poor  observations  was  not  a  serious  problem. It  appears that  it  would  downhole  source at a d i s t a n c e  amplitude  s i g n a l s are  pointed  out,  the  more  the  site.  the  The  iterative remains  the  addition, the  noise  source  signal attenuation  10  on  signal  the  data.  The  shows  be  source  is located the  has  located  using  4.5)  but  an there  constantly i s changed.  from the  lower  maximum  l a y e r i n g at  of  r e c e i v e r depth  and  is  overcome by Section  the  (1981)  through the  (See  from t h e  For  to  a  a  the  In  testhole, signal  to  s i g n a l source o f f s e t  and  normally  i n the  qualitative  l o c a t e d at  5.5  lower  consolidated r i g h t hand  comparision at  metres,  18.0  10.6  of  clay  portion  raw  test  metres depth metres,  and  from 19.8  testhole.  the  refraction.  I t was  duplicated  the  B e c a u s e of  in  of  s i g n a l s were r e c e i v e d  production  close  effect  strength  figure provide  s i g n a l source  the  s h e a r wave t r a c e s  A l l three  metres  as  the  the  that  Patel  inconvenience  s i g n a l s o u r c e as  further  Figure  deposit.  a  r e f r a c t i o n may  the  so  place  ratio.  depth  of  the  the  greater  r e f r a c t i o n i s to occur  operational  repositioning  as  testhole  analysis technique,  to  testhole  However,  from t h e  p r o b l e m of  data  advantageous  from t h e  obtained.  further  likely  be  t e s t i n g purposes the cone  hole  determined  vertical  as that  practical small  propagation  equipment c o n f i g u r a t i o n ,  plank  of  the  s o u r c e was  placed  to minimize  signal  offsets  more  closely  h o r i z o n t a l shear c l o s e s t the  source  waves. could  33  MAXIMUM  GEOPHONE  i  120  RESPONSE  1 140  TIME  FIG. 10.  mV  1 160  m sec.  1 ISO  1—•— 200  " * RECEIVER DEPTH »meters  SIGNAL STRENGTH VERSUS DEPTH  34  be  placed  was  transmission experienced However,  2.5  through  did  the plank  calculated  wave  source  from  the testhole. when  depths  i s used  short  are  assumed  source  to  that  observed  Some  noise  and d i f f i c u l t y  compression  wave  a n d down accurate  has  finite  was  arrivals.  rod  affect  Wave  source  signal  shear  wave  length,  the  from  testhole.  velocity  both  that  The  with  maintain  offsets  since  geophone  path  were ends  path  offset  the signal on  increasing  consistency  receiver  of the  eminates wave  i f  i t  signal  from  travel  the path  depth. throughout  measured  of the plank  quite  be l o n g e r  t h e ends  on  distance  shallow  lengths will from  point  l e n g t h c a n be  and  effect  always  on w h i c h  source  offsets  eminates  rapidly  to  impact,  The  on t r a v e l  travel  source.  depend  the signal  source  the signal  a  length will  i f i t i s assumed  order  Shear  path  signal  diminishes  the  source  t o measure  of the s i g n a l  In  Hz  was  testhole.  not serious  appear  The e f f e c t  used.  than  lengths  3.4  was  type  travel  the  signal  rods  the  identification.  Since  centre  not  from  identifying  the noise problem  arrival  is  the  in accurately  transmission  large  metres  from  source  a  the were  survey,  point  of  equidistant  Wave D e t e c t i o n  signal packages  detection  equipment  containing three mutually  t r a n s d u c e r s . The geophones  low pass  4094 d i g i t a l  signal  consists  filter  oscilloscope  circuit with  floppy  through  15 b i t r e s o l u t i o n disk  triaxial  p e r p e n d i c u l a r 28  are connected  to a  of  capability.  a  Hz  1000  Nicolet Details  35  of  e a c h component a r e p r o v i d e d i n t h e  3.4.1  28  Hz  velocity  geophone p a c k a g e s wire  coil  consists  suspended  by  transducer  cause  the  coil  which  leaf  s p r i n g s as  r e s i s t s movement  are  i n any  reproduced The  very  small,  orientation.  in Figure  The  of  geophone  wave t r a v e l  t i m e s w i t h d e p t h . The  inset  velocity  copper The  accelerations  scales.  The  and  Figure  response  strain  a t any  relationship  Vs,  its  rugged  inertia.  and  to The  designed to  specifications  to single  13  hammer  provides  amplitude geophone  and  a  are  relative  output  l e v e l caused  by  d e p t h d u r i n g t h e CPT  between s h e a r  peak s h e a r i n g v e l o c i t y  strain  impacts  quantative  the  shear  voltage  to the p a r t i c l e o s c i l l a t i o n v e l o c i t y  estimated  s u r v e y . The  metres.  response  comparison  be  a  12.  40  related  of  manufacturers  of  can  triaxial  and  when p a r t i c l e  because  to a depth  the  the  shown i n F i g u r e 11.  extremely  geophones showed good  directly  in  geophone h o u s i n g and magnet t o o s c i l l a t e r e l a t i v e  geophones operate  used  o f a permanent magnet  geophones g e n e r a t e e l e c t r i c c u r r e n t  on  subsections.  Geophone Response  Each  the  following  as  shear  is  shown waves  downhole s e i s m i c 7xy,  shear  wave  uy  MY 7xy  =  24 Vs  (after  White,  calculated velocity  1965)  as o u t l i n e d  can  be  u s e d . The  in Section  i s e s t i m a t e d from  4.3,  and  s h e a r wave v e l o c i t y  is  the s h e a r i n g p a r t i c l e  t h e peak geophone o u t p u t  voltage  on  36  FIG. 11. GEOPHONE CONSTRUCTION  GSC-14-L3 SEISMOMETER The GSC-1^-13 i s a v e r y s m a l l , e x t r e m e l y rugged seismometer. I t i s designed and b u i l t t o m a i n t a i n performance c h a r a c t e r i s t i c s even a f t e r being s u b j e c t e d t o h i g h shock f o r c e s . P r i n c i p a l a p p l i c a t i o n s include intrusion d e t e c t i o n , m i l i t a r y use and v i b r a t i o n m o n i t o r i n g . Standard n a t u r a l frequency i s 28 Hz, w i t h t i l t a n g l e o f o p e r a t i o n up t o 180 . SPECIFICATIONS Standard N a t u r a l Frequency  28 Hz * 5 Hz  Standard C o i l R e s i s t a n c e <s> 25°C  570 Ohms t 5%  I n t r i n s i c Voltage S e n s i t i v i t y  . 2 9 V / i n / s e c t 15%  Normalized T r a n s d u c t i o n Constant  .012 >/ Rc ( V / i n / s e c )  T i l t Angle o f O p e r a t i o n Open C i r c u i t Damping  180° 18 o f C r i t i c a l t ,0k  Moving Mass  2.15 g  O p e r a t i n g Temperature  -30°F t o +160°F  Dimensions: Diameter  .66 i n (1.7 cm)  " Height  .70 i n (1.8 cm)  Height With Terminals  .80 i n (2.0 cm)  Weight  19 g  FIG. 12.  GEOPHONE SPECIFICATIONS  FIG. 13.  OBSERVED SHEAR WAVE FROM A SINGLE HAMMER  TRACES IMPULSE  39  F i g u r e 13. Analysis that  shear  the  surface  of  Each  plank  and  i t s own  travel  at  interval  time  own  the  response  two  the  response response  were basis to  of  impulse  to  the  determine a l l  free  oscillation  f o r c o n s i d e r a t i o n . When  the  geophone  of  a  oscillation  In o r d e r t o compare  geophones  their  the  response  natural  will  f o r true  r a n d o m l y , b u t were  vibrations.  characteristics  of  f r e q u e n c i e s s h o u l d be s i m i l a r .  selected  their  a  surveys a r e c a r r i e d out  i n t h e s e i s m i c cone  initially  When  frequency  the  important.  adjacent  and n a t u r a l  oscillation  frequency.  i s used  factor  survey,  c a n be q u i t e  The g e o p h o n e s u s e d surveys  on  near t h e  s i m u l t a n e o u s l y , as i n the case  velocity  of  characteristics  blows  per cent  4  unique  natural  velocity  a r e not a s e r i o u s  interval  characteristics  indicates  i t begins t o o s c i l l a t e and t h e  measurements,  two g e o p h o n e s a r e m o n i t o r e d true  study  hammer  10-  fundamental  by an i m p u l s e  pseudo  characteristics  4.2.  its  S e c t i o n 2.2.2) t h e same geophone  wave  on  by s l e d g e  v a r y between  has  tend t o occur  When  forthis  per cent a t depth.  i s excited  oscillations  (see  6  caused  source  geophone  characteristics  phone.  data gathered  s t r a i n amplitudes  s u r f a c e and 10-  geophone  field  frequencies The  and  importance  be d i s c u s s e d  further  interval  later  paired  their  free  o f geophone in  Section  40  3.4.2  Signal  Filtering  Preferential polarization wave  generation  that  signal  filters  phase s h i f t s  ambient clear  1977)  shear  Butterworth  not  that  Our  (-6 db/1  filters  KHz)  since  filters  shear  was  1978)  wave  noise suggest  they can  cause  (Beeston  c a n be u s e d f o r  experience  indicated  that  1000 Hz low  pass  detection  were n o t u s e d h i g h f r e q u e n c y  background  shear  and made p r e c i s e  The e f f e c t  p r o v i d e d by H a l l  A t , i n t r o d u c e d by a low p a s s  of these  arrival  time  filters  was  et a l (1981).  Butterworth  The  filter  time  can  where  f  cutoff  f r e q u e n c y . Based  induced  is  one  filter  the s i g n a l  propagate  time  possible  be  using the equation  At=arctan(f/fc)/2irf  typically  &  wave  very d i f f i c u l t .  u s i n g formulae  calculated  factor  investigators  i n the  t h e s h e a r wave s i g n a l  interpretation  accurate  Hoar,  be u s e d  low p a s s  reduction.  filters  n o i s e masked  shift,  ensure  important  d e l a y . Other  suggest  waves and s h e a r  wave t r a c e s a r e o b t a i n e d by u s i n g  When  assessed  to  ( S t o k o e and  should  and s i g n a l  noise level  circuit.  Another  Some i n v e s t i g a t o r s  McEvilly,  SH s h e a r  a r e two key components  identification.  reduction.  of  at  frequency on  the  filter setting  i n h e r t z and f c i s the f i l t e r  observation  frequencies  l a g would be l e s s  than  induced e r r o r throughout  25  less  that than  0.16 msec.  were m i n i m i z e d  ah e n t i r e  survey.  shear  waves  100 h e r t z , t h e  The  effects  by s e l e c t i n g  of only  41  3.4.3 O s c i l l o s c o p e R e s o l u t i o n  Seismic packages  wave  at  to  double  by  the  were  recorded  on  a  with  floppy disk c a p a b i l i t y .  digital  capability displayed  detected  depth  oscilloscope analog  traces  and  signal  trigger  The  data  and d e s i r e d  features  enhancement and a m p l i f i c a t i o n of  d i s k programme  integration,  Conventional photographic chart are  recordings.  respond  use of  allowed  in this  preset  timing  to  the  timing  analog  stored  a t any  smoothing,  on data  time. signal  A  series  averaging,  operations. from  o s c i l l o s c o p e wave t r a c e s o r  strip  range  used  time  recording  (Hoar and S t o k o e ,  delays,  nearest  the  0.02  measurements device  1978). T h r o u g h  digital  oscilloscope  msec o r 20 usee  ten to  one  t h a t c o u l d be o b t a i n e d  must  hundred  using  in this times  conventional  data.  For signal  resolution  timing  data  downhole s e i s m i c work. T h i s p r o v i d e d the  were  or o f f i c e .  s e i s m i c wave t r a v e l  trigger  has a 15 b i t  wave forms were  s e i s m i c a n a l y s i s has  Since  digital  scope a l l o w e d  signal  i n the m i l l i s e c o n d range the s i g n a l  properly the  the  i n the f i e l d  r e c o r d s of a n a l o g  4094  accurate  to the screen  a n a l y s i s and o t h e r  in-situ  geophone  floppy disks for later  of  packages allowed  frequency  very  signals  c o u l d be r e c a l l e d  manipulation  This unit  resolution,  d e n s i t y magnetic  r e d u c t i o n . The d a t a  Nicolet  delay c a p a c i t y . Seismic  on a CRT s c r e e n  s i d e d double  triaxial  p u r p o s e s of comparison resolution  l o s s of r e s o l u t i o n sensitivity.  It  oscilloscope equated was  found  a  12  bit  analog  was a l s o u s e d  t o an e i g h t f o l d  to  digital  i n the f i e l d .  decrease  t h a t t h e low v o l t a g e  in  response  The  voltage of the  42  geophones a t depths g r e a t e r consideration  the  suitability  of t h i s  1 5b i toscilloscope  was  capable  recording  shear  wave  metres  at a sampling  traces  oscilloscope single  sampling  at  was  memory  and  very  from  to  of 4 0  t o depths  point.  clear  clear  1 2 b i t  The  shear  1 5 metres  wave  at  traces  the  same  An a n a l o g  on  amplitude  1 2  b i t  unit  voltage  signal  i s  sampled  i s stored  in a  digital  The  1 5 b i t  scope  screen.  differences  can sample  response  of  just  uV  6 . 2 5 0  to 5 0 . 0 MV differences.  of t h e geophones a t depth i s  by t h e  appeared  clock  1 5 b i t  unit.  Signals  smeared and were d i f f i c u l t t o  precisely. of poor  enhancement signal  recognition in  the  more c l e a r l y d i s p l a y e d  overcome u s i n g  multiple  i s b a s i c a l l y an e l e c t r o n i c  can sample v o l t a g e  be  signal  involves  traces  resolution  to  stacking  to provide  1 2  a  and  sufficient This  r e f r a c t i o n seismic  equipment  with  known a s s i g n a l  the  and i n t e r p r e t a t i o n .  conventional  order  resolution  a technique  enhancement a r e i l l u s t r a t e d In  per  i n t e r v a l s and t h e s i g n a l  problem  digital  of  impulses  only  oscilloscope  The  Signal  hammer  of recording  displayed  small  the  interpret  used  o f 1 0 0 Msec  the 1 2 b i toscilloscope  therefore  for  rate  voltmeter.  time  oscilloscope  can  single  impulses  digital  discrete  The  from  capable  hammer  a sensitive  while  unit for  rate.  The and  important  purposes.  The  from  t e n m e t r e s became an  assessing  research  in  than  i s common. T h e  unit  enhancement. addition  signal  technique where  b i t  amplitude i s  widely  8 b i tanalog  effects  of  to  of  signal  wave  arrival  i n Figure 1 4 .  unambiguously  determine  shear  1  SET OF POLARIZED  HAMMER  BLOWS  20-I  TIME, m s e c  FIG. 14.  EFFECTS  OF SIGNAL  ENHANCEMENT  44  times,  t h e 15 b i t a n a l o g  necessary  for  individual  signal  avoided.  research  might  enhancement precision, The  be  and  considered accepting  question  of  considerations w i l l  Since study,  engineering  satisfactory  capability  purposes.  t r a c e s was under  For p r a c t i c a l  equipment  to d i g i t a l  considered  the r e p e a t a b i l i t y of signal  enhancement  a p p l i c a t i o n s lower suitable.  a  lower  By  c o u l d be  measurement  accuracy  of  was  resolution  using  level  downhole d a t a  be d i s c u s s e d  was  signal  measurement  obtained. and  f u r t h e r i n Secton  practical  4.3.  3.5 T r i g g e r i n g S y s t e m s  Proper accurate  oscilloscope  shear  wave v e l o c i t y  Three t r i g g e r The  first  struck,  ground  geophone, trigger  and  simply  generation  second  activated New  system  striking  would an  cause  was  of  the  c u r r e n t which  would  excitation  electric  Unfortunately  source  the  rise  time  cause  premature  as  the r e s u l t  the s i g n a l  time  of  consisted  spurious  triggering  of  a  solid  state  and  inertia  Inc., Princeton,  i s designed  to close for a  of i n e r t i a l  f o r c e s on d e c e l l e r a t i o n  source.  the  measurements.  s w i t c h m a n u f a c t u r e d by 5 t h D i m e n s i o n  J e r s e y . The s w i t c h  period  investigation.  s o u r c e . When t h e s i g n a l  of  would  i n a c c u r a t e wave t r a v e l The  in this  and v a r i e d c o n s i d e r a b l y . F r e q u e n t l y  vibrations  p a r t of  c o n s i s t e d o f a geophone p l a c e d on t h e  vibrations  geophone was f i n i t e  important  determination.  to. t h e s i g n a l  the o c s i l l o s c o p e .  ground  i s a very  s y s t e m s were a s s e s s e d  system  ground a d j a c e n t  triggering  The s w i t c h  then  allowed  small  the  finite after  passage  45  of  12 V DC t o t h e t r i g g e r The  switch  increase  delay not  was  occurred  important  magnitude Stokoe,  circuitry  i n v o l t a g e over  characteristic  p o r t on t h e o s c i l l o s c o p e .  observed  that a delay known  impact  that  1978). The i n e r t i a  less  t o cause a s t e p - l i k e than  1  Msec.  b u t i t was a l s o o b s e r v e d  occurs  and  step trigger  designed  a period of  between hammer  be  electrical  was  the delay was  that i t s  checked  with  that the t r i g g e r  blow.  The d e l a y was measured a t 300 Msec p l u s o r minus 50 Msec.  and  incorrect The data  e x c e e d e d t h e maximum recommended by Hoar the  variability  velocity third  in this  of t h e type  1978).  The  MC1455 than  1  recommended by o t h e r The proper  3.6  response  Field  The advance  trigger  and  Stokoe  c o u l d have l e a d t o  s y s t e m , w h i c h was u s e d t o g a t h e r  presented  of l e s s  the delay  hammer  determinations.  trigger  time  of  the  delay  approximately  (1978),  the s t r e n g t h of  an  varied  This delay  with  It i s  be c o n s i s t e n t (Hoar &  cross  a n d i t was f o u n d  inversely  t h a t some  and scope t r i g g e r i n g .  but i t i s important  switch  This  thesis,  illustrated linear usee  a l l the  field  c o n s i s t e d o f an e l e c t r i c a l in Figure  15  integrated circuit  (Hoar  &  Stokoe,  has a s i g n a l  and use of t h e d e v i c e has  step  been  rise  highly  investigators.  s y s t e m was c h e c k e d  before  each  survey  t o ensure  and r e p e a t a b i l i t y .  Procedure  downhole s e i s m i c  survey  or  withdrawl.  penetrometer  during  rod  was a d v a n c e d  in  c o u l d be c a r r i e d  the  out during rod  Generally, the seismic conventional  manner,  cone at  a  Volt*  Hammer  Impulse Tim* 1 * U  0-TRIGGER  SIGNAL  5  1000  •*WWV\r J  —  » To To Hammer Ham i  4 •  9V. 9V ~  10/iF — p  —  r  e  Typt 555' Lintor Inltgrgltd Circuit  — ^ To Impultt Rod b-CIRCUIT  IRHC)  1  I  » To< Oicilloicop*  DIAGRAM  FIG. 1 5 . E L E C T R I C A L  S T E P TRIGGER  CIRCUIT  47  constant  rate  of  2  cm/sec  and  bearing,  pressure p r o f i l e s  were o b t a i n e d  (Campanella  Gillespie,  The  survey  selected  1981). depth  convienient withdrawl,  carry  after  was  the  of the  out  the  statigraphy low  had  amplitude  eminating  vehicle,  necessary  to decouple  during  testing.  This required  advanced. Decoupling guide  b u s h i n g and The  t h e CPT  since  rotational  slope  for  orientation the  force  assessed  using  the  CPT  between d e p t h s  was  possible  of  t o 40 m e t r e s .  source o f f s e t  measurement  significant.  Below  impulses  was  by  easily  Hole  a t t e n u a t e d such  discussed  e x c u r s i o n s were not a l w a y s  that  easily depth  the  rod  throughout  mechanism  verticallity  applies  could  be  t h e cone t i p  though  appearred signal  in  s t r e n g t h of clear  identifiable.  Section  t o work  detection  Above 3 m e t r e s t h e e f f e c t s  .30 m e t r e s t h e  using  Accurate  from  rod  well.  to  maintained  be  3.2.  30 m e t r e s ,  as  hole  pushing  measuring  data  test  procedure  day.  withdrawl  continuous  3 and  straight  crew  and  the t r u c k  i n the rod  man  field  from  the  downhole s e i s m i c s u r v e y p r o c e d u r e  best  rod  in-situ  the rods  two  time  was  rods.  f o u n d most  during  the  withdrawl  10 hour  sensor d i s c u s s e d i n S e c t i o n The  a  r o d a d v a n c e and to the  from  stand free  c o u l d be made a t any  Geophone  at  identified.  removing  a d v a n c e and  in a  I t was  a relatively  the rods  a 40 m e t r e h o l e  the survey  easily  letting  s e i s m i c cone a l l o w e d  determination  no  that  a c h i e v e d by  reasonably rapid  complete  length.  was  1981;  of t h e s h e a r wave s i g n a l s  vibrations  was  pore  performed  survey  been  and  Robertson,  then  seismic  the h i g h amplitude it  and  i n t e r v a l s d u r i n g rod changes.  to  Because  seismic  friction  of 3.3  individual  individual  shear  signal were energy wave  48  3.7 Summary  The used  following  to carry  a. P o s i t i o n  o u t t h e CPT Downhole S e i s m i c the plank  Place vehicle  b. C o n n e c t and  i s a s t e p by s t e p summary o f t h e p r o c e d u r e s  s o u r c e and c l e a r  Survey.  any d e b r i s  beneath i t .  on t h e p l a n k .  t h e cone a n d t h e hammer t o t h e o s c i l l o s c o p e  isolate  the pushing  rods  from m e c h a n i c a l  plug-in,  contact with  the t r u c k . Switch n o i s e f i l t e r s on.  c. A l i g n  t h e CPT S e i s m i c Cone w i t h t h e p l a n k  advance  d. S e l e c t on  e.  to the desired  the d e s i r e d  Induce  a  shear  g.  and  depth.  switch positions  wave s i g n a l  signal  on t h e d i s k  i n f o r m a t i o n on t h e d a t a  Polarize  into  hammer blow t o t h e p l a n k  Store the d e s i r e d the  source  and a c t i v a t e  the t r i g g e r  the o s c i l l s c o p e .  horizontal  f.  signal  the s i g n a l  source.  r e c o r d e r and  by a p p l y i n g a h o r i z o n t a l  or  repeat  by a p p l y i n g a  reference  form.  t h e o p p o s i t e end o f t h e p l a n k  h. Enhance t h e s i g n a l  t h e ground  hammer blow t o  s o u r c e and s t o r e  the  above  the s i g n a l .  procedures  d. t o  49  g. a s  i.  necessary.  Advance repeat  o r withdraw procedures  t h e cone  d. t o h.  t o t h e next  selected  depth  and  50  4.0  4.1  DATA INTERPRETATION AND  ANALYSIS  Introduction  The values  procedure from  CPT  required downhole  to  obtain  seismic  dynamic  data  s t e p s . These a r e ;  measurement  of  determination  of  shear  velocities  i n t e r v a l s and  use  data At  arise  assumptions  calculated  dynamic  This  suggested employed  4.2  and  and  The downhole arrival  over  times,  selected  depth  s h e a r modulus from e l a s t i c  theory.  uncertanties  in a cumulative error  i n the  a  detailed  discussion  used a t each  study. A q u a n t i t a t i v e error  assessment  procedures  the  s t a g e of  i s a l s o p r e s e n t e d . In  interpretation  of  of  the data  addition,  which  may  be  the c u m u l a t i v e e r r o r s are d i s c u s s e d .  Time Measurement  most  important  seismic times.  measurements reference  arrival  basic  density  a n a l y s i s procedures  and  to reduce  three  soil  result  presents  cumulative  field  Arrival  wave  reduction process various may  reduction for this  uncertainty  shear  moduli  s h e a r modulus v a l u e s .  chapter  interpretation data  t h e dynamic  s t e p i n the data and  invloves  of complementary or supplementary  to c a l c u l a t e  each  wave  shear  was  data  step is  in  accurate  Unfortunately  are  extremely  made  to.  the  of  CPT  measurement o f s h e a r  wave  accurate  difficult  three  interpretation  direct to  external  make.  travel  time  In C h a p t e r  factors  3  (trigger  51  repeatability,  signal  repeatability,  which can s i g n i f i c a n t l y 2  discussed  waves  and  the  unique  i t * was could  allow  qualitative  quantitative  of  Wave  Figure detected  recognition  of  shear  field  the  of shear  shear  procedures wave,  o f t h e s h e a r wave a r r i v a l effort.  The  s h e a r wave a r r i v a l  accurate  times  wave  but  time can  quantitative  i s d i s c u s s e d i n the  16  by  Interpretation  shows  the  package p o s i t i o n e d be  typical  transverse  at point  Stokoe,  polarized geophone  a t two d e p t h s .  identified  excursion and  preferential  Chapter  two s u b s e c t i o n s .  4.2.1 Shear  would  characteristic  be a c h i e v e d . The recommended  require concerted a n a l y t i c a l  following  that  repeatability)  t i m e measurement.  polarization  interpretation  interpretation  arrival  indicated  generation easy  affect  and geophone  as  the  shear  of  Ideally  initial  method o f i d e n t i f y i n g  traces  a triaxial  geophone  t h e s h e a r wave large  S. Numerous i n v e s t i g a t o r s  1978; S c h w a r t z  wave  arrival  amplitude (Patel,  wave  1981; Hoar  and M u s s e r , 1972) have d i s c u s s e d t h i s  arrival  times  from  polarized  shear  wave  traces. The  presence  o f n o i s e and i n t e r f e r e n c e  o f o t h e r waves  a s t h e c o m p r e s s i o n a l wave t r a i n ,  combined w i t h t h e  response  the v i c i n i t y  precise  of and  difficult. point  the  geophone  repeatable  arrival  time  I t was c o n s i d e r e d d e s i r a b l e  on t h e s h e a r wave t r a c e The  in  most  readily  of t h i s  to select  points  some  slow  point  identification  t o overcome t h e s e  identifiable  rather  such  make  rather subsequent  problems. on t h e s h e a r wave  52  FIG. 16.  POLARIZED SHEAR WAVE SIGNAL FROM T R A N S V E R S E  GEOPHONES  TRACES  53  trace  from  the  transverse  the  zero  (favorably  geophones  are  recognized  by Shannon a n d W i l s o n  particle  velocity  crossover  p o i n t s the shear  distortions The  to  wave  impulse.  As  at their  causes  the  motion  signal  trace  is  characteristics  natural to  more  oscillation  since  the  zero  by m i n o r  This  affected  by  of t h i s  and  point  velocity  t h e geophones  until  the  internal  tend  wave  oscillation  further  along the  i t was c o n c l u d e d would  Once  damping  the shear  geophone  by a  provide  that the  an  easily  reasonable r e p r e s e n t a t i v e reference point f o r time  reference  times  the voltage  each  means t h a t  study  form.  characteristics.  has d i s s i p a t e d  cease.  interpretation.  waves between t h e s o u r c e  travel  previously,  Arrival  manner however, do n o t r e f l e c t  crossover  that  transducers excited  frequency  crossover  s h e a r wave a r r i v a l this  at  T h i s was  was l e s s a f f e c t e d  t h a n by t h e s h e a r wave i m p u l s e  zero voltage  shear  rapidly  i n F i g u r e 16 d i s p l a y  described  impulse  For the purposes  identifiable  in  most  wave t r a c e  h a s i t s own n a t u r a l  oscillate  first  changing  wave forms  s h e a r wave e n e r g y  trace.  points.  (1976) who s u g g e s t e d  of e l e c t r o m e c h a n i c a l v e l o c i t y  transducer the  crossover  horizontal  and n o i s e t h a n a t o t h e r p o i n t s on t h e wave  illustrated  response shear  was  voltage  oriented)  and  and  obtained  the true t r a v e l  receiver.  p o i n t s c a n o n l y be u s e d interval  times  velocities  The  first  to obtain  over  time of  selected  zero  interval depth  increments. It a  was f o u n d  signal  trace  that from  t h e measured one  hammer  c o r r e s p o n d w i t h t h e times measured blows.  Small  differences  in  first blow on  z e r o c r o s s o v e r t i m e on did  traces  hammer  not  necessarily  from  energy  and  subsequent striking  54  orientation the  between b l o w s ,  electromechanical  and  the  geophone  repeatability sensors  limitations  caused  of  arrival  time  measurements t o v a r y . During using  a  Section  positioned an  package, interval  method  t h e cone was  geophone  modified  package  (see  i n S e c t i o n 2.2.2, t h i s  detection  of shear  illustrated  variability  was  wave t r a c e s  in  Figure  method.  As  discussed  detection  still  shear  traces  individual  hammer b l o w s a t one  m e t r e cone  hole. normal  interval.  This  method  incorporate 3.2).  a  it  17a. signal second  T h i s equipment  involves  from a s i n g l e  waves  in Figure of hammer  in  As  simultaneous  energy  Even w i t h t h i s  out.  impulse,  change,  and  signal  observed.  wave  assuming  shear  were  geophone as  illustrated  to  of  s u r v e y s t o be c a r r i e d  17b.  To a s s e s s t h e v a r i a b i l i t y multiple  times  Section  allowed true i n t e r v a l  gathered  travel  t o overcome t h e d i f f i c u l t i e s  discussed  is  as  was  and  involves  at a d j a c e n t depths,  effort  modification  study, data  s e p a r a t e hammer b l o w s a t a s i n g l e  repeatability, triaxial  pseudo  this  from  s t a g e s of the  geophone  using a  2.2.2  generated  In  initial  single  determined  is  the  The  of the a r r i v a l were  arrival  analysis  is  obtained  metre depth time  statistical  time  data  from  multiple  increments was  distributions discussed  measurements,  in  then at  over a  analyzed  each  the  20  depth  following  subsection.  4.2.2  Statistical  In  order  to  Error  Assessment  obtain  some  level  of  confidence  in  the  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.  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.  O  P S E U D O  V  I N T E R V A L  T R U E I N T E R V A L  roi  ol  V  V b)  a)  FIG.  IO]  17. COMPARISON  BETWEEN TRUE AND  PSEUDO INTERVAL  MEASUREMENT  56  measurements being the  effects  was  analyzed  times  and  normally  of  This  measurement  statistically. the true  distributed  A normal defined  made, a n d i n o r d e r  by  curve  interval  random  t h ea r r i v a l  assess  time  first  zero  crossover  travel  times  were assumed  data  arrival t o be  variables.  variable  the classic  quantitatively  variability,  The  random  to  has  bell  a  shaped  distribution normal  which  or Gaussian  i s  curve.  i s d e f i n e d by t h e f u n c t i o n  n(x;u,o)  =  1 e- ' 0  5  (U~u)/o) 2  26  2TTO  Where  TT=3. 1 4 1 5 9  e=2.71828 M=mean and  a=standard  T h e m e a n , u, time using  or interval  deviation  and standard travel  time  deviation,  a,  of a set of arrival  measurements a r e e a s i l y  calculated  t h e formulae n  '-23  Xi  27  i= 1  a 4X) -(l] ) Xi2  i=1  Xi  i=1  n(n-l)  28  57  The interval checked  goodness travel  using  f i t of  time d a t a  distribution distribution  the  arrival  time  t o t h e assumed normal  u s i n g the Chi-squared  observed expected  of  of  ( X ) goodness 2  of  d a t a and t h e  distribution  was  f i t test.  The  measurements G i was compared w i t h an  of normally  distributed  measurements  Ei  the function  k X  2  (ei-Ei)  =  2  29  Ei i =1 If  the  value  X  2  value  i s s m a l l , a good f i t i s i n d i c a t e d .  i s g r e a t e r than  I f the X  2  10, t h e f i t t o t h e assumed d i s t r i b u t i o n i s  poor. In goodness  order to of  guarantee  f i t of  a  good  number  distribution,  sampling  theory  greater  30.  this  usually  than  involved  or  mean  assessed  degree  of  assessing  depth  the  number  the f i e l d  survey  must  be  procedure shear  increment.  o f c o n f i d e n c e w i t h w h i c h t h e mean a r r i v a l  true interval  the  measurements t o t h e n o r m a l  dictates  reason,  when  t h e g e n e r a t i o n and r e c o r d i n g o f 30 t o 40  wave t r a c e s a t e a c h The  For  results  travel  times  could  be  determined  times was  u s i n g the f u n c t i o n 30  58  Where e i s t h e r a n g e  o f t h e mean, a  is  measurements  the  number  interval  of  i s the standard d e v i a t i o n , and  Z/ A  2  is  the c o n f i d e n c e  coefficient.  The  mean  calculated  pseudo  using the  interval  travel  times  u  were  easily  relationship  yx,-x, = M,- M,  where  n,  is  wave s i g n a l s time  subsequent  a t one d e p t h ,  and u, i s t h e mean r e f e r e n c e  wave s i g n a l s  t i m e s were c a l c u l a t e d  confidence intervals  Z */  2  is  the  arrival  t h e same geophone a t a of t h e p s e u d o  interval  using  t  where  from  d e p t h . The s t a n d a r d d e v i a t i o n  °* -x, = / —  The  31  t h e mean r e f e r e n c e a r r i v a l t i m e o f a s e t o f s h e a r  of a s e t of shear  travel  n  +  —  32  were d e t e r m i n e d  using the formula  confidence interval  coefficient  (1 .960 f o r  95%). During in and  the i n i t i a l  portion  of t h i s  study  t h e c o n e w i t h d u a l geophone p a c k a g e s were their  unmatched. evaluated  natural Both  frequency pseudo  in a single  from a t y p i c a l  t h e geophones u s e d selected  randomly  and o s c i l l a t i o n c h a r a c t e r i s t i c s  and  true  interval  s u r v e y . The r e s u l t s  travel  times  were were  were compared and d a t a  s u r v e y u s i n g unmatched geophones  is  plotted  in  59  Figure  18. The X  section,  for  reasonable The  this  tight  shown  travel  standard  data  Figure  generally  pseudo and t r u e i n t e r v a l In  assumed  Figure  plotted  distributions. is  in  18a  order  to  characteristics,  less  geophones  the were  results  The  matched geophones a r e p l o t t e d  reasonable  f i t t o t h e assumed n o r m a l  times  and  indicate  the  similar  that  be true  the  (magnitude of  The  reasonably standard  o f t h e mean f o r b o t h  seen  oscillation a typical  response  survey  the X  2  using values  between 4 and 6 i n d i c a t i n g  a  distribution. that  interval  chacteristics  standard  oscillation  so t h a t t h e i r n a t u r a l  free from  of  the  pseudo  interval  time data comparison  b e t t e r t h a n when unmatched g e o p h o n e s were u s e d . 19c  poor.  one  i n F i g u r e 19. A g a i n  t h i s data averaged  In F i g u r e 19a i t c a n travel  1.5%  paired  were  for  that  effects  and t h e i r  calculated  is  measurements.  assess  similar.  distribution.  geophones  than  a  between t r u e and pseudo  indicates  f r e q u e n c i e s were i d e n t i c a l very  normal  i n F i g u r e 18b i n d i c a t e 18c  in this  between 4 and 6 i n d i c a t i n g  t i m e s u s i n g unmatched  deviations  deviation  as d i s c u s s e d e a r l i e r  averaged  f i t o f t h e d a t a t o an  comparison  interval  values calculated  2  is  F i g u r e s 19b  and  of the d i s t r i b u t i o n s  are  deviation)  to  those  observed  u s i n g unmatched geophones. Ideally should  be  t h e pseudo i n t e r v a l identical.  g e n e r a l l y much l e s s on  the  following The  calculated  However  than  d a t a and t h e t r u e i n t e r v a l the  range  0.5 msec. The e f f e c t  shear  wave v e l o c i t y  will  of  travel  of t h i s  data  times i s variation  be d i c u s s e d i n t h e  section. advantages  of  true  interval  method  are  that  the  MEAN INTERVAL  STANDARD  T R A V E L TIME  DEVIATION  msec  FIG. 18.  msec  T R A V E L TIME ERROR %  COMPARISON B E T W E E N TRUE AND P S E U D O T R A V E L TIMES FOR U N M A T C H E D  INTERVAL  GEOPHONES  STANDARD  MEAN INTERVAL T R A V E L TIME msic  S  6 —  hi  TRUE  .2 •  .3 .4 i  2  o  0  2  S  4  6  - 4  m  e^  E  E  a  X H Q.  Q  o  TRUE  INTERVAL  «H  12  »  TIME ERROR %  J  INTERVAL  6  I  a  .1  —i  TRAVEL  INTERVAL  E  Si  8  7  •- P 8 E U D 0  •  DEVIATION msec  LU  12  P8EUD0  9  12  INTERVAL  16 FIG.  19.  18-1  8)  COMPARISON TRAVEL  b)  BETWEEN  TIMES  FOR  TRUE  M A T C H E D  1B-> AND  C)  PSEUDO  INTERVAL  GEOPHONES I—'  62  geophones a r e p o s i t i o n e d which  arrives  blow so t h a t The one  at a fixed  known s p a c i n g  a t e a c h geophone o r i g i n a t e d  trigger  effects  and t h e s i g n a l  from t h e same hammer  are minimized.  a d v a n t a g e s o f t h e p s e u d o i n t e r v a l method a r e t h a t  geophone  is  required  and i t a p p e a r s t h a t  unlike  i n t e r v a l method, geophone r e s p o n s e c h a r a c t e r i s t i c s  only  the true  are less  of a  factor. As  a  result  determined  that  of  this  a  single  measurements were a d e q u a t e . generation interval  and  during  sufficient  recording a survey  data  A  it  and  interval  be  used.  4.3 Shear Wave V e l o c i t y The downhole  interval  (This  travel  s h e a r wave t r a v e l  these v a r i a b l e s  the e f f e c t  velocity  of these  i s presented  the depth  provide  interval  f o r the  t i m e measurement o f  calculation  was  carried  deviation  out  o f 0.2  Determination shear  data b a s i c a l l y time  would  was  measurements).  method o f d e t e r m i n i n g seismic  involving  This  E q s . 30 and 33 a s s u m i n g a known s t a n d a r d time  pseudo  procedure  t o d e t e r m i n e a 95% c o n f i d e n c e  msec f o r t h e t r a v e l  of  field  should  p l u s o r minus 0.125 msec.  Both  geophone  assessment  o f 10 s h e a r wave t r a c e s a t e a c h  mean o f e a c h p s e u d o and t r u e  using  statistical  into  wave  involves dividing  an i n c r e m e n t  are susceptible errors  on  velocity  of t r a v e l  to error the  i n the following  from  CPT  an i n c r e m e n t path  length.  and an a s s e s s m e n t  calculated subsections.  shear  wave  62  geophones a r e p o s i t i o n e d which  arrives  blow so t h a t The one  at a fixed  known s p a c i n g a n d t h e s i g n a l  a t e a c h geophone o r i g i n a t e d  trigger  effects  f r o m t h e same hammer  are minimized.  a d v a n t a g e s o f t h e p s e u d o i n t e r v a l method a r e t h a t  geophone  is  required  and i t a p p e a r s t h a t  unlike  i n t e r v a l method, geophone r e s p o n s e c h a r a c t e r i s t i c s  only  the true  are less  of a  factor. As  a  result  determined  that  of  this  a  single  measurements were a d e q u a t e . generation interval  and  during  sufficient  recording a survey  data  A  i t  and  interval  pseudo  procedure  be  used.  involving  This  t o d e t e r m i n e a 95% c o n f i d e n c e interval  (This  travel  would  downhole  s h e a r wave t r a v e l  interval  f o r the  t i m e measurement o f  calculation  velocity  shear  data b a s i c a l l y time  these v a r i a b l e s  the e f f e c t  depth  was  carried  out  o f 0.2  Determination  method o f d e t e r m i n i n g seismic  the  time measurements).  4.3 Shear Wave V e l o c i t y The  was  provide  E q s . 30 a n d 33 a s s u m i n g a known s t a n d a r d d e v i a t i o n  msec f o r t h e t r a v e l  of  field  should  p l u s o r minus 0.125 msec.  Both  geophone  assessment  o f 10 s h e a r wave t r a c e s a t e a c h  mean o f e a c h p s e u d o and t r u e  using  statistical  of these  i s presented  into  wave  involves dividing  an i n c r e m e n t  are susceptible errors  on  velocity  of t r a v e l  to error the  i n the following  from  CPT  an i n c r e m e n t path  length.  and an a s s e s s m e n t  calculated subsections.  shear  wave  63  4.3.1  Travel  The  Time  Effects  effects  of  uncertainty  velocity  measurement  spacing,  the  precision  of the t r a v e l  fixed  accuracy  velocity  of  are  the  or  the  accuracy  illustrated  in  can  Figure  be  20. F o r example,  measurement  equipment and a n a l y s i s (500  Msec),  of a 400 m/sec  soil  spacing  o f 4 m e t r e s must  be  averaging required based  to resolve on  the  considerations all  For  of a c c u r a t e  measurement  reduced.  and  the  order  velocity This  is  velocity available to  to determine the  a c c u r a c y , a geophone  velocity  determination  d e f i n i t i o n are i n d i r e c t strata  depth  objectives  becomes masked  increments.  this conflict,  and  of  when c o n s i d e r i n g  the  Some  the  by  velocity  compromise i s  decision  data  conflict.  must  collection.  time,  and  cost  use of t h i s measurement  be The must  system  applications.  research purposes  s h e a r wave v e l o c i t y  cone p e n e t r o m e t e r logging  in  of equipment a v a i l a b i l i t y ,  be a s s e s s e d  for p r a c t i c a l  the  larger  is a  i f 5 per cent  t o the d e s i r e d  of i n d i v i d u a l  over  velocity  procedures allow p r e c i s i o n  then  stratigraphic  The d e f i n i t i o n  the  used.  the o b j e c t i v e s  detailed  and  t h e s h e a r wave or  on  geophone  tested,  interval  i s considered desirable  velocity  and  the  improved  accuracy  Clearly  being  of  t i m e measurement. The s o i l  measurement  msec  t i m e measurement  function  geophone s e p a r a t i o n  measurement  0.5  a  soil  p a r a m e t e r , however by c h a n g i n g  precision,  only  in travel  i t was  measurement  t o complement  capability  with  considered  desirable  to  allow  c a p a b i l i t i e s of the s e i s m i c  i t s conventional  stratigraphic  good a c c u r a c y . An o b j e c t i v e  of a  shear  64 SOIL  100  /  SOIL  m/s 2 0 0  C  V E L O C I T Y  V E L O C I T Y  m/8 ,3 0 0 m/s .400 m/s  SOIL  V E L O C I T Y  SOIL 100 m/s 200 m/s 3 0 0 m/s 4 0 0 m/s  V E L O C I T Y  3 Ui K  a. ui  S  ui CE  3 (0 < 111  < > OC Ul  10  H  % V E L O C I T Y T 3  G E O P H O N E  FIG.  20.  A C C U R A C Y  ~r  R E S P O N S E ,  FUNCTION AND  % V E L O C I T Y T 3  5  4  VELOCITY  20  m  G E O P H O N E  M E A S U R E M E N T OF  T "  4  R E S P O N S E ,  A C C U R A C Y  M E A S U R E M E N T  G E O P H O N E  A C C U R A C Y  SEPARATION  -r6 m  AS  PRECISION  A  65  wave v e l o c i t y  accuracy  metre  increments  depth  project.  As  equipment  was  o f p l u s o r minus was  set  explained  in  Due  to  the  and  realistic  upper bound on t r a v e l  multiple  pseudo  (Based  signal  analysis  Path  effects  of  are  measurements  (source  less  unless  discussed  in  measurements  The true of  on  1  the  one  research  the  resulting  data,  between  the  i t was d e t e r m i n e d  t i m e measurement e r r o r  true  that  would  a be  i n t e r v a l measurements and a  inaccurate  depth  to receiver) when  Section the  and  signal  when d i r e c t  are being  made.  offset  travel The  time  effects  i n t e r v a l measurements a r e b e i n g made, shallow depth. These e f f e c t s  3.3.  Of  effects  more  of  importance  signal  in  refraction  were deeper  through  a t the s i t e . conventional  shear  travel  trigonometric path  method  wave  of  analysis  surveys  interval  correction  relationship  assuming  from t h e s i g n a l  corrected  source  to  i s illustrated  travel  time  f o r b o t h p s e u d o and  involves  travel  t i m e s . The  T h i s method o f a n a l y s i s The  over  procedure).  i s at a very  are  recorded  travel  4.1,  scatter  metre  i n t e r v a l downhole s e i s m i c  interval  during  Section  p a r t i c u l a r l y important  critical  the probe  layering  cent  Effects  measurement  are'  interval  cent.  4.3.2 T r a v e l  The  early  observed  interval  per  per  measurement c a p a b i l i t i e s were n o t a s good a s had been  anticipated.  10  5  is a  the  times  into  based  on  diagonal the  conversion corrected a  simple  straight  geophone  line  receiver.  i n F i g u r e 21a.  interval  Tcorr,  equals  the  •IQNAL  SOURCE  OFFSET  S T R A I G H T LINE T R A V E L  PATH  b)  ITERATIVE TRAVEL  PATH  67  difference depths.  the  The c o r r e c t e d  vertical  path  adjacent are  between  corrected  travel  times  as i f the s i g n a l  to the testhole.  straightforward  travel  to  a r e f o r an assumed  source  were  The c a l c u l a t i o n s  and  times  easily  equivalent  located  for  done  immediately  this  on  a  adjacent  correction programmable  calculator. When the  the signal  testhole  determined possible  this that  signal  signal  contrasts analysis  cause  One  approach  involves  source cases  will  variations to  path  that  correct  constant. thickness  If  the  of each  distribution Referring  beds  would  i n each number  of which  e t a l , 1976)  21b. The into wave  layers.  in  an  analysis  a number  of  velocity i s  to infinity,  become  infintesimal  and the v e l o c i t y  a  I  refraction  was e x t e n d e d  continuous  t o the n t h bed i n Figure sin  velocity  refraction  t h e shear  as  the conventional  (Telford  c a n be d i v i d e d  was  necessary.  and  wave  i n Figure  i t  be a s s m a l l  in different  for  from  of beds  bed would become  because  Law  shown  medium  depth  length  3.3  may b e  large,  effect  of Snell's as  should  at  path  distance  In S e c t i o n  are  forthis  analysis  a small  offsets  materials  in travel  the subsoil  horizontal  larger  n o t be a c c u r a t e  the application  iterative  only  offsets  offsets  between  approach  i s offset  i s suitable.  source  exist  will  thin  analysis  but i n c e r t a i n  When  assumes  source  sin  2 1 b , we  function  with  the  depth.  have  i = p 34  Vn  Vo  Vn  AXn  Vn(z)  35  = AZn t a n in  36  68  AZn ATn  =  37 Vn c o s i  The  raypath  direction  parameter  p  i s a constant  i n which the r a y l e f t  depends upon  i ° . In t h e l i m i t  the s i g n a l  source,  that  when n becomes i n f i n i t e ,  dx — = tan i dz  By  w h i c h depends upon t h e  dt  is, i t we g e t  1 =  —  dz  38 Vcos i  integration n-1 pViAZi X = > , ^^1-(pVi)  2  pVnAZn + , Jl-(pVn)  39  1=1  n AZi T  =  y^  Vi  1-(pVi)  40  2  i=1 By r e d u c i n g  Vn = / /  X n  the e x p r e s s i o n  7!  , .,..2 -  (pVi)  f o r x, we  V  / •  ) IS  y  /  have  OJ-  \ \ pViAZi  ^T" Zn  \\2  69  A  value  is  selected  are  substituted  the  recorded a r r i v a l  assumed  into  and  calculated  a predetermined position travel  of  path  The  time  i s checked.  A  iterations  t i m e and  the convergence  new  are  and  value  for  performed  the measured a r r i v a l  p  until  time a r e  the  travel  path, thus the d e s i g n a t i o n ,  p  with is the  within  t o l e r e n c e . Changes i n t h e v a l u e of p c h a n g e  the  iterative  analysis.  iterative  performed  i s c a l c u l a t e d . Vn  t h e e q u a t i o n f o r t and  numerous  arrival  f o r p and Vn  by  analysis  hand.  A  is  extremely  computer  is  time  necessary  consuming  if  to perform  the  analysis. The  s h e a r wave v e l o c i t y  displays  the  results plot  calculated  the  higher  because  short.  The  practical be q u i t e  4.4  to that soil  shows  that  conventional  t h e assumed s t r a i g h t  differences  s o u r c e s of e r r o r  plot  in  iterative  shallow  depth  analysis  are  line  travel  Figure  w i t h the  a straight  line  downhole travel  22  travel  velocities consistently  paths  are  a r e however s m a l l when compared  associated  purposes  depth  o f b o t h c o n v e n t i o n a l and  p a t h a n a l y s e s . The using  versus  test.  too  to other For  most  path assumption  would  satisfactory.  Dynamic S h e a r  Modulus  Calculation  In  Section  1.1  and  the  study  of  wave p r o p a g a t i o n was  t h e dynamic density  acceleration  the a p p l i c a t i o n  unit  weight  of  is  of the s o i l ,  to g r a v i t y , g ) m u l t i p l i e d  elastic  theory  d i s c u s s e d . I t was  s h e a r modulus G o f a s o i l  (total due  2.2,  by  related 7, d i v i d e d  the square  shown  to by of  the the the  70  SHEAR WAVE V E L O C I T Y , V s , m / s e c  100  300  200  t  I  AO  O A  kO  i  CONVENTIONAL ITERATIVE  SIGNAL  ANALYSIS  ANALYSIS  SOURCE  OFFSET  10 m  » 5  AO  Ok AO  E *  AO  x H  AO  o.  iu 10 o  AD  A  O A  O  1 5  FIG.  O  A  -  2 2 . COMPARISON AND  BETWEEN  ITERATIVE  CALCULATIONS  CONVENTIONAL  VELOCITY  71  shear  wave v e l o c i t y  V s , by t h e r e l a t i o n s h i p 7VS G  = pVs  2  =  2  1  9 In  the  determining  previous  accurate  sections  shear  of  wave  this  travel  c h a p t e r , methods f o r  times  and  shear  velocities  have been d i s c u s s e d . I n s p e c t i o n o f t h e a b o v e  indicates  that  accuracy  of  accurately density  since  the  the  velocity  shear  measurement  a s s e s s i n g the shear  measurement  There  are  i s not as  four  wave v e l o c i t y  undisturbed  sampling,  resistance  -  correlations  was  Most  soils  kg/m , t h u s 3  introduce  for this  even an e s t i m a t e d  considered  silts  undisturbed density  samples  extremely  below.  soils,  difficult  densities  study,  d e n s i t y c a n be penetration  rather  educated  specialized  and  1600 kg/m  a  be  study  a n d 2250  would  probably  20 p e r c e n t  more soils are  returned  3  3  (Stokoe and  accurate such  as t h e c l a y s and  easily  to  assessment  the  sampled  and  laboratory for  determinations.  Cohesionless  situ  this  can  of the s o i l  making an  v a l u e o f 1900 kg/m  d e s i r a b l e . Cohesive in  soil  by  between  i n G o f no more t h a n  investigated  in  project.  Woods,1972). F o r r e s e a r c h p u r p o s e s was  important  logging,  or is  have a d e n s i t y l y i n g  an e r r o r  in-situ  neutron  l o g g i n g equipment  not c o n s i d e r e d  most  important.  determined;  e s t i m a t e . Neutron  equation  i s squared, the  m o d u l u s . The a c c u r a c y  ways by w h i c h  density  is  wave  using  t o sample  i n these a sand  particularly  coarse  sands,  are  i n an u n d i s t u r b e d c o n d i t i o n . I n -  materials  density-cone  were  determined,  bearing c o r r e l a t i o n  for  this  described  72  The relative much  determination density,  recent  of  from cone  research  soil bearing  quartz cone By  density,  sands  - relative  obtaining  disturbed maximum  situ  relative  situ  sand d e n s i t y  void  ratio  of  emax, minimum  1983).  resistance,  density sand  samples  minimum  c a n be e s t i m a t e d soil  void  ratio  at  correctly  the subject of  Though in-situ  no  unique  stress  development  of  the  i n F i g u r e 23.  selected  depths,  d e n s i t i e s , and e s t i m a t i n g i n bearing  c o r r e l a t i o n , the i n -  a t each depth  interval.  e, i s r e l a t e d t o t h e maximum v o i d emin,  and  chamber t e s t s on  c o r r e l a t i o n shown  from t h e cone  a  more  r e s u l t s of c a l i b r a t i o n  and  density  or  has been  1982) have l e d t o t h e  bearing  determining  the  the  (Baldi,  data  (Robertson,  r e l a t i o n s h i p e x i s t s between cone relative  density  and the r e l a t i v e  density  The ratio  Dr,  by  equation e=emax-Dr(emax-emin) The  specific Sr,  the  total  unit  weight  of  g r a v i t y of the p a r t i c l e s void  ratio  42  the s o i l  7 , i s r e l a t e d to the  Gs, t h e d e g r e e  e, and t h e u n i t w e i g h t  of  saturation  of water  7 W , by t h e  equation Gs + S r 7W  7S =  43  1 + e From t h e t o t a l shown  u n i t weight,  i n F i g u r e 23.  soil  density  i s easily  determined as  73  CONE 0  100  BEARING,q 200  c  300  , kg/cm* 400  500  E u  0.5 cn to  LU  rr 1.0  u b.  1.5  o M  rr o x  2.0  100% = Idmax d "dmin r e max -e dmax dmi n max min g g de1+e relative nsity water content w r bulk wet dens i ty void ratio specific gravity e unit weight water gravitational acceleration w •dry unit weight soi 1 D  Y  = -  X  Y  x  X 100%  's S.G. 1 + w Y — = X - = — — X 'w v  P  S.G.  v  Y  9  FIG. 2 3 .  SAND DENSITY - CONE BEARING  CORRELATION  (Unaged uncemented quartz s a n d s , after R o b e r t s o n ,  1983)  74  4.5  Summary  The CPT  d e t e r m i n a t i o n o f dynamic  downhole s e i s m i c s u r v e y  shear moduli  2.  Make  averaging  times  such as t h e f i r s t  an a s s e s s m e n t ten or  using the  requires a multistep procedure.  1. Measurement o f s h e a r wave a r r i v a l reference point  in soil  using  arrival  convenient  zero crossover  of the v a r i a b i l i t y more  a  point.  o f t h e measurement by  times  at  selected  depth  increments.  3.  Vectorally travel  convert times,  determinations  actual assess  and  travel the  arrive  at  times  t o pseudo  variability a  best  interval  of  these  f i t travel  time  estimate.  4. D e t e r m i n e  the t r a v e l  wave v e l o c i t i e s travel  5.  path  Calculate using  path  using  determined  interval  a  an  conventional  or  shear  interative  analysis.  t h e dynamic  the  l e n g t h and determine  elastic from  s h e a r modulus f o r e a c h relationship  supplimentary  G=pVs , 2  or  depth where  complementary  increment p  is  density  75  data.  The  research carried  indicates  that  determinations travel  time  planned  obtained than as  over  of  dependent  survey  suggested,  made.  the  cone  bearing p r o f i l e  shear  wave  modulus, minus  consider.  interval  following  velocities increments  should  velocity  i t should  and s e l e c t e d  squared  one metre d e p t h  a r e improved of  soil  over  easily  samples  soil  be  of l e s s such  density  Since  the  of shear  Gmax t o w i t h i n  larger  properties  analysis  information  increments.  which  carefully  i n the d e t e r m i n a t i o n  be p o s s i b l e t o d e t e r m i n e  25 % o v e r  averaging  is  over  w i t h an e r r o r  additional  thesis  velocity  a  c o u l d be made w i t h i n 5 % u n c e r t a i n t y .  the d e t e r m i n a t i o n s although  By  wave  and by u s i n g t h e d a t a  wave  one m e t r e d e p t h  shear  the depth  procedure shear  the  on  ten per cent. With s u f f i c i e n t  determinations  or  is  accuracy  measurements a r e  field  techniques  the  out f o r the p r e p a r a t i o n of t h i s  plus  The a c c u r a c y o f  depth  becomes  increments a  factor to  76  5.0 DYNAMIC SHEAR MODULUS FIELD MEASUREMENTS  5.1 I n t r o d u c t i o n  The p r e v i o u s c h a p t e r s a  geophone  in-situ  instrumented  dynamic  theory,  shear  rational  downhole  techniques  presents  results  three  selected  s e i s m i c cone p e n e t r o m e t e r  moduli.  intrepretation the  have i n t r o d u c e d t h e c o n c e p t  of  shear  profiles  for  modulus  with data  then shear  each  Fraser  procedures  profiles  research from  other is  correlations, conventional  testing  elastic and d a t a  This  chapter  carried  out a t  River  Delta  site.  seismic  in-situ  compared  pressuremeter  a n d dynamic The  wave  moduli  with  testing  modulus  determinations.  relationships  comparison  modulus  shear  modulus  are  determinations.  unload  bearing -  reload  modulus  moduli,  existing  w i t h CPT downhole  then Seismic  -  available. of  data  shear  measurement  c r o s s h o l e s e i s m i c d a t a where  c l o s e s by p r e s e n t i n g a  dynamic  cone  near  and t e c h n i q u e s .  opens w i t h a d i s c u s s i o n o f t h e f i e l d  wave v e l o c i t y  determined  compared  these  procedures  discussed.  field  determine  phenomena,  field  i n the  to  using  o f t h e s e i s m i c cone and p r e s e n t s cone b e a r i n g  profiles,  values  wave  been  in-situ  research s i t e s  chapter  capabilities  seismic have  V a n c o u v e r , B.C. t o e v a l u a t e This  Seismic  of  and  The c h a p t e r empirical  seismic  modulus  77  5.2 CPT S e i s m i c F i e l d  The in  location  Figure  24.  conditions, in-situ  and  of the t h r e e r e s e a r c h s i t e s  sites  accessibility,  were s e l e c t e d  and t h e  the Annacis North  pressure p r o f i l e s  bearing  profiles  o b t a i n e d . The p l a n k  on t h e b a s i s  availability  type  Langley  Pier  Site.  in  signal  Figures  source  was  waves were g e n e r a t e d  used  The f i r s t  arrival  time  times  described  were  i n Chapter  m e t r e s o f t h e cone h o l e a t e a c h  site.  and  30  calculated  The r e s u l t i n g  site  shown  moduli  shown  40  shear  in  Interval  u s i n g t h e mean i n t e r v a l  increment. are  to  and t h e  plotted 4.  in  the  ends  interval,  signal  wave  shear  Figures  true  30 t o 40  traces  and  were  delay  portion  z e r o c r o s s o v e r p o i n t s were u s e d  interpretation  30  with  to capture only the i n i t i a l  travel  t h i s data  t h e t r a n s v e r s e geophone. A p o s t t r i g g e r  signal  and  cone b e a r i n g  placed  then withdrawn and a t each metre  from  soil  25, 26, and 27 were  The  obtained  of  additional  Site  Continuous  were o b t a i n e d and from  shown  3.00  Freeway  within  shear  of  shown  t o 40 m e t r e s a t t h e M c D o n a l d s  equidistant c o n e was  is  data.  20 m e t r e s a t t h e F o r t  at  pore  cone  Capability  s e i s m i c CPT was a d v a n c e d  Farm S i t e , metres  of each These  testing  The  Testing  of  each  f o r shear  pseudo  was  wave  interval  statistical  distribution  shear  velocities  were  times over each  depth  wave  travel  wave v e l o c i t y  profiles  for  25, 26, and 27. The dynamic  i n t h e f i g u r e s were c a l c u l a t e d  using  the  as  each shear  elastic  relationship G=pVs discussed  earlier.  2  1 .  lUxnl  FIG.  24.  R E S E A R C H SITE LOCATION M A P  SCALE 1:250,000  00  79  5.2.1  M c D o n a l d s Farm  The Site)  first  on  testing  has  principal soils may  site  is located  Airport  Site  just  Sea  in  been c a r r i e d  out  research  found  site  10  deposit  normally  to  varies  generally  of  here as  the  Vancouver  Richmond, at  this  B.C.  site,  as  International  Extensive it  has  of  12 m e t r e s of  2  site  metres  of  and  1 to 2 metres  silt.  tidal  of  the  the  site  stratigraphy, organic  The  silt  extensive  water  fluctuations ground  the  Columbia  s a n d w h i c h o v e r l i e s an  consolidated clayey seasonal  The  in-situ  been  f o r t h e U n i v e r s i t y of B r i t i s h  consists  with  within  t h e M c D o n a l d s Farm  y e a r s . A c o m p l e t e d e s c r i p t i o n of  25,  overlying  depth  to  i n C a m p a n e l l a e t a l , 1983.  shown i n F i g u r e  of  north  Island  group f o r f i v e be  (referred  table but  surface  was  during  testing. The  side  shows an and The the  the  by  interesting incremental  steady  sudden d r o p a t by  the  profiles.  The  shear  increase  expected The from  Bulk  the  bulk  soil  soil  soil  silt  sand  wave v e l o c i t y  and  and  with  and  at  as  silt  and  25  profile  measurements. i n the 13  dynamic  sand  and  metres shear  modulus  c o n f i n i n g pressure  d i s t u r b e d sampling  i n the  depth  shear  d e n s i t i e s shown f o r t h e  densities  in Figure  cone b e a r i n g  velocity  consolidated clayey  density correlation  profiles  interface  wave v e l o c i t y  depth  the  wave  i n cone b e a r i n g  shear  in a normally  of  between t h e  downhole s h e a r  with  selective  bearing  comparison  increase  mirrored  then  s i d e comparison  are  modulus profiles  as  would  be  silt. sand were  from a s i t e  discussed  in  were b a s e d on  determined  specific  cone  section  4.4.  one  undisturbed  SOIL DENSITY 1700  , K G / C U  ^00  BEARING RESISTANCE  SHEOR WAVE VELOCITY 0  , M / 5 E C  '  2SO 0  ,  K  G  /  S  Q  C  M  1  DYNAMIC SHEAR MODULUS 200 0  ,  K  G  /  5  0  C  M  1  SOIL .250  PROF ILE •oil  t U T  PI*  • eft Clayey  FIG. 2 5 .  MCDONALDS FARM  CONE  PROFILE  tILT  81  sample  5.2.2  from  Fort  The  16 m e t r e s  Langley  second  Freeway  Site)  portion  of  Freeway  site  i s located  potential  for in-situ  recently  Figure  layers.  observed  The  t o be w i t h i n  The travelled  when  Trans  Canada Highway  located  Wave  on  i n the  little  trains  g e n e r a t i o n and  the  freeway  Langley,  B.C.  shows tremendous  site  stratigraphy,  with  soft  occasional  seasonally  but  shoulder  of  was  the . h e a v i l y  adjacent to a railway that  the  by heavy t r u c k t r a f f i c low  the  was  site  indicated  frequency  overpass.  allowed  detection  on  Langley  surface.  immediately  affected  generation procedure  Fort  Fort  clayey s i l t  the  field  crossed  the  e x t e n s i v e d e p o s i t of  fluctuates  However, l a r g e a m p l i t u d e ,  freight  signal  and  2 metres of the  overpass. Observations  freeway.  table  is  was  this  o f an  clay  site  wave d e t e c t i o n  near  r e s e a r c h . The  consists  water  as  e a s t of V a n c o u v e r  utilized,  normally c o n s o l i d a t e d s i l t y sandy  here  Highway  testing  26,  to  50 Km  t h e T r a n s Canada only  in  Site  (referred  Although  shown  depth.  for  on  n o i s e was The  operator  only c a r r i e d  shear  out  the  noted  impulse  type  discretion. during quiet  periods. The from  a  metres  plotted  density  s e t of c o n t i n u o u s  v a l u e s i n F i g u r e 26 were  samples o b t a i n e d between  2.8  obtained and  14.2  depth.  Both Figure  soil  26  13 m e t r e s .  the  s h e a r wave v e l o c i t y  and  s h e a r modulus p r o f i l e s  show g r a d u a l i n c r e a s e w i t h d e p t h The  i n c r e a s e i n value over  this  except  between  increment  11  in and  corresponds  FIG.  26  FORT  LANGLEY  CONE  PROFILE  83  well the  w i t h a s u b t l e but o b s e r v a b l e i n c r e a s e same i n c r e m e n t . I n s p e c t i o n o f  that  the s o i l  site  profile.  i s s a n d i e r here  5.2.3 A n n a c i s N o r t h P i e r  The Site) the  third  i s located Fraser  original  organic  continuous  a  upper  sands  silt  were  at  i t i s h i g h e r and lower  a d j a c e n t t o t h e main  out a t t h i s  stratigraphy  sand  dike  topsoil  i n the  at  encountered  shown i n  fluctuates  a  depth,  with  a p p r o x i m a t e l y 4 metres  of soil  Figure  a thin  i s underlain  during testing  arm  f o r a proposed  overlies  great  Pier  Extensive  site  overlying  which  The sand  and sand  table  indicates  t o here as t h e Annacis North  Island  deposit.  The water  encountered  metre silt  sand  samples  5 Km west o f New W e s t m i n s t e r .  3  interlayered  cone.  (referred  s t a y e d b r i d g e . The s i t e of  and  than  have been c a r r i e d  consists  available  Site  on A n n a c i s  River,  investigations cable  site  i n cone b e a r i n g o v e r  27,  l a y e r of  reasonably  by m a r i n e  silt  but  the  only  with the seismic  river  level  but  was  depth a t the time of t h e  survey. The  shear  wave  mirrors  the  dramatic  velocity  increase to  a  in  cone  bearing  s h e a r modulus The  profile  profile  in  with  Figure little  c o n t r a s t s . The most n o t a b l e  s h e a r wave v e l o c i t y  significant  stratigraphic  velocity  increase  features  in  a t 11 m e t r e s cone  are noticeably  27  subtley  i n t h e way o f  features which  are  an  corresponds  bearing  peaks.  These  amplified  on t h e dynamic  plot.  bulk s o i l  density  plot  is  based  on  sample  averages  FIG.  27.  ANNACIS  NORTH  PIER  CONE  PROFILE  85  obtained  5.3  from c o n v e n t i o n a l d r i l l i n g  Comparison  of I n - S i t u M o d u l i  Downhole moduli  can  determined. from  crosshole  determination  from  cone  or s e l f - b o r i n g  Since  from e a c h  another  of  the  of  methods  seismic  bearing  correlations data  method by w h i c h  Other  determination  sampling at the  -  in-situ  include  testing, dynamic  pressuremeter  sites,  it  direct indirect  shear  modulus  unload - r e l o a d  is  shear  and  t h e s e methods i s a v a i l a b l e  research  site.  Measurements  s e i s m i c i s o n l y one be  and  tests.  from one  presented  here  or for  comparison.  5.3.1  Self-Boring  The  Pressuremeter  dynamic  shear  s h e a r wave v e l o c i t i e s are  replotted  modulus  The  from  i n t h e sands  shear  determined  tests  program  Eldridge loading  (1982), conditions  pressuremeter  using  data  data  McDonalds  from  10  self  boring  i n h o l e s a d j a c e n t t o t h e s e i s m i c cone tests  were  (Robertson,  the p l o t t e d  at the  from s e i s m i c  i n F i g u r e 28. They a r e compared w i t h dynamic  each pressuremeter  obtain  values calculated  Site  pressuremeter  Research  moduli  Farm  values  pressuremeter  Moduli  that  1983).  test  values  carried  was  The  out  as p a r t  unload -  multiplied  initial  i s about  one  lies  above  of a  moduli  by a f a c t o r  of 5 to  by  Byrne  t a n g e n t modulus under  fifth the  PhD.  reload  ( b a s e d on a s u g g e s t i o n  the  hole.  and  static  t h e dynamic m o d u l u s ) . s e i s m i c cone d a t a but  The the  86  SHEAR M O D U L U S , Gmax, K g / c m  DYNAMIC 500  2  1000  1500  I  I  1  O  •  SELF-BORING  O  C P TSEISMIC  PRESSUREMETER DATA  A o 5H  A  SAND  A A  O  A  O  o  O  A  O 15H  o  SILT  o Note:  o  FIG.  28.  COMPARISON BETWEEN AND  SELF-BORING  MCDONALDS  FARM  SBPMT Unload - Reload moduli m u l t i p l i e d by 5 to determine Gmax.  C P TSEISMIC  PRESSUREMETER,  87  comparison that  self  cycles  5.3.2  i s r e a s o n a b l y good. The boring  pressuremeter  s h o u l d be m u l t i p l i e d  CPT  Cone B e a r i n g  data  moduli  by a f a c t o r  from  this  from  normally  c o n s o l i d a t e d uncemented q u a r t z s a n d s .  relationships  shear  modulus  combining  developed  by  correlation  relative  Baldi,  H a r d i n and In  Drnevich  Figure  29  the  was  lies  from  below  t h e CPT  density  Annacis North  Pier  values  from  the  curves  two  5.3.3  CPT  resistance dynamic  Idriss  s e i s m i c s h e a r modulus d a t a  correlation. but  The  CPT  (1970),  sand  modulus  modulus  i s quite  seismic  Site  i s compared w i t h p r e d i c t e d  t h e cone b e a r i n g c o r r e l a t i o n .  the  downhole s e i s m i c d a t a  the comparison  shear  from shear  the  The  data  from  good. the  shear  modulus  agreement  between  is excellent.  Conventional Crosshole  The  correlation  cone  by Seed and  for  (1972).  t h e cone p r e d i c t i o n  In F i g u r e 30  proposed  The  a t M c D o n a l d s Farm i s compared w i t h t h e p r e d i c t e d values  reload  (1982) a cone  (1982) w i t h e m p i r i c a l  s h e a r modulus r e l a t i o n s h i p s d e v e l o p e d and  -  3 t o g e t Gmax.  & Campanella  dynamic  by  unload  of about  bearing  developed  indicates  Correlations  In some r e c e n t work by R o b e r t s o n  was  site  Testing  s e i s m i c downhole s u r v e y a t t h e A n n a c i s  Site  was  carried  out a p p r o x i m a t e l y  5 metres  array  used  for a crosshole seismic survey.  The  North  Pier  from a t h r e e h o l e crosshole  data  88  DYNAMIC  FIG.  SHEAR MODULUS,Gmax, K g / c m  2 9 . COMPARISON AND  BETWEEN  C P T BEARING  MCDONALDS  FARM  2  C P T SEISMIC  PREDICTION,  89  DYNAMIC SHEAR MODULUS, Gmax, K g / c m * 6 0 0  0  FIG.  1000  3 0 . COMPARISON AND  BETWEEN  C P T BEARING  ANNACIS  NORTH  1500  C P T SEISMIC  PREDICTION, PIER  90  was  obtained  at  metres depth. testing  2.5  The  was  metre  holes  completed  compared  with  metres depth. crosshole 20  per  CPT The  data  but  cannot  be  this  data  after  two  the  110  crosshole  path  crosshole  between  lies  the  travel  the  lengths data  is  surface.and  consistently  s e t s of d a t a  above  30 the  compare  within  downhole s e i s m i c  survey  particularly  the  is  are  results  testing i n the  is  too  are  that  and  shear  i n Chapter SH  to support  i s suggested on  shear  installation  to  direction. this  waves  Little  this  velocity  data  detected but  and  is available the  shear  of  base  anisotropic  modulus.  the the  data  in  conclusively.Additional  t h e m a g n i t u d e of  Borehole the  S h e a r waves  e x p l a n a t i o n , and  prove  location.  the  shear  are  but  discrepancy  crosshole  effect  include  location  disturbance  cumulative  measurement e r r o r s a s s o c i a t e d w i t h Despite  velocities  waves w h i c h p r o p a g a t e h o r i z o n t a l l y  to determine  and  the  for  possible explanation  wave  2,  to account  in  explanations  effects,  used  detected  i n s t r a t i g r a p h y between  downhole  be  Numerous  waves w h i c h p r o p a g a t e v e r t i c a l l y  wave v e l o c i t y  Additional differences  SV  vertical  limited  conclusive.  s e t s o f d a t a . One  discussed  tests  literature  effects  c r o s s h o l e and  i n the h o r i z o n t a l d i r e c t i o n .  oscillate  research  between  between two  downhole  crosshole  the  31  data  g e n e r a l l y the  discrepancy  oscillate  here  Figure  downhole  affect  a n i s o t r o p i c . As  the  surveyed  ensure t h a t the  considered  may  discrepancies  in  between 5 m e t r e s and  cent.  variables  of  In  downhole  Comparisons data  were to  were a c c u r a t e l y known.  intervals  and of  and probe  inherent  each survey. »  measurement  descrepancies,  the  91  SHEAR W A V E V E L O C I T Y , m / s e c SO  100  150  200  I  I  I  5  6  A  10  4  250  300  3 5 0  —I  A  CROSSHOLE  •  DOWNHOLE  SEISMIC SEISMIC  A  i«H  A  A  & Ul O  2 0 -|  A  25  H  A  A  30  FIG.  H  A  3 1 . COMPARISON CROSSHOLE ANNACIS  BETWEEN VELOCITY  NORTH  PIER  DOWNHOLE AND MEASUREMENTS,  92  comparison  between t h e two s e t s o f d a t a  engineering  5.4  purposes  Conventional  The to  dynamic  the  would  be c o n s i d e r e d r e a s o n a b l y  f o r most  practical  acceptable.  Empirical Relationships  s h e a r m o d u l u s , Gmax, o f a s o i l  in-situ  mean  effective  stress  can by  be  an  related  empirical  r e l a t i o n s h i p o f t h e form Gmax=Kg P a ( o m ' / P a ) where Kg i s a d i m e n s i o n l e s s effective an n n  stress,  modulus  is  1.0.  (Seed  proposed  modulus  numbers  relative  d e n s i t y . The s a n d s  densities  in  which  correlation  and  (ikg/cm ), 2  Idriss,  mean  and n i s that  and c l a y s  1970; H a r d i n a n d  range  would  at  between in  indicate  (1983)  quartz  Farm  Figure  on t h e cone b e a r i n g c o r r e l a t i o n  should vary  23.  would  s e i s m i c cone s h e a r in  relative  based  Robertsons'  on t h e proposed  North  Pier  vary Site  t h a t range between 30 a n d 50 p e r c e n t i n F i g u r e 23.  indicate  that  between 750 a n d 1000 f o r t h e s e  h a s been p l o t t e d  that  t h a t t h e modulus number s h o u l d  based  correlation  have  50 a n d 70 p e r c e n t  1000 a n d 1250. The s a n d s a t t h e A n n a c i s densities  suggests  s a n d s a r e d e p e n d e n t on  McDonalds  relative  site  the  consolidated s i l t s  have  The  is  i t h a s been shown  by R o b e r t s o n  uncemented  cone b e a r i n g c o r r e l a t i o n  proposed  am'  1972).  A correlation  between  sands  0.5. I n n o r m a l l y  approximately  Drnevich,  number,  Pa i s a r e f e r e n c e s t r e s s  e x p o n e n t . F o r uncemented q u a r t z i s approximately  44  n  modulus d a t a  Figure  32  mdulus  number  sands.  from  and  the  Robertsons'  t h e M c D o n a l d s Farm  compared  with  shear  93  moduli  calculated  using  sand  exponent  0.5  of  an 1.0  depth  was  of  assumed.  i n the  sand  shows  two  was  assumed  The  resulting  that  Kg  relative  density  of  the  expected,  Kg  off  i n the  Shear  drops  modulus  are  reasonably  500.  In  a  kind  of  c o n s i s t e n c y would  The Freeway shear  moduli  above  mentioned  assuming resulting  It for  the  been  and  plotted sand.  to  discussed  a  note  Farm  modulus  value  above,  with  as  as  the  would  be  depth.  consolidated  ranging  the  exponent  depth  metres  In  modulus  Then,  normally  values  in Figure two  between  clayey  from 33  silt  400  silt,  the  and  different  function that  with  the  depth,  that  and this  Fort  compared  modulus  depth  (n  modulus  i s the  has  been  equals  400  range  The used  1).  number  same  with  numbers.  v a r y i n g between  this  Langley  The  Kg  is  and  500.  observed  data. data  from  F i g u r e 34.  with  an  shear  with  13  depth  silt  exponential relationship  with  resulting  increase  surface  using  linear  to  in  The  of  numbers.  expected.  plotted  consistent  shear  below  modulus  indicates  McDonalds  The  the  is a  is interesting  silt  with  be  empirical  plot  reasonable  been  calculated  Gmax  plot  c o n s o l i d a t e d homogeneous  shear  have  i n the  increases.  f o r the  consistent  dynamic Site  and  modulus  increases  sand  numbers  normally  different  plot  An of  depth  from  between  750  numbers  of  the  Annacis  exponent shear  a  this  0.5  modulus  value  and  of  North  1000  of at  magnitude  Pier  was  with  less  than  30  metres  would  be  Site  has  assumed  for  depth 500  shows  near  the  depth.  As  expected.  FIG.  32.  C O M P A R I S O N EMPIRICAL  B E T W E E N  DYNAMIC  MCDONALDS  FARM  CPT  SHEAR  SEISMIC  AND  MODULUS,  95  FIG. 3 3 . C O M P A R I S O N EMPIRICAL FORT  BETWEEN  DYNAMIC  LANGLEY  CPT  SHEAR  SEISMIC  AND  MODULUS,  96  FIG. 3 4 .  COMPARISON EMPIRICAL ANNACIS  BETWEEN  DYNAMIC NORTH  CPT  SHEAR  PIER  SEISMIC  AND  MODULUS,  97  5.5  Summary  The  data  confidence aquired, seismic  comparisons  to the accuracy and  the  cone.  determinations  i n sand from  However  somewhat h i g h e r part,  shear  of  t o the  than  test  Crosshole  velocity  values determined  with  cone  soils  bearing  tested,  u s i n g t h e CPT  predictions  tests  the  data  show  of  mouli  similar  SBPMT v a l u e s a r e  t h e CPT s e i s m i c v a l u e s . T h i s may be due, i n stress  unload  level  at  which  the  self-boring  - r e l o a d modulus was c a r r i e d o u t .  and CPT downhole s h e a r  appear  reasonable,  though comparison  sites  using  same  the  wave  boring pressuremeter  the  higher  pressuremeter  shear  l e n d some measure o f  a r e good. C o m p a r i s o n s w i t h dynamic  self  in  chapter  the  moduli  Comparisons  dynamic modulus  trends.  in this  signal  wave v e l o c i t y of  data  detection  from  equipment  comparisons additional is  still  required. Comparisons indicate and  that  with the  empirical  soil  modulus  relationships  s e i s m i c cone c a n p r o v i d e a r e a s o n a b l y  a c c u r a t e method o f c h e c k i n g  dynamic  shear  parameters.  both  rapid  f u n d e m e n t a l and t h e o r e t i c a l  98  6.0 CONCLUSIONS  The thesis. can  CPT downhole s e i s m i c t e s t The r e s u l t s  provide  sites  h a s been  of the data p r e s e n t e d  a rapid  chapter  summarizes  indicate  and a c c u r a t e a s s e s s m e n t  where c o n e p e n e t r a t i o n t e s t i n g some  of  the  c a n be most  discussed  in  that  this  the test  of shear moduli a t carried  out.  important  This  conclusions  discussed  i n the previous text,  presents suggestions f o r further  research  using  and  considerations  this  device  for  use  engineering  applications.  6.1  of Research  Summary  The  fundamental  develop  the  properties  it  objective  capability  the  suitable  shear moduli  stratigraphic  possible  measure  t o attempt  (ie. travel  over  In o r d e r t o  fully  of the cone,  an  p r o p e r t i e s of i n d i v i d u a l  instrument t o measure  increments.  encountered  during  the  i n c r e a s e d as f i n e r  t i m e measurement o v e r  depth  to soil  to design  Greater v e l o c i t y  larger  was  dynamic  logging c a p a b i l i t i e s  measurement e r r o r  was s o u g h t .  some  practical  research project  directly  o v e r minimum d e p t h  identification  is  in  o p e r a t i n g and d a t a a n a l y s i s p r o c e d u r e s  velocity  increments)  equipment  cone p e n e t r o m e t e r .  One o f t h e d i f f i c u l t i e s that  of t h i s  to  was c o n s i d e r e d d e s i r a b l e  and  this  discusses  Findings  with the s t a t i c  complement  of  briefly  study  was  stratigraphic smaller  measurement  depth  accurracy  i n c r e m e n t s , however t h e dynamic  stratigraphic  f e a t u r e s become masked by  99  averaging. During interval  the course  i t  interval  repeatability  The most  1.  The  was  method  CPT  2.  The  pseudo  for  both  results  method.  obtained  to  trigger  the  pseudo  satisfactory.  downhole  survey  has  distinct  testing  this  work a r e  advantages  i n that  over  i t i s much q u i c k e r  o n l y one t e s t h o l e .  survey  downhole  has  distinct  testing. and  depth  possible  determination  is  geophone  advantages  It i s faster  does not r e q u i r e a c a s e d  and  travel survey  Since  using  c o n c l u s i o n s t o come from  conventional  of  true  t h e r e was no g r e a t a d v a n t a g e  geophone)  crosshole  and  types  important  downhole  survey,  both  s t u d i e d . Because s i m i l a r  (one geophone) were  r u n and r e q u i r e s  CPT  that  (two  good,  conventional to  study  e r r o r s were n o t e d  was d e t e r m i n e d  using a true  interval  this  t y p e measurements were  t i m e measurement method,  of  grouted  over  to carry out,  borehole,  accurate  at a l l times during the  orientation  is  consistently  maintained.  3.  The  main  signal  s o u r c e s o f measurement  repeatability  uncertainty uncertain signal  about  travel  u n c e r t a n t y a r e due t o p o o r  between t h e s o u r c e a n d travel  path  source as c l o s e  path  length.  detector,  The  problem  and of  l e n g t h c a n be overcome by p l a c i n g t h e as p o s s i b l e  t o the t e s t h o l e .  Source  100  repeatability automatic  problems  r a t h e r than  repeatability mechanical of  rod  manual  signal  rods  the test  signal  high  interpretation  signals.  By  sized  of  t h e dynamic  correlations  can  this  friction  a n d t h e r o d s and  noise of  wave  measurement,  are minimized.  can s e r i o u s l y  low  amplitude  signal  a f f e c t the  shear  filtering  much  phase s h i f t s .  Any s u c h  wave sharper  used  in  s h i f t s are  and would c a n c e l when i n t e r v a l  techniques  availability  assessing  minimal  constant  free  t r a n s m i s s i o n . By d e c o u p l i n g t h e  using selective  caused  measurement  density  device  t r a c e s c a n be o b t a i n e d . The 1000 Hz f i l t e r s  reasonably  The  suitably  vibration  frequency  accurate  study  an  Detector  not a problem with  v e h i c l e d u r i n g shear  problems with mechanical  this  is  c o u p l i n g between t h e s o i l rod  using  impulse.  state pickup  s y s t e m . The u s e o f a  down  signal  energy  by  characteristics.  transmission  prevents  Background  overcome  c o u l d be overcome by r e p l a c i n g t h e  resonance  prevents  from  be  geophone w i t h a s o l i d  measurement reducer  a  problems  strong self  Down  could  velocity  a r e employed.  cone soil  be  determinations.  used  bearing data  greatly  assists in  p r o p e r t i e s . Cone b e a r i n g d e n s i t y to  complement  physical  bulk  101  7.  The  CPT  downhole s e i s m i c  between  3  and  individual  8.  signal  could  be  shear  other  6.2  in-situ  Further  at  still  compare  test  the  progress  present  of d e v e l o p m e n t  stage  equipment hole  testing  seismic  development  from  with  40  metres.  that  signals  the  CPT  downhole  p r e d i c t i o n s made u s i n g  values  calculated  of  such  of  the  offshore a  alternate  the  using  The  cone  became a p p a r e n t .  At i t s  wave s o u r c e  pursued, provided  the  suitable  and  analog  (either  signal  the  digital  primarily use  of  this  definitely  signal  source,  can  is be  cone  of  or  an  research.  use  of  of an  or v e r t i c a l )  ratio  an  require  development  torsional  filters  of  development  extension  would  to noise  is  increasing  makes  several  seismic  s e i s m i c cone  logical  a capability  an  investigation,  utilizing  tool.  cone  this  i n c r o s s h o l e c o n f i g u r a t i o n . The  shear  from  depth.  capabilities  investigation  Development  to  conceivable  and  of  topics  measurement  offshore  well  signals  relationships.  research  penetration  is  greater  methods,  penetrometer  onshore  it  effectively  Research  During additional  D e t e c t i o n of  modulus d e t e r m i n a t i o n s  survey  empirical  metres depth.  enhancement  detected  seismic  s y s t e m works most  hammer b l o w s have been d e t e c t e d  With  Dynamic  30  survey  might  the the inbe  high  enough  or  used  to s o r t  the  102  shear  wave from  other  S e v e r a l onshore could  1.  be p u r s u e d  vibrations. research topics  of  a  new  shear  control  o f t h e s h e a r wave  source  does  not  control  allow  limitations  automatic source  of  the  the  s o u r c e would  applications. possibility advancing  present  seismic  allow hammer  amplitude  mechanical  amplitude  reduce  The wave  source  and e x t e n d cone.  In  difficulties  Standard  t o be would  the present addition  associated  an with  travel  the  in to  crosshole  testing  investigate  seismic  cone  this  beside  T e s t h o l e (See O h t a ,  an  Goto,  1978)  shear  modulus  significant  to develop  way  Penetration  determinations  statistically  obtaining  quickest  would be t o r u n  Investigate in-situ downhole  penetrometer  The  Kagami & S h i o n o ,  4. A t t e m p t  and  repeatability.  2. Use o f t h e s e i s m i c c o n e  3.  shear  larger  signal of  wave s o u r c e w h i c h w i l l  amplitude.  maintained with depth. A  depth  investigation  immediately.  Development  allow  require  finer time  anisotropy  with  by  crosshole  comparing data  in  quantities.  stratigraphic measurements  logging c a p a b i l i t y over  smaller  by  depth  103  increments  ( i e . 0.5  5. C a r r y o u t p a r a m e t r i c to  further  confining under  metres).  chamber t e s t i n g  assess  6.  pressure,  soil  controlled  conditions. sand  investigate in-situ  particularly differences consolidation  in in  silts P  the  cone  It  modulus  recognized  effects,  there  f o r a l l sands.  compressional clays  velocity  characteristics.  Gillespie,  to can  wave measurements, see be  if  subtle  correlated  (See Hamdi and T a y l o r  pore p r e s s u r e  (See  be  cone  bearing,  shear  should  composition  and  wave  1981). The e x i s t i n g in  d e n s i t y and dynamic  be no u n i q u e r e l a t i o n s h i p  Further  seismic  t h e r e l a t i o n s h i p between c o n e  however t h a t b e c a u s e o f will  using the  measurement 1981)  to  Smith,  capabilities  could  be  used f o r  correlation.  7. I n v e s t i g a t e whether coefficients  may  the determination be  possible  of i n - s i t u  using  the  soil  seismic  damping cone  penetrometer.  6.3 C o n s i d e r a t i o n s  The  for Practical Application  equipment and procedures  d i s c u s s e d through  most o f t h i s  104  thesis  have  seismic  cone  For per  been  directed  toward  over  1 metre d e p t h  o b j e c t i v e . To detection  achieve  velocity  survey  and  special  statistical  data  practical larger  end,  was  analysis  signal  d e t e c t i o n equipment may f o r such  horizontally  Practical  depth  work would  a d v a n t a g e s of  shear  moduli  t h i s method o v e r  using  require  of  a  interval  data  other  was  interval  resolution  acceptable. A  cone  installation  of  transducer.  geophone i n s t r u m e n t e d  soft  10  purposes,  time  lower  the  a reasonably at  pseudo  arrival  considered  oriented velocity  application  of  be  of  signal  a p p l i c a t i o n s pseudo  increments  cone p e n e t r o m e t e r c o u l d p r o v i d e assessment  sensitive  f o r comparison  of  engineering  over  penetrometer  extremely  obtained  surveys  one  the  considered a desirable  r e q u i r e d . B o t h t r u e and  type  For  measurement a c c u r a c y  i n t e r v a l s was  this  e q u i p m e n t was  utilized.  of  penetrometer.  research purposes a v e l o c i t y  cent  only  research application  rapid  soil  and  sites.  downhole s e i s m i c  static accurate  The  major  techniques  are:  1. B e t t e r s o i l d e p t h of  2.  to r e c e i v e r coupling allowing  Controlled  Extremely  effective  operation.  receiver  orientation  for  detect ion.  3.  greater  accurate  depth  determination.  improved  shear  wave  1 05  Rapid  installation  Improved c o s t where  cone  b e c a u s e of available  and  r e m o v a l of  effectiveness penetration the  wealth  from one  of  the  geotechnical  testing of  testhole.  probe.  is  being  additional  investigations carried  out,  geotechnical  data  106  REFERENCES A l l e n , N.F., R i c h a r t , F . E . , a n d Woods, R.D., "Fluid Wave Propagation i n N e a r l y S a t u r a t e d Sand," J o u r n a l o f t h e 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, n o . GT3,' M a r c h , 1980, pp. 235-254.  Anderson, D.G., and Stokoe, K.H., I I , (1978), "Shear Modulus: A Time Dependent Soil P r o p e r t y , " Dynamic G e o t e c h n i c a l T e s t i n g . 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