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Evaluating shear wave velocity and pore pressure data from the seismic cone penetration test Gillespie, Donald G. (Donald Gardner) 1990

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EVALUATING SHEAR WAVE VELOCITY AND PORE PRESSURE DATA FROM THE SEISMIC CONE PENETRATION TEST By DONALD GARDNER GILLESPIE M.A.Sc., The University of B r i t i s h Columbia, 1981  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Ph.D.  in THE FACULTY OF GRADUATE STUDIES (Department of C i v i l Engineering)  We accept t h i s thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA JULY 1990 © Donald Gardner G i l l e s p i e  In  presenting this  degree at the  thesis  in  University of  partial  fulfilment  of  of  department  this thesis for or  by  his  or  requirements  British Columbia, I agree that the  freely available for reference and study. I further copying  the  representatives.  an advanced  Library shall make  it  agree that permission for extensive  scholarly purposes may be her  for  It  is  granted  by the  understood  that  head of copying  my or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department  of C i v i l  Engineering  The University of British Columbia Vancouver, Canada  Date August 30,  DE-6  (2/88)  1990  ABSTRACT Recent developments i n cone penetration t e s t i n g have resulted i n the addition of both pore pressure measurements and seismometers. The seismometers allow shear wave v e l o c i t y t e s t i n g t o be performed a t designated i n t e r v a l s . Both of these additions were researched t o improve t h e i r application and interpretation. The s i g n i f i c a n t factors e f f e c t i n g the pore pressure generated during cone penetration t e s t s are discussed. The importance of various factors i s e s p e c i a l l y dependent upon permeability, strength, and s t i f f n e s s . For a l l sands tested, pore pressures lower than s t a t i c were recorded behind the t i p and higher than s t a t i c were recorded on the face of the cone. I t i s believed that the large compressive stresses on the cone face r e s u l t i n p o s i t i v e pore pressures. As the cone t i p passes a s o i l element unloading and continued shearing generate pore pressures lower than s t a t i c i n a l l sands. The sign of t h i s pore pressure (higher or lower than s t a t i c ) was therefore considered p r i m a r i l y a function of the t e s t equipment. Pore pressure response and the rate of d i s s i p a t i o n of excess pore pressures were found useful i n distinguishing f i n e granular s o i l s and explaining s o i l stratigraphy. In cohesive s o i l s the d e t a i l s of pore pressure measurement were found t o be important only i n s t i f f s o i l s . Pore pressures at a l l measurement locations were found t o increase with s o i l strength i n s o f t t o firm clays but may be negative of s t a t i c i n very s t i f f clays. Pore pressures behind the cone t i p were often negative of s t a t i c i n s t i f f clays. Measurement techniques were refined t o improve the accuracy of downhole shear wave v e l o c i t y measurements. Comparisons of downhole and crosshole measurements were made a t three well documented s i t e s v a l i d a t i n g the technique. At several s i t e s i t was found useful t o consider the Gjnax values determined from shear wave v e l o c i t y and density t o d i s t i n g u i s h s o i l type. Gjnax resistance r a t i o s were shown t o vary systematically with cone resistance values i n sands. A wide range i n G^ax cone resistance was observed i n c l a y s . The dependence of both cone penetration resistance and G ^ x t o increased stress l e v e l or overburden stress i s discussed. c  t  o  o  n  e  iii TABLE OF CONTENTS Page ABSTRACT  i i  TABLE OF CONTENTS  i i i  LIST OF TABLES  viii  LIST OF FIGURES  ix  ACKNOWLEDGEMENTS CHAPTER 1.  xiii  lOTROrjUCTION  1  1.1  Purpose and Scope  1  1.2  In-situ Testing  2  1.3  CPT Testing:  3  1.4  CPTU Testing:  1.5  CPTU Interpretation and Data Reduction  5  1.5.1  Strength Determination:  Sands  5  1.5.2  Strength Determination:  Clays  6  1.5.3  Stiffness Determinations:  1.5.4  Consolidation Characteristics:  1.5.5  I n i t i a l State or Relative Density of Sands  Equipment Equipment  4  Sands Clays  7 8 9  1.6  Shear Modulus as a Geotechnical Parameter  11  1.7  Types of Seismic Waves  13  1.8  Conventional Methods of Determining Shear Wave Velocity  15  1.9  Seismic Cone Development  17  1.10 Thesis Organization CHAPTER 2.  DATA COLLECTION AND REDUCTION PRCCEDURES  17 19  2.1  j^troduction  19  2.2  The Seismic Cone Penetrometer  19  iv 2.3  2.4  2.5  2.6  CPTU procedures  22  2.3.1  Pore Pressure Measurement System Compliance  22  2.3.2  Pore Pressure Dissipations  27  Seismic Cone Testing Procedure  27  2.4.1  Sources  29  2.4.2  Velocity Measurements: Data Reduction  29  2.4.3  Shear Modulus  32  Possible Error Sources i n CPTU Testing  32  2.5.1  Zero load Stability  33  2.5.2  Resolution  35  2.5.3  Load Transfer  36  2.5.4  External Dimension Tolerances  36  2.5.5  Pore Pressure Effect  37  2.5.6  Repeatability  38  Possible error Sources i n Velocity Measurements 2.6.1  Errors Associated With The Use of Arrivals/Crossovers and Cross Correlations  2.7  Conclusions  CHAPTER 3.  40  40 44  SITE DESCRIPTIONS  46  3.1  Introduction  46  3.2  Ons0y: Site Description  46  3.3  Haga: Site Description  50  3.4  Holmen: Site Description  50  3.5  Drarnmen Clay Site:  52  3.6  No. 6 Road, Richmond: Site Description  57  3.7  McDonald Farm: Site Description  57  3.8  Pile Load Test Site:  60  Site Description  Site Description  V  3.9  Richards Island Site: Site Description  64  3.10 Schoolhouse Site: Site Description  65  3.11 Swiinming Point Site: Site Description  67  3.12 Langley Sites: Site Descriptions  70  3.13 Brenda Mines:  72  Site Description  3.14 Heber Road 2, 4, 6:  Site Descriptions  i  72  3.15 Wildlife Site: Site Description  81  3.16 New Westminster Site: Site Description  81  3.17 Summary  85  CHAPTER 4.  FACTORS AFFECTING PORE PRESSURE MEASUREMENTS  86  4.1  Introduction  86  4.2  Effect of Measurement location  86  4.3  Effect of Cone Design & Mechanical Details  91  4.4  Element Saturation  97  4.5  Effect of Cone Design/Procedure on Dissipation Tests  101  4.6  Conclusions  105  CHAPTER 5.  INTERPRETATION OF PIEZOMETER CONE DATA  106  5.1  introduction  106  5.2  Cone Resistance Corrections  106  5.3  Soil Classification From Dynamic Pore Pressures  109  5.4  Soil Classification From Pore Pressure Dissipation  114  5.5  Effect of Soil Sensitivity on Pore Pressure Measurements  115  5.6  Interpretation of CPTU Data For Stress History  117  5.7  Interpretation of CPTU Data For Undrained Shear Strength  123  5.8  CPTU data and Liquefaction Resistance  130  5.9  Conclusions  137  vi CHAPTER 6. FACTORS AFFECTING SHEAR WAVE VELOCITY DATA  140  6.1 Source Characteristics  140  6.1.1 Hammer Beam Shear Source  140  6.1.2 Explosive Sources  141  6.2 Receivers  ;  147  6.3  Identification of Shear Waves from Explosive Sources  149  6.4  Soil Layering and Resolution  152  6.5 DcwThole-Crcsshole Comparisons  153  6.6 Conclusions  158  CHAPTER 7.  APPLICATION OF  DATA  159  7.1 Introduction  ,....  7.2 Shear Modulus as an Engineering Parameter 7.3 Correlation of Velocity to Liquefaction Potential 7.4  Integration of  data into CPTU Data  159 159 160 166  7.4.1 Introduction  166  7.4.2 Application of Data i n the Interpretation of Clay Strength from Cone Resistance  167  7.4.3 Integration of Velocity Data into Soil Classification  170  7.5 Correlation Between CPTU (qp) and G^QX Data 7.5.1 Introduction  175  7.5.2 Normalization of qp, and 7.5.3  Correlation Between  175  data and qp i n Sand  176 182  7.6 Application of P Wave Velocity Data  184  7.7 Conclusions  185  CHAPTER 8. SUMMARY AND CONCLUSIONS 8.1 Summary of Pore Pressure Data  188 188  vii 8.2  Summary of Velocity Data  189  8.3  Recxammendations for Riture Research  191  PJ5FERENCES  194  viii LIST OF TABLES Table Number T i t l e  Page  2.1  Possible Sources of Error i n CPTU Testing  34  5.1 5.2  Normalized Cone Resistance and Pore Pressure Response i n Sand ... 133 Pore Pressure Response at Sand Sites 136  ix LIST OF FIGURES Figure Number T i t l e 1.1  Gjnax Attenuation with Strain  Page 12  from Seed and Idriss (1970) 1.2  Characteristics of Shear Waves  14  1.3  Conventional Downhole and Crosshole Velocity Testing  16  from Stokoe and Hoar (1978) 2.1  Dual element Piezometer Cone  21  2.2  Cone Saturation Procedure Using A Syringe  23  2.3  Cone Saturation System Using A Vacuum  25  2.4  Comparison of Pore Pressure Response at Langley  26  2.5  Source and Receiver Configuration  28  2.6  Buffalo Gun Source  30  2.7  Schematic of the Interval Technique  31  2.8  Variation i n Signals From Repeated Soundings: Holmen Sand  39  from Lunne, Eidsmoen, Gillespie, and Howland (1986) 2.9  Repeatability of Shear Waves  41  3.1  CPTU Profile at Onsoy clay site  47  3.2  Soil Description at Ons0y Clay Site from Eidsmoen, Gillespie, Lunne and Campanella (1985) Velocity Profiles at Onsoy Clay Site from Eidsmoen, Gillespie, Lunne, and Campanella (1985) CPTU Profile at Haga Clay Site from Lunne, Eidsmoen, Gillespie, and Howland (1985) CPTU Profiles at Holmen Sand Site from Eidsmoen, Gillespie, Lunne, and Campanella (1985)  48  3.3 3.4 3.5  49 51 53  3.6  Velocity Profiles at Holmen Sand Site from Eidsmoen, Gillespie, Lunne, and Campanella (1985)  54  3.7  Soil Profile at Drammen Clay Site from Eidsmoen, Gillespie, Lunne, and Campanella (1985)  55  X  3.8 CPIU Plot at Drammen Clay Site from Eidsmoen, Gillespie, Lunne, and Campanella (1985)  56  3.9 Velocity Profiles at Drammen Clay Site  58  from Eidsmoen, Gillespie, Lunne, and Campanella (1985) 3.10 CPTU Profiles at No. 6 Road Site  59  3.11 CPTU Profile at McDonald Farm  61  3.12 CPTU Profile at Pile Load Test Site  62  3.13 Velocity Profile at Pile Load Test Site  63  3.14 CPTU Profiles at Richards Island Site  66  3.15 CPTU Profiles at Schoolhoiase Site  68  3.16 CPTU Profiles at Swimming Point Site  69  3.17 CPTU and Soil Profile at Langley Research Site  71  3.18 CPTU Profile at Brenda Mines Site  73  from Campanella, Robertson, Gillespie, and KLohn (1984) 3.19 CPTU Profiles at Heber Road 2 Site  75  3.20 Velocity Profile at Heber Road 2 Site  76  3.21 CPTU Profiles at Heber Road 4 Site  77  3.22 Velocity Profile at Heber Road 4 Site  78  3.23 CPTU Profiles at Heber Road 6 Site  79  3.24 Velocity Profile at Heber Road 6 Site 3.25 CPTU Profiles at Wildlife Site  80 82  from Campanella, Robertson, and Gillespie (1986) 3.26 Velocity Profile at Wildlife Site 3.27 CPTU Profile at New Westminster Site 4.1 Pore Pressure Distribution During CPTU from Robertson, Campanella, Gillespie, and Greig (1986) 4.2 Penetration Pore Pressures at Imperial Valley Site from Campanella, Robertson, and Gillespie (1986) 4.3 Detailed Penetration Pore Pressures at McDonald Farm  83 84 87 90 92  xi 4.4  Effects of Element Osnpressibility, McDonald Farm  95  4.5  Detailed Penetration Pore Pressures at Richards Island  96  4.6  Detailed Penetration Pore Pressures at Iangley Site  98  4.7  Pore Pressure Dissipations, Examples From Two Sites from Campanella, Robertson, and Gillespie (1986)  100  4.8  Normalized Excess Pore Pressure Distribution from Gillespie, Robertson, and Campanella (1988)  102  4.9  Pore Pressure Dissipations at McDonald Farm Predicted versus Measured Dissipation Curves from Gillespie, Robertson, and Campanella (1988)  104  5.1  Correction of Cone Resistance Data, Onsoy Site  108  5.2  Undrained, Partially Drained, and Drained Response at the McDonald Farm Site  110  5.3  Soil Behaviour Type Classification from Campanella, Robertson, and Gillespie (1986)  112  5.4  Pore Pressure Response at Wildlife Site  113  from Campanella, Robertson, and Gillespie (1986) 5.5  Pore Pressure Parameters Bg vs OCR  116  5.6  Normalized Pore Pressure Difference  119  5.7  Pore Pressure Ratios vs OCR  120  5.8  Normalized Cone Resistance vs OCR  121  5.9  Cone Factor % E V S Bq  124  5.10 Cone Factor N  A U  5.11 Cone Factor 5.12 Cone Factor N  1  vs Eq± vs Bq  1#  126 Bg2  A U  127 129  from Campanella, Robertson, and Gillespie (1986) 5.13 Pre and Post Compaction Profiles at the No. 6 Road Site  132  6.1  Damped Geophone Response Profile to Hammer Shear Source  142  6.2  Accelerameter Response Profile to Buffalo Gun Source 143 from Campanella, Robertson, Gillespie, Laing and Kurfurst (1986) Geophone Response at Schoolhouse Site 145  6.3  xii 6.4 Damped Gecphone Response Profile to Buffalo Gun Source  146  6.5 Shear Wave Arrivals from Three Sources  151  6.6 Comparison of Downhole and Crosshole Velocity, Holmen from Robertson, Campanella, Gillespie and Rice (1986)  154  6.7 Comparison of Downhole and Crosshole Velocity, Drammen from Eidsmoen, Gillespie, Lunne and Campanella (1986)  155  6.8 Comparison of Downhole and Crosshole Velocity, Wildlife Site .... 156 from Robertson, Campanella, Gillespie and Rice (1986) 7.1  Shear Wave Velocity as an Index of Liquefaction Potential  162  7.2 Cone Factor N R T V S Gjnaj/qp Ratio  168  7.3  171  Stiffness - Cone Resistance Ratios i n Various Soil Types  7.4 Integration of and Pore Pressure Measurements into Cone Interpretation 7.5 Influence of stress on G^^x * P/T' ^- Y anc  7.6  Influence of stress on  7.7 Variation of G / il! C  max  c  a  and qj, Sand  Ratios with Normalized Cone Resistance  173 1  7  8  179 183  xiii  ACKNCWIEDGFlffiNTS  The writer wishes to acknowledge the encouraging support and suggestions from Dr. R.G. Campanella during the course of this study. The cooperation and suggestions from Dr. P. K. Robertson also proved invaluable.  None of the f i e l d work would have been possible without  the technical support of Messrs Art Brooks, Glen J o l l y and Dick Postgate. The  assistance of Jim  Greig who  wrote data  collection  and  processing programs i s greatfully acknowleged as was cooperative work with the Norwegian Geotechnical Institute personnel including  Tom  Lunne, and Terje Eidsmoen. Data collection was conducted mainly with Mr. John Howie who also had many technical suggestions. Financial support was provided by the British Columbia Science Council through the GREAT grant program. Special thanks  go  to my  support throughout these years.  family for their encouragement and  1 CHAPTER 1 1.1  INTRODUCTION  Purpose and Scope The  cone  penetration  test  is  investigations throughout the world.  an  important  component  of  site  S t a r t i n g as a very simple logging  t o o l the t e s t has become increasingly sophisticated both from the point of view of the amount and q u a l i t y of data c o l l e c t e d and the subsequent interpretation.  Instrumentation  advances  in  resulted i n the a b i l i t y to add multiple sensors. penetration resistance  testing, and  CPT,  l o c a l sleeve  included  cone  friction,  the  last  decade  have  E a r l y e l e c t r o n i c cone  resistance,  f , only. s  q , c  or  cone  Subsequent advances  added simultaneous measurement of pore pressure, u, and hence the term CPTU.  Pore pressure measurements were made at d i f f e r e n t locations  different  researchers  and  p r a c t i t i o n e r s and  became the most common logging t o o l .  by  piezometer cone t e s t i n g  Subsequently, a d d i t i o n a l sensors  including temperature, t , and i n c l i n a t i o n , i , were added to a s s i s t with deployment and to improve data quality. to the CPTU was  One  recent important addition  the addition of shear wave v e l o c i t y measurements made  f e a s i b l e by incorporating a suitable v e l o c i t y transducer and developing appropriate  procedures to c o l l e c t and reduce data.  Using pore pressure and shear wave v e l o c i t y data gathered at a wide v a r i e t y of s i t e s t h i s thesis addresses the following issues: 1)  What are the factors that a f f e c t each of the two measurements?  2)  How  can the data be interpreted to obtain required s o i l parameters?  3)  How  can data c o l l e c t e d from d i f f e r e n t sensors be  to a s s i s t i n the o v e r a l l interpretation?  integrated  2 1.2  I n - s i t u Testing The  investigation of s o i l types and properties can be performed i n  either  the  laboratory  or  the  field  (in-situ).  The  most  important  advantage of the laboratory methods r e l a t e s to the control of stresses and boundary conditions. the  field.  problem,  their  Often s i m p l i f i c a t i o n s are required but the most pressing  especially  maintaining  of  sands,  i s the  the  A  to  Considering  quantity  of  obtaining  further problem  i n comparison  i n the f i e l d .  materials  difficulty  and  state or even returning them to  stress conditions.  sample tested  material loaded geologic  in  samples i n an undisturbed  original  quantity  The laboratory observations are extended into  of  the  i s the  small  enormous amount of  the natural v a r i a b i l i t y of  material  tested  in  a  normal  laboratory investigation i s small. By  performing  in-situ  tests  the  complications  of  reproducing  unknown f i e l d stress conditions on disturbed samples are eliminated a  much  greater  volume  of  continuous c y l i n d e r of s o i l This  sample  is  tested.  In  CPTU  and  testing  a  i s influenced and determines the p r o f i l e .  feature r e s u l t s i n the most s i g n i f i c a n t a p p l i c a t i o n of the cone  t e s t — a s a logging t o o l . information  The trade o f f f o r obtaining such a volume of  i s that the CPTU invokes l a r g e l y unknown and  complicated  stresses on the s o i l and i t s interpretation becomes somewhat empirical.  Interpretation methods presently available, which w i l l be outlined i n t h i s chapter, to  conventional  briefly  are l a r g e l y derived from e i t h e r c o r r e l a t i o n s  laboratory  testing, f i e l d  t e s t s on large laboratory chamber t e s t s .  behaviour or  experimental  Some i n t e r p r e t a t i o n methods,  3 notably  for  theoretical theory.  the  strength  basis  One  in  of  and  consolidation  e i t h e r bearing  the  complications  enormous stresses imposed at the foundation  loads these  l o c a l i z e d crushing.  properties,  capacity of  CPTU  or  cavity  have  a  expansion  interpretation i s  the  cone t i p ; i n comparison to normal  stresses are i n a range that may  even impose  The e f f e c t s of these various problems i s further  discussed i n t h i s thesis.  1.3  CPT Testing: Equipment The  as  a  cone penetration t e s t continues tool  for  publications include: 1981;  of  site  to become more commonly used  investigation and  greatest  geotechnical  s i g n i f i c a n c e describing  the  2nd  European  Symposium  on  Penetration  equipment  design  Penetration Testing prepared  Test  was  Procedure,  F l o r i d a i n 1988 the  which  described  (deBeer, 1988).  ICSMFE 1989.  at  the  Experience,  Testing,  and ASCE I n - s i t u 86, 1986.  Technical Committee on  at  Past  ASCE Symposium on Cone Penetration Testing and  Robertson and Campanella, 1984;  due  design.  1982;  The ISSMFE  an International  ISOPT-1 conference  in  The f i n a l version of t h i s document was  The  ASTM document,  D3441, provides  some  l i m i t e d guidelines f o r CPT t e s t i n g . The  first  cone  tests  were  performed  using  mechanical  cones,  measuring e i t h e r cone resistance alone or cone resistance and mantle friction.  Loads were measured at the surface and though the t e s t  slower to perform the equipment was simple and robust. the  use  of  mechanical  Although t h i s  cones were described  report was  by  was  Guidelines f o r  Sehmertmann  (1978).  written with mechanical cones i n mind  the  4 i n t e r p r e t a t i o n methods proposed  f o r cone resistance and  pile  design  procedures remain v a l i d today. The  first  significant  channel cone, was for  much  of  description of  an  made by de Ruiter (1971).  the  future  cone  generally established as 60°  This cone set a  development.  Tip  apex  two  standard  angles  were  f r i c t i o n sleeves  immediately behind  the t i p were 'standardized' with an area of 150 cm  and a diameter the  same as the t i p at 35.7 Electronic recorded  and  e l e c t r o n i c cone, a  2  mm.  penetrometers  incorporated  built-in  separately the cone resistance and  load  cells  f r i c t i o n sleeve.  s t r a i n gauges were commonly used because of t h e i r accuracy, and ruggedness.  t h e s i s (Figure 2.1)  t h e i r own  advantages.  CPTU Testing:  by  cone used i n t h i s  2.  measurements has  significantly  t e s t i n g (the notation CPTU i s generally used to  piezometer cone t e s t i n g ) . (1975) and  The UBC  Equipment  introduction of pore pressure  changed CPT  simplicity  incorporates many of these i n i t i a l developments and  i s discussed i n greater d e t a i l i n chapter  The  Bonded  Various configurations were used i n d i f f e r e n t designs,  each of them having  1.4  that  Torstensson  The  (1975).  Campanella, Robertson and  first  two  signify  publications were by Wissa  Design considerations were discussed  Gillespie  (1981), Campanella,  Gillespie  and Robertson (1982) and Smits (1982).  Design considerations included  filter  publications  type  considered  and  location;  various  and  conferences  the s e n s i t i v i t y of r e s u l t s to the element l o c a t i o n .  considerations are discussed i n d e t a i l i n chapter  4.  These  5 1.5  CPTU Interpretation and Data Reduction The primary r o l e of the CPTU as a logging t o o l i s often overlooked  i n the continuous attempt t o enhance the i n t e r p r e t a t i o n procedure f o r the determination of s p e c i f i c mechanical parameters.  Many examples of  CPTU p r o f i l e s are shown i n chapter 3.  Various methods of i n t e r p r e t i n g  CPTU data w i l l  here and  be  discussed b r i e f l y  those areas  i n which  advancements have been made i n t h i s t h e s i s w i l l be pointed out.  1.5.1  Strength Determination:  The strength  CPT  has  become an  characteristics  Sands  important t o o l  i n sands  problems associated with sampling. suitable  for  interpreting  cone  that  f o r the i n t e r p r e t a t i o n of  are e s p e c i a l l y  to the  A l l methods presently a v a i l a b l e are resistance  through  normally consolidated, mainly quartz or feldspar sands. are empirically derived from chamber t e s t i n g , capacity theory.  prone  non-cemented, The methods  experience and bearing  Most commonly used methods are those of Lunne and  Christofferson (1983), Durgunoglu and M i t c h e l l (1975), Jamiolkowski, et al.  (1988) and Robertson and Campanella  derived (1986).  from  bearing capacity  theory  (1983). include  Additional methods  Mitchell  and  Keaveny  The M i t c h e l l and Keaveny bearing capacity method requires an  estimate of s o i l  s t i f f n e s s that reduces i t s usefulness i n p r a c t i c e .  One of the uncertainties i n a l l of the methods i s the importance of the ambient  stress l e v e l , i n p a r t i c u l a r the l a t e r a l stress.  Some methods  such as Houlsby and Wroth (1989) consider only the horizontal  stress  while others such as Been, et a l . (1986) consider both horizontal and v e r t i c a l stresses.  The commonly used methods, however, consider only  6 the  v e r t i c a l e f f e c t i v e stress and these methods are generally found t o  be  entirely  satisfactory.  The dependence  o f cone  resistance  on  increased stresses with depth i n the f i e l d was investigated i n t h i s t h e s i s i n chapter 7 and found t o be s l i g h t l y d i f f e r e n t than that found i n chamber t e s t s .  1.5.2  Strength Determination:  Four  Clays  approaches  have been used  strengths i n clays.  A l l approaches  factor  NJQI  t o derive  methods o f obtaining  are used t o determine the cone  f o r use i n : Su = (g.T - Ov) / K T N  where: q r p = t o t a l cone resistance T r a d i t i o n a l bearing capacity methods such as Janbu and Senneset (1974) and  cavity  expansion  supplemented  by t h e o r e t i c a l  method, Baligh been used  (1986).  as  Vesic  approaches,  vane, Greig  (1977)  solutions  especially  have  been  the s t r a i n  path  These three t h e o r e t i c a l methods have l a r g e l y  t o confirm the empirical  either f i e l d results,  such  correlations  that  t y p i c a l l y use  (1986), or embankment f a i l u r e or laboratory  Aas, e t a l . (1986).  Considerable d i f f e r e n c e  i n opinion  regarding the observed v a r i a t i o n i n N ^ J J with p l a s t i c i t y c h a r a c t e r i s t i c s has been reported i n the l i t e r a t u r e , Lunne, et a l . (1988) and Aas, e t a l . (1986).  Work i n t h i s  (1976), La Rochelle thesis  was directed  towards reducing the observed scatter i n N ^ r values and determining the cause of the reported v a r i a t i o n . this  thesis.  details  In the f i r s t  Two separate approaches were taken i n  case  i t was observed  and accuracy considerations  that  measurement  explained much of the observed  7 variation.  This work i s explained i n chapter 2.  In the second case,  to address the accuracy problems associated with low cone resistance i n soft  clays,  developed.  1.5.3  methods that used  the  pore  pressure measurements were  These methods are discussed i n chapters 4 and 5.  S t i f f n e s s Determinations:  Sands  A r e l i a b l e determination of large s t r a i n s t i f f n e s s properties of sands i n - s i t u i s of great p r a c t i c a l i n t e r e s t because of the problems of sample disturbance.  D i f f i c u l t i e s are encountered  i n any  theoretical  i n t e r p r e t a t i o n because modulus values are stress l e v e l and s t r a i n l e v e l dependent.  In addition the e f f e c t s of drainage and the d i r e c t i o n of  loading are l a r g e l y uncontrolled during penetration t e s t i n g . values  obtained  from  obtain or uncertain.  foundation  performance  are  also  Reference  difficult  to  As a r e s u l t of these d i f f i c u l t i e s the commonly  used methods of determining s t i f f n e s s values i n sands are derived from the r e s u l t s of chamber t e s t i n g . Robertson results  and of  Campanella Bellotti,  (1983) and  et  dependence of the r a t i o E  The commonly used methods are those of  s  al.  Bellotti,  (1989)  / q , where E T  et a l . (1989).  shows s  a  not found i n t h i s study i n the v a r i a t i o n of Gjn discussed  in  chapter  7.  The  large  i s a drained secant modulus  on the previous stress h i s t o r y or aging of a sand.  further  surprisingly  The  ax  This dependence was / q . T  determination  This t o p i c i s of  stiffness  parameters from CPT i s s t i l l uncertain although lower bound values  may  be r e l i a b l y obtained using the available methods that c o r r e l a t e cone resistance to s t i f f n e s s . thesis  show that the  The seismic cone methods discussed i n t h i s  small s t r a i n  stiffness  characteristics  can  be  8 reliably  obtained from the seismic cone.  The  state of the a r t and  improvements made are discussed l a t e r i n t h i s t h e s i s .  1.5.4  Consolidation C h a r a c t e r i s t i c s :  Clays  Other than the determination of equilibrium pore pressures perhaps the primary advantage used  t o determine  Theoretical excess  pore  of the piezometer cone t e s t  the  consolidation  solutions that e x i s t pressure that  i s that i t can be  characteristics  of  f o r the rate of decay  are most commonly used  clay  soils.  of generated  include those of  Torstensson (1977), which were confirmed by Randolph and Wroth (1979), and those of Baligh and Levadoux (1986).  The Torstensson solutions are  based on cavity expansion theory and consider c y l i n d r i c a l or spherical dissipation  of  excess  pore  pressure.  The  Baligh  and  Levadoux  solutions were developed by generating the excess pore pressure with the s t r a i n Boston  path method using parameters  Blue clay.  determined  specifically for  These methods are a l l s e n s i t i v e  to the  initial  excess pore pressure surrounding the cone, the d i s t r i b u t i o n of which i s not known. al.  (1987).  G i l l e s p i e (1981) examined these solutions as d i d Soares, et A curve matching solution by Gupta and Davidson (1986) was  not r a d i c a l l y d i f f e r e n t than the other methods.  A l l researchers have  found that the a v a i l a b l e solutions are reasonable f o r p r e d i c t i n g the c o e f f i c i e n t of consolidation.  The r e s t r i c t i o n s found i n t h i s t h e s i s ,  which are discussed i n a l a t e r chapter, r e l a t e t o commonly observed difficulties procedure. later  in  implementing  Certain  the  restrictions  solutions  and  on the solutions  difficulties  with  are discussed i n  chapters; the solutions are found t o be v a l i d  i n normally to  9 l i g h t l y overconsolidated Attempts  have  soils.  been  made  to  extend  consolidation  characteristics.  Given  consolidation  can  be  it  permeability  can  be  Determining a  drained  determined determined  the  that  is  modulus from the  the  often  using  determination  the  coefficient  reasoned drained  penetration  of  that  of the  stiffness.  part  of  the  CPT  p r o f i l e , which i s an undrained t e s t , i s not pursued here.  1.5.5  I n i t i a l state or Relative Density of Sands The  using  state of the  a r t of determining the  r e l a t i v e density,  sense  of  Been,  controversial.  et  and  al.  (1986),  incompressible,  regarded  as  difficult  (1983),  reasonable  Lunne  and  Christofferson  and  B a l d i , et a l . (1986). answers  in  (1983),  A l l of these  normally  consolidated,  non-cemented, imaged, medium grain sized sands.  r e s t r i c t i o n s are  chapter.  is  commonly used include those of Schmertmann (1978),  Campanella  provide  primarily  sands  or d i l a t i o n angle, or state parameter i n the  Jamiolkowski, et a l . (1985) and methods  state of  Most interpretation methods are based on chamber t e s t s .  Important refences Robertson  initial  the  sometimes d i f f i c u l t  effects  of  grain  to deal with and  size,  are  These  some of them,  investigated  in a  later  On the other hand the range of cone resistance experienced i n  sands i n the repeatable,  f i e l d v a r i e s by accurate  indexes  two of  orders of magnitude and density  can  usually  be  sensitive, obtained.  Furthermore the solutions of Baldi, et a l . (1986) can a l s o be used i n overconsolidated  sands.  10 1.5.6  Liquefaction Potential  The  state  of the a r t of determining l i q u e f a c t i o n  resistance of  sands from CPT cone resistance has been developed i n two separate ways depending  on the data available t o various researchers.  developed  by  commonly  used  Robertson  and  Campanella  liquefaction  (1985)  resistance  The method  recognized that  curves  for  the  the  standard  penetration t e s t were based on experience that could not be reproduced i n an analogous manner f o r the CPT. the  To use the experience developed i n  SPT curves Robertson and Campanella related the SPT N value t o cone  resistance and calculated new curves f o r the CPT.  The r e l a t i o n between  cone resistance and SPT N value was l a r g e l y based on side by side f i e l d t e s t s conducted i n the Fraser Delta, Robertson, et a l .  (1983) and Laing  (1981);  to  these  importance  tests  were  SPT  extensive  of the nonrepeatable ,nature of the SPT.  Robertson and Campanella the  sufficiently  experience  reduce  the  In t h i s manner  (1985) were able t o combine the advantage of  with  the  advantages  of  the  CPT  quality  and  continuity.  The Robertson and Campanella curves were v a l i d f o r clean  sands only.  Later publications by Shibata and Teparaksa  on  field  performance  observations  and  field  (1988), based  tests,  showed  the  s e n s i t i v i t y of the cone resistance l i q u e f a c t i o n p o t e n t i a l t o grain s i z e i n the f i n e s i l t y sand range.  In the clean sand range the Japanese and  Chinese experience published by Robertson towards solutions  and the  Campanella problem  without  the  of  Shibata and Teparaksa  curves.  Work i n t h i s  determining  a i d of  the  sampling.  confirmed the  thesis  validity  of  i s directed the  I t shows that  various  there are  s i t u a t i o n s where pore pressures or shear wave v e l o c i t y measurements can  11 be used t o r e f i n e the CPT bearing based  1.6  interpretation.  Shear Modulus as a Geotechnical Parameter The evaluation of seismic response and the response of foundations  t o dynamic loads such as machine loads r e l i e s on the determination of stiffness properties.  The  shear modulus r e l a t e s  shear  stresses and  shear s t r a i n s i n the manner of = Gy  T  where G = shear modulus T = applied shear s t r e s s 7 = r e s u l t i n g shear s t r a i n which appears  simple but as indicated i n Figure 1.1  h i g h l y s t r a i n l e v e l dependent. level  the  effects  determining  the  of  In addition t o i t s dependency on s t r a i n  stress  stiffness  the value of G i s  level  of  any  are  soil.  of  primary  Early  importance  in  work d e s c r i b i n g the  v a r i a t i o n of s t i f f n e s s i s discussed i n Hardin and Drenevich (1972).  An  indepth look at the e f f e c t s of stress l e v e l i s included i n chapter 7 of this thesis. A  study  by  Seed  and  Idriss  (1970) presented  quantitatively  the  v a r i a t i o n of shear modulus with increasing s t r a i n i n sands and c l a y s i n the manner shown i n Figure 1.1. r e a d i l y apparent  i n Figure 1.1;  The  reduction i n shear modulus i s  also very s i g n i f i c a n t i s the  plateau value a t shear s t r a i n s below approximately shear modulus a t low independent modulus.  of  strain  strains levels  10~  3  t o 10~ .  i s widely accepted as being and  i s termed G^g^,  apparent 4  The  reasonably  or dynamic  shear  o)  SANDS  F i g u r e 1.1 G A t t e n u a t i o n with from Seed and I d r i s s (1970) m a x  Strain  13 Elastic  theory can be used t o show that  c  a  n  b  determined  e  from G =  pVs  2  where Vs = v e l o c i t y of a shear wave p= mass density of the s o i l hence  shear  wave  velocity  determine shear modulus, In-situ advantages discrete  a  difficulties  of  is  bulk  samples.  especially  sampling In  process  addition  samples  can  of downhole p r o f i l e s  particular  thin  attractive compared  in-situ  disturbance  usefulness  layer  in-situ  be  used  to  of  the  G^^.  measurement of  measurements  and  to determine  because to  testing  testing  small  eliminates  reconsolidation. the properties of  i s discussed i n chapter  2 but  the  the The any  enormous  advantage of t e s t i n g an e n t i r e s o i l column, even with some averaging of properties across an i n t e r v a l , should never be overlooked.  1.7  Types of Seismic Waves Seismic wave can be  divided  into body waves that may  penetrate  deeply and surface waves that are generally considered t o t r a v e l near the surface.  Solids support two types of body waves:  compressional,  or P (primary), or longitudal, or i r r o t a t i o n a l waves; and shear, or S, waves.  Compressional waves have displacement p a r a l l e l t o the d i r e c t i o n  of propagation while shear waves have displacement perpendicular to the d i r e c t i o n of propagation. in  Figure  1.2a.  Note  A simple depiction of a shear wave i s shown that  the  direction  of  propogation  is  perpendicular t o the displacement d i r e c t i o n and that there i s no volume  14  wavefronts  ^displacement propagation  direction direction  SH waves a r e autonomous a t s o i l F i g u r e 1.2  C h a r a c t e r i s t i c s o f Shear waves  interfaces  15 change, j u s t deformation.  Shear wave deformation can be resolved into  separate components, one p a r a l l e l t o the surface (SH) vertical direction.  and one  i n the  Seismic exploration techniques commonly generate  e i t h e r P and SV waves or SH waves depending on the source used. fundamental difference between SV and SH waves i s the unique of SH waves at a boundary.  A  behaviour  SH waves are autonomous (Figure 1.2b); i f  an SH wave s t r i k e s a horizontal geologic boundary part of the energy i s r e f l e c t e d and part i s transmitted but both components remain SH waves. The d i r e c t i o n of propagation i s fixed by Snell's law.  1.8  Conventional Methods of Determining Shear Wave V e l o c i t y Two  These  methods are commonly used are  termed  conventional  to determine crosshole  shear wave v e l o c i t y .  and  downhole  methods.  Considerable l i t e r a t u r e e x i s t s that compares the two methods. references  include White  (1965) and  l a t e r geotechnical aspects were  considered by Stokoe and Woods (1972). methods.  Early  Figure 1.3  i l l u s t r a t e s the two  The s i n g l e most important d i s t i n c t i o n i s the complication and  expense of d r i l l i n g more than one hole to perform the crosshole t e s t . Downhole  testing  vertically  is  always  propagating  performed  with  a  with  SH  horizontal  waves,  which  particle  are  motion.  Conventional crosshole t e s t i n g considers h o r i z o n t a l l y propagating waves with a v e r t i c a l feasible  to  p a r t i c l e motion, SV waves, but  generate  horizontally  traveling  i t i s also shear  waves  horizonal plane, SH waves, with a t o r s i o n a l source. , The  entirely in  the  significance  of the difference i s discussed i n chapter 7, which looks at the e f f e c t s of the d i f f e r e n t stresses on shear wave v e l o c i t y .  Receiver Borehole  (0.6m) 2ft U-  Cost-ln-Ploce Concrete Block  -2ft (06m) -12 ft (3.7m) • 20ft (6.1m)  Embedded A n g l e Iron  o.-PLAN VIEW Verticol Velocity  ^-Verticol Impulse  o.- PLAN VIEW  Electricol Trigger.,  -Hommer Inclined Hommer Blo»  ^ i t r ^ i ) £i'  wsss Cosing  Ll (Not to Scole)  "*"•  -3-D Velocity Transducer Wedged in Ploce  b-CROSS-SECTIONAL VIEW  b.-CROSS-SECTIONAL VIEW  F i g u r e 1.3 Conventional Downhole and C r o s s h o l e V e l o c i t y T e s t i n g a f t e r Stokoe and Hoar (1978)  "  (06m)  Generation of Body Waves  (Not to Scale)  17 In the downhole t e s t there are two fundamental methods of obtaining velocity.  The v e l o c i t y may be determined by measuring the increment of  shear wave t r a v e l time by e i t h e r a pseudo i n t e r v a l t r a v e l method or a true  interval  travel  method.  c a r r i e d out by advancing and  measuring the  energy events.  The  pseudo i n t e r v a l  t r a v e l method i s  a single geophone to various depths i n a hole  t r a v e l time i n t e r v a l between depths from  The true i n t e r v a l technique requires the  separate  simultaneous  measurement from a single impulse event at separate geophones having a known separation.  The  relative  merits  of the  two  techniques  investigated i n depth by Rice (1984) and Laing (1985). for  some of the complications Rice  were  An explanation  (1984) discovered i s investigated  in this thesis.  1.9  Seismic Cone Development The CPT seismic cone used i n t h i s t h e s i s i s a downhole t o o l .  development Robertson  work  was  (1982).  verification although Rice  that  reported The  an  by  Rice  important  incremental  work  (1984) of  method could  and  Rice be  Early  Campanella (1984)  used  was  and the  in practice  (1984) found d i f f i c u l t i e s with the r e p e a t a b i l i t y of the  i n t e r v a l method.  Equipment considerations of these problems were made  by Laing (1985); a separate explanation i s considered i n chapter 2.  1.10  Thesis Organization Chapter 1 includes introductory remarks and  a b r i e f state of the  art of the interpretation of cone data that indicates the strengths and weaknesses of CPTU interpretation and where work was performed i n t h i s  18 thesis. Chapter 2 gives a b r i e f description  of the s p e c i a l equipment and  procedures used i n the t e s t i n g conducted i n t h i s t h e s i s .  Limitations  of the data gathered from the various sensors are addressed. Chapter 3 gives a b r i e f description of each o f the s i t e s from which data were c o l l e c t e d during t h i s t h e s i s . Chapter 4 describes the various measurement d e t a i l s that the  results  obtained  from  the  piezometer  determine  measurements  during  penetration and d i s s i p a t i o n s . Chapter Many s o i l  5 discusses the interpretation parameters  interpretation  of piezometer cone data.  are shown t o influence  f o r any one s o i l  parameter  the r e s u l t s making the difficult.  With  some  r e s t r i c t i o n s r e s u l t s can be interpreted f o r some s o i l parameters. Chapter  6 discusses some of the important d e t a i l s of shear wave  v e l o c i t y measurements and d i f f e r e n t r e s u l t s  obtained using d i f f e r e n t  sources and receivers. Chapter 7 outlines the interpretation of shear wave v e l o c i t y data for The  parameters application  i n addition of  shear  t o the small s t r a i n shear modulus, Gj^jj. wave  velocity  data  to  assist  i n the  i n t e r p r e t a t i o n of other data from other sensors i s investigated. dependence o f both v e l o c i t y and cone resistance  on stress  The  levels i s  discussed. Chapter  8 presents the major findings  recommendations f o r future research.  of t h i s t h e s i s  and o f f e r s  19 CHAPTER 2.  DATA COLLECTION AND REDUCTION PROCEDURES  2.1 Introduction This  chapter  outlines  important  aspects  of the data  collection  process used i n a l l phases of the seismic cone penetration t e s t .  The  equipment associated with seismic cone t e s t i n g i s discussed followed by a  brief  description  uncertainties,  of important  errors  procedure  and resolution  details.  of d i f f e r e n t  F i n a l l y the  measurements are  discussed.  2.2  The Seismic Cone Penetrometer Three d i f f e r e n t cone penetrometers  t h i s study.  were used most extensively i n  A l l were b u i l t a t the University of B r i t i s h Columbia, UBC:  1) UBC no. 4, f i v e channel  1  q^., f , u, i , t s  2) UBC no. 6, amplified s i x channel:  q ^ f , u, i , t , geophone  3) UBC no. 8, amplified s i x channel:  g^., f , u l or u2, u3, i ,  s  s  accelerometer, where qj,  = cone resistance of projected area 10 cm , f u l l scale capacity of 75 MPa (750 bar)  f  = f r i c t i o n sleeve resistance of projected area 150 cm , f u l l scale capacity of 1 MPa (10 bar)  2  2  s  u  = pore pressure, v a r i a b l e capacity transducers  u l = pore pressure f i l t e r on the cone t i p u2 = pore pressure behind the cone t i p u3 = pore pressure behind the f r i c t i o n sleeve i  = i n c l i n a t i o n from v e r t i c a l , f u l l scale 11°  t  = temperature  e i t h e r geophone or accelerometer oriented h o r i z o n t a l l y  20 The most sophisticated of the penetrometers other penetrometers  i s shown i n Figure 2.1, the  are mechanically s i m i l a r but lack the upper pore  pressure c a p a b i l i t y .  E a r l i e r cones such as no.  s i m i l a r but d i d not include amplified signals.  4 were mechanically  Cone no. 8 allowed the  simultaneous c o l l e c t i o n of pore pressure at d i f f e r e n t locations, both behind  (above) the sleeve and e i t h e r on the cone face or behind the  cone t i p .  Porous elements  used  in this  study  nominally sized 120 micron porous polypropylene. more  rigid  ceramic  compressibility was  filters  were  used  to  were machined  from  On several occasions verify  that  element  not r e s u l t i n g i n the generation of pore pressures;  these t e s t s are referred to i n chapter 4. F r i c t i o n measurements were made with an equal end sleeve that reduced pore pressure e f f e c t s . sleeve  load  cell  was  designed  to  be  area  friction  The t h i n walled  friction  loaded  in  tension,  thereby  eliminating possible buckling and collapse problems. A h o r i z o n t a l l y oriented Geospace GSC-14-13 miniature geophone with a standard natural frequency of 28 Hz was used as a seismic receiver i n cone  no.  6  and  a  piezoelectric  type  accelerometer  frequency of 3 kHz. was used i n cone no. 8.  with  a  natural  Advantages and properties  of each of these receivers i s discussed i n d e t a i l i n Laing (1985). A  complete  Campanella procedures.  and  description Robertson  Only  of the  UBC  (1981) who  non-standard  and  testing also  vehicle  i s given i n  discuss standard  important procedures  testing  relevant to  shear wave v e l o c i t y and pore pressure measurements w i l l be discussed here.  21 circuit board mounting  slope sensor  seismic pick-up  porous polypropylene  pore pressure transducer  Quad ring  tension load cell (friction sleeve) equal end area (friction sleeve)  taper fit  LEMO connector  compression load cell (bearing)  O-ring  —  Quad ring  Figure 2.1  Dual Element Piezometer Cone  pore pressure transducer porous polypropylene  22 2.3  CPTU Procedures Complete  d e t a i l s of CPTU t e s t i n g are discussed i n Campanella and  Robertson (1981); t h i s section describes only the most important nonstandard d e t a i l s .  2.3.1  Pore Pressure Measurement System Compliance  Rapid  pore  pressure response generally  requires  pressure measurement system be extremely r i g i d . factor  influencing  the  degree of saturation.  stiffness  that  the  pore  The most important  of the measurement  system  i s the  The compliance of the transducer, the transducer  seating and seals contribute l i t t l e t o the compliance of the o v e r a l l system.  No  apparent  difference  was  found  between miniature pore  pressure transducers with r i g i d s i l i c o n diaphragms larger  steel  saturated.  The  permeability important  diaphragm  of  the  rapid,  Saturation was  provided  importance of complete  through  sufficiently  transducers,  soil  high and  decreases.  permeability most  both  saturation Complete  soils,  important  and more compliant were  increases as the  saturation  through  i n low  systems  i s less  which  flow i s  permeability  soils.  always performed with glycerine which was selected f o r  i t s v i s c o s i t y and complete m i s c i b i l i t y with water.  Two procedures were  used i n t h i s study; they w i l l be referred t o as the syringe and the vacuum systems.  A simple system requiring only a syringe that could  e a s i l y be repeated i n the f i e l d  i s shown i n Figure 2.2.  system, pore pressure elements were saturated stored under glycerine p r i o r to use.  With  this  i n the laboratory and  A second system was used with  cone no. 8 the duel piezometer cone; t h i s procedure i s i l l u s t r a t e d i n  23  Glycerine  Syringe  Glycerine Porous F i Slip-on Saturation Cup  Figure 2.2  Cone Saturation Procedure Using A Syringe  24 Figure 2.3.  In t h i s case the cone could be assembled dry then placed  inverted i n a vacuum chamber.  A f t e r submerging the cone i n glycerine a  vacuum was applied u n t i l no bubbles were observed. and  fluid  The element type  selected helped t o maintain saturation during the period i n  which the penetrometer was removed from the saturation stage t o the ground. this  No attempt was made t o maintain the probe under f l u i d  stage.  The vacuum  chamber  system used  t o saturate  during  the duel  element cone was very easy t o perform i n the UBC t e s t i n g v e h i c l e but may not be as simple i n some f i e l d conditions.  I t was considered t o be  the most e f f e c t i v e means of saturating the pore pressure measurement system.  P a r t i a l saturation using the syringe method was indicated by  saturating the cone as well as possible using the syringe method then placing the saturated cone i n de-aired glycerine i n the vacuum chamber and  applying  measurement completely  a  vacuum.  system  Bubbles  emerging  indicated the syringe  remove a l l a i r .  For t h i s  from  the  piezometer  saturation method  reason  the vacuum  d i d not  system  was  preferred; the necessity of using a vacuum pump unfortunately makes i t a l e s s a t t r a c t i v e method f o r f i e l d use e s p e c i a l l y i n remote areas. one p a r t i c u l a r l y vacuum  difficult  system was  s i t e with  found necessary  At  a desiccated surface crust the  t o achieve  s u f f i c i e n t saturation.  Results contrasting the response obtained are shown i n Figure 2.4 which shows a sluggish response from the syringe method and a more d e t a i l e d response obtained when the vacuum method was used. the  pore pressure  with  Rapid increases i n  no changes i n stratigraphy indicated by the  other sensors r e f l e c t s a lagging response a t rod changes.  to vacuum pump  25  Section of Plexiglass Chamber w i t h Assembled Cone I n s i d e  S a t u r a t i o n Procedure: - cone clamped w i t h vacuum chamber i n place - g l y c e r i n e added and cap p l a c e d on t o p - w i t h t i p and f i l t e r removed measurement system s a t u r a t e d under vacuum 5 - 1 0 minutes - vacuum v e n t e d - previously saturated f i l t e r and t i p p l a c e d onto cone - completed cone p l a c e d under vacuum f o r 30 minutes - vacuum vented f l u i d poured o f f and cone removed ( i f membrane was used i t was added with f l u i d i n place and cone removed through t h e top)  Figure 2.3  Cone Saturation System Using A Vacuum  3D-  Figure 2.4  Comparison of Pore Pressure Response at Langley  to  <7l  27 2.3.2  Pore Pressure Dissipations  Pore pressure dissipations were automatically recorded at a l l rod break  intervals,  During rod breaks,  typically  1 m,  and at other selected  locations.  procedures i n i t i a l l y adopted required complete load  removal at the top of the cone rods.  Unloading at the top of the cone  rods i s accompanied by a relaxation of end bearing (discussed i n a later chapter).  For this reason adjustments to the data collection  system were made permitting load to be partially maintained by fixing the top of the cone rods.  This does not, however, maintain the  penetration cone resistance and a variable amount of stress relaxation invariably takes place. This procedure can be very important when pore pressure dissipations are recorded on the cone face.  The influence of  stress relaxation was assessed by recording the analogue  q,-. signals  during pore pressure dissipations.  2.4  Seismic Cone Testing Procedure Generally at the same depth as the dissipation tests, shear wave  velocity measurements were also performed.  The configuration of the  source and receiver are shown i n Figure 2.5.  Vertically propagating  shear waves with a horizontal particle motion  (SH) were generated at  either side of the beam source; this created signals that arrived with opposite signs allowing easier identification of arrivals and allowing use of crossover events. sources were checked constant.  The  Shear waves generated using the hammer beam  to maintain the source amplitude  importance  approximately  of maintaining a reasonably  amplitude i s discussed further i n section 2.6.  consistent  28  Cone Penetrometer with Seismometer (active axis p a r a l l e l to shear source)  Figure 2.5  Source and Receiver Configuration  29 2.4.1  Sources  Both compression, P, and shear, S, wave t e s t i n g was performed.  The  preferred method t o generated shear waves was with the sledge hammer source as depicted i n Figure 2.5.  In the offshore environment a seabed  device can be c o s t l y therefore some assessment explosive sources including shotgun s h e l l s and seismic caps was made.  of the a p p l i c a b i l i t y of  (Buffalo gun), Figure 2.6,  The explosive sources generate both P and S  energy and were found t o be highly reproducible provided the source was placed i n a f l u i d  f i l l e d hole.  Previous studies by Laing (1985) d i d  not f i n d the same degree of r e p e a t a b i l i t y . a  fluid  filled  hole  better  By placing the source into  repeatability  was  achieved.  Complete  descriptions and comparisons of sources and receivers i s given i n Laing (1985).  2.4.2  V e l o c i t y Measurements: Data Reduction  Velocity  measurements were generally made at 1 m  intervals  and  c a l c u l a t i o n procedures followed the pseudo i n t e r v a l technique, which i s displayed  i n Figure 2.7.  The  work of  Rice  (1984)  confirmed  the  v a l i d i t y of the procedure by comparing the procedure to a true i n t e r v a l technique.  Use of the reaction beam under the UBC  t e s t i n g v e h i c l e as  a source kept the horizontal o f f s e t small allowing the technique to be started a t a depth of approximately 2 m. introduce  greater  refraction. drilling  Very  r i g was  travel  path  Larger horizontal  uncertainties  associated  offsets  with  wave  short o f f s e t s were obtained when the weight  of a  used to hold down the source beam at Norwegian and  Imperial Valley s i t e s .  This d i d not r e s u l t i n additional rod noise.  Drop Rod  ^  0  Buffalo Gun  \  Trigger and Flange'  Prebored HoleN^  •12 GAUGE SHELL  Shell-  Ready t o F i r e a) Schematic o f B u f f a l o Gun (from P u l l a n and MacAulay, 1984)  Figure 2.6  Buffalo Gun Source  Detonated  b) O p e r a t i o n of B u f f a l o Gun  31  Figure 2.7  Schematic of the Interval Technique  32 The use of a f r i c t i o n reducer which widens the hole behind the cone probably eliminates the p o s s i b i l i t y any of the surface noise coupling with the CPT rods. For the f i r s t depth i n t e r v a l the f i r s t a r r i v a l time must be used t o c a l c u l a t e shear wave v e l o c i t y .  Over subsequent depth i n t e r v a l s the  i n t e r v a l technique can be used with any s u i t a b l e time marker. merits i n the s e l e c t i o n o f the f i r s t  arrival  or f i r s t  Relative  crossover or  other techniques are discussed i n s e c t i o n 2.6.1.  2.4.3  Shear Modulus  Shear modulus i s calculated from shear wave v e l o c i t y from e l a s t i c theory using Gmax = P * v where  v  s  2 s  p = mass density of the s o i l  = shear wave v e l o c i t y  Density may be known o r estimated  from sample information.  At some  s i t e s studied as part o f t h i s t h e s i s density was w e l l documented; at others water  content  information was known; a t others  between cone resistance and r e l a t i v e density.  correlations  density were used t o estimate  The information a v a i l a b l e a t d i f f e r e n t s i t e s i s o u t l i n e d i n  chapter 3.  2.5  Possible E r r o r Sources i n CPTU Testing A b r i e f explanation o f the sources and magnitude o f p o s s i b l e e r r o r  associated  with  each  of the CPTU measurements  determines  some aspects  summarizes  experience  i s required  of subsequent i n t e r p r e t a t i o n .  gained  i n this  study  with  as i t  This section  the UBC cones and  33 other  cones,  sites.  as  well  Some of  as  this  results  from repeated soundings at  work i s published  i n Lunne,  et  al.  several (1986).  Typical ranges of e r r o r are tabulated i n Table 2.1 and discussed below.  2.5.1  Zero Load S t a b i l i t y  The  single  most  significant  source  of  error  for  all  measurements i s lack of s t a b i l i t y of the zero load reading. range of s o i l s generally encountered during results  i n the  very  high  loads yet s t i l l  soft  soils.  Thermal  instability. temperature  are  proper  changes are  cases, be corrected f o r .  testing  designed to withstand  be usable f o r measuring the properties  shifts  Provided  The wide  cone penetration  requirement that load c e l l s be  CPTU  generally  calibration  known the  thermal  the  cause  tests  are  of  zero  performed  instability  can,  of  load and  i n many  Zero load i n s t a b i l i t y v a r i e s from load c e l l  to load c e l l but i s generally proportional to the capacity of the load cell.  For t h i s reason zero load s t a b i l i t y i s most important when the  measurement i s a small portion of the f u l l scale capacity. Table 2.1 and  As shown i n  zero load s t a b i l i t y i s a serious source of e r r o r i n bearing  friction  measurements  through  soft  soils.  To  quantify  magnitude of errors associated with zero  load i n s t a b i l i t y ,  zero  readings  were recorded  a l l tests.  shift  compared  to  Provided  expected  and  from  after the  measured  Any  temperature  load was  changes.  the observed zero load s h i f t could be explained by the known  temperature corrected  that  before  the  calibration using  calibration.  the  and  temperature  recorded  changes  temperature  a l l readings  change  and  were  temperature  TYPICAL VALUES POSSIBLE SOURCES OF ERROR IN q : c  Absolute Value of uncertainty  Relative error i n soft CLAY*  Relative error i n SAND*  Zero Load Stability  .5 bar  20 %  .5 %  Digital Resolution  .5 bar  20 %  .5 %  nil  Load Transfer External Dimensions Total Bearing Effect (qp correction) POSSIBLE SOURCES OF ERROR IN f : c  .05 mm  nil  nil  nil  nil  no significant error i f pore pressure measured behind t i p Absolute Value of uncertainty  Relative error i n soft CLAY  Relative error i n SAND"  Zero Load Stability  .05 bar  50 %  5 %  Digital Resolution  .01 bar  10 %  1%  unknown  unknown  small  possibly large  small  nil  Load Transfer External Dimensions  unknown .05 mm  Pore Pressure Effect POSSIBLE SOURCES OF ERROR IN u:  Absolute Value of uncertainty  Relative error i n soft CLAY  Relative error i n SAND  Zero Stability  .01 b a r  .4 %  1 %  Digital Resolution  .01 b a r  .4 %  1 %  * Example Soils Considered: soft CLAY SAND Note:  <3c (bar) 2.5 100.  (bar) .125 1.0  FR  %  u (bar)  5 1  2.5 1.0  - Absolute errors may be smaller - Absolute errors are typical for 10 ton capacity cones  Table 2.1 Possible Sources of Error i n CPTU Testing  35 2.5.2  Resolution  D i g i t a l resolution was t o d i g i t a l converter was  included i n Table 2.1.  used i n t h i s study.  A 12 b i t analogue  The r e s o l u t i o n becomes  s i g n i f i c a n t i s s o f t clays f o r bearing and f r i c t i o n measurements but i s i n l i n e with the zero load s t a b i l i t y .  The computer data a c q u i s i t i o n  system  achieved greater than  used  i n this  study e f f e c t i v e l y  12 b i t  d i g i t a l resolution, depending on s o i l conditions, by using an averaging procedure single  i n which 20  value.  During  readings taken this  sampling  traveled only approximately 0.013  at 30 kHz interval  were averaged the  cone would  to a have  mm.  The a b i l i t y t o quantify the properties of a s o i l layer within an interbedded sequence i s also a question of resolution. or experimental work has been done i n t h i s area. Schmertmann diameters  No  fundamental  Treadwell (1975) and  (1978) both suggest that a probe must penetrate 5 t o 10  into  a  subsequent  layer  represents  the  soil  layer  interface  properties  and  remain  i n order of  the  5 to  that  layer  a  10  diameters  reading  above a \  i n the  i n question.  Clearly  layer the  properties of the layer and the r e l a t i v e contrast of the properties of the layers i n question determines each s i t u a t i o n .  Experimental work  performed with cones of d i f f e r e n t diameter i n a layered deposit could c l a r i f y this situation. F r i c t i o n data may  be  influenced by a smaller depth of s o i l  cone resistance but no work was done to quantify t h i s . to  assess the  thickness of the  pressure measurement system.  zone of  soil  than  It is difficult  influencing  the  pore  Although i t measures a response generated  by the cone t i p i t i s influenced by a smaller zone of s o i l than the  36 cone resistance measurement. One of the best ways to evaluate the depth r e s o l u t i o n of each of the channels  i s t o compare the a b i l i t y of each t o i d e n t i f y  changes.  The  ability  of  each of  the  various  stratigraphic  sensors  to  identify  changes depends on the nature of the contrast and the s o i l conditions present. later  This t o p i c i s explored further on a s i t e s p e c i f i c basis i n  sections.  intervals,  an  In  any  interval  case,  data were c o l l e c t e d  smaller than  one  on  cone diameter.  25  mm  depth  This depth  r e s o l u t i o n appeared t o be more than s u f f i c i e n t i n the sense that many readings were recorded within a l l detected s o i l layers.  2.5.3  Load Transfer  Load can be transferred across the gap between the t i p and sleeve when s o i l  particles  fill  the  gap  between the two  pieces.  In most  s i t u a t i o n s the load transfer i s small, but occasionally, high f r i c t i o n readings are obtained and when the hole i s completed the f r i c t i o n zeros appear o f f s e t u n t i l the cone i s cleaned. with  proper  maintenance  between  The s i t u a t i o n i s best avoided  probings.  Several  probings  were  repeated i n the course of t h i s study because of t h i s problem.  '2.5.4  External Dimension Tolerances  Friction  sleeve data are e s p e c i a l l y prone to measurement errors.  Many CPTU users have l i t t l e f r i c t i o n data c o l l e c t e d .  confidence  i n the absolute value of the  Load transfer i s often regarded as the source  of the e r r o r but another possible source of error, which was noted by de Ruiter (1982),  i s the use of undersized f r i c t i o n sleeves.  This was  37 avoided by the use of properly sized f r i c t i o n sleeves.  L a t e r a l stress  conditions, which e f f e c t the f r i c t i o n reading, are highly influenced by the exact diameter o f the sleeve compared t o the cone t i p .  Care was  taken t o ensure that the diameter of the f r i c t i o n sleeve was a t l e a s t as great as that of the cone.  2.5.5  Pore Pressure E f f e c t s  The  importance  of t o t a l bearing correction has been emphasised i n  previous publications including Campanella, e t a l . (1982). pore  pressure  correction  measurements  i s simple.  are made In many  i n the correct  cases,  measurements are made on the cone face.  however,  Provided  l o c a t i o n the pore  pressure  In t h i s case an estimate of  the appropriate value behind the t i p has t o be made.  The r e l a t i o n s h i p  between pore pressures measured a t these two locations i s r e l a t i v e l y straightforward i n s o f t clays were the correction i s most In  stiff  important.  clays where the t i p resistance i s higher the pore  pressure  d i s t r i b u t i o n i s more v a r i a b l e but fortunately the correction i s l e s s important. F r i c t i o n readings are also influenced by an uneven pore pressure distribution. friction exerted.  When pore pressures are d i f f e r e n t on e i t h e r end of the  sleeve  (which has equal exposed end areas)  a net force i s  The addition of pore pressure measurements at e i t h e r end of  the sleeve allowed t h i s correction t o be checked.  The net force was  found t o be l e s s than the d i g i t a l resolution f o r a l l s o i l s i n t h i s study except s t i f f clays.  encountered  Fortunately i n s t i f f clays the high  f r i c t i o n induced by the s o i l reduces the importance  of any correction.  38 The a p p l i c a t i o n of equal end area f r i c t i o n sleeves reduces most of the pore pressure e f f e c t .  2.5.6  Repeatability  An assessment of the o v e r a l l accuracy and r e p e a t a b i l i t y of the cone penetration t e s t can be made by comparing repeated adjacent Some of the v a r i a t i o n seen may t e s t s performed that  data  be due t o natural s o i l v a r i a b i l i t y but  as part of t h i s study at several s i t e s i n Norway show  collected  on  different  l e v e l s of r e p e a t a b i l i t y , variability.  soundings.  Figure  channels  are  subject t o  not a l l of which can be  2.8  shows  a  reasonable  different  explained by  scatter  i n the  resistance traces and there i s no systematic bias of any one compared t o the average. the p r o f i l e s .  of  observed  cone  sounding  The pore pressure data are well reproduced i n  On the other hand sleeve f r i c t i o n readings are widely  scattered f o r the d i f f e r e n t p r o f i l e s . order  soil  a  factor  at  many  of two sites  Errors at t h i s s i t e are i n the  f o r sleeve f r i c t i o n .  i s that  cone  The  general trend  resistance can  be accurately  reproduced except i n s o f t clay or peat s i t e s where zero load s t a b i l i t y r e l a t e d errors may values may  be a s i g n i f i c a n t portion of the reading.  Friction  be unreliable, and pore pressure data are generally highly  reproducible and r e l i a b l e provided proper care i s taken t o saturate the cone i n f i n e grained s o i l s ,  and that pore pressure records are only  compared f o r s i m i l a r measurement locations.  Although f r i c t i o n readings  were generally found to be u n r e l i a b l e i n a l l but dense sand s i t e s i t was  generally found  that changes i n the f r i c t i o n  reading through  p r o f i l e accurately indicated the s t r a t i g r a p h i c boundaries.  The  a  I  Figure 2.8 Variation i n Signals from Repeated Soundings: Holmen Sand adapted from Lunne, Eidsmoen, Gillespie and Howland (1986)  40 apparent  lack  however,  in  of  accuracy  assessing  of  the  friction  usefulness  data of  must  be  considered,  interpretation  methods  incorporating f r i c t i o n data.  2.6  Possible Error Sources In Shear Wave V e l o c i t y Measurements Velocity  data  are  shown throughout  this  thesis.  The  order of  magnitude of the accuracy that can be anticipated i s discussed i n t h i s section.  A consideration of errors i s important considering that the  v e l o c i t y i s squared when c a l c u l a t i n g modulus values.  2.6.1  Errors Associated With the Use of Arrivals/Crossovers and Cross Correlations  Use  of  repeatable  the  pseudo time  marker  experimentally  to  interval  calculate  determined  the  shear  method allows the wave v e l o c i t y .  repeatability  of  the  use Rice  of  any  (1984)  crossover time.  Rice concluded that an averaging of up to ten blows could s i g n i f i c a n t l y improve the accuracy of the method over the use of a s i n g l e blow at each t e s t depth.  Examination  of the cause of these d i f f i c u l t i e s i n  t h i s t h e s i s d i d not reach the same conclusion. source beam and ensuring complete  Improvements i n the  ground contact greatly improve the  r e p e a t a b i l i t y of the source and subsequent marker times. Compared to the crossover event the a r r i v a l i s more repeatable but more d i f f i c u l t to define. depth.  Two  Figure 2.9 shows f i v e traces recorded at one  of the traces are nearly i d e n t i c a l ,  common pattern, they a l l have the same a r r i v a l l a r g e r amplitude have delayed crossover times.  the others show a  time but those with  The high frequency  42 component  o f both  the high  and low amplitude  waves has the same  v e l o c i t y r e s u l t i n g i n i d e n t i c a l a r r i v a l times regardless o f the source amplitude.  The subsequent  apparent divergence i s l i k e l y due t o the  d i f f e r e n t frequency content of the input s i g n a l , the higher amplitude s i g n a l has greater low frequency (slower component) and subsequently a delayed crossover.  This dispersion r e s u l t s i n the lower r e p e a t a b i l i t y  of the crossover event compared t o the a r r i v a l  event.  The maximum  v a r i a t i o n i n the crossover times was observed t o be i n the range of 0.5 ms with d e l i b e r a t e l y  different  beam and hammer source. ways:  amplitude  sources generated with the  The divergence could be dealt with i n several  e i t h e r by averaging (perhaps by summing) multiple events; or by  maintaining a repeatable source. was used  with occasional  checks  In t h i s t h e s i s the l a t t e r by t e s t i n g multiple  approach  s t r i k e s a t one  location. At  most  sites,  provided good  shear beam contact was made, the  r e p e a t a b i l i t y o f any one measurement was within 0.05 ms.  This error i n  the  interval  repeatability  typically,  5 ms  of  the measurement  over  a  time  of,  (velocity of 200 m/s) represents an error of +/- 2 %  assuming the worst case of the error being nonsystematic. At the Norwegian s i t e s tested, depth control was regulated by the rod stickup a t the back of a f l e x i b l e l i g h t weight d r i l l r i g . control was possibly as bad as 25 mm.  Depth  This error r e s u l t s i n v e l o c i t y  errors i n the i n t e r v a l above and the i n t e r v a l below and would r e s u l t i n a maximum error of 50 mm i n 1 m or a 5 % error i n i n t e r v a l v e l o c i t y . For the most uniform s i t e s tested such as the Ons0y s i t e , Figure 3.3, t h i s i s the magnitude of the v a r i a t i o n observed between soundings.  It  43 i s d i f f i c u l t t o know how much of the v a r i a t i o n observed may be due t o s o i l heterogeneity. one  depth  amplitude  In any case, the r e p e a t a b i l i t y of measurements at  i s very i s used.  good  provided  a  reasonably  When t e s t s were conducted  r e s u l t s were repeated within approximately  5 %.  consistent  i n adjacent  source  soundings,  Investigations a t the  Holmen s i t e , Figure 3.6, resulted i n more v a r i a t i o n between soundings but more s c a t t e r was observed  i n the cone resistance traces and hence  the v a r i a t i o n was considered t o r e s u l t from natural s o i l v a r i a t i o n s . Use of a r r i v a l times, observed t o be highly repeatable, d i d r e s u l t in  the additional  location. to define.  problem, however, of d e f i n i n g a s u i t a b l e marker  As shown i n Figure 2.9 the a r r i v a l event i s very d i f f i c u l t One means of defining the event was t o construct a tangent  at the point of i n f l e c t i o n a f t e r the a r r i v a l .  The i n t e r s e c t i o n of the  tangent t o the zero crossover could then be defined as an a r r i v a l . Cross  correlation  techniques  were attempted a t several s i t e s t o  c a l c u l a t e the i n t e r v a l between subsequent a r r i v a l s .  This method o f f e r s  the advantage of permitting automation of the process.  The d i g i t a l  storage oscilloscope used i n t h i s study could optimize the s h i f t i n g and comparison  of up  to  1024  points.  The  method  suffers  the same  dependency upon input source r e p e a t a b i l i t y as the crossover technique, though t o a lessor degree, as i t considers a l l of the points selected. The optimum window of data t o use f o r cross c o r r e l a t i o n appeared t o be that  obtained  between the f i r s t  arrival  and the f i r s t  crossover.  T y p i c a l l y data were c o l l e c t e d at the rate of 10 microseconds/point and about  1000 points would be  crossover.  contained  between the a r r i v a l  and the  Results from the cross c o r r e l a t i o n method were very s i m i l a r  44  to  those  of the a r r i v a l  and crossover  events  provided  reasonably  consistent signal sources were used.  2.7  Conclusions 1) Some d e t a i l s of the data c o l l e c t i o n process were described.  In  p a r t i c u l a r those areas that are non standard p r a c t i c e or not described elsewhere  were emphasised.  were described.  Cone saturation procedures  i n particular  Where high q u a l i t y pore pressure data were required i n  s o f t clay s i t e s vacuum techniques were preferred. 2) General  guidelines showing the accuracy  measurements were given. relative  error  of CPTU and v e l o c i t y  Table 2.1 gives estimates of the absolute and  associated with  the d i f f e r e n t  measurements.  CPTU  t e s t i n g i n s o f t clay i s often confined t o cone resistances l e s s than 0.1 % of the cone f u l l scale capacity. drift  related  At such low loads zero load  errors must be considered.  Temperature o f f s e t s were  found, by laboratory c a l i b r a t i o n work, t o cause much of the zero load errors.  Temperature measurements were used t o correct a l l data points.  Cone resistance measurements i n sands, much greater than  the zero  errors are i n s i g n i f i c a n t .  load  and s t i f f s i l t s or clays are  instability  errors  and  percentage  F r i c t i o n data are u n r e l i a b l e i n loose s o i l s  and s o f t clays but the r e l a t i v e changes within a p r o f i l e are r e l i a b l e . Pore pressure readings, provided saturation was good, were found t o be extremely  accurate  in a l l soil  conditions.  Errors associated with  shear wave v e l o c i t y measurements were discussed.  Possible sources of  error include the depth measurement, r e p e a t a b i l i t y of the s i g n a l , and identification  of  the  event.  A  trade  o f f between  ease  of  45 i d e n t i f i c a t i o n of the event and event r e p e a t a b i l i t y occurs between the use  of the f i r s t  arrival  and the f i r s t  crossover.  In e i t h e r  case  v e l o c i t y measurements, provided a consistent source i s used, are l i k e l y accurate t o 5 %.  46 CHAPTER 3. 3.1  SITE DESCRIPTIONS  Introduction During t h i s research program t e s t i n g was performed a t a number of  sites,  t h i s chapter i s a compilation  s i t e s investigated by the author.  of s i t e descriptions  f o r those  Each d e s c r i p t i o n includes a summary  of the s o i l properties, reference t o more d e t a i l e d descriptions where available, a CPTU p l o t , and v e l o c i t y data as a v a i l a b l e .  Occasionally,  adjacent p r o f i l e s were performed and more than one p r o f i l e i s shown.  3.2  Ons0y: The  S i t e Description  Ons0y s i t e  Fredrikstad  i s located approximately four kilometers  i n Southern  Norway.  approximately 45 m of marine clay.  The  clay  deposit  consists  and  are close t o 60 %.  s l i g h t l y more p l a s t i c  of  The top 30 m include a weathered  crust 1 m t h i c k underlain by 8 m of s o f t clay with i r o n spots, matter and s h e l l fragments.  north of  organic  Water contents are near the l i q u i d  limit  Below t h i s layer i s a s o f t homogeneous c l a y  than the clay above and having water contents  between 65 and 60 % between depths of 8 and 20 m. The  site  was  investigated with the piezometer cone i n 1982 and  again with the seismic Eidsmoen, e t a l . Lunne, e t a l .  (1985).  (1976).  sediment p r o f i l e  cone i n 1984.  Detailed r e s u l t s are given i n  A detailed site Figure  description  description  i s given i n  3.1 shows an example CPTU p l o t .  i s given  v e l o c i t y data are shown i n Figure 3.3. t h i s s i t e made i t useful i n t h i s t h e s i s .  i n Figure  A  3.2 and shear wave  The well documented nature of In addition the high  PORE PRESSURE U. kPa  MOO  a.  FRICTION RESISTANCE FC. kPa  CORRECTED CONE RESISTANCE Q T . kPa  DIFFERENTIAL P.P. RATIO AU/Q.7  FRICTION RATIO RF«FC/QT  r/.i  0 20 0 1000 0 1.0 0| i i i i | 0 i i i i i i i i i i i 0 i i i i i i o  10 -  10  10 -  10  10  15  15  15  15  15  0  UJ  o  V  2Q!  Figure 3.1  «  I  I.  . I  2Q1  ' ' ' » ' 20'  1  1  1  1  1  1  1  '  1  ' 20'  CPTU Profile at Onstfy clay site  1  '  1  1  ' 20 ' ' ' ' '  -80 i ii  47  20  40  60  Weathered CRUST  80  o 8?  •  5  CLAY with ironsulphide spots  »• <-  0 0  —"i  —(  FIELD  1  2  3  4  8  167 1.67  -we  6  •*  6  t7  t •  s  «  <  10  «>  1.67  +  6  *7« V O  6  n V  ?  o o °o oo  5  ' a«  0 o  6  * o <SW-  o  1.64  1-  •  o  7  cd ( 0 t-  CP 15  STRENGTH,  1.83 1.80 1.64 165  w« 8  CLAY  SHEAR t/m!  167  j  10  VANE  SENSITIVITY  CONTENT, •1.  BULK DENSITY,  SOIL DESCRIPTION  DEPTH, m _  WATER  7  5 5  <  +o  ?  5  o  0 1.68 p  S  1  5  + «  4  •+  4  S  5  0» +  5  20 O  4  + «&-  5  • O O•  4 4  25  4  •  4  0  •  30  35  Figure 3.2 Soil Description at Onsoy Clay Site from Eidsmoen, Gillespie, Lunne and Campanella (1985)  4  Shear wave velocity ( /sec.) m  o  100  200  XO +  *-  * 5  4  *•  **  E  J=  10  Y  15  LEGEND: + CPT 1 • CPT 2 x CPT 3  **•  *f  • X  Figure 3.3 Velocity Profiles at Onsoy Clay Site from Eidsmoen, Gillespie, Lunne and Campanella (1985)  300  50 degree  of  uniformity  made i t e s p e c i a l l y  useful to  investigate the  r e p e a t a b i l i t y of the seismic cone t e s t and CPTU measurements.  3.3  Haga:  S i t e Description  The Haga s i t e i s located about 50 km north of Oslo. is  located on  a slope above the  medium s t i f f overconsolidated from  about  30  near  the  Flomma r i v e r .  The  The t e s t s i t e Haga c l a y i s a  lean marine c l a y with an OCR  surface  to  about  2  at  7  m.  properties and an example CPTU p l o t are shown i n Figure  decreasing The  index  3.4.  The c l a y behaviour at t h i s s i t e i s unusual i n many ways, which can, i n part, be content  explained by  i s only 1 g/1  addition,  a  sand  i t s leached  marine h i s t o r y .  Present  salt  but the c l a y i s not p a r t i c u l a r l y s e n s i t i v e .  and  gravel  layer  below  the  clay  layer  In  drained  downslope into the r i v e r and created a downward hydraulic gradient of about 1. the  S t a t i c pore pressure values are near atmospheric throughout  entire profile.  No  seismic  cone work was  done at t h i s  site.  Additional d e t a i l s are given i n Eidsmoen, et a l . (1985).  3.4  Holmen: Holmen  S i t e Description  i s an  Drammen, Norway.  island  layer.  and  Drammen r i v e r  Below a sand f i l l  layer down to 22 m. Between 22  i n the  30 m,  The s i t e was  just  downstream  from  2 m t h i c k i s a very uniform  sand  The sand i s very loose, medium to coarse grained. there i s a f i n e to medium grained compact sand investigated i n 1982 with the piezocone and  later  Figure 3.4 CPTU Profile at Haga Clay Site adapted from Lunne, Eidsmoen, Gillespie and Howland (1986)  52 i n 1985 with the seismic cone. performed  i n 1985.  Three repeated seismic cone t e s t s were  The data are reported i n Eidsmoen, et a l . (1985).  The s i t e i s of i n t e r e s t because of i t s very uniform nature and the fact that comparative t e s t i n g was possible.  Tests with the UBC seismic cone  at Holmen offered a good opportunity to v e r i f y the downhole shear wave v e l o c i t y measurement technique  and  compare r e s u l t s to crosshole and  surface wave techniques these comparisons Figure  3.5  shows  parameters.  an  example  Figure 3.6  cone  are made i n section  plot  with  some  6.5.  geotechnical  shows the d e t a i l e d v e l o c i t y measurements from  the three boreholes; those i n t e r v a l s having high v e l o c i t y also had high t i p resistance measurements r e f l e c t i n g natural v a r i a b i l i t y .  3.5  Drammen Clay S i t e : The  Drammen clay  S i t e Description site  investigated i n 1985. well  documented  measurements. complete al.  at Museumsparken i n Drammen, Norway,  was  The s i t e i s used i n t h i s t h e s i s because of i t s  properties  Figure 3.7  including  shows a  other  reference  summary of the  soil  velocity  properties;  descriptions are given i n Eidsmoen, et a l . (1985), Lunne, et  (1976) and  Lacasse, et a l . (1981).  The  surface of the s i t e i s  covered with 2 m of sand underlain by a p l a s t i c c l a y deposit of marine o r i g i n with water contents varying between 55 and 60 %. index averages  30  %.  The p l a s t i c i t y  The p l a s t i c clay i s underlain by a lean clay  deposit with water contents between 30 and 35 % and a p l a s t i c i t y index of  10  %.  Figure  3.8  shows an  example CPTU p l o t  from  the  site.  Although the s i t e includes two very d i f f e r e n t clays within the p r o f i l e the only i n d i c a t i o n of a change i n s o i l type on the CPTU p r o f i l e at  PORE PRESSURE U, kPa 0 00  SLEEVE FRICTION f , kPa s  CORRECTED CONE RESISTANCE q MPa T l  FRICTION DIFFERENTIAL P.P RATIO RATIO AU/q RF=f /q . T  s  T  0  500  o  SAND FILL medium to coarse SAND D =.45-.90 D =.20-.50 5Q  10  1fJ  subrounded quartz feldspar  20 fine to medium SAND with silty sand layers D =.45-.90 D =.20-.50 5Q  30  Figure 3.5 CPTU Profiles at Holmen Sand Site from Eidsmoen, Gillespie, Lunne and Campanella (1985)  1Q  fll  5 4  Shear wave velocity ( /sec) 100  200  300  • + +  • •  •I*  x X f  X  -He  • +  x •  +  +• +  •  •  +  •  +  LEGEND: + CPT 1 • CPT 2 x CPT 3  +  •  •  — »  Figure 3.6 Velocity Profiles at Holmen Sand Site from Eidsmoen, Gillespie, Lunne and Campanella (1985)  30  40  50  60  FIELD  VANE  SHEAR  STRENGTH,  l/m!  1  2  3  4  SENSITIVITY  CONTENT,  V.  BULK DENSITY,  SOIL DESCRIPTION  DEPTH, m  WATER  FINE SAND  •  SILTY CLAY  1.81 1.79  5  o  0  a  ab  6  K  1.71  9 CO  9  (PLASTIC) CLAY  1.70  <;  1.7t 175  10  7  6  c ?o  1.76 -  SAND, GRAVEL  1.90  15 (LEAN) CLAY  8  +  &  1.93  5" •  195 1.98  i o  '-4  c  1.99  +  J  +  3  2  +  O ^ + d EC ) -^Q 9 a?  '2.5  2 +  3  07  1.97 1.98  i  9  It c  7 9 4  % a  D  O 9( 9  *>  +  2  9  2  +  9 )  1.93  20  7  2  O +  —\  3  198  3 +  25  i  "  i  a  3.5  1.94  3.5 3  + + 1.93  *  1.94  3 +  3  7  3 +  30  5  •  9 +  3 3 3  +  35  Figure 3.7 Soil Profile at Drammen Clay Site from Eidsmoen, Gillespie, Lunne and Campanella (1985)  3  PORE  P R E S S U R E U  (BAR)  F R I C T I O N FC.  R E S I S T A N C E (BAR)  BEARING QT  R E S I S T A N C E (BAR)  F R I C T I O N  RATIO  RF = F-C/Q7  !/)  D I F F E R E N T I A L PATIO  kV/UT  P . P .  SOIL P R O F I L E  fine SAND silty CLAY  plastic CLAY  lean CLAY  Figure 3.8 CPTU Plot at Drammen Clay Site from Eidsmoen, Gillespie, Lunne and Campanella (1985)  57 11 ui i s the change i n slope of the t i p resistance vs. depth p l o t . Neither in  the f r i c t i o n or pore pressure measurements r e f l e c t the change  s o i l type.  An  i n t e r p r e t a t i o n of CPTU p r o f i l e s  that r e l i e s on  the  change of one of the parameters with depth inherently assumes that a l l other factors remain the same and can be misleading  i f the s o i l type i s  not well known. A v e l o c i t y p r o f i l e i s shown i n Figure 3.9. velocities  measured at the Drammen s i t e compared well with those made  with conventional  3.6  No.  crosshole  6 Road Richmond:  The No.  As with the Ons0y s i t e ,  techniques.  S i t e Description  6 Road s i t e i s located i n the Fraser r i v e r d e l t a deposits  at Richmond, BC.  The  s i t e includes a t h i c k sand layer, extending to a  depth of 20 m which i s medium grained with a trace of s i l t . 3.10  Figure  shows a CPTU p l o t , including before and a f t e r compaction r e s u l t s .  Vibro replacement techniques were used at the s i t e and the CPTU p r o f i l e a f t e r compaction was  done i n the centroid of the stone columns.  The  s i t e i s of i n t e r e s t because of the pre and post compaction data.  3.7  McDonald Farm:  S i t e Description  The McDonald Farm s i t e i s located near the Vancouver International Airport  on  elsewhere,  Sea  Island  including  Konrad and Law  (1985).  i n Richmond, BC. Campanella,  et  al.  The  s i t e has  (1983),  Greig  been  reported  (1985),  and  Beneath the c l a y s i l t crust i s a sand deposit  Shear wave velocity  ( /sec.) m  100  4  200  + •  • 1 5  •  * +• 1  +• + •  +  15  LEGEND: + CPT 1 e CPT 2 I Figure 3.9 Velocity Profiles at Drammen Clay Site from Eidsmoen, Gillespie, Lunne and Campanella (1985)  PORE PRESSURE U (ra. of water)  0  50  CONE BEARING Qc (bar)  SLEEVE FRICTION (bar)  0  2.5  1  7.5-  7.5-  4  (_  QI 4J  OJ E  IT ft »  Q_ LU  a  15-  >  s A.  22. 5 — J  1  • • 1 1 22.5 Depth Incromont  22.5 025 m  Before Compaction A f t e r Compaction #1 A f t e r Compaction #2 a l l pore p r e s s u r e s measured behind t i p  Figure 3.10  CPTU Profiles at No. 6 Road Site  59  60 that extends to 13 m.  The sand i s medium grained, but includes s i l t y  f i n e sand layers found at i r r e g u l a r depths around the s i t e . 15 m,  a f i n e sand layer i s observed across the s i t e .  From 13 to  This l a y e r has  much lower cone t i p resistance than the material above and i s believed to be loose. properties 3.11.  A very deep clayey s i l t layer s t a r t s at 15 m.  of t h i s  This  layer are  layer behaves  included i n the CPTU p r o f i l e s , in  a  normally  consolidated  contains s u f f i c i e n t c l a y to behave as a cohesive layer  contains  Some index  numerous t h i n  lenses  of  Figure  manner  sediment.  The  sandy material that  can  and silt be  i d e n t i f i e d by increases i n the t i p resistance and drops i n the dynamic pore pressure.  3.8  P i l e Load Test S i t e : The  pile  load  Westminster, BC,  test  S i t e Description site  is  located  on  high  Below the sand f i l l  organic  road  near a major crossing of the Fraser River.  p l o t from the s i t e i s shown i n Figure 3.12. m of f i l l .  Boundary  content  in  in  A CPTU  The s i t e i s covered by 2  i s an organic s i l t deposit which has a  the  upper  few  metres.  CPT  friction  measurements at t h i s s i t e c l e a r l y indicate the extent of the peat layers.  Below the s i l t  sand u n i t .  New  rich  layer there i s a gradational change to a fine  S i m i l a r to much of the Fraser r i v e r sand deposits the sand  i s interbedded with s i l t layers which are c l e a r l y indicated on the CPTU p l o t by  lower t i p resistance, higher  drained  pore  measurements  pressure at  the  response. site.  f r i c t i o n r a t i o and  Figure  3.13  C h a r a c t e r i s t i c of  deposits the v e l o c i t y i n the s i l t u n i t i s low.  shows most  a  partially  the  velocity  organic  Compressional wave  rich  CONE BEARING Ot (bar)  200  desiccated SILT medium grained SAND with silty SAND layers, occasional organics  ID-  (/) L QI 4-> QI  loose SAND  E  fine  X r—  normally consolidated! clayey SILT PI=10 LL=35 sand 1 0 % s i l t 70% c l a y 20%  D_ LU  a  2Di  30-  1  Figure 3.11  CPTU Profile at McDonald Farm  to  SOIL DENSITY (MG/CU |) Q  Figure 3.13  . 0  SHEAR WAVE VELOCITY (M/SEC)  BEARING RESISTANCE 500 0  Velocity Profile at P i l e Load Test Site  "  ( B R R S )  DYNAMIC SHEAR MODULUS 200 0  ( M P f l )  200  64 t e s t i n g was attempted but i t was not possible t o transmit compressional wave energy through the surface s o i l s . Pore pressure d i s s i p a t i o n rates at t h i s s i t e are not reported here but appear t o have been influenced by p a r t i a l  saturation.  Sluggish  response of the piezometer and a time l a g before d i s s i p a t i o n may have been  due t o e i t h e r  saturation.  poor  piezometer  saturation  or incomplete  soil  The presence of organics and the i n a b i l i t y t o transmit  compression wave energy through the s o i l both indicate that incomplete soil  saturation was l i k e l y  response.  This  the cause of the sluggish pore pressure  application  of compressional wave measurements i s  discussed further i n chapter 7.  3.9  Richards Island S i t e : The Richards Island  Beaufort  Sea.  The  Campanella, e t a l . i n part,  S i t e Description  site  site  (1987).  i s located  i n the coastal  investigation  details  zone of the  are reported  in  The purpose of the s i t e i n v e s t i g a t i o n was,  t o evaluate the s u i t a b i l i t y of CPTU equipment  t o delineate  stratigraphy i n the winter i c e accessible coastal zone of the Beaufort Sea.  The shallow water  equipment  but  depths allow the use of surface based CPTU  determination  of  shear  wave  velocities  presented  d i f f i c u l t i e s and required the application of explosive sources. The  site  i s characterised  overconsolidated s i l t y clay  unit  down  sufficiently penetration.  2 m  of sand  and s i l t  clay which extends down t o 4.5 m.  to 8 m  fine  by  i s a dense  fine  sand  unit.  over an Below the  The sand i s  t o generate a pore pressure response during  cone  Below the sand unit a s i l t y c l a y u n i t extends down t o a  65 hard i c e bonded material that could not be penetrated. Surface  soils  near the mouth of the Mackenzie  River  are often  seasonally frozen by subzero s a l i n e water overtop of sediments flushed of s a l t during the freshette of the previous spring. Figure 3.14, in  the  shows a t h i n frozen surface layer indicated by the spike  cone  Temperature  The CPTU p r o f i l e ,  resistance  that  also  generated higher pore pressure.  measurements at the s i t e taken using a thermistor i n the  cone and i n adjacent bore holes by others, H i l l , e t a l . that  the  entire  borehole was  at  subzero  indicate the presence of i c e bonded s o i l s . of  the  soil  results  (1986), showed  temperatures  but  d i d not  The s a l i n i t y and grain s i z e  i n an unfrozen behaviour.  The  high cone t i p  resistance layer at 11 m may, however, r e s u l t from i c e bonding of a low s a l i n i t y sand layer. t h i n layer may  Very low t i p resistance measured j u s t below t h i s  r e s u l t from a b r i t t l e fracture mechanism.  Other CPTU  measurements give no consistent explanation of the type of sediment at 11 m.  Sampling  preserved  of these marginally  marginally  bonded  layers.  frozen Details  sediments  may  not have  of the pore pressure  response at t h i s s i t e are reported i n other chapters.  3.10  Schoolhouse S i t e : The  schoolhouse s i t e  S i t e Description i s located near the hamlet  of Tuktoyaktuk.  Four CPTU's were performed on a l i n e offshore from t h i s s i t e .  Soil  conditions a t each of these s i t e s were characterised by loose t o dense f i n e and medium grained sands.  V e l o c i t y measurements were made at one  of the soundings and are described by Campanella, et a l .  (1987).  99  67 Although an average v e l o c i t y p r o f i l e was  s u c c e s s f u l l y obtained  using  explosive techniques, d e t a i l e d v e l o c i t y measurements were not possible. Figure  3.15  shows r e s u l t s  from adjacent  CPTU records  pressures measured at d i f f e r e n t locations on the cone.  with  pore  Pore pressure  measurements at the s i t e c l e a r l y indicated s l i g h t v a r i a t i o n s i n grain s i z e not indicated by f r i c t i o n measurements. content  With an increase i n f i n e s  and associated decrease i n permeability response changed from  drained t o p a r t i a l l y drained. record a pore pressure  Through those s o i l s s u f f i c i e n t l y f i n e to  response, pore pressures  behind  the t i p were  always l e s s than s t a t i c ( s t a t i c conditions were measured following pore pressure d i s s i p a t i o n s to equilibrium).  This p r o f i l e was  the only  one  encountered i n t h i s study that resulted i n negative pore pressures  on  the cone face.  3.11  Swimming Point S i t e : Some d e t a i l s  thesis. (1987).  of  the  S i t e Description Swimming Point  The  site  channel and  winter i c e was  contact  discussed  i s located on the Mackenzie River and  two  in  this  was  probings were completed i n the  frozen down to the r i v e r bottom.  measurements of the  Two  testing  more nearby at the edge of the channel where  of the channel were important velocity  are  Other descriptions of the s i t e are given i n Campanella, et a l .  performed through the winter i c e . river  site  i n evaluating the r e s u l t s obtained  made with  i c e onto the  The s i t e s at the edge  soil  explosive allowed  sources  because  the transmission  waves generated using the hammer beam source. organic r i c h , very loose s i l t y sand deposits.  from  partial of  shear  The s i t e consists of an Figure 3.16  shows two  PORE PRESSURE U (m. of vater) 0 100  SLEEVE FRICTION (bar) 0 2.5  0 0-  CONE BEARING Oc (bar)  FRICTION RATIO Rf tt> 0 5  DIFFERENTIAL P.P. RATIO 4U/Qc -.2 0 .8 ""  <  '  '  INTERPRETED PROFILE  '  dense SAND with silty sand layers  DO  V  Depth  Figure 3.15  Increment i  . 025 m  CPTU Profiles at Schoolhouse Site  ID  10  15  15 Max Depth i  note: t h a t although pore pressures on f a c e a r e generally positive there are occasional zones o f negative pore pressure  15 32.65 m  <7\ CO  Figure 3.16  CPTU Profiles at Swirandng Point Site.  70 adjacent  CPTU  performed  by  profile. tip  profiles. Kurfurst  Boring  (1986) show f i n e  partially  drained  probings stop on a gravel layer. i n chapter  sand  sampling  at  throughout  the the  site  entire  different  study.  The  response.  The  More d e t a i l e d CPTU records are shown  soil  S i t e Descriptions  adjacent  sites  conditions  overconsolidation of the different  pore pressure  6.  Lahgley S i t e s : Two  from  The CPTU p r o f i l e also shows s i l t y layers, evidenced by lower  resistance and  3.12  logs  mechanisms.  i n Langley,  are  similar,  BC  were used  except that the  surface clay deposits was At  the  Langley  232nd  apparent  likely  interchange  in this  caused by site,  the  surface clays were compacted during construction of a freeway overpass. Clays below the zone of influence of the compaction process behave i n a normally consolidated manner.  At the Langley research s i t e ,  excavation  f o r road construction under a r a i l overpass has unloaded the clays,  which appear to be  response at each of these  lightly sites  overconsolidated.  i s discussed  later  Pore in this  surface pressure thesis.  Typical of many clay s i t e s that have water tables below the surface, some d i f f i c u l t y was  encountered i n maintaining saturation of the pore  pressure measurement system. Complete descriptions of the s o i l (1985), who  obtained continuous  Remarkably d i f f e r e n t  conditions were shown by Greig  samples at the Langley  research  site.  values reported by Greig f o r the two s i t e s were  reinvestigated by the author and have been a t t r i b u t e d t o measurement errors with the t i p resistance i n the s o f t clays.  Figure 3.17  shows a  PORE PRESSURE U (m. of water) 0 100  SLEEVE-FRICTION (bar) 0 .25  CONE BEARING Qc (bar) 50 s field vane average (kPa) 23 22 25 25 26 27 36 29 26 30 30 u  Depth (m)  7.5  FRICTION RATIO Rf (X)  7.5  w L  QI 4->  3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8  0  1  5  DIFFERENTIAL P.P. RATIO 4U/Qc 0 1 0  Gmax avera (MPa) 14 1617 19 20 21 21 24 25 26 30  9  29  33  10  37  34  11  37  38  12  33  44  13  38  41  14  35  39  15  42  41  16  38  45  17  38  46  18  35  47  1  7.5-  QI  E  0_ LU Q  15  15  15-  behind t i p behind sleeve 22.5  J  22.5 Depth Increment :  Figure 3.17  22.5  -J  1  1  . 025 m  CPTU and S o i l Profile at Langley Research Site  L.  22. 5  •22. 5- — 1  Max Depth  18. 9 m  72 CPTU  profile  from  the  Langley  research  site  as  well  as  averaged  strength and s t i f f n e s s information.  3.13  Brenda Mines:  S i t e Description  Piezometer cone t e s t i n g was performed at the Brenda Mines t a i l i n g s dam  and pond to evaluate s o i l c h a r a c t e r i s t i c s and  The  soil  conditions  were characterised by  medium grained sand i n the dam, silty  sand t a i l i n g s  which was  h y d r a u l i c a l l y placed  unusual condition i n the  seepage conditions.  either lightly  compacted  dry to moist or loose f i n e i n the  t a i l i n g s pond was  tailings  the existence  frozen layers buried during previous winters.  pond.  An  of remnant  More d e t a i l s of the s i t e  i n v e s t i g a t i o n are reported by Campanella, et a l . (1985). The  s i t e , with i t s uniform  i s of i n t e r e s t to the penetration t e s t i n g .  s o i l properties and very high stresses,  i n v e s t i g a t i o n of stress l e v e l e f f e c t s i n cone  The i n v e s t i g a t i o n also highlighted one of the key  advantages of the cone penetration t e s t i n granular s o i l s , which i s the rapid  determination  of  equilibrium  penetration at the s i t e was t h i s was  achieved  with  water  Maximum  almost 70 m i n the main body of the  approximately  9,000 kg  record i s shown i n Figure  3.18.  3.14  S i t e Descriptions  Heber Road 2, 4, 6:  pressures.  dam;  of thrust. This CPTU  The Heber Road s i t e i s located i n the Imperial V a l l e y , C a l i f o r n i a . The  s i t e i s of i n t e r e s t because of l i q u e f a c t i o n r e l a t e d damage caused  by the E l Centro earthquake of 1979.  The greatest uncertainty i n the  i n t e r p r e t a t i o n of measurements made at t h i s s i t e i s associated with the  Friction Ratio FR(f /q ),%  Friction, f ,bar Cone Beoring,q ,bar e  3  2  c  I  — 0 — 80  c  160 240 320 4 0 0  0  O  I  c  2  a. a> •o  c  a>  3  O  o» O  in  O a.  e  o c  >N  "O i_ o u a  (A  •o a> > w a>  tn X)  o o Z 70 ( Ibar = l O O k P o )  32°  <p:34°  Figure 3.18 CPTU Profile at Brenda Mines Site from Campanella. Robertson, Gillespie and KLohn (1984)  medium dense tailings SAND coarse fraction from cyclone separation hydraulically placed from slurry) bulldozer compacted  74 calculated  and  measured  surface  accelerations.  The  El  Centro  earthquake was a magnitude 6.6 but e a r l y reported c y c l i c s t r e s s r a t i o s of 0.75, Youd and Bennett 0.40,  Youd  made  at  (1983), have been reduced t o  approximately  (1983), based upon analysis of acceleration measurements nearby  sites.  The  CPTU  results  were  obtained  post  l i q u e f a c t i o n , but are assumed t o be representative of conditions p r i o r to  the earthquake.  The very recent nature  of t h i s deposit  increases  the uncertainty i n t h i s assumption. Based on the i n t e r p r e t a t i o n of Youd and Bennett transects an abandon r i v e r channel. be very recent.  (1983) the s i t e  The e n t i r e p r o f i l e i s believed to  Youd and Bennett give an age of only 300 - 400 years.  At a l l three cone locations, a surface sand f i l l extends to a depth of approximately  1 m.  Below the f i l l  i s a channel sand deposit, which  i s believed t o have l i q u i f i e d during the E l Centro earthquake, Youd and Bennett (1983). is  This u n i t , r e f e r r e d t o by Youd and Bennett as u n i t A , 2  of i n t e r e s t i n t h i s study.  greatly  Although properties of t h i s u n i t vary  and averaged values must be used with  caution the cone t i p  resistance values, shear wave v e l o c i t i e s , and N values a l l c o n s i s t e n t l y indicate a very loose f i n e sand deposit. is  Below the sand u n i t , which  2 to 5 m deep, are e i t h e r interbedded c l a y and sand u n i t s or dense  sand.  The clay i s p l a s t i c and heavily overconsolidated.  Complete s i t e  descriptions are given i n Youd and Bennett, (1983).  Figures 3.20,  3.22,  3.19, and  3.21, 3.24  and 3.23  also  show the CPT r e s u l t s ,  include the v e l o c i t y  and Figures  results.  Friction  measurements i n the loose sand deposit were very low and subject to  PORE PRESSURE U (m. of water)  Figure 3.19  CPTU Profiles at Heber Road 2 Site  CONE BEARING Qt (bar)  DIFFERENTIAL P.P. RATIO AU/Qt  SOIL DENSITY (MG/CU M) 1.5 Z.O  SHEAR WAVE VELOCITY 0  '  500 0  BEARING RESISTANCE (BARS) I  I  I  I  I  I  I  DTNAMIC SHEAR MODULUS (BARS) 200 0 • lQOO  SOIL PROFILE  I I  SAND F I L L loose fine SAND D =. 10-. 12 50  f i n e SAND  stiff  C  i  '  '  HEBER  " i  I  4/1  I  i J i' r  ROAD 2 .  i  i  PC2.1ST  i  i  i  I w I  CROSS.10  i i v  i i  r 'i i v-|  S O . CM S E I S M I C  Figure 3.20 Velocity Profile at Heber Road 2 Site  ^  i  i  i  i  i  CONE MARCH  i  i  i  12.  i  i  8 4 DG  CLAY  PORE PRESSURE U (m. of «ater>  Figure 3.21  CONE BEARING Ot (bar)  CPTU Profiles at Heber Road 4 Site  DIFFERENTIAL P.P. RATIO AU/Ot  SOIL DENSITY (MG/CU CU .  .  SHEAR WAVE VELOCITT (M/SEC)  „ 500 0  C n  n  BEARING RESISTANCE (BARS)  200 0  DYNAMIC SHEAR MODULUS (BARS)  SOIL PROFILE  1000  SAND F I L L  loose f i n e SAND D =. 10-. 14 50  s t i f f CLAY  i  HEBER  ROflD  Figure 3.22  4.  PC4.1ST  C R O S S . 10  I  I  I  I  I  I  I  S O . CM S E I S M I C  I  m  I  I  I  I  I  CONE MRRCH  I  I  I  12.  I  I .  8 4 DG  Velocity Profile at Heber Road 4 Site 03  Figure 3.23  CPTU Profiles at Heber Road 6 Site  ,.5  SOIL DENSITY (MG/CU  S'.O  SHEAR WAVE VELOCITY (M/SEC)  BEARING RESISTANCE l B R R S )  DYNAMIC SHEAR MODULUS 200 0  ( B f l R S )  SOIL PROFILE  SAND FILL  loose fine SAND D =.10-.14 50  dense SAND s t i f f CLAY  -I—i—i—i—i—i—i—i—i—I ">~i—i—i—i—i—i—i—i—i—i—I  —i i  i i i i i i r .  HEBER ROAD 6 . P C 5 . 1 S T C R O S S . 1 0 S Q . CM S E I S M I C CONE MARCH 1 2 . 8 4 DG Figure 3.24 Velocity Profile at Heber Road 6 Site  03  o  81 stability  related  errors discussed  i n chapter 2.  They were useful,  however, i n delineating the highly v a r i a b l e stratigraphy.  3.15  Wildlife Site:  S i t e Description  The w i l d l i f e s i t e , Imperial  Valley,  liquefaction  l i k e the Heber Road s i t e s ,  California.  damage  during  The  the  1979  wildlife El  et  al.  site  Centro  s t r a t i g r a p h i c u n i t known t o have l i q u i f i e d was  i s located i n the also  suffered  earthquake.  The  i d e n t i f i e d by Bennett,  (1981) by noting the colour of the sand extruded i n sand b o i l s .  Similar t o the Heber road s i t e the s o i l s at the s i t e are very recent. Figures  3.25  and  3.26  show CPT  and  velocity  data  from  the  site.  Additional CPT r e s u l t s are shown elsewhere i n the t h e s i s .  3.16  New Westminster S i t e : The New  Westminster,  Westminster BC.  The  S i t e Description  s i t e i s located near the Fraser River i n New site  believed t o be loose.  i s comprised  of hydraulic  fill  Below a compacted surface f i l l ,  b u i l t up with layers of interbedded f i n e s i l t y  that i s  the s i t e i s  sand and sandy  silt.  The f i n e s content i s s u f f i c i e n t l y high that the pore pressure response i s l i k e l y undrained.  As shown on Figure 3.27, the time f o r excess pore  pressure d i s s i p a t i o n s , recorded behind the t i p , of the the  t h e i r i n i t i a l value, ( t ) 5 0  sand and s i l t u n i t . time  required  to  t o reduce t o one h a l f  , was approximately 50 t o 200 seconds i n  With t  5  0  measure  values of approximately one minute, equilibrium  pore  pressures  was  approximately ten minutes. Figure 3.27 also shows the pore pressure response measured i n three  82  PORE PRESSURE U (•. of .oter)  CONE BEARING Ot (bar)  100  200  INTERPRETED PROFILE  FRICTION RATIO Rf (I) 0 10  r~0  SILT  2.5mm  SILTY SAND  CLAYEY SILT  10  10  2.5mm thick element, "B" -5 mm thick element, " c 15*  5 mm 15  15 Max D e p t h .  Figure 3.25 CPTU Profiles at Wildlife Site from Campanella, Robertson and Gillespie (1986)  1 1. 6 3 m  STIFF SILTY CLAY  SOIL DENSITY 1.5  ( M G / C U  ^.  SHERR WAVE VELOCITY (fi/SEC)  BERRING RESISTANCE (BARS)  0  _| I I I L  DYNAMIC SHEAR MODULUS (BARS) 1000  SOIL PROFILE  200 0 l n n  n  loose interbedded sandy t o clayey SILTS loose silty SAND D =.O56-.ll 50  stiff CLAY m  _  0 1  i  1 1 1 1  WILDLIFE.  0 1  I 1 1 1 1 1 1 1—1—1—I ~ l — i 1 1 1 i 1 1 1—r P C I . 1 S T C R O S S . 1 0 S O . CM S E I S M I C CON w  Figure 3.26 Velocity Profile at Wildlife Site  1—rn—1—1—1—1 1 1 MARCH 1 2 . 8 4 DG  CO  85 d i f f e r e n t places.  The pore pressure response, measured on the face of  the cone, i s highly influenced by stops i n the push. unloading  the rods at the  The  surface diminishes with depth.  e f f e c t of The  most  d e t a i l e d i n d i c a t i o n of the s t r a t i f i e d nature of the deposit i s obtained from the t i p resistance.  3.17  Summary The  types.  soils  encountered  during  this  study  cover  a wide range of  Different geologic and a r t i f i c i a l o r i g i n , density, g r a i n s i z e ,  temperature and stress l e v e l s have been investigated.  They provide a  basis f o r the comments and observations given i n l a t e r chapters of t h i s thesis.  86 CHAPTER 4. 4.1  FACTORS AFFECTING PORE PRESSURE MEASUREMENTS  Introduction There  are  many  factors that  (penetration)  pore pressures  This  addresses  chapter  procedural the  details.  measurement of  between  soil  only  those  issues  pore pressures and  properties,  by  r e l a t e d to  equipment  and  i n v e s t i g a t i n g the c o r r e l a t i o n  dynamic  pore  procedural the  pressures.  that  the  d e t a i l s i s a function of  the  influence of  discussed where necessary i n t h i s  4.2  dynamic  Chapter 5 addresses the s o i l factors that e f f e c t  parameters  type and  measurement of  i n the piezometer cone penetration t e s t .  importance of equipment and soil  e f f e c t the  soil  In  properties  i s also  chapter.  E f f e c t of Measurement Location The  single  most  measurement i s the considerable  important  parameter  l o c a t i o n of the  pore pressure  l i t e r a t u r e that addresses the  possible advantages of standardization, (1985)  and  Jamiolkowski,  et  measurement l o c a t i o n i s best  al.  effecting  pore  sensor.  pressure There i s  s e l e c t i o n of l o c a t i o n and  including Campanella, et a l .  (1985).  No  for a l l s o i l  s i n g l e pore  pressure  types or applications  and  data w i l l be shown i n d i c a t i n g that the decision should depend upon the s i t e and a p p l i c a t i o n . Data  have  been  c o l l e c t e d at  several  sites  with  pore  pressure  elements located at the centre of the cone face, behind the t i p , and behind the  friction  sleeve.  Figure  these r e s u l t s f o r a v a r i e t y of  soil  4.1  shows a summary of some of  types.  element l o c a t i o n i s a function of s o i l type.  The  importance of  The data on Figure  4.1  the  TARANTO CLAY - Cemented(CaC0 l5-30%)( Italy) LONDON C L A Y - S t i f f , uncemented, fissured (NGI - B R E ) 3  Figure 4.1 Pore Pressure Distribution during CPTU from Robertson, Campanella, Gillespie and Greig (1986)  CO  88 have been normalized (u )•  In normally  0  large  positive  by d i v i d i n g by the equilibrium water pressure, consolidated i n s e n s i t i v e  pore  pressures  pressures measured on the  are  clays and  generated  silts,  during  where  shear,  pore  face of the t i p are u s u a l l y approximately  three times l a r g e r than the equilibrium pore pressure and about 15 % greater than  the pore pressure  immediately  behind  overconsolidation r a t i o increases i n clays and pressure on the face of the t i p increases.  the t i p .  whereas the  decrease.  This i s because the area  behind  the  tip is a  but  the  and high  zone of normal  Both areas have large shear stresses and  pressures response  area  the  s i l t s the excess pore  around the face of the t i p i s a zone of maximum compression shear  As  stress  associated pore  large normal stresses dominate the  pore  pressure  on the face, whereas the shear stresses become more important  behind the t i p . In f i n e granular materials a pore pressure response observed.  Provided  penetration  is  not  completely  may  a l s o be  drained,  pore  pressures measured behind the t i p are generally negative even i n loose sands.  As shown i n Figure 4.1 pore pressures measured on the face can  reach very high values because of the high normal forces associated with t h i s l o c a t i o n . The  data  shown i n Figure 4.1  indicates that, regardless of  soil  type, the pore pressure d i s t r i b u t i o n along the face i s i n s e n s i t i v e to the  exact  location,  l o c a t i o n on the face.  either the very t i p , mid  height, or some other  Lunne, et a l . (1986) report that pore pressures  are very s i m i l a r when measured on the cone t i p or a t the middle of the cone face.  This i s an  important  f i n d i n g that allows comparison of  89 pore pressure data c o l l e c t e d  from d i f f e r e n t cone designs each having  t h e i r pore pressure element located somewhere on the face.  This i s the  primary advantage of measuring pore pressures on the cone face. Data c o l l e c t e d  i n some overconsolidated s o i l s  indicate that the  large gradient i n pore pressure immediately behind the t i p r e s u l t s i n a variation  in  measurement Valley,  the  measured  locations.  California,  For  pore  pressure  example,  for  Figure 4.2  slightly from  different  the  Imperial  shows very d i f f e r e n t pore pressure readings when  measurements were repeated with only s l i g h t differences i n measurement locations.  Although  both values were measured behind the t i p , those  c l o s e s t t o the shoulder were much higher than those j u s t 1 mm  above.  This i s an i n d i c a t i o n of the high pore pressure gradient that e x i s t s at the shoulder.  This gradient precludes the a p p l i c a t i o n of pore pressure  measurements made at t h i s location f o r quantifying the properties of s t i f f clays.  Data c o l l e c t e d simultaneously behind the t i p and behind  the sleeve indicates that pore pressures are generally s l i g h t l y behind the sleeve than behind the t i p . two  lower  This i s due t o a combination of  factors, the increased shear induced component behind the sleeve,  and the pore pressure d i s s i p a t i o n that occurs during the time required f o r the sensor behind the sleeve to t r a v e l the distance between the two sensors, G i l l e s p i e (1981). depends upon s o i l type.  The r e l a t i v e importance of the two The s t i f f c l a y s o i l s that generate  factors negative  pore pressures behind the t i p also have large cone resistance values which can be r e l i a b l y measured.  The  focus of the i n t e r p r e t a t i o n of  CPTU r e s u l t s i n these s o i l s remains the cone resistance and measurements.  friction  90  PORE PRESSURE U <<k of water)  INTERPRETED PROFILE  FRICTION RATIO Rf (X)  CONE BEARING Ot (bar)  200  10 0 »- • •— — 1  0  SILT  5  1  L  U) L 01  +J  SILTY  s  SAND  CLAYEY  Ql E  SILT  0_  LL) O  10  1  STIFF SILTY  10  -5 mm thick element,  15  C  Depth  15  Increment  I  i  .025 m  I  I  I  I  15  15 Max Depth •  Figure 4.2 Penetration Pore Pressures at Imperial Valley Site from Campanella, Robertson and Gillespie (1986)  11.63 m  CLAY  91 Figure  4.3  shows data  collected  i n normally  s i l t f o r three measurement locations. response, normal  i n t h i s type of s o i l ,  stresses  rather  component.  Values  consolidated  soils  The difference i n pore pressure  i s p r i m a r i l y due t o v a r i a t i o n i n the  than  to  as  these  such  consolidated clayey  variation  i n the  shear  are c h a r a c t e r i s t i c  and are not s e n s i t i v e  t o exact  of  induced normally  details  of the  measurement l o c a t i o n as was shown t o be the case i n overconsolidated s o i l s such as those a t the Imperial V a l l e y s i t e , Figure 4.2. Pore pressures  sensors  located behind  advantages of those behind the t i p : history;  and i n s e n s i t i v i t y  the sleeve may  o f f e r the  robustness; s e n s i t i v i t y t o stress  t o rod break procedures  (maintaining t i p  resistance, clamping top of rods, or allowing top of rods t o rebound i n an  unconstrained  location.  manner)  while  being  insensitive  to  i t s exact  As shown i n Figure 4.3, i n normally consolidated s o i l s t h i s  measurement l o c a t i o n also shows nearly the same s t r a t i g r a p h i c d e t a i l as other measurement locations.  4.3  E f f e c t of Cone Design and Mechanical Details The extreme s e n s i t i v i t y of pore pressure measurements t o the f i l t e r  element l o c a t i o n has already been discussed. there  are  reliability  still and  several accuracy  other  For any given l o c a t i o n  considerations that  of r e s u l t s .  influence the  When penetrating high  cone  resistance s o i l s there i s a p o s s i b i l i t y that a f i l t e r element w i l l be subjected t o squeezing forces from e i t h e r : - load transferred from the t i p through the element - d i r e c t s o i l forces.  Figure 4.3  Detailed Penetration Pore Pressures at McDonald Farm  93 Jamiolkowski,  e t a l . (1985) report that t i p load t r a n s f e r through the  element has been observed with several cone designs. e a s i l y checked  by rapidly loading a f u l l y assembled de-aired cone; i t  i s most common on face t i p piezometer cones. tip  also  ensures  isolated.  This problem i s  that the pore  Rapidly loading the cone  pressure transducer  i s mechanically  F i l t e r element squeeze can also be important f o r cones that  measure pore pressure a t the t i p or on the face. application suggested  of load, that  positive  the f i l t e r  pressures  element  compressibility  must  filter  i s squeezed  element  pore  during  may  permeability  be considered together.  During the i n i t i a l result.  Itis  as w e l l  as i t s  For example,  penetration  into  a  if  high  the  cone  resistance u n i t , then some p o s i t i v e pore pressure w i l l r e s u l t unless the f i l t e r  and s o i l are of s u f f i c i e n t permeability t o d i s s i p a t e t h i s  additional pore pressure. compressible  Experience gained during t h i s study with a  porous p l a s t i c  element has not shown any d i f f i c u l t i e s  r e l a t e d t o f i l t e r squeeze, l i k e l y due t o the high permeability of both the element and those s o i l s having s u f f i c i e n t cone t i p resistance to induce element squeezing. compact g l a c i a l  tills  Penetration into very f i n e dense sands or  are most l i k e l y  to result  i n element squeeze  difficulties. To  investigate the importance  of element squeeze e f f e c t s and t o  ensure that p o s i t i v e pore pressures observed a t the McDonald Farm s i t e with  face  pore  pressure  elements  were  not the e f f e c t  of element  squeeze, repeated soundings were made with p l a s t i c and ceramic porous filters. pore  size  The comparatively s o f t p l a s t i c f i l t e r s were made from 120 micron  polypropylene  and the ceramic  nominal  filters  were  94 machined  from  "aerolith". Positive  a  very  stiff  nominal  pore  size  10  micron  ceramic  The r e s u l t s of repeated soundings are shown i n Figure 4.4.  pore  pressures are  observed  with  either  filter  type  and  allowing f o r natural v a r i a b i l i t y the p r o f i l e s indicate that use of the soft  plastic  filter  does not r e s u l t  i n induced pore pressures.  v a r i e t y of ceramic elements were used i n t h i s study a t several sites.  In most cases when the sounding was  f i l t e r element was missing and presumed broken.  completed  A  sand  the ceramic  Surprisingly, i n sands  i t was impossible to t e l l , even at well documented s i t e s with repeated soundings where within the p r o f i l e the ceramic elements were l o s t .  It  appears that sand f i l l s the void l e f t by the broken f i l t e r and forms a new  filter. Careful  identify beginning  examination of the pore pressure response can generally  any of  filter a  compressibility  push of  element into the  squeeze dense  filter  problems.  sand  For example, at the  pore pressure generated  should  dissipate  very  from  quickly.  Therefore, i f a spike i n the pore pressure i s observed at the beginning of If,  a push into a uniform material element squeeze may  be a problem.  however, within a uniform s o i l large p o s i t i v e pore pressures are  maintained, then they can be considered r e a l i s t i c .  An example of t h i s  type of behaviour i s shown i n Figure 4.5 from Richards Island. the  Within  sand u n i t a high p o s i t i v e pore pressure i s maintained f o r several  metres.  Rapid d i s s i p a t i o n of excess pore pressure during rod breaks  within t h i s sand u n i t indicates that the s o i l i s nearly free draining and  i t can therefore be concluded that the measured values are the  r e s u l t of the high normal stresses created during penetration.  95  PORE PRESSURE U (m. of water)  Depth  Increment s  Figure 4.4  .025  m  Max  Depth :  21.1  Effects of Element Compressibility at McDonald Farm  m  Figure 4 . 5  Detailed Penetration Pore Pressures at Richards Island  97 4.4  Element Saturation Inadequate saturation o f the pore pressure measurement system can  lead t o inaccurate o r sluggish pore pressure measurements. details  will  be  inaccurate.  missed  and pore  Confidence i n the data  pressure  decay  rates  Profiling will  be  i s encouraged by both a rapid  return t o pre rod break values a f t e r pore pressure d i s s i p a t i o n s and a dynamic response that i s also r e f l e c t e d by changes i n e i t h e r the cone resistance or f r i c t i o n measurements. In  overconsolidated  pressures  fine  grained  soils  are generated and measured behind  large  negative  the cone t i p .  pore  Commonly,  through a desiccated surface crust or within dense f i n e sand layers negative pore pressures approach c a v i t a t i o n values.  In these instances  a cone that i s i n i t i a l l y saturated may lose saturation and subsequent performance, depending on s o i l conditions, may be affected. examples  of s o i l  conditions  through  which  Two common  saturation problems are  commonly encountered i s shown i n Figure 4.6 with measurements taken a t d i f f e r e n t locations on the cone i n adjacent holes. are measured behind 12.5  t o 13 m.  effected. Figure  4.6  When pore pressures  the t i p , c a v i t a t i o n r e s u l t s i n the f i n e sands a t  Subsequent penetration pore pressure measurements are  Examination shows  of the records  that  measurements  from other made  on  sensors  the face  shown i n are l e s s  susceptible t o the c a v i t a t i o n problem and are more useful i n these s o i l conditions. At  the same s i t e  saturation problems were encountered with the  f i l t e r element behind the f r i c t i o n sleeve a f t e r penetration through the moist surface.  A f t e r recording negative pore pressures, sluggish  PORE PRESSURE U (m. of watar)  Depth Increment i  Figure 4.6  . 025 m  Detailed Penetration Pore Pressures at Langley Site  99 response was observed.  S u f f i c i e n t resaturation a t the higher pressures  i n the underlying s o f t c l a y resulted i n s a t i s f a c t o r y performance.  When  pore pressures are measured on the face, a zone o f high p o s i t i v e pore pressure,  as shown i n Figure 4.6, the problem o f element desaturation  during penetration does not usually occur. In  very  heavily overconsolidated  soils  the large p o s i t i v e pore  pressures may require that penetration be stopped due t o overloading of the pore pressure sensor when pore pressures are measured on the cone face.  This  situation  overconsolidated  was  observed  at  a  number  of  sites  in  clays and frozen s o i l s and can be solved by e i t h e r  measuring the pore pressure a t a d i f f e r e n t l o c a t i o n o r using a higher capacity pore pressure Pore  pressure  transducer.  d i s s i p a t i o n s are not necessarily  saturation problems.  diagnostic  of  High p o s i t i v e pore pressures are observed a t the  face o f the cone i n overconsolidated s o i l s and low values are observed behind, t h i s gradient of pore pressure recorded behind of  two  pore  often r e s u l t s i n d i s s i p a t i o n s  the t i p that increase before they decrease. pressure  d i s s i p a t i o n s recorded  simultaneously  overconsolidated c l a y are included i n Figure 4.7b.  Examples i n an  Pore pressures at  the cone face s t a r t t o d i s s i p a t e as soon as penetration  i s stopped.  The response seen behind the sleeve, an increase followed by a slower decay, i s due t o the r e d i s t r i b u t i o n o f excess pore pressures  from i n  front o f the cone i n both an upward d i r e c t i o n as well as the r a d i a l direction.  This response i s i n contrast t o that generally observed i n  normally consolidated clay an example of which i s shown i n Figure 4.7a.  10  9  A) Mc D O N A L D 8  -  7  -  6  -  3  o  FARM  CfL_  Normally c o n s o l i d a t e d c l a y e y SILT (OCR = 1) Depth = 19.7 m  —B  -H  -P (0 ft  5  •Friction sleeve  a)  4-  -  d ui  3  -  ft  2  a u  1  ^1  (A CD  o ft  eaBannnnnnp  200  400  U L J u u o a 3 D Q O G 6 6 - g  600  800  1200  1000  Time ( seconds )  10 9  BJRICHARDS  8  Over c o n s o l i d a t e d s i l t y CLAY (OCR = 8) Depth = 3.87 m  3  7  o  ISLAND  6  • Friction sleeve  •H  -P  (0  5  ft d)  M 10 a) ft a) J-I  o ft —i  I—  40  80  120  160  200  Time ( seconds ) Figure 4.7 Pore Pressure Dissipations, Examples from Two Sites from Campanella, Robertson and Gillespie (1986)  r  240  101 4.5  E f f e c t of Cone Design and Procedure on D i s s i p a t i o n Tests The  for  i n t e r p r e t a t i o n of pore pressure d i s s i p a t i o n data can be done  a  quantitative  consolidation. element  assessment  the  horizontal  Theoretical solutions e x i s t  locations.  Torstensson  of  Commonly  (1977),  and  a  used  coefficient  f o r most pore  solutions  more t h e o r e t i c a l  include  and  pressure  the  complete  of  first,  solution,  Baligh and Levadoux (1986). The  effect  interpretation  of  element  location  of pore pressure  must  dissipation  be  considered  data.  in  the  A l l theoretical  solutions  f o r the interpretation of consolidation parameters r e l y  either  calculated  Pore  a  pressure  or  values  assumed  measured  initial at  pore pressure  different  distribution.  l o c a t i o n s on  the  cone,  e i t h e r simultaneously or i n repeated measurements, often bear relation  to  those  assumed  i n theoretical  recorded behind the t i p through increase before decreasing.  solutions.  on  little  Dissipations  overconsolidated s o i l s often show an  This i s l i k e l y due t o a r e d i s t r i b u t i o n of  excess pore pressures. An  examination  of the v a l i d i t y  of t h e o r e t i c a l l y  derived  initial  excess pore pressures i s shown i n Figure 4.8 which shows i n i t i a l pore pressures, pressure observed and  Levadoux  distribution lightly  a t the  along the shaft.  (1986)  solution  represents  overconsolidated  requirement  cone surface, normalized  an  Figure 4.8  f o r the  average  insensitive  f o r d i s s i p a t i o n analysis.  of  by  the excess  pore  shows that the Baligh  initial  excess  values  between  soils.  excess  This  pore  pressure  normally  i s an  and  important  In overconsolidated s o i l s where  the i n i t i a l excess pore pressure d i s t r i b u t i o n i s more complex,  102  N O R M A L I Z E D  E X C E S S  P O R E  A U/(AU), SH DEPTH (ft)  SYMBOL  O A  TEST RESULTS  3.5  3.0  2.5 OCR  45*5 60*5 85*5  •  P R E S S U R E  3*0.4 2*0.3 1.3*0.1  FROM  BALIGH  et a l . , 1978  ADDITIONAL UBC  DATA  RESEARCH  FROM SITES  •  HANEY  OCR  =4 . 0  A  LANGLEY  OCR  = 1.0  MCDONALD  OCR  = 1.0  •  7 Predicted Distribution Baligh and Levadoux 1986  60°  CONE  Figure 4.8 Normalized Excess Pore Pressure Distribution from Gillespie, Rcfoertson and Campanella (1988)  4.0  103 dissipation  solutions  Uncertainty  presently  i n the i n i t i a l  excess  available pore  are  inappropriate.  pressures around  the cone  e s p e c i a l l y i n the s o i l several diameters away from the cone makes the development of d i s s i p a t i o n solutions d i f f i c u l t . especially  around  driven p i l e s  F i e l d measurements,  i n overconsolidated s o i l s ,  may  offer  some i n s i g h t into t h i s uncertainty. Examples locations  o f pore  pressure  dissipations  i n normally consolidated s o i l  solutions i n Figure 4 . 9 .  recorded  at  different  are compared t o t h e o r e t i c a l  In general t h e o r e t i c a l solutions match the  observed behaviour reasonably well at normally consolidated s i t e s . F i e l d t e s t procedures can have a important influence on the q u a l i t y of the pore pressure d i s s i p a t i o n data.  When the rods are unloaded at  the beginning o f a d i s s i p a t i o n , a large normal stress r e l i e f may occur and pore pressures w i l l drop.  Measurements on the face of the cone are  much more s e n s i t i v e t o t h i s problem than those behind the t i p or behind the  sleeve. An  examination  of the cone resistance  d i s s i p a t i o n s w i l l reveal any d i f f i c u l t i e s . the t o t a l  stress r e l i e f  has been c i t e d  recorded during  Clamping the rods t o reduce as a possible remedy t o the  problem, but the length of the rods and t h e i r e l a s t i c response makes i t impossible  t o control  displacement at the top.  the stress  at the t i p by  Maintaining the t i p stress (cone resistance)  would not solve the problem since presumably moving.  The influence  c o n t r o l l i n g the  of unloading  the cone would continue  the t i p stress  i s especially  important when pore pressures are measured on the face of a cone  1.20  Range of 10 Test Results 1.00  0.80  o  <  0.60  -  0.40  0.20  <3  -  Range of Test Results From McDonald Farm and Predicted Dissipation curve from Levadoux and Baligh (1986) c^= 8 mm/sec  0.00  -i—i—r—i i i |— 10  1  1000  100  13 1-.20  j Range of 10 Test Results 13 CO  co  1.00  0.80  CD Q_  0.60  O  0.40'  CO CO CD O X  0.20  -  CD  CL  "O CD  -  V Range of Test Results From McDonald Farm and Predicted Dissipation curve from Levadoux and Baligh (1986) c^= 8 mm/sec  0.00 1  10  1000  100  1.20  Range of 10 Test Results  E  1.00  0.80  0.60  V  0.40  0.20  -  Range of Test Results From McDonald Farm and Predicted Dissipation curve from Levadoux and Baligh (1986) c^= 8 mm/sec  0.00 10  Figure 4.9  Time (sec)  100  1000  Pore Pressure Dissipations at McDonald Farm: Predicted versus Measured Dissipation curves recorded on the face of a 60° Piezocone from Gillespie, Robertson and Campanella (1988)  105 where the greatest unloading takes place and i s l e a s t important behind the sleeve.  No t h e o r e t i c a l solution presently a v a i l a b l e recognizes the  drop i n t o t a l stress (cone resistance)  that occurs when penetration i s  stopped.  4.6  Conclusions 1) Pore pressure response i s primarily c o n t r o l l e d by the l o c a t i o n  of  the porous  element.  The s i g n i f i c a n c e  of the element  location  depends on s o i l type and no single element l o c a t i o n best serves a l l purposes. chapter.  The v a r i a t i o n  i n measured values was discussed  i n this  S p e c i f i c d e t a i l s of the measurement system including element  compressibility were also discussed. 2)  Element  saturation  is  a  significant  problem  following  penetration  through desiccated  s o i l s ; i n addition, penetration  through  saturated  fine  also  element  desaturation. face  results  soils  may  cause  cavitation  and  In many cases, pore pressure measurement on the cone i n the generation  of p o s i t i v e  pore  pressures  and  eliminates t h i s problem. 3)  Pore  pressure  dissipation  rates  were  found  t o be  influenced by measurement location and procedural d e t a i l s .  highly  Dissipation  theory adequately accounts f o r the measurement l o c a t i o n i n normally to lightly  overconsolidated s o i l s but the stress r e l i e f associated  stopping penetration  with  and r e l i e v i n g the cone resistance may r e s u l t i n  misleading d i s s i p a t i o n rates when pore pressures are measured on the cone face.  Pore pressures measured behind the f r i c t i o n  l e a s t effected by t h i s problem.  sleeve are  106 CHAPTER 5. 5.1  INTERPRETATION OF PORE PRESSURE MEASUREMENTS  Introduction The previous chapter dealt with  cone design and t e s t  d e t a i l s that e f f e c t pore pressure data. care  must  be  exercised  i n order  interpreted i n a proper manner. CPTU  data  i s discussed  with  interpretation methods.  factors  effect  restricted  the pore  to specific  I t was shown that considerable  that  the data  collected  can be  In t h i s chapter the i n t e r p r e t a t i o n of an  emphasis on  pressure data i n t o the t r a d i t i o n a l based  procedure  integrating  cone t i p resistance and  I t w i l l be apparent  the  pore  friction  that so many s o i l  pressure data that i t s a p p l i c a t i o n must be soil  conditions and  subject t o measurement  details. There are some incentives f o r standardization of the pore pressure f i l t e r element l o c a t i o n ; easier comparison of data would be an obvious benefit.  Bearing i n mind, however, that there i s no "best" measurement  location  the s e l e c t i o n  of measurement  location  should  l o g i s t i c a l considerations and the ultimate a p p l i c a t i o n .  be based  on  Some of these  applications and necessary measurement d e t a i l s are outlined.  5.2  Cone T i p Resistance Corrections Other  simplest  than and  the establishment perhaps  most  of equilibrium pore pressures, the  important  application  of pore  pressure  measurements may be t o correct cone resistance measurements t o obtain a t o t a l stress measurement.  Since d i f f e r e n t cones respond d i f f e r e n t l y t o  the pore pressure acting behind the t i p they should a l l be corrected t o qiji  ( i n a manner now referred t o as net area r a t i o correction) by  107 q where  This  qc + (1 - a) * u2  T  <Jc  measured cone resistance  a  net area r a t i o (determined experimentally by loading assembled cone h y d r o s t a t i c a l l y )  u2  pore pressure measured behind t i p  alone may  Lunne,  et  justify  al.  measuring the pore pressure behind  (1986)  showed  that  much  of  the  scatter  the t i p . in  q^  measurements, taken with d i f f e r e n t cones, can be eliminated by net area r a t i o corrections.  Typical data from one s i t e are shown i n Figure 5.1.  This work cleary showed the importance of pore pressure corrections i n soft  clay.  discussed  Aas,  et  a l . (1986) using  the  same data  set  as  that  i n Lunne, et a l . (1986) show that much of the s c a t t e r i n  previously  published  cone  factor,  N, K  correlations  i s due  to  the  d i f f e r e n t net area r a t i o s of the cones used t o c o l l e c t g^-. values. Measurements of pore pressure taken on the face have sometimes been used f o r q  T  corrections, these values are f i r s t reduced by 10 to 20 %.  The wide v a r i a t i o n i n pore pressure d i s t r i b u t i o n around the cone i n a l l but  normally  total  consolidated s o i l s  stress correction  reduces the accuracy of q  i s made i n t h i s manner.  T  when the  Fortunately, those  s o i l s with a wide v a r i a t i o n i n excess pore pressures around the t i p also are generally overconsolidated. resistance and  q  T  These s o i l s have a higher cone  corrections are not as s i g n i f i c a n t .  measurements taken behind the sleeve, u3, the correct pore pressure, u2, observations Figure  4.8.  of  the  pore  t o use  pressure  Pore pressure  could be used t o c a l c u l a t e  for q  T  distribution  corrections using the previously shown i n  LEGEND A Average of Bat B BRE 5kN C BRE 50 kN D DELFT E FUGRO piezocone F FUGRO f r i c t i o n cone G FUGRO s u b t r a c t i o n cone M MCCLELLAND 10 cm N MCCLELLAND 15 cm U UBC No. 4 S UBC s e i s m i c cone K v d BERG f r i c t i o n cone L v d BERG piezocone WISSA W 2  2  Figure 5.1 Correction of Cone Resistance Data, Onsoy Site adapted from Lunne, Eidsmoen, Gillespie and Howland (1986)  109 5.3  S o i l C l a s s i f i c a t i o n From Dynamic Pore Pressures At the standard rate, 2 cm/s,  sands  and  coarser  conditions. generally materials  materials  Penetration takes  place  takes  into  place  fine  under  are penetrated  penetration i n medium grained clean under  sands,  partially  silty  drained  under completely  completely sands,  drained  and  silts  conditions,  finer  undrained  conditions.  An  example showing a l l three conditions i s shown i n Figure 5.2 which shows the r e s u l t s of two sand  unit  completely  from  2  drained  adjacent to  13  CPT m  p r o f i l e s from McDonald farm.  penetration  conditions.  Pore  takes  pressures  place  under  slightly  In the nearly  above  the  hydrostatic value are observed with the face t i p pore pressure element location.  These values are generally highest through the s i l t y layers  within the sand u n i t where l e s s drainage occurs.  A p a r t i a l l y drained  response i s a l s o observed from 13 to 15 m i n a f i n e s i l t y sand u n i t . When  penetration  is  stopped  to  add  push  rods  these  pressures are observed to decay i n l e s s than 30 seconds.  excess  pore  Penetration  pore pressures shown i n t h i s p r o f i l e are c h a r a c t e r i s t i c of most sands. I f the permeability i s s u f f i c i e n t l y low, and any pore pressure response i s observed, i t i s generally l e s s than hydrostatic behind the t i p and greater than hydrostatic on the face of the cone.  These pore pressures  can be useful to characterize the sand but are very small i n comparison to the cone resistance.  The clayey s i l t u n i t below 15 m i s penetrated  under completely undrained conditions, the pore pressure response shown i n Figure 5.2 soils.  i s c h a r a c t e r i s t i c of normally or l i g h t l y overconsolidated  The pore pressure values are highest on the face and decrease  with distance up the shaft.  A completely undrained response was,  in  110  Figure  5.2  Urrirained, Partially Drained, and Drained Response at the McDonald Farm Site  Ill t h i s case, confirmed by slowing the r a t e of penetration and observing no change i n the pore pressure measurement u n t i l rates where changed by two orders of magnitude, Campanella, et a l .  (1983).  The use of pore pressure parameters t o c l a s s i f y s o i l type has been proposed by Jones and Rust  (1982) and Robertson,  charts have been developed Figure 5.3  shows one  et a l . (1985).  from data c o l l e c t e d behind the cone t i p .  c l a s s i f i c a t i o n system f o r the i n t e r p r e t a t i o n of  s o i l type from cone resistance and pore pressure data. number of possible  factors that a f f e c t to  identify  resistance and  pore  These  a  soil  pore type  pressure data solely  pressure response.  on  With the great  i t was  not  the basis of the  Tip resistance and  found cone  friction  measurements were used to c l a s s i f y the material and pore pressure data were used to d i s t i n g u i s h d e t a i l e d stratigraphy and to confirm the cone resistance  and  friction  a p p l i c a t i o n of Figure 5.3  based  interpretation.  The  intended  i s f o r f i e l d c l a s s i f i c a t i o n of s o i l type, as  such i t does not use normalized resistance values. The detection of small s t r a t i g r a p h i c changes within a s o i l p r o f i l e may be easier with pore pressure data, which i s thought t o be dependent on a smaller zone of s o i l than t i p or f r i c t i o n data. in  overconsolidated s o i l s  I t appears that  the detection of s t r a t i g r a p h i c changes i s  best made with the pore pressure element on the cone face. from  the  Imperial v a l l e y  in California,  Figure 5.4,  An example  shows much more  d e t a i l within the clay unit f o r the pore pressure element on the face than behind the t i p .  In normally consolidated s o i l s i t appears that  e i t h e r l o c a t i o n gives s i m i l a r d e t a i l .  For example Figure 5.2  shows  pore pressure measured at 2 locations, where nearly s i m i l a r d e t a i l i s  112  Zone 1 2  3  4  5  6 7 8  9  10 11 12  S o i l Behaviour Type s e n s i t i v e f i n e grained organic m a t e r i a l clay s i l t y c l a y to clay clayey s i l t to s i l t y clay sandy s i l t to clayey s i l t s i l t y sand to sandy s i l t sand to s i l t y sand sand g r a v e l l y sand to sand very s t i f f f i n e grained* sand to clayey sand*  * overconsolidated or cemented.  Figure 5.3 Soil Behaviour Type Classification from Campanella, Robertson, and Gillespie (1986)  10 - 500 2 - 2 0 10 - 100 5 - 10 2 - 5 1 - 2 .5-1 0 -.5 drained drained unknown unknown  113  Figure 5.4 Pore Pressure Response at Wildlife Site from Campanella, Robertson and Gillespie (1986)  114 observed i n a l l p r o f i l e s .  Note that the p r o f i l e obtained from the  face  t i p element i s also highly influenced by the e f f e c t of stopping to add a d d i t i o n a l cone rods.  Within an overconsolidated  s o i l p r o f i l e , i f the  presence of s l i g h t v a r i a t i o n s i n s o i l type i s of i n t e r e s t , i t appears that the  face t i p element l o c a t i o n i s most u s e f u l .  .consolidated  sites  pore  pressure  measurements  At most normally  made  at  different  locations show s i m i l a r d e t a i l .  5.4  S o i l C l a s s i f i c a t i o n From Pore Pressure Dissipation In s o i l s that generate pore pressures, e i t h e r higher or lower than  the hydrostatic value, an index of the permeability  or g r a i n s i z e can  be obtained from the rate of decay of the excess pore pressure.  The  excess pore pressure d i s t r i b u t i o n i n granular s o i l s i s complex, unknown and highly dependent upon s o i l type; therefore, t h e o r e t i c a l d i s s i p a t i o n solutions s i m i l a r to those used i n f i n e grained s o i l s are not f e a s i b l e . An  alternative  means  of  interpreting  dissipation  rates  empirically correlate d i s s i p a t i o n rates to material type,  is  permeability,  percentage f i n e s or some other useful characterization of s o i l One  type.  expression of the rate of decay, which has been found to be useful  i s the time t o 50 % equalization of excess pore pressure, t$Q. values  are  resistance  useful and  in  friction  distinguishing ratios.  soils  Figure  that  5.3  have  50  % d i s s i p a t i o n , which were compiled  These  similar  tip  i s augmented with  the  addition of t y p i c a l pore pressure decay rates, expressed as the for  to  from a  large  time  variety  of  sites. A d i f f i c u l t s o i l c l a s s i f i c a t i o n problem commonly encountered i s the  115 distinction  of s i l t s  and  stiff  clays.  Very  often, due  to  accuracy  problems with f r i c t i o n data, these two s o i l s can not be distinguished. Application of the rates of decay of the excess pore pressure can then be used t o c l a r i f y the interpretation.  Guidelines f o r the s e l e c t i o n of  s o i l type based upon pore pressure d i s s i p a t i o n rates are included i n Figure 5.3.  These averaged values are compiled from a large number of  s i t e s and are r e s t r i c t e d to decays rates recorded behind the t i p with 10 cm  2  cones.  The location of the pore pressure measurement system and  procedural d e t a i l s must also be dissipation  rates.  Very  considered i n the i n t e r p r e t a t i o n of  often the drop  i n total  stress  causes  an  apparent very rapid decay i n excess pore pressure measured on the face of  the cone.  This can be misinterpreted as a d i s s i p a t i o n i n coarse  grained materials. use  Inspection of the drop i n cone resistance and the  of a d i f f e r e n t measurement location can document or reduce  difficulty.  The  integration of pore pressure decay rates and  this shear  wave v e l o c i t y data i s further discussed i n chapter 7.  5.5  E f f e c t of S o i l S e n s i t i v i t y on Pore Pressure Measurements In  for  overconsolidated s o i l s there has been an observed general trend  very high pore  pressures  behind  pressures on  the  face.  the  Figure  materials of v a r i a b l e s e n s i t i v i t y .  face and 5.5  low  to negative  shows r e s u l t s  obtained  q  q  B  q l  = (u - u ) / ( q Q  T  in  The data are presented i n terms of  the pore pressure parameter B , Senneset and Janbu (1984), where B  pore  - OV)  and i s calculated using the pore pressure on the face, u l  2.0 -  116  > •  cr x°<9> °.  o =?  Cx  ,.0  L  +  x1  O +  +  *  ****** & * * t  cr CQ  0.0  I  I I I  II 2  I 3  I I I  o  *** *  *  I I I I  I 4  I  o  I  I I  II I 5 -  I  I I  I I I  6  I  I 7  I I  I  I  II 8  o o  I I I  I  I I I I  9  1  I 0  2.0  >  o *  "  X  Z> oo  C\J  cr  CQ 0.0  | i i i i | i l O y ^ f q a i ->i ^ |»i I»I i |»i i i i» | i i i i | i i i i | i i i i | i i i i | 1 2 3 4 5 6 7 8 9 1 0  1.5  LEGEND: * langley Sites, $ Brent Cross:Lunne et al.(1986). O Haney, • Gloucester, St Marcel, Varennes, NRCC, STP, all Konrad & L a w ( l 9 8 7 ) 0 Onsoy,-s!rSt.Alban:Roy et al.(l 982), + Boston Blue Clay:Baligh & Levadoux(1980) x Haga, A Drammen, * McDonald Farm  > to i  cr O ZD I  CO =2.  0.5 - f ' * V * * * **  CO cr CQ  <  n  *  b  °  o o* o  o  o  0  *  5.5  I 1  1  '''I' 2  o o  o  *  -0.5  Figure  0  ' ' I  II I 3 -  I I  4  I  I I I I  II 5  I I I  OCR  II 6  I I I  Pore Pressure Parameters Bg vs OCR  II 7  I I  I  II 8  I  u  9  ''i' I 10  117 Bg  2  i s calculated using the pore pressure behind the t i p ,  u2  Bq  3  i s calculated using the pore pressure behind the sleeve, u3  For any given stress h i s t o r y a wide v a r i a t i o n i n e i t h e r of the pore pressure  parameters  can  parameter Bg with OCR r a t i o may  be  seen.  The  variation  i n pore  pressure  has lead to the suggestion that a pore pressure  lead to a good c o r r e l a t i o n f o r stress h i s t o r y .  The e f f e c t of  s e n s i t i v i t y , and to a l e s s e r degree s t i f f n e s s r a t i o , i s t o obscure t h i s correlation.  Whereas  low  or  negative  pore pressures  are  measured  behind the face i n highly overconsolidated clays (for example, Figure 5.4)  penetration i n s e n s i t i v e clays generally r e s u l t s i n p o s i t i v e pore  pressures regardless of measurement l o c a t i o n .  As a general trend i t i s  observed  tends  that  for  any  stress  history,  Bg  to  increase  with  s e n s i t i v i t y but t h i s aspect was d i f f i c u l t to quantify because of a lack of s e n s i t i v i t y data c o l l e c t e d i n a s i m i l a r manner.  5.6  Interpretation of CPTU Data For Stress History Stress h i s t o r y has been shown to a f f e c t the pore pressure response.  An evaluation of the c o r r e l a t i o n between Bg and OCR was performed where good q u a l i t y f i e l d data were available. pressure parameters B g The  data  decreases  shown with  lf  Bg ,  i n Figure  2  5.5  increasing OCR  usefulness of t h i s approach.  Bg  3  against the best estimate of  indicate the  Figure 5.5 presents the pore  that although  scatter  Jamiolkowski,  i n the  data  B  q  OCR.  generally  reduces  the  et a l . (1985) reported a  s i m i l a r scatter i n the Bg-OCR r e l a t i o n s h i p when data from several s i t e s were  considered.  Neither  of  the  pore  appears to give u s e f u l indications of OCR  pressure from B  a  element locations  data.  118 Other pore pressure parameters investigated ratios The  and  differences,  r a t i o s and  include pore pressure  each with d i f f e r e n t normalizing  parameters.  differences were thought to be useful a f t e r observing  that pore pressure measurements behind the t i p were much more s e n s i t i v e t o stress h i s t o r y than those on the  cone face.  S u l l y , et a l . (1988)  proposed the use of a normalized pore pressure differences. (ul-u3)/o' thesis.  v  AUI /  and  A U 3 and  AUI /  AU2  The r a t i o s  were investigated  in this  These r a t i o s were observed to be highly dependent upon stress  h i s t o r y at some s i t e s . stress h i s t o r y was  The a p p l i c a t i o n of these parameters t o predict  tested by p l o t t i n g the r a t i o s against best estimates  of stress h i s t o r y .  Figures 5.6  and 5.7  difference and poire pressure r a t i o . r e l a t i o n s considerable scatter was  show a normalized pore pressure  In a s i m i l a r manner as the Bq-OCR  observed.  The e f f e c t s of parameters  such as s o i l s e n s i t i v i t y appear to obscure those of s t r e s s h i s t o r y . A  more  correlation  successful of  normalizing CPT but cone  approach  normalized  cone  to  determine  resistance  to  data i s somewhat controversial  OCR  is  OCR.  The  the  direct  method  i n cohesionless  soils  extensive t e s t i n g at deep clay s o i l s i t e s c l e a r l y indicates resistance  stress.  should  Figure 5.8  be  normalized  with  the  Only those s i t e s with well described  used  correlation.  effective  stress h i s t o r y were  Although there i s some v a r i a t i o n between  s i t e s a reasonable i n d i c a t i o n of stress h i s t o r y can Figure 5.8.  that  shows a compilation of r e s u l t s from a v a r i e t y of  clay s i t e s . i n the  vertical  of  be  obtained from  The c o r r e l a t i o n between stress h i s t o r y and normalized cone  resistance i s expected from consideration  of normalized strength  shear strength calculations from cone resistance.  and  Assuming the shear  20n  LEGEND: * $ o if *  > to  10H  3  Langley S i t e s Brent C r o s s : Lunne e t al.(1986) Haney S t . A l b a n : Roy e t a l . (1982) McDonald Farm  oo o o oo  < '* v* 1 i  2  i  i  + i  I i i  i  i  I i  3  i  i i  |  4  i  i  i  i  5  |  i i  i  i |  6  i  i  i i  i  i  i  i i  i  8  7  i  i  i  i  10  OCR  20  n  LEGEND: * $ O •ft * A x  > 3  lo-  o  Langley S i t e s Brent C r o s s : Lunne e t al.(1986) Haney S t . A l b a n : Roy e t . a l . ( 1 9 8 2 ) McDonald Farm Drammen Haga  °° o o  o*  x  ci  i  i  i  i  I i  2  I  i  i  i  3  i  |  i  i  4  i  i  i  1  1  1  1  5  I  1  6  1  1  1  I  7  1  1  1  1  I  8  OCR  Figure  5.6  Normalized Pore Pressure Difference  1  1  1  1  I  9  1  1  1  1  1  I  0  5-  o  4-  o  o <n> LEGEND:  ro  o +  .+  o *  1 H 0  * O * * +  +  i iiiiiri i | 2 3 ft  i ii Ii iiiIiii il iiiii 7 5 6 . r~—f OCR  y s  i  Langley Sites Haney St.Alban: Roy et al.(1982) McDonald Farm Boston Blue Clay: Baligh & Levadoux (1980)  iiiii i ii iiii i 10 8  /—I  5  LEGEND: * O •k * A x + 0  4H CM => 3 <  oo O  x  x  x  0-  o  A  2  Figure  5.7  c x  O  I I I I [ I I I I  3  II  I I I  4  I  I  Langley Sites Haney St.Alban: Roy et al. (1982) McDonal d Farm Drammen Haga Boston Blue Clay: Baligh 4 Levadoux (1980) Onsoy  I I I  5  II  I I I  6 OCR  1I  I I I  7  II I 8  Co  I I [ I I I I  9  I1  I I I  I 10  Pore Pressure Ratios vs OCR O  20-  Plasticity Index > 20 (qp - OV) = 4.24 * (OCR)0 . 8 6 • X  10 -  > b  Plasticity Index < 2 0  i  ( Q j - C y ) = 2 . 7 3 * (OCR) 0  r-  80  CD O  c  CO <*-»  w w  CD  or  CD  c o O  LEGEND:  < P l a s t i c i t y Index > 20  CD  * * * * •  Gloucester: Konrad & Law (1987) St Marcel: Konrad S Law (1987) Varennes: Konrad * Law (1987) NRCC: Konrad « Law (1987) STP: Konrad & Law (1987) On soy  <f + x *  S t . A l b a n : Roy et a l . (1982) Boston Blue C l a y : Baligh & Levadoux (1980) Haga McDonal d Farm  CD N CO  E  P l a s t i c i t y Index < 20  "i  r  10  OCR  Figure  5.8  Normalized Cone Resistance vs OCR  122  strength  of normally  consolidated  and overconsolidated  clay can be  related by ( s  u  /  oVoc  =  CT' )NC * OCR  (Su /  111  v  and undrained strength calculated from cone resistance by su = ( q T  then  (q T  ov)  /  ov)  / a' = (N * v  N  /  K  K  CT' ) ) V  NC  * OCR  M  P l o t t i n g the logarithm of normalized net bearing against the logarithm of OCR results i n a slope, m, and the intercept the product of N and K  the normalized  normally  consolidated strength  ( s / o"' ) . u  v  Figure  NC  5.7 shows an increase i n normalized cone resistance with OCR raised t o the power of approximately  0.8 and an intercept of 2.75 t o 4.25.  The  dependence of stress history shown by an m value of 0.8 i s reasonable as i s the intercept which i s close t o a calculated value of 4 from the product of NJJ of 16 and (su /  CT' )NC  O  F  V  0.25.  Each of which represent  commonly used values, Jamiolkowski, e t a l . ( 1 9 8 5 ) . Allowance f o r s o i l type, indexed by p l a s t i c i t y i n the manner shown i n Figure 5.8, can improve the correlation between stress h i s t o r y and undrained higher  shear strength.  intercept as shown  normalized normalized N  K  with  Higher p l a s t i c clays are expected t o have a  strength  i n Figure  increase  with  5.8 given  plasticity.  that  both  N  K  and  The v a r i a t i o n i n  strength with p l a s t i c i t y i s well known but the increase i n  increasing p l a s t i c i t y  i s a more controversial finding  first  reported by Aas, et a l . (1986) and reversed e a r l i e r findings reported by Lunne, e t a l . ( 1 9 7 6 ) . Konrad and Law (1987) proposed a pore pressure based c o r r e l a t i o n for OCR that also requires pressuremeter data.  The parameter proposed  123 by Konrad and Law are  included  (1987) was i n s e n s i t i v e to stress h i s t o r y .  i n Figure 5.8  and  a much better  These data  indication  of  stress  h i s t o r y was observed.  5.7  Interpretation of CPTU Data For Undrained Shear Strength Undrained  shear strengths have, i n the past, been estimated from  cone resistance measurements alone using s  u = (9c ~ °v) / K N  Pore pressure measurements have been incorporated into the equation by using the t o t a l  cone resistance,  q>p  .  As  already discussed, t h i s  correction has been found to reduce the scatter obtained from cones of different  design, Lunne, et a l . (1986).  Pore pressure measurements  behind the t i p are best f o r t h i s application. Another  application  of  pore  pressure  measurements  for  the  c a l c u l a t i o n of undrained shear strength was suggested by Senneset, et al.  (1982).  They defined the e f f e c t i v e cone resistance and  suggest  determining the undrained shear strength from s  u = (9c  _  u  ) / KE N  where qc = measured cone resistance u = dynamic pore pressure N  KE  =  e f f e c t i v e cone factor  Robertson and Campanella resistance calculation.  which  was  (1983) emphasised found  Lunne, et a l .  to  be  the use of the t o t a l cone  extremely  (1985) showed that  important  in  this  varied from 2 t o 12  as a function of stress history which was also r e f l e c t e d i n Bg.  Figure  5.9, compiled i n t h i s study, shows a wide v a r i a t i o n i n Nj^ and no  124  LEGEND:  0 Ons0y  30  A a * + x  -i  D r a m m e n plastic Drammen lean McDonald Farm Langley R e s e a r c h Site L a n g l e y 2 3 2 U p p e r Site  20H  3  LU  10X X  x  t x taS^|i*Q  o I  i i i i i i i i i  r w ^ i  1.0  0.0  Bqi=(U1-Uo)/(qra ) v  Figure  5.9  Cone Factor Nj^ vs  2.0  125 apparent trend with Bg.  For any given s i t e , however, a good  c o r r e l a t i o n between Nj^g and Bq i s generally observed.  The e f f e c t s of  s e n s i t i v i t y and s t i f f n e s s r a t i o r e s u l t i n more scatter i f more than one s i t e ( s o i l type) i s considered. The  primary d i f f i c u l t y with the e f f e c t i v e resistance approach i s  that i n s o f t clays the cone resistance and the measured pore pressure are of very  s i m i l a r value.  measurement r e s u l t  When subtracted, any  errors  i n either  i n a large v a r i a t i o n i n the parameter (qij-u) and  hence i n the calculated undrained shear strength. Additional  approaches  that integrate pore  pressure measurements  into the interpretation of CPTU data f o r s o i l strength include the use of the Bg parameter t o select the most appropriate pore pressure factor N , AU  where N  = (ul - u ) / s  A U  Q  u  A reasonable c o r r e l a t i o n between N  A U  and Bq! i s shown i n Figure  5.10  which indicates that pore pressure based parameters may successfully be integrated  into  calculations.  the  The  interpretation  data i n Figure 5.10  of  CPTU  data  for  strength  l i m i t e d the drawing of  firm  correlations at t h i s time. A more reasonable application of pore pressure data was  originally  proposed by Lunne, et a l . (1985), based on t h e i r observation that the Bg parameters correlated with stress history. hypothesised that the B most appropriate Njrj.  q  Lunne, e t a l . (1985)  parameter might help i n the s e l e c t i o n of the  Using data from several s i t e s t h i s approach was  investigated f o r pore pressure data c o l l e c t e d on both the cone face and behind the t i p .  Figure 5.11 shows that there i s s t i l l considerable  LEGEND: 0 Ons^y A Drammen plastic a Drammen lean * McDonald Farm + Langley Research Site x Langley 2 3 2 Upper Site  30-i  Z3 CO  o i  20-  * vS * **** +  W  5  ±K  II  <  + + +++  10-  0 0.0  O A  5?  x  A  *  XX  *x  x x X  n—i—i—i—i—i—|—i—i—i—i—r  1.0 BqHU1-Uo)/(q -G ) T  Figure  5.10 Cone Factor N  A U  vs  v  i—i—r 2.0  LEGEND: 0  13 CO  > to r—  3 cti  Ons0y  Drammen plastic a Drammen lean * McDonald Farm + Langley Research Site x Langley 232 Upper Site it Haga o St.Alban (Roy et el. 1982)  25  2 0 -  15  10  u_  CD §  5  O  00.0  T  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1.0  1  1  2.0  Bq1=(U1-Uo)/(q cyv) r  2 5  n  CO  >  2 0 -  cr ll  15-  0 S  CO  10H  x  X  A  *  A  x  CD  S  °  •ft  *x x x  IV*  *  5  o  0i 0 0  i  .  i  i  i  i  i  i  i  i  i  i  i  i  i  i  1.0 0  5.11  Cone Factor Nj^p vs Bq  i  i  i  2.0  B q 2 = ( U 2 - U ) / (q -o ) Figure  i  l7  T  Bg2  v  128 v a r i a t i o n i n the cone f a c t o r N^p from Bg parameters when d i f f e r e n t s i t e s are considered.  Local experience  or c o r r e l a t i o n s developed  at  one s i t e appear t o give very promising r e s u l t s with t h i s approach. An  alternative  strength was excess  means  suggested  f o r the  by  determination  of  undrained  shear  Campanella, e t a l . (1985) using the large  pore pressure generated  during cone penetration t e s t i n g .  In  s o f t clays and l i g h t l y overconsolidated clays the cone resistance can be  very  small, t y p i c a l l y  less  than  1 % of the  load c e l l capacity.  Small errors i n r e l a t i o n to the capacity, e s p e c i a l l y those r e l a t e d to zero load s t a b i l i t y , may measurement.  In the same clay, however, pore pressure values may  large percentage al.  r e s u l t i n large errors i n the cone resistance  of the pore pressure transducer capacity.  be a  Lunne, et  (1986) i n an evaluation of the accuracy of cone penetration t e s t  data  report that the pore pressure measurements taken  i n s o f t clays  were considerably more repeatable than e i t h e r the cone resistance or the  friction  empirical shear  measurements.  expression  strength w i l l  Provided  i s used, be  an  appropriate t h e o r e t i c a l  therefore, the  estimate  of  or  undrained  inherently more accurate using pore pressure  data. A  semi-empirical  solution  was  proposed  by  Massarsch  and  Broms  (1981), based on cavity expansion theories but included the e f f e c t s of overconsolidation  and  sensitivity  parameter at f a i l u r e , Af. r a t i o , charts were developed in  Figure  5.12.  Clearly  by  using Skempton's pore  pressure  Incorporating the dependence of s t i f f n e s s to determine N , Au  a knowledge of the  these charts are shown shear  modulus or  p l a s t i c i t y index, PI, would a s s i s t i n the estimate of the undrained  the  Saturated Clays  A p p r o x i m a t e A f Range  Very s e n s i t i v e t o quick Normally consolidated Lightly overconsolidated Highly overconsolidated  Figure 5.12 Cone Factor N from Campanella, Robertson, and Gillespie (1986) AU  1.5 0.7 0.3 -0.5  -  3.0 1.3 0.7 0  130 shear strength. during  cone  The addition of shear wave v e l o c i t y measurements  penetration  testing  measure of the shear modulus.  promised  to  offer  an  independent  This approach i s discussed further i n  chapter 7. The tendency f o r low or negative pore pressures measured behind  the  t i p i n i n s e n s i t i v e overconsolidated clays r e s t r i c t s the a p p l i c a t i o n of t h i s technique 5.12  to normally  or l i g h t l y overconsolidated clays.  allows f o r the application of pore pressure data c o l l e c t e d on the  face i n a wider range of s o i l types. 5.12  Figure  Although the charts i n Figure  are based on cavity expansion theories, they are  semi-empirical.  The charts do, however, provide a r a t i o n a l means of s e l e c t i n g the cone factor N  .  A U  vary with OCR,  The charts c l e a r l y show how  the cone f a c t o r N  A U  will  s e n s i t i v i t y and s t i f f n e s s .  An additional approach was proposed by Keaveny and M i t c h e l l (1986) who  propose an a l t e r n a t i v e e f f e c t i v e stress determination  parameters.  The method requires estimates  of OCR,  of strength  Af, and K Q and i s  very s e n s i t i v e to K Q .  5.8  Liquefaction Resistance Several investigators have shown that pore pressure response may  an  index  of  hypothesised,  liquefaction and  susceptibility.  showed data  supporting  Schmertmann the  (1978)  be  first  idea, that loose sands  might generate p o s i t i v e pore pressures and dense sands might generate negative pore pressures during cone penetration.  As part of t h i s study  several investigations were performed before and a f t e r compaction. s i t e investigated, No.  6 Road i n Richmond, described i n section  One 3.6,  131 was compacted by vibro-replacement t o a depth o f approximately 20 m. At t h i s s i t e CPTU r e s u l t s , shown i n Figure 5.13, generally resulted i n pore pressures becoming more negative a f t e r compaction. c l e a r , however, with s o i l s  I t i s not  such as those shown i n Figure 5.13 that  behave i n a nearly drained manner, i f the change i n pore pressure response i s due t o a change i n permeability or a change i n dilatancy. The e f f e c t s of compaction would be expected t o a f f e c t both parameters. I f the void r a t i o change resulted i n response changing from drained t o p a r t i a l l y drained, i t may be expected that the pore pressure response could change t o a negative value. have  resulted  i n greater  dilation.  Alternatively,  d e n s i f i c a t i o n may  Interpretation  of the o v e r a l l  behaviour using other cone channels does not c l a r i f y the issue.  The  cone resistance increases indicates that density improvements have been made.  The proportionally higher f r i c t i o n increases might be explained  by l a t e r a l  stress increases due t o compaction.  Surprisingly,  little  change i n shear wave v e l o c i t y was observed. Attempts soils  a t using the measured pore pressure response  have been made because of the grain  resistance  measurements.  The  size  dependence  in silty  dependence o f cone  of  cone  resistance  measurements on grain s i z e makes the use of chamber t e s t data obtained using  clean medium grained  sand d i f f i c u l t .  A compilation  o f cone  resistance and pore pressure measurements a t various sand s i t e s , some of which are known t o have l i q u e f i e d , i s shown i n Table 5.1.  A clear  p i c t u r e o f the l i q u e f a c t i o n s u s c e p t i b i l i t y can be seen from the cone resistance  measurements,  a l l sites  known t o have  consistently low normalized cone resistance.  liquefied  S i t e s that have  show a  LEGEND:  Before compaction After compaction#1 After compaction#2  Figure  5.13  Pre and Post Compaction Profiles at the No. 6 Road Site  SITE  AVERAGE SIGN OF NORMALIZED DYNAMIC PORE RESISTANCE PRESSURE RESPONSE (q /fj ') °n f a c e behind t i p  SOIL TYPE  T  v  S i t e s known t o have L i q u e f i e d Wildlife  post l i q u e f a c t i o n  45  + ve  - ve  Heber Rd.  post l i q u e f a c t i o n  55  + ve  - ve  Nerlerk prior to liquefaction Reference: Sladen e t a l . (1985)  70  free  draining  Molikpaq p r i o r to liquefaction 1-65 Reference: J e f f r i e s (1988)  50  free  draining  S i t e s known o r c o n s i d e r e d not t o have l i q u e f i e d Brenda Dam  hydraulic  McDonald Farm  fill  150  dry t o moist  F r a s e r r i v e r sand  100  + ve  - ve  No. 6 Road;  F r a s e r r i v e r sand  145  + ve  - ve  Knight S t .  F r a s e r r i v e r sand  110  + ve  - ve  Annacis  F r a s e r r i v e r sand  100  + ve  - ve  Tuk Hrbr.  Beaufort sand  175  free  Richards Island  Beaufort sand  150  + ve  - ve  Schoolhouse  Beaufort sand  170  + ve  - ve  draining  Note: S i g n o f dynamic pore p r e s s u r e r e f e r s t o v a l u e i n r e l a t i o n t o the s t a t i c pore p r e s s u r e v a l u e . Values shown as + ve mean t h a t the pore p r e s s u r e was h i g h e r than s t a t i c .  Table 5.1  Normalized Cone R e s i s t a n c e and Pore Pressure Response i n Sand  134 l i q u e f i e d a l l have normalized cone resistance l e s s than 70. other  On the  hand, no c l e a r d i s t i n c t i o n between the sands emerges from the  pore pressure sands,  response.  pore pressures  I t appears that  measured behind  even i n loose  the t i p are negative  hydrostatic value due t o the large stress r e l i e f area.  Measurements  positive  taken  of the s t a t i c  compressive  stresses  on the face  value  as would  associated  with  liquefiable  associated with t h i s  are, with  few  be expected  this  of the  area.  exceptions,  from  the high  As explained  in  chapter 4 i t appears that the d e t a i l s of the measuring system are often the key t o i n t e r p r e t a t i o n of pore pressure response. The magnitude of the pore pressure gives a clue t o the reason that cone resistance i s lower i n s i l t y sands than i t i s i n clean sands. possible explanation was thought t o be the higher pore pressure penetration  through s i l t y  A  during  sands which reduced the e f f e c t i v e s t r e s s .  The magnitude o f the pore pressure  i s very small, however, compared t o  the cone resistance and i t s influence on reducing the cone resistance is  small.  showed very hence  Repeated soundings at d i f f e r e n t rates, G i l l e s p i e little  drainage.  (1981),  cone resistance dependence on changes i n rate and A more l i k e l y  explanation  i s that  the increased  compressibility of the s i l t y sand i s the dominant f a c t o r reducing the cone  resistance  compared  t o that  of a  clean  sand.  Compressible  materials become compressive at low stress l e v e l s and have lower cone resistance than l e s s compressible materials. sands  appears  to  be  as  much  a  Cone resistance i n s i l t y  function  of  compressibility  c h a r a c t e r i s t i c s as strength c h a r a c t e r i s t i c s . An  a l t e r n a t i v e means of using  pore pressures  to assist  i n the  135 i n t e r p r e t a t i o n of l i q u e f a c t i o n resistance of sands i s t o use the pore pressure  response  t o a i d the  cone resistance  based  interpretation.  Interpretation of cone resistance f o r l i q u e f a c t i o n resistance has been proposed  by Robertson  (1985) f o r clean sand with D50  and Campanella  greater than 0.25 ram and  f o r s i l t y sand with D  l e s s than 0.15,  50  by  Seed and De Alba (1986) f o r sand with D50 of 0.25 ram, and by Shibata and  Teparaksa  values. made. all  (1988)  for a  range  of  sands  specified  by  their  D  50  A l l of these methods require that an estimate of g r a i n s i z e be The  solutions are s e n s i t i v e t o grain s i z e v a r i a t i o n s  because,  other factors held constant, with a decrease i n g r a i n s i z e below  0.25  mm  there appears t o be a increase i n l i q u e f a c t i o n resistance f o r  the same cone resistance.  An accurate i n t e r p r e t a t i o n of grain s i z e i s  best made using samples c o l l e c t e d across depth i n t e r v a l s i d e n t i f i e d to be  critical  by  the  CPT  profile.  An  alternative  interpretation i s  sometimes possible using the pore pressure response. different  t  5  values  0  characteristics.  The  at  sand  sites  with  Table 5.2 shows  known  grain  size  data c o l l e c t e d at these s i t e s i n d i c a t e that a  drained response i s only observed at s i t e s with clean sands having a D  50  greater than 0.20  mm  and  l e s s than 5 % f i n e s .  Knowing that a  response i s drained or p a r t i a l l y drained can therefore be used as a guide t o s e l e c t the most appropriate resistance curve. above  methods  include  greater than 0.25 mm,  a  resistance  curve  f o r sands  A l l of the having  D50  a  a drained CPT response i s a reasonable i n d i c a t i o n  that t h i s curve should be selected.  A p a r t i a l l y drained response would  indicate that a lower resistance curve could be used. and Campanella resistance curve f o r sands with D  50  The  Robertson  l e s s than 0.15  mm  Depth Interval  Site  t (sec)  DgQ (ram)  5  0  D (mm) 10  S o i l Type  Heber Road 2  2-4 m  30-60  .10  fine SAND  Heber Road 6  3-6 m  drained response  .20  fine SAND  Wildlife PC2A  2-7 m  drained response  .15-.25  fine SAND  McDonald farm  2-13 m  10-30  .25  2-5% fines  fine-med. SAND  13-15 m  30-60  .15  10% fines  fine SAND trace s i l t  2-22 m  drained response  Holmen  .45-.90  .15-.30 med.-crs. SAND  .20-.50  .06-.15 fine SAND trace s i l t  22-26 m  10-30  Nerlerk fill  0-10 m  drained response  .25  3-5% fines  SAND trace silt  Molikpaq 1-65 core  4-20 m  drained response  .25  2-3% fines  SAND trace silt  note:  Pore pressures recorded behind t i p for a l l traces  References:  Heber Road sites, grain size: Youd and Bennett (1983) Wildlife site, grain size: Bennett et a l . (1981) Nerlerk site: Sladen et a l . (1985) Molikpaq 1-65 core: Jeffries (1988)  Table 5.2 Pore Pressure Response at Sand Sites  137 appears response  t o be appropriate i n sands through which a p a r t i a l l y drained i s observed.  Teparaksa,  based  The resistance curves proposed  on  the  most  extensive  data  base,  d e t a i l e d analysis of l i q u e f a c t i o n resistance based on 0.05  mm  and  normalized  cone resistance.  by Shibata and permit  more  i n steps of  D 5 u  Dissipation  a  rates do  not  appear to be a s u f f i c i e n t l y accurate means of d i s t i n g u i s h i n g the small v a r i a t i o n s i n grain s i z e allowed with the method proposed by Shibata and  Teparaksa.  In  addition,  pore  pressure  dissipation  rates are  c o n t r o l l e d by permeability which i s l a r g e l y a function of the grain size  of  the  resistance  finer  curves  portion,  are  often  expressed  shown t o vary  with  by  D ,  whereas  the  Nevertheless,  the  10  D . 50  d i s t i n c t i o n of a drained response and i t s appropriate resistance curve i s i n many cases s u f f i c i e n t . D  50  greater than  0.25  mm  and  The Robertson and Campanella D  50  less  than  0.15  mm  curves f o r  appear t o  be  reasonably e a s i l y selected based on the pore pressure response i n the field.  More d e t a i l e d analysis such as that proposed  by Shibata and  Teparaksa c l e a r l y requires grain s i z e information from sampling.  5.9 Conclusions 1)  One  important  application  correction of cone resistance.  The  of  pore  pressure  account  f o r much of  is  This correction has  the v a r i a t i o n  i n cone  readings  obtained with d i f f e r e n t cones at selected s o f t clay t e s t s i t e s . r e s u l t of t h i s correction a better understanding of N been achieved.  the  correction i s p r i m a r i l y required  because of the lack of uniformity i n cone design. been shown t o  data  K  As a  c o r r e l a t i o n s has  138 2) Pore pressure response i s dominated by drainage c h a r a c t e r i s t i c s and can therefore be used as an i n d i c a t i o n of s o i l type.  Within the  range of f i n e grained s o i l s , e s s e n t i a l l y i d e n t i c a l s t r a t i g r a p h i c d e t a i l is  indicated  with  overconsolidated  a l l pore  soils,  pressure  however, pore  measurement  locations.  pressure response  In  on the cone  face was found to give the most d e t a i l e d record. 3) Pore pressure d i s s i p a t i o n rates were found to be a u s e f u l index of  soil  type  but  characteristics. soft  silts  and  cannot  be  used  to  identify  exact  grain  size  A common interpretation problem i s the d i s t i n c t i o n of overconsolidated clays.  Friction  readings  i n these  s o i l s are often i n s u f f i c i e n t l y r e l i a b l e f o r c l a s s i f i c a t i o n purposes but pore pressure decay rates can be used t o d i s t i n g u i s h these s o i l s . 4) A study of the usefulness of Bg pore pressure parameters as an index of stress h i s t o r y was generally  decreased  with  performed. increasing  I t was stress  found that although Bg history  e s p e c i a l l y s o i l s e n s i t i v i t y , masked the c o r r e l a t i o n . approach t o determine  OCR  appears  normalized cone resistance to OCR. resistance with s o i l p l a s t i c i t y was  to be  other  factors,  A more successful  the d i r e c t  correlation  of  The v a r i a t i o n of normalized cone shown and was shown i n section  5.6  to be consistent with previous publications regarding the v a r i a t i o n of the cone factor N 5) The was  at  felt  t o c a l c u l a t e undrained shear strength  The use of Bg t o a s s i s t i n the s e l e c t i o n of Nj^; was  sites  variation i n % E was  with s o i l p l a s t i c i t y .  possible use of  investigated.  assessed  It  K  with  high  quality  data.  At  these  sites  was observed and no apparent trend with Bg was  that the  subtraction of two  very  a wide found.  s i m i l a r measurements  139 likely  amplifies small  errors  associated with  CPT cone resistance  measurements i n s o f t clay. 6) The use of Bg parameters t o a s s i s t i n the s e l e c t i o n o f N N  KT  d°  e s  n  considered  °t  appear  together.  promising Site  when  specific  several  different  A U  or  s i t e s are  correlations are, however, much  better. 7) A pore pressure based means of c a l c u l a t i n g undrained strength was presented.  This method was found  very  useful  i n normally or  pore  pressures  l i g h t l y overconsolidated clays. 8)  In  silty  or  fine  sand  soils  penetration may be higher or lower than the s t a t i c values. the  response  during  cone  The sign of  i s a function only of the measurement d e t a i l s .  Pore  pressures on the face of the cone i n granular s o i l s were found t o be p o s i t i v e with only very few exceptions. tip  were found  response  t o be l e s s  than  static  Pore pressures behind the cone i n almost  a l l cases.  This  r e s u l t s from the very large stress reduction associated with  the area immediately behind the cone. 9) Pore pressure response, drained or undrained, can be h e l p f u l i n determining the most appropriate CPT based l i q u e f a c t i o n analysis.  140 CHAPTER 6. 6.1  FACTORS AFFECTING SHEAR WAVE VELOCITY DATA  Source C h a r a c t e r i s t i c s  6.1.1  Hammer Beam Shear Source  I n i t i a l work with the seismic cone penetrometer Rice  (1984).  Laing  sources and receivers The  (1985)  and weighted  comparison.  This source  beam  source  i s used  was  used  as a  extensively both  environments. standard f o r  f o r downhole and  t o a well  I t was found, i n t h i s study, that proper  leveled  ground  surface was more important and  c o n t r o l l e d the r e p e a t a b i l i t y of the source s i g n a l . more important than signal  Repeatability i s  amplitude with the i n t e r v a l  c a l c u l a t i n g shear wave v e l o c i t y . to  combinations of  Rice optimised the length of the source beam t o a  length between 2 and 3 m. coupling  different  f o r use i n offshore and onshore  hammer  surface methods.  investigated  was conducted by  include the beam s t i f f n e s s .  Secondary  technique of  considerations were found  The use of metal beams resulted i n  greater s i g n a l amplitude than s i m i l a r length timber beams. An aluminum or  s t e e l beam weighted down by the l e v e l i n g jacks of a d r i l l r i g was  found t o be an excellent shear wave source. with s t e e l end caps weighted  Rice used a timber beam  down with a v e h i c l e and, although t h i s  was an adequate source, Rice found that he needed t o use the average of a t l e a s t ten blows t o reduce the v a r i a t i o n o f the resultant s i g n a l .  The  UBC i n - s i t u t e s t i n g v e h i c l e with approximately f i v e tons of reaction on its  rear s t e e l beam l e v e l i n g pad i s probably an optimum shear wave  source beam.  Very  large shear wave sources such as the "Marthor",  Layotte (1984) , use a s i m i l a r beam configuration with a 1500 kg hammer f a l l i n g 2 m with only s l i g h t l y greater reaction than that provided by  141 the UBC t e s t i n g v e h i c l e . The high q u a l i t y of data obtained using the sledge hammer and s t e e l beam l e v e l i n g pad configuration are demonstrated i n Figure 6.1.  These  traces r e s u l t from s i n g l e s t r i k e s o f each side of the source beam and hence the opposite  arrival.  Deeper penetration,  usually required the use of stacking procedures.  below about  30 m  With the addition of  ten blows very e a s i l y interpreted r e s u l t s could be obtained t o 50 m. The shear waves generated by a h o r i z o n t a l impact source, SH waves, o f f e r the advantage over other waves of not generating noise at s o i l interfaces through the conversion of incident energy i n t o r e f l e c t e d or refracted P o r SV waves.  This eliminates noise a r r i v i n g a t the same  time and masking the shear wave.  6.1.2  Explosive Sources  Some experience was obtained using explosive sources, both shotgun s h e l l s and seismic caps.  The use o f explosive sources  i s often the  only means o f obtaining a s i g n a l source i n shallow offshore conditions and  on land  Figure  6.2  oriented source designed  i s the optimum way of generating shows  the strong  accelerometer  offset  3 m  arrivals  generated  from  high  observed  by  by a b u f f a l o gun  the cone  rods.  a horizontally (shotgun  shell)  The h o r i z o n t a l receiver,  t o record shear waves i s not favorably oriented t o record P  wave energy t r a v e l i n g near v e r t i c a l l y .  Inspite of t h i s , large s i g n a l  amplitude could be observed t o a depth of over 50 m. was  energy P waves.  possible  direction.  i f the source  was  offset  further  Deep penetration in a  horizontal  Figure 6.1  Damped Geophone Response Profile to Hammer Shear Source  0  Figure 6.2  Time 80  (milliseconds) 160 240  143  320  Acx^lerameter Response Profile to Buffalo Gun Source  144 In an offshore environment explosive sources i n the water near the seabed resulted i n strong P wave a r r i v a l s .  Figure 6.3 shows the strong  P wave a r r i v a l s and r e f l e c t i o n from a permafrost boundary below. also  appears  t o be a second  P wave l i k e l y  generated  There  by a  bubble  As a shear wave source, explosives gave very mixed r e s u l t s .  Laing  expansion/collapse mechanism.  (1985) could not achieve repeatable r e s u l t s with the b u f f a l o gun. Use of a water charged hole  (for example, an auger hole b a c k f i l l e d with  water) was found i n t h i s study t o give highly repeatable r e s u l t s . degree  The  of r e p e a t a b i l i t y obtained with the b u f f a l o gun source lowered  into a water f i l l e d augured hole was as good as that from a shear beam source. The i n t e r p r e t a t i o n f o r shear wave v e l o c i t i e s from explosive sources gave very mixed r e s u l t s .  Onshore, the generation o f shear waves from  explosive sources i s enhanced by any asymmetry of the explosion. waves are also generated at sediment interfaces by P-S coupling. possible interface  i s the ground  Shear One  surface which may generate a shear  wave when an upward t r a v e l i n g P wave reaches the ground surface.  With  a l l these possible sources the d i s t i n c t i o n of any a r r i v a l can sometimes be d i f f i c u l t and may be complicated by the p o s s i b i l i t y of destructive interference.  Well  defined shear wave markers were observed  explosive sources onshore under some conditions. shear waves generated by t h i s r e s u l t s below about from  a  shear  wave  source.  Laing  from  Figure 6.4 shows the (1985) concluded  that  12 m were acceptable compared t o those obtained source  but that  a t shallower  depths  interference and ringing of the receiver masked the shear wave  P  wave  T I M E , msec.  Figure 6.3 Geophone Response at Schoolhouse Site from Campanella, Robertson, Gillespie, Laing and Kurfurst (1987)  0  Time 40 I  (milliseconds) 80 120 I  160  I  - M c D o n a l d Farm - H o g e n t o g l e r Cone - B u f f a l o gun s o u r c e  Figure 6.4  Damped Geophone Response Profile to Buffalo Gun Source  147 arrivals.  Use of damped receivers, discussed i n a l a t e r section,  was  found i n t h i s study t o reduced the ringing problem. Offshore, the explosive sources i n water only generate shear waves at  the  soil  water interface  or with  caused by s t r a t i g r a p h i c changes. are not nearly explosive  as e a s i l y  subsequent  impedance contrasts  Shear waves generated i n t h i s manner  distinguished as shear waves generated  sources onshore.  The  interpretation of signals  by  collected  offshore was  only found possible by consideration of a l l the traces  collectively  and  This  could then  marker  Figure 6.3  the recognition be  of a shear wave marker a t depths.  traced  up  through  the  stacked  shows the d i f f i c u l t y i n s e l e c t i n g shear wave a r r i v a l s from  t h i s sort of source.  I f explosive sources are necessary i n an offshore  environment the symmetry of the explosion must be reduced. at  doing  this  was  Campanella, et a l . device,  this  difficulty  profile.  made  the  Beaufort  Sea  site  investigation,  (1987), by placing the seismic cap on a blade shaped  proved  only  i n inserting  investigated.  in  An attempt  marginally  the blade  More e f f e c t i v e  into  results  effective  because  the dense s o i l may  be  of  the  at the  site  obtained by  the  near  simultaneous explosion of two sources c l o s e l y spaced on the sea f l o o r . This  source  was  not  attempted  but  similar  ideas  symmetry of explosive sources have been experimented  of  reducing  the  with i n the o i l  industry.  6.2  Receivers A v a r i e t y of receivers were used i n t h i s research.  geophones, damped geophones, and accelerometers.  They included  I t was  quite c l e a r  148 that the excellent mechanical coupling between the s o i l , the cone, and the transducer resulted these  transducers.  i n the excellent r e s u l t s obtained by a l l of  Some  consideration,  however,  transducer best suited to c e r t a i n conditions i s s t i l l Geophones or v e l o c i t y  of  the  type  of  justified.  transducers are generally used t o measure  signals having a frequency roughly between two and twenty times t h e i r resonant frequency.  The 28 Hz natural frequency v e l o c i t y transducers  used were selected p r i m a r i l y because they f i t , inside the 10 cm^  cone.  were 40 t o 60 Hz  and P waves 400 to 600 Hz.  with s l i g h t  trimming,  Typical frequencies of shear waves observed The 28 Hz transducers  therefore are reasonably well suited t o measure e i t h e r of these signals.  Velocity  transducers c h a r a c t e r i s t i c a l l y  s h i f t s near t h e i r resonant frequency.  have  large  two  phase  Hence, lower natural frequency  transducers would have reduced any concern f o r phase s h i f t i n g of the shear waves.  I t i s l i k e l y that the i n t e r v a l technique used i n downhole  t e s t i n g cancels a l l or nearly a l l of the phase s h i f t .  Laing (1985)  compared using the downhole i n t e r v a l technique r e s u l t s obtained from accelerometers and  geophones i n repeated holes and could not f i n d a  systematic difference. Damped geophones were found to be useful with explosive sources by reducing the ringing but also reduced the amplitude of both P and S wave a r r i v a l s .  Damping i s useful when recording signals generated by  explosive sources f o r shear wave v e l o c i t y . Vertically attempt  oriented  receivers  were used  by  Laing  (1985)  i n an  t o obtain P wave v e l o c i t i e s from shear sources by optimising  the orientation of the transducer with respect to the incoming wave  149 front. Sea,  I t became c l e a r , however, i n t r i a l s conducted i n the Campanella,  dominated  by  et  al.  (1987),  waves t r a v e l l i n g  that  the  down the  vertical  relatively  Beaufort  transducer rigid  CPT  was rods.  F l e x i b l e couplings are generally used i n conventional downhole t e s t i n g f o r t h i s reason but cannot be incorporated within the cone penetration test. At many s i t e s  i t i s necessary t o lower the  casing designed t o prevent l a t e r a l ice.  cone equipment down  buckling through f i l l s ,  water or  In these instances, and i n the deep offshore environment, i t can  be d i f f i c u l t or impossible to maintain the o r i e n t a t i o n of a horizontal geophone.  To  investigate  orientation, a cone was the  shear source.  acceptable  the  sensitivity  of  the  signal  incrementally rotated with repeated  I t was  found that within +  r e s u l t s were obtained.  45  the  s t r i k e s on  degrees  This means that by  to  entirely  installing  two  orthogonally placed horizontal geophones within the cone, one receiver w i l l always be oriented i n an acceptable manner.  I f the geophone was  i n a completely unfavorably o r i e n t a t i o n almost no shear wave energy was observed.  6.3  I d e n t i f i c a t i o n of Shear waves from Explosive Sources Previous  sections have showed examples of strong shear wave traces  generated from explosive sources, recognized  that  consideration  of  the traces  (Figures 6.3  interpretation recorded  over  of a  and  6.4).  these range  I t must be  traces of  depths  required and  was  generally performed by i d e n t i f y i n g shear wave a r r i v a l s at the deepest depth and recognizing the same marker recorded  at shallow depths.  It  150 was not found possible t o interpret a shear wave a r r i v a l from a single explosive  source.  Figure  6.5  shows  a  typical  trace  from  a  h o r i z o n t a l l y oreinted geophone receiver from the b u f f a l o gun source. Also shown are traces recorded a t the same l o c a t i o n but generated by a shear wave source and by a v e r t i c a l  hammer impact.  Although  these  traces were recorded a t the same depth the t r a v e l paths had s l i g h t l y different  lengths.  Using the shear wave source as a reference, the  shear wave a r r i v a l can be selected from the traces recorded from the vertical  impact  and  the explosive source.  As  with  the hammer  (horizontal) shear source i t i s observed that the f i r s t departure i s not as strong as the succeeding.  In a l l cases where there was a known  a r r i v a l time i t was found that the shear wave f i r s t departure was of opposite sign t o the P wave f i r s t departure. in  a l l subsequent  sources.  interpretation  This conclusion was used  of traces recorded using explosive  Figure 6.5 also i l l u s t r a t e s several other points.  1) The rounded and d i f f i c u l t t o interpret P wave a r r i v a l recorded on the geophone compared t o those recorded on the accelerometer (Figure 6.2). 2) The large amplitude of the shear wavelets following the i n i t i a l departure. 3) The complete lack of P wave energy from the v e r t i c a l  impact  source. The high r a t i o of shear wave energy compared t o P wave energy from the explosive source and the v e r t i c a l impact source i s due t o the combined e f f e c t s of the rapid attenuation of P wave energy i n the unsaturated surface s o i l s and the unfavorable orientation of the receiver t o record  152 v e r t i c a l l y propagating amplitude  was  unsaturated  much  P waves. stronger  surface  soils  In the offshore environment the P wave than  the  commonly  shear  wave amplitude.  encountered  onshore  The likely  contributes to the greater success at using explosive sources onshore than offshore. Sea  indicate  Conclusions that  two  from the t r i a l s conducted i n the  factors  reduce  the  effectiveness  Beaufort of  using  explosive sources i n the offshore environment: 1) The low impedance contrast at the seabed which r e s u l t s i n only small conversion of P to shear energy. 2) The saturated sediments transmit the P wave energy r e s u l t i n g i n subsequent P-shear conversion at s o i l interfaces and therefore creating multiple apparent sources.  6.4  S o i l Layering and Resolution The e f f e c t s of s o i l layering must be considered when assessing CPTU  r e s u l t s i n interbedded that  deposits.  layers l e s s than  0.5  m  Conventional  thick w i l l  rules of thumb suggest  not  achieve  full  cone t i p  resistance values representative of the properties of that layer alone. The  validity  of  such a guideline depends on  the  contrast between the properties of the layers. generally  c o l l e c t e d on  warranted. available  1 m  Beeston in  and  downhole  intervals, McEvilly  interval discuss  v e l o c i t y measurements  distance below which a layer can be detected as D = y  1  * y * Vi - V 2  t  2  where  D = resolution distance  and  V e l o c i t y p r o f i l e s were  this  (1977)  cone diameter  and  appears to the  give  be  resolution the  minimum  153 t = timing uncertainty and V 2 = v e l o c i t y above and below the contact Typical  uncertainties were  discussed  i n chapter  2.  The  timing  uncertainty i s so small that the depth r e s o l u t i o n i s on the order of a few  centimetres  f o r normally  encountered  variations  in  velocity.  Measurements made a t 1 m i n t e r v a l s appear t o be j u s t i f i e d .  6.5  Downhole-Crosshole Comparisons One means of v a l i d a t i n g the r e s u l t s obtained from the seismic cone  t e s t and the pseudo i n t e r v a l technique was t o compare r e s u l t s t o those obtained  from  conventional  crosshole  testing.  Considerable  surrounds the comparison of downhole t o crosshole t e s t s .  debate  Comparisons  between downhole CPT and crosshole t e s t s are shown i n Figures 6.6, 6.7 and  6.8.  Holmen  Test r e s u l t s obtained with high q u a l i t y procedures a t the  and  Drammen  techniques. Robertson,  An  sites  earlier  show excellent agreement between the two comparison  shown  e t a l . (1986) at the Annacis s i t e  difference between the two t e s t methods. were  by  confirmed  measurements  by  was  later  testing.  originally  The  speculated  i n d i c a t i o n of, inherent anisotropy.  Rice  (1984)  shows a  and  by  considerable  The CPT v e l o c i t y measurements d i f f e r e n c e between the two as  being  due  to, and  an  Later comparisons a t other s i t e s  which show much l e s s difference between measurements obtained with the two  techniques,  indicates that  measurement  error  i n the crosshole  t e s t i n g most l i k e l y explains the difference. Stokie,  et a l . (1986) performed v e l o c i t y  measurements  on large  cubic specimens i n the laboratory with v a r i a b l e s t r e s s conditions.  SHEAR V E L O C I T Y  0 0-J  WAVE Cm/e)  50 100 150 200 250 1 I I I  CONE BEARING Qc (bar)  INTERPRETED PROFILE  5very3  loose  10-  I  SAND  15-  CPT A  DOWNHOLE  CROSSHOLE  Figure 6.6 Comparison on Downhole and Crosshole Velocity, Holmen adapted from Eidsmoen, Gillespie, Lunne and Campanella (1985)  155  BEARING RESISTANCE 0 (bar) 10  SOIL PROFILE  SHEAR WAVE VELOCITY V (m/s) 0 50 100 150 200 250 S  FINE SAND SILTY CLAY  PLASTIC CLAY (PI = 27%)  LEAN CLAY (Pl=  10%)  • J)  CROSS-HOLE DOWN-HOLE  Figure 6.7 Comparison of Downhole and Crosshole Velocity, Drammen adapted from Eidsmoen, Gillespie, Lunne and Campanella (1985)  156  SHEAR WAVE V E L O C I T Y Cm/s)  0  50 100 150 200 250  CONE BEARING Qc (bar)  INTERPRETED PROFILE  0  SAND SILT  CO L CD •P CU E  silty SAND  CL Ld Q CLAY stiff plastic  CPT DOWNHOLE CROSSHOLE  Crosshole Velocity Data from: Nazarian and Stokoe (1984)  Figure 6.8 Comparison of Downhole and Crosshole Velocity, Wildlife Site  157 They c l e a r l y showed that stress induced anisotropy a f f e c t s downhole and crosshole measurements to exactly the same degree. that there can be no difference between the two own  results,  however,  considerable r o l e and and  indicate  that  They also state  measurements.  inherent  anisotropy  Their  plays  a  l i k e l y explains any d i f f e r e n c e between downhole  crosshole measurements.  The  small differences shown at Holmen,  Imperial V a l l e y and Drammen are l i k e l y due to inherent anisotropy.  If  anisotropy i s of i n t e r e s t one means of evaluating i t s importance i s the comparison of v e l o c i t i e s measured i n a downhole t e s t and i n a crosshole t e s t with v e r t i c a l p a r t i c l e motion. structural  anisotropy  separating  the  Research i n t o the importance of  i s complicated,  effects  of  however, by  structural  the  anisotropy  and  difficulty the  in  generally  unknown h o r i z o n t a l stress conditions. One important advantage of the downhole CPT v e l o c i t y measurement i s that  by  using  small  diameter  cone  rods  the  influence of  borehole  induced e f f e c t s including mechanical disturbance and s t r e s s relaxation are minimized. influence the  In downhole CPT t e s t i n g several square metres of s o i l measurements.  In  comparison, the  cone rods and  soil  affected by penetration around them i s very small. Incorporating downhole shear wave v e l o c i t y measurements i n t o the cone penetration t e s t has obvious economic advantages and was enhance the CPT  found to  i n t e r p r e t a t i o n of both the v e l o c i t y measurements and  interpretation  d i f f i c u l t i e s normally  (chapter  7).  In  addition,  several  of  the the  encountered i n t r a d i t i o n a l downhole or crosshole  t e s t i n g are eliminated.  These include borehole e f f e c t s such as stress  changes and disturbance e f f e c t s , and t r a v e l path u n c e r t a i n t i e s .  158  6.6  Conclusions 1) The l i m i t a t i o n s of shear and P wave sources was  t h i s chapter, numerous examples were shown. shear  wave  traces  recorded onshore  discussed i n  The high q u a l i t y of the  i s primarily  a  result  of the  excellent coupling between the s o i l and the cone penetrometer which has the  receiver  firmly bedded inside.  Secondary considerations of the  d e t a i l s of both the source and the receiver were also discussed.  The  accuracy and r e p e a t a b i l i t y of the i n t e r v a l technique appears to be very high f o r depths of penetration l e s s than 30 m.  Below t h i s depth signal  enhancement techniques become more important.  Explosive sources were  investigated  i n both the offshore and onshore environment.  In the  offshore environment, where t h e i r use i s warranted, the high degree of symmetry of an explosion underwater r e s u l t s i n poor generation of shear waves at the seabed and other s o i l  contacts.  Interpretation of the  traces obtained offshore from explosive sources required consideration of a l l traces a t the s i t e .  Additional research i n t o the development of  a repeatable, e a s i l y deployed, shear wave source f o r use offshore i s warranted. 2) The i d e n t i f i c a t i o n of shear wave a r r i v a l s from explosive sources was a s s i s t e d with the observation that the sign of the P wave and shear wave a r r i v a l s , as i d e n t i f i e d by comparison to pure shear sources, was opposite. 3)  Downhole-crosshole  comparisons  were  made  at  a  number  reference s i t e s increasing confidence i n the CPT downhole technique.  of  159 CHAPTER 7. 7.1  APPLICATION OF  DATA  Introduction Previous chapters have dealt with methods of obtaining  v e l o c i t y data from the seismic cone t e s t .  Many d e t a i l s o f the t e s t i n g  methods and i n t e r p r e t a t i o n procedures were discussed. that,  provided the CPT i s suitable at the s i t e  accurate  I t was shown  i n question,  a very  and repeatable measure o f the shear wave v e l o c i t y can be  obtained.  This section outlines some of the applications of the low  s t r a i n shear modulus. use  shear wave  o f Gjjjax data  correlation  The most important o f these involve the d i r e c t  e i t h e r as an important  t o other s o i l  parameters.  s t i f f n e s s parameter or by  Other applications  are also  proposed i n t h i s chapter, including the integration o f G ^ ^ data into conventional CPT interpretation f o r s o i l type and strength parameters. These applications sites,  previously  became apparent when i t was found that, observed  a t some  correlations between shear wave v e l o c i t y  data and CPT cone resistance data d i d not seem t o hold.  7.2  Shear Modulus as an Engineering Parameter Shear  modulus  deformation  is a  analysis.  fundamental As  soil  discussed  parameter widely  earlier,  downhole  used i n  shear  wave  v e l o c i t y measurements are made at small s t r a i n s and r e f l e c t the small s t r a i n behaviour of the s o i l . important input  For t h i s reason G ^ ^ measurements are an  into seismic analysis.  I f deformation analysis i s t o  be made a t larger s t r a i n s the small s t r a i n modulus must be attenuated to  lower  values,  r e f l e c t i n g the non  Commonly used modulus attenuation  linear  figures  behaviour  include  of  soils.  those of Seed and  160 Idriss are  (1970).  available  In many s o i l investigations  from laboratory t e s t s and small s t r a i n measurements can  be made from laboratory or i n s i t u t e s t s . at d i f f e r e n t  large s t r a i n measurements  strain levels  Knowing the modulus values  i t i s then possible  attenuation curve t o account for l o c a l  to refine  conditions.  Secondary considerations such as the e f f e c t s generally much less because  of the very  important than s t r a i n l e v e l small  shear  a modulus  strains  of s t r a i n rate are effects.  involved  In fact,  i n shear  wave  measurements, s t r a i n rates are of a s i m i l a r order o f magnitude t o those used i n conventional large s t r a i n laboratory undrained t e s t s .  7.3  Correlation of V e l o c i t y t o Liquefaction  Potential  Evaluation of l i q u e f a c t i o n potential i s perhaps the most important application  o f shear wave v e l o c i t y measurements.  The c o r r e l a t i o n of  v e l o c i t y t o l i q u e f a c t i o n i s e s p e c i a l l y important i n s i l t y sands where chamber t e s t data are unavailable and i n sands with a coarse gravel content In  f o r which both penetration and interpretation  clean  sands, which have well  described  density or cone resistance-liquefaction measurements resistance  may  be  a  useful  based interpretations.  interpretations  are d i f f i c u l t .  cone  resistance-relative  resistance  relations, velocity  independent  means  Cone resistance  t o confirm based  cone  liquefaction  have been proposed by Robertson and Campanella (1985),  Seed and De Alba (1986), Olsen (1984), Zhou (1981) and others. Three interpretation approaches t o l i q u e f a c t i o n that consider shear velocity 1)  include:  Correlation o f shear wave v e l o c i t y t o l i q u e f a c t i o n p o t e n t i a l .  161 2)  The threshold s t r a i n approach.  3)  Comparison of shear wave v e l o c i t y measurements i n the f i e l d and  the  laboratory.  With the way  of  lack  of f i e l d data c o l l e c t e d p r i o r to l i q u e f a c t i o n ,  developing an  indirect correlation  i s to use  an  SPT  N  one  value  c o r r e l a t i o n to shear wave v e l o c i t y such as that proposed by Suyama, et al.  (1986).  Based on the comparison of 1,654  et a l . propose the  following  t e s t s i n sands, Suyama,  c o r r e l a t i o n between SPT  N value and  shear  wave v e l o c i t y  where  V  s  V  s  N  = 97.0  N  = shear wave v e l o c i t y i n m/s = blows per 300  This r e l a t i o n can  mm  be used to combine the  shear wave v e l o c i t y and SPT.  0-341  the  measurement accuracy of  the  high l e v e l of experience gained with  the  The c o r r e l a t i o n i s based on Japanese SPT p r a c t i c e which t y p i c a l l y  achieves  60  consistent (1985).  %  of  theoretical  with the Figure 7.1  prediction  of  SPT  The  60  %  energy  l i q u e f a c t i o n curves proposed by  shows the addition  liquefaction  Seed, et a l . (1985).  energy.  resistance  measurements  to  velocity  i s proportional  1 to  onto the  atmosphere. a  single  stress, raised to the power 0.35. greater d e t a i l i n a l a t e r section.  is  Seed, et a l .  of shear wave v e l o c i t y f o r the  Also shown on Figure 7.1  velocity  rating  SPT  i s a means of  This  stress,  chart proposed  figure  the  correcting  assumes  vertical  by  that  effective  This assumption i s discussed i n  0.6  0.0  0  10 ^  20  30 0^)60  213  269  40  309  50  0.6  341  0.8  C  1.0  N  and C  1.2  v e  1.4  1.6  |  Shear Wave Velocity (m/s) Corrected to 1 Atmosphere using: velj = vel * 0 | v e  Figure 7.1  Shear Wave Velocity as an Index of Liquefaction Potential  to  163  The  CJJ values  shown i n Figure  from Seed, e t a l . (1985) are  7.1  close t o the C y ^ curve shown i n Figure 7 . 1 a t low s t r e s s l e v e l s . The s i m i l a r i t y between the stress correction curves i s important because the basis f o r the e n t i r e c o r r e l a t i o n are the f i e l d observations between SPT N value and shear wave v e l o c i t y , gathered over a range o f stresses and the  not corrected stress  f o r stress l e v e l s .  correction  curves  The greatest  occurs  a t high  departure between  stress.  The stress  correction curve i s very s i g n i f i c a n t varying by a f a c t o r o f two i n the normal range o f stresses considered. wave v e l o c i t y required (1983)  do not consider  to resist stress  Some c o r r e l a t i o n s f o r the shear  l i q u e f a c t i o n such as Seed, e t a l .  effects  c o r r e l a t i o n t o the upper 50 feet.  other  This s i m p l i f i c a t i o n i s not necessary  and may be unconservative a t high stresses. must be considered at low stress l e v e l s . with water tables  than t o r e s t r i c t the  near the surface  Occasionally  liquefaction  This s i t u a t i o n i s most l i k e l y  o r i n the offshore  environment.  I n s u f f i c i e n t data are a v a i l a b l e t o j u s t i f y the extrapolation of stress corrections t o higher values i n the low stress region. stress l e v e l s were d i f f i c u l t  t o evaluate a t low stresses  s o i l v a r i a t i o n s and suction conditions In addition,  The e f f e c t s of  high loads introduced  because of  i n the upper desiccated  crust.  by the UBC t e s t i n g v e h i c l e become  important a t shallow depths and make the equipment used i n t h i s t h e s i s inappropriate t o investigate stress e f f e c t s a t shallow depths. In  the manner o f the development o f the SPT based l i q u e f a c t i o n  resistance  curve,  refinement  o f Figure  7.1  requires  additional  measurements of shear wave v e l o c i t i e s a t s i t e s that d i d and d i d not l i q u e f y i n h i s t o r i c a l earthquakes.  Although Seed, e t a l . ( 1 9 8 5 ) show  164 additional resistance due  curves f o r s i l t y sands the v a r i a t i o n i s primarily  t o the s e n s i t i v i t y of penetration resistance  t o grain s i z e .  Shear  wave v e l o c i t y appears independent of grain s i z e ; therefore a v e l o c i t y based l i q u e f a c t i o n resistance curve such as Figure 7.1 i s useful over a wide range i n grain s i z e . Direct  correlations  between l i q u e f a c t i o n p o t e n t i a l  v e l o c i t y can be based upon only a l i m i t e d data set.  and shear wave Bierschwale and  Stokoe (1984) based t h e i r curve on data c o l l e c t e d a t s i t e s that d i d and did  not l i q u e f y  i n the Imperial  Valley.  The curves presented by  Bierschwale and Stokoe compare very poorly t o those developed using correlations  t o SPT N values,  unconservative.  they appear t o be very  Bierschwale and Stokoe s curves indicate  that  7  with shear wave v e l o c i t y acceleration  i n addition,  soils  greater than 140 m/s would require maximum  l e v e l s of 0.3 g or more t o cause l i q u e f a c t i o n .  Their  curves are based upon data that showed l i q u e f a c t i o n r e s t r i c t e d t o s i t e s with v e l o c i t y  less  than  records may p a r t i a l l y indicated  explain  data that  i n the  acceleration  the apparently low threshold  appears unconservative  An additional  i s that  velocity  reason that  i t i s based  their  on Imperial  c l e a r l y f a l l s on the l i q u e f a c t i o n side and does not  constrain the resistance The  Uncertainty  by Bierschwale and Stokoe.  correlation Valley  125 m/s.  curve.  second approach f o r the evaluation o f l i q u e f a c t i o n  potential  from shear wave v e l o c i t y measurements r e s u l t s i n a s i m i l a r comparison between the c y c l i c stress r a t i o required t o i n i t i a t e l i q u e f a c t i o n and shear  wave  velocity  but was  formulated  approach by Dobry, et a l . (1981).  from  a  simple  theoretical  This approach was founded on the  165 observation strain  that  under uniform c y c l i c undrained loading  e x i s t s below which no pore pressures  develop.  a threshold Knowing the  threshold s t r a i n l e v e l from laboratory t e s t i n g and the s t i f f n e s s from v e l o c i t y measurements the c y c l i c shear stresses required t o induce pore pressure  can be  calculated.  The key assumption  i n the approach  proposed by Dobry, et a l . i s that the threshold shear s t r a i n can be well defined.  The method may be more useful on a s i t e s p e c i f i c basis  where the threshold s t r a i n can be better defined laboratory t e s t i n g .  from the r e s u l t s of  Comparison t o the methods described above i s not  made here because o f the s e n s i t i v i t y t o the assumed threshold s t r a i n . The  t h i r d approach f o r using shear wave v e l o c i t y data i n important  investigations  may  be  v e l o c i t i e s together. laboratory relations  measurements. the  be  consolidation  shear used  in  a  stage.  into  incurred.  wave to  non By  the t r i a x i a l  In addition  liquefaction  and  laboratory  measured  velocity-liquefaction  carefully  evaluate  field  resistance velocity  Shear and compression wave v e l o c i t i e s can be measured i n  laboratory,  receivers  field  At important s i t e s , o r based on l o c a l experience,  derived can  t o consider  resistance  destructive  including  shear  t e s t only  t o development relation  the  manner, wave  minor of a field  following  the  transmitters  and  incremental  costs are  shear  wave v e l o c i t y -  shear  wave  velocity  measurements may also allow the evaluation of sample disturbance. the  velocities  incorrect Equivalent  If  are not comparable then e i t h e r sample disturbance or  consolidation field  stresses  have been  applied  t o the sample.  and laboratory v e l o c i t i e s o f f e r some assurance that  representative samples can be tested. (There remains the p o s s i b i l i t y of  166 o f f s e t t i n g e f f e c t s of s t r e s s v a r i a t i o n between f i e l d and laboratory and sample disturbance effects.)  7.4  Integration of  7.4.1  Data i n t o CPTU Data  Introduction  Based on previous experience  with the c o r r e l a t i o n of acoustic and  geotechnical parameters i t became apparent that a t some s i t e s i t could be  helpful  to  incorporate  the  i n t e r p r e t a t i o n of CPTU data.  velocity  measurements  into  the  Two observations highlighted t h i s need:  the d i f f i c u l t y i n d i s t i n g u i s h i n g overconsolidated c l a y s from  normally  consolidated s i l t s using CPTU data alone; and the observation that at some s i t e s v e l o c i t y data were of unexpected values. This section shows several approaches a t the i n t e g r a t i o n of seismic data  i n t o CPTU i n t e r p r e t a t i o n .  This i s a l o g i c a l approach when the  data are c o l l e c t e d together and i s based on the f a c t that shear wave measurements  reflect  CPTU measurements  only  small  strain  stiffness  properties whereas  are a function of many properties.  I t must  be  recognized that s t i f f n e s s properties that a f f e c t CPTU measurements are at  much l a r g e r stresses and deformations than those  v e l o c i t y measurements.  encountered i n  Other CPT i n t e r p r e t a t i o n measurements a l s o use  the r e s u l t s of separate sensors t o a s s i s t i n the i n t e r p r e t a t i o n . For example, permeability, as indicated by pore pressure response, i s used to  determine i f a drained or undrained  Approaches s e l e c t i o n on  that  incorporate  pore  analysis i s most appropriate.  pressure  measurements  into  the  values t o c a l c u l a t e shear strength from cone resistance  measurements were discussed  i n chapter  5.  In a s i m i l a r manner, the  167  possible use of shear waves t o enhance the i n t e r p r e t a t i o n o f CPTU data i s discussed.  7.4.2  Application of G ^ x Data i n the Interpretation o f Clay Strength from Cone Resistance Measurements  Previous success a t improving the s e l e c t i o n o f N by Lunne, e t a l . that  Nr.  could  This  observation that both N history.  Given  this  values were shown  With s i t e s p e c i f i c c o r r e l a t i o n s i t was shown  (1985).  the Bg parameter  appropriate  K  be used  empirical  K  and B  mutual  q  t o help  correlation  evaluate  the most  followed  from the  values were known t o depend on stress dependence  on stress  history  reasoned that there may also be a c o r r e l a t i o n between N more d i r e c t manner i t may also be expected that N  K  K  i t  and Bg.  In a  may also vary with  Theoretical expressions f o r N ^ ,  some measure of the s t i f f n e s s r a t i o .  based on cavity expansion theory, include a s t i f f n e s s r a t i o term. such formula from Vesic N  From  this  cavity  K  (1972)  =  1.33  expansion  gives  N  K  )  +2.57  i t i s expected  increase with the s o i l s t i f f n e s s r a t i o .  One  as  ( 1 + In G/Sy  theory  was  that  N  K  should  A knowledge o f the low s t r a i n  modulus allows a f i r s t estimate o r index of the s t i f f n e s s r a t i o t o be made.  The r a t i o G/qij i s s i m i l a r t o a s t i f f n e s s r a t i o and v a r i a t i o n i n  t h i s parameter had been observed a t d i f f e r e n t s i t e s .  The advantage of  such a r a t i o i s that both parameters are measured i n the same p r o f i l e i n the seismic cone t e s t .  Using averaged values o f cone resistance f o r  uniform  velocity  sections  with  investigated are shown i n Figure 7 . 2 .  data,  results  from  the  Very l i t t l e c o r r e l a t i o n was  sites  LEGEND: 0 Ons^y a D r a m m e n plastic a Drammen lean * McDonald Farm + Langley R e s e a r c h Site x L a n g l e y 2 3 2 U p p e r Site  2 5 h  2 0 3  s  II  + •  1 5 ++  ro 03  +  10-  A  X  CD  * ,* * x  o O  >X X X  3f  5  0 0  1—r  20  "i—i  r  '  40  I  60 'max  Figure 7.2  Cone Factor %£. vs Gmax/qp Ratio  1  —'—I  1  80  100  169 observed and an expected increase i n apparent.  with increasing G/q  In the discussion of pore pressures  was not  T  i t was shown that pore  pressures depended on s e n s i t i v i t y , strength, and s t r e s s h i s t o r y i n f i n e grained  soils.  In the same manner, i t appears that  depend on a v a r i e t y of parameters. s e n s i t i v i t y may  values  also  In t h i s study i t was observed that  be a key parameter i n determining  N  values.  K  This  value i s poorly established f o r most of the s i t e s investigated making i t d i f f i c u l t t o e s t a b l i s h the dependence of N Previous index  attempts a t using p l a s t i c i t y  of s t i f f n e s s r a t i o ,  to assist  K  on s e n s i t i v i t y .  index,  commonly used as an  i n the estimate  of N^ have also  shown considerable scatter, i n f a c t , the general trend of increasing or decreasing ruled  with p l a s t i c i t y  out  f o r most  i s unclear.  of the s i t e s  soundings have been performed. respects  but  have  presently a v a i l a b l e .  very  used  Measurement i n Figure  e r r o r can be  7.2  as  repeated  Some of the s i t e s are s i m i l a r i n many  different  N  values.  K  No  explanation  For example, large v a r i a t i o n s i n N  are reported  K  by Greig (1985) at the Langley s i t e s which are seemingly otherwise similar. Ons0y  and  The two Norwegian c l a y s i t e s Drammen,  d i f f e r e n t N^ values. ratio  which  otherwise  investigated i n t h i s  are  very  is  similar,  very  thesis,  have  very  I t would seem that the contribution of s t i f f n e s s  i n the determination  of N  K  i s small and that s i t e s p e c i f i c  N  K  c o r r e l a t i o n s remain important. Other attempts have been made to incorporate s t i f f n e s s interpretations;  f o r example,  Konrad  and  Law  s t r a i n modulus from the s e l f boring pressuremeter. method  r e q u i r i n g pressuremeter data  (1987)  use  i n t o CPT a  larger  The complexity of a  to i n t e r p r e t CPT data  makes i t  170 unattractive and d i f f i c u l t to evaluate.  7.4.3  Integration of V e l o c i t y Data into S o i l C l a s s i f i c a t i o n  The  correlation  between  CPTU  cone  resistance measurements  and  v e l o c i t y data was developed i n t h i s t h e s i s t o : 1) Provide a framework f o r estimating  values from CPTU data.  2) Distinguish s o i l types. 3) Understand the v a r i a t i o n i n v e l o c i t y with s o i l type. A synthesis of G/q values  averaged  velocity  data,  available.  r a t i o s and normalized cone bearing was made using  over  uniform  sections from  cone  resistance,  and  become  apparent  trend between G/q  T  from  sites  known  These values are shown p l o t t e d  observations developed  T  Figure  soil  T  conditions  i n Figure 7.3. 7.3.  There  were  Several  is  a  well  and normalized cone resistance i n sands.  This trend i s discussed i n d e t a i l i n section 7.5. G/q  where shear wave  A wide v a r i a t i o n i n  i n clays i s apparent, values ranged from 40 t o 80.  The v a r i a t i o n  was noted from s i t e t o s i t e and does not appear t o vary with normalized cone  resistance i n the  measurements or l o c a l  manner observed  correlations  clays than i n sands.  Ratios of G/q  those  Organic  of  a  silt.  T  for ^  f o r sands.  Site  appear more c r i t i c a l i n  i n overconsolidated clays approach  content  i s most  apparent  in  normalized cone resistance but some decrease i n the r a t i o G/q also observed peats may  a t organic r i c h  have very low G/q  peat s i t e s observed  T  specific  sites.  Highly organic s o i l s  r a t i o s of approximately 10.  i n t h i s study may  T  lowering was such  as  Some of the  gain t h e i r strength and hence  cone resistance from t h e i r fibrous nature, t h i s strengthening mechanism  TZ.T  172 i s apparently l e s s e f f e c t i v e as a s t i f f e n i n g mechanism. overconsolidation  The e f f e c t of  i n clays i s much more apparent i n cone resistance  measurements than i n the G/qiji parameter; Figure 7.3 shows a d i s t i n c t i o n between  overconsolidated  normalized  and  normally  consolidated  c l a y s using  bearing but complete overlap of the G/qtp parameter.  the This  observation lead to c o r r e l a t i o n s between normalized cone resistance and stress h i s t o r y .  Two  commonly  demonstrated here.  encountered  CPTU  interpretation  friction This  CPT  ratio  method  boundaries  interpretation, was  very  used  in a  accurately  At the Swimming Point s i t e  based only upon cone resistance and non-subjective,  computerized,  distinguished  several  manner.  stratigraphic  but predicted much f i n e r s o i l s than those a c t u a l l y present.  Additional  measurements  included  dissipation  records,  and  shear  found  to  pressures  are  The f i r s t i s i l l u s t r a t e d by r e s u l t s obtained at the  Swimming Point s i t e , shown i n Figure 7.4. traditional  situations  were  not  dynamic  pore  wave v e l o c i t y be  especially  pressure,  data. useful  Dynamic in  this  short pore case.  D i f f i c u l t i e s with dynamic pore pressure measurements and d i s s i p a t i o n s included: 1) A complex r e d i s t r i b u t i o n of excess pore pressure and a decay d i r e c t i o n inconsistent with usual theories of pore pressure d i s s i p a t i o n analysis. (Normal analysis i s f o r decreasing pore pressures with time) 2) Very low, occasionally zero, excess pore pressures.  The  PORE PRESSURE U of »oter) 100  SLEEVE FRICTION (bo-) 0 2.5 0-  CONE BEARING Oc (bar)  0 0  (sec) 10  FRICTION RATIO Rf « )  G/q  INTERPRETATION BASED UPON Qc and Rf pre-pushed  pre-pushed  Interbedded s i l t y CLAY and SILT  Interbedded SILT and sandy SILT with organic layers  silty  c l a y e y SILT with organics  T  19  1  7 11 •  ) \  20  \  10  12  5  I  30 60  )  \  k  12 > 200  *l ^ 15  Figure 7.4  15  12  6.5 14 '  S 10-  INTERPRETATION BASED UPON Qc,Rf,U,G/Qc and d i s s i p a t i o n s  20 15  CLAY  sandy SILT to c l a y e y SILT  silty  s i l t y CLAY w i t h SILT lenses  c l a y e y SILT with organics  silty  CLAY  clayey  sandy  SILT  silty  SAND  SILT SAND  CLAY-organic  CLAY-organic  silty  SAND  SAND  stopped i n GRAVEL  stopped i n GRAVEL  Integration of Gmax and Pore Pressure Measurements into Cone Interpretation  LO  174 low values were complicated further by t h e i r s e n s i t i v i t y to rod clamping  procedures.  At the Swimming Point s i t e a p a r t i a l grounding bed  at the edge of a deep channel  measurements i n the r i v e r bottom.  of i c e onto the r i v e r  allowed good shear wave v e l o c i t y  C a l c u l a t i o n of the r a t i o of G^x  cone resistance, (G/q ) ranged from 7 to 14. T  to  This range i s consistent  with previous observations i n loose sand (discussed i n l a t e r s e c t i o n s ) . Reasonably rapid decay of excess pore pressures, where generated, the G/qiji c o r r e l a t i o n s both indicate that the p r o f i l e was than  interpreted from t r a d i t i o n a l CPT  cone resistance and cone resistance and  friction.  and  much coarser  methods which r e l y s o l e l y upon  The two p r o f i l e s — o n e interpreted from  friction,  the  other considering cone resistance  f r i c t i o n pore pressure and G / q — a r e shown with the CPT data i n Figure T  7.4.  Sampling  confirmed  performed  by  others,  Kurfurst  (1986),  ultimately  the i n t e r p r e t a t i o n made by considering a l l data but d i d not  show the same l e v e l of d e t a i l shown by the Traditional q , T  than experienced  CPT.  FR interpretation i s generally much more accurate  at Swimming Point.  At t h i s l o c a t i o n a high organic  content i n the sand resulted i n very high f r i c t i o n r a t i o measurements. The  organic  content  has  the  combined  effect  of  lowering  the  cone  resistance measurements and increasing the f r i c t i o n measurements, t h i s results  i n unusually high  friction  towards a f i n e r grained s o i l . properties  expected  of  an  r a t i o s and  The profound  overconsolidated  loose noncohesive material makes d i s t i n c t i o n very important.  biases the p r e d i c t i o n  d i f f e r e n c e i n mechanical cohesive  material  of these  two  and  a  materials  This example i l l u s t r a t e s how a l l a v a i l a b l e information  175 needs to be considered f o r best i n t e r p r e t a t i o n of CPTU p r o f i l e s . A  second  difficult  area  i s the  where  d i s t i n c t i o n of  normally consolidated  silts.  cone  have  resistance  accuracy. soils  by  interpretation  and  I t was  lightly  friction  their  CPTU  be  clays  and  within  normal  be possible to d i s t i n g u i s h these  ratio.  T  can  have very s i m i l a r  measurements well  i t may  G/q  profiles  overconsolidated  These two materials may  hoped that  comparing  of  It  was  expected  that  the  overconsolidated c l a y would have a greater shear wave v e l o c i t y than a loose  silt  with  s i m i l a r cone resistance.  however, these two materials that,  may  f o r c l a y s o i l s , the G/q  As  have s i m i l a r G/q  shown i n Figure T  ratios.  I t appears  r a t i o decreases with increasing  T  h i s t o r y and becomes s i m i l a r to that observed at s i l t  7.3,  sites.  stress  The  data  c o l l e c t e d i n t h i s t h e s i s c l e a r l y show that pore pressure d i s s i p a t i o n rates  still  form the most d e f i n i t e means of d i s t i n q u i s h i n g these  two  s o i l types from CPTU t e s t i n g alone.  7.5  Correlation Between CPT  7.5.1  (q ) and G^x  Data  T  Introduction Correlations  between  discussed because the addition  well  measurements.  cone  r a t i o may  established Results of CPT  resistance  measurements and  G^x  are  r e f l e c t important s o i l properties;  ratios  reduce  the  need  chamber t e s t s reported by  for  in  velocity  Baldi  (1986)  indicate that cone resistance values are i n s e n s i t i v e to stress h i s t o r y whereas s t i f f n e s s values were found to be history.  Stiffness  dimensional loading  values  reported  by  modulus, calculated  very s e n s i t i v e to  Baldi  included  both  from response of the  stress a  one  chamber  176 sample,  E25  and  values  t r i a x i a l specimens. was  calculated  from  loading  otherwise  similar  In both cases the stiffness/cone resistance r a t i o  very s e n s i t i v e to stress history.  Baldi concluded that there  can  be no unique r e l a t i o n between cone resistance and void r a t i o that holds for a l l ranges of stress history. i n s i t u s t i f f n e s s and stress h i s t o r y may various  sand  This conclusion  implied that, i f an  cone resistance can be obtained, an estimate of  be possible.  For t h i s reason, values measured at  s i t e s were tabulated.  Before  they  can  be  compared,  however, i t i s necessary to ensure that the e f f e c t of varying  stress  l e v e l s i s not influencing the r e s u l t s .  7.5.2  Normalization of q , and G^x T  Ideally,  for the  data  comparison of shear wave v e l o c i t y data and  cone  resistance measurements, the e f f e c t s of stress l e v e l should be s i m i l a r . Data available to determine the dependence of cone resistance on stress l e v e l s come from chamber t e s t i n g and debate  centers  around  horizontal stress.  relative  importance  Considerable  of  vertical  and  Houlsby and Hitchman (1987) showed from r e s u l t s of  calibration  chamber  important.  Other  showed  the  importance  stress  i s obviously  situations.  the  f i e l d observations.  tests  that  only  chamber t e s t  data  of  the  reported by  horizontal  important,  horizontal  stress.  i t can  only be  stress  Baldi  seemed  (1986)  also  Although  horizontal  known i n  laboratory  The chamber t e s t data are often reported i n a form s i m i l a r  to that used by Baldi, where qc = C The  0  exponent  * ( CT' )  C 1  v  C  x  reported  * exp by  (C DR) 2  Baldi  is  0.55.  Similar  values  were  177 reported by Schmertmann (1976).  Although Houlsby  and Hitchman argue  that the horizontal stress l e v e l  i s the most important,  if a  single  stress i s considered, the exponent agrees with that reported by B a l d i . Field  evidence  from  this  study  indicated  a  slightly  greater  dependence of qiji on stress at normally encountered stress l e v e l s . dependence of cone resistance  on  stress  l e v e l s was  investigated  The by  p l o t t i n g the l o g of the cone resistance against the l o g of the v e r t i c a l e f f e c t i v e stress and finding the slope of the best f i t l i n e . showing  the  dependence of both  G^x  and  l e v e l s are shown i n Figures 7.5 and 7.6. averaged data.  cone resistance  on  stress  The cone resistance data were  i n the same sections as the depth  i n t e r v a l of the v e l o c i t y  Uniform sections only were considered.  from s i t e s with c l a y behaviour.  Examples  Figure 7.5  shows data  The Onsoy s i t e data are e s p e c i a l l y  important because of i t s uniform nature. the s i t e are nearly constant with depth.  Moisture content p r o f i l e s at The  influence of stress i n  the deep s o f t sediments at the McDonald Farm s i t e are shown because of the high stresses Figure 7.6. uniform.  One  involved.  Examples from  s i t e , the No.  sand  sites  are shown i n  6 Road s i t e i n Richmond, i s e s p e c i a l l y  Another s i t e , the Annacis s i t e , has greater v a r i a t i o n i n the  cone resistance p r o f i l e , t y p i c a l of sand s i t e s , and more s c a t t e r can be seen. similar  Nevertheless the dependence of both cone resistance and G^x at  each  of  the  sites.  A l l sites  consistently  showed  is an  exponent i n d i c a t i n g the stress dependency of cone resistance and of 0.70 + 0.15 An  i n sands and 0.90 + 0.1 i n clays.  analysis  of  this  type,  which  considers  field  advantageous i n that i t accounts f o r the e f f e c t s of aging.  data,  is  Ons<^y  5.0  Site  178  co D_  ^  ro E  4.0 Log Gmax = .82 L o g o V  + 2.85  CD  T3  JlCO  3.0  D_  CT o  2.0  Log QT = .88 Log av' + 1.11  o 1.0  I i i i i i — i i i i | i i i i i i i i i | i — i i i i—r—rn—r  1.0  1.5  2.0  2  Log of Vertical Effective Stress (kPa)  McDonald Farm Clayey SILT 15 to 45 m  6.0 - ,  £  5.0  x ccf  c|  Log Gmax = .76 Log av'  + 3.10  4.0  c CO  ?' cr o o  3.0 Log QT = 1.0 Log a v' + .67  2.0  1.0  1 2.0  1  1  1  1  1  1  1  2.5  Log of Vertical Effective Stress (kPa)  Figure 7.5  Influence of stress on Gmax and qp, Clay  1  1  3.0  # 6 Road Richmond  5.0 CO Q.  4.0  x  CO E CD  ~o CO  Log Gmax = .75 Log a v '  I  2.0 H  + 3.26  Log QT = .65 Log a v ' + 2.78  CO o 1.0  1.0  i iii iiiii| iiii iiiii Iii iiii iii| iiiii iii i| 1.5 2.0 2.5 3.0 Log of Vertical Effective Stress (kPa)  Annacis N —1  5.0  4.0 CO 1-  3.0  Log QT = .74 Log a v ' + 2.29  cr CO o  2.0  1.0  i iiiiiiiiIi iiii  1.0  1.5  i i i i I i i i i i i i i i I i i i i i i i i. i I  2.0  2.5  Log of Vertical Effective Stress (kPa)  Figure 7.6  Influence of stress on Gmax and qp, Sand  3.0  180 Unfortunately  unless  information  i s a v a i l a b l e i t a l s o assumes that  density and l a t e r a l stress conditions, f o r example Kq, remain constant with depth—an u n l i k e l y s i t u a t i o n .  Only at c l a y s i t e s where accurate  moisture content information i s a v a i l a b l e can an analysis of t h i s type be used with confidence.  The observations presented here are based, i n  part, on s i t e s f o r which no void r a t i o data are a v a i l a b l e ; nevertheless the conclusions are supported by observations from a v a r i e t y of s i t e s . Another report of the stress dependency of cone resistance i s that of Olsen and Farr (1986).  Based upon extensive f i e l d observations  and Farr (1986) report a normalization exponent of 0.7 At higher stress l e v e l s i t i s often observed values  do  not  increase s u b s t a n t i a l l y with  Deep CPTs reported by  Campanella,  Olsen  f o r sands.  that cone resistance  increased s t r e s s  et a l . (1984), obtained  (depth). i n moist  t a i l i n g s , showed l i t t l e increase i n cone resistance with depth beyond a v e r t i c a l e f f e c t i v e stress of approximately factors  such  characteristics,  as  crushing,  and  the  which  ambient  500 kPa.  depend  on  stress l e v e l ,  important at these greater depths.  The  influence of  density,  probably  grain  become more  I t may therefore be that the e f f e c t  of increased stress l e v e l s reduces at very high s t r e s s l e v e l s . The and  d i f f e r e n c e i n the  field  tests  may  influence of stress observed  result  from  the  effects  of  i n laboratory aging.  Other  normalization parameters such as mean e f f e c t i v e stress, which r e s u l t i n a dimensionless cone resistance, appear t o overemphasise the e f f e c t s of stress l e v e l on cone resistance and introduce the uncertain h o r i z o n t a l stress. The dependence of G^x  on stress l e v e l s was  a l s o considered.  The  181 dependence  of G  m a x  obtained  from  downhole  shear  wave  velocity  measurements was very c l e a r l y shown experimentally by Stokoe, e t a l . (1986) t o be of the form c  —  °max ~  rrt 0.25 * 0.25 l°v °h  c  This work was performed using very large (2 m * 2m * 2m) cubic samples of  dry sand  vertical  and c o n t r o l l i n g the stresses  and horizontal  e f f e c t i v e stresses  propagation and p a r t i c l e motion.  on a l l boundaries.  act i n the d i r e c t i o n s of  Stresses i n these two d i r e c t i o n s were  shown by Stokoe, e t a l . t o be equally important. stress  The  The magnitude of the  i n the t h i r d d i r e c t i o n was shown t o be unimportant.  I f the  stress dependency reported by Stokoe, e t a l . i s converted t o a single stress, either mean normal stress or v e r t i c a l stress, the influence of stress would be a single exponent 0.5.  Other values reported  include  those by Wroth, e t a l . (1984) who state that low s t r a i n G values depend on mean normal stress t o the power 0.33 and that the exponent with s t r a i n . max  G  o  n  To investigate the dependence of shear wave v e l o c i t y or  stress l e v e l , i n t h i s case v e r t i c a l stress, the log of G^Q^ was  plotted against  log v e r t i c a l e f f e c t i v e stress where G ^ x was available  at deep uniform s i t e s . Figure 7.5 and 7.6. void  increases  Examples of t h i s analysis  were included i n  As with cone resistance the e f f e c t s of changes i n  r a t i o and l a t e r a l  stress,  Ko, conditions  were not considered.  This assumption i s s t r i c t l y proven only a t the Ons0y s i t e . from a l l s i t e s showed that ^ i n laboratory  tests.  The r e s u l t s  was more dependent on stress than seen  At sand s i t e s the exponent c l e a r l y averaged 0.7  and at clay s i t e s a larger exponent averaging 0.9 was observed. the  case of the normalization of cone resistance  As i n  i t may be that the  182 e f f e c t s o f aging change the dependence of G ^ x Field  data  consistently  indicate  that  o  n  stress levels.  both  cone resistance and  Gmax data depend on stress l e v e l with a s i n g l e stress l e v e l exponent of approximately greater,  0.7 i n sands.  approaching 1.0.  The dependence  of each  i n clays i s  For a l l s o i l s tested the r a t i o ,  G/q , i s T  reasonably independent of stress l e v e l .  7.5.3  Correlation Between  and q  GJ^QX  i n Sand  T  Seismic cone data c o l l e c t e d a t sand s i t e s indicate that G ^ x can be predicted well i n sand deposits provided that density v a r i a t i o n s are accounted f o r by using normalized cone resistance. observations,  discussed  above,  cone  resistance  Based upon was  field  normalized  by  d i v i d i n g by the estimated v e r t i c a l e f f e c t i v e stress r a i s e d t o the power of  0.7.  The d e t a i l e d r e s u l t s from several  sand s i t e s are shown i n  Figure 7.7. The large v a r i a t i o n i n G/q with density, as indicated by T  normalized cone resistance,  shows that some care must be used before  assuming a r a t i o common t o a l l sands. A  commonly  p r e d i c t i o n of G sands,  loose  used m a x  ratio  from q  T  of, G/qj. =  7.5, provides  a reasonable  f o r most sands with the exception o f s i l t y  sands, and very 1  dense  sands.  The addition  of small  amounts of s i l t has the e f f e c t of lowering the cone resistance but not changing Gjjj^. permeability parameters  The addition  of s i l t  and the compressibility. may  influence  stiffness  a f f e c t i n g the cone resistance.  i n the sand a f f e c t s both the Changes t o e i t h e r of these two and  strength  characteristics  Given that the pore pressures are only  a small f r a c t i o n of the cone resistance, i t appears that the addition  183  30 - i  LEGEND: 0 x + o &  25  a A  20  oo o o  McDonald Farm # 6 Road Richmond Pile test Site Holmen, Norway Knight S t . Richmond Annacis S i t e Richards I s l a n d  o  x cd  E 1 5 H O  o  4>0  DO  0^ + D o  10  +  #b°0<>  0  0  x  1—I—I—I—I—I—I—I—I—I—I—I—1—1—I—I—1—I—I—I—I—I—I 0  100  I — I — I — I — I I—I _  200  Normalized Cone Resistance (q-r/o- v ' ) 1  Figure 7.7  Variation of Gmax/qj Ratios with Normalized Cone Resistance  7  300  184 of  silt  cone  increases  the  resistance.  In  large  s t r a i n compressibility  contrast  the  small  and  reduces  the  s t r a i n s t i f f n e s s appears  r e l a t i v e l y unaffected by the addition of s i l t . Very loose clean sand deposits observed to have high G/qp scale,  very  dense  such as the Holmen s i t e were also  ratios.  sands,  those  On  the other end  with  resistance, have a lower than average G/q t o the  cone  This i s l i k e l y  due  e f f e c t of d i l a t i o n i s manifested i n the large s t r a i n s associated  with  but  the  ratio.  normalized  The  CPT  of d i l a t i o n on  T  high  density  behaviour of dense sands.  the  influence  very  of the  i s l e s s important i n the  small  s t r a i n region  associated  with shear wave v e l o c i t y measurement. The  v a r i a t i o n of  G/q  T  shown i n Figure  7.7  appears to  indicate  thatG/q depends more on density and grain s i z e than on s t r e s s history, T  at l e a s t f o r the like  s i t e s selected.  cone resistance,  effects  and  that  the  are  I t appears that  i n s e n s i t i v e to  ratio  G^x/gpi  is  measurements,  stress h i s t o r y unlikely  to  be  and  fabric  useful  in  d i s t i n g u i s h i n g stress h i s t o r y of sands.  7.6  Application of P wave V e l o c i t y Data Compression wave v e l o c i t y data was  discussed  T h e o r e t i c a l l y , compression wave v e l o c i t y and shear  wave  velocity  characterizing s o i l s .  should  also  be  a  i n previous chapters.  r a t i o s of compression to useful  parameter  for  The type of s o i l s that permit CPT work, however,  r e s t r i c t s the range of normally encountered compression wave v e l o c i t i e s to a very small range.  In saturated s o i l s , compression wave v e l o c i t i e s  seldom are lower than 1500  m/s.  S o i l s that can be penetrated by  the  185 CPT  seldom have compression wave v e l o c i t i e s that are higher than 1700  m/s.  This narrow range, combined with measurement errors, reduces the  usefulness of compression wave measurements f o r c o r r e l a t i o n t o s p e c i f i c geotechnical parameters. One important application follows  from  influence  i t s s e n s i t i v i t y t o the s o i l  of the degree  (1967).  o f compression wave v e l o c i t y measurement  o f saturation  saturation  has been  state.  shown by Ishihara  The r e s u l t s of the experimental work performed indicate  i f a s o i l i s not completely saturated the v e l o c i t y i s much lower. does not appear t o be possible  The  that It  to d i s t i n g u i s h the degree of saturation  of p a r t i a l l y saturated s o i l s but i t i s c l e a r l y f e a s i b l e t o determine i f a  soil  i s completely  saturated.  Saturated  soils  have  velocities  greater than 1450 m/s while unsaturated s o i l s have v e l o c i t i e s l e s s than 1000  m/s.  7.7  Conclusions: 1)  Different  methods of using  shear wave v e l o c i t y  evaluation of l i q u e f a c t i o n potential were discussed.  data  f o r the  These methods are  considered t o be supplemental t o the use of cone resistance methods f o r evaluating l i q u e f a c t i o n p o t e n t i a l . correlation and  Of the methods outlined  between shear wave v e l o c i t y ,  a direct  corrected t o 1 atmosphere,  c y c l i c stress r a t i o i s considered t o be most appropriate f o r many  engineering problems.  Compared t o penetration based r e l a t i o n s v e l o c i t y  methods have the advantage of being independent of grain s i z e and may prove most useful  in silty  sands.  The major uncertainty with  this  method i s the lack of f i e l d data c o l l e c t e d p r i o r t o l i q u e f a c t i o n .  The  186 major advantage i s the accuracy and economy of simultaneous c o l l e c t i o n of cone resistance and shear wave v e l o c i t y data. Imperial  Valley  liquefaction  sites  and  do  unfortunately  not  provide  fall  much  Data c o l l e c t e d at the  clearly  constraint  on  the  side  of  to  the  relation  developed from SPT-shear wave v e l o c i t y c o r r e l a t i o n s . 2)  No c o r r e l a t i o n between G^x,  cone factor N  was  K  found.  Dependence of N  i s expected from consideration or Bg based interpretations. some cases poorly  The  K  the estimation on N  K  useful  as  on a s t i f f n e s s r a t i o term  use  especially s o i l  OCR  of a low  s e n s i t i v i t y , dominate  s t r a i n s t i f f n e s s to a s s i s t i n  does not appear to be warranted. data i n s o i l c l a s s i f i c a t i o n was  a t o o l secondary to cone resistance  interpretations.  and  I t i s hypothesised that other factors, i n  3) The a p p l i c a t i o n of G^x be  K  of both c a v i t y expansion theory and  constrained,  the v a r i a t i o n i n N .  normalized with cone resistance  An  example was  showing the v a r i a t i o n i n G/q showed the wide range i n G/q  shown and  a  and chart  f r i c t i o n based was  f o r d i f f e r e n t s o i l types.  T  found to  developed This  chart  found at d i f f e r e n t clay s i t e s but d i d not  T  indicate a reasonable means of c l e a r l y distinguishing overconsolidated clays from loose s i l t y s o i l s .  The d i s t i n c t i o n of these two  s o i l types  can be d i f f i c u l t because of f r i c t i o n measurement problems. example was  shown i l l u s t r a t i n g how  Figure 7.3  A specific  could be used to augment  cone resistance and f r i c t i o n based interpretation methods. 4)  The  dependence of G^x  investigated vertical  by  p l o t t i n g the  effective  stress  r e l a t i o n f o r each s i t e .  and  log of G  and  Both  cone resistance m a x  finding and q  T  and  the  q  T  on stress l e v e l  was  vs.  the  slope  of  the  l o g of  the  were found to be  best f i t  proportional  187 to  the v e r t i c a l  sands and 0.9  e f f e c t i v e stress raised t o the power 0.7  + 0.1  i n clays.  in  Both of these findings are contrary to  chamber based studies but are consistent with other f i e l d The  + 0.15  s i m i l a r dependence of both q  T  and  o  experience.  stress l e v e l  n  (or some  known index of i t ) allows comparison of the r a t i o Gmax/^T a t d i f f e r e n t stress levels. appears stress  The dependence of cone resistance on stress l e v e l s also  t o be dependent on cone resistance, s o i l compressibility, level.  For example at high stress l e v e l s  and  increased ambient  s t r e s s has a decreased e f f e c t on cone resistance. 5) In sands a r a t i o Gmax/^T i s often used t o estimate G^x this  ratio  was  explored  appropriate r a t i o was  i n Figure  7.7.  The  from q ,  determination  T  of  an  shown t o vary with normalized cone resistance.  No s i n g l e value was found f o r a l l sands but excellent c o r r e l a t i o n s were established provided normalized bearing was considered. 6)  P  wave v e l o c i t y  parameters but  data  should  be  measurement l i m i t a t i o n s  useful  i n determining  across the very  short  soil depth  i n t e r v a l used i n p r a c t i c e and the short range i n anticipated values i n saturated  soils  determined  with  presently downhole  limits  interval  the  application  techniques  unsaturated s o i l s from saturated s o i l s .  of  t o the  P  wave  data  distinction  of  188 CHAPTER 8. 8.1  SUMMARY AND CONCLUSIONS  Summary of Pore Pressure Data Pore pressure response during cone penetration f o r any given s o i l  i s p r i m a r i l y controlled by the location of the porous element. significance  of the element  location  depends  on s o i l  s i n g l e element location best serves a l l purposes. behind  the f r i c t i o n  sleeve gave s i m i l a r  type  The  and no  Measurements made  results  t o those  measured  behind the t i p except i n s o f t clays where pore pressures were s l i g h t l y lower behind the sleeve.  The s i m i l a r i t y of measurements behind the t i p  and sleeve makes the simultaneous measurement of pore pressures on the face of the t i p and behind corrections  then  require  the sleeve an i d e a l some  interpolation  pressure between the two measurement locations.  combination  to  obtain  but q  the  T  pore  This measurement i s  required f o r correction of cone resistance measurements because of the lack o f uniformity i n cone design and was shown t o account f o r much of the  variation  i n cone  readings  obtained  with  different  cones at  selected s o f t c l a y t e s t s i t e s . Pore pressure response  f o r any given cone design i s dominated by  drainage c h a r a c t e r i s t i c s and can therefore be used as an i n d i c a t i o n of soil  type.  The d i s t i n c t i o n  drained or undrained manner.  can be made between s o i l s  acting  in a  Pore pressure d i s s i p a t i o n rates were also  found t o be a useful index of s o i l type but cannot be used t o i d e n t i f y d e t a i l e d grain s i z e c h a r a c t e r i s t i c s . A common interpretation problem i s the d i s t i n c t i o n  o f s i l t s and  overconsolidated clays where f r i c t i o n readings are often i n s u f f i c i e n t l y r e l i a b l e f o r c l a s s i f i c a t i o n purposes.  Pore pressure decay rates can be  189 used to d i s t i n g u i s h these s o i l s . In s i l t y or f i n e sandy s o i l s pore pressures during cone penetration may  be  response  higher is  or  a  lower  than  function  only  the  static  of  the  values.  The  measurement  s i g n of  details.  the Pore  pressures on the face of the cone were found, i n granular s o i l s , t o be p o s i t i v e with very few exceptions.  Pore pressures behind the cone t i p  were found to be l e s s than s t a t i c i n nearly a l l cases.  This response  r e s u l t s from the very large normal stresses on the cone face and the reduction t o much lower stresses behind the t i p . Various  application  investigated.  Pore  of  pore  pressure  pressure  measurements  measurements were  found,  were with  r e s t r i c t i o n s , u s e f u l f o r the determination of undrained strength. The  most successful approach to determine OCR  appears to be  d i r e c t c o r r e l a t i o n of normalized cone resistance t o OCR. of  normalized  resistance  on  soil  plasticity  was  the  A dependence indicated  and  methods  for  reasonable correlations were shown. All  published  cone  resistance  interpretation  l i q u e f a c t i o n resistance are highly dependent upon g r a i n s i z e . pressure response, way  drained or undrained, was  Pore  shown to be a reasonable  of deciding the most appropriate CPTU based l i q u e f a c t i o n analysis  i n many s o i l s .  8.2  Summary of Shear Wave V e l o c i t y Data The  high  quality  of  the  shear  p r i m a r i l y a r e s u l t of two factors:  wave traces recorded  onshore i s  the excellent coupling between the  s o i l and the cone penetrometer, which has the receiver f i r m l y embedded  190 inside; and the use of SH waves.  The accuracy and r e p e a t a b i l i t y of  the  i n t e r v a l technique appears to be very high f o r depths of penetration less  than  30  m.  At  greater  depths  signal  enhancement  techniques  become more important. Downhole  velocity  measurements  were  compared  crosshole measurements at a number of s i t e s . quality  data  were  available  good  to  conventional  At three s i t e s where high  comparisons  were  obtained,  thus  increasing confidence i n the CPT downhole technique. Different evaluation  methods  of  of  using  liquefaction  shear  potential  were considered secondary to  the  wave v e l o c i t y , required  to  offers  accuracy and  to  liquefaction.  as  silty  lack of  field  and  clearly  Data c o l l e c t e d at the Imperial V a l l e y on  to the  the  side  of  liquefaction  and  sites  do  not  r e l a t i o n developed from SPT-shear wave  correlations.  The application of useful  in  economy of simultaneous c o l l e c t i o n of cone resistance  provide much constraint velocity  prove useful  being  the  fall  The  of  ratio  major advantage i s  shear wave v e l o c i t y data. unfortunately  methods f o r  advantage  major uncertainty with t h i s method i s the prior  therefore may  the  sands.  collected  and  the  These methods  the c y c l i c stress  of  data  size  for  A d i r e c t c o r r e l a t i o n between shear  independent The  grain  liquefaction  data  of cone resistance  corrected to 1 atmosphere, and initiate  velocity  were discussed.  use  evaluating l i q u e f a c t i o n p o t e n t i a l .  wave  data i n s o i l c l a s s i f i c a t i o n was  a supplementary t o o l to cone resistance  interpretations. showing the  An  variation  example was i n G/q  T  shown and  a  for different s o i l  and chart  found to  be  f r i c t i o n based was  types.  developed This chart  191 showed the wide range i n G/q-p  found at d i f f e r e n t c l a y s i t e s but d i d not  indicate a means of c l e a r l y d i s t i n g u i s h i n g overconsolidated loose  silty  soils.  The  d i s t i n c t i o n of these two  soil  clays from  types can  be  d i f f i c u l t because of f r i c t i o n measurement problems. The  dependence of  investigated.  Gjaax  Both Gm^  and  cone resistance q  + 0.1  i n clays.  r a t i o s d i d not  stress  level  were found to be proportional  T  v e r t i c a l e f f e c t i v e stress raised to the power 0.7 0.9  on  + 0.15  to  that void  vary s i g n i f i c a n t l y with depth; t h i s assumption clay s i t e .  The  the  i n sands and  The key assumption i n t h i s analysis was  only be v e r i f i e d at one  was  could  s i m i l a r dependence of both qp  and Gjnax on stress l e v e l (or some known index of i t ) allows comparison of the r a t i o Gjjjax/qrp at d i f f e r e n t stress l e v e l s .  At high s t r e s s l e v e l s  increased ambient stress has a decreased e f f e c t on cone resistance. In sands a r a t i o G^ax/qip was resistance.  8.3  shown to vary with normalized cone  The r e l a t i o n shown can be used to p r e d i c t G^ax  T  Recommendations f o r Future Research 1)  Silt  data.  remains the most d i f f i c u l t  Its  compressibility  addition and  into  sands  soil  to  greatly  thereby a f f e c t s the  i n t e r p r e t from CPTU increases  penetration  i n t e r p r e t a t i o n method that accounts f o r the e f f e c t of of  from q .  silty  soils  compressibility chamber  tests  content. easy.  is  will would  required. not have  be to  an  Accounting easy  vary  task;  stress  an  for  the  sand  resistance.  An  compressibility the  extensive  l e v e l s , density  effect series and  of of silt  Uniform placement of s i l t y sands i n a chamber w i l l not prove  Possible e f f e c t s of s o i l f a b r i c are more l i k e l y to be important  192 i n a mixed s o i l than i n the uniform sand samples tested t o date i n the chamber.  Perhaps f i e l d  testing  and d e t a i l e d  sampling  at silt/sand  s i t e s may prove more productive than laboratory chamber work. logistical  point of view the use of hydraulic f i l l  From a  preloads tested  a f t e r construction and subsampled during the unloading phase may allow density measurements t o be more e a s i l y made. 2) data.  The accurate i d e n t i f i c a t i o n o f s o i l s s t i l l r e l i e s on f r i c t i o n Equipment  improvements that  lead  t o increased accuracy and  r e p e a t a b i l i t y o f f r i c t i o n sleeve data are required. friction  The s e n s i t i v i t y of  sleeve data t o exact dimensions of the t i p and sleeve has not  been well documented. 3) and  Improvement t o d i s s i p a t i o n rate based estimates o f permeability  consolidation parameters  could  be  made  by  comparing  field  performance t o data c o l l e c t e d i n the s i t e investigation phase. 4)  Although some suggestions have been made i n t h i s t h e s i s , the  d i s t i n c t i o n of overconsolidated clays and clay s i l t mixtures i s s t i l l a difficult  problem.  Future  approaches  should  continue  t o examine  alternate  interpretations that combine data from the various sensors  already a v a i l a b l e . 5)  No  application  of  shear  consideration of damping parameters.  wave  data  has  y e t included  The v a r i a t i o n of s i g n a l  amplitude  with frequency may o f f e r a means of obtaining damping parameters from downhole t e s t i n g .  Repeatable broad spectrum  sources may be required;  the use o f true i n t e r v a l techniques should be explored as a means of d i s t i n g u i s h i n g damping e f f e c t s from geometric damping. 6)  The p o s s i b l e r o l e of aging e f f e c t s proved t o be a d i f f i c u l t  193 problem a t some of the s i t e s published l i t e r a t u r e .  encountered  i n this  study  and i n the  Some s i t e s appear not t o change with time a f t e r  compaction while others show large changes i n s o i l properties with time following soundings and  compaction.  An  investigation  that  with t e s t s a t d i f f e r e n t s t r a i n l e v e l s  cone resistance) f o r various times  includes  repeated  (shear wave v e l o c i t y  a f t e r compaction  could o f f e r  some i n s i t e i n t o t h i s phenomena. 7)  P wave v e l o c i t y measurements can give an accurate i n d i c a t i o n  that unsaturated s o i l s are present. d i f f i c u l t t o determine.  The degree of saturation i s more  Further work i n t h i s area and i n the behaviour  of p a r t i a l l y saturated s o i l s i s warranted. 8)  Stress correction  curves  are unavailable a t low stresses.  These curves could be developed with t e s t i n g i n uniform s o i l s but may require s p e c i a l l y b u i l t equipment.  194 REFERENCES Aas, G., Lacasse, S., Lunne, T. and Hoeg, K. (1986), "Use of In-Situ Tests f o r Foundation Design i n Clay", Proceedings of In-Situ 86, Geotechnical Special Publication No. 6, ASCE, Blacksburg, V i r g i n i a , pp. 1-30. 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