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Development of an electrical resistivity cone for groundwater contamination studies Weemees, Ilmar Andrew 1990

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DEVELOPMENT OF AN ELECTRICAL RESISTIVITY CONE FOR GROUNDWATER CONTAMINATION STUDIES By ILMAR ANDREW WEEMEES B . A . S c , The U n i v e r s i t y o f B r i t i s h Columbia, 1987 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of C i v i l  Engineering  We accept t h i s t h e s i s as conforming to the required  standard  THE UNIVERSITY OF BRITISH COLUMBIA September, 1990 <©  Ilmar Andrew Weemees, 1990  In  presenting this  degree  at the  thesis in  University of  partial  fulfilment  of  of  department  this or  thesis for by  his  her  representatives.  for  an advanced  Library shall make it  agree that permission for extensive  scholarly purposes may be  or  requirements  British Columbia, I agree that the  freely available for reference and study. I further copying  the  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  CIVIL  The University of British Columbia Vancouver, Canada  Date  DE-6 (2/88)  Serf 28 ,  tffO  ii  ABSTRACT  The  evaluation  increasingly  of  important  as  groundwater more  quality  industrial  has  waste  become  and  solid  domestic  r e f u s e comes i n t o c o n t a c t w i t h groundwater.  Often  quantity  and  by  extent of contamination i s  sampling of the groundwater and s o i l . detecting  contaminated  resistivity  investigated i n was  t h i s research.  electrical  The f e a s i b i l i t y  conducting cone penetrometer  of l o g g i n g  t e s t i n g has  To t h i s end a two  of  been  stage program  d e v i s e d , c o n s i s t i n g of l a b t e s t i n g and then f i e l d t e s t s of a  working  tool.  Lab to  soil.  direct  An a l t e r n a t i v e method  groundwater i s by n o t i n g the  of the contaminated  r e s i s t i v i t y while  determined  the  t e s t i n g was  evaluate  c a r r i e d out u s i n g a p r o t o t y p e probe designed  the f e a s i b i l i t y of the p r o j e c t .  c o n s i s t e d of d e t e r m i n i n g the r e s i s t i v i t y soil,  necessary were  requirements  chosen  itself  and  consists  On the b a s i s of l a b t e s t i n g the  f o r the module dimensions  tested  and  were f i n e tuned by f i e l d t e s t s . of  testing  mixtures w h i l e v a r y i n g  an i n s u l a t e d f o u r e l e c t r o d e  mounted behind a standard 15 sq cm piezo-cone  Upon  lab  of a number of d i f f e r e n t  e l e c t r o l y t e , and o r g a n i c contaminant  the c o n f i g u r a t i o n of the probe.  The  electronics The  array  module and  (CPTU).  completion of the development phase t h e instrument at  four  different sites.  determined  that  the  accurately  map  is  it  was  able  to  changes i n groundwater chemistry on the b a s i s  of  resistivity  From f i e l d cone  (RCPTU)  testing  was  was  iii r e s i s t i v i t y measurements. were  verified  changes  by groundwater sampling.  in lithological  penetration  The r e s u l t s of the r e s i s t i v i t y t e s t i n g  t e s t (CPT),  properties,  I t was  also  as determined by  that  the  cone  c o u l d i n f l u e n c e the r e s i s t i v i t y .  g u i d e l i n e s f o r the use of the RCPTU i n contaminant are p r e s e n t e d .  found  Basic  investigations  iv TABLE OF CONTENTS PAGE ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES ACKNOWLEDGEMENTS 1. INTRODUCTION 1.1 R a t i o n a l e f o r R e s i s t i v i t y Cone Development 1.2 Scope of Research  i i iv vi vii viii 1 1 4  2. ELECTRICAL CONDUCTION PHENOMENA 2.1 I n t r o d u c t i o n 2.2 E l e c t r i c a l Conduction i n Pore Water 2.3 E l e c t r i c a l Conduction i n M u l t i - P h a s e Systems 2.4 Frequency Dependent Behavior 2.4.1 Induced P o l a r i z a t i o n 2.4.2 D i e l e c t r i c P o l a r i z a t i o n  6 6 7 9 12 12 14  3. INSTRUMENT DEVELOPMENT 3.1 E x i s t i n g R e s i s t i v i t y Cone Technology 3 . 2 Lab T e s t i n g Equipment 3.3 Design Requirements and C o n s i d e r a t i o n s 3.3.1 Number of E l e c t r o d e s 3.3.2 E l e c t r o d e Spacing 3.3.3 E x c i t a t i o n Frequency 3.3.4 Measurement Range 3.3.5 Probe M a t e r i a l s 3.4 R e s i s t i v i t y Module D e s c r i p t i o n 3.5 R e s i s t i v i t y Cone C a l i b r a t i o n 3.6 BAT Water Sampling System D e s c r i p t i o n and Use 3.7 F i e l d T e s t i n g Procedures 3.8 Data R e d u c t i o n  16 16 17 18 18 21 21 22 22 23 25 26 27 29  4. SITE DESCRIPTION AND TEST RESULTS 4.1 McDonald Farm Research S i t e 4.2.1 S i t e D e s c r i p t i o n 4.2.2 S t r a t i g r a p h i c and R e s i s t i v i t y P r o f i l e 4.2 F r a s e r V a l l e y G l a c i o m a r i n e D e p o s i t s 4.2.1 Strong P i t 4.2.1.1 S i t e D e s c r i p t i o n 4.2.1.2 S t r a t i g r a p h i c and R e s i s t i v i t y P r o f i l e 4.2.2 Langley 4.2.2.1 S i t e D e s c r i p t i o n 4.2.2.2 S t r a t i g r a p h i c and R e s i s t i v i t y P r o f i l e 4.2.3 Colebrook 4.2.3.1 S i t e D e s c r i p t i o n 4.2.3.2 S t r a t i g r a p h i c and R e s i s t i v i t y P r o f i l e  31 31 31 35 37 38 38 38 40 40 42 42 42 43  V PAGE 5. INTERPRETATION AND DISCUSSION OF RESULTS 5.1 R e p e a t a b i l i t y of R e s u l t s 5.2 P r o f i l i n g C a p a c i t y 5.3 E f f e c t o f S o i l L i t h o l o g y 5.3.1 General Aspects 5.3.2 Cone Parameter R e l a t i o n s t o S o i l R e s i s t i v i t y 5.3.2.1 F r i c t i o n R a t i o R e l a t i o n s h i p 5.3.2.2 Cone Bearing R e l a t i o n s h i p 5.3.2.3 Pore P r e s s u r e R e l a t i o n s h i p 5.4 D e t e r m i n a t i o n o f Pore F l u i d R e s i s t i v i t y 5.5 I n f l u e n c e o f E l e c t r o d e Spacing on Measured Resistivity  45 45 47 50 50 51 51 53 53 55 57  6. APPLICATION OF THE RESISTIVITY CONE 6.1 A p p l i c a b i l i t y o f R e s i s t i v i t y f o r Contaminant Detection 6.2 Use o f t h e RCPTU i n Contamination Problems 6.3 Other P o s s i b l e A p p l i c a t i o n s 6.3.1 C o r r o s i o n Assessment 6.3.2 Water Q u a l i t y Assessment 6.3.3 S o i l C l a s s i f i c a t i o n  63  7. CONCLUSIONS AND RECOMMENDATIONS  72  REFERENCES  75  65 68 70 70 71 71  LIST OF TABLES TABLE  PAGE  4.1  I n - s i t u t e s t i n g program  32  4.2  Summary o f T y p i c a l R e s i s t i v i t y Measurements of F l u i d s and Bulk S o i l - F l u i d M i x t u r e s  67  vii LIST OF FIGURES FIGURE 3.1  PAGE Inner and outer e l e c t r o d e normalized measurements versus  resistivity  frequency  20  3.2  UBC R e s i s t i v i t y Cone  24  4.1  General  33  4.2  McDonald Farm Research S i t e  34  4.3  R e s i s t i v i t y cone sounding a t McDonald Farm  36  4.4  R e s i s t i v i t y cone sounding a t Strong P i t  39  4.5  R e s i s t i v i t y cone sounding a t Langley  41  4.6  R e s i s t i v i t y cone sounding a t Colebrook  44  5.1  A comparison of two adjacent r e s i s t i v i t y l o g s . made 11 days a p a r t f o r (a) The i n n e r e l e c t r o d e s , and b) The outer e l e c t r o d e s S t r a t i g r a p h i c and r e s i s t i v i t y p r o f i l e of the McDonald Farm s i t e  46  5.2 5.3  5.4  5.5  5.6  5.7 5.8 5.9  l o c a t i o n of the UBC r e s e a r c h s i t e s  48  A comparison of the r e s i s t i v i t y (outer e l e c t r o d e s ) and the f r i c t i o n r a t i o f o r two soundings from the McDonald Farm s i t e  52  Observed r e l a t i o n s h i p between apparent f o r m a t i o n f a c t o r and cone b e a r i n g normalized with respect to h o r i z o n t a l e f f e c t i v e s t r e s s  54  A comparison between the r e s i s t i v i t y of pore f l u i d samples and the r e s i s t i v i t y measured by t h e RCPTU  56  A comparison between the r e s i s t i v i t y measured by t h e i n n e r and outer e l e c t r o d e s a t McDonald Farm  59  A comparison between the r e s i s t i v i t y measured by the i n n e r and outer e l e c t r o d e s a t Langley  60  A comparison between the r e s i s t i v i t y measured by the i n n e r and outer e l e c t r o d e s a t Colebrook  61  A comparison between the r e s i s t i v i t y measured by the i n n e r and outer e l e c t r o d e s a t Strong P i t  62  viii ACKNOWLEDGEMENTS I wish t o thank Dr. Campanella f o r t h i s c h o i c e o f a r e s e a r c h p r o j e c t and h i s continued i n t e r e s t i n t h i s p r o j e c t . I would like t o thank my f e l l o w students i n the In-situ T e s t i n g Group: Dave Brown, Ross Hitchman, John S u l l y , Damika Wickremesinghe, and from G e o l o g i c a l E n g i n e e r i n g , Mark P r i t c h a r d f o r t h e i r a s s i s t a n c e i n c a r r y i n g out t h e necessary f i e l d work f o r this thesis. Many thanks t o Harold Schrempp f o r h i s work i n machining t h e resistivity cone module and e s p e c i a l l y S c o t t Jackson, who designed and b u i l t t h e c i r c u i t r y f o r t h e e x c i t a t i o n , measurement and data l o g g i n g o f t h e r e s i s t a n c e measurements f o r t h e r e s i s t i v i t y cone module. I would a l s o l i k e t o thank A r t Brookes for h i s continual role i n maintaining the i n - s i t u testing v e h i c l e , without which none o f t h e f i e l d work would be p o s s i b l e . I wish t o acknowledge t h e f i n a n c i a l support o f t h e N a t u r a l S c i e n c e s and E n g i n e e r i n g Research C o u n c i l , Canada, i n t h e form o f a research a s s i s t a n t s h i p .  1  1. INTRODUCTION  1.1 R a t i o n a l e f o r R e s i s t i v i t y Cone Development  The  detection  become  an  of  contaminated  important  aspect  geotechnical industry. has  a  direct  of  soil both  and the  groundwater groundwater  The d e g r a d a t i o n o f groundwater  effect  on t h e q u a l i t y o f l i f e  has  in  a  and  quality  region  by  p o s s i b l y t h r e a t e n i n g both t h e h e a l t h o f t h e l o c a l p o p u l a t i o n and of  wildlife  containment of  habitats. o f contaminated  potential  byproduct  Therefore,  the r a p i d  d e t e c t i o n and  s o i l i s o f wide i n t e r e s t .  contamination sources a r e :  acidic  Examples  sludge  as  from o i l r e c l a m a t i o n (Greenhouse and S l a i n e ,  leachate  from  sanitary  landfills  (MacFarlane e t  a  1986),  al,  1983),  a c i d i c l e a c h a t e from mine t a i l i n g s dumps (Morin e t a l , 1982), o r accidental  spills.  Contaminants  may be d e t e c t e d by e i t h e r d i r e c t sampling  a n a l y s i s o f groundwater and s o i l samples o r by i n d i r e c t that  operate  on the premise t h a t t h e presence o f  common  i n d i r e c t method i s t h e measurement o f t h e  electrical measure  of  conductivity.  presented  i n t h i s case s o i l . in  terms  of  property. subsurface  e l e c t r i c a l conductivity  t h e ease t h a t an e l e c t r i c a l c u r r e n t may  through a medium, are  The  methods  contaminants  w i l l change some other measurable s o i l o r groundwater A  soil  O f t e n these resistivity  r e s i s t i v i t y ) , which i s t h e i n v e r s e o f s o i l  and  be  is a passed  measurements (or  conductivity.  bulk  In most cases contaminants the  soil  because they change t h e e l e c t r i c a l p r o p e r t i e s o f t h e  groundwater. increase  The e l e c t r i c a l r e s i s t i v i t y w i l l decrease w i t h an  i n dissolved  contaminants cohesive place  solids,  and  increase  a r e p r e s e n t i n t h e groundwater.  soils  v i r t u a l l y a l l the e l e c t r i c a l  i f insulating  G e n e r a l l y f o r nonconduction  takes  through t h e pore f l u i d w i t h t h e s o i l m a t r i x a c t i n g as  insulator. mixture phase  In  many  i n s t a n c e s contaminant  sites  o f aqueous phase ( u s u a l l y conductive) ( i n s u l a t i n g contaminants).  produce  highly  conductive  Given  conductive  contaminants  non-conducting  of  influence the bulk r e s i s t i v i t y of  contain  and  U s u a l l y such  an a  non-aqueous  mixtures  will  plumes s i n c e t h e i n f l u e n c e  of the  i s g e n e r a l l y g r e a t e r than t h a t  of the  contaminants.  t h a t s o i l r e s i s t i v i t y measurements a r e a v a l i d method  d e t e c t i n g contaminants  i t becomes necessary t o  choose  method i s most s u i t a b l e t o make such measurements.  what  Generally,  t h e r e a r e two methods, g a l v a n i c measurement, and e l e c t r o m a g n e t i c (EM)  induction.  contact with  with  G a l v a n i c measurements a r e made  t h e ground w h i l e f o r EM measurements  t h e ground i s necessary.  surface or i n boreholes.  by no  Both can be employed  direct contact  from  EM measurements have t h e advantage  the of  b e i n g a b l e t o make measurements i n p l a s t i c cased h o l e s .  The o b j e c t i v e o f t h i s r e s e a r c h i s t o make r a p i d and a c c u r a t e measurements  of  penetrometer.  The cone penetrometer  acceptance  soil  resistivity  using test  a  modified  cone  (CPT) has gained wide  as t h e most a p p l i c a b l e l o g g i n g t o o l f o r s o i l i n t h e  geotechnical the  industry  (Campanella and Robertson,  a d d i t i o n of t h e r e s i s t i v i t y  that  the  CPT  will  investigations. resistivity  A  see  1982).  With  logging c a p a b i l i t y i t i s  more  use  for  likely  hydrogeological  cone penetrometer w i t h t h e c a p a b i l i t i e s of  logging  would  be  appealing  for  the  following  reasons:  1) By b e i n g pushed i n t o the ground the measuring in  intimate  c o n t a c t w i t h the ground,  as opposed t o  where a r e s i s t i v i t y probe i s deployed i n a mud  2)  Direct  measurements  measurements. electrical at  Surface  are  l e a s t a 5 t o 10% e l e c t r i c a l  (Benson  soil  et a l ,  variations. resolution  A of  than  and  surface  to  1976),  a  measure  but r e q u i r e  contaminant  assuming t h a t t h e r e a r e no  resistivity  case  c o n t r a s t between contaminated and  t o s u c c e s s f u l l y map  1985),  1%  accurate  (Telford et a l ,  the  f i l l e d borehole.  methods are commonly used  soil resistivity  uncontaminated  more  e l e c t r o d e s are  lithological  cone can measure r e s i s t i v i t y  a t the same time  plume  record  to  changes  a in  lithology.  3)  The  development of i n s t r u m e n t a t i o n f o r measuring  resistivity  is  electromagnetic  4)  Valuable  much e a s i e r t o d e s i g n and  galvanic  implement  than  for  penetrometer  is  also  induction.  i n f o r m a t i o n from the cone  r e c o r d e d i n a d d i t i o n t o the r e s i s t i v i t y  data.  1.2  Scope of  Very  little  concerning  published  technical literature  the d e s i g n and use of e l e c t r i c a l  though both D e l f t McClelland probes.  4  Research  Delft  measurements  offshore  cone  contaminants  has  sands.  been  (Horsnell,  used  1988)  published  resistivity gap cone  data,  cone  The to and  d e t e r m i n i n a t i o n of c o r r o s i v i t y p o t e n t i a l . little  1985)  cones  and  Fugro-  have s u c c e s s f u l l y operated  have used t h e i r r e s i s t i v i t y  in  resistivity  1988)  available  resistivity  (Van de G r a f f and Zuidberg,  (Horsnell,  is  for  such  density  Fugro-McClelland  profile also  conductive  used  in  the  With t h e r e b e i n g  work on the o p e r a t i o n and  such  interpretation  the purpose of t h i s r e s e a r c h i s t o f i l l  and independently penetration test  determine (RCPTU)  how  a p p l i c a b l e the  of this  resistivity  i s f o r d e t e c t i n g the presence  of  contamination.  To  meet t h i s o b j e c t i v e a r e s e a r c h program was  developed  and  is  summarized as f o l l o w s :  1.  Gather  in  soil  available l i t e r a t u r e regarding e l e c t r i c a l and  water  and  also  resistivity  conduction  testing  methods,  s p e c i f i c a l l y downhole t e s t s .  2.  Set up a s i m p l i f i e d l a b r e s i s t i v i t y  in  the  This  t e s t i n g apparatus t o a i d  s e l e c t i o n of a f i n a l d e s i g n f o r the  step  resistivity  i s meant t o check the v i a b i l i t y of measurements and t o minimize  resistivity making  the number of  cone.  accurate changes  t h a t would be needed f o r the e v e n t u a l f i e l d  3.  Field  t e s t the r e s i s t i v i t y cone t o ensure  i t is  a c c u r a t e data and then compile data from v a r i o u s  4.  Determine how  5  prototype.  collecting  sites.  the r e s i s t i v i t y measurements a r e a f f e c t e d  by  d i f f e r e n t s o i l types and groundwater c o n d i t i o n s .  5.  Outline  contaminant  Each  the  application  s t u d i e s and f o r other  of  the  resistivity  cone  to  purposes.  of these steps are examined i n the f o l l o w i n g  chapters  of t h i s t h e s i s . C o n c l u s i o n s and recommendations f o r f u r t h e r work are a l s o  presented.  6  2. ELECTRICAL CONDUCTION PHENOMENA  2.1  Introduction  An  electric  processes is  charge can be t r a n s f e r r e d by  (Telford,  1976). The f i r s t ,  conductor.  electronic, transfer the  or  ohmic c o n d u c t i o n .  migration  dominant  as  Another method  i s e l e c t r o l y t i c conduction, of  at  cations  molecular  is  and anions  conduction.  produced  due  polarization  varying e l e c t r i c f i e l d .  in  charge  an  electrolyte  in  T h i s method o f charge t r a n s f e r galvanic  With d i e l e c t r i c  t o changing  resistivity  caused  by the a p p l i c a t i o n  Conduction,  [2.1]  J =[er+<^£+  where:  J E °" 8. i -  1 0  conduction  electronic,  ionic of  a  a or  time  i n the most g e n e r a l terms,  be d e s c r i b e d by the f o l l o w i n g r e l a t i o n  The  of  as  The f i n a l method of charge t r a n s f e r i s r e f e r r e d  dielectric  current  to  a  the t r a n s f e r o f charge by  the f r e q u e n c i e s used i n  measurements.  may  b e i n g the most f a m i l i a r ,  T h i s charge t r a n s f e r i s r e f e r r e d  response t o an e l e c t r i c a l f i e l d .  to  different  the t r a n s f e r of a charge by the flow o f f r e e e l e c t r o n s i n  metallic  is  three  (Hearst ,1985).  i(<r-u/£)]E  2 c u r r e n t d e n s i t y (A/m ) e l e c t r i c f i e l d strength c o n d u c t i v i t y (S/m) dielectric permittivity angular frequency  (V/m) (F/m)  1/^1  form of the above e q u a t i o n can be s i m p l i f i e d  depending  upon  the  excitation  dielectric  frequency.  permittivity  frequency  dependent.  are  Both  the  complex  conductivity  quantities  In the case of low  and  that  frequency  are  resistivity  measurements the r e l a t i o n between the a p p l i e d e l e c t r i c f i e l d  and  the c u r r e n t d e n s i t y s i m p l i f i e s t o the f o l l o w i n g r e l a t i o n : [2.2]  J = <rE =  where:  E/p  p = resistivity  This  (ohm-m)  r e l a t i o n s h i p w i l l be v a l i d a t low  frequencies,  up  several kilohertz,  p r o v i d i n g the charges are not bound.  this  the  relationship  sometimes  referred  conductivity  may  resistivity  low  frequency  t o as the DC  resistivity),  be determined.  a t low  frequencies  The  Using  (which  or  is  conversely  f a c t o r s which  i n pore f l u i d and  s o i l w i l l be examined i n the f o l l o w i n g  2.2  resistivity  to  in  influence saturated  sections.  E l e c t r i c a l Conduction i n Pore Water  At  low  frequencies  conduction i n pore water takes p l a c e  electrolytic  conduction.  migrate  due  to  general,  the more ions p r e s e n t i n the pore f l u i d the g r e a t e r  conductivity. conductivity (1982) field  the  current  i s produced when the  a p p l i c a t i o n of an  However, of  A  a  electric  field.  an  electrolyte.  p o i n t s out t h a t the a c c e l e r a t i o n of ions i n an is  opposed by v i s c o u s  v e l o c i t y of the  drag.  This  limits  i o n s , hence i t s c o n d u c t i v i t y . The  i s a f u n c t i o n of temperature, i o n i c c o n c e n t r a t i o n ,  the  ions In  number of other f a c t o r s a f f e c t  a p a r t i c u l a r ion i n  by  the the  Keller electric maximum  amount of drag ion s i z e ,  and  valence. the  Since  conductivity  temperature increased towards  more  ionic  It  mobility  concentration  increase  conductivity t h e r e i s an  there  would  be  increased  is  the  the with  tendency  of i o n s t o  less  some  i o n s would viscous  not t h a t simple s i n c e charged  ( a t t r a c t a l a y e r of water m o l e c u l e s ) .  valence  as  increases  which r e t a r d the m i g r a t i o n  since  temperature,  be  drag.  (1985) s t a t e s t h a t the r e l a t i o n s h i p between s i z e  dependent  higher  While  will  would seem r e a s o n a b l e t h a t s m a l l e r  However, H e a r s t  solvate  a p a r t i c u l a r ion  increases.  conductive  also  of  collisions  extent.  and  f l u i d v i s c o s i t y i s a f u n c t i o n of  on the v a l e n c e of the i o n .  more charge t r a n s f e r r e d per  conductivity.  ions  tend  to  Conductivity  is  The  ion,  greater  resulting  the in  V i s c o s i t y a l s o decreases w i t h p r e s s u r e  a so  that  c o n d u c t i v i t y w i l l increase at higher  pressures,  however  this  i s a n e g l i g i b l e c o n s i d e r a t i o n w i t h the p r e s s u r e s  involved  i n cone t e s t i n g .  By assuming a l i n e a r r e l a t i o n s h i p between the of  ions  and  c o n d u c t i v i t y , a reasonable e s t i m a t e of the  d i s s o l v e d s o l i d s (TDS) [2.3]  C  where:  concentration  i n a s o l u t i o n can be  made. (CRC,  total 1982).  =crK  C - c o n c e n t r a t i o n of t o t a l d i s s o l v e d s o l i d s (mg/1) O - c o n d u c t i v i t y (^S/cm)  and K i s a constant  w i t h the f o l l o w i n g ranges.  K < 0.55 h i g h s a l i n i t y (TDS>2g/l ,6<pH<9) K = 0.55 - 0.7 low s a l i n i t y (TDS<2g/l ,6<pH<9) K > 0.7 f o r h i g h l y a c i d i c or c a u s t i c pore waters The high  high  mobility  value  of K f o r low pH pore f l u i d s i s due  of hydrogen ions i n comparison  to  other  to  the ions.  Different  ions  have  different  conductivity  factors,  the  c o n d u c t i v i t y f a c t o r being the r e l a t i v e c o n t r i b u t i o n t o the conductivity  of  concentration relative  a solution.  of  each  Using  conductivity  constituent  may  be  total  factors  estimated  the  if  the  q u a n t i t i e s of contaminants i n the groundwater are  not  changing  2.3  E l e c t r i c a l Conduction i n M u l t i - P h a s e Systems  A study by U r i s h uncontaminated  soil  (1983) determined t h a t b u l k c o n d u c t i v i t y i s a combination of a number  c o n d u c t i v i t y of the matrix and (which  unit  the t o t a l i n t e r s t i t i a l s u r f a c e  pore  volume  of  the  c o n d u c t i v i t y of the g r a i n s resistivity),  and  becomes  aqueous  the  area of the pores  per  specific  i o n i c composition of the pore water,  conductivity more  considered:  of  the  shape  in a  complicated  soil particles,  phase  liquids  surface  (which i s dependent on the pore water  c a t i o n exchange c a p a c i t y  bulk  sample,  factors:  porosity, tortuosity  i s dependent on the geometric p a c k i n g and  grains),  pH,  pore f l u i d ,  of  (CEC)  pore water  of the m a t r i x m i n e r a l s .  contaminated since  four  multi-phase components  and  air.  The  measured  of the s o i l i s a r e s u l t of c o n d u c t i o n  conduction)  through the above mentioned components and  the  (or  between  lack how  be nonbulk of the  other.  each s p e c i f i c c o n t r i b u t o r t o c o n d u c t i v i t y was relationship  system  aqueous phase l i q u i d s (APL),  (NAPL),  components i n t e r a c t w i t h each  The  must  resistivity  If  of  fluid  conductivity  considered and  bulk  conductivity describe as  be extremely c o m p l i c a t e d .  the r e s i s t i v i t y  mixing  made.  would  laws.  Formulas  i n multi-phase systems a r e r e f e r r e d t o  F o r t u n a t e l y s i m p l i f y i n g assumptions  A i r ,NAPLs,  that  can be  and sand can be c o n s i d e r e d e q u i v a l e n t w i t h  r e s p e c t t o t h e i r c o n d u c t i v i t y , i n most cases they a r e c o n s i d e r e d insulators. all  T h e r e f o r e t h e s i m p l e s t case i s t h e assumption  conduction  takes  place  through t h e pore  assumption i s t h e premise of A r c h i e ' s Formula  fluid.  pore  assumes  t h a t bulk r e s i s t i v i t y  water r e s i s t i v i t y  the  soil  (or r o c k ) .  resistivity which  i sdirectly  and t h e geometry A  t o pore f l u i d r e s i s t i v i t y  to  Archie's  related  to  spaces  in  o f t h e pore  term commonly used  relate  i s the formation  i s a f u n c t i o n o f t h e pore geometry.  This  ( A r c h i e , 1942, and  T e l f o r d e t a l , 1976), t h e s i m p l e s t o f t h e mixing laws. Formula  that  soil  factor,  A r c h i e ' s Formula  is  given as: F = P /p  [2.4]  h  where:  F = (°b = P-f = a,m = n =  For type.  m  u n c o n s o l i d a t e d s o i l a m 1,  and m i s dependent  on  soil  F o r sands t h e v a l u e o f m i s approximately 1.5, and f o r authors have  found t h a t m = 1.8 t o 3 (Jackson e t  1978).  Archie's  Formula  oversimplification the  = an"  i n t r i n s i c formation f a c t o r b u l k r e s i s t i v i t y (ohm-m) f l u i d r e s i s t i v i t y (ohm-m) constants f o r a given s o i l porosity  various clays al,  f  pore  fluid  has  been  recognized  to  be  but i s s t i l l v a l i d under t h e c o n d i t i o n resistivity  i s v e r y low o r t h e r e a r e no  an that clay  minerals  present  resistivity  can  in be  the  soil.  formation  formation  factor  factor.  is  because  a f u n c t i o n of f a c t o r s ,  geometry and f l u i d r e s i s t i v i t y , observed  This  factor. is  bulk  than  pore  which would tend t o decrease the For these  referred  The i n t r i n s i c  other  the  t o as  reasons the  the  apparent  f o r m a t i o n f a c t o r of a s o i l  measured formation  i s a function  o n l y of the pore geometry, which has been found t o be a f u n c t i o n of p a r t i c l e shape.  Jackson e t a l . (1978) r e s e a r c h e d the e f f e c t  of p a r t i c l e s i z e , d i s t r i b u t i o n and shape on the f o r m a t i o n f a c t o r and found m t o be o n l y a f u n c t i o n of g r a i n shape. measure  of  pore  tortuosity,  Thus, m i s a  with m i n c r e a s i n g  as  the  soil  p a r t i c l e s become more elongated.  Other  more c o m p l i c a t e d mixing laws have been f o r m u l a t e d  consider  the  effect  presence of c l a y . be  of m i n e r a l o g i c a l c o n d u c t i o n  to  the  An e x c e l l e n t summary of these r e l a t i o n s  may  found i n Jordan and Campbell  difficult  (1986).  These  these  factors  relations  t o put i n t o p r a c t i c e due t o the n e c e s s i t y of  the c a t i o n exchange c a p a c i t y of the s o i l . of  due  relationships may  conduction  influence is  to  is  important  resistivity.  are  measuring  However an awareness in  understanding  The  effect  important i n c l a y e y s o i l s and  of  organic  what  surface material  which have a h i g h c a t i o n exchange c a p a c i t y .  Attempts as  a  have been made by some authors t o use  method  rationale  of  being  determining that  if  hydraulic  porosity  can  resistivity  conductivity. be  estimated  r e s i s t i v i t y measurements then h y d r a u l i c c o n d u c t i v i t y c o u l d  The from also  be  estimated.  I f t h e Kozeny - Carmen e q u a t i o n i s used  representation  of  the  factors  that  influence  as  a  hydraulic  c o n d u c t i v i t y i t can be seen t h a t h y d r a u l i c c o n d u c t i v i t y depends, to  some extent,  on t h e square o f t h e pore r a d i u s ,  surface  term  and  factors  a r e measures o f pore s i z e ,  the representative g r a i n s i z e .  r e l a t i o n t o t h e formation between  formation  contradictory. formation  factor.  specific  A l l these  hence t h e r e should However r e l a t i o n s  be  some  developed  f a c t o r and h y d r a u l i c c o n d u c t i v i t y have  The  factor  a  fact  are  that  the  apparent  and  o f t e n d i f f e r e n t makes t h i s  determining h y d r a u l i c c o n d u c t i v i t y  been  intrinsic  approach  of  unfavorable.  2.4 Frequency Dependent Behavior  Frequency ascribed being  to  dependent  e l e c t r i c a l behavior i n  soils  two d i f f e r e n t p o l a r i z a t i o n p r o c e s s e s .  induced  polarization,  and  the  second  may  The  be  first  dielectric  p o l a r i z a t i o n . Both e f f e c t s r e s u l t i n a c u r r e n t out o f phase w i t h the  voltage  therefore  permittivity  to  polarization  i s noted  requiring  be d e s c r i b e d  the  as a complex  at frequencies  conductivity, quantity.  o f l e s s than  or  Induced one  hertz  w h i l e d i e l e c t r i c p o l a r i z a t i o n i s noted i n t h e mega-hertz range.  2.4.1  Induced P o l a r i z a t i o n  At  low f r e q u e n c i e s  p o l a r i z a t i o n of ions.  complex c o n d u c t i o n may occur due t o the P o l a r i z a t i o n t a k e s p l a c e due t o zones of  unequal i o n i c t r a n s p o r t p r o p e r t i e s  (Hearst,  1985).  C l a y s have  fixed  negative  clayey  soils  charges  so t h a t the c o n d u c t i o n of  i s f a v o r e d over t h a t of a n i o n s .  zones of unequal charge d i s t r i b u t i o n .  in  leads  to  This  In s o i l s c o n t a i n i n g c l a y  t h i s l e a d s t o what i s r e f e r r e d t o as the membrane When  cations  polarization.  a current i s applied to a clayey s o i l ionic  concentration  gradients  develop  i n r e g i o n s where c l a y p a r t i a l l y b l o c k s  pore  spaces.  T h i s b e h a v i o r i s i n d i c a t i v e of v a r i a b l e c l a y content.  The r e l a t i o n s h i p between p o l a r i z a t i o n and the s t a t e of the is  complex.  increases  Bodmer e t a l .  (1968)  noted t h a t  clay  polarizability  t o a maximum a t 5 t o 9 p e r c e n t c l a y c o n t e n t and  then  decreases.  Besides c o n f i r m i n g the presence of c l a y m i n e r a l s i n the polarization have  an  soil  i s a l s o i n d i c a t i v e of c o n t a m i n a t i o n i n s o i l s  initial  high  polarization.  Increased  pore  that fluid  s a l i n i t y w i l l decrease the p o l a r i z a b i l i t y s i n c e c o n d u c t i v e paths w i l l be chosen over c a p a c i t i v e paths of c u r r e n t flow. al  (1968)  noted  that  in  sand  clay  mixtures  polarizability  i s r o u g h l y p r o p o r t i o n a l t o the  capacity  of the c l a y .  would  (CEC)  decrease  organic  the  exchange  The presence of contaminants  that  the CEC c a p a c i t y of the c l a y c o u l d be noted  contaminants  soluble  that  cation  o b s e r v i n g a decrease i n p o l a r i z a b i l i t y of the s o i l . such  Bodmer e t  are cations  hydrocarbons (Hughes,  (Olhoeft,  1986),  and  Examples of  1985), also  by  water  chlorides  ( S c o t t - F l e m i n g e t a l . 1983).  Measurements of p o l a r i z a t i o n are accomplished time  domain or frequency domain ( T e l f o r d ,  1976).  in either  the  In the time  domain, once the source v o l t a g e i s removed, the observed v o l t a g e decay  curve  is  integrated.  measurements  of  resistivity  decade  apart.  resistivity,  Another uses  frequency range. al  the  frequency  are made a t  method,  resistivity  low  referred measurements  domain  two  frequencies  one  to  as  complex  over  a  large  Using the complex r e s i s t i v i t y method Towle e t  (1985) noted an i n v e r s e r e l a t i o n s h i p between g r a i n s i z e and a  c r i t i c a l frequency, resistivity  2.4.2  low  Polarization  frequencies  independent  of  increasing to  which i s d e f i n e d as the peak i n the complex  spectrum.  Dielectric  At  due  In  conduction  frequency.  free  electrolytes  As the frequency i s  increased  p r o p o r t i o n of the charge t r a n s f e r i n pore  displacement c u r r e n t s .  dielectric frequency  of  In the  p e r m i t t i v i t y of water, dependent  due  to  time  mega-hertz  fluid  is an is  range  the  and o t h e r p o l a r f l u i d s ,  is  dependent  dipoles.  At h i g h e r f r e q u e n c i e s the d i e l e c t r i c  function  of  orientation  of  permittivity i s a  frequency due t o v a r i o u s resonances of  atoms  and  electrons.  As  previously  conduction  currents  noted  displacement  at high frequencies,  currents  dominate  the frequency  range  where displacement c u r r e n t s dominate depends on the c o n d u c t i v i t y of  the  soil.  permittivity  The  advantage  of  measuring  the  of the s o i l i s t h a t i t i s c l o s e l y r e l a t e d  water c o n t e n t of the s o i l .  The d i e l e c t r i c  dielectric to  the  c o n s t a n t of water i s  weakly This  i n f l u e n c e d by s a l i n i t y and temperature f o r most is  water, constant the  because being  of the v e r y h i g h d i e l e c t r i c  highly polar,  of the s o i l matrix.  dielectric  i n comparison t o  soils.  permittivity the  dielectric  Thus the i n - s i t u measurement  constant of the s o i l c o u l d be used t o  water content, and hence v o i d r a t i o  of  of  determine  i s cohesionless s o i l s .  3. INSTRUMENT DEVELOPMENT  The  successful  contingent  on  two  development of the r e s i s t i v i t y factors:  (1)  understanding the  p r i n c i p l e s of c o n d u c t i v i t y i n s o i l s and; the  l a b t e s t i n g program.  outline  (2)  t e s t i n g program was  d e s i g n f o r the UBC  underlying  T h i s chapter commences w i t h a  of c u r r e n t l y a v a i l a b i l i t y  resistivity  cone  cone.  brief  technology.  so sparse t h a t a  necessary t o determine  resistivity  was  the completion of  A v a i l a b l e l i t e r a t u r e c o n c e r n i n g these t o o l s was lab  module  an  appropriate  The l a b t e s t i n g  apparatus  w i l l be d e s c r i b e d and r e s u l t s from t h a t program w i l l be used  in  the s e c t i o n of t h i s chapter c o n c e r n i n g d e s i g n c r i t e r i a .  3.1  E x i s t i n g R e s i s t i v i t y Cone  Electrical used  measurements  successfully  of s o i l and pore water  i n a number of i n s t a n c e s t o map  groundwater composition. are  Technology  Normally,  at  contaminated contaminant  least and plume  a  5 to  10%  electrical  uncontaminated (Benson,  s o i l to  1985),  in  surveys  Surface  methods  contrast  between  successfully  assuming  there  a  are  no  variations.  penetration  testing  resistivity  can  information.  The r e c o g n i t i o n of t h i s has l e d t o the development  much  more  made  resistivity  map  lithological  be  By measuring  been  changes  surface r e s i s t i v i t y  c a r r i e d out t o measure s o i l r e s i s t i v i t y .  require  have  accurate  while  d u r i n g cone  determinations  obtaining  of  lithological  of a s m a l l number of r e s i s t i v i t y there  has  s i t e s and  cone penetrometers.  been l i t t l e p u b l i s h e d about t h e i r use of t h e i r a c t u a l d e s c r i p t i o n .  The  However,  at  different  following i s a brief  d e s c r i p t i o n of these cones.  1)  Delft:  This  cone was  developed i n 1970 s t o be /  used  c o n j u n c t i o n with water sampling t o determine s o i l p o r o s i t y de G r a f f and presumed  Zuidberg,  that  1985).  t h e r e are two  The  cone has  8 electrodes.  s e t of f o u r e l e c t r o d e s .  in (Van  It is  Data  is  c o l l e c t e d a t d i s c r e e t i n t e r v a l s of 20 cm t o p r o v i d e a p r o f i l e of r e s i s t i v i t y with depth.  The  i n p u t s i g n a l i s a t a frequency  of  10 h e r t z .  2)  Fugro:  The  five  cm apart  from  the  Fugro cone c o n t a i n s two  (Horsnell,  rest  1988).  The  c i r c u l a r electrodes set e l e c t r o d e s are  of the cone body by a ceramic  material.  e x c i t a t i o n s i g n a l i s a p p l i e d a t an u n s p e c i f i e d low  3) ConeTec: T h i s module has two apart.  The  modular  design The  controlled  unit.  resistivity  cone.  built  t o be f i t t e d on a  probe This  is a  The  frequency.  wide e l e c t r o d e s s e t 7.5  e x c i t a t i o n c u r r e n t i s a p p l i e d a t 1000  piezocone.  3.2  10 mm  isolated  standard  fully  digital,  module was  developed  Hz.  cm  It is a  Hogentogler microprocessor  after  the  UBC  Lab T e s t i n g Equipment  The  l a b t e s t i n g equipment was  q u i t e simple  but e f f e c t i v e i n  making  resistivity  measurements.  The probe p a r t c o n s i s t e d  f o u r r i n g s t h a t s l i d along a p l a s t i c c y l i n d e r . electrodes  of  T h i s allowed the  t o be p l a c e d a t v a r y i n g d i s t a n c e s t o note t h e e f f e c t  of changing t h e e l e c t r o d e s p a c i n g . same constant  The source was b a s i c a l l y t h e  c u r r e n t c i r c u i t t h a t was i n t h e f i n a l u n i t ,  the power being  s u p p l i e d from a s i g n a l generator.  This  with allowed  f o r measurements over a wide frequency range t o study t h e e f f e c t of  varying  the  frequency.  The  voltage  e l e c t r o d e s was noted on an o s c i l l o s c o p e . was  from  the  The e l e c t r o d e assembly  submerged i n a l a r g e tank o f water and  (KC1)  output  Potassium  Chloride  was added t o the water i n t h e tank t o c r e a t e s o l u t i o n s o f  different conductivity.  3.3 Design Requirements and C o n s i d e r a t i o n s  The  following  r e s i s t i v i t y probe. benefits  i s an o u t l i n e o f t h e  requirements  Options i n t h e d e s i g n a r e c o n s i d e r e d  and problems i n v o l v e d w i t h each o p t i o n a r e  in the l i g h t  f o r the  o f t h e r e s u l t s obtained  and the  considered  from from t h e l a b t e s t s .  3.3.1 Number o f E l e c t r o d e s  Most  resistivity  electrode arrays.  probes  have  used  either  two  electrodes  and  t h e p o t e n t i a l measured with t h e i n n e r e l e c t r o d e s .  two  electrode  probe  applying  four  U s u a l l y s u r f a c e r e s i s t i v i t y methods use f o u r  e l e c t r o d e s , w i t h t h e c u r r e n t a p p l i e d a t t h e outermost  electrodes  or  the  potential  the current.  i s measured  For t h e UBC  With  across  probe  a  the  i t was  decided  t o use  across  the  a f o u r e l e c t r o d e d e s i g n w h i l e measuring p o t e n t i a l  i n n e r and  configuration  was  outer e l e c t r o d e s .  The purpose  t o observe i f t h e r e was  r e s u l t s between the two  s e t s of e l e c t r o d e s .  any  of  this  d i f f e r e n c e i n the four  electrode  probe a l s o has the advantage of being a b l e t o make low  frequency  measurements  without the i n n e r e l e c t r o d e s  Polarization  occurs due  which  produces  surrounding  an  soil.  The  becoming  polarized.  t o a b u i l d u p of i o n s a t the  electrodes  impedance  in  series  with  that  of  At the e l e c t r o d e s o x i d a t i o n - r e d u c t i o n  r e a c t i o n s must take p l a c e f o r t h e r e t o be a t r a n s f e r of ( K e l l e r , 1982). concentration  The of  transferred. electrodes  the  (redox) charge.  redox r e a c t i o n r a t e s are c o n t r o l l e d by  r e a c t i o n s t h a t accumulate as the  the  current  is  As the ions cannot r e a c t they accumulate a t c a u s i n g the p o l a r i z a t i o n .  f u n c t i o n of c u r r e n t the problem may  the  Since p o l a r i z a t i o n i s  be a m e l i o r a t e d  the c u r r e n t p a s s i n g through the e l e c t r o d e s .  by  decreasing  T h i s can be done by  employing a second s e t of e l e c t r o d e s t o measure v o l t a g e .  Since  the impedance through the v o l t a g e measuring c i r c u i t i s h i g h c u r r e n t p a s s i n g through the e l e c t r o d e s i s very s m a l l . such  an  becoming  array  can  polarized.  i n F i g u r e 3.1  be operated The  three  electrode  low  where the r e s i s t i v i t y ,  frequencies  Hz,  normalized  output i s independent of frequency, polarization configuration  of  the  inner  illustrated  i s p l o t t e d versus  with the e l e c t r o d e s s e t 3.5  Using cm  showing t h a t  electrodes.  The  without  with respect  d i f f e r e n t electrode configurations. system,  the  Therefore,  e f f e c t of p o l a r i z a t i o n i s  the r e s i s t i v i t y measured a t 1000 for  at  a  frequency a  apart, there i s  two  to  four the no  electrode  shows a frequency dependent output c h a r a c t e r i s t i c  20  2.00  FREQUENCY  F i g u r e 3.1  (Hz)  Inner and o u t e r e l e c t r o d e n o r m a l i z e d r measurements v e r s u s f r e q u e n c y  of e l e c t r o d e p o l a r i z a t i o n .  As  1000  Hz  i s approached the  of p o l a r i z a t i o n decreases,  t h i s i s because the i o n s do not have  time t o accumulate a t the e l e c t r o d e s . T h e r e f o r e ,  a two  configuration  can  the  frequency  adequate.  is  configuration  be s u c c e s s f u l l y employed i f  over  The  a  four  effect  electrode excitation  advantage  of  a  two  electrode  electrode  probe  is  ease  of  fabrication.  3.3.2  Electrode  Three used.  Spacing  factors  Smaller  are i n v o l v e d when  determining  the  d i s t a n c e s between the e l e c t r o d e s a l l o w  p o s s i b l e d e t e c t i o n of t h i n n e r l a y e r s of c o n t r a s t i n g Wider  spacing provides  should  give  resistivity. between  the  potential  a  a greater penetration  more  With  accurate  p o t e n t i a l and  electrodes  will  electrode  e l e c t r o d e s , spacings  become  spacings  if  polarized  resistivity. and  of  in-situ  the  distance  if  a  the  very  low  From a number of l a b t e s t s a t  i t was  as s m a l l as 15mm  adequate i n p r o v i d i n g a c c u r a t e  3.3.3  the  c u r r e n t e l e c t r o d e s i s too s m a l l  e x c i t a t i o n frequency i s employed. different  for  i n t o the s o i l  determination  a four electrode array,  spacing  found t h a t f o r 5  mm  wide  from c e n t r e t o c e n t r e were  determinations  of  resistivity.  E x c i t a t i o n Frequency  A l t e r n a t i n g c u r r e n t e x c i t a t i o n s u p p l i e s are used i n order avoid  electrode polarization.  An upper l i m i t t o the  chosen f o r the probe i s a few thousand h e r t z t o a v o i d  to  frequency inductive  coupling.  A  few p r a c t i c a l l i m i t a t i o n s were a l s o encountered.  S i x t y h e r t z should be avoided s i n c e n o i s e from power sources may a f f e c t the instrumentation.  The frequency  ensure a c c u r a t e AC t o RMS c o n v e r s i o n . this  frequency  must  be  high  the  effect  to  avoid  The frequency  k i l o - h e r t z . T h i s frequency  to 3.1  electrode  I t i s a l s o notable  of electrode polarization i s d i f f e r e n t f o r  fluid resistivities.  also  As seen from F i g u r e  enough  p o l a r i z a t i o n o f t h e outer e l e c t r o d e s .  must h i g h enough  that  varying  chosen f o r t h e probe was one  meets a l l t h e d e s i r e d c r i t e r i a and i s  w i t h i n t h e range 25-3000  Hz suggested  by t h e ASTM (D1125-  82) f o r c o n d u c t i v i t y measurements o f water.  3.3.4 Measurement Range  Electrical of  many  orders  insulating range  resistivity of  measured  magnitude.  contaminants  i s necessary. voltages  o f t h e ground can v a r y over a  being  With  both  considered a  With v e r y c o n d u c t i v e  to  noise  power  ratio.  conducting wide  and  measurement  contaminants  a c r o s s t h e e l e c t r o d e s may be  a c c u r a t e l y determine changes i n r e s i s t i v i t y ,  range  too  small  the to  due t o a low s i g n a l  The maximum i n p u t c u r r e n t i s l i m i t e d  by t h e  supply.  3.3.5 Probe M a t e r i a l s  The resistant  material  from which t h e probe i s c o n s t r u c t e d  t o a b r a s i o n and a b l e t o withstand  The p a r t s must a l s o be e a s i l y r e p l a c e d .  must  be  r e a c t i v e chemicals.  The e l e c t r o d e m a t e r i a l  must  be r e a s o n a b l y  non-oxidizing.  durable,  Lab and  have a h i g h c o n d u c t i v i t y ,  f i e l d t e s t i n g was  was  found  formentioned copper  t h a t the r e s u l t s from the  of  reasonably  a b r a s i o n r e s i s t a n t and  an o x i d i z e d s u r f a c e .  copper are not durable  that  stainless  steel  enough f o r f i e l d use.  r e s i s t i v i t y module,  isolated rings.  by The  the is  Aluminum  It is an  likely  electrode  a good conductor.  as shown i n F i g . 3.2,  The  i n s u l a t i o n and  c o n s i s t s of a  e l e c t r o d e s are made of b r a s s and  p l a s t i c i n s u l a t i n g s e c t i o n s and  width  of  are s e a l e d  the e l e c t r o d e s are f i e l d  voltage  the e l e c t r o d e s being  measurements  electrodes.  Conversion  are  5  made w i t h  of  mm.  by  the  The  are 0-  replaceable. with  Simultaneous  the measured AC  t a k e s p l a c e downhole.  t i p i s the c u r r e n t source.  The  to  s p a c i n g between the c e n t r e of the e l e c t r o d e s i s 25 mm,  continuous  of  beryllium  i s a good conductor.  and  the  chosen as i t  would a l s o be adequate as  four electrode array.  the  of  R e s i s t i v i t y Module D e s c r i p t i o n  The  The  three The  Brass was  m a t e r i a l s i n c e i t i s both very durable  3.4  first  however became e a s i l y p o l a r i z e d due  formation  and  b e r y l l i u m copper.  metals were e s s e n t i a l l y the same.  electrodes  be  done w i t h a number of  d i f f e r e n t metals: b r a s s , aluminum, copper, and It  and  inner  and  voltage  and outer  to  RMS  e l e c t r o d e f u r t h e s t from the  T h i s e l e c t r o d e i s s e t a t the  centre  the i n s u l a t i o n t o maximize the d i s t a n c e from the cone  body.  cone  towards  body i s grounded and w i l l tend t o draw it.  electrode,  I d e a l l y a l l the c u r r e n t should go t o the e l e c t r o d e c l o s e s t t o the t i p .  some the  current ground  The magnitude of  F i g . 3.2  UBC  Resistivity Cone.  the  constant  c u r r e n t source,  c o n t r o l l e d from t h e s u r f a c e . very  small,  potential  a t 1000  Hz,  is  Since t h e peak a p p l i e d c u r r e n t i s  t y p i c a l l y i n t h e order o f 150  measured  downhole t o  operating  across  micro-amps,  t h e e l e c t r o d e s must  t h e p o i n t where they f a l l  be  the  amplified  i n t o t h e range u s a b l e by  the data a q u i s i t i o n system.  3.5  R e s i s t i v i t y Cone C a l i b r a t i o n  The  RCPTU  electrodes. set  electrical  resistance  between  the  The r e s i s t a n c e w i l l i n c r e a s e i f t h e e l e c t r o d e s a r e  f a r t h e r a p a r t o r i f t h e e l e c t r o d e s u r f a c e area  The  i s decreased.  r e s i s t i v i t y i s t h e a c t u a l s o i l parameter and thus i t s value  should as  measures  be independent o f t h e probes e l e c t r o d e geometry as  t h e probes i n s e r t i o n i n t o t h e s o i l does n o t change  situ resistivity. lab  To convert  the i n -  from r e s i s t a n c e t o r e s i s t i v i t y  c a l i b r a t i o n was made f o r both t h e outer and i n n e r  pairs.  long  a  electrode  T h i s was accomplished by p l a c i n g t h e probe i n an  open  c y l i n d r i c a l chamber t h a t completely surrounded t h e module.  The  chamber added be  was f i l l e d w i t h water and potassium c h l o r i d e (KC1) was i n q u a n t i t i e s such t h a t measurements o f r e s i s t a n c e  made  The  a t a number o f d i f f e r e n t  resistivity  of  t h e s o l u t i o n was  c o n d u c t i v i t y meter (Omega CDH-30) to  noted  was c a l i b r a t e d with a 0.01  checked w i t h a 0.10 a  linear  M  portable  and t h e v a l u e s were  compared  M  solution.  relation  concentrations. a  t h e r e s i s t a n c e s measured by t h e probe.  meter  cone  electrolyte  could  between  with  The  conductivity  s o l u t i o n o f KC1  and  then  From t h e c a l i b r a t i o n o f t h e the resistance  and  the  r e s i s t i v i t y was d e r i v e d .  For t h e dimensions  the c a l i b r a t i o n f a c t o r , for In  penetration  of  3.2  K, (Eq. 3.3), was found t o be 0.100  t h e o u t e r e l e c t r o d e s and 0.838 an E r t e c (1987)  given i n F i g .  m  m  f o r the inner electrodes.  r e p o r t they note t h a t K i s dependent on t h e the  electric  field  into  the  ground,  or  a l t e r n a t i v e l y s t a t e d K w i l l vary with d i f f e r e n t s o i l types.  One  way  o f p r o v i d i n g some l e v e l o f c o n f i d e n c e as t o t h e v a l i d i t y o f  the  c a l i b r a t i o n f a c t o r i s by comparing t h e r e s i s t i v i t y  determined  by  Differences  i n measured  electrode soils for  sets  both  the  inner  and  outer  r e s i s t i v i t y values  w i l l be d i s c u s s e d i n Chapter  electrode between 5.  sets.  the  For  two  cohesive  l a b r e s i s t i v i t y measurements c o u l d be made on tube  samples  comparison.  3.6 BAT Water Sampling  Besides samples  fluid  making  the  resistivity at  System D e s c r i p t i o n and Use  measurements  of the  Torstensson pushed  equipment.  resistivity  of  o n l y other way o f gauging t h e r e l i a b i l i t y cone  i s t o measure t h e c o n d u c t i v i t y o f  t h e s i t e o f a RCPTU t e s t .  (1984). into In  the  this  soil  sediments  with  case a s t e e l BAT t i p ,  cone  doing  metre i n t e r v a l s a hypodermic s y r i n g e sampling  by  filter  penetration  coupled  f r i c t i o n reducer was pushed i n t o t h e s o i l w i t h AWL r o d s .  through  pore  system developed  T h i s system was designed t o have a the  tube  o f the  The e a s i e s t way o f  t h i s was w i t h t h e BAT ground water sampling  tip  results  system i s  with  a  A t one lowered  t h e rods,  p e n e t r a t i n g a rubber septum a t t h e t i p , and  e x t r a c t s a sample.  The s m a l l t i p volume i s q u i c k l y purged and a  second sample i s taken,  from which t h e c o n d u c t i v i t y i s measured  by u s i n g an Omega CDH-3 0  p o r t a b l e c o n d u c t i v i t y meter.  The BAT  and RCPTU r e s i s t i v i t y v a l u e s should c o r r e l a t e q u i t e w e l l as they are  both approximately sampling a s i m i l a r volume o f s o i l .  the  case o f t h e cone t h e o u t e r e l e c t r o d e s a r e 7.5  for  t h e BAT t i p t h e l e n g t h o f t h e porous f i l t e r  the  same d i s t a n c e .  immediately  In  cm a p a r t and  i s approximately  I f measurements o f t h e c o n d u c t i v i t y a r e made  a f t e r t h e water sample i s drawn from t h e ground  no  temperature c o r r e c t i o n s a r e necessary t o compare t h e r e s i s t i v i t y of  t h e pore water t o t h a t measured by t h e RCPTU.  are  I f t h e samples  s t o r e d and t h e c o n d u c t i v i t y measured a t a l a t e r  situ  temperature  resistivity  3.7 F i e l d  All  at  that  depth must be  by  system,  testing vehicle,  Campanella  and Robertson  o f which a d e s c r i p t i o n i s (1981).  Cone  t e s t i n g d i g i t a l data  data  was  aquisition  which has t h e c a p a b i l i t y t o s i m u l t a n e o u s l y r e c o r d e i g h t  channels.  Seven  channels  pressure,  upper  pore p r e s s u r e ,  resistivity2)  (1988).  the  T e s t i n g Procedures  c o l l e c t e d u s i n g t h e UBC i n - s i t u  These  that  t h e f i e l d work i n v o l v e d i n t h e r e s e a r c h was c a r r i e d out  provided  similar  so  v a l u e s may be c o r r e c t e d t o a common temperature.  from t h e UBC i n - s i t u  25 mm.  known  time t h e i n -  (bearing,  friction,  temperature,  pore  resistivity1,  where r e c o r d e d d u r i n g p e n e t r a t i o n a t i n t e r v a l s of  The p r e p a r a t i o n s i n v o l v e d i n r e s i s t i v i t y to  lower  those i n v o l v e d w i t h t h e s t a n d a r d  procedures  are outlined  i n Robertson  t e s t i n g are the piezocone and  test.  Campanella  The o n l y a d d i t i o n a l p r e p a r a t o r y s t e p f o r t h e RCPTU i s  t h a t t h e AC e x c i t a t i o n v o l t a g e i s s e t . controls  This e x c i t a t i o n voltage  t h e amount o f c u r r e n t s u p p l i e d t o t h e e l e c t r o d e  array  according t o the r e l a t i o n : [3.1]  I = V / 47.5kQ.  where:  V = i n p u t v o l t a g e (RMS v o l t s a t 1kHz) I = e x c i t a t i o n c u r r e n t (RMS amps)  Hence,  an a p p r o p r i a t e c h o i c e o f v o l t a g e must be made  on t h e d e s i r e d range o f r e s i s t i v i t i e s t o be measured,  based  where t h e  r e s u l t i n g r e s i s t i v i t y w i l l follow the r e l a t i o n s : [3.2]  R = V/(I*A)  where:  R I V A  [3.3]  = = = =  r e s i s t a n c e (ohm) c u r r e n t (RMS amp) output v o l t a g e (RMS v o l t ) a m p l i f i e r g a i n ( 50 f o r outer e l e c t r o d e p a i r , 500 f o r i n n e r e l e c t r o d e p a i r )  p = K*R = ( 1 / c o n d u c t i v i t y ) p = r e s i s t i v i t y (ohm-m) K = calibration factor  where:  The  maximum  corrupting results  the  input voltage i s  10  s i n u s o i d a l nature o f t h e output  V  This  A.  Therefore,  output  during V  v o l t a g e from t h e DAS exceeds 7.5  testing,  i f t h e output v o l t a g e  RMS p e n e t r a t i o n should be stopped  V  the  From  the s i t e s  to  input  Care must be  taken t o note t h e i n p u t v o l t a g e p r i o r t o each t e s t and then changes.  if RMS.  starts  and  v o l t a g e should be lowered t o an a p p r o p r i a t e l e v e l .  subsequent  The  i n p u t v o l t a g e can be a l s o l i m i t e d t o a lower v a l u e  the r e s i s t i v i t y  7  without  signal.  i n a maximum a l l o w a b l e i n p u t c u r r e n t o f 210  allowable  exceed  allowable  investigated  any  f o r this  r e s e a r c h i t was found t h a t an i n p u t v o l t a g e 5 V RMS p r o v i d e d t h e  best  accuracy  without exceeding t h e range o f t h e  DAS.  This  r e s u l t e d i n a p o s s i b l e range o f measurement o f 0 t o 119 If  higher  voltage  r e s i s t i v i t i e s were expected a t a s i t e a lower  should  be chosen.  must be maintained  due  input  The frequency o f t h e i n p u t  signal  a t 1000 Hz s i n c e a v a r i a t i o n i n t h e frequency  w i l l a l t e r t h e observed because  ohm-m.  c a l i b r a t i o n of the electrodes.  t h e behavior o f t h e e l e c t r o n i c s i s frequency  This i s dependent  t o the c a p a c i t i v e coupling of the electrodes t o  the  probe  circuitry.  Ideally  the  maintained.  This  resistivity  module  should  be  regularly  e n t a i l s cleaning the electrodes a f t e r  t e s t and p e r i o d i c a l l y c l e a n i n g and i n s p e c t i n g t h e O - r i n g After  each seals.  prolonged use t h e i n s u l a t i o n and t h e e l e c t r o d e s should be  replaced which  due may  to abrasional reduction i n t h e i r affect  the  repeatablity  of  outer the  diameter  resistivity  measurements.  3.8 Data  Reduction  In a d d i t i o n t o t h e normal c o r r e c t i o n s n e c e s s a r y t o cone data some For  data  m a n i p u l a t i o n must be done t o t h e  purposes  of p l o t t i n g , the r e s i s t i v i t y  resistivity  data must  71 cm upward t o t h e same datum as t h e cone t i p . data  from  t h e cone i s i n t h e form o f a measured  across the electrodes. based The  on  data.  be o f f s e t  The r e s i s t i v i t y voltage  from  The v o l t a g e i s converted t o a r e s i s t a n c e  t h e c o n s t a n t c u r r e n t chosen f o r t h e p a r t i c u l a r  conversion t o r e s i s t i v i t y  i s based on t h e c a l i b r a t i o n  test. done  i n water.  The r e s i s t i v i t y p r o v i d e d from t h i s c a l i b r a t i o n should  be f a i r l y r e p r e s e n t a t i v e o f t h e i n - s i t u c a l i b r a t i o n f a c t o r . applicability the  of the c a l i b r a t i o n factor i s discussed  results.  results  later  R e s i s t i v i t y i s a l s o temperature dependent.  i n t h i s r e s e a r c h have n o t been c o r r e c t e d t o  temperature  a  in The  common  The temperature changes  between  s i t e s a r e n o t l a r g e enough t o s i g n i f i c a n t l y change t h e  results.  Water  f o r comparison.  The  sample r e s i s t i v i t y v a l u e s have been c o r r e c t e d t o t h e same  temperature as t h e i n - s i t u r e s i s t i v i t y measurements.  No since  temperature  correction  particular  soil  different  soils  calibration  for a  f l u i d solution  (2% /degree C e l s i u s ) . by  forming  i s assumed  chamber.  holds  f o r any  T h i s c o u l d be t e s t e d f o r  samples around t h e cone  i n the  When p e n e t r a t i o n t a k e s p l a c e t h e  heat up due t o f r i c t i o n ,  probe  but t h e temperature o f t h e probe  w i l l n o t a f f e c t t h e measurements. at  It  t h a t almost a l l c o n d u c t i o n i s e l e c t r o l y t i c t h a t t h e same  temperature  does  c a l i b r a t i o n has been made.  I f comparisons o f r e s i s t i v i t y  a s i t e a r e b e i n g made over a long p e r i o d o f time t h e i n - s i t u  temperature  should  be  noted  c o n d i t i o n s change a p p r e c i a b l y .  i f seasonal  soil  temperature  4. RESEARCH SITES AND  All  field  vehicle.  t e s t i n g was  Testing  31  FIELD RESULTS  done from the  s t a r t e d on Oct  31,  UBC  1989.  in-situ  The  first  six  tests  The  first  test  were needed t o f i n e tune the probe e l e c t r o n i c s . with  the  f i n a l working c o n f i g u r a t i o n  was  RES  testing  89-7.  A  table  showing  the  t e s t schedule i s presented i n T a b l e 4.1.  A  map  showing  the  l o c a t i o n of the t e s t s i t e s i s shown i n F i g u r e  4.1.  Most  of  the  testing  research s i t e .  The  was  site  is  4.1  4.1.1  McDonald  Farm  along  with  a  A  description  description  of  of the  r e s i s t i v i t y p r o f i l e from each s i t e .  McDonald Farm  Site  This of  nearby  lower F r a s e r V a l l e y .  provided  s t r a t i g r a p h i c and  the  f i n a l t h r e e t e s t s were conducted i n d e p o s i t s  of g l a c i a l o r i g i n i n the each  done a t  Sea  detailed  Description  s i t e i s located Island map  a t an abandoned farm on the  as shown on the of the  area map  s i t e showing the  t e s t s i s p r e s e n t e d i n F i g u r e 4.2. +1.6  m with v a r i a t i o n s  area  is  mostly  i n elevation  covered w i t h low  (Figure  side  A  more  4.1).  l o c a t i o n of  The  north  elevation  the  various  of the  of no more than 0.5 grass  and  light  site is m.  The  deciduous  vegetation.  Sea lowlands  Island in  i s part  of the p r o g r a d i n g F r a s e r R i v e r d e l t a .  t h i s area are u n d e r l a i n by  a complex  sequence  The of  Table 4.1  Site McDonald Farm  Strong P i t Langley colebrook  m - s l t u t e s t i n g program  T e s t No. RES RES RES RES RES RES RES RES BAT RES RES RES  89-5 89-7 89-8 89-9 89-10 89-11 89-12 89-13 89-2 89-14 89-15 89-16  Date Feb Mar Mar Mar Mar Mar Mar Mar Apr Apr Apr Apr  21/89 6/89 6/89 6/89 17/89 29/89 29/89 29/89 3/89 6/89 6/89 18/89  Coordinates 210.4,28.7 29.5,0.2 29.5,-99.9 29,5,-50.2 29.5,-0.5 214.1,2.2 141.0,0.2 424,3,-16.1 215.1,2.2 n/a n/a n/a  F i g . 4.1  General L o c a t i o n o f the U.B.C. Research  Sites co  CO  F i g u r e 4.2  McDonald Farm r e s e a r c h  site  glacial,  fluvial,  and marine d e p o s i t s up t o a depth o f 300  w i t h t h e more r e c e n t F r a s e r R i v e r sediments a c c o u n t i n g 200  f o r up t o  m o f t h i s sequence. The groundwater t a b l e a t t h e s i t e v a r i e s  from  1  t o 2 metres depending on r a i n f a l l and t i d a l  During  the  winter  permeability  of  limiting vehicle  An  the  surface  overbank  representative on  of  the  site  cone  profile  i s presented  m.  in  a  grained  with of  highly  m  with  This i s followed  soil  relative  density,  to  fine  sand.  is  coarse  near t h e s u r f a c e .  the sand becomes f i n e r  This  The sand i s medium  w i t h t h i n l a y e r s o f medium  silt.  m  and  At  a  i s occasionally  T h i s t r a n s i t i o n l a y e r grades  into  a  silt.  From water  4.3.  sand and s i l t y sand.  variable  i n c r e a s i n g f i n e s content  15  interbedded clayey  Figure  a n a l y s i s from a nearby SPT show t h a t t h e sand  grained depth  (RES89-7)  This horizon c o n s i s t s of  h o r i z o n t a l l y and v e r t i c a l l y a c r o s s t h e s i t e .  Sieve  in  can be expected.  d e l t a i c and d i s t r i b u t o r y channel f i l l  coarse  thus  t h e s i t e from t h e s u r f a c e t o a depth o f 2 t o 4  by a sand h o r i z o n t o a depth o f 15  resulted  deposits,  low  Profile  resistivity  overbank sandy t o c l a y e y s i l t  has  silt  the  access.  interpreted  Typically  influence.  some s u r f a c e ponding occurs due t o  4.1.2 S t r a t i g r a p h i c and R e s i s t i v i t y  to  m,  the r e s i s t i v i t y p r o f i l e the high s a l i n i t y of the  i s evident  infiltration  of  (25 brackish  to  2 ohm-m).  This  i s due  water found near t h e  mouth  pore  t o the of the  FRICTION RATIO  ig.  4.3  SLEEVE FRICTION  Resistivity  CONE BEARING  PORE PRESSURE  Cone S o u n d i n g a t McDonald Farm, V a n c o u v e r  International  RESISTIVITY  Airport,  INTERPRETED  B.C.  CO  Fraser  River.  depth,  as  reaching  The s a l i n i t y o f t h e pore water  i l l u s t r a t e d by t h e d e c r e a s i n g  increases  with  resistivity,  until  a l i m i t i n g v a l u e i n t h e c l a y e y s i l t o f about 2  ohm-m.  The groundwater t a b l e i s noted by t h e sudden drop i n r e s i s t i v i t y a t 1.2 m.  4.2 F r a s e r V a l l e y Glaciomarine  The  current  dominated  by  ice  geology  glaciomarine  Deglaciation. depressed  surface  Deposits  of  the  Fraser  Valley  clay deposited  during  the  sheet.  m  there  During t h e r e c e s s i o n g l a c i o m a r i n e d e l t a i c d e p o s i t s  the  are  1982).  Formation  were  Mountains  so  The  deposited their  Fort  Cascade  deltaic from  mineralogy  deposits  melt  the  from  which  contain  no  i c e contact  of  raised deltas,  time and  Capilano  the  Coast  granitic  Langley d e p o s i t s were d e r i v e d from rock  g l a c i o m a r i n e sediments.  very  water  (Clague  of  i s dominated by  d e p o s i t e d i n a more s a l i n e environment.  and  distinct  same  Mountains t o t h e e a s t o f t h e F r a s e r V a l l e y .  sediments,  consist  were d e p o s i t e d .  two formations were d e p o s i t e d a t t h e  some f e a t u r e s t h a t make them  Luternauer,  types.  were  by t h e weight o f t h e c o r d i l l e r a n  of t h e C a p i l a n o and F o r t Langley Formation  While  Fraser  A t the time o f d e p o s i t i o n t h e lowland areas  by more than 200  is  of  rock the  Capilano  sediments,  were  The C a p i l a n o sediments  i n t e r t i d a l and beach  deposits  With t h e r e s u l t a n t u p l i f t o f t h e  and land  l e a c h i n g these c l a y s would have a g r e a t e r tendency t o become sensitive.  The  F o r t Langley  glaciomarine  clays  were  deposited tended  closer  to  t h e decaying g l a c i a l  t o have an o r i g i n a l l y  i c e front  lower s a l i n i t y .  and  thus  The f a r t h e r  i n t h e F r a s e r V a l l e y the lower t h e s a l i n i t y o f t h e  east  depositional  environment.  4.2.1 Strong P i t  4.2.1.1. S i t e D e s c r i p t i o n  The gravel  Strong P i t r e s e a r c h  s i t e i s l o c a t e d w i t h i n an abandoned  p i t approximately 4 km west o f A b b o t s f o r d  location  on F i g u r e  4.1).  The s i t e i s on t h e n o r t h  v a l l e y which i s occupied by Pepin Creek. by g l a c i a l outwash and c o n t a i n s contact  deposits  valley  contains  Airport  of  a  The v a l l e y was i n c i s e d  outwash sand and g r a v e l and i c e  o f t h e Sumas Formation.  was  j u s t west o f t h e f a r t h e s t l o c a l advance o f Sumas I c e d u r i n g  the  Fraser  Fort  Glaciation.  Langley  the  implying  Immediately t o t h e n o r t h  glaciomarine  surface.  deposits,  The south s i d e o f t h e that s i t e  site  i c e contact  side  (see  of the s i t e  stoney c l a y and sand i s p r e s e n t  The c l o s e p r o x i m i t y  at the  o f t h e F o r t Langley c l a y t o the  would suggest t h a t t h e c l a y t e s t e d a t t h e s i t e belongs same f o r m a t i o n .  to  The v a r i a b l e depth t o c l a y throughout t h e  s i t e may be due t o i r r e g u l a r e r o s i o n by t h e Sumas melt water.  4.2.1.2 S t r a t i q r a p h i c and R e s i s t i v i t y  The  RCPTU p r o f i l e ,  into three  zones.  Profile  as shown i n F i g u r e  The f i r s t  1.5  m  4.4,  can be  consist of f r e e l y  divided draining  f FRICTION RATIO Rf(%) O 5  ig-  4.4  SLEEVE FRICTION (MPo) 0 0.25 0  Resistivity  CONE BEARING q (MPo) 7.5 1  PORE PRESSURE U ( m of voter) 15 O 150  Cone S o u n d i n g a t S t r o n g P i t , A l d e r g r o v e ,  RESISTIVITY pfohm-m) 0 125  INTERPRETED PROFILE  b  B.C.  10 U3  sand  and g r a v e l which was  Below  the f i l l  between  originally  10  m  t h i c k a t the  i s o v e r c o n s o l i d a t e d stoney c l a y .  the f i l l  and the c l a y i s c l e a r l y  The  marked by  perched  water  desiccated  t a b l e at t h i s point.  layer  The presence  a t the s u r f a c e of the c l a y  The  lower r e s i s t i v i t y  From 1.8  f a i r l y c o n s t a n t a t a v a l u e of 35  distinct  some  i n c r e a s e i n the r e s i s t i v i t y  The  lower  t o 6.8  m  1.8  m)  resistivity.  the  of  resistivity  m  of the c l a y .  T h i s would be  The  there i s a  sand l a y e r c o n t a i n s  l a s t u n i t i n the p r o f i l e  In the sand the r e s i s t i v i t y  conducting  clay  resistivity.  i s a medium  dense  i s h i g h e r due t o the l a c k of  m i n e r a l s but more so due t o h i g h e r pore In  l a y e r , h i g h e r Qc,  4.2.2  to  harder  water and thus would tend t o l e a c h the a d j a c e n t c l a y t o  extent.  sand.  a  a  ohm-m. At 6.8  due t o the p r o x i m i t y of the sand l a y e r . fresher  of  c o u l d be due t o s u r f a c e water f i l l i n g  s m a l l f i s s u r e s i n the c l a y . is  sudden  There i s  (1.5  r e s u l t s i n a h i g h e r cone b e a r i n g and s l i g h t l y  boundary  the  i n c r e a s e i n pore p r e s s u r e and drop i n r e s i s t i v i t y .  site.  water  the sand l a y e r the more denser p a r t s of  the  a l s o have the h i g h e s t r e s i s t i v i t i e s .  Langley  4.2.2.1 S i t e D e s c r i p t i o n  The Langley B.C.  Rail  municipality upland. of  site  i s l o c a t e d approximately  overpass of  100 m  along the Trans Canada  Langley.  T h i s area i s p a r t  Highway of  The area i s u n d e r l a i n by C a p i l a n o sediments  glaciomarine  west of the  the  in  the  Surrey  consisting  c l a y w i t h numerous t h i n i n t e r b e d s of s i l t  and  42  f i n e sand.  4.2.2.2 S t r a t i q r a p h i c and R e s i s t i v i t y  A resistivity site  cone p r o f i l e i s p r e s e n t e d on f i g u r e 4.5.  increase  c l a y . The b e g i n n i n g o f t h e c l a y l a y e r i s marked by an i n pore p r e s s u r e and drop i n r e s i s t i v i t y  becomes s a t u r a t e d .  Generally  the r e s i s t i v i t y  ohm-m, i n c r e a s i n g w i t h depth,  15  ohm-m.  narrow  layers  cone  also  sand  o f f i n e sand. bearing  with  occasional  These t h i n l a y e r s a r e noted by  and low pore p r e s s u r e s .  noted by b e a r i n g  i n the  and pore  account f o r a l l t h e r e s i s t i v i t y highs, high  soil  w i t h o c c a s i o n a l peaks o f up t o  produce pronounced i n c r e a s e s  layers  as t h e  f a l l s between 6 and  The c l a y i s normally c o n s o l i d a t e d  interbeds  increased  The  The  s t r a t i g r a p h y c o n s i s t s o f c l a y o v e r l a i n by 2.3 m o f f i l l and  desiccated  9  Profile  These  sand  resistivity.  pressure  do n o t  such as a t 12.5 m. These  v a l u e s a r e most l i k e l y due t o lower pore water  salinities  i n t h e c l a y o r c o u l d be sand l a y e r s t h a t a r e t o o narrow f o r t h e cone b e a r i n g  r e s i s t a n c e t o respond t o .  4.2.3 Colebrook  4.2.3.1 S i t e  The  Description  Colebrook s i t e  i s l o c a t e d immediately west o f t h e south  abutment o f t h e Highway 99 r a i l w a y overpass. The area i s l o c a t e d w i t h i n t h e Nicomekl-Serpentine V a l l e y a t an e l e v a t i o n o f s e v e r a l metres above s e a - l e v e l .  The v a l l e y has been s u b j e c t e d  t o marine  sedimentation  throughout  (Armstrong, recent.  1984) The  most  of  the  Quaternary  w i t h t h e C a p i l a n o Formation  Capilano  sediments  i n this  Period  being the  area  most  consist  of  g l a c i o m a r i n e c l a y o v e r l y i n g p r o g l a c i a l d e l t a i c sand and g r a v e l .  4.2.3.2 S t r a t i g r a p h i c and R e s i s t i v i t y  Profile  A r e s i s t i v i t y cone p r o f i l e from t h e s i t e that  (Fig.  4.6)  t h e s t r a t i g r a p h y c o n s i s t s mainly o f marine c l a y  dense sand. clay  A t t h e s u r f a c e t h e r e i s 0.5  m  t h e r e s i s t i v i t y i s f a i r l y constant,  tendency  toward  decreasing,  r e s i s t i v i t y from 4.5 from 14 table  t o 25  to  a  suggesting  m  either  In t h e  perhaps w i t h a  between 4.5  and  The  t o 14 m has some minor v a r i a b i l i t y ,  while  o f 4.5  m  25  small  m.  From t h e water  the r e s i s t i v i t y  a change i n l i t h o l o g y o r a  fluid resistivity.  overlying  of t o p s o i l .  t h e p r o f i l e i s v e r y uniform.  depth  shows  i s much change  lower  in  pore  T h i s l a y e r o f lower r e s i s t i v i t y may be  due  t o d e p o s i t i o n o f d i s s o l v e d s o l i d s s i n c e t h e s u r f a c e i s a zone o f groundwater artesian of  discharge.  The  sand l a y e r below  upward  very  flow through  h i g h CEC,  Leaching relatively original  clay  has  pore p r e s s u r e s t h e r e f o r e t h e r e would be some component the c l a y l a y e r .  a l s o have a g r e a t e r o r g a n i c content. a  the  of  the  high  The upper c l a y  Organic s o i l s tend t o have  and h i g h e r CEC s o i l s clay  by  this  a r e more  process  resistivity forthis  would  soil,  s a l i n e d e p o s i t i o n a l environment.  s a l i n i t y may cause t h e c l a y t o be v e r y  could  conductive.  explain  considering  A lowered  sensitive.  the the  pore water  DEPTH  (meters)  o o  O2 o m  h o x z w  o 1  •  P  2  C  - o > s  ft ~ i  I  I  I  i  I  1  o 5 •  •  •  •  •  •  *  i  i  cv i  i  r-  Z) -o I- 30 mm  5. INTERPRETATION AND DISCUSSION OF RESULTS  A  number  resistivity Questions  o f o b s e r v a t i o n s may be made on t h e b a s i s cone  profiles collected  regarding;  profiling  sites.  (1) The r e p e a t a b i l i t y o f t h e RCPTU,  (2) The  o f t h e instrument,  changing s o i l l i t h o l o g y on r e s i s t i v i t y , pore f l u i d r e s i s t i v i t y of  electrode  spacing  examined i n t h i s  the  research  capability  from t h e  of  (3)  effect  of  (4) The d e t e r m i n a t i o n o f  from bulk r e s i s t i v i t y , on t h e measured  The  and (5) The e f f e c t  resistivity,  will  be  chapter.  5.1 R e p e a t a b i l i t y of R e s u l t s  With t h e development o f new i n s t r u m e n t a t i o n i t i s to  verify  the  repeatability confidence small  validity  of  the  of  the  results  measurements.  by  important  checking  Repeatability  the  provides  i n t h e r e s u l t s , e n a b l i n g t h e comparison o f reasonably  changes  in  groundwater  quality  from  different  test  locations.  Two t e s t s , eleven  days  one metre a p a r t , were conducted a t McDonald Farm apart.  The r e s i s t i v i t i e s measured from  the  two  h o l e s by both t h e i n n e r and outer e l e c t r o d e s a r e superimposed on Figure  5.1a  repeatability profiles  and  5.1b.  These  profiles  f o r both the i n n e r and  shown i n F i g u r e 5.1  outer  indicate electrodes.  o n l y d e v i a t e i n t h e upper  good The clayey  F  ig.  5.1  A Comparison of Two Adjacent Resistivity Logs Made 11 Days Apart for (a) The Inner Electrodes, and (b) The Outer Electrodes.  silt, the  t h i s i s due t o water t a b l e f l u c u a t i o n s site  from r a i n f a l l  between the time the two soundings were  at  made.  The  groundwater t a b l e i s c l o s e r t o the s u r f a c e f o r RES 89-10.  There  i s a l s o a sharp peak f o r RES 89-10,  table  f o r RES 89-7 was. at  where t h e groundwater  Due t o the h i g h l y v a r i a b l e n a t u r e o f the sand  t h e s i t e the two p r o f i l e s do not completely match up but the  same peaks and troughs a r e e v i d e n t from both t e s t s .  5.2 P r o f i l i n g C a p a b i l i t y  The r e s i s t i v i t y cone i s i d e a l f o r r a p i d l y d e t e r m i n i n g s e c t i o n a l p r o f i l e s o f groundwater q u a l i t y . be  done  cross  T y p i c a l l y t h i s would  t o d e l i n e a t e the boundaries o f a  contaminant  plume.  While t h e r e i s no contaminant plume as such a t McDonald Farm the s i t e does p r o v i d e a s i m i l a r a p p l i c a t i o n - a s a l t water t o  fresh  water  interface.  fresh  water  i s not d i s t i n c t .  dispersion gradual water,  The i n t e r f a c e between s a l t water There i s  (Bear and V e r r u i j t ,  a  zone  of  and  hydrodynamic  1988) which r e s u l t s i n a  t r a n s i t i o n between f r e s h and b r a c k i s h water.  more  The s a l t  due t o i t s h i g h e r d e n s i t y w i l l tend t o m i g r a t e below the  f r e s h water.  The  s a l t water t o f r e s h water i n t e r f a c e a t McDonald Farm i s  f u r t h e r c o m p l i c a t e d by s e a s o n a l f l u c t u a t i o n s i n r i v e r  salinity.  During  water a t  McDonald  periods Farm  of  low flow i n the w i n t e r the r i v e r  becomes v e r y b r a c k i s h  ( =0.64  ohm-m i n  February) w i t h a s a l i n i t y i n order o f t h a t o f sea water ohm-m,  sea water average, T e l f o r d e t a l , 1976).  early  ( =0.2  When the r i v e r  RESISTIVITY (ohm—m) 0  10  20  RESISTIVITY (ohm-m) 30  i i i i I i i i i I i i i i i  10m from River Fig.  5.2  Stratigraphic  0  10  20  RESISTIVITY (ohm—m) 30  i i i i »i i i t I i i i i»  60m from River  0  10 I I I  1  I  20 I  I  I  I  I  30 I  I  I  i  I  110m from River  and Resistivity Profile of McDonald Farm Site.  oo  flow i s i n c r e a s e d due t o e i t h e r prolonged or  snow  melt  r a i n f a l l i n the w i n t e r  i n t h e s p r i n g and summer  the s a l i n i t y  considerably  (^ = 14.8 ohm-m measured on May 9,  variability  i n salinity  would  be r a p i d l y  groundwater a d j a c e n t t o the r i v e r . the  salinity  seasonal  river  that  much  i l l u s t r a t e s a c r o s s s e c t i o n through t h r e e  the  river  bank.  test  a l o n g w i t h a 6 ohm-m contour and the  4.2).  m,  (RES 89-7,8,9)  The  s i t e map  As i l l u s t r a t e d by the c r o s s s e c t i o n t h e r e i s  11  m  there i s very l i t t l e  the r e s i s t i v i t i e s from the t h r e e t e s t s . t h e r e was v e r y l i t t l e  a  i s approached, as would  f o r the case o f s a l t water i n t r u s i o n .  approximately  f o r each  stratigraphy.  i s shown on the  i n the r e s i s t i v i t y as the r i v e r  be expected  RCPTU  i n a l i n e perpendicular to  The f i g u r e shows the r e s i s t i v i t y  l o c a t i o n o f the h o l e s  if  i n the  variability.  each separated by 50  of  This  reflected  n o t have  soundings,  decrease  1989).  F a r t h e r away from t h e  o f t h e groundwater would  F i g u r e 5.2  (Fig.  drops  Below a depth  d i f f e r e n c e between  T h i s would be the  case  groundwater movement below t h i s  depth.  The  r e s i s t i v i t y o f the s i l t y c l a y does not v a r y a t a l l  across  the  whole  and  t h e r e has been no subsequent groundwater flow  clay.  Near the s u r f a c e ,  resistivity table.  s i t e s i n c e i t was d e p o s i t e d i n a marine  with  environment through  the  t h e r e tends t o be an i n c r e a s e i n t h e  depth o f the overbank s i l t  below  t h e water  T h i s may be due t o d e c r e a s i n g amount o f c o n d u c t i v e  m i n e r a l s w i t h depth i n the overbank d e p o s i t .  clay  5.3  E f f e c t of S o i l  5.3.1  General  Litholocrv  Aspects  As d i s c u s s e d i n the s e c t i o n on c o n d u c t i o n i n s o i l - p o r e systems a number o f d i f f e r e n t f a c t o r s a f f e c t t o b u l k of  the s o i l .  resistivity  By  f a r t h e most  o f the pore f l u i d .  important  resistivity  factor  A t low pore water  fluid  is  the  resistivities  the a f f e c t o f s u r f a c e conduction i s i n s i g n i f i c a n t i n comparison to  e l e c t r o l y t i c conduction i n the pore f l u i d .  The s i t u a t i o n i s  analogous  t o the t o t a l r e s i s t a n c e measured by two r e s i s t o r s i n  parallel,  where the r e s i s t o r s r e p r e s e n t s u r f a c e c o n d u c t i o n and  pore water c o n d u c t i o n . 89-7),  the c l a y e y s i l t  appreciable layer.  resistivity  For example,  a t McDonald Farm (hole RES  l a y e r a t 11.8 m  does not  c o n t r a s t w i t h the sand  provide  bounding  an this  T h i s i s because a much g r e a t e r p r o p o r t i o n o f conduction  i n both s o i l s takes p l a c e through the pore water where the  soil  r e s i s t i v i t y was o n l y about 4 ohm-m.  When  t h e pore water r e s i s t i v i t y  i s h i g h e r the  s u r f a c e c o n d u c t i o n become more apparent. true  and 25  site  where t h e  ohm-m r e s p e c t i v e l y ,  and the sands have v a l u e s o f 110 and 70 ohm-m. surface  of  T h i s was p a r t i c u l a r l y  a t the Strong P i t s i t e and the Colebrook  c l a y s have bulk r e s i s t i v i t i e s o f 35  effects  In c l a y minerals  c o n d u c t i o n i s r e l a t e d t o the CEC c a p a c i t y o f the  soil.  S o i l s w i t h h i g h CEC are c l a y s , the more a c t i v e c l a y s w i l l have a g r e a t e r CEC,  and o r g a n i c s o i l s  ( O l h o e f t , 1985).  The  resistivity  measurement i s a l s o i n d i c a t i v e  water flow regimes. water  with  layer  results  opposite  of  ground  A t t h e Colebrook s i t e r e c h a r g e from ground  a lower amount of d i s s o l v e d s o l i d s than i n t h e c l a y in  a greater r e s i s t i v i t y .  T h i s was  just  the  a t McDonald Farm where b r a c k i s h pore water g i v e s  very  low r e s i s t i v i t i e s r e s u l t i n g i n almost no d i f f e r e n c e between sand and c l a y  resistivity.  5.3.2 Cone Parameter R e l a t i o n s t o S o i l  Resistivity  With t h e simultaneous measurement o f cone b e a r i n g , f r i c t i o n , and pore p r e s s u r e , to  see  how  comparisons may be made w i t h t h e r e s i s t i v i t y  changes i n mechanical s o i l p r o p e r t i e s  affect  the  resistivity.  5.3.2.1 F r i c t i o n R a t i o R e l a t i o n s h i p  The  friction ratio  cone b e a r i n g with  increasing  d e p o s i t s where in  K K  Q  f i n e s content.  affect  space  Q  expressed as a percentage,  will  and i n c r e a s i n g f i n e s c o n t e n t . i s constant R The  the r e s i s t i v i t y  content  the  stress  (R^), s l e e v e f r i c t i o n s t r e s s d i v i d e d by  f  increase In  may be used t o note i n c r e a s e s  presence of f i n e s i n a sandy s o i l in  two  ways:  (1)  increased  w i l l decrease p o r o s i t y s i n c e t h e f i n e s w i l l occupy between t h e  effect  presence  of  sand  grains.  of i n c r e a s i n g fines  sand  fines void  D e c r e a s i n g t h e p o r o s i t y has  the r e s i s t i v i t y ;  may i n d i c a t e  may  t h e presence  and of  (2)  the  conducting  RESISTIVITY ( o h m - m )  RESISTIVITY ( o h m - m )  0 5 10 15 ^ Ii i i iii i i i i i ii i i  0  20 25 30 j.ijjiiii i i i i  4  5 ii  i i i  10 ii  i i  15 j j_  >_  i i  20 25 30 i i iII i i i i i i i  6-  6-  i  | i i i i  I  8  CL  8  UJ Q  Q  10-  10  RESISTIVITY (ohm-m) FRICTION RATIO  RESISTIVITY (ohm-m) FRICTION RATIO «  12 | 0.0  I  1  i  |  l  0.2  I  i " |  0.4  i  I  i  |  l  0.6  I  I  |  0.8  I  I  I  1.0  12 i r i | i i i | i i i | i i i | i i i 0.0 0.2 0.4 0.6 0.8 1.0 FRICTION RATIO  FRICTION RATIO Fig.  5.3  A  Comparison of the Resistivity (Outer Electrodes) and the Friction Ratio for Two Soundings from the McDonald Farm Site.  ui  clay minerals,  which would r e s u l t i n a decrease  F i g u r e 5.3  McDonald Farm,  (  increased  friction ratio in  the r e s i s t i v i t y .  RES  89-5,7)  at  conduction resistivities. and  other The  resistivity  their  was  conductivity  remove  the  However,  effects the  a p p l i c a t i o n of  T h i s would suggest t h a t , a t  conduction  relationship  between  data as a f u n c t i o n of  complex  lithological  of pore  mechanisms  fluid  at  low  friction  noted by ERTEC (1987).  of  the  decreases t h i s e f f e c t becomes  t h i s being due t o the domination  over  match  t h a t f i n e s i n the sand w i l l decrease  As the r e s i s t i v i t y  l e s s pronounced,  that  decrease  G e n e r a l l y the peaks i n the r e s i s t i v i t y  this site,  resistivity.  illustrates  sandy s o i l s w i l l tend t o  the troughs i n the f r i c t i o n r a t i o . least  in resistivity.  They  ratio  normalized  friction  ratio  change from t h e i r  nature of s o i l r e s i s t i v i t y  to  data.  make  the  such c o r r e c t i o n s u n c e r t a i n .  5.3.2.2 Cone B e a r i n g R e l a t i o n s h i p  Cone  bearing  horizontal density  effective  density  effective  is  stress,  compressibility,  and  cone b e a r i n g  there  i s a similar  resistivity  to  soil  1988).  be  related and  between  by  horizontal  so i t s h o u l d be  reasonable  between  formation  s i n c e the f o r m a t i o n f a c t o r  p o r o s i t y by A r c h i e ' s  Formula.  In  s o i l s t h i s r e l a t i o n s h i p has been shown t o be  (Jackson, 1978). F i g u r e 5.4  to  relative  Relations  normalized  correlation  and n o r m a l i z e d cone b e a r i n g ,  related  accurate  has been shown t o  s t r e s s have been proposed  expect  factor  sands  (Robertson and Campanella,  relative  to  in  r e l a t e s apparent  low quite  formation  CONE BEARING /  F i g . 5.4  HORIZONTAL EFFECTIVE  STRESS  (Ko=0.55)  Observed Relationship Between Apparent Formation Factor and Cone Bearing Normalized with Respect to H o r i z o n t a l Effective Stress.  f a c t o r t o t h e normalized cone b e a r i n g . is  not  that  bearing,  or  formation  strong i t s t i l l decreased  While t h e  illustrates  relative  that  density  relationship  increased  will  cone  increase the  factor.  5.3.2.3 Pore P r e s s u r e R e l a t i o n s h i p  No d i r e c t r e l a t i o n s h i p between any pore p r e s s u r e and  resistivity  are  indicative  resistivity. behavior,  has been made. of  a  high  parameters  I n g e n e r a l h i g h pore fines  content,  pressures  thus  a  I n normally c o n s o l i d a t e d c l a y e y s o i l s ,  lower dilative  which would be i n d i c a t i v e o f sand l a y e r s , may a l s o be  r e f l e c t e d by changes i n t h e r e s i s t i v i t y .  5.4 D e t e r m i n a t i o n o f Pore F l u i d  From  Figure  resistivity measured  5.5  i t can be  determined  from  the  Resistivity  basis  possible  of to  cone r e l a t e q u i t e w e l l ,  resistivities related  by  t h e pore  with  fluid  resistivity a  formation  T h i s c o r r e l a t i o n i s expected on  A r c h i e ' s Formula. make  that  from BAT samples and t h e b u l k  f a c t o r between t h r e e and f o u r . the  seen  reasonable  from t h e r e s i s t i v i t y the formation f a c t o r .  Given t h i s , estimates cone.  i t should of  pore  be  fluid  The two q u a n t i t i e s a r e  Therefore,  t h e pore  fluid  r e s i s t i v i t y may be estimated by d e t e r m i n i n g t h e f o r m a t i o n f a c t o r by e i t h e r : fluid  (1) s i t e s p e c i f i c c o r r e l a t i o n s between s o i l and pore  resistivity;  o r (2)  A r c h i e ' s Formula assuming  a c c u r a t e e s t i m a t e o f t h e s o i l p o r o s i t y i s known.  that  an  Fig.  5.5  A Comparison Between the R e s i s t i v i t y of Pore Fluid Samples and the R e s i s t i v i t y Measured by the RCPTU.  The  estimation  o f pore f l u i d r e s i s t i v i t y  i n clay  d i f f i c u l t due t o t h e e f f e c t s o f s u r f a c e c o n d u c t i o n . apparent  formation  resistivity, apparent 10.6 This  In c l a y the  f a c t o r i s v e r y dependent on t h e pore  c l a y m i n e r a l content and type.  fluid  From Colebrook t h e  f o r m a t i o n f a c t o r was found t o be 1.43  at a  depth  of  m on t h e b a s i s o f a water sample o b t a i n e d from a BAT probe. i s c o n s i d e r a b l y lower than t h e range o f 3 t o 4  noted i n t h e sand a t McDonald Farm. Farm has an apparent Archie's  Formula  that  According  the formation f a c t o r f o r a c l a y with assuming m=2.  a  Colebrook  to void  So t h a t a t t h e McDonald  s i t e A r c h i e ' s Formula was a p p l i c a b l e s i n c e t h e pore  r e s i s t i v i t y was v e r y low.  was  The s i l t y c l a y a t McDonald  f o r m a t i o n f a c t o r o f 4 t o 5.  r a t i o o f 1 should be 4, Farm  i s more  fluid  F o r n=0.6,m=2, F - i n t r i n s i c = 2.8 f o r  as compared t o t h e F-apparent  = 1.43.  This difference  i s due t o c l a y m i n e r a l s u r f a c e conduction.  5.5  I n f l u e n c e o f E l e c t r o d e Spacing on Measured R e s i s t i v i t y  The  UBC  simultaneous electrodes.  resistivity  cone  has  measurement o f r e s i s t i v i t y This  section  been  equipped  to  make  from t h e i n n e r and outer  d e a l s w i t h t h e comparison  of the  r e s u l t s o f t h e i n n e r and outer e l e c t r o d e s and suggests why t h e r e should be d i f f e r e n c e s between t h e two measurements i n soil  different  types.  When t h e e l e c t r o d e s a r e i n a homogeneous - i s o t r o p i c the e l e c t r o d e s should respond  medium  i n a s i m i l a r manner t o t h a t o f t h e  case of water immersion. However, s o i l i s r a r e l y homogeneous and isotropic,  so  dependent caused  that  the response  electrodes  penetration.  contrasting  resistivity  resistivity  will  p e n e t r a t e d the  not  the f u l l response be  have  of the two  narrow l a y e r s .  When the e l e c t r o d e s e n t e r a  noted  until  of  due t o the change  in  the  probe  has  The  magnitude  i n F i g u r e s 5.6  t o 5.9.  In these  of  p r e s e n t e d as t o why  these  observations  some  sand.  to  figures  s i n c e i t i s the results.  suggestions  t h e r e should be a d i f f e r e n c e between the  are two  measurements.  Clean sands a t McDonald Farm ( F i g . 5.6):  measured  the  from the i n n e r and o u t e r e l e c t r o d e s  s o i l type t h a t appears t o cause the d i f f e r e n c e s i n the basis  of  f o l l o w i n g o b s e r v a t i o n s were made a t the t e s t  are superimposed and compared t o the s o i l type,  1.  fully  e l e c t r o d e p a i r s and t h e i r r e s p o n s i v e n e s s  the r e s i s t i v i t i e s determined  resistivity  soil  layer  been made between the  s i t e s and are presented  the  be  layer.  Comparisons  On  will  on the s t a t e of the s o i l and the changes t o the  by  results  of the  The  resistivity  by the o u t e r e l e c t r o d e s i s g r e a t e r i n the medium dense  In s i l t y sands t h e r e appears t o be v e r y l i t t l e d i f f e r e n c e  at McDonald Farm.  2.  Langley  almost  (Fig.  exactly  interbeds.  the  5.7): same  The  i n n e r and o u t e r e l e c t r o d e s  result  in  clay  with  narrow  give sand  59  RESISTIVITY (oh m—m) 10 20  Fig.  5.6  SOIL T Y P E 30  INNER ELECTRODES OUTER ELECTRODES A comparison between the r e s i s t i v i t y measured by the inner and outer e l e c t r o d e s at McDonald Farm.  60  Fig.  5.7  A comparison between the r e s i s t i v i t y measured by the inner and outer e l e c t r o d e s at Langley.  61  0  RESISTIVITY (ohm-m) 50  SOIL T Y P E 100 FILL; PEAT & ORGANIC SILT  CLAY  SAND  Fig.  5.8  •- INNER ELECTRODES - OUTER ELECTRODES A comparison between the r e s i s t i v i t y measured by the inner and outer e l e c t r o d e s at Colebrook.  62  RESISTIVITY ( o h m - m ) 25 50 75 100  SOIL T Y P E 125 SANDY GRAVEL  O.C. SILTY CLAY  SAND  INNER ELECTRODES OUTER ELECTRODES Fig.  5.9  A comparison between the r e s i s t i v i t y measured by the inner and outer e l e c t r o d e s at Strong P i t .  3.  Colebrook ( F i g . 5.8):  the  same  in  clay.  The  r e s u l t s of the two  However  the  s u b s t a n t i a l l y greater r e s i s t i v i t y  4.  Strong P i t ( F i g . 5.9):  the  sand  the  The  inner  e l e c t r o d e s are  electrodes  i n the l o o s e sand l a y e r .  r e s u l t s are the same i n c l a y and  l a y e r w i t h the e x c e p t i o n of the l a s t  sand  is  looser,  the  give  inner  electrodes  40 cm,  give  where  a  higher  resistivity.  In to  dense sands t h e r e i s a narrow zone of d i l a t i o n  the cone.  For l o o s e sands t h e r e i s an i n c r e a s e i n  adjacent  t o the cone.  adjacent  to  the  I f there i s d e n s i f i c a t i o n i n  cone the r e s i s t i v i t y measured  e l e c t r o d e s would be g r e a t e r .  by  of  representative undisturbed  the e l e c t r i c f i e l d the  a  Adjacent  greater  the  clays  the  r e s i s t i v i t y measurements should be  more  of  the  and c l a y ,  both NC  and  OC,  resistivity  t o the cone, when pushing through c l a y , t h e r e  of remolding.  T h i s remolding  of the  clay  volume and hence constant water content.  water content change.  the  soil.  zone  constant  inner  case  t h a t the i n n e r and outer e l e c t r o d e s g i v e c o n s i s t e n t  is  sand  In any  i n t o the s o i l and  I t has been observed t h a t i n s i l t  results.  the  For the case of a dense sand  l a r g e r the s p a c i n g between the e l e c t r o d e s the  penetration  density  the  i n n e r e l e c t r o d e s would measure a lower r e s i s t i v i t y . the  adjacent  This  of the s o i l  i s constant the r e s i s t i v i t y  i s i n f a c t the behavior  t e s t e d a t the f o u r s i t e s .  noted i n a l l  is  at  Since  the  should  not  the  By measuring r e s i s t i v i t y  silty at a  number  of  different  spacings  one  can  use  the  measurements t o note t h e a f f e c t o f sand d i s t u r b a n c e F i g u r e 5.5 has  suggests,  f o r clays,  values of undisturbed  the  resistivity  spacing  This  is  c l o s e l y spaced e l e c t r o d e s w i l l resistivity.  affected  by  In sands t h e v a l u e  soil  e f f e c t decreases w i t h  Therefore,  increased  give of from  electrode undisturbed  f o r contaminant s t u d i e s  i s p r e f e r a b l e t o have c l o s e e l e c t r o d e  because  disturbance  because more o f t h e c u r r e n t t r a v e l s through  s o i l f u r t h e r from t h e cone. it  disturbance  f a c t o r t o be more uniform.  true  penetration.  by t h e cone.  f o r the inner electrodes, that  caused t h e formation  In g e n e r a l ,  resistivity  spacing.  This  is  t h e narrow spacing w i l l i n d i c a t e t h e presence o f narrow  layers  and t h e i n f l u e n c e o f sand d e n s i t y i s reduced,  making i t  easier  to  basis  estimate  measured s o i l  pore f l u i d c o n d u c t i v i t y on  resistivities.  the  of  65  6. APPLICATIONS OF THE RESISTIVITY CONE  The  purpose  of  t h i s r e s e a r c h was  the  r e s i s t i v i t y cone f o r contaminant d e t e c t i o n . is  accessing  done.  The  such s i t e s no t e s t i n g a t following  contaminants describes  the how  investigation.  section  for  method would be  the  RCPTU  should  The  resistivity  be  of  a  Due t o d i f f i c u l t i e s  contaminant  outlines  resistivity  development  sites  was  types  of  applicable  and  what  deployed  in  cone can be used  a  site  for  other  a p p l i c a t i o n s which are d e s c r i b e d a t the end of t h i s c h a p t e r .  6.1 A p p l i c a b i l i t y o f R e s i s t i v i t y f o r Contaminant  There  a r e two g e n e r a l groups of contaminants;  phase l i q u i d s Aqueous  Detection  (APLs);  phase  1)  and 2) Non-aqueous phase l i q u i d s  Aqueous (NAPLs).  l i q u i d s c o n s i s t of both c o n d u c t i n g ( i o n i c )  and  s o l u b l e o r g a n i c ( i n s u l a t i n g ) contaminants.  The e a s i e s t contaminants t o d e t e c t by the r e s i s t i v i t y method are  conducting  aqueous  c o n t a m i n a t i o n may or  be l a n d f i l l s  mine t a i l i n g s .  Fe  due  aqueous  to  and H .  (industrial,  of  sanitary, when  such  f l y ash) oxidized,  The b e s t conductors a r e s o l u t i o n s  a c i d s , and bases.  s a l t water i n f i l t r a t i o n  phase  Sources  +  most i n o r g a n i c s a l t s , be  liquids.  P y r i t e produces a c i d water  3+ releasing  phase  of  Contamination may  of also  aquifers.  Non-ionic  l i q u i d s w i l l not be d e t e c t e d by the  resistivity  66  method.  Non-aqueous  phase  contaminants. resistivity space  The  liquids presence  (NAPLs) of  NAPLs  are i n s u l a t i n g decreases  organic  the  bulk  by b l o c k i n g pathways o f c o n d u c t i o n through the pore  of the s o i l .  NAPLs can be e i t h e r c l a s s i f i e d  as  DNAPLs,  contaminants t h a t are denser than water, o r f l o a t i n g NAPLs, t h a t have a d e n s i t y l e s s than t h a t of water.  DNAPLs w i l l s i n k under  a g r a v i t y g r a d i e n t t o some low p e r m e a b i l i t y l a y e r o r w i l l i n r e s i d u a l s a t u r a t i o n . L i g h t NAPLs w i l l f l o a t the  water  table  resistivity of  may  be d i f f i c u l t  the presence of contamination. test  effectiveness assuming  to  on the s u r f a c e of detect  site  would  be  However, necessary  the  o f the RCPTU a t d e t e c t i n g such contaminants.  By  to  approximately  estimate  c o n t a m i n a t i o n by assuming the r e s i s t i v i t y e q u i v a l e n t t o t h a t of a i r .  to  an the  used  sufficient  f i e l d work a t evaluate  NAPLs a r e i n s u l a t o r s A r c h i e ' s Formula  be  since  above the water t a b l e would be v e r y h i g h r e g a r d l e s s  appropriate  can  and  remain  (Equation the  amount  of the contaminant  2.4) of is  For the r e s i s t i v i t y method t o note a  change t h e r e would need t o be a t  least  5%  NAPL  saturation.  However,  i n most cases c o n d u c t i v e contaminants w i l l be  t a r g e t of a s i t e  investigation.  the  T h i s i s because most i n d u s t r i a l  waste w i l l have a l a r g e component o f d i s s o l v e d s o l i d s a l o n g w i t h possible are  NAPLs.  v e r y hazardous.  contamination  Very s m a l l amounts of some o r g a n i c  chemicals  I f such contaminants a r e the o n l y source of  the r e s i s t i v i t y  cone would not be a b l e t o  detect  Table 6.1 Summary of Typical Resistivity Measurements of Fluids and Bulk Soil-Fluid Mixtures ,ohm-m p f,ohm-m (fluid) (bulk soil) Seawater  0.2  -  Drinking Water  >15  -  McDonald Farm Clay Colebrook Site Clay 401 @ 232 Ave., Railway Site Clay B.C. Highway Strong Pit Clay  0.3 18.2  McDonald Farm Sand Colebrook Site Sand Strong Pit Sand  1.5-6  Typical Landifll Leachate  0.5-10  100% Ethylene Dichloride (ED)  20400  25 8 35 5-20 70 115  50% ED/50% 150 ohm-m fluid i n Wedron 7020 sand  696  30% ED/70% 150 ohm-m fluid i n Wedron 7020 sand  335  17% ED/83% 150 ohm-m fluid in Wedron 7020 sand  273  1.5  them.  The r e s i s t i v i t y  resistivity. as  cone i s used f o r d e t e r m i n i n g c o n t r a s t s i n  I f the n a t u r a l groundwater i s v e r y b r a c k i s h ,  i n a marine d e l t a ,  contaminants.  i t may  be d i f f i c u l t t o d e t e c t c o n d u c t i v e  On the o t h e r hand i f the n a t u r a l groundwater i s  h i g h l y c o n d u c t i v e i t becomes e a s i e r t o d e t e c t i n s u l a t i n g Table  6.1  number  p r o v i d e s a convenient  of s o i l types,  NAPLs.  summary of r e s i s t i v i t i e s of  s o i l contaminant mixtures,  and  Having a knowledge of the s o i l type and contamination one  such  fluids.  at a  can use t h i s i n f o r m a t i o n t o h e l p d e c i d e i f the  a  site  resistivity  method i s a p p r o p r i a t e .  6.2  Use of the RCPTU i n Contamination  Problems  By i t s e l f the RCPTU i s a v a l u a b l e t o o l i n contamination investigations. groundwater  site  Besides p r o v i d i n g i n f o r m a t i o n on the extent of  contamination  the  cone  may  also  be  used  for  determining: hydrogeological p r o p e r t i e s , s t r a t i g r a p h i c  profiles,  and  a  suggested  CPTU can q u i c k l y determine steady s t a t e pore  pressures  geotechnical  properties.  The  following  is  o u t l i n e f o r an RCPTU i n v e s t i g a t i o n .  The in  drained  measures stopped pore  Given t h a t  pore p r e s s u r e ,  the  CPTU  provides  soundings should  t o a l l o w an a c c u r a t e d e t e r m i n a t i o n of  pressure.  almost be  of  soils.  In sandy s o i l s  equilibrium  be the will  accurate  periodically equilibrium be  reached  i n s t a n t a n e o u s l y thus a l l o w i n g many such measurements  made.  silty soils  D i s s i p a t i o n of excess pore p r e s s u r e i s f a i r l y rapid.  in  to  non-plastic  In p l a s t i c c l a y s i t would not  be  practical  t o determine t h e e q u i l i b r i u m pore p r e s s u r e due t o t h e  low p e r m e a b i l i t y o f such s o i l s . a  By r e p e a t i n g t h i s procedure i n  number o f h o l e s a t a s i t e t h e d i r e c t i o n and magnitude o f t h e  h y d r a u l i c g r a d i e n t may be determined.  The  hydraulic  grained  conductivity  can  be  determined  s o i l s by pore p r e s s u r e d i s s i p a t i o n s .  D e t a i l s on  procedure may be found i n Robertson and Campanella procedure clays.  f o r fine  (1988).  initial  estimate  parameters.  Porosity  classifications  the  effective  For drained  soils  o f h y d r a u l i c c o n d u c t i v i t y can be made  b a s i s o f s o i l type c l a s s i f i c a t i o n  the  and  I n t h e case t h a t such s o i l s a r e encountered i t would be  method o f d e t e r m i n i n g h y d r a u l i c c o n d u c t i v i t y .  the  This  works w e l l f o r normally c o n s o l i d a t e d s i l t y c l a y s  worthwhile d o i n g a d i s s i p a t i o n t e s t s i n c e i t i s a c o s t  an  this  may  determined from  a l s o be e s t i m a t e d  from  and r e l a t i v e d e n s i t y e s t i m a t e s .  t h e CPT soil  type  Alternatively  p o r o s i t y may a l s o be determined by u s i n g a m i x i n g law. case o f low r e s i s t i v i t y  determine  on  In  sand A r c h i e ' s Formula may be used t o  porosity providing the r e s i s t i v i t y  o f t h e pore  fluid  i s a l s o known.  A  rapid  groundwater tests. prepared.  assessment  of  contamination  the three  dimensional  extent  can be made a f t e r a s e r i e s  of  S e c t i o n s showing s t r a t i g r a p h y and r e s i s t i v i t y By comparing t h e r e s i s t i v i t y  at. c e r t a i n  of cone  s h o u l d be, points  to  contaminant c o n c e n t r a t i o n s determined from d i r e c t water sampling the an  resistivity indication  v a l u e s may be used s e m i ^ q u a n t i t a t i v e l y t o o f contaminant c o n c e n t r a t i o n s a t  other  give  points.  The  h i g h l y accurate  allows  s t r a t i g r a p h i c p r o f i l e t h a t t h e CPT  provides  f o r t h e i d e n t i f i c a t i o n of s o i l l a y e r s w i t h h i g h  hydraulic  conductivities soils  with  aquitards obtained  that  low  may be pathways f o r contaminants.  hydraulic  conductivities  are also i d e n t i f i e d .  which  may  Also a c t as  A t t h e same time t h e i n f o r m a t i o n  from t h e CPT can a l s o be used t o determine  geotechnical  parameters.  On  the  planning and  basis  f o r other  o f an i n i t i a l  forms o f i n v e s t i g a t i o n ,  sampling w e l l s , can be made.  periodic  monitoring  contaminants.  i n v e s t i g a t i o n with  of  a  the  RCPTU  such as piezometers  The RCPTU can a l s o be used f o r  s i t e t o note  the  advance  of  any  I f b a s e l i n e r e s i s t i v i t y t e s t s a r e done changes i n  the groundwater chemistry can be e a s i l y noted.  6.3 Other P o s s i b l e A p p l i c a t i o n s o f t h e RCPTU  While  t h e r e s i s t i v i t y cone was designed w i t h t h e t h e purpose  of contaminant d e t e c t i o n i t may be a p p l i e d t o other areas.  Three  applications are b r i e f l y outlined i n the following section.  6.3.1 C o r r o s i o n  Soils  with  Assessment  low r e s i s t i v i t i e s have h i g h  concentrations  d i s s o l v e d s o l i d s which would a c c e l e r a t e c o r r o s i o n . adopted Group having  i n t h e U n i t e d Kingdom ( G e o l o g i c a l Working P a r t y , a  1988)  Society  A  of  standard  Engineering  d e f i n e s s e v e r e l y c o r r o s i v e s o i l as  r e s i s t i v i t y o f l e s s than 10  ohm-m,  and  moderately  corrosive  s o i l s having a r e s i s t i v i t y  ohm-m. S o i l s w i t h a r e s i s t i v i t y  i n t h e range o f 10  t o 100  o f g r e a t e r than 100 ohm-m a r e o f  l i t t l e concern w i t h r e s p e c t t o c o r r o s i o n .  6.3.2 Water Q u a l i t y Assessment  As  noted  earlier  there i s a  strong  between TDS and f l u i d c o n d u c t i v i t y . pore  water  measurement formation  resistivity  may  be  resistivity  can be made.  estimated  from  F o r sands,  hence  the direct by  using  an i n i t i a l estimate o f t h e pore The l i m i t o f t o t a l d i s s o l v e d  f o r p o t a b l e water i s 500 mg/1 (water r e s i s t i v i t y m)  relationship  By u s i n g a mixing law t h e  o f t h e bulk r e s i s t i v i t y . f a c t o r o f 3.5,  linear  a  fluid solids  aprx = 12 ohm-  f o r most sand a q u i f e r s t h e minimum b u l k  resistivity  s h o u l d be i n t h e range o f 35 t o 50 ohm-m.  6.3.3 S o i l  The  Classification  resistivity  classification water  cone  can be used  as  a  tool  for soil  where s o i l h o r i z o n s have d i f f e r e n t s a l i n i t i e s o r may  make  r e s i s t i v i t y measurements an i d e a l method o f d i f f e r e n t i a t i n g  such  soil  contents.  The h i g h water content o f peats  from o t h e r s o i l s w i t h lower water c o n t e n t s .  measurements  are ideal  Resistivity  f o r d e t e c t i n g t h e presence  of frozen  ground.  There  can be no m o b i l i t y o f e l e c t r o l y t e s  therefore  i t a c t s as an i n s u l a t o r and i c e content c o u l d perhaps  be i n f e r r e d by u s i n g A r c h i e ' s Formula.  in  ice,  R e s i s t i v i t y measurements  would a l s o be s e n s i t i v e t o t h e presence o f gas i n s o i l .  72  7. CONCLUSIONS AND RECOMMENDATIONS  It  was  initial  found,  through e x t e n s i v e  f i e l d tests,  d e s i g n o f t h e UBC RCPTU was s u c c e s s f u l i n  accurately  determining  resistivity.  that  the  rapidly  and  The r e p e a t a b i l i t y o f t h e  measurements and t h e f a v o r a b l e comparisons t o d i r e c t groundwater sampling proved t h e v a l i d i t y  While  in  of the r e s u l t s .  t h i s r e s e a r c h no a c t u a l contaminated  sites  were  t e s t e d t h e t e s t i n g done a t t h e McDonald Farm s i t e served w e l l t o show t h e a b i l i t y o f t h e RCPTU t o make a d e t a i l e d p r o f i l e  of the  bulk  i n the  resistivity,  amount noted  of  total  that  which i s r e p r e s e n t a t i v e o f changes d i s s o l v e d s o l i d s i n t h e groundwater.  changes i n s o i l p o r o s i t y and  i n f l u e n c e t h e bulk r e s i s t i v i t y . simultaneous inner changes  measurements  electrodes in  showed  fines  content  was  could  The f o u r e l e c t r o d e module with  o f r e s i s t i v i t y from that  It  penetration  the  outer  causes  and  localized  s o i l d e n s i t y which i n t u r n i n f l u e n c e s t h e  measured  bulk r e s i s t i v i t y o f sandy s o i l s .  Due  to  contaminants method.  the e l e c t r i c a l l y they should  Besides  insulative properties  a l s o be d e t e c t a b l e by t h e  being a t o o l f o r contaminant  RCPTU may a l s o be used f o r c o r r o s i o n assessment,  of  organic  resistivity  detection  the  d r i n k i n g water  q u a l i t y assessment, and as an a i d i n s t r a t i g r a p h i c l o g g i n g .  On  the  speed,  b a s i s of the r e s u l t s p r e s e n t e d i t appears t h a t  economy,  and r e l i a b i l i t y of the RCPTU make i t i d e a l f o r  many contaminant i n v e s t i g a t i o n s i n u n c o n s o l i d a t e d s o i l . field  testing  across  with  simultaneous  measurement  of  Lab and  resistivity  two s e t s of e l e c t r o d e s showed t h a t a two e l e c t r o d e probe  operating For  a t a frequency of no l e s s than 1000  contaminant  electrodes layers  is  and  applications  desirable  close  Hz i s  spacing  adequate.  between  as i t g i v e s good r e s o l u t i o n  tends t o reduce the i n f l u e n c e o f s o i l  measurements of sand  water sampling program be undertaken.  porosity  sites  Testing i n different  w i l l g i v e an i n d i c a t i o n of what background  Ideally,  s h o u l d take p l a c e a t a w e l l documented s i t e of  d e t e c t the presence of contaminants.  legitimize  the  RCPTU  as  a  practical  organic  Further research tool  soil  resistivities  contamination t o prove t h a t the r e s i s t i v i t y method i s v i a b l e to  in  comprehensive  c o u l d be expected when t e s t i n g a t a contaminant s i t e . testing  thin  resistivity.  v a r i o u s s o i l c o n d i t i o n s coupled w i t h a more  types  the  of  I t i s recommended t h a t f u r t h e r f i e l d work a t d i f f e r e n t with  the  in  way will  contaminant  investigations.  Further r e s i s t i v i t y would changes  f i e l d t e s t i n g c o u p l e d w i t h s o i l sampling  a l l o w f o r comparisons between changes i n r e s i s t i v i t y i n s o i l water content,  percentage of c l a y ,  and  and clay  type.  Numerical  modeling c o u l d be used t o determine the  distance  the e l e c t r i c a l f i e l d p e n e t r a t e s be  i n t o the s o i l .  Modeling  could  u s e f u l i n i l l u s t r a t i n g the i n f l u e n c e of s o i l d i s t u r b a n c e  of e l e c t r o d e s p a c i n g on observed r e s i s t i v i t y  Research structures  into  the  subject  would be a p p r o p r i a t e  of  the  and  measurements.  corrosion  of  s i n c e the measurement  buried  of  bulk  r e s i s t i v i t y i s one way of a s s e s s i n g s o i l c o r r o s i o n p o t e n t i a l .  Research permittivity measurements the  i n t o the v i a b i l i t y i n t o making i n - s i t u measurements  could  be  examined.  dielectric Dielectric  have a p p l i c a t i o n i n both contaminant d e t e c t i o n and  determination  of  soil  water  content.  This  a p p l i c a t i o n would be a p r a c t i c a l approach i n determining v o i d r a t i o of c o h e s i o n l e s s  soils.  former in-situ  REFERENCES  Archie, G.E. 1942. The e l e c t r i c a l r e s i s t i v i t y l o g as an a i d i n determining some r e s e r v o i r characteristics, Transactions American I n s t i t u t e of M i n e r a l M e t a l l u r g y E n g i n e e r i n g 146, pp. 54-62. Armstrong, J.E. 1984. Environmental and E n g i n e e r i n g A p p l i c a t i o n s of the S u r f i c i a l Geology of the F r a s e r Lowland, British Columbia. Paper 83-23, GSC. 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