Evaluation of Soil ResistivityMeasurement Techniques

Contract PR-262-0114

Prepared for the

Corrosion and Inspection Technical Committeeof

Pipeline Research Council International, Inc.

Prepared by the following Research Agency:

CORRENG Consulting Service Inc.Toronto, ON, Canada

Author:Robert G. Wakelin, P.Eng.

Publication Date:May 2006

Catalog No. L52127

Section 1 - Introduction

1.1 GENERAL ............................................................................................................................................................. 1-1

1.2 OBJECTIVES ........................................................................................................................................................ 1-1

1.3 PROPOSED WORK PLAN ..................................................................................................................................... 1-21.3.1 Preliminary Work ................................................................................................................................... 1-21.3.2 Field Trials .............................................................................................................................................. 1-21.3.3 Interpretation of Data ............................................................................................................................. 1-31.3.4 End Product ........................................................................................................................................... 1-3

Section 2 - Background

2.1 RESISTANCE AND RESISTIVITY .......................................................................................................................... 2-1

2.2 THE EARTH AS A CONDUCTOR OF ELECTRICITY ................................................................................................ 2-22.2.1 General .................................................................................................................................................. 2-22.2.2 Effect of Temperature ............................................................................................................................. 2-32.2.3 Effect of Water Content .......................................................................................................................... 2-42.2.4 Effect of Ionic Content ........................................................................................................................... 2-42.2.5 Effects of Other Factors ......................................................................................................................... 2-5

2.3 SOIL RESISTIVITY MEASUREMENT .................................................................................................................... 2-52.3.1 Types of Soil Resistivity Surveys ........................................................................................................... 2-52.3.2 General Applications for Soil Resistivity Surveys ................................................................................... 2-62.3.3 A History of Resistivity Measurement Techniques ................................................................................. 2-72.3.4 Other Electrical Geophysical Measurements Unrelated to Resistivity ................................................... 2-10

2.3.4.1 Induced Polarization (IP) ................................................................................................ 2-102.3.4.2 Self Potential (SP) .......................................................................................................... 2-112.3.4.3 Other Applied Current Methods ...................................................................................... 2-12

2.4 RESISTIVITY MEASUREMENT FOR PIPELINE CORROSION APPLICATIONS ..................................................... 2-122.4.1 Electrode Resistance Calculations ....................................................................................................... 2-122.4.2 Corrosion Risk Assessment ................................................................................................................. 2-142.4.3 Other Applications ............................................................................................................................... 2-16

Section 3 - Measurement Techniques

3.1 INTRODUCTION ................................................................................................................................................... 3-1

3.2 GALVANIC METHODS........................................................................................................................................... 3-23.2.1 General .................................................................................................................................................. 3-23.2.2 Theoretical Basis .................................................................................................................................... 3-33.2.3 Four-Pin Arrays ...................................................................................................................................... 3-5

Table of Contents

Page xii Evaluation of Soil Resistivity Measurement TechniquesTable of Contents

3.2.3.1 Wenner Arrays .................................................................................................................. 3-53.2.3.2 Theorem of Reciprocity .................................................................................................... 3-73.2.3.3 Schlumberger Array ......................................................................................................... 3-83.2.3.4 Schlumberger-Palmer Array ............................................................................................. 3-93.2.3.5 Dipole-Dipole Array .......................................................................................................... 3-93.2.3.6 Pole-Pole Array ............................................................................................................... 3-103.2.3.7 Pole-Dipole Array ........................................................................................................... 3-113.2.3.8 Lee’s Method of Partitioning ........................................................................................... 3-123.2.3.9 Box Array ........................................................................................................................ 3-13

3.2.4 Resistivity Soundings .......................................................................................................................... 3-143.2.4.1 Depth of Current Penetration .......................................................................................... 3-143.2.4.2 Effect of Soil Stratification .............................................................................................. 3-163.2.4.3 Depth of Investigation .................................................................................................... 3-193.2.4.4 Resolution ...................................................................................................................... 3-22

3.2.5 Interpretation of Resistivity Soundings ................................................................................................ 3-233.2.5.1 Apparent Resistivity Curves ............................................................................................ 3-233.2.5.2 Curve Matching - Two-Layer Soils .................................................................................. 3-263.2.5.3 Curve Matching - Multi-Layer Soils ................................................................................ 3-273.2.5.4 Partial Curve Matching - Multi-Layer Soils ..................................................................... 3-283.2.5.5 Inverse Modelling ........................................................................................................... 3-293.2.5.6 Tagg’s Method ................................................................................................................ 3-293.2.5.7 Barnes-Layer Method ..................................................................................................... 3-303.2.5.8 Point-of-Inflection Methods ............................................................................................ 3-313.2.5.9 Other Methods ................................................................................................................ 3-333.2.5.10 Effect of Lateral Variations on the Interpretation of Sounding Data ................................ 3-333.2.5.11 Further Discussion of Interpretive Methods .................................................................... 3-37

3.2.6 Resistivity Profiling .............................................................................................................................. 3-383.2.7 Instrumentation and Equipment ........................................................................................................... 3-40

3.2.7.1 General Considerations ................................................................................................... 3-403.2.7.2 Test Current Frequency ................................................................................................... 3-423.2.7.3 Specific Examples of Instruments .................................................................................. 3-443.2.7.4 Associated Equipment .................................................................................................... 3-50

3.2.8 Further Discussion of Galvanic Measurement Techniques ................................................................... 3-523.2.8.1 Wenner Versus Schlumberger ........................................................................................ 3-523.2.8.2 Notes on Other Arrays .................................................................................................... 3-54

3.3 ELECTROMAGNETIC (EM) METHODS................................................................................................................ 3-573.3.1 General ................................................................................................................................................ 3-573.3.2 Frequency Domain Techniques ............................................................................................................ 3-58

3.3.2.1 Theory ............................................................................................................................ 3-583.3.2.2 Effect of Soil Stratification .............................................................................................. 3-613.3.2.3 Interpretation of Results in Layered Soils ....................................................................... 3-63

3.3.3 Time Domain (TDEM) Method ............................................................................................................. 3-633.3.4 Other EM Methods ............................................................................................................................... 3-65

3.3.4.1 Telluric Current (TC) and Magnetotelluric (MT) Methods ............................................... 3-653.3.4.2 Very Low Frequency (VLF) ............................................................................................. 3-663.3.4.3 Plane Wave Surface Impedance ..................................................................................... 3-673.3.4.4 Audio-Frequency Magnetic Field (AFMAG) ..................................................................... 3-673.3.4.5 Radio Frequency (RF) Method ........................................................................................ 3-673.3.4.6 Aeroelectromagnetic Methods (AEM) ............................................................................. 3-67

3.3.5 Instrumentation ................................................................................................................................... 3-683.3.5.1 General ........................................................................................................................... 3-683.3.5.2 Fixed Coil/Fixed Frequency EMI Instruments .................................................................. 3-683.3.5.3 Variable Coil/Variable Frequency EMI Instruments ......................................................... 3-693.3.5.4 Fixed Coil/Variable Frequency EMI Instruments .............................................................. 3-70

3.3.6 Further Discussion of EM Techniques .................................................................................................. 3-723.3.6.1 Susceptibility to Electromagnetic Interference ................................................................ 3-723.3.6.2 Susceptibility to Structural Interference ......................................................................... 3-72

PRCI Contract PR-262-0114 Page xiiiFinal Report - May 2006

3.3.6.3 Susceptibility to Coil Misalignment Errors ...................................................................... 3-733.3.6.4 Linearity of Response ..................................................................................................... 3-733.3.6.5 Other Observations ......................................................................................................... 3-743.3.6.6 Comments Regarding Fixed Coil/Variable Frequency EMI Instruments .......................... 3-75

3.4 DIRECT METHODS ............................................................................................................................................. 3-773.4.1 General ................................................................................................................................................ 3-773.4.2 Soil Sample Retrieval and Resistivity Measurement (Soil Box) ............................................................ 3-773.4.3 Resistivity Rods ................................................................................................................................... 3-793.4.4 Direct-Push Probe ............................................................................................................................... 3-813.4.5 Electrical Well Logging ........................................................................................................................ 3-83

3.5 INDIRECT METHODS ......................................................................................................................................... 3-843.5.1 General ................................................................................................................................................ 3-843.5.2 Driven Rod Resistance Tests ............................................................................................................... 3-853.5.3 Buried Wire Resistance Tests ............................................................................................................... 3-86

Section 4 - Test Program

4.1 SELECTION OF INSTRUMENTS AND TEST METHODS......................................................................................... 4-14.1.1 Selection of Galvanic Instruments and Test Methods ............................................................................ 4-14.1.2 Selection of Electromagnetic Instruments ............................................................................................. 4-34.1.3 Selection of Other Equipment and Methods ........................................................................................... 4-4

4.2 SELECTION OF TEST SITES ................................................................................................................................. 4-54.2.1 Selection of Primary Test Sites .............................................................................................................. 4-54.2.2 Selection of Secondary Test Sites .......................................................................................................... 4-7

4.3 TEST SET-UP AND PROCEDURES ..................................................................................................................... 4-19

Section 5 - Results of Field Testing

5.1 VERTICAL SOUNDING TECHNIQUES ................................................................................................................... 5-15.1.1 Galvanic Methods .................................................................................................................................. 5-1

5.1.1.1 Wenner Four-Pin Method .................................................................................................. 5-15.1.1.2 Schlumberger Method ...................................................................................................... 5-55.1.1.3 Schlumberger-Palmer Method ........................................................................................ 5-105.1.1.4 Pole-Pole Method ........................................................................................................... 5-115.1.1.5 Dipole-Dipole Method ..................................................................................................... 5-14

5.1.2 Electromagnetic Methods .................................................................................................................... 5-155.1.2.1 Variable Coil/Variable Frequency Instrument .................................................................. 5-155.1.2.2 Fixed Coil/Variable Frequency Instrument ....................................................................... 5-17

5.1.3 Direct Methods .................................................................................................................................... 5-185.1.3.1 Soil Sampling ................................................................................................................. 5-185.1.3.2 Direct-Push Probe .......................................................................................................... 5-20

5.1.4 Indirect Methods.................................................................................................................................. 5-22

5.2 HORIZONTAL PROFILING TECHNIQUES ............................................................................................................ 5-265.2.1 Galvanic Methods ................................................................................................................................ 5-265.2.2 Electromagnetic Methods .................................................................................................................... 5-29

5.2.2.1 Fixed Coil/Fixed Frequency Instrument ........................................................................... 5-295.2.2.2 Fixed Coil/Variable Frequency Instrument ....................................................................... 5-355.2.2.3 Variable Coil/Variable Frequency Instrument .................................................................. 5-41

Page xiv Evaluation of Soil Resistivity Measurement TechniquesTable of Contents

5.2.3 Direct Methods .................................................................................................................................... 5-43

5.3 TWO-DIMENSIONAL (2D) IMAGING TECHNIQUES ............................................................................................ 5-44

5.4 INVESTIGATION OF SOURCES OF ERROR ......................................................................................................... 5-465.4.1 Effect of a Very-High Resistivity Surface Layer .................................................................................... 5-46

5.4.1.1 Galvanic Methods ........................................................................................................... 5-465.4.1.2 Electromagnetic Methods ............................................................................................... 5-48

5.4.2 Effect of Pin Depth ............................................................................................................................... 5-485.4.3 Effect of Pin Alignment and Spacing Errors ......................................................................................... 5-515.4.4 Effect of Circuit Resistance .................................................................................................................. 5-535.4.5 Effects of Lead Wires and Wire Reels .................................................................................................. 5-565.4.6 Effects of Structural Interference ......................................................................................................... 5-61

5.4.6.1 Background .................................................................................................................... 5-615.4.6.2 Effects on Galvanic Methods .......................................................................................... 5-625.4.6.3 Effects on EM Methods .................................................................................................. 5-64

5.4.7 Effects of Electrical Interference .......................................................................................................... 5-665.4.7.1 Induced AC Interference and DC Methods ...................................................................... 5-665.4.7.2 Induced AC Interference and EM Methods ..................................................................... 5-685.4.7.3 Interference from Electrical Storms on EM Methods ...................................................... 5-69

5.5 INTERPRETATION OF DATA ................................................................................................................................ 5-715.5.1 Curve Matching ................................................................................................................................... 5-715.5.2 Rule of Asymptotes Method ................................................................................................................ 5-745.5.3 Barnes-Layer Method .......................................................................................................................... 5-745.5.4 Inverse Modelling ................................................................................................................................ 5-765.5.5 Comparison of Interpretive Methods ................................................................................................... 5-81

Section 6 - Synopsis

6.1 EVALUATION OF GALVANIC METHODS ................................................................................................................ 6-16.1.1 Evaluation of Sounding Capabilities ....................................................................................................... 6-16.1.2 Evaluation of Profiling Capabilities ......................................................................................................... 6-26.1.3 Evaluation of Galvanic Instrumentation .................................................................................................. 6-36.1.4 Evaluation of Interpretive Techniques .................................................................................................... 6-46.1.5 Other Observations ................................................................................................................................ 6-5

6.2 EVALUATION OF ELECTROMAGNETIC METHODS ............................................................................................... 6-6

6.3 EVALUATION OF DIRECT METHODS .................................................................................................................... 6-7

6.4 EVALUATION OF INDIRECT METHODS ................................................................................................................ 6-8

Section 7 - Recommendations

References

Appendix A - Curve MatchingAppendix B - Data Tables

PRCI Contract PR-262-0114 Page xvFinal Report - May 2006

List of Figures

2.1 Determination of Resistivity ................................................................................................................... 2-12.2 Typical Soil and Rock Resistivities ......................................................................................................... 2-22.3 Soil Resistivity vs. Temperature for Typical Soil Samples ...................................................................... 2-32.4 Soil Resistivity (Saturated with Distilled Water) vs. Chloride Ion Content

for 400 Soil Samples Obtained from Watermain Excavations in Ontario ................................................ 2-42.5 2D Resistivity Section at Concrete Bridge Pier ....................................................................................... 2-52.6 2D Resistivity Section from Archaeological Survey ............................................................................... 2-62.7 Electrode Resistance (Normalized) vs. Electrode Length (Normalized)

for Various Two-Layer Soil Structures ................................................................................................. 2-132.8 Effect of Resistivity on Pitting Rates of Cast Iron when Coupled to Copper Piping .............................. 2-152.9 Effect of Soil Resistivity and AC Voltage on the Probability of AC Corrosion ....................................... 2-16

on a Cathodically Protected Structure .................................................................................................. 2-163.1 Effect of Contact Resistance On Measurement of Large Resistance Using 2-Terminal Ohmmeter ......... 3-23.2 Effect of Contact Resistance On Measurement of Small Resistance Using 2-Terminal Ohmmeter ......... 3-23.3 Effect of Contact Resistance On Measurement of Large Resistance Using 4-Terminal Ohmmeter ......... 3-23.4 Measurement of Resistivity Using Four-Terminal Ohmmeter ................................................................. 3-33.5 Current Flow and Potentials at a Point Electrode ................................................................................... 3-33.6 Four-Pin Method - General Arrangement ............................................................................................... 3-43.7 Wenner Array (Alpha) ............................................................................................................................ 3-63.8 Wenner Array (Beta) .............................................................................................................................. 3-63.9 Wenner Array (Gamma) ......................................................................................................................... 3-73.10 Reciprocal Wenner Array ....................................................................................................................... 3-73.11 Schlumberger Array ............................................................................................................................... 3-83.12 Schlumberger-Palmer Array .................................................................................................................. 3-93.13 Dipole-Dipole Array (Polar) .................................................................................................................. 3-103.14 Pole-Pole Array .................................................................................................................................... 3-103.15 Effect of Remote Pin Location on Measurements Using Pole-Pole Method ......................................... 3-113.16 Pole-Dipole Array ................................................................................................................................. 3-123.17 Lee’s Method of Partitioning ................................................................................................................ 3-133.18 Box Array ............................................................................................................................................. 3-133.19 Current vs. Depth in Uniform Soil ........................................................................................................ 3-143.20 AC-to-DC Current Density Ratio vs. Depth for Various Frequencies in Uniform Soil ............................ 3-153.21 Depth of Penetration vs. AC Frequency for Various Soil Resistivities .................................................. 3-163.22 Current Entering Lower Layer Versus Wenner Pin Spacing ‘a’ for Various Reflection Factors ‘k’ ........ 3-173.23 Depths of Current Penetration for Wenner Array and Reciprocal Wenner Array .................................. 3-193.24 Value of ‘L’ for Various Arrays .............................................................................................................. 3-203.25 Effects of Depth of Investigation of Various Arrays .............................................................................. 3-213.26 2D Resistivity Sections at Amistad Dam Using Various Arrays ............................................................ 3-223.27 Master Resistivity Curves for Wenner Method in Two-Layer Soil ........................................................ 3-243.28 Master Resistivity Curves for Schlumberger Method in Two-Layer Soil .............................................. 3-243.29 Master Resistivity Curves for Dipole-Dipole Method in Two-Layer Soil ............................................... 3-253.30 Comparison of Wenner, Schlumberger, & Dipole-Dipole Resistivity Curves in Two-Layer Soil ............ 3-253.31 Model Used in Barnes-Layer Method ................................................................................................... 3-303.32 Asymptotes Rule .................................................................................................................................. 3-323.33 Resistivity Profile Across a Vertical Fault ............................................................................................. 3-343.34 Effect of Lateral Inhomogeneity on Apparent Resistivity Curves .......................................................... 3-353.35 Effect of Increases in Potential Pin Spacing on Schlumberger Resistivity Curves ............................... 3-36

Page xvi Evaluation of Soil Resistivity Measurement TechniquesList of Figures

3.36 Correcting for Shifts in the Schlumberger Apparent Resistivity CurveDue to Changes in the Potential Pin Spacing ....................................................................................... 3-36

3.37 Resistivity Profiling/Sounding Data Obtained Using Wenner Method .................................................. 3-383.38 Various Soil Resistivity Instruments .................................................................................................... 3-453.39 Schematic of Ratio Ohmmeter ............................................................................................................. 3-463.40 Schematic of Single-Balance Transformer ........................................................................................... 3-473.41 Older Soil Resistivity Meters ................................................................................................................ 3-473.42 Typical Output Current and Measured Potential Using a Digital DC Instrument ................................... 3-493.43 Extra Equipment Required to Conduct a Soil Resistivity Sounding ...................................................... 3-523.44 Principle of Operation of EM Earth Conductivity Meter (Vertical Dipole) .............................................. 3-593.45 Relationship Between Transmitted and Received EM Waveforms ........................................................ 3-603.46 Orientation of Coils for Creation of Co-planar Horizontal Dipoles ........................................................ 3-603.47 Relative Contribution to HS from Soil at Normalized Depth z .............................................................. 3-613.48 Cumulative Contribution to HS from all Soil Below Normalized Depth z .............................................. 3-623.49 TEM Method ........................................................................................................................................ 3-633.50 Master Resistivity Curves for Electromagnetic Method in Two-Layer Soil (Horizontal Dipole) ............. 3-653.51 Master Resistivity Curves for Electromagnetic Method in Two-Layer Soil (Vertical Dipole) ................. 3-653.52 Fixed Coil/Fixed Frequency EMI Instrument Being Pulled on a Sled Over the Snow............................. 3-693.53 Variable Coil/Variable Frequency EMI Instrument Shown in Vertical Dipole Mode ............................... 3-703.54 Fixed Coil/Variable Frequency EMI Instrument ..................................................................................... 3-713.55 Indicated vs. Actual Conductivities for Geonics EM31 and EM34-3 ..................................................... 3-743.56 Split-Spoon Soil Sampler ..................................................................................................................... 3-773.57 Soil Box ............................................................................................................................................... 3-783.58 Various Resistivity Rods: a) Shepard Rod; b) Columbia Rod; c) Wenner Rod ..................................... 3-803.59 Resistivity Rod and Meter (Fisher Research) ....................................................................................... 3-803.60a Truck-Mounted Direct-Push Unit ......................................................................................................... 3-823.60b Remote-Controlled Track-Mounted Direct-Push Unit ........................................................................... 3-823.60c Direct-Push Resistivity Probe .............................................................................................................. 3-823.60d Top of Rod Showing Driving Pin and Instrumentation Cable ............................................................... 3-823.60e Resistivity Logger and Probe Testing Rig ............................................................................................ 3-823.60f Extraction of Rods and Probe ................................................................................................................ 4-14.1 Apparent Resistivities at the Four Primary Test Sites ............................................................................. 4-54.2 Site ‘A’ in Rodney, Ontario ..................................................................................................................... 4-94.3 Soil Resitivity Sounding at Site ‘A’ in Rodney, Ontario ........................................................................... 4-94.4 Site ‘B’ in Greenbank, Ontario .............................................................................................................. 4-104.5 Soil Resitivity Sounding at Site ‘B’ in Greenbank, Ontario .................................................................... 4-104.6 Site ‘C’ in Baldwin, Ontario .................................................................................................................. 4-114.7 Soil Resitivity Sounding at Site ‘C’ in Baldwin, Ontario ........................................................................ 4-114.8 Site ‘D’ in South River, Ontario ............................................................................................................ 4-124.9 Soil Resitivity Sounding at Site ‘D’ in South River, Ontario .................................................................. 4-124.10 Site ‘E’ in St. Martins, New Brunswick ................................................................................................. 4-134.11 Soil Resistivity Profile at Site ‘E’ in St. Martins, New Brunswick .......................................................... 4-134.12 Site ‘F’ - Lake Bernard near Sundridge, ON .......................................................................................... 4-144.13 Resistivity Sounding at Site ‘F’ on Lake Bernard near Sundridge, ON .................................................. 4-144.14 Site ‘G’ in Salina, KS ............................................................................................................................ 4-154.15 Soil Resistivity Sounding at Site ‘G’ in Salina, KS ................................................................................ 4-154.16 Site ‘H’ in Rockton, ON ........................................................................................................................ 4-164.17 Soil Resistivity Sounding at Site ‘H’ in Rockton, ON ............................................................................ 4-164.18 Site ‘I’ in Pickering, ON ........................................................................................................................ 4-174.19 Soil Resistivity Sounding at Site ‘I’ in Pickering, ON ............................................................................ 4-174.20 Site ‘J’ in City of Kawartha Lakes, ON .................................................................................................. 4-184.21 Soil Resistivity Sounding at Site ‘I’ in Kawartha Lakes, ON .................................................................. 4-184.22 Instrument Set-Up for Resistivity Soundings ....................................................................................... 4-19

PRCI Contract PR-262-0114 Page xviiFinal Draft Report - July 2004

4.23 Switch Box for Soil Resistivity Soundings ........................................................................................... 4-194.24 Wire Reels, Ground Pins, and Tape Measures for Conducting Resistivity Soundings .......................... 4-205.1 Wenner Method - Comparison of Galvanic Instruments at Four Primary Test Sites ............................... 5-15.2 Comparison of Measurements Obtained at all Four Primary Sites ......................................................... 5-25.3 Instrument Measurement Errors Using Wenner Method at Four Primary Test Sites .............................. 5-35.4 Wenner Resistivity Sounding Using Various Instruments (Site E) ......................................................... 5-45.5 Effect of Various Instruments on Accuracy of Schlumberger Method (Site B) ....................................... 5-55.6 Effect of Potential-Pin Spacing on Accuracy of Schlumberger Method

for Various Instruments (Site B) ............................................................................................................ 5-65.7 Effect of Schlumberger Pin Spacing Ratio ‘n’ on Accuracy of Various Instruments (Site B) .................. 5-75.8 Effect of Potential-Pin Spacing on Accuracy of Schlumberger Method .................................................. 5-8

for Various Instruments (Site C) ............................................................................................................ 5-85.9 Effect of Potential-Pin Spacing on Accuracy of Schlumberger Method .................................................. 5-9

for Various Instruments (Site D) ............................................................................................................ 5-95.10 Schlumberger-Palmer Method - Comparison of Galvanic Instruments at Two Primary Test Sites ....... 5-105.11 Schlumberger-Palmer Method vs. Wenner Method ............................................................................. 5-115.12a Pole-Pole Sounding at Site C (L for Pole-Pole Array is from C2 to P2) ............................................... 5-125.12b Pole-Pole Sounding at Site C (Pole-Pole Data Shifted to Align with Wenner) ...................................... 5-125.13a Pole-Pole Sounding at Site C (L for Pole-Pole Array is from C2 to P2;

Resistivities Calculated Using Eqn. 3.16) ............................................................................................. 5-135.13b Pole-Pole Sounding at Site C (Pole-Pole Data Shifted to Align with Wenner;

Resistivities Calculated Using Eqn. 3.16) ............................................................................................. 5-135.14 Dipole-Dipole Sounding at Site C ......................................................................................................... 5-145.15 Comparison of Soundings using EM-2 and Wenner Method (Various Sites) ....................................... 5-165.16 Apparent Resistivity vs. Test Signal Frequency as Measured by EM-3 at Sites B and C ....................... 5-175.17 Retrieval of Soil Samples - Site B ........................................................................................................ 5-185.18 Borehole Analysis (Actual Results and Simplified Models) ................................................................. 5-195.19 Soil Resistivity Data Obtained at Depth Using Direct-Push Resistivity Probe (Site G) ......................... 5-215.20 Wenner Resistivity Sounding at Site G vs. Geometric Mean of Five Resistivity Logs

Obtained Using Direct-Push Probe ...................................................................................................... 5-225.21 Measurement of Resistance of Buried Wire Using Fall-of-Potential Method (Site B) ........................... 5-235.22 Lower Layer Resistivities and Upper Layer Heights to Produce Resistances Equivalent

to Those in Table 5.1 ............................................................................................................................ 5-245.23 Comparison of Measured Wire Resistances with Resistances Calculated Using Soil Model ................ 5-255.24 Conducting a Soil Resistivity Profile With a Wenner Array by Advancing

the Array Using the ‘Leap-Frog’ Method .............................................................................................. 5-265.25 Soil Resistivity Profiles at Site C Using the ‘Leapfrog’ Method ............................................................ 5-275.26 Soil Resistivity Profiles at Site C Using the ‘Leapfrog’ Method

(Wenner Beta Data Separated from Wenner Alpha Data) ..................................................................... 5-275.27 Switching Arrangement to Change from Wenner Alpha to Wenner Beta Array .................................... 5-285.28 Soil Resistivity Profiles Conducted at Sites B and E

Using the Wenner Method and Instrument DC-2b ............................................................................... 5-285.29 Marker Flags Used as Ground Pins While Profiling .............................................................................. 5-295.30 Soil Resistivity Profiles to 3m and 6m Depths Using EM-1 (Sites B, C, & E) ....................................... 5-315.31 Effect of Instrument Height Using EM-1 (Sites A, B, C, D and E) ......................................................... 5-325.32 Comparison of EM-1 and Wenner Data (DC-2b) to 3m and 6m Depths (Sites B, C, & E) .................... 5-345.33 Soil Resistivity Profiles at Various Signal Frequencies Using Instrument EM-3 at Sites B and C ......... 5-365.34 Response of Instrument EM-3 at Various Frequencies (Site B) ........................................................... 5-375.35 Response of Instrument EM-3 at Various Frequencies (Site C) ........................................................... 5-385.36 Comparison of EM-3 with Wenner Method (DC-2b) at Sites B and C .................................................. 5-395.37 Comparison of EM-3 with EM-1 at Sites B and C ................................................................................. 5-405.38 Soil Resistivity Profiles Conducted to Various Depths Using EM-2 (Site A) ......................................... 5-41

Page xviii Evaluation of Soil Resistivity Measurement TechniquesList of Figures

5.39 Soil Resistivity Profiles Using EM-2 at Site A(Comparison of Horizontal and Vertical Dipole Modes) ....................................................................... 5-42

5.40 Comparison of Profiles Obtained with EM-2, EM-1 and Wenner Method (Site A) ................................ 5-435.41 Profiles Obtained Using the Wenner Method at Various Pin Spacings (Site B) .................................... 5-445.42 Resistivity Pseudosection Obtained Using Wenner Method (Site B) .................................................... 5-455.43 Resistivity Pseudosection Obtained Using EM-2 (Site A) ..................................................................... 5-455.44 Pins Driven Into Ice ..............................................................................................................................5.465.45 Pins Placed in Augered Holes .............................................................................................................. 5-465.46 Wenner Soundings Conducted on Surface of Frozen Lake (Site F) ...................................................... 5-475.47 Resistivity Profile Using EM-1 Along Line of 4-Pin Survey at Site F .................................................... 5-485.48 Resistivity Variation Over Time Using EM-1 at Fixed Position (V-Dipole) ............................................ 5-485.49 Effect of Point Source Electrode Depth on Resistivity Measured Using the Wenner Method ............... 5-495.50 Effect of Pin Depth on Resistivity Measured Using Wenner Method .................................................... 5-495.51 Effect of Pin Depth on Wenner Accuracy (0.15 m Pin Spacing) ........................................................... 5-515.52 Effect of Pin Depth on Wenner Accuracy (0.6 m Pin Spacing) ............................................................. 5-515.53 Effect of Pin Depth on Wenner Accuracy (4 Ω-m Pool Only) ............................................................... 5-515.54 Effect of Pin Depth on Wenner Accuracy (Theoretical vs. Measured) .................................................. 5-515.55 Misalignment of Potential Pin .............................................................................................................. 5-525.56 Effect of Misalignment of Potential Pin in Wenner Array...................................................................... 5-535.57 Theoretical Effect of Misalignment of Potential Pin Spacing Error (Wenner) ....................................... 5-535.58 Test Set-Up to Evaluate Effects of Circuit Resistance ........................................................................... 5-535.59 Effect of Current-Pin Circuit Resistance on Galvanic Instrument Accuracy .......................................... 5-545.60 Combined Effect of Current-Pin and Potential-Pin Circuit Resistances ................................................ 5-555.61 Effect of Wire Reel Orientation on Measurements with AC Instruments .............................................. 5-575.62 Test Set-Up to Determine the Effects of Wire Reels on AC Instruments Used for Galvanic Methods ... 5-585.63 Effect of Excess Potential-Pin Lead Wire on AC Instrument ................................................................. 5-605.64 Theoretical Effect of a Grounding Grid on Wenner Resistivity Measurements ..................................... 5-615.65 Effect of a Coated Pipeline Parallel to Wenner Pin Array ...................................................................... 5-625.66 Effect of Test Current Frequency on Measured Resistivity (Wenner Array Parallel to Coated Pipeline) 5-635.67 Effect of Coated Steel Pipeline on EM-1 Conductivities ........................................................................ 5-645.68 Error in EM-1 Measurements Due to Coated Steel Pipeline ................................................................. 5-645.69 Effect of Buried Steel Object on EM-1 Conductivities

(V-Dipole; Object Moving Perpendicular to Boom) .............................................................................. 5-655.70 Effect of Buried Steel Object on EM-1 Conductivities

(V-Dipole; Object Moving Parallel to Boom) ........................................................................................ 5-655.71 Effect of Chain Link Fence on EM-1 Conductivities .............................................................................. 5-655.72 Effect of 60 Hz AC Field on Galvanic Measurement Techniques ........................................................... 5-675.73 Effect of 60Hz AC on EM-1 Conductivities ........................................................................................... 5-695.74 Effect of 60Hz AC on EM-1 Resistivities ............................................................................................... 5-695.75 Effect of Electrical Storm on EM-1 Conductivities ................................................................................ 5-705.76 Effect of Electrical Storm on EM-1 Resistivities ................................................................................... 5-705.77 Wenner Sounding at Site J and Soil Model Derived by Curve Matching .............................................. 5-715.78 Best-Fit Curve for Wenner Data at Site J

(Determined by Manual Iteration of Soil Model for Use in Eqn. 3.26) .................................................. 5-735.79 Best-Fit Curves for Wenner Data at Site A ............................................................................................ 5-735.80 Best-Fit Curves for Wenner Data at Site C (Model Determined by Curve Fitting) ................................. 5-735.81 Rule of Asymptotes Applied at Site K ................................................................................................... 5-745.82 Barnes-Layer Model for Site J Compared to Model Obtained by Curve Matching ................................ 5-755.83 Barnes-Layer Model for Site B ............................................................................................................. 5-755.84 Alignment of Schlumberger Curve Segments by Inverse Modelling Software

to Account for Increases in Potential Pin Spacings (Site D) ................................................................ 5-775.85 Inverse Modelling of Wenner and Schlumberger Data at Site A ........................................................... 5-795.86 Inverse Modelling of Wenner and Schlumberger Data at Site B ........................................................... 5-79

PRCI Contract PR-262-0114 Page xixFinal Draft Report - July 2004

5.87 Inverse Modelling of Wenner and Schlumberger Data at Site C ........................................................... 5-795.88 Inverse Modelling of Wenner and Schlumberger Data at Site D ........................................................... 5-795.89 Inverse Modelling of Site E Wenner Data ............................................................................................. 5-795.90 Inverse Modelling of Site H Wenner Data ............................................................................................ 5-795.91a Inverse Modelling of Site F Wenner Data (On Ice - E-W) ..................................................................... 5-795.91b Inverse Modelling of Site F Wenner Data (Through Ice - N-S) ............................................................. 5-795.92 Inverse Modelling of Wenner Data at Site G (Array Orientations E-W and N-S) ................................... 5-805.93 Inverse Modelling of Site J Wenner Data ............................................................................................. 5-805.94 Inverse Modelling of Site K Wenner Data ............................................................................................. 5-805.95a Automatic Inverse Modelling of Site C Wenner Data (During Sampling) ............................................. 5-805.95b Forward Modelling of Site C Soil Sample Data ..................................................................................... 5-80A.1 Plot of Apparent Resistivity Data Versus Wenner Pin Spacing on Log-Log Graph Paper ....................... A-2A.2 Alignment of Resistivity Data with Master Curves ................................................................................. A-2A.3 Plots of Apparent Resistivity Data and Auxiliary Curve .......................................................................... A-4A.4 Alignment of Resistivity Data with Master Curves and Intersection of

Master Curve Origin (‘X’) with Auxiliary Curve ....................................................................................... A-5A.5 Log-Log Graph Paper (3x2 Decades) ..................................................................................................... A-6A.6 Master Wenner Resistivity Curves for a Two-Layer Soil Structure (Lower Layer Less Conductive) ....... A-7A.7 Master Wenner Resistivity Curves for a Two-Layer Soil Structure (Lower Layer More Conductive) ...... A-8

Page xx Evaluation of Soil Resistivity Measurement TechniquesList of Tables

2.1 Anticipated Corrosion of Steel Exposed to Soils of Varying Resistivity ................................................ 2-153.1 Depths of Investigation for Various Arrays .......................................................................................... 3-205.1 Resistance Measurements for Buried Wire Using Fall-of-Potential Method (Site B) ............................ 5-235.2 Comparison of Interpretive Methods for Wenner Data from Primary Test Sites .................................. 5-81B.1 Soil Resistivity Soundings Using the Four-Pin Method - Site A ........................................................ App. BB.2 Soil Resistivity Soundings Using the Four-Pin Method - Site B ........................................................ App. BB.3a Soil Resistivity Soundings Using the Four-Pin Method - Site C (Nov.2001) ...................................... App. BB.3b Soil Resistivity Soundings Using the Four-Pin Method - Site C (Oct. 2002) ..................................... App. BB.4 Soil Resistivity Soundings Using the Four-Pin Method - Site D ........................................................ App. BB.5 Soil Resistivity Soundings Using the Four-Pin Method - Site E ........................................................ App. BB.6 Soil Resistivity Soundings Using the Four-Pin Method - Site F ......................................................... App. BB.7 Soil Resistivity Soundings Using the Four-Pin Method - Site G ........................................................ App. BB.8 Soil Resistivity Soundings Using the Four-Pin Method - Site H ........................................................ App. BB.9 Soil Resistivity Soundings Using the Four-Pin Method - Site I ......................................................... App. BB.10 Soil Resistivity Soundings Using the Four-Pin Method - Site J ......................................................... App. BB.11 Soil Resistivity Soundings Using the Four-Pin Method - Site K ........................................................ App. BB.12 Soil Sample Data .............................................................................................................................. App. B

List of Tables