Evaluation of Soil Resistivity

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					                                                 Catalog No. L52127




Evaluation of Soil Resistivity
 Measurement Techniques

           Contract PR-262-0114




              Prepared for the

Corrosion and Inspection Technical Committee
                      of
 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
                                                     Table of Contents

Section 1 - Introduction

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

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

1.3    PROPOSED WORK PLAN ..................................................................................................................................... 1-2
       1.3.1 Preliminary Work ................................................................................................................................... 1-2
       1.3.2 Field Trials .............................................................................................................................................. 1-2
       1.3.3 Interpretation of Data ............................................................................................................................. 1-3
       1.3.4 End Product ........................................................................................................................................... 1-3



Section 2 - Background

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

2.2    THE EARTH AS A CONDUCTOR OF ELECTRICITY ................................................................................................ 2-2
       2.2.1  General .................................................................................................................................................. 2-2
       2.2.2  Effect of Temperature ............................................................................................................................. 2-3
       2.2.3  Effect of Water Content .......................................................................................................................... 2-4
       2.2.4  Effect of Ionic Content ........................................................................................................................... 2-4
       2.2.5  Effects of Other Factors ......................................................................................................................... 2-5

2.3    SOIL RESISTIVITY MEASUREMENT .................................................................................................................... 2-5
       2.3.1   Types of Soil Resistivity Surveys ........................................................................................................... 2-5
       2.3.2   General Applications for Soil Resistivity Surveys ................................................................................... 2-6
       2.3.3   A History of Resistivity Measurement Techniques ................................................................................. 2-7
       2.3.4   Other Electrical Geophysical Measurements Unrelated to Resistivity ................................................... 2-10
                    2.3.4.1             Induced Polarization (IP) ................................................................................................ 2-10
                    2.3.4.2             Self Potential (SP) .......................................................................................................... 2-11
                    2.3.4.3             Other Applied Current Methods ...................................................................................... 2-12

2.4    RESISTIVITY MEASUREMENT FOR PIPELINE CORROSION APPLICATIONS ..................................................... 2-12
       2.4.1   Electrode Resistance Calculations ....................................................................................................... 2-12
       2.4.2   Corrosion Risk Assessment ................................................................................................................. 2-14
       2.4.3   Other Applications ............................................................................................................................... 2-16



Section 3 - Measurement Techniques

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

3.2    GALVANIC METHODS ........................................................................................................................................... 3-2
       3.2.1  General .................................................................................................................................................. 3-2
       3.2.2  Theoretical Basis .................................................................................................................................... 3-3
       3.2.3  Four-Pin Arrays ...................................................................................................................................... 3-5
Page xii                                                                     Evaluation of Soil Resistivity Measurement Techniques
                                                                                                                   Table of Contents


                    3.2.3.1            Wenner Arrays .................................................................................................................. 3-5
                    3.2.3.2            Theorem of Reciprocity .................................................................................................... 3-7
                    3.2.3.3            Schlumberger Array ......................................................................................................... 3-8
                    3.2.3.4            Schlumberger-Palmer Array ............................................................................................. 3-9
                    3.2.3.5            Dipole-Dipole Array .......................................................................................................... 3-9
                    3.2.3.6            Pole-Pole Array ............................................................................................................... 3-10
                    3.2.3.7            Pole-Dipole Array ........................................................................................................... 3-11
                    3.2.3.8            Lee’s Method of Partitioning ........................................................................................... 3-12
                    3.2.3.9            Box Array ........................................................................................................................ 3-13
       3.2.4        Resistivity Soundings .......................................................................................................................... 3-14
                    3.2.4.1            Depth of Current Penetration .......................................................................................... 3-14
                    3.2.4.2            Effect of Soil Stratification .............................................................................................. 3-16
                    3.2.4.3            Depth of Investigation .................................................................................................... 3-19
                    3.2.4.4            Resolution ...................................................................................................................... 3-22
       3.2.5        Interpretation of Resistivity Soundings ................................................................................................ 3-23
                    3.2.5.1            Apparent Resistivity Curves ............................................................................................ 3-23
                    3.2.5.2            Curve Matching - Two-Layer Soils .................................................................................. 3-26
                    3.2.5.3            Curve Matching - Multi-Layer Soils ................................................................................ 3-27
                    3.2.5.4            Partial Curve Matching - Multi-Layer Soils ..................................................................... 3-28
                    3.2.5.5            Inverse Modelling ........................................................................................................... 3-29
                    3.2.5.6            Tagg’s Method ................................................................................................................ 3-29
                    3.2.5.7            Barnes-Layer Method ..................................................................................................... 3-30
                    3.2.5.8            Point-of-Inflection Methods ............................................................................................ 3-31
                    3.2.5.9            Other Methods ................................................................................................................ 3-33
                    3.2.5.10           Effect of Lateral Variations on the Interpretation of Sounding Data ................................ 3-33
                    3.2.5.11           Further Discussion of Interpretive Methods .................................................................... 3-37
       3.2.6        Resistivity Profiling .............................................................................................................................. 3-38
       3.2.7        Instrumentation and Equipment ........................................................................................................... 3-40
                    3.2.7.1            General Considerations ................................................................................................... 3-40
                    3.2.7.2            Test Current Frequency ................................................................................................... 3-42
                    3.2.7.3            Specific Examples of Instruments .................................................................................. 3-44
                    3.2.7.4            Associated Equipment .................................................................................................... 3-50
       3.2.8        Further Discussion of Galvanic Measurement Techniques ................................................................... 3-52
                    3.2.8.1            Wenner Versus Schlumberger ........................................................................................ 3-52
                    3.2.8.2            Notes on Other Arrays .................................................................................................... 3-54

3.3    ELECTROMAGNETIC (EM) METHODS ................................................................................................................ 3-57
       3.3.1  General ................................................................................................................................................ 3-57
       3.3.2  Frequency Domain Techniques ............................................................................................................ 3-58
                    3.3.2.1            Theory ............................................................................................................................ 3-58
                    3.3.2.2            Effect of Soil Stratification .............................................................................................. 3-61
                    3.3.2.3            Interpretation of Results in Layered Soils ....................................................................... 3-63
       3.3.3        Time Domain (TDEM) Method ............................................................................................................. 3-63
       3.3.4        Other EM Methods ............................................................................................................................... 3-65
                    3.3.4.1            Telluric Current (TC) and Magnetotelluric (MT) Methods ............................................... 3-65
                    3.3.4.2            Very Low Frequency (VLF) ............................................................................................. 3-66
                    3.3.4.3            Plane Wave Surface Impedance ..................................................................................... 3-67
                    3.3.4.4            Audio-Frequency Magnetic Field (AFMAG) ..................................................................... 3-67
                    3.3.4.5            Radio Frequency (RF) Method ........................................................................................ 3-67
                    3.3.4.6            Aeroelectromagnetic Methods (AEM) ............................................................................. 3-67
       3.3.5        Instrumentation ................................................................................................................................... 3-68
                    3.3.5.1            General ........................................................................................................................... 3-68
                    3.3.5.2            Fixed Coil/Fixed Frequency EMI Instruments .................................................................. 3-68
                    3.3.5.3            Variable Coil/Variable Frequency EMI Instruments ......................................................... 3-69
                    3.3.5.4            Fixed Coil/Variable Frequency EMI Instruments .............................................................. 3-70
       3.3.6        Further Discussion of EM Techniques .................................................................................................. 3-72
                    3.3.6.1            Susceptibility to Electromagnetic Interference ................................................................ 3-72
                    3.3.6.2            Susceptibility to Structural Interference ......................................................................... 3-72
PRCI Contract PR-262-0114                                                                                                                                                Page xiii
Final Report - May 2006


                    3.3.6.3            Susceptibility to Coil Misalignment Errors ...................................................................... 3-73
                    3.3.6.4            Linearity of Response ..................................................................................................... 3-73
                    3.3.6.5            Other Observations ......................................................................................................... 3-74
                    3.3.6.6            Comments Regarding Fixed Coil/Variable Frequency EMI Instruments .......................... 3-75

3.4    DIRECT METHODS ............................................................................................................................................. 3-77
       3.4.1  General ................................................................................................................................................ 3-77
       3.4.2  Soil Sample Retrieval and Resistivity Measurement (Soil Box) ............................................................ 3-77
       3.4.3  Resistivity Rods ................................................................................................................................... 3-79
       3.4.4  Direct-Push Probe ............................................................................................................................... 3-81
       3.4.5  Electrical Well Logging ........................................................................................................................ 3-83

3.5    INDIRECT METHODS ......................................................................................................................................... 3-84
       3.5.1  General ................................................................................................................................................ 3-84
       3.5.2  Driven Rod Resistance Tests ............................................................................................................... 3-85
       3.5.3  Buried Wire Resistance Tests ............................................................................................................... 3-86


Section 4 - Test Program

4.1    SELECTION OF INSTRUMENTS AND TEST METHODS ......................................................................................... 4-1
       4.1.1  Selection of Galvanic Instruments and Test Methods ............................................................................ 4-1
       4.1.2  Selection of Electromagnetic Instruments ............................................................................................. 4-3
       4.1.3  Selection of Other Equipment and Methods ........................................................................................... 4-4

4.2    SELECTION OF TEST SITES ................................................................................................................................. 4-5
       4.2.1  Selection of Primary Test Sites .............................................................................................................. 4-5
       4.2.2  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 ................................................................................................................... 5-1
       5.1.1  Galvanic Methods .................................................................................................................................. 5-1
                    5.1.1.1            Wenner Four-Pin Method .................................................................................................. 5-1
                    5.1.1.2            Schlumberger Method ...................................................................................................... 5-5
                    5.1.1.3            Schlumberger-Palmer Method ........................................................................................ 5-10
                    5.1.1.4            Pole-Pole Method ........................................................................................................... 5-11
                    5.1.1.5            Dipole-Dipole Method ..................................................................................................... 5-14
       5.1.2        Electromagnetic Methods .................................................................................................................... 5-15
                    5.1.2.1            Variable Coil/Variable Frequency Instrument .................................................................. 5-15
                    5.1.2.2            Fixed Coil/Variable Frequency Instrument ....................................................................... 5-17
       5.1.3        Direct Methods .................................................................................................................................... 5-18
                    5.1.3.1            Soil Sampling ................................................................................................................. 5-18
                    5.1.3.2            Direct-Push Probe .......................................................................................................... 5-20
       5.1.4        Indirect Methods .................................................................................................................................. 5-22

5.2    HORIZONTAL PROFILING TECHNIQUES ............................................................................................................ 5-26
       5.2.1  Galvanic Methods ................................................................................................................................ 5-26
       5.2.2  Electromagnetic Methods .................................................................................................................... 5-29
                    5.2.2.1            Fixed Coil/Fixed Frequency Instrument ........................................................................... 5-29
                    5.2.2.2            Fixed Coil/Variable Frequency Instrument ....................................................................... 5-35
                    5.2.2.3            Variable Coil/Variable Frequency Instrument .................................................................. 5-41
Page xiv                                                                   Evaluation of Soil Resistivity Measurement Techniques
                                                                                                                 Table 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 ......................................................................................................... 5-46
       5.4.1   Effect of a Very-High Resistivity Surface Layer .................................................................................... 5-46
                   5.4.1.1            Galvanic Methods ........................................................................................................... 5-46
                   5.4.1.2            Electromagnetic Methods ............................................................................................... 5-48
       5.4.2       Effect of Pin Depth ............................................................................................................................... 5-48
       5.4.3       Effect of Pin Alignment and Spacing Errors ......................................................................................... 5-51
       5.4.4       Effect of Circuit Resistance .................................................................................................................. 5-53
       5.4.5       Effects of Lead Wires and Wire Reels .................................................................................................. 5-56
       5.4.6       Effects of Structural Interference ......................................................................................................... 5-61
                   5.4.6.1            Background .................................................................................................................... 5-61
                   5.4.6.2            Effects on Galvanic Methods .......................................................................................... 5-62
                   5.4.6.3            Effects on EM Methods .................................................................................................. 5-64
       5.4.7       Effects of Electrical Interference .......................................................................................................... 5-66
                   5.4.7.1            Induced AC Interference and DC Methods ...................................................................... 5-66
                   5.4.7.2            Induced AC Interference and EM Methods ..................................................................... 5-68
                   5.4.7.3            Interference from Electrical Storms on EM Methods ...................................................... 5-69

5.5    INTERPRETATION OF DATA ................................................................................................................................ 5-71
       5.5.1  Curve Matching ................................................................................................................................... 5-71
       5.5.2  Rule of Asymptotes Method ................................................................................................................ 5-74
       5.5.3  Barnes-Layer Method .......................................................................................................................... 5-74
       5.5.4  Inverse Modelling ................................................................................................................................ 5-76
       5.5.5  Comparison of Interpretive Methods ................................................................................................... 5-81



Section 6 - Synopsis

6.1    EVALUATION OF GALVANIC METHODS ................................................................................................................ 6-1
       6.1.1  Evaluation of Sounding Capabilities ....................................................................................................... 6-1
       6.1.2  Evaluation of Profiling Capabilities ......................................................................................................... 6-2
       6.1.3  Evaluation of Galvanic Instrumentation .................................................................................................. 6-3
       6.1.4  Evaluation of Interpretive Techniques .................................................................................................... 6-4
       6.1.5  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 Matching
Appendix B - Data Tables
PRCI Contract PR-262-0114                                                                                                                                  Page xv
Final Report - May 2006




                                                   List of Figures
      2.1    Determination of Resistivity ................................................................................................................... 2-1
      2.2    Typical Soil and Rock Resistivities ......................................................................................................... 2-2
      2.3    Soil Resistivity vs. Temperature for Typical Soil Samples ...................................................................... 2-3
      2.4    Soil Resistivity (Saturated with Distilled Water) vs. Chloride Ion Content
             for 400 Soil Samples Obtained from Watermain Excavations in Ontario ................................................ 2-4
      2.5    2D Resistivity Section at Concrete Bridge Pier ....................................................................................... 2-5
      2.6    2D Resistivity Section from Archaeological Survey ............................................................................... 2-6
      2.7    Electrode Resistance (Normalized) vs. Electrode Length (Normalized)
             for Various Two-Layer Soil Structures ................................................................................................. 2-13
      2.8    Effect of Resistivity on Pitting Rates of Cast Iron when Coupled to Copper Piping .............................. 2-15
      2.9    Effect of Soil Resistivity and AC Voltage on the Probability of AC Corrosion ....................................... 2-16
             on a Cathodically Protected Structure .................................................................................................. 2-16
      3.1    Effect of Contact Resistance On Measurement of Large Resistance Using 2-Terminal Ohmmeter ......... 3-2
      3.2    Effect of Contact Resistance On Measurement of Small Resistance Using 2-Terminal Ohmmeter ......... 3-2
      3.3    Effect of Contact Resistance On Measurement of Large Resistance Using 4-Terminal Ohmmeter ......... 3-2
      3.4    Measurement of Resistivity Using Four-Terminal Ohmmeter ................................................................. 3-3
      3.5    Current Flow and Potentials at a Point Electrode ................................................................................... 3-3
      3.6    Four-Pin Method - General Arrangement ............................................................................................... 3-4
      3.7    Wenner Array (Alpha) ............................................................................................................................ 3-6
      3.8    Wenner Array (Beta) .............................................................................................................................. 3-6
      3.9    Wenner Array (Gamma) ......................................................................................................................... 3-7
      3.10   Reciprocal Wenner Array ....................................................................................................................... 3-7
      3.11   Schlumberger Array ............................................................................................................................... 3-8
      3.12   Schlumberger-Palmer Array .................................................................................................................. 3-9
      3.13   Dipole-Dipole Array (Polar) .................................................................................................................. 3-10
      3.14   Pole-Pole Array .................................................................................................................................... 3-10
      3.15   Effect of Remote Pin Location on Measurements Using Pole-Pole Method ......................................... 3-11
      3.16   Pole-Dipole Array ................................................................................................................................. 3-12
      3.17   Lee’s Method of Partitioning ................................................................................................................ 3-13
      3.18   Box Array ............................................................................................................................................. 3-13
      3.19   Current vs. Depth in Uniform Soil ........................................................................................................ 3-14
      3.20   AC-to-DC Current Density Ratio vs. Depth for Various Frequencies in Uniform Soil ............................ 3-15
      3.21   Depth of Penetration vs. AC Frequency for Various Soil Resistivities .................................................. 3-16
      3.22   Current Entering Lower Layer Versus Wenner Pin Spacing ‘a’ for Various Reflection Factors ‘k’ ........ 3-17
      3.23   Depths of Current Penetration for Wenner Array and Reciprocal Wenner Array .................................. 3-19
      3.24   Value of ‘L’ for Various Arrays .............................................................................................................. 3-20
      3.25   Effects of Depth of Investigation of Various Arrays .............................................................................. 3-21
      3.26   2D Resistivity Sections at Amistad Dam Using Various Arrays ............................................................ 3-22
      3.27   Master Resistivity Curves for Wenner Method in Two-Layer Soil ........................................................ 3-24
      3.28   Master Resistivity Curves for Schlumberger Method in Two-Layer Soil .............................................. 3-24
      3.29   Master Resistivity Curves for Dipole-Dipole Method in Two-Layer Soil ............................................... 3-25
      3.30   Comparison of Wenner, Schlumberger, & Dipole-Dipole Resistivity Curves in Two-Layer Soil ............ 3-25
      3.31   Model Used in Barnes-Layer Method ................................................................................................... 3-30
      3.32   Asymptotes Rule .................................................................................................................................. 3-32
      3.33   Resistivity Profile Across a Vertical Fault ............................................................................................. 3-34
      3.34   Effect of Lateral Inhomogeneity on Apparent Resistivity Curves .......................................................... 3-35
      3.35   Effect of Increases in Potential Pin Spacing on Schlumberger Resistivity Curves ............................... 3-36
Page xvi                                                              Evaluation of Soil Resistivity Measurement Techniques
                                                                                                              List of Figures


       3.36    Correcting for Shifts in the Schlumberger Apparent Resistivity Curve
               Due to Changes in the Potential Pin Spacing ....................................................................................... 3-36
       3.37    Resistivity Profiling/Sounding Data Obtained Using Wenner Method .................................................. 3-38
       3.38    Various Soil Resistivity Instruments .................................................................................................... 3-45
       3.39    Schematic of Ratio Ohmmeter ............................................................................................................. 3-46
       3.40    Schematic of Single-Balance Transformer ........................................................................................... 3-47
       3.41    Older Soil Resistivity Meters ................................................................................................................ 3-47
       3.42    Typical Output Current and Measured Potential Using a Digital DC Instrument ................................... 3-49
       3.43    Extra Equipment Required to Conduct a Soil Resistivity Sounding ...................................................... 3-52
       3.44    Principle of Operation of EM Earth Conductivity Meter (Vertical Dipole) .............................................. 3-59
       3.45    Relationship Between Transmitted and Received EM Waveforms ........................................................ 3-60
       3.46    Orientation of Coils for Creation of Co-planar Horizontal Dipoles ........................................................ 3-60
       3.47    Relative Contribution to HS from Soil at Normalized Depth z .............................................................. 3-61
       3.48    Cumulative Contribution to HS from all Soil Below Normalized Depth z .............................................. 3-62
       3.49    TEM Method ........................................................................................................................................ 3-63
       3.50    Master Resistivity Curves for Electromagnetic Method in Two-Layer Soil (Horizontal Dipole) ............. 3-65
       3.51    Master Resistivity Curves for Electromagnetic Method in Two-Layer Soil (Vertical Dipole) ................. 3-65
       3.52    Fixed Coil/Fixed Frequency EMI Instrument Being Pulled on a Sled Over the Snow ............................. 3-69
       3.53    Variable Coil/Variable Frequency EMI Instrument Shown in Vertical Dipole Mode ............................... 3-70
       3.54    Fixed Coil/Variable Frequency EMI Instrument ..................................................................................... 3-71
       3.55    Indicated vs. Actual Conductivities for Geonics EM31 and EM34-3 ..................................................... 3-74
       3.56    Split-Spoon Soil Sampler ..................................................................................................................... 3-77
       3.57    Soil Box ............................................................................................................................................... 3-78
       3.58    Various Resistivity Rods: a) Shepard Rod; b) Columbia Rod; c) Wenner Rod ..................................... 3-80
       3.59    Resistivity Rod and Meter (Fisher Research) ....................................................................................... 3-80
       3.60a   Truck-Mounted Direct-Push Unit ......................................................................................................... 3-82
       3.60b   Remote-Controlled Track-Mounted Direct-Push Unit ........................................................................... 3-82
       3.60c   Direct-Push Resistivity Probe .............................................................................................................. 3-82
       3.60d   Top of Rod Showing Driving Pin and Instrumentation Cable ............................................................... 3-82
       3.60e   Resistivity Logger and Probe Testing Rig ............................................................................................ 3-82
       3.60f   Extraction of Rods and Probe ................................................................................................................ 4-1
       4.1     Apparent Resistivities at the Four Primary Test Sites ............................................................................. 4-5
       4.2     Site ‘A’ in Rodney, Ontario ..................................................................................................................... 4-9
       4.3     Soil Resitivity Sounding at Site ‘A’ in Rodney, Ontario ........................................................................... 4-9
       4.4     Site ‘B’ in Greenbank, Ontario .............................................................................................................. 4-10
       4.5     Soil Resitivity Sounding at Site ‘B’ in Greenbank, Ontario .................................................................... 4-10
       4.6     Site ‘C’ in Baldwin, Ontario .................................................................................................................. 4-11
       4.7     Soil Resitivity Sounding at Site ‘C’ in Baldwin, Ontario ........................................................................ 4-11
       4.8     Site ‘D’ in South River, Ontario ............................................................................................................ 4-12
       4.9     Soil Resitivity Sounding at Site ‘D’ in South River, Ontario .................................................................. 4-12
       4.10    Site ‘E’ in St. Martins, New Brunswick ................................................................................................. 4-13
       4.11    Soil Resistivity Profile at Site ‘E’ in St. Martins, New Brunswick .......................................................... 4-13
       4.12    Site ‘F’ - Lake Bernard near Sundridge, ON .......................................................................................... 4-14
       4.13    Resistivity Sounding at Site ‘F’ on Lake Bernard near Sundridge, ON .................................................. 4-14
       4.14    Site ‘G’ in Salina, KS ............................................................................................................................ 4-15
       4.15    Soil Resistivity Sounding at Site ‘G’ in Salina, KS ................................................................................ 4-15
       4.16    Site ‘H’ in Rockton, ON ........................................................................................................................ 4-16
       4.17    Soil Resistivity Sounding at Site ‘H’ in Rockton, ON ............................................................................ 4-16
       4.18    Site ‘I’ in Pickering, ON ........................................................................................................................ 4-17
       4.19    Soil Resistivity Sounding at Site ‘I’ in Pickering, ON ............................................................................ 4-17
       4.20    Site ‘J’ in City of Kawartha Lakes, ON .................................................................................................. 4-18
       4.21    Soil Resistivity Sounding at Site ‘I’ in Kawartha Lakes, ON .................................................................. 4-18
       4.22    Instrument Set-Up for Resistivity Soundings ....................................................................................... 4-19
PRCI Contract PR-262-0114                                                                                                                             Page xvii
Final Draft Report - July 2004


       4.23    Switch Box for Soil Resistivity Soundings ........................................................................................... 4-19
       4.24    Wire Reels, Ground Pins, and Tape Measures for Conducting Resistivity Soundings .......................... 4-20
       5.1     Wenner Method - Comparison of Galvanic Instruments at Four Primary Test Sites ............................... 5-1
       5.2     Comparison of Measurements Obtained at all Four Primary Sites ......................................................... 5-2
       5.3     Instrument Measurement Errors Using Wenner Method at Four Primary Test Sites .............................. 5-3
       5.4     Wenner Resistivity Sounding Using Various Instruments (Site E) ......................................................... 5-4
       5.5     Effect of Various Instruments on Accuracy of Schlumberger Method (Site B) ....................................... 5-5
       5.6     Effect of Potential-Pin Spacing on Accuracy of Schlumberger Method
               for Various Instruments (Site B) ............................................................................................................ 5-6
       5.7     Effect of Schlumberger Pin Spacing Ratio ‘n’ on Accuracy of Various Instruments (Site B) .................. 5-7
       5.8     Effect of Potential-Pin Spacing on Accuracy of Schlumberger Method .................................................. 5-8
               for Various Instruments (Site C) ............................................................................................................ 5-8
       5.9     Effect of Potential-Pin Spacing on Accuracy of Schlumberger Method .................................................. 5-9
               for Various Instruments (Site D) ............................................................................................................ 5-9
       5.10    Schlumberger-Palmer Method - Comparison of Galvanic Instruments at Two Primary Test Sites ....... 5-10
       5.11    Schlumberger-Palmer Method vs. Wenner Method ............................................................................. 5-11
       5.12a   Pole-Pole Sounding at Site C (L for Pole-Pole Array is from C2 to P2) ............................................... 5-12
       5.12b   Pole-Pole Sounding at Site C (Pole-Pole Data Shifted to Align with Wenner) ...................................... 5-12
       5.13a   Pole-Pole Sounding at Site C (L for Pole-Pole Array is from C2 to P2;
               Resistivities Calculated Using Eqn. 3.16) ............................................................................................. 5-13
       5.13b   Pole-Pole Sounding at Site C (Pole-Pole Data Shifted to Align with Wenner;
               Resistivities Calculated Using Eqn. 3.16) ............................................................................................. 5-13
       5.14    Dipole-Dipole Sounding at Site C ......................................................................................................... 5-14
       5.15    Comparison of Soundings using EM-2 and Wenner Method (Various Sites) ....................................... 5-16
       5.16    Apparent Resistivity vs. Test Signal Frequency as Measured by EM-3 at Sites B and C ....................... 5-17
       5.17    Retrieval of Soil Samples - Site B ........................................................................................................ 5-18
       5.18    Borehole Analysis (Actual Results and Simplified Models) ................................................................. 5-19
       5.19    Soil Resistivity Data Obtained at Depth Using Direct-Push Resistivity Probe (Site G) ......................... 5-21
       5.20    Wenner Resistivity Sounding at Site G vs. Geometric Mean of Five Resistivity Logs
               Obtained Using Direct-Push Probe ...................................................................................................... 5-22
       5.21    Measurement of Resistance of Buried Wire Using Fall-of-Potential Method (Site B) ........................... 5-23
       5.22    Lower Layer Resistivities and Upper Layer Heights to Produce Resistances Equivalent
               to Those in Table 5.1 ............................................................................................................................ 5-24
       5.23    Comparison of Measured Wire Resistances with Resistances Calculated Using Soil Model ................ 5-25
       5.24    Conducting a Soil Resistivity Profile With a Wenner Array by Advancing
               the Array Using the ‘Leap-Frog’ Method .............................................................................................. 5-26
       5.25    Soil Resistivity Profiles at Site C Using the ‘Leapfrog’ Method ............................................................ 5-27
       5.26    Soil Resistivity Profiles at Site C Using the ‘Leapfrog’ Method
               (Wenner Beta Data Separated from Wenner Alpha Data) ..................................................................... 5-27
       5.27    Switching Arrangement to Change from Wenner Alpha to Wenner Beta Array .................................... 5-28
       5.28    Soil Resistivity Profiles Conducted at Sites B and E
               Using the Wenner Method and Instrument DC-2b ............................................................................... 5-28
       5.29    Marker Flags Used as Ground Pins While Profiling .............................................................................. 5-29
       5.30    Soil Resistivity Profiles to 3m and 6m Depths Using EM-1 (Sites B, C, & E) ....................................... 5-31
       5.31    Effect of Instrument Height Using EM-1 (Sites A, B, C, D and E) ......................................................... 5-32
       5.32    Comparison of EM-1 and Wenner Data (DC-2b) to 3m and 6m Depths (Sites B, C, & E) .................... 5-34
       5.33    Soil Resistivity Profiles at Various Signal Frequencies Using Instrument EM-3 at Sites B and C ......... 5-36
       5.34    Response of Instrument EM-3 at Various Frequencies (Site B) ........................................................... 5-37
       5.35    Response of Instrument EM-3 at Various Frequencies (Site C) ........................................................... 5-38
       5.36    Comparison of EM-3 with Wenner Method (DC-2b) at Sites B and C .................................................. 5-39
       5.37    Comparison of EM-3 with EM-1 at Sites B and C ................................................................................. 5-40
       5.38    Soil Resistivity Profiles Conducted to Various Depths Using EM-2 (Site A) ......................................... 5-41
Page xviii                                                         Evaluation of Soil Resistivity Measurement Techniques
                                                                                                           List 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) ................................ 5-43
        5.41   Profiles Obtained Using the Wenner Method at Various Pin Spacings (Site B) .................................... 5-44
        5.42   Resistivity Pseudosection Obtained Using Wenner Method (Site B) .................................................... 5-45
        5.43   Resistivity Pseudosection Obtained Using EM-2 (Site A) ..................................................................... 5-45
        5.44   Pins Driven Into Ice ..............................................................................................................................5.46
        5.45   Pins Placed in Augered Holes .............................................................................................................. 5-46
        5.46   Wenner Soundings Conducted on Surface of Frozen Lake (Site F) ...................................................... 5-47
        5.47   Resistivity Profile Using EM-1 Along Line of 4-Pin Survey at Site F .................................................... 5-48
        5.48   Resistivity Variation Over Time Using EM-1 at Fixed Position (V-Dipole) ............................................ 5-48
        5.49   Effect of Point Source Electrode Depth on Resistivity Measured Using the Wenner Method ............... 5-49
        5.50   Effect of Pin Depth on Resistivity Measured Using Wenner Method .................................................... 5-49
        5.51   Effect of Pin Depth on Wenner Accuracy (0.15 m Pin Spacing) ........................................................... 5-51
        5.52   Effect of Pin Depth on Wenner Accuracy (0.6 m Pin Spacing) ............................................................. 5-51
        5.53   Effect of Pin Depth on Wenner Accuracy (4 Ω-m Pool Only) ............................................................... 5-51
        5.54   Effect of Pin Depth on Wenner Accuracy (Theoretical vs. Measured) .................................................. 5-51
        5.55   Misalignment of Potential Pin .............................................................................................................. 5-52
        5.56   Effect of Misalignment of Potential Pin in Wenner Array...................................................................... 5-53
        5.57   Theoretical Effect of Misalignment of Potential Pin Spacing Error (Wenner) ....................................... 5-53
        5.58   Test Set-Up to Evaluate Effects of Circuit Resistance ........................................................................... 5-53
        5.59   Effect of Current-Pin Circuit Resistance on Galvanic Instrument Accuracy .......................................... 5-54
        5.60   Combined Effect of Current-Pin and Potential-Pin Circuit Resistances ................................................ 5-55
        5.61   Effect of Wire Reel Orientation on Measurements with AC Instruments .............................................. 5-57
        5.62   Test Set-Up to Determine the Effects of Wire Reels on AC Instruments Used for Galvanic Methods ... 5-58
        5.63   Effect of Excess Potential-Pin Lead Wire on AC Instrument ................................................................. 5-60
        5.64   Theoretical Effect of a Grounding Grid on Wenner Resistivity Measurements ..................................... 5-61
        5.65   Effect of a Coated Pipeline Parallel to Wenner Pin Array ...................................................................... 5-62
        5.66   Effect of Test Current Frequency on Measured Resistivity (Wenner Array Parallel to Coated Pipeline) 5-63
        5.67   Effect of Coated Steel Pipeline on EM-1 Conductivities ........................................................................ 5-64
        5.68   Error in EM-1 Measurements Due to Coated Steel Pipeline ................................................................. 5-64
        5.69   Effect of Buried Steel Object on EM-1 Conductivities
               (V-Dipole; Object Moving Perpendicular to Boom) .............................................................................. 5-65
        5.70   Effect of Buried Steel Object on EM-1 Conductivities
               (V-Dipole; Object Moving Parallel to Boom) ........................................................................................ 5-65
        5.71   Effect of Chain Link Fence on EM-1 Conductivities .............................................................................. 5-65
        5.72   Effect of 60 Hz AC Field on Galvanic Measurement Techniques ........................................................... 5-67
        5.73   Effect of 60Hz AC on EM-1 Conductivities ........................................................................................... 5-69
        5.74   Effect of 60Hz AC on EM-1 Resistivities ............................................................................................... 5-69
        5.75   Effect of Electrical Storm on EM-1 Conductivities ................................................................................ 5-70
        5.76   Effect of Electrical Storm on EM-1 Resistivities ................................................................................... 5-70
        5.77   Wenner Sounding at Site J and Soil Model Derived by Curve Matching .............................................. 5-71
        5.78   Best-Fit Curve for Wenner Data at Site J
               (Determined by Manual Iteration of Soil Model for Use in Eqn. 3.26) .................................................. 5-73
        5.79   Best-Fit Curves for Wenner Data at Site A ............................................................................................ 5-73
        5.80   Best-Fit Curves for Wenner Data at Site C (Model Determined by Curve Fitting) ................................. 5-73
        5.81   Rule of Asymptotes Applied at Site K ................................................................................................... 5-74
        5.82   Barnes-Layer Model for Site J Compared to Model Obtained by Curve Matching ................................ 5-75
        5.83   Barnes-Layer Model for Site B ............................................................................................................. 5-75
        5.84   Alignment of Schlumberger Curve Segments by Inverse Modelling Software
               to Account for Increases in Potential Pin Spacings (Site D) ................................................................ 5-77
        5.85   Inverse Modelling of Wenner and Schlumberger Data at Site A ........................................................... 5-79
        5.86   Inverse Modelling of Wenner and Schlumberger Data at Site B ........................................................... 5-79
PRCI Contract PR-262-0114                                                                                                                   Page xix
Final Draft Report - July 2004


       5.87    Inverse Modelling of Wenner and Schlumberger Data at Site C ........................................................... 5-79
       5.88    Inverse Modelling of Wenner and Schlumberger Data at Site D ........................................................... 5-79
       5.89    Inverse Modelling of Site E Wenner Data ............................................................................................. 5-79
       5.90    Inverse Modelling of Site H Wenner Data ............................................................................................ 5-79
       5.91a   Inverse Modelling of Site F Wenner Data (On Ice - E-W) ..................................................................... 5-79
       5.91b   Inverse Modelling of Site F Wenner Data (Through Ice - N-S) ............................................................. 5-79
       5.92    Inverse Modelling of Wenner Data at Site G (Array Orientations E-W and N-S) ................................... 5-80
       5.93    Inverse Modelling of Site J Wenner Data ............................................................................................. 5-80
       5.94    Inverse Modelling of Site K Wenner Data ............................................................................................. 5-80
       5.95a   Automatic Inverse Modelling of Site C Wenner Data (During Sampling) ............................................. 5-80
       5.95b   Forward Modelling of Site C Soil Sample Data ..................................................................................... 5-80
       A.1     Plot of Apparent Resistivity Data Versus Wenner Pin Spacing on Log-Log Graph Paper ....................... A-2
       A.2     Alignment of Resistivity Data with Master Curves ................................................................................. A-2
       A.3     Plots of Apparent Resistivity Data and Auxiliary Curve .......................................................................... A-4
       A.4     Alignment of Resistivity Data with Master Curves and Intersection of
               Master Curve Origin (‘X’) with Auxiliary Curve ....................................................................................... A-5
       A.5     Log-Log Graph Paper (3x2 Decades) ..................................................................................................... A-6
       A.6     Master Wenner Resistivity Curves for a Two-Layer Soil Structure (Lower Layer Less Conductive) ....... A-7
       A.7     Master Wenner Resistivity Curves for a Two-Layer Soil Structure (Lower Layer More Conductive) ...... A-8
Page xx                                                          Evaluation of Soil Resistivity Measurement Techniques
                                                                                                          List of Tables




                                                   List of Tables
      2.1    Anticipated Corrosion of Steel Exposed to Soils of Varying Resistivity ................................................ 2-15
      3.1    Depths of Investigation for Various Arrays .......................................................................................... 3-20
      5.1    Resistance Measurements for Buried Wire Using Fall-of-Potential Method (Site B) ............................ 5-23
      5.2    Comparison of Interpretive Methods for Wenner Data from Primary Test Sites .................................. 5-81
      B.1    Soil Resistivity Soundings Using the Four-Pin Method - Site A ........................................................ App. B
      B.2    Soil Resistivity Soundings Using the Four-Pin Method - Site B ........................................................ App. B
      B.3a   Soil Resistivity Soundings Using the Four-Pin Method - Site C (Nov.2001) ...................................... App. B
      B.3b   Soil Resistivity Soundings Using the Four-Pin Method - Site C (Oct. 2002) ..................................... App. B
      B.4    Soil Resistivity Soundings Using the Four-Pin Method - Site D ........................................................ App. B
      B.5    Soil Resistivity Soundings Using the Four-Pin Method - Site E ........................................................ App. B
      B.6    Soil Resistivity Soundings Using the Four-Pin Method - Site F ......................................................... App. B
      B.7    Soil Resistivity Soundings Using the Four-Pin Method - Site G ........................................................ App. B
      B.8    Soil Resistivity Soundings Using the Four-Pin Method - Site H ........................................................ App. B
      B.9    Soil Resistivity Soundings Using the Four-Pin Method - Site I ......................................................... App. B
      B.10   Soil Resistivity Soundings Using the Four-Pin Method - Site J ......................................................... App. B
      B.11   Soil Resistivity Soundings Using the Four-Pin Method - Site K ........................................................ App. B
      B.12   Soil Sample Data .............................................................................................................................. App. B