ASTM D6431-99(2005)
(Guide)Standard Guide for Using the Direct Current Resistivity Method for Subsurface Investigation
Standard Guide for Using the Direct Current Resistivity Method for Subsurface Investigation
SCOPE
1.1 Purpose and Application
1.1.1 This guide summarizes the equipment, field procedures, and interpretation methods for the assessment of the electrical properties of subsurface materials and their pore fluids, using the direct current (DC) resistivity method. Measurements of the electrical properties of subsurface materials are made from the land surface and yield an apparent resistivity. These data can then be interpreted to yield an estimate of the depth, thickness, and resistivity of subsurface layer(s).
1.1.2 Resistivity measurements as described in this guide are applied in geological, geotechnical, environmental, and hydrologic investigations. The resistivity method is used to map geologic features such as lithology, structure, fractures, and stratigraphy; hydrologic features such as depth to water table, depth to aquitard, and ground water salinity; and to delineate ground water contaminants. General references are, Keller and Frischknecht (), Zohdy et al (), Koefoed (), EPA(), Ward (), Griffiths and King (), and Telford et al ().
1.2 Limitations
1.2.1 This guide provides an overview of the Direct Current Resistivity Method. It does not address in detail the theory, field procedures, or interpretation of the data. Numerous references are included for that purpose and are considered an essential part of this guide. It is recommended that the user of the resistivity method be familiar with the references cited in the text and with the Guide D 420, Practice D 5088, Practice D 5608, Guide D 5730, Test Method G 57, D 6429, and D 6235.
1.2.2 This guide is limited to the commonly used approach for resistivity measurements using sounding and profiling techniques with the Schlumberger, Wenner, or dipole-dipole arrays and modifications to those arrays. It does not cover the use of a wide range of specialized arrays. It also does not include the use of spontaneous potential (SP) measurements, induced polarization (IP) measurements, or complex resistivity methods.
1.2.3 The resistivity method has been adapted for a number of special uses, on land, within a borehole, or on water. Discussions of these adaptations of resistivity measurements are not included in this guide.
1.2.4 The approaches suggested in this guide for the resistivity method are the most commonly used, widely accepted and proven; however, other approaches or modifications to the resistivity method that are technically sound may be substituted if technically justified and documented.
1.2.5 This guide offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgements. Not all aspects of this guide may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word "Standard" in the title of this document means only that the document has been approved through the ASTM consensus process.
1.3 Precautions
1.3.1 It is the responsibility of the user of this guide to follow any precautions in the equipment manufacturer's recommendations and to consider the safety implications when high voltages and currents are used.
1.3.2 If this guide is used at sites with hazardous materials, operations, or equipment, it is the responsibility of the user of this guide to establish appropriate safety and health practices and to determine the applicability of regulations prior to use.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D6431 – 99 (Reapproved 2005)
Standard Guide for
Using the Direct Current Resistivity Method for Subsurface
Investigation
This standard is issued under the fixed designation D6431; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope the resistivity method be familiar with the references cited in
the text and with the Guide D420, Practice D5088, Practice
1.1 Purpose and Application:
D5608, Guide D5730, Test Method G57, D6429, and D6235.
1.1.1 This guide summarizes the equipment, field proce-
1.2.2 This guide is limited to the commonly used approach
dures, and interpretation methods for the assessment of the
for resistivity measurements using sounding and profiling
electrical properties of subsurface materials and their pore
techniques with the Schlumberger, Wenner, or dipole-dipole
fluids, using the direct current (DC) resistivity method. Mea-
arrays and modifications to those arrays. It does not cover the
surements of the electrical properties of subsurface materials
use of a wide range of specialized arrays. It also does not
are made from the land surface and yield an apparent resistiv-
include the use of spontaneous potential (SP) measurements,
ity. These data can then be interpreted to yield an estimate of
induced polarization (IP) measurements, or complex resistivity
the depth, thickness, and resistivity of subsurface layer(s).
methods.
1.1.2 Resistivity measurements as described in this guide
1.2.3 The resistivity method has been adapted for a number
are applied in geological, geotechnical, environmental, and
of special uses, on land, within a borehole, or on water.
hydrologic investigations. The resistivity method is used to
Discussions of these adaptations of resistivity measurements
map geologic features such as lithology, structure, fractures,
are not included in this guide.
and stratigraphy; hydrologic features such as depth to water
1.2.4 The approaches suggested in this guide for the resis-
table, depth to aquitard, and ground water salinity; and to
tivity method are the most commonly used, widely accepted
delineate ground water contaminants. General references are,
and proven; however, other approaches or modifications to the
Keller and Frischknecht (1), Zohdy et al (2), Koefoed (3),
resistivitymethodthataretechnicallysoundmaybesubstituted
EPA(4),Ward (5), Griffiths and King (6), andTelford et al (7).
if technically justified and documented.
1.2 Limitations:
1.2.5 This guide offers an organized collection of informa-
1.2.1 This guide provides an overview of the Direct Current
tion or a series of options and does not recommend a specific
Resistivity Method. It does not address in detail the theory,
course of action. This document cannot replace education or
field procedures, or interpretation of the data. Numerous
experienceandshouldbeusedinconjunctionwithprofessional
references are included for that purpose and are considered an
judgements. Not all aspects of this guide may be applicable in
essential part of this guide. It is recommended that the user of
all circumstances. This ASTM standard is not intended to
represent or replace the standard of care by which the
ThisguideisunderthejurisdictionofASTMCommitteeD18onSoilandRock
adequacy of a given professional service must be judged, nor
and is the direct responsibility of Subcommittee D18.01 on Surface and Subsurface
should this document be applied without consideration of a
Characterization.
project’s many unique aspects. The word “Standard” in the
Current edition approved May 1, 2005. Published September 2005. Originally
approved in 1999. Last previous edition approved in 1999 as D6431–99. DOI:
title of this document means only that the document has been
10.1520/D6431-99R05.
approved through the ASTM consensus process.
The boldface numbers in parentheses refer to the list of references at the end of
1.3 Precautions:
this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6431 – 99 (2005)
1.3.1 It is the responsibility of the user of this guide to 4. Summary of Guide
follow any precautions in the equipment manufacturer’s rec-
4.1 Summary—The measurement of electrical resistivity
ommendations and to consider the safety implications when
requires that four electrodes be placed in contact with the
high voltages and currents are used.
surface materials (Fig. 1). The geometry and separation of the
1.3.2 If this guide is used at sites with hazardous materials,
electrode array are selected on the basis of the application and
operations, or equipment, it is the responsibility of the user of
required depth of investigation.
this guide to establish appropriate safety and health practices
4.1.1 In an electrical resistivity survey, a direct current or a
and to determine the applicability of regulations prior to use.
very low frequency alternating current is passed into the
1.4 This standard does not purport to address all of the
ground through a pair of current electrodes, and the resulting
safety concerns, if any, associated with its use. It is the
potential drop is measured across a pair of potential electrodes
responsibility of the user of this standard to establish appro-
(Fig. 1). The resistance is then derived as the ratio of the
priate safety and health practices and determine the applica-
voltage measured across the potential electrodes and the
bility of regulatory limitations prior to use.
current electrodes. The apparent resistivity of subsurface ma-
terials is derived as the resistance multiplied by a geometric
2. Referenced Documents
factor that is determined by the geometry and spacing of the
2.1 ASTM Standards:
electrode array.
D420 Guide to Site Characterization for Engineering De-
4.1.2 The calculated apparent resistivity measurement rep-
sign and Construction Purposes
resents a bulk average resistivity of the volume of earth
D653 Terminology Relating to Soil, Rock, and Contained
determined by the geometry of the array and the resistivity of
Fluids
the subsurface material. This apparent resistivity is different
D5088 Practice for Decontamination of Field Equipment
from true resistivity unless the subsurface materials are elec-
Used at Waste Sites
trically uniform. Representative resistivity values of layers are
D5608 Practices for Decontamination of Field Equipment
interpreted from apparent resistivity values obtained from a
Used at Low Level Radioactive Waste Sites
series of measurements made with variable electrode spacing.
D5730 Guide for Site Characterization for Environmental
Increasing electrode spacing may permit distinction among
Purposes With Emphasis on Soil, Rock, the Vadose Zone
layers that vary in electrical properties with depth.
and Ground Water
4.1.3 Most resistivity surveys for geologic, engineering,
D5753 Guide for Planning and Conducting Borehole Geo-
hydrologic, and environmental applications are carried out to
physical Logging
determine depths of specific layers or lateral changes in
D6235 Practice for Expedited Site Characterization of Va-
geologic conditions at depths of less than a hundred metres.
dose Zone and GroundWater Contamination at Hazardous
However, with sufficient power and instrument sensitivity,
Waste Contaminated Sites
resistivitymeasurementsaremadetodepthsofseveralhundred
D6429 Guide for Selecting Surface Geophysical Methods
metres.
G57 Test Method for Field Measurement of Soil Resistivity
Using the Wenner Four-Electrode Method 4.2 Complementary Data—Other complementary surface
geophysical methods (D6429) or borehole geophysical meth-
3. Terminology
ods (Guide D5753) and non-geophysical methods may be
3.1 Definitions: necessary to properly interpret subsurface conditions.
3.1.1 Definitions shall be in accordance with the terms and
symbols given in Terminology D653.
5. Significance and Use
3.1.2 —The majority of the technical terms used in this
5.1 Concepts—The resistivity technique is used to measure
document are defined in Sheriff (1991).
the resistivity of subsurface materials. Although the resistivity
3.1.3 Additional Definitions:
of materials can be a good indicator of the type of subsurface
3.1.3.1 apparent resistivity—the resistivity of homoge-
material present, it is not a unique indicator. While the
neous, isotropic ground that would give the same voltage-
resistivity method is used to measure the resistivity of earth
current relationship as measured.
materials,itistheinterpreterwho,basedonknowledgeoflocal
3.1.3.2 conductivity—Theabilityofamaterialtoconductan
geologic conditions and other data, must interpret resistivity
electrical current. In isotropic material, it is the reciprocal of
data and arrive at a reasonable geologic and hydrologic
resistivity. The units of conductivity are siemens per metre.
interpretation.
3.1.3.3 resistance—opposition to the flow of direct current.
5.2 Parameter Being Measured and Representative Values:
The unit of resistance is ohms.
5.2.1 Table 1 shows some general trends for resistivity
3.1.3.4 resistivity—the property of a material that resists the
values. Fig. 2 shows ranges in resistivity values for subsurface
flow of electrical current. The units of resistivity are ohmme-
materials.
tres or ohm-feet (1 Vm = 3.28 V-ft).
5.2.2 Materials with either a low effective porosity or that
lack conductive pore fluids have a relatively high resistivity
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
(>1000 Vm). These materials include massive limestones,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
most unfractured igneous rocks, unsaturated unconsolidated
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. materials, and ice.
D6431 – 99 (2005)
FIG. 1 Diagram Showing Basic Concept of Resistivity Measurement (from Benson et al, (15))
TABLE 1 Representative Resistivity Values for Soil, Water, and
measure the current, a high impedance voltmeter, electrodes to
Rock (Mooney (4))
make contact with the ground, and the necessary cables to
Regional Soil Resistivity Vm
connect the electrodes to the power sources and the volt meter
- wet regions 50–200 (Fig. 1).
- dry regions 100–500
5.3.1 While resistivity measurements can be made using
- arid regions 200–1000 (sometimes as low as 50 if the soil
common electronic instruments, it is recommended that com-
is saline)
mercial resistivity instruments specifically designed for the
Waters Vm
purpose be used for resistivity measurements in the field.
- soil water 1 to 100
5.3.2 Commonly used equipment includes the following
- rain water 30 to 1000
- sea water order of 0.2
elements:
- ice 105 to 108
5.3.2.1 A source of current consisting of batteries or a
Rock Types Vm
generator,
- igneous and metamorphic 100 to 10,000
5.3.2.2 A high-impedance voltmeter or resistivity unit,
- consolidated sediments 10 to 100
5.3.2.3 Metal stakes for the current and potential electrodes,
- unconsolidated sediments 1 to 100
and
5.3.2.4 Insulated wire to connect together all of the preced-
ing components.
5.2.3 Materialsthathavehighporositywithconductivepore
fluids or that consist of or contain clays usually have low 5.3.3 Caremustbetakentoensuregoodelectricalcontactof
the electrodes with the ground. Electrodes should be driven
resistivity. These include clay soil and weathered rock.
5.2.4 Materials whose pore water has low salinity have into the ground until they are in firm contact. If connections
between electrodes and the insulated wire are not waterproof,
moderately high resistivity.
5.2.5 The dependence of resistivity on water saturation is care must be taken to ensure that they will not be shorted out
by moisture. Special waterproof cables and connectors are
not linear. Resistivity increases relatively little as saturation
decreases from 100 % to 40-60 % and then increases much required for wet areas.
more as saturation continues to decrease. An empirical rela- 5.3.4 A large variety of resistivity systems are available
tionship known as Archie’s Law describes the relationship from different manufacturers. Relatively inexpensive battery-
between pore fluid resistivity, porosity, and bulk resistivity powered units are available for shallow surveys. The current
(McNeill (8)). source (transmitter) and the potential measurement instrument
5.3 Equipment—Geophysical apparatus used for surface (receiver) are often assembled into a single, portable unit. In
resistivity measurement includes a source of power, a means to some cases, the transmitter and receiver units are separate.
D6431 – 99 (2005)
FIG. 2 Typical Ranges of Resistivities of Earth Materials (from Sheriff, (16))
High power units capable of deep survey work are powered by 5.4.2.5 Extremely resistive materials will prevent current
generators. The current used in dc resistivity surveys varies injection into the ground.
from a few milliamps to several amps, depending on the depth
5.4.3 Interferences Caused by Ambient and Geologic Con-
of the investigation. ditions:
5.3.5 Signal Enhancement—Signal enhancement capability 5.4.3.1 The resistivity method is sensitive to electrical
is available in many resistivity systems. It is a significant aid
interference from a variety of sources. It is inherently sensitive
when working in noisy areas or with low power sources.
to electrical interference. Spatial variables caused by geologic
Enhancement is accomplished by adding the results from a
factors and cultural factors may also produce noise.
number of measurements at the same station. This process
5.4.3.2 Ambient Sources of Noise—Natural (ambient)
increases the signal-to-noise ratio.
sources of noise include lightning or natural earth currents,
5.4 Limitations and Interferences:
which may induce a voltage in resistivity cables.
5.4.1 Limitations Inherent to Geophysical Methods:
5.4.3.3 Geologic Sources of Noise—Geologic sources of
5.4.1.1 Afundamentallimitationofallgeophysicalmethods noise include local inhomogeneities near electrodes that may
liesinthefactthatagivensetofdatacannotbeassociatedwith result in measurement error and variations in the subsurface
a unique set of subsurface conditions. In most situations, that are not the object of the survey.
surface geophysical measurements alone cannot resolve all 5.4.3.4 Cultural Sources of Noise—Resistivity measure-
ambiguities,andsomeadditionalinformation,suchasborehole
ments may be influenced by nearby c
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