ASTM D6431-99(2010)
(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
SIGNIFICANCE AND USE
Concepts—The resistivity technique is used to measure the resistivity of subsurface materials. Although the resistivity of materials can be a good indicator of the type of subsurface material present, it is not a unique indicator. While the resistivity method is used to measure the resistivity of earth materials, it is the interpreter who, based on knowledge of local geologic conditions and other data, must interpret resistivity data and arrive at a reasonable geologic and hydrologic interpretation.
Parameter Being Measured and Representative Values:
Table 1 shows some general trends for resistivity values. Fig. 2 shows ranges in resistivity values for subsurface materials.
Materials with either a low effective porosity or that lack conductive pore fluids have a relatively high resistivity (>1000 Ωm). These materials include massive limestones, most unfractured igneous rocks, unsaturated unconsolidated materials, and ice.
Materials that have high porosity with conductive pore fluids or that consist of or contain clays usually have low resistivity. These include clay soil and weathered rock.
Materials whose pore water has low salinity have moderately high resistivity.
The dependence of resistivity on water saturation is not linear. Resistivity increases relatively little as saturation decreases from 100 % to 40-60 % and then increases much more as saturation continues to decrease. An empirical relationship known as Archie's Law describes the relationship between pore fluid resistivity, porosity, and bulk resistivity (McNeill (8)).
Equipment—Geophysical apparatus used for surface resistivity measurement includes a source of power, a means to measure the current, a high impedance voltmeter, electrodes to make contact with the ground, and the necessary cables to connect the electrodes to the power sources and the volt meter (Fig. 1).
While resistivity measurements can be made using common electronic instruments, it is recommended that commercial resisti...
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 groundwater salinity; and to delineate groundwater contaminants. General references are, Keller and Frischknecht (1), Zohdy et al (2), Koefoed (3), EPA (4), Ward (5), Griffiths and King (6), and Telford et al (7).
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 D420, Practice D5088, Practice D5608, Guide D5730, Test Method G57, D6429, and D6235.
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 polarizati...
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D6431 − 99 (Reapproved 2010)
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
procedures, and interpretation methods for the assessment of 1.2.2 This guide is limited to the commonly used approach
for resistivity measurements using sounding and profiling
the electrical properties of subsurface materials and their pore
fluids, using the direct current (DC) resistivity method. Mea- techniques with the Schlumberger, Wenner, or dipole-dipole
surements of the electrical properties of subsurface materials arrays and modifications to those arrays. It does not cover the
are made from the land surface and yield an apparent resistiv-
use of a wide range of specialized arrays. It also does not
ity. These data can then be interpreted to yield an estimate of include the use of spontaneous potential (SP) measurements,
the depth, thickness, and resistivity of subsurface layer(s).
induced polarization (IP) measurements, or complex resistivity
1.1.2 Resistivity measurements as described in this guide
methods.
are applied in geological, geotechnical, environmental, and
1.2.3 The resistivity method has been adapted for a number
hydrologic investigations. The resistivity method is used to
of special uses, on land, within a borehole, or on water.
map geologic features such as lithology, structure, fractures,
Discussions of these adaptations of resistivity measurements
and stratigraphy; hydrologic features such as depth to water
are not included in this guide.
table, depth to aquitard, and groundwater salinity; and to
1.2.4 The approaches suggested in this guide for the resis-
delineate groundwater contaminants. General references are,
2 tivity method are the most commonly used, widely accepted
Keller and Frischknecht (1), Zohdy et al (2), Koefoed (3),
and proven; however, other approaches or modifications to the
EPA(4), Ward (5), Griffiths and King (6), and Telford et al (7).
resistivitymethodthataretechnicallysoundmaybesubstituted
1.2 Limitations:
if technically justified and documented.
1.2.1 This guide provides an overview of the Direct Current
1.2.5 This guide offers an organized collection of informa-
Resistivity Method. It does not address in detail the theory,
tion or a series of options and does not recommend a specific
field procedures, or interpretation of the data. Numerous
course of action. This document cannot replace education or
references are included for that purpose and are considered an
experienceandshouldbeusedinconjunctionwithprofessional
essential part of this guide. It is recommended that the user of
judgements. Not all aspects of this guide may be applicable in
all circumstances. This ASTM standard is not intended to
This guide is under the jurisdiction ofASTM CommitteeD18 on Soil and Rock
represent or replace the standard of care by which the
and is the direct responsibility of Subcommittee D18.01 on Surface and Subsurface
adequacy of a given professional service must be judged, nor
Characterization.
Current edition approved May 1, 2010. Published September 2010. Originally
should this document be applied without consideration of a
approved in 1999. Last previous edition approved in 2005 as D6431–99(2005).
project’s many unique aspects. The word “Standard” in the
DOI: 10.1520/D6431-99R10.
2 title of this document means only that the document has been
The boldface numbers in parentheses refer to the list of references at the end of
this standard. approved through the ASTM consensus process.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6431 − 99 (2010)
1.3 Precautions: 3.1.3.4 resistivity—the property of a material that resists the
1.3.1 It is the responsibility of the user of this guide to flow of electrical current. The units of resistivity are ohmme-
follow any precautions in the equipment manufacturer’s rec- tres or ohm-feet (1 Ωm = 3.28 Ω-ft).
ommendations and to consider the safety implications when
4. Summary of Guide
high voltages and currents are used.
1.3.2 If this guide is used at sites with hazardous materials,
4.1 Summary—The measurement of electrical resistivity
operations, or equipment, it is the responsibility of the user of
requires that four electrodes be placed in contact with the
this guide to establish appropriate safety and health practices surface materials (Fig. 1). The geometry and separation of the
and to determine the applicability of regulations prior to use.
electrode array are selected on the basis of the application and
required depth of investigation.
1.4 This standard does not purport to address all of the
4.1.1 In an electrical resistivity survey, a direct current or a
safety concerns, if any, associated with its use. It is the
very low frequency alternating current is passed into the
responsibility of the user of this standard to establish appro-
ground through a pair of current electrodes, and the resulting
priate safety and health practices and determine the applica-
potential drop is measured across a pair of potential electrodes
bility of regulatory limitations prior to use.
(Fig. 1). The resistance is then derived as the ratio of the
2. Referenced Documents
voltage measured across the potential electrodes and the
current electrodes. The apparent resistivity of subsurface ma-
2.1 ASTM Standards:
terials is derived as the resistance multiplied by a geometric
D420 Guide to Site Characterization for Engineering Design
factor that is determined by the geometry and spacing of the
and Construction Purposes (Withdrawn 2011)
electrode array.
D653 Terminology Relating to Soil, Rock, and Contained
4.1.2 The calculated apparent resistivity measurement rep-
Fluids
resents a bulk average resistivity of the volume of earth
D5088 Practice for Decontamination of Field Equipment
determined by the geometry of the array and the resistivity of
Used at Waste Sites
the subsurface material. This apparent resistivity is different
D5608 Practices for Decontamination of Field Equipment
from true resistivity unless the subsurface materials are elec-
Used at Low Level Radioactive Waste Sites
trically uniform. Representative resistivity values of layers are
D5730 Guide for Site Characterization for Environmental
interpreted from apparent resistivity values obtained from a
Purposes With Emphasis on Soil, Rock, the Vadose Zone
series of measurements made with variable electrode spacing.
and Groundwater (Withdrawn 2013)
Increasing electrode spacing may permit distinction among
D5753 Guide for Planning and Conducting Borehole Geo-
layers that vary in electrical properties with depth.
physical Logging
4.1.3 Most resistivity surveys for geologic, engineering,
D6235 Practice for Expedited Site Characterization of Va-
hydrologic, and environmental applications are carried out to
dose Zone and Groundwater Contamination at Hazardous
determine depths of specific layers or lateral changes in
Waste Contaminated Sites
geologic conditions at depths of less than a hundred metres.
D6429 Guide for Selecting Surface Geophysical Methods
However, with sufficient power and instrument sensitivity,
G57 Test Method for Field Measurement of Soil Resistivity
resistivitymeasurementsaremadetodepthsofseveralhundred
Using the Wenner Four-Electrode Method
metres.
3. Terminology
4.2 Complementary Data—Other complementary surface
3.1 Definitions: geophysical methods (D6429) or borehole geophysical meth-
3.1.1 Definitions shall be in accordance with the terms and ods (Guide D5753) and non-geophysical methods may be
symbols given in Terminology D653. necessary to properly interpret subsurface conditions.
3.1.2 The majority of the technical terms used in this
5. Significance and Use
document are defined in Sheriff (1991).
3.1.3 Additional Definitions: 5.1 Concepts—The resistivity technique is used to measure
3.1.3.1 apparentresistivity—theresistivityofhomogeneous,
the resistivity of subsurface materials. Although the resistivity
isotropic ground that would give the same voltage-current of materials can be a good indicator of the type of subsurface
relationship as measured.
material present, it is not a unique indicator. While the
3.1.3.2 conductivity—Theabilityofamaterialtoconductan resistivity method is used to measure the resistivity of earth
electrical current. In isotropic material, it is the reciprocal of
materials,itistheinterpreterwho,basedonknowledgeoflocal
resistivity. The units of conductivity are siemens per metre. geologic conditions and other data, must interpret resistivity
3.1.3.3 resistance—opposition to the flow of direct current.
data and arrive at a reasonable geologic and hydrologic
The unit of resistance is ohms. interpretation.
5.2 Parameter Being Measured and Representative Values:
5.2.1 Table 1 shows some general trends for resistivity
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
values. Fig. 2 shows ranges in resistivity values for subsurface
Standards volume information, refer to the standard’s Document Summary page on
materials.
the ASTM website.
5.2.2 Materials with either a low effective porosity or that
The last approved version of this historical standard is referenced on
www.astm.org. lack conductive pore fluids have a relatively high resistivity
D6431 − 99 (2010)
FIG. 1 Diagram Showing Basic Concept of Resistivity Measurement (from Benson et al, (8))
TABLE 1 Representative Resistivity Values for Soil, Water, and
5.3 Equipment—Geophysical apparatus used for surface
Rock (Mooney (4))
resistivity measurement includes a source of power, a means to
Regional Soil Resistivity Ωm
measure the current, a high impedance voltmeter, electrodes to
- wet regions 50–200
make contact with the ground, and the necessary cables to
- dry regions 100–500
- arid regions 200–1000 (sometimes as low as 50 if the soil connect the electrodes to the power sources and the volt meter
is saline)
(Fig. 1).
Waters Ωm
5.3.1 While resistivity measurements can be made using
- soil water 1 to 100
- rain water 30 to 1000
common electronic instruments, it is recommended that com-
- sea water order of 0.2
mercial resistivity instruments specifically designed for the
- ice 105 to 108
purpose be used for resistivity measurements in the field.
Rock Types Ωm
- igneous and metamorphic 100 to 10,000
5.3.2 Commonly used equipment includes the following
- consolidated sediments 10 to 100
elements:
- unconsolidated sediments 1 to 100
5.3.2.1 A source of current consisting of batteries or a
generator,
5.3.2.2 A high-impedance voltmeter or resistivity unit,
(>1000 Ωm). These materials include massive limestones,
5.3.2.3 Metal stakes for the current and potential electrodes,
most unfractured igneous rocks, unsaturated unconsolidated
and
materials, and ice.
5.3.2.4 Insulated wire to connect together all of the preced-
5.2.3 Materialsthathavehighporositywithconductivepore
ing components.
fluids or that consist of or contain clays usually have low
5.3.3 Caremustbetakentoensuregoodelectricalcontactof
resistivity. These include clay soil and weathered rock.
the electrodes with the ground. Electrodes should be driven
5.2.4 Materials whose pore water has low salinity have
into the ground until they are in firm contact. If connections
moderately high resistivity.
between electrodes and the insulated wire are not waterproof,
5.2.5 The dependence of resistivity on water saturation is
care must be taken to ensure that they will not be shorted out
not linear. Resistivity increases relatively little as saturation
by moisture. Special waterproof cables and connectors are
decreases from 100 % to 40-60 % and then increases much
required for wet areas.
more as saturation continues to decrease. An empirical rela-
tionship known as Archie’s Law describes the relationship 5.3.4 A large variety of resistivity systems are available
between pore fluid resistivity, porosity, and bulk resistivity from different manufacturers. Relatively inexpensive battery-
(McNeill (10)). powered units are available for shallow surveys. The current
D6431 − 99 (2010)
FIG. 2 Typical Ranges of Resistivities of Earth Materials (from Sheriff, (9))
source (transmitter) and the potential measurement instrument 5.4.2.4 Ambiguities in interpretation arising from suppres-
(receiver) are often assembled into a single, portable unit. In sion (where resistant layers are sandwiched between more
some cases, the transmitter and receiver units are separate. conductive layers).
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 Afundamental limitation of all geophysical methods
noise include local inhomogeneities near electrodes that may
liesinthefactthatagivensetofdatacannotbeassociatedwith
result in measurement error and variations in the subsurface
a unique set of subsurface cond
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.