ASTM G57-06

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
Designation:G57–06
Standard Test Method for
Field Measurement of Soil Resistivity Using the Wenner
1
Four-Electrode Method
This standard is issued under the fixed designation G57; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope separation should be selected with consideration of the soil
strata of interest. The resulting resistivity measurement repre-
1.1 This test method covers the equipment and procedures
sents the average resistivity of a hemisphere of soil of a radius
for the field measurement of soil resistivity, both in situ and for
equal to the electrode separation.
samples removed from the ground, for use in the control of
3.2 A voltage is impressed between the outer electrodes,
corrosion of buried structures.
causing current to flow, and the voltage drop between the inner
1.2 To convert cm (metric unit) to metre (SI unit), divide by
electrodes is measured using a sensitive voltmeter. Alterna-
100.
tively, the resistance can be measured directly. The resistivity,
1.3 This standard does not purport to address all of the
r, is then:
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
r,V·cm 5 2p aR ~a in cm!
priate safety and health practices and determine the applica-
5 191.5 aR~a in ft!
bility of regulatory limitations prior to use.
where:
2. Terminology
a = electrode separation, and
2.1 Definition:
R = resistance, V.
2.1.1 resistivity—the electrical resistance between opposite
Using dimensional analysis, the correct unit for resistivity is
faces of a unit cube of material; the reciprocal of conductivity.
ohm-centimetre.
Resistivity is used in preference to conductivity as an expres-
3.3 If the current-carrying (outside) electrodes are not
sion of the electrical character of soils (and waters) since it is
spaced at the same interval as the potential-measuring (inside)
expressed in whole numbers.
electrodes, the resistivity, r is:
2.1.2 Resistivity measurements indicate the relative ability
b
of a medium to carry electrical currents. When a metallic
r, V·cm 5 95.76bR/ 1 2
S D
b 1 a
structure is immersed in a conductive medium, the ability of
the medium to carry current will influence the magnitude of
where:
galvanic currents and cathodic protection currents. The degree
b = outer electrode spacing, ft,
of electrode polarization will also affect the size of such
a = inner electrode spacing, ft, and
currents. R = resistance, V.
or:
3. Summary of Test Method
b
r, V·cm5pbR/ 1 2
3.1 The Wenner four-electrode method requires that four S D
b 1 a
metal electrodes be placed with equal separation in a straight
where:
line in the surface of the soil to a depth not exceeding 5 % of
b = outer electrode spacing, cm,
the minimum separation of the electrodes. The electrode
a = inner electrode spacing, cm, and
R = resistance, V.
1
This test method is under the jurisdiction of ASTM Committee G01 on
3.4 For soil contained in a soil box similar to the one shown
Corrosion of Metals and is the direct responsibility of Subcommittee G01.10 on
in Fig. 1, the resistivity, r, is:
Corrosion in Soils.
Current edition approved Nov. 1, 2006. Published December 2006. Originally
r, V·cm 5RA/a
approved in 1978. Last previous edition approved in 2001 as G57 – 95a (2001).
DOI: 10.1520/G0057-06.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1

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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Please contact ASTM International (www.astm.org) for the latest information.
G57–06
FIG. 1 Typical Connections for Use of Soil Box with Various Types of Instruments
cathodic protection systems. As an essential design parameter
where:
for cathodic protection systems, it is important to take as many
R = resistance, V,
A = cross sectional area of the container perpendicular to measurements as necessary so as to get a sufficiently represen-
2
tative characterization of the soil environment that the entire
the current flow, cm , and
a = inner electrode spacing, cm.
buried structure will experience.
NOTE 1—The spacing between the inner electrodes should be measured
5. Apparatus
from the inner edges of the electrode pins, and not from the center of the
5.1 At-Grade Measurements in situ:
electrodes.
5.1.1 The equipment required for field resistivity measure-
4. Significance and Use
ments to be taken at grade consists of a current source, a
4.1 Measurement of soil resistivity is used for the control of
su
...