ASTM D6938-23
(Test Method)Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)
Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)
SIGNIFICANCE AND USE
4.1 The test method described is useful as a rapid, nondestructive technique for in-place measurements of wet density and water content of soil and soil-aggregate and the determination of dry density.
4.2 The test method is used for quality control and acceptance testing of compacted soil and soil-aggregate mixtures as used in construction and also for research and development. The nondestructive nature allows repetitive measurements at a single test location and statistical analysis of the results.
4.3 Density—The fundamental assumptions inherent in the methods are that Compton scattering is the dominant interaction and that the material is homogeneous.
4.4 Water Content—The fundamental assumptions inherent in the test method are that the hydrogen ions present in the soil or soil-aggregate are in the form of water as defined by the water content derived from Test Methods D2216, and that the material is homogeneous. (See 5.2)
Note 1: The quality of the result produced by this standard test method is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection, and the like. Users of this standard are cautioned that compliance with Practice D3740 does not in itself ensure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
SCOPE
1.1 This test method describes the procedures for measuring in-place density and moisture of soil and soil-aggregate by use of nuclear equipment (hereafter referred to as “gauge”). The density of the material may be measured by direct transmission, backscatter, or backscatter/air-gap ratio methods. Measurements for water (moisture) content are taken at the surface in backscatter mode regardless of the mode being used for density.
1.1.1 For limitations see Section 5 on Interferences.
1.2 The total or wet density of soil and soil-aggregate is measured by the attenuation of gamma radiation where, in direct transmission, the source is placed at a known depth up to 300 mm (12 in.) and the detector(s) remains on the surface (some gauges may reverse this orientation); or in backscatter or backscatter/air-gap the source and detector(s) both remain on the surface.
1.2.1 The density of the test sample in mass per unit volume is calculated by comparing the detected rate of gamma radiation with previously established calibration data.
1.2.2 The dry density of the test sample is obtained by subtracting the water mass per unit volume from the test sample wet density (Section 11). Most gauges display this value directly.
1.3 The gauge is calibrated to read the water mass per unit volume of soil or soil-aggregate. When divided by the density of water and then multiplied by 100, the water mass per unit volume is equivalent to the volumetric water content. The water mass per unit volume is determined by the thermalizing or slowing of fast neutrons by hydrogen, a component of water. The neutron source and the thermal neutron detector are both located at the surface of the material being tested. The water content most prevalent in engineering and construction activities is known as the gravimetric water content, w, and is the ratio of the mass of the water in pore spaces to the total mass of solids, expressed as a percentage.
1.4 Two alternative procedures are provided.
1.4.1 Procedure A describes the direct transmission method in which the probe extends through the base of the gauge into a pre-formed hole to a desired depth. The direct transmission is the preferred method.
1.4.2 Procedure B involves the use of a dedicated backscatter gauge or the probe in the backscatter position. This places the gamma and neutron sources and the detectors in the same plane.
1.4.3 Mark the test area ...
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This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D6938 − 23
Standard Test Methods for
In-Place Density and Water Content of Soil and Soil-
1
Aggregate by Nuclear Methods (Shallow Depth)
This standard is issued under the fixed designation D6938; 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* ratio of the mass of the water in pore spaces to the total mass
of solids, expressed as a percentage.
1.1 This test method describes the procedures for measuring
in-place density and moisture of soil and soil-aggregate by use
1.4 Two alternative procedures are provided.
of nuclear equipment (hereafter referred to as “gauge”). The
1.4.1 Procedure A describes the direct transmission method
density of the material may be measured by direct
in which the probe extends through the base of the gauge into
transmission, backscatter, or backscatter/air-gap ratio methods.
a pre-formed hole to a desired depth. The direct transmission is
Measurements for water (moisture) content are taken at the
the preferred method.
surface in backscatter mode regardless of the mode being used
1.4.2 Procedure B involves the use of a dedicated backscat-
for density.
ter gauge or the probe in the backscatter position. This places
1.1.1 For limitations see Section 5 on Interferences.
the gamma and neutron sources and the detectors in the same
plane.
1.2 The total or wet density of soil and soil-aggregate is
measured by the attenuation of gamma radiation where, in 1.4.3 Mark the test area to allow the placement of the gauge
over the test site and to align the probe to the hole.
direct transmission, the source is placed at a known depth up to
300 mm (12 in.) and the detector(s) remains on the surface
1.5 Units—The values stated in SI units are to be regarded
(some gauges may reverse this orientation); or in backscatter or
as standard. The values given in parentheses are provided for
backscatter/air-gap the source and detector(s) both remain on
information only and are not considered standard. Reporting
the surface.
the test results in units other than SI shall not be regarded as
1.2.1 The density of the test sample in mass per unit volume
nonconformance with this standard.
is calculated by comparing the detected rate of gamma radia-
1.6 All observed and calculated values shall conform to the
tion with previously established calibration data.
guide for significant digits and rounding established in Practice
1.2.2 The dry density of the test sample is obtained by
D6026.
subtracting the water mass per unit volume from the test
1.6.1 The procedures used to specify how data are collected,
sample wet density (Section 11). Most gauges display this
recorded, and calculated in this standard are regarded as the
value directly.
industry standard. In addition, they are representative of the
1.3 The gauge is calibrated to read the water mass per unit
significant digits that should generally be retained. The proce-
volume of soil or soil-aggregate. When divided by the density
dures used do not consider material variation, purpose for
of water and then multiplied by 100, the water mass per unit
obtaining the data, special purpose studies, or any consider-
volume is equivalent to the volumetric water content. The
ations for the user’s objectives; and it is common practice to
water mass per unit volume is determined by the thermalizing
increase or reduce significant digits of reported data to be
or slowing of fast neutrons by hydrogen, a component of water.
commensurate with these considerations. It is beyond the scope
The neutron source and the thermal neutron detector are both
of this standard to consider significant digits used in analysis
located at the surface of the material being tested. The water
methods for engineering design.
content most prevalent in engineering and construction activi-
1.7 Limitations—This test method is not applicable to clean
ties is known as the gravimetric water content, w, and is the
gravel or clean crushed rock due to excessive surface voids
which have the potential to affect gauge measurements.
1
1.8 This standard does not purport to address all of the
This test method is under the jurisdiction of ASTM Committee D18 on Soil and
Rock and is the direct responsibility of Subcommittee D18.08 on Special and
safety concerns, if any, associated with its use. It is the
Construction Control Tests.
responsibility of the user of this standard to establish appro-
Current edition approved May 1, 2023. Published Ma
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: D6938 − 17a D6938 − 23
Standard Test Methods for
In-Place Density and Water Content of Soil and Soil-
1
Aggregate by Nuclear Methods (Shallow Depth)
This standard is issued under the fixed designation D6938; 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
ε NOTE—Editorially corrected units of measurement statement in June 2021.
1. Scope*
1.1 This test method describes the procedures for measuring in-place density and moisture of soil and soil-aggregate by use of
nuclear equipment (hereafter referred to as “gauge”). The density of the material may be measured by direct transmission,
backscatter, or backscatter/air-gap ratio methods. Measurements for water (moisture) content are taken at the surface in backscatter
mode regardless of the mode being used for density.
1.1.1 For limitations see Section 5 on Interferences.
1.2 The total or wet density of soil and soil-aggregate is measured by the attenuation of gamma radiation where, in direct
transmission, the source is placed at a known depth up to 300 mm (12 in.) and the detector(s) remains on the surface (some gauges
may reverse this orientation); or in backscatter or backscatter/air-gap the source and detector(s) both remain on the surface.
1.2.1 The density of the test sample in mass per unit volume is calculated by comparing the detected rate of gamma radiation with
previously established calibration data.
1.2.2 The dry density of the test sample is obtained by subtracting the water mass per unit volume from the test sample wet density
(Section 11). Most gauges display this value directly.
1.3 The gauge is calibrated to read the water mass per unit volume of soil or soil-aggregate. When divided by the density of water
and then multiplied by 100, the water mass per unit volume is equivalent to the volumetric water content. The water mass per unit
volume is determined by the thermalizing or slowing of fast neutrons by hydrogen, a component of water. The neutron source and
the thermal neutron detector are both located at the surface of the material being tested. The water content most prevalent in
engineering and construction activities is known as the gravimetric water content, w, and is the ratio of the mass of the water in
pore spaces to the total mass of solids, expressed as a percentage.
1.4 Two alternative procedures are provided.
1.4.1 Procedure A describes the direct transmission method in which the probe extends through the base of the gauge into a
pre-formed hole to a desired depth. The direct transmission is the preferred method.
1
This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.08 on Special and Construction
Control Tests.
Current edition approved Nov. 1, 2017May 1, 2023. Published December 2017May 2023. Originally approved in 2006. Last previous edition approved in 2017 as
ɛ1
D6938–17.–17a . DOI: 10.1520/D6938-17AE01.10.1520/D6938-23.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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D6938 − 23
1.4.2 Procedure B involves the use of a dedicated backscatter gauge or the probe in the backscatter position. This places the
gamma and neutron sources and the detectors in the same plane.
1.4.3 Mark the test area to allow the placement of the gauge over the test site and to align the probe to the hole.
1.5 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for
information only and are not considered standard. Reporting the test results in units other than SI shall not be regarded as
nonconformance with this standard.
1.6 All observed and calculated values shall conform to the guide for significant digits and rounding established in Practice D6026.
1.6.1 The procedures used to specify how data are collected, recorded, and calculated in this standard are regarded as the industry
standard. In addition, they are representative of the significant digits that should generally be retained. The procedures used do not
consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the
...
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