Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)

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. 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. It is the intent of this subcommittee that this standard replaces D2922 and D3017.
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 Adescribes the direct transmission method in which the gamma source rod 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 Binvolves the use of a dedicated backscatter gauge or the source rod in the backscatter position. This places the gamma and neutron sources and the detectors in the same plane.
1.5 SI UnitsThe values stated in SI units are to be regarded as the standard. The values in inch-pound units (ft - lb units) are provided for information only.
1.6 All observed and calculated values shall conform to the guide for significant digits and rounding established in Practice D 6026.
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 users objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.
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.

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Publication Date
30-Jun-2007
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ASTM D6938-07a - Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)
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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:D6938–07a
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope* 1.4.1 Procedure A describes the direct transmission method
inwhichthegammasourcerodextendsthroughthebaseofthe
1.1 Thistestmethoddescribestheproceduresformeasuring
gauge into a pre-formed hole to a desired depth. The direct
in-place density and moisture of soil and soil-aggregate by use
transmission is the preferred method.
of nuclear equipment. The density of the material may be
1.4.2 Procedure B involves the use of a dedicated backscat-
measured by direct transmission, backscatter, or backscatter/
ter gauge or the source rod in the backscatter position. This
air-gap ratio methods. Measurements for water (moisture)
places the gamma and neutron sources and the detectors in the
content are taken at the surface in backscatter mode regardless
same plane.
of the mode being used for density. It is the intent of this
1.5 SI Units—The values stated in SI units are to be
subcommittee that this standard replaces D2922 and D3017.
regarded as the standard. The values in inch-pound units (ft –
1.1.1 For limitations see Section 5 on Interferences.
lb units) are provided for information only.
1.2 The total or wet density of soil and soil-aggregate is
1.6 All observed and calculated values shall conform to the
measured by the attenuation of gamma radiation where, in
guideforsignificantdigitsandroundingestablishedinPractice
directtransmission,thesourceisplacedataknowndepthupto
D6026.
300 mm (12 in.) and the detector (s) remains on the surface (
1.6.1 Theproceduresusedtospecifyhowdataarecollected,
somegaugesmayreversethisorientation);orinbackscatteror
recorded, and calculated in this standard are regarded as the
backscatter/air-gap the source and detector (s) both remain on
industry standard. In addition, they are representative of the
the surface.
significant digits that should generally be retained. The proce-
1.2.1 Thedensityofthetestsampleinmassperunitvolume
dures used do not consider material variation, purpose for
is calculated by comparing the detected rate of gamma radia-
obtaining the data, special purpose studies, or any consider-
tion with previously established calibration data.
ations for the user’s objectives; and it is common practice to
1.2.2 The dry density of the test sample is obtained by
increase or reduce significant digits of reported data to be
subtracting the water mass per unit volume from the test
commensuratewiththeseconsiderations.Itisbeyondthescope
sample wet density ( Section 11 ). Most gauges display this
of this standard to consider significant digits used in analysis
value directly.
methods for engineering design.
1.3 The gauge is calibrated to read the water mass per unit
1.7 This standard does not purport to address all of the
volume of soil or soil-aggregate. When divided by the density
safety concerns, if any, associated with its use. It is the
of water, and then multiplied by 100, the water mass per unit
responsibility of the user of this standard to establish appro-
volume is equivalent to the volumetric water content. The
priate safety and health practices and determine the applica-
water mass per unit volume is determined by the thermalizing
bility of regulatory limitations prior to use.
orslowingoffastneutronsbyhydrogen,acomponentofwater.
The neutron source and the thermal neutron detector are both
2. Referenced Documents
located at the surface of the material being tested. The water
2
2.1 ASTM Standards:
content most prevalent in engineering and construction activi-
D653 Terminology Relating to Soil, Rock, and Contained
ties is known as the gravimetric water content, w, and is the
Fluids
ratio of the mass of the water in pore spaces to the total mass
D698 Test Methods for Laboratory Compaction Character-
of solids, expressed as a percentage.
3
istics of Soil Using Standard Effort (12 400 ft-lbf/ft (600
1.4 Two alternative procedures are provided.
3
kN-m/m ))
1
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
2
Rock and is the direct responsibility of Subcommittee D18.08 Special and For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Construction Control Tests. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
CurrenteditionapprovedJuly1,2007.PublishedJuly2007.Originallyapproved Standards volume information, refer to the standard’s Document Summary page on
in 200
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