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ASTM D 6938 REV A Document Information:
Title
Standard Test Method for In-Place Density and Water Content of Soil and Soil- Aggregate by Nuclear Methods (Shallow Depth)
ASTM International
Publication Date:
Jun 1, 2008
Scope:
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 replace D
2922 and D 3017.
For limitations see Section 5 on Interferences.
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.
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.
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.
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.
Two alternative procedures are provided.
Procedure A describes 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.
Procedure B involves 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.
SI Units—The 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.
All observed and calculated values shall conform to the guide
for significant digits and rounding established in Practice D
6026.
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 user's
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.
*A Summary of Changes section appears at the end of this
standard.
Keywords:
- Compaction test
- acceptance testing
- construction control
- quality control
- field density
- in-place density
- wet density
- water content
- dry density
- nuclear methods
- nuclear gauge
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