ASTM D6938-15

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.
Designation: D6938 − 10 D6938 − 15
Standard Test MethodMethods 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*
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 replace 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) 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 gamma source rod 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 source rod 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 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.
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 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.
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 May 1, 2010Aug. 1, 2015. Published June 2010August 2015. Originally approved in 2006. Last previous edition approved in 20082010 as
D6938–08a.–10. DOI: 10.1520/D6938-10. 10.1520/D6938-15.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International
...