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Field Services: Soil testing

Field Services: Soil testing

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Test Method Title

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

Reference Number

ASTM D6938


Field Soil

Test Property

Dry density and moisture content of in-situ soil

Description of Test

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. 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.

Preferred Test Sample Size

Number of Test Specimens

project specific

Test Specimen Size



Nuclear, density, compaction, gauge

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