ASTM D6938-17 Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)

Designation: D6938-17 Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)1 1. Scope 1.1 This test method describes the procedures for measuringin-pliace density and moisture of soil and soil-aggregate by useof nucear equipment (hereafter referred to asgauge""y.Thedensity of the material may be measured by directtransmission,backscatcr, or backscatterVair-gap ratio methods.Measurements for water (moisture) content arc iaken at thesurface in backscatter mode regardless of the mode being usedfor density. 1.1.1 For limitations see Section 5 on Intcrferences. 1.2 The total or wet density of soil and soill-aggregate ismcasured by the attenuation of gamma raliation where.indirect transmission, the source is placed at a known depth up to300 mm (12 in.) and the detector(s) remains on the surface( some gauges may reverse this orientation); or in backscatter orbackscatterVair-gap the source and deleclorisy both remain onthe surface. 1.2.1The density of the test sample in mass per unit volumeis calculatedd by comparing the detected rate of gamma radia-tion with previously established calibration data. 1.2.2The dry density of the test sample is obtained bysubtracting the water mass per unit volumc from the testsample wet density (Section 11). Most gaugcs display thisvalue directly. 1.3 The gauge is calibrated lo read thec water mass per unitvolume of soill or soil-aggregate.When divided by the densityof water and then multiplied by l00.the waler mass per unitvolume is cquivallent to the volumetric watcr contcnt.Thewatcr mass per unit volume is dctermined by the thcrmalizingor slowing of fast neutrons by hydrogen, a component of water. D6938-17 Standard Test Methods for In-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth