ASTM_D_6938_-_15.pdf

Designation:D693815Standard Test Methods forIn-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods(Shallow Depth)1This standard is issued under the fixed designation D6938;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This test method describes the procedures for measuringin-place density and moisture of soil and soil-aggregate by useof nuclear equipment.The density of the material may bemeasured by direct transmission,backscatter,or backscatter/air-gap ratio methods.Measurements for water(moisture)content are taken at the surface in backscatter mode regardlessof the mode being used for density.It is the intent of thissubcommittee 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 ismeasured by the attenuation of gamma radiation 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 orbackscatter/air-gap the source and detector(s)both remain onthe surface.1.2.1 The density of the test sample in mass per unit volumeis calculated by comparing the detected rate of gamma radia-tion with previously established calibration data.1.2.2 The dry density of the test sample is obtained bysubtracting the water mass per unit volume from the testsample wet density(Section 11).Most gauges display thisvalue directly.1.3 The gauge is calibrated to read the water mass per unitvolume of soil or soil-aggregate.When divided by the densityof water and then multiplied by 100,the water mass per unitvolume is equivalent to the volumetric water content.Thewater mass per unit volume is determined by the thermalizingor slowing of fast neutrons by hydrogen,a component of water.The neutron source and the thermal neutron detector are bothlocated at the surface of the material being tested.The watercontent most prevalent in engineering and construction activi-ties is known as the gravimetric water content,w,and is theratio of the mass of the water in pore spaces to the total massof solids,expressed as a percentage.1.4 Two alternative procedures are provided.1.4.1 Procedure A describes the direct transmission methodin which the probe extends through the base of the gauge intoa pre-formed hole to a desired depth.The direct transmission isthe preferred method.1.4.2 Procedure B involves the use of a dedicated backscat-ter gauge or the probe in the backscatter position.This placesthe gamma and neutron sources and the detectors in the sameplane.1.4.3 Mark the test area to allow the placement of the gaugeover the test site and to align the probe to the hole.1.5 SI UnitsThe values stated in SI units are to beregarded 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 theguide for significant digits and rounding established in PracticeD6026.1.6.1 The procedures used to specify how data are collected,recorded,and calculated in this standard are regarded as theindustry standard.In addition,they are representative of thesignificant digits that should generally be retained.The proce-dures used do not consider material variation,purpose forobtaining the data,special purpose studies,or any consider-ations for the users objectives;and it is common practice toincrease or reduce significant digits of reported data to becommensurate with these considerations.It is beyond the scopeof this standard to consider significant digits used in analysismethods for engineering design.1.7 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is the1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.08 on Special andConstruction Control Tests.Current edition approved Aug.1,2015.Published August 2015.Originallyapproved in 2006.Last previous edition approved in 2010 as D693810.DOI:10.1520/D6938-15.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 responsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil,Rock,and ContainedFluidsD698 Test Methods for Laboratory Compaction Character-istics of Soil Using Standard Effort(12 400 ft-lbf/ft3(600kN-m/m3)D1556 Test Method for Density and Unit Weight of Soil inPlace by Sand-Cone MethodD1557 Test