Designation:D6938−15StandardTestMethodsforIn-PlaceDensityandWaterContentofSoilandSoil-AggregatebyNuclearMethods(ShallowDepth)1ThisstandardisissuedunderthefixeddesignationD6938;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope*1.1Thistestmethoddescribestheproceduresformeasuringin-placedensityandmoistureofsoilandsoil-aggregatebyuseofnuclearequipment.Thedensityofthematerialmaybemeasuredbydirecttransmission,backscatter,orbackscatter/air-gapratiomethods.Measurementsforwater(moisture)contentaretakenatthesurfaceinbackscattermoderegardlessofthemodebeingusedfordensity.ItistheintentofthissubcommitteethatthisstandardreplaceD2922andD3017.1.1.1ForlimitationsseeSection5onInterferences.1.2Thetotalorwetdensityofsoilandsoil-aggregateismeasuredbytheattenuationofgammaradiationwhere,indirecttransmission,thesourceisplacedataknowndepthupto300mm(12in.)andthedetector(s)remainsonthesurface(somegaugesmayreversethisorientation);orinbackscatterorbackscatter/air-gapthesourceanddetector(s)bothremainonthesurface.1.2.1Thedensityofthetestsampleinmassperunitvolumeiscalculatedbycomparingthedetectedrateofgammaradia-tionwithpreviouslyestablishedcalibrationdata.1.2.2Thedrydensityofthetestsampleisobtainedbysubtractingthewatermassperunitvolumefromthetestsamplewetdensity(Section11).Mostgaugesdisplaythisvaluedirectly.1.3Thegaugeiscalibratedtoreadthewatermassperunitvolumeofsoilorsoil-aggregate.Whendividedbythedensityofwaterandthenmultipliedby100,thewatermassperunitvolumeisequivalenttothevolumetricwatercontent.Thewatermassperunitvolumeisdeterminedbythethermalizingorslowingoffastneutronsbyhydrogen,acomponentofwater.Theneutronsourceandthethermalneutrondetectorarebothlocatedatthesurfaceofthematerialbeingtested.Thewatercontentmostprevalentinengineeringandconstructionactivi-tiesisknownasthegravimetr...
