1、Designation: D 6938 08aStandard Test Method forIn-Place Density and Water Content of Soil and Soil-Aggregate by Nuclear Methods (Shallow Depth)1This standard is issued under the fixed designation D 6938; the number immediately following the designation indicates the year oforiginal adoption or, in t
2、he 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
3、 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 den
4、sity. It is the intent of thissubcommittee that this standard replace D 2922 and D 3017.1.1.1 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
5、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 comparin
6、g 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 r
7、ead 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 hydr
8、ogen, 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 wat
9、er 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 gamma source rod extends through the base of thegauge into a pre-formed hole to a desired depth. The directtransm
10、ission is the preferred method.1.4.2 Procedure B involves the use of a dedicated backscat-ter gauge or the source rod in the backscatter position. Thisplaces the gamma and neutron sources and the detectors in thesame plane.1.5 SI UnitsThe values stated in SI units are to beregarded as the standard.
11、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 PracticeD 6026.1.6.1 The procedures used to specify how data are collected,recorded, and calculated in th
12、is 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 obj
13、ectives; 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
14、all of thesafety concerns, if any, associated with its use. It is theresponsibility 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:2D 653 Terminology
15、Relating to Soil, Rock, and ContainedFluidsD 698 Test Methods for Laboratory Compaction Character-istics of Soil Using Standard Effort (12 400 ft-lbf/ft3(600kN-m/m3)1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.0
16、8 on Special andConstruction Control Tests.Current edition approved June 1, 2008. Published June 2008. Originallyapproved in 2006. Last previous edition approved in 2008 as D 6938 08.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.
17、org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United Stat
18、es.D 1556 Test Method for Density and Unit Weight of Soil inPlace by Sand-Cone MethodD 1557 Test Methods for Laboratory Compaction Charac-teristics of Soil Using Modified Effort (56,000 ft-lbf/ft3(2,700 kN-m/m3)D 2167 Test Method for Density and Unit Weight of Soil inPlace by the Rubber Balloon Meth
19、odD 2487 Practice for Classification of Soils for EngineeringPurposes (Unified Soil Classification System)D 2488 Practice for Description and Identification of Soils(Visual-Manual Procedure)D 2216 Test Methods for Laboratory Determination of Wa-ter (Moisture) Content of Soil and Rock by MassD 2937 T
20、est Method for Density of Soil in Place by theDrive-Cylinder MethodD 3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD 4253 Test Methods for Maximum Index Density and UnitWeight of Soils Using a Vib
21、ratory TableD 4254 Test Methods for Minimum Index Density and UnitWeight of Soils and Calculation of Relative DensityD 4643 Test Method for Determination of Water (Moisture)Content of Soil by Microwave Oven HeatingD 4718 Practice for Correction of Unit Weight and WaterContent for Soils Containing Ov
22、ersize ParticlesD 4944 Test Method for Field Determination of Water(Moisture) Content of Soil by the Calcium Carbide GasPressure TesterD 4959 Test Method for Determination of Water (Moisture)Content of Soil By Direct HeatingD 6026 Practice for Using Significant Digits in Geotechni-cal DataD 7013 Gui
23、de for Nuclear Surface Moisture and DensityGauge Calibration Facility Setup3. Terminology3.1 Definitions: See Terminology D 653 for general defini-tions.3.2 Definitions of Terms Specific to This Standard:3.2.1 nuclear gaugea device containing one or moreradioactive sources used to measure certain pr
24、operties of soiland soil-aggregates.3.2.2 wet densitysame as bulk density (as defined inTerminology D 653); the total mass (solids plus water) per totalvolume of soil or soil-aggregate.3.2.3 dry densitysame as density of dry soil or rock (asdefined in Terminology D 653); the mass of solid particles
25、perthe total volume of soil or soil-aggregate.3.2.4 gamma (radiation) sourcea sealed source of radio-active material that emits gamma radiation as it decays.3.2.5 neutron (radiation) sourcea sealed source of radio-active material that emits neutron radiation as it decays.3.2.6 Compton scatteringthe
26、interaction between agamma ray (photon) and an orbital electron where the gammaray loses energy and rebounds in a different direction.3.2.7 detectora device to detect and measure radiation.3.2.8 probea metal rod attached to a nuclear gauge inwhich a radioactive source or a detector is housed. The ro
27、d canbe lowered to specified depths for testing. Probes containingonly a radioactive source are commonly referred to as “SourceRods.”3.2.9 thermalizationthe process of “slowing down” fastneutrons by collisions with light-weight atoms, such as hydro-gen.3.2.10 water contentthe ratio of the mass of wa
28、ter con-tained in the pore spaces of soil or soil-aggregate, to the solidmass of particles in that material, expressed as a percentage(this is sometimes referred to in some scientific fields asgravimetric water content to differentiate it from volumetricwater cotent).3.2.11 volumetric water contentt
29、he volume of water as apercent of the total volume of soil or rock material.3.2.12 test count, nthe measured output of a detector fora specific type of radiation for a given test.3.2.13 prepared blocksblocks prepared of soil, solid rock,concrete, and engineered materials, that have characteristics o
30、fvarious degrees of reproducible uniformity.4. Significance and Use4.1 The test method described is useful as a rapid, nonde-structive technique for in-place measurements of wet densityand water content of soil and soil-aggregate and the determi-nation of dry density.4.2 The test method is used for
31、quality control and accep-tance testing of compacted soil and soil-aggregate mixtures asused in construction and also for research and development.The nondestructive nature allows repetitive measurements at asingle test location and statistical analysis of the results.4.3 DensityThe fundamental assu
32、mptions inherent in themethods are that Compton scattering is the dominant interac-tion and that the material is homogeneous.4.4 Water ContentThe fundamental assumptions inherentin the test method are that the hydrogen ions present in the soilor soil-aggregate are in the form of water as defined by
33、thewater content derived from Test Methods D 2216, and that thematerial is homogeneous. (See 5.2)NOTE 1The quality of the result produced by this standard testmethod is dependent on the competence of the personnel performing it,and the suitability of the equipment and facilities used.Agencies that m
34、eetthe criteria of Practice D 3740 are generally considered capable ofcompetent and objective testing/sampling/inspection, and the like. Usersof this standard are cautioned that compliance with Practice D 3740 doesnot in itself assure reliable results. Reliable results depend on manyfactors; Practic
35、e D 3740 provides a means of evaluating some of thosefactors.5. Interferences5.1 In-Place Density Interferences5.1.1 Measurements may be affected by the chemical com-position of the material being tested.5.1.2 Measurements may be affected by non-homogeneoussoils and surface texture (see 10.2).5.1.3
36、Measurements in the Backscatter Mode are influencedmore by the density and water content of the material in closeproximity to the surface.D 6938 08a25.1.4 Measurements in the Direct Transmission mode are anaverage of the density from the bottom of the probe in the soilor soil aggregate back up to th
37、e surface of the gauge.5.1.5 Oversize particles or large voids in the source-detectorpath may cause higher or lower density measurements. Wherelack of uniformity in the soil due to layering, aggregate orvoids is suspected, the test site should be excavated andvisually examined to determine if the te
38、st material is represen-tative of the in-situ material in general and if an oversizecorrection is required in accordance with Practice D 4718.5.1.6 The measured volume is approximately 0.0028m3(0.10 ft3) for the Backscatter Mode and 0.0057 m3(0.20 ft3)for the Direct Transmission Mode when the test d
39、epth is 150mm (6 in.). The actual measured volume is indeterminate andvaries with the apparatus and the density of the material.5.1.7 Other radioactive sources must not be within9m(30ft.) of equipment in operation.5.2 In-Place Water (Moisture) Content Interferences5.2.1 The chemical composition of t
40、he material being testedcan affect the measurement and adjustments may be necessary(see Section 10.6). Hydrogen in forms other than water andcarbon will cause measurements in excess of the true value.Some chemical elements such as boron, chlorine, and cadmiumwill cause measurements lower than the tr
41、ue value.5.2.2 The water content measured by this test method is notnecessarily the average water content within the volume of thesample involved in the measurement. Since this measurementis by backscatter in all cases, the value is biased by the watercontent of the material closest to the surface.
42、The volume ofsoil and soil-aggregate represented in the measurement isindeterminate and will vary with the water content of thematerial. In general, the greater the water content of thematerial, the smaller the volume involved in the measurement.Approximately 50 % of the typical measurement results
43、fromthe water content of the upper 50 to 75 mm (2 to 3 in.).5.2.3 Other neutron sources must not be within 9 m (30 ft)of equipment in operation.6. Apparatus6.1 Nuclear Density / Moisture GaugeWhile exact detailsof construction of the apparatus may vary, the system shallconsist of:6.1.1 Gamma SourceA
44、 sealed source of high-energygamma radiation such as cesium or radium.6.1.2 Gamma DetectorAny type of gamma detector suchas a Geiger-Mueller tube(s).6.1.3 Fast Neutron SourceA sealed mixture of a radioac-tive material such as americium, radium and a target materialsuch as beryllium, or a neutron emi
45、tter such as californium-252.6.1.4 Slow Neutron DetectorAny type of slow neutrondetector such as boron trifluoride or helium-3 proportionalcounter.6.2 Reference StandardA block of material used forchecking instrument operation, correction of source decay, andto establish conditions for a reproducibl
46、e reference count rate.6.3 Site Preparation DeviceA plate, straightedge, or othersuitable leveling tool that may be used for planing the test siteto the required smoothness, and in the Direct TransmissionMethod, guiding the drive pin to prepare a perpendicular hole.6.4 Drive PinA pin of slightly lar
47、ger diameter than theprobe in the Direct Transmission Instrument used to prepare ahole in the test site for inserting the probe.6.4.1 Drive Pin GuideA fixture that keeps the drive pinperpendicular to the test site. Generally part of the sitepreparation device.6.5 HammerHeavy enough to drive the pin
48、to the requireddepth without undue distortion of the hole.6.6 Drive Pin ExtractorAtool that may be used to removethe drive pin in a vertical direction so that the pin will notdistort the hole in the extraction process.6.7 Slide Hammer, with a drive pin attached, may also beused both to prepare a hol
49、e in the material to be tested and toextract the pin without distortion to the hole.7. Hazards7.1 These gauges utilize radioactive materials that may behazardous to the health of the users unless proper precautionsare taken. Users of these gauges must become familiar withapplicable safety procedures and government regulations.7.2 Effective user instructions, together with routine safetyprocedures and knowledge of and compliance with RegulatoryRequirements, are a mandatory part of the operation andstorage of these gauges.8. Calibration8.1 Calibration o
