1、Designation: D6938 17D6938 17aStandard 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 o
2、r, 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 measuring in-place density and
3、moisture of soil and soil-aggregate by use ofnuclear equipment (hereafter referred to as “gauge”). 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 backscattermo
4、de regardless of the mode being used for density.1.1.1 For limitations see Section 5 on Interferences.1.2 The total or wet density of soil and soil-aggregate is measured by the attenuation of gamma radiation where, in directtransmission, the source is placed at a known depth up to 300 mm (12 in.) an
5、d the detector(s) remains on the surface (some gaugesmay reverse this orientation); or in backscatter or backscatter/air-gap the source and detector(s) both remain on the surface.1.2.1 The density of the test sample in mass per unit volume is calculated by comparing the detected rate of gamma radiat
6、ionwith previously established calibration data.1.2.2 The dry density of the test sample is obtained by subtracting the water mass per unit volume from the test sample wetdensity (Section 11). Most gauges display this value directly.1.3 The gauge is calibrated to read the water mass per unit volume
7、of soil or soil-aggregate. When divided by the density ofwater and then multiplied by 100, the water mass per unit volume is equivalent to the volumetric water content. The water massper unit volume is determined by the thermalizing or slowing of fast neutrons by hydrogen, a component of water. The
8、neutronsource and the thermal neutron detector are both located at the surface of the material being tested. The water content mostprevalent in engineering and construction activities is known as the gravimetric water content, w, and is the ratio of the mass ofthe water in pore spaces to the total m
9、ass of solids, expressed as a percentage.1.4 Two alternative procedures are provided.1.4.1 Procedure A describes the direct transmission method in which the probe extends through the base of the gauge into apre-formed hole to a desired depth. The direct transmission is the preferred method.1.4.2 Pro
10、cedure B involves the use of a dedicated backscatter gauge or the probe in the backscatter position. This places thegamma and neutron sources and the detectors in the same plane.1.4.3 Mark the test area to allow the placement of the gauge over the test site and to align the probe to the hole.1.5 SI
11、UnitsThe values stated in SI units are to be regarded as the standard. The values in inch-pound units (ft lb units) areprovided for information only.1.6 All observed and calculated values shall conform to the guide for significant digits and rounding established in PracticeD6026.1.6.1 The procedures
12、 used to specify how data are collected, recorded, and calculated in this standard are regarded as theindustry standard. In addition, they are representative of the significant digits that should generally be retained. The proceduresused do not consider material variation, purpose for obtaining the
13、data, special purpose studies, or any considerations for the usersobjectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with theseconsiderations. It is beyond the scope of this standard to consider significant digits used in analysis metho
14、ds for engineering design.1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability o
15、f regulatory limitations prior to use.1 This test method is under the jurisdiction ofASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.08 on Special and ConstructionControl Tests.Current edition approved March 1, 2017Nov. 1, 2017. Published March 2017December 2
16、017. Originally approved in 2006. Last previous edition approved in 20152017as D693815.17. DOI: 10.1520/D6938-17.10.1520/D6938-17A.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version.
17、Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section a
18、ppears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States11.8 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on
19、Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D653 Terminology Relating to Soil, Rock, and Contained FluidsD698 Test Methods for Labora
20、tory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft3 (600 kN-m/m3)D1556 Test Method for Density and Unit Weight of Soil in Place by Sand-Cone MethodD1557 Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft3 (2,700kN-m/m3)
21、D2167 Test Method for Density and Unit Weight of Soil in Place by the Rubber Balloon MethodD2487 Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)D2488 Practice for Description and Identification of Soils (Visual-Manual Procedures)D2216 Test Methods f
22、or Laboratory Determination of Water (Moisture) Content of Soil and Rock by MassD2937 Test Method for Density of Soil in Place by the Drive-Cylinder MethodD3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used inEngineering Design and Const
23、ructionD4253 Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory TableD4254 Test Methods for Minimum Index Density and Unit Weight of Soils and Calculation of Relative DensityD4643 Test Method for Determination of Water Content of Soil and Rock by Microwave Oven Heating
24、D4718 Practice for Correction of Unit Weight and Water Content for Soils Containing Oversize ParticlesD4944 Test Method for Field Determination of Water (Moisture) Content of Soil by the Calcium Carbide Gas Pressure TesterD4959 Test Method for Determination of Water Content of Soil By Direct Heating
25、D6026 Practice for Using Significant Digits in Geotechnical DataD7013 Guide for Nuclear Surface Moisture and Density Gauge Calibration Facility SetupD7759 Guide for Nuclear Surface Moisture and Density Gauge Calibration3. Terminology3.1 DefinitionsSee Terminology D653 for general definitions.3.2 Def
26、initions of Terms Specific to This Standard:3.2.1 nuclear gaugea device containing one or more radioactive sources used to measure certain properties of soil andsoil-aggregates.3.2.2 gamma (radiation) sourcea sealed source of radioactive material that emits gamma radiation as it decays.3.2.3 neutron
27、 (radiation) sourcea sealed source of radioactive material that emits neutron radiation as it decays.3.2.4 Compton scatteringthe interaction between a gamma ray (photon) and an orbital electron where the gamma ray losesenergy and rebounds in a different direction.3.2.5 detectora device to detect and
28、 measure radiation.3.2.6 gravimetric water contentsame as water content (as defined in Terminology D653), a nomenclature used in somescientific fields to differentiate it from volumetric water content.3.2.7 thermalizationthe process of “slowing down” fast neutrons by collisions with light-weight ato
29、ms, such as hydrogen.3.2.8 volumetric water contentthe volume of water as a percent of the total volume of soil or rock material.3.2.9 test count, nthe measured output of a detector for a specific type of radiation for a given test.3.2.10 prepared blocksblocks prepared of soil, solid rock, concrete,
30、 and engineered materials, that have characteristics ofvarious degrees of reproducible uniformity.4. Significance and Use4.1 The test method described is useful as a rapid, nondestructive technique for in-place measurements of wet density and watercontent of soil and soil-aggregate and the determina
31、tion of dry density.4.2 The test method is used for quality control and acceptance testing of compacted soil and soil-aggregate mixtures as usedin construction and also for research and development. The nondestructive nature allows repetitive measurements at a single testlocation and statistical ana
32、lysis of the results.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.D6938 17a24.3 DensityThe fundamental ass
33、umptions inherent in the methods are that Compton scattering is the dominant interaction andthat the material is homogeneous.4.4 Water ContentThe fundamental assumptions inherent in the test method are that the hydrogen ions present in the soil orsoil-aggregate are in the form of water as defined by
34、 the water content derived from Test Methods D2216, and that the materialis homogeneous. (See 5.2)NOTE 1The quality of the result produced by this standard test method is dependent on the competence of the personnel performing it, and thesuitability of the equipment and facilities used. Agencies tha
35、t meet the criteria of Practice D3740 are generally considered capable of competent andobjective testing/sampling/inspection, and the like. Users of this standard are cautioned that compliance with Practice D3740 does not in itself ensurereliable results. Reliable results depend on many factors; Pra
36、ctice D3740 provides a means of evaluating some of those factors.5. Interferences5.1 In-Place Density Interferences5.1.1 Measurements may be affected by the chemical composition of the material being tested.5.1.2 Measurements may be affected by non-homogeneous soils and surface texture (see 10.2). E
37、xcessive voids in the preparedtest surface beneath the gauge can cause density measurements that are lower than the actual soil density. Excessive use of fillmaterial to compensate for these voids may likewise cause biased density measurements, or biased water content measurements,or both.5.1.3 Meas
38、urements in the Backscatter Mode are influenced more by the density and water content of the material in proximityto the surface.5.1.4 Measurements in the Direct Transmission mode are an average of the density from the bottom of the probe in the soil orsoil aggregate back up to the surface of the ga
39、uge.5.1.5 Gravel particles or large voids in the source-detector path may cause higher or lower density measurments. Where lackof uniformity in the soil due to layering, aggregate or voids is suspected, the test site should be excavated and visually examinedto determine whether the test material is
40、representative of the in situ material in general and whether an oversize correction isrequired in accordance with Practice D4718.5.1.6 Oversize particles or large voids in the source-detector path may cause higher or lower density measurements. Where lackof uniformity in the soil due to layering, a
41、ggregate or voids is suspected, the test site should be excavated and visually examinedto determine if the test material is representative of the in situ material in general and if an oversize correction is required inaccordance with Practice D4718.5.1.7 The measured volume is approximately 0.0028 m
42、3 (0.10 ft3) for the Backscatter Mode and 0.0057 m3 (0.20 ft3) for theDirect Transmission Mode when the test depth is 150 mm (6 in.). The actual measured volume is indeterminate and varies withthe apparatus and the density of the material.5.1.8 Other radioactive sources must not be within 9 m (30 ft
43、) of equipment in operation.5.2 In-Place Water (Moisture) Content Interferences5.2.1 The chemical composition of the material being tested can affect the measurement and adjustments may be necessary (seeSection 10.6). Hydrogen in forms other than water and carbon will cause measurements in excess of
44、 the true value. Some chemicalelements such as boron, chlorine, and cadmium will cause measurements lower than the true value.5.2.2 The water content measured by this test method is not necessarily the average water content within the volume of thesample involved in the measurement. Since this measu
45、rement is by backscatter in all cases, the value is biased by the water contentof the material closest to the surface. The volume of soil and soil-aggregate represented in the measurement is indeterminate andwill vary with the water content of the material. In general, the greater the water content
46、of the material, the smaller the volumeinvolved in the measurement. Approximately 50 % of the typical measurement results from the water content of the upper 50 to75 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 /
47、 Moisture GaugeWhile exact details of construction of the apparatus may vary, the system shall consistof:6.1.1 Gamma SourceA sealed source of high-energy gamma radiation such as cesium or radium.6.1.2 Gamma DetectorAny type of gamma detector such as a Geiger-Mueller tube(s).6.1.3 Fast Neutron Source
48、A sealed mixture of a radioactive material such as americium, radium and a target material suchas beryllium, or a neutron emitter such as californium-252.6.1.4 Slow Neutron DetectorAny type of slow neutron detector such as boron trifluoride or helium-3 proportional counter.6.2 Reference StandardA bl
49、ock of material used for checking instrument operation, correction of source decay, and toestablish conditions for a reproducible reference count rate.6.3 Site Preparation DeviceA plate, straightedge, or other suitable leveling tool that may be used for planing the test site tothe required smoothness, and in the Direct Transmission Method, guiding the drive pin to prepare a perpendicular hole.D6938 17a36.4 Drive PinA pin of slightly larger diameter than the probe in the Direct Transmission Instrument used to prepare a holein the test site for insertin
