1、Designation: D6639 18Standard Guide forUsing the Frequency Domain Electromagnetic Method forSubsurface Site Characterizations1This standard is issued under the fixed designation D6639; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、 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 Purpose and Application:1.1.1 This guide summarizes the equipment, fieldprocedures, and interpretation
3、methods for the assessment ofsubsurface conditions using the frequency domain electromag-netic (FDEM) method.1.1.2 FDEM measurements as described in this standardguide are applicable to mapping subsurface conditions forgeologic, geotechnical, hydrologic, environmental,agricultural, archaeological an
4、d forensic site characterizationsas well as mineral exploration.1.1.3 The FDEM method is sometimes used to map suchdiverse geologic conditions as depth to bedrock, fractures andfault zones, voids and sinkholes, soil and rock properties, andsaline intrusion as well as man-induced environmental condi-
5、tions including buried drums, underground storage tanks(USTs), landfill boundaries and conductive groundwater con-tamination.1.1.4 The FDEM method utilizes the secondary magneticfield induced in the earth by a time-varying primary magneticfield to explore the subsurface. It measures the amplitude an
6、dphase of the induced field at various frequencies. FDEMinstruments typically measure two components of the second-ary magnetic field: a component in-phase with the primary fieldand a component 90 out-of-phase (quadrature component)with the primary field (Kearey and Brook 1991). Generally, thein-pha
7、se response is more sensitive to metallic items (eitherabove or below the ground surface) while the quadratureresponse is more sensitive to geologic variations in thesubsurface. However, both components are, to some degree,affected by both metallic and geologic features. FDEM mea-surements therefore
8、 are dependent on the electrical propertiesof the subsurface soil and rock or buried man-made objects aswell as the orientation of any subsurface geological features orman-made objects. In many cases, the FDEM measurementscan be used to identify the subsurface structure or object. Thismethod is used
9、 only when it is expected that the subsurface soilor rock, man-made materials or geologic structure can becharacterized by differences in electrical conductivity.1.1.5 The FDEM method may be used instead of the DirectCurrent Resistivity method (Guide D6431) when surface soilsare excessively insulati
10、ng (for example, dry or frozen) or alayer of asphalt or plastic or other logistical constraints preventelectrode to soil contact.1.2 Limitations:1.2.1 This standard guide provides an overview of theFDEM method using coplanar coils at or near ground level andhas been referred to by other names includ
11、ing Slingram,HLEM (horizontal loop electromagnetic) and Ground Conduc-tivity methods. This guide does not address the details of theelectromagnetic theory, field procedures or interpretation of thedata. References are included that cover these aspects ingreater detail and are considered an essential
12、 part of this guide(Grant and West, 1965; Wait, 1982; Kearey and Brook, 1991;Milsom, 1996; Ward, 1990). It is recommended that the user ofthe FDEM method review the relevant material pertaining totheir particular application. ASTM standards that should alsobe consulted include Guide D420, Terminolog
13、y D653, GuideD5730, Guide D5753, Practice D6235, Guide D6429, andGuide D6431.1.2.2 This guide is limited to frequency domain instrumentsusing a coplanar orientation of the transmitting and receivingcoils in either the horizontal dipole (HD) mode with coilsvertical, or the vertical dipole (VD) mode w
14、ith coils horizontal(Fig. 2). It does not include coaxial or asymmetrical coilorientations, which are sometimes used for special applications(Grant and West 1965).1.2.3 This guide is limited to the use of frequency domaininstruments in which the ratio of the induced secondarymagnetic field to the pr
15、imary magnetic field is directly propor-tional to the grounds bulk or apparent conductivity (see 5.1.4).Instruments that give a direct measurement of the apparentground conductivity are commonly referred to as GroundConductivity Meters (GCMs) that are designed to operatewithin the “low induction num
16、ber approximation.” Multi-frequency instruments operating within and outside the lowinduction number approximation provide the ratio of the1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.01 on Surface and SubsurfaceChara
17、cterization.Current edition approved Feb. 1, 2018. Published March 2018. Originallyapproved in 2001. Last previous edition approved in 2008 as D6639 01(2008),which was withdrawn January 2017 and reinstated February 2018. DOI: 10.1520/D6639-18.*A Summary of Changes section appears at the end of this
18、standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment
19、of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1secondary to primary magnetic field, which can be used tocalculate the ground conductivity.1.2.4 The FDEM (inductive) method has been adapted for anumber of spec
20、ial uses within a borehole, on water, or airborne.Discussions of these adaptations or methods are not included inthis guide.1.2.5 The approaches suggested in this guide for the fre-quency domain method are the most commonly used, widelyaccepted and proven; however other lesser-known or special-ized
21、techniques may be substituted if technically sound anddocumented.1.2.6 Technical limitations and cultural interferences thatrestrict or limit the use of the frequency domain method arediscussed in section 5.4.1.2.7 This guide offers an organized collection of informa-tion or a series of options and
22、does not recommend a specificcourse of action. This document cannot replace education,experience, and professional judgment. Not all aspects of thisguide may be applicable in all circumstances. This ASTMstandard is not intended to represent or replace the standard ofcare by which the adequacy of a g
23、iven professional servicemust be judged without consideration of a projects manyunique aspects. The word standard in the title of this documentmeans that the document has been approved through the ASTMconsensus process.1.3 UnitsThe values stated in SI units are to be regardedas standard. No other un
24、its of measurement are included in thisstandard. Reporting of test results in units other than SI shallnot be regarded as nonconformance with this test method.1.4 Precautions:1.4.1 If the method is used at sites with hazardous materials,operations, or equipment, it is the responsibility of the user
25、ofthis guide to establish appropriate safety and health practicesand to determine the applicability of regulations prior to use.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish
26、appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for t
27、heFIG. 1 Principles of Electromagnetic Induction in Ground Con-ductivity Measurements (Sheriff, 1989)FIG. 2 Relative Response of Horizontal and Vertical Dipole CoilOrientations (McNeill, 1980)D6639 182Development of International Standards, Guides and Recom-mendations issued by the World Trade Organ
28、ization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D420 Guide to Site Characterization for Engineering Designand Construction PurposesD653 Terminology Relating to Soil, Rock, and ContainedFluidsD5730 Guide for Site Characterization for EnvironmentalPurposes
29、 With Emphasis on Soil, Rock, the Vadose Zoneand Groundwater (Withdrawn 2013)3D5753 Guide for Planning and Conducting GeotechnicalBorehole Geophysical LoggingD6235 Practice for Expedited Site Characterization of Va-dose Zone and Groundwater Contamination at HazardousWaste Contaminated SitesD6429 Gui
30、de for Selecting Surface Geophysical MethodsD6431 Guide for Using the Direct Current ResistivityMethod for Subsurface Characterization3. Terminology3.1 Definitions:3.1.1 For definitions of common technical terms used in thisstandard, refer to Terminology D653.3.1.2 The majority of the technical term
31、s used in thisdocument are defined in Sheriff (1991). An additional defini-tion follows:3.2 apparent conductivity, aThe conductivity that wouldbe measured by a GCM when located over a homogeneousisotropic half space that has the same ratio of secondary toprimary magnetic fields (Hs/Hp) as measured b
32、y other fre-quency domain instruments over an unknown subsurface.Apparent conductivity is measured in millisiemens per meter(mS/m).4. Summary of Guide4.1 Summary of the GuideAn alternating current is gen-erated in a transmitter coil producing an alternating primaryelectromagnetic field, which induce
33、s an alternating current inany nearby conductive material. The alternating currents in-duced in the earth material produce a secondary electromag-netic field, which is sensed by a nearby receiver coil (Fig. 1).Common FDEM instruments operate under the “low inductionnumber approximation”, which is a
34、function of the separationbetween the transmitter and receiver, the electrical permeabil-ity and conductivity of the ground, and the frequency of thetransmitter signal. Essentially, this means that, in the absenceof any metallic objects in the subsurface, the ratio of themagnitude of this secondary
35、magnetic field to the primarymagnetic field is directly converted to an apparent conductivitymeasurement of the earth material in a GCM. The ratio ofsecondary to primary magnetic fields (Hs/Hp) in other fre-quency domain instruments can be interpreted in terms of theground conductivity. When operati
36、ng under the low inductionnumber approximation, most of the response will be in thequadrature component. When this assumption does not hold,such as in the presence of metal, there will be a significantin-phase component to the response, and the direct correlationof the signal response to apparent co
37、nductivity breaks down.4.1.1 The depth of the site characterization is related to thefrequency of the alternating current, the distance betweentransmitter and receiver coils (intercoil spacing) and coilorientation. For the GCM, the depth of the site characterizationis related to the distance between
38、 electrodes and the coilorientation.4.1.2 The apparent conductivity measured by a GCM orcalculated from the ratio of the secondary to primary magneticfields is the conductivity of a homogeneous isotropic halfspace, as long as the low induction number condition appliesand the subsurface is nonmagneti
39、c. If the earth is horizontallylayered, the apparent conductivity measured or calculated isthe sum of the conductivities of each layer, weighted by itsthickness and depth, and is a function of the coil (dipole)orientation (Fig. 2). If the earth is not layered, that is, ahomogeneous isotropic half sp
40、ace, both the horizontal andvertical dipole measurements are equal. In either case, if thetrue conductivities of the layered earth or the homogeneoushalf space are known, the apparent conductivity that would bemeasured with a GCM can be calculated with a forwardmodeling program.4.1.3 Any variation e
41、ither in the electrical homogeneity ofthe half space, or the layers, or a physical deviation from ahorizontally layered earth, results in a change in the apparentconductivity measurement from the true conductivity. Thischaracteristic makes it possible to locate and identify manysignificant geologica
42、l features, such as buried channels, somefractures or faults (Fig. 3) or buried man-made objects. Thesignatures of FDEM measurements over troughs and dikes andsimilar features are well covered in theory (Villegas-Garcia andWest, 1983) and in practice.4.1.4 While many ground conductivity surveys are
43、carriedout to determine simple lateral or areal changes in geologicconditions such as the variation in soil salinity or location of asubsurface conductive contaminant plume, measurementsmade with a GCM with several intercoil spacings or differentcoil orientations can be used to identify up to two or
44、 threehorizontal layers, provided there is a sufficient conductivitycontrast between the layers (Fig. 4), the layer thicknesses areappreciable, and the depth of the layers falls within the depthrange of the instrument used for the measurement.4.1.5 Similarly, by taking both the horizontal and vertic
45、aldipole measurements at several heights above the surfaceresolved with a rigid fixed transmitter-receiver configuration,two or three layers within the instrument depth of explorationcan also sometimes be resolved.4.2 Complementary DataOther complementary surface(Guide D6429) and borehole (Guide D57
46、53) geophysical data,along with non-geophysical data related to the site, may be2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page
47、onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.D6639 183necessary, and are always useful, to properly interpret thesubsurface conditions from frequency domain data.4.2.1 Frequency Domain as Complementary MethodInsome cases, the frequency domain
48、 method is not able toFIG. 3 Typical Vertical and Horizontal Dipole Profiles Over a Frac-ture Zone (McNeill, 1990)FIG. 4 Cross Section of Frequency Domain Soundings (Gradyand Haeni, 1984)D6639 184provide results in sufficient detail or resolution to meet theobjectives of the site characterization, a
49、lthough for a givendepth of investigation, the EM methods usually require lessspace than linear arrays of the DC method. It is, however, afast, reliable method to locate the objective of the sitecharacterization, which can then be followed up by a moredetailed resistivity or time domain electromagnetic survey(Hoekstra et al, 1992).5. Significance and Use5.1 Concepts:5.1.1 This guide summarizes the equipment, field proce-dures and interpretation methods used for the characterizationof subsurface materials and geological structure as based ontheir properties to conduct, e
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