1、Designation: D 6639 01Standard Guide forUsing the Frequency Domain Electromagnetic Method forSubsurface Investigations1This standard is issued under the fixed designation D 6639; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 Purpose and Application:1.1.1 This standard guide summarizes the equipment, fieldprocedures, and interpretati
3、on 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, agricul-tural, archaeologic
4、al and forensic investigations as well asmineral 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-tio
5、ns including buried drums, underground storage tanks(USTs), landfill boundaries and conductive ground watercontamination.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 andpha
6、se of the induced field at various frequencies. FDEMmeasurements therefore are dependent on the electrical prop-erties of the subsurface soil and rock or buried man-madeobjects as well as the orientation of any subsurface geologicalfeatures or man-made objects. In many cases, the FDEMmeasurements ca
7、n be used to identify the subsurface structureor object. This method is used only when it is expected that thesubsurface soil or rock, man-made materials or geologicstructure can be characterized by differences in electricalconductivity.1.1.5 The FDEM method may be used instead of the DirectCurrent
8、Resistivity method (Guide D 6431) when surface soilsare excessively insulating (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
9、 coils at or near ground level andhas been referred to by other names including 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 includ
10、ed that cover these aspects ingreater detail and are considered an essential 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
11、. ASTM standards that should alsobe consulted include Guide D 420, Terminology D 653, GuideD 5730, Guide D 5753, Practice D 6235, Guide D 6429, andGuide D 6431.1.2.2 This guide is limited to frequency domain instrumentsusing a coplanar orientation of the transmitting and receivingcoils in either the
12、 horizontal dipole (HD) mode with coilsvertical, or the vertical dipole (VD) mode with 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 do
13、maininstruments in which the ratio of the induced secondarymagnetic field to the primary 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 GroundC
14、onductivity Meters (GCMs) that are designed to operatewithin the “low induction number approximation”. Multi-frequency instruments operating within and outside the lowinduction number approximation provide the ratio of thesecondary to primary magnetic field, which can be used tocalculate the ground
15、conductivity.1.2.4 The FDEM (inductive) method has been adapted for anumber of special 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 co
16、mmonly used, widelyaccepted and proven; however other lesser-known or special-ized techniques may be substituted if technically sound anddocumented.1.2.6 Technical limitations and cultural interferences that1This guide is under the jurisdiction of ASTM Committee D18 on Soil and Rockand is the direct
17、 responsibility of Subcommittee D18.01 on Surface and SubsurfaceCharacterization.Current edition approved Feb 10, 2001. Published May 2001.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.restrict or limit the use of the frequency dom
18、ain method arediscussed in section 5.4.1.2.7 This guide offers an organized collection of informa-tion or a series of options and does not recommend a specificcourse of action. This document cannot replace education,experience, and professional judgment. Not all aspects of thisguide may be applicabl
19、e in all circumstances. This ASTMstandard is not intended to represent or replace the standard ofcare by which the adequacy of a given professional servicemust be judged without consideration of a projects manyunique aspects. The word standard in the title of this documentmeans that the document has
20、 been approved through the ASTMconsensus process.1.3 Precautions:1.3.1 If the method is used at sites with hazardous materials,operations, or equipment, it is the responsibility of the user ofthis guide to establish appropriate safety and health practicesand to determine the applicability of regulat
21、ions prior to use.1.3.2 This standard guide does not purport to address all ofthe safety concerns that may be associated with its use. It is theresponsibility of the user of this standard guide to determinethe applicability of regulations prior to use.2. Referenced Documents2.1 ASTM Standards:D 420
22、Guide to Site Characterization for Engineering De-sign and Construction Purposes2D 653 Terminology Relating to Soil, Rock, and ContainedFluids2D 5730 Guide to Site Characterization for EnvironmentalPurposes with Emphasis on Soil, Rock, the Vadose Zoneand Ground Water3D 5753 Guide for Planning and Co
23、nducting Borehole Geo-physical Logging3D 6235 Practice for Expedited Site Characterization ofVadose Zone Ground Water Contamination at HazardousWaste Contaminated Sites3D 6429 Guide for Selecting Surface Geophysical Methods3D 6431 Guide for Using the Direct Current ResistivityMethod for Subsurface I
24、nvestigation33. Terminology3.1 DefinitionsDefinitions shall be in accordance with theterms and symbols given in Terminology D 653.3.2 The majority of the technical terms used in this docu-ment are defined in Sheriff (1991). An additional definitionfollows:3.3 apparent conductivity, saThe conductivit
25、y 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 by other fre-quency domain instruments over an unknown subsurface.Apparent conductivity is measured in millisiemens per meter(mS/m).
26、4. Summary of Guide4.1 Summary of the MethodAn alternating current isgenerated in a transmitter coil producing an alternating primaryelectromagnetic field, which induces an alternating current inany nearby conductive material. The alternating currents in-duced in the earth material produce a seconda
27、ry electromag-netic field, which is sensed by a nearby receiver coil (Fig. 1).The ratio of the magnitude of this secondary magnetic field tothe primary magnetic field is directly converted to a conduc-tivity measurement of the earth material in a GCM. The ratioof secondary to primary magnetic fields
28、 (Hs/Hp) in otherfrequency domain instruments is interpreted in terms of theground conductivity.4.1.1 The depth of the investigation is related to the fre-quency of the alternating current, the distance between trans-mitter and receiver coils (intercoil spacing) and coil orienta-tion. For the GCM, t
29、he depth of investigation is related to thedistance between electrodes and the coil orientation.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 induct
30、ion number condition appliesand the subsurface is nonmagnetic. If the earth is horizontallylayered, the apparent conductivity measured or calculated isthe sum of the conductivities of each layer, weighted by its2Annual Book of ASTM Standards, Vol 04.08.3Annual Book of ASTM Standards, Vol 04.09.FIG.
31、1 Principles of Electromagnetic Induction in GroundConductivity Measurements (Sheriff, 1989)D6639012thickness and depth, and is a function of the coil (dipole)orientation (Fig. 2). If the earth is not layered, that is , ahomogeneous isotropic half space, both the horizontal andvertical dipole measur
32、ements 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 either in the electrical homogeneity ofthe half spa
33、ce, 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 geological features, such as buried channels, somefractures
34、 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 carriedout to determine simple lateral or areal ch
35、anges 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 threehorizontal layers, provided there is a suffi
36、cient 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 verticaldipole measurements at several heights above the
37、 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 D 6429) and borehole (Guide D 5753) geophysicaldata, along with non-geophysical
38、data related to the site, maybe necessary, 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 method is not able toprovide results in sufficient detail or resolution to meet
39、 theobjectives of the investigation, although for a given depth ofinvestigation, the EM methods usually require less space thanlinear arrays of the DC method. It is, however, a fast, reliablemethod to locate the objective of the investigation, which canthen be followed up by a more detailed resistiv
40、ity or timedomain electromagnetic survey (Hoekstra et al, 1992).5. Significance and Use5.1 Concepts:FIG. 2 Relative Response of Horizontal and Vertical Dipole CoilOrientations (McNeill, 1980)FIG. 3 Typical Vertical and Horizontal Dipole Profiles Over aFracture Zone (McNeill, 1990)D66390135.1.1 This
41、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, enhance or obstruct the flow ofelectrical currents as induced in the ground by an alternatingelectromagne
42、tic field.5.1.2 The frequency domain method requires a transmitteror energy source, a transmitter coil, receiver electronics, areceiver coil, and interconnect cables (Fig. 5).5.1.3 The transmitter coil, when placed on or near theearths surface and energized with an alternating current,induces small
43、currents in the near earth material proportional tothe conductivity of the material. These induced alternatingcurrents generate a secondary magnetic field (Hs), which issensed with the primary field (Hp) by the receiver coil.5.1.4 Under a constraint known as the “low inductionnumber approximation” (
44、McNeill, 1980) and when the subsur-face is nonmagnetic, the secondary magnetic field is fullyout-of-phase with the primary field and is given by a functionof these variables.sa5 4/vos2! Hs/Hp! (1)where:sa= apparent conductivity in siemens/meter, S/m,v =2pf in radians/sec; f = frequency in Hz,o= perm
45、eability of free space in henrys/meter 4p310-7, /m,s = intercoil spacing in meters, m, andHs/Hp= the ratio of the out-of-phase component of thesecondary magnetic field to the primary magneticfield, both measured by the receiver coil.Perhaps the most important constraint is that the depth ofpenetrati
46、on (skin depth, see section 6.5.3.1) of the electromag-netic wave generated by the transmitter be much greater thanthe intercoil spacing of the instrument. The depth of penetra-tion is inversely proportional to the ground conductivity andinstrument frequency. For example, an instrument with aninterc
47、oil spacing of 10 m (33 ft) and a frequency of 6400 Hz,using the vertical dipole, meets the low induction numberassumption for earth conductivities less than 200 mS/m.FIG. 4 Cross Section of Frequency Domain Soundings (Gradyand Haeni, 1984)D66390145.1.5 Multi-frequency domain instruments usually mea
48、surethe two components of the secondary magnetic field: a com-ponent in-phase with the primary field and a component 90out-of-phase (quadrature component) with the primary field(Kearey and Brook 1991). Generally, instruments do notdisplay either the in-phase or out-of-phase (quadrature) com-ponents
49、but do show either the apparent conductivity or theratio of the secondary to primary magnetic fields.5.1.6 When ground conditions are such that the low induc-tion number approximation is valid, the in-phase component ismuch less than the quadrature phase component. If there is arelatively large in-phase component , the low induction numberapproximation is not valid and there is likely a very conductiveburied body or layer, that is, ore body or man-made metalobject.5.1.7 The transmitter and receiver coils are almost alwaysaligned in a plane either parallel to the earths sur
