1、Designation: D 6431 99 (Reapproved 2005)Standard Guide forUsing the Direct Current Resistivity Method for SubsurfaceInvestigation1This standard is issued under the fixed designation D 6431; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, the 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 guide summarizes the equipment, field proce-dures, and interpre
3、tation methods for the assessment of theelectrical properties of subsurface materials and their porefluids, using the direct current (DC) resistivity method. Mea-surements of the electrical properties of subsurface materialsare made from the land surface and yield an apparent resistiv-ity. These dat
4、a can then be interpreted to yield an estimate ofthe depth, thickness, and resistivity of subsurface layer(s).1.1.2 Resistivity measurements as described in this guideare applied in geological, geotechnical, environmental, andhydrologic investigations. The resistivity method is used tomap geologic f
5、eatures such as lithology, structure, fractures,and stratigraphy; hydrologic features such as depth to watertable, depth to aquitard, and ground water salinity; and todelineate ground water contaminants. General references are,Keller and Frischknecht (1),2Zohdy et al (2), Koefoed (3),EPA (4), Ward (
6、5), Griffiths and King (6), and Telford et al (7).1.2 Limitations:1.2.1 This guide provides an overview of the Direct CurrentResistivity Method. It does not address in detail the theory,field procedures, or interpretation of the data. Numerousreferences are included for that purpose and are consider
7、ed anessential part of this guide. It is recommended that the user ofthe resistivity method be familiar with the references cited inthe text and with the Guide D 420, Practice D 5088, PracticeD 5608, Guide D 5730, Test Method G57, D 6429, andD 6235.1.2.2 This guide is limited to the commonly used ap
8、proachfor resistivity measurements using sounding and profilingtechniques with the Schlumberger, Wenner, or dipole-dipolearrays and modifications to those arrays. It does not cover theuse of a wide range of specialized arrays. It also does notinclude the use of spontaneous potential (SP) measurement
9、s,induced polarization (IP) measurements, or complex resistivitymethods.1.2.3 The resistivity method has been adapted for a numberof special uses, on land, within a borehole, or on water.Discussions of these adaptations of resistivity measurementsare not included in this guide.1.2.4 The approaches s
10、uggested in this guide for the resis-tivity method are the most commonly used, widely acceptedand proven; however, other approaches or modifications to theresistivity method that are technically sound may be substitutedif technically justified and documented.1.2.5 This guide offers an organized coll
11、ection of informa-tion or a series of options and does not recommend a specificcourse of action. This document cannot replace education orexperience and should be used in conjunction with professionaljudgements. Not all aspects of this guide may be applicable inall circumstances. This ASTM standard
12、is not intended torepresent or replace the standard of care by which theadequacy of a given professional service must be judged, norshould this document be applied without consideration of aprojects many unique aspects. The word “Standard” in thetitle of this document means only that the document ha
13、s beenapproved through the ASTM consensus process.1.3 Precautions:1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.01 on Surface and SubsurfaceCharacterization.Current edition approved May 1, 2005. Published September 200
14、5. Originallyapproved in 1999. Last previous edition approved in 1999 as D 643199.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1.3.1 I
15、t is the responsibility of the user of this guide tofollow any precautions in the equipment manufacturers rec-ommendations and to consider the safety implications whenhigh voltages and currents are used.1.3.2 If this guide is used at sites with hazardous materials,operations, or equipment, it is the
16、 responsibility of the user ofthis guide to establish appropriate safety and health practicesand to determine the applicability of regulations prior to use.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of
17、 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:3D 420 Guide to Site Characterization for Engineering, De-sign, and Construction PurposesD 653 Terminology Relating t
18、o Soil, Rock, and ContainedFluidsD 5088 Practice for Decontamination of Field EquipmentUsed at Nonradioactive Waste SitesD 5608 Practice for Decontamination of Field EquipmentUsed at Low Level Radioactive Waste SitesD 5730 Guide for Site Characterization for EnvironmentalPurposes With Emphasis on So
19、il, Rock, the Vadose Zoneand Ground WaterD 5753 Guide for Planning and Conducting Borehole Geo-physical LoggingD 6235 Guide for Expedited Site Characterization of Va-dose Zone and Ground Water Contamination at HazardousWaste Contaminated SitesD 6429 Guide for Selecting Surface Geophysical MethodsG57
20、 Test Method for Field Measurement of Soil ResistivityUsing the Wenner Four-Electrode Method3. Terminology3.1 Definitions:3.1.1 Definitions shall be in accordance with the terms andsymbols given in Terminology D 653.3.1.2 The majority of the technical terms used in thisdocument are defined in Sherif
21、f (1991).3.1.3 Additional Definitions:3.1.3.1 apparent resistivitythe resistivity of homoge-neous, isotropic ground that would give the same voltage-current relationship as measured.3.1.3.2 conductivityThe ability of a material to conduct anelectrical current. In isotropic material, it is the recipr
22、ocal ofresistivity. The units of conductivity are siemens per metre.3.1.3.3 resistanceopposition to the flow of direct current.The unit of resistance is ohms.3.1.3.4 resistivitythe property of a material that resists theflow of electrical current. The units of resistivity are ohmme-tres or ohm-feet
23、(1 Vm = 3.28 V-ft).4. Summary of Guide4.1 SummaryThe measurement of electrical resistivityrequires that four electrodes be placed in contact with thesurface materials (Fig. 1). The geometry and separation of theelectrode array are selected on the basis of the application andrequired depth of investi
24、gation.4.1.1 In an electrical resistivity survey, a direct current or avery low frequency alternating current is passed into theground through a pair of current electrodes, and the resultingpotential drop is measured across a pair of potential electrodes(Fig. 1). The resistance is then derived as th
25、e ratio of thevoltage measured across the potential electrodes and thecurrent electrodes. The apparent resistivity of subsurface ma-terials is derived as the resistance multiplied by a geometricfactor that is determined by the geometry and spacing of theelectrode array.4.1.2 The calculated apparent
26、resistivity measurement rep-resents a bulk average resistivity of the volume of earthdetermined by the geometry of the array and the resistivity ofthe subsurface material. This apparent resistivity is differentfrom true resistivity unless the subsurface materials are elec-trically uniform. Represent
27、ative resistivity values of layers areinterpreted from apparent resistivity values obtained from aseries of measurements made with variable electrode spacing.Increasing electrode spacing may permit distinction amonglayers that vary in electrical properties with depth.4.1.3 Most resistivity surveys f
28、or geologic, engineering,hydrologic, and environmental applications are carried out todetermine depths of specific layers or lateral changes ingeologic conditions at depths of less than a hundred metres.However, with sufficient power and instrument sensitivity,resistivity measurements are made to de
29、pths of several hundredmetres.4.2 Complementary DataOther complementary surfacegeophysical methods (D 6429) or borehole geophysical meth-ods (Guide D 5753) and non-geophysical methods may benecessary to properly interpret subsurface conditions.5. Significance and Use5.1 ConceptsThe resistivity techn
30、ique is used to measurethe resistivity of subsurface materials. Although the resistivityof materials can be a good indicator of the type of subsurfacematerial present, it is not a unique indicator. While theresistivity method is used to measure the resistivity of earthmaterials, it is the interprete
31、r who, based on knowledge of localgeologic conditions and other data, must interpret resistivitydata and arrive at a reasonable geologic and hydrologicinterpretation.5.2 Parameter Being Measured and Representative Values:5.2.1 Table 1 shows some general trends for resistivityvalues. Fig. 2 shows ran
32、ges in resistivity values for subsurfacematerials.5.2.2 Materials with either a low effective porosity or thatlack conductive pore fluids have a relatively high resistivity(1000 Vm). These materials include massive limestones,most unfractured igneous rocks, unsaturated unconsolidatedmaterials, and i
33、ce.3For 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 onthe ASTM website.D 6431 99 (2005)25.2.3 Materials that have high porosity w
34、ith conductive porefluids or that consist of or contain clays usually have lowresistivity. These include clay soil and weathered rock.5.2.4 Materials whose pore water has low salinity havemoderately high resistivity.5.2.5 The dependence of resistivity on water saturation isnot linear. Resistivity in
35、creases relatively little as saturationdecreases from 100 % to 40-60 % and then increases muchmore as saturation continues to decrease. An empirical rela-tionship known as Archies Law describes the relationshipbetween pore fluid resistivity, porosity, and bulk resistivity(McNeill (8).5.3 EquipmentGe
36、ophysical apparatus used for surfaceresistivity measurement includes a source of power, a means tomeasure the current, a high impedance voltmeter, electrodes tomake contact with the ground, and the necessary cables toconnect the electrodes to the power sources and the volt meter(Fig. 1).5.3.1 While
37、resistivity measurements can be made usingcommon electronic instruments, it is recommended that com-mercial resistivity instruments specifically designed for thepurpose be used for resistivity measurements in the field.5.3.2 Commonly used equipment includes the followingelements:5.3.2.1 A source of
38、current consisting of batteries or agenerator,5.3.2.2 A high-impedance voltmeter or resistivity unit,5.3.2.3 Metal stakes for the current and potential electrodes,and5.3.2.4 Insulated wire to connect together all of the preced-ing components.5.3.3 Care must be taken to ensure good electrical contact
39、 ofthe electrodes with the ground. Electrodes should be driveninto the ground until they are in firm contact. If connectionsbetween electrodes and the insulated wire are not waterproof,care must be taken to ensure that they will not be shorted outby moisture. Special waterproof cables and connectors
40、 arerequired for wet areas.5.3.4 A large variety of resistivity systems are availablefrom different manufacturers. Relatively inexpensive battery-powered units are available for shallow surveys. The currentsource (transmitter) and the potential measurement instrument(receiver) are often assembled in
41、to a single, portable unit. Insome cases, the transmitter and receiver units are separate.FIG. 1 Diagram Showing Basic Concept of Resistivity Measurement (from Benson et al, (15)TABLE 1 Representative Resistivity Values for Soil, Water, andRock (Mooney (4)Regional Soil Resistivity Vm- wet regions 50
42、200- dry regions 100500- arid regions 2001000 (sometimes as low as 50 if the soilis saline)Waters Vm- soil water 1 to 100- rain water 30 to 1000- sea water order of 0.2- ice 105 to 108Rock Types Vm- igneous and metamorphic 100 to 10,000- consolidated sediments 10 to 100- unconsolidated sediments 1 t
43、o 100D 6431 99 (2005)3High power units capable of deep survey work are powered bygenerators. The current used in dc resistivity surveys variesfrom a few milliamps to several amps, depending on the depthof the investigation.5.3.5 Signal EnhancementSignal enhancement capabilityis available in many res
44、istivity systems. It is a significant aidwhen working in noisy areas or with low power sources.Enhancement is accomplished by adding the results from anumber of measurements at the same station. This processincreases the signal-to-noise ratio.5.4 Limitations and Interferences:5.4.1 Limitations Inher
45、ent to Geophysical Methods:5.4.1.1 Afundamental limitation of all geophysical methodslies in the fact that a given set of data cannot be associated witha unique set of subsurface conditions. In most situations,surface geophysical measurements alone cannot resolve allambiguities, and some additional
46、information, such as boreholedata, is required. Because of this inherent limitation in geo-physical methods, a resistivity survey alone is never considereda complete assessment of subsurface conditions. Properlyintegrated with other information, resistivity surveying is aneffective method of obtaini
47、ng subsurface information.5.4.1.2 All surface geophysical methods are inherently lim-ited by decreasing resolution with depth.5.4.2 Limitations Specific to the Resistivity Method:5.4.2.1 Interpretation methods assume horizontal (or paral-lel) layered conditions where each layer has a uniform electri
48、-cal resistivity. If subsurface conditions cannot be reasonablyapproximated by this assumption, then results will be in error.5.4.2.2 Thin layers or multiple layers with similar resistivi-ties may not be detected.5.4.2.3 Ambiguities in interpretation arising from equiva-lence (where two resistive la
49、yers carry nearly the same electriccurrent if the products of their resistivity and thickness equal).5.4.2.4 Ambiguities in interpretation arising from suppres-sion (where resistant layers are sandwiched between moreconductive layers).5.4.2.5 Extremely resistive materials will prevent currentinjection into the ground.5.4.3 Interferences Caused by Ambient and Geologic Con-ditions:5.4.3.1 The resistivity method is sensitive to electricalinterference from a variety of sources. It is inherently sensitiveto electrical interference. Spatial variables caused by geologicf
