1、Designation: D7046 11Standard Guide forUse of the Metal Detection Method for SubsurfaceExploration1This standard is issued under the fixed designation D7046; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 ApplicationThis guide summarizes theequipment, field procedures, and interpretation methods for theassessment of subsu
3、rface materials using the metal detectionmethod. Metal detectors respond to the presence of bothferrous and nonferrous metals by inducing eddy currents inconductive objects. Metal detectors are either frequency do-main (continuous frequency or wave) or time domain (pulsed)systems. A wide range of me
4、tal detectors is commonly avail-able.1.1.1 Metal detectors can detect any kind of metallic mate-rial, including both ferrous metals such as iron and steel, andnon-ferrous metals such as aluminum and copper. In contrast,magnetometers only detect ferrous metals.1.1.2 Metal detector measurements can be
5、 used to detect thepresence of buried metal trash, drums (Tyagi et al, 1983) (1)2and tanks, abandoned wells (Guide D6285); to trace buriedutilities; and to delineate the boundaries of landfill metal andtrench metal. They are also used to detect metal basedunexploded ordnance (UXO).1.2 Limitations:1.
6、2.1 This guide provides an overview of the metal detec-tion method. This guide does not provide or address the detailsof the theory, field procedures, or interpretation of the data.References are included for that purpose and are considered anessential part of this guide. It is recommended that the
7、user ofthis guide be familiar with the references cited and with theASTM standards D420, D653, D5088, D5608, D5730, D5753,D6235, D6429, and D6431.1.2.2 This guide is limited to metal detection measurementsmade on land. The metal detection method can be adapted fora number of special uses on land, wa
8、ter, airborne and ice.1.2.3 The approaches suggested in this guide for the metaldetection method are commonly used, widely accepted, andproven. However, other approaches or modifications to themetal detection method that are technically sound may besubstituted.1.2.4 This guide offers an organized co
9、llection 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 professionaljudgment. Not all aspects of this guide may be applicable in allcircumstances. This ASTM standard
10、is not intended to repre-sent or replace the standard of care by which the adequacy ofa given professional service must be judged, nor should thisdocument be applied without consideration of a projects manyunique aspects. The word “Standard” in the title of thisdocument means only that the document
11、has been approvedthrough the ASTM consensus process.1.3 The values stated in SI units are regarded as standard.The values given in parentheses are inch-pound units, whichare provided for information only and are not consideredstandard.1.4 Precautions:1.4.1 It is the responsibility of the user of thi
12、s guide tofollow any precautions in the equipment manufacturers rec-ommendations and to establish appropriate health and safetypractices.1.4.2 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
13、safety and health practicesand to determine the applicability of any regulations prior touse.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, 20
14、11. Published June 2011. Originallyapproved in 2004 as D704604. DOI: 10.1520/D7046-11.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive
15、, PO Box C700, West Conshohocken, PA 19428-2959, United States.1.4.3 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 appro-priate safety and health practices and determine the appl
16、ica-bility of regulatory requirements prior to use.2. Referenced Documents2.1 ASTM Standards:3D420 Guide to Site Characterization for Engineering De-sign and Construction PurposesD653 Terminology Relating to Soil, Rock, and ContainedFluidsD3740 Practice for Minimum Requirements for AgenciesEngaged i
17、n Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD5088 Practice for Decontamination of Field EquipmentUsed at Waste SitesD5608 Practices for Decontamination of Field EquipmentUsed at Low Level Radioactive Waste SitesD5730 Guide for Site Characterization for E
18、nvironmentalPurposes With Emphasis on Soil, Rock, the Vadose Zoneand Ground WaterD5753 Guide for Planning and Conducting Borehole Geo-physical LoggingD6235 Practice for Expedited Site Characterization of Va-dose Zone and Ground Water Contamination at HazardousWaste Contaminated SitesD6285 Guide for
19、Locating Abandoned WellsD6429 Guide for Selecting Surface Geophysical MethodsD6431 Guide for Using the Direct Current ResistivityMethod for Subsurface InvestigationD6639 Guide for Using the Frequency Domain Electromag-netic Method for Subsurface InvestigationsD6820 Guide for Use of the Time Domain E
20、lectromagneticMethod for Subsurface Investigation3. Terminology3.1 DefinitionsSee Terminology D653.3.2 The majority of the technical terms used in this docu-ment are defined in Sheriff (1991) (4), and Bates and Jackson(1997) (5).4. Summary of Guide4.1 Summary of the MethodA metal detector uses eithe
21、r apulsed or an alternating current in a transmit coil to generate atime varying magnetic field around the coil. This primarymagnetic field induces eddy currents in buried metal which inturn, induces a voltage in a receiver coil, which, whenamplified, reveal the presence of buried metal. Benson (198
22、2)(2) and U.S. EPA (1993) (3) provide an overview of metaldetectors.4.2 Complementary DataData from other surface geo-physical methods (see Guide D6429) such as electromagnetics(Guides D6639 and D6820) and ground penetrating radar(Guide D6432) may be useful in fully evaluating buried metalresponse.
23、Geologic data obtained from other complementarygeological or surface geophysical methods (Guide D6429) andborehole geophysical methods (Guide D5753) may be neces-sary to help interpret and assess subsurface conditions.5. Significance and Use5.1 Concepts:5.1.1 This guide summarizes the equipment, fie
24、ld proce-dures, and interpretation methods for using the metal detectionmethod for locating subsurface metallic objects. Personnelrequirements are as discussed in Practice D3740.5.1.2 MethodMetal detectors are electromagnetic instru-ments that work on the principle of induction, using typicallytwo c
25、oils (antennas); a transmitter and a receiver. Both coils arefixed in respect to each other and are used near the surface ofthe earth. Either an alternating or a pulsed voltage is applied tothe transmitter coil causing electrical eddy currents to beinduced in the earth. The electrical currents flowi
26、ng in the earthare proportional to electrical conductivity of the medium.Theses currents generate eddy currents in buried metallicobjects that is detected and measured by the receiver (Fig. 1).5.2 Parameter Measured and Representative Values:5.2.1 Frequency Domain Metal Detectors:5.2.1.1 Frequency d
27、omain metal detectors apply an alternat-ing current having a fixed frequency and amplitude to thetransmit coil which generates a time-varying magnetic fieldaround the coil. This field induces eddy currents in nearbymetallic objects that in turn generate time-varying magneticfields of their own. Thes
28、e eddy-fields induce a voltage in thereceiver coil. The presence of metal causes small changes inthe phase and amplitude of the receiver voltage. Most metaldetectors amplify the differences in the receiver coil voltagecaused by nearby metal and generate an audible sound or meter(analog or digital) r
29、eading.5.2.1.2 Ground conductivity meters (frequency domainmetal detectors) measure the two-components of the secondarymagnetic field simultaneously. The first is the quadrature-phasecomponent which indicates soil electrical conductivity and ismeasured in millisiemens per meter (mS/m). The second is
30、 theinphase component, which is related to the subsurface mag-netic susceptibility and is measured in parts per thousand (ppt)(that is, the ratio between the primary and secondary magneticfields).(1) Conductivity Measurements (Quadrature-PhaseComponent)Metallic objects within a few feet of the surfa
31、cewill cause induced magnetic field distortions that will result inzero or even negative values of measured conductivity. Deepermetallic objects will cause less field distortion and lead tomeasured conductivities which are abnormally high in com-parison to site background values.(2) Inphase Componen
32、tInphase measurements are moresensitive to metal than conductivity measurements. Thus,inphase anomalies may indicate the presence of metal at agreater depth than the conductivity measurements.5.2.2 Time Domain Metal Detectors:5.2.2.1 In time domain metal detectors, a transmitter gener-ates a pulsed
33、primary magnetic field in the earth. After eachpulse, secondary magnetic fields are induced briefly from3For 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 standard
34、s Document Summary page onthe ASTM website.D7046 112moderately conductive earth, and for a longer time frommetallic targets. Between each pulse, the metal detector waitsuntil the response from the conductive earth dissipates, andthen measures the prolonged buried metal response. Thisresponse is meas
35、ured in millivolts (mV).5.3 EquipmentMetal detectors generally consist of trans-mitter electronics and transmitter coil, power supply, receiverelectronics and receiver coil. Metal detectors are usually singleindividual portable.5.3.1 Typical “treasure-hunter” metal detectors provide anaudible signal
36、 and/or meter reading (analog or digital) whenmetal is detected.5.3.2 Quadrature and inphase measurements from groundconductivity meters are shown either on analog or digitalmeters. These measurements can often be recorded digitally inthe field using a small field recorder, strip-chart recorder, orc
37、omputer.5.3.3 Time domain metal detectors can consist of either oneor two receiver coils. When two coils are used, one coil istypically placed above the other. Readings from both coils arerecorded simultaneously. In order to improve detection ofdeeper metallic targets, the differential response from
38、 the tworeceiver coils can be used to suppress the response fromsmaller, shallower metallic targets. Some time domain metaldetectors are mounted on wheels, allowing for the use ofodometers to provide location data.5.4 Limitations and Interferences:5.4.1 General Limitations Inherent to Geophysical Me
39、th-ods:5.4.1.1 Afundamental limitation of all geophysical methodsis that a given set of data cannot be associated with a unique setof subsurface conditions. In most situations, surface geophysi-cal measurements alone cannot resolve all ambiguities, andsome additional information, such as borehole da
40、ta, is advised.FIG. 1 Simplified Block Diagram of a Metal Detector System (Tyagi et al, 1983) (1)D7046 113Because of this inherent limitation in the geophysical methods,a metal detector survey alone can never be considered acomplete assessment of subsurface conditions. Properly inte-grated with othe
41、r geologic information, metal detector survey-ing is a highly effective method of obtaining subsurfaceinformation.5.4.1.2 In addition, all surface geophysical methods areinherently limited by decreasing resolution with depth.5.4.2 Limitations Specific to the Metal Detection Method:5.4.2.1 Several fa
42、ctors influence metal detector response:the properties of the target, the properties of the soil/rock, andthe characteristics of the metal detector itself. The targets size,depth, and condition of burial are the three most importantfactors.5.4.2.2 The larger the surface area of the target, the great
43、erthe eddy current that may be induced, and the greater the depthat which the target may be detected.5.4.2.3 The metal detectors response decreases at a rateequal to the reciprocal of its depth up to the sixth power(1/depth6). Therefore, if the distance to the target is doubled,the metal detector re
44、sponse will decrease by a factor of 64.Consequently, the metal detector is a relatively shallow-depthdevice. It is generally restricted to detecting small objects atrelatively shallow depths or larger targets at limited depths.Generally, most metal detectors are incapable of responding totargets at
45、depths much greater than 6 m.5.4.2.4 Although the shape, orientation, and composition ofa target will influence the metal detector response, these factorswill have much less influence than will the size and depth ofthe target. Target deterioration, however, has a significantimpact. Metallic containe
46、rs will corrode in natural soils con-ditions. If a container is corroded, its surface area will besignificantly reduced, and in turn will degrade the response ofa metal detector.5.4.2.5 Because the metal detectors response weakens rap-idly with increasing distance to the target, system gain andinstr
47、ument stability are important. The size of the coil controlsthe size and depth of the metallic target that can be detected asshown in Fig. 2.5.4.3 Interferences Caused by Natural and Cultural Condi-tions:5.4.3.1 Sources of noise referred here do not include thoseof a physical nature such as difficul
48、t terrain or man-madeobstructions but rather those of a geologic, ambient, or culturalnature that can adversely affect the measurements and hencethe interpretation.5.4.3.2 Natural Sources of NoiseSome kinds of soil/rock,particularly those containing high iron content (often known asmineralized soil)
49、 affect receiver coil output strongly enough toindicate the presence of a metal target with certain kinds ofmetal detectors. Some types of metal detectors provide a meansfor compensating the output for the ground effect. This usuallyrequires the operator to position the detector near the ground(but not near a metal target) and adjust a control until the targetsignal disappears. Small variations in the soil characteristicsand stones (particularly those containing metallic compounds)can cause small changes in the detector output. Often thesechanges cause small target-li
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