1、Designation: D 7046 04Standard Guide forUse of the Metal Detection Method for SubsurfaceInvestigation1This standard is issued under the fixed designation D 7046; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. 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 ApplicationThis guide summarizes theequipment, field procedures, and interpretation methods for theassessment of s
3、ubsurface 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 o
4、f metal 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 ca
5、n be used to detect thepresence of buried metal trash, drums (Tyagi et al, 1983) (1)2and tanks, abandoned wells (Guide D 6285); to trace buriedutilities; and to delineate the boundaries of landfill metal andtrench metal. They are also used to detect metal basedunexploded ordnance (UXO).1.1.3 Benson
6、(1982) (2) and U.S. EPA(1993) (3) provide anoverview of metal detectors.1.2 Limitations:1.2.1 This guide provides an overview of the metal detec-tion method. It does not provide or address the details of thetheory, field procedures, or interpretation of the data. Refer-ences are included for that pu
7、rpose and are considered anessential part of this guide. It is recommended that the user ofthis guide be familiar with the references cited and with theASTM standards D 420, D 653, D 5088, D 5608, D 5730,D 5753, D 6235, D 6429, and D 6431.1.2.2 This guide is limited to metal detection measurementsma
8、de on land. The metal detection method can be adapted fora number of special uses on land, water, 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 detectio
9、n method that are technically sound may besubstituted.1.2.4 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 should be used in conjunction with professionaljudgmen
10、t. Not all aspects of this guide may be applicable in allcircumstances. This ASTM standard 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 manyuni
11、que aspects. The word “Standard” in the title of thisdocument means only that the document 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 a
12、re not consideredstandard.1.4 Precautions:1.4.1 It is the responsibility of the user of this 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
13、, or equipment, it is the responsibility of the user ofthis guide to establish appropriate safety and health practicesand to determine the applicability of any regulations prior touse.1.4.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is th
14、eresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory requirements prior to use.1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Subcommittee D18.
15、01 on Surface and SubsurfaceCharacterization.Current edition approved May 1, 2004. Published June 2004.2The 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,
16、United States.2. Referenced Documents2.1 ASTM Standards:3D 420 Guide to Site Characterization for Engineering, De-sign, and Construction PurposesD 653 Terminology relating to Soil, Rock, and ContainedFluidsD 3740 Practice for Minimum Requirements for AgenciesEngaged in the Testing and/or Inspection
17、of Soil and Rockas Used in Engineering Design and ConstructionD 5088 Practice for the Decontamination of Field Equip-ment Used at Nonradioactive Waste SitesD 5608 Practice for the Decontamination of Field Equip-ment Used at Low Level Radioactive Waste SitesD 5730 Guide to Site Characterization for E
18、nvironmentalPurposes with Emphasis on Soil, Rock, the Vadose Zoneand Ground WaterD 5753 Guide for Planning and Conducting Borehole Geo-physical LoggingD 6235 Guide for Expedited Site Characterization of Haz-ardous Waste SitesD 6285 Guide for Locating Abandoned WellsD 6429 Guide for Selecting Surface
19、 Geophysical MethodsD 6431 Guide for Using the Direct Current ResistivityMethod for Subsurface InvestigationD 6639 Guide for Using the Frequency Domain Electro-magnetic Method for Subsurface InvestigationsD 6820 Guide for Using the Time Domain ElectromagneticMethod for Subsurface Investigations3. Te
20、rminology3.1 DefinitionsSee Terminology D 653. The majority ofthe technical terms used in this document are defined in Sheriff(1991) (4), and Bates and Jackson (1997) (5).4. Summary of Guide4.1 Summary of the MethodA metal detector uses either apulsed or an alternating current in a transmit coil to
21、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.4.2 Complementary DataData from other surface geo-physical methods (se
22、e Guide D 6429) such as electromagnetics(Guides D 6639 and D 6820) and ground penetrating radar(Guide D 6432) may be useful in fully evaluating buried metalresponse. Geologic data obtained from other complementarygeological or surface geophysical methods (Guide D 6429) andborehole geophysical method
23、s (Guide D 5753) 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, field proce-dures, and interpretation methods for using the metal detectionmethod for locating subsurface metallic objects. Personnelre
24、quirements are as discussed in Practice D 3740.5.1.2 MethodMetal detectors are electromagnetic instru-ments that work on the principle of induction, using typicallytwo coils (antennas); a transmitter and a receiver. Both coils arefixed in respect to each other and are used near the surface ofthe ear
25、th. Either an alternating or a pulsed voltage is applied tothe transmitter coil causing electrical eddy currents to beinduced in the earth. The electrical currents flowing in the earthare proportional to electrical conductivity of the medium.Theses currents generate eddy currents in buried metallico
26、bjects 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 domain metal detectors apply an alternat-ing current having a fixed frequency and amplitude to thetransmit coil which generates a ti
27、me-varying magnetic fieldaround the coil. This field induces eddy currents in nearbymetallic objects that in turn generate time-varying magneticfields of their own. These eddy-fields induce a voltage in thereceiver coil. The presence of metal causes small changes inthe phase and amplitude of the rec
28、eiver voltage. Most metaldetectors amplify the differences in the receiver coil voltagecaused by nearby metal and generate an audible sound or meter(analog or digital) reading.5.2.1.2 Ground conductivity meters (frequency domainmetal detectors) measure the two-components of the secondarymagnetic fie
29、ld simultaneously. The first is the quadrature-phasecomponent which indicates soil electrical conductivity and ismeasured in millisiemens per meter (mS/m). The second is theinphase component, which is related to the subsurface mag-netic susceptibility and is measured in parts per thousand (ppt)(that
30、 is, the ratio between the primary and secondary magneticfields).(1) Conductivity Measurements (Quadrature-PhaseComponent)Metallic objects within a few feet of the surfacewill cause induced magnetic field distortions that will result inzero or even negative values of measured conductivity. Deepermet
31、allic objects will cause less field distortion and lead tomeasured conductivities which are abnormally high in com-parison to site background values.(2) Inphase ComponentInphase measurements are moresensitive to metal than conductivity measurements. Thus,inphase anomalies may indicate the presence o
32、f 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 primary magnetic field in the earth. After eachpulse, secondary magnetic fields are induced briefly frommoderately conductive earth
33、, 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 measured in millivolts (mV).3For referenced ASTM standards, visit the ASTM website,
34、 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.D70460425.3 EquipmentMetal detectors generally consist of trans-mitter electronics and transmitter coil, power suppl
35、y, receiverelectronics and receiver coil. Metal detectors are usually singleindividual portable.5.3.1 Typical “treasure-hunter” metal detectors provide anaudible signal and/or meter reading (analog or digital) whenmetal is detected.5.3.2 Quadrature and inphase measurements from groundconductivity me
36、ters are shown either on analog or digitalmeters. These measurements can often be recorded digitally inthe field using a small field recorder, strip-chart recorder, orcomputer.5.3.3 Time domain metal detectors can consist of either oneor two receiver coils. When two coils are used, one coil istypica
37、lly placed above the other. Readings from both coils arerecorded simultaneously. In order to improve detection ofdeeper metallic targets, the differential response from the tworeceiver coils can be used to suppress the response fromsmaller, shallower metallic targets. Some time domain metaldetectors
38、 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 Meth-ods:5.4.1.1 Afundamental limitation of all geophysical methodsis that a given set of data cannot be associated with a unique seto
39、f subsurface conditions. In most situations, surface geophysi-cal measurements alone cannot resolve all ambiguities, andsome additional information, such as borehole data, is required.Because of this inherent limitation in the geophysical methods,a metal detector survey alone can never be considered
40、 acomplete assessment of subsurface conditions. Properly inte-grated with other 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 dep
41、th.5.4.2 Limitations Specific to the Metal Detection Method:FIG. 1 Simplified Block Diagram of a Metal Detector System (Tyagi et al, 1983) (1)D70460435.4.2.1 Several factors influence metal detector response:the properties of the target, the properties of the soil/rock, andthe characteristics of the
42、 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 greaterthe eddy current that may be induced, and the greater the depthat which the target may be detected.5.4.2.3 The metal detectors res
43、ponse 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 response will decrease by a factor of 64.Consequently, the metal detector is a relatively shallow-depthdevice. It is generally restric
44、ted to detecting small objects atrelatively shallow depths or larger targets at limited depths.Generally, most metal detectors are incapable of responding totargets at depths much greater than 6 m.5.4.2.4 Although the shape, orientation, and composition ofa target will influence the metal detector r
45、esponse, these factorswill have much less influence than will the size and depth ofthe target. Target deterioration, however, has a significantimpact. Metallic containers will corrode in natural soils con-ditions. If a container is corroded, its surface area will besignificantly reduced, and in turn
46、 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 andinstrument stability are important. The size of the coil controlsthe size and depth of the metallic target that can be detected asshown i
47、n 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 difficult terrain or man-madeobstructions but rather those of a geologic, ambient, or culturalnature that can adversely affect the measureme
48、nts 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) affect receiver coil output strongly enough toindicate the presence of a metal target with certain kinds ofmetal detectors. Some ty
49、pes 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-like signals, known as “groundnoise.” These can confuse the operator because they sound likesmall targets.5.4.3.3 Cultural Sources of Nois
