1、Designation: D6430 18Standard Guide forUsing the Gravity Method for Subsurface SiteCharacterization1This standard is issued under the fixed designation D6430; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisio
2、n. 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 methods for the assessment
3、 ofsubsurface conditions using the gravity method. However, thisstandard does not address the use of marine, airborne, orsatellite gravity measurements.1.1.2 The gravity method described in this guide is appli-cable to site characterization of a wide range of subsurfaceconditions.1.1.3 Gravity measu
4、rements indicate variations in theearths gravitational field caused by lateral differences in thedensity of the subsurface soil or rock or the presence of naturalvoids or man-made structures. By measuring spatial changes inthe gravitational field, variations in subsurface conditions canbe determined
5、.1.1.4 Detailed gravity surveys (commonly called micro-gravity surveys) are used for near-surface geologic site char-acterizations and geotechnical, environmental, and archaeo-logical studies. Geologic and geotechnical applications includelocation of buried channels, bedrock structural features, voi
6、ds,and caves, and low-density zones in foundations. Environmen-tal applications include site characterization, groundwaterstudies, landfill characterization, and location of undergroundstorage tanks (1)2.1.2 Limitations:1.2.1 This guide provides an overview of the gravitymethod. It does not address
7、the details of the gravity theory,field procedures, or interpretation of the data. Numerousreferences are included for that purpose and are considered anessential part of this guide. It is recommended that the user ofthe gravity method be familiar with the references cited andwith the Guides D420, D
8、5753, D6235, and D6429, andPractices D5088, and D5608.1.2.2 This guide is limited to gravity measurements madeon land. The gravity method can be adapted for a number ofspecial uses: on land, in a borehole, on water, and from aircraftand space. A discussion of these other gravity methods,including ve
9、rtical gravity gradient measurements, is not in-cluded in this guide.1.2.3 The approaches suggested in this guide for the gravitymethod are the most commonly used, widely accepted, andproven. However, other approaches or modifications to thegravity method that are technically sound may be substitute
10、d.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 profes-sional judgment. Not all aspects of this guide may be appli-cab
11、le in all circumstances. This ASTM document is notintended to represent or replace the standard of care by whichthe adequacy of a given professional service must be judged,nor should this document be applied without consideration ofa projects many unique aspects. The word “Standard” in thetitle of t
12、his document means only that the document has beenapproved through the ASTM consensus process.1.3 UnitsThe values stated in SI units are regarded asstandard. No other units of measurement are included in thisstandard. Reporting of test results in units other than SI shallnot be regarded as nonconfor
13、mance with this test method.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 this guide is used at sites with hazardous materials,operatio
14、ns, 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.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is th
15、eresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1This guide is under the jurisdiction ofASTM Committee D18 on Soil and Rockand is the direct responsibility of Su
16、bcommittee D18.01 on Surface and SubsurfaceCharacterization.Current edition approved Feb. 1, 2018. Published March 2018. Originallyapproved in 1999. Last previous edition approved in 2010 as D643099(2010).DOI: 10.1520/D6430-18.2The boldface numbers in parentheses refer to the list of references at t
17、he end ofthis standard.*A Summary of Changes section appears at the end of this 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
18、on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.11.6 This international standard was developed in accor-dance with internationally
19、 recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3D420 Guide to S
20、ite Characterization for Engineering Designand Construction PurposesD653 Terminology Relating to Soil, Rock, and ContainedFluidsD5088 Practice for Decontamination of Field EquipmentUsed at Waste SitesD5608 Practices for Decontamination of Sampling and NonSample Contacting Equipment Used at Low Level
21、 Radio-active Waste SitesD5753 Guide for Planning and Conducting GeotechnicalBorehole Geophysical LoggingD6235 Practice for Expedited Site Characterization of Va-dose Zone and Groundwater Contamination at HazardousWaste Contaminated SitesD6429 Guide for Selecting Surface Geophysical Methods3. Termin
22、ology3.1 Definitions3.1.1 For common definitions of terms used in this standard,see Terminology D653.3.2 Additional technical terms used in this guide are definedin Sheriff (2) and Bates and Jackson (3).4. Summary of Guide4.1 Summary of the MethodThe gravity method makesmeasurements of gravity varia
23、tions at stations along a profileline or grid relative to an arbitrary selected local base stationgravity value. The gravity measurements are then corrected forother effects that cause variations in gravity. Lateral variationsor anomalies in the resulting residual gravity data can then beattributed
24、to lateral variations in the densities of subsurfacematerials, for example, buried channels, structures, or caves.The data are interpreted by creating geologically consistentdensity models that produce similar gravity values to thoseobserved in the field data.4.1.1 Measurements of variations in the
25、subsurface densityof soil and rock are made from the land surface using agravimeter (Fig. 1). The lateral variations in density are used tointerpret subsurface conditions along a profile line or grid ofgravity measurements.4.1.2 Gravity measurements can be interpreted to yield thedepth to rock, the
26、location of a buried valley or fault, or thepresence of a cave or cavity. The results obtained frommodeling can often be used to characterize the densities ofnatural or man-made subsurface materials.4.2 Complementary DataGeologic and water table dataobtained from borehole logs, geologic maps, and da
27、ta fromoutcrops or other complementary surface geophysical methods(D6429) and borehole geophysical methods (Guide D5753) areusually necessary to properly interpret subsurface conditionsfrom gravity data.5. Significance and Use5.1 ConceptsThis guide summarizes the equipment, fieldprocedures, and inte
28、rpretation methods used for the determi-nation of subsurface conditions due to density variations usingthe gravity method. Gravity measurements can be used to mapmajor geologic features over hundreds of square miles and todetect shallow smaller features in soil or rock. In some areas,the gravity met
29、hod can detect subsurface cavities.5.1.1 Another benefit of the gravity method is that measure-ments can be made in many culturally developed areas, whereother geophysical methods may not work. For example, gravitymeasurements can be made inside buildings; in urban areas;and in areas of cultural, el
30、ectrical, and electromagnetic noise.5.1.2 Measurement of subsurface conditions by the gravitymethod requires a gravimeter (Fig. 1) and a means of deter-mining location and very accurate relative elevations of gravitystations.5.1.2.1 The unit of measurement used in the gravity methodis the Gal (in ho
31、nor of Galileo), based on the gravitational forceat the Earths surface. The average gravity at the Earthssurface is approximately 980 Gal. The unit commonly used inregional gravity surveys is the mGal (103Gal). Typicalgravity surveys for environmental and engineering applicationsrequire measurements
32、 with an accuracy of a few Gals (106Gals), they are often referred to as microgravity surveys.5.1.2.2 A detailed gravity survey typically uses closelyspaced measurement stations (a few meters to approximately100 meters) and is carried out with a gravimeter capable ofreading to a few Gals. Detailed s
33、urveys are used to assesslocal geologic or structural conditions.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 webs
34、ite.FIG. 1 Gravimeter (from Milsom (4)D6430 1825.1.2.3 A gravity survey consists of making gravity mea-surements at stations along a profile line or grid. Measurementsare taken periodically at a base station (a stable noise-freereference location) to correct for instrument drift.5.1.3 Gravity data c
35、ontain anomalies that are made up ofdeep regional and shallow local effects. It is the shallow localeffects that are of interest in microgravity work. Numerouscorrections are applied to the raw field data. These correctionsinclude latitude, free air elevation, Bouguer correction (masseffect), Earth
36、tides, and terrain. After the subtraction ofregional trends, the remainder or residual Bouguer gravityanomaly data may be presented as a profile line (Fig. 2)orona contour map. The residual gravity anomaly map may be usedfor both qualitative and quantitative interpretations. Additionaldetails of the
37、 gravity method are given in Telford et al (5);Butler (6); Nettleton (7); and Hinze (8).5.2 Parameter Being Measured and Representative Values:5.2.1 The gravity method depends on lateral and depthvariations in density of subsurface materials. The density of asoil or rock is a function of the density
38、 of the rock-formingminerals, the porosity of the medium, and the density of thefluids filling the pore space. Rock densities vary from less than1.0 g/cm3for some vesicular volcanic rocks to more than 3.5g/cm3for some ultrabasic igneous rocks. As shown in Table 1,the normal range is less than this a
39、nd, within a particular site,the realistic lateral contrasts are often much less.5.2.2 Table 1 shows that densities of sedimentary rocks aregenerally lower than those of igneous and metamorphic rocks.Densities roughly increase with increasing geologic age be-cause older rocks are usually less porous
40、 and have been subjectto greater compaction. The densities of soils and rocks arecontrolled, to a very large extent, by the primary and secondaryporosity of the unconsolidated materials or rock.5.2.3 A sufficient density contrast between the backgroundconditions and the feature being mapped must exi
41、st for thefeature to be detected. Some significant geologic or hydrogeo-logic boundaries may have no field-measurable density con-trast across them, and consequently cannot be detected withthis technique.FIG. 2 Graphical Method of Regional-Residual Separation (from Butler (5)TABLE 1 Approximate Dens
42、ity Ranges (Mg/m3) of SomeCommon Rock Types and Ores (Keary and Books (9)Alluvium (wet) 1.962.00Clay 1.632.60Shale 2.062.66SandstoneCretaceous 2.052.35Triassic 2.252.30Carboniferous 2.352.55Limestone 2.602.80Chalk 1.942.23Dolomite 2.282.90Halite 2.102.40Granite 2.522.75Granodiorite 2.672.79Anorthosi
43、te 2.612.75Basalt 2.703.20Gabbo 2.853.12Gneiss 2.612.99Quartzite 2.602.70Amphibolite 2.793.14Chromite 4.304.60Pyrrhotite 4.504.80Magnetite 4.905.20Pyrite 4.905.20Cassiterite 6.807.10Galena 7.407.60D6430 1835.2.4 While the gravity method measures variations indensity in earth materials, it is the int
44、erpreter who, based onknowledge of the local conditions or other data, or both, mustinterpret the gravity data and arrive at a geologically reason-able solution.5.3 Equipment:5.3.1 Geophysical equipment used for surface gravity mea-surement includes a gravimeter, a means of obtaining positionand a m
45、eans of very accurately determining relative changes inelevation. Gravimeters are designed to measure extremelysmall differences in the gravitational field and as a result arevery delicate instruments. The gravimeter is susceptible tomechanical shock during transport and handling.5.3.2 GravimeterThe
46、 gravimeter must be selected to havethe range, stability, sensitivity, and accuracy to make theintended measurements. Many gravimeters record digital data.These instruments have the capability to average a sequence ofreadings, to reject noisy data, and to display the sequence ofgravity measurements
47、at a particular station. Electronicallycontrolled gravimeters can correct in real time for minor tilterrors, for the temperature of the instrument, and for long-termdrift and earth tides. These gravimeters communicate withcomputers, printers, and modems for data transfer. Kaufmann(10) describes inst
48、ruments suitable for microgravity surveys.Acomprehensive review of gravimeters can be found in Chapin(11).5.3.3 PositioningPosition control for microgravity sur-veys should have a relative accuracy of1morbetter. Thepossible gravity error for horizontal north-south (latitude)position is about 1 Gal/m
49、 at mid-latitudes. Positioning can beobtained by tape measure and compass, conventional landsurvey techniques, or a differential global positioning system(DGPS).5.3.4 ElevationsAccurate relative elevation measure-ments are critical for a microgravity survey. A nominal gravityerror of 1 Gal can result from an elevation change of 3 mm.Therefore, elevation control for a microgravity survey requiresa relative elevation accuracy of about 3 mm. Elevations aregenerally determined relative to an arbitrary reference on sitebut can also be tied
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