1、Designation: G187 12aStandard Test Method forMeasurement of Soil Resistivity Using the Two-ElectrodeSoil Box Method1This standard is issued under the fixed designation G187; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the equipment and proceduresfor the measurement of soil resistivity, for samples removedfro
3、m the ground, for use in the assessment and control ofcorrosion of buried structures.1.2 Procedures allow for this test method to be used in thefield or in the laboratory.1.3 The test method procedures are for the resistivitymeasurement of soil samples in the saturated condition and inthe as-receive
4、d condition.1.4 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly. Soil resistivity values are reported in ohm-centimeter.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. I
5、t is theresponsibility of the user of this standard to establish appro-priate safety and health practices and to determine theapplicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterE691 Practice for Conducting an Interlabo
6、ratory Study toDetermine the Precision of a Test MethodG57 Test Method for Field Measurement of Soil ResistivityUsing the Wenner Four-Electrode MethodG193 Terminology and Acronyms Relating to Corrosion2.2 UNS Standards:3UNS Designation S30400 where “I”is measured in amperes, “E” in volts, and “R” in
7、 ohms.3.1.2 resistivity (soil), nThe electrical resistance betweenopposite faces of a unit cube of material; the reciprocal ofconductivity.3.1.3 saturated soil, nsoil whose entire soil porosity isfilled with water.3.1.4 soil box factor, nA factor which is determined by atwo-electrode soil boxs inter
8、nal dimensions (cross sectionalarea/distance between electrode plates). The soil box factor ismultiplied by the measured resistance of a substance in the soilbox to obtain that substances resistivity.3.1.5 soil resistance meter, nAn instrument capable ofmeasuring soil resistance.3.1.6 two-electrode
9、soil box, nAnon-conductive containerof known internal dimensions with two end plate electrodes formeasuring a substances resistivity.3.2 The terminology used herein, if not specifically definedotherwise, shall be in accordance with Terminology G193.Definitions provided herein and not given in Termin
10、ologyG193 are limited only to this standard.4. Summary of Test Method4.1 The two-electrode soil box method is predicated onmeasuring the resistance between two opposite faces of a boxcontaining a substance or solution. That resistance measure-ment through the substance being tested is then converted
11、 toresistivity based on the conversion formula of Eq 1.1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.10 onCorrosion in Soils.Current edition approved Nov. 1, 2012. Published March 2013. Originallyapproved
12、in 2005. Last previous edition approved in 2012 as G18712. DOI:10.1520/G0187-12A.2For 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
13、 onthe ASTM website.3UNS (Unified Numbering System) was developed jointly by ASTM Interna-tional and SAE International.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.2 A voltage is applied to the opposing electrodes and theresultin
14、g current is measured. Ohms law reveals the resistance.The resistivity, , is then: ohm 2 cm! 5 AR/d (1)where:A = exposed area of one electrode face, cm2,R = resistance, ohms, andd = distance between electrodes, cm.5. Significance and Use45.1 The resistivity of the surrounding soil environment is afa
15、ctor in the corrosion of underground structures. High resis-tivity soils are generally not as corrosive as low resistivitysoils. The resistivity of the soil is one of many factors thatinfluence the service life of a buried structure. Soil resistivitymay affect the material selection and the location
16、 of a struc-ture.55.2 Soil resistivity is of particular importance and interest inthe corrosion process because it is basic in the analysis ofcorrosion problems and the design of corrective measures.5.3 The test method is focused to provide an accurate,expeditious measurement of soil resistivity to
17、assist in thedetermination of a soils corrosive nature. Test Method G57emphasizes an in situ measurement commonly utilized in thedesign of a buried structures corrosion control (cathodicprotection systems ground bed design, and so forth). Thetwo-electrode soil box method often compliments the four-p
18、in,in situ soil resistivity method.5.4 The saturated soil resistivity determined by this testmethod does not necessarily indicate the minimum soil resis-tivity.6. Apparatus6.1 The equipment required for the measurement of theresistivity of soil samples, either in the field or in thelaboratory, consi
19、sts of a two-electrode soil box, a soil resis-tance meter, wiring to make the necessary connections and asoil extraction tool with straightedge.Atwo-electrode soil box,soil resistance meter and its electrical connections are shown inFig. 1.4Method of Test for the Resistivity of Soils Material, Texas
20、 State Department ofHighways and Public Transportation Materials and Tests Division, Test MethodTex-129-E, November 1986.5Method for Estimating the Service Life of Steel Culverts, California StateDepartment of Transportation Engineering Service Center, California Test 643,November 1999.FIG. 1 Typica
21、l Connections for Use of Soil Box with Soil Resistance MeterG187 12a26.2 Two-Electrode Soil BoxTwo-electrode soil boxes canbe constructed in various sizes provided the inside dimensionsare known. Design and construction shall incorporate materialsthat are durable and machinable. The two end plate el
22、ectrodesshall be constructed of a clean, polished corrosion-resistantmetal or alloy (that is, UNS Designation type S30400/S30403or UNS S31600/S31603 stainless steel) that will not form aheavy oxide film or otherwise add significant resistance. Thebody of the box shall be constructed of a material th
23、at isnon-conductive and able to maintain its desired dimensions(polycarbonate plastics). The box shall be readily cleanable toavoid contamination by previous samples. See Fig. 2.6.3 Soil Resistance MeterCommercially available soilresistance meters are commonly used for measuring soilresistivity. The
24、y offer convenience, ease of use, and repeatabil-ity. Soil resistance meters yield direct readings in ohms, whichare multiplied by the appropriate factor for the specifictwo-electrode soil box. The meter utilized may limit the upperrange of resistivity, which can be measured. In such cases, theresis
25、tivity should be reported as greater than the meters upperlimit.6.4 Wiring18 to 22 AWG insulated stranded copper wire.NOTE 1It is important to make reliable, low-impedance electricalconnections. Ensure that all terminals are clean, and all wiring connectionsare made securely.7. Reagents and Material
26、s7.1 Distilled or deionized water (Type IV grade as refer-enced in Specification D1193) to saturate samples.8. Sampling Test Specimens, and Test Units8.1 Collected soil samples that are to be tested in thelaboratory shall be placed in an appropriate sealable containeror polyethylene type bag to prev
27、ent contamination. Eachsample shall be clearly marked with the location, depth,collection date, and sample temperature at the time of collec-tion.NOTE 2The resistivity of a soil sample does not typically change overtime. However, it is advisable to conduct your tests typically within a fewweeks afte
28、r sample collection to avoid any unforeseen changes. It is alsoadvisable to avoid prolonged exposure of samples to extreme heat ordirect sunlight.FIG. 2 Typical Two-Electrode Soil Box (Empty and Full)G187 12a38.2 Soil samples shall be representative of the area ofinterest. Where the stratum of inter
29、est contains a variety of soiltypes, it is desirable to sample each type separately.8.3 The collected soil sample size is dependent on thevolume of the soil box used. Be sure to collect enough soil toallow for compaction during the test. It is also advisable tocollect extra soil in case repeated tes
30、ting becomes necessary.8.4 Soil resistivity measurements shall not be conducted onfrozen or partially frozen soil samples. Soil samples to betested in the laboratory shall be allowed to reach roomtemperature (approximately 20C (68F) prior to the resistiv-ity measurement. Field measurements shall ref
31、lect the soilstemperature during testing. Soil temperatures that are abovefreezing can be corrected for a uniform temperature of 15.5C(60F) by use of the following equation:6R15.55 Rt24.51t!/40 (2)where R15.5is the resistance at 15.5C (60F) and Rtis theobserved resistance at temperature tC.9. Calibr
32、ation and Standardization9.1 The accuracy of the soil resistance meter shall beperiodically checked with a commercial resistance decade boxor several appropriate known value resistors. Meter error shallnot exceed 5 % over the range of the instrument. If errorexceeds this limit, the meter should be r
33、ecalibrated as soon aspossible. Until such time, a calibration curve can be establishedand used to correct all measurements.9.2 The two-electrode soil box can be calibrated usingsolutions of known resistivity. Commercially available solu-tions (VWR Conductivity Calibration Standards7) in the rangeof
34、 1000, 5000, and 10,000 ohm-cm are recommended for thispurpose. Calibration checks are generally performed biannu-ally.10. Procedure10.1 Procure enough soil sample for testing to accommo-date the soil box.10.2 Examine the sample for the presence of foreign mate-rial such as gravel, small stones, roo
35、ts, twigs, and so forth,which shall be removed from the sample.10.3 Fill the soil box by adding increments of soil. Mixdistilled or deionized water into each soil increment to saturateand help the ionic components of the soil go into solution. Donot oversaturate the soil. Compact each wetted soil in
36、crementas densely as possible by hand. Make certain that voids areeliminated. Continue this filling procedure until soil box isslightly over full. Using the straightedge portion of the soilextraction tool, level off the excess hand compacted soil so thesoil conforms to the total volume of the soil b
37、ox. Add a slightamount more of distilled or deionized water to ensure the handcompacted sample is saturated but not oversaturated (thepresence of a moisture sheen on top of the sample is desirable).This procedure will allow for a resistivity measurement of thesoil in a saturated condition.NOTE 3Othe
38、r soil box resistivity measurement techniques and equip-ment are available. More detailed procedures related to the addition ofwater and compaction of the soil may be employed in controlledlaboratory investigations, which should be defined in reporting the results.Where resistivity information is in
39、cluded in published information, themeasurement techniques used should be defined.10.4 Connect the soil resistance meter to the soil box asshown in Fig. 1 and record the resistance measurement.Multiply the resistance measurement value by the appropriatesoil box factor to obtain the soil resistivity.
40、10.5 When requested to supply as-received sample results,perform the same procedures of steps 10.1-10.4, but eliminatethe addition of water.10.6 The soil resistance measurement using the two-electrode soil box will include the soil resistance between thetwo electrodes and the interface resistance be
41、tween the soilsample and the electrode. Tests and experience has shown thatthis interface resistance is negligible.11. Calculation or Interpretation of Results11.1 Each individual soil box will have a unique factordependent upon the internal dimensions of the box. Example:A soil box with inside dime
42、nsions of 4 cm4cm4cmwillhave a soil box factor of 4: 5 AR/d (3) 5 4 cm4 cmR/4 cm 5 4R ohmcm!where:A = cross sectional area, cm2,R = resistance, ohm, andd = distance between electrode plates, cm.12. Report12.1 Report the following information at a minimum:12.1.1 Technician performing the test.12.1.2
43、Model of soil resistivity meter being used.12.1.3 Soil box factor.12.1.4 Measured resistance in ohms for each sample (thismay be helpful later if the calculated value below becomessuspect.)12.1.5 Calculated resistivity value for the sample inohmcm.12.1.6 Temperature of the sample at time of collecti
44、on.12.1.7 Temperature of the sample during measurement.12.1.8 Date when the sample was collected.12.1.9 Date when the sample was tested.12.1.10 Depth of the sample.12.1.11 Location of the sample.12.1.12 Any other information that may facilitate the sub-sequent interpretation.12.1.13 Any deviation fr
45、om this test method.6Davis, R.O.E., “The use of the electrolytic bridge for determining solublesalts,” U. S. Dept. Agriculture, Circular 423, 1927.7The sole source of supply of the apparatus known to the committee at this timeis VWR International, 1310 Goshen Parkway, West Chester, PA19380, USA. If
46、youare aware of alternative suppliers, please provide this information to ASTMInternational Headquarters. Your comments will receive careful consideration at ameeting of the responsible technical committee,1which you may attend.G187 12a412.2 For a sample test report, see Fig. X1.1.13. Precision and
47、Bias13.1 PrecisionThe precision of this test method wasdetermined by a statistical evaluation of an interlaboratorystudy per Practice E691. The data from this evaluation areavailable from ASTM in a research report.8A summary ofthese data is given in Table 1.13.1.1 RepeatabilityRepeatability refers t
48、o the variationin results obtained by the same operator with the sameequipment and the same operating conditions in successivetests. In the case of soil resistivity measurements, the repeat-ability may be characterized by a coefficient of variation,CV%r, representing the repeatability standard devia
49、tion di-vided by the average result and expressed in percent. The ILSresults indicate a repeatability coefficient of variation of 6.6 %.The 95 % confidence interval is 2.8(CV%r) or 18.5 %.13.1.2 ReproducibilityReproducibility refers to the varia-tion in results that occurs when different operators measure thesame soil. In the case of soil resistivity measurements repro-ducibility may be characterized by a coefficient of variation,CV%R, representing the reproducibility standard deviationdivided by the average result and expressed in
