Standard Test Method for Field Measurement of Soil Resistivity Using the Wenner Four-Electrode Method. Soil testing is performed for a variety of reasons, from agricultural to environmental. Find out why the ASTM G57 standard may be helpful for. Geotechnical and power engineers, find out how to perform a fall-of-potential or ASTM G57 test.
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The multiparticipant test program results indicate a reproducibility Cv of Do not include large nonconductive bodies such as frozen soil, boulders, concrete foundations, etc. The two-electrode technique is inherently less accurate than the four-electrode method because of polarization effects, but useful information can be obtained concerning the characteristics of particular strata.
Alternatively, the resistance can be measured directly. The electrode separation should be selected with consideration of the soil strata of interest. Surplus water should not be poured off as this will remove soluble constituents. Where regular surveys are to be made at? Where mean or median values cannot be estimated with reasonable accuracy, sequential sampling techniques can be employed. The latter method permits precise mathematical treatment, such as cumulative probability analysis.
Originally published as G 57 — A soil box can be calibrated using solutions of known resistivity. Conductive structures such as pipes and cables should not be within 1? The current can be provided by either a cranked ac generator or a vibrator-equipped dc source.
Since most pipelines are installed at depths of from 1. B57 method permits the determination of the probability of the presence of a soil with a resistivity equal to or greater than a particular value. Where a resistivity meter is used, read the resistance directly and record.
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It will also be necessary to prepare a astj sample. Risk and error must be arbitrarily selected to allow determination of the number of measurements. Sharp changes in resistivity with distance and appreciable variations in moisture content and drainage are indicative of local severe conditions. A summary of these data is given in Table 1. These commonly use two electrodes mounted on a prod that is inserted in the soil-at-grade in an excavation or a driven or bored hole. Surface contamination tends to concentrate in existing ditches with surface run-off, appreciably lowering the resistivity below the asmt level.
The sample should be reasonably large and thoroughly mixed so that it will be representative. This can be done by preparing a stiff slurry of the sample, adding only sufficient water to produce a slight adtm of surface water, which should be allowed to evaporate before the slurry is remixed and placed in the box.
The degree of electrode polarization will also affect the size of such currents.
Some soils absorb moisture slowly aastm contain constituents that dissolve slowly, and the resistivity may not stabilize for as much as 24 h after saturation.
Measurements could be made in each soil classi? Available pedological t57 should be used to facilitate interpretation. Where available, use ground water from the sample excavation for saturation. The effect of variations in compaction and moisture content can be reduced by fully saturating the sample before placing it in the box.
To evaluate contamination effects when a new route is being evaluated, soil samples can be obtained at crossings of existing pipelines, cables, etc, or by intentional sampling using soil augers.
ASTM G57 Standard
More precise procedures may be employed in laboratory investigations and these should be de? Where resistivity information is included in published information, the measurement techniques used should be de?
Otherwise, use distilled water. A superscript epsilon e indicates an editorial change since the last revision or reapproval. The resulting resistivity measurement represents the average resistivity of a hemisphere of soil of a radius equal to the electrode separation. The box should be readily cleanable to avoid contamination by previous samples. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Resistivity is used in preference to conductivity as an expression of the electrical character of soils and waters since it is expressed in whole numbers.
Since a pipeline ditch cannot be included in the span of at-grade measurements, soil box samples should be obtained where the opportunity exists.
Terminals should be of good quality to ensure that lowresistance contact is made at the electrodes and at the meter. Both materials may require heat treatment so that they are sufficiently rigid to be inserted in dry or gravel soils.
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The a spacing should equal the maximum depth of interest. In the case of soil resistivity measurements reproducibility may be characterized by a coefficient of variation, Cv, representing the reproducibility standard deviation divided by the average result and expressed in percent.
Measure the voltage drop across the inner electrodes and record both the current and voltage drop if a separate ammeter and voltmeter are used. An unaltered dc source can be used if the electrodes are abraded gg57 bright metal before immersion, polarity is regularly reversed during measurement, and measurements are averaged for each polarity. When a metallic structure is immersed in a conductive medium, atsm ability of the medium to carry current will in?
atm It is desirable to sample each type separately. The soil should be well-compacted in layers in the soil box, with air spaces eliminated as far as practicable.
The resistivity, r, is then: Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, are entirely their own responsibility.
A galvanometer type of movement is preferred but an electronic type instrument will yield satisfactory results if the meter input impedance is at least 10 megaohm.
Current edition approved April 15, Individual reprints single or multiple copies of this standard may be obtained by contacting ASTM at the above address or at phonefaxf57 service astm. If you feel that your comments have not received a fair hearing you should make your views known to the ASTM Committee on Standards, at the address shown below.