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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A nomograph for this correction is shown in Fig.
The resistivity, r, is then: Available pedological data should be used to facilitate interpretation. Alternatively, the resistance can be measured directly. It is desirable to sample each type separately. If samples are retained for subsequent measurement, correct the resistivity if the measurement temperature is substantially different from the ground temperature.
A number in parentheses indicates the year of last reapproval. This standard is subject to revision at any time by the responsible technical committee and must be reviewed every?
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Where mean or median values cannot be estimated with reasonable accuracy, sequential sampling techniques can be employed. Otherwise, use distilled water. Your comments will receive careful consideration at a meeting of the responsible technical asfm, which you may attend.
The effect of variations in compaction and moisture content can be reduced by fully saturating the sample before placing it in the box. 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.
Precision and Bias 9.
The a spacing should equal the maximum depth of interest. The sample should be reasonably large and thoroughly mixed so that it will be representative. If error exceeds this limit, prepare a calibration curve and correct all measurements accordingly. Originally published as G 57 — Summary of Test Method 3. 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. 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.
Since the number of soil sections that could be inspected is essentially unlimited, in? 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.
Since a pipeline ditch cannot be included in the span of at-grade measurements, soil box samples should be obtained where the opportunity exists. Surface contamination tends to concentrate in existing ditches with surface run-off, appreciably lowering the resistivity below the natural level. The current can be provided by either a cranked ac generator or a vibrator-equipped dc source.
Measurements could be made in each soil classi? The resulting resistivity measurement represents the average resistivity of a hemisphere of soil of a radius equal to the electrode separation. 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. This method permits the determination of the probability of the presence of a soil with a resistivity equal to or greater than a particular value.
The multiparticipant test program results indicate a reproducibility Cv of In either case, use pedological surveys in the planning and interpretation of any extensive survey. Surplus water should not be poured off as this will remove soluble constituents.
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Since most pipelines are installed at depths of from 1. The multi-participant test program results indicate a repeatability Cv of 6.
Where resistivity information is included in published information, the measurement techniques used should be de? Terminals should be of good quality to ensure that lowresistance contact is made at the electrodes and at the meter.
When a metallic structure is immersed in a conductive medium, the ability of the medium to carry current aetm in?
The latter method permits precise mathematical treatment, such as cumulative probability analysis. Where available, use ground water from the sample excavation for saturation. Conductive structures such as pipes 5g7 cables should not be within 1? 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.
It will also be necessary to prepare a mixed sample. A summary of these data is given in Table 1. Sharp changes in resistivity with distance and appreciable variations in moisture content and drainage are indicative of local severe conditions.
The degree of electrode polarization will also affect the size of such currents. The meter used may limit the upper range of resistivity, which can be measured.