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ASTM G57: Measurement of Soil Resistivity Using the Wenner Four-Electrode Method
In-situ soil resistivity by the four-pin Wenner array — the field measurement behind corrosion-rate estimates, cathodic protection design, and grounding-grid design.
| Designation | ASTM G57 |
| Setting | Field + Laboratory |
| Service line | Construction Materials Testing |
Testing is performed to the current edition of ASTM G57 referenced by your project specification. This page is a plain-language overview, not a substitute for the published standard.
What the ASTM G57 test measures
ASTM G57 measures soil resistivity in place using the Wenner four-electrode method. Four metal pins are driven into the ground in a straight line at equal spacing, a current is passed through the outer pair, the voltage drop is measured across the inner pair, and the apparent resistivity of the soil to a depth roughly equal to the pin spacing is computed. Low resistivity means the soil conducts current easily and is corrosive to buried metal; high resistivity means the opposite.
Resistivity is the primary variable in corrosion-rate estimates for buried pipelines, piles, tanks, and culverts, in cathodic protection design, and in the design of electrical substation grounding grids.
How the ASTM G57 test works, step by step
Pins are set at a chosen spacing, often 2.5, 5, 10, and 20 feet in sequence, to profile resistivity with depth. A soil resistance meter applies an alternating current to the outer electrodes and reads the resistance between the inner ones. Resistivity in ohm-centimeters equals 2 pi times the spacing times the resistance, with a correction if the pin depth is significant relative to the spacing. Readings are taken in two perpendicular directions at each location and the soil moisture and temperature conditions are noted.
What the numbers mean
Resistivity under 1,000 ohm-cm is generally rated severely corrosive, 1,000 to 2,000 corrosive, 2,000 to 10,000 mildly corrosive, and above 10,000 progressively less corrosive. MSE wall backfill specifications typically require a minimum of 3,000 ohm-cm for steel reinforcement. Because resistivity drops sharply as soil moisture rises, the wet-season or saturated value governs design.
What can throw the result off
Buried metal pipes, conduits, fences, and grounding conductors near the pin line short-circuit the measurement and read as low resistivity. Dry surface soil with poor pin contact, stray current from nearby power systems, and frozen ground also distort readings. Spacings are chosen to keep the measurement volume below shallow disturbance.
Common questions about ASTM G57
How is G57 different from G187?
G57 measures the soil in place over a volume; G187 measures a sample in a laboratory soil box. G57 captures field conditions and depth variation; G187 gives the controlled saturated value that most backfill specifications require.
How many locations are needed?
Enough to characterize variability along the alignment or across the site, typically several hundred feet apart for a pipeline and at each grounding grid corner and center for a substation.
How we help with ASTM G57 testing
Our technicians run Wenner resistivity surveys for pipeline corrosivity assessments, cathodic protection design, and substation grounding studies, and report resistivity by depth and location with the field conditions recorded.
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