Site investigation · Geophysics & monitoring
Resistivity sounding (Wenner array) calculator
Apparent resistivity for each electrode spacing from the measured resistance, the range and trend with depth, and an indicative corrosivity class for buried steel.
Standard: ρa = 2πaR (Wenner) · typical corrosivity guide for buried steel
Open the live calculator → All site investigation calculators
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Design limit (minimum ρ for the corrosion allowance used) | 20 | Ω·m |
| Readings: spacing a (m), resistance R (Ω) | 1, 15.869 2, 7.791 3, 4.986 5, 2.601 8, 1.243 12, 0.612 20, 0.276 30, 0.168 50, 0.097 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Maximum ρa | 99.71 | Ω·m |
| Trend d(log ρa)/d(log a) | -0.372 | |
| Corrosivity (typical guide, from minimum ρa) | moderate | |
| Minimum ρa | 30.47 | Ω·m |
- ✓ Minimum apparent resistivity ≥ design limit
Method, formulas and assumptions
- Maximum ρa = MAX([t.rho]) = 99.708 Ω·m
- Trend d(log ρa)/d(log a) = SLOPE([t.lr],[t.la]) = -0.37224
- Corrosivity (typical guide, from minimum ρa) = IF(MIN([t.rho])<10,"very high",IF(MIN([t.rho])<20,"high",IF(MIN([t.rho])<50,"moderate",IF(MIN([t.rho])<100,"mild","low")))) = moderate
- Minimum ρa = MIN([t.rho]) = 30.473 Ω·m
- Apparent resistivity at spacing a reflects ground to a depth of very roughly a/2 to a; invert layered models for design. Corrosivity also depends on pH, chlorides, sulfates and moisture (see AS 2159 Section 6).
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.