This is a series of short posts on Soil Resistivity Testing. And the common mistakes encountered, with practical advice on how to avoid common mistakes. Part 10 – Soil Resistivity Testing Erratic Readings.
So, when carrying out soil resistivity testing. Erratic readings can occur due to poor connections. Also, through high contact resistance. And background noise at a frequency similar to that used by the measurement equipment. Nearby buried metallic structures, equipment failure, operator error, and other factors.
Therefore, ideally, after soil resistivity testing. Measured soil relativities plotted on log-log graph paper in the field, to permit detection of irregular measurements. Thus, eliminating erratic readings so, that corrective action can be taken immediately.
So plot soil resistivity readings, compared against electrode spacing. Also, expect a smooth curve. Sharp changes suggest a need for checking the equipment set-up. Therefore, repeating your measurements. Also, taking additional measurements at shorter and larger electrode spacings close to the problematic one.
- The Wenner and Schlumberger 4-pin methods differ only in the spacing of the two inner potential electrodes.
- Note that only the area in the vicinity of the current injection electrodes wetted in this way. This will not influence the measurements significantly. But, ensure that the wetted area is small, in comparison to the inter-electrode spacing.