Investigating parameters m, n, and a in the extended Archie’s Equation for clayey soils

The resistivity of sandy soils and sediments can be explained by Archie’s Equation, whereas for clay bearing soil the extended version of the equation can be used. However, the parameters tortuosity factor (m), saturation exponent (n) and the constant (a) in this equation are not fully explored for clayey soil, although often used for calculation. In this study laboratory electrical resistivity measurements on soil samples from granitic and sandstone bedrock with increasing saturation were fitted with the extended Archie’s Equations, which was solved using physical properties measured in the laboratory. The tortuosity factor, m, shows a larger variation within the same soil type, but less difference to the other soil type. The saturation exponent, n, however, shows a larger variation between the soil types but less variation within.