Laboratory characterization and modeling of DC electrical resistivity of sandy soil with variable water resistivity and content

Soil resistivity is an important parameter for engineering applications. In this work the effects of soil characteristics and conditions on the DC soil resistivity are investigated experimentally using remolded soil samples. Several natural silica and artificial glass sands of uniform gradations were tested under variable water resistivity and content, using the two-electrode and the four-electrode soil box methods for dry and wet soil, respectively. The dependence of DC soil resistivity on soil characteristics and conditions, such as grain size, specific surface, pore water conductivity and degree of saturation, is assessed. Soil resistivity decreases with increasing water conductivity and content. It also decreases with decreasing grain size as a result of the shorter current conduction paths (lower tortuosity) and the higher amount of available electrolytes; the contribution of the latter was quantified by measuring the resistivity of several soil:water suspensions. The effects of soil characteristics and conditions on soil resistivity have been well accounted for by considering soil resistivity at saturation as reference. For degree of saturation higher than the percolation threshold soil resistivity is well approximated by Archie's law; parameter values applicable to sandy soil are proposed. A new expression has been derived on a physical basis to describe soil resistivity for degree of saturation values lower than the percolation threshold.