Estimating the electrical conductivity of clayey soils with varying mineralogy using the index properties of soils

Abstract

Electrical conductivity assessment provides the valuable information required for comprehensive subsurface characterizations. This study aims to extend the existing modified Archie's equation for capturing the electrical conductivity of soils to various clayey soils in a broad range of plasticity. Five clayey soils that involve two kaolinite-, two illite-, and one montmorillonite-dominant fines were selected, and the bulk electrical conductivity σmix for the five clay samples in slurry state prepared in a modified oedometer cell was measured in a broad range of porosity n = 0.6–1.0 and pore water conductivity σw ≈ 0.013–4.5 S/m. The results showed that surface conduction plays a critical role in the determination of the electrical conductivity of clayey soils when subjected to a relatively low pore water conductivity environment. In this context, detailed analyses revealed that there exist robust correlations between the clay index properties and the unmeasurable input parameters for the modified Archie's equation such as the matrix conductivity λ and m exponent relevant to the tortuosity for pore water conduction. Comparison between the measured and predicted electrical conductivity for the raw clayey sediment used for model validation indicated that the unique global equation extended and verified in this study can be used for the first-order estimates of electrical conductivity of the in-situ clayey sediments.