Empirical Study of the Correlation between Geoelectrical and Soil-Index Properties of Clayey Soils

Insufficient subsurface information and soil mischaracterization contribute to significant delays and cost overruns in up to 50% of all infrastructure projects. Adequate and accurate determination of soil-index properties such as plasticity index and fine/clay fraction which affect the shear strength of clayey soils help assess infrastructure stability, especially in locations with extreme wetting-drying cycles such as North Texas. Due to the inherent limitations of geotechnical site investigation methods, extensive research has been conducted to establish relationships between various soil-index and geoelectrical properties of clayey soils. However, little to no efforts have been made to quantify the effects of plasticity index, fine fraction, and clay fraction on the electrical resistivities. This paper investigates the relationship between these variables using correlation and linear regression analyses. Other influencing variables such as water content and dry unit weight were also used in the analyses. Conventional laboratory electrical resistivity tests and physical property tests were performed on 56 soil samples taken from some locations across Texas, US (842 observations). The results show statistically significant relationships between clay and fine fractions, plasticity index, and electrical resistivity. The results also show that the electrical resistivities are more influenced by the plasticity index than the fine and clay fractions. The proposed model in this paper provides practical tools to continuously determine the soil-index properties for assessing site conditions and infrastructure stability.