Electrical Resistivity Tomography (ERT) on site for survey of natural clayey soil water content

Foundations problems emphasize a lack of knowledge on parameters controlling ground movements during wet-fry cycles. To address this problem, a geotechnical characterization of a clayey formation reveal an important variability of lithological facies in depth and for very short distances, explaining a wide range of geotechnical parameters and weak correlations. The study focused on water deficits and benefits over time, related to soil composition in a heterogeneous clay formation by using Electrical Resistivity Tomography (ERT). The electrical variations obtained from ERT were compared with local effective rainfall and soil moisture measurements from Time Domain Reflectometry (TDR) down to 3 m deep. The first results show the potential of measuring soil water content variations over the seasons, and especially to detect a quick increase of humidity thanks to spatial soil heterogeneity at a centimetric or decametric scale. These measurements confirm a strong relationship of geotechnical parameters with lithological composition of soils.