Long-Term Landslide Monitoring Using Soil-Water Relationships and Electrical-Resistivity Tomography to Estimate Suction Stress and Shear Strength

Electrical-resistivity tomography (ERT) has become an increasingly popular technique for investigating landslides, providing insight into landslide type, location of the failure zone, soil and bedrock interfaces, and areas of excess moisture. Field monitoring of hydrologic variables in a colluvial slope, combined with ERT surveys, is an effective joint framework that can assess a soil's geotechnical properties. Variables such as water content, water potential, and electrical data can establish the relationships needed for geotechnical and landslide hazard investigations, particularly concerning the shallow unsaturated zone.

Volumetric water content, water potential, and electrical conductivity were measured at a shallow colluvial landslide in Kentucky and used in a framework to estimate unsaturated soil properties (soil-water characteristic curves) and suction stress. Relative constitutive equations were found to be valid for long-term soil measurements, and new equations developed from electrical data were determined to be useful to predict suction stress. The framework was then used with 2-D ERT measurements to predict shear strength. An unsaturated-soils shear-strength equation calculated shear strength based on inverted ERT values. Shear strength changed at depth, indicating landslide failure zones, specific soil horizons, and areas of low resistivity, and provided a spatial view of shear strength. This multidisciplinary approach connects geologic processes, geophysical surveys, and geotechnical parameters to assess landslide hazard and investigate slope stability.