Long-term landslide monitoring using soil-water relationships and electrical data to estimate suction stress

Soil-moisture fluctuation in the unsaturated zone of shallow colluvial landslides is influenced by many geologic, geomorphic, and seasonal conditions. Long-term field monitoring of variables such as water content, water potential, and electrical conductivity that can establish relationships used for geotechnical and landslide hazard investigations is deficient, particularly in regard to the shallow unsaturated zone. In addition, using electrical-conductivity data as a means to calculate related parameters such as shear strength and suction stress is even less common. The hydrologic conditions in the soil, rainfall, and movement were monitored within an active landslide in southeastern Kentucky to (1) assess soil moisture fluctuations within the landslide and (2) establish soil-water relationships across the slope using constitutive models and a new equation for predicting suction stress. In-situ measurements of volumetric water content and water potential were used in a framework that incorporates electrical conductivity to estimate unsaturated soil properties (soil-water characteristic curves) and suction stress. The framework proves that the relative constitutive equations are valid for long-term soil hydrologic monitoring and that electrical data can be used as a predictor of suction stress. The practical application of developing this framework is to further the understanding of the dynamic movement of water through shallow colluvial soils, which can support landslide hazard and geotechnical investigations.