Water retention and suction stress of a partially saturated sand-clay mixture subjected to hydraulic hysteresis: Laboratory investigations and model evaluation

The properties of partially saturated soils are essential for geotechnical engineering since the majority of construction work takes place in the unsaturated zone between the ground surface and the groundwater table. The presence of air-water interfaces in partially saturated soils influences both the suction and stress state of the soil, and thus important soil properties like shear strength and stiffness. This research investigates the water retention and strength properties of a partially saturated sand-clay mixture exposed to different hydraulic paths. Pressure plate and desiccator tests were performed to investigate the interaction between suction and soil water content. In the analysis of the strength characteristics, the concept of suction stress was employed. Suction stress was determined from strain-controlled uniaxial compression tests on about 100 specimens, which were previously subjected to different drying and wetting paths. In this context, the impact of hydraulic hysteresis on suction stress is thoroughly examined. This article further evaluates mathematical equations for describing both the soil water characteristic curve (SWCC) and the suction stress characteristic curve (SSCC). Equation-specific benefits and problems are addressed, using statistical evaluation and error quantification.