Effect of Sample Size, Dry Unit Weight, and Hysteresis of Expansive Soil on SWCC and Finite Slope Stability

This study investigates the influences of sample size and dry unit weight on expansive soil properties, focusing on soil water characteristic curves (SWCCs) and the stability of unsaturated finite slopes. The expansive soil collected from IIT Hyderabad, Sangareddy, Telangana, India, was compacted in both California Bearing Ratio (CBR) and relative density (RD) molds at varying water contents, ranging from 8.0% water content to saturated water content. Soil water characteristic curves (SWCCs) were systematically measured at different depths using matric potential sensors (MPS) in both CBR (2 cm, 8 cm, and 14 cm) and RD molds (2 cm, 6 cm, 10 cm, 14 cm, and 18 cm). Notably, matric suction of the soil compacted in RD molds was assessed at the maximum dry unit weight (MDU), as well as at 90%, 80%, and 70% of MDU. The results of the experiments revealed that matric suction in the CBR mold was underestimated by 14.69% when compared to the RD mold. Moreover, expansive soils compacted at MDU exhibited 68.56% greater suction than those compacted at 70% of MDU. The study highlights the depth-dependent increase in matric suction in both CBR and RD molds. Furthermore, the research elucidates the pronounced hysteresis effect in expansive soil compacted at low dry unit weight compared to MDU. Crucially, the research establishes a robust correlation between the stability of unsaturated finite slopes and the dry unit weight. The factor of safety for unsaturated finite slopes exhibited an 84.67% increase as dry unit weight increases from 12.4 kN/m³ to 17.7 kN/m³, emphasizing the significant influence of dry unit weight on location of critical failure surfaces. The present investigation provides crucial understandings into the complex interactions among soil compaction, matric suction, and slope stability. These findings offer valuable information for improving geotechnical approaches in slope design and management.