Coupled Hydro-Mechanical Analysis of Rainfall Induced Shallow Slope Instabilities

Understanding the hydro-mechanical behavior of slopes under rainfall conditions is critical to predict slope instability issues, which is the focus of this study. Coupled pore pressure-stress models were developed using SEEP/W and SIGMA/W to understand the hydrological and mechanical changes occurring in the slope. Results showed that slope inclination and initial moisture content strongly influenced deformation, with slopes inclined at 60° developing up to 1.6 times more shear strain than those at 30°. An increase in the initial moisture content from 8% to 20% further caused an increase in shear strain due to a reduction in the matric suction and shear strength. Rainfall intensity was identified as a significant factor (Logworth of 5.25) influencing the time to saturation. As intensity increased from 0.2 cm/h to 5 cm/h, the time to saturation decreased by 1.05 times in slopes with a groundwater table and by 1.8 times in slopes without groundwater table. Finite element stability analyses in SLOPE/W indicated that factors of safety consistently decreased with rainfall duration. Statistically, the factor of safety was found to be significantly influenced by groundwater table (Logworth of 19.23) followed by slope inclination (14.51) and initial moisture content (14.23). Similar findings were obtained from the finite element models, where the interaction of all factors collectively influenced the reduction in factor of safety. Rainwater infiltration caused the critical slip surface to migrate towards the ground surface, reducing the volume of the slope material was involved in a failure under saturated conditions.