The impact of rainfall characteristics on slope stability and the mitigation through sand pile reinforcement: a finite element analysis in tropical residual soils

Abstract

Abstract Rainfall-induced slope failures are widespread in tropical regions where residual soils predominate, largely due to elevated pore water pressures and the loss of matric suction during infiltration. Although numerous studies have examined rainfall-triggered instability, limited research has focused on the combined influence of variable rainfall intensity and duration on unsaturated tropical slopes, or on the effectiveness of drainage-based reinforcement such as sand piles. This study conducts a detailed finite element analysis to evaluate the transient hydro-mechanical response of a tropical residual soil slope subjected to a range of rainfall scenarios representing both short-duration/intense events and long-duration/low-intensity events. Results show that prolonged rainfall of low intensity has a more detrimental effect on stability than short, intense storms, reducing the factor of safety (FOS) from 2.72 to 1.11 under a 96-h event, a 60% reduction, primarily due to cumulative pore pressure build-up and deep suction loss. The study further evaluates the use of sand piles as vertical drainage elements and demonstrates that they significantly improve stability, yielding up to a 16% increase in matric suction, a 39% reduction in slope deformation, and a 26% increase in FOS under severe rainfall conditions. These findings highlight the dual drainage–reinforcement function of sand piles and provide practical guidance for designing mitigation measures in rainfall-susceptible residual soil slopes.