Rainfall-Induced Slope Stability and Deformation around Rajui Dam Infrastructure Using Finite Element Analysis

Abstract

Rainfall-induced slope instability poses a significant risk to dam infrastructure in tropical regions, where intense and prolonged precipitation frequently alters subsurface stress conditions. This study aims to evaluate the effects of rainfall infiltration on slope stability in the Rajui Dam area, Aceh, Indonesia, by quantifying changes in safety factor and deformation behavior under existing and high-rainfall conditions. A finite element–based numerical approach was employed using two-dimensional slope models representing critical slopes near the dam access road and spillway. Soil mechanical and hydraulic properties were derived from field and laboratory data, while rainfall was modeled as surface infiltration corresponding to a high-intensity scenario of 150 millimeters over ten days. Slope stability was evaluated using the strength reduction method, with safety factor and total displacement adopted as primary indicators of stability. The results indicate that rainfall infiltration consistently reduces the safety factor and increases slope displacement at both locations. One slope exhibited lower safety factor values, indicating higher susceptibility to instability, while the other showed greater deformation despite maintaining a marginally higher safety factor. Displacement patterns concentrated near slope toes and propagated along potential shear zones, suggesting progressive instability driven by increased pore water pressure and reduced effective stress. These findings demonstrate that identical rainfall conditions can produce different stability responses depending on slope geometry and material characteristics, highlighting the importance of site-specific evaluation.