3D FEM Assessment of Rainfall-Induced Stability of Residual Soil Slopes under Extreme Rainfall
DOI:
https://doi.org/10.69855/sipil.v2i2.698Keywords:
residual soil, slope stability, 3D finite element method, rainfall infiltration, factor of safety, hilly areaAbstract
Hilly areas underlain by tropical residual soil are susceptible to rainfall-induced slope failure as infiltration reduces matric suction and soil shear strength. This study investigates three-dimensional (3D) slope stability using the finite element method (FEM), coupling transient unsaturated seepage analysis with the shear strength reduction method (SRM) to evaluate time-dependent factors of safety (FoS). Four representative slope profiles (25°–38° inclination and 8–15 m height) in West Sumatra were modeled using laboratory-derived residual soil parameters, including effective cohesion, friction angle, saturated permeability, and soil-water characteristic curves. The slopes were subjected to a synthetic 72-hour extreme rainfall event with a peak intensity of 45 mm/h. Results showed that pore-water pressure increased from an initial matric suction of −55 kPa to near-zero or slightly positive values within 24–48 hours. Consequently, FoS decreased by 25.0–31.9% compared with dry conditions. The steepest profile (38°, 15 m height) reached a minimum FoS of 0.94 after approximately 40 hours, indicating potential failure. Critical slip surfaces occurred at depths of 1.5–3.0 m within the residual soil layer. Verification against 2D Bishop limit-equilibrium analysis was conducted under dry conditions. However, transient rainfall responses remain unvalidated. Therefore, findings indicate relative slope sensitivity rather than operational early-warning thresholds.
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