Numerical Modeling of Unsaturated Soil Slope of Bukit Mewah Using Field Data of Soil-Water Characteristic Curves

Abstract

Rainfall-induced instability is a major concern for unsaturated residual soil slopes in tropical regions, where porewater pressure and matric suction fluctuate rapidly under transient hydrological conditions. This study investigates the hydro-mechanical response of the Bukit Mewah slope in Selangor through a fully coupled flow–deformation analysis using PLAXIS 2D. Bukit Mewah slope represents a typical urban residual soil slope in a tropical environment and is located within a residential area, making it suitable for slope investigation. The numerical model incorporates sitespecific soil-water characteristic curves (SWCCs) derived from field monitoring data, allowing a realistic representation of unsaturated hydraulic behaviour. The simulation reproduced the pore-water-pressure dynamics at the monitored depths of 0.5 m and 1.0 m. At 0.5 m depth, suction during dry periods decreased to approximately –7.5 kPa, while heavy rainfall caused rapid dissipation toward about 5 kPa. At 1.0 m depth, pore-water pressure reduced to around –12 kPa after minor rainfall and rose to a peak of approximately 9 kPa during the heaviest storm. These responses aligned closely with the field sensor data, confirming the model’s ability to capture wetting-front progression, delayed deeper infiltration, and post-rainfall suction recovery. The Factor of Safety (FoS) remained relatively stable, slowly increasing from 1.35 to 1.55, but dropped sharply to about 0.9 during the first major rainfall event. A second reduction to approximately 1.07 from 1.40 occurred during the subsequent heavy storm, followed by gradual recovery as suction redeveloped. Overall, the results demonstrate that PLAXIS 2D effectively reproduces the coupled hydraulic–mechanical behaviour of an unsaturated tropical slope, providing valuable insights into rainfall-induced pore-pressure changes and stability fluctuations.