The Stability of Unsaturated Lateritic Slopes Under Rainfall Conditions Considering Shear Strength Variability

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

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.

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

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.

Review of Numerical Modeling Studies and the Influence of Compaction, Moisture, and Particle Size on Slope Stability

Rainfall-induced stability of unsaturated tropical slopes in Pagar Alam, South Sumatra, Indonesia: Effects of slope gradient and soil layering

Rainfall-induced slope failure is a recurring geohazard in tropical regions, where intense and prolonged precipitation promotes infiltration, reduces matric suction, and increases pore-water pressure within near-surface soils. This study investigates the effects of slope gradient and soil layering on the stability of unsaturated natural slopes in Pagar Alam, South Sumatra, Indonesia, using soil properties obtained from laboratory testing. Three representative slope geometries derived from terrain data were analyzed under both homogeneous and layered subsurface conditions to assess the combined influence of topography and stratification. Transient rainfall infiltration was incorporated into a numerical framework, and stability was assessed using the Morgenstern-Price limit equilibrium method in GeoStudio. The results indicate that the factor of safety decreases rapidly due to rainfall infiltration. The greater the slope angle, the greater the reduction in the factor of safety. Layered slopes generally produced lower factors of safety than their homogeneous conditions, demonstrating that stratification can reduce slope stability even when the overall failure pattern remains similar. The results further suggest that hydraulic and mechanical contrasts between soil layers influence pore-water-pressure evolution and the distribution of shear resistance during rainfall. These findings highlight the importance of incorporating unsaturated soil behavior and realistic subsurface stratification into slope-stability assessment in tropical environments. The study provides a hydro-geologically relevant basis for improving landslide susceptibility evaluation and supports the development of site-specific monitoring and mitigation strategies for rainfall-prone slopes in Indonesia.

Influence of hysteresis of bimodal soil-water characteristic curve on the stability of dual-porosity soil slope

ABSTRACT Slope failures often occur during soil wetting, yet most analyses rely solely on drying soil-water characteristic curve (SWCC), leading to results that do not reflect field conditions. This study develops a mathematical model to estimate bimodal permeability functions under both soil drying and wetting, and to investigate the influence of hysteresis on the stability of dual-porosity soil slopes. Analyses were performed under three scenarios: using only the drying SWCC, using only the wetting SWCC, and using both the drying and wetting SWCCs. Rainfall patterns were chosen according to records of rainfall intensities in central Asia. Drying and wetting SWCCs were tested in the laboratory, while the shear strength of unsaturated soil was a function of matric suction linked to the SWCC. Comparing the results of analyses using the three scenarios indicates that ignoring hysteresis provides an ‘overly conservative’ factor of safety, with differences of up to 67%. Thus, using the relevant SWCC to model drying and wetting processes in slope stability analyses is important to avoid unsafe or excessively conservative designs.

Analysis of bearing capacity and deformation of unsaturated expansive soil foundations under flood-induced lateral seepage

To investigate the impact of flood-induced seepage on foundation bearing performance, a comprehensive numerical analysis was conducted on the vertical ultimate bearing capacity of a strip foundation resting on unsaturated expansive soil. Utilizing the ABAQUS platform with the Modified Cam-Clay model, the coupled hydro-mechanical responses, seepage field evolution, and subsequent reduction in bearing capacity were systematically analyzed under both transient and steady-state conditions. The numerical results indicate that saturated hydraulic conductivity and matric suction are key parameters affecting foundation stability. Under the influence of transient hydraulic gradients, the negative pore-water pressure gradually dissipates, leading to a nonlinear decrease in matric suction and a reduction of up to 65% in the ultimate bearing capacity of the foundation. Furthermore, the infiltration process alters the subsoil failure mechanism, shifting the general shear failure observed in the initial unsaturated ground toward an asymmetric local failure concentrated beneath the footing edges. This study reveals the localized weakening mechanisms of unsaturated expansive soil foundations subjected to flood-induced lateral seepage and provides a quantitative basis for the risk assessment of infrastructure founded on unsaturated soils.