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

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.

Hydro-Geotechnical Modelling and 45-Year Trends of Rainfall-Induced Slope Failures in Tropical Regions

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.

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

Rainfall-induced slope failures pose significant risks and economic impacts globally. This study investigates the impact of rainfall on the hydromechanical behavior and stability of unsaturated lateritic slopes, commonly found in tropical regions. By employing both experimental and computational analyses, this research goes beyond traditional assumptions about soil behavior, providing an insight into the behavior of clayey and sandy lateritic soils in unsaturated condition. A probabilistic Monte Carlos analysis highlights the critical role of the variability of soil strength parameters on the assessment of slope stability. Detailed experimental design and computational modeling capture the complex interactions between hydraulic and mechanical soil behaviors, contributing substantial empirical data to geotechnical engineering fields. Notably, the shear strength prediction models adapted for unsaturated soils significantly influence slope behavior, demonstrating similar patterns in factor of safety reduction across different hydraulic models during rainwater infiltration. The analysis also confirmed hydraulic parameters with marked differences in porosity and water retention capacities between the soils impacting their susceptibility to saturation and shear strength reduction under similar conditions. This comprehensive approach not only advances our understanding of lateritic soils under changing climatic conditions but also enhances the predictive capabilities for slope stability, guiding effective risk management and engineering practices in tropical regions.

Instability Mechanism of a Soil–Rock Binary-Structure Slope Under Rainfall Conditions

Rainfall-induced instability of highway slopes with a soil–rock binary structure may be strongly influenced by the hydraulic barrier effect of low-permeability shale. This study investigated the right-side slope along the D-ramp section from DK0+230 to DK0+660 at Deze Interchange on the Zhanhui Expressway, China. A two-dimensional coupled seepage–stress model was developed based on the engineering geological conditions and rainfall records to simulate the slope response under a 72 h extreme rainfall scenario with an intensity of 175.6 mm/d. Field displacement monitoring data were used to validate the modeled deformation pattern under natural conditions. Under natural conditions, the reinforced toe zone remained stable, deformation was concentrated along the interface between the block-stone layer and strongly weathered limestone in the middle and rear portions of the slope, and the factor of safety was 1.1344, indicating a basically stable state. During prolonged rainfall, infiltrating water accumulated near the interface between the strongly weathered shale and the underlying shale owing to the hydraulic barrier effect of the low-permeability shale, forming a continuous transient saturated zone. The plastic zone progressively extended from the upper shallow weak interface to the lower deep interface and eventually became fully connected, while the factor of safety decreased to 0.9886, indicating overall instability. The results reveal a coupled mechanism involving interfacial water accumulation, increased pore-water pressure, the formation of a transient saturated zone, and a shift in the controlling zone of slope deformation and failure from shallow to deeper layers. These findings provide a reference for disaster prevention and mitigation of similar soil–rock binary-structure slopes.

Rainfall-induced instability of high road cut slopes in tropical lateritic soils: numerical assessment and stabilization performance

This study numerically assessed the stability of a high road cut slope subjected to rainfall infiltration, on the Olembe–Obala Interchange Road section near Nkolngem, in the Centre Region of Cameroon. Hourly climatic data spanning 25 years (2000–2025) were obtained from NASA POWER and cross-validated against Climate Research Unit monthly records, yielding a Pearson correlation coefficient of 0.949 and a mean relative error of 9%, confirming data reliability. Extreme rainfall intensities were extracted and fitted to the Gumbel distribution, with adequacy verified by the Kolmogorov-Smirnov test, accepted for 84% of durations analyzed. Intensity-Duration-Frequency curves were then constructed for return periods of 2 to 100 years. Infiltration modeling was performed using SEEP/W, with soil hydraulic properties estimated via the Fredlund and Xing model, under two complementary approaches namely a soil-climate interaction approach using continuous hourly time series, and a unit water flux approach simulating discrete extreme events. Slope stability was evaluated using SLOPE/W, combining the Morgenstern-Price limit equilibrium method and a finite element stress-based approach implemented through SIGMA/W, with both methods yielding consistent results within a mean relative difference of 2.72%. In the absence of stabilization, the safety factor decreased under the combined effect of rainfall intensity and duration, falling below the critical threshold of 1.3 during prolonged events exceeding 24 hours. A multiple linear regression analysis revealed that rainfall duration influences the safety factor approximately eight times more than intensity. Two stabilization techniques were evaluated. Vegetation cover, modeled using the Penman-Monteith evapotranspiration method with parameters representative of tropical grasses, increased the safety factor by 4% to 32% depending on event characteristics, primarily through a gain in superficial cohesion from root reinforcement, and maintained the safety factor above 1.3 even for 24-hour events. Masonry revetments with weep holes reduced the maximum degree of saturation by approximately 20% and raised the safety factor by more than 35% during extreme events, consistently keeping slopes above the required safety threshold. These findings highlight the high sensitivity of unstabilized tropical cut slopes to rainfall infiltration and confirm the effectiveness of both vegetation and masonry revetments as context-adapted stabilization solutions. Keywords: Rainfall-induced slope failure; Tropical lateritic soils; Transient infiltration; Limit equilibrium method; Finite element method; Slope stabilization.     Received Date: June 19, 2026 Accepted Date: July 10, 2026 Published Date: August 01, 2026 Available Online at: https://www.ijsrisjournal.com/index.php/ojsfiles/article/view/811