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

Abstract

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