Slope instability represents a major challenge for road infrastructure in mountainous regions, particularly where complex geology, intense rainfall, and shallow groundwater prevail. The Masha–Alemtena–Teppi Road corridor in southern Ethiopia has experienced recurrent slope failures that threaten public safety and infrastructure performance. This study investigates the failure mechanisms along critical road sections and identifies the most influential parameters governing slope stability. An integrated approach combining geotechnical field investigations, laboratory testing, geophysical surveys, and numerical slope stability modeling was adopted. Limit equilibrium analyses were performed using Rocscience SLIDE software to compute the Factor of Safety (FOS) under existing, saturated, and design cut conditions. The results show that current FOS values range from 0.56 to 0.89, indicating unstable to critically unstable slopes. Sensitivity analysis revealed that increasing cohesion or friction angle by up to 100% was insufficient to raise FOS above the safe threshold of 1.5, whereas groundwater conditions had a pronounced effect. Under dry conditions, FOS values increased to 2.01–2.73, while full saturation reduced FOS to as low as 0.35–0.59. To quantitatively assess parameter influence, the Taguchi method was applied using an L9 orthogonal array with cohesion, internal friction angle, and saturation as control factors. Signal-to-noise ratio analysis and analysis of variance (ANOVA) results indicate that saturation accounts for 89–91% of FOS variation across all sections, while cohesion and friction angle contribute less than 7% each. Back analysis estimated required reinforcement forces ranging from 1,283 to 2,197 kN to achieve a target FOS of 1.5. Based on these findings, site-specific remedial measures, including drainage systems, slope re-profiling, and retaining structures—were proposed, resulting in improved FOS values of up to 2.36. The study demonstrates that integrating statistical optimization with conventional geotechnical analysis provides a robust and efficient framework for slope stability assessment and mitigation design in landslide-prone regions.
Shitu et al. (Fri,) studied this question.