Geotechnical analysis and stability assessment of a landslide event in Gera Woreda, Ethiopia

This study investigates the geotechnical factors influencing a recent landslide event in Gera Woreda, Ethiopia. The primary objective was to identify the soil properties contributing to landslide occurrence and understand the triggering mechanisms. Field investigations, soil sampling from both affected and unaffected areas, and subsequent laboratory characterization were conducted. The analysis revealed a dominance of fine-grained soils, such as clay and silt, which are susceptible to weakening upon saturation, thereby increasing landslide susceptibility. Rainfall is identified as the primary trigger for the landslide. Numerical stability assessments using the Limit Equilibrium Method (software, Slide™) and the Finite Element Method (software, PLAXIS®) were performed to assess the stability of the slopes. The stability analysis revealed a notable decrease in the factor of safety (FS) under rising groundwater levels. For example, the FS for Slope 1 decreased from 1.42 under dry conditions to 0.73 at a 2 m groundwater depth. Similarly, Slope 2's FS decreased from 2.06 to 1.18 under similar conditions. These results emphasize that rainfall is the primary trigger for landslides in the area. To address this, the study proposes surface drainage systems and the planting of Vetiver grass to improve slope stability. These findings provide critical insights for developing proactive mitigation strategies to protect local communities and infrastructure from landslide hazards.