ANALYSIS OF THE SLOPE INSTABILITY AND MITIGATION MEASUREMENTS IN GURBA KEBELE ARBA MINCH TOWN, SOUTHERN ETHIOPIA

Abstract

Slope instability, whether natural or artificial, is a common challenge for geotechnical engineers. Ethiopia is often the most affected by landslides because of its steep topography, high rainfall, and dense population. The frequently occurring landslides in Arba Minch town result in economic loss, including residential houses, destroying the nearby road and electric line, damaging the physical environment, and leading to deforestation. The main objective of this study is to analyze slope instability and mitigation measurements. It began by undertaking laboratory geotechnical characterization of the soil and slope stability analysis with Plaxis 2D software. Based on the laboratory test results, above 50% of the soil was dominated by coarse-grain soils, and ranged from slightly plastic to medium plastic. The direct shear test result, cohesion, and angle of friction obtained 7.5 to 14.25 KN/m2 and 19.6 o to 33 o, respectively. Primarily, this study focused on the determination of deformation and factors of safety to evaluate a failed slope section. From the analysis, it is found that the minimum and maximum deformation and factor of safety for both drained and undrained cases. For drained analysis, deformation and factor of safety were 0.68 m to 3.5 m and 0.78 to 1.1, respectively. For undrained deformation and factor of safety, 0.78 m to 4.12 m and 0.67 to 1, respectively. The causal factors were: eroding the supporting geological material due to stream erosion, groundwater rise, and rainfall, and slope angle and slope height were identified as the triggering factors that initiated landslides in the study area. Based on causal factors, the following remedial measures were proposed: monitoring and early warning systems, gravity-retaining walls, gabions, geogrids, geonets, and vegetation, which were effective corrective measures to prevent future failure in the research area. The designed geogrid analysis output shows the effectiveness of the stabilization by the geogrid. Overall, this study found that deformations and factors of safety in the study area show the slope sections are unstable.