Investigations and Mitigation Measures of Landslide Affected Areas in Hill Roads of East Africa—Case Study on Projects of Ethiopia

Under the road development programme of Ethiopian Roads Authority (ERA) in Ethiopia, many roads spreading all over the country were upgraded from the existing gravel road to the widened asphalt road. Due to the rugged and mountainous terrain condition, natural and man-made slope failures such as landslides usually occur in almost all the hilly and mountainous terrain in Ethiopia. The main cause for the occurrences of failures at different locations along project roads which were widened either by cutting the hill slope and/or filling the valley slope was high rainfall in the area during the month of June to September. In this paper, the case study on the investigations of landslide failures along hill slope, valley slope, slope of bridge approaches, slope of hillside on upstream and valley side on downstream of culverts along project roads is described. The analysis of landslides and its different methods of mitigation measures, namely flattening of slope with or without provision of intermediate berms, provision of lateral support by gravity retaining wall at toe of hill slope or at road edge on valley slope side including proper slope protection and drainage measures adopted in the rehabilitation works along different project roads in Ethiopia, are presented here.