Geotechnical Aspects and Stability of Road Cuts in the Blue Nile Basin, Ethiopia

Road construction in the Blue Nile basin is largely determined by geotechnical factors. The area is characterized by steep slopes and has a history of landsliding. The geological formations range from Mesozoic sedimentary to Tertiary volcanic rocks making the stratigraphic makeup sensitive to deformation and failure. The heterogeneity of these rocks also means it is difficult to depend on results of stability analyses alone for road design and construction. As an alternative, ratios of cut-slope lengths to cut-slope heights have been developed in this study based on the performances of unsupported natural and artificial cuts and some stability analyses. Hence, road cuts on cliffs of hard rocks need a horizontal to vertical ratio of 0.25:1. Slopes made up of weak rocks can remain stable at a threshold angle of 45°. For heterogeneous slopes, it is advisable to use different road cuts depending on material makeup, and the degree of weathering and consolidation.