Assessment of slope stability and remedial measures around Gilgel Gibe-II Hydroelectric Project, Southwest Ethiopia

Abstract

A road constructed from Fofa town to Gilgel Gibe-II powerhouse in south-western Ethiopia passes through an extremely rugged terrain characterized by steep hill slopes and deep valleys. The present study has been carried out to identify potentially unstable slope sections and to work out proper remedial measures. In order to identify potential unstable slopes in the study area field investigations for slope stability analysis were undertaken. Further, based on the field manifestations of instabilities eight potentially unstable slopes were identified. Out of these, seven slope sections show potential for planar mode of failure whereas, one slope shows a potential for wedge mode of failure. The detailed stability study of these critical slope sections has been carried out by limit equilibrium method. The slopes having planar mode of failure were analyzed by using Sharma et al. (1995) technique, whereas the slope having wedge mode of failure was analyzed by ‘SASW’ computer program. The stability analysis was carried out for the existing and anticipated worst conditions. The results indicate that all critical slopes in the study area are stable for the existing conditions, represented by dry static conditions whereas for the anticipated worst conditions (i.e., moderately saturated slope with dynamic ground condition) slopes may become unstable. Based on the results of the stability condition, suitable remedial measures, such as safe cut slope design, rock bolt anchoring and suitable drainage requirements have been worked out for the critical slope sections.