Rock Slope Stability Assessment Using Stereographic Projection Method and Limit Equilibrium Analysis

Stability of rock slopes significantly influence by the structural geology of the rock in which the slope is excavated. Therefore, the structural and the engineering geological studies are necessary in assessment and identification of potential slope instability. Instability identification is essential to follow-up stabilization measures needed to ensure the long-term stability and integrity of the rock slope. The study was focused to identify the possible modes of failures occur during the widening of Thennekumbura—Ragala road of Sri Lanka. Hence, the study was focus to propose suitable remedial measures to stabilize the rock slope. Detailed field mapping was carried out to identify the lithological variations and to measure the orientations, intensity of discontinuities of the rock slope. Discontinuity orientation data were analyzed by stereographic projection method to identify the possible modes of failures along the road trace. In between each chainage, limit equilibrium analysis was performed to obtain the factor of safety for each mode of failure. Stability predictions were made based on the factor of safety achieved by the limit equilibrium analysis. According to the study, the predominant types of instability along the road trace were planar and wedge failures. As remedial measures, reduction of slope angle, rock benches with safe slope angle and rock bolting were proposed by analyzing the conditions of each site. In this study expected factor of safety of was 1.5. Furthermore, structural geological analysis can be used to predict the possible mode of failures in rock slope stability analysis; hence, remedial measures can be applied accordingly.