Rock slope stability modeling using kinematic and limit equilibrium methods along Woliso to Wonchi lake road, central Ethiopia

Slope failure is one of the major recurring geological hazards along the road that connects Woliso town to Wonchi Lake, Central Ethiopia. As a result, this road was repeatedly blocked by failed rock blocks that delay traffic activities and cause casualties. Thus, this study was aimed at identifying and modeling critical rock slope sections along this road by using the Kinematic and Limit Equilibrium Method (LEM). Parameters such as discontinuity and slope geometry factors, unit weight of rocks, and shear strength parameters of failure planes were used for the modeling. The discontinuity and slope geometry factors were determined via a detailed field survey while the unit weight of rocks was determined in the laboratory using a buoyancy technique. The shear strength parameters of failure planes were determined using Rocscience software. The kinematic and LEM modeling were then done on three critical slope sections (RSS1, RSS2, and RSS3) that were identified during the field survey. The Kinematic modeling revealed that slope section RSS1 is subjected to planar failures whilst slope sections RSS2 and RSS3 are exposed to wedge failures. The LEM modeling in terms of Factor of Safety (FOS) revealed that planar failures identified at RSS1 are unstable under all anticipated conditions with a FOS of less than 1. This modeling has also shown that the wedge of RSS2 is only unstable during saturated conditions illustrating a significant contribution of saturation on slope failure. Moreover, the LEM modeling results also displayed that the wedge of RSS3 which is formed due to the intersection of JS1 and JS3 is also unstable under all projected conditions. In general, from the modeling results, saturation, steep slope cuts, and low shear strength parameters of failure planes are identified as the main factors causing slope instability in the study area. This study has designed rock bolts and shotcrete to stabilize unstable rock blocks of critical slope sections. Moreover, surface and subsurface drainage systems are also recommended for better control of the effects of saturation.