Slope Stability analysis of Selected Slope Sections along Jinka to Mendir road,south omo zone,SW Ethiopia

Abstract

Slope failures are among the most common geo-environmental natural hazards in the world’s hilly and mountainous terrain causing damage to human life and the destruction of civil engineering infrastructure such as roads and open-pit mines. The road which connects Jinka to Mendir is also frequently affected by slope instabilities. Hence, this study is aimed at identifying and analyzing critical slope sections along this road by using Kinematic, Limit Equilibrium Method (LEM) and Finite Element Method (FEM). The input parameters for the analysis were determined through field investigation methods such as discontinuity surveying, in-situ Schmidt hammer test, sampling, and laboratory testing of samples. From field investigation, two critical structural controlled and one critical non-structural controlled and 2 soil slope sections were identified. Schmidt hammer rebound test conducted on the study area revealed that the Uniaxial Compressive Strength (UCS) value ranges from 68.3MPa to 72.8MPa and 95 MPa for rocks of structural and non-structural controlled slope sections, respectively. The stability analysis of structurally controlled slope sections is first done via kinematic analysis and the results showed that RSS3 and RSS4 are unstable for planar mode of failure. Further stability analysis of planar mode of failure in terms of Factor of Safety (FOS) using Rocplane 2.0 software revealed that RSS3 is unstable under static and dynamic saturated conditions due to JSS1 and JSS2. A similar analysis of planar mode of failure in terms of Factor of Safety (FOS) using Rocplane 2.0 software revealed that RSS4 is unstable under static and dynamic saturated conditions due to JSS2. Similarly, stability analysis using both LEM-based Slide 6.0 and FEM-based Phase 2.0 software has also shown that non- structural controlled, structural controlled, and soil slope sections are unstable under saturated conditions. This illustrates that rainfall/or saturation is the major factor contributing to slope failure in the study area. Moreover, the FOS obtained from LEM-based Slide 6.0 software and SRF obtained from FEM-based Phase 2.0 software are in very close agreement which validated slope instability problems in the study area. Depending on the analysis of results, a total bolt capacity of 290 and 198 t/m were designed for RSS3 to stabilize planar failure due to JS1 and JS2 respectively. Similarly, rock bolts with a total capacity of 198 t/m at RSS4 stabilize planar failure due to JS2. Moreover, for non-structural controlled sections, it is designed to reduce slope angle and height. The safety factors were computed by lowering the slope angle from the original condition and by lowering the slope height according to research increasing the factor of safety. For soil sections it is designed to flatten the slope angle from the original slope angle was modeled as (1H: 1V) and the analysis was then carried out by subsequently reducing the slope angle from (1H:1V) to (1.5H:V), (2H:1V) and (2.5H:1V),(3H:1V) by keeping the height (V) constant that enhances the factor of safety. Moreover, surface and subsurface drainage systems are also recommended in these slope sections for better control of water effects.