Slope Stability Analysis Along Selected Steep Sections of Adama Ridges Using Limit Equilibrium Method (LEM) and Finite Element Method (FEM)

Abstract

Adama town is one of the rapidly growing towns in the country, and its population is growing at a staggering rate as well. The town is bounded by the two steeply sloped ridges that strike in the NNE-SSW direction. The urbanization and population growth of the town is leading to the construction of infrastructures near these steeply sloped ridges. However, these ridges (particularly Dibibisa ridge) are frequently affected by slope instability problems posing a danger to human lives and nearby infrastructures. Thus, this study is aimed at identifying and analyzing/or modeling slope stability along the ridges of Adama town using the Kinematic, Limit Equilibrium Method (LEM), and Finite Element Method (FEM). The input parameters for these techniques were determined through field surveys and laboratory testing of samples. Accordingly, three critical structural controlled (i.e. RS1 and RS2) and four non-structural controlled slope sections (i.e. SS1, SS2, SS3, and SS3) were identified based on field manifestations. The stability analysis of structural controlled slope sections was first done via kinematic technique and the results showed that RS1 and RS2 are susceptible to planar and wedge modes of failures. LEM modeling in terms of Factor of Safety (FOS) using Rocplane 2.0 software has shown that the planar failures of both RS1 and RS2 are unstable under dynamic and saturated conditions. Similar modeling for wedge failure via Swedge 2.0 software has also shown that the two wedges of RS1 are unstable under saturated conditions while the wedge of RS2 is stable under all conditions. Similarly, stability modeling of non-structural controlled slope sections using both LEM and FEM has shown that SS1, SS2, and SS3 are unstable under saturated conditions while SS4 is stable under all conditions. 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 for slope sections SS1, SS2, and SS4 while the results show variation for slope section SS3. All the modeling results showed that the stability of the critical slopes of the study area is primarily controlled by saturation and slope geometry factors. Based on modeling results, this study has designed rock bolts and shotcrete to stabilize unstable rock blocks of structurally controlled slope sections. Moreover, for non-structural controlled slope sections, slope flattening, benching, and coupled slope flattening and benching were designed to stabilize unstable geological formations.