Rock Slope Stability Analysis along a Selected Slope Section of a Rhyolite Quarry in Adama, Central Ethiopia

Abstract

Slope instability at the rhyolite quarry site in Adama is one of the most frequent and common problems and issues in quarrying activity. The stability of the quarry slope depends on several factors, including a combination of both internal and external factors. This study aims to assess and evaluate the slope stability of the rhyolite quarry site in Adama, central Ethiopia, by using kinematic analysis, limit equilibrium, and finite element methods. Input parameters were determined through field surveys, such as the orientation of discontinuities and slope geometry, and a buoyancy technique were used in the laboratory to determine the unit weight of rocks. The strength of the intact rock was determined using a point-load laboratory test and the Schmidt hammer in the field. Rocscience software was utilized to determine the shear strength parameters along the failure plane, such as cohesion and friction angle. The kinematic analysis was used to determine the mode of failure, whereas limit equilibrium and finite element methods were used to determine factors of safety for critical slope sections of the quarry that were identified during the field survey. According to kinematic analysis, results QSS_1, QSS_3, show wedge failure, while QSS_2 and QSS_3 show planer failure. Moreover, deterministic analysis was conducted under a variety of circumstances: static dry, static saturated, dynamic dry, and dynamic saturated. According to the results, both quarry slope sections are unstable in static saturated and dynamic saturated conditions and stable in other conditions, and wedge failures at QSS_1 and QSS_3 under dynamic saturated conditions FOS are 0.95 and 0.248, respectively. For non-structurally controlled slope sections, Slide 6.0 and Phase 2 were used to determine the factor of safety of QSS_4 and QSS_5. Based on the findings, both slope sections are unstable under static and dynamic load conditions. From the analysis result, the combined effect of quarry operation by removal of rock material through excavation, steep slope cuts, and discontinuity orientation with respect to the slope face, rainfall, and seismic activity are factors that significantly affect slope stability in the quarry site. Based on the findings, the study recommends increasing the benching by multi-benched excavation systems with bench width and height of 8 m and 12 m, respectively, and reducing the slope angle to 650 of each bench with an overall slope angle of 460 as the most important aspects of stabilizing the critical slope sections of the quarry site.