The Effect of Geometrical Features of Release Surfaces on the Stability of Tectonically Disturbed Deep Rock Slopes in an Albite Open Pit Mine

Abstract

An albite deposit formed in orthogneiss has been operated using open pit mining process since 1996. However, landslides have occurred following the excavation works and heavy rainfalls. In the current state, the slopes are still susceptible to mass movement. For this reason, this study aimed to determine the root causes that are influencing continuous movements. In this context, two geometric features of the strike-slip faults that form tectonic slices in the pit were proposed. The first one (α-angle) is the acute angle between the dip direction of the overall slope and the general trend of the strike-slip fault and it was used for the kinematic evaluation of the sliding potential of the tectonic slices. The validity of α-angle was confirmed by investigating its relationship with the factor of safety values. The second one (undulation angle, i) was used to determine the effective surface friction angle (ϕeff). Thereafter, ϕeff value was used in the deterministic finite element (FE) slope stability analyses as well as back analyses. Its effect on the stability of overall slopes was investigated for static and pseudo-static conditions with different water table levels. The FE results confirmed the monitored field displacement measurements. It was found that as α-angle decreases, the ability to resist sliding also decreases since the low α-angle promotes block formation. This study also demonstrated that using the undulation angles on mapped profiles of large-scale discontinuities (≥270 m) would be a promising approach for slope stability assessments of open pit excavations in tectonically disturbed metamorphic rocks.