Numerical simulation of quarry wall stability considering the fault location in the bottom part

Purpose. The research aims to assess the impact of geological disturbances located in the bottom part of the super-deep Kacharsky Ore Quarry on the stress-strain state (SSS) of its walls and to determine the safety factor of the walls, taking into account the complex geological situation. Methods. Fault plane modelling methodology is based on 3D finite-element analysis using the RS3 Rocscience software. Fault zone is represented by a medium with a system of fractures. Fracture characteristics, such as openness, contact filler type, and surface quality are achieved by selecting the normal and shear stiffness of the contact. The strength and deformation properties of rock inside the fault zone are defined by low geological index values (GSI = 20), corresponding to the “poor” quality mass according to the Hoek-Brown classification. The main mass outside the fault zone is represented by elastic-plastic medium, where the transition to inelastic deformation stage is determined by the Mohr-Coulomb failure criterion. Findings. FEM-analysis of the stress-strain state of the Kacharsky quarry walls at various stages of mining, taking into account faults in its bottom part, provides a safety factor (FoS) that is 28-30% lower than that obtained without considering the faults. Parametric analysis shows that for normal stiffness values of the fracture-filling material up to 2.5 GPa/m, the difference in the realized shear strains is most significant. When the Er index, which characterizes the ratio of material stiffness inside and outside the fault zone, decreases from E_r = 0.2 to E_r = 0.05, the maximum shear strains in the bottom part of the quarry increase from 0.05 to 0.075, that is, by 50%. Thus, a weaker and more disintegrated medium in the fault zone provokes the development of shear strains and causes a decrease in the stability of the walls. Originality. For the first time, under real mining-geological conditions of deep ore quarry, a pattern of change in safety factor of steeply sloping walls has been identified, taking into account geological faults in the bottom part of the quarry. A dependence of shear strains on the normal stiffness index of fractures and the ratio of stress-strain modules of the rock medium inside and outside the fault zone has been found. Practical implications. The wall safety factor (FoS) value at each stage of mining is a key parameter for adoption of technological decisions and regulations. The established fact that the stability of the walls has decreased to a critical level (FoS = 1.1) at the final stage of mining due to the presence of faults may serve as a basis for revising the technological scheme of ore mining at the final stage, in particular, to reduce the slope angle of the benches.