Influence of repeated multi-seam mining on the deformation-failure mechanism and fracture network evolution in slopes of varying geometry

In mountainous environments, frequent underground coal mining activities can readily trigger collapse and landslide hazards, while complex topographic and geomorphological conditions further lead to diverse and complex deformation and failure modes of slopes. However, studies on the deformation evolution and failure mechanisms of mining-induced slopes with different geometries remain scarce. This study constructed three generalized models of mining-induced slopes, namely linear, concave, and concave-convex slopes. By combining numerical simulations combined with multi fracture index evaluation, this study systematically elucidates the deformation-failure mechanisms and fracture network evolution of these three slope types under repeated mining conditions. The results indicate that the deformation-failure modes for linear slopes are goaf caving， subsidence， creeping slip， tensile fracturing， shear sliding; for concave slope, goaf caving， subsidence， tensile fracturing， slip， bending， shearing， sliding; and for concave-convex slope, goaf caving， subsidence， tensile fracturing， toppling， shearing， ollapse. As mining advances, the fractal dimension (D) shows a “step-like” increase, the probability distribution index (b) first increases and then decreases, and the fracture number (Nf), fracture rate (Rf), and fracture entropy (Kf) increase continuously. The evolution of the fracture network can generally be divided into three stages: a rapid development stage of multiple forms (detachment fractures, vertical fractures, inclined fractures), a steady expansion stage and a compaction stage (accompanied by the formation of a small number of new faults). Under repeated mining, the fracture network undergoes a cyclic process of formation → expansion and interconnection → widening → compaction. The findings provide a scientific basis for establishing early warning criteria and implementing targeted prevention and control strategies for mining-induced slope hazards.