Jun Li

Underground mining disturbance alters the initial stress state of rock masses and is an important factor triggering large-scale slope failures in karst mountainous areas. In the karst mountains of southwestern China, dual-layered geological structures composed of carbonate rocks and clastic rocks are widely developed. However, studies integrating lithological combinations, structural discontinuities, and the transmission of mining-induced disturbances into a hierarchical identification framework remain limited. Based on data from 29 representative cases, the deformation and failure characteristics of mining-affected slopes are analyzed, and a hierarchical failure-mode identification framework controlled by dual-layered geological structures is proposed. First, according to stratigraphic structural characteristics, mining-affected slopes are divided into two basic structural types: hard-over-soft and alternating hard–soft strata. These types are further classified according to the development of karst-related structural discontinuities, deformation characteristics of the basal layer, and failure evolution sequence, resulting in nine typical failure modes. Case analyses indicate that lithological combinations and structural discontinuities jointly control slope deformation under underground mining, while deformation of weak basal layers and propagation of karst-related structural discontinuities are key factors governing different failure modes. The identification framework provides a theoretical basis for hazard investigation and identification, mechanism analysis, and risk prevention and control of mining-induced slope failure hazards.

Deep excavation reduces lateral confinement and can increase tangential stress, promoting brittle failure in highly stressed rock. However, the effects of bolt number and spacing on mechanical response and damage evolution under this stress path remain insufficiently understood. In this study, parallel RFPA^3D simulations were conducted for true-triaxial single-face unloading followed by continued axial loading, assuming perfect bonding at the bolt–rock interface. Two parameter series examined bolt numbers from zero to four (M0–M4) and bolt spacings from 10 to 80 mm. Stress–strain response, acoustic emission activity, failure morphology, damage area ratio (A_d), and box-counting fractal dimension (D_f) were analysed. Bolt reinforcement increased post-unloading peak stress and restricted the inward extent of damage, while damage persisted near the unloaded face and within the inter-bolt regions. Peak stress increased from approximately 345 MPa in M0 to 363 MPa in M3, then decreased slightly to 358 MPa in M4, showing that reinforcement gains were not proportional to bolt number. Bolt spacing had a modest effect on peak stress but a clearer influence on damage continuity and inward extent. Among the tested spacings, the 40 mm case (D40) achieved the highest peak stress of 370.0 MPa and the lowest A_d of 23.85%, with a low D_f of 1.431. In contrast, the 80 mm case (D80) exhibited more extensive and spatially complex damage (A_d = 30.78%, D_f = 1.677). A_d and D_f provided complementary descriptions of damage extent and spatial complexity. These numerical results provide a quantitative basis for comparing reinforcement configurations under the investigated specimen-scale conditions.