The Wumeng Mountain area exhibits complex geological conditions, where the development of Wumeng Mountain area exhibits complex geological conditions characterized by widespread boot-shaped dual-structure slopes (hard upper layer/soft lower layer, steep upper section/gentle lower section). Intensive underground coal mining superimposed with seasonal freeze-thaw-rainfall interactions triggers high-frequency and high-impact landslides and rockfalls during winter seasons. Taking the mining-induced collapse at Toutun in Zhenxiong County as a case study, geological structural features of the mining-disturbed slope were analyzed through field investigations and airborne LiDAR (light detection and ranging) technology. Deformation and failure processes were reconstructed using the discrete element numerical simulation method (particle flow code in 2 dimensions, PFC^2D), and an early warning threshold was proposed based on an improved tangent angle theory. The results show as follows. The Toutun collapse follows a four-stage chain mechanism: mining disturbance-roof collapse-rear tensile cracking-shearing failure. Coal extraction triggers stress redistribution, causing roof collapse. extrusion of the upper slope toward free faces initiates vertical tensile cracks at the rear. fracture networks progressively fragment the rear scarp rock mass, which extrudes along weak layers before collapsing toward steep free surfaces. The early warning threshold for mining slopes should be set at the uniform deformation stage (tangent angle 25.42°), significantly earlier than traditional critical failure criteria (45°). A novel instability mechanism is established by integrating the “thermal gradient effect” and “lid effect” theories, revealing three pathways for winter slope failure in mining areas. This research provides a quantifiable theoretical framework for early warning systems and mechanistic studies of mining-induced slope instability in seasonal freezing regions.