Disaster-causing process of steep columnar karst mountain collapse induced by mine mining -Taking Guizhou Yiziyan Collapse as an Example

To reveal the collapse disaster mechanism of steep columnar karst mountains under mining disturbance, this study taking a typical“hard-top, soft-bottom; steep-top, gentle-bottom” collapse body at Yiziyan, Jinsha County, Guizhou Province as the research object, systematically analyzes the entire deformation and failure process of the slope under multiple mining activities. It is based on field geological surveys and laboratory rock mechanics tests, conducting bottom friction physical simulation experiments, combined with PhotoInfor digital imaging system for quantitative monitoring of slope deformation and displacement. The results indicate that slope deformation caused by mining disturbance presents a four evolution stages pattern. During the initial unloading and joint development phase, unloading rebound occurs in the roof above the goaf, forming joint zones and collapse bands. The displacement areas shows a crescent-shaped distribution and has a relatively minimal impact on the slope surface. At the overburden overall subsidence and slope surface response stage, the overall collapse of roof causes significant subsidence of the surface slope, the deformation of overburden continues to intensify and extends to the slope crest area. In the fissure expansion and stress redistribution stage, mining induces secondary roof unloading rebound, causing the joint zones and collapse bands to develop further upward, promoting this reactivates and widens existing dissolution fissures at the slope crest. During shear failure and overturning collapse stage, the compressive shear stresses at the bottom of the rock mass is highly concentrated to form a continuous shear failure plane. The slope surface experiences intense compressive shear failure, with rear-edge tensile fractures progressively worsening. Ultimately, the steep inclined columnar unstable rock masses collapses toward the open face. The evolution of the shear strain field indicates that the maximum shear strain during mining process gradually increases from an initial value of 1.2 to 1.7. The stress concentration zone expands from within the collapse zone to the vicinity of the slope top fractures and the vertically overlapping regions of multiple mining voids. This study has confirmed that progressive deformation and stress redistribution of the overburden caused by multiple mining activities are the key mechanisms controlling the instability of columnar rock masses. The bottom friction combined with digital image measurement technology can effectively reveal the four-stage evolution pattern-“initial unloading- overburden overall subsidence - fissure expansion -shear overturning”-under mining influence, clarifying the deformation characteristics and mechanical response mechanisms at each stage.