Propagation of fissures and deformation and failure laws of karst slopes with deep and large structural plane mining action

Collapse and slide disasters frequently occur in high and steep karst mountainous areas in Southwest China. Long-term underground mining activities are one of the important inducements of the collapse and slide disasters in these areas. Under the action of mining, the expansion and evolution of deep and large structural plane at the back edge of the slope controls the stability and instability failure mode of high and steep karst slopes. On the basis of field geological survey, combined with indoor physical model tests and discrete element numerical simulation, the propagation and evolution laws of overlying rock fractures under underground mining disturbance are revealed, the control effects of deep and large structural plane on slope stability are expounded, and the failure modes of slope deformation are discussed. The results show that the influences of underground mining disturbance on slope stability are mainly reflected in the redistribution of overburden stresses caused by underground mining unloading and the propagation of fissures induced by mountain deformation. After underground mining, the slope body forms a "cantilever structure" on the two-dimensional section, and the original deep and large structural plane of the slope body controls the stability of the slope body. Under downward mining, the goaf range is in front of the fault, and the mountain height is small. Under the action of self weight, the "cantilever structure" rock stratum cooperates to deform towards the fault and goaf, and will not produce a large number of separation fissures. The coal seam roof only breaks and collapses and fills the goaf. After the goaf reaches the fault, the mountain at the left has collapsed and the mountain stresses are redistributed. The overburden forms a large number of tension fissures under the action of self weight, and the direct roof collapse height and fracture zone height also increase with the increase of goaf range. The evolution process of deformation and failure can be generalized as follows: underground mining unloading-stress redistribution→overburden fault subsidence-fissure propagation→slope fissure penetration-cantilever failure→deformation extrusion in the slope-rock bridge shear→overall instability failure of the slope.