Experimental Study on the Movement and Failure Characteristics of Karst Mountain with Deep and Large Fissures Induced by Coal Seam Mining

To investigate the temporal and spatial evolution process of overlying karst mountain instability caused by mining, the case of "8.28" mega landslide in Pusa, Nayong County, Guizhou Province, China, is taken as the example. Based on the results of the field investigation after the disaster, the complete process of rock strata fracture and slope instability under the descending and ascending mining conditions of gently inclined coal seam is reproduced by similitude model experiments. According to the key motion features of overburden deformation and fracture evolution law, the failure process of slope collapse controlled by deep and large karst fissures under mining action is summarized. And the change law of overburden pressure and displacement in the mining process is analyzed as well as the failure mode of slope collapse is proposed. The results show that the slope experiences four failure stages in the process of coal seam descending mining: coal seam roof caving, overburden cantilever tension fracture, overburden integral dumping subsidence and slope instability collapse, and the slope undergoes deformation toward the free surface and downward. During the ascending mining process, the slope experiences four failure stages: periodic caving of coal seam roof, upward transmission of separated fractures, overburden integral bending subsidence and slope instability collapse, and the slope undergoes deformation toward the inside of the slope and downward. The rock mass ahead of the advancing direction of working face has the phenomenon of tension-compression stress transformation. Along the mining direction, the overburden sequentially experiences the change process of pressure increase, decrease, or increase again, and stabilization. Deep and large karst fissures at the slope top are the structural basis for the occurrence of collapse. Coal mining activities have a certain promoting effect on mountain cracking and rock fragmentation. The failure mode of slope can be summarized as tension-shear-slip-toppling collapse failure. Improved understanding of the deformation movement characteristics and damage mode of slope can aid in early identification and timely warning of geo-hazards in karst area.