Investigation on the mechanism of grouting and seepage reduction reinforcement of fault-cut karst collapsed column

The combination of faults and karst collapsed columns forms a fault-cut karst collapsed column, which will form a dominant fracture water-conducting channel inside the karst collapsed column, and there is a large risk of water inrush from the Ordovician limestone aquifer. Through theoretical analysis, indoor simulation test and field data verification, the movement law of grouting slurry in karst collapsed column and the mechanism of seepage reduction and reinforcement were studied. The results show that the grouting slurry of karst collapsed column is limited by the boundary of the column and the fault cutting fracture. Under the combined action of grouting pressure, column weight and water pressure, the grouting slurry is mainly filled and diffused along the column and the fault cutting fracture to form the slurry vein skeleton. The slurry movement model was established and the theoretical formula was deduced. Combined with the on-site grouting parameters of 9 − 6 karst collapsed column in Hemei No.9 Coal Mine, the diffusion distance is 23.82 m. The mechanism of grouting and seepage reduction of karst collapsed column based on fracture closure was proposed. Under the limitation of the boundary of the column and the surrounding conditions of the fracture, the high-pressure slurry squeezed the filling of the column and caused the fracture to be closed, so as to realize the sealing of multiple fractures at the same time, thereby reducing the water yield of the column. The grouting reinforcement mechanism of karst collapsed column based on stress enhancement was explained. The high-pressure slurry increased the density of the column filling by seepage extrusion under the boundary conditions of the column boundary and the surrounding constraints of the fracture to increase the column stress of the karst collapsed column, increase the horizontal support stress of the column to the surrounding rock and the vertical stress of the lower high confined water. The research results are of great significance to guide the design and construction of grouting boreholes in karst collapsed columns, improve the grouting treatment effect of large-scale water-conducting channels like karst collapsed columns, liberate coal resources in karst collapsed columns, ensure coal mine safety production and maintain the ecological environment of mining areas.