Study On Water Inrush Mechanism And Seepage Effect Of Coal Floor By Coal Mining

The plastic failure scope of mining face was analyzed by elastic-plastic theory and Griffith criterion. Based on the plastic failure scope, the mechanical model of the plastic failure scope of mining floor was established by slip line field theory. A theory analysis method of the plastic failure scope and the maximum floor damage depth was carried out by the model. The relationship about depth of broken floor and its affecting factors was analyzed. The floor was simplified as elastic beam. Taking the pore pressure into consideration, the critical damage variable Dc was determined. Mechanical model of fracture was developed by fracture mechanics, and the calculation formula of the stress concentration factor at the floor initial crack tip was determined. Finally, the crack propagation was analyzed by damage and fracture. The calculation formula of the initial crack propagation’s release rate of damage fracture energy was developed by simplify some parameter. Finally, the effective confining bed thickness was determined. The stress-permeability model of floor fractured rock in stope was established by preferred crack angle of fracture mechanics theory, and in initial rock stress, the angle of fractured rock was determined. Based on stress-permeability model of floor fractured rock in stope, in plane stress state, the equation of permeability variation was developed by the mechanical model of fracture mechanics in stope. The relationship about permeability coefficient and its affecting factors was analyzed. It could provide a theoretical basis for prediction of water inrush from floor.The numerical simulation of different advancing distance and the different lithology of confined aquifer based on FLAC3D were applied. The distribution of plastic yielding area of stope was analyzed. The characteristic distribution of stress of along the direction and tendency of the working face was studied. The distribution law of stress of different distance from coal floor was analyzed. The characteristic distribution of displacement was studied. The distribution law of stress along the direction of working face was analyzed through the numerical simulation of different width of working face.