Abstract: Based on the mine ground pressure and strata control theory, spatial distribution characteristics of ground pressure and floor water pressure around mining field have been analyzed in this paper, and then the mechanical effects of both these pressures on the coal floor have been determined. By setting up mechanics model, the effects of ground pressure and water pressure on a set of tilted cracks have been studied from a microcosmic point of view. Based on the thin plate theory, the effects of water pressure on the effective water-resisting layer have also been studied from a macroscopic point of view. Finally, a theoretical formulae of limiting hydraulic pressure has been deduced. The results have shown that the increase of abutment pressure can lead to the decrease of permeability coefficient; the increase of water pressure can cause the attenuation of rock mass strength and the increase of fissure length. The essence of water inrush in mining field is the result of propagation of micro-cracks and fracture damage of the effective water-resisting layer caused by ground pressure and water pressure.

Key words: abutment pressure, water pressure, micro-cracks, the effective water-resisting layer, mechanism of water inrush