Investigation on failure characteristics and water inrush risk of inclined floor mining above confined aquifer

The exploitation of coal resources in China is seriously threatened by water hazards. A coupled hydrornechanical modeling ning above a confined aquifer with FLAC3D was carried out to numerically investigate the fractured behavior of inclined floor and water outburst risk. Based on the double-end plugging leak detection device, the in-situ testing of mining-induced damage depth was implemented, Furthermore, the mechanical model of inclined water-resisting key strata was constructed to theoretically calculate the stability of inclined floor under the synergistic action of the roof caving rock mass, floor mining-disturbed rock mass and non-uniformly distributed confined aquifer. Results show that obvious three-zone failure characteristics in an asymmetric state are formed in the inclined floor after excavation. The mining failure zones along the strike and inclination are approximately spoon-shaped and upper small and lower large inverted saddle-shaped, respectively, and the maximum failure depth of numerical simulation with 16.71 m is approximately equivalent to the measured result of 15.49 m. The theoretical calculation shows that the pre-failures of inclined water-resisting key strata are not located in the middle of its boundary, but occur near the normal intersection points between the curves passing through the maximum deflection position and the right or lower boundary, The pre-failure areas may intersect with each other along the boundary, and gradually extend to the whole inner region of the aquifer. The water inrush location and risk of inclined water-resisting key strata calculated by the theoretical model are in good agreement with that of numerical simulation. The research results in this paper can provide some theoretical guidance and reference for the evaluation and safety control of floor water inrush under mining with pressure.