Study on mining water inrush mechanism of buried fault under coal seam floor above confined water body

Due to the wide distribution, large quantity, strong invisibility and difficult detection, the activated water inrush of buried fault on the bottom strata has become one of the main forms of deep mining water inrush. According to the development scale and spatial location of buried fault, three modes of water inrush are summarized: water inrush due to connection of floor and buried fault, water inrush of upper and lower buried fault. According to the water inrush mode of the floor of buried fault at the bottom of coal seam above stressed water body, the development of induced floor stress during mining, the extension of buried fault and the evolution of water inrush passages during coal mining are studied by mechanical analysis, physical simulation of floor water inrush and FLAC3D numerical modelling. The results show that with the advance of working surface, the floor rock close to the coal seam is subjected to a compression-unloading-recovery process forming mining-induced failure zone. The stress within the floor is horizontal “S” shape with a boundary of the working face. Under the effect of mining-water pressure-buried fault, the buried fault blocks the extraction-induced stress with the movement of the working face. The degree of damage of the mining pressure-hydraulic pressure of the buried fault is earlier and more serious which is more likely to induce the development of water conducting fractures. The pre-existing fractures of buried fault expands and develops upward in the opposite direction of advance of the working face, forming the water inrush passages by connecting with the mining-induced destruction zone. The rise of the pressured water is closely related to the mining fracture development. The rise intensity of mining-induced pressured water and the range of strong seepage area develop gradually with the advance of the working face. The buried fault mining area above the hidden fault. The amount of water increases gradually with the advance of the working surface. On the basis of the division of the floor with buried fault into “buried fault mining activation area, water blocking area and mining-induced area”, the water inrush mechanism of floor containing buried fault above the pressurized water is revealed.