A new insight of water inrush mode and coal (rock) pillars setting in near-fault mining under high confined water

Mining-induced fault water inrush has become the most critical disaster-causing factor of mine water disasters in mines in recent years. In near-fault coal mining, the water flowing fractures caused by mining in the roof (floor) of a coal seam may connect the fault fracture zone and induce fault water inrush. The most effective way to prevent fault water damage is to set waterproof coal (rock) pillars. However, the width of coal (rock) pillars was mainly calculated by empirical formulas in the past, and the calculated results were quite different from the actual ones. This paper determines the safe water blocking zone and inelastic zone by introducing mine pressure and confined water pressure ("double pressure"). Then, the range of the mine pressure failure zone is determined by comprehensively considering the floor strata's peak stress propagation direction and the roof strata's collapse propagation angle. The hydraulic model of roof (floor) water inrush in near-fault coal mining under "double pressure" control is established. A new method for calculating the width of waterproof coal (rock) pillars in coal mining on large normal faults is derived by considering the nature of the fault, mine pressure, and confined water pressure. Finally, the research results are applied to the width calculation of waterproof coal (rock) pillars in the Jiaxiang branch fault of Xinhe Coal Mine, and the FLAC3D software is used to conduct numerical simulation and check the calculation of the pillars' width of coal (rock) under the influence of mining. The formation mode of fracture channels in the roof (floor) of a coal seam in near-fault mining is proposed, and the failure theory of surrounding rock in near-fault mining is perfected. The research results will effectively guide the layout of the near-fault working face on the Ordovician limestone confined aquifer in North China Coalfield, liberate a large number of resources threatened by fault water damage, and provide a theoretical basis for the prevention and control of mine fault water damage under other similar geological conditions.