Water-inrush Risk through Fault Zones with Multiple Karst Aquifers Underlying the Coal Floor: A Case Study in the Liuzhuang Coal Mine, Southern China

The deep Liuzhuang coal mine faces a risk of water-inrush from multi-layer Carboniferous and Ordovician karst aquifers below the coal floor. We analyzed the permeability of a major fault by in-situ water injection tests and found that its overall permeability was low. The hydraulic conductivity of test sections ranged from 3 × 10–4 to 7 × 10–4 m·d−1, with a maximum injection pressure of 1 Mpa. An analytical model of fluid–solid interaction was used to express the influence of mean principal stress and pore pressure on rock permeability, and a 3D numerical model of a pseudo-inclined working face was built to analyze the inrush risk of minor fault zones with varied occurrences and locations. The simulations showed that the risk of a delayed water inrush through the fault zones after fault exposure was greater than that of an instantaneous inrush. The risk of an inrush through the fault zone was greater near the middle of the working face than near the upper roadway; the risk of an inrush through the fault zone near the lower roadway was relatively small.