Evaluations of the risk of fault-induced water inrush hazard is an important issue for mining engineering applications. According to the characteristics of the seam floor during mining advancing, a mechanical model of fault activation is built to obtain the equations of normal stress and shear stress on the surface of fault, as well as the mechanics criterion of fault activation. Furthermore, using FLAC^3D numerical software, the stress variation on the surface of fault under two different mining advancing directions are numerically simulated, and the distribution characteristics of the plastic failure zone of the roof and floor near the fault are obtained. The results show that: (1) When mining advances from the hanging wall, the normal stress increases more greatly than that from the foot wall, the shear stress distribution changes drastically with a large peak, and it is more likely to cause fault activation. (2) When mining advances from the hanging wall and approaches the fault, the normal stress and shear stress within the fault first increases, and then decreases suddenly. When mining advances from the foot wall, the normal stress and shear stress increases constantly, and the fault zone stays in the compaction state where the hanging wall and foot wall are squeezed together, which is unfavorable for water inrush hazard. (3) When mining advances from the hanging wall, the deep-seated fault under the floor is damaged first, and the plastic failure zone of the floor increases obviously. When mining advances from the foot wall, the shallow fault under the floor is damaged first, and the plastic failure zone of roof increases obviously. (4) For a water-conducting fault, the waterproof coal pillar size of the mining advancing from the hanging wall should be larger than that from the foot wall. (5) The in-situ monitoring results are in agreement with the simulation results, which proves the effectiveness of the simulation.

In order to study the water inrush mechanism of faulted rock mass, a series of erosion seepage experiments were carried out to test the non-Darcy hydraulic properties of a limestone and mudstone mixture. The test results are employed to verify and modify a classic permeability prediction model. Based on the evolution of mass loss rate, the erosion process can be divided into four stages, i.e., particle rearrangement, severe erosion, mild erosion, and stable seepage. During the erosion, the sample height decreases gradually, the water pressure at outlet grows first and then keeps stable, and the porosity and permeability decrease slightly first, then grow gradually and finally keep stable. The hydraulic properties show a more significant variation in the sample within high mudstone particle contents. Through the comparison of test results and the predicted results by the classic Carman-Kozeny model, it is found that the accuracy of the model is greatly affected by lithology. Based on this investigation, a revised model is proposed which introduces a proportional coefficient related to the rock composition, so as to increase the predicted precision in variable rock composition. The forecast accuracy of the revised model is much higher than the classical one in permeability although it decreases with the increase of mudstone content.

To study the seepage and fracture characteristics of cemented rock strata, a series of triaxial seepage tests on cemented rock samples under different confining pressures and water pressures were carried out in this study. The triaxial strength, elastic modulus, volume strain, and the permeability of the cemented rock samples were analyzed by the seepage unit connection probability model and Kozeny-Carman model. Based on test results, the stress state of cemented rock samples was divided into four stages: nonlinear compaction stage, linear elastic stage, stress yield stage, and failure and postfailure stage. The triaxial strength of the cemented rock samples gradually increased with the increase of confining pressure but decreased with the increase of water pressure. The elastic modulus of the cemented rock sample increased with the increase of confining pressure but decreased with the increase of water pressure. Besides, the volume strain of the cemented rock sample was analyzed, and the volume strain change of the cemented rock sample was also classified into three stages: the increasing stage of crack volume strain, the stable stage of crack volume strain, and the decreasing stage of crack volume strain. Based on the results of triaxial seepage tests, the evolution of permeability was divided into the declining stage, increasing stage, and redescend stage. Through the seepage unit connection probability model and Kozeny-Carman model, the evolution of crack volume was obtained, and the evolution of crack volume with axial strain was also classified into three stages: the original pore closure stage, crack network expansion stage, and crack network closure stage. The permeability evolution and the crack volume evolution were also compared. The comparison results suggest that three stages of crack volume evolution are all ahead of three stages of permeability evolution, verifying that the crack propagation induces the formation of seepage channels in cemented rock samples. This research will provide a valuable reference for the study of instability and water inrush mechanism in cemented rock strata.