Coal-gas outburst, rock burst, and other mine dynamic disasters are closely related to the instability and failure of coal-rock. Coal-rock is the assemblies of mineral particles of varying sizes and shapes bonded together by cementing materials. The damage and rupture process of coal-rock is accompanied by acoustic emission (AE), which can be used as an effective means to monitor and predict the instability of coal-rock body. In this manuscript, considering the size effect of coal-rock, the influence of different height to diameter ratio on the acoustic emission characteristics of coal-rock damage evolution was discussed by microparticle flow PFC2D software platform. The results show that coal-rock size influences the uniaxial compressive strength, peak strain, and elastic modulus of itself; the size effect has little effect on the acoustic emission law of coal-rock damage and the effects of the size of coal-rock samples on acoustic emission characteristics are mainly reflected in three aspects: the triggering time of acoustic emission, the strain range of strong acoustic emission, and the intensity of acoustic emission; the damage evolution of coal-rock specimen can be divided into 4 stages: initial damage, stable development, accelerated development, and damage.

In order to solve the problems of roadway stability and easy instability under repeated mining of close-distance coal seam groups, the mechanism and control technology of surrounding rock instability under repeated mining were studied via indoor testing, field testing, physical similarity simulation experiment, and numerical simulation. The results show that the surrounding rock of roadway has low strength, low bearing capacity, and poor self-stabilization ability, and it is vulnerable to engineering disturbances and fragmentation. Affected by the disturbance under repeated mining, the roadway surrounding rock cracks are developed and the sensitivity is strong, and it is prone to large-scale loose and destroyed. The location of the roadway is unreasonable, and the maximum principal stress of the roadway is 3.1 times of the minimum principal stress, which is quite different. Thus, under a large horizontal stress, the surrounding rock undergoes long-range expansion deformation. On the basis of this research, the direction and emphasis of stability control of roadway surrounding rock under repeated mining of coal seam groups in close-distance are shown. A repair scheme (i.e., long bolt + high-strength anchor cable + U-shaped steel + grouting) is proposed, and reduces the risk of roadway instability.

To accurately detect the development height of the water flowing fractured zone (WFFZ) in the overlying strata of the working face after mining under water and to ensure the safety and reliability of coal mining, the coal seam located under Weishanhu Lake in the Jisan coal mine was used as the experimental system. A similar laboratory simulation and water injection-based fracturing test system were used with the working face before and after mining activity to calculate, quantitatively detect, and qualitatively analyze the development height of the WFFZ in the overlying strata. Meanwhile, a flow-stress-damage model and its criterion of fracture expansion were established based on the Mohr-Coulomb criterion, and the FLAC 3D software was used to simulate the deformation and failure of the overlying strata and the evolution of WFFZ during the mining process. The results showed that the height ranges of the WFFZ beneath Weishanhu Lake of the Jisan coal mine as established by the above three methods are 30-45 m, 30-48 m, and 30-50 m. In the process of mining, the caving zone and fractured zone are, respectively, subjected to tensile failure and shear failure. The development height of the water flowing through the fractured zone in the overlying strata is basically consistent with the range of the “breaking arch.” The flow-stress-damage model and its criterion of fracture expansion can be applied to the fracture law of overlying strata under water under similar geological conditions.