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.

The dynamic disasters of deep mining coal and rock mass are frequent and easy to be instable. Aiming at the deformation of coal-rock roadway under the coupled static and dynamic load, a new equipment which can simulate the actual situation dynamic environment is used to carry out the coupled static-dynamic loading test of coal-rock combination. The failure law and mechanical behavior of combination are studied. Test results show that weak structure significantly affects mechanical response of coal-rock combination. The coal part with lower strength firstly reaches the crack initiation stress. The strength of the combination is dominated by the coal part. The post-peak stage of the stress–strain curve under the coupled static and dynamic load presents a stepped reduction, which shows yield process. The dynamic load level has a significant effect on the mechanical behaviors of the combination. The elastic modulus decreases under dynamic loading. The peak stress of the combination is positively correlated with the dynamic load level in a certain range, and the peak strain was negatively correlated. The energy accumulation and dissipation are closely related to the failure of the samples. The strain energy is more concentrated in the area where the failure occurs first. The AE energy under dynamic load is developed from the traditional “four-stages” characteristic under static load to three stages. The interval release stage appears because of the appearance of intermittent disturbance load makes the AE energy of the sample change intermittently. The dynamic instability of samples accompanies a sudden increase in AE energy rate, hysteresis loop area and strain. Compared with the shear failure of single lithology sample, the failure mode of the combinations is mainly tensile, and it turns into tensile-shear failure under dynamic load. The fragmentation of samples is different under different failure modes. The fragmentation index can characterize the failure mode and crack propagation characteristics of coal-rock combination. The research provides reference for large deformation dynamic disasters of surrounding rock.

At present in China, short‐wall working face coal‐mining methods are among the main methods used for the high‐efficiency recoveries of boundary coal pillars and residual pillars. In traditional short‐wall mining methods, overlying roofs are supported by coal pillars. However, issues such as the excessive number of coal pillars, low coal recovery efficiency, large areas of hanging roof arches, etc, have been encountered. In view of the aforementioned issues of the current short‐wall mining technology, this study took the short‐wall mining of the Yujialiang Mine in the Shendong mining area as the project background. The study then proposed a judgment method for the key stratum on the working face of the mine using a short‐wall continuous mining and full‐caving method. The proposed method was based on the theory of elastic plates and was verified using the theoretical analysis results of similar material simulation experiments. FLAC 3D software was adopted to analyze the stress and displacement evolution processes of the overlying rock strata during the advancement of the working face using a short‐wall continuous mining and full‐caving method. The results showed that the short‐wall continuous mining and full‐caving method not only had the ability to improve the recovery rate, but was also able to realize the effective control of the roof areas, thereby avoiding any large areas of hanging arches. The short‐wall continuous mining and full‐caving method is potentially of important significance for the improvement of coal recovery rates, as well as for the safe and highly efficient mining of boundary coal pillars and residual pillars in mines under special conditions.

The large-scale extraction of coal resources in the western mining areas of China has resulted in a significant loss of water resources, which is a challenge for coordinating resource extraction with ecological preservation in the mining areas. Although underground reservoir technology can effectively solve this problem, measuring the storage capacity of underground reservoirs through engineering experiments is costly and time-consuming. Currently, there is a lack of accurate, reliable, and low-cost theoretical calculation solutions, which greatly restricts the promotion and application of underground reservoir technology. The theoretical calculation methods for underground reservoir capacity were studied based on parameters from the Shendong mining area in China. A water storage structure model for coal mine underground water reservoirs was established, taking into account the settlement boundaries of the bedrock and loose layers in shallow coal seams, based on the key layer theory and the spatial structure model of the mining roof. The mathematical expression for the load on the coal-rock mass in the goaf was derived considering the rock breaking characteristics of the mining roof. The model determined the range of each water storage area, including the zone of loose body, zone of gradual load, and the compacted zone, based on the strength of the water storage capacity. The key parameters for calculating the water storage capacity were determined using a modified model for shallow thick loose layers and thin bedrock movement. Finally, a calculation method for the storage capacity was obtained. Based on the real data from the 22,615 working face of a mine in the Shendong mining area, the water storage capacity of the underground reservoir in the goaf was jointly calculated using FLAC^3D, Surfer 12.0 and the proposed calculation method. The calculated water storage capacity was approximately 1.0191 million m³. Although this result was 2.20% smaller than the on-site water pumping experiment data, it still verifies the feasibility of the above calculation method for determining the water storage capacity of underground water reservoirs.

The instability of mine pillars has posed a serious threat to the safety of mines in China. In order to reduce the risk of pillar instability, this study used fiber-reinforced polymer (FRP) to reinforce gypsum specimens and conduct mechanical loading experiments. The study investigates the reinforcement effect of gypsum specimens with different height-diameter ratios and different FRP wrapping thicknesses, and analyzed the uneven distribution of constraint force along the height direction of FRP-reinforced gypsum specimens. An optimized wrapping method was proposed, and a stress–strain constitutive model for gypsum materials under optimized wrapping was established. By utilizing a statistical method based on strain energy density for heterogeneous rock damage identification, a simulation study was conducted on FRP-reinforced gypsum-like specimens. A comparative analysis was carried out with experimental results to verify the feasibility of the constitutive model. The research findings indicate that the use of FRP reinforcement significantly improves the uniaxial compressive strength and strain values of gypsum-like specimens. Moreover, the smaller the aspect ratio, the more pronounced the effect of FRP reinforcement on gypsum-like specimens. The stress–strain curve of FRP-reinforced gypsum-like specimens shows a distinct combination of curves and straight lines, which can be divided into two distinct stages based on different elastic moduli. The peak value of acoustic emission energy of FRP-reinforced gypsum specimens appears at the junction of the first and second stages of the stress–strain curve, and then the acoustic emission energy curve becomes relatively flat, with an increase in peak energy before failure. The constraint force acting on FRP-reinforced gypsum specimens exhibits an obvious uneven distribution along the height direction, based on which an optimized reinforcement scheme is proposed. Based on the established constitutive model, numerical simulation was conducted using real data from a specific mine. The research findings demonstrate that when the optimized reinforcement method is employed, the load-bearing capacity of the mine pillars was significantly enhanced. The maximum displacement was reduced by 33%, the maximum vertical stress was reduced by 3.2%, and the volume of the plastic zone was reduced by 39.87%.

Highwall mining, which is referred to the technique of extracting coal from the bottom of an exposed highwall, features safety, efficiency, and economy. According to existing highwall mining methods, the mining sequence has a great influence on highwall stability. Based on a highwall mining project in Australia, this study adopted the FLAC^3D numerical simulation method to investigate the stability of coal pillars with different mining sequences. The results show that different mining sequences of boreholes exert a great effect on highwall stability. Compared with sequential mining, the skip mining method achieves higher speed of highwall stabilization and smaller plastic zone of coal pillar with its maximum strength decreasing by 12. By adjusting the mining sequence scientifically, the coal pillar failure and roof collapse caused by the deviation of mining angle can be avoided. The results may provide a new angle for the studies on the coal pillar layout and stability design in highwall mining.