Mining of the coal seam adjacent to the extracted coal panel is widely practiced in China to improve coal resource recovery rates, but the energy change associated with longwall mining may present a new risk to ground stability and gateroad failure. To understand the energy change effectively, a meticulously validated numerical model, built using FLAC3D software, incorporating a double‐yield model for the gob materials and a strain‐softening model for the coal/rock masses, was developed to investigate the energy redistribution in coal seams and barrier pillars during the process of mining the coal seam adjacent to the extracted coal panel. The model results showed that the closer the region was to the LW 5301 gob, the higher the location and magnitude of the peak strain energy density. Consequently, the risk of rockburst in coal seams was greater than that in barrier pillars. Along the coal seam strike, with increasing advancing distance from the setup room, the magnitude of the peak strain energy density gradually increased to 1.88‐2.78 times the premining energy level. In addition, along the coal seam dip, the maximum distance from the peak strain energy density to the edge of the coal seam was approximately 16‐28 m, which is greater than that in the barrier pillar. The proposed numerical simulation procedure and calibrated method could be a viable alternative approach to evaluate longwall mining‐induced energy changes.

In view of the problem that the evolutionary mechanism of bit temperature during the drilling process is still unclear and the influencing factors are complex, this paper analyzes the causes of heat generation and the factors of heat production when the drill bit interacts with the coal and rock mass. Considering the stress field distribution of coal and rock mass and the dynamic characteristics of drilling, a three-dimensional mechanical structure model of bit drilling is established in this paper, based on the energy conservation theory and introducing the friction heat micro-distribution mechanism. The corresponding relationship between coal stress and the bit temperature variation rate is obtained in this paper. Therefore, the temperature rise condition model and the coal stress identification model can be verified, combined with the existing experimental data. The result shows that the temperature of bit drilling is affected by factors such as bit geometry and drilling parameters, as well as the strength and stress state of the coal and rock. Without considering other factors, the rate of increase in bit temperature is proportional to the stress of the coal and rock mass. Based on the research results, the temperature rate of the drill bit can be used as an index to identify the stress areas of coal and rock mass. Research results provide a theoretical basis for the identification of high-stress risk areas in coal mines.

The fracturing of high-position, thick, and hard roof strata overlying deep coal seams generates dynamic stress waves that can trigger rockbursts in stopes. The fractured zone serves as the primary pathway for wave transmission from the source to the stope. To investigate the propagation behavior of stress waves within fractured rock masses, this study employs a combination of split Hopkinson pressure bar (SHPB) testing and FLAC^3D numerical modeling to analyze the attenuation characteristics of stress waves in fractured sandstone of varying sizes. The findings reveal the following: (1) Under dynamic loading, the failure mode of fractured specimens significantly differs from that of intact specimens. As the size of the fractured sandstone increases, the transmission coefficient decreases while the energy dissipation ratio increases. When the impact velocity rises from 7.5 m/s to 12.5 m/s, the transmission coefficient and energy dissipation ratio of fully fragmented specimens increase by 27.3% and 13.3%, respectively; for moderately fragmented specimens, the increases are 22.9% and 14.7%. (2) The propagation of dynamic stress waves from the overlying strata to the mining site can be categorized into three stages: stress wave initiation, propagation through intact rock, and propagation through plastic rock. In the plastic rock stage, stress wave attenuation is markedly more pronounced than in the other stages. The peak particle velocity of the surrounding rock decreases by 33.8%, and the attenuation rate of elastic strain energy reaches 47%. (3) Numerous discontinuities within the fractured sandstone induce multiple transmissions and reflections of dynamic stress waves, resulting in significant energy loss. The intensified fragmentation of the sandstone further dissipates wave energy, which constitutes the primary cause of the substantial attenuation of dynamic stress waves. (4) In designing rockburst prevention measures for mining stopes subjected to strong dynamic stress, it is essential to implement zoned pressure relief in the overlying strata. By regulating the degree of overburden fragmentation, the propagation paths of dynamic stress waves can be progressively disrupted, thereby reducing their impact on the stability of the surrounding rock at the mining site. The research findings may serve as a valuable reference for the prevention and control of rockburst disasters induced by dynamic stress waves in deep mines.

To investigate the load-bearing behavior and damage evolution characteristics of the grout–sandstone composite structure formed by the consolidated grout and overlying key stratum after bed-separation grouting under mining-induced stress disturbances, uniaxial compression and multilevel cyclic loading–unloading tests were conducted on grout–sandstone composites with different height ratios. The failure modes, mechanical responses, acoustic emission (AE) characteristics, energy evolution, and cumulative damage behavior were comprehensively analyzed. The results show that the grout–sandstone composites exhibit a significant height-ratio effect, with the peak strength of the G40-S60 specimen being 51.06% higher than that of the pure grout specimen. Under multilevel cyclic loading–unloading, the peak strengths of the specimens decrease by 1.73%~24.52% compared with those under conventional uniaxial loading. The high-strain zones progressively expand with increasing stress levels, while cyclic disturbance promotes local irreversible deformation and damage accumulation, causing the composites to evolve from localized instability under monotonic loading to progressive deterioration. The energy evolution exhibits a clear loading path dependence, and significant differences are observed in the partitioning of elastic strain energy and dissipated energy among specimens with different height ratios. The damage variable established based on cumulative dissipated energy exhibits distinct stress-level-triggered and stepwise increasing characteristics. These findings provide a theoretical basis for evaluating the stability of the grout–key-stratum composite supporting structure after bed-separation grouting and for assessing the effectiveness of grouting reinforcement.