Using gangue backfilling in underground coal mining not only controls the roof deformation in the gob area but also reduces the amount of mining waste rock. However, due to the limitations of the complicated engineering conditions, backfilling mining in the steep coal seam is not widely applied. In this study, a long-distance backfilling technology with a scraper winch for a steep coal seam was proposed and applied in a flexible shield supporting working face in Datai Mine, Beijing. Aiming at the problem of the decreasing backfilling ratio in field practice, numerical simulation was carried out to research the moving law of gangue in the goaf. The gangue mainly experienced four stages: gangue landslide stage, small-scale subsidence stage, funnel-shaped subsidence stage, and large-scale subsidence stage. The moving area of the gangue could be divided into five areas including a motionless area, a landslide area, a subsidence area, a funnel-shaped subsidence area, and a to-be-backfilled area. With the increase of the inclined length of the working face, the moving time of the gangue increased gradually. Based on the simulation results, the scheme of backfilling and mining in Datai Mine was optimized, for which the inclined length of the working face was shortened, and a higher backfilling ratio was obtained.

Large‐diameter borehole destressing technology is one of the main technical measures for the prevention and control of coal mine rock burst. In engineering practice, there is generally a contradicting problem due to the presence of excess destressing which damages support system and insufficient destressing which results in high stress hardly transfer. In this paper, the mechanism of large‐diameter borehole destressing technology and its influence on anchorage support were simulated and analyzed. Based on this, a segmented enlarged‐diameter borehole destressing technology was proposed. The destressing effect at deep part and anchorage strength changing at shallow part of the coal rib were studied under different borehole parameters. Numerical simulation results show that the destressing effect increases with the increase of the borehole diameter, while borehole with oversize diameter increases the deformation of the roadway and weakens the strength of the anchorage support. The diameter‐enlarging point in segmented enlarged‐diameter borehole destressing technology is best placed between the anchorage end and the vertical stress peak point. The anchorage strength is inversely correlated with the diameter of the small‐diameter section, and the destressing effect is positively correlated with the diameter of the large‐diameter section. Based on its advantages in destressing, the segmented enlarged‐diameter boreholes and anchorage support are applied together, and a system of destressing‐support cooperative control of rock burst is presented. The roles in rock burst control of "zone of strong anchorage support" and "zone of low stress and energy dissipation" are described.

Although tectonic areas with facies change (i.e., variation of coal seam thickness, coal seam dip angle, or coal quality) are one of the three major geological structures that induce rock bursts, case studies of rock bursts in these tectonic structures are rare. The main objective of this study is to illustrate this issue and provide case studies that may inspire future research. Based on several typical cases of rock bursts induced by tectonic areas with facies change, the conditions conducive for these bursts are introduced and investigated in detail. Subsequently, numerical simulation is performed, showing that stress concentration exists in regions with variable coal seam thicknesses or dip angle. When stoping or tunnelling approaches this region, the peak stress increases rapidly. Thus, the burst occurs via a mechanism involving the superposition of high in-situ stress from tectonic areas with facies change and abutment pressure from stoping or tunnelling, leading to high stress concentration. Strategies for mitigating rock bursts are also provided. Rock bursts induced by tectonic areas with facies change can be mitigated by avoiding regions of high tectonic stress concentration and reducing mining induced stress.

The pressure relief with large‐diameter boreholes is one of the effective methods to prevent coal bumps in deep coal roadway. An unreasonable pressure relief design can cause the rockbolt support failure and aggravate the deformation of the surrounding rocks. In this paper, a coupling model of roadway sidewall considering borehole pressure relief and rockbolt support was established. The influence of the destressing borehole diameter on the rockbolt located in the plastic zone and the roadway deformation was studied by theoretical calculation and numerical simulation. The results show that there is a critical zone of the borehole diameter for the influence on the rockbolt normal stress and roadway convergence. When the destressing borehole diameter exceeds the critical zone, the rockbolt normal stress decreases sharply. Considering the existence of the broken zone in the surrounding rock, the bolehole diameters in the critical zone increase with the increase of the distance between the borehole and the rockbolt, the residual strength, and decrease with the increase of initial stress. In the engineering analysis, with the increase of the destressing borehole diameter, the ultimate pullout force of rockbolt decrease, and the plastic zone of surrounding rock, the roadway deformation, the maximum axial force, and slippage of the rockbolt all increase. Therefore, to better keep the stability of the surrounding rock in coal roadway, the borehole pressure relief needs to be coordinated with the rockbolt support. The destressing borehole diameter in the pressure relief design should not be greater than the critical zone.

Research on energy accumulation and releasing in the rock plays a key role on revealing its failure mechanism. This paper establishes a microscopic structure model of granite using Otsu digital image processing (DIP) technology and particle flow code software (PFC2D). A series of numerical compression tests under different confining pressures were conducted to investigate the macro and micro characteristics of energy evolution in granite. The results showed that the energy evolution of granite is divided into three stages: stable accumulation, slow dissipation, and rapid release. With increasing confining pressure, the strain energy accumulation ratio decreased exponentially and the peak value of strain energy increased linearly. It was found that the energy accumulation speed in the pre-peak stage increased as a linear function, while the energy release speed in the post-peak stage decreased as an exponential function. In addition, the feldspar is the main microstructure which played a major part in accumulating energy in granite. However, the unit mineral energy of mica particles was bigger than that of feldspar and quartz. When subjected to increasing confining pressure, the feldspar’s total energy growth rate was fastest. Meanwhile, the mica’s unit energy growth rate was fastest.