Rockburst caused by the fracture of thick hard roof and the instantaneous instability of residual coal pillar seriously jeopardize the deep coal mining safety. This study takes Boertai Coal Mine, Shendong, China, as the engineering background, in which dynamic instability mechanisms of the gob-side roadway surrounding rock are analyzed by integrating field research, theoretical analysis, and numerical simulation. The results show that the overlying residual coal pillar, side abutment pressures, and front abutment pressures together induce high static stresses in the surrounding rock of the gob side roadway, with peak values exceeding the in situ stress by one order of magnitude. High stresses accumulated in the goaf-side roadway surrounding rock can easily induce dynamic disaster. With the working face advanced, overburdens are caved in succession, resulting in a continuously decreasing of the overlying residual coal pillar width, once the working face entered the influence area of the residual coal pillar. As the morphology of abutment pressure in the residual coal pillar changes from “unimodal distribution” to “bimodal distribution,” the residual coal pillar gradually changes from elastic state to plastic state. When the width of the overlying residual coal pillar is less than the critical width, the thick hard roof and residual coal pillar structure (THRRCPS) lose stability suddenly, resulting in strong dynamic load on the surrounding rock of gob-side roadway. In order to prevent the rockburst of the gob-side roadway under the influence of THRRCPS, regional and local prevention measures are adopted to mitigate the accumulation of stress in the thick hard roof and gob-side roadway surrounding rock by hydraulic fracturing technology and large diameter pressure relief drilling hole.

To explore the dynamic mechanical characteristics of CRCB specimens, a separated Hopkinson pressure bar (SHPB) test device combined with ultra-high-speed camera system was used to carry out the impact compression test on CRCB specimens. The stress wave propagation, dynamic stress–strain relationship, dynamic evolution of cracks, energy dissipation law and failure characteristics of the coal–rock combined body in the case of stress waves entering coal from rock were compared and analyzed. The influence of the difference between the rock and the incident bar on the propagation of stress wave gradually weakens with the increase of the impact velocity. The strength stress and peak strain of the CRCB specimens have obvious strain-rate effects. Besides, with increased impact velocity, the incident energy increases linearly, the reflected energy proportion decreases linearly and the absorbed energy proportion change approximately as a power function. Under the same stress wave, as the strength of the rock increases, the failure degree of coal gradually increases, the broken particles gradually transition from massive to powder and the rock mode changes from splitting failure to shear failure. As a result, the average particle size of broken coal blocks decreases, and the fractal dimension of CRCB specimens increases gradually. The research results provide basic research for the control of surrounding rock of roadway under dynamic pressure.

The compound dynamic disaster of coal and gas outbursts and rockburst is a typical hazard jeopardizing the mining of the high gas content coal seam under a hard roof condition. In this study, the hard roof’s mechanism inducing this hazard is analyzed. Physical analog modeling experiments and in situ monitoring of mining-induced stress were performed during coal seam mining under a hard roof condition. The pattern of hard roof breakage effect on the stress-fissure field evolution was revealed. The elastic energy was released and propagated on both sides immediately after the hard roof breaking, leading to energy accumulation. Meanwhile, expansive roof collapse resulted in the intense weighting of the working face and rockburst. Thus, the coal and gas outburst occurred under the joint action of the impact energy generated by breaking the hard roof and gas expansion energy. In other words, the compound dynamic disaster happened. Synergistic stereoextraction integrating cross-seam drilling and along-seam drilling was combined with deep hole advanced presplitting blasting technology to cope with the compound dynamic disaster in the high gas coal seam under a hard roof condition.

Horizontal layered composite rock samples composed of white and black sandstones with large differences in physical and mechanical properties were tested to explore the dynamic characteristics of layered composite rocks under impact load. Using the split Hopkinson pressure bar test system, the dynamic compression tests of two incident states of stress waves, that is, stress waves from white sandstone to black sandstone (W⟶B) and from black sandstone to white sandstone (B⟶W), were designed and carried out under different impact velocities. Combining the ultrahigh‐speed photography system and digital photogrammetry for deformation measurement (DPDM), we obtained the stress wave propagation characteristics, failure characteristics, and particle size distribution characteristics of broken rocks of the composite rocks under the two conditions. The experimental results were compared and analyzed, while stresses and strength conditions at the interface of the composite rock samples were theoretically assessed, yielding the following main findings. The energy dissipation pattern of composite rock had an obvious strain rate effect. The reflected energy and fragmentation energy density of composite rock increased approximately as quadratic functions of the incident energy. Affected by the wave impedance matching relationship, the W⟶B and B⟶W samples were significantly different in terms of the stress wave shape, energy dissipation, average particle size, and fractal dimension of the broken rocks at low impact velocities. However, with an increase in the impact velocities, the two gradually shared the same behavior. When composite rock samples deformed and failed, the macrocracks mostly initiated from the white sandstone. When the crack tip stress of the white sandstone at the interface exceeded the strength of the weakened black sandstone, the crack continued to develop through the two‐phase rock interface due to the difference in Poisson’s ratios. The damage degrees and failure modes of the two parts of composite rocks were different: black sandstone was prone to tensile splitting with local shear failure, while white sandstone exhibited shear failure with local tensile splitting. The damage degree of white sandstone exceeded that of black sandstone.

采用高分辨X射线衍射技术对大尺寸磷酸二氢钾(KDP)晶体的晶格应变进行了测量, 并定量分析了其晶格应力. 探讨出KDP晶体容易沿着[001]方向发生开裂, 与实际工作中的开裂现象相符合; 进一步归纳总结了晶体生长过程中引入内应力而导致晶体开裂的主要因素. 研究结果为提出相应的晶体防裂措施提供了重要的理论基础.

Thick-hard roofs (THRs) govern the fracture and movement of overburden strata and control the formation and stability of stope structures. The instability of THRs acts as a core factor influencing ground pressure and serves as a primary trigger of rockbursts. This study aims to reveal the zoned energy release characteristics and dynamic response laws of gob-side roadways under THR instability. An elastoplastic foundation mechanical model was established to characterize the load-bearing behavior of THRs under mining-induced disturbances. The propagation and attenuation laws of stress waves generated by THR fracture were analyzed, and the dynamic disturbance characteristics of gob-side roadways were elucidated. Furthermore, a targeted rockburst mitigation strategy was proposed, which integrates dynamic load source isolation, static stress concentration relief, and cooperative support with constant-resistance, large-deformation, energy-absorbing anchor cables. The research findings can provide a solid theoretical basis for the prevention and control of THR-type rockbursts in deep coal mining.