The compound dynamic disaster is an abrupt and violent energy-releasing process under the combined action of gas and geological tectonic stress in deep underground coal mines. To investigate the occurrence mechanism of compound dynamic disasters, a novel experimental approach was designed and the one free-face true triaxial tests with different loading rates were conducted. Results shown that the compound dynamic disaster can be classified into several stages: initial quiet period, local particles and fragments ejecting, mid-term quiet period, external coal plate bending accompanied by gas-emitting, dynamic disaster occurring process, and the final re-stabilized period. The presence of the gas can significantly facilitate the development of cracks and enhance the kinetic energy, thus increasing the probability of the compound dynamic disasters. Under the one free-face true triaxial engineering stress conditions, the mechanical properties (e.g. deformation and strength) of coal samples are obviously rate-dependent, and the peak stress exhibits an approximate logarithmically increase trend with increasing loading rate. After failure, several tensile-shear fractures approximately parallel to the intermediate principal stress direction and perpendicular to the free face are generated. And an arc-shaped coal-burst pit on the free face of coal sample is observed, and the pit volume increases with the increase of the loading rate. Moreover, the particle ejection kinetic energy increases gradually as the loading rate increased, suggesting a higher loading rate can enhance the intensity of the disaster. The findings may provide guidance for the prevention and control of the compound dynamic disasters in deep underground coal mines.

煤与瓦斯突出、冲击地压等动力灾害严重威胁矿山安全高效生产.煤矿进入深部开采后,受原岩应力升高及地质赋存条件变化的影响,冲击与突出复合型动力灾害呈逐渐增多趋势,其发生原因、机理较单一动力灾害更为复杂.因此研究深部煤矿复合动力灾害致灾机理对于动力灾害的有效防治至关重要.本文基于自主研制的“多功能真三轴流固耦合试验系统”,进行了考虑气体影响的完整煤样和卸压孔煤样的5面加载、单面临空试验.结果 表明,复合动力灾害是煤岩在应变能和气体内能作用下非线性瞬发性破坏的动态过程.其发生过程具有明显的阶段性,主要经历颗粒弹射、碎片弹射、局部煤体破坏、煤体抛出失稳和重新平衡状态,煤样破坏后形成明显弧形阶梯状煤体抛出坑.中间主应力在一定范围内有增强煤样强度的特性,试样强度随中间主应力的增加而逐渐增加,试样破坏后形成平行于中间主应力方向的主断裂面.钻孔卸压措施可在一定程度上改善煤岩力学性质,软化煤岩结构,降低煤岩强度,增强其塑性变形特性,使集聚的弹性能量缓慢释放,降低动力灾害发生的可能性.对比试验结果表明,卸压孔平行于中间主应力时煤样产生的塑性区范围更大,塑性程度更强,钻孔后的试样破坏后形成明显的阶梯式层裂结构,与未钻孔和其他钻孔布置方式相比,致灾程度弱化,无明显动力显现特征,卸压效果更好.卸压钻孔主要通过优化能量释放结构,促进煤岩渐进式损伤,最终煤岩趋于静态缓慢式破坏.针对现场具体工程条件,提出了根据实际地应力、地质条件等布置卸压钻孔方位的技术方案和可行的治理措施.

The magnitude and direction of geo-stress undergoes complex changes following disturbance by artificial excavation in underground engineering. Tests were conducted using the self-made multi-functional true triaxial geophysical apparatus to investigate the influence of stress Lode angle on deformation, deformation modulus, and permeability of sandstone under true triaxial stress conditions (sigma(1) > sigma(2) > sigma(3)). The results indicate that principal, volumetric, and deviatoric strains, as well as permeability varied with the stress Lode angle, and eventually increased/decreased at different levels. For constant deviatoric stress and variable mean stress, the plastic strain decreased with increasing M (ratio of deviatoric stress q to mean stress p), whereas the permeability increased. For constant mean stress and variable deviatoric stress, the principal, volumetric, and deviatoric strains, as well as the permeability decreased first and then increased with the increase in M; the rock generated fracture surface when M was relatively large. The gas flow and stress axis directions significantly influence the value and changing trend of the permeability. With increasing stress Lode angle, the permeability increased first and then decreased. In our stress condition testing, the permeability value and variation range were maximum when the gas flow direction was parallel to sigma(1); when it was parallel to sigma(3), the permeability demonstrated an upward trend, but with a smaller increase range. Conversely, when it was parallel to sigma(2), the permeability decreased and the variation range was minimized. Finally, based on the analysis of the experimental results, we developed a permeability model that is expressed by both volumetric and deviatoric strains.

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