1.School of Resources and Safety Engineering,University of Science and Technology Beijing,Beijing 100083,China
2.Institute of Disaster Rock Mechanics,Liaoning University,Shenyang,Liaoning 110036,China
3.Rock Burst Prevention and Control Department,Henan Dayou Energy Co. ,Ltd. ,Sanmenxia,Henan 472300,China
4.National Key Laboratory of Intelligent Technology and Equipment for Unmanned Coal Mining,Anhui University of Science and Technology,Huainan,Anhui 232001,China
5.College of Mining Engineering,Taiyuan University of Technology,Taiyuan,Shanxi 030024,China
Studies on the mechanism of rock bursts in water-immersed coal pillars of high-stress main roadways triggered by recurrent disturbances remain limited, resulting in an insufficient theoretical basis for on-site prevention and control in coal mines. Taking the frequent rock bursts occurring in the water sump coal pillar of the main roadway in Zhaolou Coal Mine, Shandong Province, as the engineering background, this study employed field measurements and laboratory experiments to investigate the mechanical response and failure characteristics of rock-coal-rock composite specimens (RCRCS) with gradient water saturation under cyclic impact loading, and further explored the mechanism of frequent rock bursts in roadway coal pillars under high static load, recurrent disturbances, and continuous water immersion. The results show that the fractal dimension of coal fragments and the strain concentration range in the RCRCS increased continuously with increasing water saturation, with the most pronounced increase occurring within the range of 0%-33%. Compared with cyclic strong impacts (2.8 m·s-1) and combined strong-weak impacts (2.8/2.3 m·s-1), cyclic weak impacts (2.3 m·s-1) reduced the strength difference between dry and water-bearing states. The degree of local strain in the RCRCS increased rapidly and uniformly with the number of cyclic strong impacts, whereas under cyclic weak impacts, damage accumulated slowly in the early stage and macroscopic cracks increased sharply in the later stage; the strain characteristics under combined impacts were intermediate between the two. The resistance of specimens with 0% water saturation to cyclic dynamic fatigue damage was significantly higher than that of specimens within the 33%-100% range. Water immersion generally weakened the dynamic strength, although its sensitivity varied markedly under different impact modes, with the most pronounced softening effect occurring under cyclic strong impacts. Reducing the impact energy decreased the sensitivity of the strength parameters of the RCRCS to water saturation. The mechanism of frequent rock bursts in water-immersed coal pillars of high-stress main roadways under recurrent disturbances was revealed as follows: the deep water sump coal pillar remained under a high static load for a long period, and water immersion reduced the initial load-bearing threshold of the shallow surrounding rock; under repeated dynamic events such as far-field mine seismicity and mining-induced disturbances, damage accumulated continuously and drove the load-bearing threshold to decline progressively. Because the shallow water-immersed zone degraded faster than the inner dry zone, it was more prone to local instability first, which induced stress concentration toward the core zone and made subsequent disturbances more likely to trigger rock bursts. The results provide a theoretical basis for the monitoring, early warning, and targeted prevention of rock bursts in deep high-stress water-immersed coal pillars.
赵楼煤矿位于山东省菏泽市巨野煤田中部,矿区内部的开拓及准备巷道、永久硐室系统由南部大巷、七采区大巷和一集下山三部分系统组成,而本文的研究对象位于南部大巷与七采区大巷上段的相交处,如图1所示.南部大巷水仓煤柱由7#联络巷、8#联络巷、内水仓、南部辅运大巷和南部胶带大巷切割形成,其中内水仓与外水仓是全矿蓄水、沉淀和储水的中心枢纽,水仓煤柱平均埋深、长度、宽度、煤厚和倾角分别约为980,89.4,21.5,6.5 m和8.5°.受煤层赋存影响,水仓煤柱四周巷道存在局部穿层和留底煤设计,7#与8#联络巷、南部辅运与胶带大巷、内水仓巷道内最大底煤厚度分别约为3.2,1.1,2.3,6.7,2.1 m.
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