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石门揭煤诱发煤与瓦斯突出演化过程及失稳机制

Evolution process and instability mechanism of coal and gas outburst induced by rock cross-cut coal uncovering

  • 摘要: 煤与瓦斯突出(简称突出)是煤炭开采过程中一种复杂的动力灾害现象,严重威胁矿井安全生产,其中石门揭煤诱发突出的平均强度最大。为此,利用自主研发的多功能煤与瓦斯突出模拟试验系统,开展了25、50、70、100 mm突出口径条件下的石门揭煤突出物理模拟试验,发现随着突出口径的增加,煤层瓦斯压力下降速率加快,突出煤粉运移速度有所增加且破碎程度显著增强,同时相对突出强度呈线性增长趋势,分别为6.93%、25.83%、48.03%、70.31%。结合煤与瓦斯突出物理模拟试验建立了流固耦合数学模型,利用COMSOL模拟分析了突出不同阶段的多物理场演化规律。模拟结果表明:突出准备阶段,暴露面附近煤体发生应力集中和塑性变形,25、50、70、100 mm突出口径下应力集中系数分别为1.31、1.36、1.40、1.51,塑性区以环状形态分布在突出孔洞周围,分布面积分别为90.75、401.31、884.18、2250.5 mm2;突出发展阶段,煤层内依次形成球向流区、过渡区和单向流区,其中暴露面附近的球向流区瓦斯压力梯度较大,以渗透力的形式作用于煤体;计算得到4组模拟条件下最大瓦斯渗透力分别为7.87、10.15、14.94、21.73 MPa/m,与突出口径呈正相关,同时具有衰减速度快、作用范围小的特点,影响时间主要集中在煤体暴露1 s时间内,作用范围主要位于暴露面附近10 mm煤体上,使得煤壁薄层易发生拉伸破坏从而诱发突出。最后针对石门揭煤作业特点分析了石门揭煤诱发煤与瓦斯突出的演化过程、失稳机制及影响因素,并探讨了防控石门揭煤突出的思路和措施。

     

    Abstract: Coal and gas outburst (referred to as outburst) is a complex dynamic disaster phenomenon in the process of coal mining, which seriously threatens the safety production of mines, and the average intensity of coal outburst induced by rock cross-cut coal uncovering is the largest. In this study, the physical simulation of outburst induced by rock cross-cut coal uncovering under the conditions of 25 mm, 50 mm, 70 mm, 100 mm outburst calibers was carried out using the self-developed multifunctional coal and gas outburst simulation test system. It was found that with the increase of outburst calibers, the rate of decrease in coal seam gas pressure accelerates, the velocity of outburst pulverized coal increases, and the fragmentation degree of outburst pulverized coal significantly increases. At the same time, the relative outburst intensity shows a linear increasing trend, with values of 6.93%, 25.83%, 48.03%, 70.31%, respectively. A fluid solid coupling mathematical model was established based on physical simulation experiments of coal and gas outbursts, and the evolution laws of multi physical fields at different stages of outburst were simulated and analyzed by COMSOL. The simulation results show that during the preparation stage of outburst, stress concentration and plastic deformation occur in the coal body near the exposed surface. The stress concentration factors under the outburst calibers of 25, 50, 70, 100 mm are 1.31, 1.36, 1.40, 1.51, respectively. The plastic zone is distributed in a circular shape around the outburst holes, with surface integrals of 90.75, 401.31, 884.18, 2250.5 mm2, respectively. During the development stage of outburst, the coal seam sequentially forms a spherical flow zone, a transition zone, and a unidirectional flow zone. The gas pressure gradient in the spherical flow zone near the exposed surface is relatively large and acts on the coal body in the form of gas seepage force. Under the four simulated conditions, the maximum gas seepage force is 7.87, 10.15, 14.94, 21.73 MPa/m, respectively, which are positively correlated with outburst calibers. At the same time, the gas seepage force has the characteristics of fast attenuation rate and small range of action. The influence time is mainly concentrated within 1 second of coal exposure, and the range of action is mainly located on the 10 mm coal body near the exposed surface, which can easily cause tensile failure of the thin layer of coal wall and induce outburst. Finally, the evolution process, instability mechanism, and influencing factors of coal and gas outbursts induced by rock cross-cut coal uncovering were analyzed based on the characteristics of the rock cross-cut coal uncovering operations. The ideas and measures for preventing and controlling rock cross-cut coal uncovering outbursts were also discussed.

     

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