【作者】 易丽军；

【导师】 俞启香；

【作者基本信息】 中国矿业大学 ， 安全技术及工程， 2008， 博士

【摘要】 煤与瓦斯突出是在地应力和瓦斯的共同作用下,破碎的煤和瓦斯由煤体或岩体内突然地向采掘空间抛出的异常动力现象,它是煤矿最严重的灾害之一,中国是世界上突出最严重的国家。密集钻孔预抽瓦斯技术是一种防止煤与瓦斯突出的措施,钻孔在煤层中所形成的应力分布、透气性规律和瓦斯的流动过程是极其复杂的问题,本文主要采用实验室试验和数值试验进行了系统研究,即采用平面应变模型,揭示密集钻孔的透气性、应力分布、塑性区和卸压区的范围、煤层瓦斯压力变化、预抽半径和钻孔瓦斯流量等问题。研究这些问题,对人们进一步认识密集钻孔预抽瓦斯的机理和合理的布置钻孔具有重要的理论意义和工程实用价值。实验室试验得出,在不同的加载应力条件下,不论是在卸压区还是未卸压区,气体流过模型材料都符合达西定律。并用达西定律进行了密集钻孔模型的透气性规律的考察,得出在钻孔卸压区内外,透气系数与载应力的变化规律和透气系数的分布规律,在卸压区内,透气系数随着加载应力的增加而增大,在卸压区外,透气系数随着加载应力的增加而减小。实验室试验所得的卸压区范围与数值试验所得结果进行对比表明,两者较为接近。用ANSYS有限元软件,考察在静水压力条件下,煤层埋藏深度、钻孔直径、钻孔间距、内聚力和内摩擦角等因素的变化,密集钻孔的应力分布和产生的塑性区和卸压区的范围。得出在钻孔附近切向应力最大,径向应力最小。塑性区和卸压区范围随着煤层埋藏深度、钻孔的直径的增大而增加,随着内聚力和内摩擦角的增加而减小,塑性区范围随着钻孔间距的增加而减小。应用固气耦合RFPA2D-Gas数值试验系统,以煤岩-瓦斯固气耦合理论为基础,建立数值试验模型,将密集钻孔预抽瓦斯简化为平面问题,并选取合理的边界条件,为解决预抽煤层瓦斯更为接近实际。研究在透气系数、钻孔间距、钻孔直径、瓦斯含量系数和预抽时间等因素的变化,用密集钻孔预抽瓦斯,煤层瓦斯压力变化、预抽半径和钻孔瓦斯流量的变化规律,得出透气系数、钻孔直径越大,钻孔间距和瓦斯含量系数越小,煤层瓦斯压力下降幅度越大,抽采半径越大;达到消除煤层突出危险的瓦斯压力值所需要抽采的时间越短;随着钻孔预抽时间的延长,瓦斯压力下降范围将扩大,抽采半径增加。透气系数、瓦斯含量系数和钻孔直径越大,钻孔间距越小,钻孔瓦斯流量就越大,反之越小。钻孔瓦斯流量的衰减规律遵循负指数规律。最后,应用RFPA2D-Gas数值试验系统,结合芙蓉矿务局白皎煤矿用穿层钻孔预抽瓦斯和郑州煤业集团大平煤矿用顺层钻孔预抽瓦斯实例进行瓦斯预抽数值模拟对比分析,得出数值模拟的瓦斯压力降低值和瓦斯抽出量与现场实际较为吻合。更多还原

【Abstract】 The coal and gas outburst is an abnormal dynamical phenomenon that occurred with the broken coal and gas suddenly burst from the coal or rock to the mining space under the joint action of the gas and the in-situ stress. It is one of the most serious disasters in coal mine, and China is the country with most serious problem of outburst in the world. The pre-drainage technology with dense boreholes is a preventive measure for the coal and gas outburst. The stress distribution, the law of gas permeability and the flow of gas formed in the coal seam during the borehole are extremely complicated issues. This paper has systematically studied the issues by adopting mainly the laboratory test and numerical test, namely, by adopting the model for plane strain to reveal the permeability, stress distribution, the scope of plastic zone and distressed zone of the dense boreholes, the changes of gas pressure in coal seam, the pre-drainage radius, and the gas flow quantity of the borehole, etc. The research on these issues is of great theoretical significance and practical value for the engineering to layout the boreholes reasonably, as well as to raise the awareness of people about the mechanism of pre-drainage gas by dense boreholes.Laboratory tests indicate that under different stress loads, the gases penetrate through model materials are all in line with Darcy law, whether they are in stress relieving zone or not. The law of gas permeability in the dense boreholes model has been investigated with Darcy law. The coefficient of gas permeability, the changing rule of load stress, and the distribution rule of gas permeability have been obtained. In the stress relieving zone, the coefficient of gas permeability increases with the increase of the load stress. Outside the stress relieving zone, the coefficient of gas permeability decreases with the increase of the load stress. The comparison between the result of numerical test and the scope of stress relieving zone obtained from the laboratory tests shows that these two are rather close.ANSYS FEM software was adopted to study the changes of factors, such as the depth of coal seam, the diameter of borehole, the boreholes space, cohesion and internal friction angle, the stress distribution of dense boreholes, the plastic zone formed and the scope of stress relieving zone, under the hydrostatic pressure. In the vicinity of the borehole, the tangential stress is maximum and the radial stress in minimum. The scope of plastic zone and stress relieving zone increases with the increase of the depth of coal seam and the diameter of borehole; it decreases with the increase of the cohesion and the internal friction angle. Based on the coal and gas solid-gas coupling theory, using the application of the solid-gas coupled RFPA2D-Gas numerical test system established the numerical test model. The pre-drainage gas by dense boreholes has been simplified into the plane problem and the reasonable boundary condition has been selected to solve the problem of pre-drainage gas in coal seam, which is much closer to reality. Study the changing factors, such as the coefficient of permeability, the space and diameter of borehole, the coefficient of gas content, the duration of pre-drainage, etc. With the changing rule of gas flow in boreholes and the pre-drainage radius, the changes of gas pressure in coal seam, and the pre-drainage gas by dense boreholes, it can be concluded that the greater the permeability coefficient and the diameter of borehole, the smaller the coefficient of gas content and the span of the boreholes, the bigger the extent of gas pressure drop in coal seam, the larger the gas drainage radius; the shorter the time needed for pre-drainage gas to the value that can eliminate the outburst risk of coal seam. With the prolonging of the pre-drainage time, the extent of gas pressure drop will be expanded and the pre-drainage radius will be increased. The bigger the permeability coefficient, the coefficient of gas content and the diameter of the borehole, the smaller the borehole space, the larger the gas flow in the borehole, and the smaller the gas flow in the borehole on the other hand. The attenuation of the gas flow in borehole follows the law of negative exponent.In conclusion, with the application of RFPA2D-Gas numerical test system has been combined with the examples of pre-drainage gas with boreholes through coal seam used by Baijiao Mine of Furong Mining Bureau and boreholes alone coal seam used by Daping Coal Mine of Zhengzhou Coal Industry Group, the numerical simulation of gas pre-drainage has been analyzed. The value of gas pressure decrease and gas drainage amount obtained by numerical simulation are quite matched with the actual conditions on site.更多还原