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采用胶囊-密闭液封孔测定煤层瓦斯压力时,如果钻孔深度偏短,则测定结果不是原始煤层瓦斯压力;反之,瓦斯压力测定仪可能拔不出来,导致仪器损坏。首先分析了掘进头前方煤体应力及透气性系数分布规律,并提出了透气性系数的分段函数表达式;根据达西渗透定律,推导出了掘进头前方瓦斯稳态流动时的压力分段函数表达式;最后,根据瓦斯压力的边界条件和连续条件推导出了测压钻孔深度计算公式。结果表明,掘进头前方测压钻孔深度约为15.0m。
When the pressure of coal seam gas is measured by the capsule-sealing liquid sealing hole, if the drilling depth is short, the measurement result is not the gas pressure of the original coal seam; on the contrary, the gas pressure gauge may not be pulled out and the instrument will be damaged. Firstly, the distribution law of stress and permeability coefficient of coal body in front of driving head is analyzed, and the expression of subsection function of air permeability coefficient is proposed. According to Darcy’s law of permeability, the pressure section of gas flow in front of driving head is deduced Function expression; Finally, according to the boundary conditions of gas pressure and continuous conditions, the calculation formula of pressure drilling depth is deduced. The results show that the depth of pressure drilling in front of the heading is about 15.0m.