单孔增透率算法的提出及其工程应用

低透煤层增透效果的定量描述和评价一直处于盲目状态，使得煤矿瓦斯治理中致裂措施、瓦斯抽采不能因地制宜。增透率可反映采动或人工增透措施对煤岩体渗透特性的改变，并可定量评价煤层增透效果，其分布和演化规律可精准圈定瓦斯富集区域，指导瓦斯抽采钻孔的合理布置。在简化钻孔和裂隙模型基础上，求解了采动条件下钻孔的体积应变，提出了针对单孔的增透率计算方法；依托同煤矿塔山矿8212采面，开展现场裂隙探测试验，研究了工作面前方采动裂隙网络发育演化及卸压增透变化规律，并分析了单孔增透率随回采面推进的演化特征。结果表明：裂隙网络呈现“从无到有、从短变长、从窄变宽、不断贯通”的趋势，煤岩体单孔增透率随回采面推进呈现先逐渐上升后保持平稳的趋势，该成果有望直接优化煤矿现场瓦斯抽采孔的布置设计。

Algorithm of mining-enhanced permeability of a single borehole and its engineering application

How to quantitatively describe and evaluate the mining-enhanced permeability for low-permeability coal seams has always been in a blind state, which results in the inadequacy of fracturing measurements and gas drainage during coal mining for local conditions. Mining-enhanced permeability can reflect the influence of mining or other measures on permeability enhancement and also quantitatively evaluate the effect of coal seam permeability enhancement, and its distribution and evolution can be used as a guide to the location of gas enriched area and the rational layout of gas drainage boreholes. The volumetric strain caused by mining is determined by simplifying the model of borehole with cracks. A single borehole algorithm is proposed for mining-enhanced permeability. A field test for detecting mining fracture network is carried out at mining face No.8212 of Datong coal mining group. According to the fracture data of each single borehole, the evolution of mining induced fracture network and pressure are studied, and the evolution of a single borehole mining-enhanced permeability is analyzed. The results show that the fracture network evolution presents a trend of growing out of nothing, growing from short to long, growing from narrow to wide and connecting continuously, respectively. The single borehole mining-enhanced permeability rises at first and then maintains steady as the mining face advances, thus providing a foundation for the design of gas drainage at the working face.