<p>随着煤矿新技术、新设备的使用，煤矿开采强度和采掘延伸速度进一步加快，深部煤层瓦斯含量增加，瓦斯压力增大，瓦斯灾害事故越来越多，后果也越来越严重。矿井瓦斯抽采是我国煤炭开采中瓦斯灾害防治最重要的一项技术。特别是松软煤层中存在着力学强度低、瓦斯解吸速度快、瓦斯含量和压力相对较高等特征，导致松软煤层瓦斯抽采钻孔易发生塌孔和变形，难易成孔。同时，封孔后的钻孔周围煤体存在较多裂隙，导致气体渗漏，使得松软煤层瓦斯抽采难以高效稳定的进行。因此，研究多因素条件下钻孔孔周裂隙扩展规律，对实现松软煤层瓦斯高效抽采具有重要的意义。</p> <p>实验煤样选自陕西某矿松软煤层，通过型煤配比实验，制成不同钻孔参数的含孔试件。利用声发射监测技术分析不同钻孔参数试件单轴加载过程中的变形破坏特征，得到随着钻孔角度和直径增大，试件抗压强度都减小，声发射振铃计数、能量和事件数增加，试件破裂产生的裂隙数量增加；当钻孔角度增大时，试件破坏类型不变，呈X型剪切破坏；当钻孔直径增大时，试件破坏类型由X型剪切破坏变为压裂破坏。</p> <p>采用超声波实验装置，通过波速计算得到试件裂隙等效宽度，发现最大等效裂隙宽度随着钻孔角度和钻孔直径的增加呈现增大的趋势，钻孔角度0&deg;、10&deg;、30&deg;试件最大裂隙等效宽度依次为3.16&times;10^-3 mm、4.31&times;10^-3 mm、5.29&times;10^-3 mm；钻孔直径4 mm、6 mm、8 mm试件最大裂隙等效宽度依次为3.16&times;10^-3 mm、5.27&times;10^-3 mm、8.43&times;10^-3 mm。利用自主设计并搭建的固-气耦合三维物理相似钻孔模拟实验台，研究了不同钻孔角度和气体压力下声发射信号活动规律，发现随着钻孔角度和气体压力的增大，钻孔孔周裂隙分布特征由钻孔中部区域集中分布变为钻孔中部下方区域集中分布，钻孔裂隙数量与钻孔角度、气体压力呈正相关。通过分析6组含孔模型中透射波信号、波幅透射系数以及声压分布特征的变化规律，对不同钻孔角度和钻孔直径孔周裂隙区域分布特征进行了反演，发现钻孔角度和直径增加，钻孔孔周裂隙扩展区域增大，钻孔破坏更加严重。</p> <p>研究结果获得多因素条件下钻孔孔周裂隙扩展的规律，对提高松软煤矿井瓦斯灾害的治理和瓦斯资源的利用都具有积极的意义。</p>

<p>With the use of new technologies and new equipment in coal mines, the mining intensity and mining extension speed of coal mines have been further accelerated, the gas content in deep coal seams has increased, the gas pressure has increased, and the gas disaster accidents have become more and more serious. Mine gas extraction is the most important technology for gas disaster prevention and control in coal mining in China. In particular, the soft coal seam has the characteristics of low mechanical strength, fast gas desorption speed, relatively high gas content and pressure, which leads to the collapse and deformation of gas extraction boreholes in soft coal seams, and it is difficult to form boreholes. At the same time, there are many cracks in the coal around the borehole after sealing, which leads to gas leakage, making it difficult to carry out gas extraction in soft coal seam efficiently and stably. Therefore, it is of great significance to study the law of crack propagation around boreholes under multi-factor conditions to achieve efficient gas extraction in soft coal seams.</p> <p>The experimental coal samples were selected from the soft coal seam of a mine in Shaanxi Province. Through the briquette ratio experiment, the hole-containing specimens with different drilling <font color='red'>parameter</font>s were made. Acoustic emission monitoring technology was used to analyze the deformation and failure characteristics of specimens with different drilling <font color='red'>parameter</font>s during uniaxial loading. With the increase of drilling angle and diameter, the compressive strength of specimens decreased, the number of acoustic emission ringing counts, energy and events increased, and the number of cracks produced by specimen rupture increased. When the drilling angle increases, the failure type of the specimen remains unchanged, showing X-type shear failure. When the borehole diameter increases, the failure type of the specimen changes from X-type shear failure to fracturing failure.</p> <p>The ultrasonic experimental device was used to calculate the equivalent crack width of the specimen by wave velocity. It was found that the maximum equivalent crack width increased with the increase of drilling angle and drilling diameter. The maximum equivalent crack width of the specimen with drilling angle of 0 &deg;, 10 &deg; and 30 &deg; was 3.16 &times; 10-3 mm, 4.31 &times; 10-3 mm and 5.29 &times; 10-3 mm, respectively. The maximum crack equivalent widths of specimens with borehole diameters of 4 mm, 6 mm and 8 mm are 3.16 &times; 10-3 mm, 5.27 &times; 10-3 mm and 8.43 &times; 10-3 mm, respectively. Using the self-designed and built solid-gas coupling three-dimensional physical similar drilling simulation experiment platform, the activity law of acoustic emission signals under different drilling angles and gas pressures was studied. It was found that with the increase of drilling angle and gas pressure, the distribution characteristics of cracks around boreholes changed from concentrated distribution in the middle of boreholes to concentrated distribution in the lower part of boreholes. The number of borehole cracks was positively correlated with drilling angle and gas pressure. By analyzing the variation of transmission wave signal, amplitude transmission coefficient and sound pressure distribution characteristics in 6 groups of hole-containing models, the distribution characteristics of fracture areas around boreholes with different borehole angles and borehole diameters are inverted. It is found that the fracture expansion area around boreholes increases with the increase of borehole angle and diameter, and the damage of boreholes is more serious.</p> <p>The research results obtained the law of crack propagation around borehole under multi-factor conditions, which has positive significance for improving the control of gas disasters and the utilization of gas resources in soft coal mines.</p>

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