College of Mining Engineering, Liaoning Technical University, Fu Xin, Liao Ning, China.
National Engineering Research Center of Coal Mine Gas Control, China University of Mining and Technology, Xu Zhou, Jiang Su, China.
PLoS One. 2018 Jun 28;13(6):e0199835. doi: 10.1371/journal.pone.0199835. eCollection 2018.
To solve the hidden danger of high methane and low permeability gas in the coal mining process, potentially affecting the safety production in an orderly way, we propose the use of deep hole blasting technology to improve the permeability of the coal seam gas drainage, increase the quantity and rate of extraction, and reduce methane output. Taking the geological conditions of the 201 working surface of Tingnan Coal Mine as an example, it is calculated that the single drilled fracture crack extension range is 3.11~5.24 m according to the coal seam deep-hole pre-splitting blasting joint mechanism and fracture propagation mechanics model, providing a theoretical basis for choosing the appropriate hole spacing. Using COMSOL simulation software to simulate the effective gas drainage radius of a coal seam from a two-dimensional perspective on a single borehole radial, the least squares fitting method was used to analyze the simulated data, and obtained the effective drilling extraction radius after pre-split blasting in a deep hole that is 3.6 m, which is in accordance with the theoretical calculations. In order to obtain accurate and scientific calculations, Fast lagrangian analysis of continua (FLAC3D) numerical simulation software was used. After simulating the distribution of plastic zone between two blast holes at different intervals from a three-dimensional angle, and evaluating the development of cracks in the blasting hole, the white zone of the blasting space was completely eliminated when the interval between blasting holes was 7 m, and the cracks could be propagated throughout the surroundings. Therefore, a blasting hole spacing of 7 m is optimal. On-site monitoring in the Nanting coal mine showed that the quantity and rate of extraction of the single hole after pre-splitting blasting were 2.36 times and 1.62 times as much as before. By integrating the borehole drainage amount and the optimized calculation equation, it could be concluded that the permeability coefficient of the coal seam after blasting was 7.78 times as much as before. The function of time-variated drilling methane emission was obtained using multivariate statistical regressions based on the on-site monitored borehole methane emission (qt), and the drilling limit after pre-splitting blasting revealed that the limitation of methane extraction volume was 5.27 times as much as before.
为了解决煤矿开采过程中高甲烷和低透气性这一潜在的安全隐患，我们提出采用深孔爆破技术来提高煤层瓦斯抽采的透气性，增加抽采量和抽采率，降低甲烷排放量。以亭南煤矿 201 工作面的地质条件为例，根据煤体深孔预裂爆破起裂机理和裂纹扩展力学模型计算得出单个钻孔裂缝扩展范围为 3.11~5.24 m，为合理选择孔距提供了理论依据。利用 COMSOL 模拟软件对单孔径向的煤层有效抽采半径进行二维模拟，采用最小二乘法对模拟数据进行分析，得到深孔预裂爆破后的有效钻孔抽采半径为 3.6 m，与理论计算结果相符。为了得到准确、科学的计算结果，采用 Fast lagrangian analysis of continua (FLAC3D) 数值模拟软件，从三维角度模拟不同间隔两炮孔间的塑性区分布，评价爆破孔内裂纹的发展情况，当炮孔间隔为 7 m 时，爆破空间的白色区域完全消除，裂缝可以贯穿周围，因此，爆破孔间隔 7 m 是最优的。在南亭煤矿进行现场监测表明，预裂爆破后单孔的抽采量和抽采率分别是爆破前的 2.36 倍和 1.62 倍。通过整合钻孔抽采量和优化计算方程，可以得出爆破后煤层的渗透率系数是爆破前的 7.78 倍。基于现场监测的钻孔瓦斯涌出量（qt），采用多元统计回归得到了钻孔瓦斯随时间变化的排放函数，预裂爆破后的钻孔极限表明，抽采量的限制是爆破前的 5.27 倍。
