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深部高瓦斯煤层爆破致裂增透裂纹扩展规律研究

Study on propagation law of cracking and permeability enhancement caused by blasting in deep high-gas coal seams

  • 摘要: 针对深部高瓦斯煤层在地应力作用下爆破增透时裂纹扩展规律尚不明确的问题,首先根据爆破应力波的传播和叠加,从理论上分析了地应力和爆破荷载耦合作用下炮孔周围的应力分布规律;然后通过室内试验研究了不同地应力条件下单孔爆破裂纹扩展特征,在此基础上,对不同侧压系数下双孔爆破裂纹扩展机理以及贯通过程进行数值模拟研究,并结合ImageJ图像识别软件和LS-PrePost软件,以裂纹密度和扩展长度为量化指标表征地应力对裂纹发育程度的影响;最后根据室内试验和数值模拟研究结果,给出考虑地应力影响下的煤层爆破致裂增透爆破孔布置方案建议。单孔爆破室内试验结果表明:地应力可以减小爆破荷载引起的拉应力,从而抑制裂纹扩展;在非静水地应力条件下,与较大主应力方向正交的拉应力受到削弱,导致该方向的裂纹扩展受到抑制,使裂纹优先向高应力方向扩展;双孔爆破数值模拟研究结果表明:侧压系数不为1时,爆生裂纹扩展呈现出方向性,主裂纹倾向于向较高地应力方向扩展,造成爆破裂纹区域呈椭圆形,长轴和较大地应力方向一致。根据室内试验和数值计算结果,在深部煤层进行爆破致裂增透时,宜沿较大地应力方向钻孔,有利于提高爆破致裂增透效果。研究成果对深部高瓦斯煤层爆破增透时了解裂纹扩展机理以及优化炮孔布置方案具有指导意义。

     

    Abstract: Aiming at the problem that the crack extension law of deep high-gas coal seams is not clear during blasting and permeability enhancement under the action of ground stress, firstly, according to the propagation and superposition of blasting stress wave, the stress distribution law around the blast hole under the coupling effect of ground stress and blasting was theoretically analyzed. Then, the crack extension characteristics of single-hole blasting under different ground stress conditions were investigated through laboratory tests, on the basis, the numerical simulation was carried out to investigate the crack extension mechanism and the penetration process of double-hole blasting under different lateral stress coefficients, and combined with the ImageJ image recognition software and LS-PrePost software, the effect of ground stress on the degree of crack development was characterized using crack density and extension length as a quantitative index. Finally, based on the results of laboratory test and numerical simulation, the layout scheme of coal seam blasting holes for cracking and permeability enhancement considering the influence of ground stress was proposed. The results of single-hole blasting laboratory test shown that, the ground stress can reduce the tensile stress induced by the blasting load and thus inhibit crack extension. Under the condition of non-hydrostatic ground stress, the tensile stresses orthogonal to the direction of the larger principal stresses were weakened, resulting in the inhibition of crack extension in this direction, causing the cracks to preferentially extend in the direction of higher stresses. The numerical simulation results of double-hole blasting shown that, when the lateral stress coefficient was not 1, the blasting crack expansion was directionality, and the main crack tended to expand in the direction of higher ground stress, resulting in an elliptical shape of the blast crack area, and the direction of the long axis and the larger in-situ stress were consistent. According to the results of laboratory tests and numerical calculations, it was advisable to drill holes along the direction of large ground stress to improve the effect of fracturing and permeability when blasting in deep coal seams. The research results are of great significance for understanding the crack expansion mechanism and optimizing the blast hole layout scheme when blasting for permeability enhancement in deep high-gas coal seams.

     

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