高瓦斯低透气性煤层聚能爆破增透机制

为解决常规爆破增透煤层过程中煤体粉碎严重而裂隙发育不佳的难题，进行了聚能爆破煤层增透技术研究。开展了聚能爆破与常规爆破的混凝土致裂实验，对比分析了爆破后混凝土裂隙开裂程度，同时利用超动态应变仪采集了应变砖应变随时间变化的数据。利用ANSYS/LS-DYNA数值模拟再现了聚能罩压垮运移、聚能射流侵彻混凝土的过程，对比分析了聚能爆破与常规爆破应力波传播特征及内部裂隙扩展过程。最后在平煤十矿进行了聚能爆破与常规爆破的煤层增透试验，对比了爆破后抽采孔瓦斯的体积分数。研究结果表明：聚能爆破后，聚能方向上混凝土的裂纹宽度为1.1 cm，垂直聚能方向上混凝土的裂纹宽度为0.4 cm，而常规爆破后混凝土形成的4条主裂纹的宽度均为约0.3 cm。数值模拟结果显示：聚能爆破混凝土的粉碎区呈“哑铃型”，常规爆破混凝土的粉碎区呈圆形，且聚能爆破混凝土的粉碎区面积小于常规爆破的；而裂隙区呈“纺锤型”，且聚能爆破混凝土的裂隙区面积大于常规爆破的，说明聚能爆破技术可有效解决爆破增透过程中煤体粉碎区严重而裂隙区发育不佳的难题，更有利于致裂增透高瓦斯低透气性煤层。现场试验结果同样显示聚能爆破后瓦斯抽采浓度明显高于常规爆...

On infiltration enhancement mechanism of shaped charge blasting in high gas and low permeability coal seam

In order to improve the permeability of coal seam with high gas and low permeability and effectively control the disaster of coal and gas outburst, the mechanism of permeability enhancement of coal seam by shaped charge blasting is studied. Firstly, the comparative experiments of concrete cracking caused by shaped charge blasting and conventional blasting were carried out, and the sizes of concrete crushing area and fracture area after blasting were compared. Meanwhile, the strain data of the strain bricks with time were collected by the super dynamic strain gauges. Then, ANSYS/LS-DYNA is used to reproduce the whole process of the formation, migration and penetration into concrete of shaped energy jet. The stress wave propagation characteristics of shaped charge blasting and conventional blasting are compared and analyzed. Finally, the coal seam antireflection tests were carried out in Pingmei No. 10 mine, and the gas volume fraction of the extraction hole after blasting was compared. The results show that after shaped charge blasting, the crack width of concrete in the direction of energy accumulation and in its perpendicular direction was 1.1 cm and 0.4 cm, respectively; while the width of four main cracks formed in concrete after conventional blasting was 0.3 cm. Comparing the strain peaks measured from strain gauges at the same distance, it is found that the strain gauge in the direction of energy accumulation is the maximum, followed by the perpendicular direction, and the strain at the diagonal direction is the minimum. In addition, the strain peak value in the direction of energy accumulation is much larger than that under conventional blasting, and the strain peak value in the perpendicular direction is basically equal to that of conventional blasting, while the strain peak value of the diagonal direction is smaller than that under the conventional blasting. The numerical simulation results show that the crushing region of concrete after shaped charge blasting is of “dumbbell type”, and the area of crushing region is smaller than that under conventional blasting. While the fracture region is of “spindle type”, the fracture is better developed. The field test shows that the gas volume fraction of the extraction hole after shaped charge blasting is significantly higher than that under conventional blasting. It is seen that shaped charge blasting can effectively improve the permeability of coal seam with high gas and low permeability.