摘要:
在良好破碎效果的前提下,通过降低孔底冲击波峰值压力来减小上向扇形深孔孔底以上岩体振动,是降低振动保护上部建筑的有效措施。为确定合理的孔底空气柱长度,采用理论研究与现场模型爆破动态测试试验相结合的方法,研究了孔底空气不耦合装药时,空气柱长度对孔壁冲击压力的变化规律,得到了炮孔底部空气间隔不耦合装药条件下轴向不耦合系数与孔壁冲击压力随时间的变化曲线;基于岩石动态抗压强度,确定了适用于软、中、硬岩石的合理底部轴向空气间隔长度范围,研究结果表明:空气间隔层的存在,使得冲击压力作用时间显著增加,而冲击压力峰值有明显减小;当K=1.5,空气柱长度200mm时,孔底峰值压力衰减比例为73.4%,当K=4,空气柱长度1.2m时,孔底峰值压力衰减比例达到96.7%。当空气间隔层大于60cm时,炮孔底部出现压力值较低的区域。现场工业试验验并对爆破后采场顶板成型和爆堆块度的观察和拍照表明:合理的底部空气间隔长度,不仅能保证良好的爆破块度,同时也能通过减小孔底峰值压力降低爆破振动以达到保护采场顶板及其它保护对象的目的。
Abstract:
On the premise of good crushing effect, reducing the rock mass vibration above the bottom of the upward fan-shaped deep hole by reducing the peak pressure of the shock wave at the bottom of the hole is an effective measure to reduce the vibration and protect the superstructure. In order to determine the reasonable length of the air column at the bottom of the hole, the variation law of the length of the air column on the impact pressure of the hole wall when the air at the bottom of the hole is not coupled is studied by combining the theoretical research with the field model blasting dynamic test. Based on the theories of one-dimensional unsteady hydrodynamics and theoretical detonation physics, The action process and propagation law of shock wave in the blast hole after the explosion of bottom air interval charge column under the condition of cylindrical charge are discussed in stages. Considering the reflection and transmission of shock wave at the interface of different media, the parameters of shock wave front propagating in different directions and the initial shock pressure and action time acting on the hole wall in each stage are analyzed, Thus, the calculation formula and variation curve of pressure acting on the hole wall in each stage are obtained. In order to verify the above laws, six groups of 12 cylinder thick wall concrete models with different sizes were designed and made, and the bottom air interval blasting model tests were carried out. The air column lengths were 200mm, 400mm, 600mm, 800mm, 1000mm and 1200mm respectively. During the blasting process, the blast ultra high-speed multi-channel dynamic strain testing system was used to monitor the hole wall impact pressure, analyze the monitoring data and verify with the theoretical results, Finally, the variation curve of axial decoupling coefficient and hole wall impact pressure with time under the condition of uncoupled charge in air interval at the bottom of blast hole is obtained; Based on the dynamic compressive strength of rock, the reasonable length range of bottom axial air interval suitable for soft, medium and hard rocks is determined. In order to verify the rationality of the conclusion, the field industrial test is carried out, the charging blasting is carried out by using the air interval at the hole bottom, and the observation and photo analysis of the roof forming and blasting pile size after blasting are carried out. The research results show that the existence of air interval significantly increases the action time of impact pressure, The peak value of impact pressure decreases obviously; When k = 1.5 and the length of air column is 200mm, the attenuation ratio of peak pressure at the hole bottom is 73.4%; when k = 4 and the length of air column is 1.2m, the attenuation ratio of peak pressure at the hole bottom reaches 96.7%. When the air compartment is greater than 60cm, the area with low pressure value appears at the bottom of the blast hole. The reasonable bottom air interval length can not only ensure good blasting fragmentation, but also reduce blasting vibration by reducing the peak pressure at the hole bottom, so as to protect the stope roof and other protected objects.