大型地下洞室上层爆破开挖对下层围岩振动特性的影响

某地下实验厅采用上、下层同时爆破开挖,最后进行贯通的开挖施工方案。采用现场爆破试验监测的手段,研究了上层水平钻孔爆破开挖时下层围岩的质点峰值振动速度及频率特性,分析了上层爆破开挖对下层围岩动力稳定的影响。研究结果表明,大型地下洞室上层水平钻孔爆破开挖时,爆炸地震波能量主要向下层岩体传播,致使下层洞室顶拱处的振动速度大于上层底板相同距离处的振动速度;爆破振动主要以剪切波(SV波)的形式向下层岩体传播,下层洞室围岩在平行于炮孔纵轴向(实验厅纵轴向)方向上的振动速度最大;由于上层的爆破振动以体波的形式在岩体内向下层传播,下层围岩的振动频率更高。

Vibration Characteristics of Lower Rock Masses During Blasting Excavation of Upper Layers in a Large Underground Cavern

The blasting excavation of an underground laboratory was carried out with the upper and lower layers excavated simultaneously. The peak particle velocity (PPV) and frequency characteristics in the lower layer of rock mass during the horizontal-hole blasting in the upper layer were investigated by using field blasting vibration monitoring. On this basis, the influence of upper-layer blasting on the dynamic stability of lower-layer rock mass was analyzed. Results demonstrate that during the horizontal-hole blasting in the upper layer excavation, the explosion-induced seismic wave energy preferentially propagates into the lower rock mass, which results in the PPV at the roof of the lower opening to be greater than that on the upper floor at the same distance. With regard to the downward-propagating seismic waves, a significant amount of energy is transported in the shear-vertical (SV) mode. As a result, the maximum vibration velocity component occurs in the direction along the blasthole axis (also the laboratory axis). In addition, the vibration frequency in the lower rock mass is significantly higher than that on the upper floor because the downward-propagating body waves travel at depth in a relatively competent medium, while the surface vibration on the upper floor travels in a weaker layer.