Abstract: 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.

Key words: underground cavern, vibration of rock mass, blasting excavation, explosion-induced seismic wave, vibration frequency