Influence of the spatial distribution of underground tunnel group on its blasting vibration response

The spatial distribution of underground tunnels is significant to the stress redistribution in the surrounding rock masses and blast wave propagation.The field blasting tests were first carried out to study the propagation of blast-induced seismic waves through under-ground tunnels of the Xiluodu Hydropower Station in China.The results show that the peak horizontal particle vibration velocity can be used as a safety criterion for underground tunnels.The effects of in situ stresses and spatial distributions of the tunnel group on the vibra-tion velocities distribution is afterward investigated by numerical simulation.The results show that there is a significant amplification of the blasting vibrations in the adjacent tunnels,which depends on their vertical positions during the excavation of a tunnel.The peak vibration velocity decreases as the lateral separation between tunnels increases.When the separation between the tunnels exceeds the width of three tunnels,the impact of the blast waves on each part of the adjacent tunnel tends to be stable on the whole.In terms of the size of the tunnel,the blasting vibration velocity in the upper part of the straight wall on the front-blast side increases as the width increases(and then levels off),while the blasting vibration velocity in the lower part decreases as the width increases(and then levels off).Finally,a generalized formula of blasting vibration velocity considering the spatial distribution is established,which can well predict the vibration velocity of particles in underground tunnels.