Numerical Modeling of Environmental Vibration Induced by Millisecond Delayed Blasting of Tunnel Adjacent to Historical Building

The blasting-induced environmental impact of tunneling is a major concern in drill and blast excavation practice, particularly in urban areas. The present paper carries out comprehensive numerical modeling to study the vibration attenuation at the soil surface away from the blasting source as well as the resulting interactions between a historical structure and the surrounding soil, with particular attention to the effects of a millisecond delay. Special attention is given to the interpretation of the role of the local site effects in terms of the frequency-dependent changes of the vibration attenuation mechanism and the response of the historical structure. The velocity responses along the ground surface generally exhibit higher-frequency suppression and low-frequency amplification for both instantaneous blasting and millisecond delay blasting cases in the layered soil–rock site. The millisecond delay blasting can effectively avoid excessive vibration velocity and thus reduce the vibration amplitude at the ground surface by 60–70% (compared with instantaneous blasting), with the predominant frequency mainly concentrated in the high frequence band of 400–500 Hz. The empirical formulae for predicting the vibration attenuation along the scale distance in a soil–rock site has been proposed for both instantaneous blasting and millisecond delay blasting. Through the HHT spectral analyses of the velocity response of the historical structure, it is seen that the difference of structure properties between the wood-frame tower and the base masonry structure has a remarkable influence on the structural vibration. The numerical results can provide a reliable reference for the practical blasting scheme and the systematic study of the dynamic responses of historical structures subjected to blasting-induced vibrations.