Prediction of Tunnel Blasting Vibration Velocity Considering the Influence of Free Surface

Abstract

The blast vibration attenuation will change as the tunnel cut hole is blasted to create a new free surface. To guarantee safe tunnel construction and optimize blast design parameters, it is crucial to understand the impact of the free surface on blast vibration attenuation. Previous studies have often only qualitatively evaluated the effect of the free surface on blast vibration, failing to quantify these impacts on vibration attenuation. In this paper, by analyzing the decay law of the blast vibration velocity under different free surfaces, we quantitatively assessed the effect of the number of free faces and burden distance on the peak vibration velocity. Then, we introduced free-face parameters to enhance the current formula for predicting blast vibration velocity. The results show that the peak vibration velocity decreases with the increasing free surface number and increases with increasing burden distance; the free surface factor cannot be ignored in the decay of vibration velocity and contributes about 21% more to the total decay factor than the scale distance factor. The average tolerance rises from 24.79% in the Sadovsky formula to 13.32% in the correction formula, and the correction formula more precisely predicts the peak vibration velocity. The accuracy of the correction formula provides a good scientific basis for the design of tunnel blasting parameters. The research results were successfully applied to the Jiujiawan proximity tunnel on the Duyun-Anshun highway in Guizhou, effectively guaranteeing blasting safety with a minimum clear distance of 17.2 m.