Determination and application study of optimal delay time for tunnel millisecond blasting based on interference vibration reduction method

Abstract

In tunnel excavation, blasting is widely adopted as an efficient excavation method. However, the influence of vibration on tunnel surrounding rock and support structures during the blasting process cannot be ignored. In this study, based on the background of tunnel blasting construction, we theoretically analyze the reasonable range for selecting the optimal delay time, considering the wave superposition cancellation effect and rock fragmentation effect. We use field measured single-hole waveform and calculate superimposed predicted waveforms for different delay time through linear superposition. This allows us to determine the optimal delay time; it is then validated through numerical simulation and field experiment. The results indicate that, based on the principles of interference vibration reduction and rock fragmentation, the optimal delay time in theory should be in the range of 6.14–8.06 ms. By performing superposition calculation on the measured single-hole waveforms, we determined that the optimal delay time for continuous detonation of cut-holes is 7 ms. The delay time of 7 ms falls within a reasonable millisecond range and it is consistent with the results of numerical simulation. When the optimal delay time was applied to field blasting, the measured vibration waveforms exhibited uniform distribution. Compared to blasting without delay, the peak vibration velocity of the cut-holes decreased from 2.08 cm/s to 0.20 cm/s, and the dominant frequency band shifted from 20 Hz–60 Hz to 30 Hz–120 Hz. This achieved the desired effects of reducing vibration and enhancing frequency. These findings can serve as a reference for future similar engineering projects.