A Research on the Delay Time of Vibration Reduction in an Open Pit Mine Based on the Dominant Principal Frequency

Vibrations generated by blasting operations in open-pit mines can have adverse effects on nearby buildings. To mitigate these vibrations by selecting an appropriate delay time, blasting vibration monitoring experiments were conducted in an open-pit mine. The characteristics of peak particle velocity (PPV) and principal frequencies of seismic waves from single-hole and group-hole blasting were analyzed, and an equation for the decay of PPV during the propagation of blasting seismic waves was established. To address the uncertainty in the principal frequency of seismic waves from single-hole blasting, the dominant principal frequency of single-hole blasting seismic waves was defined. A method for determining the optimal vibration-reduction delay time based on the dominant principal frequency of single-hole blasting seismic waves was proposed. Using the bootstrap method, the dominant principal frequency of single-hole blasting seismic waves was estimated to be 20 Hz. Combining this with the principle of staggered-phase superposition, the optimal vibration-reduction delay time between boreholes was determined to be 25 ms. The vibration-reduction effectiveness of the optimal delay time was verified through field experiments. The results show that, compared with the original inter-hole delay time of 42 ms, a delay time of 25 ms achieves good vibration reduction, with average reduction rates of 28.3%, 19.4%, and 20.6% in the horizontal radial, horizontal tangential, and vertical directions, respectively. These research findings can serve as a reference for optimizing delay times and controlling blasting vibrations in deep-hole open-pit blasting.