Abstract
The selection of delay time will directly affect the effect of vibration reduction in millisecond delay blasting. The commonly used frequency spectrum control methods have some problems such as the difficulty of seed wave selection and the complexity of nonlinear superposition model. Based on the principle of waveform linear superposition, this study proposes a new spectrum superposition method for minimizing the vibration hazards in an open deep-hole bench blasting. This method, with no need to select the seed waves, mainly uses the ratio of the Fourier spectrum of the combined vibration waveform and the single hole vibration waveform to quantify the suppressed vibration. By defining the suppression ratio K, the suppression ratio with frequency range of 10 – 60 Hz under different delay times was calculated, and the theoretical optimal vibration reduction delay time value of 10 – 15 ms was given. A high precision digital electronic detonator was used to verify the proposed spectrum superposition method. The test results show that the best delay time of field vibration reduction is 5 – 10 ms, which is lower than the theoretical best delay time of 10 – 15 ms. It is the authors’ belief that this phenomenon is mainly caused by the joints and cracks in the rock mass, which will prolong the actual superposition time of blasting seismic waves between adjacent holes. In addition, it is found that there is a negative correlation between the delay time and the main vibration frequency, which is mainly caused by the low-pass filtering characteristic of rock medium. In order to minimize the probability of resonance failure, an optimal delay of 5 ms based on the main vibration frequency was given.
Published Version
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