Analysis of Acoustic Wave Frequency Spectrum Characters of Rock Mass under Blasting Damage Based on the HHT Method

The limitation associated with Fourier transform and wavelet analysis that they often fail to produce satisfactory resolution simultaneously in time and frequency when dealing with nonlinear and nonstationary signals is frequently encountered. Therefore, this paper aims at using the HHT (Hilbert-Huang transform) method, which is built on the basis of the EMD- (empirical mode decomposition-) based wavelet threshold denoising technique and the Hilbert transform, to analyze the blasting vibration signals in a south China lead-zinc mine. The analysis is conducted in terms of three-dimensional Hilbert spectrum, marginal spectrum, and instantaneous energy spectrum. The results indicate that the frequencies of the blasting vibration signals lie mainly within 0∼200 Hz, which consists of more than 90% of the total signal energy. At the onset of the blasting, the vibration frequency tends to be low, with the frequency that is less than 50 Hz being dominant. By using instantaneous energy spectrum, which can reveal the condition of energy release for detonator explosion, the initiation moments of detonators with 7 time-lag levels are accurately identified. This accurate identification demonstrates the superiority of the HHT method in coping with nonlinear and nonstationary signals. Additionally, the HHT method that is characterized by adaptivity, completeness, strong reconfigurability, and high accuracy provides an opportunity for reflecting signals' change features with regard to time domain, frequency domain, and energy irrespective of the limitation of the Heisenberg uncertainty principle.