Abstract
The blasting vibration signal obtained from tunnel construction monitoring is affected by the external environment, which contains a lot of noise that causes distortion during signal processing. To analyse the blasting vibration signal and determine the appropriate water seal blasting charge structure for construction, combined with wavelet threshold denoising method and HHT transformation, the blasting vibration signals of the four charge structures of conventional charge, water interval charge at both ends, water interval charge at the orifice, and water interval charge at the hole bottom are denoised and HHT is analysed. The results show that the wavelet threshold method can effectively eliminate high-frequency noise in the blasting vibration signals and retain information carried by the vibration signal itself. The frequency and energy of the blasting vibration signals of the water interval charge at both ends are densely distributed in the range of 0 s to 0.9 s and below 100 Hz. The frequency and energy of the blasting signals of the other three charging structures are reduced within the same range, sparse areas appear, and the instantaneous total energy is smaller than that with a water interval charge at both ends, which shows that the water interval charge at both ends can effectively apply explosive energy to the surrounding rock and reduce energy loss in the explosive. The blasting vibration signal energy of the water interval charge at both ends is mainly concentrated in components IMF2 to IMF5, and the corresponding frequencies are concentrated at 6 Hz to 11 Hz and 20 Hz to 70 Hz, while the blasting vibration signal energy of other three charge structures is mainly distributed in components IMF2 to IMF4, corresponding frequencies are concentrated within 20 Hz to 70 Hz, and the distribution at low frequencies is not obvious. Therefore, when using the water interval charge at both ends, it is necessary to increase the main vibration frequency of the original vibration signals by reducing the single section charge and using frequency shift technology to avoid the natural frequency of the structure and reduce resonance-induced damage.
Highlights
In the tunnel blasting process, in addition to crushing the rock, the explosive energy propagates within the surrounding rock to form a vibration signal in the form of stress waves
Li et al used multifractal analysis to analyse the singular spectrum of vibration signals and used a multifractal spectrum derived by use of the wavelet transform [11]
E Hilbert transform is applied to multiple intrinsic mode functions (IMFs) signals obtained by the empirical mode analysis (EMD) method. e instantaneous spectrum of each IMF component can be obtained. e Hilbert spectrum can be obtained by synthesising the instantaneous spectrum of all IMF components. e Hilbert transform is a type of linear transformation, which emphasises the local properties of the signal. e instantaneous frequency obtained by use of the Hilbert transform is the best definition: it avoids many spurious high- and low-frequency components produced by the Fourier transform
Summary
In the tunnel blasting process, in addition to crushing the rock, the explosive energy propagates within the surrounding rock to form a vibration signal in the form of stress waves. TM et al used MATLAB combined with wavelet analysis to analyse the energy of blasting vibration signals monitored in practice. Cao et al used the HHT method to analyse the measured blasting vibration signals from the perspective of their time-frequency and energy distribution characteristics and assessed the safety of a slope and surrounding buildings [8]. Li et al used multifractal analysis to analyse the singular spectrum of vibration signals and used a multifractal spectrum derived by use of the wavelet transform [11]. Erefore, we take the Wenquan Tunnel in Beijing Yanchong Expressway as the engineering background and combine the wavelet threshold denoising and HHT methods to compare and analyse the measured vibration signals of water seal blasting and conventional blasting signals. According to the analytical results, the appropriate water seal blasting charge structure is selected for tunnel construction
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