# Study on Blasting Vibration Control of Brick-Concrete Structure under Subway Tunnel
## 4 Spectrum and Energy Analysis of Blasting Vibration Signal  
### Signal Decomposition and Analysis  
#### 4.1.1 EMD Decomposition and Analysis of Signals  
The original signals measured in the field before and after the scheme optimization are relatively complex, so it is very difficult to analyze them directly. The primary task to obtain the signal is to decompose it, and then analyze the components obtained after decomposition. The EMD method does not require preset basis functions and has the advantages of adaptability and efficiency [42]. The original signals can be decomposed into components by the EMD method. These components are different in time scale, and these IMF components contain the original signal's own characteristics. These IMF components have specific and practical physical meanings, and they can express the most outstanding information of the original signal. The blasting vibration signal is decomposed by EMD in multiple layers, and IMF components and power spectral density (PSD) will be obtained from the decomposition. They are shown in Figure 11. Figure 11a shows the IMF component of the original signal before scheme optimization, Figure 11b shows the power spectral density (PSD) of the original signal before scheme optimization, Figure 11c shows the IMF component of the original signal after scheme optimization, and Figure 11d shows the power spectral density (PSD) of the original signal after scheme optimization. It can be seen from Figure 11a,b that twelve components of c1-c11 and R are obtained after EMD decomposition of the signal before scheme optimization. The amplitude and frequency of different IMF components are different. Most of the IMF components obtained by EMD are of physical significance; c1 represents the white noise contained in the signal, and c2 and c3 represent the high frequency of the signal. The most important part of the vibration signal is composed of c4-c6. Their vibration amplitude is relatively large. The dominant range of the frequency corresponding to c4 is 20-40 Hz, the dominant range of the frequency corresponding to c5 is 40-50 Hz, and the dominant range of the frequency corresponding to c6 is 0-20 Hz. The secondary part of the signal is composed of components c7-c11 with small amplitude and frequency of vibration velocity, whose frequency is within 20 Hz, and component R is the residual quantity of blasting vibration signal. It can be seen from Figure 11c,d that thirteen components of c1-c12 and R are obtained after EMD decomposition of the optimized signal; c1 is the white noise contained in the signal, and c2 is the high-frequency component of the signal. The most important part of the vibration signal is composed of c3-c7. Their vibration amplitude is relatively large. The dominant range of the frequency corresponding to c3 is 100-150 Hz, the dominant range of the frequency corresponding to c4 is 50-100 Hz, the dominant range of the frequency corresponding to c5 is 20-50 Hz, the dominant range of the frequency corresponding to c6 is 0-50 Hz, and the dominant range of the frequency corresponding to c7 is 0-50 Hz. The  
Figure 11: The result of EMD resolution before and after optimization (**a**) the IMF component of the original signal before scheme optimization (**b**) the power spectral density (PSD) of the original signal before scheme optimization (**c**) the IMF component of the original signal after scheme optimization and (**d**) the power spectral density (PSD) of the original signal after scheme optimization. secondary part of the signal is composed of components c8-c12 with small amplitude and frequency of vibration velocity, whose frequency is within 30 Hz, and component R is the residual quantity of blasting vibration signal. The EMD method is used to decompose the original signal, and the IMF component is obtained. The IMF component contains white noise and high-frequency of the signal with a small amount of energy.