# Study on Blasting Vibration Control of Brick-Concrete Structure under Subway Tunnel
## 5 Conclusions  
This paper is based on the underground excavation of the tunnel between Zhifang Street Station and Metro Town Station of Wuhan Metro Line 27. In order to make the subway tunnel pass through the brick concrete structure buildings safely, the blasting scheme is optimized by reducing the maximum single-section and multi-section charges, increasing the distance between the upper and lower steps, and densifying the surrounding holes. Based on the field experiment results, the HHT method and wavelet analysis are used to evaluate the advantages and disadvantages of the optimization scheme from the perspective of energy. The HHT method first decomposes the signal by EMD, then obtains the MF component and power spectral density (PSD), and finally, the distribution of frequency and PSD, the relationship between energy amplitude and time, and the Hilbert energy spectrum of vibration signal are further obtained. In the wavelet transform, db8 is selected as the wavelet base, then the wavelet components are obtained through transformation, and finally, the frequency band energy distribution and three-dimensional energy spectrum are obtained. The following conclusions are obtained:  
1. The peak velocity and frequency of vibration at monitoring points before and after the optimization of blasting schemes were monitored. The peak velocity of blasting vibration after the optimization of the blasting scheme was significantly lower than that after the optimization of the blasting scheme, and both were less than 2.0 cm/s; The blasting vibration frequency after the optimization of the blasting scheme is significantly higher than that before the optimization of the blasting scheme, which is more difficult to form resonance, and the building is safer.
2. After the blasting scheme is optimized, the peak vibration velocity is at maximum when the blasting construction is directly under the exterior wall of the brick concrete structure. When blasting to such parts, the maximum single-section charge shall be kept as small as possible, and millisecond blasting shall be used for multi-section blasting.
3. Within the monitoring range, from the back of the working face to the front of the working face, the peak velocity of surface particle vibration increases first and then decreases. The peak velocity of surface particle vibration is the largest at 5 m in front of the working face, and the cavity effect and diffraction of the stress wave are obvious.
4. From the perspective of energy, the optimized blasting scheme has a wider frequency band of measured vibration signal energy distribution, a more decentralized energy, and a safer optimized scheme than before.  
Figure 18: The three-dimensional energy spectrum of blasting vibration signal (**a**) before optimization and (**b**) after optimization.  
**Author Contributions:** Conceptualization, Q.Z. and J.W.; methodology, Y.W.; software, Y.W.; validation, Y.W., C.M., and Q.Z.; formal analysis, Y.W.; investigation, H.Z.; resources, Q.Z.; data curation, Y.W.; writing--original draft preparation, Y.W.; writing--review and editing, Y.W.; visualization, Y.W.; supervision, C.M.; project administration, Q.Z.; funding acquisition, Q.Z. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural Science Foundation of China, grant number 51404010.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data used to support the findings of this study are available from the corresponding author upon request.  
**Conflicts of Interest:** The authors declare no conflict of interest.