# Study on Blasting Vibration Control of Brick-Concrete Structure under Subway Tunnel
## 2 Blasting Scheme and Parameters
### Propagation Law of Blasting Vibration  
According to the stipulations in the blasting safety regulations GB6722-2014 [37], due to the low vibration frequency of brick concrete structure buildings, the allowable safe vibration velocity is 1.5-2.0 cm/s. Before the optimization of the blasting scheme, the measured peak vibration velocity is in the range of 0.764-4.603 cm/s. After the blasting scheme is optimized, the measured vibration peak velocity is within the range of 0.607-1.835 cm/s, which is less than 2.0 cm/s. The vibration peak velocity after the blasting scheme is optimized meets the safety requirements specified in the blasting safety regulations. According to Table 2, the relationship between the vibration peak speed and the position of the working face is drawn, as shown in Figure 8.  
In the forward direction of the subway tunnel work, the peak vibration velocity before the optimization of the blasting scheme is significantly greater than the peak vibration velocity after the optimization of the blasting scheme, which shows that the effect of the optimization of the blasting scheme is very significant. After the optimization of the blasting scheme, the peak vibration speed is relatively high when the working face mileage is DK44+219.04. This is the exterior wall of the brick concrete structure kindergarten. When the working face mileage is greater than DK44+219.04, it enters the kindergarten. When the working face mileage is less than DK44+219.04, it enters the road surface. When blasting seismic wave propagates in rock and soil, the denser the rock and soil, the higher the wave velocity, the looser the rock  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Scheme**} & \multirow{2}{*}{**Order**} & \multicolumn{3}{c}{**Vibration Peak Velocity (cm\(-\)s\({}^{-1}\))**} & \multicolumn{3}{c}{**Vibration Frequency (Hz)**} & **Mileage of** & **Charge** \\ \cline{2-11}  & & **Mexaursing** & **Measuring** & **Measuring** & **Measuring** & **Measuring** & **Measuring** & **Measuring** & **Measuring** & **Working** & **Quantity** \\  & **Point 1** & **Point 2** & **Point 3** & **Point 4** & **Point 1** & **Point 2** & **Point 3** & **Point 4** & **Point 4** & **Point 4** & **Face (m)** & **Face (s)** \\ \hline \multirow{9}{*}{ \begin{tabular}{c} Before optimization \\ \end{tabular}  } & 1 & 1.697 & 4.264 & 1,904 & 0.95 & 1.53 & 1.53 & 1.53 & 1.53 & DK44+195.04 & 9 \\  & 2 & 1.431 & 2.512 & 1.417 & 0.806 & 1.53 & 1.53 & 1.53 & 1.53 & DK44+195.04 & 7 \\  &  
and soil, the lower the wave velocity [38]. During the blasting operation in the subway tunnel, the blasting seismic wave propagates from the blasting source to the buildings on the ground. Because the materials at the foundation are relatively dense, the wave velocity of the blasting seismic wave propagating to the buildings through the foundation will be higher, and the blasting vibration effect caused by it will be greater. When the working face mileage is DK44+219.04, the foundation is below, and the bearing wall is above the foundation. The density of materials is very good, which is far greater than the density on both sides of the wall. When the blasting seismic wave propagates upward from the blasting source, because the density of the working face mileage at DK44+219.04 is greater than that on both sides, according to the theory mentioned above, the wave speed transmitted here during blasting is greater than that on both sides, and the vibration speed of the ground surface is also greater than that on both sides. According to the data in Table 2, the relationship between the vibration peak speed and the location of the measuring point is drawn, as shown in Figure 9. Digital Group1-13 in the figure represents 13 field tests. According to Figure 9, for the monitored measuring points, the peak vibration velocity increases first and then decreases from near to far from the working face, and the peak vibration velocity of the surface particle is the largest at 5 m in front of the working face.