## 4 Numerical Analysis Results
### Effects of blasting Vibration on the TBM Backup Unit Adjacent to the Blasting Point  
Because the effects of blasting vibration are typically evaluated according to the vibration velocity, the vibration velocities transmitted to the TBM backup device (bottom and side) adjacent to the blasting point were measured and compared according to rock type (hard rock, soft rock, and weathered rock) and powder factor (0.5, 0.75, 1.0, and 2.0 kg). In Figure 5, the red, yellow, green, and blue lines represent the vibration velocities at powder factors of 0.5, 0.75, 1.0, and 2.0 kg, respectively. These vibration velocities decrease with distance from the blasting point in all rock types. Specifically, the vibration velocity at the bottom point gradually decreases with increasing distance. The vibration velocity at the sidewall exhibits a sharp decrease at a distance of 3 m (6-m point on the graph) from the blasting point (3-m point). This result can be assumed to be because the TBM and NATM parallel excavation method performs blasting on the contour hole without a center-cut blasting hole, so the blasting vibration is transmitted to the sidewalls closer to the contour hole. The vibration velocity was observed to be the highest in hard rock, followed by soft rock, and weathered rock, indicating better vibration transmission in denser rock. Compared to the domestic standards for permissible blasting vibration, the vibration velocity at the sidewall is lower than the regulated value only when a distance of  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variable\(\backslash\)**:** & 4 & 8 & 16 \\
**Pilot Tunnel Length (m)** & & & \\ \hline
**Variable\(\backslash\)**:** & & & \\
**Rock Condition** & & & \\ \hline
**Variable\(\backslash\)**:** & & & \\
**Powder Factor (kg)** & & & \\ \hline \hline \end{tabular}
\end{table}
Table 7: Numerical analysis case classification.  
Figure 4: Vibration velocity measurement points.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Measurement Point** & **Position** \\ \hline A & TBM backup equipment (bottom) \\ B & TBM backup equipment (side) \\ C & Rear of TBM \\ D & Ground above the TBM \\ E & TBM tunnel face \\ F & Ground surface \\ \hline \hline \end{tabular}
\end{table}
Table 8: Numerical analysis case classification.  
at least 7 m (10-m point on the graph) is maintained from the blasting point, regardless of the rock type and powder factor. At the bottom, the vibrations in the hard and soft rocks were measured to be lower than the regulated level at a distance of at least 3 m from the blasting point [13]. Therefore, depending on the selection of the powder factor according to rock type, the separation distance (economic efficiency) can vary significantly.  
Figure 5: Cont.  
Figure 5: Analysis results for vibration velocity according to rock type and powder factor (measurement points A and B): (**a**) bottom of the TBM backup (hard rock), (**b**) bottom of the TBM backup (soft rock), (**c**) bottom of the TBM backup (weathered rock), (**d**) side of the TBM backup (hard rock), (**e**) side of the TBM backup (soft rock), and (**f**) side of the TBM backup (weathered rock).