## 4 Field Monitoring and Stress Analysis
### Monitoring Test Setup, Materials, and Methods  
The purpose of dynamic strain monitoring is to measure stress in the surrounding rock of the adjacent tunnel during blasting, verify the accuracy of the previously derived analytical stress solutions, and analyze stress variation patterns induced by blasting. An ultra-dynamic strain measurement system (Figure 13) was used to monitor dynamic strain in the tunnel surrounding rock. The testing procedure, shown in Figure 14, operates as follows: voltage signals were collected via embedded sensors, converted into strain values using Equation (26), and dynamic stress peaks are then calculated based on [PERSON]'s law (Equation (27)) [40]. \[\varepsilon=4\times U/\mathrm{K}\times U_{0}\times n\times G \tag{26}\]  
Figure 12: Blasting network diagram. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Borehole Type** & **Number of Boreholes** & **Charge per Hole (kg)** & **Total Charge (kg)** & **Delay Segment** \\ \hline \multirow{2}{*}{Cut Holes} & 6 & 1.5 & 9.0 & Segment 1 (0 ms) \\ \cline{2-5}  & 8 & 2.4 & 19.2 & Segment 2 (50 ms) \\ \hline \multirow{4}{*}{Auxiliary Holes} & 11 & & 19.8 & Segment 3 (100 ms) \\ \cline{2-5}  & 13 & & 23.4 & Segment 4 (150 ms) \\ \cline{2-5}  & 16 & & 28.8 & Segment 5 (200 ms) \\ \cline{2-5}  & 24 & & 43.2 & Segment 6 (250 ms) \\ \hline \multirow{2}{*}{Contour Holes} & 18 & & 27.0 & Segment 7 (300 ms) \\ \cline{2-5}  & 18 & & 27.0 & Segment 8 (350 ms) \\ \hline Floor Holes & 16 & 1.8 & 28.8 & Segment 9 (400 ms) \\ \hline Total & 130 & & 226.2 & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Blasting parameters of upper bench. \[\sigma=\mathrm{E}\epsilon \tag{27}\]  
where \(U\) is the peak output voltage (V), K is the sensitivity coefficient of the strain gauge, \(U_{0}\) is the bridge voltage of the strain amplifier (V), \(n\) is the number of effective bridge arms, \(G\) is the gain of the strain amplifier, and E is the elastic modulus of the rock mass (GPa). The dynamic strain test uses a half-bridge circuit, with the instrument parameters listed in Table 4.  
The operating principle of the triggered voltage signal recording system is illustrated in Figure 15. When blast loads act on the strain bar, it undergoes minor deformation, causing the bonded strain gauges to change resistance. The resistance change produces a microvolt-level output via a Wheatstone bridge. The signal is then amplified by an ultra-dynamic strain amplifier, triggering a pulse that converts the microscopic deformation into a millivolt-level voltage signal recorded by the system. The measurement point layout is shown in Figure 16. Horizontal boreholes are drilled into the sidewall of the adjacent existing tunnel, with five strain measurement points spaced at 1 m intervals (Point 1 is 1 m from the sidewall). Prefabricated strain bars, matched to \begin{table}
\begin{tabular}{c c c c} \hline \hline
**K** & **\(U_{0}\)/V** & \(n\) & \(G\) \\ \hline
2.0 & 4.0 & 1 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Key parameters of the instrument. Figure 14: Flowchart of the testing system. Figure 15: Schematic diagram of the voltage signal recording mechanism. the physical and mechanical properties of the tunnel surrounding rock, are used. Triaxial resistance strain gauges are mounted on the bars to measure strain via electrical resistance (Figure 17). The instrumented bars are inserted into the boreholes and fixed with grout. A schematic diagram of the strain bar inserted into the borehole is shown in Figure 18, where the specifications of the PVC pipe in the diagram are consistent with those of the on-site drilling. To determine the rock mass damage factor D at the same locations, a YL-LCT single-transmitter dual-receiver sonic probe (Figure 19) is used to measure P-wave velocities. Sonic testing boreholes are drilled 0.5 m from the strain measurement holes (Figure 20), ensuring spatial alignment for accurate comparative analysis.