## 4 Applicability Analysis of Theoretical Calculation Method of Loose Zone
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Working** \\ **Condition** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Surrounding** \\ **Rock Type** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Buried** \\ **(m)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Surrounding** \\ **Rock Grade** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Moulus** \\ **of** \\ **(GPa)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Poisson's** \\ **Ratio** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Friction** \\ **Angle** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Cohesion** \\ **(MPa)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Density** \\ **(Mg/m)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Range** \\ **(m)** \\ \end{tabular} } \\ \hline \multirow{2}{*}{1} & Moderately & \multirow{2}{*}{20.0} & IV & 4.0 & 0.26 & 30 & 0.2 & 2400 & 1.2-1.4 \\  & Neufengly & \multirow{2}{*}{22.5} & IV–V & 1.0 & 0.34 & 30 & 0.16 & 2200 & 1.8-2.6 \\  & Shephy weathered & \multirow{2}{*}{23.0} & III & 4.0 & 0.26 & 38 & 0.2 & 2620 & 0.6-1.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Measured data of the surrounding rock and loose zone under different operating modes. Figure 10: Monitoring waveform diagram of working condition 3: (**a**) Vault waveform; (**b**) spandrel waveform. Figure 9: Monitoring waveform diagram of working condition 2: (**a**) Vault waveform; (**b**) spandrel waveform. surrounding rock compaction area (increased stress area) and the loose area. However, it should be pointed out that the loose zone was not equal to the plastic zone but to the relaxed part of the rock mass in the plastic zone. By analyzing the measured wave velocity data, it could be ascertained that under the working conditions corresponding to moderately weathered granite, the thickness of the loose zone was 1.2-1.4 m. Under the working conditions corresponding to strongly weathered granite, the thickness of the loose zone was 1.8-2.6 m, and under the working conditions corresponding to slightly weathered granite, the thickness of the loose zone was 0.6-1.5 m. From the measured data, it could be seen that the worse the surrounding rock conditions, the greater the thickness of the loose zone. The range of the loose zone under different working conditions can be obtained, as shown in Figure 11.  
According to the field-measured data, under the same tunnel section, the higher the weathering degree of the surrounding rock, the worse the surrounding rock conditions, the deeper the burial depth, and the greater the thickness of the loose zone. Under the condition of strongly weathered and moderately weathered granite, the thickness of the surrounding rock loose zone was sorted as follows: arch shoulder > arch crown > arch waist; under the condition of weakly weathered granite, arch crown > spandrel > spandrel. The worse the surrounding rock condition, the greater the difference in the range of loose zones in different parts of the tunnel section. Through the above analysis, it could be seen that the lower the  
Figure 11: Schematic diagram of the loose zone range under three working conditions: (**a**) Schematic diagram of the loose zone range under working condition 1; (**b**) schematic diagram of the loose zone range under working condition 2; (**c**) schematic diagram of the loose zone range under working condition 3.  
from the analysis of measured data that the scope of the surrounding rock loose zone was affected by surrounding rock conditions, burial depth, and section position. Next, the stress method and work-energy relationship method described above were used to theoretically calculate the working conditions, and the results were compared with the actual values measured on site to test the applicability of these methods. During the calculation, the tunnel section was analyzed based on the equivalent circular tunnel section.