## 4 Field Application
The pre-excavation boreholes are arranged on the tunnel face (Figure 14), the rock cores are collected via pre-excavation boreholes for investigation, and the \(RBI\) value of rock mass (Table 5) for each borehole is calculated using Equation (9) and the core length measured on site. For the monitoring of surrounding rock mass deformation after excavation, the on-site monitoring point placement is illustrated in Figure 14.  
Figure 12: The overburden near monitoring section K143 + 621. Figure 13: Tunnel face (unexcavated) at K143 + 630. (**a**) Geological sketch picture. (**b**) Photo of the tunnel face. Taking Point 4 as an example, the field investigation shows that the RBI of the surrounding rock mass cores at Point 4 is about 2.8; the AWI is about 0.65. According to Table 4, the _GSI_ value is 33. For the intact phyllite rock, the Hoek-Brown constant \(m_{\rm i}=10\) and the uniaxial compressive strength \(\sigma_{c}=35\) MPa. From Equation (5), we have \(\sigma_{3 max}=\frac{\sigma_{c}}{4}=8.75\) MPa and from Equations (2)-(4), we have \(m_{\rm b}=0.916\), s = 0.000587, and \(a=0.518\). Finally, according to Equation (1), the uniaxial comprehensive strength of the rock mass \(\sigma_{r}=16.33\) MPa and the elastic modulus \(E_{0}=1.11\) GPa. The basic parameters at the other points are summarized in Table 6.  
Figure 14: Monitoring point and pre-excavation borehole placement in the tunnel (K143 + 621). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Monitoring** & **Cores** & **RBI Values** \\
**Point** & & \\ \hline
1 & & 6.763 \\
2 & & 5.626 \\
3 & & 3.748 \\
4 & & 3.748 \\
5 & & 4.331 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Cores collected via pre-excavation boring at each monitoring point and the RBI values. The fitting of the creep constitutive model (Equation (11)) to the surrounding rock mass monitoring data (Figure 15) was performed using the least square method to calculate the creep parameters of the rock mass at each monitoring point. The calculation results are shown in Table 7. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Monitoring** & \multirow{2}{*}{_RBI_} & \multirow{2}{*}{_AWI_} & \multirow{2}{*}{_GSI_} & \multirow{2}{*}{_m\({}_{\text{b}}\)_} & \multirow{2}{*}{_s_} & \multirow{2}{*}{_a_} & \(\sigma_{r}\) & \(\sigma_{3}\)=\(\frac{\sigma_{r}}{4}\) & \(E_{0}\) \\
**Point** & & & & & & & (MPa) & (MPa) & (GPa) \\ \hline
1 & 6.763 & 1.570 & 79.708 & 2.212 & 0.001418 & 0.27 & 36.8 & 45.29 & 2.69 \\ \hline
2 & 5.626 & 1.306 & 66.305 & 1.840 & 0.001179 & 0.22 & 32.28 & 37.67 & 2.24 \\ \hline
3 & 3.748 & 0.870 & 44.169 & 1.226 & 0.000786 & 0.15 & 21.57 & 25.10 & 1.49 \\ \hline
4 & 2.8 & 0.65 & 33 & 0.916 & 0.000587 & 0.11 & 16.33 & 18.75 & 1.11 \\ \hline
5 & 4.331 & 1.006 & 51.050 & 1.417 & 0.000908 & 0.17 & 22.8 & 29.01 & 1.73 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Basic parameters of the surrounding rock mass at each monitoring position. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Point No. ** & \(\mathbf{E}_{0}\)**/GPa** & \(\sigma_{r}\) **(MPa)** & \(\mathbf{E}_{1}\)**/GPa** & \(\eta_{1}\)**/(GPa-d)** & \(\eta_{2}\)**/(GPa-d)** \\ \hline
1 & 2.69 & 36.8 & 0.8 & 16.38 & 93.71 \\ \hline
2 & 2.24 & 32.28 & 0.71 & 11.22 & 88.63 \\ \hline
3 & 1.49 & 21.57 & 0.5 & 8.78 & 6.55 \\ \hline
4 & 1.11 & 16.33 & 0.4 & 7.87 & 5.62 \\ \hline
5 & 1.73 & 22.8 & 0.6  
Section K143 + 621 was chosen for numerical simulation.