## 2 Project Overview and In-Situ Monitoring
### Monitoring Arrangement  
During the construction process of the super-span transition section, detailed monitoring of the deformation and the forces of both the surrounding rock and the support structures was carried out. It can be seen from Figures 3 and 4 that the tunnel within the range of DK68+285-DK68+305 has the characteristics of the largest span and the poorest rock quality. Therefore, the middle section of the above interval, that is DK68+295, was selected as the section to be monitored. As the most commonly used tunnel monitoring instrument, total stations were used to monitor the tunnel displacement, i.e., arch settlement and horizontal convergence. The internal displacement of \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Tunnel Support Type** & **Specific Parameters** & **Installation Area** \\ \hline \multirow{4}{*}{temporary support} & \multirow{2}{*}{fiberglass anchor} & \(\Phi\)25 mm, L = 4 m, 1 m \(\times\) 1 m \\  & & (longitudinal and & \\  & & circumferential spaced) & sidewalls of Drift 1 \\ \cline{2-3}  & steel support & No.16 I-shaped steel, 0.8 m \\  & & longitudinal spaced & sidewalls of Drift 1 \\ \cline{2-3}  & shotcrete & thickness: 8 cm, concrete type: C30 & sidewalls of Drift 1 \\ \hline \multirow{4}{*}{primary support} & \multirow{2}{*}{prestressed anchor bolt} & \(\Phi\)32 mm, L = 11 m, 0.8 m \(\times\) 1.2 m \\  & & (longitudinal and circumferential & \\  & & spacing), 100 kN pretension & \\ \cline{2-3}  & \multirow{2}{*}{prestressed anchor cable 1} & \(\Phi\)15.2 mm \(\times\) 7 steel stranded wires, & \\  & & L = 25 m, 700 kN pretension & \\ \cline{2-3}  & \multirow{2}{*}{prestressed anchor cable 2} & \(\Phi\)15.2 mm \(\times\) 5 steel stranded wires, & \\  & & L = 25 m, 500 kN pretension & \\ \cline{2-3}  & \multirow{2}{*}{steel rib} & \(\Phi\)22 mm four bars lattice girders, & \\  & & 0.8 m longitudinal spaced & whole section \\ \hline \multirow{4}{*}{secondary support} & \multirow{4}{*}{shotcrete of vault} & (1) thickness: 5 cm, concrete type: & \\  & & C30, containing nano-silica and fiber & \\ \cline{1-1}  & & concrete & \\ \cline{1-1}  & & (2) thickness: 18.2 cm, concrete type: & \\ \cline{1-1}  & & C30, containing fiber concrete & \\ \cline{1-1}  & & (3) thickness: 11.8 cm, concrete & \\ \cline{1-1}  & & type: C30 & \\ \cline{1-1} \cline{2-3}  & & shotcrete of inverted arch & thickness: 25 cm, concrete type: C30 & inverted arch \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Detailed parameters of the tunnel support for Section 5-5. Figure 5: Support pattern and excavation process for Section 5-5.  
the surrounding rock was monitored using multi-point extensometers (see Figure 6). In order to reduce the relative displacement between the anchor heads and the rock around the boreholes, hydraulic anchor heads were used instead of the common anchor heads. The claws of the hydraulic anchor heads could be expanded by increasing the pressure in the oil pump and then anchored in the rock to provide additional holding power. The contact pressure between the surrounding rock and the primary supports and the contact pressure between the primary and secondary supports were monitored using vibrating-wire pressure cells (see Figure 7). In order to make the monitoring results more accurate, measures were taken to ensure that the surface of the pressure cells closely adhered to the surface of the measured mediums. Therefore, when monitoring the contact pressure between the surrounding rock and the primary supports, the steel supports were used to place the pressure cells on a relatively flat surface of the surrounding rock, and the end of these were welded to the four bar lattice girders. When monitoring the contact pressure between the primary and secondary supports, the pressure cells were fixed to the surface of the shotcrete using expansion bolts before the installation of geotextiles and waterproof boards. Ring dynamometers were used to monitor the axial forces in both the anchor bolts and cables (see Figure 8).