## 3 Three-Dimensional Laser Scanning Technology and Application Scheme
### Three-Dimensional Laser Scanning Equipment  
The Yulinzi Tunnel test section uses a Trimble SX10 scanner from Trimble, USA. The instrument integrates a 3D laser scanner, a total high-end station, and close-range photogrammetry technology, and no additional operation with a total station is required. It has a point cloud collection efficiency of 26,600 points per second and a maximum scanning distance of 600 m. The use of improved Trimble VISION technology allows for the quick and easy acquisition of high-resolution site imagery and is less susceptible to environmental disturbances. Post data and image processing are fully integrated with Trimble Access and Trimble Business Center (TBC). Compared with the conventional monitoring methods of tunnels, the instrument is more suitable for monitoring applications of tunnels in the test section. Table 2 compare the monitoring technology between 3D laser scanning technology and conventional monitoring methods. The main scanning technical parameters of the Trimble SX10 scanner are shown in Table 3.  
\begin{table}
\begin{tabular}{c c c} \hline
**Project** & **The Monitoring Scheme of This Trial** & **Common Monitoring Schemes** \\ \hline Monitoring instruments & Trimble SX10 scanner & Level/Total Station \\ \hline \multirow{2}{*}{The layout of measuring points} & Full cross-section monitoring; More & Fixed measuring points; \\  & intensive monitoring points & Fewer measuring points \\ \hline \multirow{2}{*}{Monitoring frequency} & Short-term high frequency; & Low, depending on the distance between the measuring section and the excavation surface and the displacement rate \\  & Long-term low frequency & & Low, depending on the distance between the measuring section and the excavation surface and the displacement rate \\ \hline Speed of data collection & Fast & Slow \\ \hline Monitoring process safety risks & Low & High \\ \hline \end{tabular}
\end{table}
Table 2: Comparison of monitoring technologies.  
\begin{table}
\begin{tabular}{c c c} \hline
**Scanning Performance** & **Project** & **Parameter** \\ \hline \multirow{8}{*}{General Scanning specifications} & Scanning principle & Band scanning using a rotating prism in the telescope \\ \cline{2-3}  & Measurement rate & 26.6 kHz \\ \cline{2-3}  & Point spacing & 6.25 mm, 12.5 mm, 25 mm, or 50 mm @ 50 m \\ \cline{2-3}  & Field-of-view & 360\({}^{\circ}\times\) 300\({}^{\circ}\) \\ \cline{2-3}  & Coarse scan: full dome\(-\)360\({}^{\circ}\times\) 300\({}^{\circ}\) (horizontal & \\  & angle \(\times\) vertical angle): Density\(-\)1 mrad, 50 mm & Scan time: 12 min \\  & spacing @ 50 m & \\ \cline{2-3}  & Standard scan: area scan\(-\)90\({}^{\circ}\times\) 45\({}^{\circ}\) (horizontal & \\  & angle \(\times\) vertical angle): Density\(-\)0.5 mrad, 25 & Scan time: 6 min \\ \hline \multirow{8}{*}{Range Measurement} & Range principle & Ultra-high-speed time-of-flight powered by Trimble \\  & Lightning technology \\ \cline{2-3}  & Range & 0.9 m-600 m \\ \cline{1-1} \cline{2-3}  & Range noise & @ 50 m on 18–90\% reflectivity, 1.5 mm \\ \cline{1-1} \cline{2-3}  & Scanning Angular Accuracy & 5\({}^{\circ}\) (1.5 mgon) \\ \cline{1-1} \cline{2-3}  & 3D position Accuracy @ 100 m\({}^{8}\) & 2.5 mm \\ \hline \end{tabular}
\end{table}
Table 3: Main technical parameters of Trimble SX10 Scanner.