# A Novel Visual System for Conducting Safety Evaluations of Operational Tunnel Linings
## 4 Engineering Case Analysis
### Visualized Evaluation and Result Analysis  
The monitoring data from Table 3 were input into the visualized system. The evaluation results are shown in Table 4.  
Taking the previous five sections (numbers 1-5) as an example (Table 4), the structure safety values of Sections 2-5 were 3.8307, 2.8485, 2.2418, and 2.4022, respectively. Section 2 was classified as A-level, indicating slight damage to the structure, which does not compromise traffic safety. Therefore, this section was relatively safe, and only needed continued observation, without taking special safety measures, and maintenance. Sections 1 and 3 were classified as B-level, indicating moderate damage to the structure that may potentially affect traffic safety. The evaluation of lining weakening in Section 3 was C, so the strength and thickness of lining should be of particular concern. For example, the lining strength can be improved by grouting and supporting. Sections 4 and 5 were classified as C-level, indicating severe damage to the structure that poses a threat to traffic safety and thus requires immediate action to be taken. Taking Section 4 as an example, the evaluation of lining cracking, lining weakening and lining cave were C, D, and C, respectively, which requires immediate safety measures and maintenance; lining cracks and deformation can be treated by jointing reinforcement and shotcrete, the lining strength can be improved by grouting and supporting, and lining cave can be treated by backfilling and grouting. The safety levels of Sections 4 and 5 were lower than those of the previous sections, indicating that the system has a strong sensitivity to monitoring data. Observations showed that the monitoring data in these two sections were significantly different from those in the previous sections. When the monitoring data changed in an unfavorable direction, the overall structure safety performance also weakened significantly. It was also observed that the lining crack length and width had a significant impact on structure safety, which corresponded to the weight design in the AHP model and conformed to engineering experiences. In addition, for system architecture, multi-level evaluation can enhance evaluation efficiency and quickly identify key disease indexes to focus on. For instance, Sections 1 and 3 (both B), Sections 4 and 5 (both C) had the same safety level (second-level  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Section** & \begin{tabular}{c} **Crack** \\ **Length** \\ **/m** \\ \end{tabular}  & \begin{tabular}{c} **Crack** \\ **Width/mm** \\ \end{tabular}  & \begin{tabular}{c} **Lining** \\ **Deformation** \\ \end{tabular}  & \begin{tabular}{c} **Lining Peeling** \\ **Depth** \\ **/mm** \\ \end{tabular}  & \begin{tabular}{c} **Strength** \\ **Index** \\ \end{tabular}  & \begin{tabular}{c} **Thickness** \\ **Index** \\ \end{tabular}  & \ \begin{tabular}{c} **Water** \\ **Leakage** \\ **State** \\ \end{tabular}  & \begin{tabular}{c} **Lining Cave** \\ **Depth** \\ **/mm** \\ \end{tabular}  \\ \hline
14 & 4.2 & 1.8 & 0.12 & 11 & 0.61 & 0.73 & seepage & 189 \\
15 & 1.8 & 1.3 & 0.30 & 13 & 0.87 & 0.78 & seepage & 35 \\
16 & 1.1 & 2.1 & 0.07 & 16 & 0.45 & 0.83 & seepage & 409 \\
17 & 0.2 & 0.  
evaluation or final evaluation), but there were still differences. By observing Columns 2 to 5 in Table 4 that represents the structure safety level of the first-level evaluation, it can be seen which index had a greater impact. This two-level evaluation mode can quickly find the key diseases to focus on and improve the evaluation efficiency. The visualized system interface for structure safety evaluation is shown in Figure 8.  
As for the entire tunnel structure (K+050-K+350), the absence of D-level damage (second-level evaluation) indicated that the overall safety of the tunnel structure was still within a controllable range, requiring only local reinforcement.