## 6 Discussions  
The long-term stability of deep-buried tunnels in soft rock stratum is comprehensively studied in this article. It is shown that large deformations are particularly inevitable in such tunnels, and are affected by major factors such as high stress and pore water pressure. In this situation, the host rock mechanical properties are degenerated, and considerable instability and failure in these underground structures are common [75; 76; 77]. On top of that, although the drill-and-blast excavation method causes extra damage to the host rocks [18; 78], it is imposed under complex geological and hydrological conditions of rocky media. Accordingly, to effectively guarantee the long-term stability of deeply buried tunnels in complex soft rocks, highly reliable measures must be adopted to prevent the triggering of tertiary creep. In fact, the latter is associated with huge deformations of deep-buried tunnels in soft rocks [79]. In this sense, the two variants of the novel creep constitutive model are designed in order to address, as accurately as possible, the time-varying deformations of the rocks surrounding the Weilai Tunnel. It is in the same order of ideas that the two closed-form solutions are proposed. Other variants could also be designed. For instance, as temperature variation also affects rock creep, a related variant could be conceived. However, it is very difficult to cover everything in this paper. It should be highlighted that, although the proposed creep constitutive model has the advantages of accurately capturing the comportment of deep soft rocks, it has two main drawbacks. On the one hand, it contains at least nine parameters whose evaluation for loading and unloading processes takes considerable time. On the other hand, triaxial creep tests performed under load-unload cycles are necessary for precise model applications. It should be noted that the second variant of the creep model and that of the closed-form solution better describe the conditions of the studied deep soft rock tunnel. The designed closed-form solutions are utilized to evaluate the convergence deformation in terms of creep deformations of the deep soft rock tunnel. It is shown that the tunnel exhibits large creep \begin{table}
\begin{tabular}{c c c} \hline \hline
**Host rocks and Structural** & **Type of Sensors** & **Sensor Capability** \\
**Component to be Monitored** & **Type of Sensors** & **Sensor Capability** \\ \hline Excavation damaged zone & & Monitor any stress change and \\ (EDZ) & & evolution in the EDZ. \\ Rock bolts and cable bolts & &
\begin{tabular}{c} Detect the early deficiency of \\ rock bolts and cable bolts. \\ Monitor corrosion attack at \\ the earliest stage. \\ Assess the whole condition of \\ the secondary lining. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 14: Sensors to monitor the structural health of the Weilai Tunnel. deformation, which surpasses 400 mm after only 27 days of excavation. This shows that, after excavation, the tunnel deformation increases quickly, owing to the complexity related to the regional environment (poor rock mass quality, high stress, presence of groundwater). To limit the creep deformation in this tunnel, quick installation of a suitable and robust support is strongly imposed. Despite that, to effectively ensure the long-term safety and stability of the deep-buried tunnel in soft rocks, long-term monitoring of its structure is required. In fact, not only tunnels can be considered as risky structures [80], and some uncertainties during their design and construction should be recognized [81]. Thereby, continuous monitoring of the tunnel structural health is promising. Since traditional monitoring techniques cannot regularly provide the actual tunnel health conditions [82], appropriate remote sensors are necessary to ensure the reliable operation of the tunnel at all times. Normally, each structural component of the tunnel should be adequately monitored.