## 5 Relevant Measures Guaranteeing Tunnel Long-Term Stability  
Since the convergence deformation is large, and the rocky environment of the tunnel is complex, the requirements for the supporting structure are considerable. In such conditions, stresses in the supporting structure will be very strong [58]. An adequate and robust support scheme is required to properly ensure the long-term stability of the tunnel. In spite of that, it should be recognized that the long-lasting performance of the support structure will be incontestably attacked by fatigue and ageing. This relates to all components of any given deep rock tunnel support system. For instance, the durability of typical primary support (rock bolts, cable bolts) can be diminished under the actions of major factors, including rock creep [59]. In addition, excessive deformation of soft rock tunnels can even seriously jeopardize the secondary support [60]. As pointed out by [PERSON] and [PERSON] [61], the widely employed materials for the tunnel secondary support are mostly reinforced concrete and steel plate. However, the long-term performance of these materials is affected by corrosion, which is almost inevitable in deep underground structures. In fact, as a result of groundwater leaks, deterioration and deformations in concrete structures can be increasingly severe over time [62; 63]. The deformation of the Weilai Tunnel has considerably exceeded the established limit, as shown in Table 10, where H is the height of the tunnel, which is 1000 mm. It should be noted that over the whole length of the Weilai Tunnel, the surrounding rock grades IV and V represent, respectively, 48.18% and 53.62% (right line), and 43% and 56.12% (left line). Specific values of the convergence deformation can be read in Figure 29. The extent of exceeded displacements is presented in Table 11.  
Based on the major factors affecting the performance and durability of the typical primary support [59], and related engineering practices, to ensure tunnel stability, a robust support system was offered. Concretely, the proposed scheme of the support structure is as follows: pressure aid + deep grouting + rock bolts + cable bolts + steel arch + secondary lining. Indeed, by this robust support scheme, the observed deformation in the Weilai Tunnel is properly addressed. Each component of the proposed support scheme plays a key role. For instance, note that the risk of floor heave is significant in deep soft rock tunnels, and cannot be ignored. In fact, as relayed by [PERSON] et al. [64] and [PERSON] et al. [65], the presence of groundwater and poor rock quality are among the major factors driving floor heaving in such tunnels. Pressure aid can thus address the problem of floor heave in the Weilai Tunnel. By coupling their actions, the floor pressure aid and the arch support can control enormous localized deformations in the tunnel. Additionally, referring to [PERSON] [66], in incompetent rocks, grouting holes can be made up to 6 to 10 m deep into tunnel surrounding rocks. At least, the host rocks of the Weilai Tunnel must be boosted with a 10 m deep penetration of grouting. Relevant details regarding all components of the support scheme are provided in Tables 12 and 13. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Surrounding Rock Grade** & \
\begin{tabular}{c} **Adopted Relation of the** \\ **Limit Relative Displacement** \\ \end{tabular} &
\begin{tabular}{c} **Limit Relative Displacement** \\ **(mm)** \\ \end{tabular} \\ \hline Class IV & 0.05H & 50 \\ Class V & 0.08H & 80 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Allowable relative displacement around the tunnel. Although the proposed support scheme is robust, as explained above, it is necessary to adequately and durably monitor the structural components of the tunnel. To this end, appropriate remote sensors are strongly suggested to ensure acceptable structural integrity and safety at all times [67].