## 5 Conclusions  
This paper firstly investigates the mechanical characteristic variation of soft rock with variable confining pressure and establishes the corresponding variable models for mechanical parameters of soft rock. Secondly, an improved numerical simulation method including  
Figure 17: Numerical simulation results of the LDP with different initial pressure conditions: (**a**) LDP in front of tunnel face and (**b**) LDP behind tunnel face. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Region** & **Expression** & **Fitting Result** \\ \hline in front of tunnel face (x \(<\) 0) & \(u^{*}(x)=1.12\exp\left(1.94\frac{x^{*}}{R^{*}}\right)u_{0}^{*}\) & \(R^{2}=93.95\%\) \\ tunnel face (x \(=\) 0) & \(u_{0}^{*}=25.98(R^{*})^{-0.66}\) & \(R^{2}=98.38\%\) \\ behind tunnel face (x \(>\) 0) & \(u^{*}(x)=\left[1-\left(1.14-2.45u_{0}^{*}*10^{-2}\right)\exp(-0.2x^{*})\right] *100\%\) & \(R^{2}=98.24\%\) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Improved expression of the LDP for soft rock tunnels considering confining pressure influence. these variable models is proposed to solve this current defect of the conventional simulation method, which cannot consider the confining pressure influence on the mechanical parameters of soft rock during the calculation process. Finally, for exhibiting the application of the improved numerical simulation method, an improved expression of the LDP for soft rock tunnels considering confining pressure influence is proposed. The conclusions can be summarized as follows:  
1. Mechanical parameter variation of soft rock with variable confining pressure is investigated by triaxial experiments. The experimental results indicate that with increasing confining pressure, the elasticity modulus and cohesion obviously increase, and the friction angle gradually decreases, but the Poisson ratio remains basically constant. Furthermore, variable models for mechanical parameters (\(E,\
u,c\) and \(\varphi\)) are established with confining pressure influence. 2. A transversal loop discriminant update procedure including variable models for the mechanical parameters of soft rock is proposed with the FISH language and introduced into the iteration calculation process of FLAC\({}^{\text{3D}}\), thus forming an improved numerical simulation method for soft rock tunnels. The improved simulation method can integrally consider the mechanical parameter variation of surrounding rock with variable confining pressure and realize the automatic update for the mechanical parameter of surrounding rock with its variable stress state during the calculation process. Moreover, the improved numerical simulation method is validated as accurate and correct with the experiment and elastoplastic results, and the comparison results between the improved and conventional simulation methods indicate that the results of the improved simulation method are more consistent with practical soft rock tunnel engineering. 3. As an application example for the improved simulation method, based on many displacement field results of surrounding rock obtained by the improved simulation method, an improved expression of the LDP for soft rock tunnels is proposed, which can consider the comprehensive influence of multiple factors, including the initial pressure, tunnel radius and mechanical parameter variation of surrounding rock. In this study, we investigated the mechanical characteristic variation of phyllite with confining pressure influence and established variable models; meanwhile, a numerical simulation method for tunnel excavation, which can consider this variation of surrounding rock, was proposed. In reality, natural phyllite is the joint rock, and its mechanical characteristic variations are affected by joint and confining pressure; however, this paper only considers the confining pressure influence.