# Reasonable Support Parameters for Loess Tunnel Under Different Water Contents: A Case Study
## 4 Numerical Simulation
### Simulation Analysis of Original Design Support Parameters  
#### 4.2.1 Comparison of Deformation Results  
Field measurement data reveal that the settlement deformation at the crown is the predominant form of the surrounding rock deformation within the Fengshouling Tunnel. In addition, due to the length limitations of this article, the vertical settlement deformation of the crown has been chosen as the focus for analyzing the deformation of the surrounding rock in loess tunnels. Figure 11 displays the temporal settlement deformation curves at the crown measurement points under different water content conditions, as derived from the calculation results. Additionally, Figure 12 illustrates the distribution of the proportion of crown settlement deformation throughout each process.  
Figure 11 illustrates that the vertical settlement at the crown under natural water content is 72.5 mm, which is larger than the deformation measurements from the field. The reason for this is that due to the impact of on-site construction, some surrounding rock deformations could not be obtained. Therefore, it is reasonable for the simulated calculation results to be greater than the on-site-measured results. The comparison of the deformation results shows that the simulated deformation results conform to the deformation law of the surrounding rock, and this correspondence affirms the rationality of the model's construction. In addition, the final value for the crown settlement under median water content is 124.3 mm, and this value is 189.3 mm under saturated water content. According to the allowable deformation value of 150 mm for Fengshouling Tunnel, the final value under saturated water content was larger than the deformation threshold value 150 mm, and less than the deformation threshold value of reservation deformation 250 mm under grade V [43]. The three deformation curves collectively demonstrate that the deformation characteristics of the surrounding rock in loess tunnels are not closely tied to water content variations, and can be represented by rapid growth stage, continuous growth stage, and  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Support Structure** &
\begin{tabular}{c} **Elasticity Modulus** \\ **E/GPa** \\ \end{tabular} & **Gravity \(\gamma\)/kN/m\({}^{3}\)** & **Poisson’s Ratio \(\mu\)** \\ \hline Steel rib & 210 & 78.5 & 0.22 \\ Shotcrete & 26 & 22 & 0.22 \\ Bolt & 200 & 78.5 & 0.22 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Support parameters of grade V.  
Figure 10: Numerical simulation model diagram.  
slow growth stage. By analyzing the final deformation values of the surrounding rock under three different water contents, for the same level of support strength, the deformation value of the surrounding rock in the Fengshouling Tunnel increases linearly with the rise in water content within the loess strata.  
According to the distribution diagram of crown settlement percentages under different stages in Figure 12, it is clear that the settlement deformation of the crown in the Fengshouling Tunnel, under different water content scenarios, predominantly takes place during the excavation phases of the upper and middle bench. These stages account for 60.5%, 62.1%, and 68.6% of the total settlement value, respectively. This suggests that strict control over the deformation of the surrounding rock is essential during the early construction stage of loess tunnels.