## 3 Monitoring Results and Analysis  
### Tunnel Displacement Characteristics  
Two representative sections including DK70+829 and DK70+869 in the pipe roof section and the leading ductile section were selected to show the typical tunnel displacement characteristics, including the arch settlement and the horizontal convergence at different construction stages (Figure 9; Figure 10). The monitoring results of all monitoring sections are finalized in Figure 11, Tables 4 and 5. According to the monitoring data, the representative tunnel displacement characteristics of shallow-buried large cross-section loess tunnel are as follows:  
Figure 8: Layout of the monitoring points of monitoring sections. Figure 9: Tunnel displacement–time curves of section DK70+829. Figure 11: Final monitoring values of tunnel displacement. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Monitoring**} & \multirow{2}{*}{**Pre-Support**} & \multirow{2}{*}{**Buried**} & \multicolumn{6}{c}{**Settlement Proportion/\%**} & \multicolumn{6}{c}{**Maximum**} \\  & & & **Depth** & & & & & **Settlement Rate (mm/d)** \\ \cline{3-10}  & & **Type** & **(m)** & **Stage** & **Stage** & **Stage** & **Stage** & **Stage** & **Stage** & **Stage** \\ \cline{3-10}  & & & **1** & **2-3** & **4-5** & **6-8** & **1** & **2-3** & **4-5** & **6-8** \\ \hline DK70+829 & & 16 & 53.3 & 8.2 & 24.9 & 13.6 & 4.2 & 3.2 & 2.5 & 1.4 \\ DK70+834 & & 16 & 28.2 & 41.2 & 15.7 & 15.0 & 3.5 & 2.6 & 1.9 & 1.4 \\ DK70+839 & leading & 16 & 34.6 & 49.4 & 3.6 & 12.3 & 3.9 & 4.1 & 0.9 & 1.6 \\ DK70+844 & ductile & 16 & 20.4 & 65.9 & 3.0 & 10.6 & 2.7 & 3.7 & 1.7 & 1.2 \\ DK70+849 & & 16 & 31.4 & 47.5 & 16.5 & 3.7 & 2 & 2.4 & 1.2 & 0.8 \\ DK70+854 & & 16 & 33.6 & 48.7 & 12.5 & 5.2 & 2.7 & 3.7 & 0.9 & 1.4 \\ \hline DK70+864 & & 12.4 & 23.8 & 53.3 & 13.1 & 9.8 & 2.4 & 2.8 & 2.3 & 1.1 \\ DK70+869 & & 12.4 & 34.1 & 30.9 & 20.9 & 14.1 & 2.3 & 2.7 & 2.8 & 0.7 \\ DK70+872 & pipe & 11.3 & 54.4 & 22.2 & 18.1 & 5.3 & 3.8 & 1.1 & 1.7 & 0.5 \\ DK70+877 & roof & 11.1 & 45.3 & 42.4 & _7.6_ & 4.7 & 4 & 2.5 & 1.3 & 0.7 \\ DK70+882 & & 6.2 & 56.7 & 33.5 & 1.7 & 8.2 & 4.1 & 1.7 & 0.8 & 0.6 \\ DK70+887 & & 2.1 & 34.9 & 50.0 & 3.6 & 11.4 & 3.1 & 3.7 & 0.7 & 0.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Settlement proportion and maximum settlement rate. Figure 10: Tunnel displacement–time curves of section DK70+869. (1) The excavation of loess tunnels usually caused significant tunnel displacements. As it can be seen in Figures 9 and 10, both the arch settlements and horizontal convergences of the section DK70+829 and section DK70+869 were more than 15 mm. Moreover, the maximum value of arch settlement in the concerned zone was 44.7 mm, and the arch settlement rate for more than half of the monitoring sections was more than 3 mm/d. This suggests high deformation potential of the ground, whose release was affected by the excavation of loess tunnel. Therefore, timely supporting can effectively reduce the deformation of surrounding rocks and prevent serious disasters from happening. Moreover, real-time monitoring is also essential and can provide data feedback. (2) The arch settlement is considered as the dominant displacement induced by tunneling in loess ground. In this case, the distribution range of horizontal convergence for entire monitoring sections was 9.2-17.7 mm, with a significant increase in the distribution range of arch settlement, reaching 16.6-44.7 mm. Moreover, the mean values of arch settlement for the leading ductile sections and the pipe roof sections were 2.6 and 1.9 times the horizontal convergence, respectively. This indicates a clear directional difference of the tunnel displacement in loess ground, hence the arch settlement control is essential to ensure tunnel safety. (3) A significant difference in the tunnel displacement was identified during the different stages of excavation.