## 4 Analysis of Numerical Results
### Influence of Tunnel Excavation Surface Spacing
#### 4.1.1 Ground Settlement Analysis  
Figure 5 presents the lateral variation curves of ground settlement for different tunneling surface spacing at the position of 10 m in the excavation direction, and the curves roughly conform to the form of \"normal distribution\". The curve was large in the middle and small at the ends, symmetrically distributed along the distribution center. When the distance between tunnel excavation surfaces gradually increases, the degree of mutual influence of the two line tunnels is smaller, and each tunnel tends to be constructed independently from the other. However, this influence does not increase with the spacing of the tunnel excavation surface; when the distance increases to a certain value, the influence on ground settlement is close to equilibrium. When the tunnel excavation surface spacing is small, the stress on the surrounding rock is larger, so when is later tunnel is excavated, the first tunnel surrounding rock deformation is not yet stable enough to share part of the surrounding rock stress, resulting in the cave perimeter and the ground surface producing a large displacement deformation.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Number**} & \multirow{2}{*}{**Working Number**} & \multicolumn{2}{c}{**The Tunnel**} & \multirow{2}{*}{**The Tunnel**} & \multirow{2}{*}{**The Tunnel**} & \multirow{2}{*}{**The Water**} \\  & & **Ex excavation** & & & & **Level on the** \\  & & **Surface** & & & **Depth (m)** & **Spacing (m)** & **Riverbed** \\  & & **Spacing (m)** & & & & **Side (m)** \\ \hline
1 & J100H25D13.2W29 & 100 & 25 & 13.2 & 29 \\
2 & J75H25D13.2W29 & 75 & 25 & 13.2 & 29 \\
3 & J50H25D13.2W29 & 50 & 25 & 13.2 & 29 \\
4 & J25H25D13.2W29 & 25 & 25 & 13.2 & 29 \\
5 & J0H25D13.2W29 & 0 & 25 & 13.2 & 29 \\
6 & J100H22D13.2W29 & 100 & 22 & 13.2 & 29 \\
7 & J100H28D13.2W29 & 100 & 28 & 13.2 & 29 \\
8 & J100H31D13.2W29 & 100 & 31 & 13.2 & 29 \\
9 & J10  
Figure 6 shows the three surface monitoring points set at the position of 10 m depth in the excavation direction, which is numbered and presented in the figure. Figure 7 shows the variation curve of the displacement at different monitoring points with the spacing of the tunnel excavation surface. From Figure 7, we can see that the larger the spacing of the excavation surface, the smaller the ground settlement value, and the maximum settlement values of 4.93 mm, 4.57 mm, 4.058 mm, 3.658 mm and 3.508 mm corresponding to 0 m, 25 m, 50 m, 75 m and 100 m spacing of the tunnel excavation surface, respectively, and the maximum settlement point occurs at the centerline of the tunnel. According to the above settlement law, it can be concluded that in the excavation stage of the right cavern first, the excavation load is mainly borne by the surrounding rock of the right cavern, and after the excavation of the left cavern, the load is shared by the left and right caverns, and the settlement trough is biased in the direction of the right cavern.  
Figure 5: Lateral variation curve of ground settlement for different tunneling surface spacing at 10 m depth in excavation direction.  
Figure 6: Arrangement of surface monitoring points at the position of 10 m depth in excavation direction.