# Study on the Disturbance of Existing Subway Tunnels by Foundation Sloping Excavation
## 4 Validation of the Numerical Simulation
### Results Analysis of Numerical Simulation
#### 4.3.2 Excavating Soil on Both Sides and Reserving the Middle Core Soil  
Figure 12 shows the vertical deformation cloud diagram and the vault bulge curve for the excavation method of excavating soil on both sides and reserving the middle core soil. The maximum vertical deformation of the vault is located on the right side of the existing tunnel, with a maximum deformation of 0.96 mm. After the excavation of the left side, the maximum position is shifted slightly away from the central position of the tunnel, with a maximum deformation of 1.5 mm. The excavation of the left and right sides of the soil has a minimal impact on the deformation of the existing tunnel. After excavating the middle core soil, the maximum deformation of the existing tunnel is reached, with a maximum deformation of 8.8 mm, located at the central position of the tunnel. After the excavation of the middle core soil, the tunnel deformation increased by 486% compared to the previous two excavation steps. This proves that the soil located directly above the existing tunnel is the main factor causing vertical deformation in the existing tunnel. The maximum vertical deformation was reduced by 44% compared to the block excavation method. The maximum vertical differential settlement value for the existing tunnel within the pit excavation is 0.035% and the differential settlement rate within the pit excavation is reduced by 63%. This indicates that the use of excavating soil on both sides and reserving core soil in the middle is effective for reducing the impact of unloading of the foundation excavation on the existing tunnel.  
Figure 11: Graphical presentation of the horizontal deformation of the tunnel.  
Figure 13 shows the horizontal deformation cloud and the horizontal deformation curve at the arch waist caused by the method of excavating soil on both sides and reserving the middle core soil.  
In Figure 13, the excavation of the right side of the soil shows an overall rightward deformation of the existing tunnel. After excavating the left side of the soil, the horizontal deformation of the arch waist on the left and right side shows a symmetrical distribution. The deformation values at this stage were small, with a maximum deformation of 0.1 mm. After the excavation of the middle soil, the horizontal deformation of the existing tunnel increases enormously, with a maximum deformation of 2.5 mm. The horizontal deformation of the arch waist on the left and right sides is symmetrically distributed. The soil directly above the tunnel is still the main factor determining the horizontal deformation of the tunnel, in consistency with the factors influencing the vertical deformation of the tunnel. This shows that reserving the core soil above the existing tunnel can significantly reduce the impact of the excavation on the tunnel. The method of excavating soil on both sides and reserving the middle core soil reduces the horizontal deformation of the existing tunnel by 50% compared to the block excavation method.  
The comparison between the above two excavation methods shows that when the existing tunnel is a single-line tunnel, the excavation disturbance of the existing tunnel line caused by using the method excavating on both sides and reserving core soil the middle is less than that caused by the method of excavating the middle soil and reserving core soil on both sides. Therefore, when the pit excavation is close to the existing tunnel line, the soil can be first excavated away from the tunnel.  
Figure 12: Graphical presentation of the vertical deformation of the tunnel.  
Figure 13: Graphical presentation of the horizontal deformation of the tunnel.