# Study on the Disturbance of Existing Subway Tunnels by Foundation Sloping Excavation
## 4 Validation of the Numerical Simulation
### Comparative Analysis of Calculation Results
#### 4.4.2 Excavate on Both Sides Soil and Reserve the Middle Core Soil  
In the theoretical calculations, the method of excavating soil on both sides and reserving the middle core soil only considers the effect of excavating the soil on both sides and does not consider the effect of the subsequent excavation of the soil in the middle. The vertical load magnitudes for the three unloading load distribution widths are 23,063 kPa, 8719 kPa and 12,654 kPa, respectively. The distributional width of the unloading action is 3.0 m, 7.9 m and 5.5 m, respectively. The horizontal unloading load on the sidewall is 2084 kPa and the width of the load distribution for the unloading of the sidewall is 3.0 m.  
Figure 14: Comparison of the theoretical calculations (when excavating the middle soil and reserving the core soil on both sides).  
The calculations were carried out to obtain the vertical deformation of the vault of the existing tunnel and the horizontal deformation of the arch waist caused by the excavation of the soil on both sides of the method of excavating soil on both sides and reserving the middle core soil, as shown in Figure 15.  
In Figure 15, the theoretical results are very close to the results of the numerical simulations. Unlike the results of the calculation for the method of excavating the middle soil and reserving the core soil on both sides, for the method of excavating soil on both sides and reserving the middle core soil, the minimum error with the numerical simulation results is the way in which the unloading action is at 3.0 m width and the unloading load strength is 10,919 kPa with its three load distribution cases. This means that the calculated load distribution width is chosen to be the trapezoidal short side of the slope. However, the calculation results based on the trapezoidal central line of the slope are also less inaccurate than the numerical simulation results. Therefore, it is also possible to calculate the load distribution width as the length of the trapezoidal central line of the slope. After the excavation of the soil on both sides, the removal of the soil has a very low impact on the existing tunnel. It also proves that when excavating large volumes of soil close to an existing tunnel, the soil can be excavated away from the existing tunnel side first. The excavation provides a working surface for reinforcement or counter-pressure measures, thus ultimately ensuring the safety and stability of the subsequent construction.  
By comparing the numerical simulations with the theoretical solution, the unloading width is most reasonably taken to be the length of the slope central line when adopting sloping excavation. The smaller excavation area and the lower unloaded load levels in the one-time excavation reduce the deformation of the tunnel. According to the above analysis, the results of the formulae derived in our study are less inaccurate than the results of the numerical simulations. This proves the applicability of the formulae derived in this study.