## 4 Analysis of the Numerical Calculation Results
### Surrounding Rock Displacement Analysis  
During the excavation and support process of large section tunnels, the top of the arch typically experiences the maximum vertical displacement, while the bottom of the arch tends to undergo the maximum uplift displacement. As shown in Figure 7, the deformation of the surrounding rock continues to increase with each excavation and support step until stabilization is reached. However, the extent of disturbance and deformation of the surrounding rock varies significantly depending on the construction method used. The three-benching seven-step method leads to greater disturbance of the surrounding rock and more pronounced deformation because it involves excavating all of the perimeter rock of the upper step in the first excavation step, resulting in a significant release of perimeter rock pressure. Consequently, the maximum vertical displacement caused by this method is primarily due to the settlement of the vault. Specifically, compared to the CRD method, the three-benching seven-step method increases the settlement of the arch by 23%, the vertical displacement of the arch shoulder by 18.3%, the vertical displacement of the arch footing by 9%, and the augmentation of the arch base by 9.5%. Therefore, compared to the three-benching seven-step method, the CRD method can better control the perimeter rock displacement. In the displacement monitoring of the actual construction process, it is noted that all displacement values recorded when using the CRD method are smaller than those obtained with the three-benching seven-step method. This observation confirms that the CRD method provides better control over perimeter rock displacement compared to the three-benching seven-step method. However, the actual measured displacement values are generally greater than the calculated values. This discrepancy occurs because the support in the numerical simulations is assumed to be instantaneously effective, whereas in the actual construction process, the support takes effect with some delay. Additionally, the support structures require a certain amount of time to solidify and reach sufficient strength, meaning that the observed displacement values are larger than those predicted by the simulations [43]. Figure 6: Contour map of the large principal stresses in the surrounding rock of the three working methods. (**a**) Double-sided drift method; (**b**) CRD method; (**c**) three-benching seven-step method (unit: Pa). Figure 8 illustrates the displacement of the surrounding rock at the arch crown and arch base under three different excavation methods. It shows that under the double-side drift method, the changes in both arch crown settlement and arch base uplift are minimal. Compared to this method, the displacement convergence at the tunnel arch crown is reduced by no more than 14% when using the three-benching seven-step method, and the displacement convergence at the left arch shoulder is reduced by no more than 19% compared to the other method. The difference between the two methods is that the displacement convergence at the left arch shoulder is reduced by no more than 19% compared to the other method. Figure 7: Contour map of surrounding rock displacement of three working methods. (**a**) Double-sided drift method; (**b**) CRD method; (**c**) three-benching seven-step method (unit: m). pared to the CRD method. Overall, after implementing the double-side drift method, the trend of changes in the left-side soil support is the most moderate, whereas with the three-benching seven-step method, the rate of change in the surrounding rock displacement is the greatest during the initial excavation of the upper soil. Several conclusions can be drawn from Figure 8. First, the double-side drift method demonstrates superior performance in controlling the displacement of surrounding rock, particularly in reducing the settlement at the arch crown and uplift at the arch base.