## 4 Comparative Analysis of Top-Down Method and Cut-and-Cover Method
### Comparative Analysis of Simulation Results
#### 4.2.2 Main Structure Internal Force  
The maximum longitudinal compressive stress and maximum longitudinal tensile stress of the main structure for the cut-and-cover method and the top-down method during the final construction stage are shown in Table 7. As can be seen from Table 7, the maximum longitudinal compressive stress and maximum longitudinal tensile stress of the cut-and-cover method are both larger than those of the top-down method. Specifically, the maximum longitudinal compressive stress of the cut-and-cover method is 1649 kN/m\({}^{2}\) greater than that of the top-down method, an increase of 54.9%; the maximum longitudinal tensile stress of the cut-and-cover method is 120 kN/m\({}^{2}\) greater than that of the top-down method, an increase of 6.32%. It can be concluded that the variation range of longitudinal compressive stress is greater than that of longitudinal tensile stress. This is mainly because the top-down method uses steel supports as the support system, making the main structure more uniformly stressed, while the cut-and-cover method uses the stiffness of the main structure itself to resist deformation, resulting in an uneven stress distribution of the main structure, and thus the maximum longitudinal stress of the cut-and-cover method is larger than that of the top-down method.  
The bending moments of the main structure's first floor and fourth floor for the cut-and-cover method and the top-down method during the final construction stage are shown in Figure 11. As can be seen from Figure 11, the maximum positive and negative bending moments of the first floor in the cut-and-cover method are much greater than those of the fourth floor of the cut-and-cover method and the first floor and fourth floor of the top-down method. They reach \(-\)1091.7 kN\(\cdot\)m/m and 950.0 kN\(\cdot\)m/m, respectively. This is mainly because, during the construction of the Cut-and-Cover method, the first floor of the main structure is the first to be constructed. The first floor serves as the first supporting structure of the cover excavation pit and bears most of the soil pressure during the subsequent excavation. As a result, the bending moment at the top plate of the main structure in the cut-and-cover method is the largest. Compared with the difference in bending moments between the first floor and fourth floor in the cut-and-cover method, the bending moments at the first floor and fourth floor in the top-down method are almost the same. This is because, when the main structure is poured in the top-down method, due to the effect of the internal support, the main structure and the internal support jointly bear the soil pressure, making the main structure more evenly stressed.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Method**} & **Maximum Longitudinal** & \multirow{2}{*}{**Maximum Longitudinal** **Tensile Stress/(kN/m\({}^{2}\))**} \\  & **Compressive** & **Transile Stress/(kN/m\({}^{2}\))** \\  & **Stress/(kN/m\({}^{2}\))** \\ \hline Top-Down & \(-\)4650 & 2017 \\ Cut-and-Cover & \(-\)3001 & 1897 \\ \hline \hline \end{tabular}
\end{table}
Table 7: The longitudinal stress of the main structure of the top-down and cut-and-cover method during the final construction stage.