## 3 Feasibility of Construction Plan
### Analysis of Numerical Results  
Upon the completion of the shield tunnel construction, final settlement and deformation curves for the existing underground Passages A and B were plotted and are presented in Figure 7.  
To facilitate a comprehensive comparison of settlement and deformation in both passages under different conditions, the maximum vertical displacements of the existing tunnels in different schemes are detailed in Table 3.  
Figure 7: Cross-sectional settlement of rectangular pipe jacking. (**a**) Passage A; (**b**) Passage B. Different reinforcement schemes did not alter the deformation pattern of the settlement trough in the cross-section of the existing tunnel. In the end, they all led to an asymmetric \"W\"-shaped settlement trough. However, implementing reinforcement measures effectively reduced the values of maximum settlement caused by the shield tunnel crossing the existing tunnel, as detailed in Table 3. All three reinforcement schemes met engineering safety control standards. Yet, upon comparative analysis, it was evident that the comprehensive reinforcement scheme, which combined grouting and steel supports, delivered the most effective control over the vertical settlement and deformation of an existing tunnel. Under this scheme, the maximum settlement values induced by the new shield tunnel for Passages A and B were 9.95 mm and 8.64 mm, respectively. These values represented reductions of 39.8% and 42.1%, respectively, compared to the original condition with no reinforcement measures in place. When analyzing the use of a single reinforcement method, under the sole application of grouting reinforcement, the values of maximum settlement induced for Passages A and B were 12.48 mm and 11.21 mm, respectively. Compared to the original condition with no reinforcement measures, these maximum settlement values decreased by 24.5% and 23.7%, respectively. Conversely, when relying solely on steel support reinforcement, the maximum settlement values induced for Passages A and B were 14.84 mm and 13.15 mm, respectively. Compared to the original condition with no reinforcement measures, these maximum settlement values decreased by 10.5% and 10.7%, respectively. In summary, when employing a single reinforcement method, the grouting reinforcement scheme proves to be more effective than the steel support reinforcement scheme. Steel support reinforcement strengthens the interior of the existing tunnel, resulting in better control over relative deformations between tunnel segments. However, the weight of the steel structure exerts additional pressure on the existing tunnel, which can have a somewhat unfavorable impact on controlling the overall displacement of the existing tunnel. A comparison of the maximum vertical displacement from settlements in Passages A and B under different reinforcement schemes shows that the reinforcement effect is slightly better for Passage B. This is mainly attributed to Passage B's smaller span relative to Passage A, resulting in greater overall stiffness of shorter beams compared to longer ones. Implementing reinforcement measures not only controls the settlement deformation of the existing tunnel, but also mitigates upward deformation in areas further away from the shield tunnel directly above. Similarly, the comprehensive reinforcement scheme involving grouting and steel supports demonstrates the most effective control over the upward deformation of the existing tunnel. Upon comparison, it is clear that the reinforcement effect of the comprehensive reinforcement is not simply the sum of the effects of the other two separate reinforcement schemes when it comes to controlling the settlement and deformation of the existing rectangular pipe-jacking tunnel. This indicates that the comprehensive reinforcement scheme, which combines grouting and steel support, fully capitalizes on the reinforcement effects of both methods within the strata, resulting in a \"synergistic effect\".