# Analysis of the Impact of the New Two-Lane Shield Tunnel Underpass on the Existing Tunnels
## 5 Conclusions  
Through theoretical calculations, numerical simulation of the interval project from Dongfang Road Station to Barracuda Bay Station of Dalian Metro Line 4, and on-site monitoring, the following conclusions are obtained:  
(1) By summarizing [PERSON]'s prediction formula for the new two-lane shield tunnel passing beneath the existing tunnel, the surface soil settlement deformation is calculated using the superposition principle, with additional displacement obtained by correcting the width of the settlement tank and the stratum loss rate. The vertical displacement of the existing tunnel is determined using the finite difference method, applying the balanced differential equation of displacement load-tunnel deformation. This method's algorithm is straightforward, easy to understand, and provides quick, effective guidance for the construction of urban underground projects.  
(2) For the existing tunnels, vertical deformation is primarily influenced by the vertical settlement of the arch top, which is smaller than that of the arch bottom. The settlement groove at the arch top follows a typical pattern aligned with the centerline of the new twin tunnels. In contrast, the settlement groove at the arch bottom forms a \"W\" shape due to the tunnel arch bearing part of the additional stress. The maximum settlement occurs directly beneath the crossing point of the new tunnel and the centerline of the existing tunnel. The final settlement in the existing left line is slightly larger than that of the right line. During  
Figure 12: Comparison of theoretical calculation, numerical simulation, and field data.  
construction, particular attention should be given to the impact of the shield tunnel's first crossing on the existing tunnel.  
(3) The secondary lining of the existing tunnel is in the tensile state as a whole, and the resulting additional stress value is 1.47 MPa, which is smaller than the standard tensile value of C50 concrete and meets the load-bearing requirements, but in the part of the arch at the cross position, the stress value increases significantly, and there is the possibility of pulling crack.  
(4) The grouting pressure has a large impact on the vertical settlement of the existing line, but the change in the soil chamber pressure has a smaller impact on the settlement of the existing tunnel.  
(5) Based on the measured data, the settlement values of the existing tunnels predicted by both theoretical calculation and numerical simulation methods were compared and analyzed. The results demonstrate that the predicted location of the maximum settlement value and the overall settlement trend from both methods are highly consistent, further validating the accuracy and reliability of the theoretical model.  
The above-obtained influence law of a double-line shield going through the existing tunnel can provide a reference for similar engineering practices.  
J.L.: Provision of ideas and methods. X.F.: Editing and modification, data processing. Y.Y.: Optimization of image tables and supervision. All authors have read and agreed to the published version of the manuscript.  
The research received financial support from the National Natural Science Foundation of China (Grant No. 51474045).  
Not applicable.  
Some or all data that support the findings of this study are available from the corresponding author upon reasonable request.  
The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.