## 6 Conclusions  
The excavation of the foundation pit and construction of the over-crossing shield when the existing tunnel was disturbed by excavation of the foundation pit and construction of the above-crossing shield excavation was successful owing to the foundation pit, which caused slight settlement of the existing tunnel, and the over-crossing shield caused vertical uplift of the existing tunnel. The vertical displacement caused by the above-crossing shield was far greater than the influence of foundation pit excavation. The maximum vertical displacement occurred in the middle of the crossing point between the two lines of the above-crossing tunnel and the existing tunnel. Numerical simulation software and the analysis of the measured data have led to the abovementioned conclusions.  
The foundation pit excavation induced horizontal displacement of the existing tunnel segments toward the foundation pit. Subsequently, the over-crossing shield provoked horizontal displacement of the existing tunnel in the tunneling direction. The impact of shield tunneling on the horizontal displacement of the existing tunnel far exceeded that caused by foundation pit excavation. Numerical simulation software and the analysis of the measured data can prove the above conclusions.  
In comparison to the measured values of three typical sections with the numerical simulation data, it was revealed that in the final state, the numerical simulation results for the vertical displacement are much larger than the measured values, which was 4.7 times the measured data. The numerical simulation results for the horizontal displacement agree with the measured data. Furthermore, when using numerical simulation software for evaluation, attention should be paid to minimizing the value of vertical displacement, or other numerical simulation methods should be used for comparison and confirmation.  
The existing tunnel is subjected to multiple disturbances caused by foundation pit excavation and the above-crossing shield. Vertical displacement and horizontal displacement for the construction disturbances of the two parts have opposite influences. Certainly, multiple disturbances can offset each other's partial displacement, thereby minimizing the final displacement.  
The segment structure of the existing tunnel is gathered as a whole, wherein the stiffness reduction is caused by the bolted connection between the segments, which was not considered in this study. The numerical simulation did not consider the impact of groundwater because there was sandy soil in the soil layer, and the soil bulk density and effective stress were bound to be affected by the action of groundwater. This may have affected the accuracy of the numerical simulation to some extent.  
Conceptualization, F.Y. and X.H. (Xingbo Han); methodology, H.L.; software, H.L.; validation, X.H. (Xingbo Han) and X.H. (Xin Han); formal analysis, H.L.; investigation, X.H. (Xin Han); resources, H.L.; data curation, X.H. (Xingbo Han); writing--original draft preparation, H.L.; writing--review and editing, F.Y.; visualization, X.H. (Xin Han); supervision, F.Y.; project administration, H.L.; funding acquisition, X.H. (Xingbo Han). All authors have read and agreed to the published version of the manuscript.  
This work was financially supported by the National Science Foundation of China (Nos. 51678062 and 51878060).  
Not applicable.  
Data Availability Statement: The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflict of interest.