## 7 Conclusions  
The influence of assembly error and the impact of jack thrust on the stress and structural damage of an unlooped segment is generally overlooked in the traditional shield construction process. In this paper, the interaction and damage of segments in the synchronous propulsion and assembly mode were investigated via a suite of multi-segment assembly finite element models. Through the research on the assembling position of the segment and the safety of the assembly process, the displacement, stress, and bending moment distribution of the newly assembled segment under different gravity directions were discussed. The goal of damage analysis is to explore the effects of different assembly errors, gravity directions, and the assembly process on segment damage and seam opening. The obtained results can be used to guide the smooth application of the synchronous propulsion and assembly method in practical engineering. It was found that:  
1. In the synchronous propulsion and assembly mode, the segment will rotate radially inward during the assembly process. Under the influence of the propulsion force, the unlooped segment will firstly be squeezed on one side and then clamped on both sides. The rotational freedom of the segment will gradually decrease.
2. The direction of gravity affects the radial rotation of the segment, which in turn affects the interaction between the newly assembled segments. Inward rotation is greatest when the segment is at the top. The stress concentration of the segment will gradually decrease with the clamping effect, and the stress range is between 3.5-10.5 N/mm\({}^{2}\).
3. The bending moment of the segments that are initially assembled at different positions is different, which makes the segments present different bending conditions. With the assembly of adjacent segments, the bending of segments tends to be the same as the influence of the surrounding segments.
4. In the synchronous propulsion and assembly mode of the shield, the segment may be destroyed within the assembly error range. The longitudinal thrust of the jack will be redistributed due to the posture of the segment and the interaction between the segments. The stress concentration between the contact surfaces of the segments leads to the failure of the segments. The radial deflection error is more likely to damage the segment. In actual engineering, if the assembly error reaches the segment damage angle, the operation mode of the shield needs to be adjusted.
5. The maximum opening of the segment is directly related to the assembly error mode, and its peak value is strongly linearly related to the angle of the segment assembly error. Under the effect of assembly error, the maximum opening of the segment can  
Figure 21: Maximum opening of segment joints in the presence of lateral deflection.  
reach 10.4 mm, which may cause the segment gasket to bear excessive pressure and reduce the waterproof performance of the segment.  
Conceptualization, P.L.; Data curation, J.L. and J.F.; Funding acquisition, P.L.; Investigation, X.K.; Methodology, Z.D.; Project administration, J.F.; Resources, X.K.; Visualization, J.L.; Writing--original draft, Z.D.; Writing--review & editing, P.L. and X.W. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the \"Social Development Project of Science and Technology Commission of Shanghai Municipality (21 DZ1201105)\", \"The Fundamental Research Funds for the Central Universities (21D11320)\", and \"Shanghai Rising-Star Program of China (18 QB1403800)\".  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
Thanks to research section and the members of research group for their great help in the engineering geological prospecting of the project.  
The authors declare no conflict of interest.