## 5 Conclusions  
Relying on an underground docking project of a cross-sea tunnel, this paper uses the methods of theoretical calculation and numerical simulation to study the longitudinal stress relaxation effect of segment lining and steel channel reinforcement technology after the thrust is unloaded in the process of shield docking and dismantling. The accuracy of theoretical calculations and numerical simulation is verified by comparing the openings of circumferential joints. Numerical simulation was used to further analyze the effect of key parameters, such as reinforcement range, model and quantity of steel channels, on the reinforcement effect after thrust unloading. The influence law and reinforcement  
Figure 19: The relationship curve between the opening of circumferential joints and the number of rings under different models.  
Figure 20: The relationship curve between steel channel models and the opening of circumferential joints for different rings.  
mechanism of key parameters on the openings of circumferential joints are revealed, and the following results are obtained:  
1. The reinforcement method of adding a steel channel is equivalent to transferring the internal force of the segment lining with several springs in parallel to resist the axial tension of the segment lining. This method can effectively reduce the stress relaxation effect of segment lining in the process of docking.
2. With the increase in the reinforcement range, the maximum longitudinal displacement and the openings of circumferential joints decrease first and then increase. The openings of circumferential joints are minimized when the reinforcement range just reaches the ring. When the reinforcement range is 20 rings, the maximum opening of circumferential joints reaches 5.97 mm.
3. The model and quantity of steel channels have similar effects on the reinforcement mechanism of the segment lining. With the increase in the model and quantity, the maximum longitudinal displacement and the opening of circumferential joint gradually decrease, and the reduction ratio also decreases. The farther away from the shield tail, the worse the reinforcement effect is.
4. In order to ensure that there is no sea water leakage in the process of the shield docking of the supporting engineering, it is recommended that the reinforcement range be 18-20 rings, the number of channels should be no less than 24 and the channel steel type should be no less than 14 when using channel steel reinforcement technology for the longitudinal reinforcement of segments.  
Conceptualization, Z.G. and D.Y.; methodology, Z.G. and D.Y.; software, Z.G.; validation, Z.G., D.W., Y.Z. and T.X.; formal analysis, Z.G.; investigation, Z.G., D.W., Y.Z. and T.X.; resources, D.Y.; data curation, Z.G.; writing--original draft preparation, Z.G.; writing--review and editing, Z.G. and D.Y.; visualization, D.W.; supervision, Y.Z.; project administration, T.X.; funding acquisition, D.Y. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China grant number No. U1834208.  
The data presented in this study might be available on reasonable request from the corresponding author.  
The authors declare no conflict of interest.