## 6 Conclusions  
Based on the PLAXIS 3D numerical simulation platform, this study systematically investigates the surface settlement characteristics of unreinforced soil and grout-reinforced soil during shield tunnel construction, focusing on the influence of tunnel burial depth, grouting pressure, and soil bin pressure on the surface settlement. Through comparative analysis, the following main conclusions are drawn:  
1. Flower pipe grouting reinforcement technology demonstrates significant efficacy in controlling surface settlement. Research findings indicate that, compared to unreinforced conditions, the implementation of grouting reinforcement reduces average surface settlement by 92%, with maximum settlement controlled within 3 mm. This evidence provides an effective solution for mitigating surface settlement when shield tunnels traverse sensitive areas such as long-distance railroads.
2. The numerical simulation method demonstrates high reliability in predicting surface settlement caused by shield tunnel construction. The discrepancy between the simulation results and on-site monitoring data is maintained within \(\pm\)0.5 mm, thereby validating the accuracy of the numerical model and providing a robust technical approach for predicting surface settlement in similar projects.
3. Under unreinforced conditions, surface settlement exhibits the following trends: tunnel depth is negatively correlated with surface settlement, decreasing by approximately 0.15 mm for every 1 m increase in depth; soil chamber pressure is positively correlated with surface settlement, increasing by approximately 0.08 mm for every 10 kPa increase in pressure; grouting pressure has a critical value of around 400 kPa. Below this critical value, surface settlement decreases as grouting pressure increases; however, once the grouting pressure exceeds this critical value, surface settlement increases with further increases in grouting pressure.  
Under flower pipe grouting reinforcement conditions, the influence of tunnel depth, grouting pressure, and soil compartment pressure on surface settlement is markedly diminished, with the degree of impact reduced by approximately 85-95% relative to unreinforced conditions. These results suggest that grouting reinforcement measures can effectively mitigate the effects of construction parameter variations on surface settlement, thereby providing enhanced stability and reliability for shield tunnel construction in sensitive regions.
* When the shield tunnel passes through a long-distance railway group, surface grouting reinforcement can effectively reduce the impact caused by shield tunnel excavation, so this engineering method can be usefully and effectively applied to similar projects in the future.  
Q.M., resources, supervision, and funding acquisition; X.Z., conceptualization, methodology, and writing--original draft; H.S., supervision and writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
The authors are grateful for the financial support of the National Natural Science Foundation of China (No. 52478338, No. 52078194), the National Young Top-notch Talent of Ten Thousand Talents Program, the Science Fund for Distinguished Young Scholars of Hubei Province (2022 CFA043), the Young Top-notch Talent Cultivation Program of Hubei Province, the Outstanding Young and middle-aged Science and Technology Innovation Team of colleges and universities in Hubei Province (No. T2022010), and the Innovation Demonstration Base of Ecological Environment Geotechnical and Ecological Restoration of Rivers and Lakes (No. 2020 EJB004).  
Not applicable.  
The data presented in this article are available within the article.  
The authors declare no conflict of interest.