## 8 Conclusions  
The new prefabricated SRS arch adopts high-strength seamless steel tubes as the main load-bearing parts to improve the supporting rigidity and bearing capacity, forming a supporting structure suitable for tunnels under complex surrounding rock conditions. Relying on the undercut tunnel project of Guangzhou Metro Panyu Square Station, the bearing characteristics and supporting performance of the SRS arch structure are studied by laboratory experiments, numerical analysis, and field measurement. The main conclusions are as follows:  
1. A construction system of the prefabricated SRS arch for a large cross-section tunnel in a complex urban environment is developed, which mainly includes a three-arm and three-basket multifunctional operation trolley, a high-strength SRS arch and a longitudinal connection device.
2. Through the indoor model test, the deformation characteristics and bearing mechanism of end-plate joint components and jointless components are clarified. It is verified that the SRS arch structure has good ductility and high bearing capacity and meets the joint design requirements. The research results provide a theoretical basis for the parameter design and engineering application of this structure.
3. With the help of the numerical simulation method, the stress distribution characteristics of the SRS arch and grid arch and the plastic damage of the concrete are mastered. Moreover, it is concluded that the SRS arch has a positive impact on controlling the deformation of the surrounding rock and ameliorating the stress of the support structure.
4. Through the field test of the prefabricated SRS arch, mechanized construction is realized. The measured data show that the SRS arch can be closed and formed into a ring in time, and the structural force is reasonable, which can meet the demand of support strength and provide new technical support for the development of urban underground large spaces in the future.  
Based on the stratum conditions of the underground tunnel at Panyu Square Station of Guangzhou Metro, the key technology research on the mechanized construction of large-section tunnels by the step method was carried out, but the adaptability of other construction methods and stratum conditions was not studied. Therefore, it is necessary to expand the construction technology to underground engineering construction with different construction methods, stratum conditions, and section sizes in the future.  
**Author Contributions:** M.H. and Y.S.: conceptualization, methodology, project administration and writing the original draft; X.Z.: validation, analysis, and review. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the General Program of National Natural Science Foundation of China (No. 51878037) and the National Key R&D Program of China (No. 2018 YFC0808705).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest.