## 5 Conclusions  
Based on the double-arch tunnel part of Haicang tunnel in Xiamen, the deformation and stress laws of underground pipelines in different horizontal distances, buried depth, diameter, wall thickness, shape, material and excavation methods were studied by using numerical analysis, and the following conclusions are drawn:  
1. The underground pipelines near the central axis of the double-arch tunnel deformed most obviously. Therefore, special attention should be paid to the protection of the underground pipelines above the central axis of the tunnel. The pipeline should be relocated or protected before tunnel excavation.
2. The circular underground pipelines with large buried depth, small diameter and large wall thickness were greatly affected by tunnel excavation, so protection measures should be strengthened during tunnel excavation.
3. Larger diameter and distance between the pipeline and tunnel, smaller pipeline wall thickness or square rigid pipeline resulted in smaller pipeline deformation.
4. Three-step reserved core soil excavation method reduced pipeline deformation compared with the other excavation methods which is advantages pipeline protection.
5. The relative position of pipeline and tunnel, and construction method had a great influence on pipeline deformation. Pipeline type, pipeline material, pipeline diameter and excavation method had a great influence on pipeline stress.  
The influence of several main factors on the response of adjacent underground pipelines during double-arch tunnel excavation had been discussed here with a special case. In future, further studies on a common double-arch tunnel soil type, blast damage, hydrological condition and supporting time should also be considered under certain conditions.  
Figure 20: Vertical deformation of pipeline with different excavation methods.  
**Author Contributions:** [PERSON], [PERSON] and [PERSON] carried out the main research task and wrote the manuscript. [PERSON] proposed the original idea and contributed to the revision of the obtained results and the whole manuscript. [PERSON], [PERSON] ([PERSON]) and [PERSON] performed utilization on-site. [PERSON]. ([PERSON]), [PERSON] and [PERSON] performed investigation. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Shanghai Municipal Science and Technology Project (18 DZ1201301; 19 DZ1200900); Xiamen Road and Bridge Group (XM2017-TZ0151; XM2017-TZ0117); the project of Key Laboratory of Impact and Safety Engineering (Ningbo University), Ministry of Education (CJ202101); Shanghai Municipal Science and Technology Major Project (2021 SHZDZX0100) and the Fundamental Research Funds for the Central Universities; Key Laboratory of Land Subsidence Monitoring and Prevention, Ministry of Natural Resources of the People's Republic of China (No. KLLSMP202101); Suzhou Rail Transit Line 1 Co. Ltd. (SURT01Y1S10002); China Railway 15 Bureau Group Co. Ltd.( CR15 CG-XLDYH7/2019-GC01); the National Natural Science Foundation of China (Grant No. 41907230).  
**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.