Impact of Large-span Civil Defense Tunnel Project Under-passing Construction on Structural Stability of Existing Metro Tunnel Intervals

Abstract

Objective To analyze the construction impact of new large-span civil defense tunnel on metro tunnel interval structural stability when under-passing existing metro line with a small clear distance, it is necessary to conduct a simulation study of the civil defense tunnel under-passing construction process. Method Leveraging a flat large profile civil defense tunnel under-passing existing metro tunnel interval project in Qingdao, a three-dimensional finite element model is established to simulate the whole process of civil defense tunnel excavation. The mechanical response and deformation patterns of the diaphragm wall set in the civil defense tunnel during excavation is emphatically analyzed, as well as the impact of overall construction process on existing metro station and tunnel interval. Result & Conclusion The civil defense tunnel diaphragm wall exhibits a noticeable biasing trend during the construction of both the leading and trailing holes. In the initial support phase of the civil defense tunnel, a rare ′four-quadrant′ distribution pattern is observed due to the combined effects of the existing metro tunnel upper arching effect and the diaphragm wall, with higher settlement values on the right side compared to the left side. The existing metro stations and interval structures experience a significant impact from the civil defense tunnel excavation space effect, with deformation trends moving towards the excavation side, while the deformation values are all below the regulation-specified warning limits.

Keywords

• metro tunnel
• civil defense tunnel
• small clearance under-passing
• structural stability