Numerical study on mechanical properties of large diameter double-layer shield tunnels under the elevated temperatures in fire

Abstract

As the development of underground engineering, shield tunnels in single-pipe and double-deck type have been widely used and promoted to improve the utilization rate of the effective space. For this complex structure, fire may trigger tunnel lining structure damage or even the failure of the structure. In this paper, the mechanical properties of a large diameter double-layer shield tunnel under elevated temperatures induced by fire were analyzed numerically. A thermo-mechanical coupling numerical approach was employed to implement the thermo-mechanical models in full size. Aiming at a large-diameter shield tunnel with the internal structure combining road and metro space in Jinan, China, the model is applied in a parametric study to verify the fire resistance of tunnel structures under different configurations and RABT fire exposure. The effects of the internal structure and fire location on the complicated mechanical properties of the tunnel were analyzed. Results from numerical analysis showed that the elevated temperatures have a significant impact on the mechanical properties of tunnel, and the structure subjected to elevated temperatures has obvious expansion deformation and stress change. The internal structure has a great influence on the mechanical properties of the tunnel under elevated temperatures, which is conducive to reducing the radial convergence deformation of the tunnel lining structure and improving the internal force state of the lining structure. The location of the fire in the tunnel has a major influence on the internal force and deformation of the tunnel structure. When the fire occurs in the lower space of the tunnel, the fire safety of the internal box culvert structure should be paid more attention. The key design considerations have been identified as the concrete deck slab and the tunnel lining segmental joints configuration.