Study on Time-varying Behavior of Reinforced Concrete Immersed Tunnel Structure in Chlorine Corrosion Environment

As an important public transport infrastructure, a subsea immersed tunnel should have good durability, but there are still deficiencies in the research on the life prediction and time-varying characteristics of immersed tunnel structures in a marine chlorine environment. This study used the diffusion law of chloride ions in concrete and the chlorine corrosion mechanism of reinforced concrete to develop a life prediction model for the reinforced concrete lining of an immersed tunnel under a chlorine corrosion environment based on the normal service limit state, and refined the main parameters of this prediction model based on the relevant specifications. Then, time-varying models of the reinforcement corrosion rate and concrete elastic modulus attenuation rate of a tunnel structure were established, which could be used to calculate the material parameters of tunnel structure reinforcement and concrete with different service times as the input parameters of the finite element model. Finally, the tunnel life prediction model and structural time-varying model were applied to a reinforced concrete immersed tunnel project in Dalian to predict its service life, and the time-varying mechanical behaviors of the tunnel lining materials and structures were analyzed. The results showed that ① the corrosion rate of the tunnel reinforcement and attenuation rate of the concrete elastic modulus increased nonlinearly in three stages with an increase in the corrosion time; ② with an increase in the service time (chlorine corrosion time), the internal force (bending moment and axial force) at the mid span of the vault of the immersed tunnel gradually decreased, while the settlement deformation gradually increased; ③ the plastic zone of the immersed tunnel structure first appeared in the tensile part of the structure, and this plastic zone hardly expanded before the expansion cracking of the concrete surface, but gradually expanded after the expansion cracking of the reinforcement rust on the concrete surface, and then appeared in the compression part of the structure; and ④ the maximum Mises stress of the compression part of the structure increased with the service time before the plastic zone appeared in the compression part of the immersed tunnel structure, while the maximum Mises stress rapidly decreased after the plastic zone appeared in the compression part of the structure. © 2022 Xi'an Highway University. All rights reserved.