Time-varying analysis of deterioration by chloride ion erosion for subsea tunnels under wave loads

The subsea tunnel in shallow water is in a complex fluctuating hydraulic environment. The existing theoretical researches generally reckon in the corrosion effects of free diffusion of chloride ions on the tunnel linings in the hydrostatic environment, and seldom consider the promotion effects of ocean wave force on the corrosion of the lining structures. Firstly, the wave pressure on the seabed surface is determined by using the Stokes second-order wave theory which is suitable for the shallow water, and the hydraulic response around the tunnel linings is obtained based on the Biot consolidation theory. Then, the improved Fick's second law is used to consider the diffusion of chloride ions driven by the water pressure and concentration gradient, and the exponential strength deterioration model is used to describe the deterioration effects of lining concrete during service time. Finally, considering with the erosion effects of chloride ions under wave action, the bearing capacity of the linings of the subsea tunnel is calculated. The theoretical solution for this study is compared with the numerical models and existing test results, and the solutions are in good agreement. The results show that when the promoting effects of the dynamic wave pressure on chloride ion seepage in lining concrete are neglected, the diffusion velocity of chloride ions in lining concrete will be underestimated. With the increase of wave period, the maximum depth of erosion infiltration of chloride ions inside the lining increases significantly. Without considering the deterioration effects of lining strength, the service life of tunnel structures will be obviously overestimated, which is not conducive to the safety reserve of subsea tunnel during service.