Abstract
The durability of subsea tunnels under the coupled action of stress and chloride ions was analyzed to estimate the service life and provide a theoretical foundation for durability design. The influence coefficient of the stress on chloride ion transmission at lower stress levels was discussed according to the material mechanics, and was verified by experimental data. A stress calculation model of a subsea tunnel’s lining section is proposed based on the plane-section assumption. Considering the space-time effect of the convection velocity, a partial differential equation was constructed to calculate the chloride ion transfer condition under the coupled action of stress-convection-diffusion. The numerical solution of the partial differential equation was solved and the sensitivity of the parameters was analyzed. The subsea tunnel’s time-varying reliability index was calculated following the Monte Carlo method, and was used to predict the service life. The results show that the chloride ion concentration calculated by considering the coupled action is larger and the reliability index is lower than calculated only considering diffusion. Our findings contribute to the conclusion that durability designs of subsea tunnels should consider the coupled action of stress-convection-diffusion. An effective method to improve the service life of a subsea tunnel is to reduce the water–binder ratio or increase the thickness of protective cover.
Highlights
Subsea tunnels are widely recognized as the preferred means of cross-channel transportation [1,2,3,4]and are becoming increasingly important for the development of national life and economics
Where α is the attenuation index of time; t0 is the test age of the diffusion coefficient of the concrete, which is usually evaluated as 28 days; tk is the time when diffusion coefficient tends to stabilize; D0 is the diffusion coefficient of time t0 ; and W/B is the water–binder ratio
(1) Under of the coupled was effect ofmain diffusion convection, diffusion a major role inthe the influence early period, convection the effectand during the middle period,played and during the role in the early period, convection was the main effect during the middle period, and during late period, diffusion was again responsible for the majority of the effect
Summary
Subsea tunnels are widely recognized as the preferred means of cross-channel transportation [1,2,3,4]. Liu [14] established a numerical model of chloride ion erosion and transport in segment joints, considering the coupling of pressure permeation and chloride ion concentration They concluded that the external water pressure of a tunnel has a significant impact on the velocity and depth of chloride ion transmission. Song [18] calculated the service life of a subsea shield tunnel using the reliability method, considering the effect of structural stress state on the diffusion velocity of chloride ions. A partial differential equation for chloride ion transfer under the coupled action of stress, convection, and diffusion was established, based upon which the chloride ion concentration was calculated. To determine the chloride ion transfer in both the inside and outside of tunnel lining, it is necessary to consider the coupled action of convection and diffusion. Where α is the attenuation index of time; t0 is the test age of the diffusion coefficient of the concrete, which is usually evaluated as 28 days; tk is the time when diffusion coefficient tends to stabilize; D0 is the diffusion coefficient of time t0 ; and W/B is the water–binder ratio
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