Study On Some Key Problem On The Durability Of Shield Tunnel Under River

With the development of national economy and speedup of urbanization, more and more shield tunnels under river have been built. The shield tunnel under river is an important structure and expected to serve more than 100, has bad maintainability and always requires high maintenance costs. However, it is exposed to complicated aggressive environment and by far little research work has been done on the durability of underground structures as shield tunnel under river and the study is inadequate. So, it is necessary to carry out study on the issues concerns the durability of shield tunnels under water.Based on an overall analysis on the factors that may influence the durability of subaqueous shield tunnel, this paper develop methodology and theory frame for its durability study. Main works are summarized as fellow:1. Analyzed and classified all the factors may influence the durability of river shield tunnel by their property and established corresponding tree diagram.2. Based on the cause analysis of segment crack and the discussion of relationship between crack and durability, a FEM program was developed in Matlab environment to simulate the transportation and distribution of chloride in cracked segment concrete. According to the simulation, the relationship between crack depth and rust time of reinforced bar can be well formulated with logistic function with three parameters. Besides, the paper established durability damage membership function for segment crack factors as width, depth, orientation and distribution density respectively and conducted fuzzy comprehensive evaluation for the above factors using case study.3. The soil column test was conducted on overlying grey mud clay of the Shanghai Yangtze River tunnel to study its property of chloride transportation and measure its parameters involves chloride transport. Then the paper studied the chloride transportation in soil skeleton using analytic solution and in pore water using Galerkin's method respectively. The study indicates that in normal condition, increase of chloride concentration in Yangtze estuary, decrease of thickness of overlying strata and leakage of segment lining can hardly influence the chloride concentration in soil and groundwater that contact with tunnel segment.4. A coupling model of chloride transport in seepage water in segment joints and concrete as well as corresponding FEM program was developed. The conclusion was made that joint leakage will remarkably reduce rust time of the reinforced bar of segment lining according to numerical analysis. Consequently, it is of high importances that waterproof gasket work well. Then the thermal-oxidative aging test was conducted on EPDM gasket used in Shanghai Yangtze River tunnel to study its contact stress relaxation behavior. According to the aging test, the paper predicted the service life of gasket at atmospheric temperature using trigram aging model and proposed a time-dependent constitutive model to express the contact stress relaxation of gasket. Besides, the contact stress relaxation of gasket at atmospheric temperature was simulated using Marc. The study shows the waterproof gasket employed in Shanghai Yangtze River tunnel can serve 100 years.Finally, the paper gave an appraisal on the durability of Shanghai Yangtze River tunnel based on the research finding and established methodology and theory frame for the durability study of subaqueous shield tunnel, made a summary on the research work and delivered expectation on the issues need further study.