Sealing Performance Degradation And Evolution Of Shield Lining Joints-Multiple Scale Research

In the past 30 years,shield tunneling has been extensively used in construction of urban tunnels including transportation,electricity and pipe gallery engineering.All of these infrastructures are usually designed to meet for 100 years.However,the durability of tunnels has not attracted enough attention due to the short operation time.According to the previous experience of subway tunnels,leakage is a common factor affecting tunnel operation.The waterproof of shield tunnel lining is mainly achieved through a pair of EPDM gaskets,the thermal-oxidation and viscoelasticity of EPDM will lead to contact press relaxation,as a result,leakage will gradually increase during service time,which brings great challenges to the healthy operation and service durability of shield tunnel.In view of this problem,most scholars mainly focus on the treatment measures,nevertheless,attention to understanding on the development and evolution of tunnel lining joint leakage has been little paid.In order to explore the underlying microscope process of the leakage development in shield lining joints,the long-term degradation behavior of EPDM and the leakage evolution mechanism of sealing interface were studied in this paper.Firstly,the viscoelastic and degradation behavior of EPDM were studied through experimental characterization and molecular dynamics(MD)simulation: 1)EPDM was artificially aged in a rolling-thin film oven(RTFO)to simulate aging that occurs in service,macro and micro characterization tests were carried out to study the law of service performance degradation,based on which the aging constitutive of of EPDM was conducted;2)molecular dynamics simulation was used to investigate the microcosmic mechanism of the viscoelastic and thermal oxidation of EPDM service performance,the influence of factors including temperature,stress,strain and their combined effect on the viscoelastic of EPDM were explored,the hydrocarbon free chain,carbon cross link,chain scission,hydroxyl and ether cross link were proportionally mixed into several MD systems representing EPDM at different thermal oxidation stages,the influence of thromal-oxidation on the kinetics and mechanical properties of EPDM were analyzed;3)The coupling mechanism between viscoelastic and thermal oxidation of EPDM was further explained via combining analysis of experiments and MD results.Then the underlying process of leakage development in sealing interface was revealed based on Persson contact theory: 1)A multi-scale analysis model of shield lining seam leakage was established,and various influencing factors including the gap and offset of joints,the roughness of sealing materials,the service time,and groundwater pressure were embedded into it through parameter transformation;2)the critical leakage state and the self-sealing effect were defined and the approach to calculate critical leakage pressure as well as selfsealing stress were deduced;3)taking SuTong GIL pipe gallery shield tunnel as a case,the method was valid via comparing the experiments and the calculations of critical leakage pressure,and then the influence law of each factor on the leakage of shield joints were analyzed.The experimental characterization,MD simulation and multi-scale contact mechanics were used here to study the degradation mechanism of EPDM service performance and the underlying process of shield tunnel lining joints leakage,which could provide guidance and reference for improving durability design of waterproof material and prevention as well as treatment of shield lining leakage.