Probabilistic Back Analysis Of Parameters And Reliability Analysis For Shield Tunnels Using Bayesian Method

With the acceleration of urbanization in China,planning and construction of urban subway network is the main focus of national urban transportation construction.In recent years,more and more accidents such as ground collapse,pipeline water and sand gushing arise from the uncertainties of shield tunnel parameters in construction sites.The traditional back analysis approaches of parameters belong to the category of deterministic analysis.The influence of the uncertainties of shield tunnel parameters cannot be effectively taken into account.To remove this limitation,Bayesian Updating with Structural reliability method(BUS)is introduced for probabilistic back analysis of shield tunnel parameters.Then,reliability analysis of excavation face stability induced by shield tunneling is carried out based on the estimated posterior statistics of shield tunnel parameters.The main contents and conclusions of this study are summarized as follows:(1)The basic principles of probabilistic back analysis approach of shield tunnel parameters based on BUS method are introduced.The implementation procedures of the subset simulation-based BUS method are presented.To improve the computational efficiency of probabilistic back analysis of shield tunnel parameters,the surrogate models of output responses of the shield tunnel are constructed using the stochastic response surface method.These can lay the foundation for promoting the application of Bayesian theory in the practice of shield tunnel engineering.(2)The shield tunnel project of Hangzhou Metro Line 7 is taken a typical case,the finite difference model of tunnel excavation is built with the geotechnical site exploration data.A surrogate model for the crown settlement of shield tunnel is constructed using the fourth-order Hermite polynomial chaos expansion.Probabilistic back analyses of elastic modulus and friction angle of mixed breccia layer of clay are carried out by adopting the BUS method.Meanwhile,a series of sensitivity analyses are carried out to explore the influences of the number of samples per subset simulation level,the reliability of monitoring data,the monitoring displacement and the monitoring sample size on the probabilistic back analyses of soil parameters.(3)The shield tunnel project of Nanchang Metro Line 1 is taken a typical case,sequential probabilistic back analyses of the elastic modulus of different soil layers and driving load on the road above the shield tunnel is performed by employing the BUS method with the field time-series monitoring data.Then,reliability analysis of ground settlement induced by shield tunneling excavation is conducted based on the estimated posterior statistics of shield tunnel parameters.The probability distribution of parameters and failure probability can be used to predict the instability of shield tunnel effectively.Thus,early warning of failure accidents of shield tunnels considering the uncertainties of parameters can be real-timely carried out with the aid of the collected field monitoring data.