| In general, the study of tunnel stability calculation is based on uncertainty analysis.However, the engineering geological environment of metro shield tunnel is very complex,such as geotechnical parameters and boundary conditions have a great deal of randomness and variability and the traditional calculation method can't reflect the uncertainty.It is of great significance to apply the structural reliability theory which is based on probability and mathematical statistics to the reliability and sensitivity analysis of shield tunnel.In order to understand the structural reliability of Lanzhou subway shield tunnel during the construction and determine the main factors influencing the structural reliability.This paper is based on the reliability theory of stochastic finite element method in engineering structure, relying on the Lanzhou metro shield tunnel.Considering the uncertainty of material properties, the buried depth of the tunnel,structural size,load and so on.To determine the probability characteristics of the random variables by reference to the relevant literature.The three dimensional stochastic finite element model is established by using ANSYS finite element analysis software and the limit state equation is builded on the basis of deterministic analysis.By using the Monte Carlo Latin hypercube sampling method,the reliability and sensitivity of the maximum stress,minimum stress,the maximum deformation of segment lining of shield tunnel and the surface subsidence maximum value,uplift maximum value along the tunnel axis and the maximum value of the maximum subsidence,uplift of heading face above the surface are calculated in Lanzhou metro construction process of the tunnel.Through the analysis of the simulation results obtained the following conclusions:(1)The random variables histogram fitting curves are smooth and the sampling data is continuous and in accordance with default probability distribution.It shows that the reliability calculation of cycle times is enough and the sampling is effective.(2)Based on the reliability analysis of shield tunnel,the reliability of segmental lining maximum stress is 95% and the reliability is 96.29% when segmental lining maximum deformation is less than 3.7 mm and the failure probability is 3.71%.The reliability of surface uplift and subsidence is 95%.Therefore,this section of shield tunnel is safe and reliable during construction.(3)Through the shield tunnel structural reliability sensitivity analysis,the random input variables are sorted on the degree of influence of each structural response,so as to determine the main random variables influencing the reliability of the structural response.In view of the controllable factor,the reasonable measure is taken to improve the reliability of structure.(4)By comparing the calculation results of the reliability sensitivity of shield tunnel structure analysis,effects of surrounding rock,lining and other material parameters on thereliability of tunnel structure are larger than the structure size and other factors on the reliability of tunnel structure.In addition,the tunnel buried depth has a great influence on the maximum uplift of the surface and the construction load uncertainty has little influence on the reliability of tunnel structure.(5)The results of this study can provide reference for the research on reliability of the similar tunnel structure and under the similar geological environment.This calculation can provide a basis for later operation and maintenance of shield tunnel. |
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