Numerical Simulation Of Mechanical Behavior Of Shield Tunnel Under Environmental Loads

After a long period of development,the shield tunnel has been widely used in urban subway construction in China due to its advantages of safe construction,high degree of automation and suitable for soft soil layer.With the increasing mileage of subway tunnels in various cities and the increasing operation time of subway tunnels,under the long-term environmental load,the problems of tunnel segment cracking,joint opening,ring dislocation and other diseases are increasing,which seriously affect the safety of shield tunnels.On the basis of previous studies,the following work about the mechanical behavior of shield tunnel under environmental load has been done:In the theoretical calculation method,the tunnel is simplified into Euler-Bernoulli beam model and Timoshenko beam model;then the calculation formula of shield tunnel settlement under surcharge load is deduced.By comparing with the results of similar model tests,it is concluded that the above theoretical calculation method can accurately predict the longitudinal settlement of shield tunnel under surcharge load.FLAC3D finite difference software is used to establish the stratum-structure model.The interface element is used to simulate the interaction between the soil and the lining.First,the value of the interface element parameters is studied.Then,the influence of the existence of the interface element on the longitudinal settlement and lateral deformation of the shield tunnel is analyzed.At last,the influence of the single factor of the surcharge load on the longitudinal settlement and lateral deformation of the tunnel under different soil and soil layer distribution is analyzed,and the settlement and lateral deformation of the tunnel are obtained.The ABAQUS software is used to establish a three-dimensional numerical model,the joint weakening method is used to simulate the lining segment joint structure,and the applicability of the joint weakening method is analyzed.The empirical formula of weakening elastic modulus of shield tunnel lining joint is given.and the empirical formula is extended to large diameter tunnel and super large diameter tunnel,which provides reference for three-dimensional numerical simulation of lining structure.A multi-ring three-dimensional tunnel model is established to apply the same uneven settlement to shield tunnels with different lateral deformations.Firstly,the overall deformation of the tunnel after uneven settlement is analyzed.Then the change of the internal force of the tunnel with the settlement value is analyzed.Finally,the development of segment damage in shield tunnels with different lateral deformations during uneven settlement is analyzed,and the recommended values of safe settlement for subway shield tunnels with different lateral convergence values are proposed,which provides a reference for the monitoring and maintenance of new tunnel and shield tunnel lining structure during operation.