The Refined Simulation Of Shield Tunnel-Strata And The Study Of The Longitudinal Mechanical Properties

Studies have shown that shield tunnels are prone to uneven settlement when longitudinally traversing soft and hard change strata,which in turn causes serious diseases such as segment opening,misalignment and seepage of mud and water from joints,directly threatening the safety of construction and operation of shield tunnel.The cross section of shield tunnel is mostly circular and has better resistance to deformation,while the longitudinal direction is much longer and has much less resistance to deformation than the lateral direction.In addition,shield tunnel is made of several prefabricated segments assembled by bolts,which have lower strength at the bolted joints,resulting in weaker longitudinal stiffness and highly susceptible to longitudinal deformation.Existing studies have analyzed the mechanical properties of shield tunnels under different geological conditions and engineering disturbances by various methods,providing technical support for the construction and operation of shield tunnels,but there are still deficiencies in the study of the longitudinal mechanical properties of shield tunnels,such as the treatment of the segment bolts,strata and strata-tunnel contact surface are too simple,and the longitudinal inhomogeneity of the strata around the tunnel is seldom considered etc.Therefore,this paper proposes a shield tunnel refinement simulation method and establishes a threedimensional refinement numerical calculation model of shield tunnel to address the longitudinal mechanical properties of shield tunnel and its deformation law in soft and hard change strata,simulating the real mechanical properties of shield tunnel segments staggered assembly,longitudinal and circumferential bolts and strata-tunnel interface.On this basis,the longitudinal mechanical properties of shield tunnel through soft and hard strata are studied,the influence law of stratigraphic factors is analyzed,and the effectiveness of several typical shield tunnel deformation control measures is initially discussed.The research results can further improve the longitudinal mechanical properties analysis method of shield tunnels.The main work and research results of this paper are as follows:(1)Based on FLAC 3D finite difference software,a shield tunnel refinement simulation method and 3D model are proposed in this paper.Firstly,the establishment,positioning and staggered assembly of segments are realized based on Fish language,and the longitudinal and circumferential bolts are simulated by the Link element at the precise position,and the intrinsic model and related parameters of the Link element in each direction are reasonably set according to the mechanical properties of the bolts.Secondly,by establishing the Interface element between the strata and the segmemt lining and reasonably selecting the normal and tangential intrinsic models and related parameters,the refined simulation of the strata-tunnel interface is realized.Finally,the reliability of this method is verified by the improved Timoshenko beam theory in this paper.(2)Based on a shield tunnel project in China,the longitudinal mechanical properties of a shield tunnel longitudinally traversing soft and hard change strata are analyzed,including longitudinal settlement of shield tunnel,segment opening and dislocation,segment longitudinal internal force,bolt deformation and interface relative deformation,etc.;the influence law of strata on shield tunnel longitudinal mechanical properties is highlighted by comparing two models with simplified strata and real strata,and the influence law of strata on shield tunnel longitudinal mechanical properties is demonstrated.(3)Based on the characteristics of shield tunnel longitudinal traversing soft and hard change strata,three main factors,namely the elastic modulus difference between soft and hard strata,sliding characteristics and inclination of interface,were carried out for sensitivity analysis,and the influence law of the three factors on the longitudinal mechanical properties of shield tunnel was studied separately,and the unfavorable state of shield tunnel longitudinal deformation under the three factors was determined.(4)Based on the above study of the longitudinal mechanical properties of shield tunnels through soft and hard change strata,combined with the control measures adopted in existing shield tunneling projects when the deformation exceeds the permissible range,this paper summarizes three types of deformation control measures for segment lining: applying secondary lining,improving lining strength,and improving joint strength,and studies the control effects of different measures with the help of the refined simulation method of shield tunnel,and provides a basis for deformation protection of shield tunnel projects.