Study On Influence Of Ground Surcharge On Structural Deformation And Bearing Performance Of Subway Shield Tunnel

With the development of society,the scale of the subway is growing.Under the condition of surcharge loading on the ground above the shield tunnel,additional stress will be produced to the shield tunnel structure,which will destroy the original balance of the tunnel structure and cause the stress redistribution,thus causing certain deformation.When the situation is serious,it may even lead to the phenomenon of segment joint opening,segment cracking and bolt failure.In this paper,a tunnel deformation model considering shear dislocation effect and rigid body rotation effect is established,and the calculation formulas of longitudinal deformation,displacement between loops,rotation angle between loops and shear force between loops of shield tunnel structure underground loading are derived;And select engineering cases for checking calculation.Based on the modified inertia method,a method for calculating the internal force and confining pressure of shield tunnel under surcharge loading is proposed,and the single factor analysis is carried out;Using MIDAS/GTS NX software to establish the three-dimensional finite element model of the segment ring,taking into account the bolt and bolt hole and other details of the structure,simulation analysis of the lining structure under the eccentric loading of the state of stress and deformation;Finally,the ellipticity of tunnel is proposed as an evaluation index of tunnel safety.The main research results and innovations are as follows:(1)The deformation model of tunnel considering rotation effect of rigid body and shear dislocation effect is established,and the calculated results are in good agreement with the measured data in numerical value and trend,which verifies the rationality of the new deformation model.In the vicinity of the maximum longitudinal settlement of the tunnel,there is basically no dislocation deformation and rigid body rotation deformation,and the shear force between the rings is also very small;At the back bend point of the tunnel horizontal displacement,the displacement between the rings,the rotation angle between the rings and the shear force between the rings reach the maximum.(2)Considering the influence of eccentric loading and the force between the shield lining rings,based on the modified usage,the formulas for calculating the confining pressure and internal force(moment,axial force,shear force)of the lining are derived.Finally,a numerical example is given to show the law of confining pressure and internal force of tunnel lining under eccentric loading.Eccentric loading will lead to asymmetric distribution of tunnel lining confining pressure,in which the confining pressure on loading side is greater than that on non-loading side.The influence of surcharge on the moment and shear of loading side is greater than that on the axial force(3)Through single factor analysis,the influence law of three factors on the longitudinal deformation,confining pressure and internal force of tunnel lining structure is obtained.(4)Using MIDAS/GTS NX software,a three-dimensional finite element model considering the details of bolt and bolt hole is established,and the variation of deformation and internal force of tunnnel lining under surcharge loading is analyzed.(5)In this paper,the ellipticity is proposed as an index to evaluate the safety of tunnel structure under surcharge loading.The rationality of the evaluation index is verified by the engineering example analysis and comparison with the finite element software.