Study On Stress Characteristics Of Segment Structure On The Process Of Air Pushing Through Mining Method Of Tunnel Construction

The excavation working of the basic transportation subway is the core part of the construction of the underground tunnel.Shield tunnel construction with a high degree of automation, high construction speed, quality, small effect on the ground pipeline,as well as good working environment, has been widely used in urban rail transit construction.But when excavation in compound layer, often meet composite section of hard rock, boulder group or a long formation with up part of soft and down part of hard, if still constructed by shield method, can lead to the slow speed, the tool wear, high cost high, safety risk.To solve this problem, the general use "construction by mining method,lining by shield method", namely the shield air pushed through the tunnel by mining method.which is mean the tunnel excavation forming initial support in local hard rock using mining method, then in the use of in the use of shield machine assembling segment through the tunnel. A mixture of two methods, improves the progress, reduces the geological risk, but lead to a big construction difficulty, torsion in air push, segment floating or lateral overload, low quality of the segment assembling, tunnel water seepage and so on.This paper, taking the rail line3of Wuhan metro across the han river interval by shield empty inference as the engineering background, using3D finite element software ANSYS to carry on the modeling calculation. Study on shield air pusher through the mining method in the process of tunnel construction are as follows:(1) Using elastic mechanics theory of thick-walled cylinder analysis composite lining combined by segment, backfill and the early supporting.By changing the properties of materials and the layer thickness of the backfill obtained the influence law of stress and displacement of composite support radial,When the elastic modulus of backfill layer is1/5between the elastic of the initial support and the elastic modulus of the segment, backfill layer thickness is0.4m, the mechanical properties of the composite lining of Wuhan Metro Line3in shield air pushing through mining retain the best.(2) Modeling the process of the shield air pushing through the mining tunnel model in3D numerical, Analysis the changes of the displacement of surrounding rock and the longitudinal stress of segment.we can know that the changes of the displacement of the surrounding rock,and a large deformation occurred before the shield machine pushed through the monitoring section; Just out of the shield tail crown segment in longitudinal stress rapidly became small, segment arch bottom in from shield tail after12m longitudinal stress begins to fall.Through the calculation of the above studies,not only is of instructive significance to this project,but also for the future similar design and construction of tunnel excavation of soil layer has reference function.