Numerical Simulation Of Soil Displacement In Shield Tunnel Construction Stages

To meet the increasing demand for public transportation,cities have accelerated the pace of building urban subways.The shield method,as a common method of tunnel excavation,has been used widely in urban areas.Based on the extension of the subway line D of Lyon in France,the different construction stages of shield tunnel is carried out to analyze the surface subsidence patterns.Using PLAXIS and FLAC 3D,the paper do some research on surface settlement during tunnel excavation by combining the site measurement and numerical simulation results.The main research contents are as follow:(1)The 2D numerical simulation approach uses the radial contraction and stress release method to simulate the different stages of excavation.By combining the numerical analysis and comparsion of the site measurement results,the applicability of the two methods is verified in the paper.Meanwhile,several soil constitutive models are used in the research.(2)Using FLAC 3D simulates the excavation process of the shield tunnel.The 3D approach takes more directly the physics of the problem into account: the depth of the tunnel,the layer of the soil,groundwater,the trapezoid slurry pressure at the tunnel face,the conicity shape of the shield machine,the trapezoid grout injection in the anular void,the grout consolidation and the construction of lining.(3)In this part,several factors induced the soil displacement during shield excavtion are considered,including the trapezoid slurry pressure at the tunnel face,the trapezoid grout pressure at the air surface and the grout consolidation.The purpose of studying the factors is to reduce the settlement of the soil.