Influence Analysis Of Soft Soil Foundation Pit Excavation On Adjacent Subway Tunnel Structure

With the development of the city and the increase of ground traffic pressure,a large-scale construction of subway tunnels emerges.With the rapid development of underground structures,the urban upper buildings are becoming more and more complex.In order to develop economy and improve people’s living standard,the city is also building new large-scale engineering projects.The excavation of large foundation pit will change the stress field of soil around itself,which will cause additional deformation of shield segment adjacent to the foundation pit,which lays a potential safety hazard to the normal service of the subway tunnel structure.Therefore,it is of great practical significance to study the influence of foundation pit excavation on the deformation of adjacent existing tunnel structures and put forward excavation deformation control measures for the rapid development of urban rail transit.This paper collects typical engineering cases of foundation pit excavation adjacent to the subway tunnel in Hangzhou and summarizes and analyses the main laws of influence of foundation pit excavation on deformation of adjacent tunnel.On this basis,relying on the project case of Ganglong City in Hangzhou,the research on the influence of excavation of soft soil foundation pit on deformation of adjacent tunnel structure is carried out.The concrete work contents and results are as follows:(1)Based on Winkler foundation beam and Timoshenko beam models,a two-stage method is used to establish the theoretical calculation method of tunnel deformation under the condition of foundation pit excavation.Comparing the theoretical calculation results with the measured data of the project,the verification shows that the theoretical calculation model can not be well applied in the case of complex foundation pit excavation.(2)To study the influence of foundation pit support scheme on structural deformation of adjacent tunnel.Using PLAXIS 2D software,the section models of foundation pit and adjacent tunnels are established,and the deformation laws of foundation pit support and tunnel structure during foundation pit excavation are analyzed.The orthogonal test is designed to explore the control effect of section scheme of foundation pit support on structural deformation.The result shows that the optimized foundation pit support structure type can reduce the disturbance of tunnel caused by foundation pit excavation.(3)To study the influence of excavation in foundation pit zones on structural deformation of adjacent tunnels.Using PLAXIS 3D software,three-dimensional models of foundation pit and adjacent tunnels are established,and the deformation laws of foundation pit support and tunnel structure under two zoning foundation pit excavation schemes are compared.By comparing the three-dimensional simulation results with the theoretical calculation and field measurement results,the optimum foundation pit construction scheme for the characteristics of the project is proposed.The optimized construction scheme can effectively reduce the influence of foundation pit excavation on structural deformation of adjacent tunnels.