Safety Analysis Of Existing Metro Under New Up-crossing Tunnel Construction

With the development of urbanization,the metro has become the landmark of large and medium cities.Therefore,a new foundation project is highly likely to be located near existing metro in the process of city construction.In order to guarantee the normal operation of urban transportation,some strengthening measures are usually adopted in these projects.This research aims at studying the impacts of these control measures on mitigating the deformation of existing metro under soil excavation.First,Overall 22 project cases of foundation pit excavation held above existing metro are listed to summarize the project profile,relative position,excavating scheme,strengthening and supporting condition and the final deformation of tunnel lining.Afterwards,ABAQUS finite element software is utilized to bulid three dimensional finite element models of excavation to analyze the deformation principle of existing metro tunnel under such excavation.The impacts on metro tunnel lining are analyzed of different supporting measures,including retaining wall,soil reinforcement,bracing configuration and loading,and the evacuating methods,including evacuating size and sequences,respectively.The results indicate that the primary function of retaining wall and bracings are for the overall foundation stability,but the soil reinforcement and loading can greatly decrease the top lining deformation.The results also demonstrate that the excavating time and size of soil above the metro centre has a significant impact on the maximum top lining deformation,excavating symmetrically by layer and blocks can effectively elevate the increase stability of lining deformation during the construction process.Based on these conclusions,this paper suggests the excavating design principle for such projects and proposes the optimized excavating and supporting scheme.In the end,a large three dimensional finite element model is built,based on the reconstruction project of Chengbei Road in Suzhou in which a new utility tunnel of Renming Road will up-cross an existing metro,to compare the analysis result of current design scheme and optimized scheme.The results show that the optimized scheme is better than design scheme in controlling the maximum top lining deformation,the increase stability of lining deformation and the maximum deformation difference of two metro tunnels.The results of this paper provide theoretical basis to instruct relevant project construction and serve as reference material to design excavating methods.