| Domestic cities are moving towards modernization and large scale,and many new projects such as highrise buildings,urban bridges and underground MTR and pipelines have been built at the same time.In the construction process of underground engineering,it is inevitable to pass through the existing bridge or the adjacent area,and the two is in the conflict of space position.In order to solve the problem,it is necessary to reinforce or replace the existing bridge foundation.After the foundation reinforcement,the excavation of the tunnel,the stress release causes the deformation of the strata around the tunnel,which further causes the settlement or deformation of the adjacent bridge pile foundation,and may threaten the normal use of the superstructure of the bridge.In this paper,based on the existing bridge of a subway in Beijing as the research background,the finite element model of the bridge is established by the finite element MIDAS CIVIL software.The influence of the pile foundation underpinning construction process on the settlement of the pier column and the internal force of the bridge structure is analyzed.The effectiveness of the finite element simulation results is verified by comparing the results of the simulation and the results of the monitoring.The influence of the different top lift on the settlement of the bridge is analyzed and analyzed.The finite element MIDAS GTS NX software is used to establish the two-dimensional finite element model of the subway and bridge,and the influence of the construction process of the full section shield tunneling on the settlement of the existing bridge pile foundation and the internal force of the bridge structure is analyzed and studied.The influence of the excavation sequence of the subway tunnel on the settlement of the bridge is analyzed and studied.The main results are as follows:(1)In the process of pile foundation replacement,the pier column settlement of the whole bridge is very small,only the pier column of the pile foundation is slightly larger.When the new cap is raised,the pier column has the upward 1.27mm displacement.When the old pile foundation is excised,the pier column has the downward 3.41mm displacement;the simulation result and the monitoring result change trend phase.The main reason for the error is that the choice of soil parameters is different from that of the actual project when the finite element method is used to simulate the pile-soil interaction.(2)In the process of pile foundation underpinning,when the new cap is lifted,the old pile foundation unloads most of the axial force and transfers to its new pile foundation.When the old pile foundation is excised,the load transferred from the superstructure is all borne by the new pile foundation.In the process of pile foundation underpinning,the structural internal force(bending moment,shear force)and axial force of the pier column and the axial force of the unsupported pile foundation can be negligible.(3)In the process of tunnel excavation,the first excavation of the tunnel has a great influence on the settlement of the bridge pile foundation.When the construction sequence of the tunnel is changed,the settlement value of the bridge pile foundation is different in the tunnel construction process,but the final settlement value is the same.The influence of the tunnel excavation on the pile foundation settlement is about 3 times that of the pile foundation settlement.(4)In the process of tunnel excavation,through the analysis of the maximum principal stress,minimum principal stress and maximum shear stress of the pile foundation,it is known that the stress changes of the pile foundation in the tunnel most recently when the tunnel is excavated,and the pile foundation stress changes most in the same depth with the tunnel.As the right line tunnel is distance from the bridge 2-4#pile foundation 11.12m,the distance is more than that of the bridge.Far,the excavation of right line tunnel has little effect on the stress of bridge pile foundation. |
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