| In recent years,the process of urbanization is speeding up.The urban population is increasing rapidly.It brings great pressure to the city traffic.The urban rail transit has developed rapidly because of its high efficiency,low pollution,convenient and so on.Xi'an has opened three subway lines-No.1 subway line,No.2 subway line and No.3 subway line.There are more lines being designed and built.With the continuous increase of subway lines,Project-by proximity will be more and more common.At present,main technical problems in rail transit is not only ensure the safety of a single station or a single tunnel,but also control the influence of post construction lines on existing lines in the project-by proximity.This paper is based on the project of transfer and transformation of the subway station in loess area and the key technology research of protection of existing lines.In this paper,the excavation process of the transfer Hall foundation pit near the existing subway station is studied by centrifugal model test and numerical simulation.This paper analyzes the deformation law of the existing station in the construction of Transfer Hall foundation pit.The main research contents and results include:(1)The construction of the deep foundation pit adjacent to the existing metro station is different from that of the single one.Through the investigation of domestic and foreign research data,combined with finite element analysis results,this paper analyzes the incidence of foundation pit excavation and masking effect of underground structure during the deep foundation pit near the rigid underground structure.The research results show that the excavation of foundation pit has a great influence on the soil at three times of the depth of foundation pit excavation.Within this scope of the structure(building)should be focused on.(2)This paper is based on the project of Xi'an Metro Line Five.This paper analyzes the influence of foundation pit excavation to vertical displacement of existing station,horizontal displacement of existing station,and bending moment.The results show that the foundation pit excavation make the existing subway station produce upward vertical displacement and horizontal displacement toward the side of the foundation pit.The station incline to the side of the foundation pit.(3)This paper further studies the relationship between the displacement of existing station and the distance between the new foundation pit and the existing station,and stratified thickness of new foundation pit excavation by changing the model parameters.The results show that: The effects of existing stations caused by excavation of a foundation pit is getting smaller and smaller with the increase of the distance between the foundation pit and the station;horizontal displacement and vertical displacement of the existing stations are both reduced with the increase of the number of layers and the decrease of the thickness of the foundation pit.(4)According to the results of finite element analysis,this paper studies the relationship between the different displacement of exterior-protected construction and displacement field of existing station by the centrifugal model test.The relationship between the displacement of exterior-protected construction of foundation pit and the deformation of the existing station is found out.This research will provide reference for similar projects in the future.Research shows that: The whole station rises up with the increase of the displacement of exterior-protected construction of foundation pit.The lifting capacity of the station is no longer increasing when the maximum displacement of exterior-protected construction was more than 75 mm.The Station deformation is eventually realized as settlement.The lifting capacity of station near the foundation pit is obviously larger than that away from the foundation pit.The station lean to the side without foundation pit.The results of the centrifuge model agree well with the numerical simulation results. |
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