Study On The Influence Of Deep Foundation Pit Excavation On Adjacent Subway Tunnels And Stations

With the development of urban underground space,the construction of deep foundation pit in dense urban central area with crowded surrounding environment is facing more and more challenges,including the existence of underground pipelines,underground structures and other safety problems that affect the surrounding area.Deep foundation pit excavation should not only consider sufficient safety and stability of the surrounding structure itself,but also consider the safety of soil layer deformation near the foundation pit,such as surrounding surface subsidence,displacement and deformation of overground and underground structures such as tunnels or pipelines,etc.,which must meet the requirements of protecting the surrounding environment.With the scale of foundation pit engineering increasing day by day,the space effect gradually strengthening,the factors to be considered before and after foundation pit excavation also gradually increasing,the limited underground space restriction and the safety hidden danger of the surrounding environment will inevitably become the factors to be considered in the excavation construction of tunnel and station adjacent to foundation pit.This paper combined with the world trade center of DongGuan city south of foundation pit engineering case,the side of foundation pit by tunnel line,southwest hub in great luck or blessing road station,by using MIDAS GTS NX contrast method,finite element simulation and field testing of part near the side of the tunnel and station foundation pit excavation stage of the 3 d simulation analysis,the research on the adjacent surrounding roads,tunnel excavation process and part of the station,the influence of the comprehensive analysis is done according to the simulation results,the following conclusions:(1)this paper introduces the research background of this paper,investigates the engineering cases of the influence of foundation pit excavation on the adjacent tunnel and station structure in recent years,understands the current tunnel and station deformation situation,and puts forward the research ideas and methods of this paper.(2)relevant theories of surrounding soil deformation caused by foundation pit excavation and theories of tunnel deformation caused by foundation pit excavation were reviewed,and the surrounding surface subsidence law,uplift law in foundation pit,displacement law of foundation pit enclosure structure,additional displacement factors affecting the tunnel and displacement algorithm were summarized.(3)To DongGuan International Trade Center Building Foundation Pit Engineering Project as a project example,the finite element analysis software MIDAS GTS NX,construct a three dimensional model analyzes the deformation of the retaining structure in excavation process,the changes of the anchor axial force,the surface settlement and foundation pit side compared with the test result,the analysis results show that the scheme of foundation pit excavation process pile wall appeared on "big small",present the "y" type horizontal deformation;In the excavation stage,the vertical deformation of the side tunnel and the station surface changes with the excavation,presenting a "triangle" deformation.Besides,the lateral and horizontal deformation of tunnel pipeline near the foundation pit is more obvious than that at the far foundation pit during the excavation stage.At the same time,the tunnel pipe arch roof appears the subsidence deformation,the arch bottom appears the uplift deformation.In addition,the station as a whole appears inclined deformation during the excavation stage,among which the horizontal deformation of the station side wall and column is relatively obvious,and the uplift deformation of the station structure plate appears near the foundation pit and the subsidence deformation appears at the far foundation pit.(4)by using three dimensional finite element analysis model,the deformation of excavation tunnel and station,the different retaining pile wall of built-in depth,different excavation method,different excavation depth and the deformation of foundation pit reinforcement under the condition of tunnel and station structure changes,the results show that: to a certain extent,increase the built-in depth of supporting pile wall and reduce the foundation pit excavation depth can effectively reduce the deformation of foundation pit,tunnel and station;Block excavation is more effective than bench excavation in controlling deformation of foundation pit.The method of pit reinforcement has more advantages of cost and deformation control than that of the original scheme without reinforcement,outside reinforcement and simultaneous reinforcement inside and outside the pit.The above research also provides certain reference value for the design and construction of deep foundation pit excavation adjacent to tunnel or station with similar geological conditions,so as to effectively and timely avoid the occurrence of engineering accidents.