Study On Influence Of Foundation Pit Excavation On Underlying Tunnel

With the development and utilization of urban underground space,the onstruction of the subway and its related facilities has greatly eased the pressure of urban traffic and effectively utilized the urban underground space.However,due to the development of urban underground space,underground rail transit lines and urban buildings are excessively dense,and it is often encountered that the foundation pit works are located around the subway tunnel.The construction process of the foundation pit breaks the original stress balance around the tunnel,which leads to the redistribution of the geostress field,which causes corresponding deformation of the surrounding building roads and underground rail transit structures,causing adverse effects.This paper takes the foundation pit engineering directly above the tunnel of Hefei Station to Tongling North Road Station of Hefei Rail Transit Line 3 as the background,and studies the foundation pit support design through finite element simulation.The results have been as follows:(1)According to the existing theory of soil mechanics,the deformation of the foundation pit and the phenomenon of tunnel displacement caused by excavation and unloading of the foundation pit are analyzed,and how to calculate the uplift eformation and tunnel deformation of the foundation pit are introduced;(2)Selecting the foundation pit support scheme on the premise of considering the engineering background,and designing and checking the foundation pit support;(3)The MIDAS GTS NX geotechnical engineering finite element software was used to simulate the excavation process of the foundation pit above the No.3 line of the subway,and the working conditions were calculated according to the actual construction process.The results obtained were in accordance with the engineering experience and relevant theories;The tunnel located below the foundation pit is mainly displaced in the vertical direction,showing upward bulging;the horizontal displacement is relatively small;the tunnel uplift deformation caused by one-time excavation of the foundation pit and excavation of the foundation pit is analyzed and compared.Foundation pit excavation is more conducive to controlling tunnel deformation;during foundation pit construction,backfilling can effectively control the displacement deformation of the tunnel;(4)A tunnel protection measure suitable for the foundation pit project is proposed for the foundation pit project.