Influence Of Deep Excavation On The Adjacent Subway Tunnel

The foundation pit of a plaza in Nanjing is adjacent to the subway line 2.The excavation depth of foundation pit reaches 34m,the total area of foundation pit reaches 56,000m2,and the nearest distance between foundation pit and subway tunnel is only 33m,and the subway tunnel is within the influence of foundation pit excavation.The excavation of foundation pit will affect the safe operation of adjacent metro tunnel.In this paper,the influence of deep and large foundation pit excavation on the adjacent subway tunnel structure is studied by means of data collection,field measurement and numerical simulation.The main research contents and achievements of the thesis are as follows:(1)Through extensive access and research of domestic and foreign literature,the research status of the influence of foundation pit excavation on adjacent subway tunnel is summarized from the field measurement method,numerical analysis,theoretical interpretation method,centrifuge test method,and so on.(2)The engineering situation,site geology,deformation monitoring scheme and construction progress of the foundation pit of a world plaza in Nanjing was introduced in detail.(3)Based on the field measured data of 4 years,the effect of foundation pit excavation on the horizontal displacement,vertical displacement and inner diameter of the tunnel structure is analyzed.This paper analyzes the deformation law of tunnel deformation with the increase of excavation depth,and defines the maximum working condition of tunnel deformation.(4)Using the finite element calculation software MIDAS,the finite element model of the excavation process is established.Through the measured data,the deformation of bracing structure,ground settlement and tunnel deformation in the process of foundation pit excavation are studied.The deformation of the foundation pit diaphragm wall is developed to the foundation pit,and the horizontal displacement of the tunnel corresponds to the horizontal displacement.The settlement distribution of the foundation pit is "groove" shape distribution.The horizontal displacement,vertical displacement and convergence of the tunnel are basically consistent with the measured resulS.(5)Based on the parametric analysis of finite element model,the influence of foundation pit excavation depth,different distance between tunnel and foundation pit,different thickness of diaphragm wall and different elastic modulus of diaphragm wall on the deformation of tunnel structure is studied.It is found that the deeper the excavation depth of foundation pit under the same conditions,the larger the deformation(horizontal displacement,vertical displacement and convergence)of the tunnel;The nearer the distance between the foundation pit and the tunnel,the larger the deformation of the tunnel;The larger the thickness of the foundation pit wall,the smaller the deformation of the tunnel;The larger the elastic modulus of the diaphragm wall,the smaller the deformation of the tunnel.The change of the distance between foundation pit and tunnel is the biggest influence on the tunnel deformation.