The Spatial Effect Study Of Narrow Metro Station Foundation Excavation By Step

In order to relieve the pressure of urban traffic,the economy developed cities of the nation have carried out metro project intensively in recent years.Deep foundation engineering of long-narrow subway station is a high risk project,the force and deformation of each part of the retaining structure influence each other,so the foundation excavation has obvious spatial effect.How to reasonaly avoid the adverse impact,it is necessary to research on effect of its spatial characteristics.This paper is according to a metro station of line two of Foshan city in Guangdong province and based on the current literature research status at home and aborad,carrying out theoretical analysi,field tests and numerical simulation study.The main work and achievement are as follows:(1)Summarize the current research status about foundation spatial effect at home and abroad,then points out that it is short of studying the core construction parameters of foundation spatial effect.(2)Through the calculation example of the spatial effect coefficient,it is obtained that when the partitioned length of metro station foundation is about 20m can make full use of the spatial effect.(3)Analysis and verification focus on six main indicators,namely the surface subsidence,the horizontal and vertical displacement of diaphragm wall,the bottom heave,the moment of diaphragm wall and the axial forces of internal strut,which have obvious spatial effect at three dimensional distribution of the foundation.Through PLAXIS3D finite element software,simulating two different excavation method of overall and partitioned with layer.Then compares the results of the two kinds of excavation and the simulation result with the measured data,analyzing the spatial effect of the metro station foundation during excavation process.? The results show that vertical displacement of diaphragm wall adds along the increase of excavation depth,the bottom heave can cause diaphragm wall's floating and then resulting part soil upheaval outside of foundation;? Acoording to the characteristic of horizontal displacement and moment of diaphragm wall at the boundary between expand and standard zone of the metro station foundation,the diaphragm wall at this zone has a certain degree of torrional deformation due to spatial effect;? The characteristics of the horizontal displacement at the top of diaphragm wall and the strut axial forces at the first layer indicate that the first layer concrete support may transform from press into tension in some cases.