Study On Deformation Characteristics Of Foundation Pit In Dahongmen Station Of Beijing Metro

With China's reform and opening up in 1978 and the rapid development of China's economy,the problem of traffic congestion caused by urbanization has become more and more prominent.Subway is an effective way to solve this problem.However,construction of the subway will have a lot of negative effects on the surrounding environment.In recent years,the engineering accidents caused by the construction of the foundation pit of the subway station have occurred,which also warns us that studying the deformation of the foundation pit can not be lax.Therefore,the stability study of foundation pit has become a hot topic in many scholars.This paper mainly introduces the current development of the foundation pit engineering,the engineering overview of the project,the engineering geological conditions,scheme of the excavation and support and the plan of monitoring.The general rules of excavation deformation of foundation pit are obtained by analyzing the actual monitoring data of surface subsidence,inclination of retaining structure and axial force of steel supporting.Finally,this paper mainly introduces the principle of FLAC3 D,and the numerical simulation model of foundation pit including the range of the calculation,the constitutive model,the structural element,the calculation parameter,the boundary condition and the steps of the excavation.During the process of excavation of the deep foundation pit,We carried out six steps of the excavation to analyze the surface subsidence,inclination of retaining structure and axial force of steel supporting.Compared with the results of actual monitoring,we verify the general law of deformation of foundation pit.The main results of this paper are as follows: the sedimentation curve is "pipe-like" at the same time in space;The ground subsidence value near the long side of the foundation pit is generally larger than that of the short side.The value of the maximum deformation is 11.90 mm,which is much lower than the control value and indicates the safety of the foundation pit is better.The deformation curve is gradually developed from the "forward" type to the "bow" type and the final tends to be stable.The maximum of the horizontal displacement of the wall is 13.52 mm,which occurs at a depth of about 18 m.The horizontal displacement of the wall is controlled by 20 mm,which indicates that the excavation of the foundation pit,the support system and the inner wall can better control the lateral deformation of the foundation pit and ensure the safety of the foundation pit.On the whole,the axial force of the steel support will continue to increase,especiallly the third steel support.Compared with the actual value,the numerical simulation results show that the deformation law calculated by the numerical simulation is smaller than the actual value.The trend is basically consistent with the actual one.The simulation results of this paper can be used to provide some guidance and reference for the similar engineering design in the future.