Study On The Influence Of Deep Foundation Pit Excavation On Lateral Subway Tunnel

With the rapid development of urban construction in China,especially in the first and second tier cities,in order to alleviate the traffic congestion,more and more subway lines are opened,and the subway line network is becoming more and more dense.At the same time,the development of urban underground space is becoming more and more common.With the rise of buildings along the subway,there are a lot of deep foundation pit projects near the subway tunnel.In the process of deep foundation pit excavation,the stress field and displacement field of surrounding soil will change due to the unloading of earth excavation,which may affect the structural safety of subway tunnel and the normal operation of subway.Therefore,it is of great practical significance to study the influence of foundation pit excavation on the deformation of the lateral subway tunnel.At present,the research on the influence of foundation pit excavation on the lateral subway tunnel is mostly focused on a single engineering case,and most of them are focused on the subway shield tunnel.However,the study of foundation pit deformation control based on the deformation of subway tunnel in other forms is not perfect.Therefore,this paper combines the deep foundation pit engineering of a tunnel near Metro Line 2 in Baiyun District,Guangzhou City.Aiming at the single-layer double-span rectangular frame structure of the tunnel,the three-dimensional finite element model of excavation is established by using MIDAS/GTS finite element analysis software,and the deformation of the subway tunnel structure in the whole process of deep foundation pit excavation is systematically studied.It also provides some reference for the design and construction of other similar foundation pit projects.The following studies have been done:(1)In this paper,16 examples of foundation pit engineering near the existing subway tunnel in China are collected and counted.According to the general situation of different foundation pit,the horizontal distance between foundation pit and tunneland the relative height difference between foundation pit and tunnel are taken into account,and time-space effect is taken into account in excavation.The deformation law of adjacent subway tunnel under the influence of foundation pit excavation is summarized in four aspects of foundation pit soil reinforcement.(2)Based on a deep foundation pit project in Baiyun District of Guangzhou City,a three-dimensional numerical model is established based on finite element method to simulate and analyze the influence of foundation pit excavation on the lateral subway tunnel,so as to focus on the analysis of the influence of foundation pit excavation.The horizontal displacement deformation and internal support force state of the enclosure structure,the settlement deformation of the surface soil after the enclosure structure,and the horizontal and vertical displacement deformation of the tunnel.(3)Based on the influence law of foundation pit excavation on adjacent subway tunnel based on the statistical analysis of relevant engineering examples,aiming at the different horizontal distance between foundation pit and tunnel,space-time effect excavation,foundation foundation soil reinforcement,Different finite element models are established in the four aspects of groundwater level,and the influence law of excavation on lateral subway tunnel under different factors is studied and analyzed.It also provides a reference for the design and construction of the deep foundation pit of the adjacent subway tunnel with similar geological conditions,thus effectively avoiding the occurrence of engineering accidents.