| The foundation pit of a subway station in Shanghai is adjacent to a certain subway line.The excavation depth of the foundation pit reaches 30 m.The nearest distance between the foundation pit and the subway tunnel is about 50 m.The existing subway tunnel is within the scope of the foundation pit excavation.Excavation of the foundation pit will affect the safe operation of adjacent subway tunnels.In this paper,data collection,field measurement,numerical simulation and other methods are used to study the influence of foundation pit excavation on the structure of adjacent existing subway tunnels.The main research contents and results of the thesis are:(1)Through extensive reference and research of domestic and foreign documents,the current research status of the influence of foundation pit excavation on neighboring subway tunnels is summarized from three aspects: theoretical analysis research,field measurement research,and numerical analysis method.(2)Introduced in detail the project overview,engineering geological conditions,monitoring content,items and frequency of a certain foundation pit in Shanghai.(3)Based on on-site measured data,the entire construction process is divided into six stages,and the deformation laws of each stage of the tunnel are analyzed from the three aspects of the horizontal displacement,vertical displacement and inner diameter convergence of the subway tunnel structure,as well as the final deformation state of the tunnel.(4)Using Flac3 D software,a finite element model of the excavation process of the foundation pit was established,and the reliability of the model was preliminarily verified by comparing the measured and simulated data.According to the simulation calculation results,the adjacent tunnels under the unloaded state of the foundation pit excavation were analyzed.The vertical displacement of the vault,the horizontal displacement of the arch waist,and the convergence of the inner diameter,analyze the reasons for the deviation from the actual measurement results.(5)By changing different foundation pit excavation depth,distance between tunnel and foundation pit,elastic modulus of ground connecting wall and other condition factors when establishing numerical model analysis,we can analyze these different parameter variables in the process of foundation pit excavation.The law of influence on the deformation of the tunnel structure.The calculation results show that the deeper the excavation depth of the foundation pit,the greater the deformation of the tunnel;the smaller the distance between the foundation pit and the tunnel,the greater the deformation of the tunnel;the greater the elastic modulus of the ground wall,the greater the impact of the excavation of the foundation pit on the tunnel At the same time,by comparing the deformation degree of the tunnel,it can be found that the distance between the foundation pit and the tunnel is the biggest factor affecting the deformation of the tunnel structure. |
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