Deformation Monitoring And Numerical Simulation Analysis Of Deep Foundation Pit Excavation In A Subway Station

With the continuous and rapid development of our economy,the pace of urban construction and the development and utilization of underground space are increasingly rapid.In the use of underground space,such as the construction of subway,underground passageways,underground commerce and underground garage,the utilization rate of land space has been greatly improved,and bring the convenience of people's living and travel.However,in the construction process of the actual deep foundation pit project,due to the damage of the supporting structure,the settlement of the surrounding buildings is too large and the uplift value of the foundation pit is too large,it may cause the construction period delay and additional economic losses,and even the casualties.Based on the research background of deep foundation pit engineering in a subway station in Tianjin,this paper introduces the common supporting structure types and their applicable conditions,and expounds the design theory and deformation theory of foundation pit supporting structure,and uses the finite element software MIDSA GTS NX simulate each construction stage of the deep foundation pit engineerin's actual excavation,then the simulation results are compared with the actual monitoring results,and the deformation law of the soil around the foundation pit and the deformation law of the enclosure structure during the excavation of deep foundation pit engineering are expounded.Secondly,by changing the design parameters of the foundation pit support structure in subway station such as the stiffness of the underground continuous wall,the embedded depth of the underground continuous wall,the number of steel bracing layers and the applied prestress of the steel bracing,the influence of the change of the design parameters on the deformation of the foundation pit and the surrounding environment is studied.The main contents of this paper are as follows:(1)The research of deep foundation pit engineering and the application of finite element software in the field of foundation pit engineering are reviewed at home and abroad to understand the current research situation of foundation pit engineering at home and abroad,and the research ideas and methods of this paper are put forward.(2)This paper introduces the characteristics of deep foundation pit engineering,the design status of supporting structure and several common forms and characteristics of foundation pit supporting structure,and focuses on the stress mechanism and deformationtheory of supporting structure during the excavation of deep foundation pit.(3)Taking the deep foundation pit project of a subway station in Tianjin as the research object,through the research and analysis of the relevant monitoring data of the actual excavation site,the deformation law of the enclosure structure and the surface settlement in the process of foundation pit excavation from the surface to the base elevation is summarized;besides,the station model is established by using the finite element software MIDSA GTS NX,and the simulation results are compared with the actual monitoring data,and the results of the finite element simulation are basically consistent with the actual monitoring results,which verifies the correctness of the model.(4)By studying the influence law of the change of design parameters of the support structure on the foundation pit deformation,it is concluded that increasing the stiffness and embedded depth of the underground diaphragm wall can reduce the relevant deformation of the foundation pit,but when the stiffness and embedded depth increase by a certain value,the impact on the foundation pit deformation is negligible;the less the number of steel bracing layers,the greater the deformation of the foundation pit,the foundation pit will be in a dangerous state;Increasing the applied prestress by steel support can reduce the horizontal displacement produced by underground continuous wall,but when the applied prestress value reaches a certain value,the influence on the displacement and deformation of underground continuous wall in horizontal direction can be ignored.