Monitoring And Numerical Simulation Analysis Of Construction Process Of Deep Foundation Pit In Metro Station

With the rapid development of China’s economy,the population and traffic pressure are increasing sharply,and the development of underground engineering has become an inevitable trend.But nowadays,the distance between deep foundation pit and surrounding buildings is getting closer and closer,the scale and size of deep foundation pit is getting larger and larger,the depth of foundation is getting deeper and deeper,and the supporting forms are complex and changeable,which put forward more stringent requirements for the design and construction of deep foundation pit.The excavation of deep foundation pit involves many complex disciplines,and its deformation mechan:ism is not yet clear.Therefore,it is necessary to study the deformation characteristics of deep foundation pit under various supporting structures and summarize the deformation law of deep foundation pit.This research combines the background of the project "Monitoring and Measuring Construction of Deep Foundation Pit in a Station of Dalian Metro Line 5",and carries out the following research:(1)Based on the research background of the project and combined with the engineering situation of the deep foundation pit of the station,the supporting scheme of the deep foundation pit of the station is designed as "sleeve biting pile+internal support".By calculating the internal force and displacement of the supporting structure,it is found that the maximum horizontal displacement of the pile appears in the middle and upper part of the deep foundation pit,and the shear moment at the two or three supporting positions changes obviously.The rationality of the supporting scheme is verified by the application of "Lizheng 7.0" in the deep foundation pit.(2)Combined with the actual project,considering the deep foundation pit excavation,erection of support,the whole process of prestressing,using finite element analysis software MIDAS/GTS to simplify the soil,to establish a reasonable three-dimensional model of deep foundation pit,the retaining structure of deep foundation pit construction in the process of stress and deformation regularity are studied,and the simulation data and experimental data,this paper compares and analyzes the changing trends of are the same,the numerical fitting degree is higher.The results show that the horizontal displacement of pile increases with the increase of excavation depth,and the maximum value appears in the middle of deep foundation pit.The axial force of steel support increased rapidly at the initial stage of erectio n,but slowed down after erection.The variation law of surface subsidence around is "parabolic",indicating that the numerical simulation results have a good prediction effect on the foundation pit construction process.(3)MIDAS/GTS software was used to simulate the influence of different supporting stiffness,wall thickness and soil parameters on the deformation of deep foundation pit.Qualitative and quantitative comparative analysis was conducted on horizontal displacement of pile body and surface settlement under different influencing factors,and it was concluded that soil parameters had a great influence on the deformation of deep foundation pit,among which the internal friction Angle had the greatest influence on the deformation of deep foundation pit.Support stiffness and wall thickness have a good inhibitory effect on the deformation of deep foundation pit within a certain range,and the inhibitory effect on the deformation of deep foundation pit decreases after a certain degree.Therefore,reasonable parameters should be selected in the design and construction stage to save cost on the basis of ensuring safety and provide technical reference for similar projects.