Research On Excavationd Eformation Of Deep Foundation Pit Of Metro Station In Soil-Rock Dualistic Stratum

In the study of foundation pit stability,the study of deformation of deep excavation in subways has always been the focus of research.The Deep Foundation Pit of the Second-Bridge-Park Station of the North Extension Project of Metro Line 1 is located at Taixin Road,Qixia District,Nanjing.This station is the terminal station of the North Extension Project of Line 1.The foundation project is located in the geomorphic unit of terraces and terraces and this stratum conditions are “soft and hard”.The buried depth of the foundation pit reaches 18.36m~24.04 m,and there are many pipelines around the project.The deformation of deep foundation pits is difficult to predict,especially for deep foundation pits of the geological of soil-rock dualistic stratum.For the study of deep foundation pit deformation of soil-rock dualistic stratum,the measured data of foundation pit is analyzed firstly in this paper,and then the numerical simulation of the deep foundation pit engineering of Second-Bridge-Park Station is carried out by finite element software.The numerical calculation results are compared with the measured results to verify the reliability of the model,and analyze the main factors affecting the stability of the foundation pit in order to figure out the relationship between the deformation of the foundation pit and different factors.Finally,the three-dimensional numerical model of foundation--pipeline is established,and the research and sensitivity analysis of different factors on pipeline deformation are carried out.This paper main contents are as follows:(1)The measured data of the typical section of the foundation pit is obtained,and the measured deformation of the foundation pit is carried out.The measured data include: surface settlement outside the pit,lateral displacement of the pile,horizontal displacement of the pile top,vertical displacement of the pile top and pipeline settlement.Exploring the changing rules of various factors during foundation pit excavation in order to provide guidance for construction.(2)According to the site conditions,the finite element model of this deep excavation project is established,and the values between the parameters of the soil hardening model are studied.The finite element numerical calculation results are compared with the measured results to verify the reliability of the model.(3)Analyze the main factors affecting the deformation of foundation pit,including: thickness of overlying soil layer,thickness of strong weathered rock,depth of excavation of foundation pit and rigidity of pile,and summarize the relationship between various factors and deformation of foundation pit as well as explore the deformation law of deep foundation pits in soil-rock dualistic stratum.(4)Establish a three-dimensional numerical model of foundation--pipeline,and analyze the influence of main factors on pipeline deformation.The main factors include: foundation pit excavation depth,pipeline and foundation pit spacing and pipeline depth,and then sensitivity analysis are carried out in different factors in order to study the proportion of each factor to the deformation of the pipeline.