Construction Monitoring And Numerical Simulation Of Deep And Special Shaped Foundation Pit Surrounding Existed Metro

With the development of our society and the acceleration of urbanization,the construction environment that foundation pit projects face is getting hotter and more complicated.Foundation pit projects have only engineering similarities.The deformation law of the foundation pit soil and the mechanical state of the supporting structure are of great significance for the design,construction and management of similar foundation pit projects.This paper relies on the "Research on Key Technologies for Dewatering and Excavation of Deep and Special Shaped Foundation Pits in Existing Metro Stations",and adopts two methods of site monitoring and numerical simulation to analyze the soil and surrounding buildings during the excavation process.The deformation law and the mechanical state of the support system are analyzed.On this basis,based on the fuzzy mathematical theory,the analytic hierarchy process is used to quantify the risk sources in the construction of deep and special-shaped foundation pits,and a foundation pit safety evaluation system is proposed which combines the excavation process,deformation control and risk analysis.The main research results are as follows:(1)The settlement deformation of the soil gradually increases with the excavation of the foundation pit.The maximum settlement amount is located 20 m away from the edge of the foundation pit,and the settlement value is controlled within the range of 20 mm.The settlement and deformation of the soil body appear "concave" in space.The influence range of the surrounding soil settlement is 2 ～ 3 times of the excavation depth H.(2)The horizontal deformation is 15 m below the ground surface,and the maximum horizontal displacement is 15 mm.The horizontal deformation of the soil is “convex” in the depth direction.The settlement and deformation laws of the existing building are consistent with the deformation laws of the soil at the location.(3)The annular support can effectively control the deformation of the foundation pit.The axial force value of the support system gradually increases with the excavation of the foundation pit.After each excavation,the axial force value appears as an uneven distribution feature.The value is 4000 k N.For the special-shaped foundation pit,the value of the supporting axial force in the gusset position is the largest.(4)The law of soil deformation in numerical simulation is basically consistent with the field monitoring.The settlement at the middle of the existing subway is the largest,with a maximum settlement of 32 mm.The geological layer can affect the stability of the foundation pit.At the intersection of various strata,the amount of settlement deformation is large.(5)The quantified value of the overall stability of the foundation pit is 0.32,which is in a stable state to a more stable state.A set of foundation pit multi-level evaluation system and evaluation set reference standards were established,and the method of calculating the maximum eigenvalue and eigenvector using the eig function in MATLAB was proposed to determine the weight value of each element in the judgment matrix.