Study On Bearing Capacity Of Foundation Soil Under Subway Station Uilt By Top-down Boring With Cast-in-situ Arch

Currently, there are many studies on the bearing capacity of the foundation in the the cut and cover method, but there is few research on the bearing capacity of foundation soil in the shallow tunneling method. Top-down Boring with Cast-in-situ Arch as a new type of shallow tunneling method,Increasingly used in the construction of Subway Station.However, the change rule of the ground bearing capacity is still not very clear at the Stage of Construction in the subway station of Top-down Boring with Cast-in-situ Arch. As a starting point for research,using orthogonal method, using the finite element method to analysis the influence factors of bearing capacity of shallow tunneling method,and in the engineering background of DaWangLu station of Beijing subway station,Study the foundation bearing capacity in the construction process of Top-down Boring with Cast-in-situ Arch.The main work is as follows:(1) using the orthogonal method, Consider burial depth of foundation, friction Angle, unit weight of soil and elastic modulus, cohesive force and the poisson’s ratio and other factors and levels,The significance of factors affecting the bearing capacity of foundation is analyzed, at the same time, contrast numerical method and formula of foundation bearing capacity.(2) the ultimate bearing capacity for shallow tunneling method (single and double hole hole) was studied by means of two-dimensional finite element elastoplastic.(3)Considering the change of the buried depth, diameter of column spacing and the column factors, establish a numerical model of plane strain for Top-down Boring with Cast-in-situ Arch subway, study change rule of foundation bearing capacity in the process of Construction.In this paper, the main conclusions are as follows:(1) in the cut and cover method, The order of the factors affecting the ultimate bearing capacity of foundation is angle of friction> burial depth> unit weight> Modulus of elasticity> Cohesive force> Poisson’s ratio.Compared with the formula can be obtained,Finite element numerical analysis has good reliability in terms of foundation bearing capacity calculation.(2)In the shallow tunneling method,The order of the factors affecting the ultimate bearing capacity of foundation in the single(double) hole is angle of friction> Modulus of elasticity> burial depth> unit weight> Cohesive force(Poisson’s ratio)> Poisson’s ratio(Cohesive force).(3)In the construction process of subway station with Top-down Boring with Cast-in-situ Arch,when the thickness of overburden soil is a fixed value for the station, Along with the construction process, maximum vertical stress reduced gradually, in the final stages of construction increased significantly.Step in the construction sequence is certain,with the increase of the thickness of overburden soil, the basal maximum vertical stress of the construction processes increase,With the increase of the column spacing,basal maximum vertical stress decreases; The column diameter changes in less effect on the maximum vertical stress of the basement,however,In the last stage of the construction,With the increase of the column diameter,Basal maximum vertical stress increases.