Study On Deformation And Stability Of Subway Foundation Pit Considering Soil Structure Interaction

Along with the construction of urban rail transit,the large scale development and utilization of underground space produce a large number of foundation pits,and the stability of soil and structure dominated by deep foundation pit is attracting more and more attention.The foundation pit of the city subway usually appears in the downtown area and the complex location of the surrounding environment,and now the design idea of foundation pit is changed from strength control to deformation control,therefore,the internal force and deformation in the construction process of the subway foundation pit are closely related to the overall stability of the foundation pit.It is of great theoretical and engineering significance to study the deformation and stability of the subway foundation pit.The research on the traditional foundation pit is mainly concerned with the construction technology of the subway and its influence on the surrounding environment.With the development of the nonlinear contact theory,more and more research on the deformation of the nonlinear contact in the excavation of the foundation pit has been studied.This paper combines theoretical analysis,laboratory test,numerical simulation,and engineering monitoring methods,the factors for evaluating the stability of the subway foundation pit include the displacement of pile wall,the displacement of soil behind the wall and the supporting axial force.And a systematic study of the deformation and stability of the subway foundation pit is implemented consideration of soil structure interaction.The main research work of this paper is as follows:(1)Through the collection and collation of the literature at home and abroad,the research status of the deformation and stability of the subway foundation pit construction is systematically summarized,and the similarities and differences between the subway foundation pit and the ordinary deep foundation pit are analyzed.The research status of contact theory at home and abroad is expounded,the problems and limitations of Goodman contact unit and the modified ones are analyzed.(2)The contact surface test of different soil and concrete is carried out,and nonlinear relation of stress and strain of contact surface is obtained.Based on hyperbolic relation of the Clough and Duncan tangential models,the tangential nonlinear parameters(K???n?Rf)in the contact element are obtained.Based on the second development ffunctions of ABAQUS in the three-dimensional soil structure model,a FRIC subroutine to satisfy the hyperbolic relationship between Clough and Duncan tangential models is developed.The contact mechanical properties of the penalty function method and the nonlinear method are analyzed in the numerical calculation.(3)Based on ABAQUS finite element platform and subroutine,the mechanical properties of soil structure contact and the elastoplastic deformation characteristics of soil under different contact parameters are studied.The change laws of the friction coefficient and the Clough and Duncan hyperbolic parameters of the nonlinear function model on the displacement of pile wall,the displacement of soil behind the wall and the supporting axial force of are analyzed.(4)Through the single factor analysis,the parameters of soil and enclosure structure are selected,including soil elastic modulus,Poisson's ratio,cohesion,internal friction angle,pile wall stiffness,pile wall depth and supporting stiffness.The influence of soil parameters and enclosure structure parameters on the supporting axial force,displacement of soil behind the wall and displacement of pile wall is studied.(5)Based on the actual subway engineering,the influence of different contact models(nonlinear method and penalty function method)on the internal force and deformation of subway foundation pit is studied,and the influence of the contact model between the nonlinear method and the penalty function method on the displacement of soil behind the wall,the displacement of pile wall and the supporting axial force is compared and analyzed.The numerical results of different contact models(nonlinear method and penalty function method)are compared with the actual monitoring data.The rationality and effectiveness of the nonlinear contact model in the excavation of the subway foundation pit are verified.