Mechanical Behavior Analysis Of Ballastless Transition Section Based On DEM-FEM Coupling Model

Railway engineering is a very important part of the national transportation industry,ballast railway and ballastless railway undertook all the transport undertakings in the field of railway.It is of great significance to explore the dynamic characteristics of ballast and ballastless railway for the maintenance of train safety.In view of the coexistence of continuous media and discontinuous media in two kinds of railways,this paper established the coupled discrete-finite element algorithm to analyze the dynamic characteristics of ballast track and ballastless track,and put forward the simplified algorithm of discrete element model of ballast particle.According to the stiffness difference between ballast and ballastless track,polyurethane material was used to strengthen the ballast bed,and the discrete-finite element coupling algorithm was used to analyze the dynamic response of transition zone,and the cementing effect of polyurethane material was simulated in a parallel bonding model.Settlement results and force chain distribution results show that polyurethane material can effectively improve the stiffness of the ballasted side,enhance the overall stability of the track bed and reduce the settlement.The ballast bed contains two structures of different properties: granular structure and continuous structure,and its special structure makes the single type of numerical analysis method has limitations.According to the actual situation of ballast bed,the coupled discrete-finite element algorithm method is adopted.Ballast particle is constructed by clump combination unit,subgrade and foundation are analyzed by elastic-plastic finite element method,and parameters transfer between discrete element and finite element coupling region is realized by energy conservation principle.Numerical results show that the embedded coupling algorithm can enhance the stability of the model and fit the reality more.Ballast particle under the action of train load will appear wear and pulverization phenomenon,resulting in the settlement of track bed and uneven deformation.Using geogrid to reinforce particles can improve the stability of ballast bed and reduce crushing.The discrete element method and finite element method are used to simulate Ballast particle and geogrid respectively,and the discrete-finite element coupling analysis is carried out.The discrete element model of unreinforced ballast direct shear test,the discrete-finite element coupling model of reinforced ballast direct shear test and the discrete-finite element coupling model of pull test are established.The shear stress-displacement curve,displacement vector and nominal volume strain of ballast particle all indicate that geogrid has obvious reinforcing effect on ballast bed.The computational efficiency and cost of discrete element method have always influenced the pace of scientific research.In order to solve this problem,this paper took ballast particle as an example,established a discrete element model,retained the spherical particles on the surface of the model,and removed the basic units inside.The consistency between the simplified model and the original model were verified by numerical tests,which provides a possibility for simulating largescale discrete element simulation engineering.