Discrete Element Simulation Of The Transition Zone Of High-speed Railway With Polyurethane Reinforced Ballast Bed

High-speed railway lines inevitably encounter the connection of ballasted track and ballastless track.Because of the differences in the strength,stiffness,and settlement of the ballasted track and the ballastless track,the rails are caused to bend and deform,which results in the occurrence of track irregularity and reduces the comfort,stability and safety of the train.In order to meet the requirement of high regularity of high-speed railway line,transition zones are installed to solve the problem at home and aboard.Polyurethane(Ballast glue)reinforcement technology can improve the adhesion between ballast,thereby changing the stiffness of the ballast bed and achieving the gradual change of the stiffness and the reduction of the settlement of the transition zone between the ballasted and ballastless track.The method is an effective measure to improve the mechanical behavior of the track transition zones.However,the related work is mainly focused on engineering applications and experimental studies.There are relatively few numerical studies on the microscopic interactions between ballast glue and ballast,and the mechanical behaviors of polyurethane reinforced track transition zones.In this paper,the discrete element method is used to study the mechanical behaviors of transition zones of unreinforced track and polyurethane reinforced track transition zones,respectively.The main work is as follows:1.The mechanical behaviors of the transition zones of high-speed railway are simulated by establishing the discrete element model of the three-sleeper ballast box.Aiming at the irregular geometries of ballast,two types of clumps are constructed,fine ballast grain element and simplified ballast grain element.2.The variation of the inhomogeneous settlement and the effective elasticity of the track transition zone are studied under the reciprocating load of the train,and the influences of the load size and load frequency are also analyzed.3.The change rule of the sleeper settlement and the effective elasticity of the polyurethane reinforced track transition zone are studied by using the parallel bonding model to bond the adjacent ballast particles and simulate the microscopic interaction between the ballast glue and ballast.The effects of different load parameters(load size,load frequency,different moving directions of the train)and different reinforcement parameters(reinforcement depth,strength of the parallel bond,reinforcement form)are determined.Based on the meso-scale discrete element calculations,the main factors influencing the dynamic characteristics of the transition zones with the polyurethane reinforcement are discussed.This paper provides scientific basis for the rational laying of the polyurethane reinforced ballast bed in the transition zones of the high-speed railway.