Research On Characteristics Of Ballast And Performance Of Rubber-Protected Ballast Based On Discrete Element Method

Ballasted track is widely used in railways all over the world.According to research,most of the diseases of ballasted track are directly related to the track bed.The track bed is the main structure that carries the superstructure and maintains the stability of the track.Its macroscopic characteristics such as the vertical and horizontal resistance,the stiffness,and maintenance have always been the focus of scholars.However,in the course of longterm service,the interaction between the ballast particles directly affects the overall performance of the ballast bed,and even the deterioration of the ballast particles causes the disease of the ballast bed,which affects the safe operation of the line.Therefore,the influence of the physical properties of the ballast monomer particles cannot be ignored,but research in this area is relatively lacking.In view of this,this paper analyzes the influence of the shape,density and roughness of the ballast monomer.In addition,the new ballast is a composite structure that appears due to the deterioration of ballast,and its physical properties are difficult to measure accurately.Therefore,this paper studied the shear characteristics and cyclic load performance.The main research work is summarized as follows:1.Shear performance of flakiness and elongation ballastIn this paper,based on a large-scale direct shear tester,the influence of the content of flakiness and elongation ballast on the mechanical properties of ballast bulk is studied,including the shear strength,deformation characteristics and ballast particle breakage,and the total limit of flakiness and elongation ballast content is recommended to provide a reference for the production and selection of ballast.2.Mesoscopic study of shear performance of flakiness ballastAccording to the experimental results,it is found that the flakiness and elongation ballast is very prone to rupture,and they have similar rupture rules during the shearing process.Then the meso-characteristics of flakiness ballast,such as contact force distribution,coordination number,particle displacement,etc.are studied through discrete element method,and the location of fracture ballast distribution and sensitive particle size range are analyzed.3.Influence of ballast density and roughness on mechanical characteristics of ballasted bedIn this paper,three kinds of gravel materials(steel slag,basalt and pumice)with large difference in density and roughness are selected through density test and angle of repose test.The lateral resistance of three kinds of gravel ballast under the same conditions was tested by the real-size track bed lateral resistance test.Then a sleeper-track bed discrete element model is established to systematically analyze the influence of ballast density and roughness on the lateral resistance and vertical stiffness of the track bed.4.Rubber-protected ballast shear performanceBased on the Neoballast,this paper uses ballast glue and rubber particles of different sizes to make a new ballast Rubber-Protected Ballast(RPB),using direct shear tests to study the effect of surface rubber particles on the RPB shear performance,and through discrete numerical analysis reveals the contact state and movement between the RPB particles under shear at a meso level.5.Rubber-protected ballast properties under cyclic loadingBy establishing a two-dimensional sleeper-track bed discrete element model and applying cyclic loading,new ballast RPB was used to replace the part of the conventional ballast under the sleeper.Through studying the effect of RPB rubber particle size and replacement amount on the track bed settlement and the distribution of contact force and the movement of particles provide reasonable suggestions for the use of the new ballast RPB.