Railway Ballast Mechanical Mechanism Research Based On Discrete Element Method

Railway is a basic and critical infrastructure of a country. As a green rapid and efficient mean of transportation, the railway industry has been developing rapidly under national policy support. With the advantage of discrete material, ballasted railway is becoming an irreplaceable track type and widely applied worldwide. As the core component of ballasted railway, Ballast bears the load from the rail upwards and transfers it to the subgrade uniformly. The mechanical mechanism of ballast directly influences deformation law and stability of track.However, investigation of high-speed railway ballast in china is still far from sufficient. The traditional research method of continuous medium can’t reflect the real nature of railway ballast, which seriously hindered the application of ballasted railway in China.Considering the shortage of research on high-speed railway ballast mechanics, the discrete element method (DEM) was introduced in this thesis to investigate the relation of the key parameters of ballast, such as particle shape, confining pressure, grading, compaction, axial stress, volumetric strain, axial strain and track bed elastic modulus. This research helped as a reference in the size design of ballasted track and the choosing of key parameters in construction and maintenance. Meanwhile, the distribution of contact force inside ballast sample and relative movements of ballast particles were reflected through exploring the calculation of simulation model, which would explain the service status and deterioration mechanism of railway bed. The major work and innovations in the thesis are as follows:1) Based on discrete element method, with the application of PFC3D, methods of constructing ballast DEM modeling were discussed systematically; ballast direct shear test and triaxial test model were established. A ballasted bed was also constructed according to Chinese high-speed railway standard to investigate the influence factors of lateral resistance. All the DEM models were of irregular ballast particles simulated by constructing clump particles.2) Large-scale ballast direct shear test was conducted and analyzed with simulation results. The basic mechanical mechanism of ballast through the shear process was discussed from a micro-macro perspective. 3) The servo system is embedded in the ballast triaxial tests DEM simulation, and the relationship of the related parameters, for instance the deviator stress, volume strain, confining pressure, axial strain, were analyzed. The results illustrated that the simulation proved a strong influence to deformation> maximum value and ratio of deviator stress by the confining pressure. The increasing of lateral confinements led to a reduction of ballast sample deformation, which can be used in ballasted track design and maintenance.4) A lateral resistance test according to Chinese high-speed railway standard was conducted. The relative contributions of the base, crib, and shoulder ballast to lateral resistance are quantified with both experiments and DEM simulations. The behavior of the lateral ballast resistance tests were investigated with DEM model. Through exploring the results of the experiments and DEM calculations, characters of ballast-sleeper micro-interaction, contribution and development were discussed.