Study On Energy Dissipation And Vibration Reduction Characteristics Of Ballast In Rail Transit

The ballasted track shows a better effect of absorbing the wheel-rail impact.Compared with the ballastless track,the ballasted track uses granular track bed composed of a certain gradation of ballast,so its vibration reduction principle is obviously different from the various vibration isolation and vibration reduction measures adopted in the ballastless track at present.Under the action of load,part of the wheel-rail vibration energy is dissipated by the interaction between ballast particles.Although the ballasted track has been widely used for a century,the perception of its energy dissipation is still at a perceptual level.The main concern is the energy dissipation law under different track states,such as polyurethane-mixed ballast track bed and sand intrusion,and its mesolevel energy dissipation mechanism is not clear yet.In order to make full use of the energy dissipation characteristics of ballasted track,it is necessary to carry out the research on the energy dissipation mechanism of ballasted track and related influencing factors from the macro and micro level.Based on this,ballasted track is taken as the research object,and the methods of indoor test,theoretical analysis and numerical simulation are used to study the energy dissipation characteristics characteristics of the ballast layer,the meso contact properties and mechanical behavior between ballast particles.The energy dissipation characteristics and influencing factors of ballasted track from the macro and micro levels are also explored,so as to provide a theoretical basis and reference for making full use of the energy dissipation characteristics of ballasted track.The main research contents and results are as follows:(1)The characteristics of energy dissipation distribution in each part of ballasted track and ballastless track under vehicle load are compared and analyzed.Based on the finite element method simulation model of ballasted track and ballastless track under train load,it is found that the energy dissipation of ballasted track mainly comes from the ballast layer,followed by the railpad.With the same boundary and external excitation conditions,the energy dissipation of ballastless track is less than that of ballasted track.(2)The contact properties of ballast particles under cyclic dynamic load are studied through experiments.And the existing method of calculating damping ratio is modified.The contact stiffnesses,effective radii and damping ratios of fresh and used ballast particles with different particle sizes are obtained.Based on the load-displacement curves obtained from uniaxial compression tests of fresh and used ballast particles with different particle sizes,theoretical analysis shows that the contact stiffness between ballasts is close to Hertz contact under cyclic dynamic load.Accordingly,the contact stiffnesses and Hertz contact radii of the fresh and used ballast particles are calculated.Through the processing andanalysis of the uniaxial compression test results,a damping ratio correction method suitable for nonlinear systems is proposed,that is,the area under the loading and unloading equal displacement average curve is used to represent the strain energy,.The estimation method of damping ratio correction caused by residual strain after unloading is derived.Based on the derived correction method,the average damping ratios of fresh and used ballasts are calculated.(3)The energy dissipation law of ballast during cyclic loading and unloading are explored.And the effects of ballast contact parameters,grading and initial density of ballast bed are analyzed.Based on the discrete element method model of dynamics compression ballast box test,the energy dissipation characteristics of ballast under cyclic load are analyzed.The results show that under the same conditions,the friction energy dissipation,which is the main source of ballast energy dissipation under cyclic load,is more than 4 times of the damping energy dissipation.At the initial stage of loading,the friction energy and damping energy between ballasts increase rapidly.After entering the stable settlement stage,the two increase almost linearly with the increase of loading times.With the increase of the friction coefficient,the friction energy dissipation and damping energy dissipation decrease gradually.The damping energy dissipation increases with the increase of damping ratio.In addition,the wider the ballast grading and the larger the initial ballast bed density,the smaller the corresponding friction energy dissipation.(4)The micromechanics,energy distribution and evolution characteristics of ballasted track system under simulated vehicle load are studied.According to the three-dimensional sleeper-ballast-foundation discrete element method full-scale model,for the ballasted track structure,the ballast layer is the most important energy storage and energy dissipation part.In the stable stage of track bed,the most important energy form in the ballast layer is elastic strain energy,followed by friction energy dissipation.The track structure shows the characteristics of low kinetic energy as a whole.The changes of track parameters and load amplitude will not affect this energy distribution characteristic.Through the use of sleeper pad and ballast mat,the contact forces between the ballast and sleeper / sleeper pad and the foundation are more uniform,and the stress conditions of the upper and lower ballast particles are effectively improved.At the same time,the friction energy dissipation and damping energy dissipation between ballast particles are reduced.(5)The effects of sleeper pad and ballast mat stiffnesses and load amplitude on the micromechanics and energy evolution characteristics of granular track bed are explored.Based on the established three-dimensional discrete element full-scale model of ballasted track,the influences of sleeper pad stiffness,ballast mat stiffness and load amplitude on the mechanical and energy characteristics of the ballast bed are analyzed by using the control variable method.With the decrease of sleeper pad stiffness,the peak value of average contact force between ballast-sleeper pad decreases,and the contact status is improved,The total damping energy dissipation,elastic strain energy and viscous strain energy of track structure gradually increase,while the friction energy dissipation does not change much.And the elastic strain energy among ballasts increases slightly.The reduction of ballast mat stiffness can improve the contact state between the ballast and foundation,and reduce the average peak contact force.At the same time,the friction energy dissipation,elastic strain energy inside the track and energy dissipation between ballasts are decreased,while the viscous strain energy increases.With the increase of load amplitude,the number of contact forces between the upper ballast-sleeper pad increases significantly.Similarly,the contact force amplitude inside ballast particles and between the ballast and lower foundation increases obviously,but the amount of contact force changes little.The total energy of track structure and the energy inside ballast particles raise significantly with the rise of load.