Study On TDA Delaying Ballast Degradation Characteristics Based On Discrete Element Method

As a means of transportation and means of people’s travel,railways have already occupied an important position in our country.Among them,the number of ballasted railways are accounted for the overwhelming majority.Ballasted railways are widely distributed in my country’s freight transport at this stage,and they have an irreplaceable role.However,traditional ballasted railways are often prone to ballast degradation during operation,which seriously affects the smoothness of train tracks and threatens driving safety.In recent years,a few scholars over the world have mixed tire-derived aggregate(TDA)in the ballast layer.This method can reduce the ballast crushing rate,so as to improve the performance of the ballast bed.However,experimental research is difficult to obtain real-time meso-mechanical characteristics of ballast,TDA contact,misalignment,etc.And it is difficult to in-depth reveal the mechanism of tire debris delaying the degradation of the ballast bed.Numerical simulation is needed for supplementary research.Therefore,three-dimensional laser scanning technology is used in this paper to reconstruct the geometric shape of irregular ballast,and a discrete element cluster particle model reflecting the real shape of the ballast is established.The discrete element simulation and calculation of irregular ballast and TDA are more closer to the actual engineering.This paper makes detailed analysis of the spatial displacement distribution,contact force distribution,cumulative settlement characteristics and plastic deformation and.Meanwhile,it includes deep discussion on the mechanism of delaying ballast degradation by discrete element simulation of rubber particles under different parameters.The following are the main research contents and results of the article:(1)The triaxial compression simulation found that the peak strength and initial elastic modulus of the ballast sample decrease with the increase of TDA content,and the lower the TDA content,the faster the peak strength is reached,and the highest residual strength is at 5% content.After adding TDA,the ductility of the sample increases,and the ratio of the residual strength to the peak strength increases.With the increase of the content,the average contact force between ballasts decreases,and the change trend of the average contact force between rubber-ballast and rubber-rubber gradually tends to be flat.During the loading process,the maximum contact force between particles and the degree of fluctuation are reduced.(2)Under cyclic loading,the cumulative plastic strain of the ballast specimen increases with the increase of TDA content,and it increases rapidly in the initial loading stage.As the number of cycles increases,the strain steadily occurs.Under the same number of cycles,the higher the content of TDA,the greater the maximum contact force inside the sample.The value fluctuates the most severely without TDA,and the average contact force first decreases and then increases with the increase of TDA content.TDA fills the gaps between the ballasts and increases the final mechanical average coordination number of the specimen.However,as the loading progresses,the sample undergoes dilatation,the average number of contacts between particles decreases,and the average mechanical coordination number gradually decreases.(3)With the increase of TDA content,the distribution of the contact force between the ballasts becomes more uniform,the force chain inside the sample is closer,and the number of strong chains inside the sample decreases whose degree of evolution and fracture fluctuation also reduced.This beneficial effect is most significant when the rubber volume content is 5%.The addition of TDA effectively fills the pores between the interiors,participates in the transmission of the force chain inside the sample,and makes it more stable.This reduces the internal structure dislocation and rearrangement caused by the fluctuation of the strength chain of the sample,and avoids ballast splitting and corner damage during the process of rearrangement and dislocation.(4)Comparing the influence on mechanical properties of ballast specimens under different TDA content,comprehensively integrating the macro and micro indicators such as cumulative plastic strain,contact force,coordination number,force chain distribution,and rotational angular velocity,the optimal volume of TDA is 5%.This dosage has little effect on the peak strength and cumulative plastic strain of the sample,but it can significantly reduce the contact force inside the sample and reduce the disturbance of the sample structure system under the load,so as to achieve the effect of delaying the degradation.