Influence of unsupported sleepers on the dynamic stability of ballasted bed based on wheelset impact tests

The unsupported sleeper can change the load characteristics of ballast particles and thus affect the dynamic stability of a ballasted bed.In this work,a laboratory test was constructed on a ballasted track containing unsupported sleepers.The ballasted track was excited by a wheelset,and the influence of unsupported sleepers on the dynamic stability of a ballasted bed was studied.The results show that the main frequency of the sleeper vibration appeared at 670 Hz,and the first-order rigid vibration mode at the frequency of 101 Hz had a significant effect on the condition without the unsupported sleeper.When the sleepers were continuously unsupported,the vibration damping effect of ballasted bed within the frequency range of 0–450 Hz was better than that at higher frequencies.Within the frequency range of 70–250 Hz,the vibration damping effect of the ballasted bed with unsupported sleepers was better than that without the unsupported sleeper.Owing to the excitation from the wheelset impact,the lateral resistance of the ballasted bed with unsupported sleepers whose hanging heights were 30,60,and 90 mm increased by 37.43%,12.25%,and 18.23%,respectively,while the lateral resistance of the ballasted bed without the unsupported sleeper remained basically unchanged.The unsupported sleeper could increase the difference in the quality of the ballasted bed between two adjacent sleepers.In addition,test results show that the hanging height of the unsupported sleeper had little effect on the lateral resistance of a ballasted bed without external excitation,but had an obvious effect on the rate of change of the lateral resistance of a ballasted bed and the acceleration amplitude of the sleeper vibration under the wheelset impact.

Analysis of the breakage parameters of railway ballast based on the discrete element method

During the service lives of ballasted tracks,the ballast experiences degradation,such as breakage and fragmentation,which reduces the stability of the tracks.Ballast breakage is directly related to the shapes,sizes,and stress states of particles.The key to solving this problem is to determine the breakage parameters of railway ballast.In this study,through uniaxial compression and uniaxial shear tests,the factors associated with ballast breakage for a simple stress state were obtained.Then,a refined discrete element model of railway ballast was established.The Box-Behnken method was used to design a simulation test,and a response surface method was used to obtain the optimal ballast breakage parameters.Lastly,the results of a direct shear test were compared with the simulation results to verify the correctness of the parameters and to study the shear resistance of the ballast aggregates.The results showed that for ballast particles with sizes of 22.4–63.0 mm,the characteristic stresses of compression and shear were not significantly affected by the size of the particles,but were greatly affected by their shape.In particular,long particles were more likely to break.During the direct shear test,the cumulative ballast breakage ratio gradually increased to 13.97%.The optimal breakage parameters of the ballast determined by this approach have high application value in the management of ballasted tracks.