The load generated during train operation is transmitted to sleepers through rails, and then from sleepers to trackbeds. As one of the important components of the track structure, sleepers are very important to the service-life and safety of railways. The running speed of the train will produce different load frequencies on the rails. To explore the response of sleepers under cyclical train loads, this research used the discrete element method to simulate rails and sleepers, and realizes the loading of sleepers by applying cyclic loads to the rails. The discrete element method was used to simulate the compression-failure test of the concrete sample to verify the reliability of parameters of the discrete element model. On this basis, the sleeper was simulated by the discrete element, and the change law of the mechanical parameters such as particle displacement, contact force, and stress of the sleeper under different loading frequencies were analyzed. The research results show that the sleeper particles under the rail had a large vertical displacement, and the maximum displacement and the maximum contact force of the particles in the sleeper increased with increasing loading frequency. The stress change trend of the sleeper under the left and right rails was the same, and both showed periodic changes with cyclic loading. The loading frequency had little effect on the stress of the sleeper. The vertical displacement, velocity, and acceleration amplitude of the rail all increased with increasing cyclic loading frequency, thereby increasing the force between the rail and the sleeper, and increasing the dynamic response of the sleeper.

In order to explore the influence of different particle size gradations of dirty materials on the service performance of the ballast bed, the clean track bed, the completely fouled ballast bed polluted by coarse coal and fine coal, respectively, were studied based on the discrete element method. In order to explore the influence of the multi-scale particle size gradation of the dirty material on the service performance of the ballast bed, the clean ballast bed, the completely dirty ballast bed polluted by coarse-particle coal, and the completely dirty ballast bed polluted by coarse-particle coal were simulated, respectively, based on the discrete element method, which are used to analyze the dynamic response of track bed under different working conditions under cyclic load. The model is verified by the lateral resistance and vertical stiffness of the ballast bed to prove the accuracy of the discrete element model. On this basis, the dynamic cyclic load is considered to analyze and study the mechanical response and change law of the ballast bed with different degrees of contamination. Studies have shown that after the ballast bed is contaminated, its lateral resistance and vertical support stiffness are reduced, the amount of settlement increases, the coordination number between ballasts is declined, and the fine-grained dirty material has a worse effect on the ballast bed; The displacement value of the ballast particles decreases with the increase of the depth of the ballast bed; The displacement value of the ballast particles under the rail is the largest, and the ballast particles on the ballast shoulder appear dilatancy; The displacement of the ballast particles at the laterally symmetrical position of the track structure is close to but not completely same; Dirty materials aggravate the frequency of ballast particles, and the impact of fine-particle coal powder is particularly significant.