Discrete element analysis of ballasted track mechanical behavior under rack vehicle loads on steep slopes

For addressing the design challenges of rack railways in mountainous regions, a DEM (Discrete Element Method) simulation analysis was conducted to investigate the mechanical performance and dynamic response of the ballasted track on Steep Slopes. The DEM model of the rack railway ballasted track was used to investigate the static and dynamic mechanical behaviors of steel-based sleeper and ballast under gradients ranging from 120 ‰ to 600 ‰. The macro-meso dynamic response of the ballasted track during uphill operation of the rack railway vehicle was revealed, offering theoretical insights for rack railway track design. The results indicated that when the gradient is below 400 ‰, both lateral and longitudinal resistances decrease approximately linearly with the increasing gradient. However, when the gradient exceeds 400 ‰, both resistances decay at an accelerated rate. Therefore, for rack railway lines with gradients greater than 400 ‰, it is crucial to carefully evaluate the mechanical performance of the ballasted track to ensure its stability. Under the rack railway loads, the longitudinal displacement of the sleeper increased with the gradient and was more significant when the rack bogie passed through. The average longitudinal displacement of the sleeper was 0.25 mm, 0.45 mm, 0.71 mm, and 0.97 mm when the gradient ranged from 120 ‰ to 400 ‰. Similarly, the sleeper’s vertical displacement also increased with the gradient and was greater when the rack bogie passed through. Furthermore, the rear wheel of the bogie caused a larger vertical displacement than the front wheel, due to axle load transfer effects