Dem Study on the Dynamic Performance of a Fouled Ballasted Track Under Repeated Traffic Loading

The fouling of ballast, resulting from upward intrusion of subgrade slurries, coal or other mineral ore dislodging from passing freight traffic, and the accumulation of debris among ballast grains, has been extensively reported as the primary cause for numerous disastrous railroad incidents. This paper presents a numerical study to examine the deformation and degradation responses of a coal-fouled ballasted track upon repeated traffic loading using the discrete element modeling (DEM). A particle degradation model considering Weibull statistics in tandem with a granular medium size effect is developed and employed to capture the continuous corner abrasion of angular ballast. The model had been calibrated by comparing the predicted shear stress–strain response with laboratory data obtained from large-scale direct shear testing. A series of cubical shear test simulations have been carried out to examine the dynamic performance of ballast assemblies with various coal fouling contents under cyclic loading. The results show that an increase in fouling content exacerbates the sleeper settlement, while decreasing the resilient modulus and the particle breakage in ballasted bed. Ballast beneath the sleeper experiences significant breakage compared to the crib ballast, and the extent of damage is mitigated with depth. Rigorous microscopic analysis is also presented in terms of interparticle contacts and contact network anisotropy of the ballast assembly. The micromechanical examinations show that the decrease in ballast breakage observed in fouled assemblies is predominantly attributed to the inevitable decrease in interparticle pressures as effected by the coating of ballast aggregates by the coal fines.