Simulation of fresh and fouled ballast behavior using discrete element method
Ballasted rail track is commonly used worldwide for several reasons, including economy, rapid drainage and ease of maintenance. During operation, the ballast becomes contaminated or fouled due to infiltration of fines from surface, mud pumping from subgrade, and ballast degradation under train loading. This paper presents the application of a three-dimensional Discrete Element Method (DEM) in investigating the stress-strain and volumetric behaviour of fresh and 40% VCI-fouled ballast in direct shear testing. A 'Clump logic' in PFC3D was employed to model irregular-shaped particles in which groups of ten to twenty spherical balls were clumped in appropriate sizes and positions to model representative ballast particles. Fouled ballast was modeled by adding pre-determined amount of miniature spherical particles into the voids of fresh ballast. Results obtained from DEM simulation reasonably agree with those measured experimentally. The DEM simulation indicates that when ballast becomes fouled, the peak shear stress decreases and the dilation increases compared to fresh ballast. Additionally, the distribution of contact force chain apparently explains the 'cushioning effect' of coal fines that effectively reduced maximum contact forces and associated ballast degradation. Keywords: Ballast, Fouling, Coal fines, Discrete element method.