Impact of particle degradation on repose angle of railway ballast: insights from experimental and DEM analysis

This study investigates the effects of ballast degradation on its repose angle through a series of large-scale cylinder lifting tests conducted on fresh and degraded ballast across various degradation levels. The conditions of the degraded ballast were thoroughly analysed based on particle gradation, fouling and breakage indices, and shape characteristics. The results indicate that higher degradation levels reduce the repose angle of the granular medium. Original equations have been developed to correlate the physical properties of degraded ballast with its repose angle. In addition, discrete-element method (DEM) simulations, which could precisely capture the fine content and the morphological evolution of ballast due to degradation, provided fresh insights into the micromechanical behaviour of degraded aggregates, focusing on their particle mobility, contact force distributions and structural anisotropy. DEM modelling reveals that compared to fresh ballast, degraded ballast exhibits elevated translational and rotational velocities when naturally assembled. Particle degradation compromises the interlocking capacity of the granular assembly by decreasing inter-particle contact numbers and the contact forces, ultimately diminishing the structural integrity of degraded aggregates. The findings provide valuable insights for more effective monitoring and assessment of ballast performance, particularly in addressing the demands of heavier and faster trains in modern railway systems.