Quantification of Railway Ballast Degradation by Abrasion Testing and Computer-Aided Morphology Analysis

Ballast degradation (particle breakage and abrasion) induced by repeated train loads may lead to insufficient track stiffness and excessive track settlement. For safe operation and effective maintenance of ballasted railroad tracks, an accurate assessment of the initial ballast particle size and shape properties and the morphology evolution with usage is very beneficial. Nevertheless, commonly used ballast specifications dictate only particle-size distribution or gradation testing, which is not capable of describing ballast particle morphology characteristics and those changes induced by surface abrasion and particle breakage experienced during ballast service life. To obtain morphological characteristics of ballast particles, Los Angeles abrasion testing was performed on two types of ballast materials, tuff and granulite. An enhanced particle boundary roughness treatment method was implemented in a computer-aided ballast morphology analysis system to capture and reconstruct the three-dimensional ballast geometry. By adopting this method, the degradation of ballast particles during service were assumed to be associated with the Los Angeles abrasion testing in the laboratory. Test results clearly showed the trends observed during the process of particle degradation quantified through imaging-based morphology indexes; angularity index (AI) and flat and elongated ratio (FER) typically decreased, whereas particle sphericity and convexity increased. In relation to such morphological changes, ballast abrasion was found to significantly reduce ballast material’s angle of repose.