Degradation of railway ballast under impact loading considering the morphological properties of aggregate

Abstract

Degradation of railway ballast aggregate is ensued from breakage of single particle as well as from abrasion of angular corners. The present study evaluates the change in morphological characteristics as well as particle size distribution of ballast aggregate degraded under applied impact loads to further illuminate the degradation mechanism of particles. The utilized drop-weight impact loading apparatus implemented on prepared ballast specimens is modified to take into account the real stress levels applied over ballast course. The morphological features of aggregate including angularity and surface roughness are quantified by establishment of extended image processing method. Generally, the obtained results uphold the evident effect of parent rock type on degradation mechanism. Also, the percent reduction of indices related to angularity and surface roughness are in line with increment of degradation level measured by fouling index (FI). Furthermore, the change in morphological indices is not significant in case of using particle size distribution with higher uniformity coefficient compared with more uniform gradation. Indeed, major effect of selection of broader sieve size range is exhibited on reduction of breakage of larger-sized aggregate. Meanwhile, provision of flexible subgrade instead of rigid type considerably diminishes the percentage of reduction of sharp corners and surface roughness which confirms evident effect of stiffness of underlying layer on level of abrasion of coarse particles.