Investigating Effect of Ballast Degradation on Track Dynamic Behavior using Coupled Train-Track Discrete Element Method Model

Abstract

Railroad ballast is uniformly graded coarse aggregate placed between and immediately underneath the crossties. The purpose of ballast is to provide drainage and structural support in a ballasted track. As ballast ages, degradation takes place under increased traffic when aggregate particles become more rounded and smaller in size as a result of abrasion and breakage. In this study, 10-crosstie train-track discrete element method (TT-DEM) models, containing up to 160,203 particles for clean ballast and 942,472 for degraded ballast, were generated to investigate the effect of ballast degradation on track dynamics caused by the passage of the ACELA Express passenger train used in North America. Realistic gradations and particle shape properties of clean and degraded ballast were adopted to build the TT-DEM models. Through a comparative analysis of the results of clean and degraded ballast models, the following key observations were made: 1) crossties in the degraded model experienced 30% smaller displacements and slightly lower vibration velocities as a result of higher ballast layer density and stiffness; 2) degraded ballast had more particles greater than 5 mm (0.2 in.) that indicated large movements when compared those in the clean ballast; 3) a critical particle size of 25.4 mm (1 in.) could classify the primary and secondary load-carrying structures in both clean and degraded ballast; and 4) for ballast in the crib area, two times wider ranges of principal stress rotation were observed for clean ballast than the degraded. In conclusion, the TT-DEM models developed in this study captured realistic track dynamic behavior trends much better than the individual train-track or discrete element method models.