Discrete Element Modeling of Railroad Ballast Settlement

This paper presents findings of a railroad ballast Discrete Element Modeling (DEM) research study focused on investigating ballast settlement under repeated wheel loading. In this approach, the ballast layer is modeled as an assembly of aggregate particles, AREMA No. 24 ballast gradation with different shapes and angularities and rough surface textures. The study matrix considered three different wheel load magnitudes applied on a crosstie at three different load frequencies. Varying load frequencies helped account for different load pulse durations realized under different trafficking speeds. For each DEM solution, the load was applied for up to 100 cycles and the plastic deformations were recorded to indicate resulting ballast settlement. As expected, greater load magnitudes produced larger plastic deformations at one loading frequency. Yet, at a constant applied load magnitude, lower loading frequencies often yielded higher plastic deformations. DEM simulations also conducted with two other aggregate shapes indicated similar impacts of the frequency on ballast settlement.