Abstract Summary
Ballasted track has been extensively employed in railway lines, even in high-speed railways. In recent years, with the increasing of train speed, the vibrations of the railway track become much more intense, which significantly accelerates the track deterioration, particularly leading to the excessive permanent settlement in the ballasted trackbed, consequently affecting the safety and comfort of train operation. Hence, comprehensive evaluations of the dynamic behaviors and the irreversible deformation of the granular trackbed under high-speed train loading are essential for track condition assessment and improving track maintenance practices. This study focuses on the distinct intense vibration of the track structure and the induced remarkable plastic deformation in the ballast layer under high-speed train loading, especially their particle-scale mechanisms, via a series of discrete element method (DEM) simulations. The DEM model of the granular trackbed is established with realistic polygon elements, and then validated with the measurements from full-scale model tests. Subsequently, the validated numerical model is used to simulate the response of railway ballast under different train speeds. Results indicate that the faster train speed motivates vigorous shaking of the ballast particles, manifesting as violent vibration of the track structure at the macroscopic level, thereby activating particles to move, leading to the instability of the inter-particle supporting structure in the ballast layer. Consequently, the migration and rearrangement of the ballast particles increases, and greater permanent deformation accumulates in the granular trackbed. Furthermore, the trackbed is becoming hard to stabilize with the increasing of the train speed especially when the shakedown threshold is reached, where the permanent deformation of railway ballast would rise nearly endlessly instead of presenting an obvious slow tendency. This paper discusses the dynamic response and cyclic settlement of railway ballast. These conclusions will guide the potential methods to alleviate the permanent deformation in high-speed railways.
