Dynamic Responses and Associated Permanent Deformation of Ballasted Trackbed Due to Train Passages at High Speed

Abstract The ballasted trackbed plays a crucial role in railway infrastructure. However, as train speeds escalate, it experiences heightened vibrations and substantial permanent deformation, posing a notable threat to normal train operations. This study is dedicated to investigating the dynamic response and associated irreversible deformation of railway ballast under varying train speeds, with a specific focus on particle-scale manifestations. To accomplish this, a comprehensive ballasted trackbed model, encompassing the entire transversal cross-section, was built using the discrete element method (DEM) with realistic polygonal elements. The DEM model underwent preliminary validation against measurements from full-scale model tests and was subsequently employed to simulate the mechanical behavior of the ballasted trackbed under various train speeds. The findings reveal that increased train speeds lead to vigorous shaking of ballast particles, manifesting as intense vibration at the macroscopic level of the track structure. The heightened particle activity indicates instability in the inter-particle contact network and distinctive particle migration. Consequently, a notable accumulation of permanent deformation occurs in the granular trackbed. Notably, once the train speed surpasses a certain threshold, there is observable migration of ballast particles beneath the sleeper towards both ends. This phenomenon results in the absence of a stabilized inter-particle contact network to support the upper train load, leading to rapid and significant irreversible deformation in the ballasted trackbed.