The long-term performance of ballasted railway tracks is strongly influenced by the degradation of ballast, which compromises stability, drainage, and lateral resistance. Ballast, a coarse angular aggregate placed beneath and around sleepers, is designed to distribute loads, provide stability, and facilitate drainage. However, repeated train loading, tamping during maintenance, and environmental factors gradually break down the angular asperities of ballast particles, producing fines that accumulate in void spaces and lead to fouling. This process reduces ballast porosity, promotes settlement, and weakens lateral resistance, thereby increasing the risk of track misalignment and buckling. Field studies by the Association of American Railroads (AAR) report that 75–90% of fouling originates from ballast degradation, highlighting the central role of particle breakage in track deterioration.
Despite its importance, the micromechanical processes underlying ballast degradation remain poorly quantified, limiting the accuracy of field assessments and computational models. Current experimental approaches, such as large-scale triaxial and direct shear tests, are challenged by scale effects, while field tests like single-tie push and track-loading vehicles are expensive and yield variable results. Similarly, discrete element method (DEM) simulations often rely on oversimplified contact models that fail to capture ballast’s real mechanical behavior.
This project introduces a novel grain-scale methodology that combines targeted crushing tests with interparticle shearing experiments to investigate ballast degradation. Single-particle crushing tests will be conducted on commonly used ballast rock types, such as granite and basalt, to track the evolution of particle size and shape during progressive breakage. In parallel, a custom-built interparticle loading apparatus will be used to measure key micromechanical parameters including normal stiffness, tangential stiffness, and interparticle friction. The resulting dataset will form the basis for developing experimentally validated contact mechanics models for DEM simulations, which will enable more realistic predictions of ballast degradation and its influence on lateral resistance.
By focusing on the fundamental mechanics of ballast degradation, this study will establish a new framework for linking particle-scale processes to track-scale performance. The outcomes will support friction-based ballast inspection methods, inform revisions to Gage Restraint Measurement System (GRMS) standards, enhance maintenance strategies, and ultimately contribute to safer, longer-lasting railway infrastructure.