Quantifying Railway Ballast Degradation through Repeated Large-Scale Direct Shear Tests and Three-Dimensional Morphological Analysis

To investigate the mechanism and manifestation of ballast spoilage, this study introduces a novel approach using a repeated large-scale direct shear test (involving multiple large-scale direct shear tests on the same batch of ballast aggregates) to simulate ballast degradation. Using advanced three-dimensional (3D) reconstruction technology, we obtained detailed 3D images and particle morphological feature indices before and after repeated shearing. Statistical methods were then applied to analyze these changes. The results reveal that ballast degradation primarily involves a sharp angular fracture of large particles and edge wear, leading to smoother and rounder surfaces and edges. Unlike traditional Los Angeles Abrasion tests, repeated shearing of the same batch of aggregates shortens the long, middle, and short axes of the ballast and decreases particle sphericity, highlighting an increase in sharpness. Additionally, direct shear behavior results in significant fragmentation near the shear zone and reduces volumetric grain size and surface area, while having minimal effect on the local morphological feature indices such as surface shape factor and shape factor. These findings offer a deeper understanding of ballast degradation and provide valuable insights for its maintenance, marking a significant advancement over traditional testing methods.