Application of a modern laser technique to evaluate the performance of recycled railway ballast

The performance of railway track structure is influenced by the ballast shape properties including roundness, flatness, elongation, sphericity, angularity and surface texture. The challenge is how to accurately measure the irregular shapes of ballast materials and directly link them to performance. In this paper, a modern three-dimensional laser technique was used to determine shapes of freshly produced crushed ballast and recycled ballast sampled from the heavy-haul coal line in South Africa. The objective was to investigate the effect of ballast shapes on settlement (i.e. permanent deformation). All five ballast materials were scanned in the three-dimensional laser scanning system and the data collected was processed to reconstruct three-dimensional models of the ballast particles. The results obtained were used to develop a chart to classify ballast shapes and link these shapes physically with settlement determined from a triaxial testing programme. Based on the triaxial test results, new empirical models were developed to determine settlement on the route corridor of the heavy-haul coal line. It is anticipated that outcomes of this study would assist with quality assessments and railway ballast maintenance in the field.