Appraisal of Railway Ballast Degradation Through Los Angeles Abrasion, Cyclic Loading Tests, and Image Technics

Ballast degrades through wear and breakage due to the cumulative actions of traffic. This study evaluated ballast degradation using the Los Angeles abrasion (LAA) and cyclic loading tests, changes in the ballast aggregates shape indexes (form, angularity, surface texture and volume) were also evaluated using image analysis techniques. A typical freight train with an average speed of 120 km/h and 30 tonnes capacity was simulated for the cyclic loading test. Series of LAA and cyclic loading tests were conducted on separate samples of the same gradations, and the changes in the aggregates shape indexes were determined using the Aggregate image measuring system (AIMS) package and a 3D laser scanner before and after each of the tests. The image-based assessment revealed that ballast degradation is related to the particle edge breakage and surface wear. The overall experimental results showed that ballast degradation is more profound in the ballast early stage of service, and the degradation index has a good correlation with the changes in aggregate shape indexes. The results also revealed that the two tests gave different degradation indexes, hence a relationship between the ballast degradation index and the number of load cycles with the number of LAA drum turns is proposed to reflect the effect of the number of train’s axle load cycles on ballast degradation.