Abstract
Aggregates constituting ballast layer wear due to the continuous passage of trains and during the necessary maintenance operations of the track. In order to develop efficient solutions for ballasted tracks design and maintenance, a proper knowledge of the degradation laws of ballast grains is needed. In tribology, the amount of wear due to friction when two surfaces are in contact is classically predicted by Archard’s equation. However, due to the continuous evolution of grain angularity and roughness, at the macro-scale wear coefficient cannot be assumed to remain constant, but will depend on the state of degradation of the grain surface. In order to adjust the model to this particular case, the Micro-Deval Attrition test is used. The rotating drum is stopped at intermediate stages and the amount of generated fine particles is measured. Thus the curve of mass loss along time is built. These results are then linked to Archard’s model using the values of contact forces and relative displacements extracted from discrete element simulations. Finally, a morphology analysis is performed tracking shape and roughness parameters at different stages of degradation using X-ray tomography and a laser profilometer.
Highlights
In ballasted railway tracks, ballast layer plays a crucial role in the transmission of dynamic stresses imposed by the circulation of trains to the geotechnical structure supporting the track
This quasi-linear production of fines observed after the initial stages of the test is coherent with the constant rate of friction work extracted from the Non-Smooth Contact Dynamics approach (NSCD) simulations
Taking into account the friction work extracted from NSCD simulations and the production of fines observed in the experimental tests, it is possible to link both results using Archard’s model to get a first approximation of the wear coefficient
Summary
Ballast layer plays a crucial role in the transmission of dynamic stresses imposed by the circulation of trains to the geotechnical structure supporting the track. After some years of service of the first high-speed service in France, ballast has proven not to be resistant enough, showing a faster degradation than expected. This has been partially compensated over the years by the strict selection of good quality granite for the aggregates. This selection is performed in the quarry, where some mineral samples are subjected to an attrition test called Micro-Deval (MDA) [1, 2]. Particles retained at the 1.6 mm sieve are weighted and compared to the initial weight through a dimensionless coefficient CMDA determining the resistance to abrasion of the material
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