Keywords: corrugation, ballast, degradation, rail, interaction, measurements.

Rail corrugation is a significant source of vibration in the track, causing increased degradation of the track infrastructure. As a consequence, the required maintenance increases, and so do the corresponding costs. Rail corrugation is thus a matter of great concern for the railway infrastructure manager.

The localized degradation of the ballast particles in sections of track presenting significant corrugation was observed in the Portuguese railway network. According to the observations, the ballast around several sleepers and under the inner rail was found to be rolled, which is evidence of ballast wear that significantly influences the ballast long-term behaviour.

This paper shows that corrugation leads to higher rates of degradation of the ballast. The analyses are based on numerical models of train-track interaction, considering the non-linear contact between the sleeper and the ballast with the possible inclusion of voids under the sleepers. The model represents one of the observed corrugated railway track sections. The numerical results prove that rail corrugation implies a greater cyclic loading of the ballast and significantly higher levels of vibration of the sleepers. By facilitating rolling and wear of the ballast particles, these effects lead to higher rates of degradation of the ballast.

The degradation of the ballast was found to be higher around hanging sleepers, corresponding to sleepers suspended by the rails, with no base contact with the ballast on the unloaded condition. Hanging sleepers are likely to occur in places with significant variation of the track support stiffness. The numerical simulations included the verification of the impact of such conditions to the dynamic vehicle-track system response. It was shown that the vibration level of these sleepers is significantly higher and also that the wheel-rail and sleeper-ballast force transmission is increased with the combination of rail corrugation and hanging sleepers around stiff regions of the track. From the dynamic results, it is concluded that the mechanism responsible for the observed increased degradation of the ballast particles around hanging sleepers is attrition.

The influence of the railpad stiffness on the wheel-rail and sleeper-ballast force transmission was investigated. The results show that softer railpads may significantly reduce the cyclic loading on the ballast, having therefore a beneficial effect for the long-term behaviour of the track infrastructure.

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