The effect of enhanced curving forces on the behaviour of canted ballasted track

Priest, J.A., Powrie, W., Le Pen, L., Mac, P. and Burstow, M. (2012) The effect of enhanced curving forces on the behaviour of canted ballasted track. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 227 (3), 229-244. (doi:10.1177/0954409712458623).

Abstract

The performance of railway ballast depends not only on the characteristics of the ballast itself but also the magnitude, frequency and number of axle loads imposed by the trains running on the track it supports. Recent trends towards more frequent and faster trains have highlighted some potential limitations of ballasted railway track. In particular, the introduction of tilting trains on the UK West Coast Main Line, which allowed train operating speeds to be increased over much of the route, has coincided with the sporadic occurrence of localized areas of ballast migration. This phenomenon involves ballast particles moving from the high side of a canted section of track to the low side, exposing the sleeper ends on the high (outer) side of the curve, reducing the lateral resistance of the track and therefore increasing maintenance requirements.

This paper reports the results of an investigation carried out to try to identify the underlying mechanism responsible for this behaviour. Measurements of sleeper end displacements under the passage of trains were made at two locations which had experienced ballast migration. Analysis of the measured data together with numerical modelling of the forces imposed on the track structure suggest that the increased speed and typical axle loads of the tilting trains result in larger lateral forces and larger rotation of the sleeper (in the vertical plane) than for a train consisting of a locomotive plus trailing vehicle, as was previously used on the route. It is hypothesized that this leads in turn to a slow but progressive movement of the ballast down the slope of the canted track. However, given the highly localized nature of the ballast migration sites, other factors such as an irregular sub-base stiffness and ballast depth may also contribute to the phenomenon and further work is required to determine the combinations of circumstances that may trigger this effect.

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Contributors

Author: W. Powrie

Author: L. Le Pen

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