The mechanical behaviour of fibre reinforced railway ballast

Abstract

Ballasted track is the most traditional form of railway track but is still widely predominant and able to cope with high performance demands, such as those typical of high speed lines. A major disadvantage of ballasted track is its tendency to settle with the passage of trains, mainly due the accumulation of permanent deformation in the ballast under cyclic loading. This leads to track geometry deterioration, as the settlement is unlikely to be uniform, jeopardising the safety of train operations and ride quality. Therefore, costly maintenance operations, e.g. tamping, are periodically required to restore the correct ballast level. Also, rail transport demand is growing in many parts of the world, increasing the need for track maintenance while reducing the maintenance windows. In light of this, the mechanical behaviour of ballast has been widely studied and techniques to improve it have been proposed.

A novel technique with the potential to reduce ballast settlement is fibre reinforcement, which consists of the addition of unbound randomly placed discrete fibres. It is widely accepted that fibre reinforcement provides additional strength to granular materials ranging from sand to gravel. Hence, it can potentially reduce ballast tendency to settle by increasing the particle interlocking. Fibre reinforcement seems suitable to railway ballast, as it is expected to maintain adequate track stiffness and permeability, not produce planes of weakness, and be compatible with standard maintenance operations. Moreover, fibres can be potentially obtained from recycled materials, separated from ballast after use for recycling, and added either during ballast cleaning or renewals. Nevertheless, the effect of fibre reinforcement on the deformability of granular materials, especially under cyclic loading, remains unclear.

This research investigated the mechanical behaviour of fibre reinforced railway ballast through full-size laboratory tests, reproducing a section of single-line track extended to the shoulder and subjected to a sinusoidal load representative of train passage. The tests explored the effect of fibre dimensions and content for two different types of inclusions, i.e. filament-like and tape-like fibres. It was found that the addition of properly selected fibres can reduce track settlement, increase the long-term support of the sleeper ends, and reduce ballast damage. This might be explained by the fibres inhibiting the micromovements exhibited by the particles in each load cycle, while the effect of the additional confinement was secondary. However, the holistic understanding of the mechanics of fibre-reinforcement would require further experiments designed specifically to capture ballast behaviour at the particle scale.

More information

Identifiers

ORCID for Antonios Zervos: orcid.org/0000-0002-2662-9320

Catalogue record

Export record