The effect of fibre reinforcements on the mechanical behaviour of railway ballast

Abstract

Ballast is a primary component of the railway track and it has several functions including the ability to resist vertical, lateral and longitudinal forces applied to the sleepers from the train wheels. In response to the stresses induced during a train passage, ballast typically experiences plastic settlement which can reach unacceptable magnitudes. Thus, ballast is the focus of the majority of maintenance and renewal activities. In response to the growing need for resilient track materials (including ballast) to cope with increasing train speed, load and frequency, means of optimizing its performance and minimizing maintenance requirements are required.

Ballast improvement techniques, such as the use of geogrids, have attracted a great deal of attention in terms of research, but huge potential for reducing costs through ballast improvement still exist. It has been shown from previous research that the use of randomly oriented fibres in sands can significantly improve their strength. This technique might be used to improve ballast strength and reduce track geometry deterioration. In addition, fibre reinforcements in ballast can potentially provide a new method of reinforcing ballast whilst maintaining the capability of withstanding typical tamping operations which are incompatible with geogrids. However, there is a lack of rigorous scientific understanding of the effects of fibre reinforcements on relatively large aggregates such as railway ballast.

This research examines the effect of random fibre inclusions on the packing structure of granular materials (coarse sand and scaled ballast) and describes the physical implications associated with the observed changes. The mechanical properties of fibre reinforced granular materials across different particle sizes and a hypothesis of fibre/particle reinforcement suitable for relatively large particles are presented. An image-based deformation measurement technique has also been used to investigate the effects of fibre reinforcements on the local deformation of triaxial specimens to corroborate the observed mechanical behaviour of the reinforced specimens. Finally, the mechanical behaviour of a fibre reinforced ballast layer below a cyclically loaded railway sleeper was investigated using a full scale laboratory tests.

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

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