Railways are expected to play a very important role in future transport in Australia, and its large
network should capture the essential needs for quick and safe, passenger and freight mobility. In
recent years, the increased demand of heavier and faster trains has posed greater challenges to
railway industry to improve efficiency and stability of track while reducing the track maintenance costs.
Centre for Geomechanics and Railway Engineering (GRE) has been the primary Research and
Development unit in the Australasia for developing and implementing new design and construction
concepts for modern track upgrading with clear emphasis on applying theory to practice, with the key
objectives of ensuring enhanced track longevity and minimising track maintenance costs.
In spite of recent advances in rail track geotechnology, the optimum choice of ballast for track
design is still considered critical. The major reason is that, ballast aggregates progressively degrade
under heavy cyclic loading. Research at GRE has shown that a proper understanding of load transfer
mechanisms and their effect on ballast breakage are important pre-requisites for minimising track
maintenance costs. Ballast degradation is influenced by various factors including the amplitude and
number of load cycles, particle gradation, track confining pressure, and the angularity and fracture
strength of individual grains.
Recent research projects at GRE and field trials in Bulli (near Wollongong) demonstrated that the
discarded aggregates from ballast tips could be effectively reused in track construction, if regraded
and reinforced with geogrids to rejuvenate their internal friction and load carrying capacity. This
recycling practice would directly decrease the accumulation of discarded ballast, minimise the cost of
track maintenance and reduce environmental degradation (i.e. less quarrying). Moreover, the use of
effective sub-surface drainage via geosynthetic drains has been very effective in rapidly dissipating
cyclic-induced pore water pressures in the soft subgrade (e.g. clay and silts) during the passage of
trains, and these drains have effectively prevented soil liquefaction (mud pumping). The
corresponding track behaviour models have been also developed through large-scale laboratory
simulations and computer-based numerical modelling.
This state-of-the-art paper describes field trials and prototype laboratory studies carried out to
quantify the geotechnical behaviour of ballast, including shear strength, particle breakage, effects of
increased confining pressure, supplemented with predictive and design models for practitioners
adopting user-friendly analytical and numerical approaches. The paper also highlights the proposed
changes to current standards of track design and how these new concepts have been implemented
through actual field trials that demonstrated better performance, in terms of reducing settlement and
improving drainage. Two case studies are elaborated including the Bulli and Sandgate sites enhanced
by synthetic grids and geosynthetic drains.