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University of Wollongong researchers at the UoW rail research test
facilities.
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A comprehensive understanding of the rail track substructure,
including the deformation characteristics of ballast and track, is
essential to prevent track misalignment and reduce maintenance
costs. Prior to this project, the degradation mechanisms of ballast
under low confining pressures, at high cyclic loading amplitudes
and frequencies was not understood. Accordingly, the project
incorporates three geotechnical research phases:
- Ballast behaviour and track improvement using geosynthetics.
- Ballast degradation modelling under cyclic loading.
- Formation stabilisation and drainage enhancement.
The ultimate goal is to achieve technological advancement in design
of track substructure - minimising maintenance costs by extending
the life-cycle of ballast through alternative engineering
solutions.
The project has resulted in the publication of a book, available
through Taylor and Francis at
www.crcpress.com
, titled ‘
Mechanics of Ballasted Rail Tracks: A Geotechnical
Perspective’.
The book is a guide to the design of track ballast for railway
engineers and covers track structure and loading, factors governing
ballast behaviour, testing of ballast, use of geosynthetics,
existing deformation models, a new model for ballast, track
drainage, track maintenance and recommending ballast gradings.
The benefits of the research to the rail industry include, reduced
maintenance costs for ballast repair and lower capital costs of new
track (by straightening out curves by being able to traverse
difficult terrain) for track owners. For train operators, benefits
include fewer speed restrictions due to ballast problems, reduced
incidence of track closure due to ballast problems, and straighter
tracks - reducing capital costs and operating costs. The research
was independently assessed by STEM Partnerships to have the
potential to deliver a risk-free-value of $67.2 million over 15
years to the rail industry. Taking into account the risks involved
in delivering the technology and processes, the expected value is
estimated at $39.1 million.
Progress to date:
- Development of constitutive stress-strain-degradation model under
monotonic triaxial loading completed – for ballast behaviour
based on the critical state concept and the theory of plasticity.
- Fabrication of new large-scale consolidometer to determine the
factors affecting performance of geosynthetic vertical drains
installed in soft formation clays.
- Upgrade of large-scale cylindrical triaxial apparatus with dynamic
actuator to conduct cyclic loading tests.
- Development of constitutive model for the behaviour of ballast
under static loading conditions using artificial neural networks
(ANNs) completed and comparisons undertaken with built-in
constitutive models of PLAXIS.
- Extensive laboratory testing of ballast under cyclic loads to
examine effects of particle size distribution, confining pressure
and deviator stress on ballast particle breakage and deformation.
- Development of preliminary model based on numerical analysis of
track systems completed.
- The project recommendations on ballast standards has been adopted
by RailCorp (NSW).
Future Outcomes:
- Ballast breakage model based on micro-mechanics approach by
extending the previous work (considering internal rolling, sliding
and friction, particle attrition and crushing, particle size and
shape).
- Development of a comprehensive numerical model for design of track
substructure under cyclic loads and formation conditions, and
verification of the model based on laboratory results and field
trial data.
- Development of informative Geotechnical Track Smart Tool to provide
independent assessment and advice on geotechnical aspects of rail
track including ballast and formation.
Project Leader: Professor Buddhima Indraratna (University of
Wollongong)
Project Manager: Mr David Christie (RailCorp)
