Large and frequent cyclic train loading from heavy haul and passenger trains often leads to progressive
track deterioration. The excessive deformation and degradation of ballast and unacceptable
differential settlement of track and/or pumping of underlying soft subgrade soils necessitate
frequent and costly track maintenance. A proper understanding of load transfer mechanisms and
subsequent deformations in track layers is the key element for safe and economical track design and
optimum maintenance procedures. Many simplifi ed analytical and empirical design methods have
been used to estimate the settlement and stress-transfer between the track layers. However, these
design methods are based on the linear elastic approach, and often only give crude estimates.
Given the complexities of the behaviour of the composite track system consisting of rail, sleeper,
ballast, sub-ballast and subgrade subject to repeated traffi c loads in a real track environment, the
current track design techniques are overly simplifi ed. The track design should also account for the
deterioration of ballast due to breakage and subsequent implications on the track deformations.
Considering this, an elasto-plastic constitutive model of a composite multi-layer track system is
proposed. Constitutive models and material parameters adopted in this numerical model are discussed.
A hardening soil model with a non-associative fl ow rule is introduced to accurately simulate
the strain-hardening behaviour of ballast. The breakage of ballast observed in large scale triaxial
tests is also simulated based on this model. In conjunction, numerical simulations are also performed
using a two-dimensional plane-strain fi nite element analysis (PLAXIS) capturing the effects
of ballast breakage and track confi ning pressure. The paper also demonstrates the advantages of
the proposed elasto-plastic fi nite element simulations when compared to conventional analytical
methods used by practitioners that are primarily based on a linear elastic approach.