The paper investigates reproducing the effects of confining pressure on the behaviour of scaled railway ballast in triaxial tests in discrete element models (DEM). Previous DEM work, using a standard Hertzian elastic contact law with an elastic-perfectly plastic tangential slip model, has been unable to replicate the behaviour observed in laboratory tests across a range of confining pressures without altering both the material stiffness and the inter-particle friction. A new contact law modelling damage at the contacts between particles is introduced. Particle contact is via sphericallycapped conical asperities, which reduce in height if overstressed. This introduces plasticity to the behaviour normal to the contact surface. In addition, the inter-particle friction angle is varied as a function of normalized contact normal force. At relatively low normal forces the friction angle must be increased for peak mobilized friction angles to match the laboratory data, an effect that is attributed to interlocking at the scale of surface roughness. Simulation results show close agreement with laboratory data.

Summary The paper describes the development of a technique to simulate triaxial tests on specimens of railway ballast numerically at the particle scale and its validation with reference to physical test data. The ballast particles were modelled using potential particles and the well‐known discrete element method. The shapes of these elemental particles, the particle size distribution and the number of particles (N = 2800) in each numerical triaxial specimen all matched closely to the real ballast material being modelled. Confining pressures were applied to the specimen via a dynamic triangulation of the outer particle centroids. A parametric study was carried out to investigate the effects on the simulation of timestep, strain rate, damping, contact stiffness and inter‐particle friction. Finally, a set of parameters was selected that provided the best fit to experimental triaxial data, with very close agreement of mobilized friction and volumetric strain behaviour. Copyright © 2015 John Wiley & Sons, Ltd.

The development of reliable methods for measuring deflections as trains pass has enabled valuable insights into railway track behaviour to be gained. This is especially useful for problem areas such as transitions from normal ground onto hard substructures and complex track geometries such as switches and crossings.To date, much of the research on transition zone behaviour has focussed on transitions associated with underbridges and other substructures. Switches and crossings have received some attention and level crossings generally very little. This paper describes and discusses the behaviour of a transition onto a level crossing in the south of England, UK. Measurements are presented from both trackside and on-train instruments. It is found that at this crossing, maintenance constraints have resulted in a group of unsupported or hanging sleepers on the approach to the crossing; and that this fault is not effectively rectified by tamping. Comparisons are also made between the way the fault shows up in measurements from trains of the loaded track profile and data from trackside measurements.

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Laboratory testing of railway ballast poses practical difficulties because the particle size is often too large for most standard apparatus. There are therefore advantages in developing a scaled material whose behavior is representative of the full size material. A first stage in validating such an approach is to investigate whether the particle shape is affected by the change in scale. This paper sets out methods for evaluating form and roundness (aspects of shape) and proposes a new measure for evaluating roundness, termed ellipseness. These methods are then applied to a crushed rock railway ballast over a range of particle sizes. Statistical analysis demonstrates a measurable variation in the distributions of form and roundness with particle size over a range of sieve intervals, although the differences are slight and do not necessarily rule out the use of a scaled material for investigating the factors influencing macro mechanical behavior.