Discrete element simulation of railway ballast: modelling cell pressure effects in triaxial tests

The paper investigates reproducing the effects ofconfining pressure on the behaviour of scaled railway ballastin triaxial tests in discrete element models (DEM). PreviousDEM work, using a standard Hertzian elastic contact lawwith an elastic–perfectly plastic tangential slip model, hasbeen unable to replicate the behaviour observed in laboratorytests across a range of confining pressures without alteringboth the material stiffness and the inter-particle friction. Anew contact law modelling damage at the contacts betweenparticles is introduced. Particle contact is via spherically-capped conical asperities, which reduce in height if over-stressed. This introduces plasticity to the behaviour normalto the contact surface. In addition, the inter-particle frictionangle is varied as a function of normalized contact normalforce. At relatively low normal forces the friction angle mustbe increased for peak mobilized friction angles to match thelaboratory data, an effect that is attributed to interlocking atthe scale of surface roughness. Simulation results show closeagreement with laboratory data.