A discrete element model predicting the strength of ballast stones

An extended discrete element method (DEM) is used to describe strength and failure properties of ballast stones. For this purpose, a rock material is modeled using spherical particles bonded by breakable force elements. An inflation procedure to generate dense sphere packings which is based on a particle's current coordination number is proposed. The particle bonds are enhanced by a progressive failure model that reproduces the effects of singular stress concentrations near crack tips, which are normally not present in DEM, by successive weakening of bonds. The material model is investigated in uni- and triaxial compression, where an efficient approach for the simulation of a flexible confining membrane is applied, and calibrated to granite yielding wide agreement in strength and failure properties. Furthermore, a procedure to model shape and angularity of ballast particles is proposed. Finally, the strength of ballast stones made from bonded particles is subjected to statistical evaluation and compared to published experimental results. Different measures for single particle strength are investigated with respect to the loading state which causes failure.