This paper presents an analysis of the mechanical behaviour of coarse granular aggregates using the discrete element method. A background reference for the conducted study is the set of results of a few large scale triaxial tests performed at the UPC geotechnical laboratory. The basic tool used to simulate some of the tests is the computer code PFC3D. Rockfill particles (they have the size of gravels, typically ranging from 1 cm to 4 cm) were simulated as breakable clusters of 3D balls. Particle breakage occurs in time according to fracture mechanic’s laws. The relationship between stress intensity at a given particle, the size of an initial defect (crack) and the relative humidity could be established. This information was introduced in the numerical analysis to derive criteria for particle breakage in time. The paper describes the preliminary results of the work in progress. The influence of some properties such as particle shape, porosity, toughness, and friction coefficient was studied. The actual shape of rock gravels has been approximated by means of clusters of spherical particles. Several arrangements, comprising a different number of particles, have been tested, having always as reference validation criterion the results from triaxial tests performed. The results of the modelling exercise are encouraging and test results are reasonably well reproduced. The model is fairly general and it has a number of interesting capabilities.