Discrete element simulations, with the particle-particle interaction model based on classical contact mechanics theory between two nonadhesive spheres, were carried out and compared with `sandpile' experiments using spherical particles in order to assess the validation of the simulation data. The contact interaction model is a combination of Hertzian theory for the normal interaction and Mindlin-Deresiewicz theory for the tangential interaction. To ensure the consistency of the simulations with the experiments, the measurement of sliding friction, a key parameter in DEM simulations, was highlighted. A simple experimental method for establishing the value of the friction coefficient was proposed and used in measuring the friction of the rough glass beads and steel balls to be modelled in the simulations. The simulations were carried out for two cases according to particle arrangements: the first is quasi-two-dimensional (Q2D), with a smaller flat cuboidal box containing the spherical particles inside another box for discharge, and the second case is axisymmetric (3D). For both cases, simulations and experiments were carried out for assemblies of polydisperse rough glass beads under the same conditions. Comparisons were made that showed that the profiles and hence the measured angles of repose, in each case, were in good agreement, thus supporting the validity of the discrete element model used. Further numerical-experimental comparisons were carried out for 3D conical piles using smooth monodisperse steel balls and the same conclusions were obtained. (c) 2005 Elsevier B.V All rights reserved.