A specific contact model was used in a code (discrete element method) to explain the mechanisms of energy dissipation by collision and friction during the propagation of a granular mass on a slope. The numerical model focused on both realistic block shapes and the relevance of the single-collision law that make physical parameters easily assessable. Identification of the contact parameters was carried out by means of the digital image analysis of two-body collisions. To this purpose, the dropping of single blocks on a flat surface was filmed from two angles with high speed cameras. The digital images acquired during the rebound were then analyzed to extract accurately the block kinematics (3D trajectory and velocities). The contact parameters were optimized by minimizing an error function obtained by comparison between the numerical predictions and the experimental results. Once the parameters were set, a simulation of the collective behavior of the release of piled and randomly poured bricks under the same conditions as those released experimentally as described in the literature, was carried out. The satisfactory match between the experiments and the numerical predictions showed that (i) the proposed collision laws are sufficient to describe with accuracy the energy dissipation that occurs during binary collision or during mass propagation, (ii) the optimization procedure enables correct identification of the parameters, and (iii) the initial layout of the blocks is of primary importance in this process.