Comparison of full-scale rockfall tests with 3D complex-shaped discrete element simulations

Abstract

Trajectory analysis is often needed to handle rockfall hazards. It is crucial to understand and to refine ground and rock interactions during a rockfall, which can be related to the elements involved. They include the topology, ground and rock nature, but also the volume and shape of the falling blocks. This work focuses on replicating field observations using a 3D discrete elements model (DEM) in order to further analyze the possible rockfall deposition areas, which may not be accessible due to the limited number of experimental data available. The numerical model implements blocks of more realistic shapes that were reconstructed from in situ blocks obtained by photogrammetry. The dissipation of kinetic energy at the collision point is suitably managed. In the experimental campaign, dozens of boulders (rock block) releases were conducted on two slope profiles of a quarry located in Authume (France). Block passing heights, velocities and runout distances were assessed at specific ground points. We analyzed lateral spreads, propagation distances, and energy balances computed for 3 different block geometries. These numerical results were confronted with experimental observations. Although time-consuming compared to lumped mass and rigid body dynamics models where the impact duration is zero, the DEM used in this work is versatile thanks to an explicit consideration of geometrical effects throughout the life of multiple contacts. It allows to simulate quite accurately a multitude of configurations. Among the properties of the terrain and the blocks, geometric features are shown to be crucial. For the sake of efficiency, a simplified shape coefficient based on block’s elongation is proposed.