Discrete dynamic modelling of the mechanical behaviour of a granular soil

•3D discrete element modelling of a boulder falling on a granular medium is validated by comparison with results from the literature.•Energy absorbing system within the impacted medium consists in energy transfers and energy dissipation.•Bouncing regimes exists depending on boulder sizes (in case of constant impact velocity) and medium thickness.•Boulder bouncing is related to the substantial resistance of the medium as well as the limited energy dissipation within the medium. This paper investigates the interaction between a falling rock boulder and a granular medium through numerical modelling based on a discrete element method. The boulder is modelled as a single sphere with an incident velocity, and the medium is modelled as an assembly composed of poly-disperse spherical particles. A classical elastic-plastic contact law is implemented with rolling resistance to consider the particle shape effects. The numerical modelling is validated by comparison with results from the literature in terms of impact force, impact duration and the boulder’s penetration depth of the boulder. Then the model is used to investigate the energy propagation within the impacted medium as well as the boulder bouncing. The energy propagation processes are investigated by analysing the space distribution of kinetic energy, elastic strain energy and energy dissipation within the medium over time. The boulder bouncing occurrence is studied, varying the impact conditions in terms of medium thickness and boulder size. Relations between the bouncing of the boulder and the response of the granular medium are finally discussed.