Numerical simulation of a rockfall impacting a gravel cushion with varying initial angular velocity and particle sizes

Gravel cushions are widely laid on the top of structures or rock sheds to absorb the impact energy of rockfalls in mountainous districts. Based on the discrete element method, a numerical model of a rockfall impacting a 2D mixed-size gravel cushion layer at an initial angular velocity was established in this study. The penetration depth of the rockfall, impact force of the cushion surface, and energy dissipation ratio were investigated. Increasing the initial angular velocity and decreasing the particle size of the cushion were found to evidently reduce the maximum penetration depth of the rockfall and increase the impact force of the cushion surface, respectively. The energy dissipation ratio after collision was affected by the particle size of the cushion and the ratio of the angular kinetic energy. Omitting the initial angular velocity led to an underestimation of the energy dissipation ratio, by up to 40.8%. With decreasing particle size of the cushion, the energy dissipation ratio first increased but then decreased. The study results provide a theoretical basis for the design of gravel cushions intended for rockfall protection.