DEM analyses of rock block shape effect on the response of rockfall impact against a soil buffering layer

This study investigates the mechanism of rockfall impact against a granular soil buffering layer above a concrete/rock shed via numerical simulations by discrete element method (DEM). The soil buffering layer is modeled as a loose packing of polydisperse spherical particles, while the bottom concrete/rock shed is simulated by a layer of fixed particles. The rock blocks of various ellipsoidal shapes are represented by an assembly of densely packed and bonded spherical particles. The DEM model was employed to investigate the dynamic interaction between the rock block and the soil buffering layer, including the impact force, penetration depth and bottom force. During the rockfall impact, the force chains occur immediately at the impact area and then propagate radially downward into the soil buffering layer. The force waves vanish gradually as most of the impact energy was absorbed and dissipated by the loose buffering soil particles. The numerical results show that the maximum impact force acting on the rock block increases, while the corresponding penetration depth decreases linearly with the block sphericity. The maximum force acting on the bottom concrete/rock shed is approximately twice the maximum impact force acting on the rock block, showing apparent force amplification of the soil buffering layer. The ratio between these two forces is almost independent of the rock block sphericity. These findings can finally contribute to the design of effective soil buffering layer for concrete/rock sheds.