Dynamic analysis of rockfall impact on a protective structure via FEM-DEM coupling

Rockfall is one of the most catastrophic hazards among natural calamities. The issue involving responses of discrete-continuum interactions concerning rockfall protection remains unclear. This study couples the finite element method with the discrete element method (FEM-DEM) to realize simulations of impact dynamics of falling boulder and computations of mechanical responses of a protective structure under imported loading. The FEM-DEM coupling algorithm is elucidated. The coupling approach is verified through a free-fall experiment with a block. The velocity and size effects on impact behavior of the boulder are investigated. The interactions between gravel cushion and the concrete structure are dissected. Structural responses correlated with boulder size and velocity effects are analyzed, and numerical results indicate that the two factors affect the variations of rotational velocity and the proportion of rotational-to-translational energy of block, respectively. Strengthening is observed at the bottom of cushion layer after block impact. Coupling results reveal that tensile stress is concentrated on the crown of retaining wall and the inner part of pile root, and structure deformation meets the need for stiffness. However, this type of protection carries a risk in obstructing boulders sized relatively large; additional structures should be considered in protection scheme.