Rockfall impacts on sand cushions with different soil mechanical characteristics using discrete element method

The cushioning behavior of materials, such as sand, is numerically studied using a discrete element method (DEM) for the rational design and performance evaluation of a rock shed intended for rockfall protection. Several of the numerical analysis studies, conducted thus far, have focused on the maximum impact force which depends on the layer thickness of the cushioning materials and the falling conditions. However, to investigate the cushioning performance of a sand cushion correctly and to propose effective and rational measures, the compression and expansion behaviors, which are characteristic of soil associated with deformation, should be considered. Therefore, a method is proposed here for determining the parameters of a two-dimensional DEM simulation in order to consider the soil mechanical characteristics for the problem of rockfall impacts on a sand cushion. The proposed method was validated through a comparison of the simulation and experimental results using large-scale falling-weight impacts for different layer thicknesses of the sand cushion, initial relative densities, and falling heights of the falling mass. Not only were the maximum impact forces compared, but also the changes in density of the cushioning material after the impact experiment. The present study contributes to the elucidation of the deformation mechanism of soil under high-speed loading and evaluates the performance of a sand cushion considering its deformation behavior.