Cushioning materials, such as sand cushion placed on rock sheds, are attracting attention as construction devices that can effectively disperse and reduce rock fall energy before rocks collide with rock fall protection works. To support performance-based designs for rock fall countermeasures, the present study estimated rock fall behaviors and impact forces using 2D discrete element method (2D-DEM). As one of the typical behaviors, propagated impact force can exceed impact force of falling mass. We conducted two numerical analysis focused on this phenomenon; monotonic penetration test controlling under constant penetration velocity, and removing falling mass during penetration process for any time. In addition, the effects based on some condition of sand cushion, weight of falling mass and its velocity are examined from the view point of impact force-penetration relationship of sand cushion.
