Abstract
Cushioning materials, such as sand cushion and granular mats placed on rock sheds, can effectively disperse and reduce rock fall energy before rocks collide with protection works. Although the construction costs for sedimentary layers are low, these layers are attracting attention as construction devices that can substantially improve the margin of safety ratio. To elucidate the formation mechanism that governs the impact force waveform of falling mass, this study examines the loading rate dependency of sand cushion by 2D-DEM simulation. In the simulation, particular attention is paid to the velocity of stress waves that propagate in sand cushion. The results are summarized as follows: (1) The impact force of falling mass depends only on loading velocity and penetration depth, not on loading history. (2) The larger the loading velocity, the smaller the area wherein volume strain is borne only by the loaded surface, rather than shared by the penetration of falling mass. This imbalance in support explains the loading rate dependency of sand cushion. (3) The relationships between the compressive strain of a particle group and mean principal stress are determined over dynamic and static loading. These relationships are almost the same between the loadings. (4) Using σ=ρcv to estimate the impact force waveform of falling mass produces large-scale experimental and 2D-DEM simulation results.
