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 cushioning mechanism of cushioning materials, such as sand cushion, the present study examines the transmission behavior of the impact force in a sand mat from different external forces, while paying attention to distribution of mean principal stresses and volume strain rate, which are calculated from contact force and velocity of the particle. The results obtained in this study can be summarized as follows: (1) by calculating the depth distribution of mean principal stresses, the second peak of the impact force of a falling mass was revealed to be due to the wave reflected from the bottom; (2) under the condition of equal input energy, dense and sparse waves were produced when a fast load was applied, but the sparse wave was weaker than the dense wave when a heavy load was applied; (3) in the process that a falling mass collided with the sand cushion, the internal friction angle at the time of the falling mass penetration and stress propagation was smaller than the internal friction angle at the time of the fracture; (4) under the condition of equal input energy, the transmission behavior was stable because the load received was closer to isotropic consolidation when a heavy load was applied than when a fast load was applied.
