Cushion Layer Effect on the Impact of a Dry Granular Flow Against a Curved Rock Shed

The dry granular flow produced by a landslide or mountain collapse represents an intense threat to road structures, including rock sheds in mountainous areas. In this study, we designed a set of experiments to investigate the impact mechanism of dry granular flow against a rock shed. The experimental rock shed model was characterized by a curved surface and a cushion layer of granular materials. Based on a video recording and the time history of the impact force, we determined the impact force characteristics and found that for cases without a cushion layer, the maximum normal and tangential force components are close to the end of the rock shed directly facing granular flow impact. With the addition of a cushion layer, the maximum impact force decreases and shifts approximately 30A degrees-45A degrees away from the end, which indicates that a cushion layer can not only reduce the magnitude of the impact force, but also change its distribution mode. We also verified the stronger energy dissipation capability of a cushion layer made of finer granular material. Finally, we performed a stiffness analysis, calculated the internal forces, and found that cushion layers can reduce the internal bending moment and internal shear force and increase the internal axial force. From the engineering perspective, all the changes introduced by a cushion layer positively contribute to rock shed safety.