Load distribution of rockfall impact onto rock shed through sand cushion

Sand cushion has been widely placed above rock sheds to improve their impact resistance to rockfall. The impact load distribution through a sand cushion is an important consideration for the rock shed design. To evaluate the impact load distribution through the sand cushion, this study performed impact tests and showed that the impact stress increased with the increase of rock mass and impact velocity as well as the decrease of cushion thickness and rock sphericity. This study also conducted a sensitivity analysis, indicating that the main factor influencing the peak impact stress within the sand cushion was the rock sphericity, followed by the cushion thickness, the impact velocity, and the rock mass. Based on the test results, an impact load distribution model was proposed to characterize the peak impact stress and the impact stress distribution through the sand cushion, which was verified for its reliability. Furthermore, the results showed that the stress distribution angle was independent of the rock mass, drop height, and cushion thickness when a spherical rock was used. However, when a rectangular prism rock hit the sand cushion by its minimum contact area, the impact stress distribution angle decreased with the increase of the rock sphericity. Finally, this paper proposed a procedure for designing sand cushions to protect rock sheds against rockfall impact.