Experimental investigation of geogrid-reinforced sand cushions for rock sheds against rockfall impact

Abstract

Sand cushions for rock sheds have been used to protect roads and railways from rockfall hazard. However, thick sand cushions are often needed, which lead to high construction cost. This paper investigates the use of geogrid-reinforced sand cushions to improve impact resistance as well as reduce required thickness of the sand cushion. Impact tests were conducted in the laboratory to investigate the influence of position and layer number of geogrids on the impact responses of the sand cushions under different impact energy levels. The experimental results indicate that the geogrid placed at an appropriate position in the sand cushion could allow the penetration of an impact object, distribute the impact force, reduce the distributed vertical stress and the vibration of the slab, and increase the impact duration. The test results in this study show that placing the geogrid at one-third height of the sand cushion resulted in the optimum impact resistance. In addition, the upper sand layer within the geogrid-reinforced sand cushion should have a sufficient thickness to provide good energy dissipation ability. Furthermore, the sand cushion reinforced with multiple geogrid layers should be used carefully especially when a thin cushion is used to resist high impact energy rockfall. Moreover, dynamic magnification factors are proposed to correct the vertical stresses calculated by static analysis.