Energy absorption of sand cushions in rockfall impact: Effect of impact angle

¹ Toyohashi University of Technology, 1-1 Hibarigaoka, Tenmpaku-cho, Toyohashi, Aichi, 441-8580 Japan
² Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi, 466-8555 Japan

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 1 December 2025

Abstract

Energy absorption effects of topsoil and talus in mitigating rockfall impacts should be properly evaluated to design effective countermeasures against rockfalls. However, previous studies have largely focused on scenarios wherein the impact angle is either constant or relatively small; consequently, research on the influence of varying slope gradients, drop angles and impact angles on rockfall energy absorption is limited. To address this gap, this study investigated the rockfall behaviour on horizontal and inclined granular mats through a scaled model and full-scale experiments. The results obtained are summarised as follows: (1) The energy absorption rate of rockfall on granular mats is primarily influenced by the impact angle rather than the slope inclination angle; when the impact angle remains constant, the energy absorption rate is approximately the same regardless of the slope inclination. (2) In full-scale experiments, multivariate analysis of factors such as granular mat thickness, rockfall size, impact velocity, and impact angle revealed that the impact angle had a significant effect on energy absorption. Our study findings deepen the understanding of rockfall behaviour on granular surfaces and provide important insights into the design of rockfall mitigation measures.