Full-scale rockfall impact testing on untreated logs from protective mixed forests in the Pyrenees

Rockfalls represent a significant hazard in high-mountain regions of the Pyrenees, threatening transportation routes, infrastructure, and local communities. Protective forests naturally mitigate the impact of hazards, which can be further enhanced using engineering solutions. Here, we evaluate, close to real-scale conditions, the effectiveness of nature-based engineering solutions against rockfalls made from freshly cut logs of two common Pyrenean species, Abies alba Mill. and Fagus sylvatica L. Dynamic and static impact tests were conducted using a wooden structure and steel battering ram. Dynamic tests were performed on logs measuring two and three meters in simple and palisade structures, in both paired and unpaired configurations. Additionally, static tests were conducted to evaluate the mechanical performance of these species under controlled conditions. The relative transfer energy from the ram to the logs, as well as the estimated rupture energy, were analyzed. Our results suggest that beech logs exhibited superior impact resistance compared to silver fir. In horizontal configurations, beech logs absorbed significantly more energy, making them suitable for use in rockfall retention areas. However, both species showed severe fractures under successive impacts, indicating reduced energy absorption capacity due to fatigue accumulation. Silver fir exhibited higher moisture content than beech at testing. While the static modulus of elasticity showed no significant differences, beech demonstrated a consistently higher dynamic modulus of elasticity than silver fir. These findings emphasize the potential of using natural wood-based barriers for rockfall protection and the need for larger sample sizes, numerical simulations, and broader experimental designs to optimize protective structures. • Ram allows full-scale tests to probe the reliability of fresh wood structures. • Species mechanical properties strongly influence the protective capacity of forest. • Structures should be arranged based on the species used to ensure effectiveness. • Green structures significantly enhance the forest's protective effect.