Experimental analysis of the response of fresh wood stems subjected to localized impact loading

The forest is a well known and efficient natural protection solution against rockfall. To compensate for a loss of the forest’s protective function after windstorms or maintenance tasks, some of the felled trees can be left in an oblique position on the slope as wooden protection structures. No studies have been conducted on the efficacy of these devices and particularly their resistance to rock impacts and their energy dissipation capacity. The dynamic response of fresh stems to impact was analyzed by laboratory impact experiments with a Mouton-Charpy pendulum. The experimental results allowed the definition of different impact types related to the occurrence of nonlinear processes associated with partial rupture of wood fibers. The physics controlling the stem loading force and displacement were shown to be mainly associated with inertial effects during the early stages of the impact. Second, when the stem displacements become larger, the stem response becomes quasi-static. Based on these results, a practical approach for assessing the capacity of wooden structures made of fallen trees to resist rock impact was proposed and evaluated.