Treenet: an innovative type of rockfall protection fence on forested slopes specially designed for low energy events
Résumé
This paper deals with a type of fence specifically developed for low energy events. The fence is composed of a wire mesh, three cables and two rigid rods. This fence is tightened between existing trees. The experiments successively impacted the fence in its centre with rocks of varying mass (from 30 kg to 500 kg) with the aim of evaluating its capacities. The system allowed reaching a maximal rock velocity before impact of 17m/s. This velocity was calculated thanks to image analysis obtained with a video camera and a high speed camera. A total of 17 impact experiments were performed for different fences. The first results showed that (i) angular blocks can cut wires even for low mass rocks, (ii) the wire rupture hardly propagates in the mesh during another impact, (iii) supporting cables can be cut during the impact, (iv) the fence is not perforated by the direct impact even for rocks 500 kg in mass, and (v) a reparation of a perforated mesh consisting in placing a patch is perfectly efficient. In parallel to these experiments, numerical simulations were performed based on the discrete element model developed by Bertrand et al. (2008).
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