Mitigation effects of trees on rockfall hazards: does rock shape matter?

Abstract

Does rock shape matter to the mitigation effects of trees on rockfall hazards? This question must be resolved in order to better quantify the protective role of mountain forests against rockfall. To probe this question we investigate a single rock-tree interaction using non-smooth, hard-contact mechanics that allows us to consider rock shape at impact. The interaction of equant shaped rocks with cylinder-like tree stems is modelled. The equant shaped rocks are close to spherical but have a certain shape variability governed by the rock's surface area ratio and aspect ratio. This work serves as an important follow-up study to the existing investigations from Toe et al. (Landslides 14: 1603(Landslides 14: -1614(Landslides 14: , 2017, where the effects of trees on block propagation are numerically investigated using spherical shaped rocks. The objective of our simulations is to understand how and to what extent, shape will influence energy dissipation and trajectory change. The primary results include: surface area ratio plays a more important role than aspect ratio in determining the rock's post-impact dynamics. The primary parameters governing the rock kinematics after impact (i.e. block's energy reduction, reflected rotational

Full-scale experiments to examine the role of deadwood in rockfall dynamics in forests

“…This has been shown by real-scale experiments at the slope scale in a mixed Abies-Picea-Fagus forest (Dorren and Berger, 2005) as well as on single trees of different species including Picea abies (Lundström et al, 2009) and Ailanthus altissima (Wunder et al, 2018). Implementation of these findings into threedimensional rockfall models, e.g., Rammer et al (2010), Dorren (2012), Toe et al (2017) and Lu et al (2020), has facilitated additional investigations to quantify the protective capacity of mountain forests using numerical tools at the forest stand (Stoffel et al, 2006;Woltjer et al, 2008;Moos et al, 2017) and regional (Dupire et al, 2016;Lanfranconi et al, 2020) scales.…”

Delimiting rockfall runout zones using reach probability values simulated with a Monte-Carlo based 3D trajectory model

“…disaggregation of the initial volume during the failure process and breakage after the first and subsequent impacts (cf. Giacomini et al, 2009;Ruiz-Carulla et al, 2015;Matas et al, 2020;Ruiz-Carulla and Corominas, 2020), the size and shape and change thereof of the individual rockfall fragments that propagate down the slope (c.f., Melzner et al, 2020), the transformation and dissipation of energy during rebounds on the slope surface (Caviezel et al, 2021) and impacts on standing or lying tree stems Lundström et al, 2009;Lu et al, 2020;Noël et al, 2021;Ringenbach et al, 2021), penetration depth in the soil and alteration of the terrain during impact (Pichler et al, 2005;Wang and Cavers, 2008;Guangcheng et al, 2015;Lu et al, 2019). To come up with realistic predictions of the areas that are potentially endangered by rockfall processes, modelling rockfall trajectories is one of the methods that provide an important information (Volkwein et al, 2011;Yan et al, 2020).…”

Stability of rigid body motion through an extended intermediate axis theorem: application to rockfall simulation

“…Furthermore, the need to deal with frictional unilateral constraints in rockfall simulation asks to embed the energy-momentum conserving scheme in the Moreau-type timestepping scheme, which is not a trivial task. Moreover, existing rockfall simulation codes take into account a wealth of different types of dissipation mechanisms (e.g., to take into account the effect of trees and vegetation [18]). The fully implicit coupling between position and velocity updates of most energy-momentum conserving schemes makes it difficult to judge if they can be successfully combined with these specialized dissipation and contact laws.…”