Newcastle Chapter

Forest and bio-engineering rock fall protection techniques

Dr Franck Bourrier

Abstract

A number of studies have demonstrated that forests can be an efficient and cost-effective means of protecting against rock-fall. This is especially true for events involving small blocks (< 5 m3). Incorporating the effects of forests in rock-fall propagation models is complicated by the mechanical processes that occur between blocks and trees. Although existing modeling techniques deliver efficient computation times and are able to account for forest effects at a global level, they do not simulate the physical interactions that occur between a block and a tree or its components (stem, root system, and crown).

This research is aimed at developing mechanical models for the impact of blocks on trees and bio-engineering rock-fall protection structures that are made from standing or felled trees. Different models based on the Discrete Element Method (DEM – open source code Yade-DEM), will be presented.

Models developed to simulate block impacts on single trees and coppice stools will be presented first. These models were calibrated using laboratory impact tests. The parameters governing the trajectory of a block (tree diameter, impact location, impact velocity) were identified from numerically simulated impacts. Incorporating these models into a block propagation model delivered quantitative results on the effectiveness of forests in decreasing block propagation distance and energy. Comparing the new results with those delivered by classical approaches provided information on potential improvements for the traditional methods.

A DEM model for the impact of a block on a felled tree will also be presented. This model was used in an extensive numerical study to explore the dynamic response of bi-engineering structures made from felled trees during a range of realistic block impact scenarios. The study identified the different structure responses that depend on block and tree sizes. This result is of major interest for the design of bio-engineering structures.

About Dr Franck BourrierBourrier_F

Dr Franck Bourrier completed a PhD dedicated to the numerical modeling of rock rebound on coarse soils at the University of Grenoble,France, in 2008. After his PhD, he was awarded a permanent researcher position at Irstea (National Research Institute of Science and Technology for Environment and Agriculture of France).

He has been working extensively on topics concerning the modeling of soil and tree responses to various loading conditions. The original aspect of his research combines a mechanical process based approach with statistical ones to solve problems usually treated with semi-empirical approaches. Following this framework, he obtained significant results concerning rock interaction with soil, trees, and protection structures, as well as the slope stability improvement by tree roots at the plant and at the slope scale.

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