STUDYING ROCK-FALLS THROUGH MODEL FORESTS WITH INSTRUMENTED PARTICLES

Understanding how rock-falls interact with obstacles is important when designing mitigation measures for geophysical hazards and catastrophes. These often involve the proper design and building new protective structures which can be very costly as well as aesthetically unappealing. Many countries spend millions of dollars to construct and maintain such earth surface hazards defence infrastructure. With the advent of green development initiatives, ecologically sound engineering designs that blend better with the natural landscape and are less costly (both in terms of construction and maintenance), compared to the heavy infrastructure solutions, play an increasingly important role for the prevention and control of rock-fall disasters. Specifically, the use of obstacles to rock-falls that result in decelerating rock-falls and dissipating their mechanical energy (macroscopically seen as offering an increased equivalent roughness) is of interest in this study. Roughness elements can comprise of natural vegetation or trees and in this manner systems of these elements such as forests can make up systems that can play a defensive role in slowing the geophysical flows, including rock-falls. For a given type of trees and susceptibility to certain rock-fall hazards, the density of such forest systems is a major design parameter that define its success in dissipating the energy of rock-falls. A sufficient density of trees will successfully remove energy at a greater rate than acquired during the advection of granular material or rock-falls along the inclined earth surface. The current study introduces a new physical experiment for studying rock-falls through model forests. Specifically, it is studied how the characteristics of different densities of trees affect the kinematics and dynamics of rock-falls, for fixed rock (solid density, size and shape) and surface (slope angle and roughness) characteristics. The former are accessed using a video camera and particle tracking velocimetry while the later are identified by embedding inertial sensors in an instrumented rock, to monitor its motion and impacts with the trees and the bed surface. Such experiments can benefit our understanding of the governing aspects between the highly dynamical interactions between rock-falls (and in the future, granular flows) and forests (arrays of trees) at a particle (microscopic) scale, as well as how do factors such as trees’ spacing or their diameter relative to the rock dimension, (macroscopically) affect the observed flow behaviour.