Author: Parham Ashayer

Publisher:

Published: 2007

Total Pages: 410

ISBN-13: 9780494393994

Numerical modeling can assist in predicting falling rock trajectories and reducing the destruction caused by rockfalls. The majority of existing rockfall simulations are based on particle or lumped-mass models that consider the falling rock as an infinitesimal particle with a concentrated mass. Hybrid models usually find the rock-slope contact point using techniques similar to those used in particle models, while incorporating some aspects of the rigid body collisions for bouncing. There are also some rigid body models that employ simplified mathematical impact models. In the framework of this thesis, the applications of rigid body theory and discrete element modeling to rockfall simulation are investigated. A modified version of the discrete element model (MDEM), which can model impacts using methods similar to low-compliance impact models, is offered. In this model, the normal linear dashpot is replaced by a nonlinear dashpot which dissipates the impact velocity based on the contact normal velocity. A mono-direction sliding unit is added to model low-compliance impacts and the tangential dashpot is removed. Several numerical tests strongly indicate that if shape geometries can be sufficiently approximated by a group of particles, the proposed MDEM can replicate the rebound velocities that are predicted by the application of low compliance rigid body impact models. Application of rigid body impact mechanics (RBIM), originally developed by Stronge, in rockfall simulation is studied and compared with other classical rockfall impact models. The effects of several parameters on widely-used coefficients of restitution are investigated including: rock geometry and slenderness, angle of impact, rock orientation, and slope material properties. A new geometrical rockfall simulation program, GeoRFS, based on rigid body mechanics in two-dimensional space, is developed, where rock geometry can vary from prisms with a randomly generated polygonal cross section to superellipsoids. The trajectories of different rock geometries (e.g., roll-out distances, bounce heights, velocities, and energies) during multiple impacts on flat and inclined impact surfaces are studied. The results strongly suggest that the provided simulation program can satisfactorily replicate the roll-out distances obtained from the in-situ tests performed by the Oregon Department of Transportation using different rock geometries. It is expected that the geometrical simulation tools introduced in this work will replace the particle impact model currently used in rockfall programs.