Environmental Engineering Reference
In-Depth Information
Chapter 4
Instability of Rock Masses
4.1. Introduction
Instabilities in rock cliffs are one of the major natural risks in mountainous
regions. They generally appear in an abrupt way, in the form of slides or toppling of
rock masses that lead to falls of boulders and landslides with great kinetic energy.
The impacts on the terrain and structures can be destructive if the risks are not
limited through judiciously established protective structures, designed and
dimensioned to divert or stop masses in motion.
Knowledge of the rupture mechanisms of rocky masses and of the elementary
dynamic phenomena associated with rock falls is a prerequisite for any study of a
site at potential or declared risk:
- to be able to identify the nature of possible events, limit their order of
magnitude and evaluate the extent of the zones concerned;
- to be able to interpret the observations of previous events (state of the cliffs,
survey of the fallen boulders, traces of impact on the slope or of damage to the
existing trees and structures through the use of aerial photographs, video film if
applicable, etc.);
- to check the functioning of digital models of two or three-dimensional rock
falls, by means of simplified cases (geometry of the terrain and boulders, physical
