7 Introduction
1.1 The subject of engineering rock mechanics
The term engineering rock mechanics is used to describe the engin-
eering application of rock mechanics to civil, mining, petroleum and
environmental engineering circumstances. The term mechanics, means
the study of the equilibrium and motion of bodies, which includes statics
and dynamics l. Thus, rock mechanics is the study of mechanics applied
to rock and rock masses. ’Engineering rock mechanics’ is this study
within an engineering context, rather than in the context of natural pro-
cesses that occur in the Earth‘s crust, such as folding and faulting. The
term rock engineering refers to the process of engineering with rock,
and especially to creating structures on or in rock masses, such as slopes
alongside roads and railways, dam foundations, shafts, tunnels, caverns,
mines, and petroleum wellbores.
There is an important distinction between ’rock mechanics’ and ’rock
engineering’. When ‘rock mechanics’ is studied in isolation, there is
no specific engineering objective. The potential collapse of a rock mass
is neither good nor bad: it is just a mechanical fact. However, if the
collapsing rock mass is in the roof of a civil engineering cavern, there
is an adverse engineering connotation. Conversely, if the collapsing rock
mass is part of a block caving system in mining (where the rock mass
is intended to fail), there is a beneficial engineering connotation. In the
civil engineering case, the integrity of the cavern is maintained if the
rock mass in the roof does not collapse. In the mining engineering case,
the integrity of the mining operation is maintained if the rock mass does
collapse.
Hence, rock engineering applies a subjective element to rock mechan-
ics, because of the engineering objective. The significance of the rock
mass behaviour lies in the eye and brain of the engineer, not in the
mechanics.
I It is not always realized that the term ‘mechanics’ includes ‘dynamics’, but a book
title such as ’River Mechanics’ is correct. Similarly, ’rock dynamics’, the topic of Chapter
13, is part of ‘rock mechanics’.