Engineering Rock Mechanics

4 Introduction

‘Rock Mechanics’

‘Engineering Rock Mechanics’ and

‘Rock Engineering’ Design

Figure 1.1 The distinction between ‘rock mechanics’ itself (a) and engineering applications
of rock mechanics (b). In (a), F1.. .Fn are the boundary forces caused by rock weight and
current tectonic activity. In (b) a tunnel is being constructed in a rock mass.

The distinction between ’rock mechanics’ and ’rock engineering’ illus-
trated in Fig. 1.1 is highlighted further in Fig. 1.2 which shows part of
the concrete foundation illustrated in the Frontispiece. ‘Rock mechanics’
involves characterizing the intact rock strength and the geometry and
mechanical properties of the natural fractures of the rock mass. These
studies, together with other aspects of the rock mass properties such as
rock stiffness and permeability, can be studied without reference to a
specific engineering function. When the studies take on a generic engin-
eering direction, such as the structural analysis of foundations, we are in
the realm of ’engineering rock mechanics’. This is analogous to the term
engineering geology in which geology is studied, not in its entirety but
those aspects which are relevant to engineering.
‘Rock engineering’ is concerned with specific engineering circum-
stances: in this case (Fig. 1.2), the consequences of loading the rock
mass via the concrete support. How much load will the rock foundation
support under these conditions? Will the support load cause the rock to

Figure 1.2 Portion of Frontispiece photograph illustrating loading of discontinuous rock
mass by the concrete support of a multi-storey car park, Jersey, UK.