Engineering Rock Mechanics

14 Geological setting

In the photographs in Figs 2.4 and 2.5, the significance of the likely
influence of rock structure on engineering can be imagined. The departure
from an 'ideal' material through the existence of this structure can occur
on all scales from very large faults to micro-fissures. Similarly, engineering
in rock occurs in a variety of sizes and shapes. Examples are the
Chuquicamata open-pit copper mine in Chile which is several kilometres
long and planned to be 1 km deep, and a petroleum engineering wellbore
which is a few tens of centimetres in diameter yet is several kilometres
deep. It is the interpretation of this rock structure in conjunction with the
size, shape and design requirements of the engineering that make rock
engineering a unique discipline.
Thus, rock mechanics applied to engineering is both an art and a science.
We will be explaining the principles of engineering rock mechanics in this
book, but it should never be forgotten that we cannot specify the rock
properties and the rock loading conditions: they already exist because the
rock is a natural material and in many cases is significantly stressed
naturally before engineering commences. Hence, in the remainder of this
chapter, we will develop these concepts by considering the natural rock
environments within which the engineering occurs and the specific ways
in which the geological setting directly affects both the rock mechanics and
the engineering design.

2.2 Natural rock environments

In addition to the direct properties of the rock and rock masses as described
above, we have to remember that the natural rock environment can also
have a profound effect on the engineering. In general this is basically
governed by the location of the engineering, i.e. whether a structure is
being built on the surface, whether the structure is being created by

Figure 2.4 Large-scale rock structure.