Questions and answers: geological setting 19used in engineering, such as steel, concrete and polymers, we cannot
specify the material properties beforehand: the rock is already there
and we have to find out what its properties are. We are interested in
the stiffness and strength of the intact rock and mechanical weaknesses
in the rock mass, such as bedding planes, faults, joints, and fissures,
generically termed 'fractures' or 'discontinuities'. For rock mechanics
analysis, we also need to know the natural stress state that is in the rock
before engineering begins. This stress state is determined by gravity,
tectonic forces operating and several other factors. So, for all these
reasons and depending on the project, it is helpful, if not essential, to
have a good understanding of the geological history of a site, especially
the structural geology.
The subject of this chapter is explained further in Chapter 2 of EM 1 '.
The introduction here in this section is intended as an aide-memoire to the
subject before the questions and answers in the next section. This applies
similarly to all subsequent chapters.
2.2 Questions and answers: geological setting
- I The picture below shows a limestone slope above a highway in
Spain. Comment briefly on the geological factors that could influence
rock slope stability at this location.
A2.1 The rock strata are folded and there is evidence of opening of
the bedding planes. Generally, in limestones there will be two sets of
joints perpendicular to each other and to the bedding planes. Thus, it is
Throughout the text, we will refer to OUT earlier companion book 'Engineering Rock
Mechanics: An Introduction to the Principles' as ERM 1.