Surface
77 excavation
Many discontinuities, weak rock:
effectively a continuuminstability
Few discontinuities, strong rock:
a discontinuummechanisms
In this chapter, we discuss instability mechanisms in relation to slopes and
foundations. It is possible, in an underground excavation, for the exca-
vation walls and floor to fail in a similar way to surface slopes and
foundations, but these topics are covered in the next chapter.
17.1 Slope instability
In the history of rock mechanics and rock engineering, more attention has
been paid to slope instability considerations than any other topic, and this
topic remains one of the most important today. In Fig. 17.1, there are two
slope failure mechanisms. Figure 17.l(a) illustrates slope instability when
the rock is behaving as an equivalent continuum; Figure 17.l(b) illustrates
slope instability when the rock is behaving as a discontinuum. One of our
first considerations must be to identify the basic mechanisms of slope insta-
bility. The sketches in Fig. 17.1 also highlight the CHILE versus DIANE
nature of the rock which was discussed in Chapter 10.
Figure 17.1 Slope failure mechanisms in (a) a continuum and (b) a discontinuum.