The projed objedive 31 3Figure 18.3 Unstable rock masses along Highway 22 from India to Tibet.the maximum principal stress being horizontal and parallel to the main
fault. In Fig. 18.5, one of the china clay quarries in Cornwall, UK, is
shown. The action of carbonic acid has caused the feldspathic minerals
in the original granitic rock mass to alter to the clay kaolin, which is
being mined. However, the decomposition process was not uniform,
leading to some areas of residual granite (possessing residual jointing)
and some areas of clay. Needless to say, the prediction of slope stability
in such an inhomogeneous rock/soil mass is much more difficult than in
the hard rock mass illustrated in Fig. 18.2.
The engineering objective could also be to preserve old rock structures
such as the castle in Spain illustrated in Fig. 18.6. The edge of a cliff is a
good military location for a castle wall, but not such a good location from
the rock engineering point of view. The rock face below the castle was
shotcreted in recent times, and the shotcrete has since become separated
from the rock and is now in a parlous state. Or, the rock engineer might
be asked to evaluate the stability of natural slopes such as that illustrated
in Fig. 18.7, which was the theme of the rock mass classification question
in Q14.9.