3 1 2 Design of surface excavations
Figure 18.2 Rock slope on the A82 road by Loch Lomond in Scotlandhere are foundation loading at the base, and abutment loading at the
sides. The other main issue is the secondary permeability of the rock
mass, given the final water level in the completed dam: we have to be
able to assess the potential leakage paths under and around the dam.
Fig. 18.2 shows a finished rock slope adjacent to a road in Scotland,
which was designed after a concerted study of the rock mass fractures.
Here the considerations involved the long-term stability and any re-
quired maintenance of the rock mass, both in terms of its overall stability
and the possibility of avoiding rockfalls on to the road.
Sometimes it is not possible to engineer the slopes to avoid slope
instability because of the limitations of the terrain. Fig. 18.3 shows a
portion of Highway 22, the main highway between India and Tibet.
Here, the road winds its way up the valleys, hugging the valley sides,
and so there is almost no scope for any design variations. It is also
not practical in terms of manpower resources and materials to provide
support measures or rockfall protection along the whole highway.
In mining, there is much greater scope for design variations, espe-
cially in large quarries and open-pit mining of large orebodies, because
the whole mine geometry can be arranged to optimize the extraction
conditions. Also, mining slopes only have to be stable in so far as any
instabilities do not inhibit the mining operations - which means that
some forms of minor instabilities are acceptable. An example of the
large extent of slopes present in some mining operations is illustrated in
Fig. 18.4, which shows the Kalgoorlie 'Superpit' in Western Australia.
Although mining operations provide good opportunities for obtaining
information about the rock mechanics properties, they are often located
in faulted or contorted geology - almost by definition in the case of
orebodies because the desired metal has been concentrated by geological
processes. In the case of the Kalgoorlie area, faults are present with