Additional points 33718.3 Additional points
Foundations and rock slopes are generally at the Earth’s surface and
hence will be excavated in rock masses that have been subjected to
some form of weathering. The range of this weathering varies from
that in cold regions and the effects of permafrost to that in hot regions,
where high temperatures and rainfall can cause mineralogical altera-
tion and associated mechanical degradation to significant depths. The
weathering may be expected to extend to a depth of up to 35 m -
which is of the same order as the dimension of an engineered slope.
Moreover, the weathering is likely to be non-uniform, and so the slope
will have different properties at different locations, making the analysis
and design more complex. An example of this is the heterogeneous rock
and soil strata forming the slopes of the Panama Canal, for which precise
geotechnical predictions of the performance of the slopes are difficult.
The consequence of the near-surface conditions is that rock property
characterization for slope design is always critically important, as are
sensitivity analyses of the influences of the various parameters on stabil-
ity. Furthermore, although we have given examples of quarries in which
slopes occur at all azimuths, many rock engineering structures may
contain slopes at fixed locations and orientations. Such a circumstance
may occur with the cuttings for a transport route through mountainous
terrain. Under these conditions, the engineer has little scope for adopting
a design that minimizes the risk of instability, and must instead adopt
measures that protect the transport corridor and its users. This will prob-
ably involve the installation of fences and rock fall traps. Development
of techniques for designing such protection from rock fall instability is
currently a major activity.
The principal difficulty in the design and analysis of rock slopes and
foundations is the DIANE nature of near-surface rock masses. As engin-
eers are called upon to make ever more ambitious designs, so the need
to incorporate the DIANE features into a design becomes paramount.
As a result, more sophisticated techniques for characterization of the
rock mass and analysis of the engineered structures are required. For
example, all of the questions and answers we have presented use sets of
parallel fractures, so that the analyses can be simplified for convenience.
More advanced techniques using actual field fracture data are currently
being developed, and these will assist in improved design.