Civil Engineering Reference
In-Depth Information
Figure 3.1
Photograph of typical diamond drilling equipment for hole depths up to about 300 m.
3.1.1 Geology
be given less attention during mapping than a
limited number of shears with continuous lengths
equal to that of the slope height. A design engineer
who is analyzing the data and is not familiar with
the site, may be unable to distinguish on a con-
toured stereonet the relative importance between
the many non-persistent joints and the shears.
Alternative approaches to geological investiga-
tions are as follows. First, there may be a number
of existing slopes, either natural or excavated,
near the site where the geological conditions are
similar to those on the project. In this case, strong
reliance could be placed on extrapolating the
performance of these slopes to the new design.
In these circumstances, it may not be necessary to
collect additional data, except to carefully doc-
ument existing slope performance and assessing
how this may be applied to the proposed design.
Alternatively, where there is little local experience
in cut slope stability, it may be necessary to con-
duct an extensive investigation program involving
mapping, drilling, and laboratory testing. As this
program develops, it should be modified to suit
A distinguishing feature of many investigations
for rock slopes is that it is particularly important
to focus on the details of the structural geology.
For example, the orientation of one clay-filled
fault that dips out of the face can make the
difference between stability and instability. Struc-
tural geology data provided by surface mapping,
where available, is usually more reliable than that
obtained by diamond drilling because outcrops
and cuts show larger scale features and undis-
turbed
in situ
conditions compared to the very
small volume of a drill core. Furthermore, the ori-
entation of discontinuities in core is not known
unless the core is oriented.
It is recommended wherever possible, that the
mapping be carried out by the same person or
engineering group who will carry out the design
so that the objectives of the mapping program are
clearly identified and the data collected is relev-
ant to the design. For example, a large number of
short, non-persistent joints that have little influ-
ence on the rock mass strength or stability should
