Geology Reference
In-Depth Information
always equate with dif
cult geotechnical behaviour. Conversely, an
apparently simple geological pro
lemayhavesubtlevariations
that affect the success, or otherwise, of a project.
Once the model includes the range of engineering parameters and
ground conditions that need to be considered, it becomes a design
model (Knill, 2002). It might then be used, for example, to decide
what foundation system might be required to carry the load from a
building. It is used for making decisions on how to deal with the
ground conditions. The full model will include not only geological
features but also other site factors, including environmental conditions
and in
uences such as groundwater, rainfall, wind and earthquake
loading, as well as anthropogenic in
uences such as blasting and traf
c
vibration.
The starting point of a model should usually be a three-dimensional
representation of the geology of the area and to the depth that will
be affected by the project or which the project may affect. The
rst
attempt at a geological model for a site will usually be an interpreta-
tion of published maps and the interpretation of aerial photographs
and satellite imagery, depending upon the location of the project.
Unfortunately, for some projects, that is as far as the geological
interpretation goes, sometimes with disastrous results because the
maps are either incorrect or at such small scale that they cannot
represent the site-scale features that will affect the project. Those
working in civil engineering need to appreciate that all published
geological maps are professional interpretations of relatively small
pieces of reliable data that are then interpolated and extrapolated.
Faults may have been interpreted from lineaments and might not
exist in reality. Conversely, published maps will certainly not show
all the major geological discontinuities that may be signi
cant for an
engineering project. Most features on geological maps are generally
marked as uncertain or inferred but that does not stop the unwary
assuming that they are accurate. In all cases, maps and plans that are
not site- or project-speci
c, should be taken as indicative only and a
starting point for detailed investigation, as discussed in more detail
in
Chapter 4.
Despite the inevitable limitations of published infor-
mation, a broad understanding of the geological and geomorpholo-
gical setting can be used to make predictions of what might be
encountered at the site through experience and training. For exam-
ple, if the site includes a granitic intrusion, then one might expect
certain joint styles in the granite, a metamorphic aureole around the
intrusion where the granite has cooked the country rock, and asso-
ciated minor dykes and hydrothermal alteration, as illustrated in
earlier sections of this chapter. In limestone country, one should
