Geology Reference
In-Depth Information
lled with secondary sedi-
ments, even where they have not actually been sampled at the site.
The use of earth science skills to interpret the available data as a site
history is clearly important, yet sometimes lacking in civil engineer-
ing practice (Brunsden, 2002). The best source of information on
what might be anticipated is the geological literature
expect caves and open
fissures, perhaps in
textbooks on
physical and structural geology and sedimentology in particular, as
background, together with local geological reports and memoirs,
and there are no real short cuts.
-
A particular problem with modelling rock masses is de
ning the
fracture network. As addressed earlier in this chapter, considera-
tion of geological origin and an appreciation of the history of
development of fractures can be important for creating a realistic
model. In reality, most fracture models, be they for assessing rock
strength or permeability, are generated statistically based on orien-
tation data. Persistence is extremely dif
cult to judge and most
such models start off essentially as geological guesswork that can be
adjusted and modi
field test data are collected, say in the petro-
leum industry or from large-scale pump tests associated with water
supply or nuclear waste investigations. Particular techniques are used
for discrete fracture network (DFN) modelling as in software packages
such as FracMan.
ed as
A simple model for a cut slope alongside a road is shown in
Figure 3.61.
The mass of rock and soil has been split into
five units,
largely on the basis of strength factors, as discussed in later chapters,
but discrete and possibly important elements, such as major adverse
discontinuities along which a landslide could occur, are identi
ed for
special consideration. A simple model of ground conditions for the
design of foundations of a building is illustrated in
Figure 3.62.
The various units will each give some support to the building and
the ground-structure interactions need to be assessed if the founda-
tions are to be designed cost-effectively. Models should not be overly
complex but must account for all the important features at the site,
including apparently
'
minor geological details
'
that have
'
major
geotechnical importance
, such as individual weak discontinuities
along which slippage could occur (Terzhagi, 1929; Baecher &
Christian, 2003). Many such features can be searched for speci
'
cally
during investigation, provided there is a proper appreciation of the
geological and anthropogenic history of the site, as discussed in
