Geology Reference
In-Depth Information
engineering geologist. The bias here is towards UK practice.
In traditional design, uncertainties are dealt with by adopting a FoS. This gives a broad protection against
the inherent uncertainty in models, calculations, loads, strengths, workmanship and so on. If the site conditions,
such as geological model and geotechnical parameters, are understood well or if potential consequences are
minor, then a low FoS might be adopted. Where less certain or the risk is greater, then a higher FoS is adopted.
In the Eurocode approach, rather than assuming a global FoS, it has been taken as fundamental that different
parts of the calculation are known with different certainties; this is certainly true in many situations and is a
re
nement to design philosophy. Partial factors are then applied to material properties, resistances and/or
actions (loads), according to the level of uncertainty. The Eurocode clauses are written as Principles and
Application Rules. Principles use the word
'
'
shall
and are mandatory, whereas Application Rules use the
words
and allow more judgement. Although this use of language suggests a more
prescriptive approach than in earlier codes, in practice, the Eurocodes provide a similar level of latitude for the
designer. For example, in assessing geotechnical risk, Eurocode 7 contains Application Rules that de
'
may
'
,
'
should
'
and
'
can
'
ne three
geotechnical categories, and alternative methods are allowed for assessing geotechnical risk. For routine
design cases, the geotechnical design may be assessed by reference to past experience or qualitative assessment. For
complex or high-risk situations, e.g. weak/complex ground conditions or very sensitive structures, Eurocode 7
allows the use of alternative provisions and rules to those within the Eurocode. In such situations, rational design
based on site-speci
c testing and numerical modelling might be more appropriate. Detailed guidance is given in
Bond & Harris (2008).
Limit state design approaches are used elsewhere, similar to current European practice. For example, Canadian
practice has moved in that direction and AASHTO (2007) is used in the USA and internationally for the design
of major projects such as the 2
nd
Incheon Bridge in Korea, completed in 2009 (Cho
et al
., 2009a).
ict with
others prepared in other countries or by international learned societies,
not least in terminology for soil and rock description and classi
Sometimes locally mandatory codes or guidelines con
cation,
with the same words used in different codes to mean different things.
The engineering geologist who wishes to work in different countries
needs to be aware that the standards and terms that he will need to use
may change from country to country. He also needs to be aware that
the advice given in codes and working party reports regarding geolo-
gical matters is often generalised and sometimes dif
cult to adopt; for
example, guidance prepared for temperate zones may not be applied
readily in tropical areas and vice versa. This is addressed in more detail
in
Chapter 4
and Appendix C when discussing soil and rock descrip-
tion for engineering purposes.
Despite codes of practice and standards, ground conditions con-
tinue to be the major source of
failure in civil engineering
projects
through catastrophic failure or unacceptable performance
and even more commonly due to claims, delay and litigation. In
hindsight, the problems can often be attributed to inadequate site
investigation, incorrect interpretation of the geological conditions or
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