Civil Engineering Reference
In-Depth Information
The allowable load
V
a
is given by
V
a
=
L
f
V
c
(1.5)
where
L
f
is a load factor. Values for
L
f
in geotechnical engineering are normally
in the range 1/4 to 1/3, depending on the sensitivity of the structure to movements
and the uncertainties in the analyses and determination of the loads and the soil
parameters.
1.8 Standards and codes of practice
Construction engineering is regulated by standards and codes of practice. These are
intended to ensure that structures are designed and built safely, economically and of
good quality. These have evolved over many years and are based on theories and
practices which may have become out-dated. They were drawn up by committees and
often contain an amalgamation of current practices and interests.
In the UK, construction is currently regulated largely by British Standards. In this
book I have referred to only three; BS1377 for soil testing, BS5930 for site inves-
tigations and BS8004 for foundations but there are, of course, many others. These
will soon be replaced by Eurocodes and the relevant one for ground engineering is
Eurocode 7: Geotechnical design; EN1997.
As a practising engineer you will often be required to deliver designs which meet
standards and codes of practice. You should, however, ensure that your designs do
not conflict with the basic theories for geotechnical engineering set out in this topic.
In geotechnical engineering it is essential to distinguish between a factor of safety
which is intended to ensure safety and a load factor which is intended to limit
settlements and ground movements.
1.9 Summary
1. Geotechnical engineering is a branch of engineering and deals with the anal-
ysis and design of foundations, slopes and structures made from soils and
rocks.
2. The basic theories of mechanics (equilibrium and compatibility) and of material
behaviour (stiffness and strength) apply equally in geotechnical engineering.
3. The basic behaviour of soil is influenced both by the loads on the soil grains and
the pressures in the water in the void spaces.
4. Soil mechanics describes the relationships between stresses and strains in soils.
These will be dealt with in Chapters 8 to 15. We will find that soil behaviour is
essentially frictional, compressible and largely inelastic.
5. Methods and theories for analysis and design of geotechnical structures, such as
foundations, slopes and retaining walls, and for seepage of groundwater will be
covered in Chapters 19 to 25.
6.
In geotechnical design safe loads are found by applying factors of safety while
movements are often restricted by applying a load factor.
