Civil Engineering Reference
In-Depth Information
Figure 1.5
Geotechnical structures.
causes leakage through a dam and governs the yield of a well and it also governs the
variation of pressure in the groundwater.
The structures in Fig. 1.5 clearly should not fail. There are, however, situations
where the material must fail; these include excavation and flow of mineral ore or grain
from a storage silo. Solutions to problems of this kind can be found using the theories
of soil mechanics. Other problems in geotechnical engineering include movement of
contaminants from waste repositories and techniques for ground improvement.
1.7 Factors of safety and load factors
All structural and geotechnical analyses contain uncertainties of one kind or another.
These may involve uncertainties in prediction of maximum loads (particularly live
loads due to wind, waves and earthquakes) approximations in the theories adopted
for material behaviour and structural analysis, and uncertainties in the determination
of strength and stiffness parameters. To take account of these approximations and
uncertainties it is usual to apply a factor of safety in the design. These factors may
be applied as partial factors to reflect the various uncertainties or as a single lumped
value.
All applied sciences that analyse and predict natural events involve assumptions,
approximations and simplifications because the real world is very complicated. Many
people believe that the uncertainties in geotechnical engineering are very large because
of the variability of natural soils in the ground and the apparent complexity of theo-
retical soil mechanics. It is true that geotechnical engineering is less exact than many
