Civil Engineering Reference
In-Depth Information
and stiffness. Geotechnical engineering is simply the branch of engineering that deals
with structures built of, or in, natural soils and rocks. The subject requires knowledge
of strength and stiffness of soils and rocks, methods of analyses of structures and
hydraulics of groundwater flow.
Use of natural soil and rock makes geotechnical engineering different from many
other branches of engineering and more interesting. The distinction is that most engi-
neers can select and specify the materials they use, but geotechnical engineers must
use the materials that exist in the ground and they have only very limited possibilities
for improving their properties. This means that an essential part of geotechnical engi-
neering is a ground investigation to determine what materials are present and what
their properties are. Since soils and rocks were formed by natural geological processes,
knowledge of geology is essential for geotechnical engineering.
1.2 Principles of engineering
Engineers design a very wide variety of systems, machines and structures from car
engines to very large bridges. A car engine has many moving parts and a number of
mechanisms, such as the pistons, connecting rods and crankshaft or the camshaft and
valves, while a bridge should not move very much and it certainly should not form
a mechanism. Other branches of engineering are concerned with the production and
supply of energy, the manufacture of washing machines and personal computers, the
supply, removal and cleaning of water, moving vehicles and goods and so on.
Within civil engineering the major technical divisions are structural (bridges and
buildings), hydraulic (moving water) and geotechnical (foundations and excavations).
These are all broadly similar in the sense that a material, such as steel, water or soil, in a
structure, such as a bridge, river or foundation, is loaded and moves about. The funda-
mental principles of structural, hydraulic and geotechnical engineering are also broadly
similar and follow the same fundamental laws of mechanics. It is a pity that these
subjects are often taught separately so that the essential links between them are lost.
In each case materials are used to make systems or structures or machines and engi-
neers use theories and do calculations that demonstrate that these will work properly;
bridges must not fall down, slopes or foundations must not fail and nor must they
move very much. These theories must say something about the strength, stiffness and
flow of the materials and the way the whole structure works. They will investigate
ultimate limit states to demonstrate that the structure does not fall down and they will
also investigate serviceability limit states to show that the movements are acceptable.
Notice that engineers do not themselves build or repair things; they design them
and supervise their construction by workers. There is a common popular miscon-
ception about the role of engineers. The general public often believes that engineers
build things. They do not; engineers design things and workmen build them under
the direction of engineers. Engineers are really applied scientists, and very skilled and
inventive ones.
1.3 Fundamentals of mechanics
In any body, framework or mechanism, changes of loads cause movements; for exam-
ple a rubber band stretches if you pull it, a tall building sways in the wind and
