Page 7 - Geotechnical Engineering Soil and Foundation Principles and Practice

Introduction
2 Geotechnical Engineering

Geotechnical engineering also is involved in highway engineering and in
engineering for dams.

A more recent application of geotechnical engineering is geoenviron-
mental engineering, which involves assessment, prevention, and mitigation of
ground and surface water pollution from landfills, lagoons, and hazardous
waste sites.

1.3 WHY SOIL IS DIFFERENT

It is important to recognize that soils are different from all other construction
materials. A list of top 11 differences is as follows, ranging from the obvious to the
esoteric. An understanding and utilization of these characteristics occupy a major
portion of this book, and of geotechnical engineering.

1. Soil is cheap—usually—and therefore is our most abundant construc-
tion material. Railway and highway embankments comprise the longest
man-made structures in the world, and earth dams are the largest, many
exceeding the bulk of the Great Pyramid. The interior of the Great Wall
is soil.
2. The weight of the soil itself is a major factor in design, in some instances
being so large that it cannot even support itself, so we have a landslide.
Virtually every structure ultimately derives its support from soil or from
rock; those that don’t either fly, float, or fall over.
3. Soils are extremely variable, ranging from a harsh jumble of angular rock
fragments on a steep mountain slope to massive billows of sand in dunes,
to gentle ripples of sand on a beach, to free-standing hills of loessial silt,
to soft, viscous gumbo that can mire a tank.
4. Whereas most construction materials are specified and manufactured to a
given purpose, soils are simply there, to be either used or avoided depending
on the good or bad qualities they may possess. A geotechnical engineer should
have a sufficient understanding of geology and soil science to reliably identify,
test, and evaluate the relevant soil properties and property variations at a site.
For example, many soils become stiffer and stronger with increasing depth
because of compression under the weight of the overburden. This property
is utilized by building foundations on piles that transfer load downward to
stiffer soils or strata.
5. Soils are not homogeneous solids, but are composed of mixtures of discrete
particles that are in contact and surround jagged, spider-like voids that are
filled with varying amounts of water and air. The properties of soils depend in
part on packing of the particles, which is why soils often are compacted
prior to being used to support pavements or foundations.

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