Page 12 - Geotechnical Engineering Soil and Foundation Principles and Practice

Introduction
Introduction 7

variable the soil and the more comprehensive the investigation, the lower can be
the factor of safety.

Increasing a factor of safety by as little as 0.5 can add substantially to cost, so it
often is advantageous to try and trim the factor of safety by having more soil tests
and improving statistical reliability of the results. Thus, an inexpensive test that is
performed many times may be more accurate and create more confidence than an
expensive and more sophisticated test that can be performed only a few times for
the same amount of money.

The factor of safety also may be lower where occasional failures are acceptable.
An example is highways, where periodic repairs of weak spots is more cost-
effective than overdesign of an entire project. On the other hand, an earth dam
whose failure would endanger thousands of lives obviously requires a more
reliable and conservative investigation and factor of safety.

1.8 ANCIENT APPLICATIONS OF GEOTECHNICAL ENGINEERING

The first human uses of soil and rock as engineering materials is lost in antiquity.
Neanderthal or his predecessors may have been the first to recognize the
advantage of structural engineering as they used a log to bridge a stream, but most
effort probably was focused on simply staying alive. As glaciers receded, climatic
changes raised lake levels, so people of the early Iron Age supported their lakeside
dwellings on piles. Paved highways existed in Egypt several thousand years B.C.E.,
and were used by the pyramid builders for transportation of the construction
materials. Remnants of underground cisterns, drains, tunnels, and aqueducts, and
many other structures involving soil, have been unearthed at the sites of early
Middle Eastern civilizations. Ancient engineers encountered and solved many
practical problems in soil engineering, based on experience and trial and error.

Some primitive structures reveal an unexpected level of sophistication. Early stone
arches as well as Inuit (Eskimo) igloos follow the ideal shape of a catenary similar
to the St. Louis Arch, so sides do not sustain any bending moment, compared
with the circular arches and domes of classical European architecture that
required lateral support from columns and flying buttresses. There is a Darwinian
factor in engineering, survival of the fittest.

1.9 EARLY LITERATURE ON SOIL ENGINEERING

In 1687, a French military engineer named Vauban set forth empirical rules and
formulas for the design and construction of revetments to withstand lateral soil
pressures, and nearly 200 years later, Wheeler, in his Manual of Civil Engineering,
recommended the rules of Vauban for U.S. Military Cadets.

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