Page 16 - Geotechnical Engineering Soil and Foundation Principles and Practice

Introduction
Introduction 11

Terzaghi also conducted full-scale studies of pressures on retaining walls in order
to test the Coulomb and Rankine theories, and dared to suggest that they might
be oversimplified by ignoring an influence from soil arching.

What Is the Classical Approach?
The research methods of Marston, Terzaghi, and many others may be regarded
as the ‘‘classical approach’’ in geotechnical engineering research. This involves:
(1) field observation by a trained eye, (2) development of a theory to try and
explain the observations, (3) experimentation to test and if necessary modify the
theory, and (4) simplifications to put the new-found knowledge into practice.
A fifth element is to maintain a positive outlook and never give up. Research
that omits one or more of these steps may be fatally flawed. For example, it
recently has become commonplace to publish computer-based analyses without
experimental verifications in unintended support of the adage, ‘‘garbage in,
garbage out.’’

In 1943, Terzaghi summarized classical soil mechanics theories in a book
appropriately titled Theoretical Soil Mechanics, which still is in print. In 1948 he
collaborated with a former student, Ralph Peck, to stress practical applications in
another important book, Soil Mechanics in Engineering Practice, which remains in
print in revised editions.

1.14 SOIL AS A CONSTRUCTION MATERIAL

In 1906 C. M. Strahan, a county engineer in Georgia, began a systematic study of
the distribution of particle sizes in gravel-road surfaces in relation to road quality
and performance. Strahan’s conclusions from these correlative studies provided
the basis for later research in granular soil stabilization that now plays an
important role in the design and construction of highways and airport runways.

A contribution of outstanding importance based purely on experimentation is
that of Proctor, who in 1933 defined modern principles of soil compaction by
showing a relationship between compaction energy, moisture content, and density
of a compacted soil. Proctor’s test and its derivatives now are standards used in
construction of virtually all soil structures including earth embankments, levees,
earth dams, and subgrades for foundations or pavements.

1.15 SOIL CLASSIFICATION

In the 1920s, Terzaghi and Hogentogler introduced a scheme for soil classifi-
cation that became the basis for the ‘‘AASHTO classification’’ used in highway
work. In the 1940s, Arthur Casagrande of Harvard University introduced

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