Principles of Foundation Engineering, SI Edition, 9th ed, 2019
Updated: Aug 26, 2022
The design of foundations of structures such as buildings, bridges, and dams
generally requires a knowledge of such factors as (a) the load that will be
transmitted by the superstructure to the foundation system, (b) the requirements
of the local building code, (c) the behavior and stress-related deformability
of soil that will support the foundation system, and (d) the geological conditions
of the soil under consideration. To a foundation engineer, the last two factors are
extremely important because they concern soil mechanics.
The geotechnical properties of a soil—such as its grain-size distribution, plasticity,
compressibility, and shear strength—can be assessed by proper laboratory
testing. In addition, recently emphasis has been placed on the in situ determination
of strength and deformation properties of soil, because this process avoids disturbing
samples during field exploration. However, under certain circumstances, not all
of the needed parameters can be or are determined, because of economic or other
reasons. In such cases, the engineer must make certain assumptions regarding the
properties of the soil. To assess the accuracy of soil parameters—whether they were
determined in the laboratory and the field or whether they were assumed—the engineer
must have a good grasp of the basic principles of soil mechanics. At the same
time, he or she must realize that the natural soil deposits on which foundations are
constructed are not homogeneous in most cases. Thus, the engineer must have a
thorough understanding of the geology of the area—that is, the origin and nature of
soil stratification and also the groundwater conditions. Foundation engineering is
a clever combination of soil mechanics, engineering geology, and proper judgment
derived from past experience. To a certain extent, it may be called an art.
This chapter serves primarily as a review of the basic geotechnical properties
of soil. It includes topics such as grain-size distribution, plasticity, soil classification,
hydraulic conductivity, effective stress, consolidation, and shear strength
parameters. It is assumed that you have already been exposed to these concepts in a
basic soil mechanics course.
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