Fundamental Soil Mechanics - Mathematics and Statistics for the Environment - page 317

12.10 SOIL PHYSICS
Soil is a dynamic, heterogeneous body that is non-isotropic; that is, it does not have the same proper-
ties in all directions. As you might expect, because of these properties various physical processes
are active in soil at all times. This important point was made clear by Winegardner (1996, p. 63):
“All of the factors acting on a particular soil, in an established environment, at a specified time, are
working from some state of imbalance to achieve a balance.”
Most soil specialists have little difficulty in understanding why soils are very important to the
existence of life on Earth. They know, for example, that soil is necessary (in a very direct sense) to
sustain plant life and thus other life forms that depend on plants, and they know that soil functions
to store and conduct water, serves a critical purpose in soil engineering involved with construction,
and acts as a sink and purifying medium for waste disposal systems.
The environmental practitioner involved with soil management activities must be well versed in
the physical properties of soil. Specifically, he or she must have an understanding of those physical
processes that are active in soil. These factors include physical interactions related to soil water, soil
grains, organic matter, soil gases, and soil temperature. To gain this knowledge, the environmental
engineer must have training in basic geology, soil science, and engineering construction.
12.11 STRUCTURAL FAILURE
To this point, we have reviewed the basics involved with applied mechanics. This information is
important to the environmental engineer because, without such knowledge, properly understanding
the construction, function, and operation of workplace machines, equipment, and structures would
be difficult. More importantly, a basic knowledge of applied mechanics also enables the environ-
mental engineer to understand that systems fail, what causes them to fail, and (more significantly)
how to prevent such failures. Many types of failures are possible, and failures occur for many rea-
sons. Structural failures are important to the environmental engineer because when such failures
occur they typically cause damage and injuries (or worse) to workers and others. Structural failures
can be caused by any of the following: design errors, faulty material, physical damage, overloading,
poor workmanship, and poor maintenance and inspection practices.
Design errors are not uncommon. They are usually the result of incorrect or poorly made assump-
tions. For example, the design engineer might assume some load or a maximum load for a design;
however, the actual load may be much different in varying conditions. The 1981 Hyatt Regency
Skywalk disaster (with 114 fatalities and over 200 injured) was caused by underestimating load, a
badly designed and altered structural element design, and the failure to properly calculate and check
the numbers (see Case Study 6.1).
Faulty materials cause structural failures for two main reasons: lack of uniformity of mate-
rial and changes in properties (material strength, ductility, brittleness, and toughness) over time.
Physical damage caused by usage, abuse, or unplanned events (natural or human-generated) are
another cause of structural failure.
Overloading and inadequate support are common causes of structural failure. A particular struc-
ture might have originally been designed to house an office complex and then later reconfigured for
use as a machine shop. The added weight of machines and ancillaries is a change in the use environ-
ment that may overload the original structure and eventually lead to failure because of inadequate
structural support.
Poor and faulty workmanship is a factor that must always be considered when studying structural
failures. Improper assembly and maintenance of devices, machines, and structures have certainly
caused their share of failures and collapses. In fact, one of the major reasons many companies have
employed quality control procedures in their manufacturing and construction activities is to guard
against poor and faulty workmanship.