Specialists know
that; the stability and performance of a structure founded on soil depend on
the subsoil conditions, ground surface features, type of construction, and
sometimes the meteorological changes. Subsoil conditions can be explored by
drilling and sampling, seismic surveying, excavation of test pits, and by the
study of existing data.
Elaborate site
investigation oftentimes cannot be conducted due to a limited assigned budget.
For very favorable sites, such investigation may not be warranted.
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| Site Investigation |
However, if the area
is suspected of having deep fill, a high water table, or swelling soil
problems, extensive soil investigation will be necessary even for minor
structures.
The soil engineers
should not accept jobs in problem areas without thorough investigation. Bear in
mind that in court of law, limited budgets or limited time frames are not
excuses for inadequate investigation. Differing site conditions are a favorite
tool of the contractors. They are used as the basis for extra claims on their contracts.
Since a consulting
soil engineer cannot afford to treat each site as a potential hazard area, the
amount of investigation required will generally be dictated by the judgment and
experience of the engineers. If the project is completed on time and under
budget, the consultant may still be criticized for being too conservative. On the
other hand, if problems are encountered in the project, no number of excuses can
relieve consultants of their responsibility.
Basic
Data for Site Investigation:
As a consultant,
site investigation is probably one of the most important parts of the total
inquiry or the soil report. Average owners know very little about engineering,
but they do know a great deal about the property they own. Misrepresentation of
the observations can often cause a great deal of trouble. For instance,
describing the property as located in a low-lying area may devalue the
property. Pointing out the cracks in the building owned by someone else in the
neighborhood may induce the buyer to decrease the offer and in extreme cases
may result in litigation.
Valuable information
about the presence of fills and knowledge of any difficulties encountered
during the building of other nearby structures may be obtained from talking to
older residents of the area.
Much of the site
investigation depends on the experience and good judgment of the field engineer
or the technician. An experienced field engineer has the sense of a bloodhound;
he is able to smell or sense a problem when he visits the site. A red flag will
be raised to call for thorough investigation. In a potential swelling soil
area, special attention should be paid to the condition and foundation system
of the existing
Structures: When the
site is located out of town, consulting engineering firms sometimes assign site
investigation to a technician or a field man, who has little geotechnical experience.
He may ignore some important features which should be pointed out in the
geotechnical report. An experienced technician with many years of training in a
geotechnical company can be worth more than an engineer freshly out of college with
a Ph.D. degree.
Generally, it is a
small building with inadequate funding, poor planning, and a low-bidding
contractor that presents the most trouble the owner of such project.
Generally considers
soil investigation as a requirement fulfillment rather than a protection
against foundation failure. Geotechnical engineers should ask for more details
regarding the site condition and proposed construction before accepting such assignments.
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