Soil-Structure Interaction Seminar - Foundation Performance ...

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CASE NO. 10 - THE USE OF SPREAD FOOTINGS
During a recent meeting of the Soils-Structure Interaction Subcommittee, there was a
discussion on the use of spread footings. I promised to provide information on
buildings I had inspected with such foundation types. So, here they are.
The first example is a very large home located in the Farnham Parle subdivision,
where home dollar costs can be on the order of seven digits. The relative heights
we measured on the interior floors of this building are shown in Figure 12. It is
very obvious that the floors are very flat. In addition, there was no visible
eviaence of foundation shifting. The building plans showed the foundation to be a
reinforced concrete, grade beam stiffened slab type supported on spread footings.
The soils are lenown to be of a loam consistency on the surface with strong clays
from 6 inches to a depth of 6 feet below the surface (3).
The second example ;sa residential building located in the River Dales Subdivision
of Houston, Texas. The soil type and the foundation design, at least according to
the drawings, was similar to that described in the first example; except, this
structure was over 50 years old. Further, it had not been occupied for at least 2
years and, although it was in a general run-down condition, there were no cracles in
the bricle, no cracles in sheetrocle, and all of the doors fit well in their frames,
despite the fact that no one had watered the ground next to the slab nor had pruned
the trees. The floor height measurements, contained in Figure 13, show the floors
to be comparatively flat.
Certainly, this can not be considered to be a significant statistical sample; but,
it does serve to demonstrate that there is perhaps a place for this type of foundation
design.
CASE 11 - SLOPE VERSUS FAILURE
A concern was recently made that perhaps too much emphasis was being placed in the
use of water level measurements in determining the need for repair. Since I can
only deny this allegation as it might apply to our firm, I wish to cite the two
following examples.
The first example is displayed in Figure 14. This is a one story building that has
a comparatively high degree of slope on the interior. The building is located in
West Houston on a soil that is shown to be relatively non-expansive. Our clients had
executed an Earnest Money Contract on the property and our inspection was in
conjunction with the sale. Despite this slope, there was no foundation-induced
damage on the interior or exterior of the building. Counters, frames, and sills
were level. In fact, the kitchen counter was measured to be over one inch higher
off of the floor at one end than at the other. Obviously, the counter was installed
over a sloping floor. We understand that our clients did purchase the property.
The second example is just the opposite. From Figure 15, it can be seen that the
floors are comparatively level. Yet, there was a comparatively severe amount of
damage to the front of the building. The damage seemed to indicate that the front
showed the soils to be expansive. The movement apparently occurred when gutters were
added. The sequence of events that caused the damage must be speculated. Certainly,
corner had settled but the measurements indicated that it had not. Soils testing
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