| The
condition of the soil
on which a structure
rests is essential
to the buildings stability.
Quite often,
this strategic ingredient
is overlooked by buyers,
sellers, and uninformed
inspectors.
Approximately
one-half of the land
in the United States
contains expansive
soils, which swell
and shrink with changing
water conditions,
causing billions of
dollars in damage
each year to roads,
homes, pipelines and
other structures.
What
are expansive soils,
and what, if anything,
can be done to identify
it and prevent resultant
damage from them?
A
good inspection provided
by an expert in the
field is a prerequisite.
-
Damage
due to expansive
soil usually occurs
when poorly designed
structures
are poorly
maintained.
-
Simple
and inexpensive
preventative maintenance
can greatly reduce
the
likelihood of
problems associated
with expansive
soils.
One key
to such
maintenance
is to keep the
moisture content
of the soil as
constant as
possible.
Positive
grading and the
use of soaker
holes can help.
-
Consult
with a Structural
Engineer for advice
and correct accommodations
as
each structure
has different
construction features.
The
damage to building
structures caused
by expansive soils
is the most costly
natural hazard in
the United States
on an average annual
basis.
In August of
1997, Civil Engineering
Magazine estimated
that in the United
States alone, the
annual cost of damage
to manmade structures
as a result of expansive
soils exceeded nine
billion dollars.
This astounding
number ranks expansive
soil damage with hurricanes,
earthquakes and floods.
EXPANSIVE IS
EXPENSIVE!
There has been
major class action
suits against builders,
land developers and
Realtors, resulting
in awards in the millions
of dollars.
EXPANSIVE
SOIL is found in all
fifty states; however,
higher concentrations
are found in Texas,
Colorado, Virginia,
North Dakota, Oklahoma
and Montana.
This type of
soil demonstrates
an inert ability when
exposed to water,
to expand as it absorbs
it, and shrink as
it dries.
The expansion
of the soil may be
as much as 65%.
One of the
most expansive soils,
known as Adobe, is
found in Texas and
Colorado.
A common name
for clay soils is
Bentonite.
The expansion
and contraction of
soil beneath a structure
tends to exert tremendous
pressure and stress
causing severe structural
damage.
In some cases,
the entire sidewalk
and streets have been
lifted resulting in
severe cracking and
distortion.
Map of the U.S.
Showing Swell
Potential of Reactive
Soils
[Pacific] [Rocky
Mtn] [Mid-Cont]
[Eastern]
See Map Legend
Below
 |
Unit
contains abundant
clay having
high swelling
potential |
 |
Part
of unit (generally
less than
50%) consists
of clay having
high swelling
potential |
 |
Unit
contains abundant
clay having
slight to
moderate swelling
potential |
 |
Part
of unit (generally
less than
50%) consists
of clay having
slight to
moderate swelling
potential |
 |
Unit
contains little
or no swelling
clay |
 |
Data
insufficient
to indicate
clay content
of unit and/or
swelling potential
of clay (Shown
in westernmost
states only) |
|
