If you plan basement construction in an area that has
clay in the soil, you need to take precautions to avoid structural
damage to your home. So here are a couple tips to consider before you
start basement construction in clay soils.
Before you start basement construction you need to know what type of
soil you are building on. The U.S. Department of Agriculture has soil
information on most of the United States. Soil testing can also be done
so you will know what you are working with. Another important step is to
make sure the ground is compacted. Failing to compact the ground
properly can also lead to trouble in the future.
Expansive clay soils, such as bentonite and montmorillonite, can cause
structural damage to basements and home foundations when proper
precautions aren’t taken during construction. When deciding to build a
basement in an area that has clay soil you need keep in mind the nature
of the soil that you plan to build on. Clay holds moisture and as the
seasons change the amount of moisture in the soil also changes.
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| If you build on clay when it is holding large amounts of moisture, you
can have your basement sink as the moisture content of the soil
decreases. If you build while the moisture content is low, your basement
may be pushed up when the moisture content increases. This can end up
causing structural cracks. There are several ways to deal with the
seasonal changes in the moisture content in clay when you are
constructing a basement.
Before putting in the basement, you need to be building on
stable ground. With clay in particular, it is important to make
sure you have the ground compacted properly so you do not end up
with the ground shifting under the weight of your home.
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It is possible to treat the soil
with a lime mixture to increase stability and control swelling. This is
done by removing a layer of the soil and adding several trenches under
the area you want to construct your basement or foundation. Once you
have the trenches in place you fill them with a lime mixture. This
treatment adds about a month on the time you are going to need for
construction.
Basements that are built in clay soil need to be able to breathe or move
up and down slightly with the ground water in the soil. Concrete floors
are not attached to the concrete foundation so that this movement
doesn’t cause structural damage. To allow for this movement, all
internal walls in the basement need to be “floating walls” or raised
walls. Floating walls are suspended from the first floor and have a gap
between the wall and the concrete floor slab. When you build in some
areas you are actually required to use floating walls in basement
construction. When you obtain your building permit you need to find out
of this is a requirement for your area.
When basement construction includes plumbing, a reverse of this floating
wall process is required. The floating walls are attached to the floor
to create a solid base and the space is at the top of the wall in these
cases. Expansion joints and flex lines are used for basement plumbing
when working in clay soil to allow for the natural movement with ground
moisture changes. Space must be left for pipes to reduce the risk of
pipe breakage.
U.S. Department of Agriculture
http://websoilsurvey.nrcs.usda.gov/app/
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