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From The Ground Up

Dealing with soil’s shrinking and swelling

In Colorado it is called “bentonite.” In California it is referred to as “adobe soil.”

In Mississippi, it is known as “Yazoo clay.”

“It” is expansive soil, a type of soil that contains high concentrations of clay and can shrink and swell as much as 38%. The shrinking and swelling often causes serious damage to improvements of all types on land unless proper precautions are taken.

In Mississippi, a prolonged dry spell of more than 30 days in parts of the state where outcrops of Yazoo clay are present has recently resulted in shifting of structures and breaking of underground pipes. Water mains and gas lines have been victims, causing extra work for municipalities and utility companies. Even highways have become wavy.

Homeowners in these areas of so-called shifting soil have noticed that doors and windows may not close, that floors are no longer level and that cracks are appearing in walls.
Foundation repair companies have stepped up their advertising and are staying plenty busy.

Start by understanding

So, what’s a homeowner or building owner to do?
First is to understand that it is moisture that causes the soil to shrink and swell. Engineers and foundation repair experts will usually tell homeowners that the solution to the problem is to make sure that rain water is drained away from the home. On the other hand, it might be sound advice to say that water should be directed to the home.


Actually, both pieces of advice could be sound. What is really important to understand is that the expansive soil needs to stay at the same moisture level.

In other words, it is the shrinking and swelling that is the problem, and the shrinking and swelling is caused by a change in moisture.

‘Fixing’ a problem

A home builder related a story about a neighborhood that was built on expansive soil.

It seems that just about every house except one had foundation problems. It was a two-story dwelling built on a conventional foundation. One day the house without the problem was sold. Shortly after the sale the new owner was crawling under the house while someone inside was taking a bath.

When the person finished with the bath, she or he pulled the drain plug, and to the surprise of the person under the house a stream of water came splashing to the ground under the bathroom. It seems that when the house was built, the pipe from the bathtub was never connected to the drain pipe. For years, a daily bathtub of water had been poured onto the ground underneath the house.

The next day the new homeowner had the drain connected properly so the water would drain away into the city water/sewer system. In a matter of weeks, the house began shifting, settling and generally coming apart! It was that daily dose of moisture that had kept the soil from shrinking and swelling.

If you’re building…

Expansive soil conditions are widespread throughout the United States, but especially pervasive in some areas of Texas, the Deep South and California. Some cities in California even require foundation inspections as part of their building codes if a house is to be built on expansive soil.

There are several precautions one can take when building on expansive soil.

One solution is to dig out the expansive clay soil and replace it with soil that does not expand and contract so drastically. Sloping the ground away from the structure can also help by draining away water. Another solution is to install a foundation that will withstand the shrinking and swelling. Slab foundations can be pre-tensioned and post-tensioned, as they are called, to conceivably withstand soil movement. Piers and pilings that go deep in the ground below the expansive soil are common solutions.

People building new homes should therefore consider having soil tests done to determine the presence of expansive soil. If such soil is in the area, then an engineer or foundation professional should be consulted to deal with the issue.

And for those who are buying…

Persons buying an existing home should have the foundation checked by a professional if they suspect that the neighborhood is in an area of expansive soil. That suspicion should be aroused if they drive around and notice that the streets are wavy or have dips. Another giveaway is the presence of cracks around windows and doors. If a prospective owner is inside a house, he or she should drop a marble or something round on the floor and watch whether is stays in the same place or rolls away. If it rolls away then the floor is probably not level, and that could be caused by shifting soil underneath.

People moving into a new town might want to check the Yellow Pages and note whether there are a large number of foundation repair companies listed.

Foundation repairs are expensive and can be recurring if the problem is not solved. Consumers should ask about warranties on foundation work, remembering that a warranty is only as good as the company that provides it.

Phil Hardwick’s column on Mississippi Business appears regularly in the Mississippi Business Journal. His e-mail address is phil@philhardwick.com.


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