Expansive Soils & Your Foundation Walls
Hurricanes. Forest Fires. Tsunamis. Earthquakes. No matter where you live, there’s a dreaded natural disaster, the hundred-year act of nature that can destroy your home. But most people don’t know that the most sinister foe to a home’s survival rests just below their feet. The hidden enemy that silently destroys foundations: Expansive Soil.
What is expansive soil?
Expansive soils are clay deposits packed with hydrophilic minerals. These minerals are very similar to the silica beads sold at hardware stores to control humidity in garages and basements. Expansive clays swell with water, compressing everything around them. Through hydraulic pressure, these swollen clays create immense pressure. According to geologists at Louisiana Tech University, the average expansive clay will generate over 5,500 pounds per square foot of pressure as it swells. That means during wet weather, walls set in expansive clay must bear over two additional tons of lateral force.
These clays can expand to over twice their size when wet, and any structure built atop these clays will move with them. When these clay deposits press on concrete foundations, they often cause devastating cracks and allow water a path to infiltrate your home’s foundation.
Why haven’t I heard of this before?
Expansive soil goes by many names. Common names for it expansive clay, heavable soil, shrink-swell soil, with a dozen other regional terms across the United States. It’s not something most homeowners will ever have a reason to think about, a concern of civil engineers and construction companies—until a basement wall cracks down the center
Clay Soil Foundation Problems
Continued expansion and contraction fatigues the structural components of your home. Stress fractures in concrete slabs and cinder block walls can spread unseen until major damage has occurred.
How To Prevent Expansive Soil Damage
The best way to prevent damage from expansive soil damage is to account for expansive soil’s properties before a home is built. To do this, steps should be taken to keep the soil around a home’s foundation at a consistent moisture level.
On soils with a little clay, building the home at the top of a slope is ideal. Water will naturally run down-grade and away from the foundation.
Soils with a heavy mix of clay can combine building the home at the top of a grade with drainage systems, like a french drain around the foundation. All soils naturally swell when wet, and a good drainage system can reduce the difference between wet swells and dry shrinkage that damage foundations.
If there is no option but to build a home on severely expansive soil, contractors can choose to backfill the area of a home’s foundation. First, the clay is excavated to a depth of several feet. Then a sandy, non-expansive soil is filled in. This is an effective solution, but it’s prohibitively expensive in many residential construction projects.
Post-tension foundations are a much more cost-effective measure for building a home on expansive soil. This widely used approach involves steel tendons set into the foundation slabs of a home, which are tightened after the concrete sets. By turning the foundation slap into a giant torsion box, this construction method can create a foundation able to resist the damaging effects of soil expansion.
Landscaping Mistakes that can Damage Your Foundation
Dr. Robert L. Parsons at the University of Kansas warns homeowners that while many focus on the soil as the cause for a damaged foundation, their landscaping decisions are often a major cause of the damage.
Uneven expansion on one side of a home makes the expansion-contraction cycle of clay soils even worse. Common landscaping features can exacerbate uneven expansion and defeat the purpose of drainage systems installed during construction.
Trees or shrubs planted near the edge of a home absorb water through their root systems. This dries the surrounding soil, and many homeowners imagine this might actually help to control the swelling clay soil their home sits on. Unfortunately, trees rarely help in these situations. They dry out the soil around their base, causing it to shrink and contract. The foundation near the tree will sink along with it, and this often causes cracks.
Flowerbeds can cause exactly the opposite problem. Many people enjoy a neat rosegarden running across the front of their porch or along an exterior wall. The problem is, flower beds trap water by their very nature. Potting soil is supposed to stay moist and nutritious to plants. This means the clay beneath the bed will soak up more water as well. Homes with a garden along the outer foundation will thus often develop cracks in the foundation.
If your home is already resting on a site with expansive clay soil, it’s best to use avoid landscaping decisions that trap moisture next to your home.
How to Stop Expansive Soil Damage From Spreading
All of the solutions above are great ways to prevent the problem from happening, but that’s no longer an option if a home has already been built on expansive soils and cracks are forming in the foundation.
If that’s happening, there are steps a contractor can take to stop the damage from spreading and control expansion. If the home has no drainage solution, a French Drain installation might be appropriate to keep the clay’s moisture levels uniform.
There are calcium oxide solutions (commonly called lime treatments) that can be pumped into the ground to stabilize expansive soils. These are often used on highway projects to keep the land under the roadway from buckling. More expensive polyurethane stabilizers, normally used on commercial projects, might also be used as a stop-gap measure.
Subgrade irrigation systems can be installed to keep the soil at a consistent moisture level and limit expansion. Walls may need to be braced and reinforced, and limited backfilling of soil around the foundation might come into play.
Whatever measure is taken to stall the expansion damage, the next step is to repair your foundation. A contractor familiar with basement waterproofing and repairs can assess the damage expansion has done to the foundation and help you decide what should be done to repair it.
If your home is suffering from expansive soil damage, contact Dry Basement Solutions on their website or call 609.647.4555 for a consultation. With more than 25 years of experience in foundation repairs and drainage solutions, they can help save your home from the menace of expansive soil.