Most clay minerals are hygroscopic, meaning they have a tendency to absorb moisture. As the water table naturally fluctuates with local precipitation, the soil beneath a home or other building may shrink or swell depending on the amount of clay within it. If the soil contains a large amount of expansive clays, damage may occur to the structure, especially in times of heavy rainfall or drought.
The most expansive clays (also referred to as "pipe clay") include the smectite group of clay minerals. Smectite is common in some of the formations of the Hawthorn Group. These formations occur near the surface in many parts of north Florida. The chemistry of the water that comes in contact with smectite may contribute to the shrinking or swelling effect. Contractors may recommend soil tests for various types of problem soils including pipe clay before foundation design is finalized.
Organic matter can be extremely common in some subsurface sediments of Florida. The organic matter consists of the remains of wetland plants that were deposited over hundreds of years. Other types of soils may cover these deposits so they can’t be seen at the surface. When organic matter is exposed to air, it can become oxidized and slowly destroyed. It may also lose volume or shrink due to compaction and dewatering. Slow sinking or subsidence results from these processes, and has the potential to cause foundation and structural damage.
Major signs of foundation damage due to problem soils include cracking in walls or moldings, uneven floors, and sticky doors and windows. Damage such as cracking of foundations and other structural problems can also be caused by sinkhole activity as well as problem soils. When this type of damage occurs, homeowners are advised to contact their insurance company. Various tests can be performed to determine the cause of the damage.
December 28, 2020 - 9:32am
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The Florida Department of Environmental Protection is the state’s lead agency for environmental management and stewardship – protecting our air, water and land. The vision of the Florida Department of Environmental Protection is to create strong community partnerships, safeguard Florida’s natural resources and enhance its ecosystems.