The Definition of Expansive Soils

Expansive soils can cause cracks in building foundations.

Expansive soils are soils that contain water-absorbing minerals. These soils expand as they take in water. Expansive soils can cause nightmares for homeowners and architects because they can damage buildings and other structures due to the force they exert as they expand.

Properties

Expansive soils contain clay or other minerals that cause them to expand when absorbing water. According to the Geology website, these soils often expand by 10 percent or more during a rainfall. When the soils dry out, they shrink back to their original size.

Damage While Expanding

When soils expand, they put pressure on structures. The Geology website claims they exert enough force to crack foundations, floors and walls. The most damage is usually done to the lower levels of the structure, although damage to higher levels may also be sustained if the soil expansion causes motion within the structure.

Damage While Contracting

If a structure is built while the soil is expanded, damage can occur when the soil dries out and shrinks. According to Geology, soil shrinkage can weaken structural support. This puts buildings at risk of collapse.

Soil Fissures

When soil contracts, it can cause fissures, or splits, in the soil itself. Geology claims that these splits can cause water to penetrate more deeply into the soil. This causes a cycle of expansion and shrinkage that puts continual pressure on the structure. The repetitive pressure can weaken structures.

Why Do Soils Expand?

Expansive soil expands due to the clay content. Soil with little clay content will expand only a little bit, while soil with a greater amount of clay content will expand more. According to Geology, most clay expansion is triggered by water, but some expansion can be triggered by changes in temperature.

References

• Geology: Expansive Soils and Expansive Clays--The Hidden Force Behind Basement and Foundation Problems