Expansive Soil and Expansive Clay
The hidden force behind basement and foundation problems
What is an "Expansive Soil"?
Cracked foundations, floors and basement walls are typical types of damage done by swelling soils. Damage to the upper floors of the building can occur when motion in the structure is significant.
Expansive soils will also shrink when they dry out. This shrinkage can remove support from buildings or other structures and result in damaging subsidence. Fissures in the soil can also develop. These fissures can facilitate the deep penetration of water when moist conditions or runoff occurs. This produces a cycle of shrinkage and swelling that places repetitive stress on structures.
How Many Buildings are at Risk?
Even though expansive soils cause enormous amounts of damage most people have never heard of them. This is because their damage is done slowly and can not be attributed to a specific event. The damage done by expansive soils is then attributed to poor construction practices or a misconception that all buildings experience this type of damage as they age.
Expandable, Shrink-Swell, Heavable Soils?
Expansive Soils Map
How to Interpret the Map
All construction projects should include a soil analysis to identify the types of soil present and determine their expansive properties. Local occurrences of expansive soils can be found in all of the soil categories shown on this map.
Why Do These Soils Expand?
Changes in Moisture Content Trigger Damage
The Bottom Line
- Testing to identify any problems
- Design to minimize moisture content changes and insulate from soil volume changes
- Build in a way that will not change the conditions of the soil
- Maintain a constant moisture environment after construction