AGS / Geohazards / Expansive Soils / General Information
What do we mean by "Expansive Soil"?
To understand why some soils expand, it is important to realize that many soils contain clay. Certain types of clay are capable of absorbing water. Water molecules can actually squeeze into the chemical structures of the clay minerals that make up the soil. When this happens, the clay can actually expand in order to accommodate the water. Expansion can cause significant volume increases in the soil. Swelling can actually cause the ground and anything constructed upon the ground to gradually to be effected. Expansive soils can force concrete foundations, to crack. Conversely, expansive soils can also shrink when water is removed from the chemical structure within the clay contained within the soils. Over time, the continually shrinking and swelling of the clay minerals can render significant damage to buildings and structure over time.
Link to USGS Expansive Clay Map
Expansive Soil Diagram: www.tulane.edu/~sanelson/images/clays.gif