Drainage
Different soil types (gravel, sand, silt, and clay) have different drainage characteristics. The soil in this area has a high clay content, i.e. when the expansive clay soil gets wet, it expands, when it gets dry, it shrinks. In extreme cases, expansive clay soil can exert up to 2,500 lbs of pressure per square foot on a foundation. It is highly recommended a year round water maintenance program be put in place to keep even moisture content in the soil.
All diagrams are from Code Check ® - Building, by Michael Casey, The Taunton Press, 2003. Code Check itself is based upon the International Residential Code (IRC) for 2003.