The Dirt on Problematic Soils
By: Brian Dunagan, PE
As a follow up to our article on cracks in your sheetrock, here is a brief discussion on one of the common factors that can lead to those cracks—expansive soils.
While there are a variety of problem soils, expansive soils are the most common of problematic soils in our region. Expansive soils swell and shrink with changes in moisture content and therefore, the addition and subtraction of water is the primary issue with expansive clay. A common solution in treating expansive clay is removal and replacement with structural fill; the depth of the over-excavation is dependent on the severity of the clay's expansion potential. Another option is to design structural slabs (Post Tensioned Slabs) that resist the movement of the clays or, in some cases, designing a pier foundation system to reach a soil layer that supports a relatively stable moisture content.
It is critical that your designer has as much information as possible to determine if your site has problematic soils. The following are some links that show soils information and explore the issue of expansive soils:
Foundation Repair GuideDamage to Foundations from Expansive Soils by: J. David Rogers, Robert Olshansky, and Robert B. Rogers
In some cases, we suggest engaging a geotechnical engineer to make recommendations for the building foundation design. This may be as simple as them providing a letter with soils recommendations based on other work that has been completed in the proximity of your project. Or, if problematic soils are a possibility, a full investigation may be required.
Jim Smith at Wood Rodgers has a presentation we like called Problematic Soils in Northern Nevada. It is approved for professional development hours and is available by contacting Wood Rodgers. Because of our track record working with Wood Rodgers, we recommend them as a knowledgeable resource for soils information in the Reno, Sparks, Tahoe and Truckee areas.
The more information you have about your building site—whether building a new structure or working on an existing building—the better the design decisions and outcomes.