Beyond the Building Code: Expansive Soils

As defined by ASTM, soils that are susceptible to significant volumetric changes from the addition and/or removal of external elements are deemed “expansive.” Expansive soils associated with clay soil compositions are predominantly encountered throughout the central portion of the United States as well as portions of the southeast and west regions. Although it is not well documented, expansive soils are also encountered adjacent to coal deposits throughout the Appalachian coal region in the eastern United States. Depending on the mineralogy, clay soils comprised of expansive minerals can bond with moisture, causing the volume of the soil to increase with the addition of moisture and decrease with the withdrawal of moisture. This paper will explore tools for identifying expansive soils and factors to consider in the design and construction of ground-supported structures to mitigate the risk of post-construction differential foundation movement caused by expansive soils. It will also explore consequences to ground-supported structures not adequately designed and/or constructed for expansive soils as well as potential remedial measures to address adverse foundation performance.