Geotechnical Engineering · Engineering Glossary
Expansive soils are clay-rich soils that swell significantly when wetted and shrink when dried, exerting uplift pressures on foundations and slabs that can cause severe structural damage if not properly addressed in design. They are common in arid and semi-arid climates across the western and southwestern United States.
The potential for expansion is measured by the plasticity index (PI) and expansion index (EI) from laboratory tests. High-expansion soils can exert uplift pressures of several thousand psf — far exceeding the weight of a typical light-frame structure. Mitigation strategies include deepening foundations to extend below the active moisture zone, pre-wetting and compacting the subgrade, replacing expansive soil with non-expansive fill, or using post-tensioned slabs designed to resist the differential movement. The geotechnical report will classify the expansion potential and specify mitigation measures. Apex Grid engineers foundations and slabs to match the geotechnical engineer's recommendations for expansive soil conditions.
Apex Grid Engineering maintains this glossary as a resource for architects, contractors, developers, and property owners who encounter unfamiliar engineering terminology on their projects.
View All Engineering TermsApex Grid's licensed PEs provide geotechnical engineering services across multiple jurisdictions — with fast quote turnaround and permit-ready documents.
Request a Proposal