The California Slab design was developed in the San Diego
area of California hence the name. The purpose was to provide a
simplified design approach based on span capacity for use on 1 and 2 story
residential foundations over low to medium expansive soils, typically with
an expansion index =/< 20 (UBC 29-3). When the geotechnical and
post-tensioning engineers agree along with the building official, it can
also be used over soils with an expansion index of up to 50.
Empirical in its approach, this "spanability"
design is characterized by a typically 5 inch thick slab with integrally
cast, turned down edges for both moisture cutoff and perimeter rigidity.
Interior concrete may be thickened where necessary to accommodate
excessive structural loads and/or overturning moments from shear walls.
Often this can result in significantly deepened, monolithically cast grade
beams with additional mild steel reinforcement.