Waffle slab foundation

rdf:langString Waffle slab foundation

rdf:langString The Wafflemat foundation system, also called a waffle slab foundation, is an above-ground mat foundation used to provide load-bearing capacity on expansive, rocky, compressible, or hydro collapsible soils. The slab is created by placing a series of plastic forms ("Waffleboxes") that are either 8.5 or 12 inches (220 or 300 mm) in height, and 19 by 19 inches (480 mm × 480 mm) in plan, directly on grade to create a waffle-like grid of ribs, and then monolithically pour a post-tensioned reinforced concrete slab over the Waffleboxes. The completed slab then sits on the ground as a 'raft', with the void areas underneath the slab allowing for soil movement. The waffle slab is very stiff, with the cross section providing the needed strength to resist differential swelling resulting from landscaping practices, surface drainage, or flooding from any source. It does not require presoaking underlying soil pads, and there is no need for footings, meaning no earth spoils. And, since the slab section is typically 12.5 to 16 inches (320–410 mm) above grade, it typically does not require a capillary break or moisture barrier. Current design practice provides post-tensioned on-grade slabs with stiffness equal to or better than other post-tensioned slab types, but with less susceptibility to swell pressures exerted by expansive soils. An on-grade Wafflemat foundation provides all of the elements of the in-ground rib and uniform thickness slabs, but with greater performance provided by its geometry and smaller contact area with the soils.