Floating slab for basement/parking garage
Floating slab for basement/parking garage
(OP)
Have any geotechs or structurals that frequent this forum ever used a floating slab (ground-supported slab) for the bottom slab of a building with below-grade levels (e.g. a parking garage) with expansive clay subgrade soils? Just want to know if it is practical and desirable. For example a 2-level below-grade parking garage with clay and clay-shale 50 feet deep. The ground-supported slab and vertical height considerations could accomodate several inches of heave, no? The clays are deep enough to not be affected by near surface moisture fluctuations outside the building footprint, and at depth the only water source would be thin seams of flaggy shaley limestone with groundwater, within the clay-shale formation, so to account for some possible heave, i want to be able to suggest a ground-supported floating slab and not a more expensive structurally supported slab (on the pier foundation elements). Any comments are appreciated.
The building would be water-tight i imagine, and any water infiltration along thin backfill zone behind basement walls will be collected by a drain and sump pump system.
The building would be water-tight i imagine, and any water infiltration along thin backfill zone behind basement walls will be collected by a drain and sump pump system.





RE: Floating slab for basement/parking garage
If you have swelling clays I would think that you would want to maintain the moisture content and I would try to achieve this by using a vapour retarder membrane between the slab and granular fill. In addition, to accommodate movement, I would probably use isolation joints that permit large movement; it may be necessary to undertake a long term maintenance program.
Dik
RE: Floating slab for basement/parking garage
There is at least one parking garage in Clayton, MO (a sub of St. Louis) where the lower level of the garage has swelled 18 to 24 inches. The asphalt dives down at each column, i.e. where the soil is restrained. However, the garage was constructed with enough excess head room that the swell has not caused a problem. The building is ~25 years old.
RE: Floating slab for basement/parking garage
RE: Floating slab for basement/parking garage
Dik