Parking Garage Slab - Hydrostatic Pressures
Parking Garage Slab - Hydrostatic Pressures
(OP)
I understand the physics of concrete slab uplift from installing it below the water table. It is the rho g h concept. In the case we are looking at the geotechnical report indicates that the parking garage should be installed at 321.7 metres above sea level. The water table is 0.5 metres below this level there 321.2 m ASL. The top of the parking garage floor is at 317.5 m ASL. Preliminary calculations give a load of over 1000 lb/sq.ft. This is quite high.
Can anyone provide example calculations for the uplift pressue on this slab?
Can anyone provide examples of alternative construction technologies besides making the slab 3 to 4 feet thick to resist the uplift pressue. We have considered permannet dewatering but the risk of not getting regulatory approval is too high to consider this option.
Regards,
Cvanoverbeke
Can anyone provide example calculations for the uplift pressue on this slab?
Can anyone provide examples of alternative construction technologies besides making the slab 3 to 4 feet thick to resist the uplift pressue. We have considered permannet dewatering but the risk of not getting regulatory approval is too high to consider this option.
Regards,
Cvanoverbeke





RE: Parking Garage Slab - Hydrostatic Pressures
The uplift forces can be resisted in 3 ways:
1) Mass of basement slab acts as ballast, taking advantage of concrete density being about 2.4 x water density.
2) Mass of entire building acting as ballast, by designing the basement slab to span between the columns (think of it as an upside down floor)
3) Similar to (2), except with part of the uplift force resisted by piles or rock anchors in tension.
Note that for methods 2 and 3, you must monitor the ground water to assure that the uplift force is limited during construction.
RE: Parking Garage Slab - Hydrostatic Pressures
Why not look at drainage under the slab to remove that uplift and all the grief of resisting seepage thru cracks or joints?
Sure there may be sump pumping costs, but is that water table always there?
This form of flotation resistance also can be provided by anchorage, as with rock anchors. If H-piles are used, be sure to consider only the submerged unit weights of the soil below. A rough way to figure uplift resistance from an H-pile would be to use the soil within an inverted cone surrounding the pile, with side angle from vertical no more than 20 degrees. Your geotech should be in on these calcs.
RE: Parking Garage Slab - Hydrostatic Pressures
RE: Parking Garage Slab - Hydrostatic Pressures
RE: Parking Garage Slab - Hydrostatic Pressures
RE: Parking Garage Slab - Hydrostatic Pressures
Also, I am envisioning a temporary well point system for dewatering the site for construction. This dewatering may impact the adjacent construction if the water table is lowered substantially beneath any adjacent structures.
RE: Parking Garage Slab - Hydrostatic Pressures
Richard A. Cornelius, P.E.
WWW.amlinereast.com