Parking Garage Slab Uplift From Water Table
Parking Garage Slab Uplift From Water Table
(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 Uplift From Water Table
Usually construct 'pop-outs'... These are loose panels in the slab-on-grade that are intended to fail by lifting when the water pressure is sufficient.
Dik
RE: Parking Garage Slab Uplift From Water Table
Obviously, this is not a cool idea if the high water table is year around.
Mike McCann
MMC Engineering
RE: Parking Garage Slab Uplift From Water Table
I think we are just going to build on big thick piece of concrete. We will provide as much drainage as possible to reduce uplift pressures but you cannot rely on this from a permanent strength solution point of view.
Cvanoverbeke
RE: Parking Garage Slab Uplift From Water Table
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Parking Garage Slab Uplift From Water Table
The base would have to be quite thick to take the pressure and the whole building would have to be designed as a water retaining structure. Good quality Water stops would have to be installed between the walls and the base. A check would have to be done on boyancy uplift forces of the entire structure taking in account friction forces between the soil and the wall otherwise the entire structure may pop out of the ground if the groundwater rises far enough.
RE: Parking Garage Slab Uplift From Water Table
Steve Wagner
RE: Parking Garage Slab Uplift From Water Table
I think one of your biggest problems is building the structure in those conditions, it is very difficult especially if you cannot dewater to a legal point of discharge.
RE: Parking Garage Slab Uplift From Water Table
From a simple point of view, you are right. The building is like pushing a beach ball down under water. The buoyancy forces want to pop the building up. As for your comments on the building weighing enough, there is some validity to your comments. The whole building is 17.35 metres above the average grade and it is concrete construction. We have not calculated the weight of the building yet but I believe it will be heavy enough. I will look for concrete tank designs. I appreciate your feedback.
Response To civeng80
We can get a temporary dewatering permit. That appears to be a relatively easy permit to obtain. The problem is the permanent dewatering permit. The building is a 6 storey condominium therefore the developer does not wish to lose time taking up to 6 months to obtain a permanent dewatering permit that we may not get anyway. The geotechnical engineer suggested that the easiest construction solution is temporary dewatering with a thick slab. It really is a cost issue since you have to pour alot more concrete for this situation than a normal parking garage floor. I appreciate the feeback
Cvanoverbeke
RE: Parking Garage Slab Uplift From Water Table
To cater for this you can dewater during construction and include pressure release valves in the base that will allow water up through the base flooding the garage, if water pressures become too high in the event of something going wrong with the dewatering process. Once the weight of the structure is heavy enough to resist flotation you can stop dewatering.
One thing to be very careful of when dewatering is ground movements in the vacinity which may damage nearby structures (foundation settlement)
RE: Parking Garage Slab Uplift From Water Table
RE: Parking Garage Slab Uplift From Water Table