Void forms under grade beams
Void forms under grade beams
(OP)
I have a one story building in the Houston area where the geotechnical engineer is telling me that they don't want void forms under the grade beams supporting the building because they don't want water to get in the voids. He says to instead to design the grade beams for 1" of uplift.
I have not seen grade beams designed without void forms underneath. That means that the peirs will have to be designed for some uplift load from the swelling soil. Has anyone had any experience designing grade beams without void forms?
I have not seen grade beams designed without void forms underneath. That means that the peirs will have to be designed for some uplift load from the swelling soil. Has anyone had any experience designing grade beams without void forms?






RE: Void forms under grade beams
And, yes you should check the pier for D+H load combination that could create a tension, although it doesn't seem likely you'll be lifted out of the ground unless you have a very light building.
RE: Void forms under grade beams
Closed-cell material will not absorb or transmit water, and will not transmit soil heave pressures to the bottom of the grade beam.
Just a thought.
RE: Void forms under grade beams
I ususally spec a material called 'Frost Cushion'; it's a closed cell foam material that is cut to minimise the uplift. Foam materials often have a crushing strength of 5-10 psi which adds up...
Dik
RE: Void forms under grade beams
RE: Void forms under grade beams
As I think about this problem. I realize that expansion joint material would not work at all. It would not support the weight of the wet concrete.
A bad idea from me. Glad others have good ideas.
RE: Void forms under grade beams
I think your geotech may be a bit off base here. Tell me...how in the world does the presence, or non-presence, of void forms allow water to get to the underlying soils? I see no difference. If there is water draining into the area, then the voids won't add to the presence of the water in the surrounding soils. They simply provide a reservoir for the water...but the water would have been in the soil materials regardless.
I've used void forms under grade beams in the San Antonio area and never had a problem.
RE: Void forms under grade beams
RE: Void forms under grade beams