Void Boxes under Tiltwall Panels- Useful??
Void Boxes under Tiltwall Panels- Useful??
(OP)
I'm in the commercial tiltwall construction business and have heard more and more people talking about needing to put 12" void boxes underneath the tiltwall panels spanning between the drilled piers.
How is it that a panel which weighs about 40,000 lbs. and has a thickness of only 6-7 inches can be lifted upwards by an expansive soil ?
It seems to me the shear weight of the wall would counter any potential for vertical rise or expansion of the soil.
Thanks, Pat.
How is it that a panel which weighs about 40,000 lbs. and has a thickness of only 6-7 inches can be lifted upwards by an expansive soil ?
It seems to me the shear weight of the wall would counter any potential for vertical rise or expansion of the soil.
Thanks, Pat.






RE: Void Boxes under Tiltwall Panels- Useful??
RE: Void Boxes under Tiltwall Panels- Useful??
Right. I agree, but how do i figure the 'expansive uplift pressure' exerted by the existing subsurface clay?
Is this force a function of P.I. or liquid limit? or is there some equations explaining it?
and when it expands, wouldn't some of the uplift pressure be dissipated into the sourrounding soil?
Thanks,
Pat.
RE: Void Boxes under Tiltwall Panels- Useful??
Clays are generally produced from a feldspar type of rock and may only be a few molecules thick, but are much longer and wider.
The swelling characteristics, I understand (and may be subject to being beaten for error), come from molecular scale electrical charges on these small clay 'platlets' having an affinity to water (water is a polar type molecule and would attach to the platlet surface). I would suspect that the magnitude of the molecular charge would determine the affinity to water and, hence, the degree of swelling and swelling pressures. Different types of feldspar would produce different types of clay and the variation in composition would be the determining factor. It is also likely modified by any salts that become 'attached' to the platlets.
I can see some of it being dissipated to surrounding soils as easily as I can picture the swelling surrounding soils having an effect on it.
RE: Void Boxes under Tiltwall Panels- Useful??
A narrow (6") panel doesn't have much surface area but I never knew any geotechs down there who would recommend otherwise.
RE: Void Boxes under Tiltwall Panels- Useful??
Here in Austin... it'll be solid rock for 10 feet then whammo, Super sponge clay for 10 feet...
We specialize in tiltwall construction and I'm the only engineer here... it's a pretty country-fied organization and thus there's a lot of ''That's just the way we do things''. So, I'm constantly faced with the dilemma of explaining the basics of engineering to my Superintendents.
I suppose on highly expansive soils that lay over the entire lot as shown in the soils boring report, I'll go ahead and use void boxes.
Gracias,
Hey 'JAE'... I'll be in San Antonio for the Cinco De Mayo soccer tournament this weekend... Where do I party? and particular place on the river walk? Besides the super-commercialized touristy ones like Dicks last resort? maybe a dive or two... with a Dartboard???
RE: Void Boxes under Tiltwall Panels- Useful??
You really can't go too wrong anywhere in SA. Have fun!