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Old Posted Jun 26, 2020, 3:28 AM
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ardecila ardecila is offline
TL;DR
 
Join Date: Jun 2006
Location: the city o'wind
Posts: 14,469
Quote:
Originally Posted by WestsideLA View Post
So there's no real structural reason for an underground foundation in Chicago? I'm just asking because the Study Hotel and Rubenstein Forum are side by side, as you know. They spent months digging out the foundation for the Rubenstein, but the Study Hotel is just as tall, or so it appears, and yet they built it at ground level.

Maybe this changes for a tall skyscraper but I guess at lower level you can get away with a ground level foundation.

I ask this as a layman. I'm not in the contraction business and don't really know the engineering considerations.
The basement isn't a requirement of a deep foundation system. You build a basement because you need the extra space, especially for things that are necessary but unattractive (parking, storage, utility stuff). A deep foundation in Chicago is usually a caisson system, and you can drill caissons from ground level just as easily as from Level -1.

This is for large commercial projects, of course. For homes, especially small ones, the need to put (shallow) foundations below the frost line at 5 feet down means you're already basically doing all the work to dig out a basement space, so you can either backfill that space after the foundations are poured and waste the effort, or pour a basement floor while you have it dug out and put it to good use.
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