[California] indoor SOG tied into foundation footing/wall
JX
| Posted in General Questions on
Hello, community,
my client wants to build an attached addition using 2′ continuous footing with about 2.5′ high concrete wall sitting on top, and a SOG within the foundation perimeter. Per the geotech report, the site has expansive soil and 18″ of soil under SOG will be excavated to be replaced with class-II baserock to minimize the slab cracking. In the structural design, the slab will be tied to the foundation footing/wall instead of a floating one that is typically observed with basement construction. Is “tying the slab to the foundation” acceptable here especially from the perspective of slab cracking?
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Replies
I have a Master's in structural engineering and worked in it. But that was decades back. So hopefully you'll get a reply from an SE or PE. That said, here are my thoughts.
Your concern is perhaps slab shrinkage being constrained at the perimeter, causing visual cracking. That seems to me like a valid concern that can be addressed by using a low-water mix with a plasticizer to make it workable as a slab pour. Also space your shrinkage control joints conservatively close together. For a 4" slab I'd typically go no more than 12' between joints. Here I'd opt for 10' at most. Eight feet would be better. Ideally you could pour the slab in separate sections so that you have full on construction joints. Then you could put your control joints further apart or perhaps eliminate them altogether. But that may not be economical for you.
From a structural standpoint I don't see any problems with it, so long as you follow the geotech recommendations.
"using a low-water mix with a plasticizer to make it workable as a slab pour"
Thank you Jollygreenshortguy for this great advice!
"Ideally you could pour the slab in separate sections"
Will this cause cold joint between these sections and increase the risk of water leaking through these cold joints?
Btw, this indoor slab will be 5" SOG. Client may don't like the shrinkage control joints in the slab and might worry about water leaking through these joints.