Foundation Over Foundation

[sharingamak]

Hello
In the case where we are forced to design a foundation over another foundation, What are the precaution to take in term of calculation and construction, and is this design okey?
Thank You

 

[r13]

1) Involve a geotechnical engineer, and ask for recommendations, and best practices under given situation.
2) It is not unusual to have foundations at different elevations. The important thing is the higher foundation, including soil compaction, will put additional pressure on the lower footing, and if the lower footing settles, it tends to bring down the upper foundation. Also, attention shall be set on how to stabilize the existing foundation, the structure it supports, throughout the construction period.

 

[dhengr]

Sharingamak:
In the case of the higher elev. ftgs., why not make them a little longer in the N-S direction (in & out of the page) and a little narrower across the page? Then, you would be able to lower them to the same elev. as the lower ftgs. The two larger ftgs. might be made one long ftg. to support the two cols., if the cols. are close enough to each other. As mentioned by Retired13 above, you do have to pay attention to how settlements and soil pressures due to the two different ftgs. might interact and impact each other.

 

[msquared48]

I agree with dhengr.

Mike McCann, PE, SE (WA, HI)

 

[PEinc]

I agree also. Or, put all or, at least,the higher foundations on piles. However, piles probably would be more expensive. The solution could depend on if all of the foundations are new or if the deeper foundations are existing.

http://www.PeirceEngineering.com

 

[mchen96]

I also vote for lowering the higher foundation. For something like this, I'd probably combine both footings into a single, larger rectangular one.

Having one footing on top of another just seems like asking for trouble. Besides the fact that differential settlements could be a problem, the upper footing will also impart an additional load onto the lower footing that would need to be considered when determining the geotechnical capacity.

 

[IRstuff]

Huh, so 3000 yrs from now, some archaeologist is going to find this structure, after reading about how many times ancient cities like Rome and Troy were built on top of previous versions.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[r13]

IRstuff,

You should be grounded

 

[msquared48]

Nothing new for him...

Mike McCann, PE, SE (WA, HI)