Differnetial settlement
Differnetial settlement
(OP)
Our structural office had started getting Soils Reports that indicate we should expect settlement in a thrity foot diameter circle, located anywhere across the building site. They give an expected range of settlement, just no location. Corner of the building gets real interesting.
This sounds like a CYA item their insurance company insisted they put in.
We're in So. Cal. Has anyone else out there had soils reports like that and if so, how did you handle it. Seems to me the soils guys should at least supply a spring constant for an elastic foundation analysis. The plan checkers are at a loss about what to do too.
Lonnie P.
This sounds like a CYA item their insurance company insisted they put in.
We're in So. Cal. Has anyone else out there had soils reports like that and if so, how did you handle it. Seems to me the soils guys should at least supply a spring constant for an elastic foundation analysis. The plan checkers are at a loss about what to do too.
Lonnie P.





RE: Differnetial settlement
If you want a detailed location for a specific settlement, then you had better pay for borings about 10 feet on center through the area and beyond. In any case, a phone call usually will clear up the question.
RE: Differnetial settlement
http://www.soilstructure.com/
RE: Differnetial settlement
I have a two story classroom building 150' long. Live load is 1200#/ lin. ft. Dead load is 1400#/ lin. ft. The soils engineer has given me approximate settlement numbers for both live and dead AND differential settlement numbers for both.
My question - in the thirty foot long section of footing that's 'settled', how much upward soil pressure is still present to offset the applied downward loads. Or do I assume total loss of soil pressure in that area?
Next question - If I have reduced pressure in the thirty foot area, I have to transfer the unresolved downward loading to the 'unsettled' footing on either side of the 'thirty foot settled area'. How long of a redistribution length should be used and wouldn't this area then also settle even more which would slightly reduce the differential settlement.
Obviously this a problem in indeterminate statics - hence the need for spring constants (K values?) or even two spring constants, one for the 'unsettled' footing and another for the area subject to greater settlement.
I called soils engineer with the above discussion and he said "He'd have to think about it." Still waiting.
On a similar soils report I went through the same thing and finally suggested a soils pressure profile I'd like to have and the Geotech wrote a letter suggesting that would be adequate. Not really what I was hoping for but at least we could move forward. The footing got huge! and the cantilevered condition at the end of the building got interesting.
The issue here is what to do with a long footing, not several isolated ones.
Lonnie P.
RE: Differnetial settlement
RE: Differnetial settlement
I was hoping someone who has also delt with this issue would see my post and let me know how they resolved it. On the previous project with this comment in the soils report (different Geotech), the plan checker suggested using piles. Then we thought the pilings would still be in the same 'sagging' soil, so that wouldn't work either. If fact, the sagging pile could make thing worse buy pulling downward.
I agree, I haven't supplied near enough info for a real solution. Just a general suggestion of which direction to look for a solution. I'll probably see if the Geotech more guidance than the last one did.
LonnieP
RE: Differnetial settlement
settlement is not new. differential settlement is not new. it has always been a possibility in California because of the higher potential for earthquakes and the possibility of settlement caused by them. However to expect that your building and foundation does not settle right along with the ground is not a reasonable assumption. So, not sure how this really should change your design.
RE: Differnetial settlement
RE: Differnetial settlement
LonnieP