Shallow Foundation Suggestion
Shallow Foundation Suggestion
(OP)
We are in the early structural design stages for a 100 home housing development in Florida. The houses are 2500 to 3500sqft and two storey constructed from 8" CMU. The site is a reclaimed swamp area, a few test pits indicates visually the top 3 feet is loosely compacted limestone sand fill on top of another 3 feet on medimum dense limsetone fill. No organics or clay and both layers were placed 20 to 30 years ago. The limestone fill is on top of 2 feet of loose sand, followed by 3 feet of "muck". Below the muck is limestone bedrook at 10 to 12 feet below the existing grade. Water is at 6 feet. We are going to request some SPT test on the fill material but from the visual inspection a raft foundation should be okay, however, the developer wants to raise the houses by an additional two feet. Our options are now a strip footing with 2ft stem walls or end bearing auger piles to bedrock with grade beams (costly).
How will the for additional fill under the building influence the spread strip footings' potential bearing pressure and settlement potential? Any suggestions?
What test should we have carried out now and what should we require from the geo-engineer
How will the for additional fill under the building influence the spread strip footings' potential bearing pressure and settlement potential? Any suggestions?
What test should we have carried out now and what should we require from the geo-engineer





RE: Shallow Foundation Suggestion
RE: Shallow Foundation Suggestion
RE: Shallow Foundation Suggestion
RE: Shallow Foundation Suggestion
A Member of
www.civilvillage.com
RE: Shallow Foundation Suggestion
1. As it is a major development, you will need to bring in compactors and likely need to do some grading. Then compact the piss out of the upper fill layer - this will give you a better upper couple of feet of fill.
2. As you have 8 ft of decent fill above the muck, this might/should be enough to consider house raft foundations. In that the developer wants to raise the houses, an older style grillage foundation might be perfect - just think of this as the "divider" cardboard in a case of whiskey bottles. The large D/W ratio will give you stiffness, the height will get you the extra two feet and then your floor slabs (concrete or wooden) could span the grillages.
3. I take it that in the two foot raise, this will not be done by fill.
4. With the stiffened grillage foundation, it should be stiff enough that if there is any differential movement it should be of uniform tilt.
Anyway - this is my early take on the matter - Geotech is imperative even at this early stage.
RE: Shallow Foundation Suggestion
ets1...you make two statements that bother me.....
"Just want creative alternatives before I get the usual safe solution...piles at 12 feet on center." and "I don't think the SPT test will be done because the site is so remote."
If you think you'll only get one predicted recommendation from the geotech, then you need to be a bit more discriminating in your selection. A good geotech will look at several alternatives, not just the overly conservative one. This development is large enough that you might consider paying for a 2nd opinion based on the first geotech's data.
In your second troublesome statement you state that SPT's won't be done because of remote site. Bull$#!^. Pick a geotech who has the capability to do remote sites. It won't be remote after development!
RE: Shallow Foundation Suggestion
RE: Shallow Foundation Suggestion
RE: Shallow Foundation Suggestion
RE: Shallow Foundation Suggestion
Hire an experienced geotechnical engineer. Particularly one with marine experience; the project you have described is not that unusual - I'm currently working on a similar one in South Padre Island. (Minus the organic muck and limestone, of course.)
Sounds like a fun job - where do I sign up?!
Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"