Half and half foundation-Piles & Shallow footings
Half and half foundation-Piles & Shallow footings
(OP)
So this is somewhat a theoretical question. A new proposed building 330'x200', 3 stories, in schematic design. Nearly half the borings show that the building will be OK @ shallow footings, while the west half has either to be excavated and refilled, comapacted to 8' or we can go to deep foundations.
The arch asked me if it was OK to have half the building on shallow ftgs and half on H piles. My response was that there will be significant differntial settlement since piles are somewhat rigid support compared to footings which will settle. Any thoughts?
The arch asked me if it was OK to have half the building on shallow ftgs and half on H piles. My response was that there will be significant differntial settlement since piles are somewhat rigid support compared to footings which will settle. Any thoughts?






RE: Half and half foundation-Piles & Shallow footings
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Half and half foundation-Piles & Shallow footings
RE: Half and half foundation-Piles & Shallow footings
You are absolutely right. Use one or the other but not both.
BA
RE: Half and half foundation-Piles & Shallow footings
What we did was use drilled concrete piers on one half (soft, expansive clays with shale about 30 feet deep) and on the other half used spread footings.
Now we knew that the spread footings would tend to have more settlement than the deeper, "fixed" piers so as the spread footings got closer to the piers, we started diminishing the allowable soil pressure....i.e. using larger and larger spread footings...until we got to the fault line where the footing type changed to piers and suspended grade beams.
At that point we added a building expansion joint as near to the fault line as possible.
This was in 1985 or so - no problems since.
RE: Half and half foundation-Piles & Shallow footings
RE: Half and half foundation-Piles & Shallow footings
Firstly, I would discuss this in detail with the geotech (if there is not one then get one!).
If you are bearing on the same strata with similar bearing stresses then you should be okay. But this will depend on what lies beneath i.e. thickness of this strata, depth to water table e.t.c.
RE: Half and half foundation-Piles & Shallow footings
Kieran
RE: Half and half foundation-Piles & Shallow footings
RE: Half and half foundation-Piles & Shallow footings
Why do the strains necesarily need to be incompatible? Surely for many situations it is possible to control the stress in order to negate the difference in strains. Hard work, yes, but impossible, no.
In some strata, I would say that the worst thing you could do for strains would be to locate everything on shallow footings.