Bearing Capacity of 95% compacted fill
Bearing Capacity of 95% compacted fill
(OP)
We need to place a spread footing on a 95% compacted fill. The EOR requires 5000 psf. I am getting conflicted information. One of which that with 95% compacted you cannot reach 5000 psf; the other is that you cannot use DCP to verify that; and 95% automatically gives you the 5000 psf. HELP please?





RE: Bearing Capacity of 95% compacted fill
RE: Bearing Capacity of 95% compacted fill
RE: Bearing Capacity of 95% compacted fill
What do you think?
And thanks a lot.
RE: Bearing Capacity of 95% compacted fill
RE: Bearing Capacity of 95% compacted fill
Without any other information I would guess 2000-2500 psf for a silty sand.
For a building of any size, the pressure bulb would be below any level where you could take samples and run Proctor tests.
Why is the EOR specifying the bearing capacity? This should be done by the geotech.
If you really need 5000 psf you are probably looking at ground improvement techniques such as stone columns or even piles.
How deep is the silty sand strata? Do you have underlying rock?
RE: Bearing Capacity of 95% compacted fill
RE: Bearing Capacity of 95% compacted fill
RE: Bearing Capacity of 95% compacted fill
"The Design of foundations for Buildings" by Johnson and Kavenagh, 1968 on page 163 is quoted. This is for the SM, SW and SP sands, generally below the #4 sieve.
"N valuers not withstanding, experience seems to indicate that the bearing value of sands need not be taken as less than 2 tons per square foot,, unless some special consideration of impact or vibratory loading (earthquake , for example) exists." Although they say it depends on compaction and grading.
I'd look at where it sits as to relative density. 95% of Modified probably is way up there, near 100%
"Foundation Engineering" by Peck, Hanson and Thornburn, on page225 has a chart with N values, footing width and bearing showing a 5 foot wide footing with N about 22 (high medium density, settles 1 inch on sand. No indication of what kind of sand.
I'd want to be on site and do some probing and cone tests before saying OK, along with the 95% of Modified. By force of habit, I think my usual high for sand is 4,000 psf, but mainly because it works and no settlement problems result. Plate load tests have shown that as "safe" on fine to medium sand, extrapolated to typical footing sizes. That may be conservative however.
A final statement. N values are meaningless on uniform sands in my opinion. Reason: very small range of relative density, loose to dense.
RE: Bearing Capacity of 95% compacted fill