predisting existing bearing capacity
predisting existing bearing capacity
(OP)
I have the existing plans of a house. I have calculated the soil's working stresses under the home's isolated and strip footings.
The working stress under the isolated footings is 2,000 psf.
The working stress under the strip footings is 1,000 psf.
Am I right in saying that based on this information, the soil's allowable bearing capacity is at least 2,000 psf?
And that I have a reserve of 1,000 psf under the strip footings, thus I can safely add another 1000 psf of pressure?





RE: predisting existing bearing capacity
RE: predisting existing bearing capacity
There is no soil report and there is no way of determining the type of soil, that's the whole point of my question.
The question stated in a simpler way and in more general terms is as follows:
You have two footings under an existing building, one has a working stress of 2,000 psf the other has a working stress of 1,000 psf.
Is it a valid assumption to say that based on this information, the minimum allowable bearing pressure at the site of the building is 2,000 psf?
It's a question of judgment.
RE: predisting existing bearing capacity
the more undefined soil underneath the structure, usually has bigger its SF..
But, it is important thing to ensure the settlement (cohessive has more settlement than granular) beside considering safe or allowable bearing pressure..like Big H said on above..
RE: predisting existing bearing capacity
Working stress = 2000 psf
Allowable Bearing Pressure = 2.5 * 2000 psf = 5000 psf or 239.4 Kpa..is such a little value..
well, do insitu test (eg. SPT, CPT, DCP). I'd rather do DCP test to defined bearing capacity underlaying without losing much time..(Correlation DCP to Bearing Capacity topic already discussed in geotechnical forum)
Then the DCP result (after converted), shall be at least or greater than 5000 psf..
Just suggestion...
RE: predisting existing bearing capacity
1. Have the foundations really been subjected to 2000 psf, or does that calculated stress include live loads that may or may not have occurred? If it is all dead load and known sustained live load, then you can take the individual footings as a test.
2. The ultimate bearing capacity is different for square or rectangular footings than for a continuous footing on the same soil. For clay, a square footing has about 125% of the ultimate bearing capacity of a strip footing. For sand, more like 85%. These numbers can also be affected by footing embedment.
3. A strip footing tends to settle more than a square footing of the same width, because the stress bulbs are deeper.