foundation support
foundation support
(OP)
I'm interested in opinions about how much excavating around a residential strip foundation can be done without compromising support, assuming non-problematic fairly stiff clay soil and no danger of frost. The consensus in the residential construction industry seems to be that a 45 degree pyramid running down from the bottom edges of the footing is all the soil that participates in the support, and the rest can be safely removed. The Uniform Building Code requires two feet of overburden on the outside of a strip foundation but only 8" on the inside, perhaps only out of consideration for the possibility of frost heave. Any thoughts?





RE: foundation support
RE: foundation support
RE: foundation support
RE: foundation support
It's too bad we can't post sketches. It's hard to explain in words.
RE: foundation support
RE: foundation support
I agree with the above posts. If the cut you are making near the footing is shallow, a few feet, then the 2:1 (45 degree) method works very well in good soils as you describ. As the cut gets deeper, you have to start worring about slope stability as PEinc indicated in the post just above this one.
You should also consider the value and sensitivity of the structure to settlement. Your post says it is a residential footing, so it is likely that these are not big factors, but they can be in some cases.
RE: foundation support
RE: foundation support
RE: foundation support
I believe what you are describing is when NO soil is removed from the footing sides. Once the soil is excavated its a different set of Terzaghi line of action formulas for horizontal pressures such as against sheet piling,retaining walls, underpinning situations and open cuts. I use 2 typical ratios depending on the type of soils. 2H & 1V-soft material or clay, 1H & 1V for good sands as a quick and dirty evaluation. Most good soils can go as far out as 2V & 1H.