## Soil Bearing Capacity Based on Settlement (Bowles)

## Soil Bearing Capacity Based on Settlement (Bowles)

(OP)

We have a clean sand site with average blow counts in the upper 2B (B = 12 ft. square = width of footing) of 30.

I calculate a bearing capacity of about 10,200 psf for a settlement of 1 inch per the analysis in Bowles Foundation Design (base don Terzhagi and Peck 1967).

We have column loads of about 1,500 kips so we need to recommend a bearing pressure for reasonable size of footing.

Traditional Terzhagi Bearing Equation with FS = 4 results in 15,000 psf.

Does 10,000 psf seem reasonable for a sand, some silty sand, with N average of 31 to a depth of 2B?

I calculate a bearing capacity of about 10,200 psf for a settlement of 1 inch per the analysis in Bowles Foundation Design (base don Terzhagi and Peck 1967).

We have column loads of about 1,500 kips so we need to recommend a bearing pressure for reasonable size of footing.

Traditional Terzhagi Bearing Equation with FS = 4 results in 15,000 psf.

Does 10,000 psf seem reasonable for a sand, some silty sand, with N average of 31 to a depth of 2B?

## RE: Soil Bearing Capacity Based on Settlement (Bowles)

I know that you can get a much higher value from bearing capacity and settlement analyses. But what I've read on elastic settlement analysis is that its not very accurate and mileage may vary which leads me to believe that its better to play it safe than be sorry.

Even though this is pretty basic, I'm interested in what others have to say on this topic.

## RE: Soil Bearing Capacity Based on Settlement (Bowles)

I literally used a napkin for this exercise; however.

f-d

ípapß gordo ainÆt no madre flaca!

## RE: Soil Bearing Capacity Based on Settlement (Bowles)

I am not disagreeing that 7,500 psf seems high, another option, maybe go to a mat at about 1,750 psf? hmmmm

Then give ks of 20 to 60 pci (min to max loads) with 1" settlement ?

## RE: Soil Bearing Capacity Based on Settlement (Bowles)

(I never liked the Schmertmann method. It doesn't evoke the first principals in my mind. My approach is PL/AE. You are figuring out the P, the depth to 10% stress change is the L (sub i 'cause I'll subdivide), the A is a unit square and the E should return from N-bar for the layer.)

So, what's your modulus?

f-d

ípapß gordo ainÆt no madre flaca!

## RE: Soil Bearing Capacity Based on Settlement (Bowles)

[N55/F}((B+F2)/B)^2(K) where F and F2 are 'factors' which were derived from the research and testing, and varies with B (width of square footing). The Es, I believe, is a function of the F factors. K is also a factor that was derived based upon the depth of embedment as a function of B. (Foundation Analysis and Design, Bowles 5th Edition.). N70 may also be used.

A lot of the early derivations were based on plate tests, or small scale testing, or lab testing, then extrapolated, which is why I prefer to solve with various methods, see what's reasonable, then take a reasonable average.

## RE: Soil Bearing Capacity Based on Settlement (Bowles)

## RE: Soil Bearing Capacity Based on Settlement (Bowles)