S1 in nonconstrained UBC 97 chapter 18 definition

[McEngr]

For what it's worth, I've completed lots of foundations for drilled piers and the like. However, I have been debating with a colleague whether the S1 in UBC 97 refers to 1/3 the embedment from the bottom of the embedment or the top of the embedment. Since this equation is rather difficult to weed out with engineering physical properties, I thought I'd post this question on this board and get an informed opinion rather than convince him otherwise.

Thanks.

 

[Andy Lin]

Pretty sure it's from the top since the lateral bearing pressure increases from top to bottom.

So if the lateral bearing pressure is 200 PSF/FT and you have 9 ft depth, S1 = 200 x 9/3 = 600 PSF.

That's how I interpret it.

 

[McEngr]

This is the conservative design, of course. Thanks HQ.