×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Allowable soil bearing pressure

Allowable soil bearing pressure

Allowable soil bearing pressure

(OP)
Under UBC the maximum allowable soil bearing pressure was 1000 psf (without the need for soils report). Under CBC 2013, TABLE 1806A.2, the same soil bearing pressure is 1500 psf. The same Dead load + Live load governs the design, using the working stress design. Any body know what was the reason for the increase in the allowable soil pressure?

RE: Allowable soil bearing pressure

Strictly speaking this so general,and you have to follow the soil report.

RE: Allowable soil bearing pressure

I think it was found, that unless just total trash, 1500 was pretty achievable.

RE: Allowable soil bearing pressure

I'm pretty sure a sandbox can give you 1500 psf

RE: Allowable soil bearing pressure

At the beginning of my career, about 30 years ago, we would assume 2,000 PSF for any soil, no matter how crappy. Back then, geotechnical reports would routinely allow 3,000 psf or 4,000 psf.

Now, it seems a lot of geotechnical reports allow just 2,000 psf, even when they have soil borings. And as you said, codes are also more conservative.

Have there been problems over the years with settlement?

DaveAtkins

RE: Allowable soil bearing pressure

Or maybe just the soils engineers doing a better job of selling their services?

RE: Allowable soil bearing pressure

At the risk of being shouted down by the structural engineers...

It could also be that the owners, architects, or other engineers that are selecting the geotechnical engineers on the basis of cost. So the number of borings goes down, the amount of laboratory testing goes down, the amount of time spent doing any type of analysis goes down and they send basically the same report that they have sent for the last 50 jobs, because no one is willing to pay them to actually do any engineering.

I've been in this business for over 25 years, and the cost of a geotechnical report for typical commercial projects is within 20 percent of what it was when I started.

Mike Lambert

RE: Allowable soil bearing pressure

I'm with you 100% Mike. Geotechnical reports have become commoditized to a frightening degree.

RE: Allowable soil bearing pressure

Mike - I did a job in Ontario back in 1993 where the cost of the job as 50% of the cost of a similar investigation next door (same structure and that) that it was back in the mid-60s. - I've gone overseas!

RE: Allowable soil bearing pressure

One plausible reason for the prescriptive differences in the two codes is the significant differences in the geology of Canada and the US and the resulting soil morphology. I believe the IBC has to accommodate a more diverse range of bearing soils than the CBC would. But then again....it could be as arbitrary as other code provisions!lol

RE: Allowable soil bearing pressure

I actually agree with all the above.
-- In my opinion, the Geotech services are terribly commoditized (I believe the Architects & Structurals have about the same degree of impact as the cheap developers & the atrocious Public entities).
-- Geotechs do not appear to be doing any significant field or lab work compared to 30 years + ago (In my area of Western Colorado, I am amazed at the vast range of native & fill conditions which ALL result in an allowable of 1300 to 1600 psf).
-- As development has occurred, most towns/cities have been moving into areas of poorer subsurface conditions, probably justifying the pessimism of the Codes.

RE: Allowable soil bearing pressure

That kind of provision gets voted into existence by some committee, and a different committee gives you different answers, so it's not surprising that there is not consistency there.

RE: Allowable soil bearing pressure

Ron, the CBC is presumably the California Building Code. The Canadian model code is the National Building Code of Canada (typically abbreviated to NBCC).

RE: Allowable soil bearing pressure

Also, the surface conditions of Canada vary significantly, as you'd kind of expect for something as big as it is.

RE: Allowable soil bearing pressure

TLHS....thanks. Didn't think of that. Oddly enough, the statement still applies...perhaps even more so.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources