Estimation of bearing capacity of soil type

[Laser28]

Hi gang:

Does anyone have a reference that provides estimated bearing capacities of various soil types for use in preliminary floor-on-grade or pavement design? For example, what is the estimated bearing capacity in tsf for a silty clay or silty till.

Note that the floor on grade design will be finalized based on proper soil testing. I just wanna give my contractor a reasonable estimate of the slab thickness and base plate size for columns.

 

[ERV]

Lazer28,

Hope you have the 97 UBC, Volume 2. Look on page 2-49, Table 18-IA, Allowable Foundation and Lateral Pressure. I believe this is what you are looking for.

 

[BigH]

Many older texts give presumptive bearing pressures for various soil types that, at best, get you in the right ball park. I think that Terzaghi and Peck (1967) gave some although I may be wrong - in any event, check these kind of sources.

p.s. I AM NOT saying to design with such persumptive values - but, they have, in many localities, been proven acceptable under many/most circumstances.

 

[cdh61]

Laser28,

soft silt clay - 0.5 tsf
firm to stiff silty clay - 1.5 tsf

soft silty till - 2 tsf
very stiff to hard silty till - 7 tsf

hope this helps to put you in ball park for prelim design.

regards

 

[Laser28]

Alright - I have found several references, and I want to thank all of you for the input. Of course, now I must convince the owner of the need for a proper geotechnical investigation.

 

[BigH]

Just show him a picture of the Transcona Grain Elevator or the failure shown in Tschebotarioff's book - might open your clients eyes.

 

[Laser28]

A great book on failures and their effect on engineering design and construction practices is "To Engineer is Human". Of course, the Discovery Channel has covered a lot of these stories as well.

 

[kmerl]

The best way to convince the owner is by "showing him the money". Also for slab on grade or pavement I think that the modulus of subgrade reaction (slab) and California Bearing ratio (CBR, pavement) tests/ values may be more useful to you.



Keithe J. Merl

 

[Laser28]

KMERL:

Agreed. I use the PCA and WRI methods, that use CBR or Westergaard's k for subbase/subgrade support for final design, but this project is subject to a requirement by the municipality to use a minimum 500 lb/sf soil bearing capacity. I don't normally use a bearing capacity for design, and I was looking for a correlation to CBR or k values, for estimation purposes.

 

[kmerl]

Oh, okay. I usally use the coast of repairs adn downtime on equipment to verify the use of geotechincal investigation. I have a loose correlation based on soil type to give K and CBR, it is very conservative, by use of a bar chart.

Keithe J. Merl

 

[Focht3]

What values do you consider "very conservative"?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[kmerl]

Depends on the soils, however the chart gives very loose correlations of several different values based on gradation size.

Keithe J. Merl

 

[kmerl]

Sorry, the term "very conservative" was poor wording on my part, I think that "loose correlation" is better. My apologies.....

Keithe J. Merl

 

[Focht3]

Who developed the chart? Where can I find it?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[BigH]

There is a "standard" correlation that I've seen in a number of publications and perhaps this is the one to which kmerl is referring. The one reference that comes directly to mind is Baker (editor) Highway Engineering Handbook - similar series to Winterkorn and Fang (now Fang) - probably published 1975 or so. I think it might also be in AASHTO. Will try to find.

 

[kmerl]

BigH I think you might be right. I only have a photocopy of the chart supplied to me by one of my mentors. Iis labeled as Figure 9. Approximate interrelationships of soil classifications and bearing values (page 27). It has several sources on it. If you are interested in inspecting it I could offer it as an adobe...

Keithe J. Merl

 

[BigH]

Please do - bohica@indiatimes.com . In looking further, there is another chart in Fang's Foundation Engineering Handbook, 2nd Edition (First edition was Winterkorn and Fang). It is chapter 3. Send your email and I will send off a scanned copy of it. Baker's chart is more geared towards highway engineering - R values, etc. Fang's has CPT, et. correlations with CBR, k, etc.

 

[Focht3]

[blue]BigH[/blue] - please forward [blue]kmerl[/blue]'s chart to me via the usual path -

Thanks!



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[Laser28]

Check out

http://www.usace.army.mil/inet/usace-docs/eng-manuals/cecw.htm

and download the pdf file for EM 1110-1-1905. Table 4-8 is what I was looking for, and confirms/agrees with other sources. This table is for spread footings, rather than floor slabs, and the article provides guidance for using the values in design.

Thanks to all for the help.