HELP - CBR, Atterberg limits, angle of friction correlation

[ksdphilippines]

G'day!

I have a geotechnical report on a very big area of land which contains the averaged CBR and Angle of internal friction plus the individual testing report for CPT, SPT, and even a trial fill testing.

I want to check the validity of the average and derive some specific values for an area.

Query:
1.) Can anyone point out the correlation of an angle of internal friction to CBR value or vice versa?

2.) Any other correlations from Atterberg limits, CPT, SPT reports to Soil modulus, CBR, and Cohesion? have derived Su, angle of internal friction from these but have no correlation to others. need the CBR and Es for industrial slab design.

( Im a structural engineer and would like to know more on the geotechnical aspects so i can review a geotechnical report and not just use the values recommended...)


Cheers!

 

[fattdad]

If you need this information and it's not in the geotechnical engineering study, call the geotechnical engineer and discuss it. Be wary of correlations that you are not familiar with in your local area.

f-d

¡papá gordo ain’t no madre flaca!

 

[BigH]

Also be wary of using values of parameters that are different from the soils report - may put you on the hook rather than the geotechnical engineer. fattdad is correct in using correlations that are outside your own area - but there are "universal" correlations for ballpark estimates - local correlations are obviously better. I would suggest for some of the data you are looking to look up Paul Mayne's web site (can get off the net) and view many of his papers on in situ testing. CBR values - you would want to know if the values are "soaked" or "dry". SlideRuleEra's web site has a few sheets of paper I've put to him on various correlations used in highway work.

http://www.slideruleera.net/contributions.html

 

[ksdphilippines]

g'day!

thanks for these leads and advise.

For the correlations, i just want to check the results and recommended values for validity. double checking instead of just blindly accepting the values.

and to know more about geotech which i find intriguingly challenging...

for other leads or tips. do give me more info.

ta!

Cheers!

 

[msucog]

i'll throw out another point: i'm sure that you can find correlations for darn near anything if you look hard enough...that doesn't mean that the correlations are correct for your area/geology (as mentioned in other posts). also, some correlations may be entirely inappropriate (i.e. 20bpf SPT = "good" CBR...i've seen 20+bpf soil in place turn to a CBR of 3 when compacted to 98% standard Proctor). also, how do you accurately perform SPT for subgrade soils where you need CBR values? i'm sure some of you probably have experience with evaluating the CBR in this manner, but i personally would not trust it other than for a very general idea. i'd perform the test and relate that to field experience with seeing what a CBR=3 soil looks like under a tandem axle dump truck.

in other words, as frustrating as it may be, trust your geotech. geotechnical engineering is very complicated even though it seems like it's "just dirt" to some people. if you don't trust them, you can always hire a second geotech but don't be surprised to find different results (there's always different ways to evaluate things on top of the range of test results that you'll usually see when different folks test the same material). here's a better idea, if you bought a cheap geotech, try going with a more reputable firm even if it costs more on the front end. quite often (but not always), the cheap guy will give you the more conversative (and maybe inappropriate) recommendations. either way, if you don't trust the geotech, get a new one. if you don't trust them because you don't have a clue as to what they are recommending, then i'd suggest you find a firm you trust and stick with them...firing firms over something you don't understand may not be in your best interest. if you trust them, then discuss the test results/recommendations with the firm. ask questions about how the results they provided compare to what they typically see (sometimes, there's oddball results that pop up). to learn more about the testing we do and to see some generalized results/ranges, check out the navfac/ufc library:

http://www.wbdg.org/ccb/browse_cat.php?o=29&c=4

UFC 3-220-10N Soil Mechanics

by the way, hire "the firm" (or quality), not the results that you expect them to give you as results can be widely varying from sample to sample or site to site. i often see clients (perhaps customers is more appropriate a word) end up hiring firms other than my firm simply because they were either 5% cheaper or because they will give out "cheap" rcommendations or the recommendations that they were looking for. in the end, those customers usually end up coming back to us because the other guys weren't quite worth saving a few bucks on the front end of the project. some of those customers are now clients...some are not (can't win them all i suppose).

good luck (both on the project and understanding geotechs...we're very complicated creatures).

 

[NVcaster]

I would be wary of an averaged value unless the soil types are the same for the average. CBR tests are reasonbly cheap, I would run a couple for piece of mind. msucog has a very valid point.