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correlation between CBR and shear strength such as UCS

correlation between CBR and shear strength such as UCS

I'd like to know the correlation between CBR and sheer strength such as UCS. Is there any equation?

RE: correlation between CBR and shear strength such as UCS

I suggest you search this site using 'CBR unconfined' as your search terms.  I'm fairly sure that your question has already been asked -

Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.  See FAQ158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

RE: correlation between CBR and shear strength such as UCS

A journal I read years ago published a relationship between CBR and undrained sheAr strength.  Since there should be a relationship I haven't hesitated to use it.

CBR=Su/23 where Su is the undrained shear strength in kPa.

If you need the journal I could dig it up.

RE: correlation between CBR and shear strength such as UCS

jdmm - you'll use this correlation and not the one for SPT and Su??? - just kidding.  Is this a soaked CBR or dry CBR correlation?  There are some other curves - one in Baker's Highway Engineering Handbook but not CBR to Su - I have seen another and will find reference.  Again, as with all correlations - judgment is needed - as you all know anyway!!

RE: correlation between CBR and shear strength such as UCS

Just another point - in TRRL's Overseas Research Note 31, there is a presentation of the CBR relationships vs %MDD Heavy Tamping for a couple of soil types.  They do not give, though, a relationship of CBR vs UC (or Su).

RE: correlation between CBR and shear strength such as UCS

I've just come accross this thread and I have a quick note to add to the relationship mentioned by jdmm. Quite often I will schedule a whole series of relationships on soils where I will do MC vs CBR and MC vs Shear strength on the same samples. After reading the relationship noted by jdmm, I did a qucik check on some of the values I had got recently, and found that typically the range for Glacial Lake Deposits in the north of the UK were in the range of CBR = Su/15 to CBR = Su/17 for a range of samples tested prior to the earthworks (SI stage) and during the actual earthworks.
So in light of this, I would suggest that it is always worth checking out the relationship, and not relying soley on historical values, the difference between CBR = Su/23 and Su/15 would be fairly dramatic to the final CBR.

RE: correlation between CBR and shear strength such as UCS

Thanks for the case history ian. You make a good point with correlations - they really should be site or geologically specific to be anything more than guideline values.

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