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Cohesion undrained shear strength, Cu

Cohesion undrained shear strength, Cu

Cohesion undrained shear strength, Cu

Dear College,
I have to design single pile capacity for lateral capacity, from triaxial result only C and internal friction, I also have consolidation result, NSPT value. How I calculated or correlation to get Cu value?


RE: Cohesion undrained shear strength, Cu

There are many methods which can use triaxial test data or SPT results to determine capacity. However, if you are not competent to perform the calculations - which seems to be the case as you appear unable to interpret triaxial test data - then you shouldn't be doing the calculations. Furthermore, it sounds like you have very limited data, which indicates design risk here. You should therefore seek to get an experienced geotech to perform this analysis.

RE: Cohesion undrained shear strength, Cu

A very rough rule of thumb is that Cu = 7 x N.

RE: Cohesion undrained shear strength, Cu

BTW, Retrograde's correlation is in kPa but I would not use SPT N-values to get strength values for clay (especially if you have triaxial data). If your triaxial data is from UU tests, you already have Cu. Since you said that you have also friction angles, I assume that your soil is unsaturated. Also, consider LRJ's recommendations, take your time to take a closer look at this and ask you supervisors to review your design. Good luck...

RE: Cohesion undrained shear strength, Cu

Thanks Okiryu, I forgot to mention the units.

RE: Cohesion undrained shear strength, Cu

Skempton also proposed a correlation of 5.5 x N for Cu. N is a very arbitrary value considering the variation with SPT hammers. A correlation to N60 would be better

RE: Cohesion undrained shear strength, Cu

(as a petty grievance, the CU-bar test results should NOT be conveying the C and Phi values. The actual ASTM procedure considers the interpretation of stress strain data as a professional service and is excluded from the practice. So, by co-opting the non-professional laboratories, "Free" professional service you have no protection against negligence.

If your skill set is not such, I get that. But, it is your obligation to actually vet all aspects of the lab work to confirm the strength as reported.)


ípapß gordo ainÆt no madre flaca!

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