Su and N Value Correlations

[BigH]

Was wondering if any of you would share any correlations you have developed between undrained shear strength and N values. I KNOW how cruuuuuuuddddeeee this is - but on small jobs in many areas, it is all you have. Many places are rich enough to permit/warrant CPTs or even vanes (many times, they are not available).

I am thinking of getting a handle on correlations, say, vs liquid limit - I remember seeing a relationship years ago that one would use with CL soils and with CH soils. Perhaps, we could look into CL (LL<30), CI (30<LL<50) and CH (LL>50 but less than 80, say). Anything over 80 most definitely would give one pause.

I will forward to our colleague SlideRuleEra one that I developed for the Calcutta Alluvial Plain in Howrah area of West Bengal. I just want to look up the LL values. Hopefully he will agree to post it on his site for downloading.

Interested VAD? I've had an enquiry from a colleague on this.
to all.

 

[SlideRuleEra]

BigH - Will be glad to post it.

http://www.SlideRuleEra.net

 

[MRM]

BigH,
I've got more correlations between Su, moisture content, and Atterberg Limits data for various clays, than I do with N counts. But I could probably find some of the N values that went along with them. I'll consider it homework and try to produce something over the next week or so.

I've got some great sites that have shown the textbook stiff, desicated clays near the surface, becoming softer with with depth, increasing moisture content, and decreasing Su. I can say, in general, that most of the near-NC clays I see usually have a c/p=0.2 to 0.23 or so. My clays seem to correlate well with the c/p ratios you see in most reference books. The N counts obtained on those sites show a general trend of decreasing blow counts with depth as the near-NC depth is approached. I've just never plotted the N counts out...

 

[dgillette]

I assume you are familiar with the Terzaghi and Peck and Sowers correlations in DM-7.

I've also seen:

Tavares: Su in kPa = 5 N to 8 N, with higher ratios being associated with lower blowcounts (Guabirotuba clay, about which I know zero. Don't know what reference test.)

Hegedus and Peterson: Su in ksf = 0.25 N in lake sediments; 0.33 N in clayey till. (All data from Cleveland. Reference to unconfined compression.)

Bureau of Reclamation: Su in psi = 2+N to 6+N. (Data mostly from one dam site and a cemetery in Lakewood CO, presumably before any bodies were actually interred there. All blowcounts below about 20.) This gives much higher numbers than Terzaghi and Peck, in part because it is referenced to vane and not to unconfined compression with its associated disturbance.

In the 4th Panamerican Conference, Victor deMello shows a plot of many correlations together. For q-u (not Su) in kg/cm^2, the slope ranges from .09 to 0.35, but hey! What's a factor of four between friends?

If you need full references for these, I'll dig them out.