Per quanto attiene invece alla correlazione NSPT-Cu, questo è uno degli argomenti più controversi. Ti invio una nota esplicativa di un geotecnico americano dell'USBR a proposito (attento alle conversioni!). L'ultima frase, che ho riportato in neretto, è la più eloquente:

"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?"

"Data speak for themselves" -Reverend Thomas Bayes 1702-1761
P(Ai|E)=(P(E|Ai)P(Ai))/P(E)