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N vs N(60)

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ONENGINEER

Geotechnical
Joined
Oct 13, 2011
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284
Location
CA
Hi - I am analyzing boreholes with 200-250 ft depths in predominantly silt, clayey silt or sandy silt. No Shelby but only SPT. Correlations are often through N-values, which I assume is the raw SPT obtained in the field. For example
Beta= (N//15)* (1.2 - 0.11 sqrt(Z). or Phi= 0.3N + 27 or some other soil parameter-N value plots.

Were these correlations meant for the raw SPT data or one should use his own initiative by obtaining N1(60) or N(60) and then use the above correlation formulations. In the latter case one wonders if the constants in the correlations remain the same if N, N1(60) or N(60) are used. Hope I could explain my question clearly and I would appreciate your feedback. Thank you.



 
It depends entirely on the correlation really. I'd go back and find the original research paper for the correlation and see what they did.
 
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