Dear colleagues,
I have been searching about correlations between N-SPT and drained friction angle for sands. However, some authors don't write the respective energy efficiency used for those equations. I have a doubt of the following equations obtained from Yoshida (2015) - Seismic Ground Response Analysis. Yoshida shows an equation of Japan Road Association (2002) correlated with overburden corrected N-SPT, that is φ' = 21+4.8ln[(N1)]. Also he shows other equation of Ohsaki (1959), that is φ' = 15+(20N)^0.5. So, I appreciate if you can give me the respective information about energy efficiency.
Thank you so much.
Dear,
I have found a bit different correlation for Ohsaki (1959). As you can see in the attached screenshot taken from Duncan's book (Soil Strength and Slope Stability 2nd ed.), those older correlations used the uncorrected SPT blow counts, but the hammers which deliver 60% of energy were the most commonly used, so in the book, it is recommended to use N60 with that correlation.
I hope that helps you.
Best regards,
Exneyder
Dear,
Thank you for your answer, I'm sorry to reply too late. Also I found the equation I mentioned in a research of Hatanaka & Uchida realized in 1996. Finally, I decided to use φ' = 15+(20N)^0.5 with 72% of energy efficiency. Because the equation φ' = 15+(12N)^0.5 , is the same of Dunham (1954) to Round and Uniformly graded soil particles.
Best regards,
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