Correct Answer - Option 3 : 23
Explanation
Dilatancy correction:
It is to be applied when N’ obtained after overburden correction, exceeds 15 in saturated fine sands and silts. IS: 2131-1981 incorporates the Terzaghi and Peck recommended dilatancy correction (when N’ > 15) using the equation
\(N'' = 15 + \frac{1}{2}\left( {N'-\;15} \right)\)
Given,
N value = 30
Corrected value for dilatancy is
\(N'' = 15 + \frac{1}{2}\left( {30-\;15} \right)\)
N'' = 15 + 7.5 = 22.5
∴ Corrected value N'' = 22.5 , So closet option is Option 3