The SPT value has been used to classify the consistency or relative density of a soil. Skempton (1986) added appropriate values of N’60 to Terzaghi and Pecks (1948) classification of relative density, as shown in Table 1.1.
where C DC t p A = 60 + 25 = 1 2 + 0 05 0 01 50 log , . . log( . ) and COCR = OCR0.18; Dr = relative density (in decimal form); Cp = grain-size correction factor; CA = aging correction factor; COCR = overconsolidation correction factor; D50 = grain size at which 50% of the soil is finer (mm); t = age of soil (time since deposition)(years); and OCR = overconsolidation ratio.
