SPT Formulas

Note

60 is used in this case to represent 60% hammer efficiency and can be any percentage of hammer efficiency e.g. \(N_{55}\) for 55% hammer efficiency.

Description of symbols used in SPT Corrections

Symbol	Description
\(N_R\)	Recorded SPT blow count
\(C_H\)	Hammer efficiency correction factor
\(C_B\)	Borehole correction factor
\(C_S\)	Sampler correction factor
\(C_R\)	Rod length correction factor
\((N_1)_{60}\)	SPT blow count corrected for overburden pressure
\((N_1)_{60 \, (CORR)}\)	SPT blow count corrected for dilatancy
\(N_{60}\)	SPT blow count corrected for 60% hammer efficiency
\(C_N\)	Overburden pressure correction factor
\(\sigma_o\)	Effective overburden pressure at the test depth