Before the SPT values are used in empirical correlations and in design charts, the field 'N' value have to be corrected as per IS – The corrections are .
Correction of SPT Value for Overburden Pressure. In cohesionless soils, the overburden pressure affects the penetration resistance. For SPT made at.
standardized to a specific energy level through the use of correction .. Consequently, the consistency of the SPT N values is questioned, i.e.