Standard penetration is one of the most common field investigation technique. It is generally adapted for granular soils but sometimes may be used for cohesive soils too. A hammer of 63.5 kg is used and the height of fall is uniformly maintained as 75cm. Blows are not considered during initial 15cm seating drive. The number of blows required for 30cm penetration after seating drive gives recorded SPT N-value to which corrections has to be applied.
Overburden correction and the dilatancy correction are the two types of correction to be applied as per IS standard (Graph from IS 2131-1981). Overburden corrections are used to remove the effects of confining pressure at deeper strata. For silty fine sands or fine sands below water table Dilatancy correction is applied. It is to be noted that Overburden correction is applied first followed by Dilatancy correction.
Using coorelations from corrected SPT N-value, relative density, angle of internal friction of cohesionless soils , UCS value in case of cohesive soil, dynamic properties can be determined.
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