1. Concept:

The Standard Penetration test (SPT) is a common in situ testing method used to determine 
the geotechnical engineering properties of subsurface soils. It is a simple and inexpensive 
test to estimate the relative density of soils and approximate shear strength parameters.

2.Standard Penetration Test Process

SPT, involves driving a standard thick-walled sample tube into the ground at the bottom of a
borehole by blows from a slide hammer with standard weight and falling distance. The sample 
tube is driven 150 mm into the ground and then the number of blows needed for the tube to 
penetrate each 150 mm (6 in) up to a depth of 450 mm (18 in) is recorded. The sum of the
number of blows required for the second and third 6 in. of penetration is reported as SPT
blowcount value,commonly termed  "standard penetration resistance" or the "N-value".