What is the purpose to conduct the standard penetration test on soil?

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.

This basic soil testing procedure gives reasonably consistent results in fine-grained sands and is not as consistent in coarse sands or clays.

Standard penetration test is common and widely used soil testing procedure for Engineering purpose which is relatively quick and simple to perform.

This test is also known as " In-situ penetration test " of soil. The main aim of this test is to determine the Geo-technical engineering properties of subsurface layers of soil, class of soil and to obtain the penetration resistance or N - value. 

Its come under the subject of Soil Mechanics and also very useful and helpful for Geo tectonic engineers in there study to classify the disturbed layer of soils.

Penetration tests are used in order to evaluate the liquefaction and foundation strength.