Standard penetration test (SPT)

Question 1

Properties

Answer 1

Used primarily in granular soils
It gives:
relative density and friction angle
undrained cohesion
direct estimate of settlment

Question 2

How it is done

Answer 2

After having a borehole to the depth of the soil that is wanted to be tested; a 63.5 kg hammer is dropprd a 76cm free fall on a tube sampler causing the tube sampler to penetrate, we record the number of blows of the hammer per each 6 inches (15 cm) of penetration). The SPT blow count is equal to the number of blows for the 2nd inches penetration plus the number of blows for the 3rd 6 inches penetration.
The N that we get here is called the uncorrected SPT.

Question 3

Correction factors

Answer 3

We need to correct N for Hammer type to get N60.
N60=NCe=NER/60
The we need to correct for borehole diameter, for sampling method, and rod length
implies N60=NCeCbCsCr
Finally we need to normalize N60 with CN
N160=CN*N60