N-SPT values observed during testing are not utilized directly in the assessment of soil properties. These values need to be corrected to account for hammer efficiency , borehole diameter,sampling method, rod length and the overburden pressure. Current tool sets the rules to allow the calculations for the correct SPT numbers, N60 and (N1)60.

\(x = {-b \pm \sqrt{b^2-4ac} \over 2a}\)This is an updated text

Friction angle together with cohesion defines the shear strength parameters of soil. Its definition is derived from the Mohr-Coulomb failure criterion. It can be determined in the laboratory by direct shear test or triaxial tests or from theoretical correlations with density or N SPT number.

The current tool sets the rules to calculate friction angle for granular soils based on N SPT number.