Parameters affecting strength has lot of formula so all content include a picture.
where ?p = frictional angle under plane strain conditions, as would occur beneath a very long spread footing or a long wall leaning forward under later soil pressure; ?tr = frictional angle under axisymmetric conditions (the intermediate principal stress = minor principal stress), as would occur at the tip of a pile or beneath a square footing. The adjustment of test conditions should be limited to no more than 5°.
