The inadequacy of the ordinary flow and deformation theories of plasti
city in explaining the experimental results on shear band formation in
sand has led to the development of a consistent non-coaxial plasticit
y theory. Using this theory, the theoretical predictions for shear ban
d orientation and its onset are shown to agree well with experimental
observations of biaxial tests. The decrease of shear band inclination
angle with respect to the minor principal stress direction with increa
sing confining pressure supports the hypothesis of the dependency of n
on-coaxiality on confining pressure.