Abstract：Based on the triaxial compression tests of clays and sands under different stress paths，it is theoretically proven according to the principle of interaction between plastic volumetric and shear strains that the constitutive relations of soils are dependent on stress paths，and the dependency of stress path is the combination of effects of the interaction between plastic volumetric and shear strains. The dependence of stress path includes not only the effect of pressure sensitivity but also shear-induced dilatancy. The results of triaxial compression tests for clays and sands under three different stress paths show that the shear yield surfaces and volumetric yield surfaces rotate with the change in stress paths. At the same time，the sizes of yield surfaces in the stress space vary with stress paths. This phenomenon is called rotational hardening. The mechanism of yield surface rotation is analyzed and it is explained that the rotational hardening is resulted from the dependency of stress path，which is essentially a reflection of the interaction between plastic volumetric and shear strains.
