General non-proportional loading behavior of soils

In order to clarify the necessary factors in the elastoplastic constitutive equations for describing the general non-proportional loading behavior of soils, the mechanical responses to the stress probe test and the principal stress axes rotation are examined by numerical experiments and compared with test data. The necessity of incorporating both the anisotropy in the yield condition and the vertex effect or the tangent effect, i.e., the inelastic stretching due to the stress rate tangential to the yield surface, both of which lead to non-coaxiality, are revealed in the description of the general loading behavior of soils.