A flow theory for soil: Concept of multiple neutral loading surfaces

A flow theory for soils is proposed which diverts considerably from the classical theory of plasticity. The theory is based on the concept of multiple loading surfaces defining neutral states for which irreversible deformation cease to exist. The constitutive relation has an incremental nature and the ratios of the components of plastic strain rate are functions of both the current stress and the stress rate. The concept of the yield locus is no longer involved in the formulation.