Energy dissipation and post-bifurcation behaviour of granular soils

Extensive experimental data indicate that plastic flow in granular materials is non-coaxial (i.e. the principal directions of the plastic strain increment tensor and the stress tensor do not coincide) for loadings involving principal stress rotation. The degree of non-coaxiality depends on the magnitude of principal stress rotation, hence plastic flow is also incrementally non-linear. The paper presents an analysis and discussion of the effects of non-coaxial plastic flow on the post-bifurcation response of dilatant granular materials. Significant differences are observed between the energy dissipation and stress-dilatancy response of soils before and after shear-band formation. These differences are attributed to the non-coaxiality of plastic flow during post-bifurcation shearing. In turn, the non-coaxiality is attributed to principal stress rotation within the shear band, which is consistent with the assumption that the materials inside the shear undergo simple shear deformation. Experimental data are presented to support the analytical results. Copyright (c) 2006 John Wiley & Sons, Ltd.