In the previous chapters it has been shown that the principle of effective
stress can be applied to the shear strength, the tensional strength and the volumetric
behavior of unsaturated soils. This chapter shows that the critical void ratio plotted
against the mean effective stress for samples tested at different suctions align parallel to
the virgin consolidation line of the material. This means that the critical state concept
also applies to unsaturated materials. Taking into account all these results, an
elastoplastic framework that can be used to develop general constitutive models for
soils including saturated, unsaturated and compacted materials is presented.
Keywords: Critical state concept, critical void ratio, effective stress, virgin
consolidation line, elastoplastic framework, elastic zone, constitutive models,
tensional strength, volumetric behavior, effective stress, yield surface, plastic
deformations, suction hardening, failure surface, preconsolidation stress.