ABSTRACT
An unsaturated soil is not a special type of soil, rather a state of the soil. All soils can be partially saturated with water. Therefore, constitutive models for soils should ideally represent the soil behaviour over entire ranges of possible pore pressure and stress values and allow arbitrary stress and hydraulic paths within these ranges. This paper attempts to present an overview of constitutive modelling for unsaturated soils. In particular, it focuses on the fundamental principles that govern the volume change, shear strength, yield surfaces, water retention and hydro-mechanical coupling. Alternative forms of these principles are critically examined in terms of their advantages and disadvantages. The paper also presents a short summary of implementing constitutive models into the finite element method.
