ABSTRACT
An important number of constitutive models for unsaturated soils have been presented since the formulation of the Barcelona Basic Model or BBM (Alonso, Gens and Josa, 1990). Detailed descriptions on constitutive models for unsaturated soils are available in various review articles (Gens, 1996; Wheeler and Karube, 1996; Jommi, 2000; Gens et al., 2006; Sheng et al. 2008b; Gens, 2010). Amongst them, a useful model classification, based on the constitutive variables used to formulate the model, is presented in Gens (2010) and is followed in this paper to support the discussion. According to Gens (2010) it is generally accepted that at least two constitutive variables are required to correctly represent the main features of unsaturated soil behaviour. In the light of this, the different constitutive models considered in this paper employ two different pairs of constitutive variables and, therefore, each model belongs to a separate class (see Gens, 2010).
