hello mohsen, 

as you know the BBM is a purely mechanical model that can evaluate and predict the wetting collapse, elastic domain expansion due to suction, stiffness dependency on suction etc. however, for unsaturated soils, it is important to have include the hydraulic behavior (meaning water retention behavior) in modeling since there are important linked effects. thus, BBM per se, it is enough since it neglects the hydro-mechanical behavior.

in more fundamental view, BBM is developed based on two independent stress approach by choosing net stress and matric suction as state variables. there are numerous information available about the inconsistency of two independent stress approach in evaluating the skeleton stress or effective stress to be more precise. meaning that, using two independent stress approach you cannot define a true skeleton stress field in numerical modeling. in addition, it is important to have a smooth transition from unsaturated condition to saturated condition. in two independent stress approach, this only happens through the mechanical model itself not the stress field. 

i suggest to you to take a look at wheeler et al. (2003) and Nuth (2009) constitutive models. they used generalized effective stress equation as constitutive stress in their modeling. their model has simpler yield locus but you can intertwine the hydraulic behavior with mechanical behavior more efficiently.