Modelling plasticity of unsaturated soils in a thermodynamically consistent framework

O. Coussy (1) , Jean-Michel Pereira (2)

1 navier umr 8205 - Laboratoire Navier
2 cermes - Géotechnique

Constitutive equations of unsaturated soils are often derived in a thermodynamically consistent framework through the use a unique 'effective' interstitial pressure. This later is naturally chosen as the space averaged interstitial pressure. However, experimental observations have revealed that two stress state variables were needed to describe the stress-strain-strength behaviour of unsaturated soils. The thermodynamics analysis presented here shows that the most general approach to the behaviour of unsaturated soils actually requires three stress state variables: the suction, which is required to describe the retention properties of the soil and two effective stresses, which are required to describe the soil deformation at water saturation held constant. Actually, it is shown that a simple assumption related to internal deformation leads to the need of a unique effective stress to formulate the stress-strain constitutive equation describing the soil deformation. An elastoplastic framework is then presented and it is finally shown that the Barcelona Basic Model, a commonly accepted model for unsaturated soils, as well as all models deriving from it, appear as special extreme cases of the thermodynamic framework proposed here.

Mots clés: Thermodynamics; Elastoplasticity; Suction; Pore pressures

Domaines: Mécanique des matériaux [physics.class-ph]; Mécanique des matériaux [physics.class-ph]

O. Coussy, Jean-Michel Pereira. Modelling plasticity of unsaturated soils in a thermodynamically consistent framework. Poromechanics IV - Proceedings of the 4th Biot Conference on Poromechanics, Jun 2009, Columbia University, New-York, United States. pp.252-257. ⟨hal-00525916⟩