: The objective of this work is to propose a constitutive model in order to describe coupled plastic damage behaviour of partially saturated concrete and hard rocks. Plastic behaviour is characterised by using two yield surfaces respectively for stress controlled and suction controlled plastic deformations. Effect of capillary pressure on stress controlled plastic deformation is taken into account through definition of a plastic effective mean stress. Only isotropic damage is considered in this work, which is controlled by tensile strains. The proposed model is implemented in a finite element code by using a fully coupled and implicit algorithm. One typical application case is finally studied concerning bending of a concrete beam. The results obtained seem to be relevant to show the importance of drying effect in study of strength and failure of such structures (applications to hard rocks are not presented here due to limitation of paper length).
1 INTRODUCTION
Hard rocks and concrete are widely concerned in various civil engineering constructions. There are several common features in mechanical properties of these two classes of materials, for instance, induced damage by nucleation and growth of microcracks, volumetric dilatation, asymmetric responses under compressive and tensile stresses. Further, in many structures, these materials are submitted to drying and wetting processes. As their mechanical properties are usually very sensitive to moisture content, reliable modelling of material behaviours in saturated and unsaturated conditions becomes one of key issues in durability and failure analysis. During the last thirty years, many advances have been performed for unsaturated soils and clays both in experimental investigation and constitutive modelling, for instance Alonso et al. (1987, 1990). However, significant efforts are still necessary for modelling of unsaturated hard rocks and concrete. This is probably related to technical difficulties in experimental testing for these materials. This paper addresses a numerical modelling by using an elastoplastic damage model. However, only isotropic damage is considered in this stage. The model is formulated in the framework of plasticity for unsaturated media and continuum damage mechanics. Two yield surfaces are used for the description of plastic deformation respectively controlled by stress and suction. The damage of material is characterised by extension of the damage model proposed by Mazars (1984). The proposed model is implemented into a FEM code by using fully coupled and implicit algorithm. Simulations of laboratory tests are provided to show overall quality of numerical predictions. One application example is finally presented.
