3468 - DAMAGE MODEL FOR FAILURE ANALYSIS WITH A VIEW TO HYDROMECHANICAL PROBLEMS

In some cases, the evaluation of the leaking rate through a concrete structure is a crucial step. For nuclear power plants for example, the hydraulic integrity of the containment building is a point of concern for energy producers like EDF in France. The sealing of the barrier between the inner nuclear part and the outer environmental one has indeed to be ensured even in cases of strong accidents. To estimate the durability of the structure in time (ageing process), the effect of a mechanical load on the transport properties, and especially on the hydraulic conductivity, has thus to be investigated. The main question is to quantify the evolution of the permeability with load and to determine which mechanical properties affect it. From a combined mechanical – hydraulic discrete approach, based on lattice models, it is shown how, for pre – peak situations, the value of the damage is the most appropriate variable to quantify the evolution of permeability. It also proves, for unloaded specimens, the independence of the law on the material properties of concrete, proposing a theoretical explanation to some former experimental observations (Picandet et al. [1]). From this study, the description of the damage evolution during loading becomes a crucial point. A misevaluation of this variable would indeed directly induce an error on the coupled permeability. The choice of the associated model has thus to be done carefully. For pre-peak simulations, continuum mechanics is the most adapted framework. Nevertheless, elastic damage models or elastic plastic constitutive laws are not totally sufficient to describe the concrete behaviour. They indeed fail to reproduce the unloading slopes during cyclic loads which define experimentally the value of the damage in the material. A combined elastic plastic damage model is thus proposed : damage is responsible for the decrease in the unloading slope (cracking) while plasticity reproduces the evolution of the irreversible strains. The constitutive relation is validated on a cyclic compression test. It gives the opportunity, in a view to hydromechanical problems, to highlight the interest of including plasticity if a misevaluation of the permeability needs to be avoided.