An Experimental and Numerical Investigation of the Mechanical Behaviour of a Concrete and of its Permeability Under Deviatoric Loading

This paper investigates the mechanical behaviour of a concrete under deviatoric loading. Special attention is placed on understanding the evolution of concrete permeability at different stress levels. The studied cement-based material, called CEMI, is the potential candidate for the engineering barrier of underground repositories for nuclear wastes. The description of an original experimental method, based on applying a transient flow, is firstly presented. Two groups of experimental tests are realized. The first group is conventional triaxial tests performed under different confining pressures. The other group is triaxial compression tests accompanied with simultaneous pressure evolution phases. In the pressure evolution phases, the evolutions of water pressures are measured on the upper and lower boards of samples which are mechanically loaded. The experimental investigation shows that the mechanical behaviour of concrete is characterized by: important residual strains developed in both axial and lateral directions and a progressive decrease of elastic stiffness during loading/unloading cycles. In view of this, a coupled elastoplastic damage model is proposed for studied material. In the proposed model, two damage variables are introduced in order to take into account the dissymmetric behaviour of concrete observed under tensile and compression conditions. On the other hand, the experimental results obtained during the pressure evolution phases show that the evolution of measured pressures dependents strongly the associated mechanical behaviour induced by external loading. As the movement of fluid through concrete is essentially controlled by the permeability of concrete, a phenomenological relationship for the permeability of studied material is then proposed to study numerically the evolution of pressures. Afterwards, the previous relationship is introduced in generalized hydraulic diffusion equation. The coupled hydromechanical tests (i.e. the triaxial compression tests accompanied with simultaneous pressure evolution phases) are simulated. A good agreement is obtained between experimental data and numerical simulations. Finally, the principal numerical results of a coupled hydromechanical test are analysed and discussed in order to give a good understanding the hydromechanical coupling process developed in CEMI.