Upper-bound and lower-bound solutions for the axisymmetric compression of a concrete plug

Abstract : Deep radioactive waste deposits require specific solutions to close underground galleries and avoid any radioactive migration in the environment. One investigated solution consists of a swelling clay plug that induces a swelling pressure of approximately 7 MPa on the walls of the galleries. The clay plug is confined by a concrete plug to maintain and drive the swelling pressure towards the walls of the galleries. The concrete plug must therefore be designed to endure such a pressure. This paper addresses the mechanical strength of a cylindrical concrete plug with a ring-shaped tooth, a free face and a uniform compressive stress over the other face. Two experimental tests over 1/43 reduced samples are first performed and show two collapse mechanisms: dome collapse and tooth-shear collapse. Upper- and lower-bound solutions are investigated based on the Mohr–Coulomb criterion from nonlinear criteria of concrete. The choices of parameters for the friction angle (φ) and cohesion (C) are discussed in relation to the uniaxial compressive and tensile strength of the concrete and the magnitude of the stresses in the model. The results of the simplified analytical, numerical and experimental approaches are then compared, with good agreement found between the approaches.