Optimization of concrete lining for the geological storage of radioactive waste in clay formations (en ce compris une introduction à la méthodologie de la recherche)

Abstract

The long-term geological disposal of radioactive waste requires the construction of deep underground repositories consisting of extensive networks of galleries, each supported by a concrete lining designed to ensure structural integrity over very long time scales. Given the scale of such infrastructure, optimising the lining design and, in particular, its thickness represents a significant challenge. This work investigates the mechanical behaviour of concrete linings installed in Boom clay, the host rock studied for the Belgian deep geological repository, using the finite element code LAGAMINE developed at the University of Liège. The modelling strategy is deliberately progressive: starting from a simple isotropic, purely mechanical configuration validated against analytical solutions derived from the convergence-confinement method, complexity is gradually introduced through stress anisotropy and hydro-mechanical coupling. The model represents the excavation of a circular gallery at a depth representative of the HADES underground research laboratory (225 m). A parametric study is then conducted to assess the influence of the main governing parameters such as the gap size between the lining and the rock, the initial stress state, the coefficient of earth pressure at rest and the deconfinement profile on the contact pressure acting on the lining. The results show that larger gap sizes delay the onset of contact and reduce the equilibrium contact pressure, while higher initial stresses and lower values of the coefficient of anisotropy increase the anisotropy of the loading around the lining. The introduction of hydro-mechanical coupling reveals a significant time-dependent component to the lining loads, driven by the progressive dissipation of excess pore pressures in the Boom clay over timescales of decades. These findings provide quantitative relationships between key design and geological parameters and the resulting lining loads, which can serve as practical guidelines for the optimisation of gallery linings in deep geological repositories.