Search

This paper presents a comprehensive investigation of the swelling behaviour of a compacted bentonite–sand mixture subjected to hydration under constant volume conditions. Contrary to previous studies, the tested sample was isotropically compacted before being hydrated under constant volume conditions until full saturation was reached. The total axial pressure, total radial pressures at four different heights of the sample, and injected water volume were recorded over time. The experimental data reveal a complex and non-uniform evolution of the axial and radial stresses over time, as well as anisotropy of the total stresses, which persist at the saturated equilibrated state. To gain further insights, a numerical analysis was performed using an advanced hydromechanical framework for partially saturated porous media, accounting for the evolving microstructure of the material. The complex evolution of the total axial and radial pressures with time is attributed to the advancing hydration and swelling front in the sample, along with the development of irreversible strains. The good agreement between the numerical results and the experimental data enables validation of the developed framework. Implications for engineered barriers in deep geological disposal of radioactive waste are discussed. Highlights: The swelling behaviour of an isotropically compacted bentonite-based material under constant-volume conditions is investigated. Hydration of the sample generates stress heterogeneity and anisotropy, which persist at the saturated equilibrated state. Numerical modelling shows that the complex evolution of the total axial and radial pressures can be attributed to the advancing hydration and swelling front in the sample, along with the development of irreversible strains. The relationship between the local dry density and the radial stress seems to follow the global dry density-swelling pressure trend determined on small-scale samples. [ABSTRACT FROM AUTHOR]

Bentonite-based materials have been studied as potential barriers for the geological disposal of radioactive waste. In this context, the hydro-mechanical behaviour of the engineered barrier is first characterized by free swelling conditions (as a consequence of the progressive filling of technological gaps) followed by constant volume conditions. This paper presents an experimental study conducted in order to characterize the water retention behaviour of a compacted MX-80 bentonite/sand mixture. The water retention properties upon wetting were investigated under both free swelling and constant volume conditions. In the high suction range, the water content was not influenced by the imposed volume constraints. On the contrary, swelling significantly affected the water retention behaviour at low suctions, and the quantity of water stored was higher under free swelling conditions than it was under prevented swelling. In this case, competing effects between bentonite swelling and water uptake did not lead to an increase of the degree of saturation upon wetting, as it was observed for samples wetted under constant volume conditions. The influence of the very strong hydro-mechanical coupling is further discussed. [ABSTRACT FROM AUTHOR]