Modelling the hydromechanical behaviour of a granular expansive clayey soil upon hydration using discrete element method

Bentonite-based pellet materials are considered as a sealing material for the isolation of galleries in the French radioactive waste disposal concept, owing to operational convenience. The influence of the granular nature of the material is studied through Discrete Element Method (DEM) simulations. Each pellet is modelled individually and represented by a sphere of same mass and density as real pellets. Swelling pressure tests of pellet mixtures, carried out at laboratory scale, are simulated using a model describing the hydromechanical behaviour of a single pellet upon suction decrease. The mixture behaviour is satisfactorily reproduced upon hydration from 89 MPa (initial state) to 7 MPa of suction. The model is then used to study the behaviour of large granular assemblies of bentonite pellets on the same hydration path. Results highlight that the mixture assembling process, the pellet strength and stiffness, and the mixture density have an influence on the swelling pressure development upon hydration. Numerical results obtained through DEM simulations will be of interest for future Finite Element Method simulations of the full hydration path using double structure models where pellets correspond to the microstructural level.