Hydro-mechanical behaviour of binary bentonite pellet and powder mixtures

EasyChair Preprint 4216

Abstract

Binary mixtures of high-density bentonite 80%pellets and 20% powder at hygroscopic water content are currently being considered as an alternative engineered barrier system for the long-term disposal of radioactive wastes. These mixtures display a dry density around 1.49 Mg/m3 on pouring, and the powder is underfilling the voids between coarse pellets (the degree of powder filling at hygroscopic water content is around 0.68). The mixture presents multi-modal porosity features that significantly evolve during the hydro-mechanical paths. Water retention and water permeability results are presented for each of the constituents and the mixture. Compressibility results on loading under oedometer conditions and at different hydraulic states are also discussed for the constituents and the mixture. In addition, selected test results under constant volume hydration are presented to gain insight into the coupled hydro-mechanical response of the mixture. The inflow of water volume and swelling pressure, as well as the progressive changes of the pore size distribution on wetting, have been determined. These hydro-mechanical tests have been used to calibrate a numerical model based on the discretization of pellets and powder using Code_Bright FEM. The model has been developed to study local and global responses on wetting at constant volume, such as water mass transfer between powder and pellets, evolution of local degrees of saturation and porosities –inside pellets and powder–, and mean stress evolution in pellet and powder domains. The simulation allows observing that the mixture tends towards a uniform structure of porosity as the pellets expand and the clay powder is compressed by pellets.

Keyphrases: Hydromechanical behaviour bentonite, compressibility, water permeability, water retention

@booklet{EasyChair:4216,
  author    = {Arisleidy Mesa Alcantara and Enrique Romero and Nadia Mokni and Sebastia Olivella},
  title     = {Hydro-mechanical behaviour of binary bentonite pellet and powder mixtures},
  howpublished = {EasyChair Preprint 4216},
  year      = {EasyChair, 2020}}