Thermodynamic model on swelling of bentonite buffer and backfill materials

Sato, Haruo

Swelling pressure of bentonite was estimated based on the thermodynamic data of water on the surface of smectite which is a major clay mineral constituent of the bentonite composing engineered barriers and backfill materials. The activity and the relative partial molar Gibbs free energy (dEa) of water on the surface of smectite as a function of water content in a density range of 0.6-0.9 Mg/m. The activity and dG of water decreased with decreasing water content and showed similar trend to data of Kunipia-F bentonite (almost 100wt.% smectite) reported in the past. Swelling presure was estimated from the difference in the chemical potential balance of water in equilibrium state between free water and misturized smectite, and compared to data measured for various kinds of bentonites. The calculated swelling pressures were in good agreement with the measured data. This indicates that swelling pressure of bentonite can be calculated based on the thermodynamic data of water.