Prediction Model for the Saturated Permeability Coefficient of Compacted Bentonite

Bentonite is unanimously recognized by the international community as the ideal buffer/backfill material in deep geological repositories for high-level radioactive waste. The low permeability of compacted bentonite blocks is a key factor in preventing external groundwater from corroding metal canisters containing high-level waste and preventing the outward migration of nuclides. Research on the establishment of predictive models for permeability is of paramount importance for the safe operation of repositories. Based on the dispersion of compacted bentonite into stacked montmorillonite particles after hydration and swelling, a modification of the theoretical calculation of the saturated permeability coefficient was introduced in this study, establishing a numerical relationship between the permeability coefficient and the montmorillonite void ratio. The relationship between the montmorillonite void ratio (em) and overlying stress (p) can be predicted via a fractal model, thereby deriving the relationship between the permeability coefficient (k) and the overlying stress. The permeability coefficient of commercial bentonite was determined via the consolidation method, and the permeability coefficients of the MX-80 and GMZ01 bentonites obtained by previous researchers were compared with the proposed k‒p relationship. The results indicate that the experimental data of the three types of bentonite correspond well to the theoretical values.