Measuring hydraulic conductivity and swelling pressure under high hydraulic gradients

The concept of a deep geological repository for high-level waste in the Czech Republic is based on disposal in a granite environment. The construction of an engineered barrier between the rock and canister is considered, and compacted swelling clay (bentonite) is chosen as the most suitable material for such a barrier. The most important geotechnical properties of bentonite in this context are low hydraulic conductivity and high swelling pressure. Measuring these parameters in such a low-permeable material requires much time. This study focuses on combined measurements of hydraulic conductivity and swelling pressure and on the impact of using high hydraulic gradients that are consistent with possible porewater pressures in a deep repository. High hydraulic gradients may also quicken the determination of these parameters. Results show a decrease in hydraulic conductivity with increasing saturation pressure up to a threshold dry density, with no further change at higher dry densities. The influence of saturation pressure on measured pressure decreases with dry density until a certain value is reached. For samples with lower density, the slope of the increase is close to unity.