Anisotropy of Pressure Generated by Water Absorption of Deformation-Constrained Granular Bentonite Specimens

Bentonite is being considered for use as a buffer material in the geological disposal of high-level radioactive waste, and studies of its swelling pressure have been conducted. However, most of the previous studies have measured only the vertical pressure and not the lateral pressure. In this study, the vertical and lateral pressures generated by water absorption in a granular bentonite specimen under deformation constraints were measured. The results showed that the lateral pressure converged to a value slightly greater than the vertical pressure, with a difference of about 200 kPa for a dry density of 1.6 Mg/m3 and about 100 kPa for a dry density of 1.4 Mg/m3. The larger specimen volume required more time to converge, but if the dry density were equal, there was no significant difference in the convergence value of the pressure. This suggests that the use of specimens with small dimensions is effective in obtaining pressure properties of granular bentonite in a short time.