Evaluation of the damping ratio of compacted sodium and calcium bentonites in unsaturated conditions

Bentonites are going to be part of the Engineered Barrier System (EBS) in deep geological disposal facilities for the safe disposal of spent nuclear fuel. Some of these repositories might be constructed in tectonically active locations, and some other repository locations might have seismic risks in future related to climate changes (e.g. glaciations). The damping ratio is one of the parameters considered in dynamic analysis, and it can be measured by different methods. In this work, the damping ratio was measured in two different bentonites with the resonant column device and in one of these bentonites, it was also measured with the hollow cylinder, simple shear and triaxial tests in unloading–reloading paths. The results are presented in Pintado et al. (2019; 2023). The tests were carried out at different laboratories. The samples were compacted at different dry densities and degrees of saturation and tested with different confinement pressures and strain levels to study the influence of the shear strain, degree of saturation, dry density and confinement pressure and also the influence of the test method. The two studied bentonites had different plasticity indices which was also considered in the analysis. The results showed a clear dependence of the damping ratio on the confinement pressure and the shear strain but not as clear on the degree of saturation, the dry density and the plasticity index. The damping ratio measured by the hollow cylinder test followed the tendency of the resonant column results. The triaxial test presented larger values of damping ratios than following the tendency of the hollow cylinder and resonant column tests. The simple shear test did not follow the tendency of the other tests, presenting lower damping ratio values. All tests presented large scatter.