Search

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.

Modelling of engineered barrier systems (EBS) in deep geological disposals of spent nuclear fuel requires sophisticated approaches that include highly nonlinear constitutive models. The Barcelona Basic Model for Expansive soils (BBMEx) is an extension for highly expansive unsaturated soils of the Barcelona Basic Model (BBM) for slightly-to-moderately expansive unsaturated soils. In this extension, the parameter κ (logarithmic compliance with respect to changes in net pressure) of the BBM is extended to a function of suction and a set of parameters, and the parameter κs (logarithmic compliance with respect to changes in suction) of the BBM is extended to a function of net pressure, suction, and a set of parameters. On these functions, four conditions which are satisfied in the BBM are considered. For each condition, two results are obtained: (1) the ranges of the values of the parameters such that the condition is satisfied for all positive net pressures and all non-negative suctions and (2) for given values of the parameters, the maximum net pressure and the maximum suction such that the condition is satisfied for positive net pressures and non-negative suctions. The results should help prevent unrealistic predictions of the BBMEx. The extension was used for carrying out the simulation of an infiltration test in two different bentonites and the BBMEx model parameters analysed.