Cyclic Response of Natural Onsøy Clay

Geotechnical csonstruction projects in natural clay deposits are challenging because of the complex constitutive features of these clays (e.g. inherent and stress-induced anisotropy and destructuration). Cyclic loading, on the other hand, is typical for various geotechnical applications where natural clay deposits are involved such as wind and wave loads in relation to onshore and offshore foundations, ship locks or dams. This makes important to consider cyclic loads in the numerical simulations for geotechnical applications in natural clay deposits. Therefore, in case of natural clays it is essential to have proper constitutive models accounting for the clay material response to the cyclic nature of the loading in order to have reliable predictions of the time-dependent consolidation behavior and the corresponding development of the ground settlements. Within the present study the influence of the constitutive model on the numerical simulation of the natural clay consolidation under cyclic loading is qualitatively investigated employing the experimental results for a typical natural clay reported in the companion paper Cyclic response of natural Onsøy clay – Part I: Experimental analysis. The approach followed in this paper employs an adequate hierarchical constitutive soil model based on the bounding surface plasticity (BSP) concept. The hierarchical structure of the constitutive model makes it possible to investigate the importance of a particular feature of the model such as the inherent and the stress-induced anisotropy, the structure and the destructuration by activation/deactivation of the associated constitutive parameters. Finally, the model responses (such as the evolution of the excess pore-pressure and the settlement during cyclic loading) of each model of the hierarchical family are compared and discussed with respect to the necessity of the model complexity level. In order to calibrate the constitutive parameters a number of geotechnical experiments are numerically simulated considering natural and reconstituted Onsøy clay samples under drained and undrained hydraulic conditions. Moreover, the significant influence of the destructuration and the features of the BSP concept on the model response under consolidation induced by cyclic loading is highlighted. In conclusion, it is shown that the presented constitutive model based on the BSP concept is generally capable to predict the consolidation behavior of natural clay induced by cyclic loading. The model is suitable to simulate the main phenomena such as the pore-water pressure dissipation behavior and the associated but retarded evolution of the settlement.