Viscoplastic cyclic degradation model for soft natural soils

Cyclic loading affects the long-term response of geostructures build on natural soils. Soft soils are particularly susceptible to the development of large deformations, induced by the repetitive nature of loading. A new viscoplastic cyclic accumulation model is presented, which is an hierarchical extension of the Creep-SClay1S model, to model the long-term permanent deformation resulting from undrained cyclic loading of natural soft clays. The cyclic cumulative strains are incorporated by means of an additional viscoplastic multiplier. This cyclic viscoplastic multiplier adds four additional model parameters that are derived from undrained cyclic triaxial tests. The model is calibrated using experimental data from undrained cyclic triaxial tests performed on high quality block samples of natural Onsoy clay, at different average shear stresses, shear stress amplitudes and loading periods. The accuracy of the proposed model is demonstrated by comparing the element level simulations with the experimental data. The applicability of the proposed model is further illustrated with a boundary value problem, where an embankment submitted to cyclic loading is simulated. The use of the new model enables the simulation of the response of cyclic loaded foundations on soft soils, where the serviceability limit state over a long period of time is governing the design.