Validation of a strategy to predict secant shear modulus and damping of soils with an elastoplastic model

The assessment of seismic site effects such as ground motion and permanent displacement requires the accurate description of the soil's stress-strain-strength relationship under irregular cyclic loading from small to medium and at large strains. The main objective of this paper is to enhance and validate the performance of an elastoplastic constitutive law in modelling non-linear soil behaviour, with particular attention to the stiffness and damping evolution with deformation. First, a simple and rational strategy is presented to derive model parameters related to shear hardening based on experimental data. Secondly, as the elastoplastic law tends to overestimate damping in the large strain range in comparison with experimental data (Ishihara, 1996; Puzrin, 2012), a new parameter is introduced in the model to overcome this issue. The modified model response exhibits lower stiffness than the standard one. For sands, an effective reduction of the damping factor is achieved and good agreement is obtained for hysteretic loop and straindependent stiffness and damping curves. For clays, the reduction in damping is also achieved for large strains, but it also has a significant effect on the soil stiffness. Finally, numerical simulations of one-dimensional ground seismic response show that for sands the new parameter has no visible effect on the seismic soil response due to maximum shear strain level achieved, while for clays the reduction in both damping and stiffness occurs.