A simplified three-dimensional constitutive model for seismic modeling of dense sands

Dense sands subjected to earthquake shaking may not liquefy but experience differential settlements that can cause damage or limit the serviceability of overlying structures and utilities. Such settlements can be estimated using stress and/or strain based empirical models in conjunction with one-dimensional site response analyses utilizing normalized modulus reduction and damping curves and uni-directional ground shaking. Multi-directional effects are incorporated through applying additional factors. In contrast, there are limited number of studies on the three-dimensional (3-D) modeling of shear induced seismic response of sands. In this study, a simplified, mean stress-dependent constitutive model (termed I-soil) is presented for dense sands. The model adopts the framework of a class of multi-dimensional distributed-element models for cyclic plasticity applications. I-soil extends this framework for soil applications by adding non-Masing un/reloading rules and simplified shear induced volumetric response formulation. The shear response parameters can be calibrated using shear wave velocity, widely used normalized modulus reduction and damping curves. The shear induced volumetric response is calibrated using cyclic direct simple shear tests. Default values for model parameters and dynamic curves are proposed. The resulting model was implemented in a dynamic finite-element analysis platform, LS-DYNA. It is shown that simulations can capture the seismic shear and volumetric behavior of saturated sands measured under partially drained conditions in dynamic centrifuge tests.