Numerical Simulation Of Dense Sand Behavior Under Multidirectional Seismic Loading Using A New 3-D Constitutive Model

Saturated, dense sands subjected to strong shaking from earthquakes may not liquefy but can experience total and differential settlements that can impair an overlying structure. Many available studies and procedures have focused on liquefaction-induced seismic settlements or settlements due to seismic compression in loose to medium-dense sands under uni-directional loading. In contrast, there are few studies related to the shear and volumetric response of dense to very dense saturated sands under multi-directional seismic loading. In this study, a 3-D, distributed element plasticity-based, effective mean stress-dependent constitutive model (I-soil) is introduced for dense to very dense sands. This constitutive model captures: (1) both Masing and non-Masing type hysteretic behavior; (2) small strain nonlinearity; and (3) shear-induced volumetric behavior including settlement and excess porewater pressure generation/dissipation. The model parameters defining shear stress - shear strain behavior are determined using shear wave velocity, a normalized strain-dependent modulus reduction curve, and damping curve. Shear induced volumetric response is calibrated using shear strain - volumetric strain response data from laboratory tests. The resulting model was implemented in a dynamic finite element analysis program and can capture the shear and volumetric behavior of saturated sands (with relative densities of 65 to 100%) measured in cyclically loaded laboratory specimens, as well as free-field and soil-structure system dynamic centrifuge tests. The simplicity of the mathematical formulation of the constitutive model allows the simulation of full scale 3-D soil-structure interaction problems within a couple of hours using single and multi-CPU simulations on a personal computer.