Modification of SANISAND-MSf Model for Simulation of Undrained Cyclic Shearing under Nonzero Mean Shear Stress

Adequate simulation of undrained cyclic shearing of sands subjected to nonzero mean shear stresses is crucial for understanding complex behaviors associated with seismic liquefaction. This study presents the modification of a constitutive model, SANISAND-MSf, specifically designed to capture the effects of nonzero mean shear stresses on cyclic shearing responses. The novel model introduces a new constitutive ingredient, the shear stiffness enhancement, which progressively adjusts plastic shear stiffness and dilatancy, allowing for the simulation of residual deformation accumulation in scenarios in which initial liquefaction is hindered. Additional modifications are applied to the existing memory surface and semifluidized state constitutive components to accommodate nonzero mean shear stresses and asymmetric loading conditions. The new version of the SANISAND-MSf model was validated against various laboratory experiments involving symmetric and asymmetric cyclic mobility and residual deformation accumulation responses. The generic nature of the new and modified ingredients allows their incorporation into any bounding surface plasticity model. This study contributes to the advancement of constitutive models for seismic liquefaction-induced displacements, enhancing predictive accuracy for geotechnical risk assessment and mitigation strategies.