A Drucker-Prager J2 multi-surface-plasticity sand model is modified to employ the Lade-Duncan failure criterion as the yield function. This function includes the first and third stress invariants to account for the dependence of cyclic shear stress–strain behavior on confining pressure and the Lode angle. Related modifications to the flow rule and hardening rule are described. Dependence of dilatancy on confinement is also included. Salient features of the model performance are presented under general three-dimensional (3D) loading conditions, where the yield function provides a more accurate representation of nonlinear shear response. Dynamic response analyses of a mildly inclined infinite slope are performed to illustrate the influence of excitation direction on the accumulation of liquefaction-induced lateral ground deformation.