Vortex and work from McGill University. Semi-empirical models have a number of limitations and shortcomings when they are used in multibody dynamics simulation environments. A novel approach, based on plasticity theory, was developed for wheel-soil interaction. This approach will be shown to resolve some of the shortcomings of semi-empirical models, while being compatible with the multi-body dynamic simulation environment in Vortex. In the proposed approach, a modified Drucker-Prager constitutive relation with cap hardening is used to capture soil plastic behavior. However, the formulation is general enough to include other constitutive relations developed for soil.