A Comparative Study of Spatially Mobilized Plane (SMP) Based Extensions to the Modified Cam Clay (MCC) Model for Lode Angle Dependency

The fundamental Cam-Clay constitutive model for soils did not include strength anisotropy in the deviatoric plane (i.e., Lode angle effects) through a modified failure criterion, so there was no difference in deviatoric stress between the compression and extension paths. However, the extension triaxial and true triaxial tests exhibit differences in shear resistance response compared to the compression path. This difference in shear stress response can impact numerical simulations because the stress paths can be uncertain throughout the domain of the simulated model. The paper presents three straightforward methods to incorporate Lode angle effects using the Matsuoka-Nakai criterion. Triaxial compression and extension tests under drained and undrained conditions were simulated. Several lessons were learned from these simulations about the ease of incorporating the Matsuoka-Nakai criterion and the differences between simulations using three methods. Finally, an extensive discussion focuses on identifying the most suitable alternative for simulating soil mechanical behavior. This discussion was intended as a simple improvement to the modified Cam Clay model for basic simulations or as a basis for further, more complex model development.