State boundary surface of a hypoplastic model for clays

The paper studies some consequences of the mathematical formulation of the recently proposed hypoplastic model for clays. Particular attention is paid to the question if the hypoplastic model predicts existence of the state boundary surface, defined as a boundary of all admissible states in the stress-void ratio space. It is shown that the model enables us to derive an explicit formulation of asymptotic (swept-out-memory) states in the stress-void ratio space, which constitute so-called swept-out-memory surface. Further it is demonstrated that the swept-out-memory surface is a close approximation of the state boundary surface although, in general, they do not coincide. Finally, the influence of constitutive parameters on the shape of the swept-out-memory surface is studied. For parameters reasonable for fine-grained soils its shape is similar to the state boundary surface of the Modified Cam clay model.