State boundary surface of a hypoplastic model for clays

Abstract

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.

Directional response of a reconstituted fine-grained soil—Part II: performance of different constitutive models

“…Interestingly, the response predicted by the two K-hypoplastic models is quite satisfactory when compared to the experimental data, although no such concept as a Bounding Surface is introduced in their formulation. The appearance of a state boundary surface in the model predictions is, in this case, a combined effect of the assumed barotropy and pyknotropy functions, which endow this particular version of K-hypoplasticity with a single critical state line and a unique virgin isotropic compression line (Mašín and Herle, 2005).…”

DISCUSSION: Hypoplastic Cam-clay model. D. MAšíN (2012) Géotechnique 62, No. 6, 549–553, http://dx.doi.org/10.1680/geot.11.T.019

“…Incorporation of stiffness anisotropy into hypoplasticity was, in fact, one of the motivations behind the development of the new hypoplastic approach and the author is glad that this potential of the new formulation has been recognised by the discussers. In the earlier hypoplastic models, the stiffness tensor L controlled together with N and scalar factors f s and f d the shape of the ASBS (see Mašín & Herle (2005) and Mašín (2012b)). Any modification of L thus modified also the ASBS, most likely in an undesired way.…”

Benchmark of constitutive models for unsaturated soils

“…The CU model is instead formulated in the context of the hypoplasticity theory, which does not distinguish between elastic and plastic strains but describes irreversible behaviour by means of an incrementally non-linear stress-strain relationship, where material stiffness depends on both stress state and direction of strain vector. Though being algebraically different, the CU model is based on critical state soil mechanics similarly to the other models (Gudehus and Mašín, 2009) and incorporates the so-called swept-out-memory surface (Mašín and Herle, 2005) as an alternative to the yield surface of elasto-plastic models.…”