Incorporation of a fabric tensor in sand model

摘要

This paper shows how to incorporate a fabric tensor into conventional plasticity model to reproduce anisotropy effects. This fabric tensor can be simple and have a clear physical meaning. For transversely isotropic sand, only one material constant is needed to characterize the anisotropy intensity. The fabric anisotropy effects must be described objectively, and only the relative orientation between the loading and soil fabric is relevant. Therefore, one must use joint invariants of the stress and fabric tensors to describe the anisotropy effects. It is shown that a joint invariant can be defined with a minimum of mathematical complexity, and such a joint invariant may play two roles in a plasticity model: One is passive, which simply modifies certain parameters so that the model response depends on the loading direction relative to the fabric orientation. The other is active, which acts as a loading increment for a change in this relative orientation. This active role brings a model into the category of hypoplasticity, a necessary mechanism when non-proportional loading is dominant.