Evolving Elastic and Plastic Fabric Anisotropy in Granular Materials: Theoretical and Applied Implications

In this paper a relationship between elastic anisotropy, as typically observed in clayey soils subjected to shear wave propagation tests, and plastic anisotropy, detected at yielding and leading to rotated yield loci, is proposed. Furthermore, elastic and plastic anisotropies exhibit an evolving character, as a consequence of the evolution of the fabric of the material induced, for example, by irreversible straining. First, the theoretical implications of the above evolving character of fabric, which leads to a new form of anisotropic elasto-plastic coupling, are investigated. Then, a strategy is proposed to take advantage of such a coupling to more effectively initialise the internal variables of any nonisotropic hardening plasticity model. This latter aspect is of crucial importance when numerically analysing the response of a whole deposit of soil, as for each sub-stratum it is mandatory to identify the initial orientation of the yield locus.