Description of inherent/induced anisotropy of soils: Rotational hardening rule with objectivity

The inherent/induced anisotropy of soils was described concisely by the concept of the rotation of the yield surface around the origin of stress space, called the rotational hardening by Hashiguchi (1977), whilst the description of the inherent anisotropy of natural grounds by the rotation of the yield surface was advocated by Sekiguchi and Ohta (1977). In this article the interpretation of the evolution rule for the rotation of the yield surface, i.e. the rotational hardening rule for soils is given on the pertinent physical background, revealing the similarity to the nonlinear kinematic hardening rule for metals. The rotational hardening variable is the second-order tensor and thus the material-time derivative does not obey the ordinary transformation of a second-order tensor losing objectivity. Some comments for its pertinent integration are given in brief.