SANICLAY-T: Simple thermodynamic-based anisotropic plasticity model for clays

Bounding surface rotational hardening model for overconsolidated clay accounting for evolving fabric anisotropy

“…The rotational α-γ model is proposed by Collins and Hilder, 36 in which the yield surface expression is formulated in the dissipation stress space through a dissipation function and then transformed into the true stress space through the nonzero back stress, which is different from the approach of assuming no stored energy (zero back stress) while adding an additional term in the dissipation function. 30 In fact, the back stress determines the 'center' of the ellipse yield surface in the p-q space with the deviatoric back stress being associated with the rotational angle. The yield locus in true stress space is a rotated and distorted ellipse, expressed as:…”

“…Another approach proposed by Rollo and Amorosi 30 assumes no plastic energy stored and thus the back stress term vanishes, but an additional term is added into the dissipation function as a compensation. Both approaches can result in the same total energy and yield surface, but the latter can naturally satisfy the requirement at critical state, as no restriction is imposed on the rotational angle 30 . However, Collins 31 and Li 32–34 suggested that plastic work is not fully but partially dissipated, with the remaining being frozen/stored.…”

“…Whether an oblique or non-oblique yield surface at critical state should be allowed in the modeling is still an open question, 8,19,20,30 and no corresponding experimental evidence is available. Dafalias and Taiebat 8 proposed an RH rule that resulted in an inclined yield surface at critical state owing to the tacit assumption of critical state anisotropic fabric, as evidenced by discrete element method (DEM) observations.…”

“…32,33,35 Therefore, no further accumulation in Helmholtz free energy is allowed and the deviatoric back stress should vanish. 32,33 Another approach proposed by Rollo and Amorosi 30 assumes no plastic energy stored and thus the back stress term vanishes, but an additional term is added into the dissipation function as a compensation. Both approaches can result in the same total energy and yield surface, but the latter can naturally satisfy the requirement at critical state, as no restriction is imposed on the rotational angle.…”

“…Both approaches can result in the same total energy and yield surface, but the latter can naturally satisfy the requirement at critical state, as no restriction is imposed on the rotational angle. 30 However, Collins 31 and Li [32][33][34] suggested that plastic work is not fully but partially dissipated, with the remaining being frozen/stored. The frozen/stored part can be used to interpret the physical meaning of back/shift stress in the kinematic hardening of plasticity theory.…”