Constitutive model for K0 overconsolidated clay under complex loading

After unloading, the K0 overconsolidated clay has both initial anisotropy and overconsolidation characteristics. Specifically, the characteristic of the K0 overconsolidated clay has the following three aspects: (1) When the major principal stress is loaded along the direction normal to the K0 consolidation deposition surface, the shear modulus is higher than that of the isotropic consolidation. (2) Due to the initial deviatoric consolidation, the critical state stress ratio of the K0 consolidated clay under triaxial compression is larger than that of the isotropic consolidation. (3) Cyclic loading leads to more significant overconsolidation characteristics and stress-induced anisotropy. Based on the UH model of the overconsolidated clay, a rotational axis parameter ζ, reflecting the initial anisotropy of the boundary surface, is introduced to increase the plastic modulus of the overconsolidated clay by inclining the boundary surface. By analyzing the dilatancy characteristics of the stress ratio, the state stress ratio is proposed to replace the normal stress ratio in the unified hardening parameter for reflecting the phenomenon of strain hardening and softening. The introduction of the rotational hardening rule is used to reflect the stress-induced anisotropy under complex loading paths. The unified hardening parameter is modified to reflect the plastic volume strain accumulation characteristics under cyclic loading, hysteresis and ratchet characteristics of plastic deviatoric strain and plastic deformation characteristics of unloading path. Based on the stress transformation method of t criterion, the new model is converted into a three dimensional constitutive model. By comparing the test and prediction results for a series of K0 overconsolidated clays in the undrained loading and cyclic loading paths, it is revealed that the new model can be conveniently applied to model the stress-strain relationship for K0 overconsolidated clay under complex loading paths. © 2022, Science Press. All right reserved.