Unified modeling for clay and sand with a hybrid-driven fabric evolution law.

• A hybrid-driven fabric evolution law is proposed to describe the induced anisotropy. • The fabric tensor is properly integrated into the constitutive relations. • A novel anisotropic model for clay and sand is proposed. • The performance of the model is validated under different loading paths. • The model can reasonably describe the anisotropic characteristics of both clay and sand. This paper presents a novel critical state model for both clay and sand considering the inherent and induced anisotropy, named as CASM-h. The CASM-h model is developed based on the well-calibrated CASM model and incorporates the concepts of subloading surface and fabric anisotropy. To describe the induced anisotropy, a hybrid-driven fabric evolution law is proposed, defining fabric evolution as driven jointly by stress and strain rates. Subsequently, the fabric tensor together with its evolution law is appropriately incorporated into constitutive relation by employing the anisotropic transformed stress approach, without introducing additional mechanical mechanisms. The CASM-h model is validated under a series of stress paths, including triaxial tests, simple shear tests, shear tests with fixed principal stress direction as well as principal stress rotation (PSR) tests. The simulation results show that CASM-h model can satisfactorily capture the anisotropic behaviours of both clay and sand, such as the loading direction dependency of strength, non-coaxial behaviour, PSR effects and so on. [ABSTRACT FROM AUTHOR]