The fabric anisotropy of sand significantly affects its mechanical deformation behavior. To accurately characterize this feature

a constitutive model for sand that incorporates fabric anisotropy is proposed

based on the anisotropic critical state theory and the generalized potential theory. First

a variable referred to as virtual peak deviatoric stress is introduced into the hyperbolic model to simulate both the softening behavior of dense sand and the hardening behavior of loose sand. On this basis

the conventional state parameter is replaced with a dilatancy state parameter that captures the evolving characteristics of fabric anisotropy. A stress-strain relationship considering fabric anisotropy is then established in the principal stress space. Subsequently

using the generalized potential theory and the concept of quasi-elastic-plastic deformation

this relationship is extended to the general stress space

leading to the development of a constitutive model that incorporates fabric anisotropy is established. The proposed model is finally applied to simulate drained and undrained triaxial compression/extension tests

as well as hollow cylinder torsional shear tests on Toyoura sand. The simulations demonstrate close agreement with experimental results

confirming the model’s validity. With 13 material constants

the model effectively describes the mechanical behavior of sand across a wide range of stress levels and densities

and successfully captures the influence of fabric anisotropy on its mechanical response.