Validation of a Hypoplastic Model for Sand

This paper presents the development and validation of a hypoplastic model for sand within an extended hypoplastic framework. The proposed model is constructed by augmenting the basic hypoplastic formulation underlying the so-called reference hypoplastic model with two additional tensorial terms. This modification ensures that the maximum stiffness, represented by the size of the response envelope, remains unchanged but is no longer coaxial with the stress tensor except under isotropic conditions. The performance of the developed model is evaluated against comprehensive experimental data for Karlsruhe fine sand, covering a wide range of relative densities, confining pressures, and boundary conditions. The proposed model exhibits improved accuracy in predicting peak deviatoric stresses for dense sands under drained triaxial conditions. Undrained test simulations highlight improved predictive capabilities in extension, although limitations persist in accurately modeling the behavior of dense sand in compression.