Hypoplastic model for sands

A hypoplastic model is formulated to simulate the nonlinear and irreversible behavior of loose and dense sands. Hypoplasticity provides a theoretical framework that is simpler than elastoplasticity. The failure surface that is assumed fixed in stress space is chosen as the bounding surface. All the hypoplastic properties (flow and yield directions and plastic modulus) are defined as functions of the distance to the bounding surface. The model is formulated in terms of stress invariants', the influence of Lode angle is accounted for by using an adjustable Lode dependence. The incremental stress-strain relationships are inverted and derived in a format compatible with solution techniques, such as finite element methods. The model has 12 material constants calibrated from triaxial tests. Based on the comparison of predicted and experimental results on loose and dense Sacramento River sands, it is concluded that the model is capable of predicting the drained and undrained behavior of loose and dense sands.