A modi
fi
ed bounding surface hypoplasticity model is developed to capture distinct dilatancy behaviors of loose and dense sandy
soils during various phases of undrained cyclic loading. Based on observations from laboratory tests, new modulus formulations are proposed to
improve the simulation of cyclic mobility and postliquefaction behaviors of both loose and dense sands. The state-dependent dilatancy and
effects of accumulated plastic strains on the plastic moduli are also incorporated in this model. The model demonstrates excellent capabilities
through systematic comparison between the model predictions and
a series of undrained cyclic simple shear tests on Fraser River sand.