Sand flow liquefaction instability under shear–volume coupled strain paths

Flow liquefaction of sands is commonly studied by means of undrained tests. However, experimental findings indicate that seepage-induced change in pore-water pressure after earthquake cessation may lead to shear–volume coupled strain paths and, consequently, a remarkable departure from the undrained presumption is anticipated. This paper presents the formulation of a state-dependent constitutive model for sands. A second-order work criterion is applied to predict the onset of flow liquefaction instability under various shear–volume coupled strain paths. It is shown that pore-water inflow as imposed by different shear–volume coupled strain scenarios may lead to drastic loosening of the soil load-carrying structure and, eventually, flow liquefaction instability even worse than that under undrained condition. The effective performance of the state-dependent constitutive model in the simulation of the mechanical behaviour of Fraser River sand samples subjected to shear under a wide domain of drainage conditions is demonstrated.