An effective stress model for predicting liquefaction behaviour of sand

An elastoplastic constitutive model is presented that simulates the liquefaction response of sands in a relatively uncomplicated manner. The model, UBCSAND, is based on the characteristic behaviour of the soil skeleton as observed in laboratory element tests. The model has several key features, including a hyperbolic relationship between stress ratio and plastic shear strain, a now rule for estimating plastic volumetric strain from plastic shear strain, and the ability to handle anisotropy. The simple framework which describes the observed soil response and forms the basis for the model is presented. Monotonic and cyclic results are computed using the model and shown to be in good agreement with laboratory element tests. The model is also applied to the Wildlife Site in Calfornia and the predictions compared with field measurements from the 1987 Superstition Hills Earthquake.