Seismic deformation analysis of earth dams subject to liquefaction using UBCSAND2 model

The prediction of expected seismic deformation subjected to liquefaction plays a crucial role in the design stage of earth dams located in regions of moderate to high seismicity. This technical note is a short communication following the effective stress model called UBCSAND2, which is used to assess the liquefaction-induced damages occurring at a well-documented case study of earth dams: Lower San Fernando Dam (LSFD) near the epicenter of the 1971 San Fernando earthquake. The model itself can predict the effect of the initial horizontal stress ratio K₀ (= σ′_x/σ′_y) of soil elements beneath the slopes under direct simple shear conditions. This is usually not included in predicting liquefaction when using alternative practical constitutive models. Before the numerical modeling of the case study, the model was calibrated with typically drained and undrained behaviors of single elements under monotonic and cyclic Direct Simple Shear (DSS) loading using generic input parameters for different relative densities. It was then calibrated by empirical data from liquefaction-triggering weighting curves. The numerical results indicate that the shear band development of the failure on the upstream side was consistent with the observed post-liquefaction slide analysis.