The seismic response of shallow foundations on liquefiable sand is studied herein through fully coupled effective stress analyses. The numerical methodology that is used, is based on a bounding surface model for non-cohesive soils implemented into the Finite Difference code FLAC2D. Model constants are calibrated against element laboratory tests on Nevada sand, while the simulation of centrifuge model tests of the VELACS project validates the User-Defined Model's performance on boundary value

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... blems. Using this well established methodology, parametric analyses are performed, for the common case of a thin clay cap overlying a liquefiable sand layer, in order to provide insight to the mode of failure and the mechanism of settlement accumulation. It is shown that groundwater flow during and immediately after shaking affects the response, while there is a "critical thickness" of the clay cap beyond which sand liquefaction does not lead to bearing capacity degradation is also evaluated.