Dynamic behavior of pile-foundations during earthquakes is important for the performance of many foundations. To clarify the mechanism of the soil-pile interaction, we have conducted a series of numerical analysis of a single pile foundation in the different types of a two-layer ground. Upper layer of the ground is composed of dense sand, reclaimed soils, medium dense sand or loose sand, and the lower layer of the ground is composed of clayey soils. In the liquefaction analysis, we have used a fully coupled effective stress analysis method with the cyclic elasto-plastic and elasto-viscoplastic constitutive models for sandy soils and clays. In the FEM, u-p(solid phase displacement-pore water pressure) formulation is adopted. From the numerical results, effect of liquefaction on the single pile-soil interaction has been clarified
