Mechanism of pile foundation response in liquefiable soils under seismic cyclic ground motion

The mechanism of the dynamic response of pile foundations in liquefiable soils under excitation of seismic cyclic ground motion is investigated through study of the actual behavior of pile foundations in earthquakes as well as comparison of the accelerations, displacements, interaction forces between pile and surrounding soil, dynamic p-y curves of pile, bending moments of pile and pore water pressures between shaking table tests of pile foundations in non-liquefied and liquefied soil layers under uniform and realistic seismic excitations. The results indicate that the inertia force of the superstructure controls the behavior of pile foundation. The pile bending moments and the pile-head acceleration basically follow the acceleration history. Although the lateral rigidity of the soil layer decreases with the liquefaction process, the pile-soil interaction increases significantly due to the increase of the soil displacement and the relative displacement between pile and soil during liquefaction, i.e., the effect of the increase in soil relative displacement on the increase of pile-soil interaction force is significantly larger than the effect of the decrease in soil lateral rigidity on the decrease of pile-soil interaction force. The maximum pile-soil interaction force appears at peak soil displacement rather than at soil acceleration peak. In the non-liquefied soil, soil pushes the pile and inertia force is the dominant factor, whereas in the liquefied soil, pile pushes the soil, and soil displacement is the dominant factor. The existing quasistatic method considering only soil rigidity deterioration is not suitable for simulating the response of pile foundations in liquefiable soils.