Abstract: Seismic response of micropiles in a liquefiable soil is one of the key components that must be addressed in aseismic design. In this paper, the seismic responses of a micropile in liquefiable soils, including lateral displacement and acceleration, moment distribution and pore water pressure, are analyzed based on dynamic centrifuge testing and three-dimensional effective stress analysis. A dynamic centrifuge test is performed on a saturated sandy soil of a 57% relative density, using an input excitation of a sine form with a peak shaking amplitude of 1.516 m/s2 and 1 Hz frequency under a 40g condition. A numerical simulation is conducted to investigate the distributions and variations of lateral deformation and acceleration at the pile cap, the bending moments of the pile at different buried depths, the acceleration and excess pore water pressure in the liquefiable soil. An inversion analysis is performed on the experimental results based on the three-dimensional effective stress method and the concepts of multiple shear mechanism plastic model and state surface of liquefaction front. Comparison between the physical and numerical models indicates that the computed results agree well with the measurements of the centrifuge test, and that the dynamic response of the micropile is controlled by the field condition of the liquefiable site. It is also indicated that the maximum amounts of the lateral deformation and residual deformation at the pile top are 78 mm and 30 mm respectively. The largest bending moment and residual bending moment of the micropile occur at deeper buried depths. It is shown that the seismic response of micropiles in liquefiable soil can be effectively analyzed by combining the centrifuge test and numerical simulation.

Key words: liquefaction, centrifuge test, effective stress, seismic response, micropile