Abstract: To investigate the dynamic response of pile group foundation on liquefiable ground subjected to horizontal and vertical (bidirectional) coupling earthquake excitations, a shaking table model test for a dynamic interaction system with liquefiable ground –pile group foundation–frame tube structure was conducted. Different types of earthquake motions were selected as the excitations for the shaking table test, and then the influence of bidirectional coupling earthquake excitations on the dynamic response of liquefiable ground and pile group foundation were analyzed by comparing the test results of soil acceleration, excess pore water pressure and pile group strain subjected to horizontal unidirectional and bidirectional coupling excitations. The results indicate that under the bidirectional coupling earthquake excitations, the vertical peak acceleration of liquefiable soil gradually increases with the decrease of buried depth; the liquefaction effect of saturated sand is related to the bidirectional coupling earthquake excitations and the type of input earthquake motions; besides, compared with the horizontal earthquake excitation, the peak strain in the central and bottom of pile group foundation are larger those under the bidirectional coupling earthquake excitations, the variation of peak strain of pile top is different; also, the swaying and tilting of the pile group system of the building structure are exacerbated by the bidirectional coupling earthquake excitations. The research results are of great significance to both the seismic design of pile group on liquefiable foundation and disaster prevention and mitigation.

Key words: horizontal and vertical earthquake excitations, shaking table test, liquefaction, pile-soil-structure dynamic interaction, dynamic response