Abstract: The load of marine environment is complex and unpredictable. The soil around the foundation of offshore structure is the main bearing body, which is greatly affected by the earthquake. There are a large number of sand layers in the coastal areas which have been built or are planned to be built in China. Compared with the desert Gobi area, the dynamic characteristics of the soil around the piles are significantly different. The existing studies mainly consider the evolution of soil mechanical properties under a single earthquake, and little attention is paid to the influence of earthquake sequence and earthquake history on the dynamic characteristics of soil around the foundation. With the use of the ZJU-400 centrifuge shaking table, this paper carried out a centrifuge modeling test in dry sand and saturated sand grounds, and compared the dynamic response of soil around the pile in two grounds under the earthquake. It is found that the natural frequency of saturated foundation is obviously affected by the historical effect of earthquake, while that of the dry sand ground is not. The strong pile-soil interaction can accelerate the development of excess pore pressure around the pile. Due to the historical effect of earthquake, the dilatancy characteristics of soil are gradually strengthened, the accumulation and development process of excess pore pressure around the pile is gradually slowed down, and the dissipation process becomes faster. Saturated sand ground has the characteristics of low frequency amplification and high frequency weakening. The historical effect of earthquake has no significant effect on the amplification factor of soil in dry sand ground, but for saturated ground, the amplification coefficient of soil shows an obvious increase. In the saturated sand ground, the shear modulus of soil around the pile is more affected by the excess pore pressure than the shear strain. During the shaking, the modulus gradually decreases without the phenomenon of gradual recovery in the dry sand ground.

Key words: earthquake sequence, earthquake history effect, soil around pile, centrifuge shaking table