Numerical study on the frequency response of offshore monopile foundation to seismic excitation

The potential vulnerability of the monopile foundation for the offshore structures during seismic events is a valuable research topic. In this study, an integrated 3-D numerical model is set up to investigate the dynamic behavior of monopile-seawater-seabed coupling system in the frequency domain. The pile is considered as linear viscoelastic material and Biot model is used for porous seabed. The dynamic interactions among various components including pile, seabed, and seawater, are fully considered and the perfectly matched layer is adopted as an absorbing boundary condition. The seismic responses of the coupling system, such as hydrodynamic pressure of seawater, pore pressure in seabed, acceleration amplitudes in pile and seabed, are discussed. In addition, the transient liquefaction in the seabed around the monopile foundation is investigated. At the first three peak frequencies, transient liquefaction occurs in more than about two-thirds area around the pile, rather than the whole pile circumference. In particular, only less than about two thirds of the soil around the pile could be transiently liquefied along the vertical direction. Additionally, the influences of embedment depth, pile diameter , soil shear modulus , soil damping ratio , and water depth on the earthquake-induced pore pressure around the pile are significant.