Seismic response analysis of liquefiable seabed sites: Effects of seawater-seabed interaction and bidirectional seismic motion

The scarcity of strong-motion records in marine environments has constrained our current understanding of the seismic response of liquefiable seabed sites. In this study, the Dafalias-Manzari model served as the constitutive framework for sandy soils, while an acoustic-structure coupling approach is utilized to simulate seawater-seabed interaction. The effects of bidirectional seismic intensity, along with the thickness and depth of the liquefiable layer and seawater depth, on the seismic responses of marine sites are systematically analyzed. The findings reveal that the horizontal seismic motion triggers liquefaction within the sandy interlayer, and the liquefied soil layer impedes the transmission of shear waves. As the horizontal seismic intensity increases, the degree of liquefaction in the interlayer intensifies, and the damping effect becomes more pronounced. The vertical seismic motion exerts minimal impact on the liquefaction characteristics of the site. However, more intense vertical seismic motion induces dynamic water pressure from the overlying seawater, significantly suppressing vertical motion at the seabed. As the thickness of the liquefiable interlayer increases, its damping effect becomes more pronounced; however, a critical thickness exists beyond which the energy dissipation effect slightly diminishes. Compared to the deeper liquefiable interlayers, the shallower interlayers exhibit a more pronounced damping effect. During seismic events, seawater induces significant oscillations in the pore pressure response of the soil, yet it does not influence the overall development trend of pore pressure. Additionally, seawater exerts minimal impact on the horizontal motion response of the site but significantly suppresses vertical motion, simultaneously extending the period corresponding to the peak of the vertical response spectrum.