Experimental study of bimodal spectral wave-induced dynamic responses in a silty seabed

This study investigates the dynamic responses of silty seabeds to bimodal spectral wave loading, focusing on the impact of these waves on soil dynamics and liquefaction behavior. A series of laboratory experiments were conducted in a wave flume, simulating single-peaked wind waves, single-peaked swell waves, and bimodal spectral waves, which combine high-frequency wind waves and low-frequency swell waves. The results show that the pore pressures induced by bimodal spectral waves builds up over time, leading to a reduction in effective stress and shear strength. The buildup of pore pressures can cause residual liquefaction within a silty seabed, and the depth of liquefaction increases with wave height. When liquefaction occurs, the wave energy dissipates rapidly. The findings indicate that bimodal spectral waves induce deeper and more rapid liquefaction compared to single-peaked waves, with liquefaction progressing from the surface downward. Soil motion was analyzed using Particle Image Velocimetry (PIV), revealing complex flow patterns within the liquefied layers. Under single-peaked spectral wave conditions, shear flow was observed in the liquefied layer. However, under bimodal spectral wave conditions, both shear and plug flows were observed, with plug flow forming near the surface of the liquefied layer and shear flow occurring between the plug flow and the non-liquefied layer during the reversal phase of acceleration. Additionally, the soil particle velocity spectra exhibited multi-peak characteristics due to the nonlinear interactions of stress waves within the seabed.