Mechanism of residual liquefaction of silty seabed under standing waves

The standing waves exist when the progressive waves are reflected by the breakwater or the bank wall, which leads to the water surface oscillating where it is and the waveform doesn’t advance. Seabed soil will undergo liquefaction under standing waves, resulting in the instability of seabed foundation of marine structures. Based on the silt seabed in the Yellow River Delta of China, a series of wave flume experiments are conducted under standing waves so as to investigate the liquefaction mechanism at the antinodal section. Then, a parametric study is conducted with the proposed model to investigate the effects of the soil and wave characteristics on residual liquefaction. The results indicate that the onset of residual liquefaction is linked with cyclic stress ratio. The residual liquefaction occurs when the cyclic stress ratio χ equals the critical value χ_cr, and the required χ_cr in deeper layer is larger that of the shallow layer. The required χ_cr at the antinodal section is far more than that at the nodal section, and the required wave loading time is longer and the liquefaction is smaller than that at the nodal section. The horizontal transporting of pore pressure and the accumulating of plastic volumetric strain induced by cyclic normal stress contribute to the liquefaction at the antinodal section simultaneously, and the experimental results revealthat the former and the latter contribute to 54.3% and 45.7% respectively at the depth of 0.05 m. The discrepancy of the distribution pattern of the excess pore water pressure exists between the nodal section and the antinodal section. The shallower the water depth, the higher the wave steepness, and the smaller the saturability results in a deeper liquefaction depth.