Pore pressure response and residual liquefaction of two-layer silty seabed under standing waves

Laboratory experiments and numerical simulation were conducted to study the residual liquefaction mechanism of two-layer seabed with upper crust layer under standing waves. In this study, the buildup process of pore pressure and onset of liquefaction were firstly analyzed. Furthermore, the residual liquefaction mechanism at the nodal section was discussed. In addition, a parametric study was conducted with the present model to investigate the effects of the soil and wave characteristics to residual liquefaction. The results indicate that the liquefaction occurred before the excess pore pressure reached the maximum, then the liquefaction advanced downwards to maximal depth. Different with 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. The former and latter contribute about 52.6% and 47.4% respectively at the depth of 0.15 m. The thinner upper crust layer, the smaller k(s1)/k(s2) (k(s2) = 1.2 x 10(-6) m/s), the shorter wave period, the higher wave steepness result in a deeper liquefaction depth. Additionally, the wave period and wave steepness had a more significant effect for the upper crust layer than the lower layer at the nodal section, but the opposite trend appeared at antinodal section.