Shear-sliding failure in a cohesionless seabed induced by waves and its correlation with liquefaction

Liquefaction and shear sliding (i.e., slides) are common failure modes of cohesionless seafloor under ocean waves. However, existing research has rarely focused on shear-sliding failure, especially when considering wave- induced residual pore water pressure. Additionally, the relationship between shear-sliding failure and liquefaction is not well understood. In this study, a slice method is developed to assess the shear-sliding failure in cohesionless seafloor under non-linear waves, incorporating the effect of both oscillatory and residual seabed responses. The applicability of various liquefaction criteria is discussed, based on the interrelation between the shear-sliding and liquefaction zones. The results indicate that the seabed soil is more prone to shear-sliding failure than liquefaction under wave-induced pore water pressure. When only oscillatory pore water pressure is considered, the liquefaction criteria, assuming the initial vertical effective stress vanishes due to the excess pore water pressure, better identify the liquefaction zone, which is enveloped by and overlaps with the shear- sliding zone at a factor of safety of zero. In cases where both oscillatory and residual pore pressure coexist, the unified liquefaction criterion, which also assumes onset of liquefaction at zero vertical effective stress, provides more reliable predictions of the liquefaction zone. As residual pore pressure accumulates, the difference between shear sliding and liquefaction depths becomes more pronounced. A sensitivity analysis of shear-sliding depth with varying soil parameters indicates that relative density exerts the most significant influence, followed by the effective internal friction angle, while the shear modulus has the least effect. The effect of variations in soil parameters on shear-sliding depth diminishes to some extent with prolonged wave action.