Combined nonlinear wave and current induced instantaneously-liquefied soil depth in a non-cohesive seabed

Abstract

Progressive waves usually coexist with a steady current in coastal environments. Superposing a following or opposite current onto the progressive waves could significantly alter the excess pore-water pressure distribution within the seabed. Unlike previous studies which were predominantly limited to the pure wave cases, the instantaneous liquefaction of a non-cohesive seabed is investigated analytically under the combined loading of 3rd order Stokes waves and a steady current. Explicit expressions are derived for the transient pore pressure distribution in a seabed with instantaneously-liquefied zone and the corresponding instantaneous liquefaction depth, which are verified by degradation analyses and comparisons with the existing offshore field observations. The phase lag of excess pore pressure is taken into account in the theoretical derivation. Parametric study is then performed to examine the effects of wave non-linearity and superimposing a current on the instantaneous liquefaction depth. It is indicated that wave-nonlinearity effects on the instantaneous liquefaction depth are not neglectable, especially when the wave height gets larger and the current velocity is reduced. The envelope for the variation of maximum instantaneous liquefaction depth with both wave period and current velocity is further constructed. To superimpose an opposing current onto the progressive waves with a relatively small wave period could be beneficial for the prevention of instantaneous liquefaction. Nevertheless, the variation trends of the maximum instantaneous liquefaction depth are attributed to the synthetical effect of the alternations of both wavelength and wave height during nonlinear wave-current interactions. • Analytical solutions for instantaneous liquefaction depth under combined Stokes 3rd order waves and a steady current. • To superimpose an opposing current onto waves could be beneficial for liquefaction prevention. • Variations of maximum liquefaction depth with wave number are attributed to the synthetical effect of wave-current interactions.