Combined wave-current induced excess pore-pressure in a sandy seabed: Flume observations and comparisons with theoretical models

Waves are coexisting with currents in coastal zones; nevertheless, previous experimental studies for excess pore pressure responses in a porous seabed were predominantly limited to the wave-only condition. In this study, the combined wave-current induced excess pore-pressures in a sandy seabed were experimentally simulated with a specially-designed flume, which can concurrently generate periodic waves and a following/opposing co-directional current. The effect of a current on the wave profile is firstly examined. The wave steepness is decreased by a following current, but enhanced by an opposing current. Flume observations indicate that, under combined wave-current loading, the wave-induced pore-pressure is increased for the following-current case, but reduced for the opposing-current case. Such wave-current combination effect becomes more significant for shorter wave periods. The variation trend of the excess pore-pressure distribution in the present flume observations is consistent with that of the existing analytical solutions. Nevertheless, due to the existence of wave and/or current boundary layer and non-lineartiy of wave-current interactions as indicated by the flume observations, certain deviations exist between the flume results for excess pore-pressure and the analytical solutions, which can not be ignored especially for the opposing-current case. The effects of the boundary layer on the combined wave-current induced pore-pressures in the seabed are further highlighted by supplementary numerical simulations. A favorable prediction by the analytical solution would be expected for following-current cases and smaller pore pressure amplitudes would be obtained for opposing-current cases.