Characterization of spatio-temporal distributions of wave-induced pore pressure in a non-cohesive seabed: Amplitude-attenuation and phase-lag

Abstract

While ocean waves propagating over a porous seabed, the amplitude of excess pore pressure would attenuate into the seabed (termed as “amplitude-attenuation”), which is always accompanied by “phase-lag”. In this study, the amplitude-attenuation and the phase-lag phenomena in a fine-sand bed and a medium-sand bed were physically modeled in a large wave flume. A relative rigidity of soil-skeleton to pore-fluid is introduced to evaluate the seabed compressibility. Explicit expressions of the amplitude-attenuation and the phase-lag are derived and then validated with the experimental results. Parametric analyses indicate that, for the relative rigidity of the seabed much larger than 1.0, the amplitude-attenuation and the phase-lag along the non-dimensional soil depth would become more significant for larger wave period, but for smaller values of the combined rigidity-permeability parameter of the soil. A non-dimensional parameter (Ic) is further derived to characterize the combined effects of wave parameters and soil properties. Simplified spatio-temporal correlation of transient pore pressure is finally established for Ic ≫ 1.0, indicating the more rapidly the pore pressure amplitude attenuates within the seabed, the more significant the phase-lag becomes, correspondingly.