Synthetic Pore Pressure Signals from Seabed Surface Wave Signals within Sandy Seafloors

Pore pressure data from vertically aligned sensors has been of interest in the study of momentary liquefaction from gravity and infragravity waves. As the wave-induced pressure signal propagates vertically through a sandy bed, it experiences attenuation, and possibly, phase lag which can cause the soil to liquefy and to be more susceptible to erosion. In field experiments, a limited number of available pressure sensors or the disturbance of soil during sensor installation reduces the amount of data that can be collected, as well as potentially the accuracy of the data. Previous studies introduced models to predict the pore pressure response at different depths within a porous media as a function of geotechnical and wave parameters. Here, a theoretical model and a pressure signal from the surface of a sandy seabed are used to predict the pressure signal as it propagates through the sand. To test the model, pore pressure data was collected at different sediment depths in the intertidal zone at Cannon Beach, Yakutat, Alaska, a sandy beach with an energetic wave climate, in 2018 and 2019. Preliminary results indicate the potential to derive a synthetic pressure versus time signal that exhibits the pore pressure attenuation and phase lag associated with pressure waves moving through a porous media from a single pressure signal located at the bed surface. These synthetic signals would allow for more data to be collected by reducing the amount of pressure sensors required per deployment and may increase data accuracy in relation to in-situ conditions. With regards to the assessment of momentary liquefaction, they may also improve the analysis of upward directed pressure gradients under nearshore wave conditions.