A COMPARISON OF POROELASTIC MODELS IN DESCRIBING THE VARIABILITY OF SEDIMENT THICKNESS

Poroelastic models based on Biot theory can be used to describe the response of sediments and pore fluid to wave action. However, due to the complex interaction between the wave action and seafloor, simplifying assumptions are generally made; a common simplification is to reduce the model to a 1D or 2D form. Previously, a 1D poroelastic model was applied to data collected in noncohesive sands in 6 meters of water near Oceanside, CA. Pressure data were collected from pore pressure sensors attached to self-burying cylinders, and water pressure sensors on bottom moorings. Spectral analysis methods were applied to obtain averaged auto spectral densities, from which attenuation between sensor pairs could be calculated. A nonlinear least squares regression was used to fit the model to the calculated attenuation and estimate parameters: the consolidation coefficient of the sediment, Skempton’s coefficient, and burial depth of the cylinder. Overall, the 1D model did not describe the observed pressure signal attenuation between sensors as a function of frequency. To this end, a 2D poroelastic model was applied to the calculated attenuation in order to derive the stated parameters. The results were contrasted with the 1D model results. The 2D model was found to more adequately describe the observed pressure signal attenuation, and was able to describe changes in sediment thickness over time.