Wave Attenuation, Mudslide, and Structural Analyses for Mississippi Delta/Main Pass Caisson

Abstract

The environmental loads associated with the design of a caisson-type structure in a mudslide region are largely dependent upon the interaction of waves with the seabottom. This wave-seabottom interaction results in both an attenuation of wave energy as the waves propagate over the soft soils, as well as the generation of mudslide loads at the platform site. These effects were investigated for the design of a 14-ft-dia caisson in the Main Pass region of the Mississippi Delta. The proposed structure was planned for installation in about 100-ft water depth in very soft underconsolidated soils, typical of the Mississippi Delta region. The potential for wave attenuation was investigated analytically by considering the change in response spectra from deep water to the platform site. Regional soil conditions were used for this part of the investigation. The results obtained from the analytical modeling were in good agreement with field measurements obtained from another part of the Delta. Mudslide thicknesses were determined based on site specific soil data and the design wave for the platform site. The predicted mudslides also agreed favorably with the geological interpretations for the area. Once the design waves and mudslide thicknesses were determined, structural analyses were performed to determine the bending moments and dynamic response for the caisson. Overall, the improved analytical methodology used in the investigation and the availability of field data to verify the results allowed for a more economic platform design.