Uncertainty of Model Parameters in PSDDF for Coastal Restoration

Sediment (mud and sand) from man-made diversions of the Mississippi River, dredging effluent, and other sources is being used to conserve and create land to protect the Gulf Coast. The long-Term settlement prediction of these newly deposited sediments is necessary to ensure the confined dredged disposal areas, coastal restoration, and marsh creation projects protect people and their property, wetlands, and various infrastructure over the design/service life. Long-Term settlement predictions are usually made with the software Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill (PSDDF). PSDDF is a 1D nonlinear numerical model that accounts for settlement due to self-weight and surcharge induced consolidation, secondary compression, and desiccation. This paper uses a hypothetical case study to estimate the dredged fill height necessary to maintain a surface elevation of 1.5 ft for the next 20 years. Because there is uncertainty in the hydraulic conductivity and compressibility relationships, a reliability analysis is performed to quantify the effect on long-Term settlement predictions. The uncertainty analysis indicates that the void ratio-effective stress and void ratio-permeability relationships influence the surface settlement more than the other input parameters for the dredged sediment.