Feasibility Study of General Crust Management as a Technique for Increasing Capacity of Dredged Material Containment Areas: final report

The influence of meteorological conditions and the physical, chemical, and mineralogical properties of fine-grained dredged material on the formation of crusts resulting from evaporative drying in confinement areas was evaluated. After decantation, the moisture content of the surface layer is equivalent to about 2.5 times the liquid limit. Evaporation of moisture during the first stage of drying is nearly the same as that from an open pan until the moisture content decreases to about 1.8 times the liquid limit. After this, drying proceeds at a rate dependent on the transport of moisture to the surface. As the material desiccates, surface cracks open. The volume shrinkage is equivalent to the volume of water evaporated as the crusts forms, and evidence is given that the volume change is irreversible. Rainfall is shed from the crust and drains into the cracks, from which it can run off if channels are provided to the outflow weir. Management practices, including stirring and the removal of a thin layer of crust, produced only small increases in evaporative rate for a few days. Systems were developed to dig drainage trenches in the confinements and to remove the consolidated crust. A small dredge appears to offer the most promise for cutting deep or wide surface drainage ditches.