Dredged Material Placement Under Non-Segregating Conditions
Type:
Presented during:
WODCON XVIII - 2007 Orlando, Florida, USA
Authors:
Kesteren
Abstract: With traditional methods of placing dredged material slurry submerged into a Confined Disposal Facility (CDF) by means of hydraulic fill, a sand delta often builds up around the discharge point, with fines settling farther out in the pond. This segregation process has an adverse effect on the constitution of the fill and the storage space, because this segregation of the coarse fraction in deposits reduces the consolidation of the fines slurry and will increase the final volume of the deposit. Furthermore the sand concentrations can be very sensitive to liquefaction resulting in unexpected slides, especially when the deposit will be re-used for industrial areas.
By purposeful managing the slurry flow and the shear rate during discharge, the dredged material can be deposited without segregating by particles size, allowing permanent storage of the fine particles within the voids of the larger grains.
A new approach was developed to place dredged sediments while keeping sands from segregating from the finegrained sediment.
The benefits of this operating procedure include:
- Reduced use of water
- Elimination or reduction of the need for settling capacity in the CDF
- No flocculants needed
- High efficiency packing of coarse and fine sediment, increasing the storage capacity of the CDF or shrinking its footprint
- Reduced operating costs by eliminating or reducing the need to move the discharge point
- Improved reuse potential for the entire CDF
- Substantial reduction in contaminant and particulate loading at the supernatant treatment plant
- Virtual elimination of volatile emissions from the CDF water surface
This paper goes into the mechanisms and physics of the segregation. Although an excess entrainment of ambient water allows a start of segregation, still the reduction of water entrainment leaves open a shear induced segregation. Based on the combined knowledge of these phenomena the conditions are derives that must be met to achieve the benefits of non-segregating deposition. Next to that the kinds of tests used in the evaluation are presented in order to apply this technology.
Keywords: Slurry transport, waste management, contaminated sediment, sand segregation, transition clay to sand dominated deposit.