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|Title:||Survey of equipment and construction techniques for capping dredged material|
|Authors:||Sand Hen Corporation.|
Long-Term Effects of Dredging Operations Program (U.S.)
Sanderson, William H.
McKnight, A. L.
Dredged material disposal
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: This report reviews some of the work that has been done by the New England Division (NED) and the New York District (NYD) relating to "capping" dredged material that has been deposited in open water. The objective of the report is to synthesize, to an extent, the dredging, transporting, disposal, capping, and monitoring efforts that have been performed and to supplement the information by relating it to practical engineering and plant-operating concepts. Experimentation with the capping procedure has revealed significant facts concerning the behavior of such disposed material in the Long Island Sound and at the New York Mud Dump Site. The monitoring equipment and techniques developed by Science Applications, Inc., in the course of their work with the Disposal Area Monitoring System (DAMOS) Program for NED, have created much background knowledge that can be built upon as the capping concept is perfected and applied to other regions of the country. At present, the limiting physical conditions that would permit a satisfactory capping operation are known only in approximate terms. No specific criteria have been developed for the capping procedure. There are many places in the United States that do not possess the natural physical conditions suitable for the capping concept employed in NED and NYD. Borrow pits and excavations may provide artificial locations for infrequent and emergency use. The equipment employed in work done to date was conventional and was operated in conventional fashion. There is equipment available now that if properly employed would improve the quality of each phase of the disposal/capping process. Such currently available equipment includes precision electronic positioning systems for navigation and surveillance, split hull hopper dredges, and self-propelled hopper barges for transporting and disposal. Some innovations that should be required where applicable are closed grab buckets for wire line dredges and ladder pumps for increased slurry density in hydraulic dredging. Such equipment, if specified, will immediately improve the procedure. Equipment that could be constructed with existing technology includes ladder bucket dredges that produce high density material with less turbidity than other mechanical dredges and operate with more precision and increased production. This "old" dredge type is recommended to be adopted as a research and development project by the Corps of Engineers and could lead to much improved harbor dredging. The capping concept requires precision placement of the dredged and capping material. Lessons learned by the Japanese may be worthwhile innovations. Their need for precise control led to the use of self-unloading barges that conveyed the materials to the bottom by the use of tremie pipe. Carefully controlled spreading techniques were used. Hydraulic and mechanical systems are explored in this regard. The concept of capping contaminated material deposited in open water has the potential for mitigating some serious disposal conditions. It will not work universally, and much needs to be learned about the behavior of underwater disposal sites before the potential can be fully exploited. Work to date highlights the importance of making accurate predictions concerning soil engineering, coastal and ocean engineering, as well as equipment performance characteristics. Trials should continue with careful monitoring and coordinated record keeping in order to generate credible data upon which to base performance predictions in diverse physical conditions and geographical locations.
|Appears in Collections:||Miscellaneous Paper|