Dredging Method for Soil Containing Hazardous Substances With Closed-Type Grab Bucket --Eco-Friendly Super Grab Bucket
Type:
Presented during:
WODCON XIX: "Dredging makes the World a better place" - 2010, Beijing, China
Authors:
Jotaro Miyazaki
Abstract: The sediment over the seabed had been contaminated by heavy metals, dioxins, and other pollutants. In the recent years, this contaminated sediment has become one of problems to be solved because the indiscreet removal of the sediment by dredging would scatter the contamination to the surrounding water area.
To suppress the turbidity and scattering of the contaminated sediment, the following methods had been proposed: (1) a physical method that encloses the contaminated area with curtains to prevent scattering turbidity; (2) a chemical method that promotes the settlement of particles using a flocculating agent; (3) a slow work method that reduces the working speed not to generate turbidity; and (4) development of a special construction machinery that has a innovative mechanism to prevent generation of turbidity.
The methods of (1) and (3) will decrease the speed of construction work, and (2) will be costly. Therefore, we have developed the Super Grab Bucket (SGB) Method by focusing on (4) that suggests two typical methods: the suction and grab bucket types.
However, contaminated sediment has mostly been found in areas by sites where waterfront factories used to be. In such areas, sunken obstacles and solid wastes from the factories have been left unremoved.
If a suction dredger is used, the obstacles may cause suction blockade or mechanical damage. Compared with suction dredging, grab bucket dredging has no problem against such obstacles if they are not so great. If focusing on the grab bucket, only development of the new bucket is required, and it is applicable to the existing grab bucket or backhoe dredgers advantageously.
The SGB Method uses the closed construction type grab bucket. Mud (sediment) can tightly be grasped by the grab bucket and unloaded onto a barge without scattering turbidity to the surrounding water area. Provided with the level-excavating mechanism and thin-layer excavation support system, SGB can easily and flatly excavate the sediment layer without excess.
Today, demand for dredging work of contaminated mud has increased in shallow waters such as local ports and lakes, and the SGB method has been developed for a backhoe dredger and has demonstrated good achievements in actual dredging work. This report will describe the features of the SGB Method.
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