Dredgers/dredging

Bagger, m, dredger, excavator, baggem, v.t. dredge, excavate. 

FIGURE 1-18 Simplified flow sheet to remove silt behind dams. Silt would be dredged us ing submersible pumps at predetermined locations or in association with boat dredgers. The silt would be pumped in slurry form to agricultural farmlands or to special plants for the matrufac ture of hricks. 

Commonly used dredging equipment and its use can be found in Chapter 4 Dredging equipment. Possibilities and limitations of the various types of dredgers and then-vulnerability to the physical conditions of the project site are also included. 

When assessing the soil characteristics in a potential borrow area, the important aspect will be the suitabihty of the soil as fill material. It should be kept in mind that the dredging operations might alter the in situ properties of the soil (e.g. when dredging with a trailer suction hopper dredger, most of the silt/clay fraction will be washed out). This matter is discussed in more detail in Chapter 5, Selection borrow area. 

Offshore area dredged with a trailing suction hopper dredger ... 

Example 2 ( Saath A1 Raaz Boot Field , Abu Dhabi, sand search 2010 for the creation of artificial islands) Irregular offshore dredge areas with local sand patches, to be dredged with a trailing suction hopper dredger ... 

These type of dredgers are so called stationary dredgers and they are either fixed in the dredging position by spuds or by an anchor system. 

The bucket dredger (Figure 4.7) is provided with a chain of buckets mounted on a ladder. When dredging, the ladder with the bucket chain is lowered to the seabed and material is cut by the individual buckets while the chain rotates around the top and lower end of the ladder. While dredging, the bucket dredger is anchored by means of a wire anchor system. The bucket dredger is able to dredge cohesive as well as non-cohesive material. 

Figure 4.8 A barge unloading dredger which pimps dredged materialfrom a barge alongside the dredger...

Borrow Area Capital Dredging Maintenance dredging Plain suttion dredger Cutter suction dredger Trailing suction hopper dreclger... 

Dredging operations cause the suspension of fines in the water column, called turbidity (see also section 3.4.3.3,11.3.4 and Appendix B.3.10). The cause of this turbidity is the stirring action by the dredge tool and the overflow of process water into the surrounding water by a Trailing Suction Hopper Dredger (TSHD) or the overflow of process water from a barge when hydrauhcally loaded. 

Usually dredging operations are carried out 24 hours a day, seven days a week (24/7), for which permission must be obtained from the authorities. In noise-sensitive areas the noise generation of dredgers may be a limiting factor and dredging may be restricted to day work only. 

The area required by plain suction dredgers is dictated by slope development of the borrow area as a result of the dredging process. Economics usually restrict the volume which can be extracted from a borrow pit by a plain suction dredger to approximately 2/3 of the geometrical available volume. 

Grab, and backhoe dredgers need less space, generally determined only by the size of the dredging pontoon and the area needed to handle the transport barges. 

For stationary dredgers, a limited thickness of the fill deposits will require more frequent relocation of the dredger. This will adversely affect the production rates and, hence, the economics of the dredging operations. 

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