Dredging equipment ppt
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dredging is the removal of bottom sediments from SMEARS, rivers , lakes , coastal water and OCEANS .
Types of Dredging equipment
1.Bucket ladder Dredgers
Bucket ladder dredgers
It consists of an endless chain of buckets, mounted and running round a leader , formed in the middle of the bow of a floating vessel. The ladder can be lowered or raised by the line .the bucket is provided with a pronged cutting edge . The chain of buckets is operated by a big wheel. the dug material is brought up as the chain move round and can be dumped in the hopper of the dredger herself. This can also be transferred to the barges alongside by means of a chute. The dredger is suitable for soft ground , sand , gravel hard clay . they are used where depth is not large .
Grab dredgers :-
A grab dredger picks up seabed material with a clamshell bucket, which hangs from an onboard crane or a crane barge, or is carried by a hydraulic arm, or is mounted like on a dragline. This technique is often used in excavation of bay mud. Most of these dredges are crane barges with spuds, steel piles that can be lowered and raised to position the dredge.
Dipper Dredgers :-
A backhoe/dipper dredger has a backhoe like on some excavators. A crude but usable backhoe dredger can be made by mounting a land-type backhoe excavator on a pontoon. The six largest backhoe dredgers in the world are currently the Vitruvius, the Mimar Sinan, Postnik Yakovlev (Jan De Nul), the Samson (DEME), the Simson and the Goliath (Van Oord). They featured barge-mounted excavators. Small backhoe dredgers can be track-mounted and work from the bank of ditches. A backhoe dredger is equipped with a half-open shell. The shell is filled moving towards the machine. Usually dredged material is loaded in barges. This machine is mainly used in harbours and other shallow water.
Ø It has an ability to dredge a wide variety of material ranging from soft sand , clay , shingle , soft rock, etc.
Ø Foreign materials like scrap iron , wires, etc . It can be removed.
Ø Bucket types can be changed to suit the ground conditions .
Ø IT has poor stability when moving or under towage from one site to another.
Ø Since it is mounted on pontoon , it is affected by the wave actions.
Ø It is operation is noisy.
Bed leveller :-
This is a bar or blade which is pulled over the seabed behind any suitable ship or boat. It has an effect similar to that of a bulldozer on land. The chain-operated steam dredger Bertha, built-in 1844 to a design by Brunel and now the oldest operational steam vessel in Britain, was of this type.
Krab belaar :-
This is an early type of dredger which was formerly used in shallow water in the Netherlands. It was a flat-bottomed boat with spikes sticking out of its bottom. As tide current pulled the boat, the spikes scraped seabed material loose, and the tide current washed the material away, hopefully to deeper water. Krabbelaar is the Dutch word for “scratcher”.
Water injection :-
A water injection dredger uses a small jet to inject water under low pressure (to prevent the sediment from exploding into the surrounding waters) into the seabed to bring the sediment in suspension, which then becomes a turbidity current, which flows away downslope, is moved by a second burst of water from the WID or is carried away in natural currents. Water injection results in a lot of sediment in the water which makes measurement with most hydrographic equipment (for instance: single-beam echo sounders) difficult.
These dredgers use a chamber with inlets, out of which the water is pumped with the inlets closed. It is usually suspended from a crane on land or from a small pontoon or barge. Its effectiveness depends on depth pressure.
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