Crushing drag head
Dredging in soils containing many boulders or bouldersized obstructions leads to low productions, structural damage of the draghead and very demanding circumstances for the crew that have to deal with the boulders on deck.
The use of the shaking grids that were adapted to the boulder conditions have improved the production, working conditions and safety on many jobs. But with the persepective of some major projects with numerous boulders/rock debris, the crushing head was developed to take a leap forward.
The general idea was to incroporate a crushing device in the structure of the draghead that would allow boulders to enter and crush them automatically with the movement of the visor. After crushing, the rock fragments could go to the pump.
Design
The design of the crushing head was very challenging as different elements had to be incorporated and fit the whole concept:
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the forces generated when crushing are very high meaning the head needs to be extremely strong in different areas
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building a very strong head without exceeding the maximum weight of the head
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the crushing device needs to work automatically when actuating the visor
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the crushing device must reduce the boulders to sizes that can go through the pump