Road to the ripper Road to the ripper draghead

Road to the ripper
draghead
Melbourne Channel
Deepening Project
Royal Boskalis Westminster nv
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Channel Deepening Project
Environmental Effect Statement
Conditions at the RIP:
• Maximum current : 8 knots
• Significant wave height up to 3m
• Shipping traffic
• 350.000m3 rock (1-30MPa)
Not suitable for a
cutter suction
dredger,
but what about
dredging rock
with a hopper
dredger?
Royal Boskalis Westminster nv
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Desk study for TSHD
Up scaling of TSHD’s: propulsion, suction tube, draghead weight
What force level is available?
Royal Boskalis Westminster nv
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Desk study for TSHD
What force is needed to cut the rock?
Royal Boskalis Westminster nv
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Desk study for TSHD
Similarities to ripping with a bulldozer
Layered structure of
rock formation
Ripper teeth
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Cutting Trials
Test cart at rock quarry:
similar geology & strength
• pickpoints / ripper teeth
• cutting depth
• cutting angle
• cutting speed
• rock type
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Cutting Trials
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Cutting Trials
Measurements:
• groove patterns
• rock properties
• cutting forces
• dimensions
Engineering and construction of
ripper dragheads for the
Queen of the Netherlands
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Full Scale Trial
Aim: Demonstration of the technical feasibility
Trial Area
30.000 m3
(10%)
Royal Boskalis Westminster nv
Challenges:
• Strong current
• High swell
• Irregular seabed
• Canyon edge
• Draghead control
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Full Scale Trial: survey
In-Survey
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Full Scale Trial: survey
Survey 19-08-2005
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Full Scale Trial: survey
Survey 20-08-2005
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Full Scale Trial: survey
Survey 21-08-2005
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Full Scale Trial: survey
Survey 25-08-2005
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Full Scale Trial: survey
Survey 26-08-2005
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Full Scale Trial
Measurements:
• Vessel / draghead motions
• Rock properties
• Production
• Forces in suction tube
• Bottom roughness
Conclusion:
• cutting process OK
• draghead control OK
• acceptable force levels
• suction process to be optimized
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Laboratory tests
Scale model tests at Delft Hydraulics:
• cemented gravel
• suction flow
• jet flow
• geometry of draghead
• bottom topography
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Laboratory tests
Conclusions:
• significant improvement in suction efficiency
• draghead modifications
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Channel Deepening Project
Start of dredging the Entrance in april 2008
Extensive follow up:
• measures taken for
integrity of the pipe
• periodic checks
• work method
• frequent survey
• production
• sea bottom inspection
Royal Boskalis Westminster nv
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Channel Deepening Project
Dredging the Entrance
completed:
autumn 2008
Conclusions:
• good balance between production
and load on the suction tube
• also harder rock is dredged
• limited operational damage
• very clean sea bottom
• dredging completed within time
and budget
Royal Boskalis Westminster nv
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Channel Deepening Project
• Innovative draghead design, soil limits extended
• Dredging rock possible with TSHD
• Environmentally sustainable method
• Succesfull project is result of cooperation of many parties
Royal Boskalis Westminster nv
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