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Intro Cutter Suction Dredge
Prof. Dr. Ir. C. (Cees) van Rhee
D dgi g E gi i gDredging Engineering
Delft University of Technology
Contents
• Intro
• General lay‐out
• Working Method
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• Cutter head
• Intro Cutting Theory (Sand and Rock)
• Mixing in cutter – spillage
• Operational Limits
Small < 250 kW
Cutter Cutter SSuction uction DDredgerredgerss
Large > 2500 kWMedium, 1500 kW
Components
• Pontoon
• Ladder
– Cutter head + drive system
S i li
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– Suction line
– Support system + winch
• Spuds
• Pumps + discharge system
• Side wires + winches
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LadderSpud system
Pump + suction line
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pontoon Cutter head
Sidewires
service crane
control room
stepping spud service platform
working spud
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cutterhead
main engine + pump room
laddermain engine + pump room anchor
booms
anchor wire
Working principle
• Cutter disintegrates or dislodges the material
mechanically by rotating cutter head
• Swinging around working spud
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• Swinging around working spud
• Progress by successive steps
• Material sucked up and transported through
pipeline by use of centrifugal dredge pumps
CSD Work Method (1)
Swing to starboard
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CSD Work Method (2)
Stop at starboard, push dredger forward
CSD Work Method (3)
Start swing to portside
CSD Work Method (4)
Continue swing to portside
CSD Work Method (5)
Stop at portside, push dredger forward to next starboard cut
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CSD Work Method (6)
Start swing tostarboard
CSD Work Method (7)
Stop in centre line
CSD Work Method (8)
Auxiliairy spud is lowered
CSD Work Method (9)
Main spud is hoisted up
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CSD Work Method (10)
The spud‐carrier with the hoisted main spud is moved forward
CSD Work Method (11)
Main spud is lowered
CSD Work Method (12)
Auxiliairy spud is hoisted up
CSD Work Method (13)
Dredger starts swinging / dredging
to starboard
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CSD Work Method (14)
Continuation of starboard swing
Under and over cuttingforce balance
Side winch: pullingVert: lifting force needed
Side winch: breakingVert: pushing force needed
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DsDs
Under cutting mode Over cutting mode
Discharge Methods
• Pipeline
• Barge loading
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Discharge by pipeline
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Barge loading
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Cutter Head
• General
• Teeth systems
• Cutting process
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• Mixing process
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Clay cutter Rock cutter
• Moviehouder mes
getand mes
snijtand
houder tweezijdige bevestiging
borg
pen
punttand
houder vollas
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getand mes
'serrated' mes
glad mes
houder tweezijdige bevestiging
beiteltand
houder enkel
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Vosta
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Bucket wheels
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Ellicott wheel
Cutting Theory
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Basic failure modes
Flow Type
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Shear Type Tear Type
Cutting in Sand
• Effect of pore pressure
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Forces on the blade
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TS
F
F=G tan(phi)
phi = friction angle
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G
G tan(phi)
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Dilatancy
•Dilatancy explained
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Negative pore pressure(under pressure)
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Forces on layer – effect of dilatancyT=S’ tan(phi) Coulomb
S’=S‐u
S’ : effective stress S : Total Stressu : Pore water pressure
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S 0 : S’=‐uPore water pressure is negativeIncrease in effective stressIncrease in Shear stress
u::v h/k
u pore pressure
h i d h
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h cutting depth
v cutting velocity
k permeability
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Cutting Sand:
• Larger Cutting forces with
– Lower permeability (finer sand)
– Increase cutting depth & velocity
Increase water depth
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– Increase water depth
Under and over cuttingforce balance
Side winch: pullingVert: lifting force needed
Side winch: breakingVert: pushing force needed
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DsDs
Under cutting mode Over cutting mode
Rock Cutting
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Failure modes duringCutting
Chip
Tensile crack
hShear crack
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Tool
Crushed zone
Shear plane
Shear zone
Plastic deformation
Brittle-ductile transition
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Forces during cutting
B r i t t l e & D u c t i l e C u t t i n g
8 0
1 0 0
1 2 0
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0
2 0
4 0
6 0
0 1 0 2 0 3 0 4 0 5 0 6 0 7 0
T i m e
For
ce B r i t t l eD u c t i le
Rock cutting
• Large cutting forces
– Strength Cutter and teeth
– Teeth placement important
Tooth wear
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– Tooth wear
Spillage
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spill
Spillage
Low cutterRev.
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High cutterRev.
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Cutter head production processin rock or gravel
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Cutter head productions c.q. Spillage
•The rotational speed of the cutter head causes spillage.
–Cutter acts as a pump
•The productivity c.q. spillage depends on the ratio:
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The productivity c.q. spillage depends on the ratio:
•For sand the productivity is:
•For rock the productivity is much lower
32.5 pump
rcutter
QP
R
Influence of waves on operation
• CSD is a floating object
• Response due to wave loading as with other floating structures, but ….
T i l t f t ith l dd
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– Typical geometry of pontoon with ladder
– Interaction with soil
• Spud – Spud carriage system
• Cutter head
• Numerical prediction still not satisfactory
Wave influence
• CSD not only decisive
– Aux. Equipment
– Coupling, de‐coupling of floating pipeline
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Application of CSD
• Nearly all kinds of soils (sand, clay, rock <30 MPa)
• Sensitive to wave conditions
• Stationary dredger (vulnerable for shipping)
• Some are self‐propelled for mobilisation
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• Max. dredging depth 30 m
Limiting Factors
Excavation
Soil characteristics
Available power on cutter
Side winches (max. power and velocity)
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Thickness and width of the layer to be dredged
Dredging depth (ladder angle, spuds, vacuum limit)
Pumping distance (pump‐ and pump drive characteristics)
Shipping
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