chapter 9: monolithic breakwaters
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9. Monolithic BreakwatersTRANSCRIPT
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Vermelding onderdeel organisatie
February 1, 2012
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Chapter 9: Stability of monolithic breakwaters
ct5308 Breakwaters and Closure Dams
H.J. Verhagen
Faculty of Civil Engineering and Geosciences Section Hydraulic Engineering
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important aspects of caisson walls
• Quasi static load
• Impact forces
• sliding
• turning
• placing on a mound
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historical development of breakwater in Japan
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historical development of breakwater in Japan (2)
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historical development of breakwater in Japan (3)
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schematic pressure distribution for non-breaking waves
1
1
22 cosh
igHrp
hL
wd = gh
??
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load and equilibrium diagram
o
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example of a pressure record
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changes to incoming wave front induced by high mound breakwater
H=h
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Risk of local impact forces
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Brighton Marina, UK
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Parapet damage
Damage due to typhoon Tokage (Oct 2004) Muroto Kochi, Japan
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Sketch of upright breakwater for stability analysis
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wave pressure distribution
Hiroi
Sainflou
Minikin
p = 1.5 w0H
01 02
0
02
20
cosh
/ coth
Hp p w h
h H
w Hp
kh
H L kh
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Design wave for Goda’s method
• Wave height complicated method (formula of a magician)
• Wave period Tmax = T1/3
• Angle of incidence Assume an approach of 15 degrees to the normal
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Design wave height according to Goda
1/ 3 0
max * ' * * '0 0 1 max 0 1/ 3 0
1.8 : / 0.2
min , ,1.8 : / 0.2
H h L
HH h H H h L
'0 0
1/ 3 ' ' '0 0 1 max 0 0 0
: / 0.2
min , , : / 0.2
s
s
K H h L
HH h H K H h L
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Goda’s coefficients
0.38'
1.500
0
1
0.29'0
max0
0.028 exp 20 tan
0.52exp 4.2 tan
max 0.92,0.32 exp 2.4 tan
HL
HL
0.38'
* 1.500
0
*1
0.29'
* 0max
0
0.052 exp 20 tan
0.63exp 3.8tan
max 1.65,0.53 exp 2.4 tan
HL
HL
is the
inclination of the
seabed
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Nonlinear shoaling coefficient
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surface elevation
rise of the water above the caisson:
* = 0.75 (1+cos) Hmax
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wave pressure with Goda’s formula
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pressure values according to Goda
21 1 2 0 max
12
3 3 1
0.5(1 cos )( cos )
cosh
p w H
pp
kh
p p
2
1
2
max2
max
3
20.6 0.5
sinh 2
2min ,
3
' 11 1
cosh
b
b
kh
kh
h d H d
h d H
h
h kh
hb is waterdepth at 5 H1/3
seaward from breakwater
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uplift pressure
1 3 0 max0.5(1 cos )up w H
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safety factors
against sliding (W-U)/P >1.2
against overturning (Wt-MU)/MP >1.2
MP moment of total wave pressure around the
heel
MU moment of total uplift pressure around the heel
P total thrust of wave pressure
t horizontal distance between centre of gravity
and the heel
U total uplift pressure
W weight of the unit
coefficient of friction (order of 0.6)
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Example
• “runup” = 17.2 m
• safety factors “just sufficient”
H0 = 7 m
T1/3= 11 s
= 10 º
h = 18 m hcc=11.5 m
hc = 4.5 m
seabed slope 1:50
Wc
=
FH
examples: H 7-15; Fslide; T(6) 10-15
H 7-15; Fslide; hcc(6) 10-15
H 7-15; Fslide; h(6) 15-20
H 7-15; Fslide; wc(6) 15-25
H 7-15; Foverturn; wc(6) 15-25
d=10 m
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Damage due to typhoon Togage (Oct 2004)
Susami Wakayama
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Overflow over a caisson (1)
3 4.30.2 exp b
ss
Fq gH
H
formula of Van der Meer and Franco
Fb freeboard
parapet shape factor
0.7 normal parapet
1.0 perforated caisson
1.15 is maximum value
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Overflow over a caisson (2)
TAW-report “waterkerende kunstwerken”
based on research at HR Wallingford
qgem = 5.013 10-3 kwkagHsTzexp(-20.12 kb Fb/(Tz(gHs))
kw wind effect surcharge
ka,kb correction for oblique waves
Fb freeboard
example:
Hs = 1.8 m; Tz = 3 s; Vwind = 15 m/s
Fb 0.25 - 2; q; Ftype(3)1-3
1= Van der Meer & Franco
2= Wallingford/TAW
3= Van der Waal, Delft Hydraulics
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Overflow over a vertical wall
North Wirral Coast, near Liverpool
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Hanstholm caisson
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Jarlan Caisson
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Cylindrical breakwater, Nagashima
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breakwater with wave power generating system
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semi-circular caisson (for extremely high breakers)
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The Miyazaki breakwater
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Curved slit breakwater Funakawa Port
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Composite, curved breakwater
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Honey comb wall breakwater
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erosion pattern depending on the grain size
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Vermelding onderdeel organisatie
February 1, 2012
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Do not forget the filter layers ct4310