sr443 waves forces vertical composite breakwaters hrwallingford
TRANSCRIPT
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Wave
Forceson
Vertical
and
Composite
Breakwaters
N W H Allsop
D Vicinanza
J
E McKenna
Report
SR
443
March1995, evised
March
1996
g"- Wattingford
Address
and
Registered
Office: HR Wallingford
Ltd. Howbery
Park, Wallingiford,Oxon
OX10 8BA
Tel: + 44
(0)1491
835381 Fax: + 44
(O11491
32233
ngfdod h
Engbnd No. 256m. ttR Waft{ilod l. . rtply
Md
&t3ldaty ol Hn Wanngtord
Golp Lld.
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Contract
The
work
describedn
his
eport
was
part-funded
y he
Department
f
Environmentonstruction
Sponsorship
irectorate
nder esearch
ontracts ECD
161263nd716/312.
nd
part
by
he
European nion
MAST
rogramme
nder ontractsMAS2-CT92-0047
ndMAS3-CT95-0041.
Additionalesearchupport asgiven y he Universityf Sheffield, ueen'sUniversityelfast, ndby
the
Departmentf Hydraulics
f theUniversityf Naples, ith
urther
unding
or visitingesearchers
t
Wallingford
rom he Department
f
Education
f Northernreland,
ENI,he
TECHWARE
rogramme
of COMETT,
nd he National
ouncilfor
Researchn taly,
CNR.
The
project
o-ordinatoror
heMAST l MOS-Project
nder
ontract
MAS2-CT92-0047
as
Dr-lngH.
Oumeraci f
Franzius
nstitute
f Hannover
nMersity.
he
project
fficer
or European ommission
Directorate eneral llwas
MrC. Fragakis.
The
project
o-ordinatoror
heMAST ll
project
PROVERBS
nder
ontractMAS3-CT95-0041
as
Professor
.
Oumeraci f Leichtweiss
nstitute
f University
f Braunschweig.
he
project
fficer
or
European ommission irectorateeneral ll wasMrC. Fragakis.
The DOE
nominated
fficeror
research ontracts ECD 16/263
ndT/6/312
asMr P.B.Woodhead
andHR
Wallingford's
ominated
fficers ereDr W.R.Whiteand
Professor
.W.H. llsop.
This eport
is
published
y HRWallingford
n behalf
f the
DOE,butanyopinions
xpressedre hose
of the
authors,
nd
not
necessarily
hoseof the unding epartment.
The research escribedn his
eportwas
conducted
ithinheCoastalGroup
f HR
Wallingford,t
Queen's
Universityf Belfast,
ndat
theUniversityf Naples,
nder
he overall upeMsion
f
Professor
N.W.H.
llsop.
TheHRWallingford
ob
numbers ereCAS
41,CAS
58,andCAS
169.The
HR
Wallingford ile was
ClEll/3.
Prepared y
t i n
l/lrh
rL*q-
A,rF/
96J**
l
tr
'l
fiob
iue)
Approved y
$rr.c.,,
\(
.
htr5X'r+
Date... h
oqM... l$b
il l
@ HR Wallingford
imited
1996
sB
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IV
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Summary
Wave
Forces
on Verticaland
CompositeBreakwaters
N W H
Allsop
D Vicinanza
J E
McKenna
ReportSR
443
March
995,
evisedMarch
996
This eport
ives
nformation
n
wave
oadings n vertical ndcomposite
reakwatersnd
related
harbouror coastalstrucfures.
The report
eviewsypesof
verticalbreakwaters
sedaround
he UK,
n
Europe, nd urther verseas,nd dentifiesesignmethodsnuse n heUK,Europe, ndJapan.
Analysis f
performance
n service,
ndof research
tudies,
hows
hat
present
esignmethods
underpredictave oads
under
wave mpact
onditions,nd
arenot
able o identify
eliably
eometric
wave onditions hich
ead
o such mpacts.
ComprehensMe-dimensional
ydraulic
odel estswereconducted
n a
randomwave lumeat
HR
Wallingford
o measure ave
pressures
n a wide ange f simple
nd
composite
ertical alls, nder
normalwaveattack
9=0").
The
est esults
avebeenused
o:
r
Assess
he reliability
f existing
rediction
meithods;
r
ldentify
he ranges
of
geometrb
andwaveconditions
hich ead
o wave mpacts;
r
Develop
implemethods
o estimate
ave
orces
nder
mpact onditions.
The results f
the estshave
been
compared ith
predictions
y
a
number f different
methods.
Analysis f the
percentage
f impacts elative
o all waveshas been
used o
definea
newdecision
diagramwhich
ummarises
arameter
egionsn whichwave onditions
nd
wall/ mound
geometries
lead o breaking ave
mpacts.
For
pulsating
ave onditions,
oda's
method asbeen
ound o be
generally
ppropriate,
ut or
wave mpact
onditions,t under-estimates
oads ignificantly,
ven
when
eXended
y Takahashi.
Up-liftorces
are
generally
ell
predicted
y Goda'smethod
or
pulsating
conditions,ut
againunder-estimated
or mpact onditions. or
wallconfigurations
hat
most esemble
crownwall
sections,
hemethod
n he
CIRIARockManual eveloped
y Bradbury
Allsop
gives
generally
af
predictions.
The results
f these tudies
re
ntended
o be of direct se o
engineers
nalysing
hestability
f
vertical
r composite alls
n
deepwater,
n harbours,r along
he shoreline.
he
prediction
ethods
derived ere,
and/or he
est esults
hemselves,
aybe used
o estimate
ave
oadings n a
wide
variety
f structures,
xisting
r
in
design.The report s
also
written
or other esearchers
orking
n this
field, o illustrate
he range
of
dataavailable
or moredetailed
nalysis,
dentifyegions
f
continuing
uncertainties,
nd o assist
et
priorities
or uture
tudies.
Thework eported
erewas
part{unded
y he Departmentf
Environment
onstruction
ponsorship
Directorate
nder
esearch
ontracts
ECD 161263,ECD 161312
ndCl 39/5/96,
nd
part
by
he
European nion
MAST
rogramme
nder
he MCS-Project,
ontract
MAS2-CT92-A047,
nd ater he
PROVERBS
roject,
ontractMAS3-CT95-0041.dditionalupport as
gMen
y he
Universityf
Sheffield,
ueen'sUnMersity
elfast,
nd
by he
Departmentf Hydraulics
f the
University
f
Naples,
with urther unding
or
visiting
esearchers
t Wallingfordrom he
Departmentf
Educationf
Northernreland,
DENI,
heTECHWARE
rogramme
f COMETT,
nd he
National
ouncilfor
Researchn
taly,
CNR.
Forany urther
nformation
n hese
and elated
tudies,
lease
ontact
N.W.H.
llsop,n he Coastal
Group t HRWallingford.
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VI
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Notation
A"
a
Armour
crest reeboard
Empirical oefficient
Bb Crestwidthof rubblemound erm
B"
Widthof caisson
B"*
Width
of crownwall
B"q
Equivalent idth
of rubblemound
n rontof
wall,averaged
ver
height f mound
B'' Structure
width
at staticwater evel
Bt
Width
of rubblemound t oe evel
b
Empiricalcoefficient
C. Coefficient f wave eflection
C,(f) Reflectionoefficient
unction
Cr Coefficientf wave
ransmission
D
Particle
ize
or typical iameter
Dn Nominal
article
iameter, efined
M/p)t")
or rock
and
M/p")18
or concrete rmour
Dnso Nominal
article
iameter alculated
rom he
median
article
massMuo
d
Waterdepth
over oe moundn rontof
wall
Ei Incident ave
energy
E,
Reflected
ave
energy
q
Transmitted
aveenergy
FB Buoyant p-thrustn a caisson r related lement
FF Earth
pressure
orce
on a caisson
rom he seaward
art
of the
mound
FR Earth
pressure
orce
on he caisson
rom he
harbour ide
of the
mound
Fs
Factorof
safety
Fh Horizontalforce
n caisson r crown
wallelement
Fnrr.r*
Horizontalforce
t 99.8% on-exceedance
evel
Fn.'ouo Mean
ol highest /250
orizontalwave
orces
Fu
Up-lift
orce
on caisson
r crown
wall
element
Fuo.*r.
Up-lift orce
at 99.8% on-exceedanceevel
Funso
Mean
of
highest
1/250up-liftwave orces
f
Wave requency
f, Frequencyf peakof waveenergy pectrum, llTo
g
Gravitationalacceleration
H.*
Maximum
ave
heightn a record
H,o
Significant ave
heightrom
spectral
nalysis,
efined
.0m005
H"o
Otfshore
ignificant aveheight,
un-affected
y
shallow
water
processes
H"
Significant ave
height,
verage f
highest nethird
of
waveheights
Ho^
Waveheight
exceeded
y 2"/o f waves n a
record
H'uo
Meanheight
f highest /10
of
waves n a record
h
Water
depth
hb Height f bermabove eabed
h"
Height
f rubble
mound corebeneath aisson
wall
h,
Exposed eight
f
caisson r crown
wallover
which
wave
pressures
ct
h.
Water
depth
at toe of structure
k
Permeability
Darcy),
lsousedas wavenumber
2nlL
vtl
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L Wave ength,n hedirectionf
propagation
L. Offshore ave ength f mean
T.)
period
Lo
Deepwater
or offshore
ave ength
gllZn
Le Offshore
ave ength f
peak
To)
eriod
Lps
Wave
ength
f
peakperiod
t structure
Mh Overturningoment ue o horizontalwaveorce
M,
Overturning
oment ue o up-lift
orce
Mt
Overturning
oment ue o allwave
oads
Muo
Medianmassof armour nitderived
rom
he
mass
distribution
urue
mo
Zerothmoment f the
waveenergy ensity
pectrum
m2 Second
moment f thewaveenergy
ensity
pectrum
N*o
Number f waves vertoppingxpressed
s
proportion
r
"/"
of total ncident
N.
Number f zero-crossing
aves n a
record
TRff,
nv
Volumetric
orosity,
olume f
voidsexpressed
s
proportion
f totalvolume
P
Encounter
robability
P,
Target
robability
f
failure
p
Wave
pressure
q
Meanovertoppingischarge,
er
unit
ength f
structure
Q"
Superficial
elocity;
r specific
ischarge,
ischarge
er
unitarea,
usuallyhrough
porous
matrix
R" Crest
reeboard,
eightof
crestabove
static
water
evel
Ru Run-upevel, elativeo static
water
evel
R," Run-upevelofsignificantave
Ruex
Run-upevelexceededby/" of run-up
rests
r Roughnessr run-up eductionoefficient,
sually
elative
o smooth
lopes
SF Shear
orce
at caisson
rubble oundary
S(f) Spectraldensity
sm Steepnessf meanwave
period
2nHlgTf
sp Steepnessf
peak
wave
period
zn{lgTp"
T, Meanwave
period
T*
Return
eriod
(1
-
(1
-
PJln)-l
To Wave
period
of spectral
eak,
nverse f
peak
requency
TR Length f wave ecord, uration f seastate
T" Wave
period
ssociated
ithH",notstatistically
ignificant
u, v, w Components
f velocity long
,
y,
z xes
x,y,z
Orthogonalaxes,istance long ach
xis
z
Level n water,
sually bove
eabed
c
(alpha)
Structurerontslope
ngle
o horizontal
B
(Beta)
Angle
of waveattack o breakwaterlignment
p
(rho)
Massdensity,
sually f
freshwater
p* Massdensity f seawater
P,,9", 9"
Mass
density f rock,
oncrete,
rmour
nits
A
(delta)
Reducedelative
ensity, g.
(p/p,)-l
A
(lambda)
Model/
prototype
cale atio
Froude);
lsoused
as
raction f aeration
p (mu)
Coefficientf friction,
articularly
etween
oncrete
lements
nd
ock;also
p(x)
=
mean
of x
(xi)
lribarren
umber
r surfsimilarity
arameter,
lano.lsla
vi i i
sB
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q.,
Eo
lribarren
umber
alculatedn termsof s, or
so
0
(phi)
Angle
of internalriction
f
rock
or soil
r
(tau)
Shear
strengthof rock mound
or
soil, also used
as the
time intervalbetween
samples
o
(sigma)
Stress
o(x) Standarddeviation
of
x
o' Normalised
tandarddeviation /p
on
Normal
stress
IX
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Contents
Title
page
Contract
Summary
Notation
Contents
Page
i
ii i
v
vii
xi
I n t roduc t i on
. . . . . . . . . . 1
1 .1
The
rob lem
. . . . .
1
1 .2 Te rmso f re fe rence fo r thes tudy .
. . . . . . 2
1 .3
Ou t l i neo f thes tud ies . . . .
. . . . . . 2
1 .4 Ou t l i neo f th i s repo r t . . . . . 3
Vert lcalbrealrwatersandrelatedstructures
..
. . . .5
2 .1
Purposeand fo rmo fs t ruc tu res . . . . . . . . 5
2.2
Developmentof
er t ica lbrea l
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Contents
continued
Analysisof wave orce
pressure
esults
. . .
47
6.1 Stat is t ica ld ist r ibut ionoforces
. . . . . . .48
6 .2 Ana l ys i so f impac tsand fo rces . . . . . . . 51
6 .2 .1 S imp leve r t i ca lwa l l s .
. . . . . . . . 52
6.2.2 Compositestructures,horizontalforces
.....
53
6.2.3 Compositewalls,up-l i f t forces
... . . . .56
6.3 Compar isonwi thdesignmethods
. . . . .59
6 .3 .1 S imp leve f t i ca lwa l l s .
. . . . . . . . 59
6.3.2 Composite alls,horizontalforces
. . . 60
6.3.3 Compositewalls,upJift forces
... . . . .63
6 .3 .4
Crownwa l l s .
. . . . . . . . 64
6.3.5 Overallstability f caissons n
rubble
mounds
. . .
. . 66
6.4 Pressureradientsandocalpressures . . . . . .70
6.4.1 Verticaldistributionsof
ressures
....70
6.4.2 Pressuregradients
... .72
6 .5
Pressu re
i se t imes / impu l ses
. . : . . .
. . . . . . . 73
App l i ca t i ono f
esu l t s
. . . . . . . . 75
7 .1 fn f l uenceo fsca lee f fec t s
. . . . . . 75
7.1.1
Studiesnscal ing
... .
75
7.1.2 Scaling
f impacts
romHR
Wallingford/
ristol
tudies . . .
. .. ..
76
7.2 Response
eriods
nd
mpact urations
'
... . 79
Conc lus ionsand recommenda t i ons . . . . . . . . 81
8.1
Conclusions
. . . .
81
8.2 Recommendat ionsfordesign/analysis
. . . . . .82
8.3 Recommendat ionsfor fu tureesearch
. . . . . . .82
Acknowledgements
... .
85
References
. . . . . 87
0
Tables
Table4.1
Table4.2
Figures
Figure
.1
Figure
.1
Figure .2
Figure
.3
Figure
.4
Figure
.5
Figure .6
Figure2.7
Figure .8
Figure .9
Figure .10
Figure
.11
Figure2.12
Maingeometricalarametersorwallsandmounds
Testconditions, avesteepness,
ave
height,
nd
water evels
.
Ver t ica landcomposi tebreakwaterconf igurat ions. .
. . . . . . ' .
1
Stone
lockwork,
tCatherine'sbreakwater,Jersey
996
.. ' . . . . .
6
Concreteb lockwork,EastArmBreakwater ,Dover
. . . . . . . . .
7
Tra in ingwal l lbreakwater ,or thTyne
. . . . . . .7
Layout
of
Alderney arbour,
ftercollapse
f breakwater
uter
section
.
. ' . I
TimbercaissonrGreate hest
sed
orthe
Mole,
angier,
677
... . . . . .
I
Circularcaissonssed t
Hantsholm
nd
Brighton
arina
. ..
... ..
10
Cross-section
f
Aldemey
reakwater
uring
onstruction,
855
. . .
11
Cross-sec t i ono fl de rneyb reakwa te t , . . . .
. . . . . . . .
11
Concretecaissonsforprotectionof
estr i lndustrialAirport,
938
...-. . .
12
Caisson reakwater ithset-back
rest
wall,Bagnara,
985
. . .
. - .
12
Perforatedchamberca issonbreakwateratPonza
. . . . . . . .
13
Tsunamiprotect ion
reakwateratOfunato
. . . . . . . .
13
34
35
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Contents
continued
Figure .13
Figure .14
Figure .1
Figure
.2
Figure .3
Figure
.4
Figure
.5
Figure .1
Figure .2
Figure .3
Figure .4
Figure .5
Figure .6
Figure
.7
Figure
.1
Figure
.2
Figure
.3
Figure .4
Figure
.5
Figure
.6
Figure
.7
Figure
.1
Figure
.2
Figure
.3
Figure
.4
Figure
.5
Figure
.6
Figure
.7
Figure
.8
Figure
.9
Figure
.10
Figure
.11
Figure
.12
Figure .13
Figure
.14
Figure
.15
Figure
.16
Figure
.17
Figure
.18
Figure
.19
Figure
.20
Figure
.21
Figure
.22
Figure .23
Figure
.24
Figure .25
Figure .26
Tsunamiprotect ion
reakwateratKamaish i
. . . . . . . .
14
Harbou rb reakwa te rw i thw ideca i ssona t . . . . . . . . . .
14
Decision
ree or mpulsive
reaking
onditions
. . . . . 20
Pressure
istribution
nddefinitions
or
caissons,
fterGoda
1985)
. . . . .
21
Verticaldistributions
f
pressures
sing
Goda,
Minikin, ndSPMmethods 23
Horizontal
up-liftorces n crown
wall,afterSimm
1991)
. . . .
. .
. 26
Formsof
p- l i f td ist r ibut ions,af terMcKenna(1996)
. . . . . . . .
27
Deepwave f l ume . . . . 31
Caisson/mound
eometricalparameters
...
32
Pressuret ransducerposi t ions . . . . . . .32
S t ruc tu re
. . . .
. . . . . .
33
S t ruc tu re2 . . . . . . . . . . 33
S t ruc tu re. . . . . . . . . . 34
S t ruc tu re. . . .
. . . . . .
34
Typical
pressure
vents rom est 10003
on Structure .
.
.
. . . . . . . 39
lmpactevent f romtest
0003on tructure
. . . .
. . .40
Small mpact
vent
rom
est
10003 n
. . .
. . .
40
Double-peaked
ventfromest
10003 n
Structure . . . .
. . . . . . . . 40
Pu fsa t i ngevent f romtes t10003onSt ruc tu rel. . .
. . . . . . .
41
Exampfe
ressure
timeseries
ver
height f caisson
.
.
. . . 42
Exampfe fo rce - t imese r i es
. . . . . . . . 43
Main
arameter
egions
... . . .
47
Example
Weibulldistributionf horizontalforces
or
pulsating
nd
impac tcond i t i ons . . . . . 48
Weibulldistribution
f horizontalforces,
ertical
ndcomposite
alls . . . . .
49
Weibulldistribution
f
horizontalforces,
ffect
f berm
width . .
. . . . 51
fnffuence
f H./don
%
impacts, ,,
erticalwall
. . . . 52
fnffuenceofrn.rr lHoon%impacts,,,vert icalwall
. . . . . . .
52
Dimensionless
orizontalorces gainst
H"/d, ertical
all
. . . . .
. . 53
Influence
f H./h"on % impacts,
,,high
mound
. . . . 53
fnfluence
f
Ho/h"
n % impacts,
,, ow
mound
. . ...
54
Dimensionlessorizontalorcesagainst
H",/d,
owmound
.
. . . . . .
. 54
Influence
f
H"/h"
on
o/o
impacts,P,,high
mound
. . .
. 55
Influence f H"n/d
n
o/o
impacts,P,,high
mound
. . .
. 55
Influence f B"ol\ on7" impacts,P,,highmound . . . . 55
Flow
chartof
parameter
egions or
wave
mpacts
.
. . 56
Weibull
distribution
f up-lift
orces, ,=0.04,
H"/d=0.45
. .
. . 56
Weibufl istribution
f up-lift orces,
s,=0.04,
H"/d=0.62
. . .
. 57
Weibull
distribution f up-lift orces,
s,=0.04,
Ho/d=0.98
. .
. . 57
Weibuff istribution
f up-lift
orces, .=0.04,
H"{d=2.54
...
.
57
Up- l i f t f o rces fo r0
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Contents
continued
Figure
.27
Figure .28
Figure .29
Figure
.30
Figure
.31
Figure
.32
Figure
.33
Figure .34
Figure
.35
Figure
.36
Figure
.37
Figure
.38
Figure .39
Figure .40
Figure
.41
Figure
.42
Figure
.43
Figure
.44
Figure
.45
Figure
.46
Figure
.47
Figure .48
Figure
.49
Figure
.1
Figure
.2
Figure .3
Figure7.4
Figure .5
Figure
.6
Figure7.7
Figure .8
Appendix
Measured
predicted
irizontal
orces,Goda
& Takahashi,
igh
mounds,
.300.35.
......
71
Etfect f bermwidthon vertical
istributions
f
pressures,
omposite
alls 71
Measured
istributions
nd
goda
Takahashi
redictions
or
pulsating
cond i t i ons (S t ruc tu re3 ) . . .
. . . 71
Measured
istributionsnd
Goda
Takahashi
redictions
or mpact
conditions
Structure
l . ..
..
. 72
Measured
istributionst
exceedance
evels
of 11250,99.6%
nd99.8%,
impact
onditions
Structure
) . .
.
.
.. 72
Maximum
ressures
nd
ise imes
after
Hattoriet l)
.
..
. . 73
Comparisonf experimentaldatandHattori'sredictionsor rise imes . . 74
Experimental
ata
this
tudy)
ndHattori's
rediction
ines
......
74
Pressure
mpulsesrom ield
andmodel
or
wave mpacts
n armour
nit,
f i nea r
. . . . . . . .
76
lmpact
ressures
rom ieldand
model
orwave
mpacts n armour
un i t , l i nea r
. . . . . 76
Weibull
robabilities
or
pressure
mpulses
rom ieldand
model
. .
. 77
Weibull
robabilities
orwave
mpact
ressures
rom
ieldandmodel
. . .
. .
77
Cor rec t i onac to rs fo rp ressu res. . .
. . . . . . . 77
Pressurer iset imes,modelandfie ldmeasurements
.
. . . . .
78
Weibullprobabilities
f mpact
ressure
ise imes
rommodeland
ield . .
.
78
Correct ionfactorsforr iset imes. . . . . .78
Summary
f testconditions,
tructuralonfigurations
nd esults.
xtv
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Introduction
Harbour reakwaters
nd elatedmarine tructures
aybe of
two
generalforms:
a)
lmpermeablendsolid
withvertical r
very
steep
aces;
b) Rubblemoundwith ermeablend ough ide lopes.
Much
esearch ffort
hasaddressedhe stability
nd
hydraulic
erformance
f rubble
mound
breakwaters,
ut
relativelyesseffort asbeen
directedowards
he
stability
f vertical
alls.
Relatively
liftle eliable
nformations available
n wave orces
pressures
n
vertical
composite
alls.
This eport
presents
esultsromnew esearch
tudieso derive
nformation
n
wave
orcesacting n
vertical ndcomposite allsand elatedmaritime tructures,
igure
.1.
Thestudies
ere argeted
primarily
t vertical reakwaters,
speciallyhose
ormed
by monolithic
aissons,
r by
arge oncrete
or stone
blocks
oined
o act
monolithically.ome
esults
f these
tudies
analso
be applied
o
coastal
eawalls r other teep
r
verticallyacedstructures,
nd
some
esults
an be
appliedo crown
wallson rubblemoundbreakwatersr seawalls, lthoughheeperimentalworkwasnotspecifically
configured
o addresshose
tructures.
HWL
Figure1.1 Vertical
and compositebreakwater onfigurations
1.1 The
problem
Breakwaters
nd related
structures re built
primarilyto
gMeprotection
gainst
waveattack
on
ship
moorings,manoeuwing
reas,
ort
acilities,ndadjoining reas
of
and. Designmethods
or such
structures re
generally
ellestablished,
utsome
mportant spects
f hose
design
methods
re now
seen o be uncertain
r of
limited
pplicationor someconfigurations.
ecent esearch
tudies
n
Europe aveconfirmed
hatdesignmethodsor wave orces
ased
n studies
n Japan
on caisson
breal
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1.2 Terms of
reference or the study
The
primary
bjectivef he
work ommissioned
y
DOEunder
ontractT16/312
as o
provide
esign
data
or verticalacedbreakwaters
nd elated
tructures
n
he
stability
esponse
nder
wave
attack.
The
programme
f workdescribed
t hestart
of thestudies
as
summarised:
a) describe
he strength
ndhydraulic
roperties
f
the
principalstructure
ypes
and
componentlements;
b) identify
he
principal
ailuremodes
orsuch
tructures,
nd
each
f he
main lements;
c) describe
he design
methods
sed nternationally;
d) carry
out
parametric
odel tudies
o
quantify
he
responses
f selected
tructureross-
sectionso the
appropriate
ange f
nput onditions;
e) identifyhe remaining
reas f uncertainty,
pecification
f
future
work
neededor urther
improvementn economy nd/or
afety;
0
describe
eneral
esign ules
or vertical
allstructures,
dentifyinghe
range
f application,
andsuggestingarget
actors f safety.
These ermsof reference ereexpandedo allow
he
basic est
set-up
o
be shared
with wo
related
projects.
Studies nder
he Harbour ntrance
roject
upported
y DOE
under
ontract7161263
addressedhe hydraulic
erformance
f
vertical
alls. Under
he
European
nion
MAST
esearch
programme
n Monolithic oastal tructures
MCS-Project),R
Wallingford
ssisted
y other
Europeanesearchers
xtended
hose tudies
n hydraulic
erformance
f simple
ertical
alls
o
include range
of
low
reflection"lternativetructure
ypes.
These
ncluded
aissons
ith
voided
chambers,
erforated
ave
screens,
ndarmoured
lopes
n ront
of
vertical
alls.
Results
f those
studies avebeen
presented
eparately,
ee
Allsop
1995),
llsop
t
al
(1995b),
McBride
t al
(1995a),
andMcBride Watson
1995).
The
studies
n wave oadings ndbreakwater
tability
iscussed
ere
wereexpanded
o include
contributionsrom esearchersromBelfast ndNaples evelopedn collaborationithHRand
Universityf Sheffield.
he Ph.D
project
y McKenna
t Queen's
niversity
elfast
as
ntended
o
addressn moredetailwave p-lift
ressures
n caisson
real
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HRWallingford
overall esign
f studies;
rovision
f
est
acility,
easurement
quipment,
es t
structures,echnicalnd
computingupport;eadanalysis
nd
eporting;nd
overall uperuision.
McKennarom
Belfast
upervisedy Whittaker nd
Allsop xtended
he study
o include
more
detailed nalysis
f up-lift
ressures;
ssistedn estdesign;
onducted
anyof the ests;
and
analysed p-lift orces
ndoverallorces stability.
Vicinanza uperuisedy Benassaiand alabreseromNaplesmodified ndextendedhe
analysis
rograms,
ndassisted
n
detailed nalysis
f wave
pressures
forces ndstatistical
analysis f
wave orces,
f
pressure radients
nd
mpulses.
Allsopat Sheffieldeviewed
uchof the
historicalnformation
n vertical
reakwaters
n
he UK;
provided
upport nd
supervision
or
he
visiting esearchers
t Wallingford
articularly
n analysis
of wave orces;
ndcompiled
ndedited esearch
apers
nd his
eport.
Studies nder he MASTMCS
project
weredividednto ourareas
overing:
ask1, mpact
orces
nd
structurefoundationnteraction;
ask2, scaling
roblems
nd
air entrainment;
ask3,
local
morphologicalchanges;
ndTask
4, waveovertoppingndconstructional
easures.
HRWallingford
werecontractedo contributeo Task3.1on wave eflections,ask3.3on scourat verticalwalls, nd
wasscheduledo lead
Task4.3
on constructionaleasures
o reduce
eflectionsnd
overtopping.
During
arlystages n
he MOS-Project,
t became pparent
hatadditionalwork
asneeded n mpact
forces
pressures.
nalysis
y Oumeraci t al
(1995)
emonstrated
hat mpact
oads reof critical
importancen
the stability
f caisson reakwatersgainst
rogressive
ovements,
nd
Allsop
&
Bray
(1994)
demonstrated
hat short
durationmpacts re of considerable
mportanceo the
integrity f
blockwork alls.
n the ight
of hese indings,heWallingford
Sheffield
Belfast
Napleseam
expandedheir
contribution
o the MCS
project
ithnewstudies
n wave
mpact
ressures
dded o
Task1 anddiscussed
ere. Work
underTask4.3wasalsoexpanded,
nd
hasbeen eported
n detail
in he MCSandHarbour ntranceseports,eeMcBride tal
(1996)
or a summary.
1.4 Outline
of this report
The main ypes
of vertical
walls n use n
harbours r along oastlines
redescribed
n
Chapter
, and
designmethods
vailable
o determine
he
main
hydraulic nd
structural
esponsesre
discussed
n
Chapter .
The
designof research
tudies
developed
nder his
project,
he
structure onfigurations
ested,
and
the estequipment
nd
procedures
re
describedn Chapter
.
Resulls f
thewave
pressure
lorcemeasurements
re
irstdescribed
n
Chapter
, whichdiscusses
the ormandhandling f thedatacollected, nd definitions fwavepressure forceeventsneededo
reduce
he arge olumes
f data
o moremanageable
roportions.
hedetailed nalysis f
these
measurements
re
hen
discussed
n Chapter , covering
he
distinctions
etween
ulsating
nd
impact
onditions,
ndexploring
hedifferent
rediction
ethods
eededor hesedifferent
esponse
regions.
Application
f the wave
orce
esults,
nd he
prediction
ethods
erivedrom
hemarediscussed
n
Chapter , including
discussion
n
he effects f anyscale orrections
eeded
or wave
pressures.
Overall onclusions,
nd recommendat ions
or
design analysis
ractice,
nd
or uture esearch,
re
addressed
n Chapter
.
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2 Veftical
breal
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E
Aroundhe UK,
seawalls nd
evetments
avebeen onstructed
o
defend
arts
of he
coastline
against rosion,ermed
coast
rotection";
r
o reduce
he
evel
and/or
isk
of
flooding
f
ow-lying
and
by nundation
rom he sea, ermed
sea
defence".
Seawalls
ay
be
generally
ertical
r
steeply
sloping, r they
maybe
ormed y embankments
rotected
gainst
rosion
y
armouring.
tructures
suchas seawalls
resubstantially
orenumerous
han
arge
breakwaters,
ut many
of
thedesign
methods
ndmuch
of the echnology
erive
romstudies
or breakwaters.
nalysis
design
methods
in his eport hereforeocusprimarilyn arger tructuressed o defend oastlinesndharbours,
primarily
arbour reakwaters
or commercial/
avalharbours
r
marinas;
ometimes
ntrance
channels
or agoons;
r cooling
waterbasins
or
power
tations.
hey
may
be constructed
n 5 to 50m
of
waterand,
whereexposed
o severe
waves,
ubble
r
composite
reakwaters
ay
be armoured
y
special oncrete
rmour
n sizes rom
1 to
200 onnes,
lthough
arely
bove
0 tonne.
Caissons
may
be
constructed
n sizesup o 3,000
onnes,
r even
up o
10,000
onnes.
Choices etween
ifferent onfigurations
re nfluenced
y economics
nd
availability
f
materials;
y
local onstruction
ractice
nd
availabilityf
plant;
erformancetandards
equired
rom
he structure
and ocalenvironmental
oncerns;
ndclient
designer
references.n
the UK,
blockwork
allson
rubble
oundations ere
preferred
uringhe
astcentury,
ut
ubble
mounds
avebeen
more
strongly
favoured ver
he ast50
years.
Caisson
reakwatersre are n heUK,althoughome tructures
useslice
blockwork r sheet
piles
o form
vertical
alls.
Designers
lsewhere
n Europe
ave
also
generally
referred
ubble reakwaters
or heir elative
ase
of construction,
essbrittle
ailure
modes,
reduced usceptibilityo
wave mpacts, nd
potentially
educed
nvironmental
mpact,
xcept
n taly
where onstruction
f vertical lockwork
nd
caisson
reakwaters
ates
back o
the
Roman
ra,
and
remains
revalent
oday.
Engineersn Japan
lso
strongly
avour
ertical
aissons
r,
wherewave
forcesmaybe
parlicularly
trong,
orizontally
omposite
reakwaters
ith
a mound
f
armour
nits
n
frontof thecaisson.
2.2 Development
of vertical breakwaters
ln analysingheperformancef veftical reakwatersrseawallsn heUnitedKingdom,t isusefulo
considerhe design ndconstruction
f many
historic
tructures,
articularly
hose
builtduring
he
major
period
f harbour evelopment
n and
aroundhe
UK
between
830
and
1900.
Many
breakwaters
onstructeduring hat
period
tillsurvive,
nd heir
stability
s
mportant
o the
continuing
operation f the harbours
rotected.
";*Ki: #; r:&ile*raf;
"bl'3s,"sol oi ;p; ;
Solsol,iojrb',"?liclX'*-i
Stone
blockwork,
St Catherine's
reakwater,
Jersey
1996
Themorecommonypes
of
breakwaterr seawallaround
he
UK
areof
simple
erticalor attered
slope,withwalls ormed f stoneor
concrete locks.Suchstructures
were elatively heap o construct
when abour
osts
were ow,and
useda
minimum f material.
Breakwater
alls
were
usually
double-sided,ut
many
quays
or
seawalls rebacked y
natural
r
imported
materials.
n
example
breakwater
ection rom St
Catherine'sarbour n Jersey,
constructedt about1856, hows
the drymasonry alls, he rubble
filling etweenhe walls, nd he
rubble
mound n which he
walls
are ounded, igure .1.
Figure
.1
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Quarried
tone s not naturally
vailable
n the rectangularhapes
needed
o
forma
coherent
nd
stablewall. Production f stone blocks o acceptable
izes
and tolerances
used o
be
a routine
ask
in
civilengineering, ut became ignificantly
esseconomic
s
labour
osts ncreased.
Many
breakwaters
efore 1900
herefore
used argestone blocks
o
form
the outer
skin of
the wall,
with the
core
formed
rom
smallerblocksand/or
ubble nfill. The use
of
concrete
blocks
o replacedressed
stone
blocks becamemore
prevalent
n the UK
after 1850,see
section
of
Doverbreakwater
n
Figure2.2.
y'qartryed
K"
Aara-*-
Figure2.2 Concreteblockwork, East Arm Breakwater,Dover
Blockwork
walls
wereconstructed
widely round he
UK o form
breakwaters,ockor
quay
walls,
andseawalls.Whilst
he main
purposes
f the
breakwaters ere
to
give
quiet
water
or moored
r
manoeuvringessels;
nd
provide
shelteror cargohandling
operations,heywerealsooften
usedas
quays,
upportor cranes
andotherequipment,
ndadditional
space
or
cargo. Some
breakwatersnown
s'Moles'
or
'Piers',
Figure
.3,alsoacted
as
trainingwalls
at the mouth
of a river
or estuary.
Figure2.3 Trai
ning wall/breakwater,
North
Tyne
Seawalls roundhe UKwerealsoconstructedsing imilarechniqueso halterosion f beaches,
dunes,
r softcliffs,
nd/or o limitwave
overtoppingnd
looding
uring torms.
Such
structures
re
not
he
primary
nterest
f this report,
but examples re
citedwhere
hey
give
particular
nformation
n
design echniques
r construction
ethods.
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2.2.1 Historicalbackground
Ancient
reakwaters
roundhe Mediterranean
ere
constructed
f stone
blocks,
ometimes
ith
concrete r cementitous
nfill.Roman ngineers
sed ndenvater
onstruction
ith
imber
orms
(sometimes
unken hips), nd
illing ith ement,
ozzolana,
ndbrick.
Franco
Verdesi
1993)
describe version f caisson
onstructionsed
by Herod
he
Greal's
ngineers
t Caesarea
round
20 BC,
wherewoodenormswere
illedby concrete
mortar
owered
n baskets
nto he
orms.
Littleevidence
emains f such onstruction
round
he UK,
although
ome
oundationsf
quay
walls
havebeendated o Romanimes.
Theuseof
concrete
o form
blocks
n
he
UKwas
probably
tarted
by the Romans, utdisappeared
gain romUK
construction
ractice
or
marine coastal
tructures
untilabout
1850. Few
details f
constructionf breakwaters
r
coastal
alls
are ecorded
efore he
late1600's,
ndmuchof he
nformationvailableo
Bray&
Tatham
1992)
ates
rom he
1700and
1800s.
Onenotable xceptions
provided
y he account
f
the
construction
y
British ngineers
f
theGreateMole t Tangier y Routh
1912),
iscussed
nsection
.2.2below.
The main
purpose
f
many
harbours
n he mostexposed
reas
roundhe
UK
wasdefence,
ith
naval equirementsettingheposition,rientationndplan or harbourst Dover,Portland,
lymouth,
Holyhead, t Catherine'sndAlderney,ee
ayoutn
Figure
.4. Other
harbours
ere
constructed
s
"harbours f refuge",o be usedby ishing oats
and
rading
essels
uring
torms.
Thesenew,and
often
much arger, arbours
eremucheasier
o enter
han he
small
oastal
arbours.
hen,as
now,
narrow
ntrances nd
eflective
allsof these
mall
harbours
aused
ery
dangerousonditions
lose
to the harbour ntrance,
roblems
hatstill
persist
or
manyharbours
n heUK.
These spects
re
discussedn moredetail n
he
harbour ntrances
roject,
ee
particularly
cBride
t al
(1996).
Figurd2.4 Layoutof Alderneyharbour,aftercollapseof breakwater uter
section
Many ertical
reakwaters
r
piers
wereconstructedetween
830
and 1900,
ncluding
lderney
startedn 1846,Dover
tarted
n 1847,Tynmouth855,
Holyhead
876,Fraserburgh
877.
Most
of
these
have
survivedn
heiroriginal
orm,except
Alderney
hich
s discussed
ore
by
Allsop
& Bray
(1994)
nd
Allsop t al
(199'l).
Manyof the
navalharbours
onstructed
n his
period
avesince
been
abandoned
y he navy, ndarenowused
or
commercial,
ishing
r
eisure
ctivities.
\
q/ger
7,a;
t
Litte"
\
Craby
r:
larbour\-.\
^
\ - - ' - -_- ,- { u\
Braye
Bay
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2.2.2 Construction
of breakwaters,
piers,
and seawalls
Themostcommon
orm
of
constructionsed
n he UK
or breakwaters
r
piers
wasa
rubble
mound
brought
p o a
level
slightly
elow
owwater, ndsurmounted
y
blockwork
alls.
Hewn tone,
ften
granite,
as aid n bond,
generally
t
a slight atter ff
vertical.
Blocks
were aid
dryor
n limeor
pozzolana
ortar
p
o about1900.Concrete
illing
was arely
sed,
ndcement
mortars
ecame
widely vailable
nlyafterabout
1900, lthough
imeand
other
modars
wereused
at
east
rom1650.
Concrete
ather hanstone
blocks
wasmorewidely
sedafterabout1880.Variousmethods ere
developed
o assist ransfer
ensile,
ending, r shear
oads
between
djoining
locks,
r between
courses
f blockwork,
ncludingron
cramps, eysor
oggle
oints
between
locks.
Caissons
ere arely sed n he UK before
900.One
of the
irst
uses
by British
ngineers
f
caissons
s described y
Routh
1912)
who
elateshe construction
f the
mainbreakwater
r Greate
Mole o shelter
harbour t Tangierrom he
Atlantic.
The own
wasoccupied
y
British
roops,
nd
protection
as urgently eededor he
vessels upplyinghe
garrison. heMole
wasstarted
n
conventional
ashion, ith ubble
oundations
laced
head f
blockwork
onstruction.
onstruction
started
n August 663,buthadonly
eached 50mby
August
668
due
o adverse
aveconditions
t
the site; ossof rubbleill.nto he sandbed; hesmallandoccasionalature f theworkforce howere
often
divertedo other
military)
uties;
ifficultiesn obtaining
aterials;
nd
significant
elays
n
payment
or workcompleted.
After hecontract adbeen e-negotiated,
hecontractor
eturned
n April
1670
o find he
blockwork
wallsdamaged
ndbreachedn at east wo
places.
The
construction
ethod
was
e-considered,
nd
a type
of caisson onstructionsedat Genoa
was
proposed
sing
ogreat
wooden
hests"
ound
n
iron,and illed
with
stones nd
mortar r concrete.
fter
muchdebate,
ome
of t
reported
n Samuel
Pepys' iaries,
new
contractor
asappointed
o eltend
he existing
tructure
sing aissons'
Wooden aissons f 500 o
2000 ons
Figure
.5)were owed
out
romEngland,
nd
once
on site
hey
weresunkonto he oundation ybeing illedwithstoneboundn a localmortar f Roman arras.
Progress n the newconstruction
asmore apidand
esssubject
o damage
han
he
earlier
blockwork
ections, nd
he
prognostications
ere
or a longer
ife
han
heearlier
ections.
Figure
2.5
Timber
caisson
or GreateChestused
or the
Mole,
Tangier,
1677
Workon the Mole
continued ntil
1678whenTangierwasattacked
ndall
energies
ere
divertedo its
defence.Peacewas
concludedn
1680,
nd
t was
hen
decided
hat
he
breakwater
hould
e
destroyed
est t
provide
helter
o a laterenemy.This
wascompleted
n 1684
withmore
ditficulty
han
anticipated,nd marked
n apparent
alt n significantreakwater
onstruction
y
British
ngineers,
andcertainlyn
he useof caissons, ntil he
early1800's.
20
E
7al
/uy
Ag'bay'/Vzq*,y,il,y z{'/,
c u dz/a/znzn a4/ 61a/
rdftl
l*
dlaebe
wbw,(at
/u tL
Taot
d{," aoaa{z
9a/. oL
/-Atu
y'd.61ao@,/",
a
u
/d/z
Zan/a. tL 6ta"z
o/dz 9-
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The
useof concreteor
illing reakwater alls, nd/or
o form he
acing
tartedo
be used
occasionallygain fter
bout 830, ecoming
ore
revalent
fter
bout
870.
There s no
record f
concrete eing sed or heNorthPier t Eyemouth
1767;heOld
Pier
at Wick,
823;he
piers
t
Hynish, 843, uckie, 855,
nd
WestHartlepool,858.
Pre-cast oncrete lockswerehowever sedat North
yne n
1855,Figure
.3; or
Dover reakwater,
1866,Figure .2: andat Cork n 1877.Concreteilledbags ormed foundationo Fraserburgh
breakwater
n 1877, nd or heWintonPier,Ardrossan
n 1892.Concrete
illingwasused
or
he
ater
stages f Alderney reakwater
849-1866,
he South
Breakwater
t
Aberdeen, 873;
or he NorthPier
at Aberdeen, nd he Fraserburghreakwater,oth
n 1877.
lt is nteresting
o
note hatLamberti
Franco
1994)
redit he ta lian ngineer oenCagliwith
e-introducing
ertical
allbreakwaterso
Italyaftera visit o Britainn 1896wherehe
saw he
blockwork
reakwaters
t
Dover,Sunderland,
NorthTyne,Peterhead,
nd
Wick.
Thedevelopment
f so
many
harbours roundhe UK
between
850
and 1900, nd
sulival of
manyof
thosebreakwaters,ave
significantly
educedhe need o construct
ewharbours
roundhe
UK,and
has hus esultedn relativelyewbreakwaterseing onstructedince1900.Thosenewstructures
have
generally
een ormed s rubblemoundso their
ullheight,
rotected
y rock
or concrete rmour
units, ee
particularly
ort
Talbot,Douglas,
angor, ndPeterhead.
Many imilar tructures
ave
also
beendesigned ndconstructed
y British ngineers
orking
verseas.
Exceptions
o thiswere he newharbour t Brighton,
rotected
y
breakwaters
sing ircular
oncrete
caissons, igure .6,
based n he design sed
at Hanstholm
n Denmak;
and he
vertical
ave
screen reakwaters
t SuttonHarbour, lymouth,
ndCardiff
ay
Barrage.
Brealavater
Cross beams
Access manhole
I
f
Crane ail
Figure
.6 Circutar
aissons sedat Hantsholm
ndBrighton
Marina
2.2.3
Construction f veftically-composite
realouaters
Stone
or concreteblockwork
Before
he advent
of advanced
underwater
working,construction
f
blockwork
walls was
chiefly
imited
by
the depth
o
which
diver-assisted
lacement
f
closely-fitted
locks
was
possible,
and by
the
knowledge
and
equipmentavailable or
placing
mass concrete.
Rubble
materialwas
placed
by
barge,
allowed
o consolidate,
hen rimmed o accept he
foundation tones.
In 1850,
he water
depth at which
he
foundation tones
could be
laid
was usually imited
o 12ft
3-4m)
below ow
water evel,
but by 1900,depthsof up to
50ft
(15m)
had
been
reached. After
dressing
he
mound by
divers,blockwork
was then foundedusing
he largestblocks
available.
The
breakwater
wall
was
carried
upwards n
plain
or mortaredblocks o
the top of the
wave wall.
The block size
often
reduced
as construction
limbed,as increased ime between
mmersion
allowed
more ime to
fi t
togethersmaller
blocks,
and/or
n
laying he mortar
bedding
jointing.
lndividualblocks
were often
bonded
ogether
by keys, by iron
or steel
dowels n holes hrough
he
blocks,or
by lead or mortar
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poured
o form keys
between
locks, lthough
hesecomplications
ere
moreoften
eserved
or
the
outer end of the breakwater.
The use of
iron
or steel
rail
cramps
o
hold
ogether
he outer
end
of a
breakwaters discussed y Bray& Tatham
1992).
Timber
piles
were
sometimes
sed
o take
bending
or tensile
orces,
and were occasionally
ncorporated
ithin he
breakwater
tructure.
Thesections f St Catherine nd
Alderney reakwatershown n
Figures .1and2.7-8
re
elatively
typical f the
arger
reakwaters
constructed
etween
850and
1880. Of hese wo,Alderney
s
exposed
o
substantially
ore
severewaveconditions,as
suffered ignificant,
rovides
s
with
more
nformation
n ailuremodes
and responses,ndhas
herefore
been
given
more
attention,ecently
by Allsop t al (1991) ndAllsop
Bray
1994).
At
the
andward
ndof theAlderney
breakwater,he oundation as
set
no more han
3.5mbelow owwater
levelonspring ides. Along
he
outersections,he owestntended
levelwas7.3m
2aft)
elow
ow
water,butconsolidation
f the
mound ncreasedhis o 9.1m 30ft)
towards he seaward
nd. Large
blocks f stone, ater
of concrete,
were aid
on he rubble
fter t had
been
allowedo settle or
about6
Figure .7
months.
The batter
f thewallof 2
(vertical)
1
(horizontal)
t the
nner nd
s rather hallower
han
or
manycontemporary
reakwaters, nd
was steepenedor the
outersections.
Walls
at St Catherine's
were
battered t
3:1,and
at
Aberdeen
t 8:1.
Blocks acingmost
of
the breakwatersonsidered erewere
generally
f dressed
tone.
Typical
sizes
are
n
he ranges m
x 0.3mx
0.5mup o 2.5m 1mx 1.5m.
Thesizesused
werestrongly
ependent
on hestoneavailable,nd hestone-workingkillsavailable. ery ine olerances erepossible, ut
would
generally
ave
been eservedor
elements n he opof
thebreakwater,
hose
hatcould
easily
be seen. Stone
usedas facing
n he breakwater allcould e
dressedo
give
oint
gaps
ypically
f
no more
han1-2",
about
25-50mm.At ower
evels,
where nspection
asmoredifficult,
nd
placing
timesshorter,
olerancesmay
havebeenwider,
and
oint
gaps
of
up o 75mm
mightbe expected.
The
gaps
between
djoining
lockswould
generally
avebeennegligible
hereblocks
were aid n
mortar.The
mortar
willhowever
eterioratever hestructure
ife, he
oints
henopenup,
allowing
water
nto he
hearting
r core,and
sometimesllowingheblocks
o
move.Many
ailures f
such
walls
havebeen
associated
ith he oss
of bond filling etween
locks.
Theuse
of concrete
locks,
eg
at Dover
hown n Figure
.2,avoidedmany
of he
problems
f
bonding tonework,
nd
made
t
mucheasiero makespecial rovisionsor oining locks, uchas keyways rothersteppedoints, r
cut-outsor
keyblocks.
Once
production
f
concrete locks
ecame conomic, lock izes
ncreasedramatically,
ometimes
to sizesapproaching
00
ons. Stoney
1874)
ecords
he use
of blocks
f approximately
.5m
x 6m
x
7m or
quay
construction
n 1871,
ndsuggestsheiruseat Alderney.
t washowever
greed
hat
he
Zrutttz
Cross-section
f
Alderneybreakwater
duringconstruction,855
Figure2.8 Cross-section
f Alderney
breakwater,
completed,1864
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capital
ostsof the equipment eeded o
produce,
move
and
place
such
blocks,
would
estrict
heir
use
to
large
projects.
Concrete aissons
Over the last 40-50
years,
here have been considerable
dvances
n designmethods
or vertical
breakwaters; n constructionechnology
or
prefabricated
oncrete
caissons;
n
placement
of
rubble
foundationsat depth;and these changeshave altered he balanceof advantages nd disadvantages
between ubbleand verticalbreakwaters.
The most common orm of caisson
s rectangular or square)
n
plan
and
front elevation, nd
rectangular r near square n end elevation. Caissons
may
typically
be 15-30m
ong,divided nternally
into cells. An example taliancaisson s shown
n Figure2.9.
The
caisson
tself s designed o be
floated
out, ballastedwith
water
o sink
t into
position,
hen
illed
by sand. ln this
ow tidal
range,
he
low crest
section
s
then
cast nsitu.
,
15.00
t '-
Figure2.9
Concrete aissons or
protection
of Sestri
ndustrial
Airport,1938
Theslightlymore
complex
breakwatert Bagnara
1985)
s
shownn Figure .10.Thecrest
wall s
shaped o return
ny
overtopping aves,
nd s set back
to reduce
mpact orces
nd
overtopping.
he oe armour
o this
breakwater
as
damagedn 1991,
butonly
along ts most
outerend
where
Tetrapod
rmourwas
used
at the oe.
The oe armour
long
the main
runkwas
5 t modi fied
cubes.
Figure2.10 Caisson
breakwater
ith set'back
crest
wall,
12
Bagnara,1985
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One of the main disadvantages
f a
verticalwall breakwater
s the
high
evelof
reflections.
This
problem,
nd
potentialsolutions
avebeenstudied
n the companion
Harbour
Entrance
nd
MCS
projects,
ee discussions y McBride t al(1996),
Allsop
1995),
Allsopet al
(1995b),
McBride
t al
(1995a),
nd McBride& Watson
1995).
One approach
s to modify
he seawrd
hambers
f the
caissono allowwaveenergy
dissipation
n he irst owof
chambers,r in a few nstancesn
the irst
2
or
even3 chambers. n
example
f a
2-chamber
erforated
caisson
s
shown
n Figure .11.
This
llustrateshe higher loor
levels n he
nner
perforated
chambers,
hevent hroughhe
crown
wall o reduce
ir
pressures
within he rearchamber, nd
he
use
of concreteill
o
increase
strength
nd
densityn he seaward
cells. n a few nstances,erforated
chambers re alsousedon he
harbour ide o reduce eflected
waveaction
within
he
harbour.
ee
thesection f
Bagnara
reakwatern Figure
.10. lt should
owever
e noted
hatcaissons
itha
single
erforated
hamber reunlikelyo achieveeflections
elow
C,=0.5
or any
significant
ange
of
wave
periods.
High
wave eflections
aycombine ithcurrents long
hestructure
ncreased
y nterruption
f tidal
or
wave-induced
urrents.
These
may
precipitate
ocal courof
thesea
bed,a
problem
hat
has
afflicted number f caisson reakwaters.n he UK,Ganly 1983) eportshat hecircular
aissons
t
Brighton
laced
irectly ntochalkbedrock, igure
.6,weresubject
o
substantial
arly
cour
eading
to
settlement f
3 caissons y up o 0.65m uring onstruction.
xtensive
cour
protection
easures
were hen ncluded
uring he emainderf theconstruction
eriod.
Despitehese
measures,
cour
holes
have
continued t Brighton, ith
significantxpenditure
eing
neededo
reinforce
he oe
detail
by
pumping
oncretento lexible
agsat he seaward
dgeof
and
beneathhe caissons.
Elsewhere,
scour emains neof
the
more
ditficult esign
roblems,
nd
substantial
nti-scour
easures
ave
oftenbeen equiredo avoid ocalcollapse
r ossof
support.
Thehydro-dynamic
rocessesnvolved
in scourare reviewed
y Oumeraci
1994a),
ut
ittle nformation
s
given
on
potential
revention
measures.Practical
dvicederived rom
analysis f service
performance
s
given
by Funakoshi
t al
(1994),
nd s
discussedn 2.3below.
Mostvertical
breakwatersn Europe
havebeenconstructed
round taly.
Comprehensive
eviews
f
many
Italianbreakwaters,
esign,
construction,ailures
nd repairs,
havebeendescribed
y Franco
(1994)
ndLamberti&
ranco
(1994).
Around
he world,more
harbours nd
breakwatershave
beenconstructed
ecentlyn
Japan
thananywhere lse,perhaps ven
more
han
n
the rest
of the world ogether.The
scale
of suchconstruction
s illustrated
y the
port
of
Onahama here
he
caisson onstruction
ards
ompleted
500 aissons
n 1932
1992,
with131
constructedn
1971. Much urther
nformationn caisson reakwaters
n Japan
s
given
by
Tanimoto
Takahashi
1994a,
) who
describehedevelopmentndhistorical
rogress
f
vertical
reakwaters
n
Japan,
nd
give
details
f
many
example
tructures.
Of hose
elevant
o this
eport,hree
examples
areshownn Figures
.12 2.14.
12.oom
Figure2.11 Perforated
hamber aisson
breakwater
t
Ponza
Figure2.12 Tsunami
protection
breakwater
t
Ofunato
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The sunami
protection
reakwater
at Ofunato,
967, hown n Figure
2.12
s in relatively
eep
water
at
35m, but s requiredo resist
relatively
ow wave heights. The
perforated
hamber
aissons sed
at Kamaishi, igure2.13, s built n
60m of waterusinga moundof
35m, and is the deepestbreakwater
built
n
Japan.
This
structure gain
seryesas tsunami
protection
o the
designwave heightsare relatively ow.
The widestcaisson n Japan
at 3Bm
is shown n Figure2.14. This
breakwater
t
Hedono
port
s in less
than 30m
of
water,
but
is
designed
to
resist
a designwave of H"
=
9.7m. Here he oe armour
uses64 t
Tetrapod
units
n
a
layer
about 6m
thick. The ongest aisson uilt n
Japanup to 1994,was
100m
ong,
about 20m wide,
and
was
used as a
temporary
breakwaterat
Kochi
port.
This caissonwas cast n
a ship
dock,
and towed 370 km to site.
Figure .13
Tsunami
rotection
reakwater t Kamaishi
L.w. o.o
H'w-+2'o
Figure2.14
Harbour
breakwater
ith wide caisson
at
Hedono
Moredetails nvertical reakwatersased n workup o 1992werepresentedn a special dition f
CoastalEngineering
y Oumeraci
1994),
ranco
1994),
animoto
Takahashi
1994b),
attoriet
l
(1994),
Chan
1994)
ndOumeraci& ortenhaus
1994).
These
apers
oncentrate
n nformation
from esearch
tudies, ith
some omments
n design, nd
with
a little
nformation
n
practical
examples.More
practical
nformations
given
n
he
Workshop
n
WaveBarriers
n DeepWaters
presented
t the PortandHarbourResearchnstituten Japan,
ee
particularly
animoto
Takahashi
(1994a),
amberti Franco
1994),
llsop Bray
1994),
ie
1994),
uhl
1994)
nd
Ligteringen
(1
ee4).
2.3
Performance
n seruice
Analysis
f reports
of damage r failure
of
breakwatersuggests
hat here
are hree
main
periods
of
potentialoncern uring he ifeof thestructure:heconstructioneriod;nitial eruice; nd he
extended
ervice
eriod,
ftenwellbeyondhenormal
conomic
ifeused
n
present
esign
ife
calculations.
uch
of thedamage eported ppearso
occur arly
n
he
ifeof he
structure,
ven
during
construction,
o t wouldappear hat f a breakwater
uryives
he
irst 5
years
withoutdamage
t
is
generally
ikely
o survive
he
next40-50
ears.
Thisconfirms
he
premise
hat
damage
failures
re
generally
voidablef
sufficientnformations available
n he
main
ailure
rocesses.
Relativelyittle
nformation
n service
erformance
f breakwaters
asderived
rom he
CIRIA
project
reported
y
Bray
& Tatham
1992).
Of thoseowners
rom
whom
nformation
n breakwaters
as
requested,
nly8% responded,
erhaps
uggesting
hat hese
tructures
ave
given
ittleobvious
cause
or concernn
recent
ears.
n heir eport owever,
ray
& Tatham
ote hat
ncremental
degradationf suchwalls s
oftenoverlooked,nd hat
heapparentackof problemsmaybe due
primarily
o lack
of
inspection.
n some nstances,t might e
concluded
hat
damage
ccurred
o
early
that he
structurewas
abandoned, r was replaced t a
relatively
arlystage
n its ife.
In
other
instances,
t might
be concludedhathistoricalates f
deterioration
avebeenso
slow hat
he
need
for maintenance
xpenditures small.Thiswould gnorehe
brittleness
f
the
ailuremodes
or
many
of
these tructures,
ndBray& Tatham
oncluded
hat here
s a significant
equirement
or nspection
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andmonitoringo avoid hose uddenailureshat
occurwhen
hestructure
asdegraded
o a
failure
point.
Various
ublications
etween
850and 1900
give
details f
breakwater
edormance,
ut often
ailto
distinguishlearly etween
ause nd esponse.
good
example
f this
problem
s
given
by
reports f
damage
o Wickbreakwater. tevenson
1874)
escribeshe
start
of breakwater
onstruction
n 1863
usingdry-placed locks f5 to 1O ons. During tormsn 1870, section f about380 t (115m)of the
breakwater
asdestroyed,
resumably
y
breachinghebreakwater
all. Thissection
was
hen
rebuilt sing
Portland
emento bond
heblock acing, nd
rondowels
etween
ourses.
A
storm n
February 872
gave
wave mpact
ressures
o severe
hat
acing tones
wereshattered, lthough
Stevenson's
eport oesnot dentify hetherhiswasby direct
wave mpact,
r could
have
beenby
stones
rom
he mound einghurled gainsthe ace,see
discussion
y Allsop
t al
(1991)
n
Afderney. n December 872 section f blockwork onded
ogether
nd
estimated
s weighing
350
tonsslid nto he harbour.Thiswas ollowed y a similar
ate o
another
ection
eighing 600 ons n
1873.
These
arecitedby otherauthorsncluding ornick
1969)
s
evidence f
mpact orces rom
breaking
aves.
Shield
1895)
owevereferso
informal iscussions
t
Wick,andsuggestshat
damagewasstronglynfiuencedy oundationailure, utgives ittle ther ata.
Instances re rarernowwhere hedesign r construction
eems
o
have ncorporated
significant
law
from he start,andsevere amage r ailure asbecome
pparent
uring
he
construction
eriod.
The
prime
historical xample f this n he UK s heAlderney
reakwater
here
designhat
hadworked
well n a lowwave
environmentt St Catherines
n
he
sheltered
ide
of Jersey
wasusedagain
or an
extremely xposed ite,subject o frequent nd severe
storms.
Potential
eaknesses
f the
Alderney
breakwater erenotedduring
he construction
eriod,
eading
o
steepening
f the
ront
ace o
increaseestrainingoads
n
ndividual
locks; seof
mortar/
concrete
o
fill between
locks
o reduce
internal
ressures;
eductionf themoundevel o
place
he
oundation
t
greater
epth.
Alsoduring onstructionf the breakwatert Catanian Sicilyn 1930, ery argeblocks lidbackwards
into he harbour
underwaveaftack. Thisweakness
was ascribed
o
the absence
f the
crest
blocks,
and
no
changes eremade o the design.Thedamage
washowever
epeated
n 1933
when
muchof
the upper
part
of the
breakwater lid
backwards.Analysis f
this
ailure
dentifiedhe
lackof horizontal
connectivity
etween ayers,hence he relative ase
with which
successive
ayersslid
over hat
beneath.All aterstructures
uilt
n taly nclude eys, r other
onnections
o resist
orizontal
orces.
Despite
his, ew f any
existing tructures
ere e-appraisedr
strengthened,
ndcollapses
f such
breakwaters
ontinued t Genoa
1955),
entotene(l966),
alermo
1973),
ari
1974),
nd
Naples
(1e87).
One of the major
durability
roblems
f these ypesof structures
rises
romscour
along
he seaward
face of thebreakwater.Lamberti& Franco1994)ascribe ollapse f theMustapha reakwater t
Algiers
rimarily
o
foundation
ailure,nitiated r aggravated
y
ocal cour.
Funakoshi
t al
(1994)
anafysed reakwaiers
f total ength77kmal13 Japanese
orts,
and
oundscour
up to
2m
in nearly
all
examples,
ncluding
xamples here cour
prevention
alleviation
easures
adbeen
ncluded
rom
the startof construction.
enerallyuchscourabated fter
he
irst
1-2
years.
Funakoshi
t
al
(1994)
recommendepeated
edsurveys, nd hatscour
protection
easures
or he oe
mound
hould
e
stagedover he first 2
years
afterconstruction.
In the use
of most
practical
esign
methods,
t is
assumed
hat
wave
mpacts
illeither
ot
occur,
r
that
he
pressures
ill
be so briefas not o allow ime
or massive
aisson
ections
o respond.
Limitations
f theseassumptions
reexposed y he examples
f breakwater
amage
y mpacts
describedor Mutsu-Ogawaray Hitachi1994),or Sakata ndMutsu-Ogawaray Takahshi tal
(1994a),
nd or
Amlwch y Allsop
&
Vicinanza
1996).
Mutsu-Ogawara
ort
on he Pacific
oast f Japan
wasunder
onstruction
n February
991,
when
t
was hit by waves
whichat H"=9.9m
ubstantially
xceeded oth
he
construction
eriod
esign
condition
1:10
ear)
of
H"=/p1,
nd he 1:50
ear
design ondition
f
H;7.6m.
Damage
as
particularly
everewheremounds
f armour locks
ntendedo
cover
he
ront ace
were ncomplete
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and/or
adbeendamaged. hese
art-height
ounds cted
o
rip
he
waves ausing
mpactorces
so severe
hat wo
24m ongcaissons uffered
tructural
amage,
ne
of hem
osing
mostof
its
upper
part.
Photographsakenduringhestorm
how
breaking
aves
eing
hrown
many ens
of
metresnto
the air above he breakwater,
ery
similar
o the
process
een
at Alderney
nder
evere
waves
Sakata
ort
s on he Japan
Sea,and s herefore
n heory
ess
exposed
han
he Pacific
oast. Even
so,waveconditions uring
hewinter f 1973 74 reached .o=7'2mndexceeded "o=4'$6 ;1
other
ccasions.n a
water
epth
omore han
9-10m,hese
onditions
ould
ave
eached
r
exceededhe breaking
imit, nda high oe
mound o
protect
gainst
ossible
cour
would
alsohave
increasedhe
probability
f mpacts.
Nearly ll of
the 39 caissons,
ach
20m
ongand17mdeep,
lid
duringhese torms, ome y nearly
m.
ln a
storm n
7 December 990, smallbreakwater
asdamaged
t
Amlwch
ort
on Anglesey, orth
Wales.The
breakwater
s about 0m ong,
uns
out
approximately
astwards
rom hecoastline, nd
the breakwaterxis s slightly
urved.Thestructure
asconstructed
efore
977
using oncrete
blocksaid n slices ntoa mass oncrete
oundation
late
nto
he
rockhead.
Eachblock
s thus nter-
lockedwith ts neighbouis y keyways. hebreakwaterrestwall s at+7.7mODN,nd
he structure
toe at approximately
11mODN.
Duringhe storm,
he outer
end
of he
breakwater
lidbackwards
y
about
0.1-0.2m,eaving racks own
hroughhe
sliceblockwork
n hree
places
f up o 0.075m
width.
Waveconditions t Amlwch uringhisstorm
renot
known, ut
are
estimated
s at
eastH"o=4[],
probably
ith
a
meanwave
period
f T,=gs.
The oreshore
pproaching
he structure
s verysteep,
approximately
:13,
o
allsoutside f anyestablished
esign
method.
The
water evelduring
he
storm
probably
eached t east
+3.4mODN,
iving
waterdepths
t
he oe
of 11
14m.
Allsop&
Vicinanza
1996)
stimated
imiting
nshore
ave onditions
s
H.i=4m
t MHWS,
ut
educing
o
H"i=3.6mt MLWS. Using he simplemethod
f Vicinanza
t
al
(1995),
he
horizontalforce
as
calculated s 1O4okN/mt MHWS.Withno up-Iift,
or he
blocks
irect
n concrete,
nd
p=0.5,
hese
givea factor f safety f F,= 0.9at highwater, ontrastedypredictionssinghe Godamethodwhich
gives
F"
=
1.2
at
highwater,
nd
F"
=
2.3at ow
water.
These actors
f
safety
would
be reduced
f
up'
lift
pressures
ouldacton or beneath
heblocks.
It s claimed
y
many esearchers,
articularly
n taly, apan
nd
Germany
hat
vertical
reakwaters
with
pre-cast
aissons ave ower onstruction
ostsand
much
horter
nstallation
imes
when
compared ith ubblemounds.The ormof their
nstallation
ay
also
educe
nvironmental
mpact
n
the orm
of noiseor dust
pollution,
n site,
at
he
quarry,
nd n
rdnsport
o the
site.
Once onstructed,
vertical
breakwaters ftenhave ess
visual
and spatial
mpact
which
s
particularly
ttractive
o
navigators
hostrongly islike avigatinglose
o rubble
lopes.
Caisson
reakwater
ections
lso
have he
potential
o be removed t heendof
he
project
ifeby
simply
mptying
he
ill material
nd
e-
floatinghe empty aisson ectionsor re-use lsewhere.
It s clear
rom he examples f damage
eviewed bove,
nd he
many
other
examples
escribed
n
the iterature,hat
here
emain
ignificant
ncertainties
n methods
o analyse
nd
design
ertical nd
composite
reakwaters. he arguments
n favourof these
ypes
of structure
uggest
owever
hat
t is
nowappropriate
o re-examinehe relative
dvantages
nd disadvantages
f
vertical
breakwaters,
nd
particularly
o re-examine
ethodso determine
ave oadings
n
suchstructures.
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3 Design methods
3.1
Designconsiderations
nd
failuremodes
The main activities
n
the
design
process,
strictly he analysis
process,
are to
identify
he main
ailure
processes,
and then to dimension
he selectedstructure
ype
to ensure
hat
the
principal
oadings
remainbelow
he structure's esistance
when suitably
actored.
In
the design
of
verticalbreakwaters
and
related
walls, he main emphasis
has historically
een on
balancing
he
horizontal
and
perhaps
up-lift)
orces against he caisson
weight and hence
riction
orces.
This chapter
generally
ollows
hat
approach.
3.1.1 Structural
ailures
Themain
ailuremodes or hese ypesof structures
aybe
summarised:
Sliding
backwards)
f the
wallelementselativeo the
oundation;
Rotation r overturning,
ackwards,f he
wall;
Forwardotation fthewall;
Gross ettlementf wall;
Structural
ailure f breakwaterlements;
Loss
of
integritycontinuityf structure.
Themain
oadings
cting
n hese ypesof
wallsarise rom
direct
wave
pressures;
p-lift
orces;
uasi-
hydrostaticorces rom
nternalwater
pressures;
nd
geotechnicalorces
reactions
rom backing
r
supporting
aterials.
ome
of the ailuremodes
bovemay
hemselves
e
nitiated
r ac