sr443 waves forces vertical composite breakwaters hrwallingford

7/26/2019 SR443 Waves Forces Vertical Composite Breakwaters HRWallingford

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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.

sR

443 0209/96


2/116

sR

443 0209/96


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r

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

443 02109196


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r

IV

sR

443

02109/96


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r

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.

sR

443V2tO9t98


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r

VI

sR44302t09,8


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r

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

sR

443 02/09196


8/116

r

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

4430210919


9/116

r

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

sR

443 0209/96


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r

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r

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


12/116

r

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

sR143g2l0,9t90


13/116

r

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


14/116

r

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

sR

4

qz09l96


15/116

r

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


16/116

r

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


17/116

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

.

sR

443021c'91916


18/116

r

sR

443 2y09196


19/116

r

2 Veftical

breal


20/116

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

sR

44302JO9196


21/116

r

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.

sR

443

02109/96


22/116

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

sA4430210,9,l


23/116

r

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-

sR

443 0209/96


24/116

r

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

1 0

sB

1430210'9,l


25/116

r

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

1 1

sF

443 0209/96


26/116

r

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

sR

4430200/96


27/116

r

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

13

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443 02@/96


28/116

r

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

1 4

sR

4430209/96


29/116

E

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

1 5

sR

44St2lo9l


30/116

r

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.

1 6

sR

443 02,0919


31/116

r

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

sr443 waves forces vertical composite breakwaters hrwallingford

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