Aalborg Universitet Aspects Related to Design and...

Aalborg Universitet

Aspects Related to Design and Construction of Breakwaters in Deep Water

Burcharth, Hans Falk

Published in:Symposium Design and Construction of Deep Water Maritime Works

Publication date:2007

Document VersionEarly version, also known as pre-print

Link to publication from Aalborg University

Citation for published version (APA):Burcharth, H. F. (2007). Aspects Related to Design and Construction of Breakwaters in Deep Water. InSymposium Design and Construction of Deep Water Maritime Works: Gijon, Spain, 2007

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Aspects related to design and construction of breakwaters in deep waterby

Hans F. BurcharthAalborg University, Denmark

Contents of presentation

• Introductory characterization of the environment

• Rubble mound breakwaters

Armour placement, reallocation and settlements

Armour stability

Crane capacity

Toe stability

Construction roads

Rear slope stability

• Caisson breakwaters

Determination of wave loadings

• Safety of rubble mound and caisson breakwaters

•New Breakwater at Punto Langosteira, La Coruña

Symposium Design and Construction of Deep Water Maritime Works, Gijon, Spain, 2007

Presentation by Hans F. Burcharth, Aalborg University, Denmark, e-mail: [email protected]

1

Introductory characterization of the field

Environmental conditions

• Water depth 20 m

• Exposed locations facing the ocean giving large and long design waves

• Wave climates

–Frequent storms, always some wave disturbance during construction

(generally seasonal)

–Rare (infrequent) storms, generally very little wave disturbance during

construction (typical for some tropical zones)

The main difficulties are related to the construction and depends on the

environmental conditions.

The design should minimize the difficulties.



2

Rubble Mound Breakwaters

Usual specifications for placement of main armour

Case 1 Bulky units like cubes placed in two layers

1. Random placement specified as positioning (x, y) in

accordance with a defined grid, ± m.

2. Number of units N ± X % within a given area A.

3. Porosity P% ± X % within a given area A.

4. Layer thickness t m and tolerances ± X m within a

given area A.



3

Comments:

ad. 1. Random placement

Means random orientation.

The term random placement is used by designers only to distringuish from

regular (pattern) placement. The degree of random orientation is inherent in the

defined set of N, P and t.

The accurate position of a block when placed is not known. - only the position

at the moment of hook release. Visual checking or (if not possible) advanced

sonar measurements are needed if more close control is needed, but generally

control of N, P and t should besufficient if A is not defined too large.

ad. 2. Number of units, N

Generally no problems in fulfilling N.

ad. 3. Porosity, P

Given N then P depends only on t.

ad. 4. Layer thickness t

t is always defined in drawings (theoretical layer thickness) but cannot be

verified on site unless a method of measuring the layer surface is given.



4

Link between porosity P and layer thickness t



5

/1

Porevolume concretevolume areaP

total volume t= =

Increasing surface roughness and permeability (and settlements)

Decreasing run-up and overtopping (and stability)

The layer thickness determines the porosity (degree of random orientation)

when the number of blocks per area is given. Their tolerances are linked.

ad. 1-4 The tolerances given in the technical specification should reflect the

safety margin of the design. A small safety margin demands smaller

tolerances.

Design of large structures is based on model tests. The block

placement and the related accuracies applied in the model should

correspond to the project specifications or be more relaxed in the model.

On very exposed locations I recommend to deliberately built-in

irregularities like cavities in the models, and base the design on the

performance of such models.

Regular placement (pattern placed) like a pavement is easier to

construct than irregular placement because the first layer of cubes

tends to lay on a flat side on the underlayer. The consequence is a

more smooth surface which gives more overtopping. On the other

hand, the hydraulic stabillity of the armour increases (very high

stability can be obtained if the boundaries are intact).



6

Case 2 Single layer of complex interlocking armour on steep slopes.

Compared to placement specifications for bulky units the

specifications are more restrictive with respect to orientation of the units

in order to ensure stability. Therefore, I do not recommend such

armour in exposed places where visual underwater inspection by divers

cannot be performed almost continously during placement of the armour

units.



7

Settlement of armour layers

Settlement caused by wave action cannot be avoided.

Contributing to armour settlement can be

Compaction of under layers (vertical)

Sliding of armour on under layers

Sliding of armour blocks relative to each other

Deformation of supporting toe

The higher and steeper the slope, the larger settlements (SOGREAH limits the

height of Accropode armour to 20 rows).

The higher the initial porosity, the larger settlements.

The smoother the under layer (wide gradation, relative small stone sizes) the

larger settlements.



8

Settlements generally cause opening (cavities) in the middle to upper part of the

slope.

dddddd



1:28.5 scale model of proposal for main cross

section of Punto Langosteira Port Breakwater, La

Coruña (CEDEX 2007). Main armour placed by

crane on the slope. Pattern placed on upper

berm.

150 t cubes in two layers except 50 t cubes in

three layers in six bottom rows. Toe berm of 5 t

quarry rock.

Armour layer after exposure to design waves.

(Hs = 15 m).

9



10

The major part of settlements should preferably occur in the construction period by

occurrence of wave action of some severity (but not damaging) in order to avoid

repair by refilling after construction (might be almost impossible due to lack of space

in the cavities and due to very large mobilization costs).

Armour layers with good self healing ability (generally two-layers) are to be

preferred, especially in climates where severe wave actions are so rare that

”settlement-waves” cannot be expected to occur during construction.

Settlements cannot be studied quantitatively in models due to severe scale effects.



11



Influence of limited crane capacity on toe design

12

0

50

100

150

200

4 6 8 10 12 14 16

Significant wave height Hs [m]

10%

5%

1%

Normal density cubes

=2.40t/m3, W= 150t

High density cubes

=2.80t/m3, W= 180t

Nu

mb

er

of

dis

pla

ce

d c

ub

es

in 1

80º s

ec

tor

Reduction of crane capacity by use of high-density armour units inroundheads.

Researcher Armour Weight of roundhead armour

Weight of trunk armour

Jensen

(1984)

Tetrapods 2.3

Vidal et al.

(1991)

Cubes 1.3 – 3.8

Madrigal

(1992)

Parallelepipeds

Accropods

2.0 – 2.5

2.5 – 4.0

Burcharth et al.

(1995)

Dolos 1.3 – 1.6

Berenguer

(1999)

Holowed cubes

Antifer1.3 – 2.6



13



Roundhead design by use of high mass density blocks

Block weight in the most critical sector of roundhead must be app. double of block weight in trunk.

Double crane capacity needed for placement in roundheads if mass density is not changed.

Solution: Increase mass density of blocks placed in the critical sector.

Hudson formula

Example:

14

( )1/ 3

cot

1

s

s D

s

n

HN K

Dw

= =

p

3

s D s

s

Hs = 15 m, T = 20 s, crest level +25 m, slope 1:2 (cotá = 2)

Trunk 150 t cubes, 4x4x4 m, ñ = 2.40 t/m , K = 10.9, N = 2.80

300 t cubes, 5x5x5 m, ñ = 2.40 t/mRoundhead

3

D s

3

s D s

, K = 5.59, N = 2.24

1.75 t cubes, 4x4x4 m, ñ = 2.74 t/m , K = 5.59, N = 2.24

ROUNDHEAD ARMOUR STABILITYNormal density, regular placement, waves from NW, water level +4.5 m

Hs = 13.2 m

Hs = 14.2 m



15

ROUNDHEAD ARMOUR STABILITYHigh density, regular placement, waves from NW, water level +4.5 m

Hs = 13.2 m

Hs = 14.3 m



16

Water level +4.5, Waves from NW

0

20

40

60

80

100

120

140

160

180

200

4 6 8 10 12 14 16

Hs [m]

Nu

mb

er

of

dis

pla

ce

d c

ub

es

Comparison of normal and high density armour stabilityRandom placement

1%

10%

5%

Normal density cubes, 154 t

High density cubes, 179 t

Design wave condition



17

ROUNDHEAD ARMOUR STABILITYHigh density, regular placement, waves from NW, water level +4.5



18

New stability formula for cube armoured roundheads

(Maciñeira and Burcharth 2004)

170082cot 5701404020710070

... ...%

..+= opop

R

n

s SSDgeD

Hnm

Rnm = radius at SWL in numbers of Dn



19



20



21



22

Construction roads (Landbased equipment)

Criteria

Width sufficient for crane operation and passing dumpers, trucks and

lorries

Level sufficiently high to avoid damaging overtopping (person, materiel,

road surface) during the defined limiting sea states.



23

Sufficient hydraulic performance

Construction roads Levels



24

Design for construction



25

Example:

Determination of level and

exposure of construction

road for land based

equipment.

Run-upSWL

Run-up wedge

Internal water table

+1.5mTemporary

road

Illustration of run-up on Antifer blocks

Beirut Airport breakwater

Influence of crest width on rear slope stability



26

Splash down from the large

overtopping waves hits slope

instead of water surface

Rear slope stability

a problem if

settlement occur

Hollowed blocks for rear slope armour



27



28

Spatial Distribution of OvertoppingFormula by Lykke Andersen & Burcharth, 2006

Ratio of overtopping passing travel distance x at splash down level hlevel:

where is the angle of incidence

( )( )pL0

0.150plevel1.05-

0p

total

xpassing 0,sh2.7-cos / xmaxs1.1-exp=

q

q

x(hlevel=H)

x(hlevel=0)

x

hlevel

H

Temporary construction road with high crest level



29



30

Optimum safety levels in design of breakwaters

Main types of breakwaters and typical damage development

Damage

Hs

Damage

Hs

Design wave conditions and optimum safety levels depend

on the damage development

7.2 Reliability assessment of structures

Structures subject to the actions from waves and currents should be assessed for their

reliability at the serviceability and ultimate limit states with due consideration for their economic

and social functions, environmental influences, and the consequences of failure. The nature

and extents of the uncertainties in Subclause 7.1. should be duly taken into account when

assessing the reliability of structures during their design working life.

The probability of failure during the design working life should preferably be assessed and

confirmed to be less than the minimum value assigned to a specific class of structure, which is

to be preset or approved by responsible agencies.

The probability of failure may be evaluated by the use of reliability index method or with direct

calculation by numerical integration of their probability density functions or Monte Carlo

simulations.

For a structure that permits a certain degree of deformation at the serviceability and ultimate

limit states, the expected amount of deformation should preferably be evaluated.

International standard Organization ISO

New standard ISO 21650

Actions from waves and currents on coastal structures



31

Example of safety levels specified in Spanish Recommendations for

Maritime Structures ROM 0.0

Economic repercussion index (ERI)

(cost of rebuilding and downtime costs)

Low economic repercussion ERI < 5

Moderate economic repercussion 5 < ERI < 20

High economic repercussion ERI > 20

Social and environmental repercussion index (SERI)

No social and environmental repercussion impact SERI < 5

Low social and environmental repercussion impact 5 < SERI < 20

High social and environmental repercussion impact 20 < SERI < 30

Very high social and environmental repercussion impact SERI > 30



32

From ERI is determined service lifetime of the structure

ERI < 5 6 – 20 > 20

Service life in years 15 25 50

From SERI is determined maximum overall probability of failure within

service lifetime, Pf

SERI < 5 5 - 19 20 - 29 >30

Serviceability

limit state

(SLS)

0.20 0.10 0.07 0.07

Ultimate limit

state

(ULS)

0.20 0.10 0.01 0.0001



33

Example a large breakwater in deep water protecting a container port and/or

berths for oil tanker would have ERI around 20. This means 50 years

service

life time.

SERI might be low corresponding to 5 < SERI < 20 giving the Pf – values

SLS 0.10 in 50 years

ULS 0.10 in 50 years

How does this fit with economical optimization?



34

Objective of present study

To identify the safety levels related to minimum total costs over the

service life. This includes capital costs, maintenance and repair costs,

and downtime costs.

Safety of breakwater

Maintenenance, repair

Construction costs

Total costs

Cap

ital

ized

co

sts

(pre

sen

t v

alu

and economic loss dueto downtime etc.

Optimum safety level



35

Studied influences on optimum safety levels

• Real interest rate, inflation included

• Service lifetime of the breakwater

• Downtime costs due to malfunction

• Damage accumulation

ISO prescription

The ISO-Standard 2394 on Reliability of Structures demands a

safety-classification based on the importance of the structure and the

consequences in case of malfunction.

Also, for design both a serviceability limit state (SLS) and an ultimate

limit state (ULS) must be considered, and damage criteria assigned to

these limit states.

Moreover, uncertainties on all parameters and models must be

taken into account.



36

Performance (damage) criteria related to limit states

Besides SLS and ULS is introduced Repairable Limit State (RLS) defined

as the maximum damage level which allows foreseen maintenance and

repair methods to be used.

Functional classification Tentative performance

criteria

I Wave transmission

SLS: Hs, T = 0.5 – 1.8 m

Damage to main armour

SLS: D = 5 %, RLS: D = 15

%

ULS: D = 30 %

Sliding distance of caissons

SLS: 0.2 m, ULS: 2 m

Inner basins

Outer basinJetties



37

Cross sections

4Dn

3Dn

min. 1.5m

h 3Dn

1:2 1:1.5 2Dn

Dn relates to main armour

2Dn

1.5Hs 1:2

Dn relates to main armour

h 2.3Dn

3Dn

Shallow water

Deep water

Only rock and concrete cube armour considered.

Crest level determined from criteria of max. transmitted Hs = 0.50 m

by overtopping of sea state with return period equal to service life.



38

Repair policy and cost of repair and downtime

Damage levels S (rock) Nod(cubes) Estimated D Repairpolicy

Initial 2 0 2 % no repair

Serviceability

(minor damage,

only to armour)

5 0.8 5 % repair of

armour

Repairable

(major damage,

armour + filter 1)

8 2.0 15 % repair of

armour +

filter 1

Ultimate

(failure)

13 3.0 30 % repair of

armour +

filter 1 and

2



39

Formulation of cost functions

All costs are discounted back to the time when the breakwater is built.

{ }( )+

+++==

LT

ttFFRRRRI

T r

tPTCtPTCtPTCTCTC1 1

1)()()()()()()()( min

2211

where

T return period used for deterministic design

TL design life time

CI(T) initial costs (building costs)

CR1(T) cost of repair for minor damage

PR1(t) probability of minor damage in year t

CR2(T) cost of repair for major damage

PR2(t) probability of major damage in year t

CF(T) cost of failure including downtime costs

PF(t) probability of failure t

r real rate of interest



40

Optimum safety levels for concrete cube armoured breakwater.

30 m water depth. 50 years and 100 years lifetime. Damage accumulation

included. Downtime costs of 200,000 EURO per day in 3 month for damage

D > 15%.

Lifetime

(years)

Real

Interest

Rate

(%)

Optimum design data for deterministic

design

Optimum limit state

average number of

events within structure

lifetime

Construction

costs for 1 km

length

(1,000 EURO)

Total lifetime

costs for 1 km

length

(1,000

EURO)Optimized

design

return

period, T

(years)

HsT

(m)

Optimum

armour

unit mass

W

(t)

Free-

board

Rc

(m)

SLS RLS ULS

2 1000 14.7 168 14.8 1.21 0.008 0.001 76,907 86,971

50 5 400 14.2 150 14.8 1.84 0.016 0.003 73,722 81,875

8 100 13.2 122 14.8 3.39 0.052 0.012 68,635 78,095

2 1000 14.7 168 15.4 2.68 0.013 0.002 78,423 93,440

100 5 400 14.2 150 15.4 3.90 0.029 0.005 75,201 84,253

8 200 13.7 136 15.4 5.28 0.056 0.011 72,675 79,955



41

Case 2.3. Concrete cube armour. 30 m water depth. 50 years and 100 years

lifetime. Damage accumulation included. Downtime costs of 200,000 Euro per

day in 3 month for damage D > 15 %

50000

70000

90000

110000

130000

150000

170000

190000

210000

25 50 75 100 125 150 175

Design armour weight in ton

To

tal

co

sts

in

1,0

00

Eu

ro

50 year - 2%

50 year - 5%

50 year - 8%

100 year - 2%

100 year - 5%

100 year - 8%



42

Conclusions related to rubble mound breakwaterswithout crown walls.

Optimum safety levels correponds to:

Approximately one repair of small armour layer damage (D = 5%) in 50 years

corresponding SLS repair probability of app. 1.0. (ROM specifies 0.1).

This corresponds to the use of the 200-400 years return period waves in

deterministic design!

Chances of major damage and collapse will be marginal (ULS: Failure

probability < 0.03, where ROM specifies 0.1).

Very flat cost minimum. No significant increase in lifetime costs by designing a

safer structure.

No or marginal influence of downtime costs on optimum safety levels.



43

44



45Case 12. Water depth 20 m. Deep water waves.

Economical optimization of Icelandic berm breakwaters

Structure lifetime 50 years. Interest rate incl. inflation 5% p.a.

Downtime costs in case of failure 18,000 Euro per metre structure

Rock mass density 2.70 t/m3. Wave steepness Sop=0.035.

Case 11. Water depth 11 m. Shallow water waves.



Cross sections of outer caisson breakwater

trtf

dh

hc

bf B br

h'

1:1.5

1:1.5

Caisson on bedding layer

Caisson on high mound foundation

TL

scHh = 6.0Freeboard

46



Structure part Europe Japan

Caisson

Armour layers

Foundation core

90

150

37

150

235

25

Bulk unit prices for completed caisson structure in Euro/m3

Limit states Sliding distance (m) Repair

Serviceability SLS

Repairable RLS

Ultimate ULS

0.2

0.5

2.0

No

Dissipation blocks in front, or

mound behind

Both

Limit state performances

Repair unit prices

Blocks in front of caisson: Europe, 150 Euro/m3, Japan, 200 Euro/m3

Mound behind caisson: Europe, 25 Euro/m3, Japan, 50 Euro/m3

47



48



Table 9.14. Case B1a. Optimum safety levels for outer breakwater

in 25 m water depth. 100 years service lifetime. RLS repair with

blocks in front of caisson.

49



100000

120000

140000

160000

180000

200000

220000

240000

10 100 1000 10000

design return period years

Life

tim

e c

osts

, E

uro

/m

h'/h=0.70

h'/h=0.77

h'/h=0.83

h'/h=0.90

h'/h=0.97

Fig. 9.15. Case B1a. Dependence of lifetime costs on relative height

of caisson rubble mound foundation and on return period applied in

deterministic design.

50



Table 9.16. Case S1a. Optimum safety levels for outer breakwaters

in 40 m water depth. 100 years service lifetime RLS repair with

blocks in front of caisson.

51



Fig. 9.16. Case S1a. Dependence of lifetime costs on relative height

of caisson rubble mound foundation and on return period applied in

deterministic design.

Geotechnical failure modes Caisson breakwaters

52



53



Table 9.20. Case B1b,sand 30o. Optimum safety level for outer

caisson breakwater in 25 m water depth. 100 years lifetime. RLS

with mound behind caisson.

54



case B1 - 21

100000

120000

140000

160000

180000

200000

220000

240000

260000

280000

300000

10 100 1000 10000

design return period, years

Life

tim

e c

osts

, E

uro

/m

h'/h=0.70

h'/h=0.77

h'/h=0.83

h'/h=0.90

h'/h=0.97

Fig. 9.19. Case B1b, sand 30o. Dependence of lifetime costs on relative

height of caisson rubble mound foundation and on return period

applied in deterministic design.

55



Table 9.21. Case S1b, sand 30o. Optimum safety level for outer

caisson breakwater in 40 m water depth. 100 years lifetime. RLS

with mound behind caisson.

56



case S1 - 31

200000

300000

400000

500000

600000

700000

800000

900000

1000000

10 100 1000 10000


Life

tim

e c

osts

, E

uro

/m h'/h=0.70

h'/h=0.77

h'/h=0.83

h'/h=0.90

h'/h=0.97

Fig. 9.20. Case S1b, sand 30o. Dependence of lifetime costs on relative

height of caisson rubble mound foundation and on return period

applied in deterministic design.

57



case B1 - 21

100000

110000

120000

130000

140000

150000

160000

170000

180000

190000

200000

10 100 1000 10000


Life

tim

e c

osts

, E

uro

/m h'/h=0.70

h'/h=0.77

h'/h=0.83

h'/h=0.90

h'/h=0.97

58



59



case S1 - 31

200000

250000

300000

350000

400000

450000

500000

10 100 1000 10000


Life

tim

e c

osts

, E

uro

/m h'/h=0.70

h'/h=0.77

h'/h=0.83

h'/h=0.90

h'/h=0.97

60



Conclusions related to outer caisson breakwaters allowed to slide

moderably. Sand seabed, =35º. Wide rear berm.

Optimum safety levels for cost optimized designs correspond to the following probabilities.

Failure probabilities in 50 years lifetime

Water

depthSliding

Geotechn.

slip failureROM 0.0

SLS ULS

15 m 0.027 0.023 0.042 0.10

25 m 0.011 0.006 0.022 0.10

40 m 0.004 0.002 0.034 0.10

Optimum safety levels seem much more restrictive than recommended in ROM

0.0, and are significantly higher than for conventional rubble mound breakwaters.

61



62



V JORNADAS DE PROYECTOS Y OBRAS DE LASV JORNADAS DE PROYECTOS Y OBRAS DE LASAUTORIDADES PORTUARIASAUTORIDADES PORTUARIAS

A CORUÑA, 27 DE SEPTIEMBRE DE 2007A CORUÑA, 27 DE SEPTIEMBRE DE 2007

NUEVAS INSTALACIONESNUEVAS INSTALACIONESPORTUARIAS EN PUNTAPORTUARIAS EN PUNTALANGOSTEIRA (A CORUÑA)LANGOSTEIRA (A CORUÑA)

Fernando J. Noya Arquero.Fernando J. Noya Arquero.

Subdirector General de Infraestructuras.Subdirector General de Infraestructuras.

Autoridad Portuaria de A Coruña.Autoridad Portuaria de A Coruña.

63



TRAMOS RESULTADOS

MORRO 1A 1B QUIEBRO

13.3 13.8 14.8 15.1

2A 2B 2C 2D

15.1 14.8 15.1 10.7

Hs,140 años

ANTECEDENTES:ANTECEDENTES:

BASES DE DISEÑO: OLEAJE (2/3)BASES DE DISEÑO: OLEAJE (2/3)

64



TEMPORALES

AÑO FECHA HS (m) Hmax (m) Tp (seg)

1998 29-nov 7,42 13,18 17,24

1999 18-ene 7,58 13,54 14,3

2000 06-nov 9,61 14,76 13,4

2001 28-ene 11,91 18,06 14,3

2002 22-nov 8,02 10,69 14,3

2003 21-ene 8,76 13,8 15,3

2004 18-abr 6,8 10,65 12,5

2005 01-ene 9,36 14,65 16,7

2006 08-dic 7,81 13,24 15,3

2007 10-feb 9,04 13,77 16,7

ANTECEDENTES:ANTECEDENTES:

BASES DE DISEÑO: OLEAJEBASES DE DISEÑO: OLEAJE

65



Dique deAbrigo

PROYECTO:PROYECTO:

PLANTA Y SECCIONES TIPO.PLANTA Y SECCIONES TIPO.

66



PROYECTO:PROYECTO:

PLANTA Y SECCIONES TIPO.PLANTA Y SECCIONES TIPO.

SECCIÓN PRINCIPAL DIQUE DE ABRIGOSECCIÓN PRINCIPAL DIQUE DE ABRIGO

67



AGOAGO

20072007

DIQUE DEFINITIVO



DIQUE DEFINITIVO

SEPSEP

20072007

70



71



72



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