• Introductory characterization of the environment

Aspects related to design and construction of breakwaters in deep water by

Hans F. Burcharth

Aalborg 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

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 area P = 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 w ave height Hs [m ]

1 0 %

5 %

1%

Normal density cubes

=2.40t/m³, W= 150t

High density cubes

=2.80t/m³, W= 180t

Number of displaced cubes in 180º sector

roundheads.

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

Antifer 1.3 – 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

( ^cot )

1

s s D

s

n

N H K

w D

= =

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/m

Roundhead

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 STABILITY

Normal density, regular placement, waves from NW, water level +4.5 m

H

= 13.2 m

H

= 14.2 m

15

ROUNDHEAD ARMOUR STABILITY

High density, regular placement, waves from NW, water level +4.5 m

H

= 13.2 m

H

= 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 ]

Number of displaced cubes

Comparison of normal and high density armour stability Random placement

1%

10%

5%

Normal density cubes, 154 t

High density cubes, 179 t

Design wave condition

17

ROUNDHEAD ARMOUR STABILITY

High density, regular placement, waves from NW, water level +4.5

18

New stability formula for cube armoured roundheads (Maciñeira and Burcharth 2004)

17 0 08

2 cot

57

0 . ^{0 . 07 0 . 71} _% ^{0 . 2 0 . 4} + . ^{0 . 14} .

=

op op

R n

s e g D S S

D

H

R

= radius at SWL in numbers of D

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-up SWL

Run-up wedge

Internal water table

+1.5m Temporary

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 Overtopping

Formula by Lykke Andersen & Burcharth, 2006

Ratio of overtopping passing travel distance x at splash down level h

:

where is the angle of incidence

( ( ) )

L

0.15 0p level

1.05 - 0p total

x

passing

max x / cos - 2.7 h s , 0

s 1.1 - exp q =

q

x(h

=H) x(h

=0)

x

h

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

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

Capitalized costs (present valu and economic loss due

to 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

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: H

= 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 basin

Jetties

37

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) N

(cubes) Estimated D Repair policy

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.

{ }

( )

+ + +

+

=

= TL

t R R R R F F t

T

C T C

T C T P t C T P t C T P t r

1

1

) 1 ( ) ( )

( )

( )

( ) ( )

( )

(

min

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)

H_s^T (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

Total costs in 1,000 Euro

50 year - 2%

50 year - 5%

50 year - 8%

100 year - 2%

100 year - 5%

100 year - 8%

42

Conclusions related to rubble mound breakwaters without 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

Case 12. Water depth 20 m. Deep water waves. 45 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 S_op=0.035.

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

Cross sections of outer caisson breakwater

t

t

h d

h

b

B b

h'

1:1.5

1:1.5

Caisson on bedding layer

Caisson on high mound foundation

TL s

c

H

h = 0 . 6

Freeboard

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/m

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/m

, Japan, 200 Euro/m

Mound behind caisson: Europe, 25 Euro/m

, Japan, 50 Euro/m

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

Lifetime costs, Euro/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,

. 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

Lifetime costs, Euro/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 B1

. 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,

. 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

design return period, years

Lifetime costs, Euro/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 S1

. 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

design return period, years

Lifetime costs, Euro/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

design return period, years

Lifetime costs, Euro/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

depth Sliding Geotechn.

slip failure ROM 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 LAS V JORNADAS DE PROYECTOS Y OBRAS DE LAS AUTORIDADES PORTUARIAS

AUTORIDADES PORTUARIAS

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

PORTUARIAS EN PUNTA PORTUARIAS EN PUNTA LANGOSTEIRA (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,

ANTECEDENTES:

ANTECEDENTES:

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

64

TEMPORALES

AÑO FECHA H_S (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

BASES DE DISEÑO: OLEAJE BASES DE DISEÑO: OLEAJE

65

Dique de Abrigo

PROYECTO:

PROYECTO:

PLANTA Y SECCIONES TIPO.

PLANTA Y SECCIONES TIPO.

66

PLANTA Y SECCIONES TIPO.

PLANTA Y SECCIONES TIPO.

SECCIÓN PRINCIPAL DIQUE DE ABRIGO SECCIÓN PRINCIPAL DIQUE DE ABRIGO

67

AGO

AGO

2007

2007

AGO

AGO

2007

2007

SEP SEP 2007 2007

70

71

72

73