breakwaters

What is Breakwater?

Breakwater is a structure that protects the area within it from wave attack.

What’s the Need of Breakwater?

To provide shelter from waves.

Through this shelter, to manipulate the littoral/sand transport conditions and thereby to trap some sand entrance inside the Anchorage Area.

Availability of materials of construction.

Depth of water at site of construction.

Nature of natural foundations.

Equipment available for construction.

Funds and time available for construction.

Rubble mound breakwaters (Conventional Type)

Vertical wall/front breakwaters ( Widely Used)

Reef breakwatersRarely used

Piled breakwaters

(Based on the Materials Available on Nearby Site)

Objectives :-

To be able to make an assessment of hydraulic loads against caisson breakwater

To be able to make a preliminary design of a caisson breakwater (length, width, height)

To be able to compare caisson breakwater against rubble mound breakwater ie, on basis of material usage

FUNCTIONS

Wave protection in port/channel

Protection from siltation,

currents

Tsunami protection

Berthing facilities

Access/transport facilityGijon (Spain)IJmuiden (Netherlands)Kamaishi (Japan)Marsaxlokk (Malta)Ras Laffan (Qatar)

TYPES

(breakwaters with vertical and inclined concrete walls)

Conventional type

The caisson is placed on a relatively thin stone bedding.

Advantage of this type is the minimum use of natural rock (in case scarce)

Wave walls are generally placed on shore connected caissons (reduce overtopping)

Mutsu-Ogawara (Japan)

TYPES (continued)

Vertical composite type

The caisson is placed on a high rubble foundation.

This type is economic in deep waters, but requires substantial volumes of (small size) rock fill for foundationAlgeciras (Spain)

TYPES (continued)

Horizontal composite type

The front slope of the caisson is covered by

armour units

This type is used in shallow water. The mound

reduces wave reflection, wave impact and wave

overtopping

Repair of displaced vertical breakwaters

Used when a (deep) quay is required at the

inside of rubble mound breakwater

Gela (Sicily, Italy)

TYPES (continued)

Block type

This type of breakwater needs to be

placed on rock sea beds or on very

strong soils due to very high foundation

loads and sensitivity to differential

settlements

Alderney (Guernsey, UK)

TYPES (continued)

Piled breakwater with concrete

wall

Piled breakwaters consist of an

inclined or vertical curtain wall

mounted on pile work.

The type is applicable in less severe

wave climates on site with weak and soft

subsoils with very thick layers.

Manfredonia New Port (Italy)

TYPES (continued)

Sloping top

The upper part of the front slope

above still water level is given a slope to

reduce wave forces and improve the

direction of the wave forces on the

sloping front.

Overtopping is larger than for a

vertical wall with equal level.Napels (Italy)

TYPES (continued)

Perforated front wall

The front wall is perforated by holes

or slots with a wave chamber behind.

Due to the dissipation of energy both

the wave forces on the caisson and the

wave reflection are reduced

Dieppe (France)

TYPES (continued)

Semi-circular caisson

Well suited for shallow water

situations with intensive wave breaking

Due to the dissipation of energy both

the wave forces on the caisson and the

wave reflection are reduced

Miyazaki Port (Japan)

TYPES (continued)

Dual cylindrical caisson

Outer permeable and inner impermeable cylinder.

Low reflection and low permeable

Centre chamber and lower ring

chamber fills with sand

Nagashima Port (Japan)

TYPES (continued)

“Combi-caisson”

Sloping top

Semi-circular/perforated

Perforated front wall

Perforated rear wall

What is needed?

Proper understanding of functional requirements

Proper understanding of loads and resistance

Insight in failure modes

Understanding of breaking/non-breaking waves

Functional requirements

Access

Quay facilities

Overtopping

Transmission

Requirements: acces (pedestrians, supply traffic)

Piraeus (Greece)

Requirements: acces (harbour workers, traffic, oil piping)

Marsaxlokk (Malta)

Requirements: acces (harbour workers, traffic, Liquefied

Natural Gas (LNG) piping)

Ras Laffan (Qatar)

Requirements: acces (harbour workers, traffic, conveyors)

Porto Torres (Sicily, Italy)

Requirements: quay facilities (access, warehouses, sheds)

Constantza Port (Romania)

Requirements: quay facilities (access, warehouses, sheds)

Durres Port (Albania)

Requirement: limit overtopping and transmission of water

Marina do Lugar de Baixo (Madeira, Portugal)

Vertical Wall Breakwaters - Loads and resistance

Loads and resistanceLoads:

Hydraulic loads Weight

Resistance:

Friction (mostly) Soil bearing capacity

Vertical Wall Breakwaters - Loads and resistanceFailure modes (overall)

Hydraulic failure

SlidingOverturning

U

Vertical Wall Breakwaters - Loads and resistance

Failure modes (local)

Instability of moundErosion of seabed Partial

Instability

UErosion Scour

Example overall failure: Mutsu Ogawara Port, East Breakwater (Japan)

Example local failure: Catania Breakwater (Sicily, Italy)

Disadvantages:-

Construction cost is high.

Can be easily displaced by waves.

Don’t absorb all energy due to the gaps

between breakwater.

Aesthetically seems to be bad.

Advantages:-

Easy to repair.

Protects the shore.

Functions after minor damage.

Don’t disturb the shoreline.

Protection of the Ports or Harbors from the Natural Calamities such as

Tsunami is essential. But exact prediction of Natural Calamities is not

possible, but some extent of it can be prevented by Breakwater

Construction.

Protection of the Ports or Harbors from the Siltation & Wave Action is

done by providing a economical & suitable type of Breakwaters.

Instead of using Armor Blocks the Sand Bags may be used to Protect or

Safe Guard the Shores to some extent . Shore Protection in Quatar

Indian Standard Code of practice for planning and design of ports and

harbours part 4 general design considerations [Third Revision of IS 4651 (Part

4)].

PIANC; Breakwaters with Vertical and Inclined Concrete Walls, Report WG

28, 2003.

US Army Corp of Engineers. 1985. Shore Protection Manual. Washington,

D.C., US Army Corp of Engineers.