ug breakwaters

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BREAKWATERS

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DESIGN INFORMATION ANDCONSIDERATIONS

Character of coastal currents

Cost and availability of material of construction.

Direction and force of prevailing winds.

Nature of bottom or the foundation

Probable maximum height, force and intensity of

waves

Design should be based on extreme phenomena of

wind and waves and not on mean or the average It should be seen that the material in the foundation is

not subjected to scour.

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CLASSIFICATION OF BREAKWATER

Heap or mound breakwater Rubble mound breakwater

Concrete blocks mound breakwater

Rubble mound breakwater

supplemented by concrete blocks Rubble mound breakwater supplemented by

patented stones

Mound with superstructure or composite breakwater

Upright wall breakwater

Special breakwater

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SELECTION OF TYPE OF BREAKWATER

Depends on the following: Availability of materials for construction

Depth of water at the site of construction

Nature of natural foundations Equipment available for construction

Funds and time available for construction

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HEAP OR MOUND BREAKWATER

Mount breakwater is a heap or assemblage of undressed

stones or blocks of various sizes, thrown at site without

any bond and binding materials between adjacent units

The foundations for mount breakwater is never prepared

nor even observed. Such construction is known as pell-

mell or rip-rap construction.

Because of large voids between adjacent units of

construction, settlement occurs for first few years which

reduce the crest level inviting frequent redumping ofstones at top

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COMPONENTS OF MOUNDBREAKWATER

1. Interior or hearth or core: function of core is to increase the bulkor size of breakwater which makes construction of mount

breakwater economical. Core is usually quarry waste or washed

dredged materials which is less pervious.

2. Filter or secondary armours: the size of units (stones) in filter

which is laid around the central core is larger than the size of

stones in core. Hence such layer is more pervious. The function

of filter zone units is to destroy the energy of waves that come

through armour layer of stones.

3. Armour blocks: these stones or blocks are like fighters in army,

hence the name. they resist major part of force (kinetic energy)

of wind and waves. They will be the largest in size and weight.

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CHARACTERISTICS OF MOUND BREAKWATER

Dissipation of kinetic energy by different layers of mound

Natural foundation is unprepared None of the layers of construction work are arranged in

special bond.

No binding materials are to be provided between adjacent

units of construction

No possibility of sliding between any layers with respect to

adjacent units

No possibility of overturning as there is no rigidity in

construction

No possibility of uplift

The mound is porous or pervious

The mound construction is flexible

Unskilled labour can be used in the construction of mound8


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RUBBLE MOUND BREAKWATER

Type I: In this type of construction the top core of mound

breakwater is above mean sea level. Large volume of

core is used to make construction economical. Core is

protected from all sides by filter and armour layers.

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Type II: In this type of mound the crest level of core is kept

below M.S.L by specified distance x in relation with height of

wave dividing the water coming from armour zone into jets and

making them collide among themselves.

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ADVANTAGES & DISADVANTAGES OF MOUND

TYPE BREAKWATER

ADVANTAGES: Low in initial cost of materials of construction equipment

& labour required.

No preparation of foundation.

Construction is porous or pervious, base no possibility ofuplift.

Construction is in pell-mell fashion, bases have no

chance of slippage & overturning.

Construction is flexible. Dissipates the energy of incoming water waves most

efficiently.

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Limitations

Settlement of mound takes places for first few years by

adjustment of voids between adjacent stones & rollingdown of some stones.

Pell mell form of mound construction

Projections are chipped by water

Stones become round & role down the slopeproducing gap.

Makes the mound weak.

Requires huge quantity of materials.

Large quantity of materials is likely to be wasted. Such construction cannot be analyzed.

Occupy large area of basin.

Requires large maintenance.13


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CONCRETE BLOCK MOUNDBREAKWATER

Concrete blocks having rectangular section with sharp

edges are not rough enough and their faces of adjacentblocks are likely to coincide.

Hence energy of wave water cannot be killed or dissipated

even partly.

Only a small amount percentage of energy is dissipate. Also amount of concrete required in casting such blocks will

be huge.

Casting of concrete blocks of odd shapes and sizes and

weight with required irregularity is difficult and costly. Also the transportation from the factory to the site will be

costly.

Hence concrete block mound breakwater is rare.

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RUBBLE MOUND BREAKWATERSUPPLEMENTED BY CONCRETE BLOCKS

In this type concrete blocks are laid towards seaside of

mound to act as extra armour block over the usual

armour blocks of rubble stones which are heavy and

irregular in shape. Remaining construction is similar to rubble mound

breakwater.

The concrete blocks can be laid in

Pell-mell fashion Well compacted fashion

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RUBBLE MOUND BREAKWATERSUPPLEMENTED BY PATENTED STONES

After making no. of experiments various countries have

developed different types and shapes of concrete blocks

which are hydraulically rough as well as stable in any of

their positions and do provide permeable construction.

Such units are patented by each of the companies forworldwide use.

1. Tetrapods: they are assembly of symmetrically

prepared four-legged truncated cones with proper

amount of reinforcements.2. Tribars: they are three legged connected with a plate at

mid-height. If properly placed this tribar group will get

interlocked and remain stable.

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3. Modified cubes: these are made from ordinary cubes. On

each faces of the cubes a long and wide groove is

made, which can be used to interlock adjacent units.These are much heavier than tetrapods and tribars,

hence, shall resist the forces of incoming waves by

impact.

4. Dollosse: an artificial stone is experimented to act asarmour block in South Africa.

5.Akman armour: developed in Netherland

6. Stabit armour: experimented and tried in England and

New Zealand.

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WALL TYPE BREAKWATER

It is a big regular wall raised to construct a harbour basin on

solid natural or artificial foundation to resist the forces and

their components generated by incoming water and waves.

Types of wall breakwater

Wall breakwater of smaller size units

Wall breakwaters of large size units

Mass concrete units Caissons units

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ESSENTIALS FOR WALL TYPE BREAKWATERS

This type is suitable for sheltered sites & not reliable for

very heavy seas. When depth is not great & the bottom is firm, upright wall

breakwater could be built.

These breakwaters should not be constructed in a depth

of water less than twice the greatest storm likely to visitthe site of the proposed structure.

The sea bed at the site should be resistant to erosion

and the foundations should be free from uneven

settlements. For sea bed locations having low bearing capacity, a

rubble base may be provided to distribute the load on a

wider base.

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For locations having to bed material like silt, soft clay,

etc., it is desirable to remove such strata with the

dredgers.

The sheet piles may also be driven to improve the

bearing capacity in locations having low bearing

capacity, upto moderate depths.

The design should be such that no portion of the

breakwater may overturn due to the wave pressureexerted on its surface.

It should be seen that no horizontal course of the wall is

uplifted and gets dislocated.

Wall breakwaters of small units must have proper bondand binding.

Wall breakwaters of large units like mass construction

must have discontinuity in construction joints.

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ADVANTAGES OF WALL BREAKWATER

Reduces the amount of material

Avoids dangers of unequal settlement Increases the size of harbour basin

Maintenance cost is least as compared to that of mound

breakwater

DISADVANTAGES

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Involves building a good height of wall under water

Calls for special case and costly methods of

construction


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MOUND WITH SUPERSTRUCTURE ORCOMPOSITE BREAKWATER

Such construction is adopted to get advantage of mound

at bottom as well as to get advantage of solid or rigid

construction at top.

Solid construction is adopted usually between low water

level and high water level.

Mound with superstructure are classified into the

following two types:

Mound with superstructure founded at low water level.

Mound with superstructure founded below low water

level.

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SPECIAL BREAKWATERS

Floating type breakwater

Hydraulic breakwater

Pneumatic breakwater

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