Rubble mound breakwaters are used for protection of harbours and beaches against wave action. They are also used for protection of navigation channels and beaches against sediment transportation. The figure below shows the components of a typical Rubble mounted breakwater.

 

Components of a typical Rubble mounted breakwater
Components of a typical Rubble mounted breakwater
Core -The purpose of the core is to prevent wave transmission into harbour; hence the core material is not too coarse.

Toe -The Toe functions as the foundation for the armour layer. It also may catch armour units displaced from armour layer; The Toe is normally constructed of large stones of quarry run or the most coarse filter layer.

Filter layer -The objective of the filter layer (under layer) is to prevent the core material from being washed out through armour layer. It is built of quarry run.

Armour layer -The purpose of armour layer is to protect the core from direct wave attacks by the dissipation of wave energy. Armour layers are built of large rocks or larger concrete armour units.

Superstructure -The superstructure is used either in order to reduce the crest elevation or to reduce wave overtopping, or as a roadway for traffic or pipelines. The superstructure is usually constructed of concrete.

Primary armours used in marine structures

 

There are various types of concrete armour units, that are currently been used for the construction of marine structures. Throughout the past few decades various types and shapes of primary armour units have been invented and used in the construction industry. These have the advantage of being interlocked with high permeability and porosity as armour layer, which make them more stable and more effective in dissipating wave energy. Figure below show some of the concrete armour units that are been used in the current construction Industry.

(Source: www. www.researchgate.net)

Different types of armour units have been invented throughout the past few decades, and they too have been undergone evolution. Out of the following we have selected three primary armour units that have been used from time to time for a simple comparison.
Cube

Cube

 

Tetrapod

 

Accropode

 

Shape
Cubical
Tetrahedral
Combined bard
2D
Structural
strength
Massive/ Blocky
Slender
Bulky
Stability
factor
Own weight and
Friction
Own Weight and
Interlocking
Interlocking
Number of
layers
2
2
1
Placement
method
Random and/or
Uniform
Random
Random
Cost (relative
to accropode)
200%
191%
100%
Relative volume
of concrete
220%
208%
100%
Standard
average Mass (tons) considering equal total volumes of concrete
2.2
3.2
11.8
Effectively
Less effective
Moderately
effective
Very effective

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