Components of a rubble mound breakwater

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

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