A-Jacks are a commercially made
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most ...
product used in both open channel and coastal applications. They consist of two concrete T-shaped pieces joined
perpendicular
In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It can ...
ly at the middle, forming six legs. They are a product owned and patented worldwide by Poseidon Alliance Ltd.
Applications
Open channel applications include bank stabilization, flow and grade control, scour protection for
bridge
A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...
piers Piers may refer to:
* Pier, a raised structure over a body of water
* Pier (architecture), an architectural support
* Piers (name), a given name and surname (including lists of people with the name)
* Piers baronets, two titles, in the baronetages ...
, and biostabilization. The primary mechanism of protection employed is an increase in the relative roughness of the channel bank (as characterized by the
Manning's Roughness Coefficient); the Manning's n is relatively high at 0.1. The advantage of A-Jacks over other hard armoring solutions is the comparatively large area available in the interstitial spaces for native vegetation to take root, ultimately helping to restore the
stream bank
In geography
Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, fea ...
to a more natural state while continuing to protect against erosion.
In coastal applications A-Jacks are used as
breakwaters
A breakwater is a permanent structure constructed at a coastal area to protect against tides, currents, waves, and storm surges. Part of a coastal management system, breakwaters are installed to minimize erosion, and to protect anchorages, h ...
,
revetments
A revetment in stream restoration, river engineering or coastal engineering is a facing of impact-resistant material (such as stone, concrete, sandbags, or wooden piles) applied to a bank or wall in order to absorb the energy of incoming water a ...
,
artificial reefs
An artificial reef is a human-created underwater structure, typically built to promote marine life in areas with a generally featureless bottom, to control erosion, block ship passage, block the use of trawling nets, or improve surfing.
Many r ...
, and habitat development. In breakwater applications, A-Jacks can be an economical alternative to quarried rock, which can be both heavier and unwieldy; over the course of a breakwater construction project, the number of transportation cycles to deliver product to the site can be reduced substantially, since A-Jacks are delivered flat on trucks whereas rock rip-rap would be brought in dump trucks. For example, rock can weigh between 150-175 lb;
a suitable rip-rap boulder comparable to a 96 inch A-Jacks unit (about 36 c.f.) would weigh about 5800 pounds, about 16% more than the A-Jacks unit. A-Jacks also have the advantage of being interlocking and self-stabilizing. For artificial reefs and habitat development, typical reef-building biota find areas of low turbulence within the open spaces to establish colonies.
See also
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References
{{coastal management
Wave-dissipating concrete blocks