A-Jacks are a commercially made concrete product used in both open channel and coastal applications. They consist of two concrete T-shaped pieces joined perpendicularly at the middle, forming six legs. They are a product owned and patented world-wide by Poseidon Alliance Ltd.

Applications

Open channel applications include bank stabilization, flow and grade control, scour protection for bridge

Bridge

A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...

 piers

Pier (architecture)

In architecture, a pier is an upright support for a superstructure, such as an arch or bridge. Sections of wall between openings function as piers. The simplest cross section of the pier is square, or rectangular, although other shapes are also common, such as the richly articulated piers of Donato...

, 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

Manning formula

The Manning formula, known also as the Gauckler–Manning formula, or Gauckler–Manning–Strickler formula in Europe, is an empirical formula for open channel flow, or free-surface flow driven by gravity...

); 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 interstital spaces for native vegetation to take root, ultimately helping to restore the stream bank to a more natural state while continuing to protect against erosion.

In coastal applications A-Jacks are used as breakwaters

Breakwater (structure)

Breakwaters are structures constructed on coasts as part of coastal defence or to protect an anchorage from the effects of weather and longshore drift.-Purposes of breakwaters:...

, revetments, artificial reefs, 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/c.f. http://www.usbr.gov/pmts/geology/geolman2/Chapter18.pdf; a suitable rip-rap boulder comparable to a 96" A-Jacks unit (about 36 c.f.) would weigh about 5800 lb, 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

• Artificial reef
  Artificial reef
  An artificial reef is a human-made underwater structure, typically built to promote marine life in areas with a generally featureless bottom, control erosion, block ship passage, or improve surfing....
  
  
• Breakwater (structure)
  Breakwater (structure)
  Breakwaters are structures constructed on coasts as part of coastal defence or to protect an anchorage from the effects of weather and longshore drift.-Purposes of breakwaters:...
  
  
• Gabions
• Masonry
• Integrated Armor System