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Stainless steel wire embedded in concrete helps control erosion, improve navigation
By Dr. G. Crawford
Nickel Magazine, March 2008 -- The Lower Mississippi River snakes its way
in a continuous series of meandering curves from its confluence with the Ohio River southward for about 1,600
kilometres to New Orleans after which it empties into the Gulf of Mexico.
Erosion has to be controlled along the curving concave banks of the river to prevent flooding. Toward this
end, the Mississippi Valley Division of the U.S. Army Corps of Engineers manages a “Channel Improvement”
program as part of the federal Mississippi River and Tributaries Project.
The work entails taking large rectangular slabs of concrete and piling and laying them side by side. Each
slab is 7.6 metres (m) long, 1.2 m wide and 80 millimetres (mm) thick and consists of 16 squares of concrete.
The squares are cast through a rectangular mesh of S24100 stainless steel reinforcing wires (containing 2%
nickel) about 38 mm in diameter. S24100 was chosen for its strength and wear resistance. The wires are
embedded in the concrete, with looped ends poking out of the edges of the slabs.
Holding the slabs together are copper-coated steel connector wires about 300 mm long, that are twisted
around the looped ends of the stainless wires. In this manner, the squares, which weigh about 1.6 tonnes
apiece, are strongly connected yet flexible.
Thirty five such squares are connected side to side to form an array 43 m wide and 7.6 m long on the
sloped launching deck of a river barge aligned parallel to the riverbank.
Steel launching cables roughly 12 mm in diameter are connected between each square to control the
launching of the slabs off the barge on to the riverbank and thence underwater to depths of up to 30 m or
possibly more, as required.
As the end of the first 7.6-m-long array nears the launching deck, a second array is connected end-to-end
from a supply barge beside the launching barge, forming an elongated, flexible “mattress.” This process
continues until the mattress is lowered to the required depth.
Since the mattress is flexible, it can conform to irregularities in the riverbank both above and below the
waterline. Each mattress is held in place by anchors driven into the riverbank near the waterline. The
accompanying illustrations show how the ingenious process works.
Protection of the Mississippi’s riverbank has been ongoing since the late 1800s, though the use of
concrete slabs didn't begin until the time of First World War, and stainless steel didn't enter the picture
until the mid-1970s. By now, pretty well every erosion-prone concave bank has been protected over the entire
length of the river. Every placement is checked regularly, and repaired if damaged.
“The refined design we are using on the Lower Mississippi is tried and proven, cost-effective, and
altogether an excellent product,” says Steve Ellis, a civil engineer and consultant to the Army Corps on the
Channel Improvement program.
The excellence derives largely from the use of stainless steel in the metal mesh fabric that connects the
concrete slabs together, to minimize the erosion of the riverbanks.
Dr. G. Crawford is a Mississauga, Ontario-based consultant to the Nickel Institute.
Photos: U.S. Corps of Engineers and istockphoto.com/Ian Hamilton
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