Arcosa Lightweight, in collaboration with Industrial Fabrics, has led the development of a perfect solution for coastal protection and restoration applications: large bags encapsulating lightweight aggregates. “These are really great for erosion control," says ARCOSA's Steve Rowe. "We’re working together to promote this concept to engineers looking for a way to protect and restore coastal regions,” he says.
The oversize geotextile fabric bags filled with lightweight aggregate are being used to construct protective berms to keep vital flood control walls safe from the destructive effects of collateral damage caused by hurricane-force storm driven threats. First used in 2002, Rowe says these massive lightweight aggregate filled bags are much lighter than the material that would have been traditionally used: common riprap.
“Normally, they would just build this berm out of ordinary riprap, but because of how soft the soil is all over Southern Louisiana, but especially down below the water, the rock would just sink. "These bags containing rotary kiln produced lightweight aggregate, remain in the proper cross section shape and reduce the mass or load of that berm on the underlying soil by almost half.”"-Steve Rowe, Arcosa Lightweight
The oversize aggregate bags were made by Industrial Fabrics, Inc. in Baton Rouge. Equipment to fill the bags was set up at the Mississippi River port facility owned by 234 Terminal Corp. After each bag was filled with up to 5 cubic yards of LWA, a hand-held sewing machine was used to seal the top. Once completed, the bags were then placed, using lifting loops sewn into the bags, onto barges for delivery directly to the project site.
For a recently completed marsh protection project near Terrebonne Parish, Louisiana, the bag sizes ranged from four feet containing 1.5 cubic yards of lightweight to seven feet filled with 5 cubic yards of material. In this particular project, more than 3,000 bags containing 10,000 cubic yards of lightweight were used to construct the berm. Bags of varying sizes were placed in patterns based upon water depth and design cross-section, then covered with 250-lb class riprap limestone rock. “By only covering the tops of the bags with riprap, it’s armored for protection but the overall mass is still reduced substantially,” says Rowe. “Now, if one of these bags should be punctured, and any material would happen to escape, the most you would lose is the material in that one bag.”
Rowe says the use of ordinary, heavy riprap could also lead to underwater slope failure and loss of the berm itself, a destructive issue designers were able to avoid by utilizing LWA-filled geotextile bags. “In the case of the Algiers Canal project, dredging left the canal bottom deeper than the bottom of the adjacent berm location. This condition added to the potential for an unstable berm structure,” says Rowe. “The advantage of lightweight aggregate in this particular application is that engineers can protect against or prevent slope failure underneath the berm.”
Louisiana is shrinking. By some estimates, the state loses roughly 16-square miles of coastline every year. Bays and bayous marked on nautical maps for centuries have vanished, washed away by decades of erosion and storm surge. A series of projects hopes to change that.
Oversized geotextile bags filled with Arcosa lightweight are being used to protect the shoreline and restore marshes in the Biloxi Wildlife Management Area, a vital coastal ecosystem that protects the city of New Orleans, Louisiana.
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