May 28, 2010

Mullins Dam Revamp

Mullins Pond in Evans, Ga., was designed many years ago for agricultural use. In the years that ensued, the area shifted from an agriculturally based community to a progressive and developing town. As in many other communities, the boom of development resulted in increased storm water runoff, which ultimately exceeded the capacity of the existing pond and dam structure. In time, the Mullins Pond dam was compromised by repeated overtopping and eventually became breached. In an area prone to floods, the Columbia County Board of Commissioners needed to increase the capacity and function of the pond.

Columbia County worked with W.R. Toole, a consulting engineering firm, to design the solution. Two dams were utilized on the project: one major, one minor. The minor dam created a forebay that allowed the engineers to achieve the required water quality goals of the state, and the major dam solved for the volume control. Both structures were designed to completely overtop, which allowed for maximum storage but necessitated a very durable layer of protection.

Initially, cast-in-place, roller-compacted concrete was considered for the project, but ultimately ArmorFlex articulating concrete block revetment systems replaced that idea as the best solution. ArmorFlex is a flexible, interlocking matrix of machine-compressed, cellular concrete blocks of uniform size, shape and weight. The matrix is connected by a series of cables that pass longitudinally through preformed ducts in each block, rendering them easy to install over site-specific filter fabric on a prepared surface.

Savings & Protection

ArmorFlex was chosen for this job because of the installation time and cost savings it could offer. Additionally, the mats provided a low-maintenance solution for this dam overtopping application.

“The ArmorFlex product not only met but exceeded our expectations,” said Chad Sweaney, P.E., design engineer with W.R. Toole. “It was a successful choice for our application needs.”

Blair Construction installed 81,030 sq ft of Class 70T and 32,500 sq ft of Class 30S ArmorFlex . Geotextiles were installed on the bottom layer, followed by a stone drainage layer and the ArmorFlex.

“The installation went very smoothly,” said William Mutimer, vice president of Blair Construction. “The product enabled a fast installation, which helped in overall cost savings. All parties involved were very pleased with the end result.”

The unique tapered block design of ArmorFlex offers superior protection for embankment dams, spillways and high-velocity channels and chutes. The essential design component of the ArmorFlex tapered system is a 0.5-in. taper that virtually eliminates destabilizing impact flow forces, thereby providing higher factors of safety.

The ArmorFlex mats provided an effective, economical overtopping protection for the dams, with the stability to withstand a 100-year storm event.

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