After nearly 100 years in operation, the 2,000-ft-long, 125-ft-high concrete gravity dam’s massive spillway gates showed signs of deterioration. Rather than implement a piecemeal repair/replacement program, Georgia Power elected to replace all 19 spillway gates at once—an unprecedented effort with a host of unknowns that tested the project team’s collaboration and problem-solving abilities.

Already challenged to replace all 26-ft by 21-ft, 15-ton gates in just 18 months, the project’s scope expanded with the discovery of excessively deteriorated connection elements, which had to be replaced using a meticulous demolition process incorporating measures to prevent silica dust and slurry from contaminating air and water. Accurately designing and fabricating new tainter-style spillway gates was no easier, due to considerable variations in the alignment of original trunnion pins that initially limited adjustability.

Drawing on their collective experience and utilizing advanced laser measurement and modeling technology, the project team developed a design alternative for each gate, matching original alignments while also providing greater adjustability for more efficient water flow management. Similarly, mock-ups of the connection elements helped fine-tune the components’ design and configuration as well as an intricate installation process that required precision alignment relative to the location of the trunnion pins to maximize the new gates’ operational performance.

Contractors used a 230-ton crane to support offloading, pre-assembly and demolition activities, and a 182-ton crane positioned on a 60-ft by 60-ft barge for material handling work. The project team also assembled and installed two 50,000-lb spillway gate gantry cranes and upgraded access ladders and stairs. Input from the local historical society ensured that the retrofits and alterations preserved the aesthetics of the dam’s architecture.

The repetitive nature of the work, combined with lean construction techniques, helped instill a culture of continuous improvement that also enhanced overall safety, quality and productivity. Contractors mitigated the site’s many logistical and personnel access hazards by using custom-designed scaffolding, platforms and ladders, and stringently reviewed major hoisting and rigging activities. The project team logged more than 105,000 work hours without a single recordable incident or lost-time injury.

Having overcome so many unknowns and unexpected design and constructibility challenges, the project team was hardly fazed by having to prepare for multiple hurricanes that threatened to interrupt work. As a result, the project reached substantial completion three weeks ahead of schedule.

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