LANCASTER, TN — Work crews at Center Hill Dam recently removed the first of its massive spillway gates, a pivotal first step for an ongoing project to replace all eight original tainter gates and lifting equipment that have been in continuous operation since 1948.
The U.S. Army Corps of Engineers (USACE) Nashville District and its contractor, American Bridge Company, slid the spillway gate on a platform where it could be picked up by a crane and placed onto a work barge located next to the dam on Center Hill Lake.
According to Mike Freeman, Lead Construction Inspector for Nashville District’s Eastern Tennessee Resident Engineer Office, the contractor spent most of the day prior cutting the spillway gate from the dam to prepare for its removal. He said the lift went smoothly despite some rainfall.
“It rained for about 10 minutes. It downpoured as soon as they picked up the gate. When they set it down, the sun was shining,” Freeman said. “It went as planned. Lots of planning and engineering went into this gate removal, and it was nice to see it in action.”
The successful extraction of the first spillway gate makes it possible for USACE to prepare the empty spillway bay for installation of the new spillway gate and lifting equipment.
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“During construction, removal, and installation of each gate, public safety is our top priority,” said Greg Bishop, Nashville District Project Manager. “This includes a new wire rope and drum setup, and replacement of high and low-speed gear boxes, 10 horsepower electric motor, bull and pinion gears, and the machinery base on each gate pier.”
Bishop added that the old lifting equipment had to be replaced due to the new spillway gates being heavier than the old ones, as required by the project’s new design requirements.
Replacement is needed because a Spillway Radial Gate Evaluation Design Document Report in 2016 revealed the eight spillway tainter gates are subject to overstress due to trunnion friction issues. Trunnion friction is the force generated around the trunnion pin during a gate lifting operation. It is caused by the bearing of the trunnion pin against the gates’ trunnion hub and bushing, which is the rotating point of the gate.
Each spillway tainter gate is 37 feet high by 50 feet wide. The contractor is limited to three inoperable gates at any period of time, always leaving seven operable gates. As an additional risk reduction measure, only one gate bay will be open without a gate at any given time during construction. Replacement of gates will only occur between June and November each year, which is considered the dry season, targeting lower peak summer lake elevations.
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USACE awarded the $91.25 million contract for the Center Hill Dam Spillway Gates Replacement Project to American Bridge Company in September 2022. The project is fully funded by the Disaster Relief Supplemental Appropriations Act of 2022.
