The $954M Chickamauga Lock Replacement Project by the US Army Corps of Engineers aims to replace an outdated lock unable to accommodate modern jumbo barges. The project, set to finish by the end of 2027, involves various contracts and components to enhance efficiency and safety in transporting goods through the lock.
Photo courtesy of USACE
Originally priced at $757 million, the project cost is now set at $954 million, due to a revised schedule that led to a later completion date, as well as inflation.
Seventeen years after construction began on the Chickamauga Lock Replacement Project, the U.S. Army Corps of Engineers (USACE) is about to award the final contract.
"We're expecting C.J. Mahan, the external approach wall contractor, to be off site in the summer of 2026," said Joseph Cotton, project manager for the U.S. Army Corps of Engineers, Nashville District. "We are now in the middle of our source selection process for our final contract for the entire project, which we're calling the approach walls and decommission contract. That is our close-out contract to get this lock to fully operational status. We're currently expecting that to be the end of 2027 and then to close out the entire project."
Photo courtesy of USACE
The new lock will replace an existing lock built in 1940. At 60 ft. wide by 360 ft. long, the existing lock is not suitable for today's jumbo barges, able to accommodate only one at a time.
"When the Chickamauga Lock was commissioned in 1940 by FDR, the standard size of barges was much smaller," Cotton said. "We could move four barges through at a time, and that was economical for what the industry made. Since then, they've grown to be 35 foot wide by 195 foot long and we can only get one through at a time. So, the locks downstream of Chickamauga are designed to pass nine barges through at 110 feet by 600 feet or more, and Chickamauga Locks is the bottleneck."
The existing lock also is undermined by a reaction between the alkali in the cement and aggregate, threatening the structural integrity and limiting its lifespan. The reaction was observed soon after the initial construction. Originally priced at $757 million, the project cost is now set at $954 million, due to a revised schedule that led to a later completion date, as well as inflation, Cotton said.
The current contract to C.J. Mahan Construction Company was awarded in 2021 and involves the placement of 14 8-ft. diameter concrete shafts. The shafts go down to the lakebed which is about 60 ft. and, in some instances, extend an additional 50 ft. below the surface of the lake.
"The upstream approach wall beams were pre-fabricated and are stored off site," Cotton said. "They are 8 feet by 8 feet concrete blocks that are 110 feet long, think of them as giant Legos. The contractor will lower the beams onto the piers which are on the concrete shafts that were drilled into the bottom of the Chickamauga Lake.
The approach walls and decommissioning contract involves numerous components, including the removal of the spillway, which is currently blocking access into the new lock chamber, removal of the coffer dam surrounding the work area for the existing lock chamber, and constructing a closure plug — a block of concrete — to prevent new dam surface water from passing through the old lock.
"The final feature for this contract for this project is called the thrust block," Cotton said. "It's a 35,000 cubic yard piece of concrete that we're placing underneath the highway bridge. It's basically a giant doorstop. There's alkali aggregate reaction occurring throughout the entire dam. By placing that thrust block at the very end, we're essentially keeping the entire dam stable, not just the existing lock, not just the old lock, but the entire dam we're able to stabilize.
Photo courtesy of USACE
"Throughout construction of the replacement lock, the original Chickamauga Lock has been fully operational, with close to 1 million tons going through the lock yearly. During the pandemic, that number was cut nearly half, but last year the rate climbed to 1.3 million tons. I think we're on track for close to a million and a half tons through the lock in 2024," Cotton said. "That process right now, we can only send one barge through. The significance of one barge, as opposed to nine going through an hour is it's about an hour, hour and a half process to get one barge through. A 12-barge tow going through this lock one at a time, you're looking at an over 12-hour process. Whereas we can get 12 barges through in two and a half hours, as opposed to 12 hours."
It's not only great from an efficiency standpoint, but even more important for safety.
"The lock was not really designed to accommodate these 35-foot-wide barges, so there's a lot of movement and when we have movement on our barges, it creates an unsafe environment for the workers who are having to get in there and disconnect these barges from each other. When you send them through three at a time in 110-foot lock, there isn't a lot of wiggle room. It's just a much safer work environment for the marine industry." CEG
Lori Tobias
Lori Tobias is a journalist of more years than she cares to count, most recently as a staff writer for The Oregonian and previously as a columnist and features writer for the Rocky Mountain News. She is the author of the memoir, Storm Beat - A Journalist Reports from the Oregon Coast, and the novel Wander, winner of the Nancy Pearl Literary Award in 2017. She has freelanced for numerous publications, including The New York Times, The Denver Post, Alaska Airlines in-flight, Natural Home, Spotlight Germany, Vegetarian Times and the Miami Herald. She is an avid reader, enjoys kayaking, traveling and exploring the Oregon Coast where she lives with her husband Chan and rescue pups, Gus and Lily.
Read more from Lori Tobias here.
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