A $1.5-billion project to double the length of the Kentucky Lock on the Tennessee River—an expansion project in western Kentucky 25 years in the making—has reached a milestone with construction and installation of the final structural monoliths that form the lock’s core.

The new lock will be 110 ft by 1,200 ft, twice as long as the existing lock, which was completed in 1944. The first monolith, part of a group of 51, topped out in October 2024. In total, the lock will have 64 monoliths.

The 100-acre construction site for the Kentucky Lock Addition project, a massive civil improvement effort, thrums with activity from 350 laborers, masons, carpenters, equipment operators, ironworkers, engineers, managers, supervisors and health and safety and quality control experts. The jobsite features a concrete batch plant, thousands of feet of a material conveyor system and specially built fabrication shops to manufacture elements needed for the monoliths. In combination with continued operation of the existing lock, the increased capacity of the new structure will alleviate current delays for vessels that average 10 hours, the highest of all U.S. locks, according to the U.S. Army Corps of Engineers, which is managing the project.

A carpenter installs Stay-Form, a ribbed expanded metal leave-in-place form for poured-in-place concrete within the lock wall.
Photo courtesy of Thalle Construction Co.

Building Capacity

The lock is a critical piece of infrastructure on the Tennessee River, serving as a gateway for river traffic and providing access to the Tennessee and Cumberland River basins and to the Ohio and Mississippi rivers.

Barges transport approximately 30 to 40 million tons of commercial materials through the lock each year—the equivalent of 1.4 million 18-wheel trucks. Because of its limited length, however, the lock has become a major bottleneck on the river system, leading to increased towing and other costs for companies that transport goods on the waterway.

The new lock is located immediately adjacent to the existing operational lock, both of which are owned and operated by the Tennessee Valley Authority and located in Grand Rivers, Ky.

Working toward a July 2027 deadline, Thalle Construction Co., a Tully Group company based in Hillsborough, N.C., is constructing and installing the remaining structural monoliths necessary to complete the new lock, which the Corps estimates will provide an economic benefit of about $114.3 million a year.

Brian Sharp, project executive for Thalle, says each monolith requires about 11,000 cu yd of concrete to form the walls of the lock, which, when completed, will contain a complement of massive valves, culverts and ports to allow water from Kentucky Lake to flow in and out of the lock chamber, enabling vessels to travel upstream and down.

The project site shown before Thalle Construction began work on the current phase of the lock monoliths project.
Photo courtesy of Thalle Construction Co.

“Each monolith is essentially a massive concrete block,” Sharp says. “The monoliths are founded on a prepared bedrock surface and extend to the top of the lock.”

The monoliths average 50 ft in length, 110 ft in height and vary in width between 75 ft at the bottom and 25 ft at the top.

“The monoliths are constructed in 5-ft vertical increments and require up to 23 placements to complete,” Sharp says. “These 5-ft heights are referred to as lifts and represent individual concrete placements.”

Kenneth Bowen, project executive for Thalle, adds that “in total, the 51 monoliths required to complete the downstream section of the lock included in our scope of work require over 1,200 individual concrete placements.”

In addition to the concrete, each monolith contains steel reinforcement and a host of embedded fabricated metal items that include wall armor, line hooks, floating mooring bits and interior elements such as culvert liners, valves and mechanical equipment needed to open and close the massive miter gates.

Thalle began work on its first project related to the lock in 2010 following a contract award for site excavation, construction of nine upstream monoliths and installation of the upstream miter gates. It completed its first project in 2016 and was awarded the current phase of work in 2021.

A view from the chamber floor shows the jumping formwork used to construct the monoliths, with tower placers and conveyors in the background.
Photo courtesy of Thalle Construction Co.

A Strong Foundation

says a challenge is ensuring that each monolith is on stable ground.

“Construction of each monolith starts at the foundation, where rock is blasted to a consistent elevation that is inspected and deemed competent to support the massive structure,” Bowen says.

of the foundations require extensive preparation that includes rock cleaning, dental excavation and filling of imperfections with dental concrete prior to capping with a concrete mud mat to complete the foundation preparation.

In cases where subsurface geotechnical studies have determined that the rock foundation requires additional treatment, Thalle drills into the foundation rock as deep as 60 ft and encases steel shafts in concrete to provide additional support for the structure, he says.

Middle wall monoliths extend above and over the permanent concrete cofferdam sections and are tied together with thousands of rebar dowels.
Photo courtesy of Thalle Construction Co.

Looking Up

Following the foundation preparation, work proceeds vertically.

“Formwork to contain the concrete is assembled to accommodate two 5-ft-high concrete lifts,” says Brandon Johnson, project manager for Thalle. “Steel reinforcement is installed within each lift along with other cast-in-place elements.”

Thalle imports aggregate, sand, fly ash and cement and mixes the components in an onsite concrete batch plant that is used to produce the concrete that is placed within the formwork to create the structure.

production infrastructure consists of aggregate stockpiles that are made continuously wet to maintain saturation prior to incorporation into the concrete mix. These components are fed into hoppers, combined, wet-screened, run over screens to resegregate by size and conveyed into weigh hoppers prior to being fed to the mixers.

At the plant, the aggregates are then added into the mixers along with admixtures, fly-ash and cement to produce batches of concrete. The majority of the structural concrete that is used is a mass concrete mix with a maximum nominal size of 3 in. in diameter.

“The project’s aggressive schedule requires concrete production and placement in all seasons,” Johnson says. “The onsite batch plant is equipped with chillers that cool water to 35 degrees, which is applied to the aggregates during transportation to the weigh hoppers and introduced to the mix to aid in meeting the 70 degrees maximum allowable concrete temperature during the warm weather months.”

To supplement the chillers, Thalle installed an industrial ice plant for producing and introducing ice directly in the mix during hot weather. The plant is also equipped with boilers to provide hot water that is added to the mix during the cold weather to keep the concrete above minimum temperature requirements.

“Once the concrete is batched, it then must travel over 1,000 ft by a series of conveyors, some of which are suspended in the air by tower cranes to allow them to reach their destination at each monolith location,” Bowen says.

Progress seen on land and middle side lock walls approximately a year and a half after the project start in 2021.
Photo courtesy of Thalle Construction Co.

Preplanning

The massive quantity of concrete required to complete the current phase of work and the limited options to handle concrete mixes containing aggregate sizes up to 3 in. make concrete transport from the batch plant to the point of placement a big logistical hurdle.

Planning for how to convey the concrete began during proposal development before Thalle was awarded the project. “From this early planning stage, it was decided that there would need to be enough tower cranes on site to provide full, and in most cases, dual coverage of the project footprint,” Sharp says.

This resulted in the arrangement of six tower cranes, three of which were designated to support placement conveyors. “Careful consideration of the height of each crane was needed to avoid conflicts during operation, and further consideration was needed to decide the placement to reach all necessary locations,” Sharp says.

Full-site coverage and the ability to reach all placement areas was achieved using permanently configured, dedicated equipment. This “allowed for a high level of efficiency by avoiding set-up time and equipment moves between each placement,” Johnson says, which “is critical to achieve completion of the 1,200 individual concrete placements in a period of four years.”

Thalle also maintains and operates two onsite fabrication shops. The formwork shop produces custom formwork elements and configures system formwork for use in the field. The steel fabrication shop finalizes assembly of prefabricated embedded metals and produces framing and anchorages for use during the assembly of the structures.

“Because work of this magnitude and scale is not common, many [employee] positions in these shops require a significant amount of training,” Sharp says.

Stephen Butwell, Thalle’s construction manager, adds that the firm “worked diligently to educate workers on the proper means and methods to accomplish the required work.”

“Overcoming the learning curve and being able to produce the work required to stay on schedule and adhere to the strict quality standards necessary to satisfy [Corps] requirements is a success that Thalle celebrates,” he says.

Each monolith requires about 11,000 cu yd of concrete to form the walls of the lock.
Photo courtesy of Thalle Construction Co.

Emphasis on Safety

Safety is another reason for celebration. Thalle has exceeded 1.5 million work hours without one lost-time incident.

Placement of the remaining monoliths is a significant step forward, says Jeremiah Manning, Corps resident engineer for the project. The agency “is diligently advancing the final design work to facilitate award of remaining contracts, moving us ever closer to the operational milestone of the new Kentucky Lock project,” he says.