Corps, TVA Earn National Geology Award For Chickamauga Lock
The Nashville Engineer District and the Tennessee Valley Authority received the 2026 Outstanding Environmental and Engineering Geologic Project Award on September 16.
Presented by the Association of Environmental & Engineering Geologists, the honor recognizes engineering achievements on the Chickamauga Lock Replacement Project. Craig Carrington, Nashville District deputy district engineer for project management, accepted the award on behalf of the project team.
The annual award recognizes innovative engineering solutions that resolve complex, high-risk geological challenges to protect public safety and critical infrastructure.
Concrete Expansion
Chickamauga Lock, originally constructed in 1940, has long suffered from “concrete expansion,” a chemical reaction known as alkali-aggregate reaction. The reaction between the cement and river stone causes the concrete to expand, warping metal gates, cracking walls and threatening the structural integrity of the vital shipping corridor.
To keep 318 navigable river miles accessible upstream on the Tennessee River, the Corps embarked on a massive effort to build a new 110-by-600-foot navigation lock. The project unites two federal agencies with deep ties to the region. TVA owns and manages Chickamauga Dam, while the Nashville District designs, oversees construction and operates the navigation lock.
Geologic Puzzle
The bedrock beneath the new lock presented one of the nation’s most difficult geologic puzzles. The site features steep, tilted rock layers, dissolving limestone that forms cavernous underground voids as well as multiple weak clay seams created from ancient volcanic ash. Left unaddressed, the weight of the new concrete structures could have caused lock monoliths to slide or trigger catastrophic clay blow-outs into the active construction pit.
As part of design and construction of the new lock, Corps geologists and engineers mapped every rock fracture, clay seam and void. Construction crews installed massive 74-inch-diameter drilled shafts more than 100 feet into stable bedrock, pumped specialized grout into underground voids and used concrete mud mats to seal the foundations.
“Our geologists are some of the best in the world,” Nashville District geologist William Mackie said. “They make difficult design decisions for some of the nation’s most complex infrastructure projects. The structures we build will only ever be as good as the foundations they are built on.”
Mackie said that the geologists that worked on the project are honored to be recognized by the Association of Environmental & Engineering Geologists for their role in this vital infrastructure project that will increase navigation efficiency by 800 percent.
Safe Passage
The new lock chamber opens safe passage for modern tows, handling nine large barges at once and reducing locking times by up to 80 percent. The joint effort guarantees commercial shipping and recreational boating along the full 652 miles of the Tennessee River, connecting Knoxville and Chattanooga to global ports while keeping heavy cargo off crowded highways.
The Nashville Engineer District manages critical water resources infrastructure across the Cumberland and Tennessee river basins in a seven-state region. The district delivers navigation, flood risk management, hydropower, recreation, environmental stewardship, water supply support, regulatory oversight and emergency response while operating dams in the Cumberland River Basin and maintaining navigation lock projects on the Cumberland and Tennessee river systems.
