Addressing structural concerns caused by alkali-aggregate reactivity

Chickamauga Lock Replacement

The Chickamauga Lock Replacement Project is at Mile 471.0 on the Tennessee River at Chattanooga, Tennessee. Chickamauga Lock & Dam consists of 4,390 feet of earthfill embankments, a 111-megawatt powerhouse with four units, an 860-foot-long concrete spillway section with 18 gates, and a 60- by 360-foot navigation lock. The lock, owned by the Tennessee Valley Authority and operated and maintained by the US Army Corps of Engineers, was dedicated for service in 1940.

The alkali-aggregate reactivity in the lock concrete structures causes continued expansion of the concrete. This leads to high stresses, cracking of the concrete, and movement of the concrete structures. Ultimately, it results in increased maintenance and heightened concern about the structural integrity. In support of the USACE Nashville District and the TVA, we performed studies of innovative concepts that could reduce costs and increase performance of the replacement lock. Ideas included roller-compacted concrete lock walls, integrated lock walls with permanent cofferdams, float-in guide walls, and an efficient filling system.

Our team also prepared decommissioning plans for the existing lock, which involved a closure structure concept design and structural measures to manage the AAR growth issue long-term. In the end, we consolidated the work of multiple engineering consultants to prepare final plans, bid specifications, construction schedule, and probable cost estimates for the project.