CHATTANOOGA, Tenn. (Aug. 29, 2013) -- The U.S. Army Corps of Engineers Nashville District is collaborating with industry, West Virginia University, Engineering Research and Development Center and Tennessee Valley Authority to find a better solution to unacceptable deterioration around Chickamauga Lock’s discharge ports that cannot be dewatered.
“Opened to navigation in 1939, the main section of Chickamauga Lock has grown 12 inches in length on the riverside and more than seven inches on the landside,” said Doug DeLong, Nashville District project manager. “The growth is due to a chemical reaction between the alkali in the cement and the minerals in the stone,” he added.
The growing concrete at the lock creates many problems. In some places large chunks of concrete have broken loose from the lock walls. And because the massive blocks that make up the lock have expanded at different rates, the top of the structure is uneven. Lengthwise, the lock has actually grown five inches inside the lock chamber.
“Nashville District and the TVA installed 347 post-tensioned anchors from 1995 through 2000, and we have more than 2,900 monitoring instruments from which instrumentation reports are created monthly and annually and reviewed by the Corps and TVA,” DeLong said.
Unacceptable deterioration around Chickamauga Lock’s discharge ports caused by concrete growth expansion forces and the erosive effects from hydraulic forces prompted the Nashville District to rehabilitate them. Accessibility was a challenge because the discharge ports are downstream of the gates and cannot be dewatered, according to DeLong.
Fourteen of the 15 columns dividing the discharge ports were repaired in July 2012 using the conventional method of using steel wrap with grout filler. During this period, representatives from the Corps’ Engineering Research and Development Center visited and proposed a rehabilitation method using a fiber reinforced polymer composite wrap that could potentially save installation time and material costs.
With the Nashville District’s concurrence, a research and development project began between West Virginia University and ERDC.
A preliminary meeting convened June 11, 2013 and the Nashville District, ERDC, TVA and WVU discussed details of using the composite wrap and develop the technique for its application with the dive team to confirm that it could be accomplished underwater wearing dive gear.
The installation process consists of power washing the discharge port columns to prepare the surface for a layer of polyurethane primer/adhesive system designed to bond the wrap to the concrete column. Then two layers of Aquawrap, a woven composite-looking fabric that contains a resin that reacts with water and solidifies, is applied around the column.
After the Aquawrap hardens, a solids epoxy primer/adhesive system is used to coat over the wrap material to seal the system, according to DeLong.
“Divers successfully installed the composite wrap on the discharge column between the first and second discharge port on the riverside of Chickamauga Lock during July 15-19, 2013 and it will be monitored and recorded during future dive inspections,” said Ben Burnham, Nashville District maintenance engineer.
A live video feed allowed the divers to monitor the underwater installation. The team consisted of WVU Professors P.V. Vijay and Hota Gangarao; Bob Rhea, Aquawrap Company; and Rich Lampo, lead ERDC researcher for the project.
Expansion and movements of the lock structure are expected to continue indefinitely, and an additional 3-inch or more vertical expansion, and 7-inch or more upstream/downstream expansion can be expected in the next 50 years, according to DeLong.
“The condition of the composite wrap used in this research and development project can be compared to the condition of the conventional steel wrap to see how well each stands the test of time,” Burnham said.
A total of 404 vessels locked through Chickamauga Lock in the first 40 days after the installation of Aquawrap. Nashville District Diver Keith Holley reported Aug. 28, 2013 that, “The material and installation condition looks the same as the day it was put in.” Divers will inspect the Fiber Reinforced Polymer wrap periodically to monitor its durability.
The $693 million Chickamauga Lock Replacement Project to replace the more than 70-year-old, badly deteriorating 60-by-360-foot lock with a 110-by-600-foot chamber is 27 percent completed, with $185 million obligated.
Existing construction contracts on the Chickamauga Lock Replacement Lock project will be completed this year. If no additional funding is received construction will be suspended.
“Nashville District’s goal is to complete the new lock before closure becomes necessary,” said Jamie James, project manager. “There are three navigation locks and 318 navigable stream miles upstream of Chickamauga Lock that would be isolated from the Inland Waterways System if the lock is closed. This would present difficulties in transporting materials to upstream industries, including TVA nuclear power plants, U.S. Department of Energy facilities at Oak Ridge, and the loss of transportation rate savings in that area,” James added.
U.S. Army Corps of Engineers Nashville District Divers Brandon Kennedy and Keith Holley apply a primer substance July 17, 2013 prior to installing an experimental Fiber Reinforced Polymer wrap underwater to a deteriorated discharge port at the 73-year-old Chickamauga Lock in Chattanooga, Tenn. (USACE Video)