Tennessee Valley Authority spokesperson Mary Ellen Miller said crews have begun pouring the concrete that will make up the cutoff wall embedded in the earthen embankment beside Boone Dam.
“This is the major portion of the construction at Boone Dam,” Miller said.
The wall, which will be constructed from a series of overlapping cylindrical pillars, is designed to stop underground seepage and prevent internal erosion. Crews will pour the concrete into holes drilled on top of the embankment.
Each individual cylinder will have a circumference of about 55 inches. The pillar that crews were preparing on Tuesday, Miller said, plunges to a depth of 131 feet, but she anticipates the height of the cutoff wall could vary from hole-to-hole.
There are more than 200 workers on site on a daily basis, and Miller said the agency is gearing up for more around-the-clock workdays in the fall. TVA has also constructed an onsite concrete batch plant, which allows crews to produce concrete without relying on an outside facility.
Miller said crews will be working on the wall for two years and are scheduled to complete the structure in spring 2021. During the year following that, crews will begin testing the repair work by fluctuating the dam’s water level, which TVA has tried to keep between 1,350 and 1,355 feet of elevation during the repair process. This is roughly 30 feet lower than its normal summer lake level of 1,382 feet.
She said engineers will unveil a plan for the water level fluctuations, which will be of importance to businesses and property owners around the lake, ahead of the spring 2021 completion of the cutoff wall. She said the project will be complete in July 2022.
“The project is right on schedule, within the five- to seven-year timeframe that we initially outlined,” Miller said.
In October 2014, TVA discovered a sinkhole near the base of the Boone Dam embankment. In an effort to combat erosion and seepage, TVA began a seven-year repair process that required the agency to lower the water level. To set a foundation for the concrete wall, and plug some gaps in the earthen layer, crews have injected grout mixtures into the embankment.
Miller said the agency has spent more than $160 million out of a total project budget of about $457 million.
TVA has also been mulching vegetation that has grown around the lake. According to a TVA newsletter sent Tuesday, crews have cleared 560 acres out of 650 acres of identified land. This year’s cutting program will be complete in August.
The agency had originally tallied about 500 acres of land that it planned on clearing but added extra locations based on input from members of the public.
“I’ve sensed a positive relationship with the community that we’ve worked very hard to build, and I think that the members of the community are really seeing that we’re hard at work up here and that we are working safely and that we have the safety of the community as our No. 1 priority,” Miller said.