The Tennessee Valley Authority recently paused its drilling and grouting operation to install more sensors along the Boone Dam embankment after a test of its work in November indicated the data didn’t give engineers as much information as they wanted.
Work began winding down in early spring, but during this pause, crews continued with exploratory drilling along the embankment.
“We realized that we had some areas of the embankment that we didn’t have as clear or as detailed of a data set as we needed,” said Jim Hopson, the public relations manager for the Tennessee Valley Authority. “What we’re doing is basically constructing a building up to 30 stories underground, and you’re doing that without being able to see it.”
In November, the organization raised water levels in Boone Lake to about 1,355 feet above sea level, which is the highest end of the lake’s operating range while work is underway, so engineers could conduct a test of the low-mobility grout, a thick concrete mixture being used to plug holes in the embankment.
“What we discovered is two things,” Hopson said. “One, everything that we’re doing seems to be working. So that’s the very positive aspect of that. But it also pointed out that there were some areas of the embankment where the data wasn’t as complete as we felt that it needed to be.”
These sensors, which monitor subsurface movement and water pressure, help TVA inspectors determine whether the work they’re doing is effective and safe.
With work ramping back up over the next few weeks, TVA will also install a berm on the upstream side of the earthen embankment in August to help with repairs and to ensure the embankment stays secure as crews bring additional heavy construction equipment onsite to help with the repair.
When they return over the next few weeks, workers will test the feasibility of installing a grout wall on the embankment, which officials hope will plug a great deal of the seepage along the embankment. Up to this point, crews have been injecting high- and low-mobility grout into the embankment and testing the consistencies of the mixtures.
“We saw a very clear improvement over what we had seen prior to that,” Hopson said. “So we know that what we’re doing is having a positive effect. We just got to keep doing what we’re doing and moving forward so we can get this project complete.”
In October 2014, crews at Boone Dam discovered seepage beneath the structure’s earthen embankment, which made it necessary to launch a repair effort to safeguard against erosion.
TVA initially estimated the project could take five to seven years to finish, but if work remains on schedule, the project could be finished closer to the five-year mark.
After discovering the seepage, TVA lowered the water level to an operating level of between 1,350 and 1,355 feet, about 30 feet lower than its normal summer lake level of about 1,382 feet.
Crews are working on patching the seepage and have been drilling and grouting on the earthen embankment since the beginning of 2016.