“It was bitter cold out there this morning,” said TVA spokesperson Mary Ellen Miller on Tuesday, “but they were out there drilling and grouting.”
Having finished pouring low-mobility grout into the embankment, crews are now in the middle of injecting high-mobility grout to plug smaller holes in the earthen layer beneath the dam.
The two grout mixtures being used by workers have different consistencies.
High-mobility grout is thinner and less viscous than low-mobility grout and has what Miller describes as the consistency of chocolate milk. Workers are using it to fill the smaller cracks in the bedrock beneath the embankment. The low-mobility grout, which has the consistency of ice cream, has been used to fill the larger cracks.
In November, TVA raised the water level in Boone Dam to about 1,355 feet above sea level, the highest end of the lake’s current operating range, so engineers could conduct a test of the low-mobility grout.
“What they have determined after reviewing the data is that it is meeting their design objective up to date,” Miller said.
However, Miller said that engineers will conduct another test of the work at some point in the future, likely next fall, to evaluate the efficacy of the high-mobility grout. After the completion of the high-mobility grout phase of the project, subsequent work on the dam will consist of perfecting the seepage barrier.
“Basically what you’re doing here ... is building a dam within a dam,” Miller said. “So you’re building a dam underneath the ground.”
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 have been drilling and grouting on the earthen embankment since the very beginning of 2016. As of Nov. 3, crews have drilled 700 holes and filled 540 of them with low-mobility grout since construction began.