In Sept. 10 IssueBy Greg WellsTimes Journal Managing Editor
"We're pleased with the progress on the project," said US Army Corps of Engineers' Allison Jarrett.
Jarrett, an information officer with the Corps, said the earlier estimate of April 2010 for completion of the most vital work, and a possible reconsideration of the lake's water level, was "very optimistic," but the estimate of October 2010 is more realistic.
Daniel Kozoil, the lead engineer in the technical office at Treviicos-Soletanche said they are progressing well on the repairs to the dam impounding the largest man made lake in the Eastern United States.
He explained that they are familiar with the particular challenges that working inside a dam presents.
"You work on the unseen," Kozoil said. "You know what you are working on when you are doing it but not before. It isn't like working on a tower where you can see anything that is in the way and everything you have done."
Even given that, Kozoil said they have met with no surprises so far and that they have finished nearly 25 percent of the wall through the earthen portion of the dam and into the top of the bedrock.
That first, referred to as the protective wall, is wider than the final barrier wall and goes from the level of the work platform down to a few feet inside the top of the limestone below. He explained that it provides protection for the dam from the forces generated while drilling into the hard formations below, and the concrete pumping necessary to create the new barrier wall.
That final barrier wall is drilled within the protective wall.
In addition to pushing forward with the protective wall, Kozoil said they are beginning work on the barrier wall in the "technique area."
He explained that part of the purpose for those test areas is to prefect the process of installing the deepest, longest wall of its type; calibrate the necessary equipment and work the crews through the process before beginning work on what the Corps has acknowledged is the most structurally compromised areas of the dam, the "critical areas."
Those two areas especially that area formerly referred to as the "wrap-around" where the earthen portion meets the concrete portion of the dam and another area near the north end of the dam are those areas the Corps reports having the most "voids" and instability.
In earlier presentations the Corps has explained that both areas had caves that were exposed during the construction of the dam. Technology in that period was to simply "plug" such caves by packing them with high-clay content soils.
Flaws in that method first showed themselves in the late 60s, when sinkholes appeared in the down-stream face of the dam, necessitating a repair similar to the one going on now at the dam.
Grout, a mortar like slurry pumped into the rock through drill holes and a shorter and more shallow wall was bored-and-poured through a portion of the earthen section of the dam from approximately the elevation of the road.
More recently the indications that the dam was leaking dangerously were less noticeable than those in the 60s, but the work to repair the problem has been more ambitious.
The new concrete cut off wall was proceeded by a more intensive grouting procedure, up and downstream, of the new wall position and the wall will go through the full length of the earthen portion of the dam tying, as much as that is possible, to the concrete portion of the dam and extending 275 feet down through the dam and into the rock below.
This time grouting has also been done under the concrete portion of the dam by moving drilling and grouting rigs piece by piece into passageways within the dam.
Jarrett said the house and senate have both approved more than $120 million in funding for the project in the 2010 budget year, but that expenditure will have to go through conference committee before becoming set, as it were, in concrete.
This round of repairs began in a small way in 2006, but in 2007 the level of the lake was ordered down, and repairs began at a pace that outstrips most government projects.
The estimates were in the $309 million range for the project. The contract awarded in 2008 set the price at $341 million, and estimates push that to the $360 million all-told for this round of repairs.
Repairs in the 70s were at a cost $96 million. Reports are that the original contract for construction of the project in 1941 was less than $20 million, but WWII halted progress and when work began again afterwards the cost had risen to $81 million to finish it in 1950.
In the mean time the lake has been held to the level of 680 feet above sea level, or as closely as rain storms would allow. The normal summer level of the lake is 723.
While all of this work is being done on the dam itself the Corps is also working on the power generation system within the dam.
Sam Alley, the director of the power house, said they have re-wound the two of the generators, which have been in place since soon after the dam was finished.
"They're more stable and dependable now," Alley said.
He explained that the power generation levels can be closer to their limit after the rebuilds, and there are more ambitious plans in the works.
He said the rebuilding of the turbines and generating units has been requested, but those requests are not far enough along to project which of the options if any would be approved and funded.
At this point having the capacity to generate more power is somewhat moot, since there isn't enough height in the water behind the dam to push the turbines strongly enough to generate the 45 mega-watts the dam is presently capable of producing.