In July 14 IssueBy Derek AaronTimes Journal Editor
The $584 million foundation remediation project at Wolf Creek Dam is now more than halfway complete, according to David Hendrix, the Nashville Corps of Engineers Project Manager, and at 55 percent is still slated for a December 2013 finish.
That word came late last week after the Corps invited several media outlets from Russell and surrounding counties as well as a Fox news crew out of Nashville to take a tour and view work progress on the giant structure.
"We call it a world class project because there is not anywhere else in the world where a wall similar to this is being built at a combination of the depths we're going to and with rock as hard as we have to work with," Hendrix said. "Cutting edge technology is being developed on site here."
With a television crew present, they wanted to hear the truth about a worst case scenario if, in fact, the dam did ever fail and send Lake Cumberland's impounded water down the Cumberland River toward Nashville. Hendrix said it would take about two days for the lake's waters to reach Nashville and about eight hours to reach neighboring Burkesville in Cumberland County if that did happen. Hendrix shot down the notion that the water would look like a tsunami wave but said communities would rapidly see the river's water out of its banks as sinkholes would appear on the earthen section of the dam, much like what occurred three decades ago.
"A piping develops and water rushing through creates a vacuum, drawing material into it," Hendrix explained.
But he wanted to make sure the public knew the dam was in good shape structurally at this point and there was no cause for concern about the possibility of a catastrophe.
"There is no question this structure is safer than when we started. We've injected over 900,000 gallons of grout along the embankment," Hendrix said. "We're confident that our plan is going to work."
Treviicos Soletanche JV, the foundation remediation contractor, is continuing all phases of Pile Barrier Wall construction in every area of the project except for the Critical Area I, where the earthen embankment meets the concrete structure.
"There is two key elements that are most important to us, one is to do this safely as dam safety trumps anything else that we do and the other is to do it right," Hendrix said. He noted that there was always going to be a risk in something that is man-made but he wanted folks to realize that the stability of the dam has been and will continue to be greatly scrutinized.
Current activities include directional drilling, pre-drilling, pile drilling, concrete placement and verification coring, according to the Corps.
"This new wall is down to elevation 475 into the Kathy's Limestone, which is a much more confident rock and doesn't exhibit all the imperfection of the Leiper's Limestone," Hendrix said. "That gives us a high degree of confidence that this wall is going to be a long term solution to the huge problems we've had."
The previous wall, which was installed more than four decades ago, did not go as deep into the rock inside the earthen embankment of the dam and was in much more questionable limestone, Hendrix said. This new wall also goes the entire length of the dam, which the other one did not, and is being bored by 50 inch drill bits that create overlapping holes to create the concrete barrier wall.
"Monitoring is very intense," said. Kathy Lust, the resident project manager at Wolf Creek. "We have over 400 instruments on the dam that we monitor 24/7, some of them remotely get updated every 15 minutes. People are on the dam and checking it continually while we're operating.
"It is very much like operating on a live patient," she said. "The patient isn't even anesthetized, he's awake and he feels it and we evaluate any response from the dam that we may get to make sure it is safe to continue."
Treviicos Soletanche has completed installation of the Protective Concrete Embankment Wall from station 37+50 to station 72+00 on the work platform. That represents the entire length of the earthen embankment except a 350-foot reach in Critical Area I, where grouting and drilling just began again in May by subcontractor Hayward Baker Inc. in preparation for PCEW installation. The PCEW extends down from the work platform to the top of rock. The pile barrier wall is being installed through the PCEW to a depth of about 275 feet.
"We're really on hold here in Critical Area I until we get an access road on the upstream embankment so we can get some equipment in there," Hendrix said of the most crucial portion of the dam rehab.
Treviicos Soletanche will raise and widen the work platform in Critical Area I before they can install the PCEW.
As Hendrix said, an access road must be built along the upstream embankment so traffic will not interfere with barrier wall construction on the remainder of the platform. Initial fill for the access road cannot be placed until the lake level is near elevation 680, an elevation the lake is slowly getting back to after an extremely wet spring.
All work in that area was suspended in February of 2010 after an increase in movements in the range of one inch or less was observed primarily in monitored cracks along the crest of the dam, according to the Corps.
Initial concern was that these movements might be caused by a deep slope movement in the upstream embankment but a six-month study showed the movements were not the result of deep-seated sliding of the embankment, but rather shallow movements attributed to several other causes.
Last month, vertical holes began being drilled to define the edges of the cave and core trench along the alignment of the proposed concrete barrier wall, according to Hendrix. After testing, the holes will be gravity backfilled with grout to enable safe installation of the barrier wall.
Hendrix said while the contractor is foreign they have about 130 local employees out of 170 hired to do subcontract work, which helps the local labor force in Russell and neighboring counties.
The last work to be completed will most likely be that in Critical Area I due to the work suspension from February - November 2010 due to the slope stability concerns and changes to the construction methods used on the tender portion of the dam which were outlined earlier.
If the Corps' latest information goes unchanged and the dam is completed by Dec. 2013 it would mean that the lake would have been at around 680 ft. above sea level for seven years.