The U.S. Army Corps of Engineers at the request of the Commonwealth Journal has released photographs of widening cracks in the U.S. 127 roadway atop Wolf Creek Dam. Expanding cracks are the main reason for a partial suspension of the dam’s rehabilitation in a 600-foot area near where the earthen section joins the concrete.
The Corps revealed last month that the cracks have widened between a half inch and an inch since the first of the year. Allison Jarrett, public affairs specialist for the Corps’ Nashville District, said at the time “ ... movement that our engineers are focused on now is not necessarily movement of material, but rather cracks in the roadway over the dam.” Engineers emphasized in a later news release that the cracks are not new, but existing cracks that have widened.
Responding to this newspaper’s request for a more detailed description of the cracks, Jarrett said “ ... our engineering team is getting some numbers together ... on the size of the cracks and should have that ready soon.
“Since (the cracks) vary quite a bit in size, and the crack pins really measure movement and not the overall width of the cracks, the numbers will likely be ranges and estimates ... ,” she explained.
Jarrett said current tests are evaluating significance of the cracks, and whether it indicates just surface movement, or if it is an indicator of deeper, more significant movement of the embank-ment..
“We know they could be caused by a number of things, some as harmless as temperature and weather, or by things like change in pressure due to changing lake levels, or deeper movement of the embankment,” Jarrett said.
“Our instrumentation readings now suggest the cause of the widening of the cracks is something of less concern like weather or lake levels, but we will continue the tests to be sure the embankment is stable,” she continued.
Engineers apparently have decided material movement in soft material in the cave features below Critical Area 1 that trig-gered the work stoppage in March “ ... was expected due to pressure of the grouting operation, and is not a structural concern,” Jarrett said. Critical Area 1 is one of two places in the earthen structure of the dam where initial grouting was not successful in stopping seepage.
Jarrett said engineers are “not 100 percent sure,” but it is “highly likely” the work stoppage in the 600-foot area will extend the rehabilitation project be-yond the currently projected December 2012 completion date. Jarrett emphasized that rehabil-itation is proceeding on schedule in other areas of the dam.
“End of the work stoppage won’t be deter-mined until our test results come in August and we make a determination about the way ahead and how we will treat, or fix, Critical Area 1,” said Jarrett.
Despite the problems and concerns, Lake Cum-berland should remain at the same operational levels.
“There are no current plans to lower the lake further, and we plan to maintain elevation 680 until Critical Area 1 is completed,” Jarrett said. “At that point, we'll review our instrumentation and observations and deter-mine if it's safe to do an incremental raise to the pool,” she added.
