In March 18 IssueBy Greg WellsTimes Journal Managing Editor
The Army Corps of Engineers announced late last week that they would be halting work at the dam in “Critical Area 1” for six to eight weeks.
“We just want to evaluate all the data from our instruments,” said the Corps' director for the repairs at Wolf Creek Dam, David Hendrix. “When you have instruments telling you something you don't just want to explain it away.”
He said that the inclinometers inside the dam have indicated there has been movement within it. He said the pizometers have also indicated increased water pressure within the dam.
The area they are concerned about is that portion of the dam where the earthen portion wraps around the north end of the concrete structure.
This area, also know as the “wrap-around” has been a consistent source of concern during the present round of repairs at Wolf Creek Dam, and concerns about it have halted work before.
Hendrix said they have only paused work in that area while continuing at full speed on other areas of the dam.
Allison Jarrett, a Corps spokesperson, said the contractors had been grouting in that critical area, and had switched to a thicker, lower pressure, grout and drilling method since grouting had been halted previously.
She said the instruments indicated that the work was causing movement within the larges cave that is below that area of the dam.
Cracks in the blacktop of the roadway above that area of the dam have been widening slightly and that added to concerns.
Jarrett stressed that there are not any plans to lower the level of the lake any further than the 680 foot mark they have been holding the lake at since the announcement of problems with the dam.
As for the work on the rest of the dam is proceeding apace, adding that the technique areas, where the actual barrier wall is being installed, is 60 percent completed.
Hendrix said they have decided on the method for installing that barrier wall into the critical areas of the dam.
He said they will be using overlapping column of concrete drilled deep into the bedrock. Hendrix explained that this method exposes the dam to less pressure and provides more consistent protection than the mothod of drilling columns and then milling out panels between them.
Hendrix said the delay in working on the critical area would put work behind schedule on that portion of the project, but he expected that workers freed up from that task would be working in other areas, thus preventing the project as a whole from being completed later than planned.
The most recent problems at the dam were announced in 2006 and work began in March on the $584 million project to install a diaphragm wall inside the earthen portion of the dam, as well as to inject grout into the bedrock under the entire dam, with completion of the work expected in 2012.
The dam, completed in 1949 holds back the largest reservoir east of the Mississippi River, and was build on rock formations that are prone to the formation of caves.
Several large and small caves were located below the dam during construction and they were generally “plugged” with clay at that time.
In the late 60s muddy water began bubbling up in the tailwaters of the dam, as sinkholes were appearing in the dam itself.
Extensive grouting and controls on water level and discharge were put into place in the early 70s
Work to install a shorter, more shallow, concrete barrier wall was undertaken shortly after that; whereas the project underway now intends to place a barrier wall through the whole earthen portion of the dam deeper into the bedrock than the cave bearing bedrock.