Published: March 15, 2007 09:01 am      

A solution to the dam problem?

‘Roller- compacted’ dam being considered by Corps of Engineers

The U.S. Army Corps of Engineers is considering a layered concrete structure that would, in effect, replace the 4000-foot-long earthen section of troubled Wolf Creek Dam and be an alternative to a planned diaphragm wall.

Mike Zoccola, chief of the Corps’ Civil Design Branch, said the structure being studied is a “roller-compacted concrete dam” that would tie in to the existing concrete section of dam. It would be built instead of a four-to-five-foot thick concrete wall that would extend through the earthen section to about 100 feet into the bedrock.

Zoccola emphasized at all points in his discussion that the new method to permanently repair Wolf Creek Dam is still being studied. The nearly mile-long concrete and earthen dam that impounds Lake Cumberland has been classified as a “high risk” for failure and the lake level is being kept low to ease pressure on the unstable structure.

A roller-compacted dam would be constructed with layers of concrete, each compacted with heavy equipment. Zoccola said the concrete would be a “really dry mix” unlike the more familiar soupy concrete that wouldn’t support compaction.

Noting that roller-compacted dams are not uncommon, Zoccola estimated that the structure under study would be about the same length as the existing earthen section of the dam and some 15-20 feet in width. It would be located on the downstream side of the existing earthen part of the dam and would impact the road leading to Kendall Recreation Area, the power grid and fish hatchery.

How deep a roller-compacted dam would extend into the earth, how much it would cost and how long it would take are still questions, Zoccola noted. Also still undetermined is whether construction of that type facility would require further lowering of the lake level. Grouting and the diaphragm wall in the current plan have a price tag of $309.1million and would take up to seven years.

Zoccola said the earthen section of the dam likely would remain in place as the base for U.S. 127, the road that crosses the crest of the dam. The existing concrete section of the dam would not be affected, he indicated.

The idea for a roller-compacted structure at Wolf Creek Dam “recently came up,” Zoccola said. “There are a lot of technical problems,” he added. The Corps earlier rejected a suggestion to build a completely new dam at a cost of $500 million.

According to the current timetable, the Corps plans to award a contract late this year to permanently repair the dam. Zoccola said a decision on whether the permanent fix be a diaphragm wall or a roller-compacted structure needs to be made sometime about June. The roller-compacted structure is a “Corps idea” and not something suggested by Washington, D.C., he said.

Excessive seepage was observed at Wolf Creek Dam between 2002 and 2004 when the lake level was high due to heavy rainfall. The Corps began to control the lake level in March 2005 and announced in August of that year that a major rehabilitation of the dam is necessary.

Later, the massive dam structure that impounds 101-mile-long Lake Cumberland was declared in high risk of failure. As a result, the lake level was lowered to 680 feet above sea level, or about 43 feet below the tree line, to ease pressure on the dam.

An accelerated grouting contract was awarded last December and liquid concrete currently is being pumped into the dam to control seepage.