LANCASTER – The U.S. Army Corps of Engineers Nashville District recently announced a nearly $43 million contract for further stabilization downstream of the Center Hill Auxiliary Dam – a “final major construction effort,” the agency said.
Thalle Construction Co. Inc. was awarded the $42,972,545 contract June 27 to build a concrete reinforcing berm. The work also includes stabilization of a previous rock cut near the main dam.
“This final major construction effort will reinforce the earthen auxiliary dam, also called the saddle dam, and reduce the risk of either a seepage or an overtopping failure of this structure,” Project Manager Linda Adcock said in a release.
The construction will complete a series of major construction efforts since 2008 to significantly improve the long-term reliability of the dam and to ensure public safety. The awarded contract is the third and final major contract for dam safety-related work at Center Hill Dam.
“A second, auxiliary earthen embankment, in addition to the main one, was constructed in the 1940s as part of original construction,” Adcock added. “The auxiliary dam is southeast of the main dam and…fills a low area in the landscape in order to maintain the lake; it is an integral part of the Center Hill project.”
The foundation of the auxiliary dam has the similar seepage concerns as the main dam.
The main components of work in the auxiliary dam contract awarded today are:
- A 130,000 cubic yard roller compacted concrete (RCC) reinforcing berm immediately downstream of the saddle dam;
- And excavation and stabilization of the cut slopes east of the main dam in the area commonly known as the left rim with transport of excavated material to be placed between the existing auxiliary dam and the newly constructed RCC berm
While the contract awarded will complete the auxiliary dam rehabilitation, the first two major contracts addressed seepage issues at the main dam. The 2008-2010 work included grouting at the main dam and left rim. To complete the main dam improvements, a 2012-15 foundation barrier wall was then installed through the main dam earthen embankment and deep into foundation rock.
State Highway 96/141 across the dam is expected to remain open, as well as Long Branch Campground downstream of the dam, throughout the two and one-half year contract.
The Center Hill Dam was identified in 2006 by the Army Corps of Engineers as a high risk dam, primarily due to foundation seepage.
“Much of the risk has been reduced by work completed to date,” Adcock said. “The auxiliary dam work is the final leg repair of a three-legged stool.”
In addition to this major contract, there will be several small contracts required for site restoration through 2019.
To read more on the project, the seepage problem and the fix, visit the Nashville District webpage at http://www.lrn.usace.army.mil/Missions/Current-Projects/Construction/Center-Hill-Dam-Safety-Rehabilitation-Project/.