News: Center Hill Dam rehabilitation continues with barrier wall installation
Story by Mark Rankin
LANCASTER, Tenn. - The U.S. Army Corps of Engineers Nashville District’s ongoing foundation rehabilitation project at Center Hill Dam is making progress as work crews continue to drill deep into the main dam earthen embankment to install a subsurface concrete wall. The current efforts are the second of three major contracts from 2008 to 2017 that comprise ongoing efforts to rehabilitate Center Hill Dam.
According to construction resident engineer Bill Debruyn, the problems stem from the karst limestone foundation and from the standard foundation preparation practices of the early 1940s. The foundations of the two large earthen embankments, the main dam and a smaller saddle dam, are the focus of the multi-year project. The goal is to prevent foundation seepage from potentially harming the embankments.
Today’s technology makes it possible for work crews to make the necessary repairs deep in the foundation.
“Construction is going very well and the weather is cooperating with no major delays,” said Debruyn.
Despite the arrival of cold weather and bone-chilling temperatures, workers from the Bauer Foundation Corporation are making strides at the project site located in Lancaster, Tenn., on the Caney Fork River.
According to Debruyn, an encasement concrete wall, the first major structure, is near completion. The encasement wall is made of 10-foot by six-foot overlapping-rectangular columns into the earthen portion of the dam down to the rock foundation.
“Bauer is using custom built state-of-the-art equipment to excavate vertical columns, held open with continuously circulating slurry mix,” said Debruyn. Made primarily of clay and water the slurry not only supports the hole but transports the cuttings to the surface for removal. The slurry in each encasement wall column is then replaced with concrete. The columns overlap to form a long continuous concrete wall which protects the earthen embankment while the smaller and deeper barrier wall is similarly constructed.
“Beginning in March the barrier wall will be built through the encasement wall up to three hundred feet below the top of the dam through the karst rock ending in the solid rock layers,” said Center Hill project manager Linda Adcock.
Adcock said the barrier wall is a permanent seepage barrier and is planned to be completed in the summer of 2015.
A report is undergoing final approvals to implement the best repair plan for the earthen saddle dam. A concrete berm is planned downstream of the saddle dam from 2015 to 2017 as the final major rehabilitation phase of construction.
The Corps currently manages Center Hill Lake levels targeting a summer high of 630 feet above mean sea level and a winter pool of about 620 feet; however, day to day lake levels are highly dependent on the weather. These target elevations are 10-15 feet lower than normal and are part of risk management until the repairs are complete in late 2017.
Center Hill Dam is one of the multipurpose projects that make up the Corps of Engineers’ system for development of the water resources of the Cumberland River Basin. This system is an important part of a larger plan of development for the Ohio and Mississippi Rivers. The dam controls the runoff from a drainage area of 2,174 square miles.
As a major unit in the system, Center Hill Dam and Lake function to control the floodwaters of the Caney Fork River and contribute to the reduction of flood levels at municipal, industrial and agricultural areas along the Cumberland, lower Ohio and Mississippi Rivers.
Highway 96/141 which routes traffic over Center Hill Dam is a heavily traveled road and is now restricted to one lane. The restriction is required to support the construction on the project and installation of the foundation barrier wall. During the two-year duration of construction at the site, one lane of Highway 96 will be closed and an automated traffic control system will safely manage vehicles across the dam. Debruyn said the maximum expected wait time is five minutes.
To read more on Center Hill Dam, the seepage problem, the fix and project updates visit the Nashville District webpage at http://www.lrn.usace.army.mil/CenterHill. For more information about the U.S. Army Corps of Engineers Nashville District, visit the district’s website at www.lrn.usace.army.mil, on Facebook for updates at http://www.facebook.com/nashvillecorps and http://www.facebook.com/centerhilllake, and on Twitter at http://www.twitter.com/nashvillecorps.