The U.S. Army Corps of Engineers has released a progress report on the rehabilitation of Center Hill Dam.
The plan includes grouting as well as modern concrete barrier walls to stop the seepage. Grout is generally a mixture of sand, cement, water and additives. The mixture is placed under pressure into the rock foundation. The grout will fill voids and slow the seepage beneath and around the dam. A barrier wall is a concrete wall built in sections deep into the foundation as a permanent barrier to seepage.
Work has been underway since the first of three major construction contracts was awarded in February. The Left Rim and Main Dam Grouting contract was awarded to Kiewit-A.C.T., Joint Venture in the amount of $87.4 million dollars.The scope of the contract includes;
Construction of concrete grouting platforms and staging area at Eisenhower Park (also known as Center Hill Recreation Area)
Install grout curtains along 4,100 linear feet; up to depths of 270 feet.
Fill a cave feature in the left rim
Monitor and correct water quality degradation from grouting operations to protect the Caney Fork River.
When actual grouting begins, about 1,000 holes three inches in diameter will be drilled into the foundation. It's possible more holes could be drilled.
After the first round of grouting is finished, more grouting will take place and a cut-off concrete wall will be placed through the earthen portions of the dam and adjoining rim walls.
The priority contract is planned to be completed in the spring of 2010. The first step has been to prepare the work surfaces from which the grouting is accomplished, referred to as "platforms". Grouting is planned to begin at the main dam foundation in December. Contract documents are also being prepared for the next large grouting contract at the Right Rim and Saddle Dam. This contract is scheduled to be awarded in September 2009.
Meanwhile, lake levels continue to remain low -- operating at a current elevation of 622 feet. It's anticipated Center Hill Lake could reach its lowest level since 1956 by the end of the year, from a combination of Corps efforts to keep the lake down in order to reduce stress on the dam and also from the recent shortage of rainfall in the area.
(Top Photo shows October 2008 view of the nearly completed grouting platform at the Main Dam Embankment. The view is looking northeast from the contractor’s staging area at Eisenhower Park (also known as Center Hill Recreation Area).
(Middle Photo shows an aerial view in August 2008 of the current left rim and main dam work. It shows excavation for the left rim work platform and fill at the main dam, Eisenhower Park and the area downstream of the dam.)
(Bottom Photo shows the work that is currently underway to prepare the left rim for drilling and grouting. Approximately 340,000 cubic yards of soil and rock are being excavated from the left rim, cutting through the hillside to create a work platform.)