Drilling Expansion Holes for Chickamauga Dam
June 1, 2010
S&ME of Louisville, Tenn., used a Geoprobe 7730DT to open up sawcut expansion holes at the Chickamauga Dam for the Tennessee Valley Authority (TVA), owners of the dam. Sawcuts typically are made using sawcut expansion holes in the dam to allow for natural concrete expansion, and eliminate pressure on the dam itself. Every few years, when new expansion joints need to be made, sediment is cleaned from the holes, and the TVA lowers a pulley system into the hole to cut the new joints. Four holes that were the focus of this project originally were drilled and sawcut several years ago. At that time, two of the holes were lined with a rubber, reinforced collapsible sock seal to keep the holes open and to keep sediment from migrating between the sawcut holes. For this project, S&ME used a skid-rig to open up and clean the built-up silt and sediment from the two holes without the sock seal. TVA officials had hoped to just pull the sock seals from the other two holes, but over the years, the seals had become waded up and had been pinched into the sides of the hole during the concrete’s expansion process.
S&ME used wash rotary and diamond core bits to drill through the tough rubber sock material with the skid-rig, but could not remove the material from the hole. So it brought in its 7730DT to auger and clean out the sock material. An 80-ton gantry crane, permanently mounted on top of the dam, moved the 7730DT and pallet of augers into position. S&ME used 6-inch augers to open up the 8-inch cleanout holes to 85 feet. The skid rig took approximately 8 days to clean out the first two holes and attempt to clean out the other two holes. It took 3 days, including mobilization, to complete the work on the other two holes that were plugged with the sock material. The S&ME field team was George Patrick, drilling manager; Tracy Bunch, driller; James Bunch, shop foreman; and Brian Acres, assistant driller.
The Chickamauga Dam, a hydroelectric dam that impounds the Tennessee River, is a New Deal dam project. It was constructed in the late 1930s as part of President Franklin Roosevelt’s New Deal program to spur relief, recovery and reform of the U.S. economy during the Great Depression. The dam was needed to improve navigation and bring flood control and economic development to the Tennessee Valley. The Chickamauga dam, which cost $40 million, is 5,800 feet long and 129 feet high, and took more than 500,000 cubic yards of concrete and almost 3 million cubic yards of earth and rock. The lock at the dam is 360-feet-by-60-feet, and raises boats and barges up to 50 feet to Nickajack Lake. The Chickamauga Reservoir has 810 miles of shoreline and 35,400 square acres of surface area. The dam got its name from a tribe of Native Americans that broke away from the main body of the Cherokee Nation that lived in villages along the Chickamauga Creek, which flows into the main river body just below the dam.