SOIL NAILING: HOW IT WORKS
Soil nailing is an on-site soil reinforcement technique in which metal tubes are put in the ground at intervals of three to six feet to increase the strength of the soil beneath the roadbed. As the bars are being drilled, grout is inserted into the hole to make sure the soil nail stays put. Solid bars are usually installed into pre-drilled holes and then grouted into place using a separate grout line, whereas hollow bars may be drilled and grouted simultaneously by the use of a sacrificial drill bit and by pumping grout down the hollow bar as drilling progresses. Kinetic methods of firing relatively short bars into soil slopes have also been developed.
Source: Tennessee Department of Transportation
A contract paving project is scheduled this summer to resurface a 5.6-mile section of U.S. Highway 41 from Bobby McCulley Road to McBrien Lane. Bids on this project will be opened May 23. This project will connect with a 6.5-mile resurfacing project completed last year from McBrien Lane east to the Hamilton County line.
Source: Tennessee Department of Transportation
People who have spent most of their lives on the easternmost piece of U.S. Highway 41 in Marion County say Aetna Mountain's going to win the battle for the pavement.
The stretch of Highway 41, also known as Dixie Highway, between Lookout Valley and Haletown underwent repaving work and a soil-nailing project last fall to smooth and stabilize the road, but it just keeps sliding down the mountain toward the Tennessee River.
"I remember my daddy talking about it all the time," commercial catfisherman Jimmy Legg said as he tied his fishing nets for a day of pursuing his whiskered quarry. Legg's father owned a store on 41 called Pete's Cider and Fireworks, which had a live black bear on display back in the old days.
"That road has always fallen in," said Legg, 58, leaning on a rack made for spreading out his nets beside the highway. "I don't know what they could do to stop it.
"There's already enough asphalt under there to go all the way to the river."
Almost seven miles of U.S. 41 -- starting around the Marion-Hamilton County line and twisting alongside the river toward Nickajack Lake -- has been marked with dips, humps and pockets of collapse for decades. State road crews have tried to keep it passable with patches and resurfacing efforts.
Over the guardrail on the river side of the road lie old layers of Highway 41 -- in some places a lane wide -- indicating that paving crews over the years keep edging inward on the mountain. Some large slabs of old blacktop still bear the white shoulder stripe.
Last fall, Grand Junction, Colo.-based GeoStabilization International performed a soil-nailing project at the road's highest point on Aetna Mountain and that stretch seems to be holding its own, so far, said resident Robert Payne, whose home is directly across from the site.
Crews installed 30- to 50-foot steel "nails" -- long hollow tubes driven into the earth and grouted in place -- under a section of road about 100 yards long that started to collapse last summer. Mountain movement seems to have created waves in the road, yet the pavement is still sound.
But other areas that were repaved only last fall have collapsed so much that the top of the guardrail is level with the road surface and there are deep cracks in the pavement.
A trip though the roughest area at the posted 55-mph speed limit would be harrowing for most first-timers. A motorcyclist caught off guard could easily lose control, Payne and Legg noted.
"I go through there at 35. They can just slow down and wait on me," Payne said of anyone following him.
Payne and Legg say caution signs should be posted so drivers have some warning.
Tennessee Department of Transportation spokeswoman Jennifer Flynn said any fix along the Aetna Mountain section "will be a very expensive undertaking."
Other spots on U.S. 41 are good candidates for soil nailing, too, but it was a matter of prioritizing the worst spots throughout the 24-county region, Flynn said.
"Most, but not all, of the areas along U.S. 41 can be helped by soil nailing," Flynn said, "but it is not a one-size-fits-all method."
State engineers regularly monitor the roadway for changes and damage because it is so prone to settlement and sliding, Flynn said.
Richard Howell, operations specialist in charge of the regional maintenance division, said soil-nailing the current problem area won't work and geotechnical engineers are studying a remedy.
"They are working on some way to fix that. Geotech just hasn't come up with the right solution yet," Howell said.
Meanwhile, crews will keep patching and smoothing out the rough spots, he said.
"We're going to have to put up some signs," he said of the need to warn motorists. Officials might post some reduced speed limits through the area, too, until repairs are made.
"Once we get in there and do that fix, we want it to be 'permanent,'" Howell said. "But with the way Aetna Mountain is, I'm not sure anything's permanent."
Contact staff writer Ben Benton at email@example.com or 423-757-6569.