Commuters and local residents who drive U.S. Highway 41 between Guild and Riverside in Marion County, Tennessee, can finally breathe a collective sigh of relief.
The almost $19. 2 million slide repair project is complete, according to the Tennessee Department of Transportation. The road has been reopened to two lanes and traffic is finally flowing normally in both directions after almost two years of work that dramatically changed the landscape of a mile-long piece of Highway 41 on Aetna Mountain.
Both lanes of the two-way highway were opened to traffic Nov. 5, and no new problems complicated the project as it came to a close over the summer and fall, TDOT spokesperson Jennifer Flynn said.
TDOT officials say the repairs will be long-lasting and the design will improve drainage and stabilize the earth beneath the road as it makes its path 12 miles or so around Aetna Mountain from the Marion-Hamilton county line to the Guild community on Nickajack Lake.
"As part of the project, we have re-established, reinforced and improved ditches and cross drains," Flynn said. "The project also installed horizontal drains that go 80 to 100 feet into the slopes above and below the roadway in an effort to intercept and drain subsurface water in a controlled manner."
That means fewer slides and collapses, at least in those areas.
The design uses three techniques to accomplish its work by diverting rainwater that runs down the mountain above the highway to a drainage system of ditches lined with geomembrane material that blocks water seepage, according to TDOT. Soil nails — hollow tubes drilled or driven horizontally into the ground beneath the road bed — provide support and prevent shifting and damage to the road and drainage system, officials said.
An access road built during construction will remain as a maintenance road, Flynn said.
"This area is where the horizontal drains exit the slopes below the roadway, and it provides a site for water to discharge without washing away the slopes," she said. "It also allows crews to have access to the geomembrane ditch and horizontal drains for future maintenance."
In its early days U.S. Highway 41 was the only federal highway making its way through the Tennessee River Gorge and it remains an important route now serving as a detour when an incident forces the closure of Interstate 24 at certain points. That means it must be maintained to carry heavy interstate traffic.
Across from the Tennessee Wildlife Resources Agency boat ramp on the Tennessee River, Sullivan's Store sells snacks, bait and tackle a few miles south of the project area on Highway 41. Owner Randall Sullivan has watched the battle between the mountain and Highway 41 for all his 81 years.
Until recently, he hasn't had much hope for the highway's slide fixes that slow traffic and hurt nearby businesses.
"All the red lights are gone, so tell the people it's wide open," Sullivan said Friday. "It's a durn good road. It looks sharp, it really does."
He said he hoped it would "hold all winter," knowing rains indiscriminately deal out damage to Aetna Mountain roads.
The repair project was the largest and most expensive of the state's attempts at a permanent — or at least a longer-lasting — fix for the mile-long piece of Highway 41 on Aetna Mountain's slide-prone north slope where TDOT has waged a decades-long battle with the mountain and heavy rain runoff.
The project was supposed to have been completed by the end of November 2019, but ongoing damage from rains kept forcing more repairs. Problems began in December 2018, repairs started in January 2019 and bids were opened in May 2019, with Dement Construction winning the project with a $16 million bid.
But heavy rain kept dealing out damage.
In June, Flynn said January and February 2020 rainfall totaled more than 18 inches in Marion County, after a very wet fall in 2019, which caused cracks in the road at two new locations inside the project area. TDOT decided both those locations should be fixed and added them to the original scope of the work, kicking up the total bill to $19,176,600.
It's not the first time, even in recent years, that the same stretch of road has buckled and collapsed from underground water, and as recently as 2013 the state shelled out $909,000 for a repair project very near the one just completed. The 2013 project was one of the first uses of the soil nailing technique that was used on the just-finished slide repair project, and now it's used on mountainside road projects all over Tennessee, TDOT officials said.
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
In 2014, the section repaired the year before and other areas that hadn't been really bad were beginning to crack and collapse. In the years between 2014 and 2018, several smaller repairs were made with TDOT spending approximately $100,000 on resurfacing, manual spot patching, milling, cleaning and reshaping ditches, slide and settlement repair and drainage structure repair, officials said. Add to that a paving project in October 2013 that cost $910,000, another in September 2014 that cost $925,000 and that tally nears $2 million.
The work just finished on the Aetna Mountain piece of Highway 41 brings the total over the last seven years to just more than $21 million. While rain has been Highway 41's enemy, the completed work has not been damaged by 2020's record-setting rains, officials said.
TDOT officials said the work has the standard warranty on the overall repair of seven years. The soil-nail retaining wall is designed to last 75 years.
"We hope that this fix will last forever if no movement occurs beneath the soil nail wall," Flynn said. "On average, we would hope for features like these to last at least 50 years."
Contact Ben Benton at firstname.lastname@example.org or 423-757-6569. Follow him on Twitter @BenBenton or at www.facebook.com/benbenton1.