Near the Kentucky border on southbound Interstate 75, in Ellico, TN, a displacement of soil has caused a problem that has to be dealt with quickly or it might further jeopardize travel in the area.
Time and weather eroded soil under the roadway, creating an unstable surface on which to drive.
“This is an embankment that failed,” said Max Morton of the Knoxville-based Philips and Jordan Inc. “The dirt crumbled out from underneath the roadway, which was part of the original construction of the highway.”
Crews are removing soil that slid out from underneath the road, which has been limited to one southbound lane.
“Approximately 77,000 yds. of dirt will be removed a truckload at a time. The soil will be replaced by 86,000 t of rock aggregate we will process ourselves. There is about 700 ft. of highway that will need to be repaved above the slip.”
Construction crews are trying to stabilize the crumbling embankment to avoid future problems by driving 300 long metal poles into the ground with a soil nail launcher. The launcher sounds like a 12-gauge shotgun and gives off a cloud of white smoke as it shoots the 10-ft.-long rods or “nails” into the earth at 220 mph. The attachment is mounted on a Komatsu 150 excavator.
Bob Barrett, president of Soil Nail Launcher Inc. brought in the launcher to help reinforce the slide area.
“The mountainside must be stabilized so the damage won’t spread. The Tennessee DOT and Philips and Jordan are working together to remove material and then replace it with aggregate rock,” explained Barrett. “Soil Nail Launchers are fantastic tools. What takes traditional soil nailing 15-20 days takes only four days with the launcher. The nail is shot into the soil in one operation. It is fully bonded and effective immediately. Traditional methods require drilling, then placing the nails.”
Barrett estimated this technique saves approximately $500,000 in each job.
What’s more, as crews excavated downward along I-75, the whole hillside was at risk.
“It is not only just monetary savings. This job could have been a disaster. Excavation can cause the whole operation to collapse,” Barrett said. “Time is of the essence in an emergency situation like this one.”
The soil nail launcher was invented by the British military approximately 20 years ago. The British military built two of the unusual machines, which are powered by compressed air.
“They were adapted for commercial use and put up for sale in Britain in the 1990s but nobody could figure out what to do with them,” he said.
Barrett was part of the United States Forest Service team that tested the soil nail launcher in the western states. The geotechnical division saw a potential for their use but nobody bought them. After Barrett retired, he and his partner purchased the two launchers. The machines were tested for effectiveness in beach soil erosion in North Carolina and Maine. Still, the launcher is a relatively new piece of equipment whose usefulness is still being evaluated.
“They’re going to go at least 40 ft. down the slope with the nails,” said Cecil Patterson, vice president of Phillips and Jordan. “We’re going to work 24 hours a day, seven days a week until we get the road open.”
The project was authorized March 16, mobilization started March 17 and the actual job began March 21.
“This almost $2.5 million job has a deadline date of May 26. There is a $5,000 incentive per day up to $100,000 to finish early and a $5,000 penalty for each day the job goes beyond deadline,” said Morton.
There are about 30 men who have been on the job 24/7 using Komatsu PCs and a Caterpillar 330 excavator. Volvo A-40s and super dozers will be at work until the job is done. So far the weather has been cooperating. Rain has slowed down the job a little, but workers do have all-weather access to the site.
“I would like to commend the Department of Transportation and our men from Philips and Jordan for working so hard to get the job done,” said Morton. “They have all put in a lot of effort and a lot of hours. I appreciate their families for understanding.”