TDA Rescues Failing Road Project
Tire shreds’ lightweight, sheer strength overcomes poor soils
Construction was humming along on a multi-year, $25 million road project outside of Mankato, MN on CSAH 12 when an embankment leading to a bridge failed, temporarily affecting service on the DM&E Railroad’s mainline running along the base of the embankment. To determine the cause of the failure and figure out the most effective and cost efficient remedy, Blue Earth County sought the advice of geotechnical engineers.
Steve Gale, from Gale Tec Engineering Inc, was brought in. Determining the cause required reviewing the site, which had about a 30 foot high embankment with double train tracks at the bottom. Soil borings were drilled and tests were run on samples from the road section.
“Just like a doctor would run a CAT scan and do blood tests, we do the same thing on soil,” Gale said. The determination was heavy fill on top of soft soils caused the failure and continued movement.
“In this case, because of the limited distance between the overpass and the railroad tracks, we had to take the soil load off in order to stop the movement and then rebuild that section with a material that was lightweight,” Gale explained.
Four different materials were evaluated for their engineering properties and cost effectiveness. After looking at foam, lightweight aggregate, wood chips, and tire shreds, the choice was clear.
“Shredded tires have certain properties that were advantageous in this case,” Gale said. “They have a high interface friction angle and low weight, about one-third of the weight of regular soil.”
The county engineer, Al Forsberg, agreed with the diagnosis and the remedy.
“Tires were the most economical solution and they solved the slope stability problem,” Forsberg said.
Cost savings are just one of the benefits of using tire shreds in civil engineering applications, according to Monte Niemi, CEO of First State Tire Recycling. His facility in Isanti, MN processes millions of used tires every year into Recycled Tire Engineered Aggregate R.-T.E.A. The tires are recycled into pieces ranging in size up to 12 inches which can be used as aggregate in civil engineering products.
“When compared to other fills, tires offer a remarkable list of unique and desirable characteristics: lightweight, free-draining, insulating, high internal shear strength,” Niemi said. “When the pieces get compressed, they interlock and hold the road together.”
More than 16,000 cubic yards of tire shreds were used in the Blue Earth County bridge embankment project. This would amount to about 820,000 tires used.
Tire shreds are helping Blue Earth County meet their goals of increasing safety at the interchange connection to Highway 14, and providing grade separation with the railroad and Sakatah Singing Hills Regional Trail, Forsberg said.
The project also is addressing congestion, access and economic development needs of the region. The portion is complete that includes the shredded tires approach to the bridge over the railroad tracks. Forsberg reports the entire project is nearing completion and the tire fill has corrected the problem.
This was Blue Earth County’s first road project involving tire shreds. The product has a 20 year history and has been successfully used in other counties, including Carlton, Benton, Sherburne, Isanti, Ramsey, and Hennepin, to name a few.
© Scrap Tire News, January 2012