Value engineering
Knoxville interstate clears formidable design hurdle

By Candy McCampbell

When two proposed retaining walls flanking a bridge over Interstate 40 in Knoxville were estimated at about $1,300 per sq. ft. - more than 10 times the usual cost - engineers decided to take another route.

As proposed, the $30 million concrete walls would add another 30 percent to the $62.4 million road-widening and improvement job. The retaining walls are going up near the North Winston Road overpass at one end of the project.

Saieb Haddad, geotechnical engineer in the Tennessee Department of Transportation's Knoxville office, worked with Henry Pate, engineer at TDOT's Nashville office, to find another option.

They came up with a pile-framed retaining wall that could be built in minimal space within the existing right-of-way, eliminating the need to spend $15 million to $18 million purchasing an office building and large retail store nearby, Haddad said.

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The cost of the revised plan: an estimated $75 per sq. ft.

"People come up with different types of walls, using different types of technology," Haddad said. The new wall uses a battered pile form with coping on top of it. The battered face is at a 70-degree angle.

"The longer the battered face, the longer the base will be. The more the better" because it makes the wall stronger, he said.

The area's geology - clay over irregular limestone bedrock - requires varied depths for the wall piles, some reaching more than 100 ft. Reinforcing steel encased in cement provides additional stability.

Studs were welded to the beams to hang rebar and hold temporary wood lagging. The surface was covered with a molded stone-like concrete finish.

The piling framed retaining wall can be used "in any similar situation," Haddad said, and is being considered for a major interstate project in downtown Knoxville to be let in 2005. In fact, the design has won a TDOT award and a cost-savings award from the Tennessee General Assembly's Fiscal Review Committee.

Even with the wall design changes, it was the biggest interstate highway job in the state when it was let in late 2002. Two others let since then, both on I-40 in Nashville, are bigger.

The 4-mi. Knoxville job, which starts at Papermill Road, includes 12 bridges, 16 ramps, the complete reconstruction of the Papermill Road and West Hills interchanges and the addition of a partial interchange at Weisgarber Road, said Chad Woodroof, project manager with Charles Blalock & Sons of Sevierville, Tenn., the general contractor.

A collector road is also being built on the north side of I-40 between Papermill and Weisgarber and a frontage road is to be constructed on the south side near the West Hills interchange.

It's in a high-traffic area, where both I-40 and I-75 share the same roadbed. More than 152,000 vehicles travel that stretch every day, making it the seventh busiest in the state, according to TDOT.

Woodroof said the project is eligible for early completion incentives of $7,500 a day, so "we jumped in with both feet with an unbelievable amount of resources and equipment, moving dirt and starting on walls and roads."

Planning helped minimize weather-related slowdowns in late 2003 and early 2004 so that concrete, retaining wall and utility work could continue uninterrupted. But in May, rain delays held monthly payroll to almost half its usual $1.4 million, Woodroof said.

Bridge builder McKinnon Construction Inc. of Knoxville was able to work during most of the winter when "the dirt operation shut down," said owner Mark McKinnon.

About 150 workers are presently moving 1.3 million cu. yds. of dirt, re-using 300,000 tons onsite and hauling off the rest. About 100,000 cu. yds. of rock are also being removed.

"The new road will have a base of 10 in. of stone, topped by five lifts of asphalt totaling 14.75 in. thick," Woodroof said.

Two in. of asphalt will be milled off the existing roadbed and another 2 in. added by Renfro Construction Co. of Knoxville. The milled asphalt is taken to Blalock's plant and recycled for later use.

More than 260,000 tons of base stone and 177,732 tons of asphalt will be placed during the project. Also needed are about 2.8 million lbs. of reinforcing steel, 18,000 ft. of pilings, almost 3,300 ft .of pre-stressed concrete beams and 2,700 ft. of pre-stressed concrete box beams.

McKinnon said the bridges are taking up 250 tons of steel and about 4,500 cu. yds. of poured-in-place concrete.

"Under it all is more than 5 mi. of concrete pipe - ranging from 18-in. to 54-in. diameters," Woodroof said.

He added that coordinating the utility work has been tough because much of the underground lines have been a "huge puzzle."

Brent Wilson, vice president of Pipeline Construction Inc. of Rogersville, Tenn., said his company is laying gas, water, sewer lines and underground electrical conduit, and has bored under I-40 in six locations.

The pipeline work also runs along heavily traveled Kingston Pike at the West Hills interchange.

David McDuffie, operations vice president at Pike Electric, said this is the first TDOT project where the general contractor included the utility work in his bid.

"This has given the contractor more control and improved communication at the jobsite," McDuffie added. "It has really worked well."

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For more info about east Tennessee projects, go to: http://www.tdot.state.tn.us/projects/east.htm