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75-year-old structure's foundation deepest in East Tennessee

 

Source: Knoxville News Sentinel Co.

 

SHARPS CHAPEL - Seventy feet below the waters of Norris Lake a drill gingerly peels through bedrock creating holes that no one can see for towering concrete pillars that will support a 2,100-foot-long bridge carrying 9,000 vehicles daily.

 

"This is not a typical bridge job," said Duane Manning, Tennessee Department of Transportation assistant regional construction supervisor.

 

"This bridge has the deepest foundation of almost any bridge in Tennessee, but certainly in East Tennessee.

 

"You can't see what you're doing. It's like arthroscopic bridge building. Everything is done from above. You can't send someone down to the bottom to see what you're doing," Manning said.

 

Since Nov. 4, 2009, crews with Mountain States Contractors have been working on the structure, which at $22.4 million is the second most expensive bridge project in progress in East Tennessee, Manning said. The Henley Bridge in Knoxville, at $24.7 million, is more costly.

 

Work was temporarily halted at Norris last week after the death in Knoxville of a worker on the Henley Bridge renovation. A safety review of all projects under Britton Bridge LLC and its affiliates, including Mountain States Contractors, is under way.

 

TDOT expects the safety review to take about a week.

 

For those in Union County, replacing the 75-year-old structure can't be done quickly enough. The two-lane, truss bridge that opened in 1936 has poor drainage, has claimed too many side view mirrors when large vehicles meet, is weight-restricted and even loses a lane to the rising Clinch River at times of heavy rain.

 

"It'll be good for the community and a lot safer for drivers," said Matthew Boss, a bartender at the Bubba Brews Sports Pub and Grill that's within sight of the project.

 

"It should have been done 10 years ago. Every time it rains it floods."

 

The slogging pace of work on the new bridge - and structural problems with the old one that prompted weight limits - activated the rumor mill in the county of fewer than 20,000 people.

 

"We've heard more rumors on this bridge than any project," Manning said. "It's not funded, the company has folded, the old bridge is falling down; all kinds of stuff.

 

"It's a small community, so people talk. But we're fully funded from start to finish. There are no major hiccups thus far."

 

The new bridge is slated to be carrying traffic and the old structure dismantled by June 30, 2012. Although 19 months have passed on the 32-month project, Manning said the contractor has completed less than 30 percent of the job.

 

"Without an approved extension, he (the contractor) could be looking at liquidated damages of $2,100 per day if he goes past the June 30, 2012, date," Manning said.

 

Manning said the contractor has not requested a time extension.

 

Pouring concrete

 

Workers so far have erected two sets of support pillars for the new bridge. Each pillar is 10 feet in diameter. They have four more sets of supports to construct. Each of those pillars sits upon a 32-foot-square footing embedded in the bedrock below the river silt.

 

"Footings are the most important part of it all," said James P. Braden Jr., a TDOT project supervisor with 42 years of experience. "If it moves, you've got trouble."

 

Workers on barges position a metal frame called a cofferdam on the floor of the river and install sheet pilings more than 70 feet high to drain as much water as possible from the area. Drills on the barges dig 15-20 feet into the bedrock to assure a solid foundation. Explosives inserted into the holes then loosen bedrock that is scooped out before concrete is poured.

 

Bill Malone, TDOT operations specialist 2 with 42 years of experience, said each pillar consists of up to 2,000 cubic yards of concrete and 250,000 pounds of metal rebar more than an inch in diameter.

 

Because the new bridge is within 40 feet of the old Veterans Memorial Bridge, workers can't use explosives for the new pillars closest to the old structure. Underwater explosives could undermine footings for the old bridge.

 

Pouring concrete 70 feet under water presents challenges. Manning said pressures at those depths "can float concrete." The trick, he said, is to pour a bunch of it.

 

"You can spend two or three months just doing a footing," Malone said. "It's a major effort."

 

Braden noted the existing bridge was built before Norris Dam created the lake, so those builders weren't faced with deep water issues.

 

The 1,915-foot-long Veterans Memorial Bridge replaced a single-lane, wood-deck, metal-truss structure that was built in 1916-17 called the Ousley Bridge/Miller's Ferry Bridge, Manning said. When Veterans Memorial Bridge was built, workers moved the old Ousley Bridge to Grainger County, where it carried vehicles over Hogskins Creek on Black Fox Road until about 10 years ago. The old bridge is still used by pedestrians.

 

Wider and taller

 

Pouring concrete for the pillars will require occasional closing of one lane on Veterans Memorial Bridge, Malone said. Cement trucks will use the old bridge to pour concrete for pillars in the middle spans.

 

TDOT paid Britton Bridge $20,000 to reinforce the old bridge. It is listed as structurally poor because of deterioration over the years. Although the reinforcement will allow cement trucks to sit on it, the fixes were not sufficient to lift the weight limits. Loaded commercial rigs over 35 tons now must use a 70-mile detour to avoid the bridge.

 

Once the pillars are set for the new bridge, workers will connect the three spans with metal I-beams standing 9 feet high. On top of those four strands of beams, workers will pour up to 10 inches of concrete for the deck.

 

While the old bridge carried traffic on two, 11-foot-wide travel lanes, the new bridge will offer two, 12-foot-wide lanes and a 10-foot-wide shoulder on each side.

 

"If you have car trouble, you'll have a place to pull over. Also, there's mobile home manufacturers on either side of the river, so it'll make it easier for wide loads," Manning said.

 

The completed bridge, Manning said, will resemble other interstate bridges, with a 32-inch-high concrete wall along the sides.

 

Drivers will be using the bridge months before the project is finished, Malone said. Workers will divert traffic onto the new bridge as they pave approaches of about 600 feet long on each end of the new bridge.

 

That's when drivers will notice they are traveling on a bridge that is roughly level with the top of the metal trusses of the old bridge.

 

The new bridge deck will be 50-60 feet above the water. The existing bridge is so low to the water that many houseboats can't move under it, Braden said.

 

Once the new bridge and approaches are finished, workers will begin dismantling the old one. Manning said the water is too deep to use explosives to bring it down.

 

"Removal of the old bridge is going to be a task," he said. "Basically, they dismantle it piece by piece."