Streamlining traffic
Nashville diamond interchange requires work on 10 bridges

By Mardy Fones

Construction of a new diamond interchange on the footprint of one built in the 1960s is at the heart of a $43.6 million highway project in Nashville.

The 36-month, Interstate 40/Robertson Road project includes expanding I-40 from three to five lanes, widening bridges and constructing new ones.

For Ray Bell Construction Co. Inc. of Brentwood, Tenn., the final result will be separating local traffic from through traffic without substantially altering the residential areas and small business districts that abut the interstate.

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A requirement of the project is that the existing three traffic lanes of I-40 and nearby Briley Parkway interchange remain open, since they carry 103,000 cars and 36,000 cars on a daily basis.

"Ray Bell has a reputation for taking on the toughest jobs in the industry," said Bruce Nicely, vice president of the bridge division.

Ray Bell was founded in 1970 and bridges are its specialty. That's a good thing because the I-40/Robertson Road project has 10 - six that are being widened and four new ones, including two fly-overs. One bridge is just a few feet short of a mile long.

Other Ray Bell bridge projects have included a $52 million rebuild of the I-240/I-40 Memphis interchange and the $29 million, 540-ft. clear-span bridge across the Cumberland River in Nashville.

At completion, the I-40/Robertson Road project is expected to streamline traffic flow to and from the north.

"Overall, it will be a better, more functional interchange because it eliminates double red lights and traffic tie-ups," said Jeremy Mitchell, project manager.

Traffic control planning is a big part of the job and has been ongoing and collaborative, said Larry Ridlen, the principal in transportation services for Gresham Smith Architects and engineer of record on the job.

"With Ray Bell's help, we tweak the plan every week," he added. "The difficult part is finding space (along the interstate) to work."

To date, there have been no lost-time accidents.

"It's gotten real dangerous to do road projects, said Dennis Howell, project superintendent. "It takes people with bridge experience and nerves to work 75 ft. up in the air."

Howell added that another difficulty was setting the 70-plus piers that support the bridges. The piers are located inches from speeding traffic. Most are set on caissons, others are on spread footings. All required some blasting or extensive excavation, in one case to a depth of 60 ft.

Another caisson was set within a few feet of the back of a building because a ramp of one of the bridges extends 12 ft. over it.

Protecting Rock Creek, which runs parallel with I-40 from run off, was another priority and required the construction of new box culverts and redirecting the streambed.

Purchasing rights-of-way in the densely populated area took time and was expensive. Acquisitions began in early 2000 and were completed in summer 2002 at a cost of $10.3 million. Mark Halloran, director of Region 3 for the Tennessee Department of Transportation, said only nine of the 151 tracts required litigation; 68 resident relocations and two business relocations also occurred.

The state also purchased air rights over a strip mall and bowling alley to construct one of the fly-overs.

The installation of new utility service under I-40 required Mitchell Plumbing of Nashville to hand dig a 400-ft., 54-in.-diameter tunnel. Blasting to carve through solid limestone took teams of three diggers four to five months to complete. The project also includes 20 reinforced retaining walls, 16 of which were cast in place, plus a 1,700-ft. noise abatement wall.

By February, Bell personnel were lifting into place the 313, 150-ft.-long concrete beams manufactured by Concrete Products of Memphis. That piece of the job was reserved for weekends when traffic could be cut to one lane so 300-ton cranes can be moved onto the interstate to lift beams individually into place.

Each beam is manufactured of rebar, post-tension cable and 140,000 lbs. of concrete. The beams, laid five to eight across, span the piers.

"The beams are designed to carry the load and everything is cantilevered off them once the concrete is poured in place," Howell said.

Halloran said the pre-stressed concrete beams, 80 percent of which are bulb-tee type, will total almost 10 mi.

As spans between the piers are secured, crews follow by installing the metal decking and rebar, then pumping concrete into place. Overall, the job includes 2.1 million pounds of reinforcing steel and 8,968 cu. yds. of concrete. In total, the project has 10,550 ft. of bridge length.

The project is on track to meet its completion deadline of Nov. 1, 2005. An incentive built into the job pays Ray Bell an additional $7,500 for each day the project is ready ahead of schedule, with a cap of $2.5 million. If it misses the deadline, Ray Bell pays the state $7,500 daily with no cap.

Mitchell said it's too early to predict early completion.

The second phase of the project may be let in 2006. The project was divided in half to minimize traffic and community disruption as well as to keep costs down, Ridlen said. Splitting the job also increases the numbers of contractors available to bid on it.

Ridlen said two additional flyovers will be created during phase two to accommodate traffic onto Briley Parkway from the south.