A Bridge to the Past
By K. Robert Wendel

An old bridge with unsafe ramps is making way for a brand new bridge in Tucson, with Hunter Contracting of Gilbert, Ariz. teaming with the Pima County Department of Transportation to reconstruct Veteran's Memorial overpass in southeast Tucson.

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Work on the fast- track, $18 million project started in June, with the demolition of the old Palo Verde Bridge on 44th Street and Alvernon Way.

"The bridge was just too old," said Tom Kilargis, field engineering division manager for Pima County. "It had the old style pin and hanger system that is subject to corrosion."

The project involved an extensive amount of earthwork to pull down the old abutments and build newer and larger abutments for the approaches and bridges. The older bridge also had settlement issues, so crews brought in borrow and re compacted the site.

But rains have slowed work. "The goal from Pima County is to get this bridge done in 12 months," said Hunter project manager Jeff Jones. "We are facing a double liquidated- damage standard at 12 and 16 months, so we have to get it done."

The damages could go as high as $2,500 a day.
Jones said his crews have lost two weeks because of the wet conditions in southern Arizona this year.

The project entails building up new embankments, building five bridge spans and installing interchanges. The bridge's largest span is a 77-ft. precast concrete- tub girder that spans the railway track. Shorter spans include a 60-ft. section.

The total bridge length is 350 ft. long with a 133-ft.- wide road deck. Plans call for four lanes in each direction along with dedicated turning lanes.

"It was difficult working around the railroad tracks, and the biggest challenge was the geometry of the bridge, which is curved," said Anthony Gravagne, a project manager with Tucson's Structural Concepts Inc., a structural engineering firm. "Because of the track layout we to put the piers in the right place, so we ended up with three different types of spans."

In addition to spanning the railroad, the bridges also span channels of Tucson's diversion system. Engineers and contractors teamed to value engineer the sections, saving money by using cast-in-pace concrete arches on the smaller spans. The value-engineering team also saved money by using a mechanically stabilized earth wall.

"The original design had abutments that were designed to be full height, but we decided to use a mechanically stabilized earth wall," Gravagne said. "We have steel straps running back into the earth with little nodules every few inches.

The nodules interface with the soils, we end up with a good connection and the walls and the trap function as one element."

On the bridge decks, contractors will use two courses of asphalt in two, 2.5-in. lifts. A friction coat of asphalt rubber will also be used. Contractors will eventually use 19,000 tons of asphalt and 13,000 cu. yds. of concrete.

As with many road projects in Tucson, art and architectural features are a major part of the bridge design. Plans call for a stars and stripes theme to celebrate veterans.

The project is scheduled for completion this summer.