Hoover Dam Bridge Takes Shape

By Tony Illia

With the two approaches already complete, work is now proceeding on the 1,960-ft-long bridge to bypass Hoover Dam at the Arizona-Nevada border.

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The long-awaited $234 million Hoover Dam Bypass Bridge will now finish in late 2010 instead of June 2008 due to the collapse last year of a giant cableway system under 55-mph winds.

The 1,960-ft-long, 88-ft-wide arched bridge was already postponed a year because of the two-year delay in passing SAFETEA-LU, the federal transportation bill. In 2004, however, Arizona and Nevada each pledged $50 million in bonds to keep the project moving.

The fallen cableway system was critical to shuttling materials between Nevada and Arizona 780 ft above the Colorado River. The project was about 40% complete at the time of the incident.

"Prior to the collapse of the contractors' delivery system, all aspects of the multiyear project were on track," says F. Dave Zanetell, Federal Highway Administration project manager. "Production work is occurring on a limited basis using conventional cranes to complete tasks unrelated to the highline."

The project should still finish within budget, but a $6 million contingency fund will be consumed in the process, he adds. Bids for the Nevada and Arizona approaches were 10% to 15% below the engineer's estimate, which created a financial cushion.

And while investigations are still ongoing as to the cableway collapse, initial results point to a failure in the reconditioned Nevada south tower crane. Its failure caused support cables to fail and remaining towers to fall. FHWA is not ruling the incident a force majeure.

A joint venture led by Obayashi Corp. of San Francisco, with PSM Construction USA Inc. of Brisbane, Calif., won the A+B bridge contract in 2004 with a $114 million low bid. Although 15.6% above engineer's estimate, it was still $12.9 million below the runner-up team of Peter Kiewit Sons' Inc. of Omaha and Flatiron Construction Corp. of Longmont, Colo.

Its proposed cableway erection method helped Obayashi/PSM win the job, according to Zanetell. The project carries $8,000 per day in liquidated damages after 1,217 working days.

Obayashi/PSM bought a 42-year-old cableway system from American Bridge Co. of Coraopolis, Pa., which refurbished it for $11 million. The system had two pairs of 330-ft-tall, lattice-framed towers with 2,500-ft-long, 3-in-diameter cableways strung across the Black Canyon. The system used two 13.5-ton trolley and load block assemblies, each holding a nine-part line of 7/8-in.-diameter wire rope.

The towers, which could tilt 7 degrees laterally in each direction, were capable of carrying 50 tons of materials at a maximum line speed of 400-ft per min.

The towers were secured by a combination of stay-backs and concrete foundations.

The team has since bought a replacement system from F&M Mafco of Cincinnati. Built from scratch, it's based on the original design but with "heavier components," says Jim Stevens, Obayashi's project sponsor. The joint venture didn't disclose the replacement costs.

"We expect delivery of the new cableways in August, so we're hopeful that we will be back in operation by year's end," Stevens says. "In the meantime, we have erected a stiff-leg derrick on the Arizona side to finish the approach work. And we have a Manitowoc 2250 [crawler crane] on the Nevada side working on columns and pier caps. We're doing that while we are waiting on the cableway."

Construction of the concrete-and-steel composite main span poses daunting challenges due to the Black Canyon's sheer walls and severe climate where temperatures routinely reach 120 degrees Fahrenheit. HDR Inc. of Omaha; Sverdrup Civil Inc., a unit of Pasadena-based Jacobs Engineering Group Inc.; and T.Y. Lin International of San Francisco are the bridge's design-engineer team under a six-year, $22 million contract.

FHWA increased its original estimated price tag by 15.4% after a geotechnical survey by London-based AMEC determined that the canyon slopes would need costly excavation. Contractors created 90- and 73-degree sheer drops at the Nevada and Arizona sides, respectively, to minimize the amount of excavation otherwise needed for more gradual transitions.

Controlled explosives were needed to carve-out canyon walls.

The $21.4 million, 1.8-mi-long Arizona approach from U.S. Highway 93 to the Arizona side of the Colorado River finished in October 2004. R.E. Monks Construction Inc. of Fountain Hills, Ariz., and Chino Valley, Ariz.-based Vastco Inc. completed the two-year undertaking.



The project required a 900-ft-long precast concrete girder bridge over a 200-ft-deep ravine on the east side of Sugarloaf Mountain, plus a cast-in-place intersection bridge at the Hoover Dam Access and Kingman Wash roads, wildlife crossings, parking and drainage improvements.


The $30.1 million, 2.11-mi Nevada approach built by Edward Kraemer & Sons Inc. of Plain, Wis., finished in October 2005, roughly two months ahead of schedule. It consisted of six new bridges, including a 463-ft-long, three-span, steel-girder structure that crosses over a 160-ft-deep ravine.

There is also a new four-lane highway alignment and a new traffic interchange at U.S. 93 near the Hacienda Casino, plus a 12-ft-tall by 24-ft-wide culvert wildlife crossing at U.S. 93.

The Western Power Administration paid $9.6 million to Kansas City-based Par Electrical Contractors Inc. to relocate eight steel lattice transmission towers and accompanying 230-kV and 440-kV lines from the path of the bridge. The work finished in 2003.

The two-lane U.S. 93, a key route in the North America Free Trade Agreement between the United States, Mexico and Canada, traverses the crest of Hoover Dam and handles 17,000 vehicles daily. The stretch of highway was identified as a high-priority corridor in the National Highway System Designation Act of 1995.

Since the Sept. 11 terrorist attacks, however, truck traffic over the dam has been rerouted 23 mi away, costing consumers some $30 million annually, the FHWA's Zanetell says. Other commercial four-lane route options require an additional 250 mi detour.

The bridge, which is located 1,500-ft downstream from the dam, will be North America's longest single concrete span upon completion. Congress has officially designated it the "Mike O'Callaghan-Pat Tillman Memorial Bridge."

It's named after former Nevada Gov. O'Callaghan and Army Ranger Tillman, the professional football player who was killed during the war in Afghanistan.

"The new bridge will eliminate the sharp turns, narrow roadways, inadequate shoulders and low travel speeds of the existing travel route," Zanetell says.

"This is really a historic project that has been a long time in the making."

Key Players

Owner:
Federal Highway Administration

Design:
HDR Inc.; Sverdrup Civil Inc.; T.Y. Lin International

General Contractor (bridge):
Obayashi Corp. and PSM Construction USA Inc. (joint venture)

General Contractor (Ariz. approach):
R.E. Monks Construction Inc.; Vastco Inc.

General Contractor (Nev. approach):
Edward Kraemer & Sons Inc.

Useful Sources
http://www.hooverdambypass.org/

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