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Hoover Dam Bypass Project Approaches End

Thu June 17, 2010 - West Edition
Rebecca Ragain

A 1,060-ft. (323 m) concrete arch curves 900 ft. (274.3 m) above the Colorado River, part of a 1,900-ft. (579 m) long bridge with its abutments set into the cliffs of the Black Canyon, approximately 1,500 ft. (457.2 m) downstream of the Hoover Dam.

Starting in November, traffic traveling U.S. 93 will use this monumental new bridge to cross the Colorado River between Nevada and Arizona. The current route across the top of the Hoover Dam cannot safely accommodate the 14,000 vehicles and trucks that use it each day; issues include sharp turns, narrow roadways, inadequate shoulders, poor sight distance, and low travel speeds.

The Federal Highway Administration’s remedy to these problems is the $240-million Hoover Dam Bypass Project, a 3.5-mi. (5.6 km) corridor beginning in Clark County, Nev., and crossing the Colorado River before terminating in Mohave County, Ariz.

The partially finished bridge is the most striking phase of the six-phase bypass project. At present, four of the six phases are complete:

• Relocation of portions of the Western Area Power Administration (WAPA) transmission system and switchyard, which began in 2002 and was finished in 2004

• Arizona approach: 2 mi. (3.2 km) of bypass roadway completed in 2004 by R.E. Monks Construction and Vastco Inc. Joint Venture

• Nevada approach: 3 mi. (4.8 km) of bypass roadway completed by Edward Kraemar & Sons in 2005

• Interim surfacing of the bypass: $7-million project completed June 2008 by Las Vegas Paving Corporation

Construction of the Colorado River Bridge, officially titled the Mike O’Callaghan-Pat Tillman Memorial Bridge, began in 2005. The $114-million project was awarded to joint venture Obayashi Corporation and PSM Construction USA, Inc.

The bridge is a composite concrete deck arch design. The superstructure is composite of four-steel tub girder, cast by highline cable crane system with towers 2,500 ft. (762 m) apart, plus cast-in-place concrete slab. The twin-rib arch consists of 106 individual segments — 53 in each arch.

More than 500 concrete segments used for columns and temporary pylons were fabricated at a pre-cast yard located 20 mi. (32.2 km) from the dam, delivered to the bridge site, then erected with cranes including a S-70 Derrick and a Manitowoc 2250.

By fall 2006, work on support columns on both sides of the Colorado River was approximately 50 percent complete. Then, high winds caused the collapse of two pairs of 280-ft. (85.3 m) towers supporting the highline crane system. No one was hurt in the incident, however the project was set back nearly two years from the original completion date of late 2008.

A new highline system became fully operational in January 2008. By March of that year, finished work included canyon excavation and foundations, pre-casting of column and pylon members, post tensioned column installation, integral caps, and steel tub girder fabrication. Interim cranes, employed after the collapse of the highline towers, had allowed for construction of initial arch segments and the setting in place of the steel tub girders on the Arizona approach spans.

For the next year-and-a-half, the joint venture worked to complete the construction of the 1,060-ft. (323 m) arch, reputed to be the longest in the Western Hemisphere. In August 2009, the arch was closed. Another major landmark was reached in November, when the remaining columns were constructed.

In March of this year, key activities on the bridge included completion of the girders and preparation for the placement of the deck, which will take several months. The bridge is scheduled for completion in September, a couple of months before the entire bypass is open to traffic.

“Really, our focus is on the completion of the project, on the opening of the bypass,” said Dave Zanetell, the Federal Highway Administration’s bypass project spokesperson. “Now, it’s a matter of disciplined execution of every remaining step toward that goal.

“The placement of the girders is completed in a very specific and regimented sequence.”

Next comes the placement of stay-in-place deck forms and deck reinforcement rebar, followed by the sequence of placing concrete for the deck.

“We have a deck-placing plan, so that we load the bridge in a planned and engineered way… the unique thing about it is the regimentation,” said Zanetell.

As the bridge nears completion, supporting infrastructure and equipment will be decommissioned, including the highline cable crane system.

In the meantime, Las-Vegas-based Frehner Construction is at work on a $7-million contract to complete the final roadway elements, including signing, striping, median barrier, paving, and roadway tie-ins at U.S. 93.

“There’s lots of work going on, in addition to the bridge,” said Zanetell.

Zanetell estimates that more than 1,200 trade and craft workers have been involved with the bypass project since its inception.

“We’re extremely proud of the construction contractors in the industry who participated in the project,” said Zanetell.

The high quality work done on the bypass project, which is comprised of numerous heavy civil construction projects, “is a reflection of the capability of the industry,” Zanetell added.

“We’re all honored to be a part of the bypass project…in this historic setting, in the shadow of the Hoover Dam, to be part of something we believe is great,” said Zanetell. “It’s an honor for everybody involved in the project.”

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