Hoover Dam Bypass Project, Black Canyon, USA

Currently, the top of the Hoover Dam is the route of the major road US 93 as it crosses the Colorado River. US route 93 is the major commercial corridor between the states of Arizona, Nevada and Utah; it is also on the North American Free Trade Agreement (NAFTA) route between Mexico and Canada.

The road has been identified as a major problem in the US highway system because of the traffic congestion caused by the inadequacy of the existing highway across the dam (the road across the dam will remain open for visitors to the dam but not through traffic).

The traffic volumes, combined with the sharp curves on the road in the vicinity of Hoover Dam, are potentially dangerous. A major accident has been avoided so far but it is only a matter of time before an incident causes millions of dollars in property damage to the dam and its facilities.

The clients for the project are US Bureau of Reclamation (responsible for the Hoover Dam), Arizona Department of Transportation, Federal Highway Administration (FHWA), National Park Service and the Nevada Department of Transportation.

Design for the project was carried out by HDR Inc, Sverdrup Civil Inc and TY Lin International. Environmental impact studies were carried out by CH2M HILL. The Federal Highway Administration has received Federal and State (Nevada and Arizona) money to complete the design and construction of the project.

The bridge portion of the Hoover Dam Bypass project has been officially designated by the United States Congress as the 'Mike O’Callaghan – Pat Tillman Memorial Bridge'. The bridge's name honours two prominent local citizens.

THE ALTERNATIVE COLORADO RIVER CROSSING

The route of the road had to be changed and an alternate crossing of the river developed near the Hoover Dam. This new route would eliminate the problems with the existing roadway – sharp turns, narrow roadways, inadequate shoulders, poor sight distance and low travel speeds. To this end it was decided that a new crossing of the Colorado River had to be constructed in the vicinity of the Hoover Dam to improve the traffic conditions of this busy route.

The roadway is the primary route for commerce and travel between Phoenix and Las Vegas, with more than 17,000 vehicles using the highway each day. The accident rate in the bypass area is three times higher than the rest of US 93. The new Hoover Dam Bypass will include approximately 3.5 miles of new four-lane highway and a 1,900ft-long bridge over the Colorado River about 1,500ft south of the dam, which ties into existing US 93 on the east and west.

COLORADO RIVER BRIDGE CONSTRUCTION

The construction contract for the Colorado River Bridge was awarded to the joint venture partnership of Obayashi Corporation and PSM Construction USA Inc in October of 2004 for $114m. Construction began in early 2005 and is expected to be completed in 2008. When completed, the 2,000ft-long Colorado River Bridge will span the Black Canyon (about 1,600ft south of the Hoover Dam), connecting the Arizona and Nevada Approach highways nearly 900ft above the Colorado River.

By 2006 nearly $35m worth of construction had been completed. This included substructure excavation for the abutments, approach columns, and arch skewback footings, followed closely by the erection of the temporary cableway crane system that spans the canyon to deliver materials and equipment used in constructing the bridge.

In September 2006 the temporary highline crane system collapsed during a storm and is not expected to be back in action until late 2007. This has delayed the bridge portion of the bypass project for two years and it is not expected to be completed now until 2010.

Production work is occurring on a limited basis using conventional cranes to complete tasks unrelated to the highline.

In February 2007, additional heavy cranes became fully operational, which allowed significant production work to proceed in full force. This effort will mitigate the impacts of the lost highline until the tower cranes are
re-established. Meanwhile progress continued in the precast yard where crews were working to construct the precast segments of the bridge columns and the cast-in-place arch.

The Western Area Power Administration (WAPA), a partner with the Federal Highway Administration on the bypass has completed changes to its transmission system that were necessary to accommodate the bypass project.

These improvements were made in two phases and included replacing transmission towers and conductor that were installed in the late 1930s and removing a switchyard with 50-year-old breakers and switches. These state-of-the-art improvements will enhanced the overall reliability for electrical customers.

PHASE ONE – SUGARLOAF MOUNTAIN BRIDGE

Phase One of the bypass, the Sugarloaf Mountain Bridge, signified the end of construction on the Arizona Approach. The project involved building a connection between US 93 and the Colorado River Bridge. Major components of the $21.5m project include nearly two miles of four-lane roadway, a 900ft bridge on the east side of Sugarloaf Mountain, a new traffic interchange at US 93 and Kingman Wash Road, wildlife crossings, trail access parking, improved drainage and rock staining.

The joint venture contractor, RE Monks Construction and Vastco Inc, were responsible for construction activities on the Arizona Approach. The project was completed on time by 2004.

PHASE TWO OF THE BYPASS – NEVADA APPROACH

Phase two of the bypass, the Nevada Approach, was awarded to Edward Kraemer & Sons Inc. This $30.1m roadway improvement project running from Nevada US 93 to the new Colorado River Bridge crossing was completed nearly two months ahead of schedule in 2005 (construction of this had started in October 2003).

The contractor constructed 2.11 miles of new four-lane highway alignment including six new bridges, a new traffic interchange at US 93 near the Hacienda Casino, retaining walls, wildlife crossings, and a 1.6-mile extension of the River Mountain River Loop hiking trail. To accomplish this feat, the contractor moved over 1.5 million squeare yards of blasted rock material, placed 2.8 million pounds of reinforcing steel, and poured over 12,000yd³ of structural concrete.

HOOVER DAM BYPASS PROJECT – PHASE FOUR

Next for the bypass project will be the contracting of the phase four project, scheduled for early 2008. This phase will include asphalt paving the entire four mile alignment from Nevada to Arizona, including constructing barrier railing, signage, lighting and striping.

HIGHLINE SYSTEM

The highline system is a critical part of the contractors’ operations because it allows materials to be delivered out over the canyon while work is underway on the 1,900ft-long Colorado River Bridge. Two tower cranes are built on opposite sides of the canyon, forming dual highlines. Once the highlines are erected, the entire length of the bridge becomes accessible to the crane hook for delivery of materials used in both foundation structures and the main arch crossing.

The bridge portion of the Hoover Dam Bypass project was delayed significantly when the two highline tower cranes toppled unexpectedly in 2006. They must now be redesigned and rebuilt before final construction of the arch portion of the bridge can proceed. Wind speeds of up to 55mph were recorded at the site prior to the contractors’ reconditioned south tower failure.

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