NO. 10 BRIDGE: Pier Construction

Dec. 2, 2022
Replacing U.S. 60 Pinto Creek Bridge in Tonto National Forest was no day in the park

The Pinto Creek Bridge on U.S. 60 in Arizona was structurally deficient and functionally obsolete.

In May, Ames Construction replaced it with a new, 695-foot-long structural steel bridge that rises from the canyon floor in Tonto National Forest, providing one 12-foot-wide lane for traffic in each direction and 10-foot-wide shoulders. The project team overcame numerous challenges to construct the bridge, which serves both the traveling public and commercial vehicles from nearby mines. 

Built adjacent to the existing historic bridge, the new bridge is supported by three sets of piers. At 138 feet, the tallest piers were constructed with a single continuous pour that required crew members to climb down into the formwork to ensure there were no voids in the concrete.  

During installation of the retaining wall foundations, it was determined that a modified system for subsurface support would be needed. ADOT and Wood Environment and Infrastructure Solutions, Inc., redesigned the foundation system, and the system was installed so work could continue.

The project made use of a micro-pile foundation system for several retaining wall structures that stood more than 30 feet. Micro-pile systems are not used as often as spread footings of drilled shafts. The design team developed standards and specifications that allowed the contractor to implement this system and provide a case study of using this technology and foundation system.

The design team utilized a bid alternative during the advertisement phase, which allowed the contractor flexibility to determine which foundation system—drilled shaft or spread footing—was most economical at a particular pier location.  

The site access road to the bottom of the canyon required modifications to better fit the natural terrain, minimize impacts to the surrounding National Forest lands, and facilitate access for the 400-ton crane needed to erect the new steel bridge girders. 

During bridge deck construction in 2021, a historic wildfire burned the project limits but luckily did not affect the new or existing bridges. Work was suspended for a short time to allow fire crews to control the fire. A month later, significant monsoon rainstorms caused major debris flows and flooding along U.S. 60. These floods washed out a portion of the access road in the canyon, requiring crews to perform additional maintenance and find workarounds to maintain the schedule.

On July 29, 2021, the Bloody Tanks Wash stream, located three miles east toward the town of Miami, overtopped its bank. U.S. 60 was closed and required immediate mitigation and repairs. Ames Construction, Capstone-Pinto Valley Mine and ADOT joined forces to rebuild the roadway within 72 hours. These events extended the project and required additional funds; however, the team worked well together and made the best decisions for quality and value of the project. 

Through all the project’s challenges, the team utilized ADOT’s Construction Project Partnership principles to identify and isolate the impacts and associated risks to the project as early as possible, working toward solutions to minimize impacts to the budget, schedule and the overall safety and success of the project. 

With clear, two-way communication, the team worked through turnover in personnel and COVID-19 challenges, utilizing virtual meetings when needed. Higher level managers on all sides allowed issues to be resolved at the lowest levels feasible. 

Field personnel of ADOT, Ames Construction and numerous subcontractors worked together diligently to protect the natural resources within and around the project, such as the endangered Arizona Hedgehog Cactus, the ephemeral Pinto Creek, and the surrounding Tonto National Forest lands.

Prior to construction, Arizona Hedgehog Cactus plants were transplanted from within the project footprint. They were cared for by the Arizona Desert Botanical Garden during construction, which included propagating new plants and harvesting seeds for storage. Following site restoration and seeding, the cacti were replanted within the project limits, helping to ensure the species’ survival. R&B

Project: U.S. 60 Pinto Creek Bridge

Location: Globe, Arizona

Owners: Arizona Department of Transportation

Designer: Arizona Department of Transportation

Contractor: Ames Construction, Inc.

Cost: $25,300,000

Length: 695 feet

Completion Date: May 2022

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