Crews Install I-15 Accelerated Bridge Construction Project in 57 hours

In late May, Flatiron crews completed the company’s second accelerated bridge construction project, the Interstate 15 Manderfield Bridges. The project is on I-15 in central Utah, just north of Beaver.

Crews built two new bridges on either side of the existing bridges on temporary falsework over a period of three months, and abutments were also built under the existing bridges. Crews were given a 67-hour window to move traffic to one bridge, demolish the other, slide the new bridge into place, and complete grading and paving. The same process was followed for the second bridge within the same time window. Despite some extra time spent over-excavating unforeseen soft soils, crews finished in just under 57 hours—leaving about ten hours to spare—a huge feat.

“We came up with multiple schedules, including best- and worst- case scenarios,” said project manager Chris Mari. “Each schedule allowed for asphalt paving during the required temperatures.”

The project was Flatiron’s second using accelerated bridge construction techniques. Flatiron’s first ABC project, the Interstate 80 bridges over the Weber River in Echo Junction, Utah, followed a similar construction model, but with a few key differences. First, on this project, both bridges were moved in one window, which complicated the operation.

“This was challenging because we had to incorporate a traffic switch between the two bridge moves,” said Chris. “We had to maintain one lane of traffic on I-15 at all times, which meant two crossovers north of the bridges, and two south.”

Second, the Manderfield Bridges were built with the approach slabs attached, instead of using prefabricated slabs installed after the move. This meant a bigger bridge and more falsework during construction.

Another key difference was how the bridge was moved. Crews jacked up the bridge shortly before the operation, installed slide tracks, and hooked up 75 megaton hydraulic rams to the bridge. The rams then pushed the 700-ton bridge 60 feet to its final position.

The I-15 corridor is the major north-south highway through Utah, and connects the state to Las Vegas. Before construction, the Manderfield Bridges were in need of repair—the crew had to install temporary shoring to help support the bridges before other work began.

Owner Utah Department of Transportation calls ABC construction “the future of bridge construction in Utah.” They have implemented ABC techniques on a number of projects across the state because of the decreased impacts to the traveling public, increased quality, and increased safety the technique affords.

The project originally used hybrid composite beams, but the Utah Department of Transportation changed these to traditional precast concrete girders with precast concrete deck panels. This accelerated the project even more, but required almost a complete redesign of the bridge structures.

With the bridge move complete, crews wrapped up remaining work on the project in June.