A few years ago, construction teams could replace a big, steel and concrete bridge in 61 months. With the remarkable advancement of new technologies, Rhode Island and other states have replaced bridges in 61 days. But 61 hours?
The Vermont Agency of Transportation (VTrans) replaced an Interstate 91 bridge in White River Junction in just one weekend, using an innovative technique to minimize the impact on drivers.
“We have done this kind of work on smaller scales, but not on this scale,” said Eric Filkhorn, communications specialist at VTrans.
The bridge is one of two Hartford bridges, side by side. VTrans will be replacing the parallel bridge in a similar, whirlwind amount of time.
The slide-in construction method replaced the northbound bridge in a mere three days with a Florida crew, general contractors well versed in this latest technology, working around the clock. The bridge on Interstate 91 over U.S. Route 5 at exit 11 closed on a Friday at 6 p.m. Hydraulic jacks slid the bridge over 18 in. (45.72 cm) at a time. The new bridge opened on Monday morning.
Agency Secretary Sue Minter said the technique substantially reduces the amount of inconvenience to travelers by limiting closure.
The $11.1 million project was mostly covered by federal funding. Vermont will pay 5 percent of the cost.
One Short Season
The bridge replacement was fast-tracked through VTrans’ Accelerated Bridge Program (ABP). Typically, fast track bridge projects use innovative techniques and are completed in approximately half the time it would take by conventional construction, often in just one construction season. The culmination of that season was late August and early September.
The construction method known as a lateral slide was used to replace the Interstate 91 Hartford bridge for the first time in Vermont. The slide took place over a weekend, minimizing road closures on Interstate 91 and inconvenience to travelers. U.S. Route 5 remained open while the two bridge was moved into place.
“How it works, there are two interstate bridges, side by side, with 40 ft. between them,” said Kristen Higgins, senior project manager. “We completed the new bridge construction on temporary supports adjacent to the bridges. We also constructed the supports in advance that the bridges will sit on.”
Higgins said the new bridges, comprised of steel beams and concrete rail construction, with concrete decks, are then slid over in small increments over the new supports over slide beams.
Higgins explained how these projects would typically be completed in the past.
“This project would have been crossovers and working on one bridge at a time over two construction seasons, then another season and then again,” said Higgins. “The reason we didn’t want to do this here is that it is a major interchange of two highways. There is a significant commuter issue. So putting in a crossover wasn’t a good idea. Highway 5 is a major route and traffic would have been affected for two seasons.
“So, we tackle this in one construction season. There are no dangerous crossovers and two weekends of inconvenience of rerouting over the Interstate,” added Higgins. “Get on the ramp, get off the ramp.”
While VTrans looked at bids from various local and New England general contractors, Florida-based PCL Civil Constructors Inc. was chosen as the general contractor.
“PCL has experience with slide-in bridge construction and heavy lift,” said Higgins. “We procured them while in design phase to incorporate the means and methods into the plan. We do an RFP for a contractor with experience for this type of thing, then we evaluate based on the best experience.”
According to VTrans, this is how the lateral slide single-season construction works: The new bridges are one-span, allowing the new abutments to be built without affecting traffic flow on the highway.
Building a Foundation
In the spring of 2015, construction began on a new foundation, according to the VTrans Web site. Piers and abutments, otherwise known as a substructure, were built for each new bridge underneath the existing bridges. The new superstructure, consisting of the bridge deck and support beams for both bridges was constructed on temporary supports right next to the existing highway bridges.
Traffic along Interstate 91 over the existing bridges was able to flow as usual while construction went on underneath and next to the bridges. Travel lanes on U.S. Route 5 were reduced from three lanes to two, but traffic flowed in both directions throughout construction.
Moving the Bridge
The superstructures for each bridge were moved over one weekend at a time for each structure. One side of the highway was shut down and traffic was rerouted onto a detour to allow the bridge to be connected to its new foundation, while the other side of the highway remained open.
The foundation and deck of the old bridge were demolished. Hydraulic jacks were used to push or slide the bridge in place–thus the name “slide-in bridge construction.”
Once the new bridge was installed and related work was completed, the bridge was reopened to traffic. This process will be repeated for the second bridge on another weekend.
U.S. Route 5 remained open during the lateral slide and crucial traffic detours were set in place, which minimized the effect on commuters.
Representatives of VTrans said that replacing a bridge on a single weekend was “no problem,” although the project was delayed from an original date of Aug. 21 to Aug. 28.
For more information, visit www.vtrans.vermont.gov.
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