Interstate I-91 bridge: Longest span in Vermont

by Joe Parzych

Once the remaining span of the rusted old twin I-91 steel truss bridges built in 1960 is demolished, a new steel-reinforced concrete four lane bridge will hold the title of Longest Span in Vermont. The three span 1,036-foot arching steel reinforced concrete cantilever bridge was designed by Pennsylvania’s FIGG Bridge Engineers.

Begun in May of 2013, the bridge has a completion date of spring 2017, according to Project Manager Caleb J. Linn, P.E. of PCL Civil Constructors, builders of the bridge. The four-lane bridge will carry both north and southbound lanes of Interstate 91 traffic 100 feet above the West River.

Curving cathedral piers on either side of the river support the main 515-foot span and feature stone-formed concrete facing that looks convincingly like mortared native stonework. The cantilevered box beam bridge spans the West River as well as Route 30 (W. River Rd) that runs along the river. Eight shafts, drilled to 50 feet in depth, down to bedrock, on pier 1 on the north side and a depth of 80 feet on pier 2, which is on the south side, support the bridge piers.

The shafts are 5.5 feet in diameter. They are filled with concrete surrounding rebar cages of twenty eight #18 rebars in each shaft tied with #5 spiral reinforcement inserted inside the drilled shafts. The bridge construction builds itself forward in 16-foot increments with very little falsework. The crew incorporates a JLG Ultra Boom manlift to hoist cement finisher Craig Davis aloft in order to plug the rat holes in the box beam of the bridge overhead.

Designed by FIGG Bridge Engineers of Exton, PA, the bridge has been dubbed “A Bridge to Nature”.

The base of both piers will contain viewing platforms – with railings – that blend with the natural surroundings to enable hikers, pedestrians, and visitors to admire the work of engineering and artistry of the unique bridge. The popular West River hiking trail runs along the West River near the northerly bridge pier. When viewed from below, the bridge will appear to be colored blue like the sky.

In 1960, during the original construction of I-91, the Perini Corporation built the twin steel truss bridges. The spans measured 1,016 feet in length.

Work began on the new bridges, in the fall of 2013 when PCL diverted all I-91 traffic onto one span of the old twin steel truss bridges. In 2014, the other steel deck truss bridge was demolished to make way for the new span.

Once the new bridge is operational, it will carry four lanes of traffic, and the old steel truss bridge now carrying traffic will be demolished.

A smaller bridge designated as “Bridge 8 over Dummerston Road”, with a single 85-foot span has been under construction simultaneously during this project. Sub-contractors Bazin Brothers Trucking and Construction Co. of Westminster, VT are an active and effective cog in this project. For bridge 8, FIGG Bridge Engineers specified NEXT Beams, which stands for Northeast Extreme Tee, (NEXT) developed by the Precast Concrete Institute (PCI). Pre-stressed steel cables cast in the beams give them unsurpassed strength. They have been successfully used on other projects throughout Vermont. A reinforced concrete deck was poured atop the 13 NEXT beams.

A team of 55-ton Grove & LinkBelt hydraulic cranes lifted the NEXT beams into place during construction of the smaller bridge, which is located just south of the concrete span on I-91.

Bazin Brothers Trucking and Construction has also taken part in the construction of the larger bridge as well as the approaches for both spans.

PCL Civil Constructors, Inc. are part of the PCL family of companies, a group of independent construction companies in Canada, United States, Australia, and the Caribbean engaged in a variety of building and civil construction projects.