The ABCs of Rebuilding the Bath Viaduct
The use of Accelerated Bridge Construction (ABC) techniques is speeding the replacement of the 60-year-old Bath Viaduct, which carries U.S. Route 1 over local streets and railroad lines, and also serves as the western approach to the Sagadahoc Bridge over the Kennebec River.
Reed & Reed has a $13.7 million contract with the Maine Department of Transportation (MaineDOT) to remove and replace the elevated quarter-mile roadway - and must do so in about one-third of the time it took to build the concrete and steel structure in the late 1950s. The original project was given 720 days to complete, but Reed & Reed has only 220 days to replace the old viaduct, including not only the demolition of 19 concrete piers and 20 spans of concrete and steel superstructure, but building the entire new viaduct.
The new quarter-mile structure has 20 spans of NEXT Beam superstructure supported by 19 hammerhead piers. It is being built in the footprint of the old viaduct, in a path that parallels frontage roads, Leeman Highway and Commercial Street, and is close to downtown Bath. It is also near entrance roads to Bath Iron Works where hundreds of workers are currently building the latest class of U.S. Navy destroyers. Such factors create significant traffic control requirements and other complex challenges.
To counter these issues and expedite the job, the project team of MaineDOT, Reed & Reed and designers VHB is employing ABC technologies and procedures. These have eased traffic impacts, improved work-zone safety for the public, and are expected to significantly reduce total project delivery time.
Among the ABC technologies utilized for the Bath Viaduct are prefabricated bridge elements and systems (PBES). Use of these elements has slashed the onsite construction time that would have been required to build similar structural components using conventional construction methods. And to further hasten construction, the project team has combined PBES and "Fast Track Contracting" methods with large incentive/disincentive clauses, and requirements for nighttime or off-peak hour timeframes that limit traffic impacts.
A Multi-Phase Project
Reed & Reed was awarded the project contract on March 16, 2016, and shortly thereafter began the first phase of three construction phases. Phase I included installing drainage on the frontage roads, replacement of a railroad crossing at the intersection of the frontage roads with a local street (Washington Street), and modifications to Abutment No. 1 on the western end of the project.
Phase II consists of demolishing the existing viaduct and building the new one. For this phase, MaineDOT allowed the viaduct to be closed to Route 1 thru-traffic from October 18, 2016 to May 25, 2017. Traffic has been detoured during this period to the frontage roads below the viaduct and other local streets.
Demolishing the existing 1,300-foot viaduct while having to maintain at least two lanes of traffic on the detours has been the most difficult challenge of the project, according to Ted Clark, Reed & Reed Project Manager.
"We had to take down 19 piers and 20 spans of viaduct, including 12 spans of concrete Tee Beam and 8 spans of concrete deck on steel beam. Demolition debris amounted to approximately 2,050 cubic yards of concrete superstructure, 710 cubic yards of concrete pier shafts, and 240 tons of structural steel beams. And we did it in five weeks," Clark said.
During this period, Reed & Reed employed two shifts of workers at night for demolition operations, and one shift during the day to clean up and haul the debris to approved recycling centers. They razed the old viaduct using a 518 Link Belt Crane with a wrecking ball, a Caterpillar 349 Excavator with a Gorilla GSX 180 Hydraulic Breaker, a Caterpillar 330 Excavator with an Allied Rammer 3288 Hydraulic Breaker, Kubota KX121-3 Excavator with a Caterpillar 450 Breaker, and various dump trucks, loaders and boom lifts.
Project Manager Clark outlined the carefully orchestrated "˜round the clock' activities to remove the elevated structure:
"First the crews installed wood shielding over the traffic spans and railroad span. Next they saw cut the concrete deck on the steel-beam supported spans, and also saw cut spiral shear connectors, then they removed the superstructures," Clark explained.
"Similarly, they saw cut the Tee Beam superstructures and removed them," he said.
In another timesaving ABC application, existing footings were salvaged in place and modified to support new piers. The contractor employed Caterpillar 330 and Kubota excavators outfitted with hydraulic breakers, and manually operated jack hammers, to remove pier shafts down to the top of their footings. Then a new 21-inch deep transition footing was formed and cast on top of the existing footing, with transition footing rebar doweled into existing footings.
After a transition footing is completed, a new cast-in-place pier shaft is constructed on top of the footing. Shafts are typically 6-foot 8-inches by 4-foot 6-inches, and vary in height from a few feet to approximately 19 feet.
When the concrete shaft has set and its form stripped, a precast concrete pier cap is delivered to the job site and erected on top of the shaft. The pier caps, measuring approximately 35-feet across the top and 6 feet at their greatest depth, are being prefabricated by Reed & Reed workers at the company's dockyard on the Woolwich side of the Kennebec River. The massive 60-ton caps are hauled by trucks to the jobsite as needed and erected by a 150-ton capacity 518 Link Belt crane.
The Use of NEXT Beams
The new superstructure consists of 80 precast concrete NEXT beams weighing 50 tons each. The NEXT Beam (Northeast Extreme Tee Beam) is a double-Tee design developed by northeast state departments of transportation, local fabricators and members of the Bridge Technical Committee of the Precast/Prestressed Concrete Institute Northeast. Its purpose is to promote uniformity among DOT's, engineers and industry, in planning, designing, fabricating, and constructing highway bridges that are in line with the Federal Highway Administration's philosophy of accelerated bridge construction. FHWA considers a bridge with a NEXT Beam superstructure to be a more cost-effective structure than a conventionally built bridge.
There are two basic designs, the NEXT D beam and the NEXT F Beam. The NEXT D Beam has an integral full-depth flange that acts as the structural bridge deck on which a membrane and a wearing surface such as asphalt pavement can be field-applied, enabling it to be ready for traffic almost immediately after the bridge is erected. This is the design utilized for the Bath Viaduct.
Manufactured by Canada-based Strescon, a PCI-certified producer, the NEXT Beams for the viaduct are each 8-feet 4-inches wide and are placed four to a span on the new piers. Most span lengths are roughly 60- to 70-feet, with those over the railroad crossing and Washington Street running about 75 feet.
At a staging area near the viaduct, NEXT beams are unloaded from Strescon delivery trucks by a 250-ton Manitowoc 999 Crane. Before beams are erected, forms and rebar for the deck curbs are installed on the two fascia beams. Weighing between 110,000 pounds and 145,000 pounds each, the beams are hoisted in place by two 150-ton Link Belt cranes. After the beams are in place on top of the piers, crews place concrete for the curbs.
The beams are spaced about 8 inches apart. Ordinarily, they would have to be spaced 24 inches apart if the closure gap is filled with ordinary concrete, but this project employs 20,000 psi Ultra-High-Performance Concrete for the closure, allowing a narrower gap - another ABC feature.
Beams are covered directly by High Performance Membrane that in turn is topped by a 3-inch wearing course of bituminous concrete. The viaduct rail is steel rail, similar to that of the Sagadahoc Bridge.
The new viaduct must be open to traffic by May 25 and the project complete by June 30.
Key personnel for the Bath Viaduct include, for MaineDOT, Glen Philbrook, Resident Engineer; and for Reed & Reed, Ted Clark, Project Manager, and Thomas Reed, James Whorff and Gardner Parker, Project Superintendents.