How MaineDOT Replaced an Interstate Bridge In 60 Hours By Devan Eaton, PE, and Ben Walz, PE
As departments of transportation look to replace aging bridges in high-traffic areas, the use of accelerated bridge construction (ABC) is increasingly among the delivery options they consider. In addition to its growing track record of successful weekend completions, ABC has been shown to increase work zone safety and minimize delays for the traveling public. That was the case for Maine’s Veranda Street Bridge Replacement Project. The Veranda Street Bridge carries Interstate 295 over the two-lane di - vided Veranda Street in Portland, Maine. In 2017, an inspection found the 61-year-old bridge to be in satisfactory-to-poor condition and structurally deficient. As MaineDOT began the process of replacement, we sought a demolition and construction method that would minimize inconvenience to the approximately 54,000 motorists who use the bridge daily and the more than 15,000 motorists who travel Veranda Street daily. Our decision to demolish the existing bridge and deliver the new structure by accelerated bridge construction resulted in one of the largest, fastest ABC projects MaineDOT has undertaken. We began deconstruction on Friday, April 22, at 6:45 p.m., and 60 hours later, on Monday, April 25, at 6:52 a.m., the new bridge was in place, paved, striped, and opened to traffic. Cost-benefit analysis A cost-benefit analysis revealed accelerating construction of the $21.7 million project would: • Cut construction time by 50 percent, saving the public years of con - gestion and inconvenience • Reduce traffic impacts and travel delays by 80 percent • Improve the safety of workers and the public Further, we learned ABC would eliminate the need to construct a substantial and costly temporary bridge. The money we saved and the benefits we received by not constructing a temporary bridge helped to offset the cost of using ABC. Selecting partners with experience A proven strategy for mitigating risk is to contract with partners that have significant experience and a history of delivering success for our department. Plans called for replacing the existing three-span bridge with a low- maintenance, jointless, single-span structure, featuring wide shoulders for improved visibility and safety on I-295. Because the new bridge would be shorter, we planned to convert the remaining area underneath the existing structure into embankments prior to the roadway closure.
Photo: HNTB Corporation
To avoid post-construction settlement-related issues associated with the marine clay present at the project site, the new embankments were constructed using over 9,000 cubic yards of geofoam lightweight fill. Construction of a majority of the new embankments beneath the existing bridge in advance of the closure was critical to limiting the roadway closure to a single weekend. “We knew the closure duration needed to be minimized to the absolute greatest extent possible. Achieving that meant devising a solution that allowed the existing bridge foundations to remain in place while also maximizing the amount of embankment built prior to the road closure,” said Tim Cote, project manager for HNTB who provided structural and geotechnical, as well as highway and traffic engineering services for the bridge replacement. “At the same time, post-construction settle - ment needed to be within acceptable limits. It was a complex set of challenges, but the proposed lightweight fill design was critical to the successful outcome of the project.” To minimize disruption of traffic on I-295 and Veranda Street, the upper portion of the new northbound and southbound bridges were built on temporary abutments next to the existing bridge. At the same time, the new bridge abutments were built beneath the existing bridge. This ap - proach allowed traffic to proceed on each roadway with minimal inter - ruption. Once the preparatory work was complete, I-295 and Veranda Street were closed, crews lifted the new northbound and southbound bridges off their temporary supports, and “drove” each section into place using Self-Propelled Modular Transporters. The SPMTs’ built-in jacks then raised the decks 24 feet to a new, higher bridge clearance of 15 feet 6 inches. “We were able to bring the construction of the bridge decks down in elevation to 8 feet above the ground with the incorporation of Mam - moet’s MJS 300 Cradle System, integrated with SPMTs,” said Tom Senior, project superintendent for Cianbro. “This was the first time this system was used to move this type of structure. It afforded us the flexibility to raise both structures to final elevation and lower them into final position.” A need for closure Because safety is of the utmost importance to MaineDOT, we chose to fully close I-295 and Veranda Street while the existing bridge was
November 2022 csengineermag.com
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