Better Gardiner: Two Deteriorating Bridges Rapidly Replaced
(Image Credit – MaineImaging.com)
Gardiner, Maine, is a small city (population less than 6,000) in Kennebec County. Founded in 1754 on the banks of the Kennebec River near the furthest point upriver that deep-draft vessels can reach, it’s a nationally accredited Main Street America community, and was initially famous for cutting, warehousing and shipping pristine Kennebec ice throughout the United States and internationally. A perfect storm of quaint, in other words, and the quaint extends to the handsome and mostly brick historic district. Less fortunately, in 2019, “quaint” would have been a charitable word for the two bridges over Cobbosseecontee Stream (the word Cobbosseecontee translates to “plenty of sturgeon” in Wabanaki) that provided access to Gardiner’s historic downtown.
The Maine Avenue Bridge was a single-span, 85-year-old concrete t-beam bridge on dry-laid granite abutments carrying Route 24 over Cobbosseecontee Stream. It was severely deteriorated and load-rated less than 1.0 by MaineDOT, a low rating meaning the bridge possibly wasn’t equal to some traffic loads. It also was scour critical and of insufficient span for the stream width.
The Bridge Street Bridge, which carries Route 201 over the Cobbosseecontee Stream and Arcade Street, was a four-span 102-year-old concrete t-beam structure that sat in a nest of buildings and utilities in downtown Gardiner. Because of its age, it was severely deteriorated, and the width of the bridge was too narrow to support modern traffic and parking needs.
Adjoining intersections were cramped, inconvenient and a little unsafe by modern standards; and there was no real accommodation for foot traffic. Basically, both bridges dearly needed rehabilitation and/or replacement, and everyone involved at every level, from local to state, agreed with this. But that didn’t mean the solution was straightforward or easy; beyond the obvious need to preserve Gardiner’s historic character, there were many and severe constraints. Starting in 2015, Stantec Consulting Services Inc. began design work on the “Gardiner Downtown Bridges and Trail” project, and had this to say about the challenges:
“Gardiner is a busy, historic downtown area full of residents, visitors, commuters, commercial buildings, parking and utilities. Completing two bridge replacements, two intersection updates and a new trail without negatively impacting the city was the main challenge. The Bridge Street Bridge site provided the most challenges, with two businesses attached to the bridge, a major telecommunications duct bank crossing the bridge, remnants of an historic dam on the northwest corner, a historic building at the southwest corner, and a building with a masonry foundation at the southeast corner. The Cobbosseecontee Stream is also an endangered species habitat for Atlantic Salmon and Sturgeon underneath the Maine Avenue Bridge, so there was a restrictive in-water work window. There were also contaminated soils which complicated the foundations and general excavations.”
Visible wear at Bridge Street (Top) and Maine Street (Bottom) bridges demonstrates the need for replacement.
But big challenges, when met, yield big rewards:
“The new Bridge Street and Maine Avenue bridges replaced obsolete, aging (over 100 and 85 years old, respectively) infrastructure using ABC (accelerated bridge construction) techniques, resulting in both immediate and lasting benefits. Immediate benefits included limiting construction impacts to the traveling public, which reduced user costs and allowed businesses to function with minimal interruption. The new bridges are also significantly safer for heavy loads than their deteriorating predecessors. Replacing the bridges with sustainable stainless-steel-reinforced structures also limits future rehabilitation and maintenance, reducing construction and environmental impacts.”
Stantec led project design and provided construction support for the Maine Department of Transportation (MaineDOT) and City of Gardiner project, which eventually included the replacement of the two century-old bridges, the addition of a multi-use trail and its bridge, and updates to two signalized intersections. Stantec also shepherded the lengthy public-involvement process and provided endangered-species permitting and construction support. Haley & Aldrich was the geotechnical engineering consultant to Stantec and provided contaminated soils consultation to MaineDOT. Terra Magna Services Inc. (TMSI) provided traffic-signal design, intersection design, maintenance of traffic design support and utility coordination. The utility coordination was especially tricky and involved relocation of Consolidated Communications’ main service connection to central Maine, repositioning of aerial utilities to facilitate construction, and relocating gas and water mains.
Construction was completed in August 2021, and, in 2022, all three firms were recognized with the Grand Conceptor Award—the top prize—by the American Council of Engineering Companies (ACEC) of Maine as part of its annual Engineering Excellence Awards program (italicized quote blocks in this article are taken from Stantec’s award application).
One Project, Three Bridges, A Concerned Public
Bridge Street Bridge is about a quarter mile from Maine Avenue Bridge, and simultaneous work on these, plus design and construction of the Cobbossee Trail Multi-Use Bridge—built adjacent to the Maine Avenue Bridge—made for a lot of construction work in a relatively small space and timeframe. Why was this a good idea?
“We had multiple projects that came together, and they really could have hammered Gardiner if they were done separately or if there wasn’t a high level of communication during design and construction,” explains Wayne Frankhauser, bridge program manager for the Maine Department of Transportation. “It turned out for the better, but the people of Gardiner—and everyone else involved—wanted to make sure it was for the better, since it was a pretty radical change. There was a lot of concern about how this would impact Gardiner as a whole.”
In addition to preserving community character, cost-effectiveness and impact reduction were factors. “We often look to bundle projects that are close by to get economy of scale with the contract and contractors, and that’s exactly what we did here,” adds Frankhauser. “And it helped in the long run to coordinate this—separate distinct projects over multiple years would’ve been an even bigger challenge and would’ve really dragged on the impacts to Gardiner.”
According to Stantec Principal Timothy (Tim) Merritt, P.E., “This way we’re only impacting the public once—get in and get out. Aside from that, there’s certainly some economy and efficiency in doing it this way in terms of construction costs—just having one contractor come in and do all this work one time and then get out. It also allows for one public-involvement process—as opposed to a fragmented one—and one design. You have one consultant working on the whole project rather than three or four or staggered over five years.”
Public involvement was deemed so important on this project that Stantec worked with a subcontractor, Pamela Plumb & Associates, to coordinate a lengthy process lasting several years. “We met with Gardiner locals 18 times,” says Merritt. “The two common themes we heard back from that process were everyone involved felt like they had a voice during the design, and the project delivered on what they wanted to see in a project; and it went as planned.”
One unusual constraint on design was historic businesses with entrances actually on the bridge:
“The existing Bridge Street Bridge, originally built around 1917, was in a nest of commercial buildings and utilities, making any construction, especially ABC, very difficult. At the time of design, it was the only bridge in Maine with businesses directly attached to it. One of the businesses, the A1 Diner, is in an old train diner car that is eligible for the National Register of Historic Places and was attached to the first span of the bridge. The other business, Dennis’ Pizza, was at the second pier, which limited options for span configurations because of the potential for differential movement between the bridge span and the building. The owner of Dennis’ Pizza chose to relocate with assistance from MaineDOT, and the building was demolished, making a single-span bridge and slide-in construction possible. Stantec performed a hydraulics analysis to show that removing the building and filling in the first span would not impact FEMA flood mapping. A single, long span replaced the remaining three spans. Test pits performed during the design phase identified that several of the original A1 Diner foundations consisted of stacked granite blocks that interfered with construction of the new micropile-supported approach retaining wall. Therefore, the A1 Diner was temporarily supported during construction while foundations were replaced. This protected the original structure and allowed the business to stay in service throughout most of the construction period.”
Businesses directly attached to a bridge were unique in Maine, and a major factor in Gardiner’s character. “Their primary doors, their main entrances actually were attached to the bridge sidewalk,” says Merritt. “So when you walked out of those businesses, you were walking right out onto the bridge sidewalk, which you don’t see very often. You might see that in a big urban area like New York or Chicago, but for a more-typical downtown commercial area, it’s unique. They were very concerned at first—like anybody would be as a business owner—with the potential impacts. But I think they all recognized that because of the public-involvement process, there was an opportunity for them to get involved and be heard.”
The preservation and rehabilitation of existing unique and historic buildings was one of the most visible and important features of Stantec’s design, and no doubt a major factor in winning the Grand Conceptor Award.
Small Town, Big Innovation
Aside from preserving Gardiner’s historic character, the prime consideration for Stantec designers was to mitigate impact on the small downtown and its businesses—user costs for closures were estimated to be $12,000/day. And the best way to do that was to minimize road closures and sharply limit and stagger actual time windows when bridges were out of service. To limit impacts to the city and public, the Maine Avenue Bridge was designed to be replaced with a 15-day full road closure, and the Bridge Street Bridge to be replaced with a 30-day full road closure. Off-peak single lane closures and night work were used for pre- and post-closure work. And closures were staggered in time. “The first closure was the Maine Avenue Bridge in October of 2019, and actually took just 12 days,” notes Merritt. “And the Bridge Street full closure was mid-October to mid-November of 2020.”
Two important innovations were employed by Stantec in Gardiner: an early and total commitment to 1) 3D CAD modeling for bridge information modeling (BrIM) and 2) accelerated bridge construction (ABC) methods, including a lateral slide-in for the Bridge Street Bridge, the larger and older of the two bridges. Use of BrIM on a project of this scale was a first for Stantec in Maine, and they have continued the technique on subsequent projects. And this was only the second slide-in bridge built in Maine at the time of construction as well as the first to slide over an active utility that was later raised into a utility bay under the reopened bridge.
Here’s how Stantec describes BrIM on this project:
“One solution to the highly constrained Bridge Street site was to build a 3D model of the existing and proposed conditions. This model was live referenced in the 2D contract plans, so any changes to the 3D model were carried through to the plans. This significantly simplified a complex set of drawings and allowed us to identify several conflicts between the existing and proposed structures and utilities during the early design. The model was also useful for visualizing the site during meetings with the client and stakeholders.”
Primary reasons for using BrIM were to facilitate the slide-in as well as clash detection. “It’s why we elected to model this in 3D—the Bridge Street portion at least,” explains Merritt. “There were a lot of existing utilities with potential interferences. We also had A1 Diner to contend with and figure out how to maintain access to the business during most of the construction, and what was their interface going to be with the new bridge. The biggest benefit in the 3D modeling was figuring out potential interferences and how to deal with those and get them dealt with before construction started.”
Thanks to good design and BrIM, the actual slide-in deck construction and installation took place without any hiccups. “The contractor devised a braced frame that didn’t require us to drive piles in the ground near the A1 Diner,” explains Merritt. “And then they had steel rails that had rollers on top of them—what we call Hilman Rollers—a proprietary roller system with very low friction. It was 700 tons, which is a lot of weight, but surprisingly it doesn’t take a huge amount of force to move that on these roller systems. A hydraulic jack is used and rather than pushing the bridge sideways, it’s actually pulling it sideways.
“It’s an incremental process that took seven and a half hours,” he adds. “You move it a foot or so, and then you have to stop and reset the jacks, and then you do the whole thing again, and geometry control is a very important aspect of a slide-in—you need guides in place to keep the bridge where it needs to be and check that along the way. And the contractor was very successful in all of that.”
3D CAD and the lateral slide-in were the most visible innovations in Gardiner, but Stantec extended classy engineering and innovation to every aspect of design. For example, the project also demonstrated the practical application of micropiles in bridge construction—because of the deteriorated condition of and low headroom beneath the existing bridge, traditional H-piles would have required demolition of the existing bridge. Using micropiles, which could be installed with smaller machinery, facilitated building the new substructure before any road closures needed to occur and allowed businesses to stay open before the full closure.
A Great Success
Being recognized with the Grand Conceptor Award was important to Stantec and all stakeholders, but the feedback from Gardiner citizens was perhaps even more satisfying. “There’s a letter of support from the city actually,” says Merritt. “And the mayor’s been pretty verbal about how well the project went and provided a lot of gratitude to the project team as a whole.”
Frankhauser adds, “I’ve only heard positive comments about how pleased everyone was with the limited impacts as well as keeping everybody informed.”
In paying close attention to community needs and applying excellent, innovative engineering in a small space, Stantec and subcontractors really went above and beyond to preserve and enhance a quaint and historic American downtown.