A precast concrete tunnel keeps workers safe, modernizes the Maine Turnpike.
By Matt Werner
Cutting along the coast of Maine, Interstate 95 is a main thruway for the state, well-traveled by residents and tourists. In fact, the Maine Turnpike bills itself as New England’s original superhighway and carries millions of drivers every year. The tollway was so revolutionary when it first opened in 1947 that it was even designated as a National Historic Civil Engineering Landmark in 1999.
But times have changed. Fast forward to today and more cars are on the road than ever. Fewer cars are stopping at a toll plaza to drop in money thanks to technological advances that allow cars to pass through an electronic toll booth at highway speeds.
Therefore, getting workers to their tollbooths safely has become a bigger challenge in recent years. And with lots of highly sensitive information being transmitted between the car and tolls, keeping that information secure is vital as well.
Upgrading technology, safety
To solve these issues the Maine Turnpike Authority is wrapping up a 7-year, $125 million project to upgrade its tolling facilities as many are outdated and cannot accommodate highway-speed tolling. The newer facilities are designed to be more effective, cheaper to operate and easier to maintain.
One plaza, along Interstates 95 and 295 just outside the city of Portland, was in desperate need of renovation. The Exit 44 Open Road Tolling (ORT) Project included replacing the toll plaza with a new eight-lane tolling plaza that was more conducive for ORT, constructing an administration building and numerous other highway improvements to improve traffic conditions in the area.
Erin Courtney, Maine Turnpike Authority’s public outreach and marketing manager, said the Exit 44 plaza was one of the last to be converted due to the complexity of the project. The toll plaza also had to be moved from its previous location.
With an administration building on one side of the highway, the problem became how to get workers to their stations safely as well as ensuring the electronics and utility lines were protected from Maine’s harsh winters. Luckily, the solution came in the form of precast concrete.
High design criteria
Since the purpose of the tunnel was specific, there were a lot of unique requirements for the tunnel.
“The bearing surface of the structure needed to be large due to poor soil conditions,” said Brian Holmes, project manager with Reed & Reed. “The turnpike also had a long lifespan requirement that they wanted the tunnel to be designed for without any water infiltration. They had pretty high design criteria.”
Henniker, N.H.-based Michie Corporation provided the 200-foot-long tunnel for the project plus other precast items like highway barrier, mechanical access structures, light pole bases and more.
“We have done numerous pedestrian and animal crossings of similar dimensions, but shorter overall lengths,” explained Chad Poland, engineering manager for Michie. “What really made this structure unique was the length as well as the additional structures attached to the tunnel that needed to maintain a completely waterproof connection.”
Poland said they had to get creative with the connections to ensure the tunnel was watertight, since groundwater was a serious concern.
“The tunnel was designed with a special watertight ring system and a sloped floor with a drainage trough cast in one side,” he noted. “In the event water or condensation does build up, it would have a conduit to drain freely to an interior sump pump system. The contractor also installed an exterior membrane to maintain a dry environment throughout the system, which was critical due to the extensive utilities running throughout the tunnel.”
With short construction seasons and trying to minimize traffic disruptions, the project was done in phases. This turned up the pressure for Michie. Poland estimated they were casting tunnel sections within six weeks of signing the contract.
Meeting demands and expectations
Poland said once they started casting the 29 10-foot-wide-by-8-foot-tall tunnel sections, they had few production challenges. The median barriers were some of the largest they had ever produced ranging from the standard 48 inches tall all the way up to 66 inches, which required Michie to modify their forms to get to the needed height.
“The structural and geometric design of the staircase component was particularly challenging because there were grade beams in predetermined locations that had to be incorporated in the precast layout,” Poland said. “This led to the unique sloped shape of the staircase structure.”
Delivery also had to be streamlined and coordinated in order to meet the construction schedule, but Michie was on-site to ensure everything went smoothly. Michie’s standard practice for large projects is to send a field assistance crew to help with installation.
“It was extremely helpful having their assistance as well as some of their specialty rigging and tooling,” Holmes said. “We had not installed precast tunnel or culverts to this extent so their assistance was extremely helpful for what was a smooth installation.”
From meeting the tight timeline to the challenging design criteria, all the benefits of precast were on display for the project.
“The precast tunnels are the best alternative because they were faster and easier from a construction standpoint, had less of an impact on traffic and were less expensive,” Courtney noted. “The precast tunnels also provided a better product because instead of being exposed, they were cured under controlled conditions.”
Holmes echoed those points, adding additional benefits to working with precast.
“Using precast was very user friendly,” he explained. “We could unload it off the truck and set it right into its final position. We didn’t need any double handling or anything like that.”
Under budget, ahead of schedule
From the precaster to the project owner, all parties consider the project a success. Holmes said Michie was great to work with given how extensive the review process was. He said the fabrication was done to meet their schedule, and that they were very happy with the product.
The Maine Turnpike Authority was equally pleased with the project.
“The whole project went very smoothly,” Courtney noted. “In fact, the project just wrapped up this month and was finished under budget and a month ahead of schedule.”
For Michie, hearing that is what mattered most.
“We were happy with the way everything progressed, but more importantly the contractor and owner were happy,” Poland explained. “This was our first time working with Reed & Reed, and since this project, we’ve worked on several other projects with them. We’ve begun to developed a very positive, hopefully long-term, working relationship with them, which is always our goal.”
Matt Werner is the managing editor of Precast Solutions magazine and is NPCA’s communication manager.