Friday, March 23, 2012

Trio of trusses

Written by 

Planning, coordination and structural engineering magic come together
on a project to replace three century-old bridges in Massachusetts.

Limited access is not a term used very often to describe the commuter rail situation surrounding Boston. While an active freight corridor can be found, Taunton, Fall River and New Bedford, Mass., are the only cities within 50 miles of Boston not served by commuter rail. To remedy this, Massachusetts has developed the South Coast Rail Project to restore commuter rail access to these cities and the first construction project to directly advance the South Coast Rail project was the replacement of three structurally deficient bridges in New Bedford.

Vanasse Hangen Brustlin, Inc., was contracted to perform transportation planning, engineering design and environmental and construction phase services for the South Coast Rail Project. According to Rick Carey, project manager at VHB, the New Bedford bridges play both a freight and commuter role in the region’s rail infrastructure.

“[The bridges] provide that piece of upgraded infrastructure that will serve freight right now and serve commuter rail in the future,” said Carey.

The bridges, located at Deane Street, Sawyer Street and Coggeshall Street, were each more than 100 years old and only allowed maximum freight speeds of five miles per hour due to their condition.

Carey said that an inspection of the bridges was needed prior to any freight being run over them because they were in such poor shape. The process was time consuming, especially since there was a dredging program in New Bedford Harbor where the dredging spoils were shipped via rail over the bridges.

While plans for replacement had been in the works for years, a $20 million TIGER grant awarded to Massachusetts in February 2010 sent planning into a frenzy and construction begin on the bridges in October of the same year.

“We had performed inspection on the bridges for the past 10 years so we knew they needed to be replaced,” said Carey. “One reason they could not be rehabbed beyond the condition is the clearance between the roadways below and the bottom of the bridges was deficient. We knew we had to lift these bridges up several feet in order to get a good clearance for vehicles.”

Construction challenges

Time turned out to be one of the largest challenges on the bridge project. The TIGER funding had a February 2012 completion date tied to it. Quick construction was needed and in order to meet the time constraints, the freight line was shut down.

“We determined that we needed to shut down the freight line for the construction period so that the contractor could perform the work unimpeded by maintaining freight traffic, which would have really extended the duration of the project,” said Carey. “There was a lot of coordination with the operating railroad and the public dredging project, which had to change their operation of how they shipped and stored that material because they didn’t have the railroad to use, which meant there was a lot of coordination between the freight operator, Army Corps of Engineers and the EPA. The other challenge was that we needed to close the roadways underneath the bridges for a time. There was a lot of coordination with the city police department, the school system and the Department of Public Works to make sure we were able to maintain traffic while these roads were closed in order for the contractor to have more flexibility to get the work done quickly.”

During construction, the city of New Bedford continued to express concern that shutting roadways down would wreck havoc on area traffic.

“Even though it was planned in the design process, once we were in construction, there was a higher level of concern and if the contractor wasn’t able to close these roadways down, it really would have delayed his production to get the bridges completed. What we did was work closely with the city’s traffic engineer to retime signals in the area of the project; we had police details in and around the project directing traffic. We all had a plan and implemented that plan and allowed the contractor to build these bridges quickly.”

Traffic also drove the sequencing and decision making of the project as the contractor could only close two of the three roadways affected by the project at a time. According to Carey, the contractor scheduled to perform the bridge work simultaneously whenever possible.

Carey said all the bridges were demolished at once and the contractor sequenced the construction of abutments in a continuous fashion to make sure all work was performed in an efficient manner. 

Innovative elements

In addition to the sequencing of construction, Carey notes that there were a few unique aspects of the bridge construction.
Between the three bridges, a total of 4,000 feet was elevated with retaining walls. Carey said that when the project first came together, it was unknown if those retaining walls, which were in bad shape, could be replaced and remain within budget.

“The contractor came back with an idea of installing precast walls, which speeded the construction and allowed for reduced cost,” said Carey. “Through a little creativity of using precast walls, we were able to construct all the walls and stay within budget.”
Another construction challenge that took some creative problem solving involved an existing wall that also acted as the back wall of a building.

“This building was part of the railway track walls, so we couldn’t demolish and replace that particular wall because we would have had to demolish the whole building. What we did was build a wall within a wall using the precast material. We maintained the existing wall and built a new retaining wall behind it, which would take the loads of the railroad and reduce the loads on the building. It took a lot of creative thinking, some structural engineering magic and the contractor made it happen without disturbing the existing building,” said Carey.

In November 2011, the New Bedford Bridge replacement was completed, four months ahead of schedule. The total cost of the project was $20.8 million. Carey said the majority of the funds came from the TIGER grant, while the state contributed additional funding to finish the retaining walls.

Upon completion, New Bedford Mayor Scott Lang said, “These three TIGER grant funded bridge projects advance New Bedford 100 years in rail capacity. The bridges will allow for appropriate speed freight and passenger traffic and will help spur economic development and smart growth on our waterfront and throughout our city.”

Carey believes the project’s success came from several factors including good planning, good people and coordination among all parties involved.  

“We had a good contractor, who worked with the MBTA, the city and us as a collaborative effort to make sure things moved quickly. With the addition of when the money was available for the retaining walls, there was a lot of design and review that had to happen during the construction process and had to happen quickly. There was a lot of good faith efforts from the state’s standpoint, from the contractor’s standpoint and from our standpoint to make sure we met the schedule and we actually beat it,” said Carey.
While Carey admits the project came with some very interesting engineering feats, such as building the wall within the wall and being able to find a solution for new retaining walls, the aspect of the project that stands out for him is the teamwork needed to complete it.

“Once the state received the TIGER funding, everything had to be in place and it was really a Herculean effort,” said Carey. “It’s probably one of the few times in my career where everything fell into place and everyone stepped up and out of their comfort zone of how things are typically done to make this project happen.”