Engineering and Safety Concerns have slowed development on the $15 billion Third Harbor Tunnel project
Engineering and safety concerns threaten to slow the surface development that will cap Boston's 15-year, $15 billion Central Artery/Third Harbor Tunnel project.
The Rose Fitzgerald Kennedy Greenway, the 27-acre crescent freed by the Big Dig with the removal of the elevated portion of Interstate 93, is zoned for parks, civic structures, and private development. But the complex engineering required to build over the tunnel is a major hurdle, particularly in the aftermath of July’s ceiling collapse in the Interstate 90 connector tunnel. Repair work, an engineering review of the Big Dig tunnels, and a reassessment of the Greenway could lead to further changes and delays.
Safety concerns, and politics, delayed the development agreement for the first major Greenway project, the Daniel Libeskind–designed New Center for Arts and Culture.
With the development agreement in hand, the developer would need six months to assess “all the things necessary to construct our building on that site,” says New Center chairman, developer Ronald Druker. “We don’t know what we're building on.”
Building on top of such extensive and varied underground structures will test designers and puts the onus on Big Dig officials to relay mountains of engineering data to developers.
To support aboveground structures, tunnels need an additional load capacity of about 150 pounds per square foot per floor, plus bracing for wind and seismic loads, according to James Lambrechts, professor of civil engineering at Wentworth Institute of Technology in Boston. As-built drawings, concrete core samples, and ultrasonic readings can provide critical information like the spacing and size of rebar, he adds.
"We've never built over anything that complex," says architect Moshe Safdie, whose firm is handling the $90 million Boston Museum project tentatively slated to open in 2012. "The existing [tunnel] structure has been designed to take certain loads and there are two major exits right under our building."
The $4.5 million Harbor Islands Gateway Pavilion, which is expected to open in 2009, has a proposed grade just three feet above the Central Artery tunnel, according to designer Stephen Yablon. "We proposed a lightweight glass box for an even distribution of the load and explored a waffle slab," he says. "We're going to do some as-built probes. We have all the construction documents, but was it actually built at that height?"
This summer, Governor Mitt Romney appointed a new chairman of the Massachusetts Turnpike Authority, which oversees the Big Dig and controls the Greenway real estate. The move effectively realigned the agency with the Massachusetts Highway Department, which as of press time, was still grappling with tunnel closures and repairs and had yet to full address the engineering of aboveground projects, according to spokesman Jon Carlisle. Government officials and developers estimate that it will be another 15 years or more before the reconfiguration of the waterfront district is complete.