BOSTON (AP) After months of internal debate, Big Dig officials have chosen what they said is the best fix for a faulty wall panel that sent water pouring into the new Interstate 93 tunnel last September, backing up traffic for miles.
To complete the fix, workers will leave an existing patch in place, add more grouting, cover the patch with a steel plate, and encase the entire wall panel in concrete.
The goal is to create a permanent watertight repair that will last as long as the original walls, according to Big Dig officials.
The contractor responsible for building the wall panel will pay for the repair, estimated at between $300,000 and $500,000, and will be held financially responsible if there are future problems, Big Dig officials said.
In an interview with the Boston Herald, Turnpike Chairman Matthew Amorello said he is talking privately with state officials about establishing an account to make Big Dig firms pay for future maintenance.
“An [account] that sets aside a dollar amount that would go back into the Turnpike Authority to pay for [faulty work] … is something we’re discussing weekly with the attorney general [Thomas F. Reilly],” Amorello said.
Project Manager Michael P. Lewis told The Boston Globe that the repair work will stretch into January, and require regular early morning closing of both the northbound and southbound I-93 tunnels. Since 2003, Big Dig officials have said the project mostly would be finished no later than September 2005.
Lewis also said the entrance ramp to the westbound Massachusetts Turnpike would not open until at least November of this year, and also will continue after September to construct some of the streets on the project’s surface, which surrounds the new Rose Kennedy Greenway.
In a letter dated June 27, federal Big Dig overseers from the Department of Transportation signed off on the proposed fix, citing safety concerns associated with other proposed repairs.
“We concur in your recommendation to pursue the fully redundant, concrete encased, structural steel wall option,” wrote Carl Gottschall, Big Dig project administration of the Transportation Department.
Big Dig officials had considered two other possible fixes.
One called for the construction of an entirely new wall panel next to the defective wall on the outside of the tunnel. That plan was rejected due to potential damage to the nearby Federal Reserve Bank and problems creating a waterproof seal.
A second option called for cutting out and replacing the defective sections of the wall panel.
Big Dig officials rejected that option in part because it would require workers to drain the water level outside the tunnel to prevent ground water from rushing into the tunnel when the sections were cut away.
Officials said that would be too risky. If the pumps failed during the months it would take to drain the water and finish the repair, water would begin flowing into the tunnel. Officials also worried that draining ground water could damage the Federal Reserve Bank.
In the end, officials decided on the option of a concrete-encased steel plate fix on the inside wall of the tunnel.
Critics have faulted Turnpike officials, charging them with choosing the least expensive of the proposed solutions. An independent engineering consultant fired by the Turnpike Authority earlier this year had recommended one of the other proposed solutions.
But Turnpike Spokeswoman Mariellen Burns said cost did not factor into the decision because the money was coming out of the pockets of the contractor responsible for that section of the wall, Modern Continental, and Big Dig project manager Bechtel/Parsons Brinckerhoff.
“The liability is on the contractor,” Burns said.
The wall breach was caused when workers failed to remove excess concrete that had flowed into the panel area before pouring a new section of wall in the $14.6-billion project.
Dirt and other debris became trapped in the new wall section, and washed away over a span of several years, eventually causing the leak.
Inspectors have since looked at each of the approximately 2,000 underground wall sections in the I-93 tunnels, discovering 169 defects. The majority of those panels, approximately 125, will require minor patching while another 42 will need more extensive repairs.
Two panels, including the panel that caused the September breach, need extensive repair work.
Most of the defects in the walls have occurred in the deepest portions of the tunnel. At its deepest, near South Station, the tunnel is approximately 120 ft. below the surface.
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