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Investigators probe Boston tunnel design

BOSTON—Since the July 10 collapse of a concrete ceiling panel in the I-90 connector tunnel that killed one motorist, federal and state officials have been inspecting all sections of Boston’s Central Artery/Tunnel project, conducting tests on bolts that hold the suspended panels and ventilation fans and beginning the task of reinforcing suspect sections with newly designed redundant bolting systems that don’t rely on epoxy-secured bolts. In addition, investigators are searching project documents for insight into the engineering and construction management decisions that might have contributed to the failure.

Bechtel/Parsons Brinckerhoff, which acted as management consultant for the $14.6 billion, 20-year project known as the Big Dig, issued a statement immediately after the accident expressing its support for "a prompt, non-partisan, expert, and objective review of the entire Central Artery/Tunnel project. … We urge that this review cover the entire range of potential safety-related issues, including structural integrity, structural elements over roadways and public areas, suspended ceilings, ventilation and support systems, fire and life safety, structural fire protection, utilities and lighting, communication systems, and the adequacy of operational inspection/maintenance."

Within days of the accident, Massachusetts Governor Mitt Romney sought and received authority from the state’s legislature to oversee safety audits of the tunnels, "Basically, it comes down to an issue of public confidence," Romney said. "I’m asking the legislature to act on an emergency basis to transfer to the state the authority for overseeing the inspections now underway, and for making the final call on the safety of the tunnel system."

The Massachusetts legislature appropriated $20 million for the audits. The National Transportation Safety Board and the U.S. Department of Transportation also are involved in the investigation. Additionally, Massachusetts Attorney General Thomas Reilly is trying to determine whether the accident is the result of criminal negligence.

As of press time, investigators have not released information publicly, other than the fact that many loose bolts have been found throughout the tunnels. However, issues and questions raised during the early stages of the investigation include the following:

  • design changes that resulted in the use of heavier concrete ceiling panels in the I-90 connector tunnel instead of lighter-weight panels used in the adjacent Ted Williams Tunnel;
  • the lack of steel supports in sections of the connector tunnel ceiling to which bolts holding the concrete panels could have been connected;
  • possible tunnel damage caused by blast vibrations from nearby construction of a 14-story office tower;
  • use of diamond-tipped drill bits, instead of carbide bits, in drilling holes for the bolts supporting the ceiling panels (epoxy may not hold as well in smoother holes drilled with diamond bits); and
  • the impact of cold weather during installation of the epoxy-bolt system in some tunnel sections.

"Supporting concrete ceiling panels by anchoring bolts to the roof with epoxy adhesive is widely and successfully used throughout the public transportation industry," Bechtel/Parsons Brinckerhoff said in its statement. "Determining the causes of this specific failure will require a thorough forensic analysis of design, methods, materials, procedures, and documentation."

According to an article in the Boston Globe, federal investigators also are trying to determine whether Bechtel/Parsons Brinckerhoff’s management control compromised government oversight and construction testing on the project. "There was no one checking the checkers," the Globe quoted a U.S. Representative as saying after meeting with transportation officials.

In its defense, Bechtel/Parsons Brinckerhoff said in its press release, "We firmly believe the project’s engineering, construction, and quality assurance processes were appropriate and robust. We are proud to have been a part of one of the largest, most complex, and technically challenging projects ever undertaken in an urban setting."