Thursday, 4:30 PM
Fast-drying epoxy used in Big Dig let bolts slip over time
(David L. Ryan/Globe Staff)
Raquel Ibarra Mora wiped away tears today at a hearing in Washington about the collapse of part of a Big Dig tunnel a year ago that killed her mother, Milena Del Valle. She was joined at the National Transportation Safety Board hearing by paralegal Erica Rodriguez (center) and attorney Mario Garcia.
By Sean Murphy and Andrew Ryan, Globe Staff
WASHINGTON -- Investigators for the National Transportation Safety Board said today that part of a Big Dig tunnel collapsed a year ago because the wrong epoxy was used to secure the ceiling, allowing bolts to slip or "creep" over time.
A fast-drying epoxy used throughout the Interstate 90 connector tunnel holds 25 percent less load than conventional epoxy. The "fast-set" epoxy had "exceptionally poor creep resistance" that allowed the bolts to slip, investigators said at a hearing as the NTSB released its long-awaited report on last year’s fatal ceiling collapse.
"Fundamentally what we're talking about here is the wrong glue being used," said Kitty Higgins, one of five NTSB board members, after listening to testimony.
The board today unanimously approved the report, which determined that the fast-set epoxy was the likely cause of the partial collapse of a tunnel that killed Milena Del Valle, 38, a passenger in a car crushed by the falling panels.
"It's very difficult to relive this tragedy," said Del Valle's 24-year-old daughter, Raquel Ibarra Mora, of Costa Rica, who attended the hearing and spoke to reporters through a translator. "It's a very rough time for me."
Mora said she was "extremely pleased" that NTSB seemed to be doing a thorough job investigating the tragedy.
In a press conference this afternoon, Governor Deval Patrick said last July's accident continues to be "an important wakeup call for all of us."
"As I understand the report, it confirms the utter disappointment I have and I think we all should have with Bechtel/Parsons Brinckerhoff, the engineering on the project and much of its leadership," Patrick said.
Attorney General Martha Coakley and US Attorney Michael J. Sullivan are pursuing their own investigations as to whether to press criminal charges against those involved with the connector's construction.
Bechtel/Parsons Brinckerhoff, the Big Dig's overall design and construction management consultant, released the following statement: "NTSB has performed a thorough and objective investigation of this tragic accident. We look forward to reviewing its final report."
The Globe reported in May that contractors had used the wrong adhesive to install at least some of the bolts. Invoices from the 1999 ceiling construction job showed that Modern Continental Construction Co. received and apparently used at least one case of a quick-drying epoxy to secure ceiling bolts to the tunnel roof rather than standard epoxy.
An examination of the eastern end of the tunnel ceiling after the collapse showed that other anchor bolts were in imminent risk of failing and could have caused more ceiling panels to fall, investigators said. Since the accident the tunnel has been reinforced and state officials say it is now safe.
Builders had noticed that bolts in the connector tunnel had begun to slip in 1999 and 2001 before it opened but did not remedy the problem. "It was a missed opportunity," said Bruce Magladry, the director of the board's Office of Highway Safety.
Even after traffic began using the roadway in 2003, officials did not regularly inspect the tunnels, a safeguard that "would likely have identified" that the bolts had begun to creep, Magladry said.
Inspections of the tunnel immediately after the July 10, 2006, tragedy indicated that concrete panels fell because large bolts secured to the tunnel roof with epoxy came loose.
The specifications for the epoxy used in the tunnel were performance based and did not explicitly bar the use of fast-set epoxy. "The shortcoming is that the specifications did not address the issue of the long-term characteristics of the epoxy," said Mark Bagnard, an NTSB investigator. The project managers "could have done a better job with the specifications."
While the fast-set epoxy passed short-term load tests, engineers did not study how it would hold over time.
"They were short-term load tests ... two minutes and that was it," Bagnard said. "There was no thought to long-term characteristics."
Material from the Associated Press is included in this report.