Gannett Fleming and Bechtel/Parsons B engineers blamed by safety board for killer ceiling collapse in Big Dig

The National Transportation Safety Board (NSTB) highlights poor anchor specification by design engineers of Gannett Fleming and project managers Bechtel Parsons Brinckerhoff joint venture (Bechtel/PB) as the cause of the ceiling collapse that killed a car passenger July 10, 2006 and resulted in some tens of millions of dollars of costs in traffic disruption, lost tolls and rebuilding of the suspended ceilings. Bechtel/PB project managers and the state Turnpike Authority are blamed also for failing to respond to anchor creep or slippage observed back in 1999 with followup inspections. Followup checks on the anchors likely would have produced a recognition of the danger and remedial action before the collapse, the Board says.

Gannett Fleming engineers receive the heaviest blame. The claim is made they knew that the specified adhesive anchor was good to the intended loads for short-term loading only, but still approved the anchor system for long-term use. Project engineers Bechtel/PB and the Turnpike are blamed for overlooking the creep problem and for failing to institute followup inspections after widespread creep was observed.

The safety board also proposes a prohibition on use of epoxy for sustained vertical loads pending development of tests and standards.

A synopsis released today of the incomplete final report states:

"The National Transportation Safety Board determines that the probable cause of the July 10, 2006, ceiling collapse in the D Street portal of the Interstate 90 connector tunnel in Boston, Massachusetts, was the use of an epoxy anchor adhesive with poor creep resistance, that is, an epoxy formulation that was not capable of sustaining long-term loads. Over time, the epoxy deformed and fractured until several ceiling support anchors pulled free and allowed a portion of the ceiling to collapse. Use of an inappropriate epoxy formulation resulted from the failure of Gannett Fleming, Inc., and Bechtel/Parsons Brinckerhoff (Bechtel/BP) to identify potential creep in the anchor adhesive as a critical long-term failure mode and to account for possible anchor creep in the design, specifications, and approval process for the epoxy anchors used in the tunnel."

Bechtel/PB and builder Modern Continental are also faulted for failing to monitor the state of anchors after they had extensive anchor failures in 1999.

Manufacturers of the adhesive, Power Fasteners Inc are also faulted for knowing that fast-set epoxy had poor longterm strength but for failing to associate observed slippage with the use of this epoxy.

The state's agent Massachusetts Turnpike Authority is said to have contributed to the accident by failing to implement a tunnel inspection program that would likely have revealed the ongoing creep in time to correct deficiencies before the collapse occurred.

Modern Continental largely exonerated

Builder Modern Continental is largely exonerated by the NTSB saying that they were supplied the deficient epoxy and any deficiencies in installation would not have accounted for the failures. At the time of the 1999 problems project managers Bechtel/PB blamed poor workmanship by Modern Continental workers for the problems.

Safety issues are said in the synopsis to include:

- insufficient understanding of adhesive anchoring among designers and builders
- lack of standards for testing adhesive anchors for high loads
- inadequate requirements for tunnel inspections
- lack of standards for tunnel finishes

Some of the other conclusions listed are:

- by the month of the collapse a significant proportion of adhesive anchors had crept out of their holes in the concrete above sufficiently to produce a precarious hazard in three tunnels
- design engineers at Gannett Fleming and Bechtel/PB failed to allow for epoxy creep under sustained loads over a long period
- the fast-set epoxy used was especially susceptible to creep
- the accident might have been prevented if Gannett Fleming had specified an epoxy with less susceptibility to creep
- Gannett Fleming were told that one epoxy used was good for short-term use only but specified it for longterm use
- manufacturers Power Fasteners knew their fast-set epoxy was weak in long-term use but failed to tell the builder Modern Continental
- by the nature of the task installing adhesive anchors overhead introduces voids in the adhesive that will prevent it performing to its theoretical strength and reduce the reliability of any anchoring system
- the accident might have been prevented if Bechtel/PB or the Turnpike Authority had instituted regular followup inspections after the creep incidents of 1999.

Prohibition on use of epoxy overhead

The report recommends that use of adhesive anchors in sustained tensile load situations like the Boston tunnels be prohibited until testing standards and protocols have been developed. 

Civil laws suits have been lodged by the state and the family of the killed passenger against many of the companies involved. The tough national safety board report seems to us to provide material for criminal negligence charges and professional disbarrment as well.

see http://www.ntsb.gov/events/Boardmeeting.htm

TOLLROADSnews 2007-07-10