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Boston’s Big Dig Materials Failure: It’s Got Engineers Talking
Elizabeth M. Taurasi, Executive Editor -- Design News, July 12, 2007
Visit our Big Dig special report page for full coverage and photos of the tunnel collapse.
A year after a deadly ceiling collapse inside a Big Dig tunnel, questions about who was responsible have finally been answered, investigations are complete and lawsuits will soon be filed. While those at fault have been named, where a year ago no one knew where to place blame, one thing has remained the same – engineers are still talking about it.
The National Transportation Safety Board (NTSB) determined the probable cause of the July 10, 2006 ceiling collapse in the D Street portal of the Interstate 90 connector tunnel in Boston was the use of an epoxy anchor adhesive with poor creep resistance – the epoxy formulation was not capable of sustaining long-term loads. The recent release of shocking photos of the ceiling panel collapse, along with all the world-wide coverage has engineers talking.
Whether they are speculating about who is actually at fault or what types of fasteners should have been used, Boston’s Big Dig debacle is definitely something engineers will be talking about for years to come.
One Design News’ reader, who is a mechanical engineer, says a different type of fastener might have made the difference. “After 28 years of engineering, where I have used many methods including epoxy, VHB adhesive tape and many mechanical fasteners, it seems that this application should have used mechanical fasteners (or a self-supporting structure like an arch and/or reinforced concrete,” he says.
Another gets more to the point about epoxy. “Words from a wise engineer: Pucky (epoxy, glue, etc.) is how you pave the highway to hell. What were they thinking,” he says.
Another Design News’ engineer says it’s still too early to determine who is completely to blame, though blame, he says, is certainly shared, especially noting past failures. He says it’s difficult to say if the epoxy would have failed if properly installed. He also says the installation with a 40 percent void seems to be a causative factor, but since he does not know the design requirement, the overall length of anchorage could have been adequate if the minimum length and thickness of epoxy contact were adequate. He goes on to say that to put an important design requirement in fine print seems to be asking for trouble.
“In our hometown with the early use of adhesives and wood laminates, it took three reconstructions of a college field house to master the fine points of load and long-term creep. No one was killed that I recall but I hope they continue with the (Big Dig) investigation to determine all of the contributing factors,” he says.
Last year when news broke of the accident, spurring federal and state investigations of the project, blogs and forums popped up all over the Internet where engineers and contractors alike were offering their opinions under the guise of anonymity.
One year later, they are still talking and they have a lot to say.
Dvorak Unsensored, which was one of the first blogs to cover the Big Dig mess, stayed on the topic as the situation worsened and continues to be there throughout the course of the investigation and its aftermath.
“Hanging heavy concrete overhead and then placing shallow epoxy bolts into it actually increases the load if there is no holding power to begin with!” says one reader. “I would be equally effective to paint the concrete panels with lead paint! It just seems so stupid to me.”
Another reader questioned that maybe the cost and failure both have the same problem and perhaps it’s the many different levels of oversight that might have attributed to the problem.
“It used to be the engineer who called the shots on a job and he had his reputation on the line, success or failure either made or broke you, so you didn’t allow for failure,” he says. All of these overseers get paid and no one needs to worry that their career will be destroyed by a mistake that someone else should have caught.”
One reader says the problem is that there is not enough oversight in these projects to ensure appropriate standards are being met. “We supplied some equipment for a project on a military base with 11 inch epoxy type anchors,” he says. “The equipment failed, because we were not called out to look at the failure mode until four years after the fact. When we inspected, it was at first very clear that the bolts had been installed improperly due to the presence of epoxy and concrete dust on the outside of the bolts. Further inspection showed that the bolts had been cut/shortened. We began to pull all of the bolts and found one that was only 4.5 inches long. Fortunately, this was not a life or death situation.
He goes on to speculate there was a widespread belief that the anchors used in the Big Dig tunnel design were “overdesigned” for the installation. “There was a belief that there was no way the panels would come down, and that there were probably union or worksite regulations regarding the frequency of inspection,” he says. “The big question to ask regards the necessity of the concrete paneling. Wouldn’t foam or sheet metal have worked just as well? Was there a structural necessity to have big thick concrete panels on the inside of a tunnel?”
One West Coast reader wonders if it’s the fault of developers who take shortcuts to simply get projects done.
“Being from California, I often wonder about failures that will show up in the next big quake,” he says. “Every time there is a major quake in other parts of the world that result in a lot of deaths, they talk about our high safety standards. But I can’t help but think about how many shortcuts and payoffs were done by greedy developers to bypass those standards.”
In the days, weeks and months to come, more of this investigation will be played out through news organizations, in public forums and on the Internet. It won’t be until those determined to be responsible for this disaster pay the price that the door will be closed on this engineering mishap. One thing is for certain: With the national coverage this situation is generating, laws will likely be changed and the Big Dig tragedy will serve as an example of what not to do. Hopefully this will prevent another life from being lost due to substandard construction and design.
E-mail Executive Editor Elizabeth Taurasi with your thoughts on who's most at fault in this tragic tunnel collapse.
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