You may have heard about this engineering project when part of a concrete ceiling fell, killing a passenger in the car underneath. The entire tunnel system is shut down now pending a detailed investigation. Design News has a good article with links about this emerging fiasco:
Boston's Big Dig -- One of Engineering's Biggest Mistakes?
The faulty bolt and epoxy assemblies that led to more headlines about Boston's Big Dig/Central Artery Tunnel Project was just the kind of engineering who-done-it engineers find irresistible. Was the wrong epoxy used? Was the design faulty? Or was poor installation the reason for the failure?
"Tension anchors such as this are required to have a factor of safety (by code) of at least 4. Considering that, it appears that the assembly had been holding for a while and gave way," posts a reader on Eng-tips.com. "That points more so toward an installation anomaly, likely exacerbated by vibration or other repetitive loading, or potentially a material failure (excessive creep under load, embrittlement, corrosion, etc.), or as usual, some combination of those."
The investigation, which found faulty assemblies, was sparked by the July 10 death of a 39-year-old woman after 12 tons of cement ceiling panels fell on the car her husband was driving inside the I-90 connector tunnel more than two weeks ago.
As a result, several portions of Boston's $14.6 billion Big Dig/Central Artery Tunnel Project have been shut down. Ongoing investigations by federal and state officials are uncovering additional problems almost on a daily basis.
On July 12, according to a Boston Globe report, inspectors found at least 60 faulty bolt fixtures in the ceiling of the tunnel. On that same day, Attorney General Tom Reilly says tests conducted in 1999 showed that the ceiling bolts had a tendency to come loose.
On Wednesday, July 26, the Herald reported they obtained documents revealing that Big Dig officials noted six years ago that epoxy ceiling supports were failing in the same tunnel section where the deadly accident occurred, but allowed the continued use of that "superglue" system to support 3-ton concrete slabs.
On Thursday, July 27, Mass Turnpike Authority Chairman Matt Amorello stepped down from his position, overseeing the project, just before a hearing with Gov. Mitt Romney - a strong proponent of Amorello�s resignation.
While doubts about the infrastructure's safety are only coming to light now -- a December 1998 Inspector General's Report reviewing the project's use of anchor bolts documents numerous problems with the bolts and glue used to secure the ceiling in the Ted Williams Tunnel which opened to traffic in 1995. The I-90 connector connects the Mass Pike with the Ted Williams Tunnel.
The Inspector General's Report discloses several findings which would indicate a problem could occur:poor design specifications, paying contractors to test improperly installed anchor bolts and lack of consultation with tunnel designers before allow contractors to drill through steel reinforcements in the tunnel roof.
I went to school at Boston University and worked for New England Aquarium -- at that time, traffic was served by a series of elevated arterials and rush hour was an enormous contradiction in terms. The Big Dig is a perfect example of tax and spend politics so favored by largish cities (Seattle included) -- the elevateds could have been widened but no, they had to be torn down and this new tunnel system installed. It was supposed to take seven years and cost $2.6 Billion. It is now fifteen years later and the cost so far is $14.6 Billion and the project is not yet finished. Seattle wants to do a mini-me version of this, tearing down an elevated viaduct and replacing it with a tunnel. Riiiggghhhhttt...