The National Corridors Initiative, Inc.
MA Office: 59 Gates Street, Boston MA, 02128
As appears in Destination: Freedom
James P. RePass
The Big Botch
That Sinking Feeling
BOSTON --- Most people get a little hitch when they realize they are entering a long underground passage. Some people even break out in hives. Others simply flee. Like interrogations or burns, claustrophobia comes in degrees.
But in Boston most people were getting used to their massive hole in the ground, the Central Artery Tunnel or Big Dig, which was completed (mostly) a few months ago. Essentially, the Big Dig took the old elevated central Boston expressway and shoved it underground, and added a new tunnel extending Interstate 90 to the airport. Cost: $14.6 billion.
That was until July 10, when at 11 p.m. a two-ton concrete ceiling panel crashed down upon a car driven by a Boston man, killing his wife and injuring him.
I would like to tell you that the subsequent response by officials has safeguarded the public and set in motion the repairs necessary to make the Big Dig tunnels useable again. But I cant say that, because it isnt happening. My advice is instead, Stay Out of the Tunnels until the project has addressed and solved the falling-concrete issue in full. At present, it is false-starts and half measures, poorly executed, and a proposed fix that may not be a fix at all.
Let me explain --- and this is especially for the journalists who read Destination:Freedom.
Bostons Big Botch is a difficult story, in its complexity somewhat like the Space Shuttle Challenger explosion in 1986, and most of you do not have the time to become instant experts. But once, on a very similar story 34 years ago, I did have to become a specialist in pulled bolts and falling beams, and while I am not a structural engineer, I do know what I am talking about. That is why I am very skeptical right now of any pronouncements by politicians, no matter how well-meaning, and so should you be.
In the Winter of 1972 a new shopping mall had recently been opened in Seminole, FL., a town about half-way between Clearwater and St. Petersburg. Today it has malls and sprawl, but in 1972 it was a tiny place, and the Seminole Mall was its Big Deal, such a point of pride that City Hall re-located to it. Early in the morning of February 8, 1972, a 4,000 square-foot portion of the new malls ceiling collapsed, hurting no one since the Mall was not yet opened. A reporter in the Clearwater Bureau of the St. Petersburg Times, I was assigned by my boss, Bureau Chief Tom Rawlins to get the story.
My investigation, which when completed took several weeks, lead to the manufacturer of the expansion bolts that had been used --- or rather misused --- to hold a U-shaped saddle joint to the mall concrete wall. It was these expansion bolts, whose bottom end spreads out as the bolt is tightened, to anchor it, which had pulled out. The saddle fell, and the end of the roof beam in it, and the ceiling section attached, came crashing down.
I say misused, because, as the bolt manufacturer told me, and as his product guidelines clearly stated, you cant use expansion bolts in a joint subject to movement or vibration, because the vibration slowly eats away at the concrete around the expanded anchor-end of the bolt as it moves with the vibration.
It turned out on investigation that the saddle joint at Seminole Mall had been cast in the wrong place when the wall was poured. To remove it the saddle was sliced free from the wall, leaving the prongs in place in the wall. Then, a new saddle was drilled out, and re-attached to the concrete in one of the few ways you can do that after cement has dried: with expansion bolts. The problem is that a U-saddle is designed for expansion joints, which move. Thats why you are supposed to cast it (it comes with welded on-prongs) into the wall when the concrete is poured. And in any event, the manufacturer had banned expansion bolts for that use.
As the manufacturer had foreseen, the expansion bolts moved back and forth in the holes that were drilled, and the U-saddle slowly worked away from the wall, until the concrete had been abraded away to the point where the bolts slid out. Then, of course, the ceiling fell.
When reports aired the day after the Big Dig ceiling collapse that bolts-plus-epoxy had been used to secure concrete panels weighting more than two tons, I was stunned. Those panels are subject to constant vibration, and an expansion bolt, let alone a straight bolt as had been used, would quickly work its way out, as they had in Florida many years ago --- unless epoxy technology had reached such heights that vibration was no longer an issue. If that were the case, then this would be an isolated problem of a few bolts whose epoxy had failed.
But that wasnt the case. The next day it was 20 bolts, then 60, now 1440, and suddenly the Ted Williams tunnel more bolts per unit of weight, a lighter panel, but the same design --- was found to have bolts at risk for failure. Now its ceiling has to be redone too.
No, the ceiling failure wasnt an anomaly. It was the result of a deliberate decision. But why?
Then, it got worse. A day or so later the Governor of Massachusetts was holding aloft an expansion bolt --- the very bolt design banned 34 years ago from work where vibration is an issue ---stating that it could be part of the cure.
I called a Boston reporter whom I respect, and warned him that the Governors putative cure could be just as dangerous as the problem, just pushed further into the future --- and stressing that I was not an engineer that he should start asking some pointed questions about vibration and its effects, whether these bolts would be used with epoxy, and especially whether the stress tests being done on the original bolt+epoxy fix proposals in 1999 had been static or dynamic, and whether the new tests would be dynamic as well All very technical, but pay attention, because it is literally a matter of life and death.
I also warned the reporter that the Ted Williams Tunnel that day still being cited as the safe part of the Big Dig was probably not, and that if inspections were ordered of its [similar, but more numerous] bolt pattern those bolts, too, would be found to be compromised. That day to his credit Governor Romney ordered that inspection, and found exactly what I had told the reporter would be found. Maybe we saved a life or two.
Sometimes it is depressing to cover the news, because you see things youd rather not see. The collapse problem I covered 34 years ago at the Seminole Mall in Florida is the same one they are discovering today, with different weights and materials, but the same kind of failure: you cant use bolts in concrete when dealing with heavy weights subject to vibration, unless the epoxy is perfect --- and even then, cross your fingers.
Time and the Attorney General, with the help of the best engineers we can hire, will tell. But in the meantime --- this is not a joke ---- stay the hell out of the Big Dig.
Mr. Attorney General, hire some qualified structural engineers, get out of the way, and let er rip.
Copyright © James P. RePass - 2006