Big Dig - One of Engineering's Greatest Mistakes?

Enggirl1 writes "Design News discusses Boston's Big Dig and begs the question - is it one of engineering's greatest failures? The article reveals that forums and blogs are popping up all over the Internet as vehicles for engineers and contractors to discuss, under the guise of anonymity, their skepticism, thoughts and reactions to one of the biggest infrastructure failures in the news today." From the article: "One blogger, whose profile notes that he is an ICC Reinforced Concrete Special Inspector and an ICC Pre-stressed Concrete Special Inspector, among other specialties, says he has nearly 20 years of experience performing both placement and post-placement inspections of rebar, post-tensioning systems, concrete, masonry, etc. He says if structural engineers who specify epoxy for dowels and the like believe that the work is being done correctly then they live in a world unfamiliar to him."

Comments

About rock bolts

[Anonymous Coward]

Rock bolts are a staple in the mining industry. There are darn few failures. Of course the rock bolts are specified by engineers who work for the mining company and installed by miners whose safety depends on them. You tend to do things better if your life depends on it.

In the case of the big dig, you have contractors who are trying to make the maximum possible amount of money. I also bet that there weren't enough government inspectors or that they weren't properly qualified. Cutting costs is just as dangerous in the government as greed is in the private sector. The Canadian province of Ontario laid off all their government water inspectors and a bunch of people died in the town of Walkerton. If you don't give folks the tools they need to do a job then you shouldn't be surprised if the job doesn't get done.

The concrete ceiling tiles were used to create a separate space for supplying air to the tunnel. This is typically how you would do it in a building. In the case of the Chunnel between England and France, they dug a separate tunnel for that purpose. People have wondered why the panels had to be made of concrete. Something lighter would have worked just as well and might have been cheaper and safer.

Re:Maybe not engineering's failures...

[UnknowingFool]

"throws in numbers" and tosses together a design, then sends it out with the engineer's seal on it. Or when an engineer refuses to sign off on an incomplete or incorrect design, the manager brings in a new graduate because they're more "cooperative" (read: will sign anything to get a paycheck) and they go ahead and build it that way.

I'm not saying those things don't happen. I'm saying that they are highly illegal and not common place. Signing off on a design for an engineer is like preparing legal documents without being a lawyer or giving medical advice without being a doctor.

To sign off on any engineering or construction documents, an engineer must be licensed as a Professional Engineer (PE). The requirements vary by state but in most states new engineering graduates do not qualify to be PEs. The norm is an engineering student must pass an exam (FE) near graduation, then work under a licensed PE for several years, then pass the PE test. In most states like MA, it is 4 years minimum between passing the FE and even qualifying to take the PE test. Engineers who are not PEs can do some of the work in construction and design fields but are expressly forbidden to do certain things like sign off on plans.

I agree with you that management is most likely to blame but for another reason. As projects like this become complex, it requires very good management to ensure that the important details are not overlooked. With as many problems as the Big Dig seemed to have before completion, it would seem that the management was not up to the task.

In the case of the collapse, I think the most likely scenario is that the specifications were wrong or changed at a later date. The load required was specified to be 1/2 of what it needed to be. The engineer approved a wall thickness of so many feet that was later modified and built without approval. The specifications for the wall never included withstanding water (hydrostatic pressure), etc.

Details on the failure

[MostlyHarmless]

The Boston Globe has been writing some surprisingly in-depth analysis of the failures related to this disaster. Here's what I remember from their reports:

• Yes, the epoxy-and-bolt system is extraordinarily dumb. It is not yet clear whether the epoxy was installed correctly, but even if it was, they should not have been relying on it. In some of the other tunnels, they built steel I-beams into the sides of the tunnel to hold up the ceiling panels -- a much more sensible system. The tunnel where the panels fell was not originally supposed to have ceiling panels, but they decided later on that they needed them for ventilation purposes; it was now too late to install the more sensible system, and they used this mickey mouse anchoring system instead. (That being said, there were any number of better and epoxy-free ways to design the anchors.)
• One of the subcontractors looked into using lighter (and significantly cheaper) steel panels instead of the heavy concrete ones, but they ran into problems with vibration. They eventually figured out a solution, but now the steel system would have been almost the same price as the concrete, and another authority (I forget which) had already signed the contract to buy the concrete.
• The bolts were supposed to be tested to hold twice the weight they would actually be supporting. Instead, they were tested to a margin not much greater than the weight of the concrete panels. Furthermore, it is not clear how many of the bolts were actually tested; this may have gotten swept under the rug due to the extreme cost pressure the project was under.

As usual with engineering disasters of this sort, the failure seems to have been caused by a confluence of lesser mistakes that would not have been tragic in isolation. The root causes, however, seem to be:

• Changing requirements late in the game (as any software developer would warn you against)
• Cutting corners on safety checks due to budgetary concerns
• Bad design
• Incompetence and/or curruption on the part of the contractors. Most of the fingers right now are pointing at Bechtel, but who knows what later investigations might reveal.

Anyone who has lived in Boston can tell you that this is only the latest in a string of cost overruns and management failures. The actual mode of failure (i.e. the bolts) and the immediate causes of that failure should not overshadow the idea that the contractors who screwed this one up should be held responsible. The ongoing investigations should reveal whether the contractors were merely incompetent or whether they willfully ignored problems like these and crossed their fingers that nothing would happen.

My experience on site

[Anonymous Coward]

Posting anon here - I worked on the Big Dig (environmental) during peak construction (1997-2000) and I'm currently contracting with another MA state agency, and I don't want to ruffle any state feathers. I also want to write a book someday ;)

First a couple of general statements:

• As another poster mentioned, the Big Dig needed to be built. The traffic situation was untenable. Widening the elevated artery wasn't possible because of space and structural issues. Tearing the existing artery down first and building a conventional cut-and-cover tunnel would have been faster, at the cost of completely destroying the Boston (and MA) economy. Building another highway through Boston wasn't going to happen. A slurry wall tunnel was the best of several bad options, but make no mistake - it was going to be hideously complex and expensive.
• Contrary to popular belief, there where several major transit upgrades that were (and still are) being built to help offset the traffic on the Big Dig. More transit would have been nice, but transit brings its own set of issues.
• As for the accident: it was tragic and the responsible party (or parties) must be help accountable. But please don't think that because several MA politicians (including one presidential hopeful and one gubernatorial candidate) hold daily press conferences, that we are any closer to knowing all the facts. It's a complicated problem and it's going to take time.

Now back to the facts - I have no knowledge of roof panel construction (I spent little time in that area), but I will note that working on the project during 1999 and 2000 was an interesting experience. Already at the point there was heavy pressure on project managers and contractors to reduce costs (this was before the national stories hit that led to the ouster of James Kerasiotes). It got to the point that office supplies were locked up - you had to get the office manager's permission to get a notebook or pens!

In any event, I wouldn't be surprised at all if cost pressures let to reduced safety factors, etc. The construction site was also the source of many stories about various screw-ups that I won't get into here (wait for my book!). There was of course several times that money was spent to shut people up (at least once against my direct recommendation), but the PTB felt it was needed for the project to move along smoothly. I suppose that it would have been better for B/PB to take the Vista approach, and wait for the tunnel to be "finished" but that wasn't going to happen because of the political pressures.

Now was the project a failure? I'll just say this - is used to take me 1.5 to 2 hours to drive from Braintree to Cambridge during midday traffic. I did the same trip a month or so ago during a Friday afternoon rush hour in abut 20-25 minutes.