We were one of the first blogs to cover this mess when it began, and we stayed on the topic as the situation got worse. Beyond the money, beyond the wasted time and effort, and beyond the traffic mess lies the real damage in all of this – the betrayed trust of the public. That is the biggest failure.
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?
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.
As one of the more technically-minded sites to discuss this, we even made the industry coverage:
Another site, Dvorak Unsensored, also has discussions on the failure.
“Was there a structural necessity to have big thick concrete panels on the inside of the tunnel,” posts one reader [a tip of the hat to Nate]. “My guess would be that it was not necessary.”
He [Nate] adds that he thinks the problem is due to the lack of oversight in these types of projects to ensure appropriate standards are being met.
If this problem is as large as it is feared to be, how long will the tunnel be out of service? Will it ever be completely safe? Will the public ever trust themselves to use it afterward without being scared spitless the entire time underground?
The whole BIG DIG is so Mobbed up along with a certain dirty Dem 😉 I’d never trust that thing. ! Not that I’d ever willing go to Boston mind you.
Central Coast, what do you mean “Mobbed up”? Back up your statement with facts that lead you to this conclusion please.
#2,,,,it may or may not have actual mob involvement(like so many of Bostons projects in the past) but it was 700% over budget……and now turns out not to have met even minimum specs…..dosen’t that smell like pay off to you?
#2 Mob involvement is part of any big construction project. They don’t leave a paper trail, so it would be difficult to “back up”. Why don’t you try living in the real world.
“worst engineering failure ever”
Oh come on and drop the hyperbole! Obviously you’ve never owned an American made vehicle before!
What I cannot understand is why anyone felt the need to hang huge, heavy concrete panels from the roof of the Big Dig. Apparently they play no stuctural role. Quite the opposite, they stress the roof. If the designers thought the natural stone roof unsightly, why not cover it with lighter (plastic?) panels? And of course I think back to the Romans, who solved this problem millenia ago with the Roman arch – which is self-supporting and cannot fall.
#3, joshua, No, to me it sounds more like a government project where the specifications keep changing. Most innovative Government projects will escalate in cost.
I wonder though, why did they hang such heavy panels from the roof?
Fred — but, their empire fell! Notice any parallels?
#2 – Mob… union… same difference in Boston. And there is little doubt the unions played a large part in the project.
Never Use An Expansion Bolt To Hang Something From A Ceiling.
It relies on gripping the material that surrounds it, which may not be all that strong or durable for a dead weight in tension (as opposed to a toggle bolt, which has mechanical wings to grip the opposite side of the material). Epoxy glue has such a reputation for being “stronger than the material it’s glueing to”, and it certainly is hard stuff if you mix it and prepare the surface properly, but one wonders if some folks get a little too confident in that. It apparently weathers, too (like concrete).
I worked in architecture with these epoxy-embedded bolts, from a company called Hilti (which originally made a really interesting tool that used .22 blank cartridges to fire hardened fastening pins into concrete). We used the Hilti epoxy bolts for securing building elements to prevent lateral movement, not vertical. I doubt if the structural engineering people would ever have allowed them to be used to permanently hang heavy items.
Pterocat – epoxy anchor bolts are actually better than expansion-type anchors for vertical and lateral movement. If you happen to have a Hilti or Powers Fastener catalog available, you will see that the pull-out strength on these fasteners can be extremely high, and are in common use by structural engineers worldwide. Toggle bolts would not be applicable in this case, since there would not be an opposite side to grip to, since you cannot allow perforations in tunnel work, unless you want a continual drip. It is likely that the bolts were appropriately sized for the anticipated load, but the allowable loads contained within the catalogs all assume that installation was completed properly.
You are correct in your assertion that the base material supports the load. The catalogs are also clear in noting that you cannot have an epoxy bolt that has a higher pull-out load than the substrate. However, the concrete should also be able to support this type of load. Everything I have read has pointed to improper epoxy installation, likely due to improper cleaning of the holes.
My concern with the use of epoxy does not relate to the strength of the system or the proper mixing of the epoxy, since the manufacturers seem to have good solutions for both of these issues. My concern lies with the installer improperly cleaning out the holes. Due to failures of equipment we have produced resulting from improperly cleaned holes, we have elected to no longer furnish the epoxy for further projects, alerting our customers to their need to pick an epoxy system that they feel confident will work for them. I am also tempted to simply move back to expansion anchors, knowing that they will need to be significantly oversized, but knowing that they are virtually idiot proof.
As I noted earlier, the problem is probably not corruption, since projects that are completely above-board can be failures, while the most corrupt projects can be complete successes. The problem is that there was probably not proper oversight with respect to installation inspection. This was probably an overlooked aspect of the project and should have been rethought, considering the mass of the panels and the trouble that had been experienced with anchor installation. They would have been far better off with some light gage stainless steel, if the concrete was only there for duct work.
By the way Frederick Bushman, Roman arches can fall. Like anything else, it all depends on the loads that the structure is subject to. There are fallen arches all over Europe, and that doesn’t even consider all of the tourists with bad shoes! 😉
-Nate
I would never put an epoxy bolt in pure tension like the ones described here. The best solution here is some sort of undercut type anchor that has a positive wedge to hold the bolt. These anchors are readily available, but they are ridiculously expensive, to the tune of 10 times if they are seismic rated.
The holes are vertical overhead. I’m not sure what cleaning you would need unless you were getting some caking of the concrete due to moisture.
I read about diamond bits being used in some locations to cut through rebar. Most engineers will not allow cutting of any rebar. If a rebar can be cut, what’s the point of it being there in the first place. I’d have to question if that was someone making that one up.
Proper cleaning of fasteners is important, but no contractor wants to sit there and have a worker clean bolts. You are going to have all kinds of different dirt and oils getting on the rods. I’ve never seen a contractor take a bunch of threaded rods and clean them using some sort of solvent or degreaser. They grab a box or container of rods and start sticking them in the holes. It may not be right, but that’s the way it is.
I don’t know where the rods came from, but many times, it’s cheaper to cut your own rods from 20′ stock length all-thread rod. You can bundle and put them in the band saw. Problem here is you get oil or coolant on the rods. If the oil is not cleaned off, the epoxy will not grab to it. I’ve also seen galvanized threaded rods with some sort of oily residue on them. Same deal, epoxy won’t grab.
I would like to know what epoxy bolts were used on this project.
Powers Fasteners does not manufacture any of their products. They import their low quality junk anchors from Taiwan and China and put USA made on the box. Isn’t this illegal?
I am a contractor in NYC and I would NEVER use Powers anchors. Their results are false and their products are crap. I use ITW, Wej-It, and Hilti only. Now you see why. Big Dig will be just one of the disasters, unfortunately.
It is stupid to use concrete panels as a false ceiling when much lighter materials are available. The design was probably done to make the job cost more, or the designer is a real dummy.