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Go Toward the Light-and Hurry!

July 19, 2006 By: Stephanie vL Henkel, Sensors


E-mail Stephanie vL Henkel

The ceiling collapse in one of Boston's Big Dig tunnels finally won a minute on the national news, about a week after the event. The story's focus, strangely enough, was less on the causes of structural failure and more an exhortation to fight fiscal waste. Today I'll give you a few updates on the findings so far. Then I'll tell you a bit about a sensor technology that could have kept this from happening—and from happening again.

A Quick Point-by-Point

Even before the tunnels opened, some sprang small leaks that soon became freshets. Chunks of concrete began to detach and fall onto vehicles passing through. Part of that concrete was bogus, cheesy. On July 11, a 2-1/2 or 3-ton concrete panel forming part of a suspended ceiling fell in its totality, pancaking an automobile and killing its passenger.

The gap between the tunnel roof and the suspended ceiling, both made of concrete, was part of a ventilation system (turns out the tunnel might be fine without it). Each section of ceiling was secured by a bolt, set and epoxied into a hole in the roof so as to snug a metal plate flush to that part of the roof. From these plates descended tieback rods that held the ceiling panels up. Except that one let go.

The Pointing o' the Fingers

The number of suspect bolts has grown daily. The early report gave the number as 10; by yesterday it was 1150. Pull-tests are under way. The epoxy on some bolts is brittle, indicating epoxy that never cured; some holes showed zero evidence of epoxy's having ever been in them. Oh, and one more riveting item: Tunnel authorities have known about the bolt problems since 1999. Accusations and blame are spreading out now like hot honey.

How About a Better Future?

Our July cover story, Kevin Delin's "The Sensor Web for Tough Applications," lays out in compelling detail what the Sensor Web is: A synchronous, distributed instrument in which a vast number of sensors can all communicate with one another and actually can get something accomplished, based on the information they have collected.

The properties and phenomena detected create an overview of an area that can be quite large. And hostile. As in buried under snow or mounted in a tunnel. In principle, the pods that constitute a Sensor Web could include sensors that monitor concrete and epoxy as they cure. They could report on moisture and humidity. Air quality. Vibrational and seismic activity. And roof bolts that begin to slip their moorings.

So Where's Boston's Sensor Web?

Probably not ready for prime time when serious planning for the Big Dig got under way in 1985, but it sure was when the project was finished in 2005. A year later is not too late to install such a Sensor Web, now that ceiling panels are being pulled down one after another for inspection and precautionary reasons. Those sensor-rich pods have been demonstrated as life-saving under conditions eerily similar to those that have claimed the lives of many coal miners this year—and that of the unfortunate woman in the I-90 connector tunnel.

In McNicol's and Ryan's otherwise splendid book, The Big Dig, I note that the admittedly slender appendix had no entry for "sensors." Harrumph!






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