The Superstorm known as Sandy caused an estimated $5 billion of damage to New York's subway system. Tunnels flooded, equipment was wrecked, and several lines stayed out of action for weeks.
As the storm reared on the radar, New York's Metropolitan Transport Authority blocked up some tunnels with sandbags and makeshift wooden structures, which limited some damage. But the method was hardly ideal. In one incident under the East River, some wood broke free and ended up knocking down a barrier. The tunnel, which carries the R subway line, was flooded with 27 million gallons of water.
The MTA is now looking at a more robust and deployable solution: An enormous tunnel-engorging plug. The Resilient Tunnel Plug (RTP), to give it its formal title, is being developed by the firm ILC Dover in Delaware, with help from the Department of Homeland Security. ILC demonstrated it twice this year at New York's South Ferry station (see images). And it's now making its first full installation (though the location is secret "for security reasons").
The RTF, which is taller than a double-decker bus, has three layers. On the outside is a woven fabric layer composed of strips roughly the width of a seatbelt. The second is made from the same very-strong material, but is unwoven. On the inside is an inflatable inner-tube a bit like something you would find in a soccer ball. ILC has developed gear for space travel—the fabric was also used in the Mars Rover landing system.
Dave Codogan, ILC's director of engineering, explains the RTP was initially developed for water seeping up from below. But, following Sandy, there is more interest in the plug as a top-down water barrier. It's designed to sit near where it's needed, and to be initiated remotely. It can inflate in about 30 minutes. "It will be packed in its container until an event is sensed and then deployed via inflation with air. It is possible to use water or some other medium, but air is low risk," Cadogan says.
As well as the RTP, ILC is also working on "tensioned fabric walls" using the same material. They "resemble the roll-up doors you see on NY store fronts," and would "be used in rail yard portals and over stairwells to prevent water from getting into the system," Cadogan says.