By Vicki Smith
The technology may still be a few years from installation and deployment, but researchers at West Virginia University are working with a Delaware company and the U.S. Department of Homeland Security to fine-tune giant inflatable plugs that could protect subway and vehicle tunnels from future flooding.
The Resilient Tunnel Plug has been years in development and testing, but it may be more relevant than ever: Superstorm Sandy sent a record 14-foot storm surge into New York Harbor, flooding subway tunnels that move some 5.2 million people a day.
There is no telling how well ILC Dover’s Resilient Tunnel Plug could have helped prevent damage, “but that’s the kind of thing we’re designing these things for,” Homeland Security spokesman John Verrico said Thursday as the latest testing got under way in an airplane hangar.
Packed like an air bag, the oblong balloon made of Space Age materials flopped out of the wall of a scale-model subway tunnel that WVU engineers developed several years ago, inflating in about two minutes. While contact sensors monitored the pressure, engineers with WVU, ILC and the Pacific Northwest National Laboratory visually inspected the edges to see how tightly the tube filled the tunnel.
A proper fit is critical to the plug’s success, said John Fortune, project manager for the Department of Homeland Security.
“If there’s not a good seal, we’re going to see substantial flooding,” he said. And while there will always be some leakage, the goal is to make it minimal.
The plug is first inflated with air, then pressurized with water, which adds strength and the ability to withstand external pressures, Fortune said.
When it’s fully inflated, the woven bands of the Vectran fiber blanket around it are virtually impenetrable, said ILC’s senior project engineer, Jeff Roushey.
Vectran is a yarn spun from liquid crystal polymer. Its manufacturer says that pound for pound, Vectran fiber is five times stronger than steel and 10 times stronger than aluminum. For the plug, the yarn has been woven into 2-inch wide bands that Roushey says can withstand 5,000 pounds of force.
Underneath that webbed outer shell is a second, smooth layer of Vectran that looks like a vinyl shower curtain, protecting the bladder from anything that might somehow make it through the webbing.
“The idea is redundancy and flexibility,” Roushey said.
Engineers still must design containers for the plugs, as well as effective inflation and security systems. Tunnels will have to be modified, too, and that will take time and money.
Roushey said those details may take two to three years to fully resolve, but the goal is to create and install plugs that function like air bags in a car. They sit unnoticed — until they’re needed.
The testing also helps researchers determine how much larger the plug should be than the tunnel it’s designed to seal and protect. Roushey said the idea is to develop a range — say 5 percent to 20 percent — to fit most applications.
The plug’s design has changed as newer, stronger materials have emerged.
While Homeland Security was primarily interested in protecting transportation tunnels, Verrico said the plugs could also be used to stop smoke, gases and chemicals.
“But also, the real test here is the deployment method,” he said. “How do you get this thing installed in the tunnel so that it’s able to quickly inflate, be deployed and doesn’t kink up and will seal the tunnel? There are a lot of aspects to determine.”