Project is seen as a solution to flooding that caused billions of dollars of damage in New York City's subways.
A decade-long effort to control flooding in metropolitan subway tunnels has resulted in a solution that will be manufactured in Kent County.
The device, dubbed the Resilient Tunnel Plug, will be manufactured at ILC Dover. A test was held for reporters June 6 in a facsimile subway tunnel built on the grounds of the Frederica plant.
The company leaned on experience gained in manufacturing airbags that landed four spacecraft on Mars as the basis for the plug: it uses a triple layer of Vectran material, bound by webbing and inflated to 17.3 pounds per square inch to seal off flood-prone tunnels.
Vectran is an industrial polymer known for its high strength and moisture-resistant qualities, both vital components of a system intended to hold back water resulting from natural disasters or terrorist attacks.
Development of the plug began in 2007 with the U.S. Department of Homeland Security.
“There was a question of how do we come up with the technology to protect transportation tunnels that could be rapidly deployed and could prevent the spread of flooding through the tunnel,” John Fortune, program manager for the DHS Science and Technology Directorate, said.
“In the middle of a brainstorming session, we had this wild and crazy idea of an inflatable balloon or a plug that could be stored and quickly put into place immediately.”
Many experts thought it wasn’t a viable idea, but DHS decided “to give it a shot,” Fortune said.
A test about a year later in the Washington DC Metro was successful, but DHS staff and engineers with the Pacific Northwest National Laboratory, who designed the plug, realized it had to be beefed up.
That’s when ILC and its expertise with Vectran came into the picture, Fortune said.
Tests over the years --not all of which were successful -- eventually led to the final design demonstrated Tuesday, he said.
“This is one of those things where we had an idea that was pretty simple but we needed to take that concept to reality,” Pacific Lab staff engineer Greg Holter said. “But simple ideas are not necessarily simple to implement.”
The big problem wasn’t just designing the plug, but ensuring it could be stored without interfering with trains passing through their tunnels, Holter said.
“There’s very little extra room,” he said. Additionally, tunnel interiors are dirty, wet and infested with rats and other vermin, and water in a tunnel exerts tremendous force against any object in its way, Holter added.
The plug is stored, deflated, within specially-constructed cabinets on the side of subway tunnels and can be fully inflated within about 20 minutes. The tunnels will be modified to raise the floor to the level of the train tracks to create an effective seal.
The device isn’t just a simple round cap, however. Each is built to conform to variations in the tunnel wall where it is placed; internal pressure and friction against the walls hold it in place.
It can withstand water pressure up to 12.5 psi and can be scaled up in the manufacturing process to higher pressures encountered in deeper tunnels.
The storage container holding each plug and the machinery used to inflate it also is designed to not block the narrow tunnels. Any leakage around the plug would be handled by pumps already in place in the subway system.
“That’s pretty limited compared to the flow of water what would happen if we didn’t have our plug,” Holter said.
When initial tests showed a single layer of Vectran wasn’t enough to meet DHS specifications, a final model was created using three layers of the material. ILC and DHS gained confidence in the design after the plug successfully passed a 21-day performance test where it held back water under pressures equal to those in a genuine crisis.
Back behind ILC, engineers set the demonstration into motion inside a full-scale reproduction of a typical subway tunnel. As air pumps whined the cabinet holding the plug popped open, allowing it to spill onto the floor. For safety reasons, the test article was inflated to only 1 psi before the media was allowed to examine it.
Although at minimum pressure the Vectran fabric gave somewhat when pushed with a finger, the plug returned a solid “thump” when tapped on its criss-cross of webbing material.
The test concluded successfully as the plug was brought up to full pressure and a torrent of water released behind the 32-foot-long structure.
Even as the plug was being developed, DHS was using the technology to design special curtains that can be used to hold back rising water from around buildings and to seal off subway personnel entrances. More than a dozen of these gates already have been deployed around Manhattan tunnel entryways.
The plug also can be designed to fit similar subway systems in other countries such as the London Underground or the Metro system in Paris.
ILC officials, citing industrial security and competition concerns, declined to discuss the cost of each plug system.