Could Soft Composites Have Saved NYC Subway?

The concept of the Resilient Tunnel Plug (RTP) is a huge inflatable plug that can block tunnels (subway, vehicular traffic, etc) to isolate sections of tunnel against the spread of flood waters, terrorist gas attacks, or other fluid threats.  It utilizes a layered structure of soft composite materials to create a very large ‘balloon’ that can be folded up into very compact storage.  The folded plug is deployed by permanent installation in the tunnel wall and kept ready for emergencies.  When needed, it inflates, blocking the tunnel.

The RTP Project is being implemented by the U.S. Department of Homeland Security (DHS) Office of Science and Technology (S&T) as part of the High Impact Technology Solutions (HITS) program. The RTP project is managed through Pacific Northwest National Laboratory, and research & testing services are provided by West Virginia University. ILC Dover is responsible for design and manufacture of the RTP.  ILC Dover has developed a wide range of inflatable structures, including several that have figured prominently in the US space program, such as the “air bags” used to bounce-land two of the Rover missions to Mars.

This system was successfully tested in a full-sized, pressurized mock-up tunnel last January. The test prototype was 16 feet in diameter and 32 feet long. It was tested to 25 psi with a minimum safety factor of four at design pressure, and is said to be capable of long term operation at 17 psi. It kept water leakage low enough that the dry side of the tunnel could be kept clear by pumps in real time.

The structure of this highly stressed inflatable consists of macro-woven webbing and rope assemblies, a secondary structural layer, and an underlying inflation retention layer. Structural load bearing members are fabricated from Vectran™ fibers, which provide excellent strength and flex fold characteristics, allowing small packing volumes to be achieved.  In this application, the high ratio of strength-to-size – seen in many fiber-reinforced composites – is put in service of being able to fold down very small when uninflated.

Unfortunately, the project is still in the development stage.  Only prototype plugs exist, and none are yet deployed in actual tunnels.  Several members of the development team expressed regret that it wasn’t further along when the Hurricane Sandy hit New York City.

See a video demonstration of the RTP in a mock-up tunnel.

All photos courtesy of ILC Dover