The US Department of Homeland Security (DHS) has devised a novel yet highly effective means of plugging vehicle or train tunnels during flood conditions.
The DHS-led project has turned to the principles underlying devices as commonplace and basic as the humble pump and the inflatable balloon to create a giant plug for use in underground tunnels in the case of flooding disasters.
The Resilient Tunnel Plug (RTP) measures around five metres in diameter and almost 10 metres in length, and can be used to section off and isolate tunnel sections in the event of heavy flooding, as well as other contingencies which could result in the spread of fires or the release of toxic gas.
The device is essentially a giant inflatable vessel fashioned from super-durable materials which can be deployed swiftly and with ease in tunnel environments during hazardous contingencies.
The distinctive innovation of the RTP is its ability to fill varied configurations of space when it inflates instead of just expanding into a fixed shape which gets wedged into the tunnel frame and suffers from gaps.
This is achieved via the ingenious use of zip ties, which pop at certain pressures so that different portions of the bag inflate at different times. The end result is a staged inflation of the RTP, enabling it to fill the entire space of the tunnel and more effectively seal it off.
The device achieves remarkable durability via the use of a three-layer structure partially consisting of the same space-age material which was used for the Mars Rover landing bags.
The two outer layers are made from Vectran, with the outermost layer woven into a webbing structure for enhanced strength. The innermost layer is the capsule which actually contains the medium used for inflation of the plug, with the three-part structure providing for a long term operating pressure of 17 psi.
The compact size and portability of the device when not in use also comprises a major advantage compared to solid floodgates, which are bulky, costly and difficult to both transport and install in a confined environment.
When not inflated, the device is small enough to fit inside a cloth-like bag, roughly equivalent in size of the container for a large capacious parachute. It can be inflated to full pressure in under half an hour, using either air or water depending upon circumstance.
The DHS Science and Technology Directorate commenced work on the RTP in 2007. It was developed in collaboration with Pacific Northwest National Laboratory, West Virginia University, and Delaware-based engineering firm ILC Dover.