The Department of Homeland Security (DHS) Science and Technology Directorate (S&T) in US has developed a novel technology to hold dangerous gases or flood water in tunnels and tested the technology in January, 2012.
S&T's tunnel plug uses high strength fabrics to withstand the pressures of a flooded tunnel.
The Resilient Tunnel Project (RTP) of S&T has created a huge inflatable cylinder, which is tunnel-shaped having rounded capsule-like ends resembling a large plug. The inflatable cylinder can be sealed with air or water to control flood.
The novel technology that protects important mass transit systems was developed by S&T in association with ILC Dover, producer of NASA space suits and Pacific Northwest National Laboratory, West Virginia University (WVU.
The huge plug can inflate to a length of 32 ft and a width of 16 ft and has the capacity to hold up to 35,000 gal of water. The plug can be stored in a small place within the tunnel and inflates immediately during any disaster when it receives a signal from the command center in the tunnel system.
However, due to the irregular shape of the tunnel, it cannot be fully covered by the cylindrical plug. To overcome this issue, engineers created the plug with a larger circumference than the tunnel, which provided a tight sealing to the tunnel. The plug must fit the tunnel properly and importantly, must be strong enough to withstand pressure and flexible for packing as well.
After rigorous analysis, the team settled down for a material with three layers, including, the outer webbed Vectran layer, the inner non-webbed Vectran and polyurethane layers. The outer layer is strong and gives shape to the plug, whereas, the inner layers seal water or air.
A unique test tunnel was built at Morgantown, WV, to test the performance of the plug. On the test day, the tunnel was inflated with low pressure air initially. Secondly, air in the tunnel was replaced by water to reach the design pressure and finally, the test tunnel was closed and flooded with water to create a flood condition. The plug was able to sustain the emergency conditions and hence, was a success.
Source: http://www.dhs.gov/