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Table 1 Current technology used for flooding containment in transportation tunnels [2, 41]

From: Large-scale inflatable structures for tunnel protection: a review of the Resilient Tunnel Plug project

System Description of operation Order-of-Magnitude Cost ($US) Advantages Disadvantages
Sliding Floodgates Similar to sliding gates used for controlling flow in open channels. High (H), between $3 million and $10 million, to Very High (VH), over $10 million • They are typically made of steel, which allows withstanding relatively medium to high flooding pressures.
• Typically installed close or outside of a tunnel entrance.
• These can also be installed in new tunnels at specific locations.
• Mechanically or manually operated.
• With proper maintenance, a long operative lifetime is expected.
• Relative quick deployment (< 10 min).
• It is challenging to install within existing tunnels without significant disruptions in the tunnel and surrounding areas.
• Significant vertical clearances needed for the installation of floodgates.
• Installation cost in existing tunnels can be high to very high.
• Extensive tunnel utility relocation.
• Maintenance required to ensure operability of mechanisms and prevention of corrosion.
Automated Doors These are typically designed to protect the tunnel against flooding when fully closed. Very High (VH), over $10 million • Doors can be heavy (see for example the 50,000-lb steel floodgates and other controls at the Hugh L. Carey and Queens Midtown tunnels in New York.
• They are typically made of steel, which allows withstanding relatively medium to high flooding pressures.
• Typically installed close or outside of a tunnel entrance.
• These can also be installed in new tunnels at specific locations.
• Mechanically or manually operated, and with proper maintenance, a long operative lifetime.
• Relative quick deployment (< 10 min).
• Installation cost in existing tunnels can be very high.
• Better suited for installation at the entrance of vehicular tunnels with rectangular or square cross-sections but not for circular or quasi-circular cross-sections.
• Maintenance required to ensure operability of mechanisms and prevention of corrosion.
Portable Bulkheads Similar to automated doors, but with doors stored off-site and installed when needed. Holding frames can be preinstalled in the tunnel. Medium (M), between $1 million and $3 million • Reactive flood control system potentially used as a backup system in case of faulty or failure of automated doors.
• Portable modules can be transported or craned to the site and installed in preexisting frames to provide a seal.
• Typically installed with cranes or gantries manually operated.
• Off-site storage reduces space requirement in the tunnels.
• Slow deployment due to transportation to and installation on the site.
• Limited accessibility to the tunnel during a flooding event can make installation of modules difficult.
• Supporting frames need to be pre-installed and maintained to ensure an adequate sealing capacity.
• Manual assembly may be required at the site.
Stop Logs Individual bars or logs combined typically in the vertical direction to make a seal. Holding frames can be preinstalled at entrances or portals or specific locations within the tunnel. Low (L), up to $1 million • Similar to portable bulkheads, it is typically a reactive flood control system.
• Can be used as a backup system in case of faulty or failure of automated doors.
• Relative low-cost alternative.
• Slow deployment due to transportation to and installation of logs on the site.
• Manual assembly may be required at the site.
• Supporting frames may need to be pre-installed at specific locations.
• Holding pressure depends on the material of logs, wood, metal, and concrete.
• Sealing may not be watertight.
Inflatable plugs Concept of operation similar to automobile airbag, in which a pre-folded inflatable in a compact container installed at selected locations inside the tunnel. An air inflation system deploys and pressurizes rapidly the inflatable to prevent the propagation of flooding. Low (L), up to $1 million, to Medium (M), between $1 million and $3 million, depending on the tunnel configuration and level of retrofitting needed to install the plug containers • Can be used in the proximity of tunnel entrances or within the tunnel system at selected locations.
• Can be used to compartmentalize the tunnel system in segments for localized flood control.
• Can be installed on the ceiling or laterals of the tunnels.
• Scalable and modular system that can be used to contain flooding in rail, automotive and other tunnels.
• Current membrane technology allows containment of medium flooding pressures, up to 100 kPa to 180 kPa, in 4 to 6-m diameter rail tunnels.
• A relatively low-cost system when compared to automated doors or vertical flood gates.
• Relative quick deployment (< 5 min) and pressurization (< 20 min).
• When in storage and not in use, lifetime estimated to be around 15 to 20 years.
• Requires retrofitting of tunnel location for mounting the plug container and also to maximize the sealing capacity of the inflatable.
• The structural membrane of the inflatable may be susceptible to abrasion in rough tunnel environments.
• Current materials and manufacturing technology prevent reaching higher inflation pressures, which in turn limit the flooding pressures that can be contained.
• Once used in a flooding event, the inflatable and container need to be replaced by a new or refurbished unit.