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