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OCR for page 70
70 Table 12. Relative severity ratings in transportation tunnels. Relative Low High Severity Immersed Tube Cut-and-Cover Construction Type Soft Ground Tunnel Rock Tunnel Underwater Running and Flowing Cohesive Running Fast Raveling Ground Type Firm to Raveling Highly Jointed / Weathered Rock Moderately Jointed Rock Massive Rock Rock Bolts / Dowels Shotcrete Steel Ribs and Lattice Girder Support Type Unreinforced Concrete Reinforced Concrete Steel Backfilled with Concrete Near Surface Tunnel Depth Shallow Intermediate Deep transport the payload and consolidating at a critical loca- delivery device, and ultimate target. The right side of the tables tion inside the tunnel. contain each of the major tunnel types: immersed tube, cut- Introduction of very large IEDs, which are delivered by and-cover, bored or mined in soft to firm ground, bored or ship, barge, or boat. The depth charge is dropped and det- mined in strong rock, and air-rights structure tunnels. Each onated above an immersed tube tunnel. row represents a unique hazard or threat scenario. If that sce- Fire load larger than 341 MBTU per hour (100 MW). nario poses danger to a certain type of tunnel, then that inter- secting cell describes the physical vulnerability (PV), the In addition to the size of the hazard or threat, other critical operational vulnerability (OV) and the damage potential (DP). factors considered in the damage potential rating included type The damage potential is presented in terms of the rating abbre- of tunnel construction, ground condition, ground support sys- viations given in Table 13 (from A to F). tem, and soil or rock overburden thickness. The damage poten- tial rating is divided into six categories--letters A through F--ranging from severely catastrophic (A) to negligible (F). 4.4.6 Summary Tables 14, 15, and 16 present structural vulnerabilities to the The information presented in Section 4.4 allows tunnel most likely hazard or threat scenarios for road tunnels, transit facility owners, operators, and engineers to conduct prelimi- tunnels, and rail tunnels, respectively. These tables basically nary vulnerability rating assessments of their facilities and, if combine the information given in Table 3 (hazard and threat needed, to derive priority lists of tunnel structural compo- scenarios) with the information given in Table 13 (damage nents for further study. potential ratings for transportation tunnels). The hazard and threat scenarios have been rearranged into subtables based on the "Path to Target" and the "Target." These items are located at 4.5 System Elements and the top left side of each subtable. The hazards and threats pre- Vulnerabilities sented on the left side of the tables include very large, large, 4.5.1 Key Safety Functions medium, and small IEDs and large fires. All of the hazards and threats were developed further to identify hazard and threat There are many systems serving transportation tunnels. Of scenarios that include hazard and threat, path to target, tactical these systems, many are not visible but are nonetheless

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71 Table 13. Damage potential ratings for transportation tunnels. Fire (>34 Soil or Rock Explosion Tunnel MBTU per Ground Support System Overburden Type 1 hour, or Thickness Small Medium2 Large3 100 MW) Strong < 1 x diameter E D C D All Types Rock > 1 x diameter E D C D Rock Bolts with Wire < 1 x diameter D B B B Mesh/Lattice Girder/ Shotcrete > 1 x diameter D B B B Steel Ribs with or < 1 x diameter F B B B Soft Rock/ without Liner Plate >1 x diameter F B B B Firm Bored or Mined Ground Cast-in-Place < 1 x diameter F B B C/B Concrete Liner > 1 x diameter F C/B B C/B < 1 x diameter D B A B Segmental Concrete > 1 x diameter D B B/A B Steel Ribs or Lattice < 1 x diameter D B A B Girder with Shotcrete >1 x diameter D B A B Loose/Soft Cast-in-Place < 1 x diameter F B A C/B Ground Concrete > 1 x diameter F C/B B/A C/B < 1 x diameter D B A B Segmental Concrete > 1 x diameter D B A B Unreinforced < 15' D B A C Concrete/Masonry Firm Lining > 15' D B A C Ground < 15' D B A C Cut-and-Cover Reinforced Concrete Lining > 15' D B A C Unreinforced < 15' D B A C Concrete/Masonry Loose/Soft Lining > 15' D B A C Ground < 15' D B A C Reinforced Concrete Lining > 15' D B A C Steel Tube D B A D Immersed Tube Concrete Tube D B A D Air-Rights Structure D C B D Notes: 1. Transported by foot. 2. Transported by car. 3. Transported by truck. (continued on next page)