National Academies Press: OpenBook

Making Transportation Tunnels Safe and Secure (2006)

Chapter: Chapter 4 - Tunnel Elements and Vulnerabilities

« Previous: Chapter 3 - Case Studies
Page 51
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 51
Page 52
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 52
Page 53
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 53
Page 54
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 54
Page 55
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 55
Page 56
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 56
Page 57
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 57
Page 58
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 58
Page 59
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 59
Page 60
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 60
Page 61
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 61
Page 62
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 62
Page 63
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 63
Page 64
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 64
Page 65
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 65
Page 66
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 66
Page 67
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 67
Page 68
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 68
Page 69
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 69
Page 70
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 70
Page 71
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 71
Page 72
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 72
Page 73
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 73
Page 74
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 74
Page 75
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 75
Page 76
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 76
Page 77
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 77
Page 78
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 78
Page 79
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 79
Page 80
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 80
Page 81
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 81
Page 82
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 82
Page 83
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 83
Page 84
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 84
Page 85
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 85
Page 86
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 86
Page 87
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 87
Page 88
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 88
Page 89
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 89
Page 90
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 90
Page 91
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 91
Page 92
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 92
Page 93
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 93
Page 94
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 94
Page 95
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 95
Page 96
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 96
Page 97
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 97
Page 98
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 98
Page 99
Suggested Citation:"Chapter 4 - Tunnel Elements and Vulnerabilities." National Academies of Sciences, Engineering, and Medicine. 2006. Making Transportation Tunnels Safe and Secure. Washington, DC: The National Academies Press. doi: 10.17226/13965.
×
Page 99

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

51 4.1 Introduction When considering the role of the 550 U.S. highway and transit tunnels in the overall transportation network, and considering the lessons observed from natural disasters and the transportation-related consequences of the Septem- ber 11th attacks, it is clear that loss of a critical tunnel at one of numerous “choke points” could result in hundreds or thousands of casualties; billions of dollars of direct recon- struction costs; even greater socioeconomic costs; and ancil- lary costs to other institutions in the nation’s complex, interrelated economy. For these reasons, transportation agencies must conduct systematic reviews to understand their facilities, identify their vulnerabilities, and develop pro- tection strategies. This chapter describes important elements of various tunnel construction methods used for transportation tun- nels. Discussions on the failure mechanisms associated with hazards and threats are included. In addition to the con- struction method and general tunnel vulnerability assess- ment, a comprehensive description of the various tunnel liners and structural systems is provided. The critical factors that could affect structural behavior in the event of safety- related hazards or security-related threats are then intro- duced and related to the various features of the different tunnel systems. The results of this chapter lead to the Chapter 5 guidelines for use by tunnel and facility owners and operators to iden- tify (1) critical locations in tunnel structures from the opera- tion and safety standpoints and (2) countermeasures appropriate to those critical locations. Because of the unique features of transportation tunnels, the structural response of a transportation tunnel to a hazard or threat differs somewhat from that of a surface structure. The most notable of these features are (1) a high ratio of lon- gitudinal length to cross-sectional dimension, (2) a complete confinement by the surrounding soils and rocks, (3) reflected pressures developed from the tunnel boundaries when an internal explosion occurs, and (4) a coupled behavior of air blast inside the tunnel and wave propagation through the sur- rounding ground. An understanding of the characteristics of various types of tunnels is essential in performing an accurate vulnerability assessment. For example, an immersed tube tunnel is partic- ularly vulnerable to rapid flooding in the event of an explo- sion. This high risk is due to the following features of the immersed tube tunnel: (1) the tunnel is under high hydro- static water pressure; (2) the tunnel is surrounded by porous backfill materials; and (3) there is a limited thickness of soil cover over the tunnel. The vulnerability of an immersed tube tunnel should therefore be assessed not only from a structural damage standpoint, but also from a flooding potential stand- point. Similarly, cut-and-cover tunnels are typically built in shallow depth with limited backfill above the structures; this build reduces the amount of confinement in the vertical direction when the tunnel is subjected to either internal or external explosions. In addition, cut-and-cover tunnels are usually built in soil sites and therefore tend to be less blast resistant than tunnels surrounded by rock. Conversely, bored or mined tunnels in rock with deep cover are more resistant than those in soils with shallow cover. Therefore, the type of tunnel has a major impact on the tunnel’s vulnerability to extreme events. 4.2 Types of Transportation Tunnels Tunnel types can be categorized to a certain extent by their usage, or mode of transportation. The functional types of tunnels included in this report are as follows: • Road, • Transit, and • Rail (both passenger and freight). C H A P T E R 4 Tunnel Elements and Vulnerabilities

4.2.1 Typical Road Tunnels Road tunnels that are longer than 1,000 feet (304 meters) typically have forced air ventilation systems. Prior to 1995, when the Federal Highway Administration (FHWA) approved the use of jet fans in tunnels based on results of the Memorial Tunnel Fire Ventilation Test Program (MTFVTP), the majority of tunnels were ventilated with ducted systems. A tunnel that is served by a full transverse ventilation system has a supply air duct and an exhaust air duct, and a tunnel that is served by a semi-transverse ventilation system can have either a supply duct or an exhaust duct. In cut-and-cover tunnels, the air ducts typically run side by side to save on excavation costs, as shown in Figure 1A. In bored or mined tunnels, the ducts typically fill the available space above and below the road, as shown in Figure 1B. Tunnels served by longitudinal ventilation systems typically have ceiling-mounted jet fans in the road space in lieu of the upper ducts shown in the figures. Both of the figures depict one walk- way on the right side of the road, although some multilane tun- nels may have walkways on both sides. Tunnel utilities such as power and communication conduits and fire standpipes can run along the benchwall, as is shown in both sketches, or in the opposite sidewall, as shown in the bored tube tunnel. 4.2.2 Typical Transit and Rail Tunnels Typical transit and rail tunnels are shown in Figure 2. Shorter tunnels can be ventilated naturally by the train’s pis- ton action. Longer tunnels without forced ventilation typi- cally have intermittent ventilation shafts that relieve the tunnel pressure through sidewalk gratings, as shown in Fig- ure 2D. Longer tunnels with forced air ventilation can be served by midtunnel and/or end-of-station-platform fan shafts. Individual tracks in cut-and-cover transit and rail tun- nels can be separated by columns, porous dividing walls, or solid dividing walls. Similar to road tunnels, utilities are routed along the tunnel benchwalls. 4.3 Tunnel Construction Methods In the U.S. transportation system, tunnels have been con- structed by a variety of methods, as shown in Table 6. In gen- eral, the types of tunnels are identified by the principal types of tunnel construction and include (1) immersed tube tunnels, (2) cut-and-cover tunnels, (3) bored or mined tun- nels, and (4) air-rights structure tunnels. Determination of the appropriate method of construction typically depends on the depth, cross section, and soil/rock/groundwater condi- tions along the alignment. Other constraints include geo- graphical and environmental factors, presence of existing structures and utilities, and constructability issues. The dif- ferent materials (i.e., structural and geological), tunnel con- figurations, and construction procedures used for these tunnels impact their resistance to hazards and threats. It is therefore important to identify the various types of tunnels and the factors that could have a major impact on their vul- nerability to hazards and threats. 4.3.1 Immersed Tube Tunnels Immersed tube tunnels are employed to traverse a body of water. Tunnel sections, usually 300 to 450 feet (91 to 137 meters), are placed into a pre-excavated trench. The tunnel construction method involves (1) construction of tunnel sections in an offsite casting or fabrication facility that are finished with bulkheads and transported to the tunnel site; (2) placement of the sections in a pre-excavated trench, joint- ing and connecting together and ballasting/anchoring; and (3) removal of temporary bulkheads and backfilling the exca- vation. The top of the tunnel should be at least 5 feet (1.5 52 (A) Typical cut-and-cover road tunnel. (B) Typical bored tube road tunnel. Figure 1. Typical road tunnels.

53 (A) Typical bored tube rail tunnel. (B) Typical mined horseshoe rail tunnel. (C) Typical cut-and-cover rail tunnel. (D) Typical cut-and-cover transit tunnel. Figure 2. Typical transit road tunnels.

meters) below the original bottom to allow for an adequate protective backfill. Two distinct types of immersed tube tunnel construction have emerged over the years: (1) steel shell immersed tunnels; and (2) concrete immersed tunnels. Steel shell immersed tun- nels are categorized according to the construction method: single-shell or double-shell construction. The first trans- portation tunnel constructed by immersed tube methods in the United States was completed in 1910 for the Michigan Central Railroad Tunnel under the Detroit River. The 1993 report by the International Tunnelling Association (ITA) pro- vides a technical inventory of 91 immersed tube tunnels com- pleted since 1910 [Ref. 3]. For the steel single-shell construction, an outer steel shell serves as a permanent watertight membrane and an exterior form for the final concrete lining. The steel shell also takes flexure forces along the exterior face of the tube before and after the placement of the concrete lining. The steel shell tube behaves as a composite steel-concrete structure after the inte- rior concrete is completed. Figure 3 shows a typical single-shell tube for two rapid tran- sit tracks, separated by a service gallery and an emergency ven- tilation exhaust air duct. For this example, the shell plate is 3/8 of an inch (9.5 millimeters) thick and stiffened by interior transverse steel ribs spaced 6 feet (1.8 meters) on center and two longitudinal vertical interior trusses encased in the rein- forced concrete walls of the gallery. The interior lining of rein- forced concrete has a minimum thickness of 2 feet 3 inches (68.5 centimeters). The exterior shell is protected against cor- rosion by a cathodic protection system. Ballast pockets 2 feet 6 inches (78.2 centimeters) deep on top of the tube are filled with gravel to provide adequate weight to overcome buoyancy during sinking of the tube. The basic elements of the double-steel-shell tube is a steel shell that forms a watertight membrane and, in combination with a reinforced concrete interior lining, provides the neces- sary structural strength for the completed tunnel. Figure 4 represents a typical double-steel-shell tube, which shows the cross section of a two-lane tunnel on an Interstate highway. In this example, the circular steel shell has a diameter of 36 feet 2 inches (11 meters) and is made of five-sixteenths inch (8 millimeters) welded steel plate. It is stiffened by external diaphragms spaced 14 feet 10 inches (4.5 meters) apart and external longitudinal stiffening ribs. The interior is lined with a minimum thickness of reinforced concrete. An exterior con- crete envelope of 2-foot (61-centimeter) minimum thickness, 54 Type Description Sketch Immersed Tube Tunnel • Employed to traverse a water body • Preconstructed sections are placed in a pre- excavated trench and connected • Typical materials include steel and concrete immersed tunnel sections • After placement, tunnel is covered with soil Cut-and- Cover Tunnel • In urban areas • Excavated from the surface, then constructed in place and backfill placed to bury structure • For subway line structures, subway stations, and subsurface highway structures • Typically concrete cast-in-place or precast sections • Steel framing and concrete fill Bored or Mined Tunnel • In urban or remote locations in land, on mountains, or through water bodies • Bored using a variety of techniques • Supported by initial and final support systems • Soft ground or rock tunneling • Structure may have various liner systems, including rock reinforcement, shotcrete, steel ribs and lattice girder, precast concrete segment, cast-in-place concrete, and fabricated steel lining Air-Rights Structure Tunnel • In urban areas • Created when a structure is built over a roadway or trainway using the roadway’s or trainway’s air rights • The limits that an air-rights structure imposes on the emergency accessibility and function of the roadway or trainway that is located beneath the structure should be assessed Table 6. Types of transportation tunnels.

confined by one-quarter inch (6.4-millimeter) steel form plates attached to the shell, protects the shell against corro- sion and acts as a ballast against buoyancy. The space below the road slab forms a fresh air supply duct. The segment above the ceiling is an exhaust duct. Concrete immersed tube tunnels are generally rectan- gular reinforced concrete sections. The concrete thickness is determined largely by the weight required to prevent uplift. Crack controls to achieve impermeability of the concrete and independent waterproofing membranes are considered to accomplish water tightness. Typical waterproofing membranes used in concrete immersed tunnels are steel membranes made of one-quarter inch steel plates, multiple-ply membranes of fabric and coal-tar layers, and plastic membranes made of syn- thetic neoprene (or vinyl-type rubbers) with epoxy coatings. Figure 5 represents a typical concrete immersed tube for a four- lane highway tunnel with two 2-lane sections and ventilation ducts on both sides. Prestressed concrete has also been used to construct immersed tube tunnels. 4.3.2 Cut-and-Cover Tunnels Shallow-depth tunnels in land are frequently designed as structures to be constructed using the cut-and-cover method. The cut-and-cover tunnel construction method involves braced, trench-type excavation (“cut”) and placement of fill materials over the finished structure (“cover”). The excava- tion is typically rectangular in cross section and only for rel- atively shallow tunnels (typically less than 45 to 60 feet [14 to 18 meters] of overburden). Cut-and-cover tunnel structures may be divided into three types of structures in transporta- tion systems: subway line structures, subway stations, and subsurface highway structures. Figure 6 represents a typical “line” cut-and-cover structure constructed between subway stations. In the line structures, the subway tracks are usually enclosed in a reinforced concrete double-box structure with a supporting center wall or beam with columns. The track centers are normally located as close together as possible. The typical cut-and-cover subway station is a two- or three-story reinforced concrete structure in a rectangular excavation 50 to 65 feet (15 to 20 meters) wide, 500 to 800 feet (152 to 244 meters) long, and 50 to 65 feet (15 to 20 meters) deep. Figure 7 represents a cross section of a typical subway station. Cut-and-cover structures for older transit facilities were constructed using steel frame construction with rein- forced or unreinforced concrete between the frames. This method is referred to as jack arch construction. Cut-and-cover highway tunnels are often used in urban areas. In addition, they are often constructed at the approaches to subaqueous vehicular tunnels due to the depth required. Fig- ure 8 represents a typical highway cut-and-cover cross section. This type of tunnel is often under the groundwater table and typically consists of massive reinforced concrete structures. 4.3.3 Bored or Mined Tunnels When a tunnel is located at significant depth or when over- lying structures exist above the tunnel alignment, bored or 55 Figure 3. Steel single-shell immersed tube tunnel.

56 Figure 4. Steel double-shell immersed tube tunnel. Figure 5. Concrete immersed tube tunnel.

57 Figure 6. Cut-and-cover tunnel, subway line structure. Figure 7. Cut-and-cover tunnel, subway station.

mined underground tunnel construction is typically the pre- ferred method. Bored tunnels are often excavated using mechanical equipment, such as TBMs, and are usually circu- lar. Mined tunnels may be excavated using manual or mechanical methods and may be rectangular or horseshoe- shaped. Bored or mined tunnels are typically divided into two groups based on the type of surrounding ground: soft ground tunnels and rock tunnels. For bored or mined tunnels in soft ground (i.e., soft ground tunnels), the main concerns during excavation are associated with groundwater conditions and stability charac- teristics of the soil along the alignment. The control of groundwater is of utmost importance in soft ground tunnel- ing. Typical methods for controlling groundwater are dewa- tering, using compressed air, grouting, freezing, and using pressurized face TBMs. Recent improvements in grouting have made grouting a valuable tool in both groundwater con- trol and soil stabilization for soft ground tunneling. For bored or mined tunnels in rock (i.e., rock tunnels), sta- bility problems in blocky jointed rocks are generally associ- ated with gravity falls of rock wedges from the roof and side- walls. A tunnel in an unweathered, massive rock with few joints does not usually suffer from serious stability problems unless stresses in the rock exceed the strength of the rock. As the below-surface depth increases or as the number of close- together excavations increases, the rock stress increases to a level at which failure is induced in the rock surrounding the tunnels. This failure may range from minor spalling or slab- bing in the surface rock to major rock bursts involving failure of significant volumes of rock. Various tunneling methods used in rock and soft ground are summarized in Tables 7 and 8, respectively. When surrounding ground is massive and rock mass is sta- ble, the tunnel may require no support system or minimal support systems at portals and weak rock zones. When the ground is unstable, the initial support system is installed before, during, or immediately after excavation to stabilize the excavation. The final lining system is then placed to provide permanent support and to provide a durable, maintainable, long-term finish. Tables 9 and 10 show the initial support and 58 Figure 8. Cut-and-cover tunnel, subsurface highway structure.

lining systems and the typical application of the initial sup- port and lining systems, respectively. 4.3.4 Air-Rights Structure Tunnels Air-rights structure tunnels are defined by the National Fire Protection Association (NFPA) [Ref. 5] as structures that are built over a road using the road’s air rights, thereby imposing on the accessibility and operation of the road or train during emergency operations. Air-rights structure transportation tunnels have been constructed to enclose both road and rail operations. Figure 9 shows a typical air-rights structure tunnel. The structure is supported by intermittent columns. The structure above the tunnel can be a building of any type, a transit or rail station, a parking garage or a parking lot. These structures create transportation tunnels and may be as dangerous as the air-rights structures constructed above the roads or trains because of the relative ease of access. The damage potential of an incident in an air-rights tunnel can also be greater than those for other tunnel types because occupancy loads include the people located in the structure. 4.4 Structural Elements and Vulnerabilities 4.4.1 Ground Characteristics Terzaghi published the Tunnelman’s Ground Classifica- tion System, which describes representative soil types and their predicted behavior during various tunneling con- struction methods [Ref. 6]. As shown in Table 11, Heuer modified this classification system to present the informa- tion in engineering terms that reflect current technology and usage [Ref. 7]. 4.4.2 Modes of Tunnel Failure Tunnel failure can range from local spalling (i.e., local fail- ure), local breach, partial or complete collapse, or inundation with water (i.e., global failure) to progressive failure. Figure 10 demonstrates how a threat can lead to progressive failure. Tunnel failure modes can start from an overstress in the lining caused by explosion or fire. This overstress may lead to failure of the lining if the strength of the lining material is less than the applied stress. The failure of the lining may be restricted to be a local failure such as spalling or local breach. When the tunnel lining is damaged locally or globally, fail- ure of surrounding ground (i.e., collapse) and/or inundation with water (i.e., flooding) may follow. These failures are considered global failures. It is considered a progressive failure when instability of adjacent underground structures and/or damage to surface structures is involved. Flooding of the transportation system may also be considered a progressive failure. Lining Failure from Explosion When an explosion occurs in a transportation tunnel, frag- mentation of the liner is expected near the detonation point. Then, the peak blast pressures and gas pressures from the explosion may overstress the lining and the initial support systems. The fragments and overstress may induce failure of the liner and support systems. The extent of failure depends on charge weights, charge shapes, detonation points, types and materials of tunnel liner and support systems, thickness 59 Type Description Sketch Tunnel Boring Machine (TBM) • Full face advance • Circular sections • High advance rate Roadheader • Partial face advance • Any cross section • Usable in rock with less than about 15,000 psi of unconfined compressive strength • Most effective if the unconfined compressive strength of rock is less than 5,000 psi Drill and Blast • Conventional method • Full or partial face advance • Any cross section • Cycle involves (1 ) drilling; (2) charging with explosives; (3) blasting and ventilation; (4) loading and hauling (mucking); (5) scaling and cleaning; and (6) installation of a support system Table 7. Tunneling methods for rock tunnels.

60 Type Description Sketch Blind Shield • A closed face (or blind) shield is used in very soft clays and silts • Muck discharge is controlled by adjusting the aperture opening and the advance rate • Used in harbor and river crossing in very soft soils; often results in a wave or mound of soil over the machine • Not used nowadays Open Face, Hand-Dug Shield • Good for short, small tunnels in hard, noncollapsing soils above groundwater tables • Usually equipped with face jacks to hold breasting at the face • If soil conditions require it, this machine may have a movable hood and/or deck • A direct descendent of the Brunel Shield • Seldom used nowadays Semi- Mechanized • Similar to open face, but with a back hoe and boom cutter; often equipped with “pie plate” breasting and one or more tables • May have trouble in soft, loose, or running ground • Compressed air may be used for face stability in poor ground • Seldom used nowadays Mechanized • A fully mechanized machine • Excavates with a full face cutter wheel and pick or disc cutters • Manufactured with a wide variety of cutting tools • Face openings (doors, guillotine, etc.) may be adjusted to control the muck taken in versus the advance of the machine • Compressed air may be used for face stability in poor ground Slurry Face Machine • Uses pressurized slurry to balance the groundwater and soil pressure at the face • Has a bulkhead to maintain the slurry pressure on the face • Good for water-bearing silts and sands with fine gravels; may accommodate boulders • Best for sandy soils; tends to gum up in clay soils; with coarse soils, face may collapse into the slurry • Can be equipped with disk cutters to bore through boulders or rock in mixed face conditions Earth Pressure Balance (EPB) Machine • A closed chamber (bulkhead) face used to balance the groundwater and/or collapsing soil pressure at the face • Uses a screw discharger with a cone valve or other means to form a soil plug to control muck removal from the face and thereby maintain face pressure to “balance” the earth pressure • Best for clayey soils with acceptable conditions • Acceptable for silt and clayey and silty sand • Often uses foams and/or other additives to condition the soil • Can be equipped with disk cutters to bore through boulders or rock in mixed face conditions EPB High- Density Slurry Machine • A hybrid machine that injects denser slurry (sometimes called slime) into the cutting chamber • Developed for use where soil is complex, lacks fines or water for an EPB machine, or is too coarse for a slurry machine Table 8. Tunneling methods for soft ground tunnels (as modified by Zosen [Ref. 4]).

61 Type Description Sketch Rock Reinforcement • Untensioned rock dowels or tensioned rock bolts • To help rock mass self-support capacity and to mobilize the inherent strength of the rock mass • May provide only temporary support until a final lining is placed • To protect against spalling and fallout of rock wedges between reinforcements, a surface skin may be required such as chain link mesh or shotcrete Shotcrete • Early construction support in rock with limited stand-up time to prevent loosening of the rock mass and raveling failure • Used in soft ground tunnels when a sequential excavation method (SEM) is used. • Sometimes used as a permanent lining • May be reinforced for additional long-term ductility in poor or squeezing ground Steel Ribs and Lagging • Considerable appeal in poor rock conditions • Lateral spacer rods (collar braces) are usually placed between ribs • For soft ground tunnels, the ground between ribs is stabilized by lagging or by segmental plates Precast Concrete Segment Lining • Usually associated with soft ground tunneling • Bolted or unbolted segments • One- or two-pass lining system • Segments are bolted with a gasket for water tightness Cast-in-place Concrete Lining • Plain or reinforced • Commonly used second stage lining in two-pass lining system • Waterproofing membrane layer may be installed between initial support systems and the inner lining Fabricated Steel or Cast Iron Lining • Required when leakage through a cracked concrete lining is a concern. Designed for an exterior water pressure and furnished with external stiffeners for high- external-pressure conditions • Concrete placement is required to ensure firm contact between steel and ground Ground Rock Bolts Rock Bolts with Wire Mesh Rock Bolts with Shotcrete Steel Ribs and Lattice Girder Cast-in- Place Concrete Concrete Segments • • • • • • • • • • • • • • • • • • • Strong Rock Medium Rock Soft Rock Soil Table 9. Initial support and lining systems. Table 10. Typical application of initial support and lining systems.

62 Classification Behavior Typical Soil Types Firm Heading may be advanced without initial support, and final lining may be constructed before ground starts to move. Loess above water table; hard clay, marl, cement sand, and gravel when not overstressed. Slow Raveling Raveling Fast Raveling Chunks or flakes of material begin to drop out of the arch or walls some time after the ground has been exposed, due to loosening or overstress and “brittle” fracture (ground separates or breaks along distinct surfaces, as opposed to squeezing ground). In fast-raveling ground, the process starts within a few minutes; otherwise, the ground is slow raveling. Residual soils or sand with small amounts of binder may be fast raveling below the water table and slow raveling above. Stiff fissured clays may be slow or fast depending on degree of overstress. Squeezing Ground squeezes or extrudes plastically into tunnel, without visible fracture or loss of continuity, and without perceptible increase in water content. Ductile, plastic yield, and flow due to overstress. Ground with low frictional strength. Rate of squeeze depends on degree of overstress. Occurs at shallow to medium depth in clay of very soft to medium consistency. Stiff to hard clay under high cover may move in combination of raveling at execution surface and squeezing at depth behind surface. Cohesive Running Running Running Granular materials without cohesion are unstable at a slope greater than their angle of repose (±30–35). When exposed at steeper slopes, they run like granulated sugar or dune sand until the slope flattens to the angle of repose. Clean, dry, granular materials. Apparent cohesion in moist sand, or weak cementation in any granular soil, may allow the material to stand for brief periods of raveling before it breaks down and runs. Such behavior is cohesive running. Flowing A mixture of solid and water flows into the tunnel like a viscous fluid. The material may enter the tunnel from the invert as well as from the face, crown, and walls, and may flow for great distances, completely filling the tunnel in some cases. Below the water table in silt, sand, or gravel without enough clay content to give significant cohesion and plasticity. May also occur in highly sensitive clay when such material is disturbed. Table 11. Tunnelman’s ground classification for soils. Figure 9. Typical air-rights structure tunnel.

of liner, size and shape of tunnel, and type and amount of sur- rounding ground confinement. When tunnel linings are subjected to extreme blast load- ings, the stress–strain relationship of reinforced concrete is quite different from that under static load. This difference is due to the increased dynamic compressive and tensile strengths and the increased displacement capacity at ultimate stress. For reinforced concrete, dynamic strength magnifica- tion factors as high as 4 in compression and as high as 6 in tension for strain rates in the range of 102 to 103 per second have been reported by Grote et al. [Ref. 8]. For steel members, the U.S. Army recommends that dynamic yield strength 10 percent greater than the static yield strength be used [Ref. 9]. When the blasting induced peak overpressure is greater than the dynamic strength of the lining materials, the lining is con- sidered overstressed. Therefore, estimation of the blasting induced peak overpressure provides a critical input in tunnel lining vulnerability assessment. Breach failure potential may be determined by comparing breach threshold thickness and effective thickness of the tun- nel lining. The liner may be considered breachable when the effective thickness of the liner is less than the breach thresh- old thickness. The effective thickness of the lining includes the final lining thickness and the thickness of the portion of the initial support system that can be considered a permanent application, such as shotcrete. Breach threshold thickness of normal reinforced concrete with a strength of 4,000 psi (2,812,400 kilograms per square meter) for a spherical deto- nation is shown in Figure 11. Breach threshold thickness is expressed as a function of explosive charge weight and set- back distance (i.e., the distance from the face of the lining to the center of the charge) [Ref. 10]. Note that Figure 11 is not applicable for contact charges. This information allows a rough assessment of the tunnel lining vulnerability to an explosion inside the tunnel. Joint Failure Joints between immersed tube segments or between the end tube and the connecting structures (e.g., ventilation buildings) may be potential weak points in the structural sys- tem and may be more susceptible to flooding in case of 63 Threat Failure of Liner Overstress in Liner Failure of Ground Inflow & Flood Progressive Failure Range from lining face to charge center of gravity (ft) 0 2 4 6 8 1 0 1 2 1 4 1 6 Br ea ch th re sh ol d th ick ne ss (in ch ) 0 20 40 60 80 100 Large Medium Small Figure 10. Path to progressive failure. Figure 11. Breach threshold thickness for reinforced concrete [Ref. 10].

breach. There are various types of joints used in immersed tube tunnels: • Tremie joints: These joints have been used in a number of steel shell tubes in the past, but have rarely been used recently. The tremie joints in one particular underwater tunnel are steel formed in soil trenches and rock encased in rock trenches. For these tremie concrete joints, the steel reinforcement and the steel plate were welded and continued through the joints after internal dewatering. Thus, in this case, they are as strong as the main body of the tunnel. The tremie concrete is anticipated to provide additional resistance to loading resulting from blast waves. • Flexible joints: The initial seal of the flexible joint is pro- vided by the compression of rubber or neoprene gaskets attached to the face of one tube and bearing against a smooth surface on the adjoining tube. Many tunnels in the United States have used temporary gaskets that may form a seal, but the load is carried on solid stop bars. The two most recently built tunnels in the United States have used Gina-type joints that have soft noses and bodies capable of carrying the compressive load. Particularly in seismic areas, the flexible joints are designed to carry expected shear and tension loads and may sometimes be referred to as seismic joints. In such cases, a joint cannot open or have offset dis- placements under seismic loading conditions, which could lead to life-threatening ingress of water. This type of joint presents potential weakness for ingress of water and flood- ing under blast wave conditions resulting from detonation of an explosive. • Rigid joints: Rigid joints may be designed to have the same section properties as the rest of the tunnel, effectively mak- ing the tunnel continuous without joints. The resistance of the joints is therefore the same as the tunnel lining. Cross Passageway Failure The general lining response of cross passageway tunnels subject to blast loading is approximately the same as described above. Special attention should be given to the fol- lowing considerations: (1) high stress concentration may occur at the junctions with main tunnels and (2) given the same amount of explosive charge, the resulting blast peak pressure in a cross passageway tunnel may be greater than that in the main tunnel due to its smaller cross-sectional geome- try. Therefore, cross passages are more vulnerable to damage. In general, however, from an operational standpoint, cross passageway tunnels are not considered to be more critical than the main running tunnels because (1) there is generally more than one cross passageway tunnel (i.e., greater degree of redundancy) and (2) local failure or collapse of one or more of the cross passageway tunnels may not affect the stability of the main tunnels or prevent their continuous use, except when flooding results. Portal Failure From a stability standpoint, the tunnel portal area is gen- erally one of the critical locations due to the inherent slope stability problem. Landslide, rock fall, or even collapse at and near tunnel portals may be triggered by certain extreme events, such as earthquakes and blast waves, thereby blocking the passageway and potentially affecting structures or facili- ties at the top of the slope. Tunnel portals are therefore con- sidered to be particularly vulnerable during such extreme events. However, at the portal, the blast is less confined and the energy will dissipate. To stabilize the portal area, soil anchors or rock reinforcement systems are often used. Other remedial measures, such as flattening the earth slopes or using various ground improvement treatments, may also be effec- tive. Nevertheless, the damage potential of a portal failure is generally considered to be less than that of a tunnel lining fail- ure because the repair for a portal failure can be done in the open space. In addition, flooding is normally not an issue when a portal is damaged or collapses, so the repair time and associated costs are relatively low compared with the other parts of the tunnel. Ground (Soil and Rock) Failure Blasting may also cause the geological media surrounding the tunnel to yield or fail, particularly when the tunnel liner is breached or in unlined tunnels (such as those constructed in sound rock). The post-yield behavior of the surrounding geological media depends on the types of the materials encountered and their characteristics under high-energy transient loads. Following is a brief description of post-yield behavior of various types of soils and rocks: • Sand and gravel: These materials may quickly collapse into the tunnel. When sand and gravel are saturated with water, semi-flowing to flowing conditions may occur. Flooding of the tunnel could also happen if the surrounding material is very porous (such as gravel or rock fill) under a high groundwater level. This is particularly true for immersed tube tunnels. • Soft cohesive soils: Because of its low strength, soft cohe- sive soils, such as clay and silt, could demonstrate slow flowing behavior (i.e., creeping), eventually collapsing into the tunnel. • Stiff and highly overconsolidated cohesive clay: Local failure of this type of material into the tunnel is likely. 64

The material falling into the tunnel should be confined to the area where the liner is breached. • Shear zone, broken, or decomposed rocks: Depending on whether the shear zone is saturated with groundwater, the materials may advance into the tunnel under flowing, swelling, and squeezing conditions. • Plastic, ductile rock: This type of rock, such as shale, behaves similarly to the overconsolidated clay described above. It may yield without losing its coherence and thus provides self-support capability for a short duration. • Fractured rock held in place by support of dowels or shotcrete: The rock mass may yield with small to moder- ate displacements along fractures. Fresh fractures could be generated, thereby resulting in some loosened rock pieces falling into the tunnel. • Fractured rock without reinforcement: Upon blasting loads, this material tends to become severely loosened, thereby resulting in a raveling situation. • Stronger, brittle rock: Fractures and local spalling could occur. Chunks of rock loosened by the explosion could fall into the tunnel. Water Inflow and Flooding Transportation tunnels are intensively concentrated and interconnected in urban areas. Therefore, failure of an under- water tunnel ranging from collapse or complete inundation with water due to local breaching of the liner may lead to flooding in the underground transportation system. Flooding may also introduce large quantities of sand, silt, gravel or shear zone debris. Significant lengths of tunnel can become filled with debris or mud in short periods of time, causing tunnel structures to become buried. In addition, loosening of the soil under foundations can undermine structures above or adjacent to the tunnel. Progressive Failure Failure of the tunnel liner and surrounding ground may cause instability of adjacent underground utilities and dam- age to surface structures by piping and differential settle- ments. Flooding of the entire transportation system may also be considered a progressive failure. 4.4.3 Effects of Other Extreme Events Tunnel Lining Behavior During a Fire There are three primary adverse effects on concrete or shotcrete tunnel linings that are subjected to fire: • The lining may lose its effective section area by spalling, • The material strength and load-carrying capacity of the lining may be degraded when exposed to high tempera- tures resulting from the fire, and • Tunnels tend to be thermally restrained in both longitudi- nal and transverse directions, resulting in increased struc- tural demand under fire conditions. Fires in tunnels may lead to a high risk of explosive spalling of the concrete liner, particularly for concrete with high mois- ture content, such as shotcrete, or for high-performance or high-strength concrete with low permeability. Explosive spalling occurs in the temperature range where chemically bound water is released from the concrete. Explosive spalling of high-performance or high-strength concrete is directly related to internal pressures generated during the attempted release of chemically bound water. Lawson et al. characterized the residual mechanical prop- erties of high-performance or high-strength concrete after the concrete is exposed to elevated temperatures [Ref. 11]. Using results from a combination of a heat transfer analysis and a nonlinear structural analysis conducted for a range of service loads, concrete mixes, and fire types, Caner et al. pro- posed a guideline for assessing fire endurance [Ref. 12]. The effects of temperature-induced material degradation and ground tunnel liner interaction were considered in these analyses. Caner et al. also recommended techniques for repair of damaged concrete tunnel liners, as summarized below: • Concrete sections: Concrete sections exposed to tempera- tures in excess of 300°C (570°F) should be investigated. They should be removed or replaced if they are found to be deficient. The depth of fire-damaged concrete may be determined by using heat transfer analyses and should be verified by condition assessment. Voids and spalls should be patched with patching materials of similar characteris- tics as the concrete mix design used for the original tunnel to maintain its structural integrity. • Reinforcement: If the concrete is removed around the reinforcement, reinforcement shall also be removed. High- strength alloy bars may lose 40 percent of their initial strength at 500°C (930°F). The new reinforcement should be properly spliced to the existing reinforcement. • Micro-polypropylene fibers: Use of micro-polypropylene fibers in concrete will reduce explosive spalling because the fibers will melt over 130°C (270°F), making the concrete more porous, thus accommodating water vapor during a fire. An evaluation of the need for major repair should be determined on a case-by-case basis. Furthermore, with the more permeable concrete, the chance of explosive spalling may be minimal in the event of another fire. • Insulation materials: If the tunnel lining is insulated by the placement of coatings, and the insulation materials are 65

damaged, they should be replaced by the same type of material because of the fire performance history of the material. For practicality, spray-on insulation materials may be used to patch the damaged area. The MTFVTP consisted of 98 full-scale fire tests conducted in the abandoned Memorial Tunnel. Various tunnel ventila- tion systems and configurations were operated to evaluate their respective smoke and temperature management capa- bilities. The fire sizes ranged from 34.1 to 341 MBTU per hour (10 to 100 MW). For fires below 170.5 MBTU per hour (50 MW), only cosmetic damage to the tunnel structure was observed (mainly loss of ceramic tiles from the walls and ceil- ing). For the 170.5 MBTU per hour (50 MW) tests, spalling of ceiling concrete was observed. The areas that resulted in exposed reinforcing steel were repaired with reinforced shot- crete. The repaired areas were not further damaged during the 341 MBTU per hour (100 MW) tests. Test results are available from Bechtel/Parsons Brinckerhoff [Ref. 13] and on CD at www.tunnelfire.com/cd.htm. Full-scale fire tests were also conducted in Norway’s Runehamar Tunnel in association with the UPTUN (UPgrading methods for fire safety in existing TUNnels) Research Program [Ref. 14]. Insulated boards with high- temperature resistance were installed to protect the tunnel surfaces. A total longitudinal distance of 75 meters was pro- tected. The boards were installed along the first 25 meters downstream of the fire site. Ceramic curtains were installed beyond the boards; 9 meters upstream and 41 meters down- stream were covered. The highest gas temperature measured was 1,365°C. Significant spalling of the tunnel material occurred both upstream and downstream of the passive fire protection system. Earthquake Effects on Tunnels Underground structures are generally less vulnerable to earthquakes than surface structures, such as buildings and bridges, because the surrounding ground confines under- ground structures. As long as the surrounding ground is sta- ble and experiences only small ground deformations, the tunnel tends to move along with the surrounding ground and maintains its structural integrity. In a broad sense, earthquake effects on underground tun- nel structures may be grouped into two categories: • Ground shaking refers to the vibration of the ground pro- duced by seismic waves propagating through the earth’s crust. The area experiencing this shaking may cover hun- dreds of square miles near the fault rupture. As the ground is deformed by the traveling waves, any tunnel structure in the ground will also be deformed. • Ground failure broadly includes various types of ground instabilities such as faulting, landslides, liquefaction, and tectonic uplift and subsidence. Each of these instabilities can be potentially catastrophic to tunnel structures, although the damage is usually localized. It is often possi- ble to design a tunnel structure to account for ground instability problems, although the cost may be high. For example, with proper and often expensive ground improvement techniques and/or earth-retaining measures, it may be possible to remedy the ground conditions against liquefaction and landslides. Vulnerability Screening for Geotechnical Hazards and Threats. The discussions above show that it is important to perform a tunnel vulnerability screening study for ground failure potential (i.e., geotechnical or geological hazards and threats) prior to more detailed evaluation. The objective of the vulnerability screening process is to identify which sec- tions of the tunnel structures may have risk of poor perform- ance during earthquakes. For sections identified to have low earthquake risk, no further evaluations are required. Other- wise, further assessments may be needed. Factors to be con- sidered during this screening process include, but are not limited to, the following: • Liquefaction potential: Liquefaction potential exists in loose granular soils below the groundwater table only. To assess site-specific liquefaction potential in areas where liq- uefaction is possible, procedures based on the standard penetration test (SPT) blow count number from soil bor- ings and/or based on cone penetration test (CPT) data can be used. Both methods compare the soil liquefaction resist- ance (through SPT or CPT data) with the earthquake induced dynamic stresses. Detailed information about liq- uefaction and the recommended procedures for evaluating liquefaction procedures are documented in the report from the 1996 workshop sponsored by the National Center for Earthquake Engineering Research (NCEER) [Ref. 15]. • Slope stability: In general, a seismically induced landslide through a tunnel can result in large, concentrated shearing displacements and intense damage to the structure. Evalu- ations should focus on the following areas: (1) at tunnel portals (in soil as well as in rock), (2) in shallow parts of the tunnel alignment adjacent to soil slopes, and (3) in areas where existing slopes have displayed signs of movement under static conditions. The commonly used pseudo-static method of analysis can be used for evaluating the seismic stability in areas of concern. If a pseudo-static seismic sta- bility analysis indicates an insufficient safety margin against the landslide movements, then a more refined deformation- based method of analysis should be used to estimate the 66

movements. The impact of the potential slope movements on the affected structures should then be assessed. • Shear/fault zones: If a shear/fault zone crosses the tunnel alignment, the potential relative movement along the weak plane and its effects on the tunnel structure need to be eval- uated. In general, it may not be economically or technically feasible to build a tunnel to resist potential faulting dis- placements, particularly if the magnitude of the fault dis- placement is large (e.g., several feet). However, avoidance of faults may not always be possible, especially for tunnel systems that are spread over large areas. In highly seismic areas such as California, it may be inevitable for the tunnel to cross a fault. The design approach to this situation is to accept the displacement, localize the damage, and provide means to facilitate repairs. • Abrupt changes in structural stiffness or ground condi- tions: Stress concentrations often occur in abrupt stiffness change conditions. Special attention should be paid to the following locations: (1) at a tunnel’s junctions; (2) where a tunnel section traverses multiple distinct geological media with sharp contrast in stiffness (such as a shaft ris- ing from solid rock formation up through soft soil over- burden to the ground surface); and (3) where a regular tunnel section in soft ground is connected to rigid station end walls or a rigid, massive structure such as a ventilation building or shaft. Tunnel Response to Ground Shaking. The response of a tunnel to seismic shaking motions may be described in terms of three principal types of deformations: (1) axial deformation, (2) curvature deformation, and (3) ovaling (for circular tunnels such as bored tunnels) or racking (for rectangular tunnels such as cut-and-cover tunnels). Axial deformations are induced by components of seismic waves that propagate along the tunnel axis (i.e., longitudinal response of the tunnel). When the component waves pro- duce particle motions parallel to the longitudinal axis of the tunnel, they cause alternating axial compression and tension strains, as illustrated in Figure 12A. Curvature deformations result from component waves that produce particle motions in the direction perpendicular to the tunnel axis. The cur- vature deformation results in bending and shear demands on the tunnel structure, as shown in Figure 12B. The oval- ing or racking deformation (i.e., the transverse response of the tunnel) is caused primarily by seismic waves propagat- ing perpendicular to the tunnel longitudinal axis. Vertically propagating shear waves are generally considered the most critical type of waves for this mode of deformation, as shown in Figure 13 [Ref. 16]. Tunnel Damage Potential Due to Ground Shaking. Dowding and Rozen reported 71 cases of tunnel response to 67 Figure 12. Longitudinal deformation of tunnels. Figure 13. Transverse ovaling and racking of tunnels.

earthquake motions [Ref. 17]. The main characteristics of these case histories are as follows: • These tunnels served as railway and water links with diam- eters ranging from 10 to 20 feet (3 to 6 meters). • Most of the tunnels were constructed in rock with variable rock mass quality. • The construction methods and lining types of these tunnels varied widely. The permanent ground supports ranged from no lining to timber, masonry brick, and concrete linings. Based on their study, Dowding and Rozen concluded, pri- marily for rock tunnels, the following: • Tunnels are much safer than aboveground structures for a given intensity of shaking. • Tunnels deep in rock are safer than shallow tunnels. • No damage was found in both lined and unlined tunnels at surface accelerations up to 0.19 g. • Minor damage consisting of cracking of brick or concrete or falling of loose stones was observed in a few cases for surface accelerations above 0.25 g and below 0.4 g, • No collapse was observed due to ground shaking alone up to a surface acceleration of 0.5 g. • Severe but localized damage, including total collapse, may be expected when a tunnel is subject to an abrupt displace- ment of an intersecting fault. Owen and Scholl documented additional case histories (making a total of 127), including cut-and-cover tunnels and culverts in soils [Ref. 18]. Owen and Scholl’s conclusions form their study echoed the findings by Dowding and Rozen dis- cussed above. In addition, Owen and Scholl suggested the fol- lowing: • Damage to cut-and-cover structures appeared to be caused mainly by the large increase in the lateral forces from the surrounding soil backfill. • Duration of strong seismic motion appeared to be an important factor contributing to the severity of damage to underground structures. Damage initially inflicted by earth movements, such as faulting and landslides, may be greatly increased by continued reversal of stresses on already dam- aged sections. Using the data presented above as well as additional data from the 1995 Kobe, Japan, earthquake (with a moment mag- nitude of 6.9), Figure 14 summarizes empirical observations of seismic effects on the performance of bored tunnels [Ref. 19]. The damage state is presented as a function of ground shaking levels (represented by peak ground acceleration) and tunnel lining types. The data apply only to damage due to shaking. Data for cut-and-cover and immersed tunnels are not included in the figure. 4.4.4 Critical Factors in Vulnerability Assessment of Transportation Tunnels Because of the nature of underground structures, the vul- nerability of a tunnel must be assessed by considering the interactive effects of the blast pressure, the structure, and the surrounding ground. The critical factors that could have an impact on structural vulnerability in response to hazards and threats are summarized below: • Type of tunnel (i.e., construction type): In general, immersed tube tunnels and cut-and-cover tunnels are more vulnerable than bored or mined tunnels because of the typical shallow soil cover and the nature of the back- fill material surrounding the tunnels. If an immersed tube tunnel is breached, the result could be rapid flood- ing in the tunnel and potential flooding of significant portions of the underground transit system if they are connected. • Geological medium (i.e., ground type): Stronger and more competent rock (accounting for the rock joints and discontinuity effects) provides better tunnel confine- ment and therefore more resistance to explosions. Even a large blast inside a tunnel in good rock will likely induce only limited local damage and could be easily repaired within a reasonably short period. Tunnels constructed in soil tend to be more vulnerable than those in rock. Tun- nel structure elements in very soft soil will induce larger bending and shear demands under blast loading condi- tions. Underwater tunnels surrounded by very porous material (such as immersed tunnels backfilled with gravel or rock fill) are particularly vulnerable to the inflow of large volumes of water mixed with surround- ing materials. • Soil or rock overburden: Structural damage potential increases with decreasing soil or rock cover. Deeper cover provides better tunnel protection from both interior and exterior explosions. • Groundwater conditions: For a tunnel surrounded by semi-flowing water (e.g., an immersed tunnel backfilled with gravel-sized backfill) or flowing water (e.g., an immersed tunnel backfilled with coarse rockfill material), the damage potential may be severe because of flooding and associated damage to the operating systems. For a tun- nel on land, better tunnel performance can be expected when it is surrounded by a dry geological medium (i.e., when there is a low groundwater level) than when it is sur- rounded by a wet geological medium (i.e., when there is a high groundwater level). 68

• Properties of structure, liner, and initial support: In gen- eral, a structural liner with greater thickness, greater rela- tive structure or ground resistance, more confinement reinforcement (in concrete lining), higher ductility, and better framing design (e.g., moment-resisting properties) tends to perform better under extreme loading events, especially if high external confining pressures exist. As mentioned previously, Figure 11 presents a rough estimate of the required tunnel liner thickness (for reinforced con- crete) as a function of the explosive charge weight and the charge standoff distance. Table 12 presents relative severity ratings of tunnels based on some of the critical factors discussed above. The infor- mation in this table is based on recent tunnel security proj- ect experience and expert opinion. This chart has been prepared in a qualitative manner, and therefore should be used as such. 4.4.5 Damage Potential Rating of Tunnels Based on the data and discussions presented herein, as well as the hazard and threat scenarios discussed in Chapter 2, Table 13 shows a damage potential rating chart for trans- portation tunnels. For rating purposes, the following primary hazards and threats were considered from the structural eval- uation standpoint: • Introduction of small IEDs, which are delivered via one to five aggressors transporting the payload in suitcase-type bags on foot and consolidating at a critical location inside the tunnel. • Introduction of medium IEDs, which are delivered either by vehicle (car) or by multiple persons acting in concert to transport the payload and consolidating at a critical loca- tion inside the tunnel. • Introduction of large IEDs, which are delivered either by vehicle (truck) or by multiple persons acting in concert to 69 Figure 14. Empirical correlation of seismic ground shaking induced damage to bored tunnels [Ref. 19].

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

71 Explosion Tunnel Type Ground Support System Soil or Rock Overburden Thickness Small1 Medium2 Large3 Fire (>34 MBTU per hour, or 1 00 MW) < 1 x diameter E D C D Strong Rock All Types > 1 x diameter E D C D < 1 x diameter D B B B Rock Bolts with Wire Mesh/Lattice Girder/ Shotcrete > 1 x diameter D B B B < 1 x diameter F B B B Steel Ribs with or without Liner Plate >1 x diameter F B B B < 1 x diameter F B B C/B Cast-in-Place Concrete Liner > 1 x diameter F C/B B C/B < 1 x diameter D B A B Soft Rock/ Firm Ground Segmental Concrete > 1 x diameter D B B/A B < 1 x diameter D B A B Steel Ribs or Lattice Girder with Shotcrete >1 x diameter D B A B < 1 x diameter F B A C/B Cast-in-Place Concrete > 1 x diameter F C/B B/A C/B < 1 x diameter D B A B Bo re d or M in ed Loose/Soft Ground Segmental Concrete > 1 x diameter D B A B < 1 5’ D B A C Unreinforced Concrete/Masonry Lining > 1 5’ D B A C < 1 5’ D B A C Firm Ground Reinforced Concrete Lining > 1 5’ D B A C < 1 5’ D B A C Unreinforced Concrete/Masonry Lining > 1 5’ D B A C < 1 5’ D B A C Cu t-a nd -C ov er Loose/Soft Ground Reinforced Concrete Lining > 1 5’ 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. Table 13. Damage potential ratings for transportation tunnels. (continued on next page)

72 Damage Potential Definition A = Severely Catastrophic • Collapse—requires several months to 1 year to repair • Rapid flooding B = Catastrophic • Explosion - moderate to large area breach failure - potential flooding - facility closure over several weeks to months • Fire - significant liner damage (e.g., deep fire induced spalling through concrete liner; local failure of load carrying structural elements) - requires several weeks to months to repair C = Critical • Explosion - local breach failure - significant water inflow - requires a few days to weeks to repair • Fire - moderate liner damage (e.g., 6-inch [1 5-centimeter] fire induced concrete spalling; steel reinforcement exposed) - requires a few days to weeks to repair D = Serious • Explosion - local damage of liner—no breaching - controllable water inflow - repairable within 24 hours to a few days • Fire - local damage of liner (e.g., 2- to 3-inch [5- to 7.6-centimeter] fire induced concrete spalling) - repairable within 24 hours to a few days E = Marginal • Explosion - minor damage—spalling, cracking, lining overstress - repairable within 1 hour • Fire - minor damage (e.g., less than 1 -inch [2.5-centimeter] fire induced concrete spalling) - repairable within 1 hour F = Negligible • Explosion - no damage • Fire - no damage Table 13. (Continued). important to the ability of owners to effectively and safely operate any transportation tunnel. Systems serving trans- portation tunnels handle the following key safety functions: • Emergency ventilation, • Fire protection, • Drainage, • Power supply, • Lighting, • Signals, • Train control, • Traffic control, • System control, and • Communications. 4.5.2 Categorization of Systems The systems serving the above key safety functions have been categorized into five primary categories to simplify the designation of critical elements: • Ventilation – Emergency ventilation • Life safety – Fire protection – Drainage • Electrical – Primary – Ancillary – Traction – Emergency • Command and Control – Traffic control – Train control – Signals – System control • Communications Ventilation includes all of the systems, equipment, and facilities required to provide ventilation of a tunnel during an emergency.

Path to Target: Tunnel Roadway Target: Tunnel Liner Bored or Mined Tunnel Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Immersed Tube Tunnel Cut-and- Cover Tunnel Soft to Firm Ground Strong Rock PV insufficient liner thickness; relative proximity of threat to liner OV no inspections at portals to limit vehicle type, size, or cargo 1H Large IED Truck DP A A A-B C PV insufficient liner thickness; relative proximity of threat to liner OV no inspections at portals to limit vehicle type, size, or cargo 2H Medium IED Car/Van DP B B B-C D PV insufficient liner thickness; relative proximity of threat to liner OV public access to roadway; inadequate surveillance 3H Small IED Backpack DP D D D-F E PV insufficient liner thickness; relative proximity of threat to liner OV no vehicle inspections at portals to limit size, type, or cargo 4H Large Fire1 Tanker DP D C B-C D Path to Target: Tunnel Roadway Target: Column/Wall/Roof Slab Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Air-Rights Structure PV insufficient protection of column, wall, or roof slab; relative proximity of threat to column, wall, or roof slab OV no inspections at entrances to limit vehicle type, size, or cargo 5H Large IED Truck DP B PV insufficient protection of column/wall/roof slab; relative proximity of threat to column/wall/roof slab OV no inspections at entrances to limit vehicle type, size, or cargo 6H Medium IED Car/Van DP C PV insufficient protection of column/wall/roof slab; relative proximity of threat to column/wall/roof slab OV public access to roadway; inadequate surveillance 7H Small IED Backpack DP D PV insufficient fire protection of column/wall/roof slab OV no vehicle inspections at entrances to limit size, type, or cargo 8H Large Fire1 Tanker DP C Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Note: 1 . More than 341 MBTU per hour (100 MW) Table 14. Structural vulnerabilities to most likely hazard or threat scenarios for road tunnels. 73 (continued on next page)

Table 14. (Continued). 74 Path to Target: Tunnel Roadway Target: Portal Bored or Mined Tunnel Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Air- Rights Structure Immersed Tube Tunnel Cut-and- Cover Tunnel Strong Rock PV insufficient portal strength OV no vehicle inspections at portals to limit size, type, or cargo 9H Large Fire1 Tanker DP C D C B-C D Path to Target: Waterway Target: Portal or Shaft Wall Bored or Mined Tunnel Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Immersed Tube Tunnel Soft to Firm Ground Soft to Firm Ground Strong Rock PV insufficient portal or shaft wall strength OV uncontrolled ship traffic movement through channel over tunnel with uninspected cargo 10H Very Large IED Depth Charge or Ship DP A A A Path to Target: Waterway Target: Top of Tunnel Bored or Mined Tunnel Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Immersed Tube Tunnel Soft to Firm Ground Strong Rock PV insufficient roof slab thickness; inadequate tunnel cover OV uncontrolled ship traffic movement through channel over tunnel with uninspected cargo 11H Very Large IED Depth Charge from Ship DP A A C Path to Target: Surface Roadway over Tunnel Target: Roof Slab Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Cut-and-Cover Tunnel Air-Rights Structure PV insufficient roof slab thickness; inadequate tunnel cover OV if parking structure, no vehicle inspections to limit size, type, or cargo 12H Large IED Truck DP A A PV insufficient roof slab thickness; inadequate tunnel cover OV if parking structure, no vehicle inspections to limit size, type, or cargo 13H Medium IED Truck or Multiple Backpacks DP B B Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Note: 1. More than 341 MBTU per hour (100 MW)

75 Path to Target: Trackway Target: Tunnel Liner Bored or Mined Tunnel Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Immersed Tube Tunnel Cut-and- Cover Tunnel Soft to Firm Ground Strong Rock PV insufficient liner thickness; relative proximity of threat to liner OV insufficient inspection in rail yards and shops 1T Large IED Transit Car/ Engine DP A A A-B C PV insufficient liner thickness; relative proximity of threat to liner OV insufficient inspection in rail yards and shops; uncontrolled access through ancillary facilities (i.e., stations, exits/stairs) 2T Medium IED Transit Car/ Engine or Multiple Backpacks DP B B B-C D PV insufficient liner thickness; relative proximity of threat to liner OV insufficient inspection in rail yards and shops; uncontrolled access through ancillary facilities (i.e., stations, exits/stairs); inadequate surveillance 3T Small IED Backpack DP D D D-F E PV insufficient liner thickness; relative proximity of threat to liner OV insufficient inspection in rail yards and shops 4T Large Fire1 IED on Transit Vehicle DP D C B-C D Path to Target: Trackway Target: Column/Wall/Roof Slab Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Air-Rights Structure PV insufficient protection of column/wall/roof slab; relative proximity of threat to column/wall/roof slab OV insufficient inspection in rail yards and shops 5T Transit Car/ Engine DP B PV insufficient protection of column/wall/roof slab; relative proximity of threat to column/wall/roof slab OV insufficient inspection in rail yards and shops; uncontrolled access through ancillary facilities (i.e., stations, exits/stairs) 6T Transit Car/ Engine or Multiple Backpacks DP C PV insufficient protection of column/wall/roof slab; relative proximity of threat to column/wall/roof slab OV insufficient inspection in rail yards and shops; uncontrolled access through ancillary facilities (i.e., stations, exits/stairs); inadequate surveillance 7T Backpack DP D PV insufficient fire protection of column/wall/roof slab OV insufficient inspection in rail yards and shops 8T IED on Transit Vehicle DP C Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Note: 1. More than 341 MBTU per hour (100 MW) Large IED Medium IED Small IED Large Fire1 Table 15. Structural vulnerabilities to most likely hazard or threat scenarios for transit tunnels. (continued on next page)

76 Path to Target: Trackway Target: Portal Bored or Mined TunnelScenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Air- Rights Structure Immersed Tube Tunnel Cut-and- Cover Tunnel Soft to Firm Ground Strong Rock PV insufficient portal strength OV insufficient inspection in rail yards and shops; uncontrolled access to rail cars and engines; no cargo restrictions; insufficient inspection of cargo containers at origin 9T Large Fire1 IED on Transit Vehicle DP C D C B-C D Path to Target: Waterway Target: Portal or Shaft Wall Bored or Mined TunnelScenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Immersed Tube Tunnel Soft to Firm Ground Strong Rock PV insufficient portal or shaft wall strength OV uncontrolled ship traffic movement through channel over tunnel with uninspected cargo 10T Very Large IED Depth Charge or Ship DP A A A Path to Target: Waterway Target: Top of Tunnel Bored or Mined TunnelScenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Immersed Tube Tunnel Soft to Firm Ground Strong Rock PV insufficient roof slab thickness; inadequate tunnel cover OV uncontrolled ship traffic movement through channel over tunnel with uninspected cargo 11T Depth Charge from Ship DP A A C Path to Target: Surface Roadway over Tunnel Target: Roof Slab Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Cut-and-Cover Tunnel Air-Rights Structure PV insufficient roof slab thickness; inadequate tunnel cover OV no vehicle inspections to limit size, type, or cargo 12T Truck DP A A PV insufficient roof slab thickness; inadequate tunnel cover OV no vehicle inspections to limit size, type, or cargo 13T Medium IED Truck or Multiple Backpacks DP B B Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Very Large IED Large IED Note: 1. More than 341MBTU per hour (100 MW) Table 15. (Continued).

77 Path to Target: Trackway Target: Tunnel Liner Bored or Mined Tunnel Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Immersed Tube Tunnel Cut-and- Cover Tunnel Soft to Firm Ground Strong Rock PV insufficient liner thickness; relative proximity of threat to liner OV insufficient inspection in rail yards and shops 1R Rail Car/ Engine DP A A A-B C PV insufficient liner thickness; relative proximity of threat to liner OV insufficient inspection in rail yards and shops; uncontrolled access through ancillary facilities (i.e., stations, exits/stairs) 2R Rail Car/ Engine or Multiple Backpacks DP B B B-C D PV insufficient liner thickness; relative proximity of threat to liner OV insufficient inspection in rail yards and shops; uncontrolled access through ancillary facilities (i.e., stations, exits/stairs) 3R Backpack DP D D D-F E PV insufficient liner thickness; relative proximity of threat to liner OV insufficient inspection in rail yards and shops 4R IED on Rail Vehicle DP D C B-C D Path to Target: Trackway Target: Column/Wall/Roof Slab Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Air-Rights Structure PV insufficient protection of column/wall/roof slab; relative proximity of threat to column/wall/roof slab OV insufficient inspection in rail yards and shops 5R Rail Car/ Engine DP B PV insufficient protection of column/wall/roof slab; relative proximity of threat to column/wall/roof slab OV insufficient inspection in rail yards and shops; uncontrolled access through ancillary facilities (i.e., stations, tunnel exits/stairs) 6R Rail Car/ Engine DP C PV insufficient protection of column/wall/roof slab; relative proximity of threat to column/wall/roof slab OV insufficient inspection in rail yards and shops; uncontrolled access through ancillary facilities (i.e., stations, tunnel exits/stairs); inadequate surveillance 7R Small IED Medium IED Large IED Backpack DP D PV insufficient fire protection of column/wall/roof slab OV insufficient inspection in rail yards and shops 8R Large Fire1 IED on Rail Vehicle DP C Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Note: 1. More than 341 MBTU per hour (100 MW) Large Fire1 Small IED Medium IED Large IED Table 16. Structural vulnerabilities to most likely hazard or threat scenarios for rail tunnels. (continued on next page)

78 Path to Target: Trackway Target: Portal Bored or Mined TunnelScenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Air- Rights Structure Immersed Tube Tunnel Cut-and- Cover Tunnel Soft to Firm Ground Strong Rock PV insufficient portal strength OV insufficient inspection in rail yards and shops; uncontrolled access to rail cars and engines; no cargo restrictions; insufficient inspection of cargo containers at origin 9R IED on Rail Vehicle DP C D C B-C D Path to Target: Waterway Target: Portal or Shaft Wall Bored or Mined TunnelScenario No. Hazard and Threat Tactical Delivery Device PV/OV/DP Immersed Tube Tunnel Soft to Firm Ground Strong Rock PV insufficient portal or shaft wall strength OV uncontrolled ship traffic movement through channel over tunnel with uninspected cargo 10R Depth Charge or Ship DP A A Path to Target: Waterway Target: Top of Tunnel Bored or Mined TunnelScenario No. Hazard and Threat Tactical Delivery Device PV/OV/DP Immersed Tube Tunnel Soft to Firm Ground Strong Rock PV insufficient roof slab thickness; inadequate tunnel cover OV uncontrolled ship traffic movement through channel over tunnel with uninspected cargo 11R Depth Charge from Ship DP A C Path to Target: Surface Roadway over Tunnel Target: Roof Slab Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Cut-and-Cover Tunnel Air-Rights Structure PV insufficient roof slab thickness; inadequate tunnel cover OV no vehicle inspections to limit size, type, or cargo 12R Truck DP A PV insufficient roof slab thickness; inadequate tunnel cover OV no vehicle inspections to limit size, type, or cargo 13R Truck or Multiple Backpacks DP B A A A B Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Large Fire1 Very Large IED Very Large IED Large IED Medium IED Note: 1. More than 341 MBTU per hour (100 MW) Table 16. (Continued).

Life safety includes all of the systems, equipment, and facil- ities required to provide protection during an emergency to the tunnel and its inhabitants. Electrical includes both normal and emergency power for ancillaries, systems, and train traction. Command and control includes traffic, train, and system control, along with signals. Communications includes all communications systems required to make the tunnel functional and safe. To create the above five primary categories of systems, the research team started with an initial list of safety systems serv- ing road, transit, and rail tunnels. Table 17 shows this initial list of safety systems, along with the tunnel functions associ- ated with each system. After careful review of the data in this table, the research team made several decisions. One decision was to combine the categories of passenger rail tunnels and freight rail tunnels in this report because the vulnerabilities and damage potentials are similar. The other decisions involve the elimination of some elements (such as emission control, emission monitoring, and normal lighting) because they do not affect the vulnerability of particular tunnels. In the end, the research team decided on the above five primary categories of systems. These revised primary categories are depicted in Table 18. 4.5.3 Degree of Impact on Safety and Operations When systems are disrupted, the degree of impact on the safety and operations of the tunnel can vary. Table 19 pro- vides a subjective evaluation of the different impacts and mit- igation requirements. This evaluation is consistent with the FTA’s ranking system [Ref. 20]. System paralysis can occur if a coordinated attack is aimed at specifically related systems. For example, if a multiple- point attack focuses on the electrical power supply as well as any emergency backup systems and is successful, most of the tunnel’s MEC systems will be disabled. Such threats may cause synergistic effects and may require systemwide checks to be conducted before tunnel operations are resumed. Tables 20, 21, and 22 subjectively highlight the impact of system element disruption on each of the transportation tun- nel function types. These subjective impact ratings are based on single-point attacks. In the case of multiple-point or coor- dinated attacks, the disruption to the tunnel systems would obviously become more severe. 4.5.4 Potentially Critical Locations A careful assessment of the potentially critical locations was made for each tunnel function type. This assessment was combined with the system element impact list to develop the draft guidelines. The results of the combined assessment and list are presented in Table 23 as a list of potentially critical locations where each of the tunnel systems is vulnerable. The table records the level of vulnerability as “Low,”“Medium,” or “High.” Table 24 estimates the vulnerabilities of critical locations. Tables 25, 26, and 27 present system vulnerabilities to the most likely hazard or threat scenarios for road tunnels, tran- sit tunnels, and rail tunnels, respectively. These tables com- bine the information given in Table 3 (hazard and threat scenarios) with the information given in Table 24 (vulnera- bilities of critical locations). The hazard and threat scenar- ios have been rearranged into subtables on the basis of the “Path to Target” as well as the “Target.” These items are located at the top left side of each subtable. The hazards and threats presented on the left side of the tables include the introduction to the tunnel property of large, medium, and small IEDs; large fires; hazardous materials; C/B/R; and cyber attack. All of the hazards and threats were developed further to identify scenarios that include hazard or threat, path to target, tactical delivery device, and ultimate target. Each of the hazard or threat scenarios was considered for each of the five primary system categories presented in Sec- tion 4.5.2. Each row presents a unique set of vulnerabilities (both physical and operational) and a set of damage poten- tials. This should provide the owner or operator with a clear guide to the types of hazard and threat scenarios possible for tunnels. 4.5.5 Summary Nonstructural (i.e., tunnel systems) guidelines have been developed to provide the owner or operator with a simple method to identify the critical elements and locations within his or her tunnel based on the hazard or threat, path to target, tactical delivery device, and ultimate target. Each of the criti- cal systems has been assessed, and a set of vulnerabilities and damage potentials have been identified for each reasonable hazard or threat. 4.6 Chapter Summary The information presented in this chapter allows tunnel facil- ity owners, operators, and engineers to conduct preliminary vulnerability rating (i.e., screening) assessments of their facili- ties and, if needed, to derive priority lists of a tunnel’s structural components and system components for further study. To determine the countermeasures available to the tunnel owner or operator, the research team applied comparative analysis to the hazard and threat scenarios to discern com- mon themes. From this analysis, it was determined that the 79

80 Tunnel Function Safety System Road Transit Freight Rail Passenger Rail Transverse Ventilation •Ventilation System Type Longitudinal Ventilation • • • • Ventilation Buildings • Ventilation Shafts • • Vent Ducts (Transverse) • Ventilation System Facilities Intake Louvers • • • • Central Fans (Transverse) • Jet Fans (Longitudinal) • •Ventilation System Equipment Shaft Fans (Longitudinal) • • Emissions Control • •Ventilation System Function Smoke Management • • • • Plumbing Drainage • • • • Fire/Smoke Detection • Note Note 1 1 Fire Standpipe/Hydrants • • • • Fire Apparatus • Portable Fire Extinguishers • • • • Fixed Fire Suppression2 Notes 3 & 4 Notes 5 & 6 Note 6 Emergency Exits • • • • Cross Passages • • • • Life Safety Systems CCTV8 • Auxiliary Power • • • • Traction Power7 • •Electrical Power Emergency Power • • • • Normal Lighting •Lighting Systems Emergency Lighting • • • • Train Signals • • •Signal Traffic Signals • Emergency Phones • • • • SCADA8/Data • • • •Communications Control Center • • • • Automatic • • • • On-Site • • • • Remote • • • • Control Systems Emissions Monitoring • Notes: 1. Fire/smoke detection are only in stations and ancillary facilities. 2. This category includes all fixed fire suppression systems such as sprinklers, mist, and deluge systems. 3. Fixed fire suppression systems are only in ancillary facilities. 4. There are three road tunnels in the United States with sprinkler systems in the roadway. 5. There are some U.S. transit stations with under-car sprinkler systems on tracks. 6. Fixed fire suppression systems are only in stations and ancillary facilities. 7. Traction power is in all transit and rail tunnels with electrified train vehicles. 8. CCTV = closed-circuit television; SCADA = supervisory control and data acquisition. Table 17. Initial categories of safety systems.

81 Tunnel Function Safety System Road Transit Rail Ventilation Transverse Ventilation Ventilation Type Longitudinal Ventilation Ventilation Buildings Ventilation Shafts Vent Ducts (Transverse) Ventilation Facilities Air Intakes Central Fans (Transverse) Jet Fans (Longitudinal) Ventilation Equipment Shaft Fans (Longitudinal) Ventilation Function Smoke Management Life Safety Drainage Drainage Fire/Smoke Detection Note 1 Note 1 Fire Standpipe/Hydrants Fire Apparatus Portable Fire Extinguishers Fixed Fire Suppression2 Notes 3 & 4 Notes 5 & 6 Note 6 Emergency Exits Cross Passages Fire Protection CCTV8 Electrical Ancillary Power Traction Power7Power Emergency Power Lighting Emergency Lighting Command and Control Train Control Traffic Control System Control Signals SCADA8/Data Control Command and Control Center Communications Communications Emergency Telephones Notes: 1. Fire/smoke detection are only in stations and ancillary facilities. 2. This category includes all fixed fire suppression systems such as sprinklers, mist, and deluge systems. 3. Fixed fire suppression systems are only in ancillary facilities. 4. There are three road tunnels in the United States with sprinkler systems in the roadway. 5. There are some U.S. transit stations with under-car sprinkler systems on tracks. 6. Fixed fire suppression systems are only in stations and ancillary facilities. 7. Traction power is in all transit and rail tunnels with electrified train vehicles. 8. CCTV = closed-circuit television; SCADA = supervisory control and data acquisition. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Table 18. Revised categories of safety systems.

82 basic platforms for disruption emanated from four major cat- egories of sources: • Large fires; • Explosive devices; • Hazardous materials, including chemical/biological/radio- logical (C/B/R) agents; and • Cyber attacks. The research team then analyzed the damage potential of a disturbance emanating from each of the four major categories of sources. Damage is the loss of use of the tunnel. Minor dam- age may result from a disabled car blocking one lane, and major damage may result from a fire that closes the tunnel to traffic. The scope of the functional loss is significant, and the damage potential reflects the potential percentage loss of the tunnel use. The percentage loss of the tunnel use is important, more so than the hazard or threat that triggered the incident. Given this importance, the research team began to match the greatest damage potential, or potential loss of use of the tun- nel, to the hazards and threats. The research team finally sum- marized the hazards and threats that have the greatest damage potential, or the potential for total loss of tunnel use. Large fires and explosive devices had a similar damage potential as that of all other hazards and threats examined. Fire, as a primary or secondary hazard (i.e., accidental com- bustion) or threat (i.e., arson) can cause severe damage to the tunnel because of closure. An explosion can cause similar dis- ruption to the tunnel. Each of these main hazards and threats exhibited damage potential to both the structure and systems of the tunnel. Therefore, the hazard and threat platforms were fully described as a series of scenarios, including the type and size of hazard or threat, the tactical delivery device, and the tar- geted tunnel element. A lengthy list of scenarios was com- pressed to reflect the common hazard and threat platforms. The vulnerabilities of various tunnel types to these hazard and threat scenarios, as well as the relative damage potential, appear in Tables 14, 15, and 16 for road, transit, and rail tun- nels, respectively. The vulnerabilities of various tunnel safety system types to the same set of hazard and threat sce- narios, along with relative damage potentials, appear in Tables 25, 26, and 27 for road, transit, and rail tunnels, respectively. These tables present the groundwork for the presentation of countermeasures, which is discussed in the next chapter. Impact Rating Life Safety Tunnel Operations Operation Restoration Severely Catastrophic Incident impacts life safety sufficiently to require tunnel closure Incident impacts tunnel operations sufficiently to require complete shutdown Incident impacts operation restoration, taking several months to 1 year Catastrophic Incident impacts life safety sufficiently to require tunnel closure Incident impacts tunnel operations sufficiently to require complete shutdown Incident impacts operation restoration, taking several weeks to months Critical Incident impacts life safety Incident impacts tunnel operations sufficiently to require a disruption of operations Incident impacts operation restoration, taking a few days to weeks Serious Incident impacts life safety Incident impacts tunnel operations sufficiently to require a disruption of operations Incident impacts operation restoration, taking 24 hours to a few days Marginal Incident impacts life safety Incident impacts tunnel operations sufficiently to require a modest disruption of operations Incident impacts operation restoration, taking less than 1 hour Negligible Incident does not impact life safety Incident does not impact tunnel operations Incident does not impact operation restoration Table 19. Degree of impact on safety and operations.

83 Safety System Life Safety Tunnel Operations Operation Restoration Ventilation Transverse Ventilation Catastrophic Catastrophic Catastrophic System Type Longitudinal Ventilation Catastrophic Catastrophic Catastrophic Ventilation Buildings Catastrophic Catastrophic Catastrophic Ventilation Shafts Catastrophic Catastrophic Catastrophic Vent Ducts (Transverse) Catastrophic Catastrophic Catastrophic Facilities Air Intakes Catastrophic Catastrophic Catastrophic Central Fans (Transverse) Catastrophic Catastrophic Catastrophic Jet Fans (Longitudinal) Catastrophic Catastrophic Catastrophic Equipment Shaft Fans (Longitudinal) Catastrophic Catastrophic Catastrophic System Function Smoke Management Catastrophic Catastrophic Catastrophic Life Safety Fire/Smoke Detection Catastrophic Catastrophic Catastrophic CCTV Critical Critical Catastrophic Fire Standpipe/Hydrants Catastrophic Catastrophic Catastrophic Fire Apparatus Critical Serious Critical Portable Fire Extinguishers Critical Marginal Critical Fixed Fire Suppression Catastrophic Catastrophic Catastrophic Systems Drainage Critical Critical Catastrophic Emergency Exits Catastrophic Catastrophic Catastrophic Facilities Cross Passages Catastrophic Catastrophic Catastrophic Electrical Auxiliary Power Catastrophic Catastrophic Catastrophic Traction Power - - - - - - - - - - - - - - - Power Emergency Power Catastrophic Catastrophic Catastrophic Lighting Emergency Lighting Critical Critical Critical Command and Control Train Control - - - - - - - - - - - - - - - Traffic Control Catastrophic Catastrophic Catastrophic System Control Catastrophic Catastrophic Catastrophic Signals Catastrophic Catastrophic Catastrophic SCADA/Data Critical Critical Critical Command and Control Command and Control Center Catastrophic Catastrophic Catastrophic Communications Communications Emergency Phones Catastrophic Critical Critical CCTV = closed-circuit television; SCADA = supervisory control and data acquisition; dashes = data not available. Table 20. Disruptive impacts in road tunnels.

84 Safety System Life Safety Tunnel Operations Operation Restoration Ventilation Transverse Ventilation - - - - - - - - - - - - - - - System Type Longitudinal Ventilation Catastrophic Catastrophic Catastrophic Ventilation Structures Catastrophic Catastrophic Catastrophic Ventilation Shafts Catastrophic Catastrophic Catastrophic Vent Ducts (Transverse) Catastrophic Catastrophic Catastrophic Facilities Air Intakes Catastrophic Catastrophic Catastrophic Central Fans (Transverse) - - - - - - - - - - - - - - - Jet Fans (Longitudinal) Catastrophic Catastrophic Catastrophic Equipment Shaft Fans (Longitudinal) Catastrophic Catastrophic Catastrophic System Function Smoke Management Catastrophic Catastrophic Catastrophic Life Safety Fire/Smoke Detection Catastrophic Critical Critical CCTV Critical Critical Critical Fire Standpipe/Hydrants Catastrophic Catastrophic Catastrophic Fire Apparatus Critical Serious Serious Portable Fire Extinguishers Marginal Negligible Negligible Fixed Fire Suppression Critical Serious Serious Systems Drainage Marginal Marginal Critical Fixed Fire Suppression Critical Serious Serious Emergency Exits Catastrophic Critical Catastrophic Facilities Cross Passages Catastrophic Critical Catastrophic Electrical Primary Power Catastrophic Catastrophic Catastrophic Auxiliary Power Critical Critical Critical Traction Power Catastrophic Catastrophic Catastrophic Power Emergency Power Catastrophic Catastrophic Catastrophic Lighting Emergency Lighting Critical Serious Serious Command and Control Train Control Catastrophic Critical Critical Traffic Control - - - - - - - - - - - - - - - System Control Catastrophic Catastrophic Catastrophic Signals Catastrophic Catastrophic Catastrophic SCADA/Data Critical Serious Serious Command and Control Command and Control Center Catastrophic Critical Critical Communications Communications Emergency Phones Catastrophic Serious Serious CCTV = closed-circuit television; SCADA = supervisory control and data acquisition; dashes = data not available. Table 21. Disruptive impacts in transit tunnels.

85 Safety System Life Safety Tunnel Operations Operation Restoration Ventilation Transverse Ventilation - - - - - - - - - - - - - - - System Type Longitudinal Ventilation Catastrophic Catastrophic Catastrophic Ventilation Structures Catastrophic Catastrophic Catastrophic Ventilation Shafts Catastrophic Catastrophic Catastrophic Vent Ducts (Transverse) Catastrophic Catastrophic Catastrophic Facilities Intake Louvers Catastrophic Catastrophic Catastrophic Central Fans (Transverse) - - - - - - - - - - - - - - - Jet Fans (Longitudinal) Catastrophic Catastrophic Catastrophic Equipment Shaft Fans (Longitudinal) Catastrophic Catastrophic Catastrophic System Function Smoke Management Catastrophic Catastrophic Catastrophic Life Safety Fire/Smoke Detection Serious Serious Critical CCTV Serious Serious Critical Fire Standpipe/Hydrants Critical Critical Critical Fire Apparatus Critical Serious Critical Portable Fire Extinguishers Negligible Negligible Negligible Fixed Fire Suppression Negligible Negligible Negligible Systems Drainage Marginal Critical Critical Emergency Exits Serious Serious Serious Facilities Cross Passages Serious Serious Serious Electrical Primary Power Catastrophic Catastrophic Catastrophic Auxiliary Power Catastrophic Catastrophic Catastrophic Traction Power Catastrophic Catastrophic Catastrophic Power Emergency Power Catastrophic Catastrophic Catastrophic Lighting Emergency Lighting Marginal Marginal Marginal Command and Control Train Control Catastrophic Catastrophic Critical Traffic Control - - - - - - - - - - - - - - - System Control Catastrophic Catastrophic Catastrophic Signals Catastrophic Catastrophic Catastrophic SCADA/Data Critical Serious Serious Command and Control Command and Control Center Catastrophic Catastrophic Catastrophic Communications Communications Emergency Phones Critical Marginal Marginal CCTV = closed-circuit television; SCADA = supervisory control and data acquisition; dashes = data not available. Table 22. Disruptive impacts in rail tunnels.

86 Tunnel Function Critical System Critical Location Road Tunnel Transit Tunnel Rail Tunnel Tunnel Low Low Low Portals Low Low Low Ventilation Structures High High High Ventilation Shafts High High Medium Stations ------- High High* Ventilation Ducts High Low Low Control Center High High High Ventilation Utilities High High High Tunnel Medium Low Low Portals Low Low Low Ventilation Structures Medium Medium Medium Ventilation Shafts Low Medium Medium Stations ------- High High* Ventilation Ducts Low Low Low Control Center Medium Medium Medium Fire Protection Utilities High High High Tunnel High Medium Medium Portals Medium Low Low Ventilation Structures Low Medium Medium Ventilation Shafts Low Low Low Ventilation Ducts Medium Low Low Stations ------- Low Low* Control Center Low Low Low Drainage Utilities High High High Tunnel High High High Portals Medium Medium Medium Ventilation Structures High High High Ventilation Shafts Low Low Low Ventilation Ducts Low Low Low Stations ------- High High* Control Center High High High Electrical Utilities High High High Tunnel High High High Portals Low Low Low Ventilation Structures Low Low Low Ventilation Shafts Low Low Low Ventilation Ducts Low Low Low Stations ------- High High* Control Center High High High Communications Utilities High High High Tunnel High High High Portals High High High Ventilation Structures Low Low Low Ventilation Shafts Low Low Low Ventilation Ducts Low Low Low Stations ------- High High* Control Center High High High Command and Control Utilities High High High * Stations only in passenger rail tunnels. Table 23. Vulnerabilities of potentially critical locations.

87 Primary Hazard or Threat Critical Location Critical System or Element DEI egraL DEI m uide M DEI lla mS eriF egraL s u odraza H slaireta M R/ B/C kcattA rebyC Ventilation F F F F D F F Life Safety F F F E D F D Electrical C C C D D F D Command and Control C C C F D F D Tunnel Shell Communications C C C D D F D Ventilation F F F F D F F Life Safety F F F E D F D Electrical C C C D D F D Command and Control C C C F D F D Portals Communications C C C D D F D Ventilation B B C B D C D Life Safety B B C B D C D Electrical B B C C D C D Command and Control B B C C D C B Ventilation Structures Communications B B C C D C D Ventilation B B C B D B B Life Safety C C D B D C D Electrical C C D C D C D Command and Control C C D B D C D Ventilation Shafts Communications C C D B D C D Ventilation C C B B D B B Life Safety D D C C D C D Electrical D D C C D C D Command and Control D D C B D C D Ventilation Ducts Communications D D C B D C D Ventilation B B C C D B B Life Safety B B C B D C C Electrical B B C E D C C Command and Control B B C C D C C Stations Communications B B C B D C D Ventilation B B C C D C B Life Safety B B C C D C C Electrical B B C C D C C Command and Control B B C B D C B Control Centers Communications B B C B D C B Ventilation C C C D D C F Life Safety C C C D D C F Electrical B B B D D C F Command and Control B B B D D C F Substation Communications B B B D D C F A = Severely Catastrophic D = Serious B = Catastrophic E = Marginal C = Critical F = Negligible Table 24. Vulnerabilities of critical locations.

88 Path to Target: Surface Access Roadway Target: Stand-Alone Command and Control (C&C) Center Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 14H Large IED Truck DP N/A N/A N/A total loss total loss PV Insufficient perimeter protection OV Insufficient surveillance 15H Medium IED Car/Van DP N/A N/A N/A total loss total loss PV Insufficient perimeter protection OV Insufficient surveillance 16H Small IED Backpack2 DP N/A N/A N/A total loss total loss Path to Target: Surface Access Roadway Target: Stand-Alone Substation Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 17H Large IED Truck DP N/A N/A total loss N/A N/A PV insufficient perimeter protection OV insufficient surveillance 18H Medium IED Car/Van DP N/A N/A partial loss N/A N/A PV insufficient perimeter protection OV insufficient surveillance 19H Small IED Backpack2 DP N/A N/A total loss 8 8 8 N/A N/A Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 25. Vulnerabilities to most likely hazard and threat scenarios for road tunnels.

89 Path to Target: Surface Access Roadway Target: Ventilation Structure3 Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 20H Large IED Truck DP total loss total loss total loss total loss total loss PV insufficient perimeter protection OV insufficient surveillance 21H Medium IED Car/Van DP partial loss total loss partial loss partial loss partial loss PV insufficient perimeter protection OV insufficient access surveillance 22H Small IED Backpack2 DP partial loss total loss partial loss 8 8 8 partial loss partial loss Path to Target: Tunnel Roadway Target: C&C Center Above or Adjacent to the Tunnel Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV accessibility via public tunnel OV no vehicle inspections at portals 23H Large IED Truck DP N/A N/A N/A total loss total loss PV accessibility via public tunnel OV no vehicle inspections at portals 24H Medium IED Car/Van DP N/A N/A N/A partial loss partial loss Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 25. (Continued). (continued on next page)

90 Path to Target: Tunnel Roadway Target: Ventilation Structure Above or Adjacent to the Tunnel3 Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV ventilation shafts and ducts provide a clear path for blast wave to propagate from tunnel to ventilation building OV no vehicle inspections at portals 25H Large IED Truck DP total loss total loss total loss total loss total loss PV ventilation shafts and ducts provide a clear path for blast wave to propagate from tunnel to ventilation building OV no vehicle inspections at portals 26H Medium IED Car/Van DP total loss total loss total loss total loss total loss Path to Target: Tunnel Roadway Scenario No. Hazard or Threat Tactical Delivery Device Target PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV public access into roadway OV inadequate surveillance 27H Small IED Backpack Exposed Ductbank DP N/A N/A partial loss7,8 partial loss7 partial loss7 PV uncontrolled vehicle access OV no cargo restrictions 28H Large Fire1 Tanker Portal4 DP loss6 loss loss 8 8 8 loss loss PV uncontrolled vehicle access OV no cargo restrictions 29H Large Fire1 Tanker Any Tunnel Location Adjacent to Critical Facility5 DP partial loss6 partial loss partial loss8 partial loss partial loss PV uncontrolled vehicle access OV no cargo restrictions 30H HazMat Truck Any Tunnel Location DP function loss9 function loss9 function loss9 function loss9 function loss9 PV uncontrolled vehicle access OV no vehicle inspections at portals 31H C/B/R Vial/ Aerosol/ Package in Vehicle Tunnel Occupants DP function loss9 N/A N/A N/A N/A Abbreviations: Notes: PV = Physical Vulnerability 1. More than 341 MBTU per hour (100 MW) OV = Operational Vulnerability 2. Assumes perpetrator gets inside DP = Damage Potential 3. Assumes transverse system or longitudinal with fans housed in central location Vent. = Ventilation 4. Worst case is downhill, unidirectional tunnel Dist. = Distribution 5. Such as ventilation buildings, substations, emergency generators, or C&C centers C&C = Command and Control 6. Partial loss of emergency ventilation due to high temperatures Comms. = Communications 7. Potential loss of downstream MEC systems or power to them HazMat = Hazardous Material 8. Unless you have dual power supply from both ends of the tunnel C/B/R = Chemical/Biological/ Radiological 9. Would require decontamination N/A = Not Applicable 10. Blast wave could propagate through station and destroy MEC equipment Table 25. (Continued).

91 Path to Target: Tunnel Air Supply System Target: Tunnel Occupants and Surrounding Population in Discharge Plume Area Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent. System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 32H C/B/R Vial/ Aerosol/ Package on Foot DP functions as weapon delivery device9 N/A N/A N/A N/A PV insufficient perimeter protection OV insufficient access surveillance 33H C/B/R Vial/ Aerosol/ Package in Motor Vehicle DP functions as weapon delivery device9 N/A N/A N/A N/A Path to Target: Virtual Target: C&C Center Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient or outdated electronic protection software OV insufficient or outdated electronic protection software 34H Cyber Attack Digital Virus Code DP N/A N/A N/A total loss of or inappropriate traffic and MEC equipment control N/A Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 25. (Continued). (continued on next page)

92 Path to Target: Surface Access Roadway Target: Standalone Command and Control (C&C) Center Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 14T Large IED Truck DP N/A N/A N/A total loss total loss PV insufficient perimeter protection OV insufficient surveillance 15T Medium IED Car/Van DP N/A N/A N/A total loss total loss PV insufficient perimeter protection OV insufficient surveillance 16T Small IED Backpack DP N/A N/A N/A total loss total loss Path to Target: Surface Access Roadway Target: Stand-Alone Substation Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 17T Large IED Truck DP N/A N/A total loss N/A N/A PV insufficient perimeter protection OV insufficient surveillance 18T Medium IED Car/Van DP N/A N/A partial loss N/A N/A PV insufficient perimeter protection OV insufficient surveillance 19T Small IED Backpack 2 2 DP N/A N/A total loss 8 8 8 N/A N/A Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 26. Vulnerabilities to most likely hazard or threat scenarios for transit tunnels.

93 Path to Target: Surface Access Roadway Target: Ventilation Structure3 Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 20T Large IED Truck DP total loss total loss total loss8 total loss total loss PV insufficient perimeter protection OV insufficient surveillance 21T Medium IED Car/Van DP partial loss total loss partial loss8 partial loss partial loss PV insufficient perimeter protection OV insufficient access surveillance 22T Small IED Backpack2 DP partial loss total loss partial loss8 partial loss partial loss Path to Target: Surface Access Roadway Target: Station Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 23T Large IED Truck DP total loss total loss total loss8 total loss total loss PV insufficient perimeter protection OV insufficient surveillance 24T Small IED Backpack2 DP partial loss10 partial loss10 partial loss8,10 partial loss10 partial loss10 Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 26. (Continued). (continued on next page)

94 Path to Target: Trackway Scenario No. Hazard or Threat Tactical Delivery Device Target PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV public access into trackway OV inadequate access surveillance 25T Small IED Backpack Exposed Ductbank or MEC Equipment DP N/A partial loss7 partial loss7, 8 partial loss7 partial loss7 PV open access to station OV no personal inspections 26T Small IED Backpack on Foot in Train Station DP partial loss10 partial loss10 partial loss10 partial loss10 partial loss10 PV uncontrolled access to trains OV no cargo restrictions; no personal inspections 27T Large Fire1 IED on Train Any Tunnel Location Adjacent to Critical Facility5 DP partial loss6 partial loss partial loss partial loss partial loss PV uncontrolled access to trains OV no cargo restrictions; no personal inspections 28T Large Fire1 IED on Train Portal4 DP partial loss6 partial loss partial loss partial loss partial loss PV uncontrolled access to trains OV no cargo restrictions; no personal inspections 29T HazMat Device on Train Any Tunnel Location DP function loss9 function loss9 function loss9 function loss9 function loss9 PV uncontrolled access to trains OV no cargo restrictions; no personal inspections 30T C/B/R Vial/ Aerosol/ Package on Foot in Train Tunnel/ Station Occupants DP function loss9 function loss9 function loss9 function loss9 function loss9 Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 26. (Continued).

95 Path to Target: Tunnel Air Supply System Target: Tunnel Occupants and Surrounding Population in Discharge Plume Area Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 31T C/B/R Vial/ Aerosol/ Package on Foot DP functions as weapon delivery device9 N/A N/A N/A N/A PV insufficient perimeter protection OV insufficient access surveillance 32T C/B/R Vial/ Aerosol/ Package in Motor Vehicle DP functions as weapon delivery device9 N/A N/A N/A N/A Path to Target: Virtual Target: C&C Center Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient or outdated electronic protection software OV insufficient or outdated electronic protection software 33T Cyber Attack Digital Virus Code DP N/A N/A N/A total loss of or inappropriate traffic and MEC equipment control N/A Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 26. (Continued).

96 Path to Target: Surface Access Roadway Target: Stand-Alone Command and Control (C&C) Center Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 14R Large IED Truck DP N/A N/A N/A total loss total loss PV insufficient perimeter protection OV insufficient surveillance 15R Medium IED Car/Van DP N/A N/A N/A total loss total loss PV insufficient perimeter protection OV insufficient surveillance 16R Small IED Backpack2 DP N/A N/A N/A total loss total loss Path to Target: Surface Access Roadway Target: Stand-Alone Substation Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 17R Large IED Truck DP N/A N/A total loss8 N/A N/A PV insufficient perimeter protection OV insufficient surveillance 18R Medium IED Car/Van DP N/A N/A partial loss8 N/A N/A PV insufficient perimeter protection OV insufficient surveillance 19R Small IED Backpack DP N/A N/A total loss8 N/A N/A Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 2 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 27. Vulnerabilities to most likely hazard or threat scenarios for rail tunnels.

97 Path to Target: Surface Access Roadway Target: Ventilation Structure3 Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 20R Large IED Truck DP total loss total loss total loss8 total loss total loss PV insufficient perimeter protection OV insufficient surveillance 21R Medium IED Car/Van DP partial loss total loss partial loss8 partial loss partial loss PV insufficient perimeter protection OV insufficient access surveillance 22R Small IED Backpack2 DP partial loss total loss partial loss8 partial loss partial loss Path to Target: Surface Access Roadway Target: Station Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 23R Large IED Truck DP total loss total loss total loss8 total loss total loss PV insufficient perimeter protection OV insufficient surveillance 24R Small IED Backpack DP partial loss10 partial loss10 partial loss8, 10 partial loss10 partial loss10 Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 27. (Continued). (continued on next page)

98 Path to Target: Trackway Scenario No. Hazard or Threat Tactical Delivery Device Target PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV public access into trackway OV inadequate access surveillance 25R Small IED Backpack Exposed Ductbank or MEC Equipment DP N/A partial loss7 partial loss7, 8 partial loss7 partial loss7 PV open access to station OV no personal inspections 26R Small IED Backpack on Foot in Train Station DP partial loss10 partial loss10 partial loss10 partial loss10 partial loss10 PV uncontrolled access to trains OV no cargo restrictions; no personal inspections 27R Large Fire1 IED on Train Any Tunnel Location Adjacent to Critical Facility5 DP partial loss6 partial loss partial loss partial loss partial loss PV uncontrolled access to trains OV no cargo restrictions; no personal inspections 28R Large Fire1 IED on Train Portal4 DP partial loss6 partial loss partial loss partial loss partial loss PV uncontrolled access to trains OV no cargo restrictions; no personal inspections 29R HazMat Device on Train Any Tunnel Location DP function loss9 function loss9 function loss9 function loss9 function loss9 PV uncontrolled access to trains OV no cargo restrictions; no personal inspections 30R C/B/R Vial/ Aerosol/ Package on Foot in Train Tunnel/ Station Occupants DP function loss9 function loss9 function loss9 function loss9 function loss9 Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 27. (Continued).

99 Path to Target: Tunnel Air Supply System Target: Tunnel Occupants and Surrounding Population in Discharge Plume Area Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent. System Life Safety Systems Power Dist. C&C Comms. PV insufficient perimeter protection OV insufficient access surveillance 31R C/B/R Vial/ Aerosol/ Package on Foot DP functions as weapon delivery device9 N/A N/A N/A N/A PV insufficient perimeter protection OV insufficient access surveillance 32R C/B/R Vial/ Aerosol/ Package in Motor Vehicle DP functions as weapon delivery device9 N/A N/A N/A N/A Path to Target: Virtual Target: C&C Center Scenario No. Hazard or Threat Tactical Delivery Device PV/OV/DP Vent.System Life Safety Systems Power Dist. C&C Comms. PV insufficient or outdated electronic protection software OV insufficient or outdated electronic protection software 33R Cyber Attack Digital Virus Code DP N/A N/A N/A inappropriate or total loss of traffic and MEC equipment control N/A Abbreviations: PV = Physical Vulnerability OV = Operational Vulnerability DP = Damage Potential Vent. = Ventilation Dist. = Distribution C&C = Command and Control Comms. = Communications HazMat = Hazardous Material C/B/R = Chemical/Biological/Radiological N/A = Not Applicable Notes: 1. More than 341 MBTU per hour (100 MW) 2. Assumes perpetrator gets inside 3. Assumes transverse system or longitudinal with fans housed in central location 4. Worst case is downhill, unidirectional tunnel 5. Such as ventilation buildings, substations, emergency generators, or C&C centers 6. Partial loss of emergency ventilation due to high temperatures 7. Potential loss of downstream MEC systems or power to them 8. Unless you have dual power supply from both ends of the tunnel 9. Would require decontamination 10. Blast wave could propagate through station and destroy MEC equipment Table 27. (Continued).

Next: Chapter 5 - Countermeasures »
Making Transportation Tunnels Safe and Secure Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB’s National Cooperative Highway Research Program (NCHRP) Report 525: Surface Transportation Security and TRB’s Transit Cooperative Research Program (TCRP) Report 86: Public Transportation Security series publications have jointly published Making Transportation in Tunnels Safe and Secure. The report is Volume 12 in each series. The report is designed to provide transportation tunnel owners and operators with guidelines for protecting their tunnels by minimizing the damage potential from extreme events such that, if damaged, they may be returned to full functionality in relatively short periods. The report examines safety and security guidelines for owners and operators of transportation tunnels to use in identifying principal vulnerabilities of tunnels to various hazards and threats. The report also explores potential physical countermeasures; potential operational countermeasures; and deployable, integrated systems for emergency-related command, control, communications, and information.

NCHRP Report 525: Surface Transportation Security is a series in which relevant information is assembled into single, concise volumes—each pertaining to a specific security problem and closely related issues. The volumes focus on the concerns that transportation agencies are addressing when developing programs in response to the terrorist attacks of September 11, 2001, and the anthrax attacks that followed. Future volumes of the report will be issued as they are completed.

The TCRP Report 86: Public Transportation Security series assembles relevant information into single, concise volumes, each pertaining to a specific security problem and closely related issues. These volumes focus on the concerns that transit agencies are addressing when developing programs in response to the terrorist attacks of September 11, 2001, and the anthrax attacks that followed. Future volumes of the report will be issued as they are completed.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!