The first two chapters of this report discuss the general attributes of underground space. This chapter examines how underground space use underpins the long-term sustainability of urban areas, what additional research may be necessary to enhance underground engineering practices, and what developments in underground engineering would further support urban sustainability. This report does not develop arguments for specific sustainable urban development approaches; rather, it examines how the underground can support or contribute to those approaches shown or suggested to be sustainable and how underground use directly affects identified sustainability issues. Some key aspects regarding sustainability of urban communities will be briefly explored. This chapter discusses the urban setting as a system of systems, and the broadest relationships between underground space use and the essential elements for urban sustainability. Physical qualities of infrastructure related to transportation, shelter, food, water, and key material resources that contribute to sustainability or make them vulnerable to hazards are described. The chapter then focuses on more direct relationships in terms of maintaining enduring, livable communities and enhancing risk mitigation through the use of appropriately planned and designed underground facilities. Chapters 4, 5, and 6 examine advances in human safety issues, analytical techniques for lifecycle cost assessment of underground facilities and the broader “triple bottom line” analysis (financial, economic, and social performance), and specific technological advances associated with enhanced sustainability, respectively.
Sustainability is dependent on more than having enough clean water, food, and material goods. As urban areas grow, strategic growth of infrastructure systems is also necessary to allow for efficient and sustainable delivery of water and sewerage service, food, energy, industrial and commercial goods, and information. Locally created products or services need to be transported or exported, other goods need to be imported, and wastes need to be removed. Physical infrastructure systems are thus critical to the urban system of systems and underpin both a sustainable economy and quality of life.
How does the growth of urban populations, the expansion of urban lands, and their associated facilities and infrastructure enhance or hinder the provision of essential materials and services and the creation of stable, sustainable, socially desirable urban communities? What is the role of the underground? As described in Chapters 1 and 2, the underground is best thought of as a resource designed and managed using a system of systems approach to achieve the most sustainable solutions. Infrastructure is a substantial shaping force in urban and regional development. In developed areas, underground infrastructure may offer one of the few acceptable ways to encourage or support the redirection of urban development into more sustainable patterns because new support infrastructure can be added relatively unobtrusively. A well-maintained, resilient, and adequately performing underground infrastructure is essential to future sustainability of cities. Much, however, can be done to improve the sustainability aspects of underground facilities themselves.
Urban sustainability will be more likely if it becomes the expectation among urban planners and managers that the urban setting includes the space resources both above- and belowground, and that both contribute to the healthy functioning of a city. This chapter discusses some urban resources and their potential roles in a holistic accounting of urban systems; the following section specifically highlights certain uses of the urban underground that greatly contribute to urban sustainability.
Sustainability planning requires forethought regarding operation and maintenance issues for the entire life cycle of the infrastructure. Allowing ease of access for maintenance, repairs, and upgrades is a means of insuring that such work can be completed at lower costs. Experience from subway construction and other large underground works has led to interest among some subsurface utility providers in combining utility services in common utility tunnels—often termed “utilidors” (or “galleries” in Europe; see Box 1.4, Figure 2 for an example of a utilidor) (APWA, 1971). Utilidors provide continuous maintenance access
to utilities without the need for digging in the street, are designed to minimize subsurface displacements and other Influences that may cause damage to buried and aboveground facilities, and are a more efficient use of underground space than are separately buried utilities. A study by researchers in Spain (Riera and Pascal, 1992) found a distinct economic benefit from locating services in a common tunnel when the value of the underground was included in the calculations during construction of the Barcelona Ring Road. In fact, shared utility tunnels are frequently constructed in Europe where narrow rights-of-way and strong centralized decision making have favored their use.
It has proven difficult to develop utilidors as extensively in the United States. Obstacles include the need to abandon investment in existing service infrastructure, concerns about operational liabilities and risk in a shared or co-located utility environment (e.g., water or gas lines in the same tunnel as electric lines), and administrative concerns related to access to utility lines by others. In addition, initial connection costs may be higher than those for dig and place utilities. Operational issues such as risk and security concerns for utilities, if installed in utilidors, could be circumvented with improved sensor and security systems. The viability, value, and benefits of utilidors may be effectively communicated with (1) development of workable scenarios for secure multi-utility facilities; (2) development of workable scenarios for effective transitioning from current configurations; (3) lifecycle cost-benefit analyses comparing separate and combined utility corridors; and (4) demonstration projects. In the United States, utilidors have been built typically as part of major old and new developments or underground transportation improvements (e.g., Disney World in Orlando, Florida, with its extensive underground service “city” and the Chicago freight tunnel network). If the United States is to improve the sustainability of its urban utility services and preserve underground space for more cost-effective sustainability opportunities for future services, then this impasse needs renewed attention.
Underground Transportation Facilities
The long-term sustainability of urban areas is positively affected by the availability of underground transportation systems. Cities such as Singapore have benefited from master plans designed around transportation systems (Hulme and Zhao, 1999). Well-planned underground transportation systems tend to reduce urban sprawl, saving landscapes and protecting biodiversity, and can positively impact land use and development decisions (Bobylev, 2009; Sterling et al., 2012). They provide safe and efficient transportation and decrease the need for and use of automobiles, reducing congestion and travel times, which in turn reduces fossil fuel use and emissions (Besner, 2002).
Underground transportation assets can address multiple growth-related challenges in urban areas, but many challenges also remain to be addressed (see Box 3.1). Today, many cities have urban transit subway systems, underground
Specific Challenges and Opportunities for Transportation Systems
Underground transportation systems will benefit strongly from technical advances as discussed throughout this report. In design and construction, for example, new lining and underground construction technologies are needed that reduce material use and improve long-term facility performance. Underground transportation systems in major cities, however, usually represent key infrastructure elements that are pivotal in terms of the urban mobility that sustains the economy and provides quality of life and hence have a special importance in terms of underground space use. Because they are large public investments and subject to many policy and funding constraints, underground transportation systems may not be designed, operated, and maintained for their maximum contribution to overall urban sustainability. The construction of major underground transportation projects often requires significant relocation of in-situ underground utilities along public rights of way. However, the major excavation work and relocation needs of the project provide key opportunities for renewing and rationalizing utility provision in an area to provide for easier future maintenance of those systems. While this represents an extra burden on the transportation project, it can provide an overall benefit to the urban community using a system-of-systems analysis rather than a project-by-project analysis. Furthermore, in a planning context example, the long-term sustainability of an underground transportation system is improved when system designs allow as much flexibility as possible, taking into account future uses, potential for additional transportation lines, and intermodal connections. This again can increase initial costs but provide for better long-term sustainability.
express arterials and highways, and grade-separated dedicated freight movement corridors for railroads or trucks. High Speed Rail (HSR) service that includes both above- and belowground components is common in Europe and Asia. Each system has unique characteristics to suit its purpose and location. All will likely improve quality of life and long-term sustainability benefits to the urban center(s) served (Jehanno et al., 2011).
Underground transportation, as described in the next sections, can serve to increase community resilience against many natural or manmade hazards including earthquakes and acts of war than their surface counterparts. Box 3.2 provides an example of the performance of transportation infrastructure crossing San Francisco Bay following the Loma Prieta earthquake in 1989. Different types of underground transportation elements and systems and their roles in sustainable urban development are described.
Underground Urban Roads and Highways
Overloaded and congested urban surface arterial roads can be relocated to aerial or underground alignments to obtain grade separation (e.g., transportation routes at multiple elevations) and exclusive rights-of-way. This can relieve the
surface of crowded traffic, noise, air pollution, and congestion. The multiple transportation levels provided by tunnels may allow dysfunctional arterial roads to be replaced with functional surface roads that improve the quality of life for neighborhood residents and transportation mobility for the city. The physical barrier and visual blight that an elevated arterial road may represent can be removed. Adjacent neighborhoods once separated by the road may be able to reunite as a community (see, for example, Einstein, 2004). Removing traffic to a tunnel may also result in a brighter and quieter environment, new land use opportunities, and improved neighborhood property values—all indicators of more livable and sustainable neighborhoods (Parker, 2004).
Underground urban roads and highways typically traverse deep below a city from portals at each end that tie into existing service road networks. By going deep, the tunnels avoid building foundations and other in-place services, and leave space closer to the surface for future installations. In most cases tunnels constructed at depth will be the lowest cost among alternative underground solutions if a lifecycle cost analysis is prepared (Parker and Reilly, 2009) and geologic conditions are respected. Barriers to free-flowing traffic can be bypassed, travel times shortened, and carbon emissions reduced for the same distances traveled by surface road. Further, diversion of traffic from streets allows more pedestrian-friendly environments in the city. However, decisions to build underground roadways, regardless of the benefits, are regularly contested (for example in Seattle, Washington; see Box 3.3). The decision to proceed often requires a vote of the people and a coming together of city, county, state, and federal representatives to reach agreement. This process is often time consuming and can result in increased project costs.
Public Transit Subways
Public transit is a vital part of many urban areas and an integral part of a sustainable urban environment. Rapid transit facilitates efficient movement of people of every economic class and ethnic group to and from their homes, school, work, health services, places of worship, airports, recreational activities, and other amenities available to urban life. Public transit provides needed mobility to those without cars, and connects and unites neighborhoods and communities to function more smoothly and take advantage of community services. Many cities make public transportation available in the form of bus systems. As populations grow to between 1 million and 3 million, regions may see advantages in electrified rail transits (light rail) (APTA, 2009) that allow faster transit for larger numbers of people. Such systems can operate on streets used by normal traffic, in limited access rights-of-way, and exclusive and grade-separated rights-of-way (for example, elevated or underground as developed for the Muni transit system in San Francisco, California, and the MAX transit system in Portland, Oregon). Heavy-volume transit systems—so called “heavy rail” systems—are needed when populations increase to more than 3 million (APTA, 2009). These are grade
Performance of Transportation Infrastructure Following the Loma Prieta Earthquake, 1989
Underground transportation systems can remain operational during, or quickly resume operation following, natural hazardous events such as earthquakes, tornadoes, lightning, and thick fog or dust conditions. According to a review of several studies documenting earthquake damage, large diameter underground tunnels have historically suffered less damage than surface structures (Hashash et al., 2001). The San Francisco Bay Area Rapid Transit (BART) system operates through cut-and-cover and mined tunnels and serves multiple destinations including San Francisco and Oakland, California, through a 5.5 kilometer subaqueous trans-bay immersed tube tunnel between the two cities. This system improved disaster resilience for this urban area following the Loma Prieta earthquake in 1989 by allowing the continued functioning of the economies of these communities.
The Loma Prieta earthquake was a magnitude 6.9 event that caused serious physical damage to local infrastructure (USGS, 2009) including damage to connections, bearings, and members of the San Francisco-Oakland Bay Bridge, forcing its closure for more than a month. A 15 meter, 5-lane roadway section dropped from the upper eastbound roadway deck onto the lower westbound deck (see the Figure), killing one person (Dames and Moore’s Earthquake Engineering Group, 2004).a BART crosses San Francisco Bay underground almost directly beneath the Bay Bridge alignment. It was temporarily shut down by the earthquake, but there were no passenger injuries, and service resumed in half a day following damage inspection and power restoration. BART patronage rose quickly from an average of 218,000 riders per day to more than 308,000, and service continued around the clock, seven days a week until the Bay Bridge reopened more than a month later (Dames and Moore’s Earthquake Engineering Group, 2004). The Bay Area economy,
separated, often in subways such as in the BART system constructed in 1962 in the San Francisco Bay area, and the New York City Transit System, constructed beginning in 1900 (Bobrick, 1981).
Subway rapid transit provides the same safe, environmentally sound, fast, low-cost, and comfortable transportation to all people who use it. It has already been mentioned that choosing subway transit because of its relative comfort, savings in time and money, or predictability of the ride reduces the number of commuters on surface roads. Commuters who use rapid transit daily rather than drive personal vehicles cut their carbon footprint significantly (APTA, 2008), and may realize personal health benefits through minimizing stress associated with traffic, accidents, and congestion. From the regional perspective, regional transit system stations attract development of urban centers—small urban communities—because access to the urban areas becomes a major attraction for those relocating to the region. The location and services that support more dense, compact development in the vicinity of transit stations—as opposed to the development of urban sprawl—can affect the overall cost to the taxpayers in terms of provision
although damaged by the earthquake, recovered more quickly than would have been the case without the underground BART because significantly large numbers of people were able to get to work (USGS, 1998).
FIGURE Collapsed section of the San Francisco-Oakland Bay Bridge following the 1989 Loma Prieta Earthquake. The bridge remained closed for more than a month while the BART subway tunnel located almost directly beneath the bridge was running within a day of the earthquake. SOURCE: sanbeiji (CC-BY-SA 2.0), available at http://www.flickr.com/photos/sanbeiji/220645446/sizes/m/in/photostream/.
aSimilarly, the upper roadway of a 2 kilometer length of highway of the Cypress Street Viaduct in the San Francisco Bay area crashed onto the lower roadway, killing 42 and injuring several hundred more.
of essential services such as schools, police, fire and EMS protection, hospitals, water, sewer, electrical, natural gas, food, and other supply sources, all necessary attributes of developing a sustainable urban environment.
The ability to update and replace subway system components such as conduit, electrical and fiber optic cables, water lines, waste water lines, ventilation systems components, lighting, signage, escalators and elevators, and information systems makes it reasonable to expect useful service of subway tunnels for more than 100 years. Transit tunnels built in the 1860s in London are still in service today. The long life of underground components tends to reduce lifecycle costs and also reduce demands for both renewable and non-renewable resources (Parker, 2004). All these characteristics contribute to sustainability and justify new rapid rail subways from a lifecycle analysis point of view.
Grade Separated and Underground Freight Railroads
Combining normal surface and freight traffic, particularly the movement of ubiquitous freight container units, can result in heavy traffic, especially in port
Replacement of the Alaskan Way Viaduct, Seattle, Washington
Recent experience in Seattle, Washington, planning the replacement of the earthquake-damaged Alaskan Way Viaduct (AWV) illustrates how difficult the decision to reroute to the underground can be. The current AWV is a double-deck urban expressway (see Figures 1 and 2) running along the Seattle waterfront. It is similar in design and construction to the 1950s-era San Francisco Bay Area Cypress Street Viaduct and Embarcadero Freeway that both failed as a result of the Loma Prieta earthquake in 1989 (USGS, 2009). The AWV sustained non-reparable damaged as a result of the 2001 Nisqually earthquake (PNSN, 2002) and must now be replaced (WSDOT, 2004). Alternative solutions included a new, wider, two-level viaduct on the same alignment, a replacement of the viaduct by a wide surface street carrying significant levels of through traffic, the relocation of the highway on a bridge or tunnel over or under Elliott Bay, and the “do nothing” alternative intended to limit traffic growth and create a demand for better public transit through continued, more disruptive road congestion. The alternatives were studied and publicly discussed. Ballot measures to determine the preferred solution were intensely debated at the local, city, and state levels.
Ultimately, the decision was made to bore an urban underground bypass expressway, remove the damaged viaduct, and restore an accessible scenic waterfront (see Figure 2). The 3.2 kilometer, four-lane bypass roadway tunnel (Figure 3) will be located deep enough under the city to avoid the century old Burlington Northern Santa Fe railroad tunnel in daily use, a large interceptor sewer, and existing building foundations. Seattle will recover views of Elliott Bay, Puget Sound, and the mountains when
FIGURE 1 Seattle Washington’s Alaskan Way Viaduct is a double-deck expressway along the city’s waterfront. SOURCE: http://en.wikipedia.org/wiki/File:Alaskanviaduct.jpg.
the viaduct is removed. Major disruption of traffic patterns to and through downtown Seattle will be avoided (FHWA, 2011). A landscaped boulevard on the waterfront is planned, similar to that constructed in San Francisco following the failure of the Embarcadero Freeway. Negative effects of the old viaduct on the city were not fully appreciated until the debate for its replacement took place (e.g., Garber, 2009; Lindblom and Heffter, 2009). Proponents of the plan argue that downtown Seattle will benefit from improved open spaces and green zones.
FIGURE 2 (Left) Arial view of Seattle, Washington, water front and the prominent Alaskan Way Viaduct and (Right) early concept of proposed new Alaskan Way Street of same area. The new concept increases pedestrian access to the waterfront and improves general access to adjacent commercial enterprises. SOURCE: WSDOT.
FIGURE 3 Early concept of the proposed State Road 99 bored tunnel. SOURCE: WSDOT.
Grade Separation of Freight in Greater Los Angeles
In the greater Los Angeles area, the Ports of Los Angeles and Long Beach have grown to be, if taken together, the largest container terminal in the country (AAPA, 2011). They provide a major gateway for containerized goods in and out of Asia. The principal mode of transport of containers away from the ports to the rest of the country is rail. Three major railroads—the Southern Pacific, the Union Pacific, and the Burlington Northern Santa Fe (BNSE)—had tracks into the ports from their national track junctions. Historically, railroads have right-of-way over crossing traffic, and so much freight movement at grade brought traffic in a large area of southern Los Angeles County to a standstill multiple times daily as 200-car-long freight trains moved slowly over three separate rail networks to join their national track networks east of the urban area.
Concerns over congestion and associated air pollution led to the development of the Alameda Corridor Project (ACTA, 2012a), a plan to build a 32-kilometer (20-mile)-long freight rail expressway including a 16-kilometer (10-mile)-long top braced open trench, 15 meters wide and 10 meters deep with space on its floor for three tracks and a service road called the “Mid-Corridor Trench.” The Alameda Corridor Transportation Authority (ACTA) was proposed, organized, and authorized by legislation (ACTA, 2012b). ACTA has authority to raise funds, receive government grants, own and receive property, contract for construction and operations, and do those things necessary to implement the plan. In 1994, with the purchase of the Southern Pacific Railroad’s Alameda Corridor track and right-of-way, the corridor project began in earnest.
The 10 meter (33 feet) depth of the Mid-Corridor Trench easily provides the ability of BNSF Railway and Union Pacific Railroad, via their trackage rights, to move double-stacked container freight rail flat cars, 200 at a time, in both directions, at 40 mph from the ports to their respective national rail system connection (ACTA, 2012a). First operations began in 2002, and the more than 200 at-grade railroad crossings where cars and trucks previously had waited
cities. Drivers may encounter long lines of traffic waiting for freight trains to clear grade crossings or trucks in long queues waiting to clear signalized intersections. Significant air pollution from train and truck exhaust, as well as from the traffic waiting to pass, can degrade air quality (Hricko, 2006) and has the potential to negatively impact the quality of life and the economies of nearby neighborhoods (for example, Palaniappan et al., 2006).
Grade-separating freight movement from surface streets is part of the solution. Open braced trenches that provide natural ventilation for diesel exhaust have been a preferred solution in places such as southern California for freight trains powered by diesel-electric prime movers (see Box 3.4). In southern California, significant investment in grade separation infrastructure is the result of collaboration between the ports, a number of affected cities, the county, state, and federal governments, and the railroads.
Some traffic problems can be eased with dedicated and signalized surface
Outcomes include sustainability benefits for the region, and operational improvements for the ports and railroads, restoring some of their competitive edge by decreasing freight delivery times. Peak movements were reached with 60 train movements per day in October 2006. Benefits to air quality result from more direct rail routes traveled at greater speeds, reduction of vehicular exhausts at grade crossings, and the increase in the amount of cargo that can be transported by rail instead of by truck (Weston Solutions, 2005). ACTA is designing and will soon construct the Alameda Corridor East project, with more braced trench design and a $500 million construction project to grade separate the long freight trains from the grade crossings throughout a part of the city of San Gabriel.
FIGURE A container train of the Alameda Corridor Freight Line in California. The trains travel in an open-braced trench that provides ventilation for the engines and grade separation for container traffic. SOURCE: Courtesy of the Alameda Corridor Transportation Authority market. Grade-separation tunnels would be a part of the answer, and sustainability benefits will be among those analyzed by planners to justify such a facility.
streets or grade-separated viaduct roadways for freight movement by truck during times other than commute periods. Tunnels also can be used to provide exclusive or preferred lanes for freight movement by truck. For example, in Miami, Florida, a tunnel boring machine-driven tunnel beneath Biscayne Bay is being constructed to create a direct connection from the Port of Miami to local highways and reduce traffic in the downtown area (Port of Miami Tunnel, 2010). In the greater New York metropolitan area, tentative planning has begun again on a freight-only tunnel that would pass under a part of Eastern New Jersey, the Hudson River, Manhattan Island, and part of Brooklyn, New York, possibly providing for the movement of freight trains and trucks between the vicinity of the New Jersey Turnpike and the Long Island Expressway (FHWA/PANYNJ, 2010). The ambitious plan indicates growing recognition that not enough surface area exists to provide for the needs and services required to remain competitive in a global
There has been persistent recurring interest in underground pipelines for transporting parcels or freight, for example the use of extensive networks of pneumatic tubes in Paris, France, Vienna, Austria, Berlin, Germany, and Prague (now of the Czech Republic), since the second half of the late 1800s (Uffink and Admiraal, 2012). Such systems involve the transport of freight in a capsule, propelled by liquid (hydraulic capsule pipelines) or gas (pneumatic capsule pipelines) through a network of pipes (Liu, 2000). Pneumatic capsule pipelines were used in the former Soviet Union, and a commercial system is in place in Japan for transport of construction materials, limestone, and similar commodities (Liu, 2000). Other systems have been studied elsewhere in the world, particularly in port areas (Uffink and Admiraal, 2012). Specific plans for U.S. freight tube systems have been studied (e.g., Goff, 2001; Roop et al., 2003; Liu, 2004) but have not been implemented due to cost competition from other modes of freight movement and various environmental issues.
High Speed Rail
Broader sustainability benefits can accrue when regional rail transportation systems compete with airlines in terms of travel times and costs. High speed rail (HSR), for example, could deliver large numbers of people over long distances with a significantly smaller carbon footprint (Baron et al., 2011; Ledbury and Veitch, 2012). HSR systems are in service in Japan, France, Germany, Italy, China, and Taiwan, and accommodate home-to-work trip commuting by providing long-distance point-to-point transport on a reliable schedule. In the United States, California voters passed a bond issue in 20081 enabling the construction of HSR from Los Angeles to San Francisco (see Box 3.5).
HSR is typically planned with no more than 1.0 to 1.5 percent vertical grades to maintain maximum speeds, and very long radius vertical and horizontal curves to accommodate high ground speeds of up to 220 mph.2 Higher grades and smaller turn radii can be accommodated with commonly used technologies, for example grades of 3.5 to 4.0 percent on some HSR lines in Europe, but speeds may be compromised. These speeds require that rights-of-way be exclusive and protected from access to other vehicles, people, or large animals, and to achieve such HSR makes use of viaducts, open top trenches, and tunnels. When HSR approaches a destination city, it slows and slips underground to penetrate the city center below existing infrastructure. One or more large underground rooms are located beneath the city center to house the station, supporting facilities, and personnel required to deliver the service product. Vertical delivery systems lift
1 CAL. S.B AB 3034 (2008).
2 See, for example, http://www.cahighspeedrail.ca.gov/project_vision.aspx.
High Speed Rail in the United States: The California Example
High speed rail (HSR) may become a reality in the United States in the next two decades. HSR can be economically viable in between major metropolitan areas that are 160-800 kilometers apart, with sufficient populations (50,000 and higher) and economic productivity and a demonstrated travel market (Hagler and Todorovich, 2009). State and federal support, funding, and financing would need to accompany local interest in HSR service. Planning, environmental impact statements and mitigation measures, rights-of-way acquisition, and design and commitment to construction efforts would be significant, and engineering, geotechnical, historical, and archaeological investigations and reports would be important to the timely development of the project. Much earth science and seismic investigative and analysis work would be required to support the design solutions, especially given the need to survive and remain in service following a significant seismic event.
In 2008 California voters passed a $10 billion bond issue to enable the construction of an HSR system between Los Angeles and San Francisco, California, eventually to be extended south to San Diego and north to Sacramento. It is in the early stages of conceptual design, working through alternative designs, section by section, and filing state environmental impact reports. Total track length is estimated to be 2,775 kilometers, with most of the line to be two-track. Between 160 and 200 track kilometers of tunnel are planned. San Francisco and Los Angeles stations will be reached through deep tunnels, delivering passengers to the Transbay Terminal in San Francisco and to Union Station in Los Angeles. The tunnel designs are being developed for train speeds of 350 kilometers per hour (217 miles per hour). To provide the needed rights of way in other populated areas, significant use of open cut, open top, braced reinforced concrete box structure system for two operating tracks and a service road are being considered. The cross section is similar to that used with the Alameda Corridor Project.
passengers and luggage to street level. HSR, however, is very expensive and often subsidized.
Shelter in urban areas in the United States ranges from low-density developments of single-family homes to high-density apartment and condominium properties. Low-density developments offer self-reliant sustainability possibilities in terms of on-site energy collection, food production, and local management and recycling of some wastes generated by the occupants. However, energy expenditures for transportation in low-density urban areas greatly exceed those in high-density urban areas (Newman and Kenworthy, 1999) because of longer travel distances and limited public transportation options. Providing centralized services to low-density developments requires increased lengths of utility
FIGURE 3.1 The earth-sheltered home is partially underground, providing greater strength and energy efficiency. SOURCE: http://www.monolithic.com.
services as compared to the same population served in high-density areas. Highdensity housing increases the dependence of occupants on centralized services, but increases options for a non-automobile-based urban lifestyle, because public transportation can be provided more economically and basic shopping opportunities can exist within walking distance for many residents. Urban development trends in the United States show a continued increase in urban sprawl, but also a trend toward increased population densities in urban downtowns (for example, Greene, 2006), motivated in part by the desire for a more urban living experience without long and expensive commutes by car.
Most people do not choose to live underground. Urban underground use related to housing is in the form of utility and transportation services for residents, storage, or expanded living space (e.g., basements). In low-density suburban and rural housing developments, some earth-covered or earth-bermed structures have been built for their ecological, isolation, and energy attributes (see Figure 3.1), but initial costs, moisture control issues, acceptance, and resale issues limit their widespread construction.
Urban Commercial, Industrial, and Institutional Facilities
Sustainable urban areas must provide necessary commercial, industrial, and institutional infrastructures that support and manage a viable economy, provide jobs, and deliver support including education and social services. The relationship between urban density and land prices tends to create a market for large, multi-story, commercial and institutional buildings in the high-density core(s) of urban areas, and more low-rise structures in the surrounding urban and suburban areas. As discussed elsewhere in this report, it can be desirable under certain
circumstances to place various types of commercial, industrial, and institutional facilities underground. However, this is not the only use of the underground that is important in the urban core. Increased size and density of buildings in the urban core require an increase in the capacity of urban utility and transportation services, both in the core and in outlying areas that are connected socially and economically. Increased reliance on such systems means that the systems must be robust and reliable. The underground can offer protection to these systems, keeps them near the populations they serve, and allows provision of critical lifeline services and emergency response—all while preserving aboveground real estate for other uses.
Sustainable Food Production and Distribution
Prime agricultural land is being covered by low-density suburban development in many parts of the United States (Carver and Yahner, 1997). There has been a historic tendency for populations to concentrate in areas with good agricultural, trading, or transportation potential, often along rivers or coastlines. Hence, as cities expand, they often sprawl out from the population center and supplant good farmland. Many existing infrastructure and taxation practices actually encourage urban sprawl by supporting construction of new regional infrastructure needed to service the growing suburban areas (Brueckner, 1999). The market forces that underlie conversion of farmland to developed land represent important long-term issues that have potential impacts on the cost, availability, and impact of food supplies. Abandoning good farmland close to markets and developing poorer farmland farther away must be balanced by efficiency improvements if regional sustainability is to be achieved.
Placing facilities underground reduces claims on surface land, which can have the effect of preserving agricultural land. Careful holistic urban planning and placement of underground facilities can serve to direct urban growth in the most sustainable manner. Holistic planning considers not only how productive agricultural lands may be preserved, but also how food is made readily accessible to urban populations through transportation infrastructure, temperature-controlled storage facilities, means of distribution and sales, and the energy necessary to operate each part of the delivery/storage chain. Maximum sustainability benefits are achieved if all of these infrastructure requirements are considered as part of the overall urban system of systems. Such facilities do not necessarily need to be underground, but underground facilities do provide some inherent thermal advantages in terms of food storage and warehousing. Warehouses and retail food outlets, for example, are typically windowless facilities that have little need to occupy the surface, especially when surface space is scarce.
Water is essential to human survival, and loss of a hygienic water supply impacts survival and can cause the spread of disease more rapidly than loss of food supply. Urban areas typically draw their water from surface water (rivers, lakes, and reservoirs) or groundwater sources. Water resources are controlled largely by the hydrologic cycle, but can be damaged by poor practices associated with land development. As urban areas grow and reliable and hygienic surface and groundwater supplies are no longer adequate to meet demand, efficient water use, reuse of “grey” water (wastewater from domestic activities such as bathing and laundry) and “black” water (sewage), and creation of new water supplies become more important. Cities, especially those in arid regions, are forced to seek ever-more-distant or deeper water supplies as urban populations grow and the demand for water increases. Aging or poorly maintained water supply infrastructure leaves urban water supplies vulnerable to leakage3 and to disruption. There is also growing competition for water between urban areas and agriculture regions where irrigation occurs on a widespread scale (FAO, 2011). Holistically thinking, the export of agricultural products from a region can be considered a loss in water resources—even as it may be a boon to the regional economy.
Long-term urban sustainability implies that an urban area has balanced its water supply possibilities. Where groundwater is an important water resource, a sustainable water supply would not be depleted (for example, by over extraction), polluted, or diverted in detrimental ways (see Box 3.6). Construction activities may produce runoff with sediments and pollutants, such as pathogens and metals, that may negatively impact water quality or quantity (EPA, 2005). Agricultural practices may also have long-term impacts on water quality and the regional environment. For example, increased salinity of surface water and groundwater caused by evaporation and dissolution (CA Water Resources Control Board, 2010), and attendant changes in habitat for flora and fauna, can be the direct result of water use practices.
Good stewardship of underground water resources can include use of the underground for urban development because more natural landscape can be preserved for groundwater recharge. Water distribution facilities can be placed underground, allowing land to be developed in ways that enhance quality of life in compact cities. However, careful analysis and construction and operation approaches are needed to avoid detrimental changes in groundwater levels, flow patterns, and pollution. Groundwater pollution can become a major issue; the pollution legacy of underground gasoline storage tanks at service stations is a well-recognized example (Meehan, 1993), as are superfund cleanups of major industrial pollution sites.4
3 For example, see Hull, 2010.
Groundwater Flow Under the Duisburg (Germany) Subway
Underground tram stations in Duisburg, Germany, were designed for future traffic expansion with two platform levels and cross-platform changing in each direction. In 2000, a 3.6 kilometer extension of the Stadtbahn tunnel from north under the river Ruhr to Meiderich opened (UrbanRailNet, 2007). When the Duisburg line was being built, the slurry (diaphragm) walls were carried down to a clay layer aquaclude (impermeable layer) and would have permanently impeded northward flow of water under the city, causing a buildup of water levels on the upstream (southern) side and dropping water levels on the downstream (northern) side. This potential change in groundwater conditions was unacceptable. The Municipality of Duisburg and the prime contractor designed a system that would be watertight during construction then permeable after construction. Dense bentonite (clay) slurry would fill and support the sides of the trench until cast-in-place concrete or concrete panels replaced it. An approximately 1.3 meter gap was built between 5.4-meter-long cast-in-place panels of impermeable diaphragm wall. The gaps were frozen before excavation for the necessary ground support, creating an impermeable barrier. The freezing pipes were removed when construction was finished and the slurry thawed, permitting groundwater to pass under the tunnel (Hooks et al., 1980).
In this circumstance, issues beyond construction were considered, and a solution to a potentially serious problem was applied. However, this example illustrates the potentially large-scale problems that can occur during subsurface construction without the appropriate sensitivity to the impacts of underground design, construction, and operation on an entire urban system.
Key Material Resources
Sustainable use of a non-renewable resource seems contradictory, but in practical terms, sustainable use can be considered a question of the rate of use of a resource over a meaningful timescale. Key material resources derived from earth materials, for this discussion, fall into the categories of fluid and gaseous energy sources (principally oil and gas), energy sources in solid form (e.g., coal, oil shale, tar sands, wood, and peat), industrial minerals (e.g., iron ore and bauxite), high-value or critical strategic minerals (e.g., gold, uranium, rare earth elements), and construction-use materials (e.g., gravel, sand, building stone, Portland cements, and brick-quality clay). Consideration of the interdependencies of the energy and mineral sources, available reserves, strategic concerns, and environmental impacts is beyond the scope of this document. However, issues that arise in the interaction between urban development, energy and mineral extraction, and the use of urban underground space are justified for discussion in this report, and brief and general descriptions of some issues are provided.
Estimates vary for how long world oil, gas, and other energy reserves will last given current consumption rates. Usage rates and the extents of proven accessibility of reserves depend in part on the unit prices of the resources.
Oil and gas are important feedstock for the plastics and chemical industries, complicating price and policy interactions. When alternatives are available, there may be stronger incentives to switch to alternate resources. Wind energy, solar energy (e.g., thermal power, passive solar heating, and photovoltaic electric energy), biomass (e.g., rapidly replenished sources for hydrocarbon fuels and direct burning for electric power generation), geothermal (both hot rock power applications and ground-coupled heat exchange systems), and wave energy capture systems are among the more commonly discussed options. Considering these options in the long term is essential in urban development, including making the means available to respond to growing energy demand as energy sources and technologies change.
Industrial minerals include a range of ore types and extraction methods. Most markets are price sensitive, and many industrial ores are mined outside the United States. Such globalization has resulted in the closing of many U.S. mines and, consequently, fewer options for educating mining engineers in the United States (see Chapter 7 for additional discussion of this topic). Expending greater resources to extract minerals of high strategic importance may be justified, but domestic sources are often ignored in favor of less expensive foreign sources (NRC, 2008a). Construction materials are mostly constrained to local extraction, transport, and use because of their high bulk and low price potential. They are, however, important to urban building and infrastructure construction. Poor local availability can significantly increase construction costs and hamper development.
Important natural resources may gradually become inaccessible as a result of urban development—essentially becoming quarantined beneath expanding urban areas. New technologies may be needed for successful and safe extraction in developed areas. For example, local aggregate resources are frequently obtained from nearby open gravel pits or open rock quarries. As an urban area encroaches on the resource, open excavations become an increasing nuisance of noise, dust, vibrations, competition for road transportation capacity, and other disturbances. Land value increases also may encourage sale of the land for development.
An alternative to abandoning rock quarry resources is a change to resource recovery through underground mining. Under the right combination of rock quality and economic conditions, an aggregate supply can be maintained and newly created underground space in large mined caverns can provide a stable natural temperature and a high degree of separation from other urban or recreational uses on the land surface above. The Kansas City area is a prime example of what can be developed. Approximately two-thirds of the industrial space in the Kansas City area is located in large mined limestone caverns (Nadis, 2010) (see Box 3.7). Other mined spaces around the world have been used as facilities to store everything from paper and electronic archives; energy, waste, and agricultural products; frozen foods; and compressed air. They also have been used as museums and tourism facilities, sports facilities, education facilities, hospitals,
Underground Commerce Centers: Turning Mining Excavations into New Commercial Resources
Developers in U.S. locales such as Lawrence County, Pennsylvania, and Kansas City, Missouri, have converted their underground excavations into warehouse, office, manufacturing, and educational space (see Figure). Limestone mining began in Kansas City in the late 1800s. By the mid-1900s, mine owners strategically excavated to utilize space left behind (Buzbee, 2011). “SubTropolis” encompasses approximately 7.62 million square meters of leasable space. As of 2010, 55 businesses were located in the underground facility that includes a 3.2 kilometer network of rail lines and 9.7 kilometers of paved roads (Nadis, 2010). Constant underground temperatures result in 50 to 70 percent savings in total energy costs (Hunt Midwest, 2009). No heating costs are incurred in the winter, and very little energy is required for cooling and humidity control in the summer. Space use is diversifying as the company develops a 61,000 square meter data center with redundant power and cooling systems and protection from natural disasters.
In 1991, the facility had a major and difficult-to-control fire that burned for weeks in a large storage area in spite of firefighter efforts to control it. The underground fire was too hazardous for direct fire suppression by fire fighters, and no fixed fire suppression system such as sprinklers were in place at the time. Cleaning compounds, pesticides, paper goods, and cooking oil contributed to the fire that approached 1,100°C (2,000°F) (Buzbee, 2001). Similar problems were encountered at another underground facility located in Louisville, Kentucky. As a result of such fires, the National Fire Protection Association established a Technical Committee on Subterranean Spaces, and new fire protection standards were developed related to distance to and numbers of exits, ventilation, communication in the underground, and underground wayfinding (Lake, 1998). Kansas City has since adopted new safety language into its code for underground spaces that establish minimum safety requirements.a SubTropolis and other underground facilities now include fire suppression systems and safety practices.
FIGURE Underground warehouse space in mined limestone caverns approximately 100 feet beneath Kansas. Roads and facilities can accommodate 18-wheeler traffic. SOURCE: Hunt Midwest, http://huntmidwest.com/press.html.
laboratories, and for a variety of retail, office, and manufacturing purposes (Peila and Pelizza, 1995). Of course, such mining must be executed carefully to ensure the long-term stability of the surface and underground space. There are many examples around the world of cities growing over old mine workings that were not excavated with long-term stability in mind. Such mines may pose collapse and subsidence hazards for surface development, as well as provide a pathway for degradation of area groundwater through leaching of harmful chemicals from the mine workings.
Local Urban and Natural Environment Preservation
Beyond having food, water, shelter, a viable economy, and a supply of key resources, a sustainable urban environment requires that natural processes are sufficiently maintained to preserve an ecological balance over the long term. A sustainable and healthy urban environment is fundamentally linked to a sustainable and healthy natural environment. A deteriorating natural environment may directly and deleteriously impact food and water supplies, and ultimately degrade quality of life and health to unacceptable levels. Key environmental parameters for sustained urban quality of life include carefully considered air and water quality standards, noise control, and safety and sanitary standards. Basic living standards in even the poorest neighborhoods need to be met for urban systems as a whole to be sustainable. Aspiring beyond basic levels of environmental preservation means creating an urban environment that is appreciated by all citizens and that offers a variety of social, cultural, and recreational opportunities with easy access to the natural environment. As has been discussed, underground facilities can have many specific impacts on preservation of the surface environment at the site of a facility, or along a transportation network. In broad terms, placing facilities underground allows preservation of more natural space for the benefit of the community.
Underground construction—as compared to surface or elevated construction—can mitigate noise and vibration and can offer greater air quality control and beneficial reuse of waste construction materials, including soil and rock removed from the site. On the other hand, to contribute to the sustainable urbannatural environment system, infrastructure placed underground needs to be constructed with consideration of issues associated with water quality, groundwater flow, potential changes to soil geochemistry, or changes in underground temperatures or heat flow that might impact the natural and built environments.
To limit future pollution, current groundwater, soil, and infrastructure monitoring practices for urban areas may need to be intensified to more effectively identify and address potential problems (see Chapter 6 for detailed discussion). Sustainable practices suggest that environmental problems need to be looked at comprehensively and on a common risk-cost-reward basis.
The form and operation of urban areas has regularly responded to known risks. In historic times, threat of attacks resulted in establishment of walled cities and secure water and food supplies that could last many months. Massive fires, such as the Great Fire of London in 1666, led to changes in both construction practices and street design in major cities (Schofield, 2011); and attention to improved water supply and sanitation in the modern era occurred when the link between cleanliness and disease was established. Natural underground conditions or phenomena such as presence or absence of gases, radiation (radon), excessively high or low temperatures, and water may represent hazards to underground infrastructure and people in or dependent on it. For example, gases such as methane, sulfur, and carbon dioxide naturally exist underground and can threaten human health in certain concentrations or exposures. The lack of naturally occurring oxygen is also a hazard. Human habitation of the underground, therefore, requires continuous ventilation from the surface in a failsafe delivery system. Water also poses a hazard to underground infrastructure and its occupants and can swiftly inundate and damage subterranean structures and safety systems (see Box 3.8). Such risks can be minimized and managed at acceptable levels, but only if identified, understood, and responded to. A successful risk management strategy is one that is tightly integrated with design and operations processes. Robust monitoring systems are needed that ensure overall performance, and human and technological capacities are needed that can design, operate, and respond to substandard performance when encountered.
In recent years, different or new types of hazards have been recognized in the urban environment and require increased attention. Some are related to ongoing urban concerns such as air quality, personal safety, and security; others are associated with vulnerable and deteriorating urban infrastructure systems. Another type of hazard is linked to extreme events including those associated with war, terrorist acts, and natural disasters. Existing data resources are too sparse to allow thorough understanding of complex systems’ responses to extreme events or allow reliable behavior modeling and prediction. Extreme events can represent opportunities for large-scale demonstrations, responses can be observed, and design and performance prediction through computational simulations can be improved. This requires pre-organization and preparation (including identification of funding) as well as identification of the cross-sector teams that can be rapidly mobilized to investigate in the aftermath of an event. Teams are mobilized to investigate the aftermath of major earthquakes worldwide, but the focus proposed here is on the understanding and validation of interdependency models.
Security needs also have changed markedly from even 10 years ago, and planners and engineers need to mitigate hazards and risks not previously examined while maintaining societal expectations for well-being and quality of life. Further, facility, materials, and space usage have changed over expected infrastructure
The Great Chicago Flood of 1992
“The Great Chicago Flood of 1992” occurred the morning of April 13, 1992, as a result of the placement of a support pillar into the Chicago River bottom during construction work. The ceiling of an antiquated tunnel located beneath the river was damaged, and extensive flooding jeopardized human lives and severely damaged the infrastructure of the Chicago business district (Arnold, 1992). The tunnel is part of a system (see Figure) that ranges from depths of 6 to 15 meters below the river (Inouye and Jacobazzi, 1992); 946 million liters (250 million gallons) of water flooded downtown sub-basements (cbs2chicago.com, 2007). After unsuccessful attempts by city workers and contractors to plug the hole, Mayor Daley asked President Bush to declare the Chicago Loop a national disaster area. On April 15, the Federal Emergency Management Agency was charged with the federal response to the disaster, and the Corps of Engineers began its work with the contractors to carry out the plugging operation. The work was completed 37 days later (Inouye and Jacobazzi, 1992).
Intended to carry telephone and telegraph wires and cables, the 100 kilometer hand-constructed freight tunnel system constructed in the early 1900s was used to transport merchandise and remove solid waste from more than 80 buildings until no longer viable. The tunnels are now used to store power and fiber-optic cables (Wren, 2007). The river flooded the tunnel network “crisscrossing downtown Chicago and connecting to building basements” (Wren, 2007, p. 35). Researchers replicated the tunnel failure in a geotechnical model and explained the dramatic load increases, breach, and flooding. The southeast abutment of a bridge was previously protected by two dolphin pile clusters (tight clusters of piles). During renovations, the piles were removed and the breach was caused by the driving of new piles 1 meter to the south—and closer to the tunnel. The breach was discovered before flooding started, and repairs to the tunnel were planned. Flooding was delayed by slower water seepage through relatively impermeable soil, but the soil ultimately became displaced when the piles were removed. A conduit formed between the river bottom and the tunnel (Wren, 2007).
Reports vary about the economic and human costs of the extensive flooding. The total contract cost for “dewatering” and structural repairs was reported to be approximately $5.5 million (Inouye and Jacobazzi, 1992). The flooding shut down the Loop, a major financial and retail center and seat of government for Chicago, at an estimated cost of between $1 billion (Wren, 2007) and $1.95
life cycles. Few codes and regulations have been developed for application specifically to underground facilities, and fewer still accommodate changing security needs. Wisdom is required in the choice of new codes, regulations, and metrics to measure success. Sustainability is dependent on the ability of planners and engineers to anticipate and be flexible to emerging issues, technologies, and societal expectations over the duration and beyond the life cycle of the infrastructure they design, build, and operate. They need to accommodate the constantly evolving urban environment.
billion (cbs2chicago.com, 2007). It was reported that the Chicago Mercantile Exchange lost $25 billion in trading. Thousands were affected because people had to be evacuated, subways were shut down, buildings and businesses were left without power (some for several days), and the flooding destroyed everything from merchandise and restaurant food supplies to government records. The lower floors of the Art Institute building also were damaged. Eight city officials, including the acting commissioner of the Department of Transportation, either resigned or retired, were held accountable because they knew in advance that a potentially serious problem had developed at the breach site (cbs2chicago.com, 2007).
Figure Map showing the Chicago freight tunnel network in 1928 (courtesy of the Chicago Department of Transportation) and the location of the 1992 breach that flooded much of downtown Chicago. SOURCE: CDOT.
Identifying Hazards to Infrastructure
For the enhanced security and increased resilience of urban areas, the merits, deficiencies, and interactions of infrastructure elements need to be properly evaluated using a risk-informed approach. All hazards need to be identified, appropriate data collected, and models and methodologies developed to allow comprehensive analyses to understand risk. The complexity of our infrastructure systems of systems increases as more demands are made on infrastructure and as more infrastructure is placed underground. It is possible to model individual
systems and their functionalities, but there is little certainty that models are faithful to reality. Uncertainty in behaviors of interdependent systems is relatively high, and integrated and validated models of systems of systems have not yet been developed. Our systems lose robustness as existing systems are operated more frequently and at closer to full capacity. More frequent slowdowns or shutdowns of infrastructure (e.g., traffic jams, electricity brown- or black-outs) are the result. Even though the amount of sensing and control has increased (e.g., through supervisory control and data acquisition [SCADA] systems), these systems are more vulnerable to intentional attack, unexpected failures, and loss of service (Hildick-Smith, 2005). Infrastructure sector managers can be surprised by the cascading evolution of problems across sectors. With this increasing appreciation of SCADA- and control-system vulnerabilities, anticipatory strategies need to be developed to investigate events and hazards. Problems are exacerbated because society has underinvested in rehabilitation of existing infrastructure systems, leading to deterioration, inadequate capacity, and lack of adaptation to new demands and challenges—all leading to increased vulnerability. There has been little systematic study of either the integrated risks posed by underground infrastructure systems, or of the contribution to risk posed by the increased use of the underground for the placement of critical systems.
In order for urban areas to be sustainable, infrastructure system design needs to account for successful long-term use and service as well as for the periodic and short-term critical responses to potential extreme natural or human-induced events. When extreme events occur, engineers and planners need to be educated and trained to consider them as test beds to understand complex systems behaviors, interdependencies among systems of systems, and validation of computational models of system performance.
Sustainability of underground infrastructure and the broader community is dependent, in part, on the ability to be resilient to the risks associated with natural hazards including earthquakes and floods. Underground structures located in seismically active areas, for example, are subject to ground shaking and can experience failure if not properly designed (e.g., the Daikai Subway station, Japan; Nakamura et al., 1997). In general, underground structures perform well during seismic events due to the lower amplitudes of vibration experienced by buried facilities and the robustness of structure design and construction (Hashash et al., 2001). However, some characteristics such as depth and rock or soil properties can make underground structures more or less susceptible to damage. Hashash and others (2001) observe that deep tunnels seem less vulnerable to shaking than shallow tunnels and that facilities built in competent rock suffer less damage than those built in soils. Large earthquakes, however, can still cause significant damage on underground structures, especially near earthquake epicenters. Significant
effort has been directed toward the development of design technologies to evaluate the seismic performance of underground structures (Hashash et al., 2001; Huo et al., 2005; see Box 3.1). In increasingly urban environments, however, more complete understanding of the seismic interactions between above- and belowground infrastructure and the seismic effects on complex underground facility configurations is needed.
Flooding caused by excessive rains, hurricanes, and tsunamis is a concern in coastal and many low-lying areas. For example, storms in New York City during high tides can cause flooding of part of the subway system, necessitating the protection of surface access points against water level rise. A single storm, given the right circumstances, can result in a sustained storm surge of several feet above normal high tide levels and cause serious flooding and intrusion of saltwater into underground works, as was experienced during Hurricane Sandy on October 30, 2012 (see Box 3.9). Events such as these underscore the need for understanding risk to all hazards. Recovery from this event also can serve as a laboratory that can inform future infrastructure development and recovery planning and efforts. Underground engineers and urban planners have a unique opportunity to catalog their findings as they undertake recovery efforts, and they have the opportunity to rebuild and upgrade infrastructural systems to be more resilient and sustainable.
Flooding can occur as a result of other events or circumstances. Large magnitude subduction zone earthquakes, as in the case for parts of the western United States, may cause sea level rise that threaten infrastructure. Tsunamis also can have devastating impacts on the buildings and infrastructure of a coastal area as was demonstrated in the 2004 Indian Ocean earthquake and tsunami and the 2011 earthquake and tsunami in Japan. Interestingly, underground structures are better protected from water pressure and debris impacts of moving floodwaters if entrances are protected and sealed before an event. Areas not historically subject to flooding may not have been developed to mitigate the effects of flooding, and even some areas prone to flooding have underground infrastructure at risk (see Box 3.10 for a description of the cascading effects that flooding can have on urban infrastructure). The impacts of flooding on underground infrastructure require further research and study.
Hazards Associated with Climate Change and Sea Level Rise
The widespread environmental changes such as more frequent and intense storm events, sea level change, and flooding expected as a result of climate change will affect many urban areas (NRC, 2008b, 2010b, 2011a, 2012). Sustainability depends on the ability to respond and adapt to such changes. Although debate on climate change science is not a focus of this report, it is appropriate
Preliminary Lessons from Hurricane Sandy
Hurricane Sandy, the largest Atlantic hurricane on record, impacted the eastern United States from the Carolinas to Massachusetts on October 30, 2012 (e.g., USGS, 2012). Youssef Hashash, a member of the study committee, led a National Science Foundation-sponsored Geotechnical Extreme Events Reconnaissance (GEER) team to examine the behavior of underground and coastal infrastructure during and following Hurricane Sandy in Manhattan, Queens, Staten Island, and Rockaway Beach in New York, and in New Jersey. The GEER team’s report will be released online (see http://www.geerassociation.org/), but Dr. Hashash shared preliminary observations with the committee regarding some of the impacts in Manhattan.
A 13-foot storm surge flooded lower Manhattan and destroyed or heavily damaged surface infrastructure and overtopped entrances to subways and other underground infrastructure not designed to protect against high water levels. All eight under-river subway tunnels were flooded. Although all underground infrastructure was inundated, many structures were successfully pumped and dry within days, allowing access for the GEER team. The structural integrity of these structures appeared sound, but auxiliary and life support systems (e.g., power and ventilation) were exposed for an extended period to highly corrosive and conductive seawater. To ensure safety, electrical systems could not be tested or used until inspected by qualified personnel. Many structures were “yellow tagged,” indicating infrastructure owners still awaited electrical inspections; thus, at the time of the reconnaissance, the true extent of the damage could not be known.
There were more than 100 deaths in the United States as a result of Hurricane Sandy. Although many were related to drowning, none of the drowning victims was reported to have been found in public underground infrastructure (NY Times, 2012). In this way, the underground infrastructure was well-managed to avoid more casualties although little could be done to avoid infrastructural damage. Public underground infrastructure owners and operators assessed the impending hazards and risks associated with the storm and took
to bring attention to ways that development and use of underground space may mitigate potential climate change effects. Underground engineering may affect climate change drivers (e.g., land use, greenhouse gas emissions), and may increase the ability of urban communities to adapt to changing climate conditions.
Climate change refers to a statistically significant variation in either the mean state of the climate or its variability over an extended period, typically decades or longer, that can be attributed to either natural causes or human activity (IPCC, 2007). The National Research Council has reported on the consequences of climate change for the infrastructure and operation of U.S. transportation systems and identified five climate changes of particular importance including increases in number and frequency of very hot days and heat waves, increases in polar temperatures, rising sea levels, increases in intense precipitation events, and increases in storm intensity (NRC, 2008b).
General risks to infrastructure from climate change is well documented
appropriate action to clear the underground of occupants. Much of Manhattan is recovering as services are being restored. Subway service was restored to lower Manhattan as of December 3, 2012 (NY MTA, 2012a), but, as of December 10, 2012, tunnel service from Manhattan to Brooklyn had not been restored. The most heavily flooded subway tunnel (the Montague) was filled with seawater from “track to ceiling” for close to a mile (NY MTA, 2012b). It took several days to remove mud and debris from the tunnels once water could be pumped. Inspection teams found damage to signal relays, track switches, stop motors, and wiring. Debris washed into the tunnel, some with enough force to have bent metal, according to the MTA.
This is the first severe coastal flooding of a heavily urbanized part of the United States that depends extensively on underground infrastructure. The committee makes no determination about whether this event was in response to global changes in climate patterns; however, it acknowledges that more frequent or intense storms have been predicted as a result of expected climate change (e.g., IPCC, 2007; NRC, 2010). Seawater inundation experienced during this storm also serves as a reminder of expected sea level rise in many parts of the world (e.g., NRC, 2012). Observations and lessons learned from Hurricane Sandy could be collected to inform future urban sustainability decisions as emerging issues are identified and addressed.
Because many large urban areas are located along coasts and their infrastructure is already in place, more thought must be devoted to how to increase the resilience of urban areas to ensure sustainability—a difficult prospect given the age and deterioration of much of the this infrastructure. Resilience and sustainability of urban systems and infrastructure in light of all hazards and risks will necessarily be factors to consider during the decision making process. Urban planners must understand that it may be possible to reduce or mitigate the risks associated with high-intensity storms and sea level rise, but it is impossible to remove all risk. Engineers need to incorporate resilience and increased ability for disaster recovery (e.g., designing electrical components that can withstand prolonged exposure to seawater) into their technical decision making. All need to collaborate to understand what hazards infrastructure can safely accommodate.
(IPCC, 2007; CCAP, 2009; NRC, 2008b, 2010); however, addressing the consequences of climate change through better use of underground space for a more sustainable future has not been extensively studied. Further, climate change effects will vary regionally as a result of variability in natural and anthropogenic factors, so no solutions to emerging issues may be universally applicable. Issues may include the need for redesign of coastal wastewater discharge systems, better protection against flooding for underground road and rail systems, and better protection for underground utility vaults and tunnels. Making the necessary adaptations for the design of new systems and in a planned manner for existing systems will be important for the continued effective functioning of these systems. Known risks and the means to mitigate, reduce, or transfer risk will need to be considered. Options such as relocation or migration of urban centers away from areas susceptible to environmental changes could be considered but are not addressed in this report. Rethinking the placement of critical services—such as
Flooding in New Orleans Following Hurricane Katrina
The impacts of Hurricane Katrina on New Orleans provide a recent lesson regarding resilience and are discussed in detail elsewhere (e.g., Colten et al., 2008). Flooding due to levee system failure set in motion cascading failures and extensive damage to physical and social systems from which the city has not fully recovered years later. Because the pumping station used to pump storm water was not itself protected from flooding, it had to be shut down, dewatered, and dried before operations could start. Houses and buried infrastructure lines became buoyant during flooding (NIST, 2006), in many cases causing the severing of buried utility services (especially gas and water) at entry points into buildings. This created so many leaks in water and gas supply systems that supply pressures were lost and piping systems filled with unsanitary and salty water (NIST, 2006). The loss of water supply affected fire-fighting abilities and greatly slowed the return of normal living conditions. Flooding
emergency generators and fuel—in basements or flood-prone areas would be prudent. Other consequences of climate change may be unknown and warrant exploration. For example could the impacts of rising sea level on underground infrastructure include increased incidence of waterborne disease or the inability to supply water at sufficient pressure for fire-fighting during a disaster?
Some problems may emerge from placement of infrastructure underground, but the underground may offer some solutions. Questions related to underground construction, for example, include (a): can underground construction, e.g., through reduced fossil fuel consumption and carbon output, be a means to decrease human contribution to climate change? and (b) can underground construction mitigate damage or risk from environmental changes resulting from climate change? The first question involves a series of complex national or global evaluations, including calculation of the lifecycle net energy efficiency and carbon footprint of underground infrastructure versus surface counterparts (this will be discussed further in Chapter 5).
The second question regarding damage and risk mitigation relates to the use of underground space as a physical means to protect against some of the consequences of climate change, such as heavy storms, floods, and sea level rise (Bobylev, 2009). Although unprotected underground facilities can be inundated during floods, they offer increased protection against structural damage caused by water surge and debris impact. Changes in structural forces on buried facilities during storm or flood events are predictable and can be accommodated during design. It may be possible to avoid flooding by raising or protecting entrances to exclude the possibility of water ingress. Sea level rise associated with climate change poses significant risk to underground infrastructure. Global sea levels are projected to rise 8-23 cm by 2030 relative to 2000 levels, and 50-140 cm by 2100 (NRC, 2012). Some systems under construction are being designed in anticipation of future water levels. The difficulty, however, of protecting a whole
of the low-pressure gas distribution system caused corrosion of valves and meters and required extensive replacement. Shallow-buried utility lines were damaged by tree root systems when mature trees were blown over during the storm. Heavy cleanup equipment often damaged hydrants hidden by debris, and shallow-buried utilities were often driven over by such equipment, causing collapse or damage to those utilities. The lack of good or accessible records of utility line, shut-off valve, and other infrastructure element locations hampered utility and emergency services response. In addition, many normal landmarks for locating services were obliterated by hurricane damage and flooding. Recovery was slowed by the loss of urban services such as power, fresh water, and sanitation—people could not easily return to their neighborhoods even once flooding had receded. Without the residents there to clean up, many administrative and legal issues arose concerning interfaces between personal and emergency response service responsibilities (U.S. Executive Office of the President, 2006).
low-lying city from rising sea levels is daunting, examples of which can be found in the Netherlands and New Orleans, Louisiana. The low points of land in the Netherlands and New Orleans are 6.8 m and 1.5-3 m below mean sea level, respectively (Burkett et al., 2003). Underground facilities may require, among other things, special design (e.g., entrances) to make them suitable for sea level rise conditions.
Another potential engineered use of the underground in need of greater evaluation is the isolation of energy-related waste products within geologic features. The injection of carbon dioxide into geologic features for the purpose of carbon sequestration (NETL, 2010) and the isolation of high-level radioactive wastes (McCombie, 2003) are methods being studied for reliability, potential risk to people and the environment over the short and long terms, and interference with other potential underground applications. Sequestration of carbon dioxide is intended to decrease the amount of carbon dioxide—a greenhouse gas—released into the atmosphere. Underground isolation of high-level nuclear waste generated from nuclear-fission-produced electricity may indirectly reduce greenhouse gas emissions because such energy production does not result directly in greenhouse gas emissions. If the political and technical issues surrounding underground isolation of waste can be resolved, or if self-contained underground nuclear plants (each with its own long-term underground storage) were able to minimize the political, transport, and risk factors associated with both nuclear plants and waste storage (McCombie, 2003), reassessment of planning as it relates to climate change could be justified. Such issues are yet to be addressed but are outside the scope of this report.
To what heights of sea level rise is it practical to protect cities with walls and levees? Is it reasonable for threatened cities to consider abandoning existing ground floor levels, essentially raising “ground level” up one story as has been done for various reasons in parts of Seattle, Washington (Richard, 2008)?
If this occurred then the existing ground levels could become new levels of pseudo underground space, as has been accomplished in La Defense and La Rive Gauche in Paris, France (Duffaut, 2006) and Tsukuba Science City in Japan (Dearing, 1995) to create improved service infrastructure coupled with a more pedestrian-friendly environment. Given such scenarios, underground engineering technologies could assess whether existing underground pipe and cable networks could withstand additional depths of burial or flood pressure loading, how existing building basements might be reinforced against such load increases, and the potential for increased corrosion, among other characteristics.
The potential impacts of climate change on inland cities and communities could also be significant. For example, climate change–induced natural hazard events creating high-intensity rainfall activity will require system designs that capture and convey larger volumes of water to reduce or avoid flood damage and economic loss. Changes in annual rainfall will likely impact regional groundwater tables, causing changes in available groundwater supplies. Impacts on existing underground and surface structures caused by changing groundwater levels and the resulting changes in the properties of soil, rock, and materials used in underground construction also may be likely. A long-term and regional view of water management likely will be a key element in establishing resilience for local areas from such climate change effects, as will a more complete understanding of soil, rock, and construction material behavioral changes caused by changing groundwater conditions. Insurance and reinsurance, as a component of risk management of climate change events for underground systems, likely will be necessary because, although some events may have a low probability of occurrence, the consequences of their occurrence can have far-reaching spatial (geographic) and temporal economic impacts. Short- and long-term performance and infrastructure maintenance requirements will have to be understood in order to enhance resilience and sustainability.
As discussed in Chapter 1, resilience represents the ability to respond and adapt to change in the environment. In this discussion, resilience includes the ability of an urban community to mitigate the intensity and spatial distribution of damage caused by extreme events or long-term environmental changes (for example, economic recession, climate change). The ability to respond and deliver service functionality quickly following extreme events, and to reduce economic impacts caused by the events, are demonstrations of resilience. Building resilience applies to all manner of hazards already discussed and requires removing or minimizing vulnerabilities in essential systems that place the systems at risk. It requires a system of systems approach and consideration of cross-systems interdependencies to avoid the cascading failures of individual systems.
Disasters such as Hurricane Katrina (see Box 3.10) can yield some good if
society can learn from experience. How, for example, can underground infrastructure be designed to mitigate buoyancy effects as occurred during the flooding of New Orleans? How can the effects of corrosion of physical infrastructure be avoided? Chapter 2 described aspects of cascading failure caused by the collapse of the World Trade Center (WTC) towers following the terrorist attack of September 11, 2001. The attacks were tragic, but there are lessons from which planners and future responders can learn to apply to underground infrastructure design and operation:
• Con Edison Company of New York (electric, natural gas, and steam providers to New York City) used trailer-mounted portable generators to provide spot power and routed temporary feeder lines—called shunts—belowground to connect live to dead networks and restore power (O’Rourke et al., 2003; Mendonca and Wallace, 2005).
• Redundancy in subway system lines meant that access to most areas was restored in a few days (O’Rourke et al., 2003).
• Core stair systems in the World Trade Center towers resulted in evacuation routes from high in the towers that were discontinuous or became severed (underground infrastructure escape routes can suffer similarly).
• The hazards of dust on air and water quality were not immediately appreciated and were ultimately proven to be health hazards for first responders.
• A lack of readily available engineering information related to the World Trade Center towers and foundations hindered the ability to assess the potential for building collapse and stability of the foundation wall system.
The importance of the robustness of individual systems to overall resilience is highlighted by the above examples. Perhaps more importantly, the interdependencies among whole system of systems—social, economic, information, and physical systems are exposed.
Resilience of urban design depends on a multihazard approach to disaster preparation and integrated system design. A mulithazard approach necessitates planning for the most likely risk scenarios and includes enough flexibility to accommodate the unexpected (e.g., NRC 2011b). Integrated and coordinated systems planning includes the need to plan for critical redundancies in systems that, for example, allow adequate response and recovery when part of a system fails. Surface and subsurface infrastructure assets need to be designed and operated as integrated systems with lifecycle maintenance, risk, reliability, and real-time responsiveness in mind. Urban planners and engineers need trusted and validated risk-informed approaches to project planning and design that can balance project needs in terms of service delivery, initial cost, resilience against extreme events, and effective maintenance and operations so that whole life performance is satisfactory. Through adoption of this type of approach for underground space and infrastructure (occupied or not), the consequences of extreme events can be
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