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Innovative Underground Technology and Engineering for Sustainable Development

Geotechnologies and related science and engineering fields make it possible to use underground space to support livable, resilient, and sustainable cities. Geotechnical applications have supported the design and construction of underground facilities, and will continue to be critical to the delivery of underground facilities with lower initial costs and risk, and better lifecycle performance. To contribute to a more resilient and sustainable future, geotechnology will need to more closely integrate the many disciplines related to site investigation, design, construction, operation, and risk management of underground facilities. A better understanding of the sustainability of underground use—for example, minimizing deterioration, increasing resilience, making holistic decisions concerning subsurface hydrogeologic and thermal environments—also will be necessary. Improvements in underground technologies have enabled great strides in urban development in recent decades, but the complexity and unpredictability still inherent in underground construction are indications that many challenges remain.

This chapter provides a brief overview of the state of the art in various technologies that support underground construction and facility operation. Highlighted are technologies that provide opportunities for significant improvement in the delivery of cost-effective lifecycle performance for underground facilities, contribute to improvements in underground space usage, and contribute to resilient and sustainable urban solutions.



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6 Innovative Underground Technology and Engineering for Sustainable Development G eotechnologies and related science and engineering fields make it pos- sible to use underground space to support livable, resilient, and sustain- able cities. Geotechnical applications have supported the design and construction of underground facilities, and will continue to be critical to the delivery of underground facilities with lower initial costs and risk, and better lifecycle performance. To contribute to a more resilient and sustainable future, geotechnology will need to more closely integrate the many disciplines related to site investigation, design, construction, operation, and risk management of under- ground facilities. A better understanding of the sustainability of underground use—for example, minimizing deterioration, increasing resilience, making holis- tic decisions concerning subsurface hydrogeologic and thermal environments— also will be necessary. Improvements in underground technologies have enabled great strides in urban development in recent decades, but the complexity and unpredictability still inherent in underground construction are indications that many challenges remain. This chapter provides a brief overview of the state of the art in various technologies that support underground construction and facility operation. High- lighted are technologies that provide opportunities for significant improvement in the delivery of cost-effective lifecycle performance for underground facilities, contribute to improvements in underground space usage, and contribute to resil- ient and sustainable urban solutions. 145 Underground Engineering Camera-Ready.indd 145 2/6/2013 3:16:58 PM

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146 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT EVOLUTION OF TECHNOLOGY Technological innovation can advance engineering practice and increase the appeal of underground space. Technological and engineering advances have always been crucial to efficient and economical underground development. Many technological developments have been motivated by practical challenges encoun- tered during construction of a project (e.g., the development of the tunnel shield by Brunel), and the tunneling industry has contributed to or been instrumental in many of these. The highly automated modern tunneling boring machine is an example of an an industry led development as are water proofing and ground improvement technologies that have been introduced and popularized. In close partnership with academia, industry has developed many analysis and design tools (e.g., finite element analysis methods). Since the time of the Pharaohs, tunnels have been built by cut-and-cover construction methods (El Salam, 2002). The invention of the tunnel shield— which supports unlined ground to reduce the risk of collapse, Sir Marc Isambard Brunel and his son Isambard Kingdom Brunel were able to excavate a tunnel under the Thames River (London) between 1825 and 1843 (Muir Wood et al., 1994; Skempton and Chrimes, 1994) (see Figure 6.1 for a drawing of Brunel’s shield). Previous projects involving tunnel boring in soft, saturated soils had been extremely difficult or impossible to complete. The tunnel created an important connection between the north and south banks of the Thames that is still in use almost 170 years later. The application of this new technology heralded the era of shield tunneling. Electrically powered locomotives ushered in the era of modern subway systems around the turn of the twentieth century. Electrification alleviated concerns about hazardous diesel or coal fumes and allowed long-distance underground train travel. Innovations in large-scale ventilation systems permitted underground roadway development. Climate control systems, improved lighting, and more effective signage made the underground environment more hospitable, comfortable, and appealing for retail functions and mass transportation. Advances in materials technology, computer science, robotic construction technology, and laser guidance have allowed improved subsurface excavation using modern slurry shield and earth pressure balance boring machines1 (Figure 6.2) and rock tunnel boring machines (Figure 6.3). Those technologies made it feasible to construct tunnels exceeding 50 kilometers in length and at diameters approaching 20 meters, and to tunnel under challenging geologic conditions (e.g., in soft flowing ground or highly fractured rock under high ground and water pressures). Ground modification technologies—e.g., injecting cementitious agents to strengthen and reduce permeability of soil and rock, or temporarily freezing of water-bearing 1 Slurry shield and earth pressure balance boring machines for boring in saturated soils are designed to withstand water under pressure. Underground Engineering Camera-Ready.indd 146 2/6/2013 3:16:58 PM

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INNOVATIVE UNDERGROUND TECHNOLOGY AND ENGINEERING 147 FIGURE 6.1 Brunel’s tunnel shield. Marc Isambard Brunel developed this tunnel shield technology to build the first subaqueous tunnel beneath the Thames River (1821-1825). Brick walls were built at the faces of the tunnel and held in place while alternate shields were pushed forward 6 inches. The completed tunnel was 38 feet wide and accommodated two carriageways. SOURCE: http://en.wikipedia.org/wiki/File:Thames_tunnel_shield.png (accessed June 27, 2012). Public Domain. FIGURE 6.2 Cross-section of earth pressure balance tunnel boring machine. This tunnel- ing technology is ideal for homogenous soft soils. A screw conveyor is used to transport spoil from the face and helps to control pressure with the coordinated advancement of the machine. The excavation chamber is filled to support the face and allow the machine to be reactive to earth and groundwater pressures. SOURCE: E.J. Cording. Underground Engineering Camera-Ready.indd 147 2/6/2013 3:16:58 PM

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148 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT FIGURE 6.3 Cutter head of a rock tunnel boring machine used to excavate the Chat- tahoochie tunnel. Disk cutters cut grooves approximately 4 inches apart in this example. SOURCE: E.J. Cording. materials (Figure 6.4)—broadened the geologic and hydrologic conditions under which underground construction may occur. Horizontal directional drilling revolutionized installation of many utilities and greatly reduced the need to close streets to traffic and disrupt life in urban situations. Many of the technologies described above led to changes in engineering practice, and in some cases, to new paradigms in urban planning. Similarly, today’s engineering and technology developments will be crucial to an economi- cally constructed, functional, attractive, energy efficient, and sustainable urban environment. This chapter is grouped under the following themes: • technologies for underground site characterization, including geologic setting, rock and soil properties, and existing underground infrastructure; • technologies for design and analysis for underground technologies; • technologies for construction of underground space; • technologies for effective asset management; and • technologies that promote sustainability and resilience. These themes are not necessarily sequential or independent. Observations made during the application of each may inform decision making during any phase of development or operation. Infrastructure design may identify further site charac- terization needs, and unanticipated conditions encountered during construction Underground Engineering Camera-Ready.indd 148 2/6/2013 3:16:59 PM

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INNOVATIVE UNDERGROUND TECHNOLOGY AND ENGINEERING 149 FIGURE 6.4 Artificial ground freezing is applied in the excavations extending under the Danube River. Freezing groundwater around an excavation improves the load carrying capacity of the soils and provides temporary support during construction. (Left) A cross- sectional diagram with the locations of the freezing pipes indicated. SOURCE: IMWS, 2009. Reprinted with permission. (Right) Photograph showing excavation with freezing pipes in place. SOURCE: http://www.tunneltalk.com/images/BudapestMetro/6-Budapest- Metro-GroundFreezingApplied.jpg. may require revisions in design. Monitoring and characterization ideally should occur throughout the infrastructure life cycle. Observations can lead to a type of informed decision making called observational method (e.g., Peck, 1969; Institute for Civil Engineers (Great Britain), 1996) that can improve economy and safety. Many geotechnical engineers refer to the framework for this method originated by Peck and described in a publication by Nicholson and others (1999). The discussions within each theme are illustrative of technologies in use or that have significant potential for the future. By their nature, disruptive technolo- gies are difficult to anticipate, but can fundamentally shift the way underground space is developed and used. Many of the technologies described in this chapter depend on the use of the observational method for effective decision making. Suggested are technologies for analyses that allow improved application of the observational method. TECHNOLOGIES FOR UNDERGROUND SITE CHARACTERIZATION Engineering urban underground space requires detailed knowledge of the underlying geology and the geologic and human-development histories of a site, alignment, and adjacent areas that may affect or be affected by proposed develop- ment. Better subsurface characterization supports better decision making. Mini- Underground Engineering Camera-Ready.indd 149 2/6/2013 3:17:00 PM

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150 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT mizing unanticipated ground conditions may allow optimized design and more judicious use of resources during construction. Detailed understanding of how the site relates to the broader natural and urban systems allows more complete understanding of the existing engineering challenges and informs underground infrastructure locations and alignments, design, choice of construction methods and tools, and long-term operation of the facility and adjacent structures. Site characterization activities often begin through study of existing data and published information. Currently, relevant information must be gathered from many sources and may not provide adequate—or accurate—information about the geological setting or existing underground structures. Ongoing advances in computational capabilities (e.g., massive database systems, data mining) and georeferencing of data (e.g., survey-grade global positioning systems and geo- graphical information systems) could be of great use in the future. These issues are further explored later in this chapter. Characterizing Geology, Geologic Material Properties, Contamination, and Natural Hazards A geologic perspective in site characterization is necessary to appreciate, quantify, and manage uncertainties in and variability of soil and rock properties and behavior (e.g., composition, stress-strain behavior, permeability, abrasivity, thermal conductivity) and groundwater conditions, ultimately minimizing costs or avoiding overly conservative design (NRC, 2006; FHWA, 2009). Preliminary field and laboratory work supports preliminary project design and construction planning, but further characterization narrows uncertainties and provides detail on important geologic features (e.g., boundaries of geologic units, fault zones), supports design of specific underground works (e.g., shafts, rooms), and provides information related to other special requirements (e.g., avoiding environmental contamination or in situ stress evaluation). The natural underground environment is inhomogeneous, anisotropic, and highly variable over short spatial extents. Large volumes of geologic material often must be characterized in great detail to detect stratigraphic changes and discontinuities important for predicting ground response to construction. A broad range of invasive and noninvasive technologies and tools are available to carry out in situ field investigations (see for example, FHWA, 2009), but existing assessment tools cannot provide complete spatial coverage, accurate zonation, and in-situ material properties. At a project scale, hazardous materials encountered during underground construction can add large and unexpected costs to a project and delay project delivery. Characterizing natural and anthropogenic hazardous materials (e.g., chemical contamination and radiation) and their effects on the natural and built environments for particular construction and operation activities is vital. Under- standing any hazardous materials that may be released or transported as a result of construction and operation is important to long-term sustainability and resil- Underground Engineering Camera-Ready.indd 150 2/6/2013 3:17:01 PM

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INNOVATIVE UNDERGROUND TECHNOLOGY AND ENGINEERING 151 ience. Similarly, identifying adequate design approaches to protect underground infrastructure from natural hazards such as earthquakes or floods is critical to a resilient and well-functioning underground facility. Because these topics have a broad connection to sustainability and resilience, their characterization is dis- cussed later in the chapter. Environmental concerns that extend to underground storage and disposal also need to be considered. For example, society is grappling with the risks associated with the emerging technology of carbon dioxide sequestration. As more large- scale sequestrations are planned, the need to examine their potential impacts on the ability to develop underground space becomes even greater, because, for example, carbon dioxide could seep into underground space. Therefore, the solu- tion of one problem could inadvertently result in another problem. A recent NRC report explored the risk associated with induced seismicity as a result of carbon capture and storage and makes specific research recommendations related to, for example, factors other than pore pressure that influence seismicity, and develop- ment of physiochemical and fluid mechanical models for carbon dioxide injection into potential underground storage reservoirs (NRC, 2012). Choice of characterization tools depends on a number of factors including depth of interest and ground conditions (e.g., soil versus rock; saturated versus partially saturated). Both traditional in situ technologies (e.g., direct measure- ment) and noninvasive technologies (e.g., geophysical) can be used to character- ize natural and manmade features. Some construction sectors provide guidance on site characterization technology choices through extensive lists of tools and techniques (e.g., FHWA, 2009). Training and experience in the proper use of the tools, however, is usually as critical as the choice of technology itself. Invasive Technologies In situ testing tools provide direct physical measurement of material proper- ties. In soils, for example, standard penetration tests and cone penetrometer tests (e.g., electric, piezocone, and seismic tools) are used to sample or test soil layers directly by drilling or thrusting sampling tools into the ground. Rock sampling and testing can be borehole based or conducted on the removed core. Borings are used to characterize properties such as soil strength, stiffness, dynamic shear wave velocity, and groundwater properties and quality, and the geology at the borehole location. An individual boring may or may not represent the subsurface only a short distance away given the potential variation in geology. Directionally inclined and horizontal boreholes and oriented probing tools also can be used to investigate specific features or the distribution of materials. Horizontal probing allows exploration of the subsurface along the length of the alignment of a tunnel or other infrastructure. The use of oriented exploration tools, while common in the energy exploration industry, is less common for civil underground structure development. This may be due to cost, but perhaps also to unfamiliarity with the technique among site investigation professionals. It may be argued that incentives Underground Engineering Camera-Ready.indd 151 2/6/2013 3:17:01 PM

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152 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT for efficiency are less evident for engineers than for contractors and owners who realize savings from efficiency. Recent developments in boring technologies include cryogenic drilling capa- bilities for boring in difficult materials and measurement while drilling (MWD) systems that provide early information on the materials useful for guiding future borings and planning an efficient testing program. The profession has yet to widely adopt these techniques. Noninvasive Technologies Noninvasive site characterization tools include remote sensing (e.g., satel- lite and terrestrial light detection and ranging (LIDAR), digital photogrammetry, radiometric technologies, and interferometry methods) and ground geophysical techniques (e.g., seismic refraction and reflection, spectral analysis of surface waves (SASW), crosshole tomography, geoelectric, electromagnetic, and poten- tial field methods [gravity, magnetic]) that provide data from which subsurface conditions may be inferred. Noninvasive techniques are best used in combina- tion with invasive techniques to provide a more complete understanding of underground conditions. Advantages of noninvasive technologies are the speed with which they can be used and that larger volumes of the subsurface can be characterized. Disadvantages are that data generally must be reduced from their raw form—inversion modeling is often required to evaluate ground zonation and materials properties. Such models are non-unique (e.g., a single data set can yield infinite models), and hence special skills and knowledge are required to reduce and interpret data. The cost of some of these methods can also be high, but as the methods become more common and the technologies continue to improve (e.g., laser scanning), the cost of data acquisition and analysis will go down. There is significant opportunity to improve data gathering related to ground properties and the presence and location of existing structures using noninvasive technologies, but there are physical limitations in terms of the scale of objects to be characterized and the material property differences that can be identified rela- tive to the depth of investigation possible. There is, for example, a practical limit for pipe detection using surface-based ground penetrating radar (GPR), reported to be the ratio of approximately 12:1 for the detection depth to the detectable pipe diameter, even under favorable soil conditions (Sterling et al., 2009). This means that a 1-foot diameter pipe can only be detected if within 12 feet of the surface, and a 1-inch pipe can only be detected up to a depth of 1 foot. Research into the fusion of multi-sensor data that would allow noninvasive technologies to accom- modate a wider range of ground conditions and to improve their ability to resolve ground properties and the presence and location of buried objects is under way both in the United States and overseas. Similarly, research by the military into the detection of land mines and deep covert tunnels can have significant benefits in broader civil engineering applications. Underground Engineering Camera-Ready.indd 152 2/6/2013 3:17:02 PM

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INNOVATIVE UNDERGROUND TECHNOLOGY AND ENGINEERING 153 Characterizing Existing Infrastructure and Legacy Construction Materials Failing to locate existing infrastructure before repairing existing or installing new infrastructure is a potential source of accidents. Legacy construction mate- rials, including unmapped abandoned piles, foundations, or tiebacks that once provided support during previous construction, are regularly encountered during underground construction. Identifying and characterizing these artifacts is a nec- essary part of site characterization. Historical records found in planning depart- ments can be used to identify locations of some legacy materials, but the records are often incomplete, inaccurate, or missing, thereby necessitating a greater reli- ance on exploration technologies, especially noninvasive, for characterization. Unmapped or inaccurately mapped underground infrastructure poses poten- tial hazards and risks for underground construction workers, the construction site, other infrastructure, and other people in the vicinity. Encountering unexpected infrastructure may necessitate revised construction planning or repairs. Existing or legacy infrastructure may be avoided, but sometimes must be protected with support designed to avoid displacement or damage to existing or planned infra- structure. The committee notes that every open-cut excavation, bore, or tunnel is an opportunity to assess and document the ground properties and structures encountered for present and future applications. The hundreds of thousands of open-cut excavations for utility work made every day in the United States, for example, offer repeated opportunities to collect and archive such data. However, the fidelity of nonivinasive techniques to identify subsurface infrastructure needs to be improved. Additionally, investigation technologies need to be integrated with new physical tools and administrative structures to capture this type of infor- mation. Mechanisms that allow dynamic archiving (e.g., continuous updating and modification) of these data are critical to the sustainability of urban infrastructure. Interpreting and Integrating Site Characterization Data Site characterization information and data must be processed and evaluated to develop interpretative geologic models and to generate the engineering param- eters to be used in underground facility design (see examples in Box 6.1). Many field techniques used for preliminary property classification have been applied for decades and are subject to gross differences in interpretation. Typically, field clas- sification cannot substitute for laboratory verifications. Many tools aid interpreta- tion of, for example, rock classification including empirically based procedures such as the Q-system (for rock quality classification) (Barton et al., 1974), the Rock Mass Rating system (Bieniawski, 1976, 1989), and the Geological Strength Index (Hoek, 1994) (see Figure 6.5 for example classification). Classification schemes for characteristics such as strength and stiffness also are used to establish the input for advanced numerical analysis procedures. Underground Engineering Camera-Ready.indd 153 2/6/2013 3:17:02 PM

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154 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT BOX 6.1 Three-dimensional Geologic Modeling Three-dimensional modeling of ground conditions that incorporate geo- technical and geophysical data is conducted extensively in the United States for development activities including resource exploration and extraction and infrastructure development. Similar modeling techniques can be applied to urban infrastructure planning, risk modeling, and resource management as is done by the British Geological Survey (see Figure 1). Such models can provide multiple “views” (e.g., orientations), be “exploded” (e.g., layers can be visually separated to isolate specific features or units), and otherwise manipulated to identify predicted physical properties at depth, the locations of anthropogenic structures, aquifer vulnerabilities, and other qualities. Such comprehensive FIGURE 1 Example of three-dimensional engineering geological modeling employed by the British Geological Survey for visualizing variability in geologic materials and their physical properties. SOURCE: Reeves, 2010. Reproduced by permission of the British Geological Survey. © NERC. All rights reserved. CP12/073. From a broad perspective, however, insufficient use is made of all the clas- sification and material testing that is carried out on the thousands of individual projects that occur in a medium- to large-sized city every year. Collection and integration of such data remain difficult because, to be useful, the data must be carefully documented and referenced as to location, depth, other properties, and pedigree (e.g., data sources, what tests were run, and was test equipment properly calibrated). Also, and perhaps the most telling, are the significant disincentives for project owners and their consultants to release data because of concerns related to liability and loss of proprietary knowledge. Nevertheless, regulations exist, for example, that require well boring operations to submit their boring logs to state geological surveys. Steps to usefully capture more of the geotechnical Underground Engineering Camera-Ready.indd 154 2/6/2013 3:17:02 PM

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INNOVATIVE UNDERGROUND TECHNOLOGY AND ENGINEERING 155 views of data can enhance decision making and help to quantify uncertainties that historically are a source of difficulties in contracting and litigation. Confi- dence maps can be created based on data density and geologic complexity that indicate areas of low or high uncertainty in models (see Figure 2). Given variability of geologic conditions and the spatial limitations of underground characterization tools, information about the underground is often limited and includes significant uncertainties. FIGURE 2 A bedrock confidence map produced for an area in Glasgow, Scotland. The green points represent actual data points; the roughly vertical planes represent faults. Contours represent levels of uncertainty based on data density and geological complexity of modeled surface (red indicating high uncertainty). Such maps provide valuable insights regarding where more data may be needed. SOURCE: Reeves, 2010. Reproduced by permission of the British Geological Survey. © NERC. All rights reserved. CP12/073. data generated represent important ways to help enable the sustainability of the urban underground and the regions it serves. To move toward engineering practices that are consistent with such sustain- ability goals, data related to underground infrastructure development need to be archived in formats and with tools that make them retrievable and accessible for the infrastructure life cycle—and beyond (to account for infrastructure artifacts in place well after closure or decommissioning). These issues will be discussed in a later section related to the critical challenges of archiving infrastructure- related data. Underground Engineering Camera-Ready.indd 155 2/6/2013 3:17:03 PM

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176 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT limited maintenance to the best of current ability, they also must be reliable and accurate, self-calibrating, small in size, reasonably priced, easy to operate and maintain, and upgraded at routine intervals. Sensor systems are expected to provide data around the clock for years and withstand dust, pollutants, moisture, and stray currents, and in the most useful case, provide immediate notification of failure. Sustainable systems require that failure of an individual sensor does not take down the entire system. Power to operate sensors must be obtained through replaceable power packs or remotely acquired when a measurement is taken (i.e., a passive sensor), or by “scavenging” energy from the sensor environment (e.g., local vibrations, fluid flow). Additionally, sensors need to be hardened against vandalism or accidental damage. The longevity of many sensor systems, however, is not known. Data retrieval that allows real- or near real-time reception and data interpre- tation is important for operational decision making. Many of the same challenges that exist for transmitting construction data also exist for transmitting operational data. Hard-wired data transmission systems that require dedicated lines are reli- able but can be costly (especially in long tunnels), and they are not suitable everywhere. The number of sensors employed is limited to how many sensors can be wired. The use of wireless data transmission has recently increased, driven by advances in wireless Internet protocol access, wireless local area networks (LANs), and the proliferation of cellular-based mobile phone services. Wireless data transmission avoids the cost of wiring, but data transmission deteriorates significantly in underground and confined spaces, especially in long tunnels. Wireless data transmission is vulnerable to security breaches that can compromise the system operation (Stajano et al., 2010). Location-based information (e.g., global positioning system [GPS] data) can provide locations of system elements needing repair, relay real-time information regarding conditions in underground space, and map locations of automated sensing and maintenance devices, but GPS and cellular signals are difficult to receive underground. In addition to infrastructure operators, some underground infrastructure users (e.g., rail passengers) may rely heavily on location-based services and are accus- tomed to easy accessibility. Further development of location-based technolo- gies that allow for seamless transition from aboveground to belowground may encourage underground use by those who do not want to lose that functionality. Further, real-time traveler information (e.g., arrival and departure information) on flat screens in small businesses within or near mass transit systems, or via text messaging and email alerts to mobile devices, could help to ease congestion in and around transit stations (Zhang et al., 2011). Many other opportunities remain to develop new sensors and integrated systems for enhancing operation of underground transport systems. For example, technologies that employ security camera images for structural evaluation may prove beneficial. Selected trains or maintenance vehicles could be equipped with high speed cameras or laser scanners for periodic documentation of tunnel Underground Engineering Camera-Ready.indd 176 2/6/2013 3:17:13 PM

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INNOVATIVE UNDERGROUND TECHNOLOGY AND ENGINEERING 177 conditions and compared using image reasoning algorithms to evaluate changes in structures. Linking Data and Asset Management and Analytical Capabilities Continuous streams of numerical and visual data can inform day-to-day operations, maintenance, and predictions of longer-term infrastructure perfor- mance and operations programs. However, interpreting the large streams of numerical and visual image data in real or near-real time can easily overwhelm human operators. Important information requiring action may be missed. Meth- ods and automated systems to interpret these data and report problems to an operator would enhance optimal operation and maintenance of underground systems. Enhanced data management technologies can aid understanding of the performance of underground infrastructure as part of the larger urban system and allow planners to anticipate interdependencies and interferences that affect func- tionality and quality of service. Data management technologies such as Build- ing Information Modeling (BIM) processes (e.g., Smith and Tardif, 2009) may make it possible to evaluate in greater detail the impact of new construction on existing systems installations, to evaluate the impact of existing systems on con- structability of a new project, and to design sensing systems tailored for new and rehabilitated systems as part of an integrated urban system of systems. However, although these methods are extremely important, the technologies employed may become dated, and budget limitations make necessary data updates and accessi- bility challenging. Some data may need to remain secure. Private-public collabo- ration may be necessary to link, analyze, manage, and access system-wide data. Systematic, standardized documentation of case histories related to under- ground infrastructure could help to expand fundamental understanding of excava- tion and support processes. Indeed, case histories are an important way to learn about the underground because they benchmark the state-of-practice, and provide information that may validate or disprove assumptions and models. Archiving of data and records associated with site characterization for infrastructure develop- ment, design, operation and maintenance, rehabilitation, reuse, and decommis- sioning would allow improved future planning and management in a manner that promotes sustainability long after the data are collected. Information Security Preserving, maintaining, and protecting data integrity against neglect, van- dalism, time, or technological obsolescence are serious issues that threaten sus- tainable management. Capturing subsurface information is difficult enough; properly cataloging and maintaining it over long periods (e.g., 50 to 100 years and longer) is a significant challenge. Electronically archived data can become obsolete within just a decade or two when technologies change and the media Underground Engineering Camera-Ready.indd 177 2/6/2013 3:17:13 PM

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178 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT on which they are stored can no longer be accessed. On the other hand, paper hardcopies of data have survived for nearly a century for some tunnel projects, but only if properly cared for. The security of data during transmission or storage in central computer sys- tems is an increasingly serious concern. The data can be accessed, manipulated, and corrupted by unauthorized parties to the detriment of safe or smooth opera- tion of underground facilities. Because sensor data inform decisions affecting, for example, life safety (e.g., traffic operations, ventilation), the well-being of underground infrastructure occupants depends on the secure and proper function- ing of the system. The concern becomes more serious when sensors are used in automated feedback loops (such as traffic management or supervisory control and data acquisition [SCADA] systems). Data sabotage can immediately impact underground facility operations. The cause of the troubles may be hard to track down. As use of networked sensing and automated decision making becomes more pervasive, there is a need to develop secure data networks and authentication mechanisms to prevent malicious or accidental data corruption and manipulation. The most hardened networks are still potentially vulnerable to malicious attacks, and the National Research Council (NRC) has published multiple reports on issues related to information technology security (e.g., NRC, 2010a,b). In 2007, the NRC developed a strategy for cyber security research and promoted catego- ries of research that included limiting impacts of security compromise (e.g., the design of secure systems, evaluation of security), enabling accountability (e.g., attribution, remote authentication), promoting deployment of security designs (e.g., “usable security”), deterrence (e.g., legal policies and measures), and specu- lative, “out-of-the-box” approaches to security (NRC, 2007). Resilience needs to be built into sensor systems, including human-in-loop decision making for critical components to mitigate against corrupt data. TECHNOLOGIES THAT PROMOTE SUSTAINABILITY AND RESILIENCE This section draws attention to some key issues related to the sustainability and resilience impacts of underground facilities, and specifically to how tech- nological developments could promote improvements in these areas. Many of these issues already are considered in some form in the design and operation of underground facilities, but they take on special importance when considered in light of overall community sustainability and resilience. Other issues, such as the understanding and control of highly interrelated systems of systems, represent new areas of study with great future importance. The interconnections and inter- dependencies between individual infrastructure systems and the overall function- ing and well-being of the social community and systems need to be considered. Underground Engineering Camera-Ready.indd 178 2/6/2013 3:17:14 PM

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INNOVATIVE UNDERGROUND TECHNOLOGY AND ENGINEERING 179 Materials Improving the possibility of sustainability necessitates consideration of the economic use of materials. To be considered are the materials used, their resource availability, the processes needed to create construction-ready products, the long- term availability of the materials, the energy (and carbon footprint) implications of use, and long-term environmental impacts. For example, even commonly used materials such as sand and gravel may be in short supply because of a lack of regional availability or to urban development and planning decisions that render sand and gravel resources inaccessible. In terms of energy use (see next sec- tion), concrete, a significant element in most forms of underground construction, requires a high level of energy input for its creation (termed embodied energy). Some commonly used construction materials have been proven to be detrimental to the environment and public health (e.g., various types of volatile organic com- pounds used in pipes that can contaminate groundwater systems, and asbestos used in cement piping). Excavated materials from some tunneling projects could prove to be a resource for nearby construction projects. Millions of cubic yards of material may need to be removed from an excavation. Some of this material could be a source of sand, gravel, and rock. Some of this material, however, may end up being classified as hazardous and therefore need special handling and disposal. Still, a large volume of material may be suitable for other construction uses, or may be part of the solution to other sustainability issues. Box 6.5 describes the case of the reuse of excavated materials from the Boston Central Artery/Tunnel project to help reclaim a solid waste facility and turn it into a park operated by the National Park Service. Disposal or reuse of excavated materials is a serious issue that warrants further attention. More sustainable use of materials could mean choosing underground design and construction options that use smaller quantities of materials or materials with improved performance, or it could mean incorporating more waste or by- product materials derived from other applications into design (e.g., geopolymers made principally from waste flyash). The lifecycle costs and benefits, however, need to be factored into decisions. For example, integrating primary (support for construction) and permanent ground support systems may allow for the use of less construction materials, but may affect the efficiency of construction opera- tions. Maximizing the ability of the ground to be part of the support system, or reusing excavated materials from within or near a project, would help to increase efficiency in material use or reuse. New lining and underground construction technologies are needed that reduce material use and improve long-term facility performance. More informed decision making requires making available better information about the sustainability aspects of construction materials (e.g., avail- ability, embodied energy) to the the designers. Underground Engineering Camera-Ready.indd 179 2/6/2013 3:17:14 PM

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180 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT BOX 6.5 Reuse of Excavated Materials from the Boston Central Artery/Tunnel Project Spectacle Island in Boston (Massachusetts) Harbor is the site of a munici- pal solid waste facility in use until 1959. From 1959 until 1993, the landfill re- mained an uncapped source of leaching into Boston Harbor. Uncontaminated excavation material from Boston’s Central Artery/Tunnel (the Big Dig) project was used to stabilize slopes on the island and fill and cap the landfill to convert it to recreational use. Excavated material was transported in more than 4,400 barge loads to the island beginning in 1992 (Barnett and Chin, 1998) and was used to cap the landfill with a 2-foot clay cap (MassDOT, 2012). The cap cre- ated an impervious layer that would serve to keep precipitation from mixing with the wastes beneath and leaching into the harbor. Excavated fill was mixed with biosolids from several waste composting facilities in New England to cre- ate topsoil that was subsequently vegetated to keep the cap in place (NEBRA, 2012). Approximately 2,400 trees and 26,000 shrubs were planted on the fill (MassDOT, 2012). In 2006, a 114-acre park opened after 15 years of cleanup activities. The park is operated by the National Park Service and houses a visi- tor center, several miles of hiking trails, and a swimming beach (NPS, 2012). Energy and Carbon The cost, availability, security of supply, and climate impacts of energy use have received worldwide attention in recent years, and scientists and engineers have been working toward developing calculators of the energy embodied in a variety of infrastructure and geotechnical systems (e.g., Chester and Horvath, 2010; Hammond et al., 2011; Soga, 2011). Without such calculators, it is difficult to understand the true energy costs of underground infrastructure. The under- ground offers multiple options for promoting energy efficiency and ameliorating climate change that are described throughout the report, but there remain plan- ning, design, construction, maintenance, and other sustainability challenges to be better understood or integrated into practice to maximize the energy savings of underground infrastructure. More efficient or alternative methods to excavation or concrete production—both energy-consuming processes—may result in greater energy efficiency during construction. Underground space use requires significant quantities of energy for ventila- tion, temperature control, lighting, fire detection, and other systems throughout the life of underground facilities. Some advances allow greater efficiency, but higher installation costs could deter their adoption. Development of technolo- gies and space configurations that increase the efficiency of these systems will benefit facility operators and society at large. Light fixtures that accept lower energy demand lamps have been designed and are being specified for some new tunnels and retrofits. Ventilation systems are designed to minimize smoke danger associated with a large-scale fire and therefore have much higher installed-energy demands than needed for everyday operation. Minimum requirements for peri- Underground Engineering Camera-Ready.indd 180 2/6/2013 3:17:15 PM

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INNOVATIVE UNDERGROUND TECHNOLOGY AND ENGINEERING 181 odic ventilation system testing result in regular spikes in energy use. However, standards could be reviewed and changed to determine if less frequent or different testing methods can assure safe operation and thus reduce energy consumption over the life of the system. New technologies and processes that increase energy efficiency, and development of new and smaller space configurations that reduce the use of energy resources, will benefit facility operators and society at large. Underground facilities can be constructed and used to conserve energy and create systems that achieve ground heat exchange with subsurface geologic materials in the urban underground. Important research on underground heat transfer issues began in the 1970s and 1980s (e.g., Geery, 1982; Bloomquist, 1999). Ground-coupled heat exchange systems have since grown in popularity in Europe (Sanner et al., 2003). However, they have not been used extensively in urban communities, and their long-term efficiencies when used in close proxim- ity with each other have not been evaluated. Investigation of thermal effects and long-term impacts on both underground climate and underground space usage is warranted. The use of lower temperature geothermal resources can help to reduce net emissions of greenhouse gases through the use of ground source heat pumps or similar heat exchange systems for heating or cooling structures and potable and nonpotable water for residential use. Such systems exchange heat from the earth to a structure in the winter, and vice versa in the summer, and in some cases, can be incorporated directly into the foundations of infrastructure. Although energy savings can be significant (DOE, 2012), there are environmental implications to be explored, including the selection of refrigerants (e.g., Forsén, 2005), and the long-term effects of potential ground temperature changes on aquifers and groundwater flow, chemistry, biota, and on underground infrastructure itself. Other subsurface use may become restricted in some areas because of the pres- ence of a “forest” of geothermal boreholes. The issues of energy and resource production and energy-related waste storage are not investigated in this report, but they are relevant in the context of underground engineering and sustainable development. Extraction of con- ventional energy and resources from below the surface could be made more efficient with improved excavation and extraction rates, for example. Oil and gas production from deep wells, coal mining, uranium mining, and more recently gas production from deep shale formations are all part of the complex interaction of the underground with our energy future. There is also interest in the use of carbon sequestration and other waste disposal technologies at relatively shallow depth. These technologies often generate intense public policy discussions about actual or possible environmental impacts and the relative merits of pursuing dif- ferent policies for energy conservation or energy production. Often missing are the critical data and analyses in the public domain that properly assign benefits and liabilities to the various options that can appropriately inform critical future options regarding energy and climate. Underground Engineering Camera-Ready.indd 181 2/6/2013 3:17:15 PM

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182 UNDERGROUND ENGINEERING FOR SUSTAINABLE URBAN DEVELOPMENT Nontraditional energy sources could be better and more efficiently exploited with advances in underground engineering technologies. Geothermally active regions can be exploited, for example, by drilling into hot rocks and using the naturally high temperatures to produce steam and electric power (Duffield and Sass, 2003). Known conventional geothermal resources have the potential to produce approximately 9,000 MWe, and an additional mean power potential of 30,000 MWe are estimated from undiscovered sources (USGS, 2008). An estimated additional 518,000 MWe could potentially be generated from noncon- ventional geothermal methods including engineered geothermal systems (EGS) (USGS, 2008). Issues such as corrosion from the highly corrosive groundwater in geothermal fields have to be addressed. Similarly, long-term operation and maintenance issues are not well understood for EGS systems, especially given the high pressures and flow rates expected of EGS wells. Reliable high-temperature submersible pumps suitable for EGS development, for example, have been identi- fied as a technology gap (DOE, 2008). Another major impediment to geothermal resource use is proximity of resources to where the power is needed. REFERENCES ASCE (American Society of Civil Engineers). 2009. Report Card for America’s Infrastructure. Res- ton, VA: American Society of Civil Engineers [online]. Available: http://www.infrastructurere- portcard.org/report-cards (accessed July 3, 2012). Barnett, C.J., and K. Chin. 1998. Soil contamination assessment and characterization in urban tun- neling. Pp. 79-86 in North American Tunneling ’98, L. Ozdemir, ed. Rotterdam, Netherlands: Balkema. Barton, N.R., R. Lien, and J. Lunde. 1974. Engineering classification of rock masses for the design of tunnel support. Rock Mechanics and Rock Engineering. 6(4):189-236. Bennett, P.J., K. Soga, I. Wassell, P. Fidler, K. Abe, Y. Kobayashi, and M. Vanicek. 2010. Wireless sensor networks for underground railway applications: Case studies in Prague and London. Smart Structures and Systems. 6(5-6):619-639. Bickel, J.O., T.R. Kuesel, and E.H. King. 1996. Tunnel Engineering Handbook, 2nd Ed. New York: Chapman & Hall. Bieniawski, Z.T. 1976. Rock mass classification in rock engineering. Pp. 96-106 in Exploration for Rock Engineering, Proceedings of the Symposium, November 1976, Johannesburg, Z.T. Bi- eniawski, ed. Cape Town: Balkema. Bieniawski, Z.T. 1989. Engineering Rock Mass Classifications. New York: Wiley. Bloomquist, R.G. 1999. Geothermal Heat Pumps Four Decades of Experience. GHC Bulletin (De- cember):13-18 [online]. Available: http://geoheat.oit.edu/bulletin/bull20-4/art3.pdf (accessed June 4, 2012). Broch, E., R. Sterling, J. Zhao, and C. Rogers, eds. 1986. Tunnelling and Underground Space Tech- nology. Oxford, UK: Elsevier Science. Chester, M., and A. Horvath. 2010. Life-cycle assessment of high speed rail: The case of California. Environmental Research Letters. 5(1):014003. DOE (U.S. Department of Energy). 2008. An Evaluation of Enhanced Geothermal Systems Technol- ogy. U.S. Department of Energy, Energy Efficiency and Renewable Energy [online]. Available: http://www1.eere.energy.gov/ geothermal/pdfs/evaluation_ egs_tech_2008.pdf (accessed July 6, 2012). Underground Engineering Camera-Ready.indd 182 2/6/2013 3:17:15 PM

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