Burying such infrastructure as the Transbay Tube, part of Bay Area Rapid Transit system, can protect it from the effects of natural and man-made disasters and improve the resiliency and sustainability of cities, according to a new report. Wikimedia Commons/Eric Fischer
A new National Research Council report examines how moving infrastructure underground, and improving the planning of belowground spaces, can add to the resiliency and sustainability of urban environments.
March 19, 2013—The National Research Council published a new report this month, entitled “Underground Engineering for Sustainable Urban Development,” that examines the main steps necessary to improve the link between the underground engineering of infrastructure in urban environments and sustainable design. The connection between the two might not seem immediately obvious, but according to the report a strong bond between underground planning and green design is essential to the future U.S. economy, urban settlement patterns, and improved community resilience in the face of such extreme events as earthquakes, hurricanes, tornadoes, and terrorist attacks.
“In modern cities, underground infrastructure has become an essential component in providing the necessary services to support a strong economy and a high quality of life,” said Raymond L. Sterling, Ph.D., P.E., F.ASCE, professor emeritus at Louisiana Tech University and a member of the committee who created the report. Sterling wrote in response to written questions submitted by Civil Engineering online. “As questions are asked about the future sustainability of our way of life, it is important to examine how underground infrastructure and underground facilities can contribute to greater sustainability and how engineering understanding and education can maximize those benefits,” he said.
For the purposes of the report, the authors defined “sustainability” as the practice of meeting the current needs of a population without compromising the ability of future generations to meet their own needs. Resilience is a key attribute of sustainability, according to the report’s authors, because it ties a community’s ability to respond to a change in the environment—for example, a natural or human-made disaster—with minimal impact to critical infrastructure operations.
Sustainability is about more than having enough clean water, food, and material goods, the report notes. The transportation of those elements—and people—must also be protected and developed in response to urban expansion and population growth, according to the report.
Because ground is at such a premium in urban locations, burying infrastructure can maximize the available space for future urban growth as well as potentially protect all types of infrastructure from damage during significant events. A prime example of this, according to the report, occurred during Northern California’s magnitude 6.9 Loma Prieta Earthquake in 1989. During the earthquake, significant damage occurred in the San Francisco Bay Area; one of the most visible infrastructure failures was the collapse of a 15 m long, 5-lane section of the upper deck of the San Francisco-Oakland Bay Bridge onto the lower deck, killing one person. The Bay Bridge was closed for a month while repairs were undertaken.
In contrast to the damage sustained by the bridge, the Bay Area Rapid Transit (BART) System, which operates in cut-and-cover and mined tunnels and crosses the bay almost directly beneath the Bay Bridge’s alignment, was closed for just half a day for necessary inspections and power restoration after the earthquake, according to the report. The Transbay Tube and BART reopened and operated on a 24-hour, 7-day-a-week schedule for the next month until the bridge was repaired. During its closure, daily usage of BART jumped from an average of 218,000 riders to 308,000, according to the report.
Common utility tunnels—known as utilidors—could also benefit communities by increasing accessibility of underground infrastructure for maintenance, repair, or upgrades, according to the report. And grade-separating or burying rail lines; water resources; food distribution systems; commercial, industrial, and institutional facilities; and even housing could also benefit urban communities by maximizing the aboveground space, opening up sight lines, and offering added protection to the infrastructure—if the designs are undertaken appropriately.
The report notes that flooding of underground spaces—such as that experienced in Manhattan as a result of Hurricane Sandy in 2012—is of particular concern in coastal and low-lying areas. However, as long as entrances are protected and sealed prior to an event, underground structures are actually better protected from water pressure and the debris impact of moving floodwaters than aboveground structures, according to the report.
Some of the most important conclusions of the report, according to Sterling, include the findings that underground facilities represent a major contribution to quality of life, especially in large cities, and have significant sustainability benefits because of their longevity once constructed and their ability to provide a more livable environment in compact cities.
However, there are major issues and areas that need to be improved, according to Sterling. “Infrastructure provision in general and underground engineering in particular lacks coordination of practice, research, and education at most levels of government,” he said. “This lack of attention has serious implications for maximizing the cost effectiveness and sustainability of underground infrastructure and for the future of U.S. technological leadership in the field.” Coordinated efforts at system management, communication between stakeholders in planning underground growth, and the maintenance and care of underground facilities all need to be prioritized, according to the report. Additionally, improved research into underground engineering needs to receive greater attention from universities and academics.
“Underground infrastructure provision is usually carried out on a piecemeal basis—each new project has to fit around what has been built before and, often, choices on what to put underground are made primarily on the basis of [initial] cost,” said Sterling. “Thus, a critical first step is to start to plan the urban underground as a complement to the types of planning that currently only deal with a city as a two-dimensional space,” he said. “Good planning requires a better knowledge of what is already built underground and the geological environment in a three-dimensional format.”
According to the report, forward-thinking planning of underground infrastructure also needs to include full life cycle assessments so that long-term developments and future upgrades to meet changing economic, ecological, and social needs are also possible. “The need for sustainable and resilient urban solutions requires development of better analysis methods, examination of existing examples to derive data for triple bottom line assessments, and the development of design approaches for underground infrastructure that facilitate ongoing asset management,” Sterling said. Interdisciplinary work between engineers and various other urban development fields and the development of greater numbers of U.S.-trained underground engineers will be of crucial importance to meet these goals.
“In the short term, the critical goal is to raise the recognition of the importance of underground infrastructure so that it is planned and used more effectively,” Sterling noted. “In the long term, we need to enhance the cost effectiveness, sustainability, and resiliency of underground solutions through targeted research and education.”
Doing so will improve the performance of existing and future underground infrastructure, both under normal conditions and in the aftermath of extreme events.