and address geologic, hydrologic, environmental, thermal, and social issues that exist or may arise over time. Technologies have improved in the past decades, but, interestingly, many of the general areas in which improvements are regularly cited as being needed have not changed. For example, in 1989, the National Research Council identified the ways in which geotechnology impacts the U.S. economy, the environment, and national security (NRC, 1989). Multiple research themes deserving special attention were identified that could contribute to infrastructure development and rehabilitation including:
• Influences of construction on nearby structures;
• trenchless construction technologies for installing and rehabilitating utility pipe networks (see Box 7.4);
• development and use of new materials such as plastic pipe, polymers, and geosynthetic materials to address infrastructure system needs;
• maintenance and renewal of aging infrastructure systems, including remote sensing systems to locate and assess infrastructure system quality; and
• an interdisciplinary approach to solving the diverse needs of complex infrastructure systems.
Research in many of these areas has improved U.S. capacity to develop underground systems, but research in these same areas is still warranted today, especially given national interest in sustainability and resilience. Chapter 6 provides a detailed discussion on needed technology innovations associated with site characterization, and underground infrastructure design, construction, operation, monitoring, and maintenance that could contribute to sustainable development.
Some specific technology development challenges and opportunities for research that would aid a more holistic approach to integrated urban system design and operation are highlighted in previous chapters and in Boxes 7.4 and 7.5.
Observation: Few data exist regarding the environmental and social impacts and lifecycle sustainability of urban development that can inform technology and administrative decisions related to long-term (decades to centuries) infrastructure operation, maintenance, and reduced costs.
Conclusion 8. Comprehensive and scientific retrospective studies of the direct and indirect costs and impacts of various types of underground projects are needed to evaluate usefulness and economic, environmental, and social impacts so that future planning can maximize sustainability.