FIGURE 6.3 Cutter head of a rock tunnel boring machine used to excavate the Chattahoochie 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 economically 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 characterization needs, and unanticipated conditions encountered during construction

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