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 encountered 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.

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