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 tunneling 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.