Vehicular Tunnels in Rock—Direction for Development

Difficulties in tunneling are contributed by the large size required for vehicular tunnels, the inflexibility of design location, and necessity to handle whatever conditions are encountered in alignment, whether they be solid rock, fault zones, or mixed face of rock and soil below the watertable. Contractors around the world have been turning to mechanized systems of excavation utilizing tunnel boring machine shield systems, precast concrete segments, or other lining systems offering maximum flexibility for adapting to varying ground conditions. Contrary to a commonly-held belief, the primary development frontier is not how to cut hard rock cheaper and faster, but how to develop a mechanized system that will reliably advance a tunnel heading in the widely varying conditions often encountered. Several case studies illustrate new approaches taken by progressive contractors in vehicular tunnels around the world.