Tunneling

Tunneling and drilling operations fall into two broad categories: (1) operations in which excavation is carried out by attacking the rock face selectively, and (2) operations that use a device to advance the whole cross section of the excavation simultaneously. The first category includes all drill-and-blast and manual methods, and flexible mining machines such as roadheaders or continuous miners. These methods allow a tunnel of any cross section or any curvature to be driven, provided the machine and its mucking system can negotiate the curve. They are typically used in mining operations where great flexibility in size, cross section, and curvature of the excavation is needed.

The second category consists of excavations in which the whole face is advanced simultaneously, and includes those driven by tunnel boring machines (TBMs), raise borers, and all small-diameter holes drilled by the use of a drill bit. Such holes are almost always of circular cross section, because the excavation method consists of rotating some form of cutter head against the rock face. The drive mechanism for the cutter head is normally quite bulky and is rigidly attached to a cutter head because of the need to transmit the required power. Such drilling assemblies tend to be long relative to their diameters and tend to fit tightly in the hole. Changing the direction of the hole is then a matter of making the cutter head cut sideways and getting the drive mechanism to follow. This operation, whether for a shallow exploratory core hole for prospecting purposes, a production oil well, or a full-size freeway tunnel, has certain basic requirements, even though the equipment used in each case may be very different.