ABSTRACT
The various methods of tunnel excavation that are commonly used in the industry including drill and blast, roadheader, and tunnel boring machine (TBM) should be thoroughly evaluated as part of any design for a proposed tunnel with consideration of historical information from previous projects constructed in similar geological conditions. The minimum construction size for tunnels in rock is subject to today's safe working practices including ventilation and practical equipment space requirements. In some jurisdictions the minimum acceptable dimensions are governed by safety authorities. The drill and blast method of excavation is typically adopted for the construction of tunnels in rock of length less than 4 km for economic reasons. While drill and blast excavation for the construction of tunnels can certainly be used for good rock conditions, the method is generally preferred for variable rock conditions of poor to fair quality that includes numerous geological faults whereby greater flexibility exists to facilitate the installation of tunnel support.
