ABSTRACT
Tunnels here include mainline haulage ways in mines and other important, semi-permanent underground passageways as well as conventional tunnels with surface portals at both ends. Like shafts, “tunnels” may be used for transporting personnel, underground supplies, waste rock and for haulage of ore inmines. Like shafts, tunnels also serve as conduits for ventilation air and as pathways for compressed air and water lines. Because of their long service life, tunnels must be carefully designed and constructed with an adequate factor of safety. Tunnel support may be natural with only occasional rock bolting and screening. Support may also be in the form of a permanent, continuous concrete liner, discrete steel sets or both. Use of large bolts placed on an engineered pattern may also be used for robust tunnel support. In the case of naturally supported tunnels, strength failure of the rock mass walls can be designed against using a stress concentration approach, with due consideration of joints. Indeed, in shallow ground tunnels, fall of rock blocks defined by intersecting joints is often the primary threat to safety and stability. In case of parallel ormultiple tunnels, pillars between tunnels may be designed using an average stress approach, again with due consideration of joints.
