Tunnel Boring Machine may be suitable for excavating tunnels which contain competent rocks that can provide adequate geological stability for boring a long section tunnel without structural support. However, very hard rock can cause major wear of the TBM rock cutter and may slow down the progress of the tunneling works to the point where TBM becomes useless and uneconomical and may take longer time than the drill and blast tunneling method.
Bored tunneling Benefits
• Possible environmental impacts in terms of dust, noise and visual on sensitive receives are much reduced and are restricted to those located near the launching and retrieval shafts
• Compared with the cut and cover approach, trouble to local traffic and associated environmental crash would be much reduced