Tunnels, from wikipedia, describe as an underground passageway, except for openings for entrance and exit, commonly at each end.
Most of the tunnels in the worlds built by Tunnel Boring Machine (TBM). It's possible to bored all ground condition except in rocks with much water with high pressure (>8-12 Bar) and also in soil with pressure range from 5 to 8 bar.
Boring using TBM give smooth profile, which is perfect for water tunnels and usually it has a good stability. Although high investment needed to drill using TBM, it is environmentally friendly because TBM doesn't use explosive, unlike if we drill tunnel with Drill and Blast Method.
