A tunnel is relatively long and narrow; the length is often much greater than twice the diameter, although similar shorter excavations can be … See more

A major tunnel project must start with a comprehensive investigation of ground conditions by collecting samples from boreholes See more

Owing to the enclosed space of a tunnel, fires can have very serious effects on users. The main dangers are gas and smoke production, … See more

Much of the early technology of tunneling evolved from mining and military engineering. The etymology of the terms "mining" (for mineral extraction or for siege attacks), … See more

Tunnels are dug in types of materials varying from soft clay to hard rock. The method of tunnel construction depends on such factors as the ground conditions, the groundwater … See more

Double-deck and multipurpose tunnels
Some tunnels are double-deck, for example, the two major segments of the San Francisco–Oakland Bay Bridge (completed in 1936) are linked by a 160-metre (540 ft) double-deck tunnel section through See more

In history
The history of ancient tunnels and tunneling in the world is reviewed in various sources which include many examples of these structures that were built for different purposes. Some well known ancient and … See more