A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is enclosed except for the portals, commonly at each … See more

Much of the early technology of tunneling evolved from mining and military engineering. The etymology of the terms "mining" (for … See more

Double-deck and multipurpose tunnels
Some tunnels are double-deck, for example, the two major segments of the San … See more

A tunnel is relatively long and narrow; the length is often much greater than twice the diameter, although similar shorter excavations can be constructed, such as cross passages between tunnels.
The definition of what constitutes a tunnel can vary widely … See more

A major tunnel project must start with a comprehensive investigation of ground conditions by collecting samples from boreholes and by other geophysical techniques. An … 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

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