USA HISTORY

Detailed explanation-1: -Tunnels through mountains or underwater are usually worked from the two opposite ends, or faces, of the passage. In long tunnels, vertical shafts may be dug at intervals to excavate from more than two points.

Detailed explanation-2: -The first tunnel built whose engineer is known was excavated in the island of Samos. The engineer Eupalinos de Megara, built this tunnel in the 530 b.C to supply with water the capital of the island and was, with its 1 km length, considered as one of the three marvels of the helenic world.

Detailed explanation-3: -For centuries, tunnels in rock were driven by building fires against the rock faces, which would cause expansion and spalling, often accelerated by dousing the hot rock with water, then picking the fractured rock away with picks and wedges (Wahlstrom, 1973).

Detailed explanation-4: -There are three basic types of tunnel construction in common use. Cut-and-cover tunnels are constructed in a shallow trench and then covered over. Bored tunnels are constructed in situ, without removing the ground above. Finally, a tube can be sunk into a body of water, which is called an immersed tunnel.