túnel

tünel is a man-made passage largely excavated or bored through earth and rock to provide a route for people, vehicles, trains, water, or utilities beneath the surface. Tunnels enable transportation beneath mountains, under rivers, or beneath urban areas, and they are also used for utility conduits and mining access. The Turkish word tünel is borrowed from Western European languages; Turkish spelling uses the umlaut ü to represent a sound found in the borrowed term.

Construction methods vary by ground conditions and purpose. Cut-and-cover tunnels are built from the surface by excavating a trench, constructing the tunnel lining, and then restoring the surface. Bored tunnels are created with tunnel boring machines or traditional methods, with lining such as concrete segments, cast-in-place concrete, or steel ribs. Modern tunnels include ventilation, drainage, fire safety, emergency exits, and monitoring systems.

Types include road tunnels, rail tunnels, metro tunnels, underwater or subsea tunnels, utility tunnels, and mining or drainage tunnels. Notable examples worldwide include the Channel Tunnel, the Gotthard Base Tunnel, Marmaray under the Bosporus in Istanbul, and the Eurasia Tunnel in Istanbul. In Turkey, the historic Tünel in Istanbul opened in 1875 as an urban funicular and is among the oldest underground passenger railways in the world, illustrating early urban tunneling technology.