Tunnlar
Tunnlar are man-made passages built underground or underwater to provide transportation routes, utility corridors, or access to enclosed spaces. They can be bored through rock or excavated in soil, sometimes formed by cut-and-cover methods or as immersed tunnels joining prefabricated elements under water. In Swedish, tunnlar is the plural form of tunnel. Typical cross-sections are circular, horseshoe-shaped, or rectangular, and tunnels are reinforced with linings to carry earth and water loads and to support ventilation and drainage.
The most common modern method is tunnel boring using tunnel boring machines (TBMs), which cut a circular
Tunnlar serve a variety of purposes, including road tunnels, rail tunnels (including metro and long-distance lines),
Design and safety considerations include proper ventilation, fire protection, lighting, signaling, emergency exits, and monitoring. Groundwater
Notable examples include the Channel Tunnel between Britain and France (opened 1994), the Gotthard Base Tunnel