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 tunnel while installing a lining. Cut-and-cover builds shallow tunnels by excavating from the surface and then rebuilding the cover. Immersed tunnels are built of prefabricated elements sunk into a body of water and connected.

Tunnlar serve a variety of purposes, including road tunnels, rail tunnels (including metro and long-distance lines), and combined or immersed tunnels for utilities. Underground utility tunnels carry cables, pipelines, or data networks. Civil projects also use mining tunnels, drainage tunnels, and pedestrian tunnels.

Design and safety considerations include proper ventilation, fire protection, lighting, signaling, emergency exits, and monitoring. Groundwater management and structural lining materials, typically reinforced concrete segments, are crucial for stability and longevity. Maintenance and inspection are ongoing requirements in most programs.

Notable examples include the Channel Tunnel between Britain and France (opened 1994), the Gotthard Base Tunnel in Switzerland (opened 2016), and the Severn Tunnel in the United Kingdom (opened 1886). Tunnels have ancient roots in water supply and mining, and modern tunneling enables long, efficient routes through mountains and beneath seas, albeit at high capital costs and with significant safety and environmental considerations.