Alternatively, horizontal boreholes may sometimes be drilled ahead of the advancing tunnel face. This smaller tunnel is less likely to collapse catastrophically should unexpected conditions be met, and it can be incorporated into the final tunnel or used as a backup or emergency escape passage. To give more information, a pilot tunnel (or "drift tunnel") may be driven ahead of the main excavation. This may be a particular concern in large-diameter tunnels. It is common practice to locate a tunnel deeper than otherwise would be required, in order to excavate through solid rock or other material that is easier to support during construction.Ĭonventional desk and preliminary site studies may yield insufficient information to assess such factors as the blocky nature of rocks, the exact location of fault zones, or the stand-up times of softer ground. In planning the route, the horizontal and vertical alignments can be selected to make use of the best ground and water conditions. An informed choice can then be made of machinery and methods for excavation and ground support, which will reduce the risk of encountering unforeseen ground conditions. Geotechnical investigation and design Ī major tunnel project must start with a comprehensive investigation of ground conditions by collecting samples from boreholes and by other geophysical techniques. In Ethiopia, the Siqurto foot tunnel, hand-hewn in the Middle Ages, crosses a mountain ridge. It is the second known tunnel to have been excavated from both ends, after the Siloam tunnel in the neighbourhood of Silwan in eastern Jerusalem. The Tunnel of Eupalinos is a tunnel aqueduct 1,036 m (3,399 ft) long running through Mount Kastro in Samos, Greece, built in the 6th century BC to serve as an aqueduct. ![]() The first Qanats are known from before 2000 B.C. Predecessors of modern tunnels were adits to transport water for irrigation or drinking, and sewerage. The etymology of the terms "mining" (for mineral extraction or for siege attacks), "military engineering", and " civil engineering" reveals these deep historic connections. Much of the early technology of tunneling evolved from mining and military engineering. Joralemon Street Tunnel on 1913 postcard, part of the New York City Subway system For example, in the United Kingdom a road tunnel is defined as "a subsurface highway structure enclosed for a length of 150 metres (490 ft) or more." In the United States, the NFPA definition of a tunnel is "An underground structure with a design length greater than 23 m (75 ft) and a diameter greater than 1,800 millimetres (5.9 ft)." History The definition of what constitutes a tunnel can vary widely from source to source. Terminology An entrance of the Rantaväylä Tunnel in the northern part of Tampere, Pirkanmaa, Finland A fabric tunnel in Moulvibazar District, BangladeshĪ 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. ![]() Tunnels can be connected together in tunnel networks. Special tunnels, such as wildlife crossings, are built to allow wildlife to cross human-made barriers safely. ![]() Secret tunnels are built for military purposes, or by civilians for smuggling of weapons, contraband, or people. Utility tunnels are used for routing steam, chilled water, electrical power or telecommunication cables, as well as connecting buildings for convenient passage of people and equipment. Some tunnels are used as sewers or aqueducts to supply water for consumption or for hydroelectric stations. The central portions of a rapid transit network are usually in the tunnel. A pipeline is not a tunnel, though some recent tunnels have used immersed tube construction techniques rather than traditional tunnel boring methods.Ī tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Tunnel in Col du Galibier, France Tunnel in Fort de Mutzig, France Decorated entrance to a road tunnel in Guanajuato, Mexico Utility tunnel for heating pipes between Rigshospitalet and Amagerværket in Copenhagen, Denmark Tunnel on the Taipei Metro in Taiwan Southern portal of the 421 m long (1,381 ft) Chirk canal tunnel, WalesĪ tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. For a tunnel for pedestrians, see Subway (underpass). For the John Foxx song, see Underpass (song).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |