Tunnel

Signalisation routière entrée sud tunnel du Galibier

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14-46-35-f-mutzig

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Tunel en Guanajuato

Heatpipe tunnel copenhagen 2009

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A crossover on the south side of Zhongxiao Xinsheng Station

Southern portal of Chirk canal tunnel - geograph.org.uk - 1293092

Tunnel is an underground or underwater passageway, dug through the surrounding soil/earth/rock and enclosed except for entrance and exit, commonly at each end. A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. The central portions of a rapid transit network are usually in the tunnel. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers. 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.

Design and Construction

Designing and constructing a tunnel involves understanding geological conditions, hydrogeology, material properties, and the stress behavior of the surrounding ground. The method of tunnel construction depends on such factors as the ground conditions, the ground water conditions, the length and diameter of the tunnel drive, the depth of the tunnel, the logistics of supporting the tunnel excavation, the final use and shape of the tunnel, and appropriate risk management.

Methods of Tunnel Construction

The two main methods of tunnel construction are:

• Cut and cover: This method involves excavating a large trench or pit and covering it after the tunnel structure is placed. It is most suitable for shallow tunnels.
• Tunnel boring machine (TBM): Also known as a "mole", TBMs are used for the construction of tunnels in varying ground conditions. The machine excavates the tunnel by rotating a cutting head and applies a circular cross-section, allowing for the placement of concrete linings to support the excavated tunnel.

Other methods include:

• Drill and blast: This method is used primarily for hard rock conditions where a TBM is less effective. It involves drilling holes into the rock, filling them with explosives, and blasting the rock to form the tunnel.
• Immersed tube: Used for underwater tunnels, sections are constructed elsewhere, usually in a dry dock, then floated to the site, sunk into place, and covered with backfill.

Safety and Ventilation

Safety is a critical concern in tunnel design and construction, especially in cases of fire. Modern tunnels often include emergency exit passages, fire-rated doors, and state-of-the-art ventilation systems to manage air quality and smoke movement.

Ventilation is crucial for removing toxic gases during construction and operation. It also controls the temperature and provides fresh air, ensuring the safety and comfort of users. Ventilation methods vary depending on the tunnel's use, length, and the volume of traffic it supports.

Historical Significance

Tunnels have been used for military and strategic purposes, transportation, water distribution, and sewage systems since ancient times. The engineering skills and innovations developed through tunnel construction have contributed significantly to our understanding of geotechnical, civil, and environmental engineering.

Notable Tunnels

Some of the world's most famous tunnels include:

• The Channel Tunnel, connecting the United Kingdom and France, is one of the longest underwater tunnels.
• The Gotthard Base Tunnel in Switzerland is the world's longest and deepest rail tunnel.
• The Seikan Tunnel in Japan is the longest and deepest operational rail tunnel, especially notable for its underwater section.

Environmental Impact

Tunnel construction can have significant environmental impacts, including disruption of landscapes, ecosystems, and groundwater systems. However, tunnels also offer environmental benefits by reducing surface congestion and pollution, and by providing more direct routes that save on fuel consumption.

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