See also: Tunnel (homonymy)
Tunnel is a word tardily appeared in the French language, borrowed from English “tunnel” which would derive itself from French “ arbor ” evoking the form of the barrel.
It indicates an underpass.
Definition
Although this definition is not completely allowed, one often considers who a tunnel must be at least twice larger than it is not broad to deserve this designation. It must moreover be closed on all the sides, except with each one of its ends, which differentiates it of a passage in trench.
Types of very varied tunnels
A tunnel can be used to allow the passage of people (Piéton S, Cycliste S, road traffic, rail traffic, channel).
The improvement of average the techniques, and the political pressure to facilitate displacements, make it possible to consider very ambitious works like the Channel tunnel, and more generally under the straits, or the large transalpine basic tunnels, in construction (Saint-Gothard) or project (Lyon-Turin, Brenner). The long tunnels are very often assigned to the railroad (and with its derivatives as the maglev) because the accident risk is less and the long underground ways would be tiresome for individual transport; moreover, that avoids the gas emission pollutants in confined surroundings and simplifies the problem of the Ventilation.
The construction of a covered trench is rather simple and can apply to the not very deep tunnels. A ditch is excavated then covered. The retaining walls must be set up to prevent that the tunnel does not crumble on him.
The not very deep tunnels are often trenches covered, whereas the deep tunnels are excavated, often using what is called a tunneller. For the intermediate depths, the two methods can be used.
Until little, the largest tunneller ever built at summer used to dig the tunnel Groene Binder (tunnel of the green Dutch heart) on a highway route in Pas-Bas. Its diameter was of 14.87 meters.
Currently, four large tunnellers are in activity: two for the boring of the highway skirting of Madrid and two for the tunnel Chong Ming with Shanghai. These machines respectively make 15.2 m and 15.4 m diameter. The two Spanish tunnellers were built by a consortium joining together Mitsubishi, Dura Fuelgo and Herrenknecht, and the Chinese tunneller was it by Herrenknecht.
There exist many examples for which one chose to cross rivers or arms of the sea by building a tunnel rather than a bridge: Holland Tunnel, Lincoln Tunnel between the New Jersey and Manhattan, Westerscheldetunnel in the Netherlands, Channel tunnel.
At least a project (abandoned) in Europe considered among other solutions another form of “bridge-tunnel” with a road to some extent locked up in a tunnel, but posed on a viaduct, so as to cross the the natural Scheldt and the Scheldt channeled) while limiting the impacts of the vehicles on the natural environment. The bridge indeed brought the vehicles directly in the Canopée of two main forests, of limited size, but single in this particularly deforested area. And it cut an important corridor of animal Migration, before biological vocation of corridor of great value (European importance) and single in the area of the project. It was thus a question of reducing the noise and the disturbances related on the véhihcules and the light. It was proposed to test the vegetalisation piles of the bridge and envelope forming the tunnel , which could perhaps have conferred on this structure a function of écoduc. the Tunnel of Lærdal in the west of the Norway, between Lærdal and Aurland, is the longest road tunnel of world (24.5 km). the Tunnel of Hsuehshan is the longest road tunnel of Asia with 12,90 km. In Finland, the Aqueduc of Päijänne is the longest tunnel dug in the rock in the world. Its 120 kilometers length supply the capital Helsinki out of drinking water.
To design a tunnel for a city, it is also to worry to preserve the inheritance, the peace of the vicinity and to reduce pollution.
Several tunnels were built these last years in towns of Europe: Moscow (Tunnel Lefortovo), Rome (Tunnel Giovanni XXIII)… If, at the beginning one sees only progress there, with the use one becomes aware of the nuisances: many accidents fatal, sound pollution…
Rock mechanics Work of art
Simple: Tunnel
D' other tunnels had function of Aqueduc, only built to transport water - intended for consumption, the routing of waste water or the food of Barrage S hydroelectric - whereas others still are dug to convey cables of telecommunication, electricity, Hydrocarbure S etc
Some secret or strategic tunnels were also built with fine soldiers, to enter sector prohibited (Tunnel of Củ Chi in Vietnam or tunnels connecting the Gaza Strip to Israel).
History of the tunnels
Various strengthened installations were equipped with more or less secret tunnels making it possible their occupants to flee or circulate without being seen. Many tunnels were consruits within the framework of mining activities.
It is the development of the Railway network at the 19th century which involved at the 19th century the boring of very many tunnels to avoid the important slopes (not only because of weak the adherence of the wheels on the rails, but also of the ratio poor power/weight of the locomotive with vapor). Nowadays, it is rather the need for having the best profile in plan (large radii of curvature) for the oars at high speed which leads to the construction of tunnels (the section of LGV Florence-Bologna in construction comprises 73 km of tunnels on 78 km overall length, the first French LGV Paris-Lyon does not comprise any tunnel, but at the price of sensitive slopes (3.5%). It is also the obstruction of the ground and the difficulty in restructuring the existing Urbanisme in the urban centres which pushes with the use of the basement, in particular with the Métro S in spite of the tripling of the cost and some Claustrophobie of the travellers.
Construction
The tunnels can be dug in various types of materials, since clay to the hardest rocks, and the techniques of excavation depend on the nature of the ground.
Sliced covered
Tunnellers
The Tunnelier S are machines which can be used to automate the process of boring of the tunnel. There exists a large variety of tunnellers being able to be used in very diverse situations, going since hard stone until with the soft aquiferous ground.
There are certain which is pressurized and which can thus be used under ground water. The interior of the tunneller is pressurized, to compensate for the pressure exerted by water on the walls of the machine. Consequently, the operators working in the tunneller are subjected to pressure raised, and must undergo cycles of decompression before being able to turn over to the free air, just like the plunger S.
New Austrian method
The new Austrian method (NMA, or English NATM) developed in the years 1960. It finds all its interest in the zones of friable rocks. The general idea of this method is to use the intact rock located at some meters of the tunnel to stabilize that which is located more close to the work. With this intention, of long steel stems are inserted in the rock then bolted.
Underwater tunnels
It is possible there too several to build underwater Tunnels. The method most frequently used consists in building a submerged tube. It is what was made in the wearing of Sydney and for the tunnels of Posey and of Webster which connect the towns of Oakland and Alameda in California to the United States.
Tunnel, laces, viaduct or passage in “earthwork” ? Elements of choice
The tunnel when it long and is bored in a hard stone or on the contrary at the risk of Solifluxion, is very expensive investments. In addition some serious accidents (ex: Tunnel of Mont Blanc) made its image gravitational. However in a difficult context (strong slopes, risks crumbling or of landslides.) it can be in the long term less expensive and more making safe that long roads in laces. And in addition to a great safety and a protection against the bad weather (if it is well conceived), it has the advantage of not cutting the biological Corridors where they exist and thus not to contribute to the Fragmentation écopaysagère. From this point of view it is preferable with the viaduct which in addition to its landscape impact, can affect the migration of birds and the night environment, if it is enlightened.
Quand it is short, one sometimes compares it to a écoduc. Its construction, which is often done in ecologically significant zones (ecosystems of mountain) must be accompanied by a good impact study and a good management of extracted materials and air polluted by the vehicles, the Train and the Ferroutage being from this point of view of the alternatives which develop (in Suisse in particular).
Tunnel or bridge? Elements of choice
To cross a river or an arm of the sea, a tunnel is generally more expensive to build than a bridge. There exists however much of reasons to choose a tunnel rather than a bridge:
Mixed alternatives, solutions?
Remarkable tunnels
Tunnels in urban environment
See too
Internal bonds
External bonds
Random links: Trajan | RS Gimnástica de Torrelavega | François Décorchemont | Theory of the constraints | Boulevard circular of Defense