A tunnel is a horizontal or inclined artificial passage underground. Such objects are created for different purposes. There are pedestrian, bicycle, automobile, railway, tunnels of underground communications, metro, trams, etc.
The most "tunnel" mode of transport is the subway. Most of its lines are laid through passages, which can be located at different depths underground. Road and rail tunnels are being built under mountains and hills to shorten the overall length of the route. Sometimes it makes more sense to build a tunnel than build a bridge.
History
People have been creating these objects since ancient times. The first artificial structures of this type appeared already in the Stone Age. Caves, catacombs, quarries, mine shafts were cut through the rocks. The countries where this was done earlier than anywhere else were Egypt and Greece, as well asthe cities of Rome and Babylon. There, tunnels were dug for the purpose of mining, during the construction of temples, tombs, and laying water conduits. During the work, the simplest tools were used, and the rocks in which the passage was cut were not fixed.
The very first underwater tunnel was built under the Euphrates River around 2160 BC.
Sometimes tunnels were built in the Middle Ages, mainly for military purposes. In the late phase of the Middle Ages, navigable passages were actively created. The first railway tunnel appeared in 1826-1830. And the first automobile was built in 1927 under the Hudson River.
In the USSR, underground railway facilities were built especially often. They were laid through the Urals, the Caucasus, Crimea. The construction of automobile tunnels became relevant with the increase in the number of cars after the collapse of the USSR.
What is it?
Tunnel is an artificial void of elongated shape, laid in the rock. If the rock is strong, then the passage is not fixed, and if it is loose, then artificial fixing structures are installed. They are called lining and take on a significant part of the mountain loads, and also participate in waterproofing. So-called portals are built at the entrances and exits. They may have an architectural appearance.
Tunnel construction methods
There are two types - closed and open. The first method is used for laying passages at great depths (more than 20 meters), as well as for shallow tunnels. Open are used when layingshallow moves. The advantage of this method is the lower cost, and the disadvantage is the need to divert communications and transport routes located in its zone from the construction site.
Closed tunneling methods
The choice of the method by which the tunnel will be built depends on the type of rock to be cut through and the purpose of the object. Closed methods are often used in the construction of the subway tunnel and railway tunnels. Soils can be strong, soft, fractured, watered.
- During the mining method of laying, drilling and blasting are used. The main element of penetration is the placement of an explosive and the implementation of a directed explosion. Fragments of the destroyed rock are removed from the face to the surface. The resulting cavity is first strengthened, and then the lining is carried out. Use this method when the rocks are stable and strong.
- Combine type gasket is also based on the destruction of the rock. However, special tunneling equipment is used for this. These are the so-called combines for digging tunnels. Just like the previous one, this method is used in the case of high and medium rock strength.
- The New Austrian tunneling method is used for soft and fractured rock. It is based on the creation of temporary fastenings by spraying concrete on the surface of the rock, as well as strengthening with anchors. This increases the stability of the arch in the bottomhole zone. As for the permanent lining, it can be performed at a distance from the placeslaughter, for which high performance mechanisms are used.
- The shield method of laying is based on the use of a tunneling shield, which is used to lay a tunnel over the entire section, after which the lining is carried out. This method is also applied to loose and fractured rocks.
- In the presence of a high degree of water cut, instability of soils and the presence of aggressive environments, special methods of penetration are used. For this, fixing with a special solution, freezing, drainage, work with compressed air can be used. Shield methods can also be used, supplemented by active face weight.
Open tunneling methods
The use of an open tunneling method is advisable when digging shallow passages. The following technologies are used:
- The pit method is to create a pit for the entire width and depth of the object under construction. The walls can be artificially reinforced, or correspond to the natural occurrence of rocks. After lining the tunnel, the pit is filled up. This method was used in the construction of the subway in Berlin.
- The shield method of building tunnels is to use a rectangular shield for lining.
- The trench method is often used when laying pedestrian tunnels. It consists of digging a pit piece by piece.
Conclusion
Thus, the construction of a transport tunnel can be carried out in different ways, depending on the deliveredtasks and features of soils. The most common are railway and subway tunnels.
