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 utilities, metro, trams, etc.
The most “tunnel” mode of transport is the metro. Most of its lines are laid with passages that can be at different depths underground. Car and railway tunnels are laid under mountains and hills to shorten the total length of the route. Sometimes it’s better to build a tunnel than to build a bridge.
History
People have been creating these objects since ancient times. The first artificial structures of this type appeared in the Stone Age. Caves, catacombs, quarries, mine mines were cut in the rocks. Countries where they began to do this earlier than anywhere else were Egypt and Greece, as well as the cities of Rome and Babylon. There tunnels were dug for the purpose of mining, during the construction of temples, tombs, and the laying of water conduits. During the work, the simplest tools were used, and the rocky rocks, in which the passage was cut, were not fixed.
The very first underwater tunnel was built under the Euphrates River in the area of 2160 BC.
Sometimes tunnels were built in the Middle Ages, mainly for military purposes. In the late phase of the Middle Ages shipping 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, railway underground structures were especially often built. They were laid through the Urals, the Caucasus, and 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 like?
A tunnel is an elongated artificial void laid in a rock. If the breed is strong, then the passage is not fixed, and if loose, then artificial fastening structures are installed. They are called lining and take on a significant part of the mountain loads, and also participate in waterproofing. The so-called portals are being built at the entrances and exits. They may have an architectural appearance.
Tunnel Construction Methods
There are two types - indoor and outdoor. The first method is used for laying passages at great depths (more than 20 meters), as well as for shallow tunnels. Open apply when laying shallow moves. The advantage of this method is the lower cost, and the minus is the need to take away from the construction site the communications and transport routes located in its zone.
Closed tunneling methods
The choice of the method by which the tunnel will be built depends on the type of rock to be breached and the purpose of the object. Closed methods are often used in the construction of a subway tunnel and railway tunnels. Soils can be strong, soft, fractured, flooded.
- With the mining method of laying, drilling and blasting are used. The main element of penetration is the laying of explosives 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 lined. Use this method in the case when the rocks are stable and strong.
- Combine laying is also based on rock breakdown. However, they use special tunneling equipment. These are the so-called tunnel digging combines. Like the previous one, this method is used in the case of high and medium strength rocks.
- The New Austrian tunnel construction method is used for soft and fractured rocks. It is based on the creation of temporary fasteners by spraying concrete on the surface of the rock, as well as reinforcing with anchors. This increases the stability of the arch in the bottomhole zone. As for the constant lining, it can be performed at a distance from the bottom of the face, for which high performance mechanisms are used.
- The paneling method of laying is based on the use of a tunneling shield, which is used to lay the tunnel throughout the section, after which lining is carried out. This method is also used for 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 sinking are used. For this, fixing with a special solution, freezing, drainage, working with compressed air can be used. Shield methods can also be used, supplemented by active slaughtering.
Open Tunneling Methods
The use of an open method for the construction of tunnels is advisable when digging shallow passages. The following technologies are used:
- The excavation method consists in creating a foundation pit for the entire width and depth of an object under construction. Walls can be artificially strengthened, or correspond to the natural occurrence of rocks. After lining the tunnel, the foundation pit is filled up. This method was used in the construction of the metro in Berlin.
- The shield method for building tunnels is to use a rectangular shield for lining.
- The trench method is often used when laying pedestrian tunnels. It consists in digging a pit in parts.
