World’s Longest Undersea Tunnel: Seikan Tunnel

The Seikan tunnel is the longest railway undersea tunnel in Japan, which is 53.85 km long between both openings and having its 23.3 km long portion below the seabed. The track laid down in the Seikan tunnel is 240m below the sea level; on the other hand the track is 140m below the seabed.This discussion allows us to know all about an undersea tunnel specially the SEIKAN TUNNEL, advantages and disadvantages of the tunnels over bridges. To know more keep reading the post onwards…..

What you mean by a Tunnel??

A fully closed underground path or passage only with two openings for entrance and exit, is named as Tunnel. Tunnel is a great transportation system or pathway which may be used by vehicles, Railway and even by human beings on their feet. Tunnel can also be used as the sewers, water supply aqueducts, or for many other functions.

Basically the idea of tunneling is evolved from early time “mining”. In early ages the process of mining was carried out for excavating the valuable substances below ground.

In 1805-1809 a group of miners tried to dig the first tunnel but they failed. The Thames Tunnel is the first tunnel in the world built in 1825-1843. This was the first tunnel successfully constructed below a river. This tunnel was 35 m wide, 6 m high and 396 m which was built 23 m below the surface of river.

What is an Undersea Tunnel??

A tunnel which is fully or partially constructed below a water body is named as a undersea tunnel. The Thames Tunnel described above is the first underwater tunnel constructed by man. The undersea tunnels are mainly constructed where the construction of the bridges are not possible.

when the undersea tunnels are compared with the bridges, many of the considerable facts comes in front of us. While talking about these all elaboration will as further-

Advantages of tunnel over bridge -: 

• Special areas which come under non disturbance zone may use tunnel as an advantage.
• Congested Areas like high density towns or any projects where enough space for bridge construction is not possible tunnel construction is useful.
• An undersea tunnel allows traffic inside it as well as shipping on surface of water, where a low height bridge over water body must be opening or Swing Bridge for allowing same.
• The tunnels has a lot of functional varieties like vehicle, railway, metro, water diversion, utility tunnels and also mix up of them. On the other hand bridge is capable of functionality with vehicles and railway.

Disadvantages of tunnel over bridge -: 

• Casting cost of tunnel is higher than a Bridge.
• Highly graded technologies and equipments are required for tunnel construction as compared to bridges.
• Time period required for constructing a tunnel is more than the bridges.
• In case of shipping on water surface a bridge at required height may be provided which will replace the tunnels.

World’s Longest Undersea Tunnel: Seikan Tunnel

 The Seikan tunnel is regarded as the world’s longest undersea water tunnel. Seikan tunnel is a railway tunnel in Japan which connects island Honshu and Hokkaido with each other. This tunnel takes place below the Tsugaru Strait (a narrow waterway which connects two water bodies). The depth if the track from water surface of this strait is 240 m, where track is 140 m below the bed of strait. The distance between the both openings of the Seikan tunnel is 53.85 kms. While its 23.3 kms long portion is below the Tsugaru Strait. This tunnel was opened on 13 March 1988.

  

The initial geological investigation of the tunnel occurred from 1946-1963, which involved drilling the seabed, sonic survey, submarine boring, seismic and magnetic surveys. Beneath the Tsugaru strait, the use of tunnel boring machine (TBM) was restricted after 2 km boring, hence dynamite blasting and mechanical picking were used to excavate.      

Seikan Tunnel is longest as well as the deepest tunnel of the world till now, but in 2017 Gotthard Base Tunnel in Switzerland will be will be longer one including the undersea portion and remaining below earth surface. If the talk is about the longest undersea portion then it will be the Channel Tunnel between United Kingdom and France.  Working on such a project must be ambition of all of us.

Tunnel Extension	53.85km in which 23.30km is under the sea bed.
Cement Used	Approximately 85,000 tons.
Steel Used	Approximately 17 thousand tons (approx. Similar to Tokyo Tower).
Soil Dug	Approximately 630 thousand square meters.
Explosive Used	Approximately 2,900 tons
Workers	Approx. 14 million
Completion Period	Approx. 24 years
Total Cost	70290300 $

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