The world’ largest tunnel under the sea

February 5th, 2009 | 2 Comments

The Channel Tunnel

Eurostar speeds you through the Channel Tunnel, one of Europe’s biggest infrastructure projects to date. The $15 billion Channel Tunnel makes the old dream of a ground link between Great Britain and continental Europe a reality for the first time since the Ice Ages.
The tunnel consists of 3 interconnected tubes: 1 rail track each way plus 1 service tunnel. Its length is 31 miles, of which 23 miles are underwater. Its average depth is 150 feet under the seabed. The channel crossing time for Eurostar is only 20 minutes.

The Channel Tunnel, in French it is called “le tunnel sous la Manche”, in English it is often nicknamed the Chunnel, is a rail tunnel beneath the English Channel at the Straits of Dover, connecting Cheriton in Kent, England and Sangatte in northern France.
A long-standing and hugely expensive project that saw several false starts, it was finally completed in 1994. It is the second longest rail tunnel in the world, surpassed only by the Seikan Tunnel in Japan. It is operated by Eurotunnel plc.

The world\' largest tunnel under the sea

In 1957 the Channel Tunnel Study Group was formed. It reported in 1960 and recommended a railway tunnel of two main tunnels and a smaller service tunnel. The project was launched in 1973 but folded due to financial problems in 1975 after the construction of a 250 m test tunnel.

In 1984 the idea was relaunched with an Anglo-French government request for proposals to build a privately funded link. Of the four submissions received the one most closely resembling the 1973 plan was chosen and announced on January 20, 1986. The Fixed Link Treaty was signed by the two governments in Canterbury, Kent on February 12, 1986 and ratified in 1987.

The planned route of the tunnel took it from Calais to Folkestone (a route rather longer than the shortest possible crossing) and the tunnel was to follow a single chalk stratum (which meant the tunnel was deeper than the previous attempt). For much of its route, the tunnel is nearly 40 m under the seafloor, with the southern section being deeper than the northern.

The world\' largest tunnel under the sea

Digging the 95 miles of tunnels took 15,000 engineers, technicians and workers over seven years, with tunnelling operations conducted simultaneously from both ends. The prime contractor for the construction was the Anglo-French Transmanche Link, a consortium of construction companies.
Engineers used large tunnel boring machines (TBMs), mobile excavation factories that combined drilling, material removal, and the process of shoring up the soft and permeable tunnel walls with a concrete liner. After the British and French TBMs had met near the middle, the French TBM was dismantled while the British one was diverted into the rock and abandoned.
Almost 4 million cubic metres of chalk were excavated on the English side, much of which was dumped below Shakespeare Cliff near Folkestone to reclaim 90 acres (360,000 m²) of land from the sea. Equivalent to 68 football fields, this area has been made into a park.
The volume of rubble removed from the tunnel is three times greater than that of the Cheops Pyramid in Egypt.

The Channel Tunnel consists of three parallel tunnels: two primary rail tunnels, which carry trains north and south, and a smaller access tunnel. This access tunnel, which is served by narrow wheeled vehicles, is interconnected, by means of transverse passages, to the main tunnels at regular intervals.
It allows maintenance workers access to the tunnel complex, provides a safe route for escape during emergencies, and dissipates the aerodynamic shockwave that would otherwise accumulate in front of a train travelling through a main tunnel at full speed.


Opening of the Channel Tunnel by Queen Elizabeth II and French President François Mitterrand When the two tunnels met 40 m beneath the English Channel seabed on December 1, 1990, in what was to become one of the “crossover halls” that allow diversion of trains from one main tunnel to the other.
It became possible to walk on dry land from Britain to mainland Europe for the first time since the end of the last ice age, over 13,000 years ago. The British and French efforts, which had been guided by laser surveying methods, met with less than 2 cm of error.

The tunnel was officially opened by Queen Elizabeth II and French President François Mitterrand in a ceremony held in Calais on May 6, 1994.


The Channel Tunnel is 50 km (31 mi) long, of which 39 km (24 mi) are undersea. The average depth is 45 m (150 ft) underneath the seabed. It opened for business in late 1994, offering two principal services: a shuttle run for vehicles, and the Eurostar passenger service linking London with Paris and Brussels. Nearly 7 million passengers take the 35 minute journey through the tunnel every year. At completion, it was estimated that the whole project cost around £10 billion.

The American Society of Civil Engineers have declared the tunnel to be one of the modern Seven Wonders of the World.


Interior of Eurotunnel shuttle (vehicle train)The tunnel is operated by Eurotunnel plc. Four types of train services operate:

Eurostar, a high speed passenger service. This connects London’s Waterloo station (incidentally, named for the Napoleonic battle between the UK and France) with the Gare du Nord station in Paris and with Brussels Midi/Zuid station, with stops at Ashford, Calais-Frethun and Lille.
Eurotunnel shuttle, a rail ferry service. These carry cars, coaches and vans between Sangatte (Calais/Coquelles) and Folkestone. Enclosed railcars with minor amenities, some double-decker, permit drive-on and drive-off operation; passengers stay with their vehicle. (Formerly marketed as Le Shuttle.)
Eurotunnel freight shuttle trains. These carry lorries on open railcars, with the lorry drivers travelling in separate passenger coaches.
Eurotunnel rail freight service. These trains carry conventional rail freight or container loads between a special transfer yard in France to destinations in England.
Although Eurostar trains travel at high speeds in France (where the tracks are modern and custom-made for the standard TGV cruising speed of 300 km/h (186 mph), and within the tunnel at up to 160 km/h (100 mph), their speed in Kent is limited by the relatively low-speed tracks over which they must run.
The Channel Tunnel Rail Link project, a partly government-funded scheme to build a dedicated high-speed line from London to the tunnel entrance, is expected to be completed in 2007. A first stage of the link, running from the tunnel to North Kent, was opened in 2003.



2 Responses to “The world’ largest tunnel under the sea”

  1. Phani Bhaskar

    I think a plan of such sort could be made linking panvel mumbai under sea !…but in a country like India the cost dynamics involved is too much….but surely a thought that could be thought of !!!

  2. roller garage doors

    This is a really interesting article. It is a great feat of engineering!

Leave a Reply