The Channel Tunnel (French: Le tunnel sous la Manche), also known as the Chunnel (a portmanteau word), is a 50.5 km (31.4 mi) undersea rail tunnel linking Folkestone, Kent in England with Coquelles near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point it is 75 m (250 ft) deep. It has the longest undersea portion of any tunnel in the world, although Japan’s Seikan Tunnel is longer overall at 53.85 km (33.5 mi) and reaches a depth of 240 m (790 ft).

The tunnel carries high-speed Eurostar passenger trains, Eurotunnel ro-ro vehicle transport and international rail freight trains. In 1996 the American Society of Civil Engineers identified the tunnel as one of the Seven Wonders of the Modern World.

Overview

Ideas for a cross-Channel fixed link existed as early as 1802 but the eventual successful project, organised by Eurotunnel, began construction in 1988, opening in 1994. The cost overran predictions by 80%, and concessionaire Eurotunnel overestimated tunnel traffic and has met financial difficulty. Fires have disrupted operation of the tunnel. Illegal immigrants and asylum seekers have used the tunnel to enter Britain, causing a minor diplomatic row over the siting of the Sangatte refugee camp, which was eventually closed in 2002.

Eleven tunnel boring machines working from both the UK and France cut through chalk marl to construct two rail tunnels and a service tunnel. Rolling stock using the tunnel includes Eurostar passenger trains based on the French TGV and vehicle shuttle wagons that are the largest in the world; the tunnel has its own fleet of service vehicles. The vehicle shuttle terminals are at Cheriton (Part of Folkestone) and Coquelles, and are connected to the British and French motorways

History

Proposals for a fixed link across the English Channel go back to Albert Mathieu’s 1802 plan involving horse-drawn carts and an artificial mid-Channel island. For over 150 years, British political and press pressure over compromised national security stalled attempts to construct a tunnel. In 1974, French and UK government-funded construction commenced on both sides of the Channel, but the project was cancelled by the UK government over financial concerns. In 1985, the UK and French governments invited submissions for a fixed link. Eurotunnel, a group of ten construction companies and five banks, was awarded the project, a triple-bore railway tunnel based on the 1974 attempt. Tunnelling commenced in 1988, and the tunnel began operating in 1994. In 1985 prices, the total construction cost was £4650 million (£10,153 million inflation-adjusted to 2007), an 80% cost overrun. At the peak of construction 15,000 people were employed with daily expenditure over £3 million. Ten workers died during construction between 1987 and 1993, the majority being killed in the first few months of boring. Of the 10 deaths, 8 were British workers.

Three services use the tunnel: Eurotunnel Shuttle (formerly Le Shuttle), a roll-on roll-off shuttle service for road vehicles including lorries; Eurostar passenger trains; and freight trains. Eurotunnel”s traffic predictions for the tunnel were overestimates and the group has been challenged financially. In 1996 and again in 2006 and 2008, heavy goods vehicle shuttle wagon fires caused damage and restricted use of the tunnel, although nobody was seriously hurt in any of the incidents. Five years after the opening of the tunnel there were few and small impacts on the wider economy, and it was difficult to identify major developments associated with the tunnel. In 1996 the American Society of Civil Engineers, with Popular Mechanics, selected the tunnel as one of the Seven Wonders of the Modern World.

Proposal and Attemps

In 1802 French mining engineer Albert Mathieu put forward a proposal to tunnel under the English Channel, with illumination from oil lamps, horsedrawn coaches, and an artificial island mid-Channel for changing horses In the 1830s Frenchman Aimé Thomé de Gamond performed the first geological and hydrographical surveys on the Channel, between Calais and Dover. Thomé de Gamond explored several schemes, and in 1856 he presented a proposal to Napoleon III for a mined railway tunnel from Cap Gris-Nez to Eastwater Point with a port/airshaft on the Varne sandbank at a cost of 170 million francs, or less than 7 million pounds sterling.

In 1865, a deputation led by George Ward Hunt proposed the idea of a tunnel to the Chancellor of the Exchequer, William Ewart Gladstone. After 1867, William Low and Sir John Clarke Hawkshaw promoted ideas, but none were implemented. An official Anglo-French protocol was established in 1876 for a cross-Channel railway tunnel. In 1881, British railway entrepreneur Sir William Watkin and French Suez Canal contractor Alexandre Lavalley were in the Anglo-French Submarine Railway Company that conducted exploratory work on both sides of the Channel. On the English side a 2.13-metre (6.99 ft) diameter Beumont-English boring machine dug a 1,893-metre (6,211 ft) pilot tunnel from Shakespeare Cliff. On the French side a similar machine dug 1,669 metres (5,476 ft) from Sangatte. The project was abandoned in May 1882 owing to British political and press campaigns arguing that a tunnel would compromise Britain”s national defences.

In 1955 defence arguments were accepted to be irrelevant because of the dominance of air power. The British and French governments supported technical and geological surveys. Construction work commenced on both sides of the Channel in 1974, a government-funded project using twin tunnels on either side of a service tunnel, with capability for car shuttle wagons. In January 1975, to the dismay of the French partners, the British government cancelled the project. The government had changed to the Labour Party and there was uncertainty about EC membership, cost estimates had ballooned to 200% and the national economy was troubled. By this time the British Priestly TBM was ready and the Ministry of Transport was able to do a 300 m experimental drive.

In 1979 the “Mouse-hole Project” was suggested when the Conservatives came to power in Britain. The concept was a single-track rail tunnel with a service tunnel, but without shuttle terminals. The British government took no interest in funding the project but Prime Minister Margaret Thatcher said she had no objection to a privately-funded project. In 1981 British and French leaders Margaret Thatcher and François Mitterrand agreed to set up a working group to look into a privately funded project, and in April 1985 promoters were formally invited to submit scheme proposals. Four submissions were shortlisted:

  • A rail proposal based on the 1975 scheme presented by Channel Tunnel Group/France–Manche (CTG/F–M),
  • Eurobridge – a 4.5 km span suspension bridge with a roadway in an enclosed tube.
  • Euroroute – a 21 km tunnel between artificial islands approached by bridges.
  • Channel Expressway – large diameter road tunnels with mid-channel ventilation towers.

The cross-Channel ferry industry protested under the name “Flexilink”. In 1975 there was no campaign protesting against a fixed link, with one of the largest ferry operators (Sealink) being state owned. Flexilink continued rousing opposition throughout 1986 and 1987. Public opinion strongly favoured a drive-through tunnel, but ventilation issues, concerns about accident management, and fear of driver mesmerisation led to the only shortlisted rail submission, CTG/F-M, being awarded the project.

Fires

Three fires have occurred in the Channel Tunnel, all due to lorries carried on the heavy goods vehicle trains.

1996

On 18 November 1996 a fire broke out on a heavy goods vehicle shuttle wagon in the tunnel but nobody was seriously hurt. The exact cause is unknown, although it was not a Eurotunnel equipment or rolling stock problem; it may have been due to arson of a heavy goods vehicle. It is estimated that the heart of the fire reached 1,000 °C (1,800 °F), with the tunnel severely damaged over 46 metres (151 ft), with some 500 metres (1,640 ft) affected to some extent. Full operation recommenced six months after the fire.

2006

The tunnel was closed for several hours on 21 August 2006, when a lorry on a shuttle train caught fire.

2008

On 11 September 2008 a fire occurred in the Channel Tunnel at 13:57 GMT. The incident started on a freight-carrying vehicle train travelling towards France. The event occurred 11 kilometres (6.8 mi) from the French entrance to the tunnel. No one was killed but several people were taken to hospital suffering from smoke inhalation, and minor cuts and bruises. The tunnel was closed to all traffic, with the undamaged South Tunnel reopening for limited services two days later. A third of the north tunnel remains closed.

Engineering

Surveying undertaken in the 20 years before tunnel construction confirmed earlier speculations that a tunnel route could be bored through a chalk marl stratum. The chalk marl was conducive to tunnelling, with impermeability, ease of excavation and strength. While on the English side the chalk marl ran along the entire length of the tunnel, on the French side a length of 5 kilometres (3 mi) had variable and difficult geology. The Channel Tunnel consists of three bores: two 7.6-metre (25 ft) diameter rail tunnels, 30 metres (98 ft) apart, 50 kilometres (31 mi) in length with a 4.8-metre (16 ft) diameter service tunnel in between. There are also cross-passages and piston relief ducts. The service tunnel was used as a pilot tunnel, boring ahead of the main tunnels to determine the conditions. English access was provided at Shakespeare Cliff, while French access came from a shaft at Sangatte. The French side used five tunnel boring machines (TBMs), the English side used six. The service tunnel uses Service Tunnel Transport System (STTS) and Light Service Tunnel Vehicles (LADOGS). Fire safety was a critical design issue.

Between the portals at Beussingue and Castle Hill the tunnel is 50.5 kilometres (31 mi) long, with 3.3 kilometres (2 mi) under land on the French side, 9.3 kilometres (6 mi) under land on the UK side and 37.9 kilometres (24 mi) under sea. This makes the Channel Tunnel the second longest rail tunnel in the world, behind the Seikan Tunnel in Japan, but with the longest under-sea section. The average depth is 45 metres (148 ft) below the seabed. On the UK side, of the expected 5 million m³ of spoil approximately 1 million m³ was used for fill at the terminal site, and the remainder was deposited at Lower Shakespeare Cliff behind a seawall, reclaiming 74 acres (30 ha) of land. This land was then made into the Samphire Hoe Country Park. Environmental impact assessment did not identify any major risks for the project, and further studies into safety, noise, and air pollution were overall positive. However, environmental objections were raised over a high-speed link to London.

Tunnelling

Tunnelling between England and France was a major engineering challenge with the only precedent being the undersea Seikan Tunnel in Japan. A serious risk with underwater tunnels is major water inflow due to the water pressure from the sea above under weak ground conditions. The Channel Tunnel also had the challenge of time – being privately funded, early financial return was paramount.

The objective was to construct: two 7.6-metre (25 ft) diameter rail tunnels, 30 metres (98 ft) apart, 50 kilometres (31 mi) in length; a 4.8-metre (16 ft) diameter service tunnel between the two main tunnels; pairs of 3.3-metre (11 ft) diameter cross-passages linking the rail tunnels to the service tunnel at 375-metre (1,230 ft) spacing; piston relief ducts 2-metre (7 ft) diameter connecting the rail tunnels at 250-metre (820 ft) spacing; two undersea crossover caverns to connect the rail tunnels. The service tunnel always preceded the main tunnels by at least 1 kilometre (0.6 mi) to ascertain the ground conditions, experience with tunnelling through chalk had occurred in the mining industry. The undersea crossover caverns were a complex engineering problem. The French cavern was based on the Mount Baker Ridge freeway tunnel in the USA. The UK cavern was dug from the service tunnel ahead of the main tunnels to avoid delay.

Precast segmental linings in the main TBM drives were used, but different solutions were used on the English and French sides. On the French side neoprene and grout sealed bolted linings made of cast iron or high-strength reinforced concrete were used. On the English side the main requirement was for speed, and bolting of cast-iron lining segments was only carried out in areas of poor geology. In the UK rail tunnels eight lining segments plus a key segment were used, on the French side five segments plus a key segment. On the French side a 55-metre (180 ft) diameter 75-metre (246 ft) deep grout-curtained shaft at Sangatte was used for access. On the English side a marshalling area was 140 metres (459 ft) below the top of Shakespeare Cliff, and the New Austrian Tunnelling method (NATM) was first applied in the chalk marl here. On the English side the land tunnels were driven from Shakespeare Cliff, the same place as the marine tunnels, not from Folkestone. The platform at the base of the cliff was not large enough for all of the drives, and despite environmental objections tunnel spoil was placed behind a reinforced concrete seawall, on condition of placing the chalk in an enclosed lagoon to avoid wide dispersal of chalk fines. Owing to limited space the precast lining factory was on the Isle of Grain in the Thames estuary.

On the French side, owing to the greater permeability of water, earth pressure balance TBMs with open and closed modes were used. The TBMs were of a closed nature during the initial 5 kilometres (3 mi) but then operated as open, boring through the chalk marl stratum. This minimised the impact to the ground and allowed high water pressures to be withstood, and it also alleviated the need to grout ahead of the tunnel. The French effort required five TBMs: two main marine machines, one main land machine (the short land drives of 3 km allowed one TBM to complete the first drive then reverse direction and complete the other), and two service tunnel machines. On the English side the simpler geology allowed faster open-faced TBMs.

Six machines were used, all commencing digging from Shakespeare Cliff, three marine bound and three for the land tunnels. Towards the completion of the undersea drives the UK TBMs were driven steeply downwards and buried clear of the tunnel. The French TBMs then completed the tunnel and were dismantled. A 900 mm gauge railway was used on the English side during construction.

In Fiction

The tunnel was featured in the explosive climax of the 1996 blockbuster film Mission: Impossible, where a helicopter entered the tunnel. The tunnel mouth, the inside of the tunnel, the TGV train and the helicopter in the film were all computer generated imagery, with the entrance to the tunnel shot against scenes of a railway line in Scotland. This was necessary because of significant deviations from reality: the tunnel in the film had two tracks in a single tube (to allow space for the helicopter and to have passing trains), and there was no overhead line (to allow descent from the helicopter). The type of train seen computer animated in the film, TGV Réseau, (which, unlike the Eurostars, can only be powered from overhead wire) does not run through the tunnel. Other inaccuracies included the train changing from one side of the track to another in various shots.

An episode of the popular sitcom Seinfeld featured a fictional action movie named Chunnel, the premise of which included the President of the United States” daughter being trapped in the Channel Tunnel