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Channel Tunnel

The Channel Tunnel (Le tunnel sous la Manche), also known as the Chunnel, is a 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 deep. It has the longest undersea portion of any tunnel in the world, although Japan's Seikan Tunnel is longer overall at and reaches a depth of .

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

Key dates
1802 Albert Mathieu put forward a cross-Channel tunnel proposal.
January 1974 A UK–France government backed scheme that started in 1974 was cancelled.
February 1986 The Treaty of Canterbury was signed allowing the project to proceed.
June 1988 First tunnelling commenced in France.
December 1988 UK TBM commenced operation.
December 1990 The service tunnel broke through under the Channel.
May 1994 The tunnel was formally opened by the Queen and President Mitterand.
Mid 1994 Freight and passenger trains commenced operation.
November 1996 A fire in a lorry shuttle severely damaged the tunnel
November 2007 High Speed 1, linking London to the tunnel, opened.
September 2008 A second lorry fire closes the tunnel, with 32 people evacuated

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.

Proposals and attempts

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 diameter Beumont-English boring machine dug a pilot tunnel from Shakespeare Cliff. On the French side a similar machine dug 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, and
  • 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.

Organisation

The Channel Tunnel Group consisted of two banks and five construction companies and the French equivalent, France–Manche, consisted of three banks and five construction companies. The role of the banks was to advise on financing and secure loan commitments. On 2 July 1985 the groups formed Channel Tunnel Group/France–Manche (CTG/F–M). Their submission to the British and French governments was drawn from the 1975 project, including 11 volumes and a substantial environmental impact statement.

The design and construction was done by the ten construction companies in the CTG/F-M group. The French terminal and boring from Sangatte was undertaken by the five French construction companies in the joint venture group GIE Transmanche Construction. The English Terminal and boring from Shakespeare Cliff was undertaken by five English construction companies in the Trankslink Joint Venture. The two partnerships were linked by TransManche Link (TML), a binational project organisation. The Maître d'Oeuvre was a supervisory engineering body employed by Eurotunnel under the terms of the concession that monitored project activity and reported back to the governments and banks.

In France, with its long tradition of infrastructure investment, the project garnered widespread approval and in April 1987 the French National Assembly gave unanimous support and after a public inquiry the Senate gave unanimous support in June 1987. In Britain, select committees examined the proposal, making history by holding hearings outside of Westminster, in Kent. In February 1987 the third reading of the Channel Tunnel Bill occurred in the House of Commons, and was carried by 94 votes to 22. The Channel Tunnel Act passed into British law in July.

The Channel Tunnel is a build-own-operate-transfer (BOOT) project with a concession. TML would design and build the tunnel, but financing was through a separate legal entity: Eurotunnel. Eurotunnel absorbed CTG/F-M and signed a construction contract with TML; however, the British and French governments controlled final engineering and safety decisions. The British and French governments gave Eurotunnel a 55- (later 65-) year operating concession to repay loans and pay dividends. A Railway Usage Agreement was signed between Eurotunnel, British Rail and the Société Nationale des Chemins de fer Français guaranteeing future revenue in exchange for the railways obtaining half of the tunnel's capacity.

Private funding for such a complex infrastructure project was of unprecedented scale. An initial equity of £45 million was raised by CTG/F-M, increased by £206 million private institutional placement, £770 million was raised in a public share offer that included press and television advertisements, a syndicated bank load and letter of credit arranged £5 billion. Privately financed, the total investment costs at 1985 prices were £2600 million. At the 1994 completion actual costs were, in 1985 prices, £4650 million: an 80% cost overrun. The cost overrun was partly due to enhanced safety, security, and environmental demands. Financing costs were 140% higher than forecast.

Progress

A small two-inch (50-mm) diameter pilot hole allowed the service tunnel to break through without ceremony on 30 October 1990. On 1 December 1990 Englishman Graham Fagg and Frenchman Phillipe Cozette broke through the service tunnel with the media watching. Eurotunnel completed the tunnel on time, and the tunnel was officially opened by Queen Elizabeth II and French President François Mitterrand in a ceremony held in Calais on 6 May 1994. The Queen travelled through the tunnel to Calais on a Eurostar train, which stopped nose to nose with the train that carried President Mitterrand from Paris. Following the ceremony President Mitterrand and the Queen travelled on Le Shuttle to a similar ceremony in Folkestone.

The Channel Tunnel Rail Link (CTRL), now called High Speed 1, runs from St Pancras railway station in London to the Channel Tunnel portal at Folkestone in Kent. It cost £5.8 billion. On 16 September 2003 UK Prime Minister Tony Blair opened the first section of High Speed 1, from Folkestone to north Kent. On 6 November 2007 the Queen officially opened High Speed 1 and St Pancras International station, replacing the original slower link to Waterloo International railway station. On High Speed 1 trains travel at speeds up to , the journey from London to Paris taking 2 hours 15 minutes and London to Brussels taking 1 hour 51 minutes.

Usage and operation

Services offered by the tunnel are:

Both the freight and passenger traffic forecasts that led to the construction of the tunnel were largely and universally overestimated. Particularly, Eurotunnel's commissioned forecasts were over-predictions. Although the captured share of Channel crossings (competing with air and sea) was forecast correctly, high competition and reduced tariffs has led to low revenue. Overall cross-Channel traffic was overestimated – a cost benefit analysis of the Channel Tunnel indicated that the British economy would have been better off if the Tunnel had not been constructed.

Channel Tunnel passenger volumes were overestimated, peaking at 18.4 million in 1998, and down to 14.7 million in 2003. At the time of deciding to build the tunnel 15.9 million passengers were predicted for Eurostar trains in the opening year. In 1995, the opening year, actual numbers were 2.9 million. Passenger numbers in 2001 were 6.9 million. Tunnel freight traffic volumes have been erratic, with a decrease during 1997 due to a closure caused by a fire in a freight shuttle. The total freight crossings increased over the period, indicating the substitutability of the tunnel by sea crossings. The tunnel has achieved a cross-Channel freight traffic market share close to or above Eurotunnel's 1980s predictions but Eurotunnel's 1990 and 1994 predictions were overestimates. The first year freight prediction was 7.2 million gross tonnes, however, the 1995 figure was 1.3 million gross tonnes, in 2001 this had increased to 2.4 million tonnes. Freight traffic growth has occurred since opening, with 18.4 million tonnes recorded in 2003.

Shares in Eurotunnel were issued at £3.50 per share on 9 December 1987. By mid-1989 the price had risen to £11.00. Delays and cost overruns led to the share price dropping; during demonstration runs in October 1994 the share price reached an all-time low value. Eurotunnel suspended payment on its debt in September 1995 to avoid bankruptcy. In December 1997 the British and French governments extended Eurotunnel's operating concession by 34 years to 2086. Financial restructuring of Eurotunnel occurred in mid-1998, reducing debt and financial charges. Despite the restructuring The Economist reported in 1998 that to break even Eurotunnel would have to increase fares, traffic and marketshare for sustainability.

Under the terms of the Concession Eurotunnel was obliged to investigate a cross-Channel road tunnel. In December 1999 road and rail tunnel proposals were presented to the British and French governments, but it was stressed that there was not enough demand for a second tunnel. A three-way treaty between the United Kingdom, France and Belgium governs border controls, with the establishment of control zones wherein the officers of the other nation may exercise limited customs and law enforcement powers. For most purposes these are at either end of the tunnel, with the French border controls on the UK side of the tunnel and vice versa. For certain city-to-city trains the train itself represents a control zone. A binational emergency plan coordinates UK and French emergency activities.

Eurotunnel's freight subsidiary is Europorte 2. In September 2006 EWS, the UK's largest rail freight operator, announced that owing to cessation of UK-French government subsidies of £52 million per annum to cover the Channel Tunnel "Minimum User Charge" (a subsidy of around £13,000 per train, at a traffic level of 4,000 trains per annum), freight trains would stop running after 30 November.

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 , with the tunnel severely damaged over , with some 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 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..

Regional impact

A 1996 report from the European Commission predicted that Kent and Nord-Pas de Calais had to face increased traffic volumes due to general growth of cross-Channel traffic and traffic attracted by the tunnel. In Kent, a high-speed rail line to London would transfer traffic from road to rail. Kent's regional development would benefit from the tunnel, but being so close to London restricts the benefits. Gains are in the traditional industries and are largely dependent on the development of Ashford International passenger station, without which Kent would be totally dependent on London's expansion. Nord-Pas-de-Calais enjoys a strong internal symbolic effect of the Tunnel which results in significant gains in manufacturing.

The removal of a bottleneck by means like the Channel Tunnel does not necessarily induce economic gains in all adjacent regions, the image of a region being connected to the European high-speed transport and active political response are more important for regional economic development. Tunnel-induced regional development is small compared to general economic growth. The South East of England is likely to benefit developmentally and socially from faster and cheaper transport to continental Europe, but the benefits are unlikely to be equally distributed throughout the region. The overall environmental impact is almost certainly negative.

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.

Asylum and immigration

Illegal immigrants and would-be asylum seekers have been known to use the tunnel to attempt to enter Britain. By 1997, the problem had already attracted international press attention, and the French Red Cross opened a refugee centre at Sangatte in 1999, using a warehouse once used for tunnel construction; by 2002 it housed up to 1500 persons at a time, most of them trying to get to the UK. At one point, large numbers came from Afghanistan, Iraq and Iran, but African and Eastern European countries are also represented. Most migrants who got into Britain found some way to ride a freight train, but others used Eurostar. Though the facilities were fenced, airtight security was deemed impossible; refugees would even jump from bridges onto moving trains. In several incidents people were injured during the crossing; others tampered with railway equipment, causing delays and requiring repairs. Eurotunnel said it was losing £5m per month because of the problem. A dozen refugees have died in crossing attempts. In 2001 and 2002, several riots broke out at Sangatte and groups of refugees (up to 550 in a December 2001 incident) stormed the fences and attempted to enter en masse. Immigrants have also arrived as legitimate Eurostar passengers without proper entry papers.

Local authorities in both France and the UK called for the closure of Sangatte, and Eurotunnel twice sought an injunction against the centre. The United Kingdom blamed France for allowing Sangatte to open, and France blamed the UK for its lax asylum rules and the EU for not having a uniform immigration policy. The cause célèbre nature of the problem even included journalists detained as they followed refugees onto railway property. In 2002, after the European Commission told France that it was in breach of European Union rules on the free transfer of goods, because of the delays and closures as a result of its poor security, a double fence was built at a cost of £5 million, reducing the numbers of refugees detected each week reaching Britain on goods trains from 250 to almost none. Other measures included CCTV cameras and increased police patrols. At the end of 2002, the Sangatte centre was closed after the UK and France agreed to take shares of the refugees.

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 had variable and difficult geology. The Channel Tunnel consists of three bores: two diameter rail tunnels, apart, in length with a 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 long, with under land on the French side, under land on the UK side and 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 below the seabed. On the UK side, of the expected 5 million 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 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.

Surveying

Marine soundings and samplings by Thomé de Gamond were carried out during 1833–67, establishing the seabed depth at a maximum of 55 m and the continuity of geological strata (layers). Surveying continued over many years, with 166 marine and 70 land-deep boreholes being drilled and over 4000 line kilometres of marine geophysical survey completed. Surveys were undertaken in 1958–59, 1964–65, 1972–74 and 1986–88.

The surveying in 1958–59 catered for immersed tube and bridge designs as well as a bored tunnel, and thus a wide area was investigated. At this time marine geophysics surveying for engineering projects was in its infancy, with poor positioning and resolution from seismic profiling. The 1964-65 surveys concentrated on a northerly route that left the English coast at Dover harbour, using 70 boreholes an area of deeply weathered rock with high permeability was located just south of Dover harbour.

Given the previous survey results and access constraints a more southerly route was investigated in the 1972–73 survey and the route was confirmed to be feasible. Information for the tunnelling project also came from work before the 1975 cancellation. On the French side at Sangatte a deep shaft with adits was made. On the English side at Shakespeare Cliff the government allowed of diameter tunnel to be driven. The actual tunnel alignment, method of excavation and support were essentially the same as the 1975 attempt. In the 1986–97 survey, previous findings were reinforced and the nature of the gault clay and tunnelling medium, chalk marl that made up 85% of the route, were investigated. Geophysical techniques from the oil industry were employed.

Geology

Successful tunnelling under the channel required a sound understanding of the topography and geology and the selection of the best rock strata to tunnel through. The geology generally consists of northeasterly dipping Cretaceous strata, part of the northern limb of the Wealden-Boulonnais dome. Characteristics include:

  • as observed by Verstegan in 1698, the chalk of the cliffs on either side of the Channel is continuous, and contains no major faulting
  • the cliffs consist of four geological strata, marine sediments laid down 90–100 million years ago; pervious upper and middle chalk above slightly pervious lower chalk and finally impermeable Gault Clay. A sandy stratum, glauconitic marl (tortia), is in between the chalk marl and gault clay
  • a 25–30 metre (82–98 ft) layer of chalk marl (French: craie bleue) in the lower third of the lower chalk appeared to present the best tunnelling medium. The chalk has a clay content of 30–40% providing impermeability to groundwater yet relatively easy excavation with strength allowing minimal support. Ideally the tunnel would be bored in the bottom 15 m of the chalk marl, allowing water inflow from fractures and joints to be minimised, but above the gault clay that would increase stress on the tunnel lining and swell and soften when wet.

On the English side of the channel the strata dip less than 5°, however on the French side this increases to 20°. Jointing and faulting is present on both the English and French sides. On the English side only minor faults of displacement less than exist. On the French side displacements of up to are present owing to the Quenocs anticlinal fold. The faults are of limited width, filled with calcite, pyrite and remoulded clay. The increased dip and faulting restricted the selection of route on the French side. To avoid confusion microfossil assemblages were used to classify the chalk marl. On the French side, particularly near the coast, the chalk was harder and brittler and more fractured than on the English side. This led to the adoption of different tunnelling techniques on the French and English sides.

No major geological hazards were identified, however the Quaternary undersea valley Fosse Dangaered, and Castle Hill landslip located at the English portal were concerning. Identified by the 1964–65 geophysical survey the Fosse Dangaered is an infilled valley system extending below the seabed, south of the tunnel route, located mid-channel. A 1986 survey showed that a tributary crossed the path of the tunnel and so the tunnel route was made as far north and deep as possible. The English terminal had to be located in the Castle Hill landslip, which consists of displaced and tipping blocks of lower chalk, glauconitic marl and gault debris. Thus the area was stabilised by buttressing and inserting drainage adits. The service tunnels were pilot tunnels preceding the main tunnels so that the geology, areas of crushed rock and zones of high water inflow could be predicted. Exploratory probing took place in the service tunnels in the form of extensive forward probing, vertical downward probes and sideways probing.

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 diameter rail tunnels, apart, in length; a diameter service tunnel between the two main tunnels; pairs of diameter cross-passages linking the rail tunnels to the service tunnel at spacing; piston relief ducts diameter connecting the rail tunnels at spacing; two undersea crossover caverns to connect the rail tunnels. The service tunnel always preceded the main tunnels by at least 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 diameter deep grout-curtained shaft at Sangatte was used for access. On the English side a marshalling area was 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 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.

Railway design and rolling stock

There are three communication systems in the tunnel: concession radio (CR) for mobile vehicles and personnel within Eurotunnel's Concession (terminals, tunnels, coastal shafts); track-to-train radio (TTR) for secure speech and data between trains and the railway control centre; Shuttle internal radio (SIR) for communication between shuttle crew and to passengers over car radios. All tunnel services run on electricity, shared equally from English and French sources. Power is delivered to the locomotives via an overhead catenary system. A cab signalling system is used that gives information directly to train drivers on a display. There is automatic train protection (ATP) that stops the train if the speed differs from that indicated on the in-cab display. TVM430, as used on TGV Nord, is used in the tunnel. The American Sonneville International Corporation track system was used in the tunnel, ballasted track was ruled out owing to maintenance constraints and a need for geometric stability. The Sonneville system has UIC60 rails on 900A grade resting on microcellular EVA pads, bolted into concrete.

Initially 38 Le Shuttle locomotives were commissioned, working in pairs with one at each end of a shuttle train. The shuttles have two separate halves: single and double deck. Each half has two loading/unloading wagons and 12 carrier wagons. Eurotunnel's original order was for 9 shuttles. 46 Class 92 locomotives for hauling freight and overnight passenger trains were commissioned, which can run on both overhead AC and third-rail DC power. Freight shuttles also have two halves, with each half containing one loading wagon, one unloading wagon and 14 carrier wagons. There is a club car behind the leading locomotive. Eurotunnel originally ordered 6 freight shuttles. 31 Eurostar trains, based on the French TGV with many modifications for safety within the tunnel, were commissioned, with split ownership between British Rail, French National Railway Company and National Railway Company of Belgium. British Rail ordered seven more for services north of London.

Services

The service tunnel is used for access to technical equipment in cross-passages and equipment rooms, to provide fresh-air ventilation, and for emergency evacuation. The Service Tunnel Transport System (STTS) allows fast access to all areas of the tunnel. The service vehicles are rubber-tyred with a buried guidance wire system. 24 STTS vehicles were made, and are used mainly for maintenance but also for firefighting and in emergencies. "Pods" with different purposes, up to a payload of 2.5–5 tonnes, are inserted into the side of the vehicles. The STTS vehicles cannot turn around within the tunnel, and are driven from either end. The maximum speed is when the steering is locked. A smaller fleet of 15 Light Service Tunnel Vehicles (LADOGS) were introduced to supplement the STTSs. The LADOGS have a short wheelbase with a 3.4 m turning circle allowing two-point turns within the service tunnel. Steering cannot be locked like the STTS vehicles, and maximum speed is . Pods up to 1 tonne can be loaded onto the rear of the vehicles. Drivers in the tunnel sit on the right, and the vehicles drive on the left. Owing to the risk of French personnel driving on their native right side of the road, sensors in the road vehicles alert the driver if the vehicle strays to the right side of the tunnel.

The three tunnels contain 6000 tonnes of air that needs to be conditioned for comfort and safety. Air is supplied from ventilation buildings at Shakespeare Cliff and Sangatte, with each building capable of full duty providing 100% standby capacity. Supplementary ventilation also exists on either side of the tunnel. In the event of a fire, ventilation is used to keep smoke out of the service tunnel and move smoke in one direction in the main tunnel to give passengers clean air. The Channel Tunnel was the first mainline railway tunnel to have special cooling equipment. Heat is generated from traction equipment and drag. The design limit was set at , using a mechanical cooling system with refrigeration plants on both the English and French sides that run chilled water circulating in pipes within the tunnel.

Trains travelling at high speed create piston-effect pressure changes that can affect passenger comfort, ventilation systems, tunnel doors, fans and the structure of the trains, and drag on the trains. Piston relief ducts of diameter were chosen to solve the problem, with 4 ducts per kilometre to give close to optimum results. Unfortunately this design led to unacceptable lateral forces on the trains so a reduction in train speed was required and restrictors were installed in the ducts.

The safety issue of a fire on a passenger-vehicle shuttle garnered much attention, with Eurotunnel itself noting that fire was the risk gathering the most attention in a 1994 Safety Case for three reasons: ferry companies opposed to passengers being allowed to remain with their cars; Home Office statistics indicating that car fires had doubled in ten years; and the long length of the tunnel. Eurotunnel commissioned the UK Fire Research Station to give reports of vehicle fires, as well as liaising with Kent Fire Brigade to gather vehicle fire statistics over one year. Fire tests took place at the French Mines Research Establishment with a mock wagon used to investigate how cars burned. The wagon door systems are designed to withstand fire inside the wagon for 30 minutes, longer than the transit time of 27 minutes. Wagon air conditioning units help to purge dangerous fumes from inside the wagon before travel. Each wagon has a fire detection and extinguishing system, with sensing of ions or ultraviolet radiation, smoke and gases that can trigger halon gas to quench a fire. Since the Heavy Goods Vehicle (HGV) wagons are not covered, fire sensors are located on the loading wagon and in the tunnel itself. A 10-inch (254-mm) water main in the service tunnel provides water to the main tunnels at intervals. The ventilation system can control smoke movement. Special arrival sidings exist to accept a train that is on fire, as the train is not allowed to stop whilst on fire in the tunnel. Eurotunnel has banned a wide range of hazardous goods from travelling in the tunnel. Two STTS vehicles with firefighting pods are on duty at all times, with a maximum delay of 10 minutes before they reach a burning train.

Terminals

The terminals sites are at Cheriton (Folkestone in the United Kingdom) and Coquelles (Calais in France). The terminals are unique facilities designed to transfer vehicles from the motorway onto trains at a rate of 700 cars and 113 heavy vehicles per hour. The UK site uses the M20 motorway. The terminals are organised with the frontier controls juxtaposed with the entry to the system to allow travellers to go onto the motorway at the destination country immediately after leaving the shuttle. The area of the UK site was severely constrained and the design was challenging. The French layout was achieved more easily. To achieve design output, the shuttles accept cars on double-decks; for flexibility, ramps were placed inside the shuttles to provide access to the top decks. At Folkestone there is of mainline track and 45 turnouts with eight platforms. At Calais there is of track with 44 turnouts. At the terminals the shuttle trains traverse a figure eight to reduce uneven wear on the wheels.

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.

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