Channel Tunnel

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Map of the Channel Tunnel

The Channel Tunnel (French: Le tunnel sous la Manche) is a 31-mile undersea rail tunnel linking Folkestone, Kent with Coquelles near Calais in northern France beneath the English Channel at the Straits of Dover.

The tunnel carries three sorts of service: passenger rail services ("Eurostar"); freight trains; and roll-on/roll-off vehicle transport ("Eurotunnel Shuttle"). The Eurotunnel Shuttle is the largest such service in the world. The tunnel connects end-to-end with the LGV Nord and High Speed 1 high-speed railway lines. In 1996 the American Society of Civil Engineers identified the tunnel as one of the "Seven Wonders of the Modern World".

At its lowest point, the tunnel is 46½ feet below sea level.[1][2][3] At 23½ miles, the Channel Tunnel has the longest undersea portion of any tunnel in the world, notwithstanding that the Seikan Tunnel in Japan is longer overall.

History

Ideas for a cross-Channel fixed link appeared as early as 1802,[4][5] during the Napoleonic Wars. It resurg=faced in peacetime, but British political and press pressure over compromised national security stalled attempts to construct a tunnel.[6]

A tunnel was actually begun during the nineteenth century, but was abandoned having barely bored beneath the sea. A more organised project began as a government project in 1974, but this too was abandoned for financial and practical reasons.

The eventual successful project began with the Treaty of Canterbury between the British and French governments. It was to be a privately funded project: on the British side Parliament forbade the Government from spending any money on it. The joint venture company which won the task of building the tunnel was Eurotunnel, and the company began construction in 1988. The tunnel opened in 1994, having come in at 80% over its predicted budget.[7]

Problems

Since its construction, the tunnel has faced several problems. Fires have disrupted operation of the tunnel. Illegal immigrants and asylum seekers have attempted to use the tunnel to enter the United Kingdom,[8] causing a minor diplomatic disagreement over the siting of the Sangatte refugee camp, which was eventually closed in 2002.[9]

Origins

Proposals and attempts

Key dates
1802 Albert Mathieu put forward a cross-Channel tunnel proposal.
1875 The Channel Tunnel Company Ltd[10] began preliminary trials
1882 The Abbot's Cliff heading had reached 897 yards and that at Shakespeare Cliff was 2,040 yards in length
January 1975 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 boring machine commenced operation
December 1990 The service tunnel broke through under the Channel
May 1994 The tunnel was formally opened by HM The Queen and President Mitterrand
Mid 1994 Freight and passenger trains began to run
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 Another fire in a lorry shuttle severely damaged the tunnel
December 2009 Eurostar trains stranded in the tunnel due to melting snow affecting the trains' electrical hardware

In 1802, French mining engineer Albert Mathieu put forward a proposal to tunnel under the English Channel, with illumination from oil lamps, horse-drawn coaches, and an artificial island mid-Channel for changing horses.[4]

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[11] at a cost of 170 million francs, or less than £7 million.[12]

Thomé de Gamond's 1856 plan for a cross-Channel link, with a port/airshaft on the Varne sandbank mid-Channel

In 1865, a deputation led by George Ward Hunt proposed the idea of a tunnel to the Chancellor of the Exchequer of the day, William Ewart Gladstone.[13]

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 Edward 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 British side a 7-foot diameter Beaumont-English boring machine dug a 1.18-mile pilot tunnel from Shakespeare Cliff. On the French side, a similar machine dug 1 mile from Sangatte. The project was abandoned in May 1882, owing to British political and press campaigns asserting that a tunnel would compromise Britain's national defences.[6] These early works were encountered more than a century later during the TML project.

In 1919, during the Paris Peace Conference, British Prime Minister David Lloyd George repeatedly brought up the idea of a Channel tunnel as a way of reassuring France about British willingness to defend against another German attack. The French did not take the idea seriously and nothing came of Lloyd George's proposal.[14]

In 1929 there was another proposal for the building a channel tunnel, but nothing came of this discussion and the idea was shelved. Proponents estimated construction to be about US$150 million. The engineers addressed the concerns of both nations' military leaders by designing two sumps—one near the coast of each country—that could be flooded at will to block the tunnel. This design feature did not override the concerns of both nations' military leaders, and other concerns for hordes of undesirable tourists who would disrupt British habits of living.[15]

In 1955, defence arguments were accepted to be irrelevant because of the dominance of air power; thus, both the British and French governments supported technical and geological surveys. A detailed geological survey was carried out in 1964–65.[16] 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; an election had brought a Labour government and there was uncertainty about EEC membership, cost estimates had ballooned to 200% and the national economy was troubled. By this time the British tunnel boring machine was ready and the Ministry of Transport was able to do a 330-yard experimental drive.[6] This short tunnel was reused as the starting and access point for tunnelling operations from the British side.

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 bridge with a central span consisting of a suspension bridge 2.8 miles long, the roadway in an enclosed tube;
  • Euroroute: a 13-mile tunnel between artificial islands approached by bridges; and
  • Channel Expressway: large diameter road tunnels with mid-channel ventilation towers.[6]

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.[6] 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.[6]

Arrangement

The British Channel Tunnel Group consisted of two banks and five construction companies, while their French counterparts, France–Manche, consisted of three banks and five construction companies. 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.[6]

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 Kentish Terminal and boring from Shakespeare Cliff were undertaken by the five British construction companies in the Trankslink Joint Venture. The two partnerships were linked by TransManche Link (TML), a bi-national project organisation.[6] 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.[17]

In France, with its long tradition of infrastructure investment, the project garnered widespread approval. In April the French National Assembly gave unanimous support and, in June 1987, after a public inquiry, the Senate gave unanimous support. In Britain, select committees examined the proposal, making history by holding hearings not in of Westminster but in Kent. In February 1987, the third reading of the Channel Tunnel Bill took place in the House of Commons, and was carried by 94 votes to 22. The Channel Tunnel Act 1987 gained Royal assent and passed into law in July.[6] Parliamentary support for the project came partly from provincial members of Parliament on the basis of promises of regional Eurostar through-train services which have never materialised; the promises were repeated in 1996 when the contract for construction of the Channel Tunnel Rail Link was awarded.

The Channel Tunnel is a build-own-operate-transfer (BOOT) project with a concession.[7] 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, which are now in the hands of the Channel Tunnel Safety Authority. The British and French governments gave Eurotunnel a 55- (later 65-) year operating concession to repay loan facilities 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 loan and letter of credit arranged £5 billion.[6] 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.[18] The cost overrun was partly due to enhanced safety, security, and environmental demands.[7] Financing costs were 140% higher than forecast.[19]

Construction

Working from both the British side and the French side of the Channel, eleven tunnel boring machines cut through chalk marl to construct two rail tunnels and a service tunnel. The vehicle shuttle terminals are at Cheriton (part of Folkestone) and Coquelles, and are connected to the British and French motorways (the M20 in Kent and the A16 autoroute in France respectively).

Tunnelling started in 1988, and the tunnel began operating in 1994.[20] In 1985 prices, the total construction cost was £4.650 billion; an 80% cost overrun. At the peak of construction 15,000 people were employed with daily expenditure over £3 million.[21] Ten workers, eight of them British, were killed during construction between 1987 and 1993, most in the first few months of boring.[22][23][24]

Completion

The first passenger trains, 7 May 1994

A small, two-inch diameter pilot hole allowed the service tunnel to break through without ceremony on 30 October 1990. On 1 December 1990, Briton Graham Fagg and Frenchman Phillippe Cozette broke through the service tunnel with the media watching.[25] Eurotunnel completed the tunnel on time,[7] and the tunnel was officially opened one year later than originally planned by Queen Elizabeth II and the 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.[26] Following the ceremony President Mitterrand and the Queen travelled on "Le Shuttle" to a similar ceremony in Folkestone.[26] The tunnel was thus "officially" open but not in reality: a full public service did not start for several months.

Channel Tunnel Rail Link

The Channel Tunnel Rail Link (CTRL), now called "High Speed 1", runs 69 miles 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 the Prime Minister, Anthony 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,[27] replacing the original slower link to Waterloo International railway station.

On High Speed 1 trains travelling at speeds up to 186 miles an hour, the journey from London to Paris takes 2 hours 15 minutes and London to Brussels takes 1 hour 51 minutes.[28]

Engineering

The Channel Tunnel exhibit at the National Railway Museum in York

Surveying undertaken in the twenty 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 British side the chalk marl ran along the entire length of the tunnel, on the French side a length of 3 miles had variable and difficult geology.

The Channel Tunnel consists of three bores: two 25-foot diameter rail tunnels, 100 feet apart, 31 miles in length with a service tunnel in between of diameter 15 feet 9 inches. 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. British 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 British 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 in Folkestone the tunnel is 31 miles long, with two miles under land on the French side, 5¾ miles under land on the Kentish side and 23½ miles under the sea.[2] This makes the Channel Tunnel the longest rail tunnel in the world after the Seikan Tunnel in Japan, but the tunnel with the longest under-sea section.[29] The average depth is 147½ feet below the seabed.[30] On the British side, of the expected 6½ million cubic yards of spoil approximately 1.3 million cubic yards was used for fill at the terminal site, and the remainder was deposited at Lower Shakespeare Cliff behind a seawall, reclaiming 74 acres[21] of land.[31] 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.[7]

Geology

Geological profile along the tunnel

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

  • Continuous chalk on the cliffs on either side of the Channel containing no major faulting, as observed by Verstegan in 1698
  • 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
  • An layer of 80-10 feet 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 49 feet 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.[32]

On the British 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 British and French sides. On the British side, only minor faults of displacement less than six feet exist. On the French side, displacements of up to 49 feet 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 more brittle, and more fractured than on the British side. This led to the adoption of different tunnelling techniques on the French and British sides.[33]

The Quaternary undersea valley Fosse Dangaered, and Castle Hill landslip, located at the British portal, caused concerns. Identified by the 1964-65 geophysical survey, the Fosse Dangaered is an infilled valley system extending 260 feet below the seabed, 1547 yards 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 British 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.[34] 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.[35]

Surveying

Marine soundings and samplings by Thomé de Gamond were carried out during 1833–1867, establishing the seabed depth at a maximum of 180 feet and the continuity of geological strata. Surveying continued over many years, with 166 marine and 70 land-deep boreholes being drilled and over 4,000-line-kilometres of marine geophysical survey completed.[34] Surveys were undertaken in 1958–1959, 1964–1965, 1972–1974 and 1986–1988.

The surveying in 1958–1959 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 1964–1965 surveys concentrated on a northerly route that left the British coast at Dover harbour; using 70 boreholes, an area of deeply weathered rock with high permeability was located just south of Dover harbour.[36]

Given the previous survey results and access constraints, a more southerly route was investigated in the 1972–1973 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 British side at Shakespeare Cliff, the government allowed 820 feet of 14' 9" diameter tunnel to be driven. The actual tunnel alignment, method of excavation and support were essentially the same as the 1975 attempt. In the 1986–1997 survey, previous findings were reinforced and the nature of the gault clay and the tunnelling medium (chalk marl that made up 85% of the route) were investigated. Geophysical techniques from the oil industry were employed.[36]

Tunnelling

Typical tunnel cross section

Tunnelling between Great Britain and France was a major engineering challenge. 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 important.

The objective was to construct:

  • Two 25-foot diameter rail tunnels, 98 feet apart, 31 miles in length;
  • A 16-foot diameter service tunnel between the two main tunnels;
  • Pairs of 11-foot diameter cross-passages linking the rail tunnels to the service tunnel at 1,230-foot spacing;
  • Piston relief ducts seven feet in diameter connecting the rail tunnels at 820-foot spacing;
  • Two undersea crossover caverns to connect the rail tunnels.[37]

The service tunnel always preceded the main tunnels by at least a thousand yards to ascertain the ground conditions. There was plenty of experience with tunnelling through chalk 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 America. The British 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 British 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 British 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.[38] On the French side, a 180-foot diameter, 246-foot deep grout-curtained shaft at Sangatte was used for access. On the British side, a marshalling area was 459 feet below the top of Shakespeare Cliff, and the New Austrian Tunnelling method (NATM) was first applied in the chalk marl here. On the British 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.[34]

On the French side, owing to the greater permeability to water, earth pressure balance TBMs with open and closed modes were used. The TBMs were of a closed nature during the initial three miles, but then operated as open, boring through the chalk marl stratum.[34] 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, and two service tunnel machines. On the British side, the simpler geology allowed faster open-faced TBMs.[39] Six machines were used, all commenced digging from Shakespeare Cliff, three marine-bound and three for the land tunnels.[34] Towards the completion of the undersea drives, the UK TBMs were driven steeply downwards and buried clear of the tunnel. These buried TBMs were then used to provide an electrical earth. The French TBMs then completed the tunnel and were dismantled.[40] A 900 mm gauge railway was used on the British side during construction.[41]

In contrast to the British machines, which were simply given alphanumeric names, the French tunnelling machines were all named after women: Brigitte, Europa, Catherine, Virginie, Pascaline, Séverine.[42]

Operation

Services offered by the tunnel are:

  • Eurotunnel Shuttle (formerly Le Shuttle) roll-on roll-off shuttle service for road vehicles,
  • Eurostar passenger trains,
  • Freight trains.[43]

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.[7] 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.

With the liberalisation of international rail services, the tunnel and High Speed 1 have been open to competition since 2010. There have been a number of operators interested in running services including Deutsche Bahn, through the tunnel and along High Speed 1 to London.

Terminals

A Peugeot 807 entering a shuttle wagon at the French end

The terminals sites are at Cheriton, Kent (by Folkestone) and Coquelles (near Calais). The terminals are unique facilities designed to transfer vehicles from the motorway onto trains at a rate of 700 cars and 113 heavy vehicles an hour. The British 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 British site was severely constrained and the design was challenging, while 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.[34] At Folkestone there are 12 miles of mainline track and 45 turnouts with eight platforms. At Calais there are 19 miles of track with 44 turnouts. At the terminals the shuttle trains traverse a figure eight to reduce uneven wear on the wheels.[34] There is a freight marshalling yard west of Cheriton at Dollands Moor Freight Yard.

Outside links

References

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  11. Whiteside pp. 18–23
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  13. William Ewart Gladstone (1902). A. W. Hutton & H.J. Cohen. ed. The Speeches Of The Right Hon. W. E. Gladstone On Home Rule, Criminal Law, Welsh And Irish Nationality, National Debt And The Queen's Reign. The Speeches And Public Addresses Of The Right Hon. W. E. Gladstone, M.P.. X. London: Methuen And Company. 
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  33. Kirkland
  34. 34.0 34.1 34.2 34.3 34.4 34.5 34.6 Kirkland pp. 255–270
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  39. Kirkland p. 29
  40. Wilson p. 44
  41. Kirkland pp. 117–128
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