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Channel Tunnel

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The Channel Tunnel is a rail shuttle tunnel that runs under the English Channel crossing at the Strait of Dover. Commonly also known as the “Chunnel”[1] and the “Eurotunnel,”[2] the Channel Tunnel connects the U.K. to France starting in Folkestone, Kent, England and ending in Coquelles, near Calais in France. Described as one of the Seven Wonders of the Modern World[3], the Channel Tunnel is the second longest underwater or marine tunnel in the world next to Japan’s Seikan Tunnel. Completed and officially opened for travel in 1994, the Channel Tunnel consists of three tunnels, two of which are full sized and accommodate rail traffic as well as transport passengers in their motor vehicles and even buses. The third tunnel, smaller and positioned in between the two rail shuttle tunnels, operates as a service tunnel and escape route. There are also many cross passages.

The length of the tunnel is 31 miles (50 km) long[4] with a below-sea level depth averaging between 150 feet (45 to 50 m).[5] The construction of the tunnel was carried out by the engineering firm Transmanche Link and cost an estimated nine billion pounds[6] or an equivalent of US$21 billion.[7] At the time of construction, the Channel Tunnel was the most expensive project ever undertaken in the world.


[edit] Construction History

Connecting France to Britain by a bridge or tunnel is a concept that was entertained as far back as nearly two centuries ago way before the present day Channel Tunnel even saw the light of day. Most of these early schemes were wishful thinking and beyond current technological ability to construct. Some schemes were so "out of the box," such as a sketch of transcontinental bridge, that they resembled something more out of science fiction. However, such schemes were the vision of sheer engineering ingenuity and helped pave the way to make the Channel Tunnel as it is constructed today, a reality.

[edit] Early Tunnel Schemes

[edit] Desmarest

In 1750 an engineer by the name of Nicolas Desmarest first suggested a transcontinental link. The Academy of Amiens launched a competition inviting individuals to come up with a means of crossing over the English Channel and Desmarest came up with a proposal to actually build a tunnel. Many were surprised when he won the contest figuring the Academy would find such a concept outlandish for such a tunnel was beyond the ability to even build at the time.[8]

[edit] Mathieu-Favier

In 1803 Alberta Mathieu-Favier, a French mining officer, presented the scheme of a road tunnel under the English Channel to Napoleon Bonaparte. The tunnel was to be lit by oil lamps and ventilated by chimneys at different intervals. An artificial island, to be constructed midway in the channel, would be used to change horses. Napoleon was fascinated by such a concept and an Anglo-French group was even formed in 1803 to begin construction. The British were wary however of Napoleon’s motives and ceased to cooperate with the project.[9]

[edit] Gamond

During the 1830s other schemes gained some credibility mainly from the efforts put forth by a French engineer named Thome de Gamond. In total, Gamond produced eight different concepts between 1833 and 1856 that included tube, bridge, and tunnel designs.[10] In 1857, Gamond developed the idea of an underground railway tunnel that became widely accepted in England and France. He also conducted the first geological and hydrographical surveys for a possible route by performing many dangerous solo dives to the bottom of the English Channel to observe the seabed.[11]

His plan featured a port built midway on an artificial island on the Varne sandbank. Steam trains would operate from a Paris-Amiens-Boulogne line on a double track through a single gas-lit tunnel with ventilation being provided through an opening at the Varne.[12]

Both French and English engineers felt such a feat of building a tunnel under the channel was achievable, as other engineering projects of a mass magnitude such as the building of the Suez Canal in 1869[13] had been accomplished.

[edit] Potential Problems

Gamond’s underground rail tunnel design poised three unique problems not easily overcome. First, a lack of adequate knowledge about the geology of the seabed at the bottom of the channel had to be checked to see if boring a tunnel all the way was even remotely possible. What was needed was a stretch of unbroken bed of some sort. Second, ventilation was another issue. How would the smoke from steam trains be circulated and released without choking passengers in such a long tunnel? The third problem was British fear of creating an easy route for invaders.[14] For centuries, the British reveled in the fact that they were “an island unto themselves.” Being surrounded by a natural moat worked to their advantage and to form a cross channel link would instantly compromise the country’s national defense.

[edit] The English Channel Tunnel Co.

In 1866 Gamond completed his last scheme for a tunnel before joining forces with W. Low in 1868 to revise a scheme for twin tunnels that Low had previously collaborated on with a man by the name of J.Brunlees. Low and Gamond submitted their idea to the British Channel Tunnel Committee. In 1869, the committee gave the go ahead for two pilot tunnels to be drilled. This was followed by the formation in 1872 of the English Channel Tunnel Co. that wanted to promote the idea of a tunnel designed by J.C. Hawkshaw. It was important because it was the first design that considered the technology available at the time. In 1876, an Anglo-French commission signed a protocol on the Channel Tunnel.[15]

[edit] The First Drilling Attempts

During the 1880s the first drilling attempts for geological surveying were conducted in the channel to find exactly what was under the seabed between Dover and Calais. These first exploratory drilling attempts were successful and the first time both countries had agreed to work on a joint tunnel together. Sir William Watkin, who stood behind Low’s idea for a twin tunnel, carried out the work. Drilling commenced on the English side using a Beaumont-English tunnel boring machine that was an improved model, patented in 1875.[16] The machines were driven by compressed air and worked so well that the machine’s pumps had to be switched on only half a day every two weeks to prevent flooding of which there was very little.[17]

Alexandre Lavalley, owner of the Anglo-French Railway Co. and a Suez Canal contractor, assisted with the drilling process. At Dover, a tunnel measuring seven feet (2.13 m) in diameter and 6,211 feet (1,893 m) was completed. A similar tunnel was drilled measuring 5,475 feet (1,669 m) long on the French side near Sangatte.[18] However, again because of growing military resistance to bridging Britain to the rest of continental Europe, further tunneling was banned in 1883.[19]

Further drilling attempts didn’t resume until 1919 when the Channel Tunnel Co. published a new geological report and put forth the idea that another pilot tunnel be drilled. Using a Whitaker tunneling machine, and under the supervision of P.C. Tempest, a 490-foot- (149-m-) long trial tunnel was drilled in the Folkestone Warren.[20]

In 1929 two more tunnel schemes surfaced, one presented by the Channel Tunnel Co. and another rival bid presented by the London and Paris Railway. The bid proposed by the latter included a new rail route that would bridge Paris to London via the Channel Tunnel. The proposal executed by the Channel Tunnel was substantially smaller, suggesting twin tunnels of 18 feet (5.5 m), six inches (15 cm) wide and 36 miles (58 km) in length with 24 miles (39 km) of that extending under the sea. Construction of the tunnels would be divided equally between the French and British with six and half years slated for completion. It came as no surprise when the British halted construction in the name of national defense. This didn’t change until well after World War II was over.[21]

[edit] Post-war Construction Attempts

By 1956 military opposition to the tunnel concept died down. In the same year the Channel Tunnel Study Group was formed. Between 1964 and 1974, further marine studies were undertaken.[22] It seemed the British were warming up to the idea of transcontinental link for various reasons. In 1973, Britain had finally joined France in the Common Market.[23] As trading within the European community expanded, Britain discovered it was being cut off and falling behind its continental competitors. One reason for this was that the cost of transporting goods across the English Channel was becoming increasingly expensive. There was only one way to haul freight and that was by trucks then transported over the channel by ferry.[24] Air travel was also the only means aside from ferry to get from the U.K. to continental Europe. Flying from London to Paris for example, could easily take up a whole day and this translated into a loss of precious business time. As a result, the British business community and the general public were more and more becoming sold on the idea of a tunnel.[25] But once again construction was abandoned when Harold Wilson, then Britain’s incoming prime minister, opposed the idea due to a volatile economic climate and surging oil prices.[26]

[edit] The Realization of an Old Dream

The realization of a two-century vision of bridging the U.K. to the rest of Europe finally came to fruition during the Thatcher era of power. In 1979, Margaret Thatcher was elected as Britain’s Prime Minister. In 1981, Thatcher met with French president Francois Mitterand to form a working group that would examine the subject of constructing a link between the two countries. At the time, she described a would-be tunnel as a “project that can show visibly how the technology of the age has moved to link the continent and Britain closer together.” [27] It was a clear message of unity. However, there was a catch. The project would have to be carried out without the assistance of government financing, meaning that the private sector would have to foot the entire bill. Further technical and financial studies were undertaken and eventually the development of a series of both bridge and tunnel schemes were presented by different engineering groups. Four were finally chosen and observed with closer scrutiny. These included:

  • A motor suspension bridge
  • A tunnel accommodating a road and rail line.
  • A combination of a bridge and a submerged tube system
  • A train shuttle tunnel that would transport both passengers and passenger vehicles

In January 1986, the winner of the final proposal was announced. The government selected the train shuttle concept devised by the consortium Channel Tunnel Group Ltd. and France-Manche S.A. The proposal was later dubbed the “Eurotunnel.”[28]

On February 12, 1986, both Thatcher and Mitterand signed the Treaty of Canterbury that laid the financial, legal, and administrative ground rules the two countries would abide by in the construction of the tunnel. In July 1987, the Channel Tunnel Act was passed by British Parliament and received Royal Assent.[29]

[edit] Project Financing

At an estimated nine billion pounds to complete, the construction of the Channel Tunnel was made entirely possible by private sector financing. As a joint project between U.K. and France, financing for the Channel Tunnel was arranged through the legal entity Eurotunnel, who were granted a 55-year concession. Due to project cost overruns as a result of higher than expected costs in digging out the tunnels and lower than anticipated tunnel traffic levels, Eurotunnel was left with a huge debt load and continues to struggle financially to this day in recouping construction costs.[30]

[edit] Geology of Channel Seabed

Transmarche Link used seismic profiling, a technology used in deep sea-oil exploration to check the actual composition of the English Channel seabed. This technology was extremely resourceful in guiding excavations away from the soft clay, permitting the tunnel to have a sturdy foundation in solid bedrock known as the Chalk Marl, a basal unit of chalk that is a layer of soft impermeable or waterproof rock.[31] At 100 million years old, the Chalk Marl is a marine deposit comprised of small fossil deposits that because of clay deposits, make it somewhat impervious to water. An estimated 85 percent of the tunnel was constructed in the chalk marl.[32]

[edit] Boring the Tunnels

According to John Neerhout Jr. project chief executive of the Channel Tunnel from 1990 to completion, in his article, “The Making of the Channel Tunnel,” boring through the chalk marl allowed the tunnel boring machines (TBMs) to be designed for rapid advance with an average of 984 feet (300 m) of tunnel being bored weekly. Overall, it took approximately three years for the tunnel boring machines to drill their way from France to England.[33] Boring of the tunnels through the chalk marl first broke ground in December 1987, with actual breakthrough of both tunnels occurring in December 1990.[34] On the British side, six “open face” tunnel boring machines were used to drill and construct about 52 miles (84 km) of tunnels with 492 feet (150 m) being the average amount being drilled per week.[35] On the French side, five “earth pressure balance” tunnel boring machines were used drilling a total of 43 miles (69 km) of tunnel with 361 feet (110 m) being the average amount drilled per week.[36] The tunnel boring machines used in the project were mammoth, equaling the size of two football fields, and were capable of drilling up to 250 feet (76 m) a day. To make the project more interesting, the British and French workers even tried to race to see who could drill to the midway point the fastest. The British won.[37] The largest amount of chalk drilled by a TBM in a single week on the British side was 1,398 feet (426 m) and on the French side, 1,056 feet (322 m). In total, about four million cubic yards (3.1 million m3) of chalk were actually excavated on the English side.[38]

[edit] Tunnel Construction

The Channel Tunnel Under Construction
Actual construction of the tunnels was a massive feat requiring 13,000 workers, engineers, and technicians.[39] Overall, labor equaled 170 million man-hours.[40] Two tunnels with internal diameters of 25 feet (7.6 m) were constructed to carry both through and shuttle trains. These two tunnels were adjoined to a third tunnel measuring 15.7 feet (4.8 m) in diameter. The third tunnel, constructed to function as a service corridor, also came equipped with its own mini transportation system. Each of the two adjoining tunnels was excavated at 98 feet (30 m) apart and 26 feet (8 m) apart from the walls of the center service tunnel. The service tunnel was also linked to the adjoining rail tunnels by cross passages every 1,230 feet (375 m) and further, by piston relief ducts every 820 feet (250 m) to release the air pressure caused by high-speed train traffic.[41] Two enormous additional undersea crossover caverns were excavated to facilitate trains crossing from one track to the other.[42] These crossovers divide the three different tunnels in equal sections permitting any one to be closed off in case of an emergency or for maintenance.

Each tunnel was lined with pre-cast concrete segmented rings except where there was poor ground, tunnels connections or intersections. In these instances, ductile iron linings were used. Both materials are common in tunneling. The concrete used in the tunnel construction was of very high strength and density providing added protection to the steel reinforcements. In total, 18 design development studies were carried out to ensure no aspect of the system was overlooked. The lining was also created with a lifespan of 120 years meaning it had to be durable enough as not to deteriorate within that timeframe.[43]

Today the tunnels are kept dry with five pumping stations and pumps, three of which are built under the sea and one of each shore. In addition another unique feature of the tunnels is a cooling system designed to counteract heat build-up produced by the trains that can travel up to speeds of 100 miles (161 km) per hour.[44] Tunnel temperatures are regulated with chilled water pumped through cooling pipes.

[edit] Channel Tunnel Fire

In November 1996 a shuttle train carrying heavy goods caught on fire in the tunnel. The design of tunnel was put to the test and remarkably none of the 31 persons trapped inside the tunnel at the time were injured, managing to escape to safety through the central service tunnel that was designed to act as an emergency exit as well. Obviously, fires are just one of many safety concerns that must be considered in the construction of tunnels.

[edit] Equipment Used

[edit] Refurbishment/Recent Projects/Renovations

[edit] CTRL Project

In 1996, the British government approved construction of two sections of the 69-mile (111-km) high-speed Channel Tunnel Rail Link (CTRL). Now called Highspeed 1, the new line starts in London and extends to the Channel Tunnel portal at Folkestone in Kent. The project cost 5.8 million pounds and was officially completed in November 2007.

[edit] Unique Facts

  • The Channel Tunnel was the most expensive project ever paid for by private financing, costing the equivalent of building the Golden Gate Bridge seven times over.[45]
  • The project was completed at a very high standard and ahead of time, breaking many construction records in the process, including the speed of advance of tunnel boring machines.[46]

[edit] References

  1. PBS. Wonders of the World databank: Channel Tunnel (Chunnel). Building Big, 2008-09-25.
  2. Official Euro Tunnel website
  3. Seven Wonders of the World: Channel Tunnel. American Society of Civil Engineering, 2008-09-25.
  4. PBS. Wonders of the World databank: Channel Tunnel (Chunnel). Building Big, 2008-09-25.
  5. Channel Tunnel., 2008-09-25.
  6. Machines and Engineering: Channel Tunnel Discovery Channel, 2008-09-25.
  7. PBS. Wonders of the World databank: Channel Tunnel (Chunnel). Building Big, 2008-09-25.
  10. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  12. Channel Tunnel., 2008-09-25.
  13. Channel Tunnel., 2008-09-25.
  14. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  15. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  16. Channel Tunnel., 2008-09-25.
  17. Channel Tunnel., 2008-09-25.
  19. Channel Tunnel., 2008-09-25.
  20. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  21. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  22. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  23. Channel Tunnel., 2008-09-25.
  26. Channel Tunnel., 2008-09-25.
  30. Channel Tunnel., 2008-09-25.
  32. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  33. PBS. Wonders of the World databank: Channel Tunnel (Chunnel). Building Big, 2008-09-25.
  35. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  36. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  37. The Channel Tunnel., 2008-09-25.
  38. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  39. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  42. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.
  44. PBS. Wonders of the World databank: Channel Tunnel (Chunnel). Building Big, 2008-09-25.
  45. Machines and Engineering: Channel Tunnel Discovery Channel, 2008-09-25.
  46. Harris, C.S. Channel Tunnel Facts. Geology Shop, 2008-09-25.