bid had been selected. Foreign Affairs Ministers of both countries signed the Franco-British Treaty in Canterbury. The Concession Agreement was awarded to the two concessionnaires The Channel Tunnel Group Ltd / France-Manche SA for a period of 55 years. Formation of the Eurotunnel Group and the signature of the construction contract between Eurotunnel and TransManche Link. In 1987, Margaret Thatcher and François Mitterrand ratified the Treaty of Canterbury, paving the way for the Channel Tunnel to become a reality.
The problems that confronted them under the Channel were ancient and still far from solved. Passage tunneling - as distinct from mining - began more than four thousand years ago in the Middle East. The first towns needed to have water inside their defensive walls, and tunnels were the most secure way of assuring a supply. Thus were the waters of Perseus's spring led inside Agamemnon's citadel at Mycenae. These were not trivial operations; the ancient water tunnel that served Aleppo, in Syria, was more than twelve kilometers long.
Hezekiah, King of Judah, learned of tunneling's difficulty around 700 B.C. when, faced with an impending siege by Sennacherib's Assyrian army, he ordered a tunnel dug to carry water from the Gihon Spring to the Pool of Siloam inside Jerusalem's walls. The aqueduct, like the Channel Tunnel, was dug from both ends toward the middle. The workers lost their way and had to dig several vertical shafts to the surface to see where they were. They wandered for 1,680 feet to cover the less than 656 feet between the spring and the pool. The tunnel is still in pretty good condition, though, and you can see, in its wall, the pick marks where laborers changed direction as they groped the last few meters toward each other.
Even rough success evoked great praise. Herodotos ranked a thousand-meter-long water tunnel on Samos, built in the sixth century B.C. by the engineer Eupalinus of Megara, as one of the greatest of Greek engineering feats - despite the fact that the tunnelers, working from both sides of a hill, missed each other by 20 feet in the horizontal and 10 feet in the vertical. The teams made sharp turns to find each other, leaving the tunnel with a kink.
Nothing was, or is, more difficult and dangerous than tunneling under water. History provides eloquent testimony to this: The first underwater tunnel, a 2,953 foott pedestrian passage under the Euphrates at Babylon, was finished in 2180 B.C. The second underwater tunnel, a 1,198 foot passage dug under the Thames at London by the great French-born engineer Marc Isambard Brunel, was finished in A.D. 1843.
In fact, it is likely that the Thames Tunnel was really the first subaqueous tunnel, to use the term favored by engineers. There is much doubt about whether the Babylonian tunnel ever existed; the only mention of it was by Diodorus Siculus, a Sicilian-born Greek historian who was a contemporary of Julius Caesar. Diodorus cited a tradition that Semiramis, the legendary founder-queen of Babylon, had built such a tunnel, and he supplied some interesting details about its construction. But no trace of it has ever been found.
Through all the centuries between, no tunnel ventured under water (although Leonardo da Vinci, in a resume he submitted to Ludovico Sforza, Duke of Milan, said he thought he could dig one if it were necessary). The normal ration of danger was far greater under water. In the Hudson River railroad tunnels, built late in the last century to bring rail traffic into New York, each work crew of forty to fifty men could expect to have one fatality per month.
For the Thames Tunnel, Brunel sidestepped the navigation problem by digging from one side of the river to the other, from Rotherhithe to Wapping. It took sixteen years and two months, drained its public and private investors of money and broke Brunel's health and spirit. There was not enough money even to complete the approach ramps that would have let vehicles use it. Without access for vehicles, this monument to endurance and fortitude became a gloomy pedestrian pathway. The toll was a penny, cheap enough to attract London's homeless, some of whom no doubt owed their poverty to the industrial revolution whose triumphs the tunnel echoed. The poor used the Thames Tunnel as a makeshift shelter for years, calling it the "Hades Hotel," until the East London Railway bought it in 1869, lined the roof with sheet iron and began running trains through it.
Railroads brought in the great age of tunneling late in the last century. The Alps quickly were riddled with rail tunnels: The Frejus Tunnel, opened in 1871. The St. Gotthard, 1882. The Arlberg, 1884. The Simplon, 1906. The Lotschberg, 1912. These were only the largest tunnels, those judged worthy of a name. The 10-mile Lotschberg, for instance, was only one of thirty-four tunnels in a 36-mile stretch of rail that, in all, ran more than 14-miles underground.
But the problems that bedeviled Eupalinus lingered, as surveyors discovered in the 12-mile-long Simplon tunnel in 1901. Surveying by then was a demanding but reliable skill, at least on the earth's surface. Tunnels were different. The Simplon engineers decided to use a sort of gunsight to keep their tunnel headings, which were to be driven straight toward each other, on line. They built two steel frames outside each portal; each of these had a steel plate with a slit in it. They were placed with the utmost care; surveyors measured more than nine hundred angles in setting them. Surveyors could peer from within the tunnel to see if the slits were aligned. This worked well for a while, but the tunnel face, following the earth's curve, appeared to descend 3 feet in each 2-miles. The gunsight had to be moved into the tunnel, and engineers worried that this could cause serious surveying errors.
After three years of work, when the miners stopped to celebrate the feast of their patron, Saint Barbara, the engineers moved in to make some accurate measurements. They were badly surprised by what they found. The surveyors set up a light outside the portal and sighted back from more than 3-miles inside the tunnel. The earth's curvature and refraction - the bending of light as it passed through layers of air, the effect that makes a stick seem to bend where it enters a pool of water - depressed the image of the light almost two meters.
But instead of seeing one light, the observers saw two, one above the other. And the square tunnel opening, which the earth's curvature should have cut off to appear as a horizontal rectangle, instead appeared as a tall vertical rectangle. Further, this tall rectangle, two and a half times as high as it was wide, seemed to be leaning to the right. Persons passing the entrance also appeared to be bent over to the right, and so did the mysterious upper flame.
It dawned on the Simplon engineers that refraction in long tunnels created a very complex environment for a light beam. The air nearest the walls is warmer than the air in the center, because of ambient heat in the rock. This would not be a terrible problem in a perfectly round tunnel, with perfectly still air, if you could sight straight down the middle: The light would not be moving between layers of air, speeding up and slowing down as the density changed, pitching and yawing like a sailboat in heavy weather. But everything in a real tunnel - hot walls and cool center, cold air sliding in from the outside, hot air rising and eddying, air pushed in and pulled out by ventilating fans, air stirred by the actions of men and machinery - tended to toss light around in a most unpredictable fashion. In Simplon on that St. Barbara's Day, the engineers discovered that all of their measurements were wrong and had to be rethought, recalculated, redone.
Construction on the service tunnel began on December 1, 1987 from both the UK and French shores (On February 28th, 1988 was the start of service tunnel boring on the French side), and on December 1, 1990 the service tunnels broke through at the halfway point. TML carefully staged the break through for maximum effect: TML tunnellers Phillipe Cozette and Graham Fagg cut a heading between the two drives under the watchful eye of the media.
Digging the tunnel took 15,000 workers over seven years, with tunnelling operations conducted simultaneously from both ends. The prime contractor for the construction was the Anglo-French TransManche Link (TML), a consortium of ten construction companies and five banks of the two countries. Engineers used large tunnel boring machines (TBMs, mobile excavation factories that combined drilling, material removal, and the process of shoring up the soft and permeable tunnel walls with a concrete lining). In all, eleven TBMs were used on the Channel Tunnel:
- three French TBMs driving from Sangatte to under the Channel,
- one French TBM driving the service tunnel from Sangatte cofferdam to the French portal,
- one French TBM driving one running tunnel from Sangatte cofferdam to the French portal, then the other running tunnel from the French portal back to Sangatte cofferdam,
- three British TBMs driving from Shakespeare Cliff to the British portal,
- three British TBMs driving from Shakespeare Cliff to under the Channel.
The main rail tunnels met on May 22, 1991 and on June 28, 1991, each accompanied by a breakthrough ceremony. When each pair of TBMs met, the French TBM was dismantled while the British one was diverted into the rock, concreted in place, and abandoned. The next few years were spent refining, equipping, and finishing the tunnels. In 1994 the Channel Tunnel was considered completed.
In the end, almost 5 million cubic yards of chalk were excavated on the British side, much of which was dumped below Shakespeare Cliff near Folkestone to reclaim 90 acres of land from the sea. Called Samphire Hoe, the area is now a popular park. In all, 10.5 million cubic yards of soil were removed, at an average rate of 2,400 tonnes/hour.
The British and French efforts, which had been guided by laser surveying methods, met first with the completion of the undersea service (access) tunnel. A small pilot hole broke through without ceremony on 30 October 1990, England and France were linked. The difference in the centrelines of the two ends of the tunnel was surveyed as just 14.1 inches horizontally and 2.3 inches vertically. When the two ends of the undersea service tunnel met 130 feet beneath the English Channel seabed on 1 December 1990 it became possible to walk on dry land from Great Britain to continental Europe for the first time since the end of the last ice age 8,500 years ago. The tunnel was officially opened by Queen Elizabeth II and French President François Mitterrand in a ceremony held in Calais on 6 May 1994.
