Tunnel visionaries 20 years of the Channel Tunnel

TUNNEL VISIONARIES

For hundreds of years, probably since the English Channel was created after sea levels rose, schemes have been made to span the 21 miles of water separating the UK from the rest of Europe with tunnels and bridges. Robert Williams celebrates 20 years of the Channel Tunnel.

The first plan in recent times was developed by Albert Mathieu Favier. In 1802 the French mining engineer proposed to tunnel under the English Channel with illumination from oil lamps, horse drawn coaches and an artificial island mid channel for changing horses. Napoleon supported the plan but the British vetoed it, fearing that he wanted to build the tunnel in order to invade England (although one would think that soldiers emerging from a tunnel would have been rather easy to stop…).

There were many other plans that never left the drawing board until, in 1973, Prime Minister Edward Heath and French President Pompidou signed an agreement to push ahead with a Channel tunnel. Work actually started on this tunnel, although it was soon abandoned. Then, in 1984, French president Francois Mitterrand and UK Prime Minister Margaret Thatcher jointly agreed to construct a link across the Channel.

There were ten proposals, including various tunnels and bridges. The proposal that won was the plan for the Channel Tunnel, submitted by the Balfour Beatty Construction Company (this later became Transmanche Link). The tunnel would be the longest undersea tunnel in the world with 38km out of the 50km length under the sea.

The geology of the Channel was examined and digging began simultaneously from the British and the French coasts, with the finished tunnel meeting in the middle. On the British side, construction began near Shakespeare Cliff outside Folkestone; the French side began near the village of Sangatte. The short stretch of tunnel dug in 1974 was used as the starting and access point for tunneling operations from the British side for today’s tunnel.

Huge tunnel boring machines, (TBMs), cut through the chalk marl, collected the debris, and transported the debris behind it using conveyor belts. As the TBMs bore through the chalk, the sides of the newly dug tunnel had to be lined with concrete. This concrete lining was to help the tunnel withstand the intense pressure from above as well as to help waterproof the tunnel (although the tunnel is, on average, 40metres below the sea bed).

The project used eleven boring machines each of which were the length of two football fields and capable of chewing though 250 feet of earth a day. On the British side six were lowered into an excavation near Dover’s Shakespeare Cliff. Three were pointed toward the channel to make the underwater portion of the tunnel and three toward the mainland to make the tunnel approaches. In France the same thing was done with five machines at an excavation near Sangatte.

The Channel Tunnel is actually two parallel railway tunnels and a third, smaller, service tunnel that is used for maintenance, including communication cables and drainage pipes. One of the most challenging tasks on the project was making sure that both the British side of the tunnel and the French side actually met up in the middle. Special lasers and surveying equipment was used; however, with such a large project, no one was sure it would actually work.

© Eurotunnel

Englishman Graham Fagg and Frenchman Phillippe Cozette carried out the ceremonial break through on 1 December 1990. It took until 6 May 1994, however, before the tunnel was official opened for business in a formal ceremony involving British Queen Elizabeth II and French President François Mitterrand.

Crossover tunnels, land tunnels from the coast to the terminals, piston relief ducts, electrical systems, fireproof doors, the ventilation system, and train tracks all had to be built, as well as the two large train terminals at Folkestone and Coquelles. Overall, the project cost £4.65 billion (equivalent to £12 billion today), 80 per cent more than expected.

The tunnel today

The two rail tunnels are 7.6m in diameter and 30m apart. Each rail tunnel has a single track, overhead line equipment and two walkways (one for maintenance purposes and the other for use in the event of an emergency evacuation and on the side nearest the service tunnel). The service tunnel is a road tunnel used by electric and diesel-powered vehicles, where air pressure is higher to prevent smoke in case of a fire in one of the rail tunnels. The walkways are also designed to maintain a shuttle upright and in a straight line of travel in the unlikely event of a derailment.

Two undersea crossovers allow trains to switch from one tunnel to the other during night maintenance periods so that individual sections of the tunnel can be isolated.

The overhead power lines are also divided into sections, so that maintenance work can be carried out in stages. Electrical power supplying the tunnels, drainage pumps, lighting and the trains, is provided by substations on each side of the Channel. In the event of loss of power from one side, the entire system can be supplied from the other side.

As well as being the world’s longest undersea railway tunnel, more than 270 trains run each day, that is one train every 3 minutes at peak times. The Truck Shuttles carry up to 32 heavy goods vehicles and some of the Freight Shuttles weigh in at 2,500 tonnes. These 800-metre long trains run at 140 kph. The Passenger Shuttles travel at the same speed and transport up to 120 cars and 12 coaches. The Eurostar trains travel at 160 kph below the sea.

The Channel Tunnel is a true feat of engineering. At the height (or depth) of construction 15,000 people were employed. When you next take a journey under the Channel, you should remember the ten workers, eight of them British, who were killed during construction, most in the first few months of boring.

And mark the words the Queen observed in her speech to open this Wonder of the World, “The mixture of French elan and British pragmatism, when united in a common cause, has proved to be a highly successful combination. The tunnel embodies that simple truth.” n

© Eurotunnel