Channel Tunnel Facts


C. S. Harris

A summary of Channel Tunnel facts, selected for you by a professional geologist who was consultant geologist during Channel Tunnel construction.

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(Links to: Channel tunnel facts and brief history; Detailed geology on each side of the Channel Tunnel; Chalk, the basic facts; Chalk, the White Cliffs; Landslips of East Kent; Channel tunnel, a detailed sequence stratigraphy)



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 "Linking France and England will meet one of the present-day needs of civilization," wrote French writer, Louis Figuier, in 1888. He was only restating a conviction that had been expressed from time to time by many of his compatriots for more than 137 years. Britain and France were the world's leading maritime and commercial powers, and they were a mere 34 kilometers apart. Yet, trade between them was an extremely hazardous affair. The shortest route - across the Pas de Calais or Straits of Dover - was also the most difficult. Travelers making the current- and storm- besieged crossing could, with a fair wind and a skillful captain, be at their destination in six or seven hours. They could equally be delayed days or weeks and be extremely seasick by the time they reached the opposite shore. So, early on, quality-of-life issues spurred on engineering imagination.

The often-considered idea of constructing a tunnel under the English Channel was revived in 1986 by the United Kingdom and France. A rail tunnel was chosen over proposals for a very long suspension bridge, a bridge-and-tunnel link, and a combined rail-and-road link. Digging began on both sides of the Strait of Dover in 1987-88 and was completed in 1991. The tunnel was officially opened in May 1994.

It was constructed by an Anglo-French consortium of construction companies called Trans Manche Link, or TML for short, for their client EUROTUNNEL. Eurotunnel now own and operate the rail tunnel between England and France that runs beneath the English Channel. It consists of three tunnels: two for rail traffic and a central tunnel for services and security. The tunnel runs between Folkestone, England, and Sangatte (near Calais), France, and is used for both freight and passenger traffic. Passengers can travel either by ordinary rail coach or within their own motor vehicles, which are loaded onto special rail cars. Trains can travel through the tunnel at speeds as high as 100 miles (160 km) per hour; the trip takes about 35 minutes.

 The next stage of this rail project, the fast rail link between the Channel Tunnel and London, the CTRL (Channel Tunnel Rail Link), is currently under construction. Photographs for this project can be viewed.

The author of this page was consultant geologist to TML, the builder's of the Channel Tunnel and as such has made available articles on the geology of the Channel Tunnel, the geology of Kent and the Boulonnais, and a new detailed sequence stratigraphy of the Chalk Marl, the main tunnelling horizon (links at top of this page).

Channel Tunnel Construction Facts

The Channel Tunnel is regarded by many people as one of the most remarkable construction achievements ever; indeed some might say as one of the wonders of the world. However, as much of it is underground, with only the two terminals at either end being obviously connected to the project, it is now difficult to visualise the scale of the project.

In the final analysis of the construction program and despite some early difficulties and setbacks in tunnelling due to poor ground conditions. the entire civil engineering construction component of the project were completed to an extremely high standard and ahead of schedule; an achievement which even today has not been widely appreciated or acknowledged. Indeed, many construction records were broken in the process including the speed of advance of the TBM's (tunnel boring machines) and the size of the undersea Crossovers. All the contributors to the project can be justly proud.

The following are some of the more important construction facts:

  • In designing the tunnel lining, a total of 18 design development studies were carried out to ensure that no aspect of the system's operation was overlooked. In addition, the lining was also designed for a 120 year life, which meant that no significant deterioration in performance could occur over a period of 120 years.

  • 13,000 engineers, technicians and workers help construct the tunnels.

  • The Channel Tunnel comprises 3 tunnels; two Running Tunnels and a smaller Service Tunnel (Figure).

  • The undersea tunnels are an average of 50m below the seabed (Figure).

  • The tunnels were mainly constructed in the Chalk Marl, which is the basal unit of the Chalk. It is a marine deposit that is mainly comprised of small fossils which because of its high clay content is relatively impervious to water, unlike the bulk of the Chalk (Figure). 85% of the tunnels were constructed in the Chalk Marl.

  • The Chalk is of Cretaceous age. The Chalk Marl is about 100 million years old. Dinosaurs were still wandering the landmasses when the Chalk Marl was deposited.

  • Between the two terminals at Folkestone and Coquelles, near Calais, the tunnels are 51 Km in length, of which 37.5 Km is undersea.

  • 84Km of tunnels were constructed on the English side and 69Km on the French side.

  • The Running Tunnels have a 8.2m outer, and 7.6m inner diameter while the Service Tunnel has a 5.0m inner diameter.

  • The two main tunnels are 30m apart.

  • 6 tunnel boring machines were used on the English side and 5 on the French side. The English machines were 'open face' while the French were 'earth pressure balance' machines.

  • The TBM's were typically 200m long and telescopic, allowing he construction of the concrete segmental lining.

  • The French undersea tunnels were lined with a water-tight bolted and gasketed segmental concrete lining.

  • The English tunnel lining was a concrete expanded segmental lining. The voids behind the lining were grouted to control water ingress.

  • The tunnel lining rings are 1.5m (1.4m, 1.5m and 1.6m) in length. The average build time for each ring cycle was 50 mins.

  • On the English side an average of 150m/week tunnel progress was achieved while in France the weekly average was about 110m/week. This difference was due to the different TBM design due to more adverse tunnelling conditions.

  • Best week for a single TBM in the UK saw 426m of tunnel constructed while in France it was 322m.

  • The two Running Tunnels each carry a single track railway and these are connected to the Service Tunnel by Cross Passages every 375m (Figure).

  • Pressure relief ducts connect the Running Tunnels at 250m intervals.

  • Two caverns were excavated undersea to allow trains to change tunnels if required. These are known as the English and French Crossovers.

  • The tunnel system is kept dry by five pumping stations and sumps, three built under the sea and one on each shore. An unusual feature in the rail tunnels is the installation of a cooling system designed to counteract the buildup of heat produced by fast-moving trains. Chilled water is pumped through cooling pipes so that the tunnel air is maintained at a comfortable temperature.

  • The service tunnel started on 1st december 1987 and broke through in December 1990. The northern rail tunnel broke through on the 22nd May 1991 and the southern tunnel on the 28th June 1991.

  • Almost 4 million cubic metres of chalk were excavated on the English side.

  • The UK has increased in size by 90 acres due to the tunnel spoil being deposited in the undercliff area at Shakespeare Cliff in a number of lagoons. This area now known as Samphire Hoe has been landscaped and is a popular venue for walks, picnics and fishing.


History of the Channel Tunnel

  The Channel Tunnel project had one of the longest gestation periods in history - its ideas, plans, and efforts span well over two centuries. And, it may be the best example and most complex one where technology issues were integrated with those related to quality of life. Its challenges included overcoming the technological issues, gaining consensus among the politicians, overcoming the concerns of the British military, and obtaining finance.

  The following is a brief summary of this history:


Concept of a first, all weather Channel crossing first suggested, when the Amiens Academy held a competition to find a new means of crossing the Channel.


A tunnel for horse-drawn traffic was proposed by Albert Mathieu, a mining engineer in the Department du Nord following the signing of the Treaty of Amiens.


The first systematic geological and hydrographic survey of the Channel was undertaken by Thome du Gamond.


Du Gamond produced 8 major tube, bridge and tunnel designs.


Du Gamond's last scheme for a tunnel.


W.Low and J. Brunlees proposed a scheme for twin tunnels linked by cross-passages.


Low and Du Gamond worked on a revised scheme which was submitted before a British Channel Tunnel Committee.


The committee gave the go-ahead for two pilot tunnels.


The English Channel Tunnel Company was formed to promote a scheme designed by J.C. Hawkshaw. It was only at this time that the schemes began to be designed considering the available technology of the time.


An Anglo-French commission signed a protocol on the Channel Tunnel.


E.W. Watkin promoted Low's scheme and work began at Abbot's Cliff with the excavation of a 7 foot diameter tunnel under the direction of F. Brady, using an early (Beaumont) tunnelling machine, which completed 840 yards. It was the moved to Shakespeare Cliff where it completed a tunnel of 2020 yards under the sea towards Dover harbour.


Military opposition in England to the construction of the Channel Tunnel became very vocal and construction stopped in 1883.


The first mineable coal in Kent was proven from the Shakespeare cliff site.


The Channel Tunnel Company and l'Association du Chemin le Fer Sous-Marin entre La France et l'Angleterre proposed a new scheme consisting of two 20 foot diameter tunnels for electrical rail traffic following Brady's tunnel alignment.


The Channel Tunnel Company published a new report on the geology and propose that a pilot tunnel be driven. Under the supervision of P. C. Tempest a new experimental heading using a 12 foot diameter Whitaker tunnelling machine drove a 490 foot long trial heading in the Folkestone Warren.


A British Royal commission was set up to study the matter. Two tunnel schemes from the Channel Tunnel Company and a rival bid from the London and Paris Railway were discussed. The latter included a new rail route from London to Paris via the Channel tunnel. The Channel Tunnel Company proposed a smaller pilot tunnel and two 18 foot 6 inch, 36 mile long tunnels, of which 24 miles would be beneath the sea. Half would be constructed by British and half by French companies, taking an estimated 6.5 years.


The Imperial Defence Committee declared against the project.


All of the previous schemes had essentially been halted by British military opposition, however, by 1956 military opposition to the tunnel was minimal.


The Channel Tunnel Study Group was formed.


The first comprehensive geological site investigation was undertaken.


A White Paper was published which supported a scheme with twin rail tunnels.


Further marine surveys were carried out.


A further site investigation was undertaken.


The Channel Tunnel project began at the Shakespeare Cliff site with the excavation of two inclined headings and an erection chamber for a Priestley tunnelling machine. A 250m test section was completed.


The project was again cancelled.


Margaret Thatcher and Francois Mitterrand announced their support for the project.


A Channel Tunnel Bill was given Royal Assent.


Further marine and land site investigations were undertaken.


The first tunnelling machine in the marine Service Tunnel began excavation in December and this broke through to the equivalent French tunnel on December 1st 1990.


Breakthrough of the two Running Tunnels.


Opened for passenger traffic.


Photograph 1

The Folkstone terminal showing a loading ramp in the foreground with lorries waiting to board a shuttle. Taken from the top of the N. Downs escarpment.