Heritage

Crossing the English Channel, one of the most turbulent and dangerous sea passages in the world, can be an unpleasant experience. Since before the advent of cross Channel steamers when sailing ships were at the mercy of tide and wind plans have been proposed for a Channel Tunnel to link Great Britain with the Continent and end the vulnerability of the traveller to bad weather.

The long history of the Channel Tunnel began in 1802 when a French mining engineer, Albert Mathieu, prepared a plan, as impractical as it was precocious, linking France and Britain via an artificial island built around the Varne Sandbank which lies about 8 miles south of Dover. The tunnel was to have been ventilated by chimneys reaching above the waves. A year later hostilities with France were resumed and Napoleon approved a scheme for the invasion of England. Fears and threats of invasion were to dog the Channel Tunnel for the next 150 years.

Mathieu was almost completely ignorant of the geology of the channel bed but another Frenchman, Thome de Gamond (1807 – 1876), was the first to investigate the practicability of a Channel Tunnel by taking soundings to determine the depth of the water and by collecting samples from the sea bed. The similarity of the rock outcrops on either coast led de Gamond, correctly, to conclude that the strata of rock beneath the sea bed were continuous from one side to the other.

In fact the geology of the sea bed is generally favourable for tunnelling as a continuous stratum of chalk marl under the sea bed extends from England to France. The high clay content makes it almost impervious to water; it is firm yet sufficiently soft for boring machinery.

Proposals for a Channel Tunnel have generally been confined to the area between Folkestone and St Margaret’s Bay on the English side and Cap Griz Nez and Calais on the French side. Here Britain is separated from France by only 20 miles or so of sea and the maximum depth is only about 220 feet.

Plans proposed during the early nineteenth century included an underwater causeway and various schemes for prefabricated submerged tube tunnels resting on the sea bed. The first practical attempt to construct a tunnel was made in the 1880’s from the foot of the Shakespeare Cliff and financed by Sir Edward Watkin, Chairman of the South Eastern Railway.

In 1880, in order to test the Beaumont compressed air rotary tunnelling machine, a 74 foot deep shaft was sunk at the Abbots Cliff and a level heading driven 897 yards. The first 300 yards of this tunnel are still accessible. A second heading at the Shakespeare Cliff site was driven 2024 yards before Parliament intervened to stop the project on defence grounds. At Sangatte in France where there was little opposition to the scheme the tunnel was 1100 yards under the sea at high water before work ceased.

The idea of a Channel Tunnel was repeatedly revived during the first half of the twentieth century but it was not until 1955 that the British Government announced that defence objections to a tunnel had been lifted. The Channel Tunnel Study Group, a consortium of British and French companies, was subsequently formed to conduct joint studies resulting in the second attempt in 1974.

The scheme proposed was a railway tunnel comprising two main running tunnels and a service tunnel. As in the current design vehicles were to be driven on to special wagons at the passenger terminals near the tunnel mouth. Work started with an access tunnel being driven from the top of Shakespeare Cliff to the base of the cliff and a second access tunnel from the lower site down to a level where the tunnelling machine would begin driving the pilot tunnel.

The project was unilaterally abandoned in January 1975 by the British Government on complex grounds including national economic necessity but not before the tunnelling machine drove some 250 metres of the 4.5 metre internal diameter pilot tunnel which cut through the 1881 Beaumont tunnel.

In 1980 the British Government announced that there was no objection to a privately financed cross channel fixed link and after a further Joint Study promoters were invited to submit schemes. Joint choice was a twin bored tunnel taking passengers, freight and shuttle trains proposed by Channel Tunnel Group – France Manche, later renamed Eurotunnel.

From a point where the 1974/75 pilot tunnel ended Eurotunnel will drive two 7.6 metre diameter running tunnels and a connecting 4.8 metre diameter service tunnel towards France and landward some 6 miles back towards the site of the Folkestone terminal.

The biggest project of its kind ever attempted, the 50 km Channel Tunnel will stretch the limits of engineers’ experience. Due to be completed in 1993 with a planned breakthrough of the service tunnel in 1990 preliminary work has already started at both sites, the finance has been raised and the massive project, after nearly 200 years of talk, is all set to roll into action.