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.