rail lines plunge into the Channel Tunnel near Coquelles,
France for their 31 mile underground/underwater run. (Photograph
Holger Weinandt licensed under the Creative Commons Attribution-Share
Alike 3.0 Germany license)
a French mining engineer named Albert Mathieu had a wonderful
idea. After years of war between France and England the two
European powers were finally at peace. Suppose one took advantage
of this reconciliation to forge a permanent tie involving the
two nations? Not just an effort to create goodwill between the
two, longtime rivals, but a project that would physically link
the two countries together. Something that would give them a
way to move people and goods across the 20 miles of water of
the English Channel without relying on the small, erratic ferries
that made passengers seasick as they were knocked about by the
unpredictable waves.What if one connected the two great nations
together using an underground tunnel?
presented his idea to the then current ruler of France, Napoleon.
Unfortunately for Mathieu the "Peace of Amiens" lasted only
a year and his idea was soon forgotten, but only after being
ridiculed by the British Press in a cartoon showing French troops
invading England via balloons and a tunnel.
31.35 miles (50.45 km)
depth under sea level: 490 feet (150m)
May 6th 1994
Folkestone,Britain, to Calais, France
of: Two parallel rail tunnels and a smaller service tunnel
constucted of steel and concrete.
Could have been constructed a century earlier if not
for political squabbles between Britain and France.
probably for the best that Mathieu's idea was put on the shelf.
His early designs showed a tunnel propped up by wood beams and
illuminated by candles so that horse drawn carriages could make
the twenty mile trip between the nations. While such passageways
were practical for the mines of that day, it is doubtful that
such a scheme would have succeeded under the Channel. At that
time nobody even knew what the geology was like under the sea
floor. Were there cracks that might let the seawater disastrously
Proposed Victorian Tunnel
idea did not die, however, and was revived by another French
engineer named Thomé de Gamond in 1857. By then railway engine
had been invented and tracks crossed the length and breadth
of both continental Europe and Britain. The train, instead of
Mathieu's carriages, seemed a much more practical way of moving
people and goods through a long tunnel. That same year, in fact,
a similar project was already underway in the Alps. The Fréjus
Rail Tunnel was being dug under the mountains between France
and Italy: a distance of 8.5 miles. By then tunnels had even
been built underwater. In 1843 a walkway had been completed
under the Thames River in London.
1802 tunnel design by the Albert Mathieu depended on horse
drawn carriages to make the 20 mile trip.
reasoned that as long as the geology permitted, a tunnel could
be constructed under the channel. To check the channel floor
he made a number of risky solo dives to the sea bed using the
primitive diving equipment of the day. His explorations led
him to believe that a layer of chalk ran under the channel from
Cap Blanc Nez, in France to Dover, in England. The chalk was
soft enough to dig, yet self supporting, waterproof and would
provide a good medium for a tunnel. De Gamond's design had the
passageway surface at an artificial island on the Varne sandbank
about midway between the nations. The island would serve as
an international port and provide ventilation for the tunnel.
until the mid 1870's that politics made further work on the
tunnel possibe. In the wake of the Franco-Prussian war of 1870-71
the French and British became much more friendly because they
saw a potential common enemy in the Germans. The French Channel
Tunnel Company was founded and given permission to do some more
digging to check the geology. By 1881 serious tunneling got
under way from both sides of the channel using new tunnel boring
machines invented in 1875. It was estimated a 7 foot diameter
pilot tunnel would be completed within 5 years.
steam engines would pollute the tunnel air with smoke, it was
decided that special trains driven by compressed air would be
used to move cars through the tunnel. The invention of the electric
train would probably had made this design obsolete, however,
before the tunnel even opened.
political cartoon showing a French invasion using balloons,
boats and a tunnel. Fear of this caused the British to
canel the project.
of a French Invasion
tunneling was abruptly put to an end. The French and British
governments were squabbling over the Suez Canal and colonies
in Africa. The British military complained that if war came
the tunnel might provide an easy way for the French to invade.
The tunnel company volunteered to build a valve that could be
used to flood the tunnel in an emergency and a fortress on the
British side to close it with explosives if necessary, but their
ideas fell on deaf ears. The British military leaders' vision
was shortsighted however. During World War I they sorely wished
that the tunnel had been built as it would have made supplying
their troops France much easier.
until the 1970's that another serious attempt to build a tunnel
was again made. Unfortunately a bad economy caused the British
to pull out of the project and the digging was abandoned.
Engineering the Modern Tunnel
1980's permission was given to a company to build the tunnel
using private funds. It was decided that the tunnel would be
designed to only accommodate trains. The public favored a drive
through tunnel, but because of the extraordinary length, it
was felt that access should be limited. It would be too easy
to have a major traffic accident underground shut down the whole
operation. Cars and trucks would be able to use the facility
by driving to terminals on either side where they would be loaded
onto special extra-large shuttle trains that would carry them
through the tunnel.
"chunnel," as it was nicknamed, was actually designed as three
tunnels: Two 25 foot diameter tubes running parallel to carry
trains and a 16 foot diameter service tunnel between them. To
speed the digging the company used eleven tunnel boring machines
tunnel boring machine similar to that used on the chunnel.
The disc at the front rotates, cutting the rock.
had first been used as far back as 1825, but became the standard
way of constructing tunnels after 1953. The machines cut a round
passage through the earth by using a disc-like head with tungsten
teeth that rotates to break up the rock. The rock is then sent
by conveyer belt to the rear of the machine were it can be transported
out of the tunnel by rail cars or other vehicles. Boring machines
are also capable of reinforcing the tunnel interior surface
by erecting concrete walls as they go along. Such re-enforcement
was necessary on the French side of the channel where the geology
was less stable.
project used eleven boring machines each of which were the length
of two football feilds and capable of chewing though 250 feet
of rock 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
1st of 1990, the service tunnels, which proceeded in front of
main tunnels so they could assess the geology, were connected
in a ceremony watched by the press. It took until May 6th 1994,
however, before the tunnel was official opened for business
in a formal dedication involving British Queen Elizabeth II
and French President François Mitterrand.
cross section of the chunnel showing the rail tubes, service
tube and interconnections.
took eight years and cost $21 billion making it the most expensive
constrution project in the world up to that point. The result
was a tunnel 31.35 miles (50.45 km) long going underground at
Folkestone in Britain and emerging again at Calais in France.
At the time that it was opened it was the second longest tunnel
in the world, but with longer portion of its run underwater
(23 miles, 37km) than any other subway. It runs an average of
148 feet (45m), with a maximum depth of 490 feet (150m), below
the English Channel. With the addition of a high-speed track
from Dover to London in 2006, passengers can travel between
the British and French capitals in just two-hours and fifteen
minutes by train. New proposed higher-speed trains might shorten
that trip to under two hours in the future.
the trains that run through the tunnel are electric powered
helping to eliminate the problem of having fumes underground.
However there are several diesel locomotives available for service
and emergency work should the power fail. The tunnel has experienced
two fires large enough to close down at least one of the two
tubes for an extended length of time. Nobody was killed in either
the Channel Tunnel on the French side.
service tube that runs down between the rail tunnels not only
allows work men and equipment to move through the tunnel without
blocking the trains, but is connected to the rail tunnels at
regular intervals to provide a way for the air pressure in front
of an oncoming train to be relieved. About halfway through the
tunnel all three passages come together at a "canyon." At that
location switches allow the trains to move from one tube to
another, giving the operators greater flexibility should a section
of a rail tunnels be shut down.
Channel tunnel was one of the largest construction projects
of the 20th century and remains a marvel of engineering even
today. It was selected by American Society of Civil Engineers
as one of the Seven Wonders of the Modern World in 1996.