Introduction
"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:
1751
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.
1752
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.
1833
The first systematic geological
and hydrographic survey of the Channel was undertaken by Thome du Gamond.
1833-1856
Du Gamond produced 8 major
tube, bridge and tunnel designs.
1866
Du Gamond's last scheme for
a tunnel.
1867
W.Low and J. Brunlees proposed
a scheme for twin tunnels linked by cross-passages.
1868
Low and Du Gamond worked on
a revised scheme which was submitted before a British Channel Tunnel Committee.
1869
The committee gave the go-ahead
for two pilot tunnels.
1872
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.
1876
An Anglo-French commission
signed a protocol on the Channel Tunnel.
1881
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.
1882
Military opposition in England
to the construction of the Channel Tunnel became very vocal and construction
stopped in 1883.
1890
The first mineable coal in
Kent was proven from the Shakespeare cliff site.
1906
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.
1919
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.
1929
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.
1930
The Imperial Defence Committee
declared against the project.
1955-56
All of the previous schemes
had essentially been halted by British military opposition, however, by
1956 military opposition to the tunnel was minimal.
1956
The Channel Tunnel Study Group
was formed.
1958-59
The first comprehensive geological
site investigation was undertaken.
1963
A White Paper was published
which supported a scheme with twin rail tunnels.
1964-65
Further marine surveys were
carried out.
1972-74
A further site investigation
was undertaken.
1974
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.
1975
The project was again cancelled.
1984
Margaret Thatcher and Francois
Mitterrand announced their support for the project.
1987
A Channel Tunnel Bill was given
Royal Assent.
1986-88
Further marine and land site
investigations were undertaken.
1987
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.
1991
Breakthrough of the two Running
Tunnels.
1994
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.
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