“Fog over Channel, Continent Cut Off” was a famous "London Times" headline from the 1930s that epitomized British insularity. The Channel Tunnel, colloquially called the Chunnel and later Eurotunnel, a subsea rail link between the southern English and northern French coasts, eliminated the fog obstacle and joined Britain to the European continent.
In 1751, French geologist Nicolas Desmarets was the first to propose a tunnel under the English Channel. It was to be illuminated by gas lights, and travelers would be transported by horse-drawn carriage. In 1802, French mining engineer Albert Mathieu-Favier suggested a two-tier tunnel -- the upper for transport and the lower for drainage -- with an artificial island halfway across used to change horses. In 1856, another French mining engineer, Aime Thome de Gamond, was the first to propose an underground rail tunnel. His geological studies indicated that a uniform layer of chalk marl -- a soft rock consisting of chalk and clay -- was present 131 feet below the sea floor. He believed this rock was impermeable to water and ideal for tunneling.
British - French Political Agreements
British politicians greeted French proposals for a tunnel link with suspicion, primarily for security reasons. Initial tunneling work started in 1880 on the English side and ceased three years later under orders from a British military commission. The commission feared the link would be used for an invasion from France. This ban was lifted only in 1955. In 1973, British Prime Minister Edward Heath and French President Georges Pompidou agreed to a new tunnel project. This was abandoned in 1975 because of the economic impact of the international oil crisis at the time. In 1987, British Prime Minister Margaret Thatcher and French President Francois Mitterrand revived the 1973 tunnel project in the Treaty of Canterbury. Construction lasted from 1988 to 1994, and cost nearly $15 billion.
The completed tunnel links Folkestone on the southern English coast with Coquelles on the northern French coast. These two terminals connect with their respective national rail systems. This is the world’s longest subsea tunnel -- 31.4 miles coast-to-coast -- with an average depth below the sea floor of 131 feet, and 246 feet deep at its lowest point. The tunnel consists of three separate conduits: one service and two rail tunnels. One rail tunnel carries passenger trains and the other carries vehicles on a shuttle train. Tunneling began simultaneously from both sides of the English Channel with breakthrough -- the point where the two boreholes met -- in December 1990. The first rail shuttle ran in June 1994 from England, followed by the first passenger train in November 1994 from France.
When work began on the tunnel the precise subsea geology along the tunnel route was unclear. Engineers believed that the French side of the channel posed a greater problem with fractures in the sea bed and potential water ingress than did the English side. Actually, the reverse was the case. Special waterproof tunneling machines capable of supporting water pressures up to 10 times the Earth's atmospheric pressure were designed for the work. In 1996, the American Society of Civil Engineering named the tunnel one of the Seven Wonders of the Modern World.