The Channel Tunnel was the 20th century's greatest engineering project, and Halcrow is proud to have played a major role, fielding more than 50 engineers at the tunnelling and maritime sites in Dover.
The Channel Tunnel is a 50.5-kilometre undersea rail tunnel, beneath the English Channel, linking Folkestone, in Britain with Coquelles, in northern France. At its lowest point it is 75 metres deep and at 37.9 kilometres the Channel Tunnel possesses the longest undersea portion of any tunnel in the world, although the Seikan Tunnel in Japan is both longer overall and deeper below sea level.
The company’s early input into the scheme was during World War II, when of Sir William Halcrow was invited by the War Office to comment on the possibility of the Germans building a tunnel surreptitiously to invade Britain. He concluded that the arrangements for silt disposal would have been too easily detectable by air reconnaissance.
In 1960 the Halcrow was part of the Channel Tunnel Study Group which proposed a twin tunnel railway carrying ordinary passenger trains and a special shuttle service, in many ways similar to the final concept. A further major geological survey was carried out in 1964 and eventually in November 1973 after 16 years’ debate the British Government gave permission for the construction of a trial tunnel 2km long from each coast.
However, euphoria was relatively short lived, for after much further debate and opposition during 1974, the scheme was abandoned by the British Government with only 350m of the service tunnel constructed.
David Wallis, then deputy resident engineer, recalls the depression of all those involved, "but I was always optimistic that the scheme would be resurrected during my career." And so it was, as the project finally came to fruition in 1987.
The earlier surveys had confirmed that a tunnel route could be bored through a chalk marl stratum that was conducive to tunnelling, with impermeability, ease of excavation and strength.
Two 7.6-metre diameter rail tunnels, 30 metres apart with a 4.8-metre diameter service tunnel in between were bored using TBMs (tunnel boring machines). The service tunnel was used as a pilot tunnel, boring ahead of the main tunnels to determine the conditions. English access was provided at Shakespeare Cliff, while French access came from a shaft at Sangatte.
On the UK side, 1 million cubic metres of the 5 million cubic metres of spoil was used for fill at the terminal site, and the remainder was deposited at Lower Shakespeare Cliff behind a seawall, reclaiming 74 acres of land.
The tunnel carries high-speed Eurostar passenger trains, Eurotunnel Shuttle roll-on/roll-off vehicle transport and international rail freight trains.