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Digging the Channel Tunnel



In our look back over the last 50 years of engineering we reach 1994 and a project that brought two nations together and connected the British Isles to mainland Europe - the Channel Tunnel.

The origins of the tunnel’s engineering go back further than you might think - in fact it was almost two centuries prior to its opening that the first proposals were put forward. French mining engineer Albert Mathieu-Favier came up with a design that would allow horse-drawn carriages to travel through a tunnel lit by oil lamps. His plans included construction of an artificial island halfway across for changing horses. 

The idea resurfaced several times over the years, with Napoleon III considering proposals in 1856, William Gladstone in 1856 and David Lloyd George in 1919. Winston Churchill was a longtime advocate for a Channel Tunnel, bringing its potential up in essays published in the Weekly Dispatch and Daily Mail throughout the 1920s and 30s. 

Finally the two nations would make an agreement to begin conducting technical and geological surveys in 1964. But concerns over cost and uncertainty about whether the UK would join the EEC (the precursor to the European Union) meant that construction was delayed in the mid-70s - despite both sides having completed specially-made boring machines and beginning work on access tunnels. 

The project was eventually handed over to the private sector, with Channel Tunnel Group/France-Manche (CTG/F-M) being awarded the project with their proposal for a rail-based Channel Tunnel.

Construction began in 1988 and lasted six years. Eleven boring machines were used, digging simultaneously from the English and French side with plans to meet in the middle. In fact the English side was slightly longer than the French side when they finally met up. The ceremonial “break through” was accomplished on the 1st December 1990, by Englishman Graham Fagg and Frenchman Phillippe Cozette. 

At the height of construction the Channel Tunnel employed 13,000 workers - a number of whom, we’re pleased to say, were contracted by Fircroft!

The Engineering of the Channel Tunnel

The Channel Tunnel actually comprises three tunnels - two for trains (travelling in opposite directions) and a smaller service tunnel that can be used for evacuation in case of emergencies.  

For most of its length the tunnel had to bore through a chalk marl stratum - a geology that is fortunately conducive to tunneling thanks to its strength, ease of excavation and impermeability. This was common in the mining industry, which provided the necessary tunneling experience - but tunneling underwater presents its own unique challenges. Hydrostatic pressure and weak ground conditions make water inflow a serious safety problem that had to be overcome. 
The tunnel boring machines (TBMs) were designed and manufactured by a joint venture including Robbins Company of Kent, Markham & Co and Kawasaki Heavy Industries. Each was as long as two football pitches, and together they weighed a total of 12,000 tonnes. 

The TBM drives used precast segmental linings, while additional lining segments were added on each side to further strengthen the tunnels and safely bore 50m below the seabed. On the French side for the first 5km before the tunnel reaches the chalk marl stratum, the geology had a greater permeability to water. Modified earth pressure balance TBMs with open and closed modules were used. The closed TBMs were used in this initial 5km which minimised impact to the ground, allowing high water pressures to be withstood and alleviating the need to grout ahead of the tunnel.

The completed Channel Tunnel is 31.3 miles long - making it the 13th longest tunnel in the world with the longest undersea portion of any tunnel (23.5 miles).

The Channel Tunnel was first opened to lorry shuttles in May 1994, with the Eurostar passenger trains operational by November and car shuttles going by December. Today 60,000 passengers pass through the tunnel each day, with 4,600 trucks, 140 coaches and 7,300 cars. The journey takes just 35 minutes. 

The lining of the tunnel is designed to last for 120 years. Construction took six years and cost the equivalent of £12 billion in todays money. It was recognised as one of the “Seven Wonders of the Modern World” by the American Society of Civil Engineers. 

Fircroft has been supporting engineers on some of the world’s most ambitious projects since 1970.

Register with us today so our experienced recruitment team can help you find your next engineering job.

Recent Comments
I was there that’s running tunnel north land
Mark bates, 23 July 2020
Tunneling actually commenced in 1987 in the UK service tunnel. I have seen this 1988 commencement used in several places but I was working on the Howdens service machine in 1987.
Paul Darbishire, 25 July 2020
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Digging the Channel Tunnel - Time to read 4 min
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