RETIRED CHARTERED ENGINEERS ASSOCIATION.
Eighteenth Cooch Memorial Lecture, Friday 25th November, 1988.
by Mr. Peter Marten.
The Chairman welcomed Mr. Marten, who is engaged as a Quality Assurance Engineer in the construction of the Railway Tunnel between England and France. He has gained a wide knowledge of the whole concept, and is well qualified to give this lecture.
Mr. Marten introduced himself as a non specialist with an engineer’s appreciation of the construction and proposed operation of the tunnel.
Historically a number of previous attempts have been made to build a tunnel under the Straits of Dover, the first in 1802. Napoleon favoured this, perhaps with a military object in mind! Britain objected! In 1881 Col. Frederic Beaumont and Captain Thomas English invented a boring machine powered by compressed air piped from the surface. They
had bored about a mile from the English side and 1$ miles on the French side when British military objections stopped the work. One consequence was the start of the Kentish coal field, as they found a strata of coal in the chalk. Other proposals were made in 1905 and 1930’s. British military objections were not withdrawn until 1955.
A further start was made in 1973, but after modest progress was dropped by the U.K. Government because of cost. The machines for this, costing H million each, were similar in principle to Col. Beaumont’s.. The design proved successful in a trial bore of about 200 yards.
The present project started in 1985 is an updated revival of the 1974 scheme. It will be some 50 km long, with 4 km under French and 9 km under English mainland, and 37 km under sea. Shuttle traffic will travel between Cheriton near Folkestone and Coquelles near Calais.
The access tunnel gradients are 1 in 90, which determines the length of the underground access to reach the surface – the downs at Folkestone and the much lower surface at Calais. There will be two single track rail tunnels 30 m apart and 7.5 m diameter and a service tunnel between them of 4.8 diameter with cross passages every 375 m. and two rail cross-over passages dividing each tunnel into three to facilitate maintenance and emergency action. The service tunnel provides for ventilation, with fans at each end, and for maintenance and safety. Air build up in front of the trains will be relieved by ducts directly linking the running tunnels at about 200 metre pitch. Roll-on – Rolloff terminals provide a closed loop for the shuttle trains, with platforms alongside numerous sidings to which traffic will be directed as appropriate. They will also include Customs and Immigration facilities.
III. Shuttle trains will be divided into tourist “rakes” and freight “rakes” Tourist rakes will each comprise 13 carrying waggons with a loading waggon at each end, single deck carriages for coaches, caravans etc., and double deck for cars only. There will be a locomotive at each end.
Freight trains will comprise 25 waggons with a loading waggon and a locomotive at each end. Carrying capacity of the double deck is up to 126 cars, single deck some 65 “car equivalent” vehicles per rake; for freight, 25 lorries up to 44 tons each per shuttle. Coaches will be well lit, warm and sound insulated. The journey will take 30-35 mins, at a maximum speed of 100 m.p.h. and overall time including access and loading for passenger traffic will be 55 to 75 minutes from leaving the M20 to joining The French roads.
B.R. and S.N.C.R. main line railways will be allocated sequence “slots” in which to use the tunnel – some 50% of tunnel traffic. Journey times from London to Paris/Brussels will be 3i hrs. and 2 hrs. 55 mins, respectively. If B.R. build a high speed rail link from London, some 20 or 30 mins, will be lopped off! Through trains will run from Scotland etc. to various other European cities. B.R. will build an international station near Ashford as well as a special section at Waterloo, to provide Customs and Immigration facilities, both French and English, thus cutting down through transport time.
Construction. The boring machines are a modern development of that devised by Beaumont in 1881 and the proven design of 1974. Behind the cutting head is a ring of slightly less diameter, with pads that when thrust radially outwards against the tunnel wall firmly fix the ring, and from which jacks thrust forward behind the cutting head asembly when cutting. The jacks are hydraulically operated and can be adjusted accurately to “steer” the bore. Access through the machine is provided for trucks on narrow gauge rails to remove spoil from the cutting face and to bring in the 1| metre wide segments of tunnel lining which are placed immediately behind the anchor ring.
A re-enforced concrete lining segment weighs 11 tons and there are 6 segments for each ring. The overall length of these machines is some 250 metres. Each one costs f.6| million, for the rail tunnels. The favourable chalk marie on the English side, being impervious to water, enables progress of about 200 metres a week. French conditions are less favourable, and progress will thus be slower until they reach the chalk marie. Because the tunnel lining segments
are fitted behind the bore head and anchor ring there is no means of retracting the machine – it can only go forward. Dismantling would be difficult and expensive; the plan is therefore that when opposite borings are just short of meeting the machines will be deflected from the tunnels line, sealed up and abandoned under the sea.
On the English side the spoil is tipped into lagoons built in the sea at the base of Shakespeare Cliff, extending the existing spoil area created by cliff clearance for the Folkeston – Dover railway last century, and from which the old adit goes into the tunnel.
On the French side some large concrete structures built by the Germans for artillary bombardment of Dover in the second World War are being used in damming up a valley into which spoil is tipped.
The rail gauge is standard European 4 ft. 8 1/2 inches with 25 kV overhead catenary conductors for the traction supply. A continuous strong platform will run both sides of each tunnel to provide for maintenance and emergency access. This reduces the noise level from the rails, and should derailment occur, would keep the train reasonably upright.
Finance to the tune of £6 billion has been raised Worldwide to cover the estimated construction costs plus contingencies etc. 198 banks are involved, and the expenditure is expected to be re-couped within the concession period of 55 years – at which points the governments will “inherit” the project; it is expected that they will then re-negotiate a concession to operate. The design life is 120 years. No government capital is involved in the project.
Of the estimated costs 50% is for “Target works” costs – that work for which no firm quotation could be given -i.e. tunnelling. Procurement items such as locomotives take 10% and 40% covers all above ground work.
Discussion. This was well informed and further points of interest arose e.g.
Power supply is from both E.de F., and S.E.E.B., and each side can cover the whole demand.
Emergency and accident arrangements include the procedure to break off coaches each side of a seriously damaged coach to drive on, or back. Also for a special high speed exit to an emergency siding for ambulances, fire fighting etc.
Control and signalling uses radio and laser, each cab being given information of the location etc. of other trains running in its tunnel. The tunnel runs some 30 to 40 metres below sea level in the deeper part.
An exhibition is open to the public at Folkestone – well worth a visit; it cost 2 or 3 million pounds!
A warm vote of thanks was proposed by Mr. K. Lambert and carried with acclamation.