THE CHANNEL TUNNEL
By ROLT HAMMOND
[M. de Monzie, the French Minister of Public Works, stated in the Chamber this month that the construction of a Channel Tunnel would' be one of the first public works to be undertaken after the war] FOR more than half a century the idea of driving a tunnel under the English Channel has been discussed from every angle. Volumes have been written on the subject and many different schemes have been put forward, some of them utterly fantastic, but there is no doubt that in the present conflict this tunnel would have been of inestimable value.
Practically invulnerable, alike from attack by aeroplane and submarine, it would have formed an unrivalled line of communication for the rapid passage of troops and munitions to France. Furthermore, it would make available all French and British ports on the Atlantic ; recent events have shown all too clearly that ships bound for this country have to converge upon English ports for unloading their cargoes, which facilitates attacks upon them by mine and submarine.
It is not generally realised that the Channel Tunnel Com- pany is still in existence, an offshoot of the original parent company known as the Submarine Continental Railway Com- pany, founded in the year 1881. There is only one share- holder of this company still alive, the octogenarian Mr. Charles Sheath, who still retains his original enthusiasm for the scheme and is thoroughly optimistic about its eventual success. Some years ago more than 2,000 yards of a pilot tunnel were driven below the sea near Dover, and it is significant that at one time five well-known British public works contractors agreed to pool their resources for the purpose of carrying out the project. French opinion has been very much in favour of a Channel Tunnel, and Marshal Foch went so far as to say that it " would make war in Western Europe impossible." Some idea of the importance which the French Government attaches to the scheme is provided by the fact that the French Chamber recently passed a favourable vote upon it, strongly supported by the Foreign Affairs Committee. Since this happened at a time of grave crisis, shortly before the out- break of war, the whole matter has had to be postponed indefinitely. The additional fact that General Weygand recently joined the board of the Channel Tunnel Company is further proof of French military interest in its strategical value.
In an admirable article published in The Spectator recently, M. Dautry, chairman of the French Channel Tunnel Committee, suggested a tunnel with a length under the sea of about twenty miles, to be built at a cost of some 3o million pounds ; the depth of its lowest portion would be about 300 feet below sea level. He quotes the agreement reached between British and French experts that the receipts in the first year would be about 557 million francs, and that the tunnel would be a financially self- supporting organisation.
Just before the war considerable interest was aroused by a detailed scheme brought forward by the eminent French civil engineer, M. Andre Boisdevant, who proposed a thirty- *mile road tunnel with a road width of 22 feet and a height from road level to roof of 18 feet ; in this case the deepest point would be about 450 feet below sea level. The route of the proposed tunnel would start at Marquise, pass under Cape Gris Nez and emerge on the British side near Folkestone. The Boisdevant plan is estimated to cost about 42 millions ; the reason for the great increase' over the Com- mittee's plan being the increased length and depth. It is probable that M. Boisdevant wishes to avoid any possibility of earth movements near the cliffs on each side of the Channel affecting the structure of the tunnel. From the technical standpoint the constructors would be faced with many grave difficulties, but during the last few years the art of tunnelling has advanced by leaps and bounds. It would be no exaggeration to say that there is practically no type of ground which the modern tunneller could not tackle, in view of the vast amount of experience which he has accumulated. Perhaps his greatest enemy, apart from loose ground and heavy rock pressure, is water ; this can now be kept at bay by many ingeniou's methods, such as compressed air, chemical consolidation of the strata, freez- ing and cementation, effected by injecting cement grout into the rock fissures. The two latter methods are often employed in mining work and for sinking shafts through heavily waterlogged ground.
Although it is known that the tunnel would pass through a bed of homogeneous and impermeable material known as Rouen chalk, it is believed that the greatest obstacle would be the glacial morain said to exist in the centre of the Channel. This is a vast area of tumbled boulders left behind by the passage of a glacier in remote geological times. Pene- trating such difficult and dangerous ground involves tunnell- ing skill of the highest possible order, and the great depth at which the work would have to be carried out in this section would involve special methods. Freezing of the ground water would probably be employed for keeping the water back, since at such depths the air pressure would be so great that no human being could work in it.
By freezing that portion of the ground directly in front of the working face, the constructors would be dealing with similar conditions and problems to those commonly asso- ciated with hard rock tunnelling. It is probable that the best method of carrying out the work would be to drive two small-diameter pilot tunnels side by side for the entire length of the finished tunnel, working from both sides of the Channel and meeting in the centre, in the course of which a complete section of the ground through which the main tunnel would have to pass would be obtained.
Only after driving these pilots could the engineers reach some definite conclusion as to the ultimate cost of the tunnel, since during their perforation they would be able to obtain cores of the surrounding strata by means of diamond drills. They would also inject cement both for the purpose of consolidating the -ground and gaining an idea of its porosity. The pilot tunnels would afterwards be enlarged to the full section of the main tunnel.
Until. comparatively recently this great scheme was shelved for reasons of national defence, but now that we are so closely linked economically and politically with France the proposed tunnel once again assumes great importance in any scheme of post-war planning. Indeed, it should form a vital artery of trade and transport in that United States of Europe which so many of us would like to see emerging from the present disorder.
Clearly this vast undertaking will now have to wait upon events, but it is both encouraging and refreshing in these times to examine a project of this kind in relation to that era of construction which we all hope to see at the end of this war. Even under the most favourable conditions it would probably entail a construction period of at least five years in which to complete the tunnel, and it is obvious that it could only be carried through successfully with the backing of the French and British Governments. Commer- cial considerations would be of secondary importance when compared with the political and strategical aspects of the scheme.
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