THE CHANNEL TUNNEL.

Dominion, Volume 6, Issue 1863, 24 September 1913, Page 8

THE CHANNEL TUNNEL.

BETWEEN ENGLAND AND FRANCE,

VARIOUS SCHEMES,

DIPS INTO OLD PIGEON-HOLES

The revival of tho scheme for construction of a tunnel across tho English Channel from England to Franco calls to mind various cross-Channel ideas which have been discusscd in the past and 'pigeon-holed. Tho idea of a bridge, like that of a tunnel, is not new; it is indeed nourlya century since definite plans of a bridge were published by Thome de Gamond, who alterwards allied himsolf with thoso who believed a tunnel to bo the best remedy. for the disadvantage of a Channel passage. None of the proposals then made —the indefatigable tie Gamond bad at least fivo different bridges in viewwon the support of linglish engineers, although iu France one design for t a bridge to be built in a series of granite arches was received with some favour. It was thought that tho the arches above water level, s<ft-. at centres, would meet the requirements of the ships then m eurvico, bub "jantime opposition was to bo placated by the provision of one swinging spau.

Fantastic proposals. A succeeding generation further elaborated the plan for a Channel bridge. It was in 1867 that Boutet prepared plans and models for a bridge between Capo Blaucnez and Dover, which wag to bo built in spans up to thrce-quar-tors of a mile in length, a then impossible engineering proposition. The Boyd Bridge, tho details '?f which were made public almost simultaneously with thoso of Boutet, wero for a bridge between Dover and Capo Grisnez. This was to bo constructed on iron girders, rising from towers, 190 in number, 600 ft. high, and a similar distanco apart. Tho cost of these schemes— Boyd contemplated an outlay of £30,000,000—and engineering and other considerations put them out of court. In the Mottier box bridgo the estimate of cost»was reduced to £12,000,000, but it, was a hazardous proposal to apply to tho Engli'sh Channel the principles of bridge construction which had enabled Stephenson tlio Monai Straits, and this scheme met tlio fate of its predecessors ir. being pigeon-holed. It was left to the Channel and Railway Company, s formed in 1886, to attack the bridgo problem on sound engineering lines. Experience in bridgo construction and the improvements in the materials available for the work, had reached a point when the idea of a Channel Bridge could be seriously entertained. No less «m authority than Sir Benjamin Baker, who had designed the Forth Bridge,- was associated with the preparation of the plans for a bridge between Folkestone and Capo Grisnez, in spans ranging up to 010 yards in length, at a cost of £34,000,000. The original plans would have enabled tho Vame and Colbard Shoals to have been utilised as pier foundations, but surveys indicated that good foundations could be obtained for a ' bridge threo miles shorter between Cape Blancnez and the South Foreland, at a cost of £28,320,000, and tlies chcme was modified to that extent.

Railway Interests. The railways associated with crossChannel traffic have never, since that redoubtable champion Sir Edward \vatkin first advocated it, wavered in their allegiance to the tunnel project. The altitude they have assumed is that while tho train ferry could effect something, a tunnel could acliicvo so much more that it is hardly worth while incurring the cost of establishing a tram ferry which would bo. certain, sooner or later, to bo superseded by tho tunnel A Channel tunnel would, it is claimed, not only make provision for a far largei traffic than a train ferry, both in passengers and goods, but would, enable tho timo of tho journey between London and Paris to bo cut to five hours, with a corresponding acceleration to all Continental destinations on the direct route. Much has happened since the Joint Committeo of both Houses of Parliament, by six votes to four, reported against tho proposal thirty years ago; there have been changes which | might even bo deemed revolutionary since the last Channel Tunnel Bill was withdrawn in 1907. Tho result has been to encourage the advocates of tho Channel Tunnel to mako another attempt. ■ Long Tunnel Problems. Much experience has accumulated during recent years on tunnelling under rivers and harbours, where provision has to bo mado for dealing with possible inrushes of water. No tunnel has, of course, been constructed under an arm of the sea comparable in length to the proposed Channel tunnel, -but tunnels have been driven under mountain rangers' wliero no intermediate shafts aro possible, and where special attention has had to bo given to tlio ventilation question. Considorablo advances in economy and speed _of construction have also been made since tlio driving of the St; Gotthard tunnel, nine and a third miles in length, in the '70's. What can now bo achieved is indicated by tho scheme for a railway tuniiol 22 miles long tho Caucasus Mountains. The question of tlio ventilation of a Channel tunnel was m early schemes proposed to be achieved by shafts rising to above sea level, which were open to tlio obvious objectiai of being a danger to navigation. Tlio experience gained in Alpine tunnels and tho certainty that the traffic in a Channel jtuimel would bo operated by electric traction liavo removed some of tlio objections which wore formerly raised as to tlio ventilation of tho tunnel. It is believed that mechanical methods aro now available which should do all that would be required to maintain tlio tunnel air at tlio required degreo of purity.

To Cost Sixteen Millions. Tho present plans for the tunnel aro practically the samo aB those for which approval was asked in 1907, a.tunnel through the lower or grey chalk from ii point inland near Dover to a point adjacent to Calais on tho French coast Tho under-sea section of the tunnel would be 24 miles long, and the total length of tho tunnel, including approaches, 30 miles. Tho scheme embodied in tho Bill of 1907 proposed two single-track tunnels of circular section, 18ft in diameter and 36ft. apart, centre to centre, but communicating at certain points to' facilitate ventilation, winch was to be effected by hydraulic turbines. It was proposed to adopt tho plan of driving a pilot beading, partly to test tho strata and partly to serve as a drainage driftaway. Tho tunnel for the greater part of its length would be drivon on tho level at a point oyer 100 ft. below the bed of the sea. _ An objection raised in tho discussion on tho proposals then made was the maximum gradient, 1 in 54.8, at which the tunnel was driven in tho first section of the descent to below sea level. A gradient of this order is severe for main line traffic on a route over which it' was proposed to run olcctnc trains at 48 miles per hour. It is true that tho rapid acceleration oil gradients >\ lucli _is Olio of the features of electric traction to some extent minimises this objection. The cost of the tunnel works is estimated in the light of modern knowledge at £16,000,0®, half of which would have to bo found by British interests and half by tno French.