THE CHANNEL TUNNEL.

Star (Christchurch), Issue 6788, 27 February 1890, Page 3

THE CHANNEL TUNNEL.

A great steel bridge across the English Channel is projected. The bridge will stretch over the shallowest and narrowest arb of the Channel between Cape Grisnez and Folkestone, and will be supported by columns resting on the bottom of the sea. Ihe amount of metal and machinery to be provided would represent an aggregate weight of about 1,000,000 tons, the assumption being that each country will have to supply one-half of this amount. Eegarding the cost of the work, a rough calculation gives, with reasonable certainty, 380,000,000 francs for masonry supports and 480,000,000 francs for the metallic superstructure— in all, 800,000,000 francs, or The time required for the undertaking may be fixed at about ten years. The whole of the pillars will occupy a little over one-twelfth of the section of the channel. The distance between the piers, fixed at 500 and 300 meters for the large spans will not be less than 200 and 100 meters respectively for the small onfis, and •will be sufficient to prevent their proving an obstacle to the free navigation of sailing vessels. As for the metallic superstructure, the metal columns firmly placed upon the platforms of the supporting piers of masonry are of a distinctly cylindrical shape, and vary in height between 40 and 4278 meters, and on them will be placed the main girders of the bridge. There will thus be between the lower part of the beams and the level of the sea at low ■water a free space varying in height between Gl and G3-78 meters, which height at high water will be reduced to 54 and 5678 meters, respectively. This height is amply sufficient for the passage of vessels of whatsoever description or tonnage. By placing the flooring upon vertical cylindrical columns the minimum height of 54 meters is kept throughout the whole width of the span, a result not achieved in the bridge over the Forth. The girders are to be simple, unlutticed and trussed, so as to insure the proper distribution of all stresses. The level of the permanent way is 72 meters above the lowwater level. There will be a double set of rails, and the width of the flooring proper will be 8 metres. The width of the bridge is variable, the greatest distance being between the axes of the main girders, 25 metres, a space necessary to ensure the stability of tho structure under the action of violent gusts of wind. The roadways are of the ordinary width of 15 metreß between the axea and the rails, the latter set in grooves to obviate accident. The floor, made of ribbed sheet iron, is to cover the bridge throughout its length so as to make every part accessible to the men appointed for its supervision. Between and outßide the roadways pavements are provided for the men to stand on, and thus keep out of the way of passing trains. On the flooring may be set up refuges, stations for the guards, signal-boxes, switches, &c. All these arrangements can be multiplied according to the requirements of the traffic, and scattered over any convenient points and spans on the piers. Lighthouses may be erected to indicate obstacles to be avoided. The various kinds of lights used in lighthouses may also serve to indicate to shippers the distance from the Colbart and Varne banks. To meet military objections arrangements could be made for making the span at either end of the bridge unfit for use; the two end spans, notably, which are in contact with the abutments, might be removable or revolve.