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Floating Tunnels and Submerged Viaducts The Merits and Possibilities as Compared to Other Systems for Crossing Navigable Channels HE structures described in this paper include two kinds, (1) floating tubular bridges which are' borne: either onthe surface of the water or beneath it, and (2) sub- merged viaducts which rest beneath the water on piers. Bridges of almost every other kind, both fixed and movable, have been built at one time or another, but none of the types considered here have yet been constructed. The condi- tion is rather surprising, since these types have some undoubted advantages, including that .of economy, over high level bridges and tunnels. Lack of prec- edent is, no doubt, a serious obstacle to progress in this direction, for capital is not easily interested in new and un- tried inventions. Another barrier in the way of introducing these types is, that whether floating or submerged, these bridges are all tubular and are subject to many of the same objections as sub-aqueous tunnels, being artificial- ly lighted and ventilated, and often provoking that uncomfortable and un- canny feeling which accompanies travel underground. Collision with ships and the possibility of flooding have also influenced against them, and yet nearly all revolutionizing inventions have had much opposition to meet and overcome. The structures are suitable for cross- ing wide or very busy channels where movable bridgés of any kind would too greatly interfere with traffic on both road and water, and they may often be considered in competition with high level bridges or tunnels. Historical Data An invention, which is probably the first of its kind, in recent times at any rate, was patented in England in Au- gust, 1812, by J. J. Alexander McCarthy, who proposed a pontoon or floating tube with its center part deep enough below the water to allow ships to cross. This appears to have been the basis for the similar but later projects which ap- peared during the first half of the last century, several of which, including two by French and five by English engi- neers, were advanced for crossing the English Channel. Since the water in the channel is 180 feet at the center, and pier building therein would be difficult and expensive, a plan was pro- posed prior to 1830, by Delafons and Littlewort, for bridging it with float- ing piers or rows of barges, held in place by chains and anchors to maintain the piers at uniform elevation and pre- vent their rising or falling with wave or tide. These floating piers were io be surmounted with metal towers sup- porting the chains of a _ suspension bridge. Tunnels of Wrought Iron Tubes In the year 1845, M. De la Haye, of England, proposed building tunnels of wrought iron tubes in sections, which were to be sunk and afterwards con- nected together, and his estimate for one of this kind over the channel was $40,000,000. A plan was also proposed by a French engineer for an arched roadway on the channel bottom, the cost of which would not exceed $50,- 000,000. To execute the work would require forty sub-aqueous boats, 4,300,- 000 cubic yards of material, and the services of 1,500 men. More than 50 vears ago James Chalmers -- pre- pared plans for a double track tunnel to connect the railway systems of Eng- land and the continent. He proposed using two wrought iron tubes lined with brick, floating at first from their buoyancy, and then anchored down by | weight boxes filled with stone, After settling to the channel bottom, the tubes were to be covered with an em- bankment 150 ft. wide and 40 ft. high, the top of which would be 40 to 120 ft. below the water surface. These tubes were to be circular, and air was to be supplied through three vertical shafts at equal intervals throughout their length, the air circulation being forced with fans. Mr. Chalmers pub- lished a book describing his project, the cost of which he placed at $60,000,- 000. Somewhat similar schemes were afterwards advanced by Charles Mars- den and Zerah Colburn. Projects for crossing the English Channel in floating tubes were revived again, a few years later, by Martin, M. le Gay, of France, and J. F. Bate- man, the last contemplating cast iron \ By Henry Grattan Tyrrell, C. E, tubes, and one year later it was again agitated by J, S Story, Tr. © B Le bret also outlined a scheme for a "channel railway ferry" on floating piers anchored to the bottom, and he pub- lished and circulated a pamphlet de- scribing his invention. Instead of lay- ing tubes on the bottom, W. H. Barlow explained and advanced a method of using submerged steel tubes on_ piers, and the scheme was further developed by P. W. Barlow, but was afterwards abandoned. The tube idea was taken up again in 1876 by the celebrated Eng- lish engineer, Thomas Page, who de- signed many of the finest bridges in Great Britain. He favored sunken tubes as outlined by Messrs. Barlow, and intended building them in sections and then floating them out and sinking them in their proper places, as he had previously done across the harbor at Rio de Janeiro. A method somewhat similar to this was afterwards proposed, about thirty years ago, by Maynard and. Cook, for placing another tunnel under the Thames, with a 38-ft. road and two 8- ft. walks. The tube was to consist of wrought iron plates and arch ribs lined with brick and concrete casing 3%4 to 8 ft. thick. Sections 60 ft. long, with closed ends, were to be built on shore and then floated into position and sunk, the method being similar in some _ re- spects to that proposed in 1845 and revived twenty or more years after- wards, for crossing the English channel. Crossing the Sound A scheme for crossing the sound 2% miles wide, from Elsinore in Sweden to Helsingborg in Denmark, was ad- vanced a few years later by Rudolf Lilljeqvist, whose plans showed pro- vision for a single line of railway with a submerged tube resting on piers 100 feet apart on centers. It was to con- sist of inner and outer tubes, the small- er one having a diameter 3 ft. less than the outer one, and the space between - them was to be filled with concrete. The piers were to consist of iron cais- sons filled with concrete and the esti- mated cost of the whole undertaking was $3,000,000 to $4,000,000. A similar