Caissons Sinking Tubes

SINKING TUBES, CAISSONS, COFFER-DAMS, ETC.

In 1845, De la Haye, in England, doubtless having in mind the tedious and difficult work of the Thames tunnel, proposed to make tunnels under water by sinking large tubes on a previously pre pared bed and connecting them together. Since then many in ventors have proposed similar schemes. In 1866 Belgrand sank twin-plate iron pipes, 3.28 ft. in diameter and 512 ft. long, under the Seine at Paris for a sewer siphon, and there have since been numerous examples of sunk cast iron subaqueous water-pipes.

First Subaqueous Trench Tunnel.

It is believed that the first tunnel of this class, large enough for men to move upright in, was by H. A. Carson, assisted by W. Blanchard and F. D. Smith (in in the outer portion of Boston harbour, for the metropolitan sewer outlet. The later tubes were about 9 ft. ex terior diameter, in sections each 52 ft. long weighing about 210,000 lbs., made of brick and concrete, with a skin of wood and water tight bulkheads at each end. A trench was dredged in the harbour bed and saddles were accurately placed to support the tubes. The latter, made in cradles above the water alongside a wharf, were lowered and towed 1 to m. to their final positions. After suf ficient water had been admitted they were lowered to their saddles by travelling shears on temporary piles. The temporary joints be tween consecutive sections were made by rubber gaskets between flanges which were bolted together by divers. The later opera tions were backfilling the trench over the pipes and, in each sec tion, pumping out the water, removing its bulkheads and making good the masonry between consecutive bulkheads, this masonry being inside the flanges. This work, about 1,500 ft. in length, was done without contractors, by labourers and foremen under the immediate control of the engineers and was found perfectly sound.

The double-track railroad tunnel at Detroit, made in 1906-09, for the Michigan Central railroad, was built under the direction of an advisory board consisting of W. J. Wilgus, chairman, H. A.

Carson and W. S. Kinnear, chief engineer. The tunnel is 1.5 m. long, with a portion of o.5 m. directly under the river. A

trench was dredged with a depth equal to the vertical dimension of the tunnel below the river bed and about 7o ft. below the river surface and grillages were accurately placed in it to support the ends of thin steel tube forms, inside of which concrete was to be moulded and outside of which deposited. These tubes, each about 23 ft. in diameter and 262.5 ft. long, were in pairs (one tube for each track) and were joined together at intervals of 12 ft. by thin steel diaphragms surrounding the tubes. The planking, to limit the concrete, was secured to the outside edges of the diaphragms. The tubes were made tight, bulkheaded at their ends, floated into place, sunk by admitting water, set on the grillages and the ends of successive pairs connected together by bolts through rubber gaskets and flanges.

The second (1913-15) tunnel crossing of the rapid transit sys tem at New York beneath the Harlem river from Lexington ave nue, in Manhattan, to Mott avenue, in the Bronx, consists of four tubes LoSo ft. long. The general design and method of construc tion were modifications of those used in the Michigan Central railroad tunnel at Detroit. The tunnel was built in five sections, 199 to 220 ft. in length. A trench was dredged with a width of 81 ft. and side slopes of 45°. The sections (77o tons) were erected on timber falsework and, to launch them, flat boats were run beneath the sections at low tide and the rising tide lifted them from the falsework. The ends of the tubes were provided with timber bulkheads to make the tubes float, and when free from the falsework they were towed by a tug into the river, where the flat boats were scuttled and sunk by opening valves provided for the purpose. The tubes then floated on their own bottoms and were towed to the tunnel site and sunk on the timber caps provided for their support in the river. (See Plate, fig. 5.) The water was then pumped from the tubes and they were lined with concrete. The tunnels were completed without the use of compressed air for any part of the work. Alfred Craven was chief engineer for the Public Service Commission and the contractor was the Arthur McMullen and Hoff Company.