Scientific NewsThe Illustrated London News, vol. 40, no. 1125, p. 30.
January 4, 1862
Pneumatic Pile-Bridge—Mr. C. C. Martin, the American engineer who completed the Brooklyn Waterworks, carried on the erection of a bridge across the Savannah River until interrupted by the civil war. This bridge is on the line of the Charleston and Savannah Railroad, about sixteen miles from the latter city. When completed, it will consist of six fixed spans and a swing-bridge, with an aggregate length of 900 feet. The two abutments and seven piers are to consist of pneumatic piles—the abutments and four piers to be of two piles each, the piers at the end of the swing-bridge to consist of four cylinders each, and the pivot-pier of five. The cylinders are cast in sections, nine feet in length and six feet outside diameter, with two inches of metal. The apparatus for sinking these piles consists of a large flat boat, upon which is placed a 16-horse power steam-engine, and two double-acting air-pumps, hoisting apparatus, &c. In the Journal of the Franklin Institute, Philadelphia, appears an interesting account of the process of sinking the cylinders, with illustrative woodcuts. Two portions of cylinder are made airtight by whitelead, and held in proper position by "guys," &c. The pumps are set in action, and the cylinder sinks into the sand (about six feet in three minutes) on the application of a vacuum. As the process proceeds, a syphon pipe and other apparatus are employed. When at last a stopcock is opened, and the compressed air is allowed to escape suddenly, the upward pressure from within is removed and the cylinder, by its own weight, forces itself deeply into the sand. The amount of sand which enters the cylinder under the bottom when the pressure is allowed to escape is astonishing. When a cylinder sank less then a foot the sand rose inside it twenty-two feet (equal to twenty-one cubic yards), which was brought in by the rushing water in a few minutes. On one occasion, when the men were at work in a cylinder, they suddenly heard a sound like the report of a cannon, and all became as dark as night. The report was occasioned by the sudden removal of the pressure from without, while within the air was condensed. The darkness was occasioned by the rapid condensation of the vapour held in invisible suspension in the condensed air, forming a thick fog.