Handbook of Railroad Construction; For the use of American engineers. / Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States.

by George L. Vose

DR. POTTS’S ATMOSPHERIC SYSTEM.

280. All methods of placing foundations in difficult positions must yield to the above plan, which consists in exhausting the air from a hollow cast-iron cylinder; when the pressure upon the surface of the ground, outside of the cylinder, forces the earth immediately under the pile to its interior; at the same time the pile sinks into the opening thus made, both by its weight and by the atmospheric pressure from the outside. The earth is moved from the interior of the pile; and when sunk to the necessary depth, the interior is filled with concrete.

A very successful application of the above system was made at the Goodwin Sands, at the mouth of the Thames River, (England). These sands change their position with every violent storm, and are yet so compact that a steel bar could be driven only eight feet with a sledge hammer; and a pointed rod three inches in diameter, when sunk thirteen feet deep, required forty-six blows from a one hundred lbs. ram falling ten feet to drive it one inch. But a hollow pile two and a half feet in diameter was sunk seventy-eight feet, at the rate of ten feet per hour for a part of the time. In case of meeting with rock, the pile may be converted into a diving-bell, and the obstruction moved.

The pile is cast in lengths of ten or twelve feet, and flanged together with cemented joints.

In founding a bridge at Rochester, (England,) a pile of this nature was loaded with thirty tons of iron rails, which caused a settlement of three fourths of an inch. The rails being removed and the air exhausted, by a single effort the pile descended six and a half feet. One hundred tons of rails were then placed upon the pile, when the settlement was again three fourths of an inch. (This small depression was owing to the compression of the soil.)

The piles supporting the Shannon bridge, on the Midland Great Western Railroad, (England,) were sunk by this system; and are ten feet in diameter, and filled with concrete.

After wooden piles have been driven, they are cut off at the proper level to receive the lower courses of the masonry. In some cases square timber caps are placed upon the pile heads, and thereon a plank floor. In others, the spaces between the piles are filled with cement and concrete.