Page:The American Cyclopædia (1879) Volume III.djvu/562

 556 CAISSON air in the chamber. He therefore arranged a cock which served the purpose of ventilation also. In the same year (1841) William Bush patented in England a method of sinking a cais- son by excavating within and beneath it in compressed air, the caisson becoming a part of the pier. A sectional view of his caisson is shown in fig. 1, which represents the air cham- ber A below a second air chamber B B, in which is the air lock C, leading to the air shaft D. The problem of disposing of the excavated material, which is always in such cases a serious one, was solved by using the second air cham- ber B B as an anteroom or receptacle, it being of considerable size and provided with a door above and below. The small air lock was for the passage of men without the loss of so much air as the opening of the large lock would occasion, and also to serve as a lock when in process of filling it became desirable to remove the diaphragm or partition between A Fro. 1. Bush's Caisson. and B B. Dr. Potts about 1847 patented a pro- cess of sinking hollow piles by air pressure by ex- hausting the air within. This was sold to Messrs. Fox and Henderson, who used it successfully at Anglesea with piles that were 12 in. in diam- eter ; it was also used at Windsor and at Hun- tingdon ; but on attempting the same process at Rochester in 1851, with cylinders 7 ft. in di- ameter, it proved unsuccessful, and the opposite or plenum process which is above described was adopted, and two air locks designed by Mr. Hughes were used. These locks, placed at the top of the air shaft, were D-shaped, and extended into the shaft so that the lower door opened on the side; the earth was raised in buckets and swung into the locks. The same plan was pursued at Chepstow on the Wye. Brunei used the same locks in sinking caissons on the Saltash 37 ft. in diameter ; he also used pipes and pumps for removing the water, so as to require less pressure of air. In 1854 Pfan- muller presented a design for a caisson at Mentz on the Rhine, which was to be constructed en- tirely of iron. It had supply shafts represented about 20 in. in diameter, running through the top of the caisson, with a door at each end for the purpose of conveying down the materials necessary for filling in the air chamber; it rep- resented the air lock near the air chamber. In 1855 Mr. L. J. Flemming recommended Potts's process to be used on the Great Pedee rivei 1 ; but encountering a log, he with Major Gwynne used the plenum process. He had two pipes, one for air, the other for removing water. In 1857 the same arrangement was used on the Santee river. Similar arrange- ments were used by Stephenson about the same time on the Nile, where was also used a caisson 28 by 19 ft., which would hold 40 men. In 1857 a caisson was sunk at Szegedin, Hungary, on the Theiss, which had a siphon pump for the removal of water, with a lock ex- tending into the air chamber, as at Chepstow. In 1858 this method was also used near St. Germain des Fosses, France, on the Allier. In 1859 the caisson for the Kehl bridge over the Rhine was sunk ; it had two shafts with air locks at the top, but provided with doors at the lower end of the shaft, converting the whole into a lock when required. A chain dredge running in a water shaft raised the materials excavated. This work was executed by Castor, who afterward sunk the foundations at Argenteuil. The same year a caisson was sunk at Kovno, Russia, on the Niemen, with two separate air shafts and locks, arranged so that when a bucket passed up one shaft another passed down the other. The same year, also, Gen. William Sooy Smith sunk several cylinders on the Savannah, Ga., in which he made two very important improvements. The first was a spout or trough extending out through the side of the air lock, through which by means of valves and cocks he could send out the ma- terial brought up into the lock expeditiously, and with little waste of air. But his most val- uable improvement was the method of blowing the sand out through pipes by means of the compressed air. In 1860 the same process was used at Harlem, New York, by W. J. McAlpine. In 1862, at Argenteuil, France, on the Seine, the double locks at the top of the two air shafts were connected with each other by a pipe so as to allow the air escaping from the one to partially fill the other. The caissons at Konigsberg, Prussia, on the Pregel, and at Lorient, France, on the Scorf, the former with working chambers 50 by 20 ft., and the latter 39 ft. 6 in. by 11 ft. 5 in., were sunk like that at Kehl ; the latter were sunk in 1866 by Des- noyes, as were also those on the Loire near Nantes. About the same time a circular cais- son 26 ft. in diameter was sunk at Stettin on the Parnitz, in which a siphon pipe 2J in. in diameter, with a cock 6 ft. above the bottom, was used for ventilation and removal of water. In 1868 Burmeister and Wain used a removable caisson in excavating for and building piers at Copenhagen. At Perpignan, France, on the Tet, an iron cap with an air lock attached was secured to the top of a cylinder of masonry,