'78

On the Pneum:ltic 2tletlwd adopted in construcling the Foundations of the nzw BJi:tge across the g~leJway, at Rochester. By Joule HtJ~HEs, Assoc. Inst. C. E.* This bridge was describe l as being designed to consist of three large

openings, a central one of 170 feet in width, and two others; each of 140 feet in width, spauned by cast h'on segmental girders, and of a passage to admit masted vessels to the upper parts of the river, across which a move- able bridge would be placed. Each of the river piers occupied an area of 1118 square feet, and rested upon a series of cast iron cylinder piles, 7 feet in diameter, placed 9 feet apart longitudinally, and 10 feet trans- .versely, so that there were fourteen under taeh pier. The cylinder piles m the abutments were 6 feet in diameler, of which the "Strood" abutment required thirty, and the "Rochester" abu',ment twelve. Each pile was co,nposed of two, three, or more cylinders, 9 feet in length, bolted together through st~ut tlanches; the bottom length had its lower edge bevelled, so as to faciliate the cutting lhrough the ground. The bed of the river was origin.ally presumed to consist of soft clay, sand, and graveli overlying the chalk, and accordingly the application of Dr. Potts' pneu- matic melhod fi~r tbrciag the cylinder piles in:o the ground, which had been successfully carried out in similar positions, was contemplated; but afWr a few trials, the ground was found to consist of a compact mass of Kentish ragstone, so flint the mere atmospheric action upon the piles, induced by a partial vacuum, would be inefliective in such a situation. It was therefore deeid~d, that the pneumatic process should be reversed, so as to give each pile the character o{' a diving-bell; for which purpose one of the cylinders, 7 feet in diameter, and 9 feet inlength, had a wrought iron cover securely bolted to it, through which two east iron chambers, D shaped in plan, with a sectional area of about 6 square feet appropri- ately called "air locks," projected 2 l~et 6 inches above the top of the cylinder, and 3 feet 9 inches below the cover. The top of each "air lock" was p~ovided with a circtdar opening 2 feet in diame- ter, with a flap working on a hc~r!zontal hinge, and an iron door, 2 feet by 3 tbet 4 inch~:s, with vertical binges below the cover; each air lock was also furnished with two sets ~,f cocks, the one for forming a commu- nication between the cylinders a:~.t the chamber, and the other between the chamber and the atmosphere Compressed air was supplied to the cylinder pile by a double-barrelled pump, 12 incites in diameter, and 18 inche~ stroke, driven by a six horse power non-condensing steam engine. At first tim expelled water was made to pass into the river, from beneath the lower edge of the piles, but when the stratum became so compact as to oppose a high degree of l esistanee to ihe passage of the air, an outlet was tbrmed through the side of the uppermost cylinder, by the introduc- tion of a pipe having the tbrm of a syphon, the long leg of which reached to the bottom of the pile, m~d was sul~ject to the pressure of the condensed air on 1he surt:ace of the water within, whilst the short leg leading into the river, had the effect of relieving 1he am, rant of compression, provided a vacuum was once obtai~,ed in the body of the syphon. Such aa effect was readily produced by crnmeeting the summit with the exhaust side of the air pumps, by a pipe, which could be opened or closed at pleasure. To insure the downward motion of the pile, and to give it a weight

• Fl'cm the London Architect, for June, 1851,

Railway over the ,.%emmering .Moun&in, .3ustria. 79

which should be at all times superior to the upward pressure, two s tout trussed timber beams were laid on the top of the cylinder, in a direction suitable for bringing the adjacent piles into action as counterbalance weights, by four chains passing over cast iron sheaves.

Two light wrought-iron cranes were fixed inside the cylinder, the jibs of which swept over the space between the air locks and windlasses, inside and outside, for the purpose of hoisting the loaded buckets, and lowering the empty ones.

The method followed in worl~ing the apparatus was found to be so simple in detail, as to be perfectly intelligible to all the workmen employ- ed. The pumps being set in motion, the flap of one of the air locks and the door of the other, were closed; a few strokes compressed the air within the pile sufficiently to seal the joints, anti whilst the pumping was in progress, the men passed through the air locks to their respective stations. When the water was shallow, the pile descended, by scarcely sensible degrees, as fast as the excavation by hand permitted; when the water was deep, the excavation was carded down full 14 inches below the edge of the pile, which then descended, at once, through the whole space, as soon as the pressure was eased off

The most perfect certainty and success had attended the employment of this simple system, and as it promised to aflbrd considerable assistance to engineers in the prosecution of similar works, the author laid the ac- count before the Institution with the sanction of Mr. Cubitt, President Inst. C. E., the engineer-in-chief, and Messrs Fox, Henderson, and Co., the contractors for the works ~Proc. Inst. Cir. Eng..May 13th, 1851.

Railway over the Soernznering .Mountain, .,~ustria.

This railroad is assuredly one of the most important public works ever executed in :Europe, both as regards the fact of its establishing a com- munication with the Adriatic, and the considerable height it has to pass. The number of persons employed, when the greatest activity was dis- played in pushing the work forward, amounted to 16,000 men, and 2000 women and children. The cholera broke out last season among these workpeople, in consequence of their not being properly housed, which in some degree even interrupted the progress of the undertaking:

The height of the Soemmering at the spot where the railroad will pass, is 3066 feet above the level of the sea ; but a tunnel is to be bored in the mountain at a height of 2790 feet. 1200 men and twelve steam engines o f an aggregate power of 200 horses, are employed in this tunnel, which is called the Soemmering Haupt Tunnel, and the length of which is about one English mile. Four millions cubic feet of stone and earth will have to be displaced, at a cost of 150,000l. The esti- mated cost of the whole Soemmering railway, is 800,000l., but will probably amount to a million. As the length is 5 German miles, (20 English), each mile will require an outlay of nearly 200,000l. This sum is large ; but the railroad on the Prussian and Belgian frontiers exceeded

From the London Architect, for June, 1851.