For works with similar titles, see Caisson.
The American Cyclopædia
Caisson by William H. Paine
CAISSON (Fr. caisse, a case or chest), inarchitecture, a panel sunk below the surface insoffits or ceilings. In civil engineering, the term isapplied, first, to a hollow floating box, usuallyof iron, which serves to close the entrances ofdocks and basins; and second, to a box-likestructure used in constructing or sinking thefoundation of piers under water. Of the latterthere are at least three different varieties: theordinary, the bottomless or open, and theinverted, which includes the pneumatic. 1. Theordinary caisson is a large box with bottom andsides, made of timbers or planks, in whichmasonry is built and sunk to its desired positionunder water. The first caissons of this descriptionof which we have any account were usedin laying the foundations of the Westminsterbridge, England, in 1738-'40, by CharlesLabelye, a Swiss. Frère Romain had in 1685laid the foundation of the bridge of the Tuileriesin what has sometimes been called a caisson,but it answered more nearly to what is nowtermed a crib, the stones being cramped togetherwith timbers and sunk by the aid of guidepiles. Baskets and even barges filled withstones had been sunk at various places; but asthe idea of making a tight box in which masonrycould be properly laid, and the sinking ofit done gradually and under full control, seemsto have originated with Labelye, it is mentionedas a new system of laying foundations indeep water. These caissons, of which therewere twelve, were oblong and pointed at eachend. They were 80 ft. long from point to point,30 ft. wide, and 18 ft. high. The bottoms wereformed of timbers 12 in. square laid lengthwiseand close together. Under these were a courseof planks 3 in. thick, and over them a course oftimber 9 in. square, both laid across the firstcourse and secured to it. The sides were builtof fir timbers laid up horizontally on each otherand pinned together with oak treenails. All thecorners excepting at the ends were framedtogether, and further secured by three oak kneeseach; the two points were secured by irons,which were capable of being unfastened, so thatthe sides could be removed and used for theother caissons. When the masonry was builtin these caissons the water inside was controlledby pumps so as to lower the whole graduallyto its proper position. De Cessart had justinvented a saw for cutting off piles under water,and was about to use it at Saumur on the Loire,when the success of Labelye caused him tochange his plans, and he used caissons not onlyat Saumur, but later at Dieppe, Toulon, andRouen. Bayeux used caissons at Tours on theLoire in 1755, Bellecour at Lyons on the Saônein 1789, Deschamps at Bordeaux, and Beaupréat Sèevres, besides many other distinguishedengineers down to the present time. 2. Open orbottomless caissons. Curbs or a species ofmovable coffer dam have been used of a varietyof forms and sizes, and as many of these havebeen called caissons by the best engineers, theyare included under this head. The most prevalentform of these curbs or caissons has beencylindrical, and they have usually been madeof iron. The usual method of sinking them hasbeen to lower them down so that they standvertically on their lower edge; then, by weightsor building on flanges, to force them as far aspossible into the bed of the stream. When bydredges or pumps the material on the inside hasbeen excavated and the whole gradually loweredtill a bed has been reached so impervious asto permit the water to be all removed from theinside, workmen have completed the excavationand filled the interior with masonry orconcrete as desired, the whole forming aportion of the pier. In 1842-'4 the Royal Terracepier at Milton below Gravesend, England, wasso constructed, iron cylinders being used by Mr.Redman. At Peterborough, in 1851, WilliamCubit sunk cast-iron caissons 6 ft. square.Hawkshaw at Londonderry and at CharingCross used cylinders of cast iron, which at thelatter place were 14 ft. in diameter at thebottom. At Parnitz cylinders 20 ft. in diameterwere used, and at the new Victoria bridge castironcylinders of 21 ft. The new Blackfriarsbridge piers were each placed on six caissons,four rectangular and two pointed; the rectangularwere 36 by 18 ft. At Point du Jour,Paris, large wooden caissons were used. Theywere also used by Chanute at Kansas City, aslarge as 70 by 22 ft., and 67 by 30 ft., besidesmany others similar, in this and other countries.At the dock in Glasgow Mr. Bateman sunkcylinders of brick laid in cement. In India brickcylinders have been very generally used forfoundations. In Hungary stone has beensubstituted, and Mr. Butler proposes Ransome'sartificial stone for the same purpose.—Theintroduction of compressed air as an agent inconstructing subaqueous foundations has enlargedthe use of caissons, which are inverted and sunkto the bed of the stream, with the open spacebeneath filled by means of air pumps or compressorswith air of sufficient density to expel andkeep out the water, and admit of workmenbeing employed in excavating under them.This method dates back to about the year 1841,when M. Triger, a French engineer, sunk ashaft under the bed of the river Loire to a coalstratum, which made more fully known thecapabilities of the method; but it had been fullydescribed and patented ten years before byLord Cochrane in England, including even theprinciples of the air lock as now used. The airlock is a small anteroom through which men andmaterials pass to and from the air chamber withonly a moderate loss of compressed air. It isusually an upright closed cylinder of iron madeair-tight, having a door opening into it fromthe outside above, and another door openingfrom it into the chamber of compressed airbelow. To obtain access to the air chamber,it is first necessary to enter the lock, close theouter door, and open a cock which permits thecompressed air to come in from the chamberand fill the lock until it becomes of the samedensity, when the lower door can be opened,and entrance is gained to the main chamber,the pressure being transferred to the upperdoor. In returning, the lower door and thecock are closed, while another cock communicatingwith the outside is opened, and the airsoon becomes rarefied so that the upper doorcan be opened and the exit made. M. Trigerascertained that by making an aperturethrough a pipe some distance up from the bottomof the chamber, the current of air thusescaping would carry out a column of watertwice as high as was due to the pressure ofair in the chamber. He therefore arranged acock which served the purpose of ventilationalso.
Fig. 1.—Bush's Caisson.
In the same year (1841) William Bushpatented in England a method of sinking a caissonby excavating within and beneath it incompressed air, the caisson becoming a part ofthe pier. A sectional view of his caisson isshown in fig. 1, which represents the air chamberA below a second air chamber B B, inwhich is the air lock C, leading to the air shaftD. The problem of disposing of the excavatedmaterial, which is always in such cases a seriousone, was solved by using the second air chamberB B as an anteroom or receptacle, it beingof considerable size and provided with a doorabove and below. The small air lock wasfor the passage of men without the loss ofso much air as the opening of the large lockwould occasion, and also to serve as a lockwhen in process of filling it became desirable toremove the diaphragm or partition between Aand B B. Dr. Potts about 1847 patented aprocess of sinking hollow piles by air pressure byexhausting the air within. This was sold to Messrs.Fox and Henderson, who used it successfullyat Anglesea with piles that were 12 in. in diameter;it was also used at Windsor and atHuntingdon; but on attempting the same process atRochester in 1851, with cylinders 7 ft. indiameter, it proved unsuccessful, and the oppositeor plenum process which is above describedwas adopted, and two air locks designed byMr. Hughes were used. These locks, placed atthe top of the air shaft, were D-shaped, andextended into the shaft so that the lower dooropened on the side; the earth was raised inbuckets and swung into the locks. The sameplan was pursued at Chepstow on the Wye.Brunel used the same locks in sinking caissonson the Saltash 37 ft. in diameter; he also usedpipes and pumps for removing the water, so asto require less pressure of air. In 1854Pfanmüller presented a design for a caisson at Mentzon the Rhine, which was to be constructedentirely of iron. It had supply shafts representedabout 20 in. in diameter, running through thetop of the caisson, with a door at each end forthe purpose of conveying down the materialsnecessary for filling in the air chamber; itrepresented the air lock near the air chamber.In 1855 Mr. L. J. Flemming recommendedPotts's process to be used on the Great Pedeeriver; but encountering a log, he with MajorGwynne used the plenum process. He hadtwo pipes, one for air, the other for removingwater. In 1857 the same arrangement wasused on the Santee river. Similar arrangementswere used by Stephenson about thesame time on the Nile, where was also useda caisson 28 by 19 ft., which would hold 40men. In 1857 a caisson was sunk at Szegedin,Hungary, on the Theiss, which had a siphonpump for the removal of water, with a lockextending 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 overthe Rhine was sunk; it had two shafts withair locks at the top, but provided with doorsat the lower end of the shaft, converting thewhole into a lock when required. A chaindredge running in a water shaft raised thematerials excavated. This work was executedby Castor, who afterward sunk the foundationsat Argenteuil. The same year a caisson wassunk at Kovno, Russia, on the Niemen, withtwo separate air shafts and locks, arranged sothat when a bucket passed up one shaft anotherpassed down the other. The same year, also,Gen. William Sooy Smith sunk several cylinderson the Savannah, Ga., in which he made twovery important improvements. The first wasa spout or trough extending out through theside of the air lock, through which by meansof valves and cocks he could send out thematerial brought up into the lock expeditiously,and with little waste of air. But his mostvaluable improvement was the method of blowingthe sand out through pipes by means of thecompressed air. In 1860 the same processwas used at Harlem, New York, by W. J.McAlpine. In 1862, at Argenteuil, France, onthe Seine, the double locks at the top of thetwo air shafts were connected with each otherby a pipe so as to allow the air escaping fromthe one to partially fill the other. The caissonsat Königsberg, Prussia, on the Pregel, and atLorient, France, on the Scorf, the former withworking chambers 50 by 20 ft., and the latter39 ft. 6 in. by 11 ft. 5 in., were sunk like thatat Kehl; the latter were sunk in 1866 byDesnoyes, as were also those on the Loire nearNantes. About the same time a circular caisson26 ft. in diameter was sunk at Stettin onthe Parnitz, in which a siphon pipe 2½ in. indiameter, with a cock 6 ft. above the bottom,was used for ventilation and removal of water.In 1868 Burmeister and Wain used a removablecaisson in excavating for and building piers atCopenhagen. At Perpignan, France, on theTet, an iron cap with an air lock attached wassecured to the top of a cylinder of masonry,and so carried down. In 1867 Gen. SooySmith planned a caisson of an annular ellipticalform, with two air locks by which the foundationsof the lighthouse at Waugoshance weresunk. The cylinders of the Omaha bridgewere sunk in 1868-'9 by Mr. Sickles on Gen.Smith's plan. In 1869-'70 Capt. Eads sunk thefoundations of the St. Louis bridge, using verylarge caissons and going to the great depth of110 ft. below the surface of the water with oneof them. The caisson of the east pier served atwofold purpose, a coffer dam being erected onthe top of the inverted lower portion, in whichthe masonry was built. This caisson was madeof iron, of a hexagonal form, with the air chamberunder its whole area. The air locks wereplaced partly within the air chamber, to whichaccess was had both by stairs and an elevatorrunning down the air shafts. The excavationwas made by a water siphon designed byCapt. Eads, by which the sand was carried outby the force of water, which passed down onepipe and returned through another, bringingthe sand with it. This is probably the mosteffective method of removing sand or softmaterial under such circumstances. Capt. Eadsalso introduced glass globes in which lightswere burned under the normal air pressure,and the smoke conveyed out of the caisson.He practically demonstrated the possibility ofcarrying down a larger mass of masonry to agreater depth than had ever before beenaccomplished; and when it is understood thatthe consequent maximum air pressure was 54lbs. per square inch within the air chamber, thegreat hazard of the undertaking may beimagined; but it was entirely successful. Amongthe many other caissons worthy of note maybe mentioned those at Leavenworth by Gen.Smith and Mr. Sickles, at St. Joseph by Col.E. D. Mason, at St. Charles by C. ShalerSmith, all on the Missouri river; while on theFio. 2. Danube alone may be added those at Steyeregg,Mannshausen, and Nussdorf.
Fig. 2.—Caisson of East River Bridge.
The largest caissonthat has ever been sunk was for the NewYork tower of the East river bridge, by Col.W. A. Roebling, in 1872; and as it embraces avariety of features, a view of the longitudinalsection is presented in fig. 2. Its base isrectangular, being 172 ft. long and 102 ft. wide,with an air chamber 9½ ft. high, the roof 22ft. thick, and the sides carried up to a heightof 82 ft. from the extreme lower edge. It wasused in a double capacity, having a coffer damabove as well as an air chamber below. Itwas built of timber and lined with thin boileriron, the whole held together by angle ironsand bolts. It contained 4,200,000 ft. boardmeasure of timber, 235 tons of iron, exclusive of385 tons of bolts, and weighed when completed13,271 tons, in which was already laid 30,000tons of masonry. It had two double air locksextending into the air chamber, similar to thosein the Saint Louis caisson, in which coils ofsteam pipe were introduced for keeping anequable temperature. Two air shafts extendedup through well holes in the masonry, with anelevator in one and a double circular staircasein the other. Two water shafts, each 7 ft. 9in. in diameter, extended below the level ofthe edge of the caisson, in which powerfuldredges grappled the stones and coarsermaterials that were deposited beneath them, andraised them to cars above, which conveyedthem away; while the sand was blown out bythe air pressure, on Gen. Smith's plan, throughpipes, of which there were more than 40 invarious parts of the caisson. Gas was employedto illuminate the interior, which was forceddown into tanks and from thence distributedby pipes below. Communication wasconstantly kept up with the interior by means ofa mechanical telegraph. Four supply shaftsabout 2 ft. in diameter, each having doors attop and bottom, with equalizing pipes andcocks, served as the avenues for the introductionof materials for the concrete with whichthe whole interior was finally filled. Thiscaisson was carried to a depth of 78 ft. frommean high tide, requiring a maximum air pressureof about 34 lbs. above the normal pressure.To supply this immense amount of air, 13 largecompressors were provided; the air wasconveyed by mains and rubber hose to shaftswhich communicated with the interior. Thesinking was successfully accomplished, as hadbeen that of a caisson nearly as large on theBrooklyn side the year before. (See Bridge.)