Bridge construction, bridge vs. tunnel
THE BROOKLYN BRIDGE. Description of tho Caisson and Us JLny in tf Tho Foundation ol tho Brooklyn Bridget The 31anvfacturcr mid, Builder for the current current liionth contains an interesting article on tiro Brooklyn Brooklyn Bridge, illustrated by a section of the caisson now being built, and by a handsome view of the structure as it will appear when completed. This monthly magazine, magazine, it is bnt just to say, is not made up of odd cUp - phigs, from foroign papers, and advertising puffs of individuals individuals and their inventions insertod as editorials, but containB on almost.ovory pago information readable by ovory intelligent man, whilo Bpocially interesting to tho mechanic or tho scientific reader. Among tho points mado in its bridge article is tho prediction of a futuro DANQEB TO EAST BIVEE NAVIGATION. Tho amount of water passing through tho EastBivor at every tide is enormous ; the velocity of tho eurrout, always great, has increased with tho improvement of the Hell Galo channel ; and (when all tho obstructions shall have been removed from that channol, tlio current current will bo still moro inoonvenient, chiefly to tho Bteam forry - boats, which to - tho number of twenty - live, by Boven different forries, now transport weekly ono million million porsons aoross this river, between Now York ond old Brooklyn, not to speak of tho eastern district of BrooKlyn, formerly called WiUiamaburgh, whioh is connected connected with Now York City by means of Boven othor steam ferries, all crossing tho same river, IMPBACTICABIUTY OP A QUEENS COUNTY CANAL, One onthuBinstie party suggested the formation of a new Ensfc Rivor, east of Brooklyn, by uniting Jamaica Bay with Flushing Bay by moans of a ship - oanah This would bo equivalent to cutting off a slico from Long Island Island and annexing it to Manhattan Island, to double the size of the latter. Such a now canal would, however, however, soon be Bwept out to au enormous depth and width; all tho full tido now pouring - through tho East ltiver would expend its force on tho new canal ; and tho possible disastrous results of this dangorous undertaking undertaking can scarcely be foreseen. Those plans wero nover considered worth noticing by those in authority, who rightly concluded that tho East Kivor muBt not only bo maintained, but, in tho course of time, possibly wiil liccomo tho main ontranco to Now York harbor, when the Sandy Hook channel wilt perhaps havo followed tho example of several othor similar channels, aud beoomo so far filled up with sand that tho large ocean vessels cun only enter it with difficulty, or not at all. These vessels aro ffouBtantly being increased in draught year by year. A TUNNEL COSTLY AND DIFFICULT. A tunnel has beon proposed, in imitation of tho tunnel tunnel under tho Thames, in - London; or the Chicago sub - fluvial tunnels; or tho one now to be mado under tho Detroit River. Bnt the circumstances aro vory different different : tho depth of the Thames is only some twenty feet, and that of tho Detroit River forty; and both flow on a bed of uniform clay, easily cut and supported with water water water - tight brick masonry. Tho East Rivor, on the other hand, is sixty feet deep in tho channel ; and tho bed is composed of rock, interrupted by cractts rilled with earth and boulders. This heterogeneity of tho substratum would present great difilcultics ; and, although tho tunnel tunnel cannot bo pronounced impossible, the oxponse of its construction would be very great. It will be lef Lto posterity posterity to construct ono, when cxperionco aud knowlodgo in this kind ol work have sufficiently advanced to uu - dorlako such a gigaut.c work, with a proper confidence of success. No doubt, in tho course of years, not only eteiim ferries and bridges, but also tunnels, will bo needed. TJio population of Now York aud its onvirons will, at the present rate of growth, in half a century sui puss that of London at the present day. In fact, if we compare the favorable situation of New York, with re.ipcct to the chances of growth , Willi the situation of other great citieB, wo can but declare that nothing but a grand earthquake cau prevent New York city irom he - coming tho greatest metropolis of tho world. The plan of a bridge is preferred to those of a causeway causeway and a tunnel, and considered at the present day tho most dcsirablo and practicablo: aud, as the dopth of water and tho requirements of navigation preclude tho building of arches on plors, nolhing is loft but the cou - siruction of a suspeusiiu bridge. The article goes on to givo the history and geuer?j description oi the Roebling plans ond intended struc. lure, with which our readers aro familiar. It then pro ecids to describe, in a moro detailed and precise man. ner than has yet hoeu dono in public print, tho FOUNDATION OF THE BROOKLYN TOWEIS. The New York tower will bo situatod where now a dilapidated pior, known n& No, 29, is located; that of Brooklyn, in the east slip of the Fultuu ferry. Tho labor on the latter was commouced on Monday, Jan. 3d, 1870 ; and has since been continued by moans of dredging, dredging, machines, etc., preparatory to sinking tho colossal caiston, which iB now being built at Grcenpolnt, and has advanced considerably toward completion. The caisson is building at the yard of Messrs. Webb &Bcll: and under tho superintendence, on behalf of tho Bridjio Company, of Colonel William H. Puiuo. It was expected that it would bo ready to launch during, March; but, making allowance for inevitable though unforeseen delay's, wo will say April. The river shoro will be dredged out to low - water line, and tho caisson floated into position at high tido. When tho. water recedes, recedes, it will bo anchored or seated. To explain the manner in which it will be sunk to tho required depth, it is necessary to desoribe its construction. '. DESCRIPTION OF THE CAISSON. A caisson is literally a ohest. Applied to bridgc - buildiug, tlie term signilles a wooden box or frame of strong timbers, used for laying tho foundations of a bridge in situations whore the coffer - dam can not bo employed. In the present instance, there having been no suitable rock foundation found on tho Brooklyn shore, tho caisson itself will form part of tho foundation, foundation, as wo shall show. Tho system adopted involves also the principle of the pneumatic pile, which is usually usually a tubular pilo or cylinder of largo dimensions, forced down by atmospheric pressure. In this case, however, the atmospheric prossuro is assisted by the continual excavatiou of material beneath the mass. In fact, there is also something of the diving - bell in this apparatus. The caisson proper, or chamber within which TEE WORK OF EXCAVATION will bo carried on, is rectangular in shapo, 108 feet long and 102 feet wide on tho outsido,and about 13 feet high. The sides are wedge - shaped in section, tho lower edge being eight inches, and the upper eight feet three inches thick. The roof resting on these sides is fivo t oot thick, leaving a working chamber (tho dimensions of roof ana sides being allowed for) 100x98 feet in ground - area, and 0 feet in height. Tho whole is constructed of yol - low - pine timbers, a foot square ; the soams aro paved with a vcgctablo tar, to ronder thorn imporvious to water; and between tho outer layers of timber, is a Bheathing of tin, between two of felt, iutended to prevent prevent air from leaking through. As tho sharp - lower edges are intended to facilitate tho sinking of tho caisson, caisson, they aro made vory strong. The first course of timber timber is oak ; to this is bolted a cust - iron shoe,eight itichou Wide, ntltl oval on ito laea, nn.iujT Mtrp inonoa nur.K in the centre. Around tho shoo is placed an armor of holler holler holler - iron, extending three feet above, on both sides of tho wall, tlio wholo being strengthened by heavy interior angle - irons. Especial pains is taken to provout tho corners at the bottom from "spreading" under tho groat pressure to which they will be subjoctod. At each corner, corner, in the second course, is insorted a knee of hardwood hardwood timber, extending twenty feet each way. The timbers of the caisson arc all bolted together vertically, horizontally, and diagonally, with l'x - inch bolls, varying varying iu length from two to seven foot. Tho bolts are, on an average, eighteen inches none more than two feet eight inches apart throughout the whole structuro; aud (ho heads and nuts aro made air - tight by rubber washers. As this hugo framo is Bunk to its desired position, thirty feet below lbw - tide, additional course of timber will he laid on tho top, to tho height of fifteen feet, and filled in wilh concreto; aud when tho whole mass has Income fixed in its final resting - place THE TOWER WILL HE BUILT on (he solid foundation thus obtaiuod. Six Bhalts, lined with half - inch bailer - iron, pass through the roof of tlieoaisson. Tho two outside ones are rectangular, and six feet six inches by seven feet in Bize. These are the water - shafts, in which the water collecting in tho caisson will rise by the atmospheric pressure to (he height of tho tide outside. Next to these aro the two man - shafts or supply - shafts, circular in form. Through theso tho workmen will pass, and tho earth be hoisted. The last pair are the air - shafts, also circular and forty - two inches in diameter. The shafts are made in couples, both for convenience and for safety. Through tho air - Bhaits largo air pumps will force air into the caisson, expelling tho water, and enabling the workmen to descend and work upon tho bottom. The earth excavated will be deposited around the square walcr - shaits; and a Cumming's dredging - maclmio will lift the mud and damp it into scows. As the oxcavations progress, tho caisson will sink. During this operation, it is to bo hoped that the edges will como upon no lar'o boulders. It is of the' utmost importance that tbis heavy structure, which will not he very manageable when it is once under water, shall move downward with quiet uniformity: aud lortunate - y we have no reason to expect in the sand of the Brooklyn shore any serious obstacles to this part of tho work. Gas is to bo introduced for lighting the caisson. The following figures will givo. to somo readers readers a better notion of tho sizo and importance of this, construction: Length of caisson, 168 feet; width 102 foot; height, 15 feet; holght, inoluding suporincumboiit timber and concrete, 30 ioct; timber in caisson, 1.5C0 - 000 feet, (105,000 cubio feet ;) weight of caisson, 2,500 lo3000 toiiB;wTOUght - iron employed in bolts, angle - irons, and plates, 100 tons ; lumber in launohing - frames and ways, 127,000 feet.