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Les diagrammes suivants illt'itrent la mdthode. 1 2 3 4 5 6 1 Tirf (Alt rights reserveit ADVANCE il»ll>&OF— (-S'l/ftjeci to revision). Tliis proof is sent to you for discussion only, and on the oxpras undersUnding that it is not to be used for nny other purpose wbu- ever.— (^f. 47 of the Vonttitution). I (^aimdiai) ^ocidy of ^ioil ^ngincers. I INUOUPOUATED 1887. TBANBACTIONS. N.B.--'riiis Society, an ii Imdy, iloos not bold itsplf responsible for tbe facts and opinions ftatcJ in any of its pubbcutions. I rHK RESISTANCE OF PILES. By Hknry F. Pkrley, M.Ciin.Soo.O.E. Piles iiro used under varying circumstanci's .—(1) to form a found- ation where the soil is o" such a nature as to preclude tli» supei-iinpos- ins of a structuro on it, but wbioli, by tbe use of piles, is compacted to such an extent as to aft'oid sufficient resistance to a sinking or settle- ment of the piles which earry the load; (2) as a ready niJans of ob- taining a foundation where a loose or solt stratum overlies a firm and compact material, to or into which the piles ate driven and derive their support; (3) to serve as columns of support, as in the case when driven in clusters, or singly, as in pile-bridging an-l wharting, where the piles are capped and eariy only the superstructure, and a dead or a live load, but ate subjeeled, it may be, to the lilting power or action of ice ; (4) where they arc driven to form a cotter-dam, and are not subjected to any vorticJil pressure, their object being to provide a watertight structure, strong enough to resist the unequal side pres- sures to whicli they may be subjected ; and (5j to form a retaining or revetment wall. The resistance to which a pile is subjected is of a twofold nature (1) that which it meets with wliilst being driven, and (2) that which it offer.s in sustaining either a vertical load or a lateral pressure. In the literature on "pile-driving," the subject appears to be treat- ed in a very protbund m.inner, iuid we have no end of wonderful calcu- lations and still more wonderful furmulii- to perplex the brain of the practical man, and needlessly worry bin, willi their purely theoretical assumptions, eomp'ex forms, and variable const;ints; and ;ill the more so, seeing that the fornuihi which miyht apply in one case would not apply at all to others, and thus the adoption of the majority of the foimuliv to be found in pocket-books and manuals is to be deprecated. With regard to the resistance a pile offers in sustaining a load, a complication ensues, as it may be so pl;i?ed tl. t t;inue varying witli liie nature of the soil or ;;roiii.d, tlie ilepth driven, and (he superficial area of tlic pil*.' iu euut lut wiih tho earth ; and (3j the ubility dl' the pile to withstand erushiof!;, rupture, or def'urmatiun ol .in) kii.d whilst Ik ini:; (lri\eu, ni at auj tiiui^ liuriiig its use. Supposing a pile 12 inches Sijuure to be driven 15 ieet into tiiu Hiouud, thou thu'e must have been 15 cubic feet of earth displaced, for wliiel'. room ean only be found by a partial risiiii; of the surface, and by ii c( lupactiuu or a eouipressicin (j1 the eaith -urrounding tli,, pile. The su] crliciid una of the portioij driven is GO sf|Uare feel, liiid theiefoic each superficial loot of [ ile suilace di.sjilnees J:' = 0.25 cubic foot, ccjual to a Him of earth 12 inches square anil :t inclies thick, 'i he iknsily 01 com|iactnes» ol this film is ilependent up>)n the ehiiracter of the caith or j^iound into wliicli the pile is driven, and nO dnubl the resisliiuce to the dowiiwiiid niovtmint of the pile iluriniriiriv. iiig, and its stability allerwards, an due, to a f^reiiteror less extent, to the trictional lesisianci' set u]i iiy this eompre.ssed lilui, — a resistanc equal to the irreatest load or weifj;ht which the pile would support up t„ the moment wben a movement or setileuieiit takes place, ahvays assum- ilij;; that the load is not ureater than what would erusb and destroy the pile. There is a ;.;ivat difference between « ili/nnmic force and u. stiitif pteamre, the former being represented by a blow from a ram falling fioni a height, puidiieing an effeet in a iiiiiiute portion of time ; and the latter by a load, applied, it may be, gradually during a longer or short- ened period, or in increments defined or undefined as to amount. As an illustration, the following data is assumed : — Weight of rain, Fall of ram at last blow, Sot under last blow. Length of pile driven in ground, hiniensions of pile, From these data the dynamical force, or the " energy " of the ram de. voloped at the moiiicni of impact, and impaiied to the pile, will — usiii"- WV" 2000 lbs. 5 feet. 0,5 inch. 20 feet. 12x 12 ineho.-. the well-known forninla lor energy, itiiouiit to 10,000 foot- pounds, or the amount which would sink the pile to a depth of one foot in a stratum oflering a resistance uf ]0,00d lbs. to thi^ descent of tho pile in that distance. In the data as.-umed the pile was driven to a depth of 0.5 inch only, or, llie resistance to the downward iiiovement vasso great thai the energy developed was only siiffieieiit to eause a " set" of 0,5 inch, umler the last blow of the ram falliuj; fr.ima height of 5 feet ; hence the actual amount of energy di.-played becomes 240,000 foot-pounds. Thi.s amount lias a two-fold 10,000 X 12 0.5 signification, for it represents (1 ) the trictional resistance of the eiirth to the descent of tho pile : and (2) the load which the pih' will be.'ir without .settlement. It is assumed that the pile has been driven to a depth of 20 feet, and further assuming, for the sake of simplicity, that the point of the jiile does not supliort any porlion of tlu> load, then the area in contact with the earth will he 20 x 1 x 4 = 80 superficial feet, then 240,000 ^ 80 = aOOO lbs., or the iiveragc resistance of the earth per square loot of the driven suifnce. The area of t lie pile is f41 s(|uare inches: then 240,000 -i- 144 = 1607 lbs, per square inch, which is in excess of the weight, as a perma- nent load, to which the pile should bo subjected. Assuming a factor of safety of 8, the load becomes 208 Ib.s per .MjUare iiieh. In 1849, Major Sanders, U. S, I'Ingiiieer, dediieed Irom his exper- iments at Fort Delaware, " that .1 pile will s^ifely bi'.ir, wilhoiit danger of a further subsidence, as many times the weight of the ram as the distance which th(> pile is sunk the last blow is contained in the distance through which the ram falls in making the last blow, divided by eijft/," ,,., or expressed as a formula, Z WIl , wlioii \V is llic woii,'ht ol' till' nun. H tliu tall in innhPR, (1 tliu (iistauce suuk by iliu liiHt blow, and L tlio sai'e loud. Apply iiii; till! us-uiiiod diitii to this furuilu, v.i' liiivc : 21100 X ^5 12; ^ ;i((,00U lb.s., ami if lliis amount be multi|ilied by 8, 8 X 0.5 wo jitt L'40,0(H) llis., ur the aiiitiuiit tlciivuJ tnnu tho ealciiUitiou for incigy. During ;ho driving ol' a piU', the oavtli hurruiinding it is iti a state ipI nxtion or vibration, auil it' tin blows of tlic ram follow in quick suo- tt'Hsioii, as ill the casu of a .-teani pilndrivcr, thu partiules of larth are ktpt vibiatini; and tl.i tmdincy to settle is prevented, ai;d thus ihe I'lle may be ilrivin di i imt and mmi ((oiekly ihan by the u.'ual machine worked by luind powei, by wliieli ilu blows are rendered al ^eonipara- tively lung iutirvais. It is well knciwn that a holt eau bj driven more quickly into a hole smalli r in diun:eter than it-ell in timber, when two hiimiiiem in.stuid <>i miv i.re used, beeause tin tlLres of the timber aie pievinitd lu.m 'Mtiing'' oi liiigying the boll by ihe lapid .-ucccssion ol^ blowfc tu the tame exti i.l ibey would utlieiwise do. A heavy ram falling irom a siiiail In ij;l.t will do bitter and quicker ^work than a lighiei lain falling Irom a greiitei height, and a greater number of blowh pel unit ol linie euii be given ; and besides lliip, the ehanceu of biooiuiiij; ur erushinj; the head ol Ihe pile are reduced to a iiiiuiiiium, lui.ee the successful use of the tteaiu pile-drivei. In ihe eonslruetion of works lin- the e.\tensii n of llio^dockyard afc '' I'orismonth, England, it was fuund that on the resumption of pile- * I'r(.ce('.hni;s Inst. C. li.. Vul. lit, |i. 1(14. driving alter an intcnal ol some hours, the "fot" of the pile was invariably uiueli less than that observed on the cessation of driving, the fall id' 'the ram heiim; the same ; and this result was accounted for in a ^leai imasiire by the fact, that during the process of driving, the ground was to a L'reat extent di-turbed, and the vibration ot tho pile eauseiLlhe hole f ion i 1 lie surface downward to be slightly enlarged, thus relieving the pile from the tull friciional resistance. On the cessation of driving, '.be ground settles or expands, and thus grips the pile to such an extent as lo materially increase the fiictional rtsisiance. To determiiic the amount ot iiiereased resistance accru- ing Ironi (juiescenco, sjiecial obseivations wore made on a number of )/iles, the driving ol which had been completed before closing the work liir tlie night. On the following morning one test blow was given, and the resulting ".set " eemjaied wlili that uf the previous evening | and It was shown that o!) be, eh pihs. which had an aveiage •' set" of 0.054 tt. on completion of driving, when hsteii the following morning, iiave an average set of 0.0234 It., showing an increased resistance of 2.3 to 1.0. :>eventy tour lir piles, wliieh had an average "set" of O.tl.'ilMl fi., gave, atiir iiu interval (4' 14 Inmrs, an avciage '-set" of II.OKJ It., or an increased resistance ol 2.81 lo 1.0. Ising these •' sets,'' the data previously given, and Major 5:anders' rule, we have ; J'or heech pile>, sale hiad at night, 23,14b lbs. do dn in niorniiig, 53,360 " For tir do 'ii' at night. 34,090 " do ilo dii in morning, 00,154 " An examination ot the>e ie>ulls shows the great amount of uneer- tainlv connected with the delennination of the sale load which should he imposed on a pile, tor it may be cilhir under or overloaded, when the iiigiit (n- nicunin; " set " is taken ,is the eorioct factor, and it is this action wliic), lendivs all liie formiiln' lor ileterunning the resisting to a groat extent hypothetical. Besides the resistance to tiirtiier dcnvinvard movenjcut due to (lie dead and live loads, a ])ile in some instances has (o wiili.-tand in cold countries an upward or diawing movement due to the at'tion of ice, by which, as in the ea>e ol |iih-bi idging or whaiting, it is encompassed. In li'Uil rivers or baibonrs whuv the ice is in constant motion, a tilm or coating liirnis on the surface of piles against which the moving ice rubs, and theretbre does not produce any injuiious eft'eets; but a dif- ferent action takes jilace when piles have been driveu in bodies of Hlill-wntxT ill wliicli nil iiK^roiiBu in volunio in iiftUHod liy lui influx of wntir, anil ion>ci|iiciiily a rise in uh.vation ensues. In rivers und Biuall lakes, wheru their volume is auj;nienteil by tlifi nieilinn of snow, ete., the ice buriounilinj;: ami iiillierini,' to a pile acts as a iilatlorni wliieli is rai>ctl by the influx nl water ; aud il'tlie lil'linj: juiwer dis- played is f^icaler than the resixling power of iho pile to withdrawal, then an upward movement must take place ; but whcri! (he pile has an excess of resistance, the ice fractures and breaks away without eausiiif; damage. Ice, We know, is water in its solid form, und we also know tluil il8 spteilic gravity is less than that of water, or as 0.9175 to 1.0;— or, in other words, a cubic foot of ice weighs .57..'W lbs., as against (!2.r) lbs. the (accrpl(d) weight td' a cubic foot of water; and tlic lifting power of ice under tlie iiiliuc nee of rising water is therelore 02.50 — 57. HI! or 5.17 lbs. per s-uperficial fool, one font thick. According to apaper by Mr. J. Y. James, .M, Inst. C. Jl!.,-^^ the adhe- sion of iee to timber is 'l^A'A lbs, per sc|uare inch. Trautwiiie states that the adliesion raiiiies from 30 lo 10 lbs. per .'•i|uaie inch. There is iioi any iloubt but that the power to draw a pile is much less than the powei to drive it. especially in the case of a round pile, which is tapering, and when once stiirted is free to be moved easily up- wards. Mr. .lame.- made a number of expcriu cuts on the " Force required (0 draw a pile,' with what may lie classed as rods, ranging from 1 inch to 2 inches square, I to 2 inches in diiimeter, aud 3J by 1 inch in section; and Iroiu the results of 40 exiierimeut.- ho determined a co- efficient (' to be 0.;i285, or thai the power re(|uired to draw is to tlie power required lo drive as 0.328.") lo I. 'Ijjus, in ixperiment 17, a pile 1^ inches square w:.8 driven by a laui weighing 22.5 lbs., falling 7.2 feet at the last blow, the ".set" beiog 0.b!15 iiieb, the driven length being 18.5 inches, aud a Ibice of 727 lbs. was e.xerted lo draw it. Using Major Sanders' rule, omitiing the factor H. and ihe foregoing data. have . 80 = 17.280 lb,M.,and the area of iee to he aetid on by risiua water to just move the pile 17.280 will .5.17 =: :i.342 supcrlici.d fi'et, o»( foot thick ; or the jiilt! must stand i.s. I'JI. siiro, nnd aro lari,'n enough nnd strong enoua;h tn rnn.lor the service f'xpoetpd fVmii tliiiin. Kngincbr.-, iis a rule, wlirn dealing with pilodiiviiijr, are too apt to I'nllow a wi^lltr.Mldon path by sp<'cifvin- hard and fiiHt rf.|iiircment«, irri'Npi'otivo of the service a piln hiis to piTfortn : .md, in tho opinion of the writer, fnll eonsideriition of Miiidi wrvicc HJiouid be given Uifore a Hpeciticution k completed. In exphinutioli ul ll.in, the following iH offered;: A miisoiiry pier.auiiportini; the ends of two iron trusHcs of 160 leet span is to bo built on a pile foun.lation coinprisin-; 00 piles, capped and covered with two tiers id' tinibi r 24 inches decji. Now, the (h'ud load to l;e born.! by liO piles will be c(|Uil to the timber caps and ttoorinji, the masonry pier, a proportionate purtofthe trus.ws and track; and the live load will be cjual to that of tlio heaviest train whieli can be placed in ene span, which thoiifih intermittent in its action must b.' provided lor. As.sumin- ,tli« weight of the dead and the live load to ;iinount to 1,800,000 ll)s., the weight to be borne by each pile will I e ;!0,0(IO lb.. Uning eight as a factor of safety, the "ener^'y " t" be developed by th(! ram employed will be 240,000 loot- pounds. Using previniis data as to the weight of laiii and fill, it can ea.sily be determined Ironi Major .Sanders' rule that a "set" of 0,5 in. will be required. Now, if it be specified that the piles shall be driven' by a Mui weighing 2000 lbs., falling from a height of 5 ti