296

PIL

the driving of the timber guide-piles. The deepening infront, which, to give the required depth of 10 feet at lowwater, was as much as 12 feet, was not done until near theconclusion of the work; to have effected it in the firstinstance would, without any countervailing advantage exceptsome saving in the driving, have been attended with thedouble expense of removing the ground forming the originalbottom between the old and new lines of wharfing, andafterwards refilling the void so left by a material that wouldrequire time to make it of equal solidity; and even if thishad been otherwise, such an attempt would have endangeredthe old wall, or rather would have been fatal to it. The per-manent piling was next begun, the main piles being drivenfirst at intervals of seven feet, and the intermediate spaces orbays then filled in, working always from right to left, towardswhich the drafts of the sheet-piles were pointed. Theground is a coarse gravel, with a stratum of the hard Black-wall rock occurring in places, and some trouble was occa-sionally experienced from its tendency to turn the piles fromthe proper direction; but due attention being paid to theform of the points, the drawing was, on the whole, effectedpretty regularly, but few of the bays requiring closing pilesmade specially for them, so that the work may be said to benearly iron and iron from end to end ; at the same time, thevertical joints of the piling being all covered, as will be noticedpresently, any slight imperfection, in this respect, is no seri-ous detriment to the work as a whole.

“ The main piles are in two pieces, the lower end of theupper one being formed so as to fit into a socket on the topof the under length, and the joining made good by means ofa strong screw-bolt; the only object of this was to insure asupply of truer castings, and lessen the difficulty of trans-porting such unwieldy masses from Northumberland andStaffordshire to London . Each sheet-pile is secured at thetop by two bolts to the uppermost wale of the woodworkbehind, and the edge of the end-ones of each bay, it will beobserved, pass behind the adjoining main pile, while theother joints are overlapped by the bosses with which all thesheet-piles, except the closers, are furnished on one side.Besides adding to the perfection and security of the works,by breaking the joints, so that the water, if it penetrate, (as,even with the best pile-driving, it will,) cannot draw thebacking from its place, these projections appear to me torelieve the appearance of the otherwise too uniform space,and a like effect is produced by the horizontal fillets on thelower edges of the plates above, which also mask the joints.These plates filling up the space over the sheet-piling, arebolted to the main piles and to each other, in the mannershown, and the joints stopped with iron cement. Where themooring-rings come, the plates are cast concave, with a holeperforated in the middle, to allow a bolt to pass through, andthis bolt is secured, as well as the land-ties, from the mainpiles to the old wharf, which was not otherwise disturbed, orto needle-piles driven adjoining to it. The backing consistsof a concrete of lime and gravel, in the proportion of aboutone to ten, extending down to the solid bottom. The coping,with the water-channel in its rear, is of Devonshire granite;the water is conveyed from the channel at intervals by pipesextending from gratings in the bottom, in a slanting line, tothe lowermost plate, and discharging themselves immediatelyabove the sheet-piling. The main piles w r ere originally pro-posed to be hollow, but this was given up on further consi-deration of the uncertainty of procuring sound castings ofthe intended form, and of the greater liability to break after-wards from a blow sideways.

“ The solid form was therefore adopted, according to whichthe lower lengths weighed about 28 cwt., and that this was

not too much, was shown by the circumstance of

the piles, particularly the early ones, breaking in the l p“ eV eH

j __i _:_* *. 1 . _ p_*_ii.. ,-,rrPl' 0* ,i.,>

or driving, and showing in the fracture the danger

a slight defect. The greater care subsequentlyfoundry, and probably also greater experience m j a ter

made accidents of this kind of rare occurrence in ' r0 of

i b» d P

the

no

IK

stages of the work; and it may be mentioned as ^ - j nC iof the care of all parties, that of upward of 600 P’I e p e jngding both descriptions, only 16 broke in driving-^' ca se 3one sort, and 9 of the other: the failure was in il ' 1 ^ c!lS t-attributed to strains in driving, and to imperfections c0 n-ing in the other eleven. The sheet-piles, which uS ei'siderable resemblance in their general outline to

those

at Downes wharf ten years before, were proposed "^eirinch thick, but it was found necessary to increasesion, and some of them were IT inch thick; the

to

be

an

ick ; , aC h p 1

however, was not above 1^ inch, and weight °f j tb®17 cwt.; the length of the wharf is about 720 fee > ‘whole weight of iron used, upwards of 900 tons j,ead s 0“ The crab engine was employed invariably, tn ^ e 10>ithe piles being covered with a slip of three-quartet i ^ 311“to distribute the force of the blow equally over the lj|so prevent jarring. The monkeys used, weigb e t j l6 fato 15 cwt. each, and it was found necessary to hffl ^ th®to a height of 3 feet 6 inches, and sometimes less > sbo' ve eresistance proved more than usually great, the P 1 T^®a tendency to turn from its straightforward at

driving throughout was very hard, more especn ^7 ^ gt dwest end, where the sheet-piles in four bays, coU j n t"’°forced to the full depth, the space above being^ t j l6 otb®them made up with two plates in height, and 1 t 0 f t 1two admitting only one instead of three, as in t' oJ , j n d®®work. Driving was the only means resorted »practicable, in the gravelly soil that prevails plan ^bottom been clay, or other similar substance, ^ ^eei* pa ^boring, to receive the points, might probably h® f j sh° U j ttially adopted in the main piles with advantage; u pt>nsay, certainly not to the extent of depending noafor getting the piles home to their places.” 3 jn tf> a _

Piles similar to the above have been empi l >cU* e ° 'situations, differing only in matters of detail,not think it requisite more fully to describe. a dap te< * patPiling of cast-iron seems to be very ' ve ‘ w0 rks> U ]rcoffer-dams, wharf-walls, embankments, and suc^ ed ff [fareis not to be substituted for timber when em P^ unl , the) g{tdations, for unless based upon a very firn 1 st '‘* ] e( ] ; Il ° l ’ 1j iilnot so secure against sinking when heavily l°‘ conl pi'C s9 j nl eaccount of their small sectional area, do they ^ t pe s>consolidate the soil through which they P^^gatly aS j)iefextent as timber pilings, and this compression A 1 ' 0 t j,e

in forming a solid foundation for the su P el ® t . lU II)a tei'ii 1 '’ 0 adisadvantage which attends the use of this oftv» teJ ' 1deterioration which it undergoes by the act ply

moveable strata, an pad

it, and especially of sea-water.

The screw-pile introduced by Mr.adapted for loose and

very useful in situations where all othei ® , jgpgt .'Wa’i

This pile consists of a spindle of the reqm j je ]jca 0 fa broad cast-iron plate or disc, in a sp ua v by ^attached to the lower end, so as to form a sc r ^ e fo , pywhich the pile is secured in the S 10l,n y a p n P er 1

account of them is taken from a sumniaiy r ji)£>

co tempo Iil 'a v .uioo>

the

Mr. A. Mitchell, and published in a“ The origin of the screw-pile waswhich was designed for the purpose 0especial purpose, a greater holding povveiby either the ordinary pile, or any 0

scr

eW' )

fo> -

obtab’^sse^

than ' va 1 m o° 1 '

llSU a)