OiiAP. XIV.

ON PILES AND PILE-UU1VING.

1071

rubble work, in such a manner as to leave no fear of their bending under the weight; ifisolated at a certain height, it is necessary that their strength should be rightly calcu-lated, and the power of their resistance made greater than the load they have to bear ; theirheight out of the ground should be considered in the nature of an upright piece of timber,and the rules relative to its strength and power of support duly followed. The bendingand breaking of piles is not of so much consequence as their being driven out of a perpen-dicular position : it often happens that when they have penetrated beds of slight consis-tency, and have not a hold in firm soil, the foundation placed on them exerts a lateralpressure, which acting as on the arm of a lever, greater in proportion to the length of thepile, causes it to diverge ; this may sometimes be prevented by inclining the external pilesoutwards, and driving them in an oblique direction, or in the line of the thrust to whichthey are subjected : with respect to the weight which piles are capable of sustaining, Per-ronet thinks that one of 12 inches in diameter should not be loaded with more than 50tons, and those of 9 inches in diameter with half that weight.

Piles for foundations are either of oak, elm, fir, or beech timber : those used at the NewLondon Bridge averaged 12 inches in diameter, were 20 feet long, shod with wrought-ironshoes, weighing 30 pounds each, and had iron hoops of the same weight, to prevent themfrom splitting whilst driving. 'Die piles under the foundations of the abutments were drivenat right angles to the inclination of the foundations, those for the piers perpendicularly,and the whole more than 18 inches below the under side of the platforms that wereplaced upon them. They were placed at distances from 3 to 4 feet from centre to centre,and when arrived at their proper depths, the heads were cut level and even, and the earthbetween them taken out to the depth of 9 inches below, the space between being filled withKentish rag-stone well beat down, and racked in with sharp gravel and lime-screenings tothe level of the pile-heads, on which the sills of the timbers laid transversely were spiked :when oak piles are used, their diameter is generally about the twentieth or twenty-fifthpart of their length ; they should be very straight, and barked and dressed with care; thehead is cut at right angles to its length, and rounded to receive the movable hoop of iron ;the lower end is sharpened by cutting each side to the length of about 18 inches, in sucha manner as to bear upon the iron shoe, which is spiked or nailed to the end of the pile ;sometimes it is only necessary to sharpen the end of the pile, and char it in the fire ; thisis sufficient for the scaffold pile, or for those which are for a temporary use : when sheetpiling is used for a cofferdam, or the facing of a wharf or jetty, it is generally from 4 to 6inches in thickness, and the width about 12 inches, the length of the piles depending onthe nature of the soil they are to penetrate, and the depth to which the neighbouring pileshave been driven ; the sheet piles do not generally descend so low, and they are often requiredto be shod with iron; when they are to be exactly joined, there is on the side of eachpile a groove, into which the plank enters, though this adds to the difficulty of driving,for which as well as for the piles the beetle is sometimes made use of, but generally a ma-chine constructed for the purpose.

When it is necessary that either the points of the planks or piles should penetrate a hardsoil, holes may be pierced with an iron-shod piece of timber or rod of iron working perpen-dicularly through a frame or hole cut in a large stone, which serves to guide the in-strument, and the hole so formed may be sufficiently enlarged by an auger to admit them,which ensures greater stability.

The timber now generally employed for piles is either Dantzic or Memel, and too greatcaution cannot be used in the selection of it, to ascertain if it be perfectly sound ; insome works beech or Scotch fir are employed, and if kept always under water are foundequally durable : below London Bridge, on the Thames , and particularly where the wateris at all brackish, the ravages made by the Teredo navalis upon fir piles is so great that afew years are sufficient entirely to destroy them above the level of low water ; sheathingwith copper and iron is found of little use in protecting them, as the worm enters fromthe mud, and pursues his ravages in a vertical direction, until the entire pile is com-pletely hollowed out

The Three-hand Beetle is a large maul made of a block of hard wood, hooped with iron,having two long handles radiating from its centre, put at such a distance that it can beworked by'two men, assisted by another in lifting it, who holds by a short handle oppositeto them : this has considerable power, and is used when the piles to be driven are not of sogreat a length as to require the engine.

The Pile Engine varies in size and construction ; when small, and the block which is letfall does not exceed 2 or 3 cwt.. it is worked by a single rope passing over a large pulley,where i,t is divided into as many smaller ropes as may be required, at each of which a manworks, and when the weight is raised, the whole let go together. This kind of machinecan only be used for driving short piles, as the weight cannot be lifted beyond the heightto which the men’s arms can reach, hut it has the advantage of being easily and rapidlyworked.

For larger operations a ram of from 8 to 10 cwt. is used, set in a frame of woodwork,placed on a base formed by four timbers framed and bolted together at right angles, and to