1072

THEORY AND PRACTICE OF ENGINEERING.

Rook II

which is screwed or securely attache d a crab, with a cylindrical barrel and two handles,worked by four or six men : on this framing is placed on one side two upright piecesof timber, on the other an inclined ladder, the whole securely braced together : at thetop a wheel is fixed, over which the chain worked by the crab passes, and is attachedto the monkey, which has a plate in front and at the back, so that it is confined to worka saw up and down the perpendicular pieces of timber, which are protected by platesof iron.

The rope, fastened at the top, elevates the monkey, and the nippersbeing applied at the bottom are enabled to hold the ram untilthey are elevated to the inclined planes at top, where they are com-pressed, by which means the bottom part, which holds the ram, isopened, and it is suffered to fall the entire height of the machineupon the pile head below. The monkey and nippers immediatelyfollow by their own weight; the latter open again, and admit tiiehoop or ear of the ram to be ready to be lifted by the men at thecrab: the higher the ram is lifted, the greater will be the blow givento the head of the pile; the time of raising it is increased, thoughnot in proportion to the advantages gained, but in a higher ratio,the velocity being as the square root of the height, whereas the timeis as the height merely.

The rams are of oak, of a cylindrical form, strongly hooped roundfor common purposes ; but generally cast-iron is preferable, and ismore durable. Coulomb valued the daily action of a man em-ployed at the pile-engine as 75*2 kilogrammes, and capable of rais-ing 1000 metres.

The pile is placed vertically in the spot where it is to be driven,and is generally lowered by the chain of the engine being attached toit at about one-third of its length ; it is then maintained in itsposition, and allowed to descend until it lias fixed itself in the soil ;arrived below the frame of the engine, and the ram can no longer reach it, the driving iscontinued by means of a false pile, or piece of timber bound with iron at the two extremi-ties, and having a gudgeon of iron entering into a hole at the head of the pile; but graftingthe piles with others securely fastened and bound with iron hoops is perhaps the mostsimple method, as well as efficacious, when they are to descend far into the soil.

Great care must be taken that the piles are driven in a vertical position: to insure this,and prevent their swerving during the action of driving, they are passed through a pieceof framing attached firmly to the scaffold, which obliges them to descend perpendicularly ;sometimes a large stone will change the direction of the point; it should then be with-drawn, and the stone be either crushed or removed ; for if a pile takes a wrong direction,it is better to pull it up and replace it, than persist in endeavouring to right it: in orderthat the piles may each have its proper position, it is requisite to trace their places on theplatform, or to fix lines, which represent by their intersection their true positions; or,where the situation will permit, stakes may be placed to indicate this, and these preliminaryoperations are highly necessary when the engine is placed in boats or lighters.

The same means are adopted for driving the planks as for the piles; their use beingto enclose a certain space, it is highly important that their joints should be rendered osclose as possible ; this is done by framing together two pieces of timber on the scaffold, inthe manner of a groove, between which the plunks are driven.

Frames are formed by the rails, which are disposed on each side of the planks, and aresecured by a pin placed in a mortice horizontal in them and vertical in the plank, in order toafford some play in the driving. The planks in the middle of the frame are driven first,and when those at the extremities which carry the rail are arrived at. the peg must be removedto the next plank, where a similar mortice has been made : a lower frame is used, whennecessary, to more perfectly regulate the driving : short planks may be carried to theirposition, and placed vertically by the side of each other, and when made to enter a littleinto the soil, a blow on their heads is sufficient to establish them ; they may be held intheir places by a cramp or iron ; driving planks as well as piles is often performed fromtwo boats coupled together, carrying a timber frame. The same force made use of to drivethe pile might be applied by machinery, but it would be difficult to construct it of suffi-cient strength, and free from friction : a weight, for instance, of 500 pounds, falling througha height of 50 feet, may drive a pile at each stroke 2 inches, and if the resistance beconsidered uniform, the magnitude must he about 150,COO pounds ; the same moving power,with a mechanical advantage of 300 to 1, would perform the work in the same time;but the strain upon some parts of such a machine would be equivalent to the draught of600 horses.

The ends of the piles are variously cut, according to the soil thev arc intended to pene-trate : being shod with iron they are prevented from splitting as they enter a hard stratumor come in contact with stone.

U L

Fig. 1038.

when the pile has