Ti) draw piles out of the ground when they have been driven fast, requires a very great force. There are different methods of exerting this force: one for drawing them in water, is by having a very strong barge, with a windlass at one end to receive a strong chain, which is passed several tunes round the head of the pile, and made fast to the barge; two long beams are laid upon the barge, to form a railway for a small waggon to run upon from one end to the other, loaded with stones of several tons weight; when this is wheeled to one end of the barge, it will, of course, depress it in the water. elevating the other ; then, in this state, the lowest end of the barge is chained to the pile, by putting a very large bolt through it, and passing a chain round the pile under this bolt a great many times; the carria.re is then wheeled to the other end of the bar:T• by a windlass and rope; this tends to raise the end to hie]) the pile is fixed ; and when the carriage is so th• advanced that it exerts a sufficient power, it will draw up the pile, if the chain is pro perly fixed ; and then the carriage is retnrned to draw another pile. A plan was a(b>pted at Waterloo for drawing the useless piles by one of :11r. Bramah's hydrostatic cylinders. This is represented in Figure 10, where A is supposed to be the top of a range of piles forming the coffer dam, and 13 the pile to be drawn. A chain, a, is made bust to the pile. and carried many times round a large beam, c the end, n, of which rests upon a fulcrum, or support, E, consisting of a block, supported on the head of a neighbouring F is a block of two pieces of wood, screwed toge ther in two places, and enclosing between them a east-iron cylinder, It, into which is fitted the piston, or cylinder, d, the joining being made tight by a collar of leather; e is a small copper pipe, communicating with the cylinder, and also with a small forcing-pump, the. piston,./, of is actuated by the lever, g 11, ; the pump is fixed upon the top of a small cistern, 1•, to contain water. Now, by working the lever of the pump, water is injected into the cylinder, L, which pro trudes the piston, d, from it with a force, proportioned to the force exerted upon the lever, in the same degree as the areas of the pump to that of the cylinder multiplied by the propor tions of the lever, It. By this means, the power of or two men is increased to such a degree as to draw up the largest pile; the copper pipe, e, is made to unscrew at seve ral joints, \ai•' are provided with leather, to make them tight ; by which the pump is separated when the machine is to be removed. As it has no connection with the bean or lever, a, the e? finder is frequently employed in the manner of a hand-jack, for any purposes where enormous weights are to be lifted for a small space. The same also shows a very complete way of catching fast hold of the pile, in-tead of putting a bolt through the pile-head to stop the chain under: it is simply a strong iron ring. /, large enough to drop over the pile, loosely, and having a strong shank or eye, 712, projecting from it to run the chain through ; when this is drawn, the ring jambs so forcibly upon the wood of the pile as to draw it out of the ground rather than slip ell; for it holds faster in proportion to the force.
The theory of Mr. Valotte's engine depends on the following principles, viz.—I. lf the resistance of the groutn1 and the masses of the piles be equal, the depths to which they will be driven with a single blow will be as the product of the weight of the ram into the height through which it fal s.
2. If the masses of the ram, and heights throng!' which it falls. are both equal, the depths to which the piles wi.l be driven will he in the inverse ratios of the masses of the piles into the superlicies of that part of them which is already immersed in the earth.
3. If all these be unequal, the depths will be in a ratio compounded of the direct ratio of the heights through which the ram falls into its mass, and the inverse ratio ( f the mass of the pile into its immersed superficies.
4. If the weights of the rain be equal, and also the weights of the piles, the depths to which they will be driven will be as the heights through which the rant falls ,ind the immersed superficies of the piles. t/r, because the immersed superficies arc as the depths through which the piles are already driven into the earth, these depths arc simply as the square roots of the heights through whb-h the ra.n These principles are founded on the general supposition that tlm.ugh which the weight falls is estimated by the product of its mass into the square of its velocity, or into the height through which it falls.
11ence it is inferred, that the distance through which a pile w ill be driven by each succeeding blow, will he less and less, as the superfieics of that part of the pile which is immersed in the ground increases; and, consequently, that there is a certain depth, beyond which a pile of a given mass mid scantling cannot be driven ; the mass of the ram and the height ww hieli it fills at first being assigned.
At the close of the year 1813, a new inethod of sinking piles by atmospheric agency, was patented by Dr. Putts. In this invention the piles are of cast-iron, and hollow, and are lowered by drawing out the sand or soil through the centre by means of an air-pump. The pile is closed at the top with an airtight cap, through wwlNiell a pipe passes to a receiver, and from this again another pipe connected with an air pump. By this means a communication is kept, up between the pump and the interior of the pile, and by working the former the air is exhausted from the pile, the sand rises through the interior into the receiver, and the pile gradually sinks into the vacuity so produced. This method of piling
has been successfully employed on the Goodwin Sands by the Trinity Board, the piles being driven through the sands to a depth of 75 feet, when they reached a solid foundation. These piles are especially adapted for such situations; they are attended, however, in many instances, with some disad vantage, for by removing the earth occupied by the piles, they lose that firmness of position which is ensured in the old method by its compression. This defect, is somewhat compensated for by the injection by hydraulic pressure of certain chemical solutions, and hydraulic cements round the feet of the to consolidate the earth on which they stand, and give them a firm bearing.
The most important of all inventions for this purpose is Nasmyth's steam-hammer, which Consists of a steam cylinder, through a steam-tight aperture in the bottom of which the piston-rod passes, haying the hammer, or " monkey," sus pended from it. The steam admitted at the bottom of the cylinder raises the piston with the monkey attached to it, mid in so doing, closes the induction and opens the eduction pipe, which reverses the motion, and the monkey falls with great force upon the head of the pile beneath. The following description of the action of this machine is extracted from a contemporary, and has especial reference to its employment at 11I orice Town, Devon.
"There are two features which most remarkably distin guish this important invention from all pile-driving machines. These consist, in the first place, in the direct manner in which the elastic power of ihe steam is employed to lift up the mass of iron by Ns hose fall on the head of the pile it is driven into the ground ; secondly, in the peouliar manner in which the block of iron and its guide-ease and cylinder are made to sit, as it were, on the shoulders of the pile, so as to predispose and assist it in its descent into the ground. In this manner, the entire dea/bweight of this part of the apparatus is rendered available, and made to act in a most important degree as a portion of the pile-driving agency, and as the entire part of the apparatus follows the pile down, it never ceases for one instant to yield a most important assistance towards the attainment of the desired object. The energy and rapidity Or the blows, which are dealt out on the head of the pile at the late of upwards of 70 per ndnute, is such, that, assisted by the dead-weight of the apparatus sitting upon the shoul ders of die pile, it is seen to sink into the ground in steps varying from 6 feet to 3 inches per stroke,—the whole opera tion of driving the pile, 60 feet in length, occupying little more than from two and a halt to four minutes,—in fact, such is the ease and rapidity with which these enormous piles are driven into the ground by these powerful machines, when compared with the old system, that the spectator is as much inclined to laugh at the ridiculous contrast, as to be astonished at its vast powers, and the perfect control under which it is placed. The whole movements are governed by one handle, regulating the supply of steam from the boiler to the cylinder and piston, which yields the requisite rising and falling motion of the monkey or hammer that drives the pile. We are par ticularly attracted by the simple and efficient contrivance which Mr. Nasmyth has adopted ibr carrying the steam from the boiler to the cylinder on the head of the pile, namely, by wrought-iron jointed pipes, which fold up in the most beau tiful manner in a succession of joints or lengths, so as to accommodate the length of steam at all the various heights of the apparatus, which, having to descend through a per pendicular space of upwards of 50 feet in following down the sinking, double up or fold together in the most perfect yet simple manner. The same boiler which supplies the steam to the actual pile-driving apparatus, likewise supplies steam to a small engine, which is employed to give the requisite locomotive action to the whole apparatus in either direction, so as to cause it to move from pile to pile. The same small engine hoists and pitches the piles in the most perfect man ner; also raises the pile-driving apparatus to the head of the highest pile, some of which are 66 feet in height, and places it on the shoulders of the pile with the utmost ease and exact ness. Some idea of the performance may be formed when we state, that it drives a pile of 66 feet in length in four minutes, while, with the ordinary machines, upwards of 15 or 20 hours would be occupied in doing the same work, to say nothing of the entire absence of all damage to the head of the pile, which, in the case of the employment of Mr. Nasmyth's machine, is not in the sliLditest, degree injured ; while in driving such a pile by the ordinary machine, the head of the pile is so shattered by the repetition of its destructive and ineffectual blows, as to require to be cut off and reheaded several times during the operation. Practical pile-drivers will have some idea of the remarkable superiority in the action of Mr. Nasmyth's machine, when we inform them, that the iron hoop hitherto employed to preserve the head of the pile from being split into matches, is, in the steam pile-driver, entirely dispensed with, and the heads of the piles, after driving, hear scarcely any evidence of force having been applied to them."