621 



PILASTER. 



PILE-ENGINE. 



623 





K which is closed at the top, open at the bottom, and graduated into 

 equal parts. It has a ring of lead at the bottom to keep it immersed, 

 and being full of air it readily indicates by 

 its compression the amount of pressure 

 applied to the water by the piston. By 

 the law of Marriotte [ELASTICITY], the 

 diminution in the bulk of aeriform bodies 

 is proportional to the pressure, so that by 

 observing the degree to which the air is 

 compressed in the tube by the rise of 

 water in it, the pressure exerted by the 

 piston and that sustained by the water in 

 the bottle is always known. In this way it 

 was ascertained that water is compressed 

 46i' th milliontlis of its bulk for every 

 atmosphere of 151bs. on the square inch. 

 Of course by filling the apparatus with 

 some other liquid its compressibility could 

 be ascertained, and taking mercury as 

 unity in milliontlis of an inch, alcohol was 

 found to be 20, sulphide of carbon 30, 

 water 46'1, sulphuric ether 60. 



The results obtained by Messrs. Colladon 

 and Sturm differ considerably from those 

 of Oersted. Those physicists state that a 

 correction should be made for the com- 

 pression of the substance of the tube and 

 bottle, in consequence of the pressure 

 sustained by them within and without. 

 M. Poisson has given a simple rule for this 

 correction, the necessity for which is denied 

 by Oersted, who states that, the recession 

 of water in the capillary tube is about It 

 niillionths greater when bottles of lead ana 

 tin are used instead of bottles of glass. 

 Piezometers with bulbs of different ma- 

 terials, filled with some liquid of known compressibility, have been 

 used for ascertaining the cubic compressibility of the material of the 

 bulbs. Thus it has been ascertained by Professor Forbes, that the 

 cubic compressibility of caoutchouc is about the same as that of 

 water, for when a piezometer with a caoutchouc bulb filled with 

 water is compressed, the index remains nearly stationary in the 

 stem. 



PILASTER. [COLUMN.] 

 PILE. [GALVANISM.] 



PILE. A piece of timber, or of iron (either cast or wrought), 

 driven into the ground for the purpose of acting in the manner of a 

 column, to transmit the weight of a superincumbent structure to an 

 inferior resisting stratum, when the surface stratum is of so com- 

 pressible a nature as to be unable to support the weight intended to be 

 put upon it, and is so thick that it cannot be removed. Piles may be 

 used either in water, or on land ; and they may be used either isola- 

 tedly, or in close rows, retaining strictly the name of files, in the first 

 case, or those of gauge pilet, whole piling, or sheet piling, in the latter. 

 The gauge piles are those driven to mark out the position the close 

 piling is intended to enclose ; the whole piling is a close enclosure 

 of whule baulks of timber; and the sheet piling is a similar enclosure 

 formed of half baulks. When cast-iron piling is used, the gauge 

 piles are made with grooves on the side, into which plates with stiffen- 

 ing ribs are inserted ; whereas in the case of wood piling, the close 

 piling is made, in the best description of works, with grooves and 

 tongues, and is kept in its position by being driven between whaling 

 pieces, or horizontal ties. 



The descriptions of wood used for piles, in England at least, are 

 beech, elm, larch, Baltic fir, rock elm, live oak, green heart, and the 

 sabacu from Guiana. Of these woods the beech decays rapidly when 

 exposed to alternations of dryness and of humidity, but it resists well 

 when constantly immersed ; elm resists changes of condition more 

 successfully ; and fir, when free from sap, is still more durable ; the 

 American hard woods, such as the rock elm and live oak, are preferable 

 to the soft woods when the piles have to be driven into hard gravel, 

 And they appear to be very durable ; and it may be observed that the 

 green heart and the sabacu have been used to a great extent on account 

 of their supposed immunity from tho attacks of the teredo. It is, 

 however, now ascertained that those destructive creatures will attack 

 the green heart with nearly as much readiness as they will attack any 

 other kind of wood ; and inasmuch as the lymexylon attacks the green 

 heart on land, there can be little d priori reason for supposing that the 

 limnoria should avoid it in the water. In fact, the result of all 

 the enquiries or experiments which have been made with respect to 

 the value of the processes for the preservation of piles, or to the un- 

 assisted resistance of woods in such positions, has hitherto been to 

 show that nothing but the careful injection of creosote is able to 

 prolong, even temporarily, their durability. As the boring worms, 

 however, do not attack wood which is entirely buried in the ground ; 

 and as the durability of the wood itself is infinitely greater when it is 

 protected from the action of external atmospheric influences by being 

 buried; the common sense of the use of piling appears to be to carry 



the solid masonry or concrete foundations below the ground line, 

 so as to ensure that the piles shall always be covered. 



Wooden piles are generally pointed and shod with iron at the lower 

 end, and they are temporarily hooped at the top, in order to prevent 

 their heads from being split or beaten up during the operation of 

 driving. Occasionally piles are driven with their broad ends down- 

 wards, when foundations are required to be executed in soft mud of 

 indefinite thickness, as in the case of the port of L'Orieut. It is con- 

 sidered that in such cases, the piles only act to resist compression by 

 the friction developed upon their surfaces, and that their resistance is 

 only equivalent to about 45 Ibs. per foot superficial of those surfaces ; 

 but in addition to this small amount of resistance, piles, such as are 

 thus described, are exposed to the great inconvenience of being likely 

 to be deflected from the perpendicular by any subsequent compression 

 of the subsoil. If, however, such a mode of driving piles be resorted 

 to, and indeed in almost all cases of piled foundations, it is advisable to 

 commence with the outer rows, and to drive inwards, or towards the 

 centre of the mass, in order to compress the enclosed ground as much 

 as possible under the seat of the intended foundations. Of late years, 

 the introduction of the Mitchell's screw piles has greatly facilitated the 

 execution of works of this description, in homogeneous and soft 

 foundations ; but they do not act in any way to compress the ground, 

 and are of more use for the purpose of fixing piles intended to resist 

 lateral strains, than for driving piles intended to resist vertical weights. 



In calculating the weight a pile should support, it is not customary 

 to take into account the assistance it receives laterally from the ground 

 into which it is driven ; and the number of piles, and the load to be 

 brought upon them are ascertained upon the supposition that they 

 must be able to support that load if they were really isolated ; or in 

 other words, the longer the pile the less must be the weight it is made 

 to bear. Rondelet, in his ' Art de Batir," gives a series of tables of the 

 respective weights which may safely be brought upon piles of variable 

 ratios between the diameters and height; and it may suffice here to say, 

 that when that ratio does not exceed 16 times the diameter, Rondelet 

 considered that the load brought upon the pile permanently, might 

 safely be carried to between 430 and 500 Ibs. per inch superficial of the 

 sectional area. Morin, after verifying Mr. Eaton Hodgkinson's tables 

 of the resistance of columns to compression, increased the value of the 

 resistance of piles ; and the proportionate (permanent safety) loads to 

 be brought upon them are considered at the present day to be nearly 

 as follows : 



ter . . I 13 

 is., per \ ,, 

 rficUl / | " 9 



271 



40 



21S 



Ratio diameter . . | 12 14 16 18 20 22 24 32 

 Weight in Ib 

 inch supei 



When piles are being driven, they should be made to advance so far 

 into the earth that the effort exercised upon their heads, or the driving 

 weight, should virtually exceed the statical effect of the intended 

 permanent load ; and when this is attained, the pile is said to have 

 attained id refusal. There are no recorded experiments upon which to 

 found a theory for ascertaining the conditions regulating the descent of 

 piles ; and therefore, the rules for fixing their refusal must be con- 

 sidered as being simply empirical. It is, however, customary to consider 

 that a pile has attained a satisfactory refusal, if it be intended to 

 support 25 tons, and will not descend more than jths of an inch, 

 under a series of 30 blows from the monkey of a ringing engine, 

 weighing 12 cwt., and falling a distance of 4 feet ; or under a series of 

 10 blows from a monkey of the same weight falling a distance of 

 12 feet; if the weight be reduced to 12J tons per pile, the refusal is 

 diminished to Jths of an inch ; and if to 5 tons, to 2 inches. At the 

 bridge of Neuilly, where the piles support a weight of 52 tons each, 

 Perronet adopted a refusal of l-5th of an inch for a series of 25 blows 

 with a 12 cwt. monkey falling 4 feet 8 inches. It is important to 

 observe, in all these cases, that the piles may often appear " to refuse," 

 after having been struck by frequent blows succeeding one another 

 rapidly, perhaps on account of the superinduction of a state of vibra- 

 tion in either the piles themselves, or in the ground ; and that if the 

 driving be recommenced, after an interval long enough to allow the 

 vibration to cease, the pile will begin to descend again. In practice, 

 therefore, no pile should be considered to have attained its-refusal, 

 until the trial has been repeated at the interval of at least one day 

 after the first observation upon its conditions of descent. 



In regularly piled foundations, it t now the custom to surround the 

 heads of the piles with concrete, to a depth of three feet below tho 

 timber platform, and to extend the concrete at least three feet beyond 

 the outer line of the piles. The platform is usually made of two 

 courses of planks, the lower one tenonting upon the pile-heads, and the 

 upper one halving upon the lower. The whole of this timber is again 

 buried in concrete to a depth of two feet above its uppermost surface. 

 It is sought, in cases where these precautions are taken, to render the 

 whole of the foundation homogeneous, and to guard against any lateral 

 displacement by the piles turning over on their lower external edges, 

 an accident which often occurs when a lofty quay wall is built upon a 

 compressible subsoil ; and although the precautions may be costly, the 

 result of the works executed in many of our own, and in many foreign, 

 sea-ports, proves that they cannot safely be dispensed with. 



PILE-ENGINE. The machinery used for the purpose of driving 

 piles is rather varied ; but it is only within a very finv years that it 



