IT* 



r<T\TUTIOX8. 



IPATIONS. 



190 



count the resistance of Uut material will depend upon the nature of 

 the lime or cement of which it is composed ; but as, under ordinary 

 circumstances, the concretes made with the moderately hydraulic limn 

 fulfil all the requisite conditions, iU resistance may be taken u the 

 limit of the wifely load it w desirable to bring upon * natural foundation. 

 Vicat eatimatea it at about 80 pound* per miperficial inch, after the 

 lime baa bad time to net fairly. 



Foundations may be laid to be partially natural, when the inequalities 

 of level of the ground on which the building is about to be erected are 

 so great as to require that they should be compensated for by the 

 interposition of some extraneous substance ; or when the resistance of 

 the natural surface would not be sufficient to enable it to support the 

 superincumbent weight. When the former of these conditions pre- 

 vails, it is essential that precautions should be taken to obviate any 

 danger which might arise from the movements of a different nature 

 likely to occur in the natural and in the artificial portions of the 

 foundations. When the latter condition occurs, the modes of dealing 

 with the foundations so closely resemble the ones it is advisable to 

 adopt with the more exclusively artificial class, that they are at once 

 referred to it. Strata which are exposed to lateral displacement fre- 

 quently require the execution of works of so complicated a nature, 

 before a building can safely be erected upon them, that they can 

 hardly be considered to belong to the category of the partially natural 

 foundations, even when the natural surface of the ground is but slightly 

 altered. 



Artificial foundations are those which are required when the strata 

 occurring at the surface of the ground, upon which it is proposed to 

 erect a building, are of a highly compressible or of a moveable nature, 

 and of such a thickness as to render it dangerous to bring a heavy load 

 upon them, and impossible to remove the bulk of the soft material 

 which thus covers the harder substratum. These conditions usually 

 occur in situations wherein the surface stratum is composed of alluvial 

 matter, or upon the shores of the sea, of lakes, rivers, or in morasses, 

 peat deposits, ftc., and the ordinary difficulties attending the execution 

 of foundations in such positions are increased by the necessity for 

 dealing with the water which accompanies those deposits. The nature 

 of the works required to form artificial foundations will therefore 

 depend mainly upon the question as to whether or not it be necessary 

 to execute them in the open air ; and when it is possible to avoid 

 laying dry the surface to be operated tipon, it becomes important to 

 consider the effect of the water upon the durability of the materials 

 which enter into the composition of the artificial foundations them- 

 selves. 



In such cases as those which occur near the embouchures of the 

 Kuropean rivers, where in fact a fine alluvial clay, sufficiently mingled 

 with s-ind to allow water to permeate the mass, commonly overlies a 

 more ancient and denser geological formation, it is customary to form 

 artificial foundations by means of piles or baulks of timber, which are 

 driven vertically, wherever it is possible so to do, through the alluvious 

 into the harder substratum. Sometimes these piles act merely by the 

 compression they produce upon the ground into which they are driven, 

 but as a general rule they serve to support the superincumbent weight, 

 somewhat in the manner in which pillars would do in the open air. 

 In the former of these cases, the number of the piles is the most 

 important consideration ; and, as the resistance they have to overcome 

 in driving is insignificant, their shape is a matter of indifference : nay, 

 it may happen even that (as near 1'Orient, where artificial fonn 

 have been established upon soft mud of practically indefinite thickness) 

 it would be desirable to drive the piles with their butt end downwards : 

 to trust, in fact, to the friction upon the sides of the pile for the 

 limited degree of stability to be thus obtained. In the latter case, or 

 when the piles have to transmit the weight to the resisting substratum, 

 it U necessary to proportion the length and the transverse section of 

 the piles to the load, and to cut the driving end in such a form as to 

 ensure their entry into the bearing stratum. As they have to over- 

 come considerable resistances in the course. of their descent, they 

 require to be shod either with cast or wrought iron, and to be hooped 

 or bound with iron at the heads. The necessity for the latter pre- 

 caution increases with the violence of the blows struck upon the head 

 of the piles ; and it has been even found that when the Nasmyth's 

 hammer has been used, the frequent heavy blows at times either 

 derelope so rapid a compression of the fibres as to set the piles on fire, 

 or they beat the heads into a spongy maun. The piles are also occa- 

 sionally exposed to be split, if the shoe should encounter any very hard 

 substance in its descent. 



The description of wood used for piles ought to be a matter of 

 serious consideration to the architect or engineer. Fir timber resists 

 alternations of drynexs and moisture better than either elm or beech 

 (which arc the other woods employed for this ]irtiruhr pnrpo- 

 if it should contain much sap at the time of its being driven, tin- t^r 

 will rapidly decay. Beech resists the constant action of v. : r. but if 

 it should be exposed to alternations of dryness it will rot : whilst 1m 

 timber present* an intermediate degree of durability umli-r those cir- 

 cumstances. The boring worms constitute, it may be observed, one of 

 the most fatal sources of danger to pilot driven in the districts where 

 then creatures abound, and they have naturally exercised the ingenuity 

 of both theoretical and practical men to devise some protection against 

 them. Sometimes the whole surface of the piles is, for this purpose, 



studded with copper nails ; at others the wood is steeped in a variety 

 of solutions, such aa oreasoto, or corrosive sublimate ; but unfor- 

 tunately it does not Mem to be possible to depend on the successful 

 results of any of those o|wrations. [PHOI.ADIDJE, 7Vm/. in NAT. 

 I MV. ] It is said that the great heart w the wood which is the 

 most free from the attacks of these destructive creatures, and that 

 creascting ordinary timber to some extent guarantees its immunity. 



Piles are known by distinct names, according to the position they 

 may occupy in a foundation. Thus, the piles which define the limits 

 of the ground to be inclosed are known as the guagt ],<!..<. \\'l 

 space Iwtween the guage piles is filled in with other piles of the same 

 scantling, the latter are called dote pile* ; but if they should be of less 

 thickness, they are called ikeet pile*. All these piece* of timber are 

 tied together with horizontal vhalrt, or by cross braces. Generally 

 speaking, in foundations intended to support heavy structures upon 

 very soft strata, an inclosure of either close or sheet piling is driven all 

 round the intended situation ; and then isolated piles, of about 

 14 inches square, are driven at distances of about 8 feet from centre to 

 centre. Upon the projecting ends of these piles sleepers are laid, and 

 close planking is fixed to them. At the present day, the heads of the 

 piles and the sleepers are bedded in concrete, which is carefully rammed 

 up to them, and levelled to receive the close planking. In many cases, 

 also, in England, the planking is replaced by a layer of Yorkshire 

 landings. In driving the piles, it is desirable to work from the outside, 

 inwards ; because in that manner the compression of the ground pro- 

 duced by the mere act of driving the piles tends to increase the solidity 

 of the bearing surface. No notice is taken, however, of the additional 

 strength thus obtained ; but the load to be brought upon the piles is 

 calculated as though they were intended to sup]K>rt the weight in the 

 air without any lateral support. Evidently, under these circumstances, 

 the safe load a pile may bear will depend upon the length of tic pile 

 itself. In practice, this consideration is frequently neglected, and i in- 

 structors content themselves with the rough general rules, " that the 

 diameter of a pile should be ' 4 th of its length, and that the safety-load 

 of such a pile should be about 400 Ibs. on the superficial inch of the 

 sectional area." Under no circumstances, Imwevi r. should piles of less 

 than 7 or 8 inches in diameter be used. 



The piles themselves are driven by several descriptions of engines, 

 according to the resistance to be overcome, and also according to the 

 magnitude of the work. If the pile* have to be driven in soft uniform 

 ground, such as that which is usually met with in the Fen ilistricts of 

 the eastern counties, or in Holland, the old-fashioned ringing engine 

 will suffice ; but if the ground should become gravelly, it may be 

 necessary to use the heavy monkey worked by a crab, or the Nasmvt h's 

 hammer, or the pneumatic pressure upon the system of 1 >r. 1' 

 or upon that of the adaptation of compressed air ; although pi 1 1 

 two last-named methods of forming foundations are more particularly 

 applicable to tubular foundations than M piled ones. The v.. 

 the monkey used in ordinary ringing engines is about 12 cwt.. . 

 fall attainable is about 4 foct or 4 feet 8 inches; in the case <: 

 engines worked by machinery, the weight of the monkey 

 16 to 22 cwt., and the fall ranges between 12 and 18 feet ; in the 

 Nasmyth's hammers, the monkey is made from 32 to 45 cwt., but the 

 fall docs not exceed 2 feet 6 inches. Butwl l.iinrv 



adopted for the pile-driving, that operation must 1 1 until 



the pile refuses to advance under a certain effort. dcp<-ndnt \\\ 

 nature of the effort itself. This is usually fixed, empiric ally, a- foil, .us: 

 Assuming that the weight to be brought upon each pile i- _'."> (on 

 pile is considered "to refuse" when a series of thirty blow* from a 

 ringing engine, with a monkey of 12 cwt. falling through 

 4 feet, will not cause it to advance more than half an 

 series of ten blows has been given by a monkey of the same weight 

 worked by a crab, and falling through a height of 12 feet ; or 

 a series of seventeen blows from a Nasmyth's hammer, weighing 

 84 cwt., and falling through 2 feet 6 inches, has been given, 

 producing a greater advance. 



In the system of foundations known by the name of Dr. Potts's 

 patent, the piles at times act in a manner which makes that word 

 inapplicable to them ; for they become, indeed, wells, or tubes, subse- 

 quently to IK) filled in with concrete. Thus Dr. Potts used occasionally 

 small piles of wrought iron: but at. other times, and as a mat- 

 choice, he used large ones of about 6 or 7 feet in diameter ; but both 

 the large and the small piles bore upon a sharp continuum edge, instead 

 of upon a point, as in the case of ordinary solid piles. The den 

 the tubes was produced by the application of pneumatic pressure ; 

 there was fitted upon the head a cast irn plate, the air was then v.'-!, 

 drawn from the interior, and the pressure of the atn. n the 



cap. forced th" tube into the ground, until the air in the interior was 

 compressed sufficiently to resist the pressure on the cap. 'n. 

 was then removed from the interior of the tube, and. win -n tl<e 

 latter had been sunk deep enough, the interior was filled in with 



A curious method of founding bridges upon deep sands is used in 

 India, to which attention may be called here. It e Inking 



brick linings in all respects like those \uuil in well*, anil these linings 

 are sunk in precisely the same maiim-r. Tin- brick-work is tmi. 

 a wooden curb, and the ground in the interior and upon 

 then removed, just as is done in will sinking; and tin interior 



