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FOUNDATIONS. 



FOUNDING; FOUNDRY. 



182 



sequently filled in with rubble or with concrete. It is said that the 

 Indian divere carry on the operations of sulking these linings under 

 great depths of water. A good description of the mode of executing 

 the Indian well foundations will be found in the ' Excerpt Minutes of 

 the Institution of Civil Engineers,' for May 12th, 1857, and in those 

 for February, 1842. 



The greatest improvement which has lately been introduced in the 

 method of founding important structures, in situations wherein the 

 natural surface of the ground was not adapted to receive them, is, 

 perhaps, the system adopted in founding the bridges of Rochester, 

 Saltash, of the Quarantaine at Lyons, Macon, Bordeaux, Kiel, and 

 Szegedin. In these eases, large tubes were placed in the positions 

 designed for the piers, and an air-tight lock, or chamber, was formed 

 at the top, through which the workmen and the materials were passed. 

 The earth within the tube was dredged out as far as possible by the 

 ordinary processes ; and, the various valves being closed, the water 

 was forced through a syphon pipe by compressing the air in the inte- 

 rior. A pressure of one atmosphere (above that of the external air) 

 was usually found to be sufficient for this purpose ; but, in order to 

 prevent any rising of the water, or any blowing of the sand, the air in 

 the interior of the cylinders was compressed to about three atmospheres. 

 The workmen then passed to the bottom of the seating, and removed 

 into buckets, which were extracted through the air-locks, the earth 

 which rose above the edge of the tube ; and when subsequently the air 

 in the interior was reduced to Hs normal pressure, the mere weight of 

 the tube and the machinery upon it caused the tube itself to descend 

 in a manner analogous to the descent of a well-curb. In the Rochester 

 and Saltash bridges the tubes were sunk through the permeable, 

 moveable strata until they reached the rocks able to constitute a 

 natural foundation. In the Szegedin Bridge, however, the tubes were 

 merely sunk so far as to obviate any danger of. the undermining of the 

 foundations by the action of the river, and a piled bottom was formed 

 in them to receive the concrete. In some cases the tubes were formed 

 of wrought, in others they were of cast iron. 



One curious observation was made on the occasion of an accident to 

 a tubular foundation of this description at Macon. A barge drove 

 against a cast-iron tube, and broke it ; and on attempting to repair the 

 damage so done, it was found that, although the upper portions of the 

 concrete filling (which had been executed with mortar made of the 

 best hydraulic lime) had set, nevertheless the portions which had 

 been immersed in deep water had not commenced to solidity. It 

 would thence appear that there are some hitherto unexplained con- 

 ditions, with respect to the solidification of mortar under great 

 hydraulic pressure, to which the attention of engineers requires to be 

 directed. 



The various descriptions of artificial foundations mentioned above, 

 are supposed to be continued to such a height above the water-line of 

 the neighbourhood, as to allow the superstructure to be erected in the 

 ordinary manner. In tidal rivers or in streams exposed to floods and 

 sudden changes of level, it is however often desirable to carry the 

 bottom courses of the substructure to such a depth below the normal 

 water-line, as to obviate any danger from the removal of the sand, or 

 earth beneath them. If the depth requisite for this purpose should 

 not exceed S feet, a simple dam of impermeable earth will suffice to 

 protect the works, and to allow the workmen to lay the masonry in the 

 dry. But in such rivers as the Thames, where the tide rises from 14 

 to 18 feet, it becomes necessary to resort to the use of COFFER DAMS 

 when it is required to carry the springing courses to any considerable 

 depth below the low- water line. A description of these structures has 

 already been given ; as also has been given a description of the 

 CAISSONS so much employed in the course of the last century ; but it 

 may here be added that the practice of engineers at the present day is 

 decidedly to avoid the execution of either of these methods of forming 

 artificial foundations, on account of the expense of the former, and of 

 the uncertainty of the latter. The system now most generally 

 adopted is to inclose the site of the intended structure with a close 

 ng, to dredge out the interior very carefully, and to fill in the 

 space thus formed with piles or concrete. Evidently the stability of 

 a foundation of this description must depend upon the depth to which 

 the protective sheeting is driven ; it must be carried below the 

 extreme range of the scouring power of the river. 



Of late years cast iron has been very successfully substituted for 

 in the piles and plates, or sheeting, intended to inclose an 

 artificial foundation. Examples of this desertion of structure are to 

 be seen at the Blackwall Railway Quay, the Victoria Docks, &c. 



When buildings are to be erected upon soft compressible peat, 

 and the hydrographical conditions of the district are not likely to be 

 changed, it may suffice to inclose the whole area of the foundations 

 with aipiled or plated sheeting, and to replace a portion of the peat 

 by a layer of sharp eilicious sand. In fact sand to a great extent acts 

 like an incompressible fluid under a heavy load, and the effort 

 exerted upon one portion of the surface is distributed over the whole, 

 provided the sand be prevented from spreading. Care must, however, 

 be taken that the subjacent peat should not be subject to lateral 

 :ement, and that whatever compression may take place should 

 My take place in a vertical direction. The seating* of some of 

 tki! ilerman railways, carried over the immense peat bogs of that 

 country, are occasionally thus formed upon pillars of sand, formed by 



filling large square holes sunk through the body of the peat itself ; and 

 in some other instances" holes were bored through the peat, and sub- 

 sequently filled in with sand. 



A method of forming artificial foundations was formerly much 

 resorted to in the neighbourhood of London, and in other analogous 

 positions, in which the superstructure was carried upon timber plat- 

 forms so designed and put together as to distribute the weigtjjt 

 over a very large area. The success of this system depends, firstly, 

 upon the strength of the platform, which must be sufficient to resist 

 the partial actions of the load ; and secondly, upon the durability of 

 the platforms themselves. If any change in the conditions of the 

 moisture of the ground should take place, by improved drainage, or 

 otherwise, the timber may rot, and of course the building erected upon 

 it will be dangerously affected. This danger, it may be added, is far 

 from an imaginary or theoretical one ; for in the southern districts of 

 London the changes made of late years in the sewerage have so 

 modified the ordinary state of the surface strata, that the old timber 

 platform foundations are generally decaying. 



Whatever may be the description of artificial foundations used, or 

 whatever may be the character of the natural foundations resorted to, 

 it is essential that the weight of the superincumbent structure should 

 be distributed in the most regular possible manner, over the whole 

 bearing surface of the foundations. It is for this purpose that the 

 best builders make a practice of carrying the lower courses of their 

 structures, evenly, under all the walls, and of executing them with 

 the largest and most homogeneous materials they can obtain. The 

 footings, as these lower courses are specially called, are made wider 

 than the upper work, and even when large openings have to be made 

 in the elevation, the weight thus thrown upon the piers, by the sides 

 of these openings, is distributed over the whole area of the footings by 

 means of inverted arches. In countries where brickwork is principally 

 used, and where cement is accessible, it is often customary to intro- 

 duce, immediately above the footings, a deep band of brickwork in 

 cement, which serves not only to tie together the mass of the wall, 

 but also to intercept the capillary action of the materials of the upper 

 wall upon the moisture in the ground. Where, however, this system 

 cannot be carried into effect, it is essential that precautions should be 

 taken to ensure the strength of the masonry in this part of the 

 structure, and to distribute the effort exercised upon any one portion 

 of it over the widest possible area by the use of the largest blocks in 

 the footing courses. These courses, it may be added, should be made 

 to project on either side of the vertical walls, and to present a number 

 of sets-off proportionate to the weight and character of the super- 

 structure. The width or projection of each set-off should in no case 

 exceed the height of the course itself ; but perhaps the most 

 important general remark to be made upon this branch of construction 

 is after all that the materials used in the footing courses should be of 

 the hardest and most impermeable descriptions, and those which would 

 be the least likely to decay under the action of alternations of dryness 

 and humidity. The durability of a building in fact depends so much 

 on the measures which may be taken to prevent the absorption of 

 moisture by the foundations, that it is impossible to exaggerate the 

 precautions to be observed in the selection of their materials. [LIMES ; 

 MATERIALS FOR BUILDING.] 



FOUNDING ; FOUNDRY. Founding or casting is one of the 

 mechanical arts which embraces all the operations of reducing ores, 

 and of smelting and casting metals. There are various branches of the 

 art ; and some difference prevails in the minor details of the processes 

 as in iron-founding, brass- and bronze-founding, cannon-founding, 

 type-founding, and bell-founding. The finishing operations of chasing, 

 burnishing, plating, &c., are also parts of the founder's art. Under 

 the names of the chief metals, as well as in such articles as BELL, 

 CANNON, TYPE, &c., various processes of founding are described ; in 

 the present article we shall treat of the general features of the art, 

 especially in connection with large iron castings. 



It is certain that the art of founding is of very high antiquity. 

 From the passages in the Old Testament referred to under BRONZE, we 

 find that Tubal Cain was skilled in working in metals, and that the 

 arts of metallurgy were known and practised very extensively by the 

 early Israelites. The extent to which metal-working was carried on by 

 the ancient Egyptians, Assyrians, Phoenicians, Oreeka, Etruscans, and 

 Romans, and the excellence to which it was occasionally carried in the 

 fine arts, are too well known to need further observation in this place : 

 a general history of it, as a branch of sculpture, has already been given 

 in the article BRONZE, which also contains some notices from the 

 ancient writers on the different methods adopted of solid hammer- 

 working, hammer-work in plates, and casting; as well as on the 

 varieties and composition of metals. In all the practical points of 

 ancient founding our information is however very limited ; the writers 

 of antiquity having confined themselves, generally, to a description of 

 finished productions, and leaving us little or nothing by which we can 

 judge of the mode of working. 



It appears that furnaces of considerable size, and producing a great 

 tonnage of metal, were constructed in this country as early as the 

 reign of Elizabeth; but it was not till the beginning of the 17th 

 century that there was effected any great change in the character and 

 importance of founding. Prior to that date all the operations of 

 melting, Ac., had been performed by means of wood fuel ; but the 



