A Treatise On The Principles And Practice Of Dock Engineering

IKON CYLINDERS. 189 single piece : for large cylinders, such a base would be inconvenient and im- practicable; it is generally composed of segments bolted together. Details of a wrought-iron curb for a bridge foundation in India * are shown in figs. 116 and 117. The height of the curb is 4 feet, and the width of the brickwork base, 3 feet 7 inches. The diameters of the outer and inner edges of the curb are 12 feet 6 inches and 5 feet 4 inches respectively. “ The gusset plates, A, twelve in number, framed with angle irons, E, were fixed in position and temporarily bolted to the outside circular plates, from which they radiated inwards, forming in cross-section a V shape ; the top of the V being the top segmental plates, C, which were placed upon the gusset frames and fixed with bolts and drifts to the angle-iron ring, H, the whole being riveted together. Finally, the inside sloping plates, D, were fixed and riveted to the angle irons, E, which finished the operation.” The spaces between the gussets were filled in with concrète. Upon eurbs similar to the foregoing the brickwork, or steining, is founded, vertical bolts (K, fig. 116) being employed to firmly connect the two parts. Excavation, carried on in the interior of the cylinder and beneath its base, causes the cylinder to descend, the action of the cutting edge being assisted by the weight of brickwork above. As the cylinder sinks, brick rings are added continuously until the required depth is obtained. Great care has to be taken during these operations to maintain the per- pendicularity of the cylinder. This, of course, depends upon the equal and uniform settlement of the cutting edge. The most trying time is during the sinking of the first 10 feet or so, and it is recommended that, where possible, the curb should be sunk alone to this depth. The first layer of brickwork may then be some 5 feet in height, and no succeeding layer should be more than 10 feet. It is further recommended that the topmost course of brick- work of each layer should be removed before commencing the next layer, so as to ensure a joint perfectly clean and free from any trace of fallen earth. Where there is much side friction, the mere intrinsic weight of the cylinder may not be sufficient for the purpose of driving. Additional weight is best added in the form of iron rails and kentledge, which are compact and easily handled. The actual amount of friction to be encountered will depend on local circumstances, but under ordinary conditions it has been found to vary between 3 and 5 tons per square yard. The average rate of sinking in the instance quoted above was 6 feet in eight hours. Iron Cylinders.—Metal cylinders are almost invariably built of cast or wrought iron, in tiers of tubular castings or of circular plating, the cutting edge being furnished by the lower edge of the bottom tier. Adjacent parts in the case of cast iron are connected by internal flanges, and in the case of wrought iron by fish-plates also arranged internally, with tie and angle- iron stiffeners at intervals. Horizontal flanged joints offer facilities for the * “Cylinder Foundations” by Imrie Bell and John Milroy, Min. Proc. Inst. C.E., vol. xxviii.