A Treatise On The Principles And Practice Of Dock Engineering

190 DOCK ENGINEERING. placing of iron kentledge for weighting purposes, and brackets may be specially cash for the same object. This method was adopted in the case of foundations for the piers of a bridge in the River Clyde, the bed of which is running sand to a depth of 80 feet.* Four piles were driven as vertical guides for each cylinder, and uniform subsidence was obtained by systematic distribution of the kentledge. Brackets, 6 inches long, were cast on the lower flange of each length (6 feet 6 inches) of the cylinder, which last had a diameter of 8 feet 4 inches. The kentledge was cast in the form of circular segments, 12 inches thick, so as to fit the concavity of the sides of the cylin- der, and rest upon the brackets. In this way lOj tons dead weight was deposited in five rings upon each tier. Owing to their symmetry and the Fig. 118.—Quay Wall, Newcastle-on-Tyne. mutual support afforded by contiguous sur- faces, there was no tendency to displacement in any of the pieces. The rate of sinking was 5 feet per working day. Cast-iron cylinders, 5 feet diameter and 25 feet apart longitudinally, centre to centre, were adopted for the substructure of the earlier quays at Newcastle-on-Tyne (fig. 118).t They were sunk under atmos- pheric pressure. Over the intervening spaces, masonry and brick arches were turned, springing from cast-iron beams which connected the front and back cylinders. Crescent-shaped rows of metal sheet piling joined the front cylinders below low water level. The superstructure consisted of ashlar facing with concrete backing and granite coping. The wall, however, showed signs of weakness before the dredging in front of it had reached the intended depth, and the work had to be strengthened by a trench of concrete at the back. Elliptically shaped “cylinders” of cast iron in continuous rows were then experimented with, the sheet piling being discarded, but the result was equally unsuccessful. They were found to be too weak to resist lateral pressure. Apparently the failure was due to insufficient thickness of metal, for the substructure of the deep water quays at Cork was satisfactorily carried out in oval-shaped “ cylinders ” of concrete (figs. 119 and 120). Concrete cylinders present no essential structural difference from those of bi'ick, as already described, their only distinguishing feature being the employment of concrete instead of brickwork for the steining. Perhaps at * Min. Proc. Inst. C.E., vol. xxviii. + Scott on “Deep Water Quays, Newcastle-on-Tyne,” Min. Proc. Inst. C.E. vol. cxix.