A Treatise On The Principles And Practice Of Dock Engineering

PIERS AT SUNDERLAND HARBOUR. 297 so that each tier is | inch less in diameter than that immediately below it. The caisson was furnished with four 12-inch sluice valves, fitted to the outside of the eighth tier, 27 feet 7 inches from the bottom. Eighteen 3-inch wrought-iron pipes, rivetted over 3-inch holes in the bottom, were also provided for the purpose of grouting the rubble base beneath the caisson. They were built to a height of 50 feet, in three lengths, with screw ends. This great height was necessary, as the base could not be grouted until the caisson was nearly filled with concrete, but it entailed considerable difficulty in affixing successive lengths, a step which had to be undertaken while the caisson was afloat and by no means quiescent. Eeing too slender to support themselves, they had to be stiffened by bracing to the sides of the caisson, an arrangement which interfered with the lowering of material and plant. Any damage, moreover, to the pipes below the water line would, in all probability, have involved the foundering of the caisson. The caissons for the north and south pierheads were similar in construc- tion, with the exception that the former had an additional bracing of three transverse bottom girders, 2 feet deep, rivetted over the tops of the other ten, at right angles to them. The north caisson was brought over from England in sections and put together, to a height of 23 feet, within a temporary dock or enclosure on the beach. At this stage it was launched, and received a solid floor of concrete 4 feet thick. Above this floor, concrete was deposited, to a height of 3 feet, in such a manner as to leave seven circular wells or pits, which, with the exception of the centre one, used as a tide gauge-well, were filled later. The lining for these and the sides was built by means of wooden moulds, 5 feet 6 inches in height, set upon wooden putlogs as the sides were raised. When the iron sides with their concrete lining were completed the caisson drew 36 feet of water. At this draught it was berthed over the site, which had a prepared rubble founda- tion, with a slight inclination, to cause the caisson to tilt slightly inwards towards the blockwork of the pierhead and the wave-breakers, which would lean against it. When in position, the sluice valves were opened, the caisson grounded, and about 500 tons of water were admitted, sufficient to keep it secure. The pits were then utilised for the reception of a number of concrete blocks, ranging from 25 to 150 tons in weight, and the caisson was subse- quently emptied of water by a pulsometer. After this, the work of completing the concrete interior was proeeeded with without interruption. The sluices were removed at the close of the work. Piers at Sunderland Harbour. These piers consist of two curved arms, projecting from the shore line and converging to a distance apart of 480 feet at the pierheads. The area thus enclosed is 100 acres. The Roker Pier (fig. 244), on the north side of the River Wear, has a