A Treatise On The Principles And Practice Of Dock Engineering

194 DOCK ENGINEERING. “The bottom ring, differing from the others, is called a corbelled ring, because it is made less in thickness all round the bottom edge, in order to fit into a cast-iron shoe (figs. 123 to 126), and is tapered inwards and upwards to the füll thickness of 1 foot 11 inches. The shoe is of V-shape, 2 feet deep, of 1-inch metal, and the same external size as the rings ; the under side of the bottom concrete ring rests on a shelf in the shoe, 6 inches from the top. The wedge-shaped space below is filled with concrete. The shoe weighs about 4| tons, and is in six parts for convenience of placing in the trench, which was excavated along the line of the quay wall. The bottom of the trench was about 2 feet below low-water level, where it was made 19 feet wide, the sides sloped upwards with a batter of 1J horizontal to 1 perpendicular. Staging was erected to carry the travelling cranes and digging apparatus. On the bottom of the trench the shoes were placed exactly along the line of the quay wall, and the corbelled ring, being placed on the shelf in the shoe, was bolted to it by thirteen l|-inch bolts. A malleable-iron washer plate, 5 inches broad by | inch thick, was sunk into the top surface of the corbelled ring, in which the recess for this plate and the holes for the bolts passing through the ring had been made in the moulding of the concrete ring. The cylinders, being triple, were placed in the trench so as to dovetail into one another —one in front and two behind, alternating with two in front and one behind. The sides of the groups, where they pressed against each other, were flattened Fig. 126a.—Method of forming Joint at J, fig. 123. for a breadth of 5 feet so as to ensure a good bearing. “ When the building-up of the rings forming one group of cylinders was completed to the full height, the sand and gravel were dug out, simul- taneously, from within each of the three cylinders by means of cranes or excavators specially designed for that purpose. From 400 to 500 tons of cast-iron segmental weights, of the same shape as the rings, were generally required to force each group of cylinders down to the required depth, which is nearly 60 feet below the coping level of the quay. The tops of the cylinders finish about 12 inches above low-water level. The average rate of sinking was about 1 foot per hour; in good working sand as much as 3 feet per hour was attained. When the group had been sunk, each cylinder was cleaned out by means of the excavators to the level of the bottom of the shoe, and was then filled to the top with Portland cement concrete. On this foundation the quay wall is built. In order to effectually close up the apertures between the adjoining groups of cylinders a timber chock pile, 30 feet long by 12 inches square, was driven behind, angleways, so that a sharp corner bears hard against each of the adjoining cylinders. “ The walls are of concrete rubble, and many of the stones weigh from 2 to 3 tons each. The walls are faced with concrete ashlar, in courses ranging from 18 to 15 inches thick ; the concrete blocks are not less than